Oscillating 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. 

FIGURE 5.13 Torque-time curves obtained with the same rubber sample using the oscillating die rheometer (ODR) and the moving die rheometer (MDR). 

Oscillating die rheometer Oscillating die rheometer BS ASTM ISO Gibitre, Italy available from Negretti Automation ... 

A development of the moving die rheometer where the operation of the unit is fully computer controlled. The rate of oscillation, temperature and level of strain can all be run through a series of options. The torque measurements are also highly sophisticated. As a consequence, the unit can be set up to monitor processing parameters, then the cure behaviour and finally the finished dynamic properties of the cured material. It is manufactured by Alpha Technologies. 

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. 

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 Gibitre oscillating die Rheocheck available from Negretti Automation is a moving die rheometer which enables the vulcanisation curve for any compound to be produced rapidly at closely controlled temperatures. It is designed for rapid computer-controlled quality checks in a production environment. 

Rheometer a cure meter which determines and plots a cure curve, illustrating the state of cure for a given time and temperature typically either an oscillating disk rheometer (ODR) or a moving die rheometer (MDR). 

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