A magnetorheological fluid (MR fluid) is mainly composed of soft magnetic particles, surfactants, and the base carrier fluid. Among these, soft magnetic particles and the base carrier fluid influence the MR fluid significantly in a high-temperature environment. Therefore, a study was carried out to investigate the changes in the properties of soft magnetic particles and base carrier fluids in high-temperature environments. On this basis, a novel magnetorheological fluid with high-temperature resistance was prepared, and the novel magnetorheological fluid had excellent sedimentation stability, of which the sedimentation rate was only 4.42% after heat treatment at 150 °C followed by one-week placement. At 30 °C, the shear yield stress of the novel fluid was 9.47 kPa under the magnetic field of 817 mT: higher than the general magnetorheological fluid with the same mass fraction. Moreover, its shear yield stress was less affected by the high-temperature environment, reducing by only 4.03% from 10 °C to 70 °C. The novel MR fluid can be applied to a high-temperature environment, effectively expanding the application range of MR fluid.

The traditional vertical-shaft-impact sand-making machine has the problems of uneven discharge particles and discharge port wear. To solve these problems, the influence of the main structural parameters (number of impact rotors, angle of impact plates, angle of anvil, and number of teeth on the anvil) on sand production is researched through orthogonal testing and polar analysis. The results show that the parameters’ degrees of influence on the sand production rate are as follows: the angle of impact plates, the number of impact plates, the angle of the anvil, and the number of teeth on the anvil. The double rotor exhibits the best crushing effect when the number of impact rotors is six, the angle of the impact plate is 0°, the angle of the anvil plate is 0°, and the number of teeth on the anvil plate is 89. By taking the working speed of the double rotors as a factor, an equal-level uniform design table is constructed for the double-rotor crushing system. Polynomial regression analysis shows that the best crushing effect occurs when the accelerating rotor speed is 1200 r/min and the impact rotor speed is 585 r/min. Finally, the crushing characteristics of the double-rotor vertical-shaft-impact sand-making machine are simulated and analyzed to obtain the kinetic energy distribution of particles in the crushing chamber. The kinetic energy of particles in the main crushing area is determined, and the wear pattern of the discharge port and parts is identified.

This study investigates the temperature distribution characteristics, temperature rise behavior, and the thermal effects on the output torque in a Permanent Magnet/Magnetorheological Fluid (PM/MRF) variable-stiffness drive joint through a combined approach of simulation and experimentation. First, a thermal simulation model of the joint was established using COMSOL Multiphysics, and steady-state and transient temperature field analyses were conducted under slip powers ranging from 25 W to 100 W. The steady-state results show that, when the joint reaches thermal equilibrium under 100 W, its internal maximum temperature is 113 °C, which falls within the allowable operating temperature range of the MRF. Transient simulations indicate that, within 180 s, the temperature in the working area of the joint continuously rises, but the rate of temperature increase gradually slows down, with a maximum temperature rise of 18.35 °C observed in the transmission mode. Furthermore, an experimental test system was constructed to conduct temperature rise characteristic tests and torque temperature characteristic tests on the joint. The experimental results show that the maximum actual temperature rise measured within 180 s in transmission mode was 17.36 °C, slightly lower than the simulated prediction. Within the temperature variation range of 10 °C to 50 °C, the maximum reductions in driving torque and braking torque were 14.1% and 14.9%, respectively. The study demonstrates that, under short-term operating conditions, the effect of the internal temperature rise on the output torque is predictable and can be mitigated through closed-loop current compensation. These findings provide theoretical and experimental foundations for the thermal safety design and high-precision control of PM/MRF variable-stiffness joints.