Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1993-11-12
1996-04-16
Aftergut, Karen
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
264 405, B28B 300
Patent
active
055079962
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and to apparatus for manufacturing building blocks by molding under high pressure a mixture of a hydraulic binder such as plaster, an inert filler such as sand, and water.
Such building blocks and the method of manufacturing them have already been described in international patent application WO 88/03916 of the same inventor.
That method consists essentially in molding under high pressure the mixture of plaster, sand, and water, for a sufficient length of time, of the order of 2 minutes to 3 minutes, corresponding to the hydration under pressure of plaster which gives rise to an opposed expansion of the plaster inside the mold, and also to densification and reorientation of its crystal lattice.
Building blocks obtained in this way have remarkable characteristics: compression strength considerably greater than 100 kg/cm.sup.2, hardness equivalent to that of soft stone, good resistance to damp and to frost, and dimensional accuracy of the order of one-tenth of a millimeter, thereby enabling them to be placed directly one on another without interposing traditional jointing between the blocks.
In addition, the blocks are ready for use in building on being unmolded, without drying.
In building, that provides considerable savings both in the time and in the skills required of the workers, such that the costs associated with building proper are divided by a factor of not less than 2 or 3.
An object of the present invention is to provide considerable improvement to that method, and to the means for implementing the method, thereby enabling the characteristics of the above-specified building blocks to be further improved, enabling their quality to be made more uniform, and enabling their cost price to be reduced.
Another object of the invention is to provide means enabling such blocks to be manufactured in large quantities and at a high rate.
To this end, the present invention provides a method of manufacturing building blocks from a mixture of a hydraulic binder such as plaster, an inert filler such as sand, and water, the mixture being molded under pressure during a period of time that is sufficient for obtaining hydration under pressure of the hydraulic binder and densification of its crystal lattice, the method being characterized in that it consists in placing a measured quantity of the mixture in a mold having undeformable side walls and top and bottom horizontal plates that are movable in vertical translation inside the mold with small clearance relative to the side walls, then in slowly displacing at least one of the plates in the mold over determined strokes successively to settle the mixture inside the mold and then to impart a predefined height to the block that is to be obtained by progressively exerting high pressure on the mixture in the mold, in keeping said plates in place during the above-mentioned period of time during which opposed expansion of the hydraulic binder takes place in the mold, and then in moving one of the plates away for the purpose of unmolding the block by displacing the other plate towards the inside of the mold.
The slow compression of the mixture placed in the mold has the following effects in succession: settling the mixture in the mold, with its bulk factor being reduced; expelling the air contained in the mixture and accelerating wetting of the mixture by putting the water under pressure; expelling from the mold any water that may be in excess relative to the exact quantity of water required for hydrating the plaster; and accurately defining the height (i.e. the dimension between the horizontal plates of the mold) of the building block that is to be obtained. By keeping the mold plates in place in the positions they occupy at the end of the compression stage, it is possible to conserve this height during the following stage which is a stage of hydration under pressure and of opposed expansion of the plaster in the mold.
The building blocks produced in this way are of well-defined dimensions and they have compression strength that is not less
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Aftergut Karen
TECFIM
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