Machining Precise Parts

Hydrostatic spindle bearings ensure maximum part precision, excellent tool life and high machine availability with low servicing costs. Article by Hyprostatik Schönfeld GmbH.

In turning, grinding or milling machines, spindle bearings with roller bearings have been used predominantly up to now. Growing demands for shaping accuracy, dimensional stability, surface quality and removal rate, however, are bringing spindles with roller bearings ever closer to their limits.

Spindle Bearings with Rolling Bearings Quickly Reach Their Limits

While new high quality spindle bearings with roller bearings can achieve concentricity qualities of approximately 1 µm, the running quality decreases rapidly at high stresses and speeds. This means that the bearings in fast-turning interior grinding spindles have to be replaced after only a few months.

Spindle bearings with roller bearings are only slightly damped. This has direct effects on the surface quality of the part. It also means that tool working lives and the boundary cutting line are somewhat limited.

In addition, fast-running spindle bearings with roller bearings frequently develop very high temperatures, through which the thermal stability of machine suffers, despite costly cooling measures.

This is where hydrostatic spindle bearings come into their own. If spindle bearings with roller bearings are compared with hydrostatic spindle bearings, hydrostatic embodiments achieve the following advantages:

• Freedom from wear

Hydrostatic bearings are contactless and therefore free from wear.  The properties therefore remain unchanged regardless of the duration of use, stress and speed.

• Concentricity

Depending on the spindle size, maximum speed and spindle configuration, the concentricity of hydrostatic spindle bearings and turntables is between 0.03 µm and 0,3 µm, typically 0.1 µm – and this regardless of the duration of use.

• Damping 

Ideally designed hydrostatic spindle bearings have damping that is many times greater than roller bearing spindles. In addition to longer tool lives, better surface qualities and lower shaping errors are achieved. Chattering only occurs at significantly higher cutting rates. 

• Temperature behaviour

With hydrostatic bearings, frictional power only occurs in the oil. As this is transported very quickly from the bearing with less wetted surfaces, the bearing remains cool even at very high speeds. The bearing fluid is cooled outside the bearing.

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