Oscillating-disk viscometers

Oscillating-disk viscometers consist of an axially symmetric disk placed between two fixed parallel plates and suspended fi om a torsion wire, so that it performs oscillations in the fluid about its axis of symmetry. Such a viscometer has been used by several researchers as an instrument for viscosity measmements (see, for example, DiPippo et al, 1966 Kestin et al, 1977, 1978a,b, 1980 Correia et al., 1979 Correia and Kestin, 1980 Kestin and Shankland, 1981b, 1984b and Krall et al, 1987, 1992). The theoretical and experimental problems of this technique have been... 

As it will be shown in the following paragraphs, this natural length scale is important in the selection of the dimensions of oscillating-disk viscometers. 

For the oscillating-disk viscometers consisting of a tiiick disk oscillating in an infinite fluid i.e. a fi ee thick disk), and provided that 5 dll and R 5, file analytical solution for D(s) is Kestin and Shankland (1981b)... 

The torsional pendulum of a dense disk moving slowly in a viscous medium has been developed by J. Kestin and co-workers about 1980 to measure simultaneously the density and the viscosity of the fluid [5.11]. This work was based on a couple of papers reporting on oscillating body viscometers using cups, spheres, cylinders, etc. published already in the period 1930-1960 [5.12]. Today pendulum viscosimeters are used to measure the viscosity of both gases, liquids, and even molten metals and salts at extreme temperatures (Ir(liquid melting state) 2,800 K) and pressures (100 MPa), [5.13-5.15]. 

The results of low-temperature measurements (below 473 K) are not given usually in the Appendix. Numbers separated by a slash (/) show the minimal temperatures or pressures available in the publications (before a slash) and in the Appendix tables (after a slash). Sat. means that equilibrium pressure is not shown in the publications but was near (above) the saturation vapor pressure at measured temperature, a) - CF -capillary flow OD- oscillating disk QV-quartz viscometer FB-falling-body... 

The Mooney Viscometer test is one of the oldest processability tests in the rubber industry. Many processors now prefer the oscillating disk rheometer (ODR) for measming cme time and cme rate, but the Mooney Viscosmeter is usually preferred for viscosity and scorch time measmements. 

Oscillatory shear measurements can be done with the parallel-disk arrangement in a manner similar to the case of the cone-n-plate viscometer and, similarly, the material fimcdons i), G, C, and others can be generated. However, a slightly different tedinique [36] is at times used wherein the polymer melt sample is deformed between two oscillating parallel eccentric disks as shown in Fig. 3.2. In this case, too, it has been shown that the fluid elements undergo a periodic sinusoidal deformation and the forces exerted on the disk are thus interpreted in terms of G and G" [4]. 

Dynamic mechanical analysis is used to determine the response of a polyethylene sample to an oscillating force. In its most general form a sample is attached to a pair of movable probes, one of which applies a sinusoidal oscillatory motion while the other measures the force transmitted by the sample. The temperature of the sample and the frequency of oscillation (to) can be varied independently. The sample may be in either its solid or molten state. In the case of molten polyethylene, the sample typically takes the form of a disk sandwiched between a metal drive plate and a torque transducer. Rotation of the drive plate induces shear deformation within the sample, which is measured by the transducer. The basic configuration of the apparatus is similar to that of the cone-and-plate rotational viscometer shown in Figure 9. With appropriate modifications the same equipment can be used for both types of analysis. 

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