Sorted by the size of the sample contact area, the area of the concentric cylinder rotor is larger than the area of the parallel plate and the cone plate. The rotor with a larger diameter can have more contact area with the sample than the rotor with a smaller diameter. Therefore, within the same measuring torque range of the same rheometer, the larger the area, the lower the viscosity that can be measured. If the sample with high viscosity and high shear stress is to be measured, the small diameter rotor should be selected. At present, the smallest diameter rotor that can be selected in a commercial rheometer is 8 mm, and the maximum diameter is 60 mm. Various forms of parallel plates, cone plates and concentric cylinders are available.
If you want to measure a sample that is lower than the viscosity of water, you can also choose a new double-slot concentric cylinder rotor.
However, there are still a few technical issues to explain:
1. Many people don’t know what the parallel plates and cones of the same diameter are for? How to use different taper plates with different taper? Simply put, the parallel plate test has a gradient of shear rate (shear strain) inside the sample, and the sample change is uneven. However, this method is simple, easy to operate, and can also be used for temperature change experiments. The cone and plate test can be close to a uniformly changing shear field, and the smaller the cone angle, the better. However, the problem is that samples with large particles should not be tested with cone and plate, and cone and plate are not recommended for temperature change experiments.
2. A theoretical premise of concentric cylinder testing is that the slits are small enough to approximate the shear flow field. However, due to the demand for different viscosity tests, many designs have gradually deviated from such a principle.
3. The sample volume of the concentric cylinder is larger than that of the parallel plate and the cone plate test sample, and it takes longer for the sample temperature to be uniform.
There are also a few special occasions:
1. For the cured crosslinked sample, a disposable rotor made of aluminum can be provided;
2. For samples requiring optical measurement, a parallel plate rotor made of quartz glass may be used;
3. If it is a sample of current change, you can choose an insulated rotor;
4. The rotor under high temperature and high pressure conditions can withstand up to 700 atmospheres and 300 °C extreme conditions.
