The instron rheometer

It was shown some years ago by one of the authors (R. S. Higginbotham) that measurements of viscosity at a shearing stress of about 4500 dynes/cm² were especially useful for predicting the behaviour of colour pastes used for printing textile fabrics on engraved-roller machines. Such measurements could be made with various types of equipment, the most convenient to use being theFerranti-Shirley cone and plate viscometer, but it was felt that there was a need for a viscometer specifically designed for this purpose, and as cheap, simple, robust and easy to use as possible. A first attempt to produce such a viscometer (Higginbotham andBenbow, J. Sci. Instr.29, 221, 1952) was not entirely successful but a satisfactory, direct reading, cone and plate instrument has now been produced. It employs a permanentmagnet motor driven under conditions of constant torque to provide a constant shearing stress. The cone speed is then inversely proportional to the viscosity of the fluid under examination. A photoelectric tachometer with an associated electronic circuit generates a voltage proportional to the viscosity and the result is displayed on a linearly calibrated meter. The instrument has been tested in two printworks over a period of several months, and it has been shown to be suitable for the control of screen printing, as well as roller printing, pastes.