Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Stratified or layered articles
Patent
1987-09-21
1991-09-24
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Stratified or layered articles
126261, 126262, 264112, 264120, 264334, 264DIG57, B29C 4320
Patent
active
050512200
DESCRIPTION:
BRIEF SUMMARY
Heating elements are known in the form of a flat cake or lozenge comprising a layer of thermally insulating refractory material, a reactive layer constituted by means of a finely divided metal or metalloid, mixed with at least one oxidant, which is likewise finely divided, and a heat conducting and diffusing layer, the refractory layer comprising perpendicular walls creating a reaction path for the reactive layer. Elements of this type are described for example in European Patent No. 0084532.
These elements may be obtained by successive casting steps. The insulating layer may for example be constituted by plaster reinforced with a fibrous material such as glass fibre. The glass fibre/plaster mixture is in admixture with water and the liquid mass thus obtained is poured into an appropriate mould, such as to obtain a flat cake having a deep channel on one of its faces, formed by ribs shaped perpendicular to the plane of the cake, said channel forming a predetermined path. After solidification of the plaster, the cake is removed from the mold and the reactive exothermic mixture, provided in a fluid state by the addition thereto of a liquid which can contain a binder, is poured into the channel. This liquid may for example be water in admixture with a small percentage of silicate. A part of the liquid is progressively absorbed by the plaster and the reactive mass densifies. As soon as the reactive mass has attained an adequate consistency, the diffusing and conducting layer is placed on its surface, which layer may be either a film of metal, such as of aluminium or a pulverulent layer consisting of a metallic powder or other heat conducting element with the addition of an incombustible binder, such as silicate. Subsequently the assembly thus formed is heated in order to evaporate off the liquid elements which it contains. If this process is relatively easy to put into effect, it nevertheless has a certain number of disadvantages which render the manufacture of the elements slow and costly. The solidification of the plaster necessitates a minimum time of 15 minutes, and likewise the densification of the reactive layer takes an appreciable time. It is know that to facilitate its pouring, plaster should have an equal weight of water added to it and evaporation of this water necessitates use of a large quantity of energy.
The object of the present invention is to permit the rapid manufacture of the heating element in question in great numbers. This invention lends itself to the constitution of an entirely automated chain of manufacture, permitting the production of these elements in a very simple manner at a very low price.
To this end the present invention provides a process of manufacturing a heating element in the form of a flat cake comprising a support of generally flattened form and of thermally insulating refractory material, this support having walls substantially perpendicular to its length, these walls defining a hollow path therebetween in which is disposed an exothermic, finely divided, reactive mixture, said process being characterised in that a layer of the reactive mixture is deposited on a temporary support and provided with the mirror image of the said hollow path and a layer of a liquid or pulverulent refractory material is deposited on the reactive mixture layer thus formed, this layer of refractory material being subsequently subjected to a treatment effecting its hardening.
The accompanying drawings show schematically two examples of the process according to the present invention, and in which:
FIG. 1 is a section through a first flat cake along its principal plane.
FIG. 2 is a section along the line II--II of FIG. 1.
FIG. 3-7 show successive stages of the process of manufacture of the heating element according to FIGS. 1 and 2.
FIG. 8 is a section through another flat cake along its principal plane.
FIG. 9 is a section along the lines IX--IX of FIG. 8.
FIGS. 10-13 show successive stages of the process of the manufacture of the heating element according to FIGS. 8 and 9.
FIGS. 1 and 2 show a h
REFERENCES:
patent: 461890 (1891-10-01), Richardson
patent: 1345377 (1920-07-01), Linbarger
patent: 1792844 (1931-02-01), Knecht
patent: 3034393 (1962-05-01), Lieberman et al.
patent: 3255278 (1966-06-01), Smith
WO83/00425, Feb. 1983.
Spreter Victor
Zellweger Conrad
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