Two stage magnetic fluid vacuum seal for variable radial clearance

Abstract A two-stage magnetic fluid seal (shaft diameter: 20 mm) is designed and tested for its performance under variable rotational speed (up to 5000 rpm) and radial clearance (0.3–0.5 mm). The influence of geometry of focusing structure, radial clearance and fluid magnetization on differential pressure is simulated using FEMM. Two different fluids having magnetization 34.69 kA/m and 53.44 kA/m were synthesized for this experiment. The test rig was developed to test the designed seal for variable rotation of the shaft up to 5000 rpm (peripheral velocity, v = 5.23 m/s) under 10−2 mbar pressure. Results show that because of the combination of wedge shape pole pieces, optimum aspect ratio, higher field gradient as well as higher fluid magnetization (with optimum fluid volume) the pressure holding capacity of fluid plug increases and it makes it capable to sustain the differential pressure at higher rpm and larger radial clearance only with the two stages. Such seal can work as the bearing protection in rough vacuum devices with large shaft diameter, low-pressure chemical vapour deposition (LPCVD) and as an exclusion seal in stepper motor, robotic arm, etc.