High Pressure Capabilities of Slender Squeeze Gaps of Magneto-Rheological Fluids

In the last decade ample of academic and industrial research work in the area of magneto-rheological fluids (MRF’s) has been done. Most of the concepts and products developed in this time period (e.g. MRF brakes and clutches) feature a shear mode operation. Hence a majority of the published work is addressing this mode. Nevertheless, the MRF squeeze mode becomes more and more attractive (for damping applications for instance) due to its higher reachable force densities compared to the other modes. In this paper attainable MRF squeeze mode pressures for very small squeeze gaps are experimentally investigated. For squeeze gaps down to few hundredth of a millimetre the mean squeeze pressure reaches nearly 100bar. On the other hand, especially in the squeeze mode, the problem of MRF segregation occurs. In this work three different methods to avoid or to reduce this phenomenon are experimentally tested and discussed. Finally, a simplified analytical relation for the MRF squeeze mode pressure characteristics is presented and compared to experiments. This comparison shows that the analytical model predicts the MRF squeeze pressures with a satisfactory accuracy such that it can be used for dimensioning purposes.