【正文】 當大量的型腔必須組合在一起時，或在型腔的形狀不同時，通常采用兩級分流 道系統(tǒng)的方法。 可是當型腔的形狀和尺寸不同時，也許要采用圖 所示的布置方法。不過，這種短流道并不都可以采用。即采用平衡澆口。在計劃一個流道布置方式時，有兩個方面要重點關注。 流道截面的選擇也受到流道系統(tǒng)的頂出是否實際可行的影響。使用的是公制單位。不過對于硬 PVCs 和聚丙烯除外，這是由于它們所具有的高黏度決定的，其可用的直徑可以達到 13 毫米。對于具有復雜分型面的模具，或對于多模板模具，由于圓形流道的兩半圓難以精確地吻合，應該采用梯形的或 U 形截面的流道 。 流道截面的選擇也受到流道系統(tǒng)的頂出是否實際可行的影響。其后的料流將穿過這些已經(jīng)固化的材料中心，由于大多數(shù) 熱塑性塑料所具有的低熱傳導率，已固化的材料起到了隔熱作用并維持了中心料流的溫度。梯形流道的體積在相同尺寸的（ W=D,圖 ）情況下，大約比圓形流道大25%。 流道設計效率的評判標準從壓力傳遞的角 度來看流道應該具有最大的橫截面積，而從熱量傳遞的角度來看，應該和周邊有最小的接觸面積。 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 . The large impression is shown being fed directly from the sprue via a short runner, while the smaller ponents are fed via a branch and main runner system. Balance in the feed system is ultimately attained by adjustment of gate size OTHER MULTIIMPRESSION 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 . 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 bees progressively more impracticable as the runner length, which is a function of the pitch circle diameter, is also increased. This results in largediameter 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 . 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 eightyimpression mould is shown in Plate 2. 注塑模具設計 流道設計 流道基礎 流道是在模板上加工出的連接主流道和進入（澆口）型腔的一條溝槽。. There are some other considerations for the designer to bear in mind: (i) the shape of the cross section of the runner, (ii) the size of the runner. Runner crosssection shape The crosssectional shape of the runner used in a mod is usually one of four forms (Figure ): fully round (a), trapezoidal (b), modified trapezoidal (c) and hexagonal (d). The reason why these particular forms are used in preference to others are outlined below. The criterion of efficient runner design is that the runner should provide a maximum crosssectional area from the standpoint of pressure transfer and minimum crosssectional area to periphery will, therefore, give a direct indication of the efficiency of the runner design。 the runner section are giver in Figure . As can be seen, the various types of standpoint。在兩板式基本模具中，流道設置在分型面上而在較復雜的設計中流道也許設置在分型面的下面。因此橫截面積和周長的比率將直接可以指示流道設計的效率。為了減少這個不同，并且仍然維持相同的尺寸，改進后的梯形如圖 所示，這個體積比之圓形的增加量大約只有 14%。因此理論上，澆口應該位于流道的中心線上，從中心料流獲得材料。例如，考慮兩板式模具中已經(jīng)在分型面的兩邊加工成圓形流道的情況。 流道尺寸 在決定流道尺寸時，設計者必須考慮以下因素：（ 1）塑件的壁厚和體積 ,（ 2）主流道或分流道距離型腔的尺寸，（ 3）流道冷卻條件，（ 4）模具 工使用的刀具尺寸范圍和（ 5）所使用的塑料。 尺寸的選擇應該在模具工常備的刀具尺寸范圍之內(nèi)。圖 表示的是英制單位。例如，考慮兩板式模具中已經(jīng)在分型面的兩邊加工成圓形流道的情況。 流道的長度應該總是維持到最小，以減小壓力損失，流道系統(tǒng)要平衡。 單型腔模具 單型腔模具通常用一個直接的主流道注入型腔（圖 ）。這是因為，如下所要討論的，大多數(shù)澆口的正確位置，也許并不在模具的中心線上。大的型腔可見直接從主流道通過短的流道注入，而較小的塑件通過一級分流道和兩極分流道注入。這種分流道布置的模具示例在圖 中表示。這就要求大直徑的流道從而延長了注塑周期并且產(chǎn)生較多的廢料（盡管可以回用）。在這種情況下，型腔等分120 度布置在圓周上；這種設計允許流道能維持最短的長度。（ b）是最簡單的例子，其兩個型腔之間的流道長度最短。在這些情況下，充模的平衡可以用修改澆 口的尺寸來實現(xiàn)。（圖 ） 流道的布置 流道系統(tǒng)的布置取決于下列因素：（ 1）型腔數(shù)目，（ 2）塑件的形狀，（ 3）模具的類型（