Shear Tester Operation

Follow the directions given in the instrument manual for shear testing methodology. The routine procedure can be summarized as follows  

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Tyres are very definitely fatigued during use and, as mentioned for fabric/rubber adhesion above, it is very important to carry out dynamic tests to assess bond efficiency. Methods have not apparently been standardised but a variety of procedures have been reported71 79 Some workers have used the same or a similar test piece as in static tests and applied a cyclic tensile stress or strain, whilst others have used some form of fatigue tester operating in compression/shear to repeatedly stress or strain cord/rubber composite, or even to flex samples in the form of a belt. Khromov and Lazareva80 describe a method using test pieces cut from tyres. 

Operational Qualification The OQ document certifies that the equipment works as desired and defined by the manufacturer and the purchaser. An example is the acquisition of a new high-shear mixer/granulator where the paddle is put on rotation with a real calibrated rotation speed tester and, if the value obtained meets the specifications, the mixer paddle rotation passes the OQ test. If not, additional requalification must be performed. All the test results must be introduced and verified in the OQ report that is approved by the company at the end. The OQ document must describe several tests and related specifications to perform on the equipment in order to evaluate if it is working well, and the test to be performed must be described and approved by the manufacturer and the purchaser. Therefore, tests must be performed on the equipment, and for each one a description and signature of who performed and verified the test are required. Usually the tests are performed by the manufacturer and verified by the purchaser. These tests usually consist of evaluating if the mechanical and electric components of the equipment are working as desired. 

Middleman [M24], Goldstein [G8], Furuta et al. [Fll], Lobe and White [LI4], Toki and White [T7], Montes et al. [M37], Osanaiye et al. [OlO], and K. J. Kim and White [K8a]. The apparatus (with constant-temperature chamber) may be placed in a tensile tester and operated in a mode with a fixed velocity V giving a constant shear rate. It may, on the other hand, be used in a creep mode with hanging weights. This provides constant stress experiments. At low stress levels one needs to compensate for the weight of the central member which exerts a gravitational stress [OlO]. At very low stresses one may accurately determine the yield value of rubber-carbon black compounds. Osanaiye et al. [OlO] have made measurements at shear stresses below the yield value. 

The majority of published work on extrusion behaviour deals with compounded stock. Those papers reporting work on raw rubbers have usually been on the use of capillary rheometers to determine extrusion properties at higher shear rates than are possible with Mooney viscometers. Capillary rheometers are, in principle, quite simple to use, and the application of electronic, minicomputer and laser technology has reduced the operation and data analysis to a routine task. There are no standard ASTM or other test procedures, but under a specific set of conditions, once a material is characterized, the data can be used as standard for comparison of all subsequent batches. It is readily possible to characterize a raw rubber by an extrusion experiment to determine the viscosity/shear rate curve, extrudate swell, and stress relaxation.Both Sezna and Karg have shown how the Monsanto Processability Tester (MPT), a modified, computerized extrusion rheometer, can be used in predicting mixing behaviour. The MPT (shown schematically in Fig. 7) is a most versatile instrument. It has a larger than conventional barrel for minimal pressure drop in the barrel, a pressure transducer at the entrance to the orifice, a microprocessor system, and a laser device for... 

High shear testing machines such as the Wallace rapid plastimeter, the Monsanto processability tester and extrusion viscometers may better differentiate between natural rubber and polyisoprene, and even between polyisoprenes from different suppliers. None of these machines alone, however, will accurately predict the behaviour of the polymer or batch for all processing operations. Thus Mooney viscosity plus practical experience remain the principal factors in categorising factory processing. 

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