Paper Manufacturing Q & A

 General Paper Making

★ What is typically contained in a paper making ""furnish""?
Ans: "Furnish" refers to the suspension of fibers, fillers, and chemical
additives in water that is used to produce a sheet of paper or board.
Furnish components vary according to the desired sheet properties for
different paper grades.

★ What is the function of the headbox on a paper or board machine?

Ans: The headbox distributes the furnish evenly onto a continuously
moving fine mesh screen (also referred to as a "forming fabric" or "wire")
at one end of the machine.

★ Why is it important to remove as much water as possible at the "wet

end" of a paper or board machine?
Ans: It is desirable to remove as much water as possible at the wet end
(which consists of the forming section and press section), because the
removal of water by mechanical means costs less than the removal of water
by evaporation, which is used in the next section - the dryer section.

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★ What is the purpose of the white water system on a paper or board
machine?
Ans: The white water system collects much of the water that is removed
from the sheet on the machine and makes it available for re-use as dilution
water and shower water.

★ How are softwood and hardwood fibers different from each other?
Ans: Softwood fibers tend to be long and flexible, which contributes to the
strength characteristics of paper. Hardwood fibers tend to be short and
stiff, which contributes to the bulk, smoothness, and opacity of paper.

★ Why is paper that is made from mechanical pulp called "wood-

containing paper"?
Ans: Mechanical pulps contain all of the constituents of wood, including
the lignin, and so they are referred to as "wood-containing."

★ What is the "liquor" that is used in chemical pulping processes?

Ans: "Liquor" is the name of the water-based chemical solution that is used
to cook wood chips in chemical pulping processes.

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★ What happens to the chemicals in the cooking liquor after the pulping
process?
Ans: The chemicals are washed out of the pulp and then they are recovered
so that they can be reused.

★ Pulping and papermaking processes require a lot of steam heat. Where

does this steam come from?
Ans: As part of the chemical recovery process, many organic compounds
from the wood are burned to produce steam.

★ What dangers are present in papermaking and paper converting

facilities?
Ans: Pinch points, nips, sharp surfaces, hot surfaces, slips, trips, falls,
airborne particles, high noise levels, chemicals, confined spaces, water and
air hoses, and fires.

★ What behaviors can contribute to injuries?

Ans: Complacency due to routine, taking shortcuts to save time, and lack
of focus or distractions can contribute to injuries.

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★ What are the leading causes of fall injuries?
Ans: Objects left on the floor, slippery fluids on the floor, insufficient or
missing railings, incorrect ladder use, insufficient fall protection, and people
being unaware of their surroundings.

★ Why is paper dust hazardous?

Ans: Dust can accumulate and create a slippery surface. When airborne, it
can get into operator's eyes or cause respiratory problems. Dust is also a
risk for fire or explosion.

★ What precautions can be taken to avoid paper machine hazards?

Ans: Hazards can be avoided by wearing the proper PPE, following LOTO
procedures, and maintaining good housekeeping. E-stops should be used
when there is imminent or actual danger to personnel or equipment.

★ What is "latent heat"?

Ans: Latent heat is the heat energy that is required to convert a liquid to a
gas - for example, liquid water to steam.

★ Why is it important that steam contains latent heat?

Ans: When steam contacts a surface that is at a lower temperature than it,
the steam will condense on the surface and transfer its latent heat to that
surface.

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★ What is superheated steam?
Ans: Superheated steam is steam that has been heated above its boiling
point (for the current pressure).

★ Why is superheat sometimes added to steam, and then removed?

Ans: Steam is superheated to prevent it from condensing in steam supply
piping. Once it reaches its final destination, this superheat is often removed
to encourage condensation and improve heat transfer.

★ Why is it important to try and recover the condensate from steam-

heating systems?
Ans: Condensate still contains large amounts of sensible heat and it may
contain boiler feed water treatment chemicals, so it reduces costs if it can
be recovered and reused.

★ Why are flexible, self-conforming doctor blade holders used on some

rolls?
Ans: Flexible, self-conforming blade holders utilize two fluid-filled or air-
filled tubes to load the blade against a roll surface. They maintain a uniform
pressure on the blade across the machine and automatically compensate for
changes to the roll surface, including roll deflection.

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★ Why should you avoid increasing the load on a used doctor blade?
Ans: This can cause the blade tip to lift up, which greatly increases the risk
of the sheet wrapping the roll.

★ Why are double doctors used on some suction rolls?

Ans: The first blade removes surface water and creates a vacuum pulse that
pulls water out of the holes in the roll shell. This water is then removed by
the second blade.

★ Where are air doctors used on paper and board machines?

Ans: Air doctors are used on drilled and grooved surfaces to prevent the
type of damage that can be caused by contacting doctor blades.

★ Why is it important to change doctor blades on a regular basis?

Ans: This is important because as blades wear, blade angles change, which
makes them less efficient.

★ What are the two basic types of paper machine doctor blade holders?
Ans: Rigid and self-conforming. Rigid holders are fitted to the roll initially
and they do not automatically adjust. Self-conforming holders use one or
two tubes to load the blade and they do automatically adjust to match the
roll surface.

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★ What are the three materials from which paper machine doctor blades
are made?
Ans: Metals, composites (usually of resins and fibers), and plastics (usually
a type of polyethylene).

★ What technique can be used to detect blade wear patterns that are more
difficult to observe?
Ans: Lay the worn blade on the floor next to the straight back edge of
another blade for comparison.

★ What could cause a blade edge to become feathered?

Ans: A feathered edge can be caused by a low blade angle, excessive blade
loading pressure, or blade material that is too soft.

★ Why is it important to not increase a blade load after a blade has been
used?
Ans: This can cause the tip of the blade to lift up (called "bird mouthing"),
which can lead to debris getting trapped under the blade and sheet
wrapping.

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  Stock Preparation

★ Why is it important to control stock consistency in the thick stock

system?
Ans: Consistency control is important because it can affect refining, sheet
formation, moisture and weight profiles, and vacuum levels on the
machine.

★ Where is consistency typically controlled in a thick stock system?

Ans: Consistency is measured and dilution white water is normally added at
the suction of stock pumps to help blend the stock and white water
together.

★ Why is pH control important in the thick stock system?

Ans: Good pH control is crucial to steady machine operation because pH
plays a major role in refining, additive efficiencies, and drainage. Also, it is
easier to control machine pH when the incoming stock pH is consistent.

★ What is the purpose of savealls in thick stock systems?

Ans: Savealls (also called thickeners or deckers) are used to recover fiber
and filler from white water, thicken stock, or both. Saveall designs include
gravity drum, vacuum drum, and vacuum disc.

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★ What is the role of the machine chest in the thick stock system?
Ans: The machine chest dampens any remaining fluctuations and supplies
an uniform stock slurry to the thin stock system.

★ Why is it important to control consistency in a paper or board machine

stock system?
Ans: Consistency affects refining, screening, and cleaning operations in the
stock system, and moisture and basis weight profiles, sheet formation, and
vacuum levels on the machine, among other things. Therefore, it can
significantly impact both product quality and machine run-ability.

★ How is consistency controlled in a paper or board machine stock

system?
Ans: Consistency is usually controlled by adjusting a dilution water flow
into a stock flow.

★ What different control strategies are available to control consistencies in

stock systems?
Ans: Some control strategies currently in use include feed forward,
feedback, cascade, and a combination of cascade and feed forward. The
strategy used depends on the stability of the stock flow and the dilution
water supply.

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★ Why is it important to control pH in paper and board machine stock
systems?
Ans: Soluble ions affect pH and interfere with the surface charge
interactions which dominate the interactions amongst stock constituents.
Among other things, pH affects additive efficiencies, refining, and drainage
and formation on the former.

★ How is pH controlled on a paper or board machine?

Ans: Acidic and caustic chemicals are typically used to control pHs on
paper and board machines.

★ What is the purpose of high density cleaners?

Ans: Their main purpose is to separate heavy contaminants from fibers in
fiber-water suspensions in order to protect downstream equipment from
wear and damage.

★ Where are high density cleaners typically used?

Ans: They are often used in secondary fiber systems, pulp mills, paper and
board machine thick stock systems, and broke systems.

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★ How are high density cleaners different from other forward cleaners
used in the production of paper and board?
Ans: High density cleaners are larger in size physically, discharge their
rejects intermittently rather than continuously, and operate with higher feed
stock consistencies than other forward cleaners.

★ What is the purpose of the elutriation water in a high density cleaner?

Ans: A continuous stream of elutriation water is used to flush fibers out of
the rejects chamber, at the bottom of the cleaner, during cleaner operation.

★ How often are the junk traps on high density cleaners emptied?
Ans: The frequency of the junk trap dump cycle and the length of the
purge depends on the level of contaminants in the stock suspension.

★ What is the purpose of paper and board machine refining?

Ans: The main purpose of most paper and board machine refining is to
improve certain sheet properties, including strength and density-related
properties.

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★ What happens to the fibers during refining?
Ans: The fiber cell walls are delaminated, allowing them to absorb more
water and increasing their flexibility. External fibrillation of the fiber
surfaces increases the surface area available for bonding, and some fiber
cutting and creation of fines takes place.

★ Why is it important to keep the flow rate through a refiner steady?

Ans: Flow rate determines the amount of time the fibers are available for
treatment in the refiner. Low flow can lead to fiber cutting, fiber
channeling in the plate grooves, and poor strength development. High flow
can cause plugging and poor fiber development.

★ Why do broke fibers and recycled fibers not respond as well to refining?
Ans: Broke and recycled fibers have already been refined and contain some
shorter fibers, which don't respond as well to refining. Also, they have been
previously dried, so don't absorb water as readily, making them more
difficult to refine.

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★ How does high consistency refining differ from low consistency
refining?
Ans: Low consistency refining increases the fibers' surface area available
for bonding and several sheet strength properties. However, it reduces
freeness and drainage. High consistency refining creates micro-compressed
and curly fibers, which improve sheet stretch and porosity, as well as some
strength properties, like tear. It also reduces freeness and drainage, but to a
lesser degree.

★ On what paper or board grades is high consistency refining used?

Ans: High consistency refining is well-suited to the production of craft sack
papers and other similar grades which must withstand high levels of strain
during use.

★ At what consistency is high consistency refining performed?

Ans: High consistency refining is performed above 20% consistency, and
consistencies between 30 and 40% are quite common.

★ How is 30 to 40% consistency stock transported to the high consistency

refiners?
Ans: Screw conveyors are typically used to move high consistency stock
from the presses to the refiners.

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★ What happens to the filtrate that is removed from the stock by the
presses that are positioned ahead of high consistency refiners?
Ans: This filtrate can be used to re-dilute the stock after it has been refined,
before it is metered back into the paper making process.

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  Stock Approach:::::::

★ Why do thin stock cleaning and screening systems often use multiple
stages?
Ans: The later stages are used to recover the fibers in the rejects from the
first stage. This minimizes fiber losses and improves the overall efficiency
of the system.

★ What is the difference between a forward cleaner and a reverse cleaner?

Ans: In both types, the denser components exit from the bottom and
lighter components from the top. Forward cleaners remove small dense
contaminants, so the fibers exit from the top. Reverse cleaners remove
lightweight contaminants, so the fibers exit from the bottom.

★ Why are fan pumps usually double suction pumps instead of centrifugal
pumps?
Ans: Fan pumps are typically double suction pumps with low-pulse
impellers to minimize pressure pulsations in the stock going to the
headbox, which can occur with regular centrifugal pumps.

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★ What is the difference between cleaners and screens?
Ans: Cleaners remove small contaminants based on density differences
with fibers, while screens remove larger contaminants based on size
differences with fibers.

★ What is the purpose of the attenuator in a thin stock system?

Ans: Attenuators use air pads to remove any remaining pressure pulsations
in the stock flow to the headbox, which is especially important for
hydraulic headboxes.

★ What is the purpose of cleaners?

Ans: Centrifugal cleaners are used to remove contaminants and protect
downstream equipment from damage and wear.

★ What are forward cleaners?

Ans: Forward cleaners separate heavy particles from pulp by centrifugal
force.

★ What is a cascade cleaner system?

Ans: Rejects from a set of cleaners often contain good fiber. In a cascade
system, additional stages are used to process the Primary stage rejects and
recover the fibers.

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★ What are reverse cleaners?
Ans: Reverse cleaners separate lightweight contaminants from fibers.
Lightweight contaminants include wax, plastic, and other stickies.

★ Why is pressure drop important for cleaning efficiency?

Ans: If the pressure drop is too low, the stock will rotate too slowly inside
the cones and contaminant removal will suffer. If the pressure drop is too
high, the stock will pass too quickly through the cones.

★ Are there multiple forms of entrained air?

Ans: There are three forms of entrained air that can exist in stock
suspensions and white water - free, bound, and dissolved.

★ What are the differences between free air, bound air, and dissolved air?
Ans: Free air consists of larger bubbles that can be removed with time,
bound air consists of smaller bubbles that can attach to fibers and be
difficult to remove, and dissolved air only presents a problem if it converts
into free or bound air.

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★ Is deaeration necessary on every machine?
Ans: The amount of entrained air that is tolerable in a paper or board
making process depends on many things. So, though all paper and board
machines would benefit at least a little from deaeration, not all of them use
it.

★ How do deaerators remove entrained air from the stock suspension?

Ans: They use three means: they use vacuum to ""boil"" the stock to
remove air, they spray the stock to expose more surface area to the
vacuum, and they impinge the stock on hard surfaces to separate the
bound air from the fibers.

★ Can a deaerator cause pulsations in the stock flow to a headbox?

Ans: Pulsations in the stock flow to the headbox can be caused by
excessive air in the stock going to the deaerator, an undersized or
underperforming vacuum system, or low stock flows to the deaerator,
which can cause the level inside the vessel to rise and fall, leading to
fluctuations in the stock flow to the fan pump.

★ What is the purpose of thin stock screening?

Ans: Screening removes dirt, small pieces of plastic, wood and other
contaminants. It also helps break up fiber clumps.

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★ What are disadvantages of vibratory flat screens?
Ans: Vibratory screens have high maintenance and foaming issues.

★ How are pressure screen basket openings created?

Ans: The baskets can have drilled holes, milled slots, or welded wedge wire.

★ What are typical screen opening sizes?

Ans: In thin stock systems, hole sizes range from about 1.2 to 3 mm (0.05-
0.12 inch), with an open area of 10 to 25%. Slot widths vary from about 0.2
to 0.5 mm (0.008-0.02 inch), and open area is generally 7 to 15%.

★ What debris properties affect removal efficiency?

Ans: Large, 3D particles are easiest to remove. 2D debris, such as wet
strength flakes, can be removed, but some orientations pass through the
baskets easily. Small contaminants like shives are most difficult to remove
by screens.

★ What is the primary purpose of a pressure screen?

Ans: The purpose of a pressure screen is to separate unwanted debris from
desirable fiber in a pulp stream.

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★ What is the purpose of the spinning rotor in a pressure screen?
Ans: The purpose of the spinning rotor within the screen basket of a
pressure screen is to keep the screen clean and increase the flow of fiber
through the screen.

★ What advantage is gained by using cascaded screens?

Ans: No separation process is perfect. Some good fiber is rejected with the
unwanted debris in a pressure screen. Rescreening the rejected fiber
permits the recovery of the good fiber. Rescreening multiple times is
referred to as "cascading" screens, and ensures a high fiber recovery rate.

★ What is a good strategy for unplugging a pressure screen?

Ans: A plugged screen can often be unplugged by reducing or stopping the
accepts flow, giving the basket an opportunity to clear itself through the
rejects line, and re-opening the accepts valve.

★ What could be some causes of poor accepts quality?

Ans: There are many potential causes of poor accepts quality, but some of
the more common possibilities are: low reject rate, a hole or gap in the
screen basket, unusually high level of contaminants in the feed or worn
slots or holes in the basket.

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  Headboxes::::::::::
★ What are the four basic functions of a headbox?
Ans: To deliver the stock uniformly onto the forming fabric in the cross-
machine direction and the machine direction, create controlled turbulence
to reduce fiber flocking and develop uniform fabric distribution,
coordinate the speed of the stock jet with the speed of the wire, and to
ensure that the flow of stock from the slice opening strikes the wire at the
correct angle and location.

★ What is the purpose of the headbox?

Ans: The purpose of the headbox is to distribute the stock onto the
Fourdrinier wire to form the sheet. There are several components inside an
air-padded headbox that are designed to distribute the stock evenly across
the machine and generate turbulence to keep the fibers dispersed.

★ What is the primary function of the flow spreading device?

Ans: The primary function of the flow spreading device is to evenly
distribute the stock across the width of the headbox and the machine.
Other flow spreading devices are also in use.

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★ What are rectifier rolls and what do they do?
Ans: An air-padded headbox contains rotating, perforated rolls, call
rectifier rolls. The stock flows through the holes of the rectifier rolls,
generating a pressure drop that dampens out large-scale turbulence and
evens out the velocity profile across the headbox width.

★ How is the air pad maintained?

Ans: The air pad inside the head box is maintained by a source of
pressurized air. The source can be mill compressed air or a dedicated air
compressor for the headbox. The pressurized air is piped to the top of the
headbox and regulated to maintain the stock level inside the headbox.

★ Why is sheet formation so important?

Ans: Formation is important because it affects the appearance and
performance of the sheet. It affects appearance in that a well-formed sheet
will look very even, and it affects performance because the distribution of
fibers directly affects the distribution of fiber-to-fiber bonds which hold
the sheet together. If formation is poor, there will be thin, weak spots
which will fail under load.

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★ What is the "stock jet geometry"?
Ans: The term "stock jet geometry" refers to a set of measurable,
observable physical characteristics of the stock jet after it exits the
headbox.

★ Which stock jet geometries are important for a roll type gap former?
Ans: Jet length, jet angle, and jet impingement are all important.

★ Why is it important to have a short free jet length?

Ans: A short free jet length reduces the time available for the fibers to re-
flocculate before the sheet sets, and if there are multiple layers, it minimizes
mixing between the different layer furnishes.

★ Should the angles between the jet and the fabrics be low or high?
Ans: The jet angles should be low because if the jet is directed too much
into either roll, water can start "pumping" around the roll, which can
disrupt sheet formation.

★ What is the jet impingement angle?

Ans: On a Fourdrinier machine, it is the angle between the stock jet and
the wire as the jet strikes the wire.

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★ Why is the stock jet geometry so important?
Ans: Stock jet geometry is important because it affects sheet formation,
and sheet formation affects both the appearance and the performance of
the sheet.

★ What is the difference between "pressure forming" and "velocity

forming"?
Ans: Pressure forming occurs with very high jet angles, where the stock jet
is forced down into the wire. Velocity forming occurs with low jet angles,
and the stock jet lands more gently on the wire.

★ What is the "jet-to-wire ratio"?

Ans: It is the ratio of the stock jet speed and the wire speed, and it greatly
affects the orientation of the fibers in the sheet.

★ What is the "L/b ratio" and why is it important?

Ans: It is the ratio of the horizontal spacing to the vertical spacing between
the slice lip and apron lip. It is important because it affects the jet landing
point and the jet impingement angle.

★ Why are multi-layer headboxes increasingly popular?

Ans: Because they allow for efficient fiber usage and optimization of
desired sheet properties.

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★ Are the stock systems for multi-layer hydraulic headboxes and non-
layered headboxes the same?
Ans: No. Because the different layers can have different furnish
compositions, each layer has its own stock preparation and delivery system.

★ What are the advantages of dilution profiling systems over traditional

slice lip adjusters?
Ans: Dilution profiling systems eliminate the cross-flows in the stock jet
and fiber orientation variability that were caused by slice lip adjustments.

★ What is the purpose of the tubes, chambers, drilled plates, and flat
sheets or vanes in hydraulic headboxes?
Ans: These items induce turbulence in the stock flows to keep the fibers
separate and help break up flocs before the stock reaches the forming
fabrics.

★ What happens when the slice opening is widened slightly?

Ans: The pressure inside the headbox initially drops, so the fan pump
speeds up to increase the headbox pressure, which increases the total flow
through the headbox. The end effect is a drop in the headbox consistency.

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  Forming::::::

★ How does a paper or board machine's stock delivery system affect sheet
formation?
Ans: The shear forces created by agitators, pumps, valves, cleaners, and
screens in the stock system help keep the fibers dispersed in the dilute
stock suspension and prevent flocs from forming before the stock reaches
the headbox, which ultimately improves formation.

★ How does headbox design influence sheet formation?

Ans: Rectifier rolls, tube banks, converging channels, and other internal
headbox elements are designed to create turbulence and shear. This helps
keep the fibers dispersed until they reach the forming zone.

★ Why aren't all headboxes run at lower consistencies, since this helps
keep the fibers separate and improves formation?
Ans: The headbox consistency can only be lowered until the drainage
capacity of the former has been reached. If it is lowered further, the sheet
will be too wet going into the press section.

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★ Does the addition of starch affect sheet formation?
Ans: Starch is sometimes added to stock to increase sheet strength
properties and improve drainage and retention. This can improve
formation to a point, but over-use can lead to foam in the stock, which
hurts formation and drainage.

★ How can the forming section influence sheet formation?

Ans: Breast roll shake mechanisms, formation showers, dandy rolls, foil
box angles, and vacuum levels on the former can all affect sheet formation.

★ What are the two main jobs of a forming fabric?

Ans: To retain as much fiber and other furnish components as possible,
and to allow water to drain through as quickly as possible.

★ What are the most common fabric styles or weaves used in forming
fabrics?
Ans: The most common fabric styles are single layer (one MD and one CD
strand), double layer (one MD and two CD strands), double layer with
support shute (one MD and three CD strands), and triple layer (two MD
and three CD strands).

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★ What is the difference between "mesh" and "count"?
Ans: Mesh refers to the number of MD yarns per inch of fabric, while
count refers to the number of CD yarns per inch of fabric.

★ Why can't air permeability (which measures air flow) be used alone to
predict the drainage capacity of a fabric?
Ans: Because it does not take into account the impact of the fibers and
furnish on drainage. Surface topography and fabric construction both
affect furnish retention and so can also affect the dewatering capacity of
the fabric.

★ How can you tell if a forming fabric is misaligned?

Ans: Most forming fabrics are manufactured with a colored stripe across
their width. If this stripe is not straight, this means that the fabric is skewed
or misaligned.

★ In addition to furnish retention and dewatering capacity, what else is

required of a forming fabric?
Ans: The forming fabric must be able to withstand the wear caused by
stationary elements and vacuum devices on the former.

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★ Relatively high fabric tension is desirable because it improves drainage
and reduces slippage on driven rolls. However, what happens if the tension
is too high?
Ans: Excessive fabric tension can reduce drainage capacity by narrowing
the openings in the fabric, damage the wire seam, or cause roll deflections
and warping, which can lead to ridges in the fabric.

★ What is the problem with low fabric tension?

Ans: Very low fabric tension can cause slippage at the driven forming
section rolls, and wire flexing at the gravity foils and vacuum boxes. This
can lead to wire abrasion, and guiding and speed control issues.

★ What is the purpose of seam straightening?

Ans: A skewed seam or colored stripe on the forming fabric indicates a
misalignment in the forming section. Straightening the seam evens out the
fabric tension, which evens out the dewatering capacity of the fabric across
the machine.

★ What is the basic principle of fabric guiding?

Ans: The fabric will move or ""steer"" toward the end of the roll that it
contacts first.

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★ What exactly is a Fourdrinier ""wire""?
Ans: Contemporary wires are fabric loops that are woven from polyester
monofilaments, and traditional textile variables (weave pattern, yarn count,
and yarn diameter) allow them to be customized to each machine and grade
mix.

★ Why are different devices used on a Fourdrinier to remove water from

the sheet?
Ans: Vacuum levels increase on the Fourdrinier table because water
becomes increasingly difficult to remove from the sheet. Foil boxes help
remove water early on, and flat boxes with slotted covers are used later
because they provide better sheet support at higher vacuum levels.

★ Why must Fourdrinier wires be stretched or tensioned?

Ans: Constant tension on the wire allows the wire to maintain its retention
and drainage characteristics as it ages and stretches. Tension is also
required to properly drive the wire.

★ How do guide rolls work?

Ans: Guide rolls work on the principle that when a wire contacts a roll, it
will ""steer"" toward the end of the roll that it contacts first.

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★ What is the purpose of the separators on the drive side of a
Fourdrinier?
Ans: The air-water mixture pulled from the sheet into each vacuum box is
pulled first into a separator, which separates the air from the water. The air
flows out the top to the vacuum source, and the water exits from the
bottom to a seal pot or tank.

★ What are some benefits of twin-wire formers over Fourdrinier formers?

Ans: Twin-wire formers reduce sheet two-sidedness, wire instability, and
the length of the forming section. Also, twin-wire formers double the
drainage area and can run at higher speeds.

★ What are some potential problems presented by twin-wire formers?

Ans: Space limitations restrict the addition of more water-removal devices.
Fibers can build up preferentially on the two fabric surfaces, which
increases the likelihood of sheet de-lamination. Fabric selection is critical
and there is a high potential for fabric and equipment damage because the
fabrics operate in close proximity.

★ What is a roll former?

Ans: Roll formers are characterized by the stock jet being captured in a
long nip created between two fabrics traveling together around a
perforated suction forming roll.

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★ What is a blade former?
Ans: Blade formers are characterized by a stock jet impinging into a gap
between two forming fabrics which are forced together by a number of
fixed blades in a vertical forming section.

★ What is a roll/blade former?

Ans: Roll/blade formers try to combine the advantages of roll and blade
formers and avoid their problems. Two forming fabrics wrap around a
perforated suction roll then there is a blade section to provide additional
pulsed drainage.

★ How can multi-ply forming reduce costs?

Ans: For high basis weight grades; multi-ply forming can run at higher
speeds than are possible with single-ply forming. Also, more economical
furnish components can be used in some layers, and expensive
components can be concentrated in the layers where they can make the
most impact.

★ What are three basic ways that a multi-ply sheet can be formed?
Ans: A multi-ply sheet can be formed by forming additional layers on top
of an existing sheet, separately forming multiple layers and then combining
them together while they are still moist, or using a multi-layer headbox.

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★ What are some of the downsides of multi-ply forming?
Ans: Additional equipment must typically be installed and operated to
prepare and deliver different furnishes to the different layers. Also,
bonding between the plies or layers can be a problem.

★ What kinds of products are made using multi-ply forming?

Ans: Multi-ply forming was originally used to produce heavy weight grades,
but it is now used to produce a wide range of products, including tissue
and towel, and printing and writing, grades.

★ How can cylinder formers be used to produce a multi-ply sheet?

Ans: A cylinder former forms a sheet on its mesh-covered surface and then
transfers it to an absorbent felt that is pressed against it. When multiple
cylinder formers are arranged in series with a single felt, each additional
former adds another layer to the sheet that is forming on the felt.

★ Why do sheet breaks on a paper or board machine often originate at the

sheet edges?
Ans: The edges of the sheet tend to have issues with formation because the
stock flow abruptly cuts off at the edges, which can lead to poor formation
at the edges and cause sheet breaks.

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★ What is the purpose of deckle boards?
Ans: They keep the stock from flowing off the edges of the wire.

★ Why have water jet deckles replaced deckle boards on many paper and
board machines?
Ans: Water jet deckles use a curtain of water to contain the stock. Because
there are no longer boards for the stock to deflect off of, this minimizes
the formation of deckle waves or wakes.

★ Why is the position of the end deckles on forming section suction

boxes so critical?
Ans: If they are too far in, this can cause wet sheet edges. If they are too far
out, air will be sucked in to the box at the edges, reducing the overall
vacuum level. Also, they should be staggered to reduce wire edge wear.

★ What is the purpose of curling boards?

Ans: Curling boards help contain the stock on the wire at a low angle,
which helps prevent the formation of deckle wakes.

34
★ Why are the edges of the sheet removed at the end of the forming
section?
Ans: The sheet edges are removed because they tend to have issues with
formation, which can cause sheet breaks to originate at the edges.

★ Why is the shower water supplied to the trim squirts filtered?

Ans: Trim squirt nozzles have very small orifices which are prone to
plugging, so it is critical that the water supply be clean and free of debris.

★ On machines with multiple trim squirts or multi-orifice nozzles on both

sides, why is the alignment of the nozzles or orifices so critical?
Ans: If they are not aligned properly, the edge cuts can be too thin or too
wide, which can lead to issues with edge separation and even sheet breaks.

★ Why do edge showers often follow the trim squirts?

Ans: If the edge stock is not removed from the wire, stock would tend to
stick to it, which could lead to problems with build-up, deposits, and sheet
transfer.

35
★ Which wet end components of a paper or board machine are actively
involved in establishing the sheet edges?
Ans: The deckles, curling boards, and trim squirts all help establish the
sheet width and sheet edges.

36
  Wet Pressing::::::
★ What are the objectives of wet pressing?
Ans: Wet pressing removes water from the sheet, consolidates the sheet,
and improves the wet strength of the web so it can remain intact in open
draws.

★ How does wet pressing affect sheet properties?

Ans: Pressing increases density, surface smoothness, and dry and wet
strength properties. Bulk, caliper, and stiffness typically decrease.

★ What are the phases of water removal in presses?

Ans: Water removal can be divided into compression and expansion
phases.

★ What is the purpose of the wet felt?

Ans: Wet felts act as a transfer device or belt to move the wet sheet
without damage, absorb water from sheet, and maintain an even, smooth
surface for the wet sheet.

★ What types of rolls are used for pressing?

Ans: Wet pressing can be accomplished by using solid rolls, variable crown
rolls, suction rolls, and shoe presses.

37
★ Where are suction rolls typically located on a paper or board machine?
Ans: Paper and board machines are typically equipped with multiple
suction rolls in the forming and press sections.

★ What are suction press roll shells constructed from?

Ans: Suction roll shells are typically constructed of bronze or stainless steel.

★ What is the flushing shower in a suction roll used for?

Ans: The flushing shower is used when the paper machine is down to clean
and flush stock build up out of the vacuum box and the holes in the roll
shell.

★ What are the most common roll cover materials?

Ans: Rubber and polyurethane are the two most common roll cover
materials. Rubber is very versatile, while polyurethane is tough and wear
resistant. These materials can be designed for use in many different
applications.

★ Where are ceramic roll covers used?

Ans: Ceramic roll covers are extremely wear resistant and have very good
release properties. They are often used on center press rolls.

38
★ What is the purpose of a steam box?
Ans: Steam boxes are used to increase the after-press dryness of the paper
by increasing the temperature of the sheet.

★ What is the difference between a profiling and non-profiling steam box?

Ans: Profiling steam boxes are divided into sections across the width of the
machine. The steam flow to each section can be adjusted to produce a
uniform CD (cross direction) moisture profile. Non-profiling steam
showers apply steam evenly across the entire width of the machine, so
while they do improve dewatering, they cannot address moisture streaks.

★ Why are steam boxes usually positioned over vacuum boxes or opposite
vacuum rolls?
Ans: Vacuum helps pull the steam through the sheet so that it condenses in
the sheet and not just on the surface. The goal is to have a uniform sheet
temperature.

★ What variables affect heat transfer efficiency?

Ans: Steam box heat transfer is affected by basis weight, sheet permeability,
sheet moisture, and initial sheet temperature. Heat transfer is also affected
by steam flow, the distance to the sheet, vacuum level and position, and the
dwell time.

39
★ What is the impact on total machine drying efficiency?
Ans: Even though steam boxes use steam, total paper machine steam
consumption usually decreases. For every pound of steam used in the press
section, up to 3 pounds less steam is needed in the dryer section.

★ Why is the sheet frequently separated from one or both felts soon after
a press nip?
Ans: To minimize "rewetting," where in the sheet reabsorbs some water
from the felt or felts.

★ Are press rolls usually solid rolls?

Ans: In a conventional roll press, the roll surfaces can be solid, blind-
drilled, grooved, or blind-drilled and grooved.

★ What are the limitations of fixed crown rolls?

Ans: A "fixed crown" roll has a crown ground in to the roll face, and it is
only appropriate for a single nip loading. On machines where nip loadings
vary because different grades are made, a variable crown roll may be a
better choice.

40
★ Are controlled-crown rolls used in top or bottom roll positions?
Ans: Controlled-crown rolls can be used in both top and bottom roll press
positions. In bottom positions, they typically have softer covers that are
grooved or blind-drilled to enhance water removal.

★ How do controlled-crown rolls create the crown?

Ans: CC rolls use hydraulic pressure in a sealed chamber or applied to
cross-machine cylinders to create the crown.

★ What is the main advantage of a shoe press over roll press?

Ans: With the increased nip width, the dwell time (the amount of time that
the sheet is exposed to the nip pressure) is up to 10 times longer.

★ On which grades are shoe presses used?

Ans: Shoe presses were initially used on machines producing heavier
weight grades, like board and corrugating medium. They are now used
effectively in making printing, writing, and tissue, as well as container board
and carton board, grades.

★ What are shoe press sleeves made out of?

Ans: Most shoe press sleeves are made from a woven substrate with a
coating of polyurethane, which may be grooved, blind drilled, or smooth.

41
★ What are the functions of the hydraulic fluid in a typical shoe press?
Ans: The hydraulic fluid is used to pressurize the shoe loading pistons,
provide lubrication for the shoe-to-sleeve interface, and provide cooling.

★ Does the entire shoe press rotate during press operation?

Ans: No. The roll journals, heads, and sleeve rotate around the stationary
support beam and press shoe assembly.

★ Why is it important for press felts to be centered on the machine?

Ans: To completely cover the sheet width to ensure uniform water removal
in the press nips. Also, to keep the felts from running off the front or back
of the machine.

★ What is the basic principle of fabric guiding?

Ans: The basic principle of fabric guiding is that the felt moves or "steers"
toward the roll end that it contacts first.

★ By what mechanism does the movement of the guide palm cause the
auto-guide to move?
Ans: The guide palm movement closes or opens a bleed air valve, which
increases or decreases the air supply pressure to an air bag which moves
the auto-guide end of the guide roll.

42
★ What is the purpose of the hand guide or manual guide?
Ans: Its purpose is to keep the auto-guide end centered in its travel. This
ensures that the auto-guide always has some adjustment available in both
directions.

★ What is the recommended roll wrap (in degrees) for a felt guide roll?
Ans: Guide rolls need to have a roll wrap of 25 to 35 degrees to ensure
sufficient friction for the roll to move the felt.

★ Why are press felts usually replaced?

Ans: Press felts are usually replaced because they have either filled with
contaminants or have compacted to the point that their dewatering
capacity is insufficient.

★ How many showers and uhle boxes are typically used on each press felt?
Ans: A typical system utilizes 3 or 4 showers on each wet felt, followed by
one or two uhle boxes.

★ Where are the lubricating showers installed in press felt runs?

Ans: A lube shower is usually installed ahead of each uhle box to help
reduce wear on the felt and box cover, and also act as a seal at the uhle
box. They should spray into the ingoing nip.

43
★ Why are high pressure needle jet showers on press felts oscillated from
front to back?
Ans: They are oscillated in the cross-machine direction to evenly distribute
the water and prevent damage to the felts; these showers should be
interlocked to shut off if the oscillator or press section stops.

★ Where are uhle boxes typically positioned?

Ans: Uhle boxes are usually located on the face- or sheet-side of the felt
after the press nip and all major showers.

44
  White Water and Filtrate Systems:::::::
★ What is the difference between rich and lean white water?
Ans: The white water removed from the sheet early on the former tends to
contain more solids (fibers, fines, and fillers), and so it is often called "rich"
white water. Water removed later on the former is often referred to as
"lean white water" because it contains fewer solids.

★ Where is rich white water collected?

Ans: Rich white water is typically collected in a wire pit, or a wire tray and
flume, and directed to a silo.

★ Where is lean white water collected?

Ans: Lean white water that is removed from the sheet by suction boxes in
the forming section and press section is often piped to a separator on the
back side of the machine.

★ What is clarified white water used for?

Ans: Clarified white water is used for shower water and dilution water.

45
★ What are the objectives of the white water system?
Ans: The white water system should provide adequate quantities and
qualities of white water to all points in the process, maximize reuse of
white water in order to reduce fiber and energy losses and minimize
effluent loads, and minimize fresh water makeup, as fresh water must be
heated up to process temperatures and may require pH adjustment.

★ What are the benefits of white water clarification?

Ans: Clarification benefits include reduced water usage, sewer flows, energy
costs, and raw material cost.

★ What types of equipment are used to clarify white water?

Ans: Disc filters, rotary drum filters, dissolved air flotation systems, filters,
and strainers can all be used for white water clarification.

★ What is a saveall?
Ans: Saveall is a not her name for a disc or drum filter.
★ What does DAF mean?
Ans: DAF stands for Dissolved Air Flotation. It is a clarification process
that removes suspended solids from water using air.

46
★ What are filters and strainers used for?
Ans: Filters and strainers are usually used for additional clarification of
lower white water flows, such as shower water.

★ What are the benefits of reusing white water?

Ans: Reuse of white water reduces the fresh water usage, sewer loads and
losses, and energy usage.

★ What is the purpose of the short circulation loop?

Ans: To dilute the stock to the desired headbox consistency and to prevent
foam and entrained air from entering the thin stock system.

★ Where is white water added to thick stock?

Ans: The primary cleaner pump or fan pump receives the thick stock flow,
plus dilution white water from the silo, and pumps the resulting mixture
through the thin stock system.

★ How is white water in the long (secondary) loop clarified?

Ans: The white water in the long circulation loop is typically clarified by a
disc saveall, drum saveall, or dissolved air flotation (DAF) unit to separate
the fibers and fines from the water.

47
★ What is secondary white water used for?
Ans: Clarified white water in the secondary circulation loop is typically used
as machine shower water, dilution water for consistency control to various
stock pumps, dilution and sluicing water to pulpers, and make-down water
for chemical systems.

★ What is the difference between a strainer and a filter?

Ans: Technically speaking, a filter is any device that separates solids from a
fluid, so a strainer is a filter. However, in industry, the term "strainer" is
used for devices that use a perforated metal plate or wire mesh screen to
remove larger particles, while "filter" is used for devices with more
substantial filter media that remove smaller particles.

★ What is the difference between a duplex strainer and a twin strainer?

Ans: Both have two basket strainers so the flow can be alternated between
them to allow for online cleaning. Duplex strainers use shared internal
valving and experience higher pressure drops, while twin strainers have
separate external control valves and lower pressure drops.

★ How can the cleaning cycle be initiated for an automatic self-cleaning

strainer?
Ans: It can use a differential pressure switch, timer, pushbutton start, or a
combination of these.

48
★ What is a surface filter?
Ans: Surface filters trap particles on one side of the filter media and have
limited holding capacity. Coffee filters are surface filters.

★ What is a depth filter?

Ans: Depth filters use a porous filtration medium which captures the
particles throughout its depth. Home air filters are usually depth filters.

★ How are tiny fiber fines removed from suspension in a dissolved air
flotation system?
Ans: Tiny fibers attach to small air bubbles and are carried to the surface of
the DAF clarifier.

★ What types of chemicals are added to the DAF process to assist in

particle separation?
Ans: Coagulants and flocculants can be added to DAF units in order to
increase their separation efficiency.

★ What is the purpose of prescreening ahead of DAF units?

Ans: Prescreening the feed stream to a DAF unit reduces the solids loading
on the unit.

49
★ Where in the DAF unit is new feed added?
Ans: Incoming feed is released at the bottom of the unit, giving a chance
for dissolved air bubbles to form and collect suspended particles as they
rise.

★ What happens to the separated material that floats to the top of a DAF
unit?
Ans: Separated material is skimmed from the surface of the DAF unit. If
the unit is treating paper machine white water the float may be recycled.

★ What is the term for an aqueous suspension of particles that are too
small to settle out under the influence of gravity?
Ans: An aqueous suspension of particles that are too small to settle under
the influence of gravity is called a colloidal suspension.

★ How are tiny fiber fines removed from suspension in a dissolved air
flotation system?
Ans: Tiny fibers attach to small air bubbles and are carried to the surface of
the DAF se parathion vessel.

50
★ What do flocculants do in a colloid?
Ans: Flocculants combine microflocs formed by coagulation into larger
aggregates of flocs.

★ What do coagulants do in a colloid?

Ans: Coagulants neutralize the electrical surface charge on colloidal
particles which allows them to combine to form microflocs.

★ If both chemicals are used, in what order should coagulant and

flocculant chemicals be added to a suspension?
Ans: When coagulants and flocculants are used together, coagulants should
be added to the suspension first.

51
  Paper Machine Dryers:::::::::::
★ What is the purpose of dryer fabrics on multi-cylinder machines?
Ans: Dryer fabrics improve heat transfer and help control cross-machine
direction shrinkage and sheet distortions by holding the sheet tightly
against the can surfaces. They also drive dryer cans on some machines.

★ What is the purpose of dryer hoods?

Ans: Originally, hoods were used to improve machine room conditions.
They have evolved and their current purpose is to improve control of air
flows, temperatures, and humidites around the sheet as it dries.

★ What are single-tiered dryer sections?

Ans: Single-tiered dryer sections have one level of heated dryer cans, plus
one level of rolls. They typically utilize a serpentine-shaped "unirun" fabric
that supports the sheet through the entire section.

★ Why are single-tiered dryer sections often followed by double-tiered

sections?
Ans: Because only one side of the sheet contacts the dryers in single-tiered
sections, they are often followed by double-tiered sections to make the two
sides of the sheet more equal in appearance.

52
★ What is the purpose of pocket ventilation systems?
Ans: Pocket ventilation, or PV, systems introduce hot dry air across the
machine in dryer pockets to keep the air around the sheet from becoming
saturated and improve drying. This helps ensure a flat moisture profile at
the reel by maintaining uniform humidities across the machine.

★ What are some of the weaknesses of conventional multi-cylinder dryer

systems?
Ans: Multi-cylinder dryer systems have relatively low drying rates so require
a lot of space, they respond rather slowly to control changes, and they
inherently offer poor control of cross-machine moisture profiles.

★ Can Yankee dryers be used in the production of non-tissue grades?

Ans: Yankee dryers can also be used to produce machine-glazed (MG)
papers. On these machines, there is no dryer coating, steam pressures and
temperatures are lower, and additional dryers are necessary to assist in
sheet drying.

★ How does through-air drying increase the bulk, softness, and water
absorbency of the sheet?
Ans: Through-air drying machines do not employ any wet pressing, so the
sheet is never crushed.

53
★ Infrared drying is not usually very economical, so why is it used at all?
Ans: Infrared dryers are small so they are sometimes used to add
incremental drying capacity. They can also provide additional control over
cross-machine moisture profiles, or non-contact drying for paper coatings.

★ What is air impingement drying?

Ans: Air impingement drying involves blowing hot dry air onto a wet sheet.
Yankee dryer hood systems involve this type of drying, and air
impingement is also used in flotation dryers.

★ Why does a dryer "felt" look less like a felt and more like a regular
woven fabric?
Ans: Modern dryer felts are woven to be as porous as possible to allow
water vapor to escape. Felted materials do not allow enough air and water
vapor to pass through.

★ Are different styles of dryer felts used in the different dryer sections on
a paper or board machine?
Ans: Felts closer to the wet end, where the sheet is wetter and weaker, are
often more tightly woven in order to "pump less air" and prevent sheet
flutter and sheet breaks.

54
★ What is the purpose of a positioner?
Ans: The purpose of the positioner is to keep the auto-guide centered so
that it can make adjustments in both directions at all times.

★ Why is it important for the felt stretch roll to have a lot of "wrap"?
Ans: The high roll wrap ensures that the stretch roll movements serve only
to change the felt length, and do not affect fabric guiding.

★ Why are the bottom felts often missing in later dryer sections?
Ans: The sheet is mostly dry in later dryer sections, and the absence of a
bottom felt makes them somewhat self cleaning during threading and sheet
breaks.

★ What is a "unirun" felt run?

Ans: "Unirun" felts have a serpentine shape to support and transport the
sheet around all of the cans in a section, which is especially important for
the wetter, weaker sheet in early dryer sections.

★ Why are there two names: dryer felts and dryer fabrics?
Ans: They were originally called "dryer felts" because they were
constructed of wool and cotton, and more closely resembled felted fabrics.
Today, they are more often called "dryer fabrics" because faster machine
speeds require more permeable fabrics.

55
★ How are the dryer fabrics used in early dryer sections different from the
fabrics used in later dryer sections?
Ans: Generally speaking, dryer fabrics with lower permeabilities are used in
earlier felt sections to "pump less air" and improve stability and support for
the wetter, weaker sheet.

★ Why are surface characteristics important for dryer fabrics?

Ans: Surface characteristics are important because a rough surface can
mark the sheet. It can also carry along more "boundary layer air," which
can lead to sheet flutter and even sheet breaks.

★ Why are dryer fabrics heat set by the manufacturer before they are
delivered?
Ans: "Heat set" means that the fabrics are subjected to high temperatures
for a period of time. This improves their mechanical stability during use.

★ What is a "cascade steam system"?

Ans: In a cascade steam system, fresh steam is introduced to one of the
later steam groups, and the flash and blow-through steam from the
condensate tank is cascaded back through the previous steam groups, in
order.

56
★ Is a cascade steam system the only system that re-uses the flash and
blow-through steam from the steam groups?
Ans: No, thermo compressor steam systems also re-use the flash and blow-
through steam, except they re-use it within each group.

★ Why do cascade steam systems sometimes use condensers and vacuum

pumps?
Ans: Because there are several pressure drops as the steam cascades
through the groups, the condensate header for the wet end group is often
under vacuum. A condenser can be used to supply vacuum to this
condensate header. A vacuum pump is sometimes used to remove air and
other NCGs from the system.

★ How do cascade steam systems make control of the moisture at the reel
more difficult?
Ans: Fine steam pressure adjustments, such as those used for reel moisture
control, are difficult to achieve because a change to one pressure will cause
several other pressure changes.

57
★ How do cascade steam systems automatically account for the decrease
in drying rate that occurs as the sheet dries on a paper or board machine?
Ans: "Drying rate" is the rate at which water ca n be removed from the
sheet. In a cascade steam system, because the steam cascades from the dry
end to the wet end, steam pressures and temperatures automatically stair-
step upwards as the sheet dries. This naturally compensates for the
decrease in drying rate.

★ What is a steam group on a paper or board machine?

Ans: A steam group is a set of dryer cans that are supplied steam at a
controlled pressure from a single steam header, and typically discharge all
of their condensate to a single common condensate header.

★ What is a thermo-compressor?
Ans: A thermo-compressor is a device that uses high pressure "motive"
steam to pull in lower pressure steam in order to boost it to a more useful
steam pressure so it can be re-used.

★ How does a thermo-compressor like a valve?

Ans: Because the size of the nozzle opening can be changed by an actuator,
which changes the flow of motive steam and therefore the amount of
lower pressure steam that is pulled in, a thermo-compressor basically acts
like a valve.

58
★ Why is that thermo-compressor steam systems can respond more
quickly to production rate changes than cascade steam systems?
Ans: Thermo-compressor systems allow for independent control of the
steam pressures in the groups so the system response is faster.

★ How do thermo-compressor steam systems account for the decrease in

drying rate that occurs as the sheet dries on a paper or board machine?
Ans: Steam header pressures (and therefore temperatures) are often lower
toward the wet end and higher toward the dry end to compensate for the
decrease in drying rate.

★ What is the difference between "open" hoods and "closed" hoods?

Ans: Open hoods have walls and a roof, but are open at the operating level.
Closed hoods have movable walls at the operating level to fully enclosed
the dryers, and totally closed hoods are also enclosed at the basement level.

★ What are the advantages of closed hoods?

Ans: Lower exhaust air flows so exhaust fan requirements are lower and
heat recovery is possible. Also reduce building heating load because they
have dedicated supply air systems.

59
★ For a machine with closed hoods, should the supply air flow be equal to
the exhaust air flow?
Ans: Modern hoods should have 65% to 75% of the exhaust air flow
supplied as dry heated air. The remainder is supplied by infiltration around
the hood seals and doors to prevent hot humid air from escaping into the
machine room.

★ How can the heat that is recovered from hood exhaust air be used?
Ans: It can be used to preheat the hood supply air, heat process water, or
heat ventilation air to the building.

★ Can hood performance be evaluated somewhat easily?

Ans: Yes. Hood performance indicators include the hood supply air flow,
hood supply air temperature, and hood exhaust air humidity, which are all
measurable.

★ What is the purpose of surface sizing?

Ans: The purpose is to improve the sheet's resistance to the penetration of
fluids like ink, and improve certain sheet properties, such as surface
strength, internal bond, stiffness, and porosity.

60
★ Where is surface sizing usually applied to the sheet?
Ans: Traditionally, surface sizing is applied at a "size press" that is located
between drying sections, though it can also be applied at a calender stack.

★ How is cationic starch different from regular starch?

Ans: Cationic starch is starch that has been treated to produce cationically-
charged starch that better adheres to the anionically-charged fibers in the
sheet.

★ Where is surface sizing usually applied to the sheet?

Ans: It is the weight of surface size picked up by the sheet per unit area.
You must know the sheet weight before and after the size press in order to
calculate it.

★ Why do sheet breaks often occur at the size press?

Ans: Because the sheet is re-wetted at the size press, there is an increased
possibility of sheet breaks here, especially if there is a weak spot or hole in
the sheet.

61
  Dry End Equipment::::::::
★ How often should carrier ropes and rope runs be inspected?
Ans: The condition of the ropes and rope runs should be checked on all
levels every few hours.

★ What should be done during these regular inspections?

Ans: Remove broke or debris that is safe to remove during this check. Also
look for problems such as wobbling or slow moving sheaves, and listen for
squealing and clattering which could indicate bearing problems.

★ What is the safest technique for pulling loose tail from a rope run?
Ans: Pull tails from rope runs upstream at about a 45° angle. If your grip
on the tail is lost, this ensures that the ropes will pull the tail away from
you, not toward you. And don't grip the tail too tightly, as you may need to
release it quickly if it gets pulled in.

★ When preparing to replace a rope, why is it a good idea to leave the old
rope in place until the new rope is ready?
Ans: The new rope can be tied to the old rope, and the old rope can be
used to thread the new rope correctly through the rope run.

62
★ If a rope does break and come off the machine, what tools can be used
to help thread a new rope through the rope run?
Ans: A magnet, magnetic belt, or rubber hose can be used to thread the
rope around the dryer cans or from dryer felt nip to dryer felt nip.

★ What is a "dog leg" in a carrier rope system?

Ans: A "dog leg" release transfer refers to a rope transfer sheave setup that
facilitates the dropping of loose tails and broke after a transfer point during
threading. This improves threading and carrier rope life.

★ If a carrier rope needs to change direction on a sheave, how should the

sheave be set up?
Ans: The rope should enter the sheave square to the groove and exit on the
required angle. The straight-on entry angle helps keep wads and broke
from rolling the rope out of the sheave. The exit angle should be within the
groove profile to minimize rope abrasion on the sheave edges.

★ What is the most common cause of premature rope failures?

Ans: Poor sheave condition is the most common cause of premature rope
failures. Secondary grooves worn in the root of the sheave will abrade the
length of the rope, and especially hammer and wear the splice (which tends
to be slightly bigger around than the rope) as it passes through.

63
★ Why is rope tension reduced after threading?
Ans: Rope tension should be reduced after threading to allow the ropes to
recover from the higher threading tension and help them maintain their
natural elasticity. It also helps minimize rope wear by reducing the effects
of abrasion.

★ Why are carrier ropes sometimes coated or treated?

Ans: Size press and coater sections tend to use coated or treated rope to
combat the effects of the chemicals present in these sections.

★ How can ropes be used to thread a paper or board machine?

Ans: Carrier rope systems are comprised of multiple sections, each
containing 2 or 3 ropes which travel together along the sheet path. During
threading, a ""tail"" (a narrow section of the sheet) is pinched and carried
along between the ropes in each section.

★ How are carrier ropes driven?

Ans: They can be driven by the driven rolls or dryer cans in their section,
or by a separate rope drive in their return run.

64
★ Doesn't that take a lot of rope? What happens if you run out of rope?
Ans: Carrier ropes consist of endless loops which travel along the sheet
path with the tail through their section, and then separate and return to the
beginning of the section. On their return run, they are tensioned and
sometimes driven.

★ How is the tail transferred between rope sections?

Ans: Each rope section can be set up to release the tail directly into an
ingoing rope nip in the next rope section, or an auxiliary device (an air
shower or belt conveyor) can be used to transfer the tail.

★ Why is rope tension reduced after threading?

Ans: Reducing the rope tension after threading allows the ropes to recover
and maintain their elasticity.

★ What are the three main dangers associated with carrier rope systems?
Ans: A paper machine carrier rope system poses three major dangers above
and beyond those inherent to the paper machine: nip points, burns, and
rope breakage.

65
★ What is a nip point?
Ans: A nip point is created wherever a moving or rotating object contacts
another moving, rotating, or stationary object and creates a pinch point.
Nip points are places where clothing, tools, and body parts can be grabbed
and drawn into the machinery.

★ Where are nip points and pinch points located in carrier rope systems?
Ans: Rope systems introduce a number of new nip points, including rope -
to-rope nips, rope-to-sheave nips, rope-to-dryer can nips, and tensioner
sheave carriage nip points.

★ Why is it important to approach an area that contains carrier ropes

cautiously?
Ans: There is always a chance of rope breakage, and if a rope breaks, it can
easily get tangled in an adjacent rope and create a hazard. The fact that the
ropes move so quickly and have the power of the entire paper machine
behind them presents a considerable possibility for injury.

66
★ If you must cross under a rope, how should you proceed?
Ans: Stop before you cross and observe the rope run. Watch long enough
to see the entire length pass by and look for rope damage or an unusual
rope movement. Look in both directions to make sure that the rope is
properly moving through the sheaves. Listen for any unusual noises, like
squeaky sheave bearings, and the sheet break horn. If everything appears
normal, pass under the rope run quickly.

★ Why are multi-nip calender stacks with 3 or more rolls used on some
paper grades?
Ana: Multi-nip calender stacks are used in the production of smooth, high
gloss paper grades, like magazine paper.

★ What is a "queen roll"? What is a "king roll"?

Ans: In single-nip calender stacks, the top roll is called the "queen roll" and
the bottom roll is called the "king roll." In multi-nip stacks, the "king roll"
is at the bottom and the next roll up+G186 is often called the ""queen
roll.""

67
★ What adjustment can be made at the calender stack to "fix" soft edges
at the reel without changing the nip load?
Ans: Soft edges at the reel indicate low caliper at the edges. If one of the
calender rolls is a variable crown or controlled crown (CC) roll, increasing
the roll deflection will increase the caliper at both edges without changing
the overall nip load.

★ What if only one edge is soft?

Ans: If only one of the edges of the reel is soft, there are two options:
either decrease the load on that edge, or decrease the load on the other
edge AND decrease the roll deflection in the variable crown or controlled
crown (CC) roll.

★ What is "zone profiling"?

Ans: Zone profiling works by deforming one of the calender rolls (often
the king roll) to adjust the nip pressure at multiple cross-machine positions.
The localized nip pressure variation is achieved by increasing or decreasing
the diameter of the "zone-controlled roll." Hot or cold air and nozzles, or
induction heaters, can be used to heat or cool the zones and change the roll
diameter by zone.

68
★ Why is it called "wet stack" calendering?
Ans: In a wet stack, water is added to the sheet surface in one or more
nips. This added moisture improves the transfer of the smooth calender
roll surface to the surface of the sheet, so it enhances calendering results.

★ How is the water applied to the sheet on a wet calender stack?

Ans: "Water boxes" are positioned at one or more nips. They contain
heated water which contacts the sheet briefly to moisture only the sheet
surface, in order to concentrate the calendering action on the surface.

★ Can anything be added to the water that is used to moisten the sheet?
Ans: Dyes, lubricants, and binders like starch can be added to the water
going to the water boxes, if desired.

★ How are wet calender stacks loaded?

Ans: Stack loading is typically provided by the weight of the rolls, which
means that the nip loads increase from top to bottom. Jacking bolts or
compensators may be provided on the ends of the upper rolls to adjust
edge loads, if necessary.

69
★ Are variable crown rolls used in wet calender stacks?
Ans: To maintain uniform cross-machine nip pressure profiles in a wet
stack, the king roll and queen roll (if there is one) are either fixed crown or
variable crown rolls. Fixed crown rolls are designed for a single nip loading,
while variable crown rolls can be adjusted for different nip loadings.

★ What variables are typically measured by dry end QCS scanners?

Ans: Commonly measured variables include moisture, basis weight, and
caliper. Both machine direction and cross-machine direction results are
reported.

★ Can I work safely around a dry end QCS scanner that contains a
radioactive measuring device?
Ans: Even though they are shielded and emit only very low levels of
radiation, avoid working on or near the scanner heads for an extended
period of time in order to minimize your exposure risk. Only qualified
technicians should clean or work on the sensors and scanner heads.

★ Where are caliper adjustments made on the machine?

Ans: Caliper profile adjustments can be made at a calender stack, either by
changing a roll deflection or using a zone profiling system.

70
★ Are any of the profiled variables related to each other?
Ans: Typically, there are interactions between the profiled variables. For
example, if there is a high weight zone, that zone will mostly likely
experience high moisture. There may also be a caliper issue in that zone.

★ What are the benefits of flatter sheet profiles?

Ans: A dry end QCS scanner system can yield benefits in costs, sheet
quality, and machine productivity. Improved runnability is related to all of
these, and is perhaps its biggest benefit.

★ How is the parent reel speed controlled if it is not driven?

Ans: The building parent reel is held against and driven by the driven reel
drum, whose speed is matched to the rest of the paper or board machine.

★ What is ""double nip loading""?

Ans: "Double nip loading" occurs when both the primary arm hooks and
the secondary arms are in contact with the spool, after the primary arms
have set the spool on the rails and the secondary arms have loaded. A time-
delay pressure switch is typically used to keep the double loading to a
minimum.

71
★ Why are reel drums grooved?
Ans: Reel drums are often spiral grooved to allow the boundary layer air
traveling with the sheet to evacuate and allow the sheet to lay flat on the
drum.

★ How are reel spools started?

Ans: A driven rubber tire or belt accelerates the empty spool in the primary
arms up to, or just above, the current machine speed before the spool is
lowered to its turn-up position, on top of the reel drum.

★ Why are ""bubble"" turn-up systems only used on lower weight grades?
Ans: A bubble-type turn-up system uses a pocket of air blown in under t he
sheet just ahead of the reel to transfer the sheet to a new spool. The air
"bubble" is caught up in the reel drum/spool nip and the rotating spool
pulls and tears the sheet. This works better on lighter weight sheets, which
tear more easily.

★ Which web or webs are guided and spread on a paper or board

machine?
And: On paper and board machines, fabric loops require web guiding and
spreading to keep them running correctly, and the sheet requires guiding
and spreading at the dry end and winder to ensure the success of dry end
and winder operations.

72
★ I've heard that guide rolls must be ""in traction"" with the sheet in
order to properly guide the sheet. What does that mean?
Ans: "In traction" means that the sheet and guide roll surfaces are in
contact and moving at approximately the same speed.

★ What is the ""law of normal entry"" for webs?

Ans: This law states that a web will seek entry to a roll at 90 degrees to the
roll's axis at each point of contact. This is how a spreader roll's bow causes
the web to be directed outward, toward the roll ends, when it is set up with
its bow pointing downstream.

★ How should bowed spreader rolls be oriented?

Ans: Pointing the bow in the downstream direction utilizes the law of
normal entry and spreads the web outward, but bowed rolls are sometimes
rotated into or out of the web to compensate for a baggy center or slack
edges.

★ Where are dual spreading devices used?

Ans: Dual spreading devices are sometimes used after slitters to separate
the slits and then straighten their paths.

73
★ Why are there so many different coater designs?
Ans: The coater design used must take into account properties of the base
sheet, properties of the coating mixture, number of sides to be coated,
number of coats on each side, and the desired final coated sheet properties.

★ Why is some coating done on-machine and some off-machine?

Ans: There are advantages and disadvantages to each method. In general,
on-machine coating is better suited to light to moderate coating
applications with less stringent quality requirements. Most coaters can be
used either way.

★ Which type of coater is best at filling in low spots in the sheet to create
a smooth printing surface?
Ans: Because blades are quite rigid, blade coaters do a rather good job of
filling in low spots on the sheet, at the expense of the uniformity of the
coating layer thickness.

★ What is a ""contour coater""?

Ans: Air-knife and roll coaters are ""contour coaters"". This means that
they create a coating layer with a relatively even thickness that follows the
contour of the sheet surface.

74
★ Why are other types of dryer equipment, besides steam-heated dryer
cans, used to dry paper coatings?
Ans: Dryer cans dry by contacting the sheet. The coated side of the sheet
must be sufficiently dried before it contacts a dryer can to prevent sticking
or picking of coating on the dryer surface.

★ Why are some paper and board grades coated?

Ans: Paper and board grades can be coated to enhance printability, visual
properties (brightness, opacity, gloss), or functionality (ink holdout,
glueability) of the sheet.

★ What does a typical paper or board coating mixture contain?

Ans: Some coating mixtures contain 10 or more ingredients. A typical
print-grade coating formula might contain 83% pigment, 13% binder and
4% additives (by percent of dry weight). These ingredients are typically
dispersed in water.

★ What is the purpose of pigments in coating mixtures?

Ans: Pigments used in paper and board coatings govern the final optical
and printing properties of the sheet. They do this by providing brightness,
whiteness, smoothness, and opacity.

75
★ Why do some coating mixtures smell like latex paint?
Ans: Latex can be used as a binder in coating mixtures and also in latex
paints. Binders hold pigment particles to each other and to the sheet, help
fill voids between pigment particles, and influence the viscosity and water
retention of the solution.

★ Anti-foamers and defoamers can be used to control foam in coating

systems. What is the difference?
Ans: Anti-foamers prevent foam from forming, while defoamers help
eliminate foam after it has formed.

76
  Broke Systems:::::::
★ Why is it important to feed broke back into the system in a controlled
manner?
Ans: Broke behaves differently than virgin fiber - it holds less water, so
dries more easily. However, it can negatively affect sheet quality and
machine runnability, so the amount used needs to take into account all of
its effects.

★ Why is wet broke easier to repulp than dry broke?

Ans: Wet broke is more easily rewetted and repulped because its moisture
content is already much higher.

★ What are the differences between under-machine repulpers at the wet

end and dry end?
Ans: Dry end repulpers are usually of heavier duty construction so they can
handle larges labs of broke. They are usually larger to allow for the extra
retention time needed to properly slush dry broke.

★ How much broke storage should a paper or board machine be equipped

with?
Ans: Ideally, a broke storage system would be able to handle around 2
hours of full machine production, though in reality it is usually much less.

77
★ Why is it important to control consistency during repulping?
Ans: Repulpers are designed to create a vortex that draws broke down to
the rotor blade. If the consistency is too low, there will be excessive
turbulence, but if the consistency is too high, the suction effect of the
vortex will be weakened.

★ List some common sources of broke to off-machine broke repulpers.

Ans: Trim and waste from converting operations, loose dry broke, and
broke rolls that have been cut down by a guillotine.

★ What are the major components of an off-machine broke repulper?

Ans: A vat, one or two driven agitators or rotors, an extraction plate at
each rotor, one or more pumps, piping, and consistency and level controls.

★ How is broke typically fed to off-machine broke repulpers?

Ans: By blowers, fork trucks, and/or belt conveyors.

★ How is consistency typically controlled in an off-machine broke

repulper?
Ans: A consistency control loop utilizes a signal from a consistency
transmitter on a recirculating stock line to adjust dilution water flows to the
vat and pump suction in order to maintain the consistency at or near a set
point.

78
★ How is the vat level typically controlled in an off-machine broke
repulper?
Ans: A level transmitter on the vat sends a signal to a level controller which
controls an automatic makeup water valve position.

★ What is the purpose of under-machine repulpers?

Ans: To process the broke generated during the production of paper or
board so that the fibers and other valuable components of the sheet can be
reused.

★ Where are under-machine repulpers normally located?

Ans: Under the couch roll at the end of the forming section, under the
press section, under the reel, and sometimes under other major machine
sections and/or the winder.

★ What are the typical components of an under-machine repulper?

Ans: A vat, showers, one or more agitators, and one or more pumps.

★ What type of broke is collected in a couch pit?

Ans: Wet edge trim during normal production, and the full sheet during
start ups and sheet breaks.

79
★ What is the purpose of the ventilation/exhaust system on a reel
repulper?
Ans: To create a partial vacuum in the broke chute.

★ Why is it important to maintain broke storage chest levels in the 25 to

35% range during normal operations?
Ans: This helps ensure sufficient storage capacity during process upsets,
such as sheet breaks, threading, and start ups.

★ Why is broke often thickened so that it can be stored at a higher

consistency?
Ans: The removal of water on broke thickening equipment increases the
storage capacity of the broke chests.

★ Why is it important to control the level in repulper vats during slushing?

Ans: This allows the rotor to effectively circulate and slush the broke, using
the least amount of energy and minimizing repulping time.

★ Why are dry end repulpers typically of heavier construction than other
under-machine repulpers?
Ans: Dry end repulpers are normally of heavier construction because they
must often handle slabs from reels and cull rolls.

80
★ Why is it important for the seal pit liquid level to be kept above the
dropleg openings from a drum or disc thickener?
Ans: To make sure that the dropleg opening is not exposed to air, which
would cause the thickener to lose vacuum.

★ Why would you need both cleaners and screens? Don't they both
remove contaminants from broke?
Ans: Broke systems often use both high density cleaners and pressure
screens. HD cleaners remove heavy contaminants, while screens remove
large contaminants and help break up fiber flakes.

★ What are the process flows for a typical broke system?

Ans: Typically, broke is pumped from a broke storage chest to a high
density cleaner, through a deflaker, and on to a broke screening system,
before it is blended back in to the machine furnish.

★ Why is it important to control broke consistency?

Ans: Consistency swings can negatively affect the machine-direction weight
profile. Also, if the consistency is too high, this can cause pressure screens
to mat over and plug.

81
★ How does broke fiber differ from virgin fiber?
Ans: Broke fiber has already been screened, cleaned, refined, and perhaps
chemically treated or dried. Therefore, it does not hold water as well or
respond as well to refining.

★ Where is broke typically added back to the paper or board making

process?
Ans: Broke is typically reintroduced to the process at the blend chest or
machine chest in the thick stock system.

82
  Finishing:::::::
★ What are the TNTs of winding?
Ans: The structure of finished roll sets is largely dependent on three
winding variables - sheet tension, nip load, and winding torque. These are
often referred to as the TNTs of winding - Tension, Nip and Torque.

★ Why are there spreading devices both before and after the slitters on a
winder?
Ans: Spreading devices straighten the sheet before the slitters to ensure
good quality cuts and then keep the slit sections separate as they enter the
winding section. They help prevent the sheet from weaving back and forth
between adjacent rolls in the roll set.

★ Where is sheet tension controlled on a typical two-drum winder?

Ans: During winding, the sheet is tensioned by the driven drums in the
winding section and a mechanical brake or regenerative brake motor in the
unwind section. The braking force is used to control sheet tension.

83
★ What is the difference between wound-in-tension and residual tension?
Ans: Wound-in-tension is the amount of tension present in the sheet as it
is being wound. Once a roll set has been built, the wound-in-tension
converts to residual tension. Residual tension is usually positive in the
outermost layers of the roll, and negative or negligible in the center and
middle.

★ Why do winders run at such high speeds?

Ans: Because there is usually one winder per machine and a winder may
only run 50% of the time (due to parent reel changes, slitter adjustments,
maintenance, blade changes, and repairs), a winder must run at least twice
as fast as the paper machine in order to keep up with production.

★ Why are bottom slitters driven slightly faster than the sheet?
Ans: The over speed prevents buckling and bunching up of the sheet at the
entrance to the slitters.

★ There are several different slitting methods - water jet, razor,

score/crush, and shear. Which is the most common?
Ans: Shear slitting is the most common method used on paper and board
machine winders because it gives high quality cuts on a wide range of
grades at relatively high speeds.

84
★ Why is each bottom slitter driven instead of mounting all of the bottom
slitters on a driven carrier roll?
Ans: Because the carrier roll diameter must increase as the winder speed
and machine width increase, in order to control vibrations, individual
motor slitters have become more popular.

★ They are often referred to as ""knives,"" but only the top slitters look
sharp. How do most slitters cut the sheet?
Ans: On most winders, the top slitters are sharp circular blades and the
bottom slitters are bands. The top blade slightly overlaps the bottom band
and is loaded from the side to cut the sheet using a shearing action, like
scissors.

★ When roll sizes change, how are the slitters repositioned?

Ans: Slitters can be repositioned manually or automatically. Manual
positioning exposes workers to hazards and takes longer, so is more
appropriate when slit widths don't change very often.

★ Why must winders run so much faster than paper and board machines?
Ans: Because they must stop occasionally to load new reels, eject finished
roll sets, reposition slitters, and change blades, winders must run much
faster in order to keep up with the machine's production.

85
★ How can workers be protected from the fall hazard presented by broke
holes (openings in the floor)?
Ans: Guards and/or covers on broke holes should be interlocked with light
curtains or safety gates, and current fall protection guidelines must be
followed when working around unguarded broke holes.

★ What kinds of hazards are presented by the hydraulic systems used by

many winders and rewinders?
Ans: Hydraulic fluid is pressurized and is heated during operation. If a
fitting or coupling were to come loose, the fluid would present burn, fluid
injection, and fire hazards, as well as the hazards presented by any flailing
lines or hoses.

★ What is recommended or required for platforms and catwalks around

winders?
Ans: All walking surfaces should be slip-resistant, and elevated surfaces
should be equipped with top rails, mid-rails, and toe boards.

★ Do winders and rewinders have any cutting hazards?

Ans: The slitters and set change device (a cut off knife or guillotine) both
present nip point and cutting hazards to operators.

86
★ Why are rolls wrapped?
Ans: Rolls are wrapped to protect them from physical damage, moisture,
and foreign debris during handling transport and storage.

★ What materials are used to wrap rolls?

Ans: Paper rolls are usually wrapped with unbleached craft paper. The craft
paper can be coated and sometimes a clear film is applied in conjunction
with craft paper.

★ What are headers?

Ans: Headers are paper or board discs that are placed on the ends of the
rolls for protection.

★ What is an upender?
Ans: An upender takes a roll from its side and stands it on end so a clamp
truck can pick it up.

★ How are rolls secured to prevent damage during transport?

Ans: Roll damage during transport can be prevented by following the
correct loading pattern and securing the rolls with air-filled bags,
honeycomb and contoured void fillers, risers, and non-metallic strapping.

87
★ How is market pulp made?
Ans: A thick pulp web is formed and pressed using equipment similar to a
paper machine. Usually, the pulp sheet is dried in an airborne dryer. After
the pulp is dried, it is cut in to sheets. The sheets are collected into bales
which are compressed, wrapped, and strapped.

★ What is an airborne dryer?

Ans: An airborne dryer is a large enclosed structure. The pulp web enters
the top of the enclosure and makes several horizontal passes around
unheated rolls. Fans force air through blow boxes and onto the pulp web.
The air removes water and carries it away from the pulp web.

★ What are blow boxes?

Ans: Blow boxes are air headers that direct air onto the pulp sheet. The
pulp web travels between upper and lower blow boxes. The lower boxes
blow air to help hold the sheet above the box.

★ How is the pulp web cut into sheets?

Ans: The pulp web is cut lengthwise by slitters. Then a rotary cutter cuts
the sheet width-wise.
★ How are the bales wrapped?
Ans: Two larger sheets of pulp are folded around the stack of cut pulp
sheets and secured with either wires or straps.

88
  Paper Machine Auxiliary Systems:::::::
★ What is the purpose of the showers at the wet end of a paper machine?
Ans: Showers keep the wet end fabrics clean and open, provide lubrication
between moving and stationary elements, and prevent stock buildup and
deposits on surfaces.

★ How much water should be used in a flooding shower?

Ans: For optimal results, the shower flow should exceed the void volume
of the fabric, which can be provided to you by the fabric supplier.

★ Where are high pressure showers used on the wet end?

Ans: High pressure showers are typically installed on the wire run and on
the sheet-contacting surface of each wet felt, and often on grooved and
drilled roll covers.

★ Why are high pressure showers oscillated in the cross-machine

direction?
Ans: To provide uniform coverage and prevent damage to the fabrics and
roll covers.

★ When are flushing showers in suction rolls used?

Ans: High volume flushing showers are used to flush out the openings in
suction roll shells when the sheet is off.

89
★ What is a line shaft drive system?
Ans: A line shaft system uses one prime mover to power the whole
machine instead of a different one for each section.

★ What is draw?
Ans: Draw is the speed difference between two adjacent sections of the
paper machine.

★ What are the types of line shaft drives?

Ans: There are two main types of line shaft drives: cone pulley drives and
non-pulley direct drives. In both types, power is transmitted the length of
the machine by a line shaft running parallel to the machine.

★ What is a helper drive?

Ans: Helper drives are electric motors installed on some parts of the
machine to supply auxiliary driving energy.

★ How are line shaft drives started up?

Ans: First, the line shaft drive is accelerated with all the machine sections
unclutched or disconnected. Then, one by one, each section is accelerated
up to speed by engaging or closing the section clutch.

90
★ What is draw?
Ans: Draw is the speed difference between the sections of a paper machine
and is usually expressed as a percentage.

★ How do DC drives work?

Ans: DC drives control the speed of the motor by varying the voltage. A
DC motor's speed varies proportionally with the applied voltage.

★ How do AC drives work?

Ans: AC drives control the speed of the motor by changing the frequency
supplied to the motor. The motor speed is directly proportional frequency.

★ What are common sectional controls?

Ans: Each section of the machine usually has run, stop, jog, crawl or slow,
slack take-up, and draw controls.

★ What is a regenerative drive?

Ans: Under braking conditions, regenerative drives convert mechanical
energy of the motor and connected load into electrical energy.

91
★ What are some hazards of hydraulic systems?
Ans: Hydraulic fluid is highly pressurized and becomes very hot during
operation, which can cause burns or start fires. Hydraulic systems should
be de-pressurized and isolated prior to any work. Also, pinhole leaks can
inject hydraulic fluid under the skin, which can be very serious.

★ What are the components of a hydraulic system?

Ans: Each system consists of a hydraulic power unit (tank with one or
more pumps), filtration equipment, heat exchanger, distribution and return
piping, various valves, actuators, and instruments and controls.

★ What type of pump is used to pump hydraulic fluid?

Ans: Positive displacement pumps are typically used because they move the
same volume of fluid with each revolution and the flow volume is relatively
unaffected by the discharge pressure.

★ What analysis can be performed to determine if the hydraulic fluid is

suitable for use?
Ans: Fluids can be analyzed for dirt content, water content, oxidation, and
particulate levels.

92
★ What is the purpose of an accumulator?
Ans: Accumulators can be used to maintain hydraulic pressures for short
periods of time, dampen pressure pulses in fluid flow, and to allow
equipment to slowly return to a lower energy state if hydraulic pressure is
lost.

★ How is vacuum used in the forming section of a paper or board

machine?
Ans: In the forming section, vacuum is used at vacuum foil boxes and flat
boxes to remove water from the stock.

★ Why are vacuum levels usually stair-stepped (gradually increased) in the

forming section?
Ans: Vacuum is increased because the water becomes harder and harder to
remove as the sheet forms, and also to prevent the sheet from sealing early
on, which makes it harder to remove the remaining water.

★ Where is vacuum used in the press section of a paper or board

machine?
Ans: In uhle boxes to remove water and debris from the press felts, and in
suction rolls for multiple reasons, including sheet transfer, pulling in steam,
and preventing sheet flutter.

93
★ What devices are used to produce vacuum on paper and board
machines?
Ans: Liquid-ring vacuum pumps, centrifugal blowers, and steam ejectors.

★ How do bleed valves work in vacuum systems?

Ans: Bleed valves work by letting in air to reduce the vacuum level (or
increase the pressure). They are opened to lower vacuum levels and closed
to increase vacuum levels.

★ Why does water boil at lower temperatures at higher elevations?

Ans: The phase of water (solid, liquid, or gas) is determined by its
temperature and pressure. Atmospheric pressures are lower at higher
elevations, and liquid water boils at lower temperatures at lower pressures.

★ What is condensate?
Ans: When water molecules in steam contact a cool surface, they lose
energy to that surface and change into a liquid. The resulting liquid water is
called "condensate."

★ What is superheated steam?

Ans: Superheated steam is steam that has been heated above its boiling
point for the current pressure.

94
★ How can superheated steam cause problems with the rotary joints on
dryer cans?
Ans: The moisture in saturated steam lubricates the carbon rings in the
rotary joints. Without this lubrication, the rings will wear more rapidly and
could even crack if they get too hot.

★ Why is it important to collect and reuse the condensate from a paper or

board machine?
Ans: The condensate still contains heat, which is valuable because it lowers
the amount of heat needed to produce additional steam.

★ How is the seal water used in liquid-ring vacuum pumps?

Ans: It seals in the pumping chambers and it also cools the incoming air.

★ Why is it important for vacuum pump seal water to be cool?

Ans: It helps cool the incoming air, which increases its density and the
vacuum level produced. It also helps avoid vaporization inside the pumps,
which would reduce capacity and efficiency.

★ How is vacuum used on a paper machine?

Ans: To help dewater the stock in the forming section, to dewater and
clean the felts in the press section, and to help transfer the sheet between
sections.

95
★ What is the difference between a centrifugal fan and a centrifugal
blower?
Ans: The American Society of Mechanical Engineers uses the "specific
ratio" - the ratio of discharge pressure over suction pressure. Fans have a
specific ratio up to 1.11, while blowers have specifications of 1.11 to 1.20.

★ Is a thermo-compressor a type of steam ejector?

Ans: Yes. A thermo-compressor is a steam ejector whose purpose is to
recover the latent heat content of low pressure steam.

★ What advantages do grease lubricants have over lubricating oils?

Ans: Grease lubricants offer some advantages over oils: they adhere better
to metal surfaces, do not easily leak out, protect against corrosion, and
provide some sealing action

★ Are there any disadvantages to using a grease lubricant instead of a

lubricating oil?
Ans: Greases do not remove heat or debris away from equipment, like the
lube oil in a circulating lube oil system can.

96
★ What kinds of chemical additives are used in lubricating oils?
Ans: Lube oils can contain preservatives and performance-enhancing
additives, such as viscosity modifiers, corrosion inhibitors, detergents, and
extreme pressure additives, to name a few.

★ What can be determined by the lab analysis of lube oil?

Ans: A typical analysis will determine the dirt content, water content, wear
metals present, and level of oxidation of lube oil.

★ How can the lube oil flows to a paper or board machine be monitored?
Ans: Optical devices like sight glasses and rotameters require regular
observation by operations to confirm flows, while digital flow meters can
send the flow information to computer control systems.

97
  Chemical Additives::::::
★ What is "wet end chemistry"?
Ans: "Wet end chemistry" involves the chemistry of and chemical
interactions between the components of a paper making furnish. The
furnish contains whole fibers, fiber fines, and chemical additives in a large
amount of water.

★ What are "colloids"?

Ans: "Colloids" are particles that do not easily settle out of a solution under
the influence of gravity. They have very small particle sizes and very large
surface areas, and tend to carry electrical charge on their surfaces from the
presence of anionic (negatively charged) and cationic (positively charged)
groups.

★ What are "anionic trash" and "cationic demand"?

Ans: The furnish coming to a paper machine typically contains some
negatively-charged materials that are collectively called "anionic trash" or
"cationic demand". These colloidal and dissolved materials can build up in
the recirculating water loops and preferentially adhere to cationically-
charged additives, reducing the effectiveness of the additives. They can also
play a role in deposit formation, spots and defects in the sheet, and reduced
sheet strength properties.

98
★ Where does "anionic trash" come from?
Ans: Anionic trash can include wood components that are dissolved or
dispersed during the pulping and bleaching processes, plus defoamer, talc,
and other residual chemicals from these processes. It can also be generated
from pulp fibers during refining and storage, or enter with the fresh water,
chemical additives, broke fiber, or recycled fiber inputs.

★ Why is pH important?
Ans: Consistent pH is crucial to steady paper machine operation because
pH indicates the level of ions, and ions can interfere with colloidal surface
charge interactions. Among other things, pH affects chemical additive
efficiencies, pulp refining, water removal on the former, and dryer coating
characteristics.

★ How do paper making process additives differ from functional paper

making additives?
Ans: Process additives affect process operations on or near the machine,
while functional additives directly improve properties of the sheet.

★ Where does "anionic trash" come from?

Ans: Anionic trash can enter the paper making process in several ways. It
can enter with the incoming fresh water, broke pulp, or purchased pulp, or
with virgin slush pulp as residuals from pulping or bleaching operations.

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★ Why is good retention important?
Ans: Improved retention decreases the fines concentration in the white
water, improves drainage, decreases press felt filling, reduces sheet two-
sidedness, improves additive efficiencies, and improves overall machine
cleanliness.

★ What is the best pitch control additive for my machine?

Ans: In acid systems, alum can be used to attach pitch to fibers. In alkaline
systems, dispersants can be used to prevent pitch from precipitating, or
fillers can precipitate the pitch onto the furnish. Lowering calcium and
magnesium levels, or adding chelating agents, can also help. The best
approach must often be determined by trial and error.

★ What is the difference between a defoamer and an anti-foamer?

Ans: A defoamer works by breaking down the foam, while an anti -foamer
prevents the foam from forming.

★ Most chemical additives are delivered as ""aqueous"" solutions. What

does that mean?
Ans: The chemical is dissolved or dispersed in water, and delivered as a
liquid in a tote or tanker truck.

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★ What is the difference between the two main types of additives -
functional and process?
Ans: Functional additives are added to impart or enhance a property of the
sheet, while process additives are added to improve operations or the
runability of the paper machine.

★ What are the different ways that the dry strength of a sheet can be
improved?
Ans: In general, dry strength can be increased by using longer fibers, less
filler, more wet pressing (higher nip pressures or longer dwell times), or
more refining. It can also be improved by the addition of dry strength
additives.

★ How do wet strength additives work?

Ans: When paper gets wet, the fiber-to -fiber bonds are replaced by water-
fiber bonds and the sheet falls apart. Wet strength additives work by
creating additional water-resistant bonds between the fibers.

★ What kinds of additives are used to change the color of a sheet?

Ans: Acid dyes, direct dyes, basic dyes, and colored pigments can all be
used to change the color of a sheet of paper or board.

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★ How is starch used in the production of paper and board?
Ans: Starch can be used as an internal sizing, dry strength, or surface sizing
additive, as a binder in coating formulas, or as an adhesive in corrugated
board.

★ What four things are required to cook starch and prepare it for use at a
mill?
Ans: Water, time, temperature and agitation.

★ Describe how starch can be cooked using a batch process.

Ans: Steam is used to heat a starch-water slurry in an agitated tank for at
least 20 minutes at 200 to 210 degrees F.

★ Describe how the continuous jet cooking process can be used to cook
starch.
Ans: Steam is injected into a starch-water slurry as it travels through a
mixing device and the temperature is usually around 250 degrees F.

★ How can the cooking method affect the viscosity (or flow resistance) of
the starch solution?
Ans: When more thermal or mechanical energy is put into the starch
cooking, the starch molecules will be less entangled and so the viscosity will
be lower (it will flow more easily).

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  Paper Properties and Testing::::::::
★ What is consistency?
Ans: Consistency is the weight percentage of dry fiber in a mixture of fiber
and water.

★ What is first pass retention?

Ans: First pass retention represents the percentage of the solids delivered
to the former that are retained in the sheet and is an indication of how well
fines are retained.

★ What is freeness?
Ans: Freeness measure the drainage rate of water from a dilute pulp
suspension. The faster the water drains, the higher the freeness.

★ Why is charge demand important?

Ans: Anionic trash or cationic demand is important to measure because
undesirable dissolved materials in the paper machine white water reduce
the effectiveness of additives and can cause runability problems.

★ Why is pH control important?

Ans: pH affects chemical additive efficiency and retention, refining,
retention, drainage, and formation.

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★ Which standardized test methods are most commonly used in the U.S.?
Ans: The standards managed by the Technical Association of the Pulp and
Paper Industry (TAPPI) are most common.

★ What is basis weight?

Ans: Basis weight refers to the weight in pounds of a ream of paper, where
a ream is defined as 500 base size sheets. Different grades have different
base sizes so basis weight cannot be directly compared across grades.
Grammage (grams per square meter) is another way to express the weight
per area, and values can be directly compared.

★ What is caliper?
Ans: Caliper is the thickness measurement of paper or board.

★ How is smoothness measured?

Ans: There are many different ways to measure smoothness (optical,
friction, profile measurements, ink contact area) but air flow measurements
are must commonly used.

★ Why is porosity measured?

Ans: Porosity determines the ability of a sheet to absorb ink or water,
protect certain products, or act as a filter.

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★ What are the main benefits of improving the uniformity of CD profiles?
Ans: The two potential benefits of improved CD profiles are reduced cost
and improved runnability.

★ Why are QCS scanners often installed ahead of size presses?

Ans: Sheet moisture is often monitored before a size press because
moisture greatly affects the sheet's ability to absorb the sizing solution.

★ Are QCS scanners installed around coating operations?

Ans: Sheet weight is often measured before and after coating operations in
order to monitor the applied coat weight and coating uniformity.

★ Are profiling systems ever installed in dryer sections?

Ans: Rewet showers are sometimes installed in dryer sections to flatten the
CD moisture profile at the reel.

★ Why are some profiling adjustments made manually?

Ans: Manual profiling adjustments might be made if a system has a limited
number of cross-machine zones or if automatic actuators are not available.

★ How does light interact with a paper surface?

Ans: The incident light can be reflected, transmitted, scattered, or
absorbed.

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★ What are common optical tests for paper?
Ans: Common optical tests include brightness, opacity, gloss, and color
and formation.

★ What is brightness and how is it tested?

Ans: Brightness is the visual impression of scattered light from the sheet
surface. It is tested using blue light with a wavelength of 457 nanometers.

★ What is gloss?
Ans: Gloss measures the amount of light reflected from the sheet surface
at an angle equal to the incident light.

★ What is formation?
Ans: Formation is an optical test that measures the uniformity of the sheet
structure and orientation of fibers. Poor basis weight uniformity, thick and
thin spots, equals poor formation.

★ Why is sample conditioning important?

Ans: Water interferes with fiber bonding so the moisture content of the
sheet affects many paper properties, especially strength properties.
Temperature also affects results because air can hold different amounts of
water vapor at different temperatures.

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★ What factors can impact strength properties?
Ans: Paper strength depends on the strength and arrangement of individual
fibers, the number and distribution of fiber-to-fiber bonds, and additives.
Fiber strength can be affected by pulping, bleaching, and refining and
bonding can be impacted by refining and wet pressing.

★ Why is it important to keep track of the machine direction for a sample?

Ans: MD and CD strength properties can be significantly different. Many
grades have specific requirements. For example a high MD strength might
be required for converting.

★ What are the major strength tests?

Ans: The most common tests are tensile, burst, stiffness, tear, internal
bond, and ring crush.

★ What is zero-span tensile?

Ans: Zero-span tensile is a modification of the tensile test that eliminates
the gap between clamps. Zero-span tries to measure the fiber strength
instead of the sheet strength and is considered the maximum tensile
strength of the sheet.

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  Storage and Shipping:::::
★ What is the purpose of ware housing product?
Ans: Ware houses provide space to sort and store product prior to it being
shipped to a customer.

★ When in the storage and shipping process are labels applied?

Ans: Labels are applied to product as it is received in a ware house so that
it can be tracked during storage and shipping.

★ What does FIFO stand for and how does it apply to ware housing?
Ans: FIFO stands for First In First Out and refers to a common method
for storing and retrieving products in the order that they were received.

★ What should be listed on a bill of lading?

Ans: The bill of lading applies to a truck or railcar and should include the
date and location of loading, the products loaded, the carrier name and the
destination of the load.

★ What are hot loaded rolls?

Ans: "Hot loaded" refers to rolls which are not stored, but shipped
immediately after production.

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★ What type of label is commonly used to automate tracking of rolls?
Ans: Tracking labels applied to rolls usually include a printed barcode with
a universal product code number that can be read by a laser scanner and
perhaps an RFID tag.

★ How is roll damage prevented when handling paper rolls?

Ans: Damage can be minimized by wrapping the roll with a protective
outer layer, selecting and maintaining the right equipment, following
standard handling procedures, and by avoiding any unnecessary handling of
rolls.

★ How is the proper roll clamp truck selected?

Ans: The proper equipment depends on the roll weight, width, and
diameter, the paper type, and handling and storage requirements.

★ What is the clamp force factor?

Ans: The clamp force factor (CFF ) is used to determine how much force
can be applied to a roll without causing damage. It is the ratio of the
clamping force to the weight of the roll. The CFF varies by paper grade.

★ What are common roll damage categories?

Ans: Most damage falls into the following 4 categories: structural (e.g. out
of round), end, edge, and belly damage.

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★ How can out of round rolls be prevented?
Ans: From an equipment stand point you should ensure the clamps pads
are in good condition and the appropriate clamping force is applied.

★ What are two important safety procedures to complete before starting

to load a commercial truck trailer?
Ans: Before loading, truck and trailer wheels should be chocked and the
ICC bar of the trailer should be secured to the dock.

★ In terms of weight, what is the goal when loading a commercial truck

trailer?
Ans: The goal is to maximize the loaded weight in the trailer without
exceeding the safe and legal limits for the individual axle loads and the
overall truck and trailer weight.

★ What are some of the items used to secure rolls in trailer and keep them
from moving?
Ans: Some of the equipment used to secure rolls in trailer include blocking,
bracing, friction mats and strapping.

★ What method of securement is mandatory for a split load?

Ans: When groups of rolls are separated, they must be held together by
strapping.

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★ What happens if a truck trailer is overweight?
Ans: A loaded trailer which is overweight must be unloaded and reloaded
in such a manner that is under the legal and safe weight limit.

★ What should you be looking for when inspecting a railcar before loading
it?
Ans: Railcars should be checked for sturdy, clean, dry, hole-free flooring.
The floors and walls should also not have any nails, bolts or protrusions
which might damage loaded rolls.

★ What are common types of dunnage?

Ans: Dunnage includes corrugated fillers, risers, rubber mats, tapered roll
wedges and inflatable air bags.

★ What are common railcar sizes?

Ans: The railcars typically used by paper mills are either 50 or 60 foot long,
high cube or standard box.

★ What is T-loading?
Ans: T-loading is the term used for placing a roll on its side, or "bilge
position", on top of the rolls set on the floor of the railcar.

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★ What is a dock plate?
Ans: Dock plates are reinforced steel plates used to span the gap between
the dock and railcar to support loading clamp trucks.

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