The wood composition boards
Fiberboard (纖維板)
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Fiberboards Fiberboards
The term fiberboard includes hardboard,
hardboard medium-
medium- To make fibers for composites, bonds between
density fiberboard (MDF),
(MDF) and insulation board.
board the wood fibers must be broken.
Several things differentiate fiberboard from In its simplest form, this is accomplished by attrition
particleboard, most notably the physical milling (refiner).
configuration of the comminuted material.
Fibers can be made from
many lignocellulosics and
form the raw materials for
many composites, most
notably fiberboard. Fibers
are typically produced by
the refining process.
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Fiberboards Fiberboards
Attrition milling, or refining as it is commonly called,
can be augmented by water soaking, soaking steam
cooking,
cooking or chemical treatments.
treatments
Steaming the lignocellulosic weakens the lignin
bonds between the cellulosic fibers.
As a result, the fibers are more readily separated
and usually are less damaged than fibers
processed by dry processing methods.
Chemical treatments, usually alkali, are also used
to weaken the lignin bonds.
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Fiberboards Fiberboards
All of these treatments help increase fiber quality
and reduce energy requirements, but they may Single-
Single-revolving-
revolving-
reduce yield as well. disk mill
Refiners are available with single- or double-
rotating disks, as well as steam-pressurized and
unpressurized configurations.
Two types of pressurized refiners are being used
and they shall be differentiated here as the single-
single-
and double- Double-
Double-revolving-
revolving-
double-revolving disc which is the same
classification as used to identify the atmospheric disk mill
refiner.
For MDF,
MDF steam-pressurized refining is typical.
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Fiberboards Fiberboards
Pressurized refiner (Single-
(Single-revolving-
revolving-disk) Pressurized refiner (Single-
(Single-revolving-
revolving-disk)
0.55-
0.55-1.05 MPa
(160-185oC)
(160-
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Fiberboards Fiberboards
Pressurized refiner (Double-
(Double-revolving-
revolving-disk) Pressurized refiner (Double-
(Double-revolving-
revolving-disk)
Up to 1.05 MPa
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Fiberboards Fiberboards
Pressurized refiner (Double-
(Double-revolving-
revolving-disk)
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Fiberboards Fiberboards
Dry-
Dry-process fiberboard
Fiberboard is normally classified by density and
can be made by either dry or wet processes.
processes
Dry processes are applicable to boards with
high density (hardboard) and medium density
(MDF).
(MDF)
Wet processes are applicable to both
high-
high-density hardboard and low-
low-density insulation
board.
board
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Fiberboards Fiberboards
Dry-
Dry-process fiberboard Dry-
Dry-process fiberboard
Dry-process fiberboard is made in a similar fashion Short-
Short-retention time blender
to particleboard.
Blow-
Blow-line blending (This system is used in dry-
dry-process fiberboard
Resin (UF, PF) and other additives may be plants)
Attrition-
Attrition-mill blender
applied to the fibers by spraying in short-
retention blenders
introduced as the wet fibers are fed from
the refiner into a blow line dryer
add the resin in the refiner
The adhesive-coated fibers are then air-laid into a
mat for subsequent pressing, much the same as
mat formation for particleboard.
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Fiberboards Fiberboards
Dry-
Dry-process fiberboard Dry-
Dry-process fiberboard
Pressing procedures for dry-process fiberboard
differ somewhat from particleboard procedures.
After the fiber mat is formed, it is typically pre-
pressed in a band press.
The densified mat is then trimmed by disk cutters
and transferred to caul plates for the hardboard
pressing operation;
for MDF, the trimmed mat is transferred directly
to the press.
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Fiberboards Fiberboards
Dry-
Dry-process fiberboard
All dry-formed boards are pressed in multi-
opening presses at approximately 140°
140°C to 165°
165°C
for UF-
UF-bonded products and 190°
190°C for PF-
PF-bonded
products.
products
Continuous pressing using large, high pressure
band presses is also gaining in popularity.
Board density is a basic property and an indicator
of board quality.
Since density is greatly influenced by moisture
content, this is constantly monitored by moisture
sensors using infrared light.
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Fiberboards Fiberboards
Wet-
Wet-process Hardboard Wet-
Wet-process Hardboard
Wet-process hardboards differ from dry-process Secondly,
Secondly some wet-process boards are made
without additional binders.
fiberboards in several significant ways.
If the lignocellulosic contains sufficient lignin and if
First,
First water is used as the distribution medium for lignin is retained during the refining operation,
forming the fibers into a mat. lignin can serve as the binder.
binder
As such, this technology is really an extension of
Under heat and pressure, lignin will flow and act
paper manufacturing technology.
as a thermosetting adhesive,
adhesive enhancing the
naturally occurring hydrogen bonds.
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Fiberboards Fiberboards
Wet-
Wet-process Hardboard
Refining is an important step for developing
strength in wet-process hardboards.
The refining operation must also yield a fiber of
high “freeness;” that is, it must be easy to remove
water from the fibrous mat.
Wet-process hardboards are pressed in multi-
opening presses heated by steam.
The press cycle consists of three phases and lasts
6 to 15 min.
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Fiberboards Fiberboards
Wet-
Wet-process Hardboard Wet-
Wet-process Hardboard
The first phase is conducted at high pressure, Post-Treatment of Wet- and Dry-Process Hardboard
and it removes most of the water while bringing
the board to the desired thickness. Several treatments are used to increase the
dimensional stability and mechanical
The primary purpose of the second phase is to performance of hardboard.
remove water vapor.
The final phase is relatively short and results in the Heat treatment
final cure.
Heat treatment—exposure of pressed fiberboard to
A maximum pressure of about 5 MPa is used. dry heat— improves dimensional stability and
A high temperature of up to 210°C is used to mechanical properties, reduces water adsorption,
increase production by causing faster and improves interfiber bonding.
evaporation of the water.
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Fiberboards Fiberboards
Wet-
Wet-process Hardboard Wet-
Wet-process Hardboard
Tempering Humidification
Humidification is the addition of water to bring the
Tempering is the heat treatment of pressed boards,
board moisture content into equilibrium with the
preceded by the addition of oil.
air.
Tempering improves board surface hardness and
Air of high humidity is forced through the stacks
is sometimes done on various types of wet-formed
where it provides water vapor to the boards.
hardboards.
The entire process is controlled by a dry-bulb-wet-
It also improves resistance to abrasion, scratching,
bulb controller.
scarring, and water. The most common oils used
include linseed oil, tung oil, and tall oil. Another method involves spraying water on the
back side of the board.
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Fiberboards Fiberboards
Insulation Board Insulation Board
Like the manufacture of wet-process hardboard,
insulation board manufacture is a modification of Insulation board is usually cold-pressed to remove
papermaking. most of the free water after the mat is formed.
Insulation boards typically do not use a binder, The wet mats are then dried to the final moisture
and they rely on hydrogen bonds to hold the content.
board components together.
The board is generally dried in stages at
Sizing agents are usually added to the furnish temperatures ranging from 120°
120°C to 190°
190°C.
(about 1%) to provide the finished board with a
modest degree of water resistance and Typically, about 2 to 4 h are required to reduce
dimensional stability.
stability moisture content to about 1% to 3%.
3%
Sizing agents include rosin, starch, paraffin, resin,
asphalt, and asphalt emulsions, etc.
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Fiberboards Fiberboards
Properties and Applications Properties and Applications
Medium-Density Fiberboard—Minimum property
requirements, as specified by the American This standard is typically updated every 5 years
National Standard for MDF, A208.2 or less.
The furniture industry is by far the dominant MDF
market.
Medium-density fiberboard is frequently used in
place of solid wood, plywood, and
particleboard in many furniture applications.
It is also used for interior door skins, mouldings,
and interior trim components (Youngquist and
others 1997).
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Fiberboards Fiberboards
Dry-
Dry-process fiberboard Properties and Applications
Hardboard—basic hardboard physical properties
(ANSI/AHA A135.4)
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Fiberboards Fiberboards
Properties and Applications Properties and Applications
The uses for hardboard can generally be grouped as
For application purposes, the AHA siding classifies
construction, furniture and furnishings, cabinet and
into three basic types:
store work, appliances, and automotive and rolling
stock. Lap siding—boards
siding applied horizontally, with each
Typical hardboard products are prefinished paneling board overlapping the board below it
(ANSI/AHA A135.5), house siding (ANSI/AHA A135.6), Square edge panels—siding
panels intended for vertical
floor underlayment, and concrete form board. application in full sheets
Shiplap edge panel siding—siding
siding intended for
Examples of grade stamps: grade vertical application, with the long edges
stamp for siding conforming to
incorporating shiplap joints
ANSI/AHA A135.6 standard
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Fiberboards Fiberboards
Hardboard panels have a variety of uses.
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Fiberboards Fiberboards
Properties and Applications Properties and Applications
Insulation Board—Physical and mechanical properties Insulation board products can be divided into
of insulation board are published in the ASTM C208 three categories: exterior, interior, and industrial.
standard specification for cellulosic fiber insulation Exterior products
board. Physical properties are also included in the Sheathing—board
Sheathing used in exterior construction because
ANSI standard for cellulosic fiberboard, ANSI/AHA of its insulation and noise control qualities, bracing
A194.1 strength, and low price
Roof decking—three-in-one
decking component that provides
roof deck, insulation, and a finished interior ceiling surface;
Examples of grade stamps: grade insulation board sheets are laminated together with
mark stamp for cellulosic
waterproof adhesive
fiberboard products conforming
to ANSI/AHA A194.1 standard. Aluminum siding backer board—fabricated
board Insulation
board for improving insulation of aluminum-sided houses
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Fiberboards Fiberboards
Properties and Applications Properties and Applications
Insulation board products can be divided into Insulation board products can be divided into
three categories: exterior, interior, and industrial. three categories: exterior, interior, and industrial.
Interior products Industrial products
Building board—general
board purpose product for interior Mobile home board
construction
Expansion joint strips
Ceiling tile—insulation
tile board embossed and decorated
Boards for automotive and furniture industries
for interior use; valued for acoustical qualities; also
decorative, nonacoustical tiles
Sound-
Sound-deadening board—special
board product designed to
control noise levels in buildings
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Fiberboards Fiberboards
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Fiberboards Fiberboards
Moisture-
Moisture-Resistant Composites
Sizing agents,
agents wax,
wax and asphalt can be used to
make composites resistant to moisture.
Sizing agents cover the surface of fibers, reduce
surface energy, and render the fibers relatively
hydrophobic.
Sizing agents can be applied in two ways.
In the first method,
method water is used as a medium to
ensure thorough mixing of sizing and fiber.
In the second method,
method the sizing is applied directly
to the fibers.
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Fiberboards
Moisture-
Moisture-Resistant Composites
Rosin is a common sizing agent that is obtained
from living pine trees, from pine stumps, and as a
by-product of kraft pulping of pines.
Rosin sizing is added in amounts of less than 3%
solids based on dry fiber weight.
Wax sizing is used in dry-process fiberboard
production; for wet processes, wax is added in
solid form or as an emulsion.
Asphalt is also used to increase water resistance,
especially in low-density wet-process insulation
board.
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