Stern Rubber Company uses a rubber Rheometer to measure the viscoelastic properties of elastomeric and rubber compounds before, during and after curing. During rubber vulcanization, a Rheometer determines the plasticity, including the cure rate and examines the behavior of the rubber mixture of after it has been vulcanized. Data is transferred to a computer and displayed on a monitor that has measured the torque, viscous and elastic components for the upper and lower halves of the test chamber.
A Rubber Rheometer is a device that is used in laboratories to test raw rubber flow in response to applied forces. The origin of the word Rheometer is derived from the Greek meaning of a device that measures flow. After electricity was widely used in the early part of the 19th century, a Rheometer was used to measure electrical current, but it also measures flow of liquids. Once the term Rheology was coined, it was applied to instruments that measure the characteristics rather than quantity of flow.
Variation of the quantities of these ingredients can be measured on a Rheometer: polymer, vulcanizing agent, cure activator, cure accelerant, softeners, tackifiers, process acid, plasticizer, protective agents, fillers, pigments and blowing agents. The tests that are performed on the Rheometer are done in about 3-5 minutes and are used to identify the possible problems in a compounded rubber formula. The Rheometer measures the change in the properties of the rubber compound during the course of vulcanization. The Rheometer applies force to the associated test piece of raw rubber, including cyclic strain to test the rubber before, during and after vulcanization. The test is carried out at a constant temperature and the stiffness measured is recorded continuously as a function of time.
The Mon Tech Moving Die Rheometer, which is considered the most modern version of Rheometers, is what our quality assurance lab uses at Stern Rubber Company. In fact we have a Rheometer in every building, one in our main Quality Lab at our main facility, one in our rubber extrusion facility and the third at our Aitkin facility. We run a Rheometer test on every batch of material that we manufacture, or purchase.
The raw rubber sample is placed between two dies, in which the lower die oscillates with a ±0.5 degree movement and the upper die is connected to the torque sensor to measure the torque response of the rubber at the deformation. The raw rubber is heated to a working temperature that is between 170⁰C and 190⁰C. We use plastic film which is usually polyamide or polyester that is placed between the samples to prevent cross contamination of the dies during the testing of different products.
The results of the test on the Rheometer are transferred to a computer screen and the results of the processing phase shows the cross linking characteristics and viscous behavior of the compound, creating working information about the how easy the material will process and how the rubber will act inside the molds.