A rheometer is a specialized testing system that is able to measure the way that a liquid or a semi-solid response to the application of different types of stress. This stress can test for elongation, viscosity and shear stress.
The machines that test for shear stress and the extensional rheometers that test for elongation will have different operations and testing parameters. Most of the types of machines used to test shear stress will use a capillary, dynamic shear or rotational cylinder design.
Those used to test for extension or elongation will vary based on the viscosity ranges of the materials to be tested. The vast majority of equipment used to test polymers will include spinning or the drawing for a vertical melt strand at a constant, linear or exponentially accelerating velocity.
What to Consider
The use of a rheometer and the subsequent action of the fluid or semi-solid when exposed to shear stress and other test parameters is essential in many different applications.
It will be critical to consider the functions of the given rheometer, particularly when it is important to have highly accurate results. Different types of devices may have features such as an extended speed control for pull-off, increased measurement range and the ability to operate in both online and at-line modes for optimal consideration for specific applications.
There may be the need to consider equipment that offers advanced shear rate ranges as well as the ability to ingrate different components to the base system to extend the range of testing ability. For example, some systems allow for the ability to change out the deflection head to a round hole or slit die to use the equipment to test both blown and flat film.
There may also be the need to add a melt return or a melt return and bypass. These options will eliminate the waste from the testing process, something that is important in most applications.