Patent GB-1445863-A (GB)
Title: Cooling thermoplastic material during extrusion through a die
IPC: B29C48/05
Filed: 1973-09-07
Abstract: 1445863 Cooling material in extrusion dies CUMBERLAND ENG CO Inc 7 Sept 1973 [8 Sept 1972] 42187/73 Heading B5A In the extrusion pelletization of a plastics material, e.g. polyethylene or polypropylene, the material is extruded through at least one die passage comprising a fluid permeable sleeve, e.g. of sintered stainless steel, through the walls of which pressurized water is delivered to effect lubrication between the material and the passage and to cool the outer surface of the extruding material in partly vaporizing. The cooling produces a solidified skin which enables knives, cutting the extrudate into the pellets, to be mounted at a clearance from the outlet face of the die, thereby avoiding wear of the die face and smearing of plastics thereon, which would otherwise arise from knives contacting the die face. In the Fig. 2 embodiment, the die face comprises a cylindrical surface 154 to which extrudates are delivered through a plurality of passages defined by sleeves, which are radially aligned in a die assembly 38, from a die inlet passage 54 and via passages 56 and an annular manifold 58. The permeable sleeves 110, Fig. 5, may be removably mounted, by nuts 106, in the assembly 38 comprising a member of parts welded together and providing an annular channel 98, and bores 100 for the delivery of the water and through which the sleeves 110 extend. The sleeves each connect to the manifold 58 via a bore 82 on either side of which is provided, for the circulation of heating oil, annular channels 80 which are interconnected between the bores 82. Alternatively, Fig. 6 (not shown), the sleeves (122) may be fixedly brazed in position within a similar die assembly comprising brazed together parts. In the Fig. 2 embodiment, the die 52 is clamped, by swing bolts 42, 44, to a pelletizing housing 16 within which the knives, e.g. six to twelve, are each secured to a holder 150, for rotation by a plate 149 which is fixed for its rotation to a sleeve 147, rotated by keyed engagement with a sleeve 139 by a hollow shaft 20 extending into the housing 16. The sleeve 139 and shaft 20 respectively rotate upon a die fixture 142 and a pipe 24 fixed thereto and through bores 24, 145 of which cooling water is delivered, via fixture bores 254, to flow across the die face 154 to carry the pellets through an outlet 26 of the casing 16. The die 52 and casing 16 are mounted on a wheeled carriage for movement into clamping engagement with the extruder, and the casing 16 is provided with glass inspection windows 28. The knife holders 150, Fig. 7, are secured to the plate 149 by bolts 180, and the knives 160 are clamped to the holders 150 by members 162 and bolts 164, and their clearance from the die face 154 is adjustable by screws 170. In the Fig. 11 embodiment, the permeable sleeves 216 are aligned in parallel to extrude at a planar die face, from which the pellets are cut by a pair of knives 246 each mounted to an arm 242 of a shaft 230 having a bearing 240 within the die. In this embodiment, the knives rotate in a housing 232 from which the pellets are removed by water, circulated via housing inlets and outlets 234, 236. Extrusion is commenced in the absence of cooling water either passing through the permeable sleeves, or circulating through the housing.