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Tham khảo tài liệu 'plastics technology handbook 2011 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3-44 Plastics Technology Handbook motor FIGURE 3.34 Scheme of a Weissenberg Rheogoniometer. which is measured by means of a transducer. The polymer sample is placed in the space between the cone and plate and the torque experienced by the stationary cone is measured for different rotational speeds of the plate. Relating the shear stress at the cone surface to the measured torque and the shear rate to the angular velocity of the plate the expression for the viscosity h is obtained as 3KỠ sin a h Z 2pRpu 3.114 where K is the torsional constant and q is the deflection of the spring Rp is the radius and u is the angular velocity of the plate and a is the angle of the cone. While q and u are experimentally determined quantities K and a are obtained by calibration on other materials. The cone and plate viscometer gives reliable experimental data over an extensive range of shear rates 10 4 104 sec-1 . Not only can it be used to measure viscosities in simple shear but it can also be used to determine the dynamic properties of viscoelastic materials. The unit is also set up to measure the normal stresses exhibited by viscoelastics i.e. those perpendicular to the plane of shear. 3.2.17.2 Capillary Rheometers These rheometers are widely used to study the rheological behavior of molten polymers. As shown in Figure 3.35 the fluid is forced from a reservoir into and through a fine-bore tube or capillary by either mechanical or pneumatic means. The fluid is maintained at isothermal conditions by electrical temperature control methods. Either the extrusion pressure or volumetric flow rate can be controlled as the independent variable with the other being the measured dependent variable. Under steady flow and isothermal conditions for an incompressible fluid assuming only axial flow and no slip at the wall the viscous force resisting the motion of a column offluid in the capillary is equal to the applied force tending to move the column in the direction of flow. Thus RAP 2L 3.115 .
