Extrusion resistance test

Evaluation of the extrusion resistance of an elastomer is facilitated by a useful test method developed by the American Petroleum Institute (API) in the 1950s. The test is run on a standard ASTM compression set pellet. One modification was the drilling of a hole in the tester body for a thermocouple so that the test temperature could be accurately controlled. Die standard annular extrusion gap set up by the API was 0-34 mm (0 0135 in) on each side, as shown in Fig. 3. 

This test method was designed to be quick so that numerous samples can be run, yet accurate enough to give meaningful data. An arbitrary rating scale was then devised based on deflection test data so that a simple judgement could be made easily on the extrusion resistance of the rubber compound tested. 

COMPOUNDS USED IN EXTRUSION RESISTANCE EVALUATION USING API TEST... 

This test could be used as the basis of a screening test for extrusion resistance in a specification for elastomeric parts for oilfield performance (see Section 6). 

Extrusion resistance a test similar to the API test described earlier in this chapter (Section 5.2). 

The Ml test equipment is easy to operate, provides repeatable results, and low cost to operate. It is widely used for quality control and for distinguishing between members of a single family of plastics. Specifically, this MI makes a single-point test that provides information on resistance to flow at only a single shear rate. Because variations in branching or MWD can alter the shape of the viscosity curve, the MI may give a false ranking of plastics in terms of their shear rate resistance to flow. To overcome this problem, extrusion rates are sometimes measured for two loads, or other modifications are made. 

ISO 1872-1 1993 Plastics - Polyethylene (PE) moulding and extrusion materials - Part 1 Designation system and basis for specifications ISO 1872-2 1997 Plastics - Polyethylene (PE) moulding and extrusion materials - Part 2 Preparation of test specimens and determination of properties ISO 1969 2004 Fibre ropes - Polyethylene - 3- and 4-strand ropes ISO 3458 1976 Assembled joints between fittings and polyethylene (PE) pressure pipes -Test of leakproofness under internal pressure ISO 3459 1976 Polyethylene (PE) pressure pipes - Joints assembled with mechanical fittings - Internal under-pressure test method and requirement ISO 3501 1976 Assembled joints between fittings and polyethylene (PE) pressure pipes -Test of resistance to pull out... 

ISO 7246 1984 Pipes and fittings of acrylonitrile/styrene/acrylester (ASA) - General specification for moulding and extrusion materials ISO 12092 2000 Fittings, valves and other piping system components made of unplasticized poly(vinyl chloride) (PVC-U), chlorinated poly(vinyl chloride) (PVC-C), acrylonitrile-butadiene-styrene (ABS) and acrylonitrile-styrene-acrylester (ASA) for pipes under pressure - Resistance to internal pressure - Test method... 

Many of the comments in the previous chapter about the selection of grade, additives and mixing before moulding apply equally in preparation for extrusion. It is important of course that the material should be appropriate for the purpose, uniform, dry, and free from contamination. It should be tested for flow and while many tests have been devised for this it is convenient to classify them as either for low or high rates of shear. The main terms used in such testing ( viscosity , shear rate , shear strain , etc.) are defined in words and expressed as formulae in ISO 472, and it is not necessary to repeat them here. Viscosity may be regarded as the resistance to flow or the internal friction in a polymer melt and often will be measured by means of a capillary rheometer, in which shear flow occurs with flow of this type—one of the most important with polymer melts—when shearing force is applied one layer of melt flows over another in a sense that could be described as the relationship between two variables—shear rate and shear stress.1 In the capillary rheometer the relationship between the measurements is true only if certain assumptions are made, the most important of which are ... 

However, when a suitable clay is present, the behaviour changes radically. Clay, with a much smaller particle size and with chemical affinity for water severely reduces the movement of water through the particle matrix. If we now do the footprint test, no dry region arises around where the foot has been placed and the material sticks to the sole of the shoe. Liquid is now retained in the particle matrix because there is a very much greater resistance to liquid flow and the stress applied remains borne by the liquid. This, in turn, ensures that the particles remain lubricated around the points of contact and this has the consequence that the material is mouldable and amenable to extrusion using an auger. 

Scorch resistance is usually measured by the time at a given temperature required for the onset of crosslink formation as indicated by an abrupt increase in viscosity. The Mooney viscometer is usually used [4]. During this test, fully mixed but unvulcanized rubber is contained in a heated cavity. Imbedded in the rubber is a rotating disc. Viscosity is continuously measured (by the torque required to keep the rotor rotating at a constant rate) as a function of time. The temperature is selected to be characteristic of rather severe processing (extrusion, calendering, etc.). 

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