Patent GB-794454-A (GB)
Title: Method and apparatus for the manufacture of sheet foam rubber
Filed: 1955-12-29
Abstract: 794,454. Making latex foam sheet material; foam rubber. TALALAY, J. A., TALALAY, A. and TALALAY, L. Dec. 29, 1955, No. 37309/55. Classes 70 and 87(2). [Also in Group VIII] Air, rubber latex and zinc oxide are mixed in a mixing head or foamer 12 into homogenized foamed latex which is directed to form a bank 17 between trough members 21, 22 from which a foamed latex sheet 23 is spread on a conveyer belt 19. The belt 19 passes through a refrigerating chamber 24 whereby the foam is subjected to a temperature low enough to freeze the water in it and thereby to produce a permeable structure which allows free passage of a coagulating gas and obviates collapse of the foam during coagulation. Next, the belt carries the frozen foam through a chamber 25 containing a coagulating gas and a sol-gel transformation is thereby effected. The solidified and coagulated foam is carried through a tempering or partial thawing zone 26 to eliminate pock marks from its surface before entering an oven 27 in which the foam rubber sheet is vulcanized. After leaving the oven the foamed rubber sheet 23 is removed from the belt and passed through a washing chamber 28 and a drying oven 29, being finally wound up as a roll 30. A fabric backing may be applied to the foamed latex, either by drawing it from a fabric roll on the surface of the belt and under the bank of foam, the latex sheet being spread on top of the fabric, or by guiding the fabric backing under a doctor blade which spreads the foam on the belt and introduces the fabric on top of the foamed latex sheet. A suitable form of spreader, Fig. 2, for depositing the latex sheet comprises a tube 20a, between trough members 37, 38, with a slot 32 which can be altered in width by exerting pressure on the tube by screw clamps 33, 34. The conveyer belt may be of steel or other metal, or of rubber with protrusions 40, Fig. 3, which act as core pins to form depressions in the sheet. A sheet smooth on both sides may be produced by twisting it through 180 degrees so that its other broad surface comes in contact with the belt. Latex foam sheet smooth on both sides may be produced by an arrangement as shown in Fig. 4. Latex passes through a metering pump and line 45a, zinc oxide through a metering pump and line 44a and a metered air supply through a reservoir 42 to a foamer 43 comprising alternating rotary and stationary blades with projecting fingers. The belt 50 on which a layer of foam has been spread passes through a tunnel 52 on rollers 69 where air at a low temperature, e.g., -20‹ to -30‹F., is circulated at about 1000 to 2000 ft. per min. above and below the belt. To preserve a constant width of sheet edge doctoring blades or moving side belts should be provided. In the coagulating chamber 53 carbon dioxide mixed with air or scrubbed flue gas is circulated at a temperature about 0‹F. to prevent the foam from thawing, and permeates the porous mass of the foam and causes irreversible coagulation of the latex. The sheet is guided by edge doctor belts. Instead of carbon dioxide the coagulating gas may be selected from the group of water soluble gases with acid aqueous reaction consisting of carbon dioxide, sulphur dioxide and gaseous hydrochloric acid. Infra-red ray lamps 56 partially thaw the foam which is then guided to a belt 57 below the belt 50 and moving in the opposite direction, the foamed sheet, with its other surface now in contact with the smooth belt, thus being carried through a vulcanizing chamber 60 in which steam at atmospheric pressure, which may be superheated, is introduced in jets 62, which do not impinge on the foam, to maintain the required temperature, assisted by steam coils 61. Preferably the vulcanization takes place in an atmosphere of inert gas, e.g., a mixture with the steam of nitrogen or carbon dioxide.