GB789965A - Apparatus for method for moulding plastic material - Google Patents

Abstract

789,965. Moulding rubber rings, washers &c. DUNLOP RUBBER CO., Ltd. Sept. 3,.1954 No. 25585/54. Class 87(2). Plastic material B, Fig. 1, is plasticised on a warming mill M which forms it into a strip S, and the strip is passed between successive pairs of dies 36, 37 mounted on a wheel 10 that rotates about a horizontal axis 100. The die 37 is fixedly mounted in a ring 14, Fig. 3, forming part of wheel 10, by means of a screw 38, but the die 36 reciprocates to and from die 37 to cut an annular piece of material from the strip S and mould it into a ring R, Fig. 7, the mould cavity being formed by recesses in the meeting faces of the dies. The die 36 is fixed in a plunger 18, Fig. 3, that slides in a bore 16 in another ring 13 forming part of wheel 10. The plunger 18 is slid to and fro by a stationary cam track 26 through the intermediary of roller 26<SP>1</SP> on slide bar 25, fork 24, roller 23 on one arm of a bellcrank lever 22, and link 21. The other arm of the bellcrank lever is pivoted at 30 to one end of a slide 31 the other end of which is engaged by a compression spring 32 backed by an adjusting screw 33. When the bellcrank lever moves from the retracted position of Fig. 4 to the advanced position of Fig. 3, it passes beyond a dead centre and locks, toggle-wise. If the dies meet excessive resistance the spring 32 will yield. The dies are hot (rings 13, 14 being heated) and material moulded therein expands, thus temporarily compressing spring 32 and allowing egress of material from the mould cavity, Accurate registration of the dies is effected by the engagement of wedges 80, Fig. 4, on ring 78 on die 36 with ramps 54 on die 37. The ring 78 limits the approaching movement of the dies. The waste central portion 56 is blown through a bore 55 in die 37 into a receptacle 61, by hot compressed air supplied from a pipe 69 via spring-pressed conduit 70 and passages 62, 63, 64 in plunger 18 and die 36. The waste strip S<SP>1</SP> may be torn off the closed dies and carried back to the mill by power-driven rollers 46 via guide rollers 45. To facilitate this tearing off, the strip is engaged by the dies near one edge 58, Fig. 7, and this edge breaks away from the dies: To facilitate the breaking a slit may be made in the edge 58 by a cutter on the dies, Fig. 12 (not shown). Fig. 14 shows the moulding of a washer having one flat side and one conical side. In this case the Fig. 20 cam (see below) is used, the dies being opened to permit removal of the waste strip and then closed. A pin 87 ejects the moulded washer. A hole may be made in the washer by a tubular cutter 88, the waste emerging as a rod through passage 90. Fig. 20 shows a schematic view of a form of cam 26. A part 26a closes the dies to the Fig. 7 position, 26b opens the dies to allow removal of the waste strip and other unwanted material from between the dies, 26c closes the dies to mould the rings and 26d opens the dies. An undulating cam surface 26e, slightly opens and closes the dies to permit escape of gases. A modified cam, Fig. 19 (not shown) omits the part 26b. When the moulding cavity is large a ribbed strip, Fig. 18, may be used. Sprays 82, Fig. 4, lubricate the dies. Specifications 789,966 and 789,967 are referred to.