Abstract
In the first part of the paper a numerical calculation for the pressure distribution of the screw seal is given using the Finite Element Method (FEM). Inertial forces areneglected. The threads are considered rectangular and completely filled with a Newtonian liquid. Contrary to the stationary flow of the concentric seal the flow in the eccentric running seal is non-stationary. It is described how to treat it is a quasi-stationary problem which is computable. Sealing coefficient and pressure distribution of the concentric running screw seal is computed for a wide range of geometrie parameters. The resulting forces in the seal, due to the pressure distribution, are also calculated using the FEM.
In the second part the pressure distribution of the eccentric running screw seal is determined. Because high pressure gradients appear in the eccentric case it is necessary to idealise the integration area with a great number of finite elements and therefore a large system of linear equations has to be solved. A computer program has been developed to solve these equations. It is shown that the sealing coefficient is decreasing exponentially with increasing eccentricity. At the beginning of the threads in the diverging gap the pressure becomes partially negative and is defined as “tensile stress” in the liquid. The experiments are described in the third part. The experimental results are in good correspondence with the calculated values. The tensile stresses have been proved in the experiments and it is shown that these are responsible for the degassing of the liquid which may result in a seal-break-down.
Users
Please
log in to take part in the discussion (add own reviews or comments).
