Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CONTINUOUS PROCESSING EQUIPMENT FOR MAKING FIBERBOARD
Cross Reference to Related Applications
This application relates to U.S. Patent 5,171,366,
and U.S. application Serial No. 642,834, filed
January 18, 1991. U.S. application Serial No. 642,834 is
abandoned, but is available to the public because it is
listed in the "Related U.S. Application Data" appearing on
U.S. Patent 5,632,848.
This application is also related to application
Serial No. PCT/US90/05867 published as WO 91/05744
in 5/1991.
Field of the Invention
This invention relates to equipment for the
continuous processing of gypsum-containing fiberboard, and
more particularly, to wet processing equipment for producing
fiberboards of high strength at minimum cost.
Background of the Invention
Gypsum fiberboard is a construction material made
from admixing water, stucco and cellulosic fibers to form a
wet mixture, and permitting the stucco, also known as gypsum
hemihydrate, to cure to form a set gypsum dihydrate-
containing board. Unlike paper-faced wallboard, which
is really a
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laminar construction including a weak gypsum core disposed
between two relatively heavy paper sheets, fiberboard is
typically unfaced. It is generally known that wallboard
relies upon these paper facings to provide as much as 90% of
the requisite bending strength, whereas fiberboard relies upon
an intimate mixture of gypsum dihydrate crystals and
cellulosic fibers which adhere together to distribute applied
forces uniformly throughout the composite structure. This
unique feature of fiberboard has made it attractive in
applications requiring a high degree of mechanical strength,
such as in fire door cores and edge banding.
Early fiberboard manufacturing processes, such as
the one disclosed in Porter et al., U.S. Patent No. 2,076,349,
taught the mixing of calcined gypsum hemihydrate, paper
fibers, and "excess water" (over and above that required to
fully hydrate the hemihydrate gypsum) together to form a
slurry. The slurry was placed into a mold and then subjected
to a pressure of up to about 1,000 psi so that most of the
excess water could be squeezed from the mixture. The
resulting "green board", i.e. not fully set, contained about
30-35 wt.o moisture which was later removed by drying in a
kiln oven. Fiberboards produced by this process were strong,
having modulus of rupture values approaching as high as 1,750
lbs. per square inch, but low efficiency and the costs
associated with removing all that water made the boards too
expensive. Porter suggested a continuous operation for
producing endless webs of fiberboard, which could have helped
to alleviate these costs, but his disclosure failed to provide
sufficient details for practicing such an operation.
In some of the more modern processes, Such as in the
method described in Take et al., U.S. Patent No. 4,645,548,
sheet making equipment has been employed to promote more
continuous manufacturing of fiberboard. Moreover, readily
available and inexpensive forms of gypsum dihydrate, such as
flue gas desulfurization and phosphoric acid dihydrate
industrial by-products have been employed as a filler in these
boards to further reduce costs. Take discloses forming a
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slurry with a mixture of hydraulic gypsum, gypsum dehydrate,
organic and inorganic fibers, a setting retarder, and water.
The slurry is takE~n up ~on a sheet making roll, which is
partially immersed in t:he slurry bath, and which transfers the
slurry to a passing belt. The resulting green sheet is then
cut to length, laminated to another board and press-molded.
Although this refs~rence teaches that as much as 50 wt.% gypsum
dehydrate could bE: added to the fiberboard initial slurry
without significantly affecting board strength, Take's method
fails to take ful:L advantage of the bonding properties of
gypsum, which are largely due to the crystallization of the
hemihydrate into t:he di:hydrate form. Thus, the use of
dehydrate as a fi:Ller h,as not been particularly popular.
Recent developments in Germany, such as those
disclosed in Kraerner et al., "Gypsum Fibre Boards for the Dry
Interior Finish Construction", Holz-Zentralblatt, Stuttgart,
Vol. 111, No. 11 ;January, 1985), suggest that fiberboard can
be produced in a continuous "dry process". The dry process,
commercialized by G. Siempelkamp GmbH & Co., Krefeld, Germany,
begins with a dry mixture of plaster, gypsum, and paper fibers
which is thoroughly blended in a high-speed continuous flow-
mixer. The mixture is conveyed to a bunker of a matformer,
where it is then i:ormed into an endless mat of a dry plaster-
gypsum-fiber mix on a spreading belt. The endlessly formed
mat is then transi:erred onto a screen belt and wetted with a
minimum amount of water. Vacuum boxes located beneath the
wetting unit facilitate the penetration of water through the
cross section of i:he mat. The wetted mat then enters a
movable, open cycle press, where it is pressed between a
plastic coated te:~ture belt running synchronously on top of
the mat. The watEar squeezed out from the mat is drained into
a press pit. Aft~ar the expiration of the pressing time, the
press opens and returns into its initial starting position.
The pressed mat i:~ then ready for cutting and subsequent
setting and curin<~ operations.
Although the dry process is now used extensively
in Europe, compar~~tive testing of gypsum fiberboards produced
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with the dry and wet processes has demonstrated that boards
produced frrm a slurry containing water over and above that
required to hydrate the hemihydrate are more homogeneous in
appearance and are about 70% stronger in flexural strength
tests than comparable thickness, dry process boards.
Other manufacturers, such as Vogt, U.S. Patent
No. 4,840,688, have sought to combine the benefits of using
cheap industrial dehydrate waste as a starting material and
the uniformity and strength provided by a wet process in a
single manufacturing line. Vogt teaches the wet shaping of
gypsum dehydrate and wet-digested fibers, followed by the
removal of water, the dry recrystallization of the dehydrate
to hemihydrate by heating at atmospheric pressure, and then
the subsequent conversion back to the dehydrate by the
addition of water. Despite his aggressive attempt at using
multiple recrystallizations of gypsum to maximize strength,
the complexity and costs associated with Vogt's process
detracts from its commercial value.
Accordingly, there is a need for continuous
processing equipment for manufacturing gypsum fiberboards
having a high degree of uniformity and great strength. This
equipment should also be easy to implement and not require
complicated elements which would be difficult to maintain
and run.
Summary of the Invention
Processing equipment for the continuous
preparation of gypsum fiberboard is disclosed by this
invention. According to the present invention, there is
provided an apparatus for forming boards containing a gypsum
based core, the improvement characterized by alternatively
and selectively forming wallboard or fiberboard from
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equipment comprising: admixing means for mixing a
hydratable gypsum, a source of paper fiber, and water to
form a substantially homogeneous slurry; dewatering means
for removing a portion of said water from said slurry formed
by said admixing means to produce a substantially continuous
wet web; pressing means for configuring said wet web with a
compressive force to form a substantially continuous green
board; cutting means for cutting said substantially
continuous green board into individual uncured lengths; pin
mixing means for distributing a gypsum slurry onto a
continuously moving substrate; a first wallboard carrier
belt located past said pin mixing means for carrying said
substrate or said individual uncured lengths; setting belt
means disposed between said cutting means and said first
wallboard carrier belt to receive said individual uncured
lengths and carry said uncured lengths to said first
wallboard carrier belt; and means for selectively
introducing and withdrawing said setting belt from operative
association with said uncut lengths.
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Accordingly, a cost efficient manufacturing line for
5 making unfaced fiberboard is provided by this invention. This
equipment can be adapted for retrofitting to existing
wallboard machinery to permit multiple products, such as
glass-faced and paper-faced wallboard and fiberboard, to be
produced on the same manufacturing line. This apparatus
permits in-line dewatering and is capable of manufacturing
fiberboards from about 1/8 to about 1.5 inches in thickness by
varying the number and size of wedge presses and press rolls,
and varying the belt speed.
The process equipment of this invention can include
textured rolls for creating light or heavy patterns, such as
wood grains, into gypsum and cement fiberboards. Contoured
press rolls can be incorporated during pressing for making
stepped sheets suitable for siding or roofing applications.
Boards having densities of about 30 lbs./ft.3-85 lbs./ft.3 and
varying in width from about 6 inches to in excess of about 12
feet are possible. Full wall sections of about 8 feet by 60
feet long can also be fabricated for interior and exterior
surface sheathing applications.
Property-improving additives can also be
incorporated into the fiberboards of this invention in wet or
dry form either through stucco metering or through pulping
systems. The pulping system of this manufacturing line can
also be used to include water-resistant additives, such as
polyhydrogensiloxane, asphaltic wax emulsions, and
siliconates, or water-soluble polymers which can~be added to
increase product strength. Additionally, flue gas
desulfurization gypsum, recycled paper, and waste gypsum
wallboard can be employed to further reduce the cost of the
finished board.
In a more detailed manufacturing line of this
invention, a continuous manufacturing line is provided which
includes pulping means for mixing paper, water, and hydratable
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gypsum to form a homogenous suspension, dewatering means
including a continuous travelling mesh belt for removing a
portion of the water from the homogenous suspension to produce
a substantially continuous wet web, pressing means including a
wedge press and/or a plurality of press rolls having an
increased diameter for forming a substantially continuous
green board, cutting means including hydraulic cutters for
cutting said substantially green board in at least two
directions, and heating means including a multi-layered kiln
for curing said individual uncured lengths to form gypsum-
dihydrate-containing fiberboards.
Statement of the Obiects
It is therefore an object of this invention to
provide continuous processing equipment for manufacturing
gypsum fiberboard from hydratable gypsum and paper fiber.
It is another object of this invention to provide an
apparatus for removing large amounts of water efficiently and
continuously from a wet gypsum-containing web.
It is a further object of this invention to provide
a retrofitted or original equipment manufacturing line which
is capable of producing gypsum-containing unfaced fiberboard
as well as paper-faced versions of board products.
With these and other objects in view, this invention
resides in the novel construction, combination, arrangement of
parts, and methods substantially as hereinafter described, and
more particularly defined by the attached claims.
Brief Description of the Drawings
The accompanying drawings illustrate preferred
embodiments of the invention as well as other information
pertinent to the disclosure, and in which:
FIG. lA: is a diagrammatic view of the raw material
feeding and dewatering sections of the preferred continuous
processing manufacturing line of this invention; and
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FIG. 1B: is a~ diagrammatic view of the press
section, cutting station, and setting belt portion of the
manufacturing line of this invention.
Detailed Description of the Invention
This invention is directed to a continuous wet
processing equipment for the manufacture of fiberboard. This
equipment can be operated in unison with a conventional
wallboard machine so as to permit the manufacture of multiple
products from the same production line. As used herein, the
term "hydratable gypsum"' refers to both the hemihydrate and
the anhydrous forms of calcium sulfate.
Fiberboard Composition and Properties
The preferred ingredients and properties for the
fiberboards of this invention will now be described. The
preferred fiberboard hay; a density of about 30-85 lbs./ft.3,
preferably greater than about 50 lbs./ft.3, flexural strength
of at least 30 lbs. (1/2. inch thick material), and screw-
holding capacity, measured as defined hereinafter, of at least
about 400 lbs. These fi.berboards preferably do not include a
paper facing, which is desirably absent to promote fire and
water resistance properties. The composition of the preferred
fiberboards is a uniform distribution of solids, which
includes by weight, about 65% to about 90% set gypsum
dihydrate, about 7% to about 30% cellulosic fiber, and
preferably about 1.5% to about 35% of a performance booster
selected from inorganic fiber, clay, starch, vermiculite, and
binder polymer.
One of the essential constituents of the gypsum-
containing fiberboards of the present invention is hydratable
gypsum. This constituent is derived from the hydration of any
form of calcium sulfate which is capable of reacting with
water to form set gypsum, such as, anhydrous calcium sulfate
or calcium sulfate dihydrate. It is believed that the
hemihydrate form of calcium sulfate will be used most widely.
Of the "alpha" and "beta" forms of the hemihydrate, use of the
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latter is preferred. The hemihydrate can be produced from the
naturally-occurring gypsum mineral by heating, or calcining,
the dihydrate.
For many applications, it is not important to
inquire into the crystalline form of the hemihydrate; however,
with respect to fiberboards of this invention, a preference is
made. It is known that calcium sulfate hemihydrate can exist
in two different crystalline forms, namely a non-fibrous form
and a fibrous form, for example, elongated needles, such as
the fibrous alpha-calcium sulfate hemihydrate disclosed in
U.S. Patent No. 4,239,716. In the practice of
this invention, the non-fibrous form of
calcium sulfate capable of reacting with water to form set
gypsum is preferred. It should be understood, however, that a
minor amount of a fibrous form of gypsum can be used as an
optional constituent.
As mentioned above, one of the advantages of the
present invention is that waste-type materials can be used in
fabricating the fiberboards. For example, there can be used
as the source of the calcium sulfate the material known as
"desulfurized by-product gypsum" which is produced by the
desulfurization of flue gas. Another example of a waste- or
scrap-type material that can be used in the practice of the
present invention is scrap gypsum wallboard, which can be used
as a source of both calcium sulfate and the paper constituent
of the building product. For this purpose, scrap paper-faced
gypsum wallboard can be ground into suitably small particles
which are calcined in water under pressure and in the presence
of a crystal modifier to form calcium sulfate hemihydrate.
Scrap gypsum wallboard can also be transformed into a suitable
material for use in the practice of the present invention by
grinding and calcining it at atmospheric pressure. Sufficient
water can be used to form the desired pulp-type material from
which the product is conveniently made. This invention can
employ any of the above-disclosed individual sources of
calcium sulfate, but a mixture of the different sources of
calcium sulfate can also be used.
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In the use of an aqueous dispersion to make the
gypsum-containing fiberboards, the non-fibrous calcium sulfate
generally will comprise between about 53% and about 78% by
weight of the total solids, preferably between about 55% and
about 70% by weight, depending upon the specific application.
The gypsum dih,ydrate content of the preferred
fiberboards of this invention will be approximately 17-18.5
wt.~ greater than the non-fibrous calcium sulfate content of
the compositions from which they are made, the difference
representing the added water of hydration in the set gypsum
dihydrate. That is, by weight, the set gypsum will broadly be
within the range of about 65% to about 900, and preferably
between about 70% and about 85% of the overall set
composition.
The composition of the preferred fiberboards of this
invention also employs a. substantial amount of cellulosic
fiber. Cellulosic fiber includes the fibrous component of
plants, such as cotton, linen, and flax, for example. Among
the various sources of c:ellulosic fiber, paper stock is
conveniently employed. That is, the solid component involved
in each of the aforesaid. aspects of the invention preferably
includes by weight about. 7% to about 30~ paper fiber, more
preferably between about. 10% and about 17%. Building
materials intended for u.se in various specific products may
contain somewhat different amounts of paper fiber. The
presence of the paper fiber makes it possible to produce
building materials having good physical characteristics such
as flexural strength, screw and nail holding ability, and
surface hardness without. having any separate surfacing
membrane such as the paper facing used on conventional gypsum
wallboard.
The paper fiber can be derived from either virgin
paper stock, or previously used, waste paper stock. The
source of the paper can be wood, cotton or linen rags, straw,
etc., the origin or history of the paper not being important
factors. The paper may be a product of the sulfite process,
the sulfate (Kraft paper') process, or other processes. Among
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the types of paper stock that have been successfully employed
are virgin and brown Kraft papers, and especially, newsprint.
Waste newspaper provides very satisfactory results, is
inexpensive, and its use helps to overcome an environmental
pollution problem. And, as mentioned above, the source of the
paper stock can include the paper of ground paper-faced gypsum
wallboard.
Fiberboards within the scope of this invention
desirably and preferably include one or more performance
boosting additives, their specific nature depending to some
extent on the intended utility of the final product. In
almost every case, there will be desirably used one or more
defoaming agents, dispersants, and accelerators, ingredients
which are well-known in the art and are employed at low
concentration levels, generally each at less than about 1% by
weight of the solids. In the aggregate, the performance
booster generally will comprise about 1.5°s to about 35% by
weight of the solids and will preferably be selected from
starch, inorganic fiber, clay, vermiculite, and binder
polymer.
Inorganic fiber, as that term is employed herein,
includes glass textile fiber and mineral wool. These latter
terms are defined in U.S. Patent No. 4,557,973, and those
definitions are incorporated herein by reference. Briefly,
the term "mineral wool" means glass or other mineral fibers
prepared by attenuating a melt of glass, basalt, blast furnace
slag or other vitreous mineral composition from the face of a
heated centrifugal rotor or the like. This process is in
contrast to that used to produce textile fibers, where the
melt is drawn through an orifice. An especially useful and
readily available type of mineral wool is glass wool as found
in glass wool insulation material. Glass textile fiber and
glass wool, jointly or severally, are referred to herein as
"siliceous fiber." As employed in this invention, the glass
textile fiber, also referred to herein as "fiberglass",
generally will be chopped, e.g., the fibers may be about 1/2
inch long.
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The fiberboards of this invention also preferably
include siliceous fiber. Siliceous fiber improves the fire
resistance of the building materials and other products of
this invention, apparently by decreasing the tendency of the
gypsum construction to crack under thermal stress. The
siliceous fiber preferably comprises up to about 7% by weight
and may include glass ts:xti:le fiber and, in addition, glass
wool, depending upon the specific product.
The performance booster may also include either clay
or vermiculite, or both, especially if the intended board or
panel requires excellent: fire resistance. Both of these
materials may be present: in amounts up to about 6%, preferably
about 3% to about 4% by weight of the solids. The clay to be
employed will generally be kaolin clay, which is effective to
control the shrinkage of: fiberboards under extreme heat. The
vermiculite is preferab7~.y raw, or unexpanded vermiculite,
which swells when heated, helping to control shrinkage of the
construction and p~ossib7~e cracking. The requirement for the
presence of these materials depends somewhat on the intended
use for the final produces.
The composition of the preferred fiberboards of this
invention may also include a binder. The binder affects the
physical properties of t:he fiberboards, especially their
flexural strength, and also permits good fastener retention at
lower density. Fu.rtherrnore, the binder improves the surface
characteristics of the board such as smoothing the surface and
making it easier t.o fin:ish. Both natural binders, such as
raw, uncooked starch, and binder polymers, further described
below, are available for providing these characteristics.
The bincler polymer, when present, may comprise up to
about 15% by weight of i~he solids, but preferably about 1% to
about 3% by weight:. A number of different polymeric materials
may be employed asc the binder polymer, including homopolymers,
such as polyvinyl. acetate) and polyacrylate, as well as
copolymers, such as poly(ethylene)-co-(vinyl chloride),
poly(styrene)-co-('butad:iene), and polyvinyl acetate)-co-
(methyl acrylate). Among the various binder polymer
WO 94/03318 PCT/US93/07273
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possibilities, esters of polyvinyl alcohol) are especially
effective, and polyvinyl acetate) homopolymer is preferred.
It is also convenient in most cases to introduce the binder
polymer as an aqueous emulsion, many of which are commercially
available. Tn selecting the binder polymer it is preferred to
employ thermoplastic, resins, which when applied to the surface
of the fiberboards tend to form a tough, forgiving film,
rather than a brittle film or one which is soft and has a very
low tensile strength. Thermoplastic resins are also preferred
since the heat required to set a thermosetting resin tends to
calcine the gypsum in the preferred fiberboard compositions of
this invention. One particularly useful resin emulsion, which
is suitable for use as the resin polymer of the preferred
fiberboard composition is UCAR-130 poly-(vinyl acetate)
polymer by Union Carbide.
The composition for preparing the fiberboards of
this invention can also include water in an amount in excess
of that required to react with and hydrate the calcined non-
fibrous gypsum. That is, preferably at least about 15-fold,
and more preferably, about 20- to 25-fold excess water can be
present in wet processes.
Fiberboard Continuous Process and Equipment
Although the fiberboard compositions of this
invention may be formulated in many different ways, and any
number of different techniques may be employed, including both
"dry" and "wet" processes, to produce the panels and boards of
this invention, a manufacturing line which is preferred for
making these structures is illustrated diagrammatically in
FIGS. lA and 1B. As used herein, "dry" processes employ a
minimum amount of water necessary for hydration of the gypsum
dihydrate, or only a minor amount of excess water, for
example, from about 17-100% water (based upon the weight of
the gypsum dihydrate), where as "wet" process employ over
about 1500 water, and preferably in excess of about 250%
(about 15-fold the amount necessary for complete hydration).
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Hydratax~le gypsum, or in certain instances, cement,
is delivered from gypsum bin 22 to a metering system, such as
a feeder screw 25. If gypsum is used, it preferably comprises
stucco, i.e., gypsum hemihydrate. The stucco may be mixed
with cut glass fivers from bin 23 and other ingredients from
bin 24, such as clay, vermiculite, and starch. Waterproofing
agents, such as silicones (e. g. polyhydrogensiloxane),
siliconates, such as potassium of sodium siliconate, asphalt
wax emulsions, and. combinations thereof, can be added directly
to the slurry in the mixer 26, the pulper, or into the gauging
water.
Preferred starting compositional ranges and starting
weights for the primary ingredients are as follows:
TABLE I: Initial Fiberboard Slurry Composition
Weiaht/Ing~redier,t Broad Ranae Narrow Ranae Target
7,619 lbs. water 65-85 wt.% 70-80 wt.% 78.2 wt.%
275 lbs. paper .5- 6 wt.% 1- 4 wt.% 2.8 wt.%
1,850 lbs. stucco 10-30 wt.o 15-25 wt.% 19.0 wt.%
9,744 lbs. TOTAL 100.0 wt.%
The preferred wet composition contains about 412
wt.% water (based upon the dry weight of stucco; or about
24.6-fold in excess of that required to completely hydrate the
gypsum) and about 13 wt.% paper (from a 3.6% pulp solution)
5 based on the dry weight of paper and stucco. Of the 7,619
lbs. of water added to the initial composition, it is expected
that 6,109 lbs. will be drained during dewatering, 310 lbs.
will be incorporated in the fiberboards to hydrate the stucco
to form gypsum dehydrate, and 1,299 lbs. will be lost to
10 evaporation in the: dryer.
The paps:r fiber, which composes a major ingredient
in the fiberboard, is preferably recycled newspaper which is
pulped, in at least about 20 times its weight in water into
individual fibers in a pulper 20, preferably to about a 3-5
wt.% pulp-in-water solution; although some modern pulpers are
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known to accommodate about a 6 -9 wt.~ pulp-in-water solution.
In order to reduc6~ the length of the dewatering operation, a
vacuum filter may be employed to reduce the water content of
the pulp, following wet fiberization, to about a 20-25 wt.~
pulp-in-wager soluti.on..
Additionally, siliceous fiber, such as glass wool,
may be pulped sep~rrately or with the paper in at least about
20-25 times its weight. in water, and added to the pulp feeder
21 with the paper fiber. In contrast to that which has been
to taught previously in t:he gypsum arts, such as in U.s. Patent
No. 4,557,973, it is not necessary in the process described
above to pretreat the glass wool with powdered gypsum prior to
its use.
The pulped ingrQdients are then pumped to a slurry
mixer 26 where the paper pulp, and other pulped ingredients if
desirable, are intimat=ely mixed with the gypsum and other dry
additives. The slurry mixer 25 can be a conventional
wallboard gypsum mixer, a high-torque centrifugal pump, or the
like. The slurry mixer 26 preferably receives the dry gypsum
and other ingredients, thoroughly mixes the ingredients, and
pumps them through to a slurry roll or head box 2~.
The head box 27 holds the mixture of gypsum, pulp,
and other ingredients in suspension and spreads them e~renly as
a slurry 17 onto a travelling mesh belt. 2s. The thickness of
~:5 the slurry 17 which is deposited onto the belt za is
determined by the. consistency of the inlet material and the
speed of the belt: 28. The starting slurry thickness for
producing a .5 inch board is preferably about 1.6-2.0 inches,
more preferably ~~bvut i.7 inches.
~tp . The tr~welling mesh belt 28, as with all the belts
in this prowess, moves approximately 25-loo ft./min,
preferably about 50 ft./min. The dewatering of the slurry 17
through the mesh is assisted by a caries of drain pipes 29
which can~be vacuum-assisted for facilitating the removal of
:35 Water.
3:'ollow:~ng the initial dewatering step, the slurry 17
is reduced to a soft web 3? which is introduced to an
~A
X941804
adjustable prepresf; roll 30. The soft web 37 at this point in
the process has a thickness of preferably about 1.1-~1.3
inches, mare preferably about 1.2 inches, and a water content
of about 70:2 wt.%. The prepress roll 30 can be set for
5 various nip thickneases arid can be equipped to introduce
poxous top and bdtt:om belts 33 and 31.
The web a7 is then delivered by the porous belts 31
and 33 to wedge Areas 32, which may contain vacuum boxes,
suction slices, and/or perforated metal plates for helping to
10 remove water which enters through the belts. The thickness of
the web 37 at this point in the process is approximately .s5-
.925 inches, preferably about .s9 inches, and the water
content is about 6i!.2 wt.%.
The wet vreb 37 then enters a first press roll,
15 section shown in F7:G. 2, which includes three 18 inch press
rolls 36 and suction slices 38. The porous belts continue
through this first press section. The thickness of the web at
this point in the lrxocessing is approximately .540-.690
inches, preferably about .67 inches, and the water content is
about 52.8 wt.%.
The web :7 then enters a second press roil section
which includes three 24 inch press ro7.ls 40 and the same top
and bottom belts 3~ and 31 with vacuum-assisted suction slices
42. The thickness of the web 37 at this stage is
approximately .53-.550 inches, preferably about .54 inches,
and the water cont~:nt is about 44.b wt.%.
Finally the web 37 is introduced into the last press
roll section which includes three 38 inch press rolls 44 and
vacuum-assisted suction slices 46. At.this point in the
pressing, a new bottom belt 53 is preferably introduced,
although the board now has sufficient green strength to be
processed on rolls 50, without belts. The thickness of the
web is now about .."~ inches and the water content is about 41.5
wt.%, which represents the 310 lbs. flf water needed for
hydration and the 1,200 lbs. of water to be evaporated in the
dryer. The above-d.escr.ibed dewatering and pressing operations
can be summarized as follows:
R
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TABLE II: Thickness of Web or Board vs. Wt.% HZO
Wt . % of H20
Based on Total Wt.%
of Ingredients,
Web or
Board
Line Thickness Broad
Location linchey Ranae Target
Head Box 1.70 60-100 78.2
Pre-Press Roll 1.20 60-80 70.2
Baby Rolls .89 50-70 62.2
1st Press Section .67 40-60 52.8
2nd Press Section .54 40-50 44.6
3rd Press Section .50 35-45 41.5
Although specific press sections have been
described, the pressing operation of this invention may
consist of anywhere from about 4 to about 28 press rolls, and
may contain contouring, profiling, or embossing rolls for
individual product needs. Additionally, the rolls in each
press section may contain ridges or drilled holes for carrying
away water from the wet web. The main purpose of the press
section of FIG. 2 is to define caliper and density while
simultaneously removing water.
As the web leaves the press section, it is in a form
of a "green" board 47, i.e., is not past its initial
stiffening point. See U.S. Patent No. 4,643,771 for an
explanation of the various curing stages of gypsum boards.
The green board is preferably cut to length
and trimmed with water jets, as
illustrated in FIG. 3. The water jets preferably use about
1,800-2,600 psi, more preferably about 2,200 psi water
pressure and include side trimmers 39 and a chain driven
length cutter 41 angled at about 45° to the processing line
for cutting the running board square. Because the green board
47 is very soft, the water jets cut effortlessly through the
thickness to trim the boards to about their final length and
width dimensions.
14~~0~
I7
The proc~sss also includes repulpers 43 following the
trimmers 39 for re~~eiv~.ng the edge trim refuse, as well as
entire scrap board;b, which can be reground, mixed with water
from nozzle 45 to ;form a slurry, and transferred back to the
starting tanks ox :~lurz~y mixer for recycling.
The nut-ito-size, green boards 57 are then
transferred to a scatting belt 48 which permits the gypsum to
slowly set as it i:a convwyed. The setting belts of a
conventional wallboard line can alternatively be used as a
setting belt, which would carry the fiberboards past the
conventional pin m:Lxer 51 and shaping roll ~2. The
substantially set boards are then oven dried prior to
conventional trimWng of the water-cut ends and edges,
sanding, and s.iliec~ne sealing operations.
In an important aspect of the conveyance of the pre-
cut green fiberboazvds when a conventional wallboard line is
used, an adjustment: table 49 is provided which preferably adds
a setting belt 48 t_a the conventional wallboard machine prior
to the first board line carriQr belt. This separate bottom
belt is of sufficient length to carry the cut fiberboards
through to the start of the first conventional wallboard
carrier belt. The adjustment table 49 further preferably
includes a lift mechanism for (1) selectively introducing the
belt: when fiberboard is running, (2) lifting the wallboard
paper handling equipment out of the way while replacing it
with carrier rolls for the bottom belt, and (3) withdrawing
the belt when wallboard is being manufactured downline.
The continuous wet fiberboard process described
above permits on-line dEawatering and facilitates the
3D manufacture of nominal ..125 inch to about 1.5 inch thick
fiberboard products. This equipment can be adapted for
different types of :boards by alternating the. number of press
rolls as well as th~a speed of the belt. cement and/or gypsum
can be used in the :;tart:ing materials and the final boards can
be erubossed with light car heavy patterns, such as wood grains,
The process of this invention can permit the manufacture of
fiberboards having ~~ density of about 30--85 lbs. /ft.3 and
a
1~~8~~
widths from about 6 inches to about 12 feet. Additives can be
introduced in both the wet or dry state either through the
stucco metering or the pulping systems, such as the gauge
water. This novel pro<:ess oan also produce different
formulations of layers depositod through s:parate head boxes
onto the moving belt for achieving different densities and
finishes on the face and back of selectQd boards.
F~iberboard._~xox~ertias
The processes of the pr~asent invention can be used
1C1 to make unfaced ! i,berboard which has a substantially uniform
and homogeneous composition throughout its thictcness. The
term "unfaced" is used herein to mean that the fiberboard
layer is preferab7.y not faced with a sheet material, fop
example, the paper- or glass fiber mat that is often used as a
1~i facing material for gypsum wallboard, although structrually
improved faced-prc>ducts can be readzly produced by employing
the fiberboard compositions of this invention in the cores of
such boards.
As mentioned above, it is desirable that the
20 fiberboard layer of th.e present inventian have a density
within the broad ~:ange: of about 30-85 lbs.Jft.~, and preferably
about 50-65 lbs./:Et.'. In order to achievQ the flexural
strength and screw-holding capacity values referred to above
(30 lbs. and 400 :Lbs. respectively) in fiberboards having
25 densities much below E.0 lbs./ft.', there should bQ included in
the composition from whl.ch the building material is made
relativQly high amounts of binder polymer, for example, about
wt.% to about 35 wt.% based upon the solids content. For
applications in which such flexural strength characteristics
30 and screw-holding capacity are not considered important, the
use of a binder polymer can be absent or provided in smaller
amounts. The density of the fiberboard can be controlled by
the use of pressure in forming the product and/or by the use
of a low-density material, fax example, expanded perlite.
35 The flexural strength of fiberboards within the
scope of this invsntic~n generally should be at least about.30
~,~e.,,
s ,. "' ;
T~TaL F.DS
CA 02141804 2004-03-16
69275-126
19
lbs., preferably at least about 40 lbs. (1/2 inch thick
sample tested in accordance with a modified ASTM C 473-86a
procedure, as described in U.S. Patent No. 5,171,366). In
general, the screw-holding capacity of fiberboards within
the scope of this invention is preferably at least about
400 lbs., and in a building board to be used as fire door
edge banding, preferably at least about 600 lbs., and most
preferably in excess of about 700 lbs., when tested in
accordance with the procedures otherwise described in U.S.
Patent No. 5,171,366 for one inch samples.
Although various process and equipment embodiments
have been illustrated, this was for the purpose of
describing and not limiting this invention. Various
modifications, which will become apparent to one skilled in
the art, are within the scope of this invention as set forth
in the attached claims.
