Plastic article or earthenware shaping or treating: apparatus – Means casting fluent stock operably associated with shaping...
Patent
1982-11-01
1985-12-17
Anderson, Philip
Plastic article or earthenware shaping or treating: apparatus
Means casting fluent stock operably associated with shaping...
264 458, 264 462, 264 469, 264 51, 264DIG84, 264 453, 425817C, B29D 2704
Patent
active
045590036
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an apparatus for manufacturing webs of polymer foam and to the product obtained.
The technique sector covered by the invention is that of equipment for making webs of supple or rigid foam.
It is known that, in the process of polyurethane foaming, two simultaneous reactions are produced between, on the one hand the isocyanate and the polyol (or polyalcohol) and on the other hand between the isocyanate and water, which produces the main expanding agent: carbon dioxide gas. This latter reaction, possibly combined with the physical phenomenon of boiling of an auxiliary swelling agent (methylene chloride or trichlorofluomethane) provokes the expansion of the foam. In this way, a porous, thermosetting material is obtained which may either be supple or rigid depending on the degree of cross-linking of the polymer.
Presently known continuous-casting processes consist mainly in distributing as uniformly as possible the liquid reactive mixture over the width of an inclined conveyor, formed by a bottom and two lateral walls which move perpendicularly to the distribution of the liquid. This distribution of a mixture of liquid, only slightly viscous reagents, of rapid reactivity, involves a retention zone capable of containing the liquid poured for the time necessary and sufficient for this operation. In this design, the inclination of the conveyor is generally from 4.degree. to 6.degree. over the length necessary for the expansion of the foam and gelification thereof: between fifteen and twenty meters. Displacement takes place thereafter on a horizontal plane up to the transverse cutting equipment: about fifty meters from the point of casting.
The most conventional devices comprise a casting head adapted to be moved in a transverse to and fro movement and the retention zone of the reagents if formed, upstream, by the bottom of the conveyor, generally constituted by a sheet of supple material: sheet of paper or of polyethylene, laterally by continuously advancing walls constituted by the same material as that of the bottom and, downstream, by the product itself which enters its initial reactive phase, called the "cream line". It is specified that the term "cream line" designates the state of the mixture of the reagents occurring immediately after the liquid phase and in which this mixture attains a high viscosity preceding the formation of the foam. The product in the viscous state adheres to the bottom support and constitutes a constantly renewed barrier to the flow of the liquid mixture along the slope of the conveyor. In order to compensate for the absence of mixture in this state, an obstacle is placed downstream of the casting head at the beginning of manufacture, whose role is to retain the liquid mixture at the start.
On this principle, a process is known, described in French Pat. No. 1 579 795 according to which a transverse element of determined profile is placed beneath the supple support to communicate an ascending movement of said support over a very short distance and thus form the downstream wall of the retention zone. This process makes it possible to improve the distribution of the liquid mixture over the width of the conveyor and to reduce and even eliminate the to and fro movement of the casting head.
This principle is also applied in the process described in French Pat. No. 72 76616 in which a cylindrical bar is used, protected by a supple upper support, for example a web of paper, which laminates the liquid mixture at the precise point of the cream line, thus creating, by a constantly monitored adjustment appropriate to each manufacture, a fragile balance between the arrival of liquid and its evacuation in the expansion zone. According to this process, the downstream wall is formed by the cylindrical bar in combination with the cream line which immediately follows it.
Another known process is described in French Pat. No. 71 31528, which consists in distributing the liquid mixture over the conveyor by means of a container or trough, in which the reagents are introduce
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