MANUFACTURE OF CALCIUM HYDROSILICATE BOUND FIBERBOARD

FABRICATION DE PANNEAUX DE FIBRES LIES AEC DE L'HYDROSILICATE DE CALCIUM

English Abstract

Calcium hydrosilicate bound
fiberboard, in particular double-deck board, is manufac-
tured in a process wherein a fiber-binder-filler mixture
having a water content of 40 to 45 % by weight and a
solids content of 55 to 60 % by weight is prepared by
digesting cellulose fibers in an amount of from 2 to 12 %
by weight of the solids content with water and mixing
them with the binder comprising cement and/or lime
hydrate and substances containing reactive calcium
silicates and also the fillers to form a thick pasty
mixture, whereupon the thick pasty mixture is introduced
in a predetermined amount into the frame of a bottom mold
of a single-shot press which further includes a top mold,
essentially leveled out, formed by closing top and bottom
mold, and, via dewatering fabrics and channels in the top
and bottom molds, dewatered, compacted and vented,
whereupon the raw board thus formed is demolded and
autoclaved.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for manufacturing calcium hydrosilicate
bound fiberboard in a double-deck board, comprising the
following steps: pulping cellulose fibers; mixing said
cellulose fibers with a binder including cement and/or lime
hydrate and reactive calcium silicate and a filler to form a
pasty fiber-binder-filler mixture having a water content of
about 40 to about 45% by weight and solids content of about 55
to about 60% by weight, said solids content including about 2
to about 12% cellulose fibers by weight; introducing said
pasty fiber-binder-filler mixture in a predetermined amount
into a frame of a bottom mold of a single-shot press, said
press including a top mold; substantially leveling said pasty
fiber-binder-filler mixture; closing said top and bottom
molds; compressing said top and bottom mold to form a raw
board by compaction under dewatering and venting said pasty
fiber-binder-filler mixture via dewatering fabrics and
channels in said top and bottom molds; demolding said raw
board; and autoclaving said raw board.
2. The process of claim 1, wherein the solids content
includes from about 4 to about 7% by weight of cellulose
fiber.
3. The process of claim 1, wherein the cement is
Portland, iron Portland or blast furnace cement.
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4. The process of claim 1, wherein the solids content
includes from about 2 to about 12% by weight microsilica, and
about 10 to about 20% by weight of latently hydraulic
substances selected from the group consisting of pozzuolanic
substances, wherein the remainder of said solids content
includes cement and said cellulose fiber.
5. The process of claim 4, wherein the pozzuolanic
substances include fly ash.
6. The process of claim 4, wherein said solids content
includes from about 6% to about 10% by weight micro silica.
7. The process of any one of claims 1 to 6, wherein the
pasty fiber-binder-filler mixture further comprises a liquid
hardening accelerant for the cement.
8. The process of any one of claims 1 to 6, wherein
said pasty fiber-binder-filler mixture further comprises
finely ground quartz powder as co-reactant to lime hydrate and
as filler.
9. The process of any one of claims 1 to 6, wherein the
step of leveling is effected by riddling, raking or spreading
by means of a plunger.
10. The process of any one of claims 1 to 6, wherein the
frame and the dewatering fabrics of the single-shot press are
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each sprayed with a release agent.
11. The process of any one of claims 1 to 6, wherein the
cellulose fibers used are selected from the group consisting
of paper, pulp fibers and comminuted waste paper.
12. The process of any one of claims 1 to 6, wherein the
solids other than the cellulose fibers are premixed dry and
mixed into the pulp formed by the cellulose fibers.
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Description

`r , a~o 7Ll ~o
Manufacture of calclum hydrosilicate
bound fiberboard
The present invention relates to a process for
manufacturing calcium hydroslllcate bound flberboard.
In relatlon to cement bound fiberboard it ls known
to apply a slurry contalning a mlxture of cellulose flber and
cement to a wlre-cloth wlth a large excess of water to produce
thln layers whlch are superposed on one another ln the moist
state and then pressed together, to be finally cut to size and
autoclaved. The use of the wire-cloth of a papermaker's
machine limits the thickness of the indlvidual layers
accordingly, and the consequently necessary layering has the
effect that, in certain clrcumstances, layers having dlfferent
moisture contents are arranged on top of one another. It ls
true that this layering, given an appropriate offset
arrangement, can to a certain extent eliminate the anisotropy
in the mechanlcal propertles of the flberboard, produced ln
any one layer by the use of water as transport medlum, but lt
ls also costly. The layerlng, moreover, ls responslble for
the fact that, when the raw board thus produced ls autoclaved,
lt ls prone to dlshlng, l.e. dlsh-llke warpage at the edges,
whlch impairs product quality and makes working over
necessary.
It ls an ob~ect of the present lnvention to provlde
a process of the kind mentloned at the beglnnlng whereby
flberboard of unlform and conslstent quallty ls produclble ln
a slmpllfled manner.
Thls ob~ect is achieved by a process for
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manufacturlng calclum hydrosllicate bound flberboard ln a
double-deck board, comprlslng the followlng steps: pulplng
cellulose flbers; mlxlng sald cellulose flbers wlth a blnder
lncludlng cement and/or llme hydrate and reactlve calclum
slllcate and a filler to form a pasty flber-blnder-flller
mlxture havlng a water content of about 40 to about 45% by
welght and sollds content of about 55 to about 60% by welght,
sald sollds content lncludlng about 2 to about 12% cellulose
flbers by welght; lntroduclng sald pasty flber-blnder-flller
mlxture ln a predetermlned amount lnto a frame of a bottom
mold of a slngle-shot press, sald press lncludlng a top mold;
substantlally levellng sald pasty flber-blnder-flller mlxture;
closlng sald top and bottom molds; compresslng sald top and
bottom mold to form a raw board by compactlon under dewaterlng
and ventlng sald pasty flber-blnder-flller mlxture vla
dewaterlng fabrlcs and channels ln sald top and bottom molds;
demoldlng sald raw board; and autoclavlng sald raw board.
In the course of the process, the blnder cement, for
example Portland, lron Portland or blast furnace cement, or
rather lts llme content, or the free llme used as llme
hydrate, reacts wlth reactlve calclum slllcate durlng
autoclavlng to form strength-produclng CsH phases. Sultable
reactlve calclum silicates are microslllcate (in particular if
cement is used), finely ground quartz powder, latently
hydraulic substances such as pozzuolanas, for example fly ash
or SiO2-rich slags, which in part react with the free or freed
lime and in part can also act as filler or addltlonal filler.
Inter alia, fly ash, which can be added in a proportion of up
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to 25 % by welght of the sollds content, has a favorable
effect on the flber-blnder-flller mlxture ln that lt reduces
the water requlred and makes the mixture more malleable.
The cellulose flbers are preferably used ln an
amount of from 4 to 7 % by welght of the sollds content of the
mlxture and preferably as sulfate cellulose and optlonally
together wlth other relnforclng flbers.
Advantageously, the sollds content of the mlxture ls
prepared as a whole or ln part from 2-12 % by welght, ln
partlcular 4-7 % by welght, of cellulose flber, 2-12 % by
welght, ln partlcular 6-10 % by welght, of mlcroslllca and up
to 25 % by welght, ln partlcular 10-20 % by welght, of
latently hydraullc substances, ln partlcular fly ash.
The lnventlon wlll now be more partlcularly
descrlbed wlth reference to the accompanylng process flow
dlagram.
The cellulose flbers, whlch may be paper and/or pulp
flbers wlth or wlthout a proportlon of commlnuted
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waste paper, are digested in a pulper 1 while at the same
time the other solid components are mixed in a dry
mixer 2. The pulp from pulper 1 and the dry mixture from
dry mixer 2 are mixed in a wet mixer 3 to form a thick
pasty mixture, to which may additionally be added a
liquid solidification accelerant for the cement, if the
mixture contains cement.
The thick pasty mixture is introduced in the
necesæary amount, which can be measured gravimetrically
or volumetrically, into a bottom frame 4 surrounding a bottom
mold 5 of a single-shot press 6. The mixture, which initially forms
a heap with a low tendency to flatten, is essentially leveled
out in the bottom frame 4. This can be effected for
example by riddling, raking or spr~A~ing apart by means
of a plunger. Since the mixture has the consistency of a
thick paste, it would otherwise not be sufficiently
distributed over the area bounded by the bottom frame 4
within the single-shot press 6, which would result in
quality-reducing thickness fluctuations which might also
make costly working over necessary. The leveling, by
contrast, produces fiberboard of uniform, consistent
quality.
After leveling, the mixture is formed within the
single-shot press 6 into board of appropriate dimensions,
determined by bottom frame 4, by closing top mold 7 and
bottom moid 5. At the same time the mixture is dewatered,
the fibers forming a fleece. For this purpose, the top
and bottom molds 7, 5 have each been provided with a
dewatering fabric and channels, and a wire mesh is
advantageously arranged between dewatering fabric and
upper and lower mold 7, 5, respectively, in order to prevent the
dewatering fabric being pressed into the openings of the
dewatering channels. The top mold 7 is advantageously
movable up and down within a top frame 8, which is itself
movable up and down and which, on pressing, closely
engages the bottom frame 4 and, after the raw fiherhoArd
has been formed, holds it back in order to deposit it on
a transfer means for transferring raw board into an
autoclave 9. The raw board thus produced in one operation

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-- 4 --
is then autoclaved to initiate the strength-producing
reactions, i.e. especially to form CsH phases.
Subsequently, a small amount of grinding may be necessary
as working over.
S The thickness of the fiberboard is determined by
the amount of mixture introduced into the bottom frame 4,
assuming constant molding pressure. The molding pressures
are of the order of 50 kp/cm2.
Prior to every molding operation the parts of the
press 6 which come into contact with the mixture are
sprayed with release agent in order to avoid caking.
This avoids the production of any anisotropy as
well as a multilayered structure or a cutting of raw
board to size or the proneness to dishing. Similarly, the
amount of water to be removed from the mixture is
significantly reduced.

Representative Drawing