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1、Lesson 6 Runner,The runner is a channel machined into the mould plate to connect the sprue with the entrance to the impression. The wall of the runner channel must be smooth to prevent any restriction to flow.,Also, as the runner has to be removed with the molding, there must be no machine marks lef
2、t which would tend to retain the runner in the mould plate.,To ensure that these points are met, it is desirable for the mould designer to specify that the runner is polished in line of draw.,There are some other considerations for the designer to bear in mind: (i) the shape of the cross section of
3、the runner; (ii) the size of the runner; (iii) the runner layout.,Runner cross-section shape,The cross-sectional shape of the runner used in a mould is usually one of four forms (Figure 6-1): (a) fully round, (b) trapezoidal, (c) modified trapezoidal and (d) hexagonal.,Figure 6-1 Runner profiles,The
4、 criterion of efficient runner design is that the runner should provide a maximum cross-section area from the standpoint of pressure transfer and a minimum contact on the periphery from the standpoint of heat transfer.,The ratio of cross-sectional area to periphery will, therefore, give a direct ind
5、ication of the efficiency of the runner design; the higher the value the greater the efficiency. Ratios for various types of runner section are given in Figure 6-2.,As can be seen, the round and square types of runner are the two most satisfactory designs from this standpoint; whereas the ratios exh
6、ibited by the semicircular and rectangular types make their use generally undesirable.,Figure 6-2 Efficiency of various runner profiles,Runner size,When deciding the size of the runner the designer must consider the following factors: (i) the wall section and volume of the molding; (ii) the distance
7、 of the impression from the main runner or sprue; (iii) runner cooling considerations; (iv) the range of mould makers cutters available; (v) the plastics material to be used.,Runner layout,The layout of the runner system will depend upon the following factors: (i) the runner of impression; (ii) the
8、shape of the components; (iii) the type of mould (i.e., two-plate or multi-plate mould); (iv) the type of gate.,When designing a runner system there are two main considerations.,The runner length should always be kept to a minimum to reduce pressure losses, and the runner system should be balanced.,
9、Runner balancing means that the distance the plastic material from the sprue to the gate should be the same for each molding.,This system ensures that all the impressions will fill uniformly and without interruption providing the gate lands and the gate areas are identical.,Figure 6-3(a)(b)(c) shows
10、 examples of mould all based on the balanced runner principle.,Figure 6-3 Runner layout,It is not always practicable, however, to have a balanced runner system and this particularly applies to moulds which incorporate a large number of differently shaped impressions (Figure 6-3(d).,In these cases ba
11、lanced filling of the impression can be achieved by varying the gate dimensions that is by balanced gating.,Notes, The criterion of efficient runner design is that the runner should provide a maximum cross-section area from the standpoint of pressure transfer and a minimum contact on the periphery f
12、rom the standpoint of heat transfer.,高效率的流道设计标准是：从压力传递角度来看，分流道应该提供最大的横截面积，从热传递角度来看，分流道应该提供最小的表面积。 句中that引出的从句作谓语动词is的宾语从句，只起连接作用本身无意义。, It is not always practicable, however, to have a balanced runner system and this particularly applies to moulds which incorporate a large number of differently shaped impressions.,然而，采用平衡式分流道系统并不是完全可行的，尤其在具有不同型腔的多型腔模具中。 句中it是形式主语，真正的主语是不定时短语和省略that的从句。,
