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

Sealing is one of the most important characteristics of carrying out enhanc ed lubrication in high-performance machining work. High-speed spindles requ ire non-contact sealing mechanism types. To minimize leakage, the flow cont rol mechanism should incorporate an optimum seal design. This paper categor izes the geometry of commonly used non-contact seal types and analyses the leakage characteristics of each type in minimizing leakage on the sealing a rea. The non-leaking property is estimated by the amount of pressure drop i n the leakage path. Gas or liquid had previously been considered as the wor king fluid for most non-contact seal types including the labyrinth seal. Ho wever, it is more reasonable to apply a two-phase flow because high-speed s pindles use oil mist or oil jet lubrication. Thus, a working fluid is regar ded as comprising two phases: mixed flow of oil and air. Both turbulence an d compressible flow models are introduced in the computational fluid dynami cs (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 exc ellent sealing effects for oil mist lubrication. The minimum clearance shou ld 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-contac t seal types. The model entails the combined geometry of a protective colla r type and an air jet type. Experimental measurements are carried out to ve rify improvements in sealing efficiency with the use of the adapted model. The sealing effects of employing the leakage clearance and air jet magnitud e are studied using various parameters. The effected sealing improvement is attributed to the decrease in leakage clearance caused by air jetting. Thu s, the seal effect is improved by the amount of air jetting but the clearan ce level becomes higher at the same time.