Patent EA-000313-B1 (EA)
Title: Apparatus and process for producing polymeric foam
Inventor: BLACKWELL JAMES BRIAN
IPC: B29C44/00
Filed: 1996-07-08
Abstract: 1. An apparatus for producing polymeric foam, wherein reactive foam components and a low-boiling point frothing agent are brought together, sufficient pressure is applied to maintain the frothing agent in a liquid state, and the mixture is passed through a permeable discharge head through which the mixture is discharged and wherein the pressure is reduced and froth is formed, characterised in that the discharge head comprises at least one diffuser element (46) having a structure such as to require division, divergence and convergence of flow paths in three dimensions within the axial thickness of the diffuser element, considered in the direction of flow therethrough. 2. An apparatus as claimed in Claim 1, wherein said at least one diffuser element (46) is made of bonded or sintered composite material. 3. An apparatus as claimed in Claim 2, wherein said at least one diffuser element (46) is made of sintered wire. 4. An apparatus as claimed in Claim 1, wherein said at least one diffuser element (46) comprises a mass of loose, particulate material, or a compressible fibre material contained between permeable support plates. 5. An apparatus as claimed in any of Claims 1 to 4, further comprising means which permits backwashing of the or each diffuser element. 6. An apparatus as claimed in Claim 5, wherein the backwashing enabling means is adapted to allow said at least one diffuser element to be selectively displaced through 180 degree  to enable discharged material itself to provide backwashing. 7. An apparatus as claimed in Claim 6, wherein the diffuser element is held in a rotary member (150) of a rotary valve, the member (150) being selectively rotatable by means of a rotary actuator (152) to invert the diffuser element relative to the flow path through the valve. 8. An apparatus as claimed in any of Claims 1 to 7, including a frothing control means, which controls frothing such as to enable the diffuser element to be used for longer periods between down times for servicing. 9. An apparatus as claimed in Claim 8, wherein said frothing control means is adapted to enable backpressure at the diffuser element to be selectively adjusted during foaming. 10. An apparatus as claimed in Claim 9 in which said back-pressure adjustment facility is achieved by containing the diffuser element: material (178) between a pair of support plates (170,172) whose relative spacing is adjustable to enable adjustment of the compression level of the diffuser material. 11. An apparatus as claimed in any of Claims 1 to 10, further including means, which enables cleaning of the diffuser element whilst foaming continues. 12. An apparatus as claimed in Claim 11, wherein to enable said cleaning whilst foaming continues, there are at least two said diffuser elements (C1, C2) disposed in parallel, with the flow of reactive constituents thereto selectively controllable by a variable inlet flow path. 13. An apparatus as claimed in any of Claims 1 to 12, wherein said diffuser element has an effective area of variable size. 14. A process for producing polymeric foam comprising bringing together reactive foam components and a low-boiling point frothing agent, applying pressure to maintain the frothing agent in a liquid condition and discharging the components through a permeable discharge head to form a froth the discharge head comprising at least one diffuser element having a structure which causes division, divergence and convergence of flow paths within the axial thickness of the diffuser element, considered in the direction of flow there through.