模具方面的外文资料翻译(共8页).doc

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1、精选优质文档-倾情为你奉上外文资料翻译：PLASTIC PRODUCT FAILURE DUE TO DESIGN,MATERIAL OR PROCESSING PROBLEMSBy Myer Ezrin, Gary Lavigne and John Helwig University of Connecticut, Institute of Materials ScienceAbstractSeveral examples are given in which design, processing, or an aspect of the material were primary cont

2、ributors to failure of plastic products. A common pattern is failure to realize the consequences of seemingly inconsequential practices or decisions. Mold design was a factor in some cases. Material factors and processing were involved in other cases. Frequently design, material and processing are s

3、o closely related that failure cannot be ascribed solely to one of the three (8).1. IntroductionIn many cases of failure the cause is at least partly due to failure to know or realize the potential consequences of seemingly safe practices or decisions. In many of the cases cited failure occurs at th

4、e manufacturing stage, either in primary processing, such as injection molding, or in secondary operations. All failures can be traced to the design, the material, or processing, assuming service conditions are not unusually severe. The interdependence of the three main causes of failure is such tha

5、t often all are contributors. Material and processing are particularly strongly linked.The material contribution to failure may be in the polymer itself or in an additive. Processing imposes on plastics thermal and mechanical stresses that frequently are the most severe a part will experience in its

6、 entire lifetime. Failure is often due to lack of realization of how severe the stresses in processing are and of the effect on the material. Examples are given of failures due to part design, mold design, material selection and processing.2. Part Design2.1 Polypropylene (PP) caps for a packaging ap

7、plication required that the top of the cap be flexed substantially due to direct contact with a round ball at the top of the container. Fracture occurred with some caps from the high flexural load and deformation. The gate was at the center of the top of the cap where stress was greatest in service.

8、 The design and material can withstand the service stresses only if the material properties are in control, which was not the case. Inadequate antioxidant and regrind use were the main causes of molecular weight being out of control. This case illustrates a failure to realize how readily certain pol

9、ymers, in particular PP, degrade during processing and that a small reduction in molecular weight (MW) may be sufficient to cause failure. The design played a part in that the fracture initiation is at the gate which is inherently weak.The effect of processing on the material can be monitored by how

10、 much melt index or melt flow rate increases in processing. Generally an increase of more than 10-20% in most cases may be too much, unless the part experiences very little stress in service. The corresponding decrease in MW may be only about 5%, yet that may be more than the design and the service

11、stresses will tolerate. Fortunately, melt index is a convenient and sensitive test which takes advantage of the fact that melt viscosity is a function of the 3.4 power of MW above about 20,000 MW ( = KM3.4). Another relatively simple test that provides a measure, in effect, of antioxidant content is

12、 oxidative induction time by differential scanning calorimetry (DSC) (ASTM D3895). This test is particularly applicable to polyolefins (PE, PP). Without adequate antioxidant, PP and PE are very susceptible to oxidative degradation during processing. While this case is cited as an example of part des

13、ign, it also illustrates how material and processing considerations are also involved.Presented at National Manufacturing Week, Design for Manufacturability of Plastic Parts, March 16, 1999, Chicago.PLASTIC PRODUCT FAILURE DUE TO DESIGN, MATERIAL OR PROCESSING PROBLEMSby Myer Ezrin, Gary Lavigne and

14、 John Helwig2.2 An O ring made of plasticized PVC was in contact with a polycarbonate part in an assembly that requiredthat the PC move freely when the O ring pressure was removed. In service there was sticking, i.e., separation did not occur readily as designed. Plasticizer at the surface transferr

15、ed to the PC, which is not completely impervious to plasticizer. In effect, the plasticizer became an adhesive between PC and PVC. This failure was probably also due in part to the fact that plasticizers are less compatible in PVC under pressure. In this case the effect of plasticizer on PC, an amor

16、phous polymer, was not realized, as well as the pressure effect on compatibility. ABS is also adversely affected by contact with plasticizer from PVC. 2.3 Bottle caps were spray painted for color and scratch resistance. The bottom of the caps were to be bonded to another part of the cap with silicon

17、e adhesive. The adhesive failed to bond to the plastic in some cases. The cause was that some spray paint contacted the bottom surface. Waxy ingredients in the paint, for scratch resistance, interfered with the bond that normally would have been made to the silicone. The design and processing did no

18、t take into account the need to protect the bottom surface while the cap above was spray painted. It should have been realized that even traces of contaminant on a surface can reduce bond strength very strongly.3. Mold Design3.1 An ABS injection molded part of a syringe needle holder (4) consisted o

19、f two flats on the inside 180Eapart. A metal eyelet and tubing inserted after molding were held in place by stress at the flats. The design called for the flats, which are high stress points, to be 90E removed from the parts two weld lines. In some mold cavities the flats were not located as intende

20、d, so that the flats were at the weld lines, contributing to failure.3.2 A hollow ABS injection molded part had a top ring of ABS ultrasonically welded into the insidediameter of the part. Some welds had a protrusion at one point in the circumference, which was thought to be flash from the welding.

21、These defects occurred with parts from one of a two cavity mold. Lowering the force of insertion of the top ring during welding did not eliminate all defects. Examination of molded parts for frozen-in stress by immersion in acetic acid (ASTM D1939) showed very little stress. A check for out of round

22、ness showed that bad parts were out of round as much as 0.0025, compared to 0.0005 for good parts. Figure 1 is a cross-sectional view of a welded junction obtained by sanding down a welded unit. The failure is a fracture of the outer wall of the molded part, which occurred only with out of round par

23、ts. Figure 2 is a sketch of how good and bad parts fit together with the insert. Fracture was due to flash pushing the edge of the part outwards as the ring insert was forced down. In good welds all the flash moved downward inside the part. In this case the human failure was not to check if parts or

24、 the mold cavity were perfectly round.4. Material4.1 A glass-filled PBT (polybutylene terephthalate) part had a hole in the center in which a threaded metalpart moved freely back and forth. In oven aging at 160EC to simulate under the hood automotive service the metal part lost its ability to move f

25、reely in the PBT part, which had shrunken slightly. Shrinkage was due mainly to further crystallization in service beyond the degree of crystallinity as molded. DSC showed that the heat of fusion increased approximately 20%, corresponding to a like increase in degree of crystallinity. The crystallin

26、ity developed on aging at 160EC is seen as a new peak at approximately 200EC. Shrinkage would not occur if the part was fully crystallized. It would not be a problem if the fit or tolerance between metal and plastic was not so tight. Possibly a nucleating agent in the PBT would give complete crystal

27、lization as molded, so that shrinkage as molded would not occur in service. What was not realized was that crystalline polymers may shrink in service if not fully crystallized.4.2 A prototype part was machined from a block of plastic believed to be acetal homopolymer. It performed in trial runs in s

28、ervice below expectations. Consideration was being given to redesign or to a change inPLASTIC PRODUCT FAILURE DUE TO DESIGN, MATERIAL OR PROCESSING PROBLEMSby Myer Ezrin, Gary Lavigne and John Helwigmaterial. A check of the material by infrared spectroscopy and DSC showed that it was HDPE, not aceta

29、l. The trial run results were consistent with what would be expected of HDPE. The failure was in assuming incorrectly what the type of material was.5. ProcessingAs indicated in the Introduction, a common failure is not to realize that the most severe and potentially damaging stage in a plastics enti

30、re experience is the thermal and mechanical stresses of processing. This problem is particularly serious for condensation polymers (nylon, PET, PC, PUR) and for polyolefins, although it is a problem for all materials. In the former case, hydrolysis to lower MW can take place if water content is abov

31、e about 0.01%. The requirement of practically complete dryness in the melt cannot be overemphasized. For polyolefins like PE and PP, oxygen is the enemy, together with free radicals (reactive carbon atoms lacking one hydrogen atom) (5). Without adequate and effective antioxidant, the stage for failu

32、re is set in the molding machine or extruder. Section 2.1 above refers to the 3.4 power relationship between melt viscosity and MW. For even a small increase in MW, the melt viscosity penalty is high, making processability even more difficult. At the same time, the curve of properties (strength, tou

33、ghness, chemical resistance) vs. MW is leveling off (6), so that the gain in product performance may come at a high price in processability. The lesson seems to be to design so that properties can be achieved at the lowest MW possible (highest MI). The interdependence of design, material and process

34、ing is very high. This is noted in some cases above.5.1 In injection molding of a PC part requiring high resistance to outdoor exposure, a deposit formed onthe mold, requiring shutdown and cleaning more often than was usually experienced with PC. It also contaminated the surface of the part. Analysi

35、s identified the deposit as a UV absorber present at a relatively high concentration because of the light stability requirement. It was near its compatibility limit and the high temperature and pressure of moldingdeposited a small amount each time. Over a two week period, what was not noticeable at

36、first became a real problem. lower temperature might help reduce the problem, but change in amount or type of UV absorber may also be needed.5.2 A brominated hydrocarbon flame retardant in nylon 6 is making it difficult to process and to retain thedesired properties. Such materials act as flame reta

37、rdants by decomposing and releasing bromine (Br2) and hydrogen bromide (HBr), which act as a blanket to exclude air. But when the bromo compound does that during processing, even to a small extent, the HBr, in contact with any water present, becomes H+Br-. H+ acid is a strong catalyst for hydrolysis

38、 of condensation polymers; nylon 6 is a polyamide (-NHCO-). Hydrolysis occurs at the nitrogen-carbon bond. Processing in this case is a virtual tightrope walk.5.3 A polyurethane containing a metal carbonate for radiopacity gave porosity in extrusions. Analysis bythermal desorption gas chromatography

39、/mass spectroscopy (7) identified carbon dioxide in the extruded material. This was traced to the carbonate, which contained CO2 as received, and decomposed further in processing. Elimination of the problem is focusing on removing the initially present CO2 in the carbonate and molding so as to cause

40、 very little to form during processing.6. SummarySuccessful manufacture of plastic parts is a far more complicated matter than may be realized. Thetechnology involved cannot be used most effectively without knowledge of the basic organic chemistry and physical chemistry that underlie the materials,

41、including polymers and additives, and the rheology that is involved in melt flow processing. A major category of failure has not been dealt with in this paper, i.e., orientation and frozen-in stress and the consequences in environmental stress-cracking, warpage, etc. Orientation is affected very str

42、ongly by polymer molecular weight and composition, as well as processing; design also plays a role. Failure to understand the ways in.PLASTIC PRODUCT FAILURE DUE TO DESIGN, MATERIAL OR PROCESSING PROBLEMSby Myer Ezrin, Gary Lavigne and John Helwigwhich design and material affect processing and, in t

43、urn, how all three affect product performance is the underlyingcause of many plastic problems.译文：塑料产品故障由于设计， 材料或处理问题 由迈尔埃兹林，加里Lavigne和约翰埃尔格 康涅狄格大学，材料科学研究所 抽象 给出几个例子中，设计，加工，或者是物质方面的主要贡献者 在塑料产品的失败。一个常见的模式是无法实现的后果看似无关紧要的做法或决定。模具设计是在某些情况下因素。物质因素和加工都参与了 其他案件。常见的设计，材料和加工是如此密切相关，失败不能完全归咎于以一对三。 1.介绍 在许多情况下，

44、失败的原因至少部分是因无法知道或意识到的潜在后果 看似安全的行为或决定。在许多案例列举失败时，或者在生产阶段 在初级加工，如注塑，或在二级操作。所有的失败可以追溯到设计， 材料，或加工，假设服务条件并不特别严重。这三个相互依存 失败的主要原因是这样的：往往都是贡献者。材料和加工特别强烈的联系。 该材料的贡献失灵可能会在聚合物本身或在添加剂。在塑料加工规定 热和机械应力的经常是最严重的一个部分将在其整个一生的经验。失败 往往是由于在如何处理讲严重缺乏和实现上的重大影响。 给出失败的例子，由于零件设计，模具设计，材料选择和加工。 2.0零件设计 2.1 聚丙烯（PP）的上限为包装应用要求，该顶帽子

45、被大幅弯曲,由于直接接触在容器的顶部圆球。骨折的发生与一些帽高负荷和弯曲变形。那门却是在那里的上限应力最大的顶部中心服务。在设计和材料可以承受的服务强调只有在材料性能的控制，都是情况并非如此。抗氧化剂和不足进行再研磨使用分子正在走出重的主要原因控制。这一案例说明了如何轻易未能实现某些聚合物，尤其是聚丙烯，降解过程中在处理和分子量（MW）的小型减少可能足以导致失败。该设计所扮演一开始在该断裂在大门口这本身就是弱者的一部分。在处理过程中具有重大影响，可监视多少熔融指数或熔体流动速率增加处理。一般来说，在大多数情况下，超过10-20的增长可能会太多，除非部分经验很少强调服务。在兆瓦相应减少可能只有约

46、5，但可能以上的设计和服务讲会容忍。幸而，熔融指数是一种简便，敏感试验其中注意到这一事实熔体粘度的优点是对20,000兆瓦以上的3.4兆瓦的幂函数。另一种相对简单的测试，提供了有效的措施，抗氧化剂含量是氧化诱导时间扫描量热法（DSC）（美国ASTM D3895）差别。这个测试特别适用于聚烯烃（聚乙烯，聚丙烯）。如果没有足够的抗氧化剂，PP和PE是很容易受氧化降解过程处理。虽然这种情况下是作为一个部分的设计例子，它也说明了材料和加工考虑也参与。在国家制造周主办，塑料件的设计，1999年3月16日，芝加哥可制造性。塑料产品故障由于设计，材料或处理问题由迈尔埃兹林，加里Lavigne和约翰埃尔格 2

47、.2 O形圈的塑聚氯乙烯在接触中的一个集会的一部分，需要聚碳酸酯筹委会自由移动时，O型圈的压力已被取消。在服务有坚持，即不分离容易出现按设计。增塑剂在转移到个人电脑，这是不完全不透水的表面增塑剂。实际上，增塑剂成为PC机和PVC胶。这种失败可能是由于还一部分这一事实是不兼容增塑剂在PVC压力下（2）。在这种情况下，增塑剂的影响在PC，一无定形聚合物，没有得到实现，以及对指数的压力的影响。 ABS是也不利受由聚氯乙烯（3）增塑剂的接触。 2.3 瓶帽被喷涂颜色和耐划伤油漆。底部的盖子被人保税的另一个与硅酮胶帽的一部分。胶粘剂没有保证金，以在某些情况下塑料。该原因是，一些喷漆表面接触的底部。在涂料

48、糯成分，为抗划伤性，干扰了正常情况下已作出的硅债券。设计和加工并没有采取考虑到需要保护的底面以上，而上限是喷油漆。它应该已经实现即使是微量污染物表面上可以减少粘结强度非常强烈。 3.0模具设计 3.1 的ABS注塑成型的一个注射器针头的持有人的一部分成两个组成单位。除了一个金属管插入孔和成形后举行了应力发生在单位。所谓的设计 单位，这是高应力点，可从两个部分拆除抯焊接线90E。在某些模具腔 单位未设应有作用，使单位在焊缝线条，造成失败。 3.2 ABS的注塑中空部分有ABS的顶环超声波焊接成内 直径的部分。一些曾在焊接中的一个圆周，这被认为是一个突出闪点 从焊接。这些缺陷的发生，以一个两腔模具

49、1件。降低插入力 在顶部环焊接过程并没有消除所有的缺陷。考试的模塑部件冻结在应力 在乙酸（美国ASTM D1939浸泡）显示非常小的压力。一种新的圆度进行检查表明，坏件出了多达正负0.0025：“一轮相比正负0005”的好的地方。图1是一个跨部门的观点 交界处的一个焊接打磨焊接装置获得了1。失败是对成型零件外侧壁骨折， 只发生圆零件了。图2是一个如何好的和坏的零件配合插入一起素描。 断裂是由于闪存作为推进环插入的部分向外边缘被迫下降。在所有焊缝良好 向下移动的闪存内的一部分。在这种情况下，人类的失败是不检查的零件或模具型腔 是完美的圆形。 4.0材料 4.1 玻璃填充型PBT（聚对苯二甲酸乙二醇酯）的一部分，在一中心孔，其中一个线程金属部分自由移动来回。在160EC老化炉在模拟引擎盖下的金属部分汽车服务丧失了行动能力，在PBT的一部分，这已略有萎缩自由。收缩，主要是因为进一步在服务结晶超出了作为塑造结晶度。 DSC分析表明，融合热增加约2