Wear on Injection Molds

Development work has been going on for several years at The Carborundum Company on p-oxybenzoyl polymer systems. 3 The early work mainly focused on the homopolymer (EKONOLjI This polymer has excellent thermal stability and also very good friction and wear properties and has found use recently as an additive to PTPB for molded shapes and coatings. The homopolymer however is very difficult to fabricate by itself and this has led to the development of copolymer systems which retain the excellent thermal stability of the homopolymer but have sufficient flow for compression and injection molding. 

Although it is one of the oldest types of machinery for plastics processing, the single-screw extruder has not yet reached the end of its development—as can be seen in improvements over the past few years, based on the continuing industrial demand for improvements. Output, a major focus years ago, remains paramount but qualities such as wear and versatility are of equal importance. Improvements in all equipment are ongoing, with additional new developments occurring in injection molding machines (Chapter 2). 

Consequently, many injection molding machines monitor and/or control oil temperature. Typically, hydraulics are run prior to molding to heat the oil to an acceptable temperature, and an oil temperature setting or window is often an interlock on the molding cycle. Oil is also cooled by water that is forced through a cooling manifold. This prevents degradation of the oil. Oil is also filtered to prevent wear in the hydraulic cylinders and lines. 

Other applications are a fluid dam and a valve system washer in a new generation of viscous fan drives for the on-highway truck and agricultural vehicle markets by Borg Warner Automotive Turbo Systems. JCL3030 was selected for the superior combination of thermal resistance, dimensional stability at elevated temperatures under load, wear resistance, and close tolerance by injection-molding capability [2]. 

The specimen is a diamond-shaped obstruction in the center of a flow channel. A commercial wear test apparatus based on this geometry is the Tribotest from Bra-bender OHG in Duisburg, Germany. This test is often referred to as the Siemens-Method wear test. Eichler and Frank [6] modified this test to make it more suitable for injection molding. Entirely different test geometry was developed at the DKI (Deutsches Kunststoff Institut, Darmstadt). This test utilized a flat plate geometry as shown in Fig. 11.6. 

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