Rheometer moving disc

Various techniques have been developed in turn the Mooney viscometer, the Wallace-Shawbury curometer, the oscillating disc rheometer (ODR), and the moving disc rheometer (MDR), in addition to the calorimetry techniques. The isothermal calorimetry and its counterpart in scanning mode, the isothermal moving disc rheometer (MDR), and the improvement of this last technique with the rubber process analyzer run in scanning mode, are considered. 

FIGURE 6.1 Torque -time (temperature) curves obtained with the oscillating disc rheometer (ODR) and the moving disc rheometer (MDR). 

The degree of vulcanisation of a rubber compound is assessed technically by the indefinite terms of undercure, correct cure, optimum cure and overcure. It may be given precision by (a) measurement of stress-strain relationship of a range of cures, (b) measurement of the modulus at 100% elongation, (c) measurement of the volume swelling in benzene, or (d) by the use of instruments such as the oscillating disc rheometer and the moving die rheometer. 

The oscillating die rheometer (ODR) and the moving die rheometer (MDR) have been developed and maiketed by Monsanto, the MDR being introduced in 1985 [16]. In the MDR, a thin sheet of rubber, around 2 mm thick, is placed between the two dies kept at the desired temperature the lower disc oscillates and a reaction torque/ pressure transducer is positioned above the upper disc. It has been found that the MDR gives shorter times of cure than the ODR because of better heat transfer and higher torque values, owing to the die design. 

However, as shown in Figure 6.1, tracing the torque as a function of time obtained with the isothermal oscillating disc rheometer (ODR), the temperature of the sample varying with time according to an unknown law, it is not easy to determine the conditions of time and temperature for the scorch of cure, which are associated with the minimum torque value. Moreover, the moving die rheometer (MDR), gives a shorter... 

Newer versions of the cure meter have been introduced (e.g.. Figure 7.6). The cavity is much smaller and there is no rotor. In this type of cure meter, one-half of the die (e.g., the upper half) is stationary and the other half oscillates. These instruments are called moving-die rheometers. The sample is much smaller and heat transfer is faster. Also, because there is no rotor, the temperature of the cavity and sample can be changed more rapidly. In either case (oscillating disc or moving die), torque is automatically plotted against time. Such a chart is shown in Figure 7.7. 

The most common dynamic method is oscillatory testing, in which the sample is subjected to a sinusoidal oscillatory strain, and the resulting oscillatory stress measured. The more sophisticated rotational viscometers have the additional capability of dynamically testing liquid-like materials using small angle oscillatory shear. A parallel disc viscometer can be set up for testing solid-like materials (e.g., butter), in oscillatory shear. Some UTM-type solids rheometers, in which the moving crosshead can be made to reciprocate sinusoidally, can be used to test solid-like materials in oscillatory deformation in compression, tension or shear. 

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