Adhesive bonding and miscellaneous chemical manufacture – Methods – Plaster board making
Patent
1993-02-08
1994-11-29
Weston, Caleb
Adhesive bonding and miscellaneous chemical manufacture
Methods
Plaster board making
156 44, 156 45, 264112, 264128, B32B 3114
Patent
active
053686632
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national phase of PCT/EP91/01359 filed Jul. 19, 1991 and based in turn upon German national application P 40 25 797.5 filed Aug. 15, 1990.
FIELD OF THE INVENTION
The invention relates to a process for producing plate-shaped bodies from a mixture of plaster and fibrous materials, comprising the following process steps:
a) preparing a wet mixture of plaster and fibers;
b) spreading the mixture to form a mat;
c) compressing the mat into a raw plate; and
d) setting and drying the raw plate.
In addition, the invention relates also to an installation for implementing the process with
a) a device preparing a wet mixture of plaster and fibrous materials;
b) a spreading device spreading the wet mixture onto a molding line to form a mat;
c) a press through which the mat lying on the molding line is passed in order to be compressed into a raw plate;
d) a setting station wherein the plaster in the raw plates sets; and
e) a drying station wherein the set raw plates are dehumidified.
BACKGROUND OF THE INVENTION
A process and an installation of this kind are described in DE-OS 38 01 315. This publication describes the problems encountered when trying to set the water content of the wet plaster-fiber mixture and the possible solutions which have already been found. In the process described in DE-OS 38 01 315 the wetting of the mixture is carried out in two steps. A first portion of the required water is mixed into the dry mixture; the still spreadable mixture is then molded to a mat in several layers, similar to the process of producing pressed particle boards. The balance of the required water is then sprayed onto the individual layers of the spread mixture. The mat produced this way is then compressed into a raw plate in a press. The strength of the plates produced this way is very good, however it has been found that further improvement is possible.
OBJECT OF THE INVENTION
it is the object of the present invention to an improved process and apparatus for producing plate-shaped bodies with higher strength can be obtained in a simple manner.
This object is obtained in the process of the invention in that between the process steps (c) and (d) (i.e. between compressing and drying the following further process steps take place:
e) subsequent wetting of the top and bottom faces of the raw plate; and
f) subsequent compression of the subsequently wetted raw plates with a maximum pressure not exceeding the pressure used in process step (c), i.e. the original compression.
The process of the invention is based on the fact that a prewetted mixture after the first compression step at the highest pressure used in the total process is mechanically so stable that it is self-supporting. It is thus possible to further wet the bottom face. The subdivision of the total compression into two steps has various advantages:
The compression process which always also removes the air from the mat, is thus separated from the surface formation of the raw plate.
For the production efficiency of an installation it is always of particular importance that the air locked in the mat be expelled quickly and completely during compression. In practice this is achieved by using vent screens which are inserted between the press surfaces and the mat surface. As a result the pattern of the screens imprints itself on the surface of the raw plates and the imprint has to be subsequently removed by grinding, at least on one face. In the process of the invention it is possible to operate in the second compression step with a smooth press surface, instead of a screen. The water enrichment in the surface area of the raw plates causes a certain plasticity, so that the screen pattern can be substantially flattened during compression.
In the state of the art the plate-shaped body cannot be directly covered with a coating during its formation, because of the necessity to remove the air. However, in the second step of the process according to the invention, when air no longer has to be removed, it is p
REFERENCES:
patent: 4417931 (1983-11-01), Li
patent: 4840688 (1989-06-01), Vogt
patent: 4942003 (1990-07-01), Boyd
Babcock BSH Aktiengesellschaft Vormals Buttner-Schilde-Haas AG
Dubno Herbert
Kateshov Yuri
Weston Caleb
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