Leakage characteristics of non-contact seal types for high-speed spindles

Abstract

Sealing is one of the most important characteristics of carrying out enhanced lubrication in high-performance machining work. High-speed spindles require non-contact sealing mechanism types. To minimize leakage, the flow control mechanism should incorporate an optimum seal design. This paper categorizes the geometry of commonly used non-contact seal types and analyses the leakage charcteristics of each type in minimizing leakage on the sealing area. The non-leaking property is estimated by the amount of pressure drop in the leakage path. Gas or liquid had previously been considered as the working fluid for most non-contact seal types including the labyrinth seal. However, it is more reasonable to apply a two-phase flow because high-speed spindles use oil mist or oil jet lubrication. Thus, a working fluid is regarded as comprising two phases: mixed flow of oil and air. Both turbulence and compressible flow models are introduced in the computational fluid dynamics (CFD) analysis. As the results of the CFD analysis in various geometric cases reveal, a protective collar type and an air jet type seal exhibit excellent sealing effects for oil mist lubrication. The minimum clearance should be located between the wall on the flow inlet and the collar, while seal size should be minimized by taking into account the thermal expansions and deflections of spindles. Based on the analytical results, an adapted model is introduced to improve the sealing capability of conventional non-contact seal types. The model entails the combined geometry of a protective collar type and an air jet type. Experimental measurements are carried out to verify improvements in sealing efficiency with the use of the adapted model. The sealing effects of employing the leakage clearance and air jet magnitude are studied using various parameters. The effected sealing improvement is attributed to the decrease in leakage clearance caused by air jetting. Thus, the seal effect is improved by the amount of air jetting but the clearance level becomes higher at the same time.