【正文】 一級(jí)分流道只不過是一些二級(jí)分流道的集合。 可是隨著型腔數(shù)目的增加，由于流道長度是等分圓直徑的函數(shù)，所以設(shè)計(jì)的流道長度隨著等分圓直徑的增加變得不現(xiàn)實(shí)。澆注系統(tǒng)的平衡最終通過調(diào)整澆口的尺寸來達(dá)到。 三型腔模具 圖 表示了三個(gè)類似型腔的平衡式流道系統(tǒng)。 假如我們考慮圖 ，圖示了兩個(gè)矩形塊的模具平面，單從模具布置的角度來看要求型腔側(cè)邊之間如圖所示有較短的流道，這樣可以使得模具的尺寸保持在最小。 雙型腔模具 各種不同的雙型腔流道布置如圖 ， c和 d 所示。因此不需要流道系統(tǒng)。 可是具有平衡的流道系統(tǒng)并不總是可行的，尤其是組合了許多不同形狀型腔的模具（圖 ）。 （ 1） 流道的橫截面積必須滿足允許熔體在流道凍結(jié)之 前通過和充滿型腔，并且使得補(bǔ)縮所需要的保壓壓力能作用到型腔。如果這時(shí)設(shè)計(jì)了圓形流道的話，流道系統(tǒng)可能會(huì)粘滯在流道壁上，使得流道廢料的去除發(fā)生困難。這種情況下，當(dāng)開模時(shí)，模具一側(cè)的流道廢料被從流道中拉出，然后在另一半模具中或直接被頂桿頂出或被連接在塑件上的澆口廢料帶出。對(duì)六角形流道也有類似的問題。例如，一個(gè) 120 克的聚乙烯塑件，流道長度是 50 毫米（ 2in），所要求的直徑是 7 毫米（ 5/16in 理論上，主流道的橫截面積應(yīng)該等于或超過由主流道供料的分流道的橫截面積的組合。 （ 2）計(jì)算后的尺寸應(yīng)該向上圓整到合適的刀具尺寸。實(shí)際上以下是較常用的尺寸： 213 毫米，在公制范圍內(nèi)以每 1毫米為間隔； 1/81/2in，在英制范圍內(nèi)以 1/16in 為間隔。流道的橫截面積越大，它所包含的材料體積也越大從而由于要使這部分材料冷卻到模具可以開模頂出塑件和流道的時(shí)間周期也越長。 （ 1） 流道的橫截面積必須滿足允許熔體在流道凍結(jié)之前通過和充滿型腔，并且使得補(bǔ)縮所需要的保壓壓力能作用到型腔。如果這時(shí)設(shè)計(jì)了圓 形流道的話，流道系統(tǒng)可能會(huì)粘滯在流道壁上，使得流道廢料的去除發(fā)生困難。這種情況下，當(dāng)開模時(shí)，模具一側(cè)的流道廢料被從流道中拉出，然后在另一半模具中或直接被頂桿頂出或被連接在塑件上的澆口廢料帶出。對(duì)六角形流道也有類似的問題。這種效果可以從整圓流道得到（圖 ），也可以從六角形流道得到（圖 ）。這點(diǎn)尤其適用在流道寬度尺寸少于 3mm 的情況。 六角形流道基本上是兩個(gè)梯形，在分型面上相對(duì)吻合。 可是，方形的流道由于另一個(gè)原因，也不能另人滿意：就是頂出困難。這個(gè)值較高時(shí)，效率也高。模具中用到的流道橫截面形狀，通常是四種形式之一（圖 ）：整圓（ a），梯形（ b） ,U 型（ c），和六角形（ d）。 流道的 壁必須光滑，防止料流受到阻礙。o edge gate (for example when sprue marks must not appear on the main surface) in which case a short runner as shown in Figure may be used. But note that by gating a single impression in this way the impression itself must be offset, This is undesirable, particularly with a large impression, as the injection pressure will exert an unbalanced force which will tend to open the mod one side and may result in flashed moldings TwoImpression MOLDS 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 , 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 Tshaped runner extends beyond the impressions and is then connected to the gates by short branch runners (Figure ), 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 twoimpression molds THREEIMPRESSION MOLDS Figure illustrate a balanced runner system for three similar impressions. In this case the impressions are placed on a pitch circle diameter 120176。 whereas the ratios exhibited by the semicircular and rectangular types make their use generally undesirable. Unfortunately, the square runner is not very satisfactory either, but for another reason: it is difficult to eject. In practice, because of this, an angle of 10176。s desirable for the mod designer to specify that the runner(channel) is polished 39。in line of draw39。is incorporated on the runner well, thus modifying the square to the trapezoidal section. The volume of the trapezoidal runner is approximately 25% greater than that of a round runner with corresponding dimensions (W=D, Figure ). To reduce this difference and still maintain corresponding dimensions, a modified trapezoidal form has been developed (Figure ) in which the volume is only 14% greater (approximately) than its round counterpart. The hexagonal runner is basically a double trapezoidal runner, where the crosssectional area of this runner type is about 82% of that