【正文】 。但是當已經(jīng)達到建議的最大直徑時這種關(guān)系可以忽略。（圖 ） 可是對于多模板的模具，流道系統(tǒng)的可靠頂出是不可能的。因此很少使用小于 2 毫米（ 3/32in）直徑的流道，甚至這種尺寸的流道通常限于在長度在 25 毫米（ in）以下的分流道上使用 . 流道平衡意味著對于每個塑件而言，塑料從主流道到澆口的流通距離應(yīng)該是相同的。但是，還是需要一個邊緣澆口，（例如在不希望主流道痕跡出現(xiàn)在主要表面時），可以采用一個如圖 所示的短流道。可是，在另一個方面，比如在進澆特性的方面，也許需要澆口開在型腔的兩端。 其他的多型腔模 具 對于四個或更多型腔模具的流道布置設(shè)計只是前述方案的延伸。型腔的數(shù)目和形狀將決定流道的確切布置，但是從模板加工的角度來看，采用直的一級分流道（ c）或設(shè)計一級分流道成十字形式（ d）是較為方便的。從流道平衡的角度考慮，把型腔分布在圓周的等分點上直接從主流道通過分流道注入每個型腔的方法，遠比通過一級分流道和二級分流道系統(tǒng)的方法簡便。 倘若，兩個型腔在尺寸和形狀方面大致相等時，通常設(shè)計雙型腔模具的平衡式流道不會遇到什么困難。尤其是大的型腔這會帶來一些麻煩，由于注塑壓力的作用將會引起力的不平衡從而使得模具的單邊有打開的趨勢，也許會造成塑件的溢邊。圖 顯示了所有根據(jù)流道平衡的原則確定的例子。然后在重力的作用下，從模板之間自然下落。所以把這兩個流道精確地吻合防止流道系統(tǒng)發(fā)生不良組合和效率受阻的現(xiàn)象。 這個公式必須和前述的注釋聯(lián)合使用 . （ 1） 流 道直徑應(yīng)該不小于 2 毫米，不超過 10 毫米（或在適當時不超過 13 毫米）。例如，一個 5毫米（ 3/16in）直徑的流道也許適合于一個距離主流道 25 毫米的重量為 60 克（ 2 oz）的塑件，但與 主流道的距離為 100 毫米的同樣塑件卻要求 7毫米直徑的流道 （ 3） 流道的橫截面積應(yīng)該不影響到注塑周期，盡管對于非常輕的塑件來說這是不可避免的。然后在重力的作用下，從模板之間自然下落。所以把這兩個流道精確地吻合防止流道系統(tǒng)發(fā)生不良組合和效率受阻的現(xiàn)象。某些模具工認為，六角形流道和圓形流道相比前者在兩半模上的吻合較為方便。而半圓和矩形的比率使得它們通常很少使用。 另外還有一些要求設(shè)計者用心考慮的：（ 1）流道的橫截面形狀，（ 2）流道的尺寸和（ 3）流道的布置。s not having to carry in stock a multitude of different! sizes of cutters. In practice the following are the more mon sizes: 213 mm in I mm steps in the metric range and ~? in With ~ in steps in the imperial unit range. The following empirical formula is suggested as a guide of the size of the runner or branch runner for moldings weighing up to 200g(I g (7 oz), and with wall sections less than 3 mm ( in). For the rigid PVCs and the acrylics, increase the calculated diameter by 25%. The formula is used in conjunction with the notes given previously. (i) The runner should not be below 2 mm (3/32 in) diameter, nor above 10 mm (3/8 in) diameter (or 13 mm (1/2 in) diameter where applicable). (ii) The calculated size should be increased to the next suitable cutter size Figure shows a plot of diameter versus length of runner for various weights of molding, adopting the metric system of dimensioning. Figure shows a corresponding plot using the Imperial dimensioning system. For example, a 120 g (4 oz) molding in polyethylene being fed by a 50 mm (2 in) long runner will require a diameter of 7 mm (5/16 in). Theoretically the crosssectional area of the main runner should be equal to, or in excess of, the bined crosssectional areas of the branch runners that it is feeding. This relationship is, however, ignored when the maximum suggested diameter is reached The main objection to the fully round runner is that this runner is formed from two semicircular channels machined one in each of the mod plates. It is essential that these channels are accurately matched to prevent an undesirable and inefficient runner system being developed. A similar argument applies to the hexagonal runner system. The fact that these channels must be accurately matched means that the mod cost for a mod containing round or hexagonal runner will be greater than for one containing trapezoidal runners. The choice of runner section is also influenced by the question whether positive ejection of the runner system is possible. Consider, for instance, the case of a twoplate mod in which a circular runner has been machined from both parting surface. In this case, as the mod opens, the runner is pulled from its channel in one mod half and it is then ejected from the other mod half either directly, by ejector pins, or by relying on its attachment to the moldings by the gates (Figure ). For multiplate molds, however, positive ejection of the runner system is not practicable. Here the basic trapezoidaltype runner is always specified, the runner channel being machined into the injection half from which it is pulled as the mod opens. In this way the runner is free to fall under gravity between mod plates. If a circular runner had been specified, however, the runner system could well adhere to its channel and make its removal difficult layout The layout of the runner system will depend upon the following factors: (i) the number of impressions, (ii) the shape of the ponents, (iii) the type of mod (., twoplate or multiplate mold), (iv) the t