模具設(shè)計的外文翻譯-- 注塑模具設(shè)計

1、<p>　　The Injection Mold</p><p>　　--The design of Runner</p><p>　　1.The basic</p><p>　　The runner is a channel machined into the mod plate to connect the sprue with the entranc

2、e(gate) to the impression. In the basic two-plate mod the runner is positioned on the surface while on the more complex designs the runner may be positioned below the parting surface</p><p>　　The wall of the

3、 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 left, which would tend to retain the runner in the mod plate. To e

4、nsure that these points are met, it's desirable for the mod designer to specify that the runner(channel) is polished 'in line of draw'.</p><p>　　There are some other considerations for the design

5、er to bear in mind: (i) the shape of the cross section of the runner, (ii) the size of the runner.</p><p>　　Runner cross-section shape The cross-sectional shape of the runner used in a mod is usually one of

6、four forms (Figure 4.2): 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.</p><p>　　The

7、criterion of efficient runner design is that the runner should provide a maximum cross-sectional area from the standpoint of pressure transfer and minimum cross-sectional area to periphery will, therefore, give a direct

8、 indication of the efficiency of the runner design; the runner section are giver in Figure 4.3. As can be seen, the various types of standpoint; whereas the ratios exhibited by the semicircular and rectangular types mak

9、e their use generally undesirable.</p><p>　　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 10

10、76;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=

11、D, Figure 4.2). To reduce this difference and still maintain corresponding dimensions, a modified trapezoidal form has bee</p><p>　　The hexagonal runner is basically a double trapezoidal runner, where the cr

12、oss-sectional area of this runner type is about 82% of that of the corresponding round runner. Naturally if similar cross-sectional areas are required, then the value for D(Figure 4.2c) must be increased accord the hexag

13、onal runner compared with matching the two halves of a round runner. This point applies particularly to runners which are less 3mm (1/8 in) in width.</p><p>　　As the plastic melt progresses through the runne

14、r and mod system the melt adjacent to the cold mod surface will rapidly decrease in temperature and solidify. The material which follows will pass through the center of this solidified material and, because of the low th

15、ermal conductivity that most thermoplastics posses, the solidified material acts as an insulation and maintains the temperature of the central melt flow region. Ideally, the gate should therefore be positioned in line w

16、ith the cent</p><p>　　The basic trapezoidal designs (Figure 4.2b and c) are not as satisfactory in this respect since the gate cannot normally be positioned in line with the central flow stream. </p>

17、<p>　　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 p

18、revent 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 co

19、ntaining round or hexagonal runner will be greater than for one contain</p><p>　　The choice of runner section is also influenced by the question whether positive ejection of the runner system is possible. Co

20、nsider, for instance, the case of a two-plate 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 th

21、en ejected from the other mod half either directly, by ejector pins, or by relying on its attachment to the moldings by the gates (Figure 4.5).</p><p>　　For multi-plate molds, however, positive ejection of t

22、he runner system is not practicable. Here the basic trapezoidal-type 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

23、is free to fall under gravity between mod plates. If a circular runner had been pecified, however, the runner system could well adhere to its channel and make its removal difficult (Figure 4.6).</p><p>　　Sum

24、ming up the points concerning cross-sectional shape, we can say that for simple two-plate molds which have a flat parting surface the fully round runner or hexagonal runner is to be prefaced, the increased mod cost being

25、 relatively small. For molds which have complex parting surface, where it would be difficult to match accurately the semicircular channels of the round runner or, for multi-plate molds, the trapezoidal or modified trapez

26、oidal section should be used.</p><p>　　2.Runner size</p><p>　　When deciding the size of the runner the designer must consider the following factors: (i) the wall section and volume of the moldin

27、g (ii) the distance of the impression from the main runner or sprue, (iii) runner cooling considerations, (iv) the range of mouldmaker's cutters available and (v) the plastics material to be used.</p><p>

28、;　　(i) The cross-sectional area of the runner must be sufficient to permit the freezes and for packing pressure to be applied for shrinkage compensation if required, Because of this, runners below 2 mm (3/32 in) diameter

29、 are seldom used and even this diameter is normally limited to branch runners under 25mm (1 in) in length.</p><p>　　(ii) The further the plastic melt has to travel alone the runner the greater is the resista

30、nce to flow. Hence the distance the impression is from the sprue has a direct bearing on the choice of cross-sectional size of the runner. For example, whereas a 5mm (3/16 in)</p><p>　　(iii) The cross-sectio

31、nal area of the runner should not be such that it controls the injection cycle, although this is sometimes unavoidable for very light moldings The larger he cross-sec ~tion area of the runner the greater is the bulk of m

32、aterial it contains and the longer the period it takes to cool sufficiently to enable the mod to be opened and the moldings and runner ejected. For this reason it is undesirable to make the runner larger than 10 mm (] in

33、) diameter for most materials. However</p><p>　　(iv) The size chosen for the runner should be in a range consistent with the mouldmakers's not having to carry in stock a multitude of different! sizes of

34、cutters. In practice the following are the more common sizes: 2-13 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 th

35、e 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 (0.1</p><p>　　The formula is used in conjunction with the notes given previously. (i

36、) 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&l

37、t;/p><p>　　Figure 4.7 shows a plot of diameter versus length of runner for various weights of molding, adopting the metric system of dimensioning. Figure 4.8 shows a corresponding plot using the Imperial dimens

38、ioning 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).</p><p>　　Theoretically the cross-sectional area of the ma

39、in runner should be equal to, or in excess of, the combined cross-sectional areas of the branch runners that it is feeding. This relationship is, however, ignored when the maximum suggested diameter is reached</p>

40、<p>　　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

41、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 c

42、ontaining round or hexagonal runner will be greater than for one contain</p><p>　　The choice of runner section is also influenced by the question whether positive ejection of the runner system is possible. C

43、onsider, for instance, the case of a two-plate 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 t

44、hen ejected from the other mod half either directly, by ejector pins, or by relying on its attachment to the moldings by the gates (Figure 4.5). </p><p>　　For multi-plate molds, however, positive ejection of

45、 the runner system is not practicable. Here the basic trapezoidal-type 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 runne

46、r 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 </p><p>　　3.Runner layo

47、ut</p><p>　　The layout of the runner system will depend upon the following factors: (i) the number of impressions, (ii) the shape of the components, (iii) the type of mod (i.e., two-plate or multi-plate mold

48、), (iv) the type of gate. There are two main considerations when designing a runner layout.The runner length should always be kept to a minimum to reduce pressure losses, and the runner system should be balanced.</p&

49、gt;<p>　　(i) The cross-sectional area of the runner must be sufficient to permit the freezes and for packing pressure to be applied for shrinkage compensation if required, Because of this, runners below 2 mm (3/32

50、 in) diameter are seldom used and even this diameter is normally limited to branch runners under 25mm (1 in) in length.</p><p>　　(Runner balancing means that the distance the plastic material travels from th

51、e sprue 1o 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 4.9 show

52、s example~ of molds all based on the balanced runner principle.</p><p>　　It is not always practicable, however, to have a balanced runner system and this particularly applies to molds which incorporate a lar

53、ge number of differently shaped impressions (Figure 4.10). In these cases balanced filling of the impression can be achieved ~y varying the gate dimensions. That is by balanced gating (Section 4.3.2).</p><p>

54、;　　Single-Impression MOLDS</p><p>　　Single-impression molds are usually fed by a direct sprue feed into the impression (Figure 4.14) and hence no runner system is required. However, it may be desirable ;o ed

55、ge gate (for example when sprue marks must not appear on the main surface) in which case a short runner as shown in Figure 4.9a may be used. But note that by gating a single impression in this way the impression itself m

56、ust be offset, This is undesirable, particularly with a large impression, as the injection pressure will exer</p><p>　　Two-Impression MOLDS </p><p>　　The various alternatives for feeding two imp

57、ressions 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 beca

58、use, as shown in the following discussion, the most desirable position for the gate may not be on the centerline of the mold</p><p>　　If we consider Figure 4.9b, which schematically shows the plan of a mod f

59、or 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 o

60、f 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</p><p>　　To achieve these end gates it

61、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

62、of an S, sweeps round 1o the gales (d), without the necessity for branch runners. </p><p>　　In general, providing that the impressions are approximately the same size and shape, no difficulty should be exper

63、ienced in designing balanced runner systems for two-impression molds</p><p>　　THREE-IMPRESSION MOLDS </p><p>　　Figure 4.9e illustrate a balanced runner system for three similar impressions. In t

64、his case the impressions are placed on a pitch circle diameter 120° apart; this design allows the runners to be kept to a minimum length.</p><p>　　When, however, the impressions are of different shapes

65、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

66、in the feed system is ultimately attained by adjustment of gate size</p><p>　　OTHER MULTI-IMPRESSION MOLDS </p><p>　　For four or more impression molds the design of the runner layout is simply a

67、n 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 t

68、o 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. </p><p>　　As the number of impre

69、ssions 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

70、 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 bra

71、nch runner system is therefore usually</p><p><b>　　注塑模具設(shè)計</b></p><p><b>　　--流道設(shè)計 </b></p><p><b>　　流道基礎(chǔ) </b></p><p>　　流道是在模板上加工出的連接主

72、流道和進(jìn)入（澆口）型腔的一條溝槽。在兩板式基本模具中，流道設(shè)置在分型面上而在較復(fù)雜的設(shè)計中流道也許設(shè)置在分型面的下面。</p><p>　　流道的壁必須光滑，防止料流受到阻礙。另外，由于流道廢料必須和塑件一起取出，所以流道壁上必須不留下任何加工痕跡，避免流道廢料滯留在模板上。為了確保這些要點(diǎn)得到滿足，要求模具設(shè)計者在圖紙中注明這條流道需要沿取出方向拋光。</p><p>　　另外還有一些要

73、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。模具中用到的流道橫截面形狀，通常是四種形式之一（圖4.2）：整圓（a），梯形（b）,U型（c），和六角形（d）。為什么采用這些特殊的形狀而不采用其他形狀的理由說明如下。</p><p>　　流道設(shè)計效率的評判標(biāo)準(zhǔn)從壓力傳遞的角度來看流道應(yīng)該具有最大的橫截面積，而從熱量傳遞的角度來看，應(yīng)該和周邊有最小的接觸面積。因此橫截面積和周長的比率

74、將直接可以指示流道設(shè)計的效率。這個值較高時，效率也高。各種類型流道橫截面的比率如圖4.3所示。可見從這種角度考慮圓形和方形的流道是兩種最滿意的設(shè)計。而半圓和矩形的比率使得它們通常很少使用。</p><p>　　可是，方形的流道由于另一個原因，也不能另人滿意：就是頂出困難。實(shí)際上由于這個原因，在流道的直壁上，設(shè)計了一個10度的斜度，從而修改成梯形截面。梯形流道的體積在相同尺寸的（W=D,圖4.2）情況下，大約比圓形

75、流道大25%。為了減少這個不同，并且仍然維持相同的尺寸，改進(jìn)后的梯形如圖4.2c所示，這個體積比之圓形的增加量大約只有14%。</p><p>　　六角形流道基本上是兩個梯形，在分型面上相對吻合。其橫截面積大約是對應(yīng)圓形流道的82%。當(dāng)然，假如要求相似的橫截面積，則D值（圖4.2d）必須相應(yīng)地增加。某些模具工認(rèn)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。這點(diǎn)尤其適用在流道寬度尺寸少于3mm的情況。

76、　</p><p>　　當(dāng)塑料熔體通過流道和模腔時，鄰近冷的模腔表面的熔體將快速降溫而固化。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(dǎo)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。因此理論上，澆口應(yīng)該位于流道的中心線上，從中心料流獲得材料。這種效果可以從整圓流道得到（圖4.4a），也可以從六角形流道得到（圖4.2d）。</p><p>　　一般的梯

77、形流道設(shè)計（圖4.2b和c）難以在這方面得到滿足，因?yàn)槠錆部谕ǔ２荒芏ㄎ辉诹狭鞯闹行木€上。（圖4.4b）</p><p>　　整圓流道的主要問題是這種流道是由分別加工在兩塊模板上的兩個半圓合成的。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。對六角形流道也有類似的問題。由于這些流道必須精確地吻合，使得采用圓形或六角形流道的模具比梯形流道的模具的成本高。</p><p>

78、;　　流道截面的選擇也受到流道系統(tǒng)的頂出是否實(shí)際可行的影響。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。這種情況下，當(dāng)開模時，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。</p><p>　　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。這時，總是采用基本的梯形流道設(shè)計，其流道開在注射半模上，當(dāng)開模時流道廢料被拉出。然后在重力的作用下

79、，從模板之間自然下落。如果這時設(shè)計了圓形流道的話，流道系統(tǒng)可能會粘滯在流道壁上，使得流道廢料的去除發(fā)生困難。</p><p>　　總結(jié)有關(guān)橫截面形狀的幾點(diǎn)，我們可以說，對于具有平面分型面的簡單兩板式模具選用整圓或六角形流道較好，模具的成本增加相對較少。對于具有復(fù)雜分型面的模具，或?qū)τ诙嗄０迥＞撸捎趫A形流道的兩半圓難以精確地吻合，應(yīng)該采用梯形的或U形截面的流道。 　 　

80、 </p><p><b>　　流道尺寸</b></p><p>　　在決定流道尺寸時，設(shè)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。</p><p>　　（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

81、得補(bǔ)縮所需要的保壓壓力能作用到型腔。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</p><p>　?。?） 此外，塑料熔體必須克服流道內(nèi)的流動阻力。因此型腔和主流道之間的距離，直接和流道橫截面尺寸的選擇有關(guān)。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

82、毫米的同樣塑件卻要求7毫米直徑的流道</p><p>　?。?） 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。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間周期也越長。由此對于大多數(shù)材料來說不希望流道的直徑大于10毫米（3/8in）。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(dá)到13毫

83、米。</p><p>　　尺寸的選擇應(yīng)該在模具工常備的刀具尺寸范圍之內(nèi)。實(shí)際上以下是較常用的尺寸：2-13毫米，在公制范圍內(nèi)以每1毫米為間隔；1/8-1/2in，在英制范圍內(nèi)以1/16in為間隔。建議以下列經(jīng)驗(yàn)公式作為流道或分流道尺寸的確定指導(dǎo)，用于塑件重量在200克（7oz），而且所有的壁厚小于3毫米（0.125in）。對于硬PVCs和聚丙烯，計算得到的直徑值增加25%。</p><p>

84、;　　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(dāng)時不超過13毫米）。（2）計算后的尺寸應(yīng)該向上圓整到合適的刀具尺寸。</p><p>　　圖4.7表示的是不同塑件重量時，流道長度和對應(yīng)流道直徑的關(guān)系圖。使用的是公制單位。圖4.8表示的是英制單位。例如，一個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</p>

85、<p>　　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。但是當(dāng)已經(jīng)達(dá)到建議的最大直徑時這種關(guān)系可以忽略。</p><p>　　整圓流道的主要問題是這種流道是由分別加工在兩塊模板上的兩個半圓合成的。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。對六角形流道也有類似的問題。由于這些流道必須精確地吻合，使得采用圓形或六角形流道的模具比梯形流道的模具的成

86、本高?！?流道截面的選擇也受到流道系統(tǒng)的頂出是否實(shí)際可行的影響。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。這種情況下，當(dāng)開模時，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。（圖4.5）</p><p>　　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。這時，總是采用基本的梯形流道設(shè)計，其流道開在注射半模上，當(dāng)開模時流道廢料被拉出

87、。然后在重力的作用下，從模板之間自然下落。如果這時設(shè)計了圓形流道的話，流道系統(tǒng)可能會粘滯在流道壁上，使得流道廢料的去除發(fā)生困難。（圖4.6）</p><p><b>　　流道的布置</b></p><p>　　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（即，兩板式或多板式模具），（4）澆口的類型。在計劃一個流道布置方式時，有兩個方

88、面要重點(diǎn)關(guān)注。流道的長度應(yīng)該總是維持到最小，以減小壓力損失，流道系統(tǒng)要平衡。</p><p>　?。?） 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。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.</p><p>　　流道平衡意味著對于每個塑件而言，塑料從主

89、流道到澆口的流通距離應(yīng)該是相同的。假如澆口的長度和截面積相同，系統(tǒng)要求確保所有的型腔將均勻地充滿而沒有阻斷現(xiàn)象。圖4.9顯示了所有根據(jù)流道平衡的原則確定的例子。</p><p>　　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4.10）。在這些情況下，充模的平衡可以用修改澆口的尺寸來實(shí)現(xiàn)。即采用平衡澆口。</p><p><b>　　單型腔模具 &

90、lt;/b></p><p>　　單型腔模具通常用一個直接的主流道注入型腔（圖4.14）。因此不需要流道系統(tǒng)。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4.9a所示的短流道。這里要注意的是采用這種方法澆注單一型腔時，型腔自身必須要有一個偏置。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。

91、</p><p><b>　　雙型腔模具 </b></p><p>　　各種不同的雙型腔流道布置如圖4.9b，c和d所示。（b）是最簡單的例子，其兩個型腔之間的流道長度最短。不過，這種短流道并不都可以采用。這是因?yàn)?，如下所要討論的，大多?shù)澆口的正確位置，也許并不在模具的中心線上。 </p><p>　　假如我們考慮圖4.9b，圖示了兩個矩形塊的

92、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?？墒?，在另一個方面，比如在進(jìn)澆特性的方面，也許需要澆口開在型腔的兩端。 </p><p>　　要達(dá)到這種兩端澆口的目的，必須采用其他的流道布置設(shè)計方案，其中既可以用圖4.9c延伸到型腔一邊的T形流道再以短的分流道連接到澆口的方案；也可以用圖4.9d中S形，延伸到澆口，不需分流道的方案。</p>&

93、lt;p>　　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。</p><p><b>　　三型腔模具 </b></p><p>　　圖4.9e表示了三個類似型腔的平衡式流道系統(tǒng)。在這種情況下，型腔等分120度布置在圓周上；這種設(shè)計允許流道能維持最短的長度。</p><p>　　可是當(dāng)型腔的形狀和

94、尺寸不同時，也許要采用圖4.10a所示的布置方法。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。澆注系統(tǒng)的平衡最終通過調(diào)整澆口的尺寸來達(dá)到。</p><p><b>　　其他的多型腔模具 </b></p><p>　　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。例如，含有四腔、五腔、六腔和八腔模具的平衡式流道如圖4.

95、9所示。從流道平衡的角度考慮，把型腔分布在圓周的等分點(diǎn)上直接從主流道通過分流道注入每個型腔的方法，遠(yuǎn)比通過一級分流道和二級分流道系統(tǒng)的方法簡便。</p><p>　　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)計的流道長度隨著等分圓直徑的增加變得不現(xiàn)實(shí)。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）。當(dāng)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