Note: Descriptions are shown in the official language in which they were submitted.
~q3 5~73~
Fibre-bearing building members can be produced by mixing
fibrous substances such as for example cellulose fibres, glass
wool, rock or mineral wool, fibre asbestos and the like, with
hydraulic or non-hydraulic binding agents and water, with shaping
of the mixtures.
When hydraulic binding agents are used, an aqueous suspen-
sion can be made continuously from the binding agents and the
fibre substances. The excess water is removed by a suction
action from the aqueous solution, after it has been produced and
shaped. The remaining moulding material is dried after the
pressing operation. The removal by suction is effected on a con-
tinuously moving endless suction support which can be in the form
of a water-pervious belt such as a cotton belt or a metal sieve
belt. The water is,sucked from the shaped suspension through
the water-pervious belt, by vacuum suction heads which are arrang-
ed below the belt. After removal of the moulding, the remains of
the moulding material are removed from the water-pervious belt
with knocking means and by sponging off with water. The water
which is removed by the suction action, and the cleaning water,
are used to make the supsension which is used as the starting
material.
If fibre-bearing building members are to be produced using
non-hydraulic binding agents, the starting materials can be
produced in the presence of an amount of water which is suffi-
cient for, or which is in excess of the amount required for,
setting the non-hydraulic binding agent, and the starting mater-
ials may possibly be pressed, and then dried.
28 An example of producing plates from fibres and gypsum as the
~ - 2 - i~
~ .
105973~
non-hydraulic binding agent is found in German patent specifica-
tion No 647465,- published June 17, 1~37. In accordance with this
specification, gypsum, asbestos fibres and water are formed into
a mixture which is dry to the touch and which is subsequently
pressed into mouldings~ After the pressing operation these
mouldings are moistened with size water, and dried.
.
- 2a -
1~159~736
In accordance with German patent specification No. 934395,
published September 22, 1951 spinable glass fibres can also be dry
mixed with gypsum, and then water added. It is however also
possible for the spinable fibres to be mixed simultaneously with
gypsum and water. These mixtures which should contain approxlmately
the amount of water necessary for setting of the gypsum, are then
caused to set, while being shaped.
German patent specification No. 1123244, published August 16,
1962 discloses another possible way of producing plat~s. In ac-
cordance with this specification, in a dry condition or with the ad-
dition of an extremely small amount of water, the starting materials
such as fibres, hydraulic or non-hydraulic binding agents, are
shaped in the form of plates which are provided wi~h coverings
such as wet fine muslin cloths, from which water can be evaporated
into the plate blank moulding while this is being pressed.
In accordance with French patent specification No. 1461690,
published December 9, 1966 it is said to be of advantage to intro-
duce into a mould gypsum or other sulfate-bearing binding agents
in the form of dry dust or grains, and subsequently or simultaneously
to moisten them with water. The water required for this purpose
can be introduced in the form of steam or water bound on other
substancesO
German Offenlegungsschrift No. 1571466, published December 17,
1970 also discloses a method of producing plates and shaped
members from gypsum, wherein the gypsum which is mixed with the
fibr~ component is introduced in a dry condition into a mould, and,
during or after this step, moistened with an amount of water which
is just sufficient for setting of the gypsum. It can also be of
advantage for the moulding to be compacted by the action of a
i(~3~ pressure.
~- - 3 -
~S9736
German Offenlegungsschrift No. 2103931, published August 31,
1972, discloses a method wherein fibres and gypsum are mixed on
a conveyor belt, a so-called pre-shaping belt. This mixture is
then transferred on to a second conveyor belt r a ~o-called
pressing belt, and at the same time moistened with an amount of
water which is approximately sufficient to cause the gypsum to
set. The plate in web form which is produced in this manner is
pressed and cut into plates from which a residual moisture
content of from 10 to 15% by weight must then be removed by
drying.
When using a gypsum-water mixture of pourable consistency,
which may possibly contain fibre substances, in which the amount
of water is from 3 to 6 times the amount required for setting of
the gypsum, the excess water must be removed by drying in a method
step following the shaping step. The best known example of
such an operation is the production of gypsum pasteboard plates.
In this case thepourable gypsum-water mixture is placed on a
pasteboard web whose longitudinal eclges are folded upwardly.
The pasteboard web which is filled wi-th the gypsum-water mixture
is subsequently covered with an addi~ional pasteboard web.
After the gypsum has set, the excess water is removed by drying
from the plate web, which is cut into plates. In this method the
relationship by weight of water to gypsum is from approximately
0.6 to 1Ø
As disclosed in German patent specification No. 928219,
published April 28, 1955, however it is also possible to put into
a mould glass fibre fleeces whose fibre thicknesses are more than
0.025 mm, together with a gypsum-water mixture, and to allow this
to set. In German patent specification No. 825377, published
3~ November 15, 1951, it is recommended that a fibre belt should be
~ - 4 -
~L059736
drawn through a gypsum-water mixture of suitable consistency,
and introduced into moulds, the excess water being pressed out.
: In accordance with German patent specification No. 1092361,
published August 27/ 1964, textile fibre substances, asbestos
or cellulose can also be used for the production of gypsum
plates/ if they are firstly suspended in ample water and a mixture
of glass fibre bunches which are fixedly connected, with gypsum
and water, is introduced into the resulting suspension. The
excess water in the resulting mixture is removed by suction
after the shaping operation, and the remaining
.
- 4a -
1059736
residue is pressed into the form of plates which are then dried.
It has also already been proposed, in German patent specifi-
cation No 1104419, published May 5, 1966, to produce an aqueous
suspension from fibres and sulfatic binding agents such as
gypsum. The aqueous suspension includes a large excèss of water
over and above the amount necessary for setting of the sulfatic
binding agent, and also retarding agents. This suspension is
continuousl~ formed into a fleece configuration from which the
water is removed before the sulfatic binding agents begin to set.
Several layers of this fleece are wound on to a roller and, being
firmly pressed one upon the other, removed therefrom. The plate
blank is dried after setting of the binding agent.
` Accordingly, the technical development in the production of
fibrebearing gypsum plates led to three main possible methods.
In accordance with one of these methods; attempts were made to
keep the amount of water to be added to the starting materials,
as low as possible. In this case use was made of the observa-
tions that, in the presence of an amount of water which is
approximately sufficient to cause the gypsum present to set, the
gypsum which sets to calcium sulfate dihydrate forms a solid
body of low pore volume. In this way it shoul~ be possible to
produce building members of suEficient strength.
The second possible method is producing a pourable mixture,
from gypsum, fibres and a limited excess of water, and performing
a casting process with the mixture to produce building members
with the strength values which satisfy the requirements set in
connection with the particular intended use. In this method the
28 excess water is removed only by drying.
~L~59736
The third possibility for producing fibre-bearing gypsum
plates is substantially characterised in that the moulding
materials contain substantially larger amounts of water than are
required for making the mixture pourable and for setting of the
amounts of gypsum which are contained in such materialsO In
order to produce a building member of sufficient strength, it
is necessary for the moulding materials to be compacted by the
main amount of excess water being removed mechanically therefrom,
before the gypsum sets. These last methods suffer from techni-
cal disadvantages particularly when the hemihydrate gypsum ismade into a suspension by using the water which was removed as
excess water from a-previous such suspension. This excess water
contains dihydrate crystals which, upon being mixed with calcium
sulfate hemihydrate, act as crystallisation seeds, to promote the
precipitation of small calcium sulfate dihydrate crystals out
of the fluid component of the gypsum-bearing suspension, and thus
act as setting accelerators. It is known that the conversion,
which is referred to as setting, of calcium sulfate hemihydrate
into calcium sulfate dihydrate in the presence of water is based
on the fact that the hemihydrate is more highly soluble in water
than the dihydrate. Accordingly, the formation of dihydrate
crystals can be retarded by reducing the solubility or the speed
of dissolution of the hemihydrate crystals. The retarding agents
which are required for the purpose however also cause a reduction
of the dihydrate crystals in the excess water which is produced
when making the plates and which can be used again as the mixing
water. With manipulation it is possible to find an equilibrium
28 between the accelerating act~on ofthe crystallization seeds
- 6 -
~ S973~ i
and the effects of the retarding agent, such as to ensure a
stiffening time which is suitable for continuous production
of plates. For these previously known methods, use is made of
a mixture comprising fibre substances and plaster of Paris in a
ratio by weight of 0.1 to 0.4, which mixture is made into a
suspension with an amount of water which is ten times the weight
of gypsum, and then formed into a fleece from which the major
part of the excess water is removed again by suction. In this
the fibre component acts as a filter accessory in the excess
1~ water suction removal operation. ~s however, as is known,plaster 7
of Paris disperses very finely in water, an over-increased amount
of fibres had to be added to the fibre-gypsum-water mixture ln 7
order for the suction removal operation to be carried out in a
technically acceptable time; without causing excessive finely
divided gypsum to be removed from the fleece due to an excessive
suction action. Obviously these necessary conditions frequently
cause the strength, and the degree of dewatering, of the end
products to be reduced. In addition there is the danger that
an excessive amount of calcium sulfate dihydrate is contained in
crystalline form in the excess water. As in many cases the
excess water cannot be used again for forming the suspension, and
can only be discarded, disproportionately high losses of water
and binding agent must be accepted.
The attempt was therefore made to find ways of reducing such
losses of water and binding agent, and nonetheless avoiding an
unnecessarily high proportion of fibres, when producing puilding
members which are produced from a mixture of fibres, sulfatic
binding agents and water, wherein the water content of such mix-
29 tures should be a multiple of the amount of water necessary for
~059736
setting of the sulfatic binding agent. However, the reduction
in the proportion of fibres should not be accompanied by a reduc-
tion in the strength of the building member.
There was found a method of producing fibre-bearing build-
ing members, in particular plates, by forming a fleece from
mixtures of fibrous substances with sulfatic binding agents and
an amount of water which is a multiple greater than the amount
of water necessary for setting of the sulfatic binding agents,
wherein the main amount of excess water is removed mechanically
from the fleece before the setting process begins, and the fleece
is shaped into a moulding, possibly with a pressing treatment,
the moulding being dried after the setting process. In accord-
ance with this method the sulfatic binding agent used is a
calcium sulfate hemihydrate in which the particle specific
surface area does not alter or alters only to an unsubstantial
extent, in the aqueous suspension, until the main amount of
excess water is removed mechanically from the fleece.
The method of the invention is based on the observation that,
~ in the case of all hemihydrate gypsums which are produced in dry
; 20 methods, the individual gypsum particles decompose immediately
after they are moistened with water. The gypsum particles seem
to swell from the inside outwardly, and break up. The rapidity
and the extent of decomposition depends on the degree of purity
of the raw gypsum, and on the nature of the calcining method.
The rapidity and extent of decomposition is particularly high when
using a very pure raw gypsum which is dewatered under a very low
steam partial pressure, in accordance with the technical conven-
tional modes of operation.
29 Due to the decomposition of the individual particles of the
-- 8 --
~0~;9736
calcium sulfate hemihydrate upon contact with water, the number
of very fine gypsum particles and thus the specific surface area
of the gypsum is quite considerably increased. This increase in
the number of very fine gypsum particles, and the corresponding
increase in the specific surface area of the gypsum, results
however in a considerable extension in the time required for
removal of the excess water by a suction action. In spite of this
increase in the suction removal time, the degree of dewatering of
the fleece is poorer, so that the fleece retains a high water
content which must be removed by drying in the final stage of the
method, which requires the application of a considerable amount
of energy. The very fine gypsum particles, which are produced
by the calcium sulfate hemihydrate particles decomposing in an
apparently explosion-like manner, when in the presence of water,
rèmain suspended as solid matter in the excess water, and are
removed by suction with the excess water, due to the extremely
fine nature of such particles. Th:is disadvantage can be overcome
to a limited extent by an over-increased proportion of fibres so
that they can perform to the desired extent their function as a
filter when the water is removed by suction. It was however also
noted in this connection that the strength of the fibre~bearing
building members is reduced again when using higher proportions
of fibre than those which are the optimum for the respective
fibre-bearing building member in question.
It was found that these disadvantages can be overcome if the
sulfatic binding agent used is a calcium sulfate hemihydrate in
which the specific surface area of the particles does not alter,
or alters to an only inconsiderable extent, in aqueous suspension,
29 until the main amount of the excess water has been removed from
g _
~159736
the fleece. This delay in decomposition of the particles is not
iaentical to the known action of retarding the setting time,
which is caused by adding so-called retarding agents. It may
even be desirable to add to the gypsum-fibre suspension so-called
accelerating agents, such as potassium, iron or zinc sulfate,
; which take effect after the main amount of excess water has been
removed and which shorten the time for stacking of the fibre-
bearing building member, to that of setting. It was further
recognised that it is particularly advantageoùs to use a calcium
sulfate hemihydrate whose specific surface area, measured in
accordance with the slaine method, in aqueous suspension, is from
500 to 6000, preferably from 1500 to 4000 sq.cm/g. Calcium
sulfate hemihydrates of thiskind can be producedby means of any raw
materials which are conventionally used in the gypsum industry
and which preferably contain less than 3% by weight of clay,
these being referred to hereinafter as 'raw gypsum'.
The raw gypsum used can be for example natural or synthetic
calcium sulfate dihydrates which are converted in per se known
; manner into a hemihydrate with the above specified specific
surface area. In addition, the ca~cium sulfate hemihydrates to
be used in accordance with the invention can also be produced by
crystalline transformation of calcium sulfate hemihydrate having
a different specific surface area; the addition of additives which
influence the crystallisation tendency can be of advantage. Also,
25 - calcium sulfate hemihydrates which can be used in accordance with
the invention can equally be produced by dehydrating set calcium
sulfate hemihydrate, in which case small amounts of additives
such as chlorides of magnesium, calcium, cobalt or tin, or
29 potassium or magnesium perchlorate can possibly be added to a raw
-- 10 --
~L~S9736
gypsum of this kind.
With the above ~pecified specific surface area of the hemihydrate
used, in aqueous suspension, the calcium sulfate hemihydrate
enjoys optimum suitability for the method according to th~e inven-
tionl whose aim is to maintain this optimum suitability during
the processing time until the main amount of excess water has
been mechanically removed from the fleece.
The above-mentioned optimum specific surface area of the
hemihydrate can be achieved by the particular particle size of -
the dry calcium sulfate hemihydratel being at least substantially
unaltered due to the action of the watex over the period in
question. Thus, the mechanical decomposition of the individual
particles of the calcium sulfate hemihydrate in the presence of
water can be controlled for example by the calcium sulfate hemi-
; 15 hydrate to be used, being produced from a raw gypsum which is
previously ground to the necessary degree of fineness, by heat-
ing in aqueous suspension or by dry cooking in the presence of
chlorides of magnesium, calcium, cobalt or tin, or in the pre-
; sence of calcium or magnesium perchlorate, in the amounts of
from 0.05 to 0.8 and preferably from 0.1 to 0.4% by weight. The
above-mentioned additives prolong the decomposition time of the
gypsum particle. The suitable amount of such additive substances
can be easily determined in each case by simple preliminary tests.
It is also possible however for decomposition of the calcium
sulfate hemihydrate particles to be prevented by protective
coatings. The method according to the invention can therefore be
advantageously carried out by using a calcium sulfate hemihydrate
which was produced from a raw gypsum which was previously ground
29 to the necessary degree of fineness, by cooking in the presence
-- 11 --
~6~S973i6
of substances which form around the gypsum particles a coating
layer which retards decomposition of the gypsum particles in an
aqueous medium. Such layer-forming substances are for example
polyvinyl acetate or silicone. The method of the invention can
be carried out in a particularly advantageous manner: by using
a calcium sulfate hemihydrate which was produced by cooking from
a raw gypsum which was previously ground to the necessary degree
of fineness, in the presence of from 0.05 to 1.0 and preferably
; from 0.1 to 0.5% by weight of silicone emulsion.
The essential action of this alternative operation lies in
retarding decomposition of the calcium sulfate hemihydrate parti-
cles, calculated from the moment of admixing the water, at least
until the end of the operation of removing by suction the excess
water contained in the fleece.
Maintaining the protective layer substantially beyond this
moment would result in retardation of the setting process which
in many cases is not desired. The life of the protective coating
which is required in each specific case can be easily determined
by means of simple preliminary tests, with reference to the
description given herein.
Instead of using calcium sulfate hemihydrate as the sulfatic
binding agent, it is also possible to use a mixture of calcium
sulfate hemihydrate with less than 10% by weight and preferably
from 3 to 6~ by weight of cement. -
It has also been found advantageous for from 0.001 to 0.2%
by weight of a flocculating agent, preferably polyacrylamide, to
be added to the suspension con-taining the calcium sulfate hemihy-
drate.
29 In accordance with a variant of the invention, the calcium
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59736
sulfate hemihydrate used is a calcium sulfate hemihydrate in the
a-form, which is produced by dehydration from raw gypsum or from
hemihydrate by crystalline transformation, and in which the mean
ration between the largest and the smallest diameters of a
particle lies between 1.0 and 4.0 and preferably 1.5 and 3Ø
Calcium sulfate hemihydrate in its a-form frequently occurs
in needle or plate-shaped crystals or bunch-like crystal com-
plexes. A calcium sulfate hemihydrate in its a-form which is
present in approximately mono-crystal form, is particularly suit-
able for carrying out the method of the invention. This calcium
sulfate hemihydrate does not decompose in aqueous suspension,
but changes its particle size only by virtue of the dissolution
of its particles, which is necessary for the setting process.
The specific surface area of the particles of the calcium
sulfate hemihydrate in its a-form, as measured in accordance
with the Blaine method, in aqueous suspension, should advanta-
geously be from 500 to 6000 and preferably from 1000 to 4000
~ s~. cm/g.
1/ It is unimportant, for carrying out this method according
to the invention, whether the a-form calcium sulfate hemihydrate
is produced directly with the necessary level of grain fineness,
or whether it is ground down to the necessary level of fineness,
from a coarser grain range, in a dry or a wet process.
The method according to the invention can also be carried
out by using a calcium sulfate hemihydrate in the form of an
a-hemihydrate which was produced from gypsum which occurs in the
production of phosphoric acid, by cooking in the presence of
additives which influence the crystallisation tendency. A by
29 product which occurs when producing phosphoric acid from raw
- 13 -
~)5973~ii
-- phosphate and sulfuric acid is a gypsum which comprises for
example approximately 90% o calcium sulfate dihydrate, and which
includes only small amounts of acid. This gypsum can be convert-
ed into the a-hemihydrate, for example by heating in a 35~
calcium chloride solution. However, this firstly results in
needle-like crystals with properties which are unfavourable from
the point of view of technical application. For this reason
substances were added to the~crystallisation pan, which improve
the crystallisation tendency of the resulting a-hemihydrate
gypsum such that this occurred in the form of short, compact and
uniform crystals. Additives which have been found particularly
suitable and which are preferabiy used for influencing the
crystallisation tendency are cis-ethylene dicarboxylic acids,
for example maleic acid or the anhydride thereof, in aadition
the alkaline salts of citric acid phthalic acid and the anhydride
thereof, and sulfite lyes.
Obviously the method according to the invention can
also be carried out by using mixtures of calcium sulfate in
the ~-hemihydrate form and the -hemihydrate form, if the ~-hemi-
hydrate fulfils the condition that the specific surface area ofits particles in aqueous suspension does not alter or alters only
to an unsubstantial extent, until the main amount of excess water
has been mechanically removed from the fleece. In this case the
sulfatic binding agent used is p~eferably a mixture of ~-hemihy-
drate and from 30 to 70% by weight of a-hemihydrate.
Instead of using pure a-calcium sulfate hemihydrate or
a mixture of a- and ~-calcium sulfate hemihydrate as the sulfatic
binding agent, it is also possible to use a mixtu-e thereof with
29 less than 10% by weight and preferably from 3% to 6% by weight of
cement.
- 14 -
~L~59736
Carrying out the variant of the method according to the
invention avoids very fine gypsum particles being produced by
calcium sulfate hemihydrate particle decomposition, which is
thought to occur in the manner of an explosion, in the presence
of water. Such very fine gypsum particles firstly remain
suspended in the form of solid matter in the excess water, and
are sucked away therewith because of their extreme fineness.
Evr~n i~ the last-mentioned disadvantage can to a limited extent
be overcome by a super-increased amount~of fibres which act as
a filter when the excess water is removed by suction, these
higher levels of fibre content frequently result in end products
whose strength is not at an optimum.
It is particularly advantageous for this method according to
the invention to use a calcium sulfate hemihydrate, in particular
in a-form, whose specific surface area, as measured in accordance
with the Blaine method, in aqueou~; suspension, is from 500 to
6000 and preferably from 1000 to ~1000 sq. cm/g. As the individ-
ual particles of the-~a-calcium sulfate hemihydrate do not
decompose in the presence of water, it is possible for this
specific surface area of the a-calcium sulfate hemihydrate to be
maintained during thè whole processing time of the f~leece which
is formed from calcium sulfate, fibres and a large excess of
water, in fact until the moulding is produced.
The a-calcium sulfate hemihydrate which is to be used in
accordance with the invention has little sensitivity of reaction
on dihydrate seeds and therefore makes it unnecessary to add -
setting retarding agents to the mixture comprising sulfatic
23 binding agents, fibres and an excess amount of ~ater.
- 15 -
~059736
As already mentioned, the method according to the invention
provides that the particles of the calcium sulfate hemihydrate
used to not change, or change only to an unsubstantial extent,
in respect of their particle size, until the moulding is produced,
even though the particles are in aqueous suspension. This pre-
vents the occurrence of very fine calcium sulfate particles
which require an increase in the amount of fibres in the fleece
to be produced. However, the reduction in the amount of very
fine calcium sulfate particles also results in a considerable
increase in the speed of suction removal, without substantial
amounts of calcium sulfate and fibres being entrained wlth the
water removed. In this way the starting mixtures`icomprising
fibres, sulfatic binding agents and water can also be more rapidly
introduced into a mouldO
In accordance with the method of the invention, when produc-
ing gypsum plates, the production capacity of the apparatus used,
in particular winding roll machines, can be considerably increas-
ed in comparison~with the previously known methods. In additio~
when using the method according to the invention it is now
possible to carry out the manufacture of flbre-bearing construc-
tion material plates, using sulfatic binding agents, on Four-
driniers, which can also be provided with metal sieves. It was
not possible for these plate producing machines to be used for
carrying out the previously known methods, as excessively long
suction removal times and unacceptable fouling of the conveyor
belts had to be tolerated. These disadvantages are eliminated
by means of the method according to the invention.
28 In addition, the method according to the invention provides
- 16 -
,~ .
l~S'~736
fibre-bearing construction members which always remain constant
in quality, in particular as regards strength.
The moulded members which remain after the excess water has
been removed by the suction action still contain from 5 to 30%
,~
by weight of free water which is removed by drying in per se
known manner.
- - 17 -
