GB842977A - Improvements in methods and apparatus for measuring gel strength and viscosity - Google Patents

Abstract

842,977. Testing physical qualities of materials. BRITISH RUBBER PRODUCERS RESEARCH ASSOCIATION, and SOUTHORN, W. A. Sept. 12, 1957 [June 14, 1956], No. 18402/56. Class 106 (2). The strength of a weak gel is measured by applying a very small cyclic torsional stress, first in one sense and then in reverse, and recording the stress required to produce the constant maximum strain at .the end of each cycle, the strain being in all cases below the yield value of the material. and applied so slowly as to discriminate between viscous and structural effects. Apparatus for measuring the strength of rubber latex coagulum, for example, comprises a motor-driven oscillatory head 1 which transmits a stress down a torsion wire 2 to a bob 5 located within the material to be tested held in a glass cup 6 fitted in a double-walled vessel through which water at a controlled temperature may be circulated. The stem of the bob 5 carries an arm 7 ending in two platinum contacts which touch alternately silver plates 8, 9 to operate a series of relays which reverse the motor and cause a pen to make a mark on a sheet of paper on a constant-speed drum, thus producing two symmetrical curves whose separation at any point on the time axis is an approximate measure of the elastic modulus of the coagulum. A correction for the viscosity of the latex and the physical constants of the apparatus may be applied by subtracting from the subsequent readings the separation of two parallel lines obtained by first making a blank run with latex in the cup without coagulant. The head 1 is arranged to rotate extremely slowly, e.g. one revolution per five minutes; the record drum speed may be varied and is usually one revolution an hour or a day; the bob may be of stainless steel and 1¢ inches in diameter and the cup 2¢ inches in diameter; platinum contacts may be fitted to give a permitted travel of the bob of 1 or 5 degrees of arc and the range of the apparatus can be varied over a wide range by providing a series of calibrated wires 2.