Rotating disc viscometer

Viscosity, Mooney A measure of the viscosity of a rubber or elastomer determined in a Mooney shearing rotation disc viscometer (ASTM D1646). 

Viscometers can be divided into rotational instruments and axial flow instruments. Rotational instruments include concentric cylinder (cup and bob), cone and plate and parallel disc viscometers, while axial flow instruments include capillary, slit and extrusion rheometers. 

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. 

Some rotational viscometers employ a rotating disc, bar, paddle or pin at a constant speed (or series of constant speeds). It is extremely difficult to obtain tme shear stress, and the shear rate usually varies from point to point in the rotating member. In particular, the velocity field of a rotating disc geometry can be considerably distorted in viscoelastic fluids. Nevertheless, because they are simple to operate and give results easily, and their cost is low, they are widely used in the food industry. While they may be useful for quality control purposes, especially Newtonian foods, the reliability of their values should be verified by comparison with data obtained with well defined geometries (capillary/tube, concentric cylinder, and cone-plate). 

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.). 

The Mooney plastimeter is a rotational shearing-disc viscometer (Figure 9.2). The temperature of the machine cavity dies can be preset to typical... 

Mooney viscosity—measure of the resistance of raw or unvulcanized rubber to deformation, as measured in a Mooney viscometer. A steel disc is embedded in a heated rubber specimen and slowly rotated. The resistance to the shearing action of the disc is measured and expressed as a Mooney viscosity value. Viscosity increases with continued rotation, and the time required to produce a specified rise in Mooney viscosity is known as the Mooney scorch value, which is an indication of the tendency of a rubber mixture to cure, or vulcanize, prematurely during processing. 

Rotational Viscometers. Rotational viscometers are the most widely used instruments for the measurement of the rheological properties of a fluid (e.g., a pure liquid, emulsion, or suspension). The test fluid is placed in a gap formed by either two coaxial rotating cylinders, two flat discs, or a flat disc and a cone. The major advantages of the rotational viscometers are... 

The apparatus with a cylinder rotating in liquid in a fixed cylinder is usually called the Couette viscometer in the Pochettino viscometer6 the two cylinders rotate in opposite directions. In Searle s7 apparatus (Fig. 6.VIIIE) a brass cylinder C of radius a is supported on a vertical spindle A pivoted at its ends, and dips to a depth / in a liquid in a cylinder B of radius b. The cylinder C is rotated by weights mg in scale pans which pull on cords passing round a drum of diameter d attached to the spindle, on the top of which is a disc a used with an index b to measure the period of rotation, t0. Then ... 

For filled polymer studies, rotational viscometers with either the cone-plate or parallel-disc configuration are used. 

The cone and plate viscometer is a widely used instrument for shear flow rheological properties of polymer systems [21-32]. The principal features of this viscometer are shown schematically in Figure 3.1. The sample whose rheological properties are to be measured is trapped between the circular conical disc at the bottom and the circular horizontal plate at the top. The cone is connected to the drive motor which rotates the disc at various constant speeds while the plate is... 

Figure 3.2 Schematic diagram showing the principal features of a parallel eccentric discs rotational viscometer.

One of the simplest and cheapest viscometers on the market today is the Brookfield viscometer based on a thin disc rotating in large volume of liquid. While the viscosity is normally quoted as the equivalent Newtonian viscosity as a function of rotation speed in rpm for a given spindle, it is possible to evaluate the power-law parameters k and n for suitable liquids using the following equations [4]... 

Many types of rotational rheometers and viscometers have been developed. The cone and plate, couette (coaxial cylinder), torsional, and disc spindle types are the most common. 

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