Plastics material selection

More specifically, data bases are now available which are designed as aids to plastics material selection. One estimate in 1993 was that there were 300-400 systems in the field.Systems vary as to whether they are limited to the products of a particular company, to a particular area of activity and to the depth of coverage over a broad area. 

The first interactive electronic encyclopedia for users of plastics, materials selection is carried out using 3 search routines. The Chemical Resistance Search eliminates materials that cannot meet user specified chemical resistance requirements. The other search routines ( Elimination and Combined Weighting ) eliminate candidate materials based on 72 properties, falling within one of the following groups General and Electrical, Mechanical, Cost Factors, Production Methods and Post Processing. All data is evaluated and based on independent tests conducted in RAPRA s laboratories. 

With this continued growth in variety of plastics materials, selection and matching of optimum combinations between materials and applications becomes a major problem. With at least 50 types of commercial plastics already available, each in a variety of copolymers, molecular weights, and different manufacturers, there are already too many for rational manual choice of the optimum material for any specific application and the situation is growing worse at an alarming rate. 

In addition to their inclusion in the CAS databases, CAS Registry Numbers are used in many public and private databases. Currently, the cluster of databases on STN International containing Registry Numbers includes 7 CAS databases and 53 non-CAS databases. Among the latter are such diverse files as AIDSLINE, BIOSIS, Design Institute for Physical Property Data File (DIPPR), MEDLINE, Natural Products Alert (NAPRALERT), Pharmaceutical News Index (PNI), and Plastics Materials Selection Database (PLASPEC). 

The physical and mechanical properties of RPs, including URPs, have some significant difference from those of familiar metallic materials. Consequently in the past those not familiar with designing RP or URP products may have had less confidence in plastics and in their own ability to design with them. Thus, plastic material selection and optimization was confined to the familiar steel materials approach resulting in overdesign, or failures that may have occurred in service. 

Physical dimensions of many processed parts must be held to fairly close tolerances to ensure proper assembly of parts into a complete structure, as, for example, molded fender panels bolted to steel chassis cars, plastic screw caps for glass jars, etc. In general, the final dimensions of the processed part will differ from the dimensions of the mold cavity or the pultrusion die. Such differences are somewhat predictable, but are usually unique to the specific material and to the specific process. The dimensions of a mold cavity for a phenolic part requiring close tolerances will often be different from dimensions of a cavity for an identical polyester part. Both the part designer and the mold or die designer must have a full understanding of the factors affecting final dimensions of the finished product, and often need to make compromises in tolerances of both part and cavity dimensions (or even in plastic material selection) in order to achieve satisfactory results with the finished product. 

IPS (International Plastics Selector, D.A.T.A. Business Publications, San Diego, CA). Plastics material selection database reviews of more than 10,(XX) grades with up to 50 properties for each material. Includes physical, mechanical, electrical, flammability, and other characteristics. 

Kusy, P. F. Plastics Materials Selection Guide. No. 760663. Society of Automotive Engineers, Sept. 1976. 

Plastic Materials Selection System [PLASCAMS]. Shrewsbury, England RAPRA Technology, Ltd. 

Examples of hard copy databases for plastic material selections are listed in Chapter 5 and the Bibliography sections. 

This book is meant to be a guide in the process of plastics material selection. It is based on the simple premise that we all make things, and that we have a fundamental understanding of how to use materials— based on our heritage as human beings. 

As a general rule, I try not to get involved in these kinds of questions. It is a sign that the questioner is not experienced with plastic material selection. As a consultant, and someone engaged in new business development, you might ask. How could you pass up a new client opportunity The truth of the matter is, working with clients like this is often more of a bother than it is worth. And sometimes the questions they ask make you shake your head. 

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