Automatic Rotational Viscometer and High-Pressure Apparatus for the Study of the Non-Newtonian Behavior of Materials

Abstract

The automatic concentric‐cylinder rotational viscometer described here records flow curves of shear stress versus rate of shear. It provides an automatic means of increasing and decreasing the applied rates of shear and an automatic control of the time that each shear rate is applied to the sample. In as much as flow properties may change rapidly with time and shear rates, this automatic control is important for materials which are time dependent. Presently, with proper selection of the axle and transmission gears, the cup's rotational speed can be automatically varied from zero to 1830 rpm. A switch permits the operator to select a constant shear rate and record shearing stress changes as a function of time at any point of this range. By simply replacing the gear sets, a speed of approximately 2750 rpm can be achieved. The time required for the speed to change from zero to a preset maximum, at constant acceleration, is controlled by voltage changes through a Variac which affords a continuous range from 11 to 300 sec. Shear rates of up to 4090 sec⁻¹ are obtained. The cup and bob are aligned coaxially and mechanically fixed. Added cup‐bob features for bob‐flushing effectively control effects of frictional heating within the sample. Other apparatus described here provides a means to measure the consistency of greases, near the ``pseudo solidification'' point induced by high pressures. The flow curves of greases which have a critical solidifying pressure reveal characteristics suggesting stiffer consistencies at increasingly high pressures. A 6‐tank ``reservoir'' of hydraulic fluid is used where the fluid under compression and the tensile stresses in the steel of the tanks are used to completely eliminate the antagonistic ``ripples'' in the pressure which are caused by the action of the pump. Pressures of 0–50 000 psi are easily and safely obtainable with this apparatus.