Shearing equipment designs

Since fluid shear rates vary enormously across the radius of a capillary tube, this type of instrument is perhaps not well suited to the quantitative study of thixotropy. For this purpose, rotational instruments with a very small clearance between the cup and bob are usually excellent. They enable the determination of hysteresis loops on a shear-stress-shear-rate diagram, the shapes of which may be taken as quantitative measures of the degree of thixotropy (G3). Since the applicability of such loops to equipment design has not yet been shown, and since even their theoretical value is disputed by other rheologists (L4), they are not discussed here. These factors tend to indicate that the experimental study of flow of thixotropic materials in pipes might constitute the most direct approach to this problem, since theoretical work on thixotropy appears to be reasonably far from application. Preliminary estimates of the experimental approach may be taken from the one paper available on flow of thixotropic fluids in pipes (A4). In addition, a recent contribution by Schultz-Grunow (S6) has presented an empirical procedure for correlation of unsteady state flow phenomena in rotational viscometers which can perhaps be extended to this problem in pipe lines. 

The most critical step in cryopelletization is droplet formation, which is influenced not only by formulations-related variables such as viscosity, surface tension, and solids content but also by equipment design and the corresponding processing variables. The diameter and design of the shearing edge of the holes on the container plates are critical. For instance, the diameter of the holes determines the flow rate, which,... 

Based on the machine design parameters, high-shear granulation equipment of the same type will usually vary less in tip speed, Froude number, and RSV upon scale-up in equipment size. The differences in Froude number and RSV among high-shear mixers of different types are less as the size of the equipment increases. Therefore, development and scale-up are easier if the same type of high-shear equipment is used. 

When new drugs and drug-delivery systems are developed in the laboratory, the correlation of the necessary production equipment may be very difficult indeed. For example, the shear needed to create the desired particle size of an emulsion with the help of laboratory equipment may pose serious problems in the selection of plant equipment necessary to reproduce the attributes of the product. Recording the speed of a laboratory mixer is not sufficient by itself for this task definition of the operating principle and equipment design is necessary to accomplish the task. 

Among the factors impacting binder performance in high shear equipment are the binder quantity, binder addition method (wet vs dry), solvent quantity, solvent addition rate and method (spray vs open tube), wet massing time, impeller speed, chopper speed, and equipment design and these parameters need to be optimized during the development process, typically with the aid of a statistically designed set of experiments. 

When selecting shearing equipment, it is essential that the buyer understands the advantages and disadvantages of each design, the operating variables, and the principles of shearing to ensure that the machine of choice is one that is most suitable for his particular operation. 

Only a very small amount of PP is processed by the blow moulding technique. As a blow moulding material, PP has never enjoyed the success of HOPE. This is in large measure because mouldings of PP require more attention to equipment design and operating conditions. The initial development of the machinery for blow moulding was optimised for HOPE due to its earlier invention. The difficulty with PP is that its melt viscosity is far more sensitive to temperature and shear rate than is the case for PE. 

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