Extrusion rheometer for characterizing thixotropic materials

A special form of extrusion rheometer has been developed for characterizing thixotropic pastes and high viscosity materials. It consists of a cylinder with an orifice situated halfway along, and has a piston at each end. In use, a sample plug of material is forced through the orifice at a uniform rate by one of the pistons, and the load required is recorded. After a given recovery period the material is forced back through the orifice by the other piston, and the load again recorded. If the material is thixotropic, it will have a reduced viscosity on the second ’’pass,’’ and the percentage reduction in load will be related to the thixotropy of the sample. This rheometer was developed for testing resin adhesive pastes, but other possible applications might include the testing of paints, foodstuffs, cosmetics, toothpaste, printing inks, and greases.