A modified pin-on-disc tribometer was developed to investigate the friction and wear characteristics of magnetorheological (MR) fluids under controlled magnetic fields. The design incorporates an inclined pin (0.1°) to establish hydrodynamic conditions, achieving a maximum magnetic flux density of 138 mT at the pin–disc interface.

The schematic of the tribometer based on pin-on-disc arrangement is shown in Fig. 1. The designed tribometer has several components such as a coil core, coil, pin holder, pins, disc, disc holder, lower yoke, side yoke, and green zone indicates the MR fluid at the pin and disc contact. Fig. 2 shows the fabricated part of the MR tribometer assembly and pin-on-disc arrangement setup used in the test, three pins have been symmetrically attached at an angle of 120 to the pin holder to avoid any deflection due to eccentricity under axial load. The pin is fixed at a radius of 20 mm from the center and the pin diameter is 5 mm. MR fluid is uniformly distributed on the disc surface. The pin is brought in contact with a disc with the help of a stepper motor-based linear actuator, and load is applied from the bottom side of the disc with the help of a low-powered linear actuator. In order to generate the magnetic field DC current is supplied to the electromagnet, which activates the MR fluid in the pin and disc contact zone. We preferred a clearance fit with 0–2 µm tolerance between the pin and the holder assembly to avoid the misalignment error.

Fig. 3(a) presents the experimental setup of the developed tribometer. It consists of an AC servo motor (2000 rpm, 2 kW) with a speed controller. The speed controller of the servo-motor has an AC-regulated power supply with output voltage (0–200 V) and current (0–9 A, 3-phase). A 100 Nm torque sensor with rpm output is connected to the servomotor through a jaw coupling. The other side of the torque sensor is connected to the shaft of the pin holder of the MR tribometer through a flexible coupling. To replace the MR-fluid after testing, a linear ball screw slider with DC input voltage (20–72 V) and output current (2A–6.5 A) is used to move the pin holder in the upward direction and vice versa. To activate the MR fluid placed on the disc, DC current is supplied to the copper coil through a programmable PFC DC supply (30 V,20 A). The low-powered linear actuator is connected to the disc, and the disc is pressed to apply load at the pin and disc contact zone. A low-powered linear actuator has been used to apply load on the pin during testing, and a load cell is used to measure the load applied on the pin. Fig. 3(b) illustrate the variation in the coefficient of friction (COF) for the steel pin-disc pair. The COF remained relatively constant throughout the test duration. However, a noticeable increase in COF was noted with an increase in magnetic field intensity.