Patent GB-1365942-A (GB)
Title: Device for moulding heated material under pressure
IPC: C03B11/12
Filed: 1971-09-07
Abstract: 1365942 Pressing glass PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 7 Sept 1971 [10 Sept 1970] 41702/71 Heading C1M [Also in Division B5] A press for glass articles, e.g. lenses, prisms, television screens and lamp glasses, comprises two pressing elements such as 1 and 8 which co-operate to define a pressing space 17, each pressing element being hollow and the cavity 4, 11 within each element containing a heattransfer medium which conveys heat from the wall of the pressing surface 2, 9 to a second wall 3, 10 by changing state from the liquid to the vapour phase adjacent the pressing surface wall and then condensing back to liquid at the second wall. Alternatively this heat-transfer process may be reversed to heat the pressing surface. Each cavity also contains porous material, e.g. in the form of a lining 5, 12 which enables the condensate to be returned by capillary action. By this means the pressing surface is kept at the same temperature all over to avoid uneven temperature distribution in the articles being pressed. Heat is provided, e.g. by an electric element 6, 13, or a gas burner, which heats the second wall 3, 10, or alternatively these walls are cooled by cooling coils or spray. To strengthen the pressing walls internal supports may be provided in the cavity; these may be of perforated metal plate, folded metal gauze, rods or pipes but preferably take the form of a compressed porous mass filling the cavity, the pores being so much larger than those of the porous lining that condensate flow will be restricted to the latter, leaving the pores of the filling mass free for flow of vapour. A formula relating pore sizes in the two porous materials is given. A further refinement, which may be provided to cater for deviations from the nominal working temperature of the pressure surfaces consists in providing a container 55 or 52 (Fig. 4), communicating with the element cavity 36 or 28 and containing an inert control gas. The vapour/gas interface is arranged, by balance of pressures, to be located adjacent the second wall 35 or 27 as shown by the dotted line, so that the vapour does not contact the entire wall and its heat-transfer rate is restricted accordingly. Reduction or increase in vapour pressure due to variation in temperature of the pressure wall will cause the vapour/gas interface to move, thus presenting less or more of the second wall surface for heat transfer to compensate for the aforesaid temperature variation. In alternative embodiments (Fig. 5, and 6, not shown) the control gas container is either formed by an extension of the cavity, or is contained within the cavity, and in either case is lined with the porous material so that any vapour which enters it may condense and be returned by capillary action. The porous material of the linings may be, e.g. ceramic, sintered metal powders, gauzes of glass fibres or of metal wires. The preferred material for the porous support filler is compressed steel wool. The heat-transfer medium may be water vapour or, for higher temperatures and with the cavity evacuated may be, e.g. liquid sodium, potassium, lithium, cadmium, indium, lead, or silver; metal salts such as various metal halogens, nitrates, nitrites or mixtures thereof.