GB726814A - Improvements in or relating to a mould for forming an article by compression moulding - Google Patents

Abstract

726,814. Moulds for rubber &c. SCHERER CORPORATION, R. P. Nov. 14, 1952 [June 24, 1952], No. 28756/52. Class 87 (2) Relates to moulding cup shaped or tubular articles from material such as rubber and consists in. a self-trimming mould comprising two co - acting mould halves having narrow lands or parting surfaces rendering said mould halves subject to damage on over-stressing, plates having aligned recesses for slidably receiving said mould halves, and a generally columnar member in one of said recesses for spacing the mould half seated in said one recess from the bottom thereof, said columnar member being more readily deformed than the mould half supported thereby on overstressing of said mould half, and said columnar member retaining resiliency even after permanent deformation. The object is to mould an article without leaving any fin or flash. A plurality of male mould halves 20 are slidably fitted in bores 24 in a die plate 26 and female mould halves 22 are slidably fitted in bores 30 in a die plate 32. Between the mould halves in both plates and the cover plates 28, 34 are spool-shaped back-up members 72. The die plates 26, 32 are accurately aligned by dowels 50 and are fitted with handles.to enable them to be lifted in and out of the press and separated from one another. Each male mould half 20, Fig. 11, tapers to a die 90, and formed in the tapering surface is an annular shoulder 94. Each female mould half 22 projects beyond the die plate 32, tapering to an annular surface 106, and has a recess 102 which forms the mould cavity. 94 and 106 are the parting surfaces between the mould halves. 94, being wider than 106, projects inwards to form the edge or lip of the finished article, Fig. 13. All the parting surfaces in each die half must be accurately aligned, but the need for careful machining for this is obviated by the hack-up members 72, which when first fitted are slightly oversize and are deformed by the pressure of the initial moulding operations to the exact length required for accurate alignment of the parting surfaces. The cross-section and material of the back-up members are such as to give them the correct deformation, the latter being a metal with a modulus of elasticity less than 20 x 10<6> lb. per sq. in., e.g, brass, bronze or aluminium. The spool-shaped back-up members may be plain-walled, as shown, or they may be corrugated. The deformability of the back-up members enables them to yield if excessive local pressures arise, due, e.g., to hand particles in the moulding material, so guarding against crushing of the parting surfaces. The back-up members are easily replaceable. Before the moulding operation an excess of material over the amount required for the size of the article is placed in each recess 102. As the die 90 enters the recess, material M, Fig. 13, is squeezed out between the parting surfaces, which are narrow enough for all the material to be displaced and no fin or flash formed.