Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – With reshaping or surface embossing of formed article
Patent
1991-10-03
1992-08-25
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
With reshaping or surface embossing of formed article
264122, 264DIG31, B29C 4302, B29C 4700, B29C 6902
Patent
active
051416883
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with mineral-filled resin products, and methods for the production thereof.
It is known to make mineral-filled resin products, such as roofing tiles, by moulding a mixture of mineral particles and a thermosetting resin. The problem with roofing tiles produced by this method is that they have a "synthetic" appearance, because their surfaces are smooth and uniform.
According to the present invention, there has been devised a method of producing mineral-filled resin products whereby the surfaces of the resulting products have a more natural-looking appearance.
The method according to the invention comprises: thoroughly mixing a powdered mineral material with a minor proportion of a thermosetting resin material; extruding a batch of the resulting formulation, of predetermined weight, through a substantially rectangular section die to form an elongate extrudate of predetermined length; pressing the extrudate between a pair of generally planar plates each substantially of the predetermined length, one of the plates being a cast metal body which has been cast in material bearing an impression of a textured finished building product; and permitting the pressed extrudate to cure.
All the ingredients of the formulation, except the glass fibre, are generally initially mixed together to form a dough, followed by mixing the resulting dough with glass fibre reinforcement.
The resulting reinforced formulation is then weighed out as batches of predetermined weight, which are individually fed to an extruder (the latter being typically hydraulically operated), and extruded in the form of a longitudinally extending, square- or rectangular-sectioned, body of predetermined length. These lengths are then pressed according to the invention between plates, one of which has thereon the impression of a textured finished building product, as described above. It is particularly preferred that a plurality of the extruded lengths are simultaneously pressed in a stack, one above the other, with an alternating stack of the plates described above, such that each extrudate is pressed between a face of one plate have the impression of the textured finished building product, and a further face of a further plate.
The mixing carried out in the method according to the invention is typically carried out by means of a tumbling mixing vessel, preferably provided with interior baffles or agitators. The mixing vessel may, for example, be tumbled about a horizontal axis.
The cast metal body used in the method according to the invention is generally a cast steel plate, which is a reversed facsimile of the original textured finished building product, the latter being typically a roofing panel, such as a slate. It is accordingly preferred that the impression of the textured finished building product is that of a natural slate. Such a steel plate therefore generally includes protuberances corresponding to weakened recesses required in the resulting roofing panel for location of nails to be passed through the formed panel for nailing the latter to rafters or purlins. The steel plate is generally cast in a granular refractory material bearing the required impression. An example of such a granular refractory material is sand, which is traditionally used in the process known as sand casting.
The plates used in the method according to the invention are preferably thermostatically heated, at a temperature such that the extruded formulation can be thermally deformed, and cured. In one embodiment of the invention, the plates may be hollow, with channels therethrough for the flow of heated gas or steam to control the temperature of the plates.
The pressed extrudate may be subsequently allowed to cure, with only the region adjacent each end supported; this ensures that when the final product is a roofing slate, it has a small degree of "sag" corresponding to that desired for this product.
The powdered mineral-filled resin product produced in the method according to the invention may be a roofing panel, such as a slate, a wall-cl
REFERENCES:
patent: 4420351 (1983-12-01), Lussi et al.
patent: 5017320 (1991-05-01), Velazquez Garcia
Olway Industries Limited
Theisen Mary Lynn
LandOfFree
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