模具专业英语 作者 王浩钢 14456第8章.pptVIP

Lesson 8  Parting Surface 　　The parting surfaces of a mould are those portion of both mould plates, adjacent to the impressions, which butt together to form a seal and prevent the loss of plastic material from the impression①. 　　The parting surface is classified flat and non-flat. Flat parting surface 　　The mature of the parting surface depends entirely on the shape of the component. For instance, the parting surface of the rectangular molding is shown in Figure 8-1(a). 　　The cavity for this article can be die-sunk into one mould plate. The position of the parting surface will therefore be at the top of the molding, the parting surface itself being perfectly flat. 　　For appearance this is the ideal arrangement as the parting line is not noticeable unless flash develops. 　　A further consideration is that the parting surface must be chosen so that the molding can be removed from the mould. 　　　Figure 8-1(b) shows the parting surface of a flat rectangular molding which incorporates a double-bevel edge. 　　The suitable choice for the parting line is on the centre of the double-bevel which allows for half of the required form to be die-sunk into each of the two mould halves. 　　The parting line must occur along the line round the position of maximum dimension when viewed in the draw direction. Non-flat parting surface 　　Many moldings are required which have a parting line which lies on a non-planar or curved surface. In these cases the mould’s parting surface must either be angled (a), profiled (b) or stepped (c) (in Figure 8-2). Balancing of mould surfaces 　　When the parting surface is not flat, there is the question of unbalanced forces to consider in certain instances. Figure 8-3 shows a mould with a stepped parting surface. 　　The plastic material when under pressure within the impression, will exert a force which will tend to open the mould in the lateral direction (see Figure 8-3(a)). If this happens some flashing may occur on the angled face