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1、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 contributors to f
2、ailure 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 so closely rel
3、ated 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 the manufacturi
4、ng 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 that often all a
5、re 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 entire lifet
6、ime. 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 application req
7、uired 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. The design a
8、nd 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 polymers, in par
9、ticular 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 much melt in
10、dex 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 stresses will
11、 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 oxidative in
12、duction 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 design, it also
13、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 John Helwig2
14、.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 transferred to the PC,
15、 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 amorphous polymer
16、, 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 silicone 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 resis
