Deciding whether to buy a viscometer or a rheometer is not always simple. This guide will walk you through the differences and how a rheometer can better suit your needs.
What is the Difference?
Typically, viscometers employ mechanical bearings that limit the speed and torque capabilities of the instrument, while rheometers use low-friction air bearings. This means that viscometers can be a solution for materials, process or production testing where simple flow measurements (where viscosity is independent of shear rate) are required for Newtonian materials, but with rheometer performance to better characterize flow, deformation and even is sticky.
Adhesion describes the interaction between two layers of the same (self-adhesive) or dissimilar (cohesive) material, i.e. surface tack.
Viscosity of the material (for Newtonian and non-Newtonian)
A non-Newtonian fluid is a fluid whose viscosity changes with applied shear rate or shear stress.
non-Newtonian materials).
Viscometers can provide portability for on-site or remote testing. Rheometers, although generally more expensive than viscometers, are more versatile and have a wider dynamic range of control and measurement parameters.
Measure Viscosity
Measuring viscosity is the most common application of a viscometer or rheometer. For most products, the viscosity is required to be higher at low shear rates to prevent settling or slumping, but thinner at higher shear rates to facilitate application or processing. Therefore, a single viscosity measurement is insufficient to describe the viscosity of such materials and the viscosity should be measured over a range of shear rates or stresses.
Typically, viscometers can measure from about 0.1 to 103 s-1, while rheometers extend the measurement range from 10-6 to 105 s-1. The wider measurement range makes it possible to obtain relevant data by exposing the sample to conditions similar to those applied during the manufacture or use of the product.
Due to the rheometer’s low torque capability, processes such as sedimentation are best suited for analysis using a rheometer. The high speed control of the rheometer also enables the analysis of very high shear rate processes such as spray coating.
Yield Stress
Besides viscosity, yield stress is perhaps a more routinely measured rheological property, since many consumer products gain value by having it.Compressive stress at yield is defined as the level of force exerted on a sample with a well-defined cross-section. (stress = force/area). Samples with circular or rectangular cross-sections can be compressed or stretched. Elastic materials such as rubber can stretch to 5 to 10 times their original length. Stress varies with temperature and time scales, during which compressive stress is defined as the level of force exerted on a sample with a well-defined cross-section. (stress = force/area). Samples with circular or rectangular cross-sections can be compressed or stretched. Elastic materials such as rubber can stretch to 5 to 10 times their original length.
put pressure on. Rheometers can provide more relevant yields. Pressure stress is defined as the level of force exerted on a sample with a well-defined cross-section. (stress = force/area). Samples with circular or rectangular cross-sections can be compressed or stretched. Elastic materials such as rubber can stretch to 5 to 10 times their original length.
By applying these methods extensively, better stress data than viscometers can be obtained. Apply a Compressive stress is defined as the level of force exerted on a sample with a well-defined cross-section. (stress = force/area). Samples with circular or rectangular cross-sections can be compressed or stretched. Elastic materials such as rubber can stretch to 5 to 10 times their original length.
Stress ramps are considered the easiest way to use a rheometer.
Which is best for me?
Enhanced versatility and performance make the rheometer an excellent tool for research, product and process development, and quality control testing. Viscometers and rheometers are complementary, and it is not uncommon for viscometers to be used within a single organization for quality control testing of products developed using rheometers.
