The various alternatives for feeding two impressions are shown in Figure 4,9b. c and d. The simplest case (b) is where the runner takes the shortest path between the two impressions. Unfortunately, it is not always possible to adopt this short runner. This is because, as shown in the following discussion, the most desirable position for the gate may not be on the centerline of the mold
  If we consider Figure 4.9b, which schematically shows the plan of a mod for two rectangular blocks, it is seen that solely from the viewpoint of mod layout it is desirable to have tine impressions positioned as shown with short runners to the sides of the impressions, thus enabling the size of the mod to be kept to a minimum. However, there are other constructions, such as that of correct gating, and it may be desirable to gate at one end of the impression
  To achieve these end gates it is necessary to alter the design of the runner layout, so that either a T-shaped runner extends beyond the impressions and is then connected to the gates by short branch runners (Figure 4.9c), or the runner, in the form of an S, sweeps round 1o the gales (d), without the necessity for branch runners.
　In general, providing that the impressions are approximately the same size and shape, no difficulty should be experienced in designing balanced runner systems for two-impression molds
  THREE-IMPRESSION MOLDS
Figure 4.9e illustrate a balanced runner system for three similar impressions. In this case the impressions are placed on a pitch circle diameter 120° apart; this design allows the runners to be kept to a minimum length.
  When, however, the impressions are of different shapes and sizes the layout may be as shown in Figure 4.10a. The large impression is shown being fed directly from the sprue via a short runner, while the smaller components are fed via a branch and main runner system. Balance in the feed system is ultimately attained by adjustment of gate size
  OTHER MULTI-IMPRESSION MOLDS
For four or more impression molds the design of the runner layout is simply an extension of the previous discussion. For example, balanced runner systems for molds containing four, five, six and eight impressions are shown in Figure 4.9. From the runner balancing standpoint it is simpler by far to situate the impressions on a pitch circle diameter and feed each impression directly from the sprue via a runner rather than to incorporate a main and branch runner system.
As the number of impressions increase, however,the pitch circle diameter design becomes progressively more impracticable as the runner length, which is a function of the pitch circle diameter, is also increased. This results in large-diameter runners being required which progressively length the moulding cycle and more scrap   (although reprocessable) is producd. When a large number of impressions are of greatly dissimilar shape, the alternative main and branch runner system is therefore usually adopted. Examples of moulds with this form of runner layout are shown in Figure 4.10. The main runner acts simply as a manifold which which feeds a number of branch runners. The number and shape of the impressions will determine the precise layout but from the bloster machining standpoint convenient either to adopt a straight main runner (c) or design the main runner in the form of a cross (d) An eighty-impression mould is shown in Plate 2.
流道是在模板上加工出的连接主流道和进入（浇口）型腔的一条沟槽。在两板式基本模具中，流道设置在分型面上而在较复杂的设计中流道也许设置在分型面的下面。
流道的壁必须光滑，防止料流受到阻碍。另外，由于流道废料必须和塑件一起取出，所以流道壁上必须不留下任何加工痕迹，避免流道废料滞留在模板上。为了确保这些要点得到满足，要求模具设计者在图纸中注明这条流道需要沿取出方向抛光。 注塑模具流道设计英文文献和中文翻译(4):http://www.youerw.com/fanyi/lunwen_5507.html