When a piston subject to an axial pressure drop has to be moved periodically along a bore sticking often occurs owing to hydraulic locking between the piston and the bore. The locking is caused by the hydrostatic pressures acting along the annulus between the two surfaces. The hydraulic instability may be reduced by using a piston tapered to give a converging film shape in the direction of flow, and this paper considers a large number of tapered configurations. The hydraulic pressures are calculated by a solution of Reynolds' two-dimensional equation using a digital computer, and the resultant force and its line of action are obtained. From these results empirical equations for the locking force and its line of action are derived which are valid for a wide range of conditions. The values predicted by the equations agree well with experimental and theoretical results given in the literature.

A mathematical model simulating the gas carburising of steel components has been developed for the prediction of optimum process parameters. The utilisation of optimised process parameters has given rise to increases in furnace throughput of ~ 20%. The implementation of the optimised process parameters has demanded faster, more accurate process control than that achieved with conventional furnace control equipment. The required degree of control has been achieved with systems based on either a minicomputer or a microcomputer in which furnace atmosphere analysis is effected with oxygen probes.