A Simplified Extrusion Plastometer for Unvulcanized Rubber

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Abstract
An extrusion plastometer operating at rates of shear comparable with those existing in rubber tubing machines has been described previously. This plastometer was not designed to be a routine testing instrument, but rather was intended for use in the determination of the value of a high speed extrusion test for the factory control of rubber stocks. The plastometer served satisfactorily in the capacity of a research instrument, and has for some time been in constant use as a physical testing instrument where great rapidity of operation is not essential. The results obtained with this plastometer were found to correlate with tubing machine behavior. It was also found that the extrusion plastometer results agreed better with factory experience with various types of masticated rubber than did the Williams plastometer results. It was learned by experience with the extrusion plastometer, when used as a physical testing instrument, that its results agreed closely with calender behavior. In many cases, it was found that the extrusion plastometer results did not correlate with the Williams plastometer results and that, in general, the extrusion plastometer appeared to be much more sensitive than the Williams plastometer. The next step after establishing the value of the high speed extrusion test was to design an extrusion plastometer suitable for routine control testing. Such an instrument must be rugged in construction, rapid and simple in operation, and must yield precise results. The extrusion plastometer, which is described in this paper, was designed to fulfill these requirements and at the same time to give the same type of test results as those given by the original experimental plastometer.

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