Lubrication hydrostatic

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Hydrostatic Lubrication. Slow-moving or even static "gliders" can be separated form the bearing surface by a fluid film if Ihe hydrostatic pressure required 10 earn Ihe load is provided by an external source, as for instance... 

See ZN/P curve. A less common form of full-fluid-lubrication is hydrostatic lubrication, wherein the oil is supplied to the bearing area under sufficient external pressure to separate the sliding surfaces. 

Bassani R, Piccigallo B (1992) Hydrostatic lubrication. Elsevier Science, Amsterdam... 

Hydrostatic Lubrication. Hydrostatic conditions occur when fluid is pumped between the bearing surfaces with enough pressure to separate them.The surfaces may or may not be moving with respect to each other. 

R. Bassani and B. Picdgallo, Hydrostatic Lubrication, Elsevier, Amsterdam, 1992. 

Wear Particles From the Cradle to the Grave (Dowson et al.. Editors) Hydrostatic Lubrication (Bassani and Piccigallo)... 

The hydrostatic testing is the first test used on the lube system. The system is tested while assembled or partially assembled, based on the particular system. A test pressure of VA times the maximum allowable working pressure, a minimum of 20 psi for the oil side, is used for the test. For the oil-wetted parts, the test fluid should be light oil, which is normally the recommended lubricant for the compressor train. The test period is the length of time needed to inspect for leaks, or a minimum ol thirty minutes. Acceptance is based on the lack of leaks as visually observed or the lack of a drop in the test pressure. 

To generate a lubricating film within a bearing, the opposed surfaces must be forced apart by pressure generated within the fluid film. One way is to introduce the fluid under sufficient pressure at the point of maximum loading, but this hydrostatic method, although equally effective at all speeds, needs considerable power and is consequently to be avoided whenever a satisfactory alternative exists. 

To avoid the instabilities of wedge-shaped oils films, a lubricating film can be maintained by the application of pressurized oil (or, occasionally, air) to the bearing. The hydrostatic bearing maintains a continuous film of oil even at zero speed, and induces a strong stabilizing force towards the center that counteracts any displacement of the shaft or spindle. Disadvantages include the power... 

Externally pressurized gas journal bearings have the same principle of operation as hydrostatic liquid-lubricated bearings. Any clear gas can be used, but many of the design charts are based on air. There are three forms of external flow restrictors in use with these bearings pocketed (simple) orifice, unpocketed (annular) orifice, and slot. 

Many of the disadvantages of ram extrusion are eliminated in hydrostatic extruaon, where the piston is replaced by high pressure fluid. As shown in Fig. 15, the billet stands clear of the cylinder walls, so that this element of friction is eliminated. The pressure transmitting fluid also lubricates the interface between the die and the billet, so that the deformation is essentially plug-flow (i.e. an extensional deformation, identical to drawing polymer with a free surface). Homogeneous oriented sections are therefore produced. A small haul-off force is applied to provide control of the extrusion process, and this also serves to ensure that the extrudates are straight. 

This dimensionless term is known as the hydrodynamic factor , where Fig. 8.2 represents the Stribeck curve in the log scale and shows that a compromise must be made with respect to lubricant viscosity, between the friction losses in the region of hydrodynamic (HD) lubrication, and bearing wear when passing through the regime of mixed friction. Both hydrodynamic and hydrostatic bearings operate with infinite service life below some critical value of load and above a critical value of speed assuming other modes of wear such as corrosion and erosion are not experienced. 

In the discussions of Chapter 13 there was no categorical separation of unlubricated and lubricated wear. Given the existence of an unbroken film of liquid lubricant between two surfaces, it is generally expected that no wear will occur. This is not always so transmission of hydrostatic pressure through the film can plastically deform the bodies which it separates, and tangential tractive forces in the film can do the same. These are wear phenomena as defined in Chapter 13, and since they occur in the presence of lubricant they can be formally classified as lubricated wear. However, in this chapter we shall not concern ourselves with these particular aspects of lubricated wear. We shall be concerned instead with the course of wear in situations where the behavior of the lubricant does not. conform fully with the laws of hydrodynamics or elas-tohydrodynamics. The inference, of course, is that the lubricant at the rubbing surfaces is not there as an unbroken film. 

A hfth regime, sometimes referred to as dry or unlubricated, may also be considered as an extreme or limit. In addition, there is another form of lubrication that does not require relative movement of the bodies either parallel or perpendicular to the surface, that is, as in externally pressurized hydrostatic or... 

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