Sheet Forming and
Formers
Jim Atkins
Atkins, Inc.
TAPPI Paper Machine Operations Course
Water Removal
Most water removal occurs in the
Forming Section forming section. Since fibers are
5,947 gpm hydrophilic, water removal gets
increasingly difficult.
Press Section
124 gpm
Dryer Section
72 gpm
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Types of Formers
Fourdrinier
Hybrid or Top Wire
Twin Wire or Gap
Twinwire or Gap
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Board & Packaging – MultiPly Formers
Two ply using
secondary headbox
2
Two ply using mini
top fourdrinier
Three ply using
multiple fourdriniers
2
2
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Fourdrinier Terminology
Typical forming table layout
Breast roll
Forming board
Foil boxes
Low vacuum boxes
Flatboxes or high vacuum boxes
Couch roll
Wire turning roll
Wire return rolls (including guide and stretch rolls)
TAPPI Paper Machine Operations Course
Fourdrinier Basic Functions
Forms and consolidates the fibers into a web
Increase consistency of the sheet from <1% at the
slice to 20-25% at the couch.
Retain the fiber and filler – typically around 85%
first pass retention.
Provide the best Z-direction uniformity possible –
one of the limitations for fourdrinier machines.
Transfer the sheet into the presses.
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The Problem of Flocculation
Most papers formed at
less than 0.7%.
Fibers like to form
networks call flocs.
Flocs result in lumpy
paper, poor formation.
TAPPI Paper Machine Operations Course
Forming Process
Forming is a combination of three hydro-dynamic
processes:
Drainage Oriented Shear Turbulence
Each occurs simultaneously and can be controlled within limits by
the papermaker.
It is the control of these processes that will ultimately determine
the characteristics of the paper produced.
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Forming Process
Drainage
TAPPI Paper Machine Operations Course
Forming Process
Drainage
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Controlling Slice Flow
The way the jet hits on
the forming wire
controls initial fiber mat
formation.
Retention of fines and
filler depend on good
mat formation.
TAPPI Paper Machine Operations Course
Controlling Slice Flow
L = bottom lip extension
b = slice opening
L/b ratio.
L/b determines jet
angle.
Velocity forming vs.
pressure forming.
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Pressure forming vs.
Velocity Forming
TAPPI Paper Machine Operations Course
Shear at slice impingement
The speed of the jet leaving
the headbox can be faster or
slower than the forming
fabric
This creates shear on the
bottom side of the jet
This speed difference is
called rush/drag or jet-to-
wire
It can stated as a speed ratio
or as the exact speed
difference in fpm
Point of shear
TAPPI Paper Machine Operations Course
Forming Process
Turbulence
Turbulence is
added to the
forming zone to
minimize floc
formation
Turbulence doesn’t
last.
Smaller the scale,
faster it dissipates.
Must constantly be
added
TAPPI Paper Machine Operations Course
Forming Board
First drainage
element on the
former
First blade is wider
and has a rugged
mount system
Blades are flat
(usually)
Gap should open up
as the front wall
follows down the
breast roll
TAPPI Paper Machine Operations Course
Forming Board
Supports the
forming fabric
Catches the
headbox jet
Must be very rigid to
avoid deflection and
vibration under load
Usually fix mounted Weavexx Adjustable FB
but some models
can be moved on
the run
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Forming
Two examples of jet delivery over the forming board
Case 1 Case 2
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Foil Unit
Blade angles are fixed. Must be removed
to change the angle and stock activity.
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Gravity Foils - Concept
Machine Direction
Slurry Activity
Mat
Forming Wire
Suspended Layer
Foil Blade
Dewatering
Positive
Foil Pressure Profile
0
Negative
TAPPI Paper Machine Operations Course 20
Blade Spacing
Pulse Profile
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Relationship Between Foil
Spacing And Pulse Frequency
Frequency (Hz) = Fabric Speed (mpm)
.06 X Blade Spacing (mm)
<30 Hz Difficult to agitate stock
30-40 Historical design standard
80-100 Hz Present design standard
100 Hz Maximum possible for fourdrinier
150+ Hz Gap or top-wire formers
TAPPI Paper Machine Operations Course
Operation of Foils
Foil blade angles and widths are variables used
to develop controlled activity.
Maximum foil angle of 3 degrees for slow
machines and typically 0.5-1.0 degrees on fast
machines.
Experience and trial and error is used to find the
right set up
Goal is fine scale turbulence and controlled
drainage
Long fiber furnish is more difficult to agitate
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Examples of Activity Level
MD
Low
Transition High
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Foil box activity
Initiate Activity Maintain Activity
Note the two different types of blade construction
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Moveable Angle Foil Units
IBS Hydroline foil units with adjustable
angles and height.
TAPPI Paper Machine Operations Course
Low Vacuum Boxes
Bottom discharge Lovac
• high flow capacity
• low P potential
• require pan depth or modification
to w/w tray for leg height
End discharge Lovac
• low flow capacity
• high P potential
• can fit in shallow pan area
• require space on back side
of machine for drop leg
TAPPI Paper Machine Operations Course
Low Vacuum Boxes
Lovacs take over at 2-3%
consistency.
Lower drag and energy
than high vacs.
Capable of up to 10%
consistency (6% more
common).
Use blower for vacuum
needs-- 5-50” water. Bottom discharge
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Low Vacuum Boxes
Low vacs should be Vacuum Blower
connected to a separate
vacuum blower.
Each box needs a
separator.
Special control valves
designed for low
Vacuum
vacuum operation are
Header for
normally used Low Vacs
Alternately a hand valve Separator w/
can be used on the box Drop Leg
to bleed air into the box
reducing the vacuum
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Low Vac Operating Limits
Lovac Body Forming fabric
Wire to
vacuum inlet Vac
In
Wire to overflow
Maximum
Allowable Drop
Vacuum Leg
Seal Pot
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Low Vac Operating Limits
Vacuum exceeds
maximum allowable
TAPPI Paper Machine Operations Course
Pulsative Drainage Units
Controlled activity without sealing the
sheet.
Early attempts with lovacs after the
forming board unsuccessful.
Two types of pulsative drainage units
broken plane
step foils
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Broken Plane Unit
TAPPI Paper Machine Operations Course
Step Foil Unit
TAPPI Paper Machine Operations Course
Moveable Element Lovac Units
IBS Varioline flovac units with height
adjustable t-bars and control blades.
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Flatbox (Hivac) Operation
Take over from lovacs
Vacuum levels of 5-50
kPa (1.5-15”Hg)
Consistency of 14-19%
before couch
High drag load so want
to minimize the number
of boxes
High quality ceramic
covers a must on high
speed machines
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Flatbox (Hivac) Operation
TAPPI Paper Machine Operations Course
Couch
Vacuum of 15-25” Hg
Takes the sheet from 16% consistency up to 22-24%.
Consolidates the sheet.
Shower water 1.6 gpm/100”
Rewetting
outgoing side past deflector
incoming side past the wipe
Double doctors result in drier sheet to presses
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Couch Rewet
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Double Doctor On Couch
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Forming Drainage Elements
Couch Roll Setup
Full Width Correct Setting,
Sheet Rewetting Packing Strips Throw-Off goes in
Saveall
Hi Lo
Vacuum Box Vacuum Box
Saveall
Saveall
Couch Roll Adjustment
Deckle
Worn Gear
Adjusters
Adjuster
Couch Roll Vacuum Box Adjustment
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Forming
Example of Good Couch Throw-off
TAPPI Paper Machine Operations Course
Sheet Forming and
Formers
Jim Atkins
Atkins, Inc.
TAPPI Paper Machine Operations Course
