Correction of torque transfer lag in magnetic coupling rheological test system

In this study, a mathematical model for the magnetic coupling transmission process was set up to solve the problem of torque transfer lag in magnetic-coupled rheological testing systems. This model was developed on the basis of torque balance in a magnetic coupling rotatory rheometer test system, which considered friction loss for the jewel bearing, as well as the inertia of both the motor and fixture. Taking the HAAKE-MARS60 high-pressure rheometer as an example, the rheological properties of Newtonian fluid at the initial measuring stage under controlling constant stress conditions were tested to verify the accuracy of the model and using the model to modify the rheological test results. The results show that the load torque mainly influences the alternating frequency of the rotational speed and the hysteresis degree of the inner and outer magnetic rings, the larger the load torque, the greater the deviation of the magnetic coupling test results of the rotational rheometer. The results of the apparent viscosity test are modified under different loading conditions, and the rheological curves of the initial shear phase of the Newtonian fluid are coincident with the steady-state test results, showing the true viscosity of the Newtonian fluid, which conforms to the cognition of Newtonian fluid rheology being independent of time. The results of the initial start test of gelling crude oil were modified, the yield stress and yield time were reduced, and the lower the test temperature and the higher the shear rate, the more obvious the correction effect was. Under different shear rate conditions, the yield strain corresponding to the modified yield stress was close and the yield strain was approximately not changed with the shear rate. The results can provide a basis for understanding the rheological properties of materials in the start-up transient process under high pressure conditions.