Torque rheological property

The impeller method is a technique commonly used to determine rheologic properties of fluids subject to particle settling. The impeller method utilizes a viscometer along with Newtonian and non-Newtonian calibration fluids to obtain constants that relate shear stresses and shear rates to experimentally measured values of torque and rotational speed. Newtonian calibration fluids are used to determine the impeller constant, c, and non-Newtonian calibration fluids are used to calculate the shear rate constant, k. These constants are then used to aid in the determination of rheologic properties of a selected non-Newtonian fluid, such as wet grains. 

Two Brookfield viscometers were used to collect the data necessary for rheologic property studies of wet grains a Brookfield RVDV III viscometer with a cone-and-plate spindle and a Brookfield HBDV III viscometer with a double helical ribbon impeller attachment. The Brookfield RVDV III had a full-scale torque of 7187 dyn-cm, and the HBDV III had a full-scale torque of 57,496 dyn-cm. Each viscometer had a maximum rotational speed of 250 rpm. Both viscometers had accuracy limits of 5% full-scale torque. 

In general, shear stress at one location (e.g., the bob surface in a concentric cylinder viscometer) is calculated from the dimensions of the sample gap and the measured or applied torque. Shear rate is calculated at the same location from sample gap dimensions and rotational speed. By making experimental measurements over a range of speeds or torques, the flow curve (shear stress versus shear rate) of the sample can be established. Suitable mathematical treatment of the flow curve data yields the sample s constitutive equation and rheological properties. 

The existence of a stress-free meniscus introduces a boundary discontinuity on both upper and lower rims. This discontinuity is bound to result in sharply enhanced stress build-up at the upper and lower contact lines. It may produce an effective slip layer on the sample/plate interfaces at the meniscus, yielding an overall torque, which is less than anticipated on the basis of Fig. 7a, since a large portion of the measured torque on the plate arises from the stress contribution at the rim r=R. This correction may increase with lowering the gap distance. Without a proper analytical treatment, it remains unknown how the magnitude of such an apparent slip depends on the rheological properties of the sample and whether the reported slip like behavior [ 19,33] is a manifestation of such a plausible edge effect. 

A torque rheometer is a device that provides an off-line measurement of torque required to rotate the blades of the device and this torque can be used to assess rheological properties of the granulation. It has been extensively used for end-point determination.The torque values thus obtained were termed as measure of wet mass consistency. ° ... 

Rowe, R.C. Sadeghnejad, G.R. The rheological properties of microcrystalline cellulose powder/water mixes-measurement using a mixer torque rheometer. Int. J. Pharm. 1987, 38, 227-229. 

Plant food dispersions such as tomato concentrates and concentrated orange juice are important items of commerce. The viscosity function and the yield stress are two important rheological properties that have received considerable attention. Corrections for slip, due to the formation of a thin layer of fluid next to solid surfaces, in a concentric cylinder viscometer depended on the magnitudes of applied torque and on the shear-thinning characteristics of the dispersion. Mixer viscometers were used for obtaining shear rate-shear stress and yield stress data, but the latter were higher in magnitude than those obtained by extrapolation of flow data. 

Another group of possible errors arises from the characteristics of apparatus, evaluation of rotation velocity of cylinders and torque, measured as net torque [15]. These problems do not appear in the case of Newtonian or Bingham fluids, while the tixotropic one reveal several problems because the gradient of velocity in the space between the cylinders depends on the paste rheological properties which ate to be tested. There are different ways to resolve this problem Nagataki and Kawano [17] measured directly the distribution of velocity gradient in the space between the cylinders. The assumption that this gradient is linear is not a correct approach, particularly when it appears later that this is not true it is an error and not the approximation [15]. 

In an attempt to follow the effect of concentration of stearic acid on the rheological properties, compounds from SBR rubber -filled with 50 phr carbon black N550, ZnO, and with varying the stearic acid concentration (0 0.5 1.0 1.5 and 2 phr) were prepared. Using Brabender plasticorder and capillary viscometer these compounds were studied. The observed effective (apparent) viscosity (30-5-120%) (Figure 1) and torque maxima (104-20%) (Figure... 

There are several techniques for studying rheological properties, but in this chapter we present the two techniques for rheological characterization that are used to determine the flow properties of the natural rubber reactive blending. First, the Mooney viscosity can determine the natural rubber that is related directly to the inherent property of its molecular weight. It is the most common instrument used to measure the bulk viscosity of rubber. It is defined as the shearing torque that can resist the rotation of a cylindrical metal disk/rotor... 

The torque variation of blends during compounding can also indicate effect of MDI distribution. As expected, the addition of MDI increased the torque of pure PLA, due to molecular weight increase [45]. Similar results for other polyesters such as polycaprolactone (PCL) and poly(butyl-ene succinate adipate) (PBSB) have also been observed [44]. The highest torque values were recorded for the blends where MDI was distributed in the PLA phase, which further confirms the benefits of PLA phase distribution of MDI. The results of a detailed study of the rheological properties of the various blends will be reported in a separate paper. 

Torque rheometry is used extensively for measuring rheological properties and for determining melt flow values, thermal stability of polymers, degradation time, and characterization of different formulations. Chapter 12 discusses torque rheometry in detail. 

The cone-n-plate viscometer is a widely used instrument for measurement of shear flow rheological properties of polymer melts [9-20]. The principal features of this viscometer are shown schematically in Fig. 3.1. The sanaple, whose rheological properties are to be measured, is trapped between the circular conical disk at the bottom and the circular horizontal plate at the top. The cone is connected to the drive motor which rotates the disk at various constant speeds, whereas the plate is connected to the torque-measuring device in order to evaluate the resistance of the sample to the motion. The cone is truncated at the top. The gap between the cone and plate is adjusted in such a way as to represent the distance that would have been available if the untruncated cone had just touched the plate. The angle of the cone surface is normally very small (0o 4° or 0.0696 radians) so as to maintain [4] cosec Op = 1. The cone angles are chosen such that for any point on the cone surface, the ratio of angular speed and distance to the plate is constant. This ensures that the shear rate is constant from the cone tip to the outer radius of the conical disk. Similarly, the shear... 

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