1998-02-23

Accelerated Glass Reveal Molding Test 980718

Over the past 20 years, polyvinyl chloride (PVC) has almost replaced metal in stationary glass reveal moldings with dramatic part cost savings on cars and trucks world-wide. The process of assembly is generally simple and convenient but to replace a reveal molding can be difficult. Many times, in order to replace the molding, it may also be necessary to replace or reseal the glass. In short, PVC reveal moldings, relatively inexpensive parts, are very expensive to service.
Outside of general assembly and processing issues, there are 5 variables that may cause a failure in the performance of a stationary glass reveal molding. They are as follows: material degradation, crystallization, plasticizer loss, material properties, and molded-in stress. Because of modern standard PVC formulations and the material requirements of most automotive companies, material degradation, crystallization and plasticizer loss do not commonly cause failure. Material properties and molded-in stress do.
The automotive industry has developed many extreme-temperature component tests to model PVC reveal molding failures seen on full vehicle tests without a thorough understanding of the mechanism of failure. These test methods, although effective, are expensive and require engineering time.
By understanding the PVC failure mechanism and standardizing a test method for evaluating these and similar parts, engineering time efficiency will be improved, OEM PVC molding suppliers will be less confused by many different required testing procedures, and testing costs will be significantly reduced if not eliminated. This paper reviews the 5 variables above and suggests a simple standardized procedure developed from tested parts which eliminates the future need for an elaborate validation test.

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