Hyprostatik Schönfeld
Ultra-precise surfaces require high precision grinding spindles.

Hydrostatic Motor Grinding Spindle Bearings

Feb. 22, 2023
Spindles that guarantee concentricities of < 0.1 µm over the entire range of speeds promote improved machining quality, higher availability and longer working life.

HYPROSTATIK SCHÖNFELD spindle bearings help grinding machine operators achieve ultra-precise finishes: When grinding, the best surface finishes are achieved if the tips of the abrasive particles rotate in an absolutely true circle both while dressing and while grinding. To achieve this, a concentricity in the region of 0.1 µm, with high rigidity, perfect balancing, and excellent damping are required.

This performance cannot be achieved with conventional roller bearing spindles. The concentricity error of roller bearing spindles varies over a range of 2 to 5 µm; in rare cases 1 µm. Furthermore, these are damped to only a limited degree. As time use increases, the quality of the concentricity of conventional roller bearing spindles deteriorates.

Hydrostatic high precision motor grinding spindles guarantee concentricities of < 0.1 µm over the entire range of speeds. For this, hydrostatic spindle bearings have damping some 100 times greater than spindles in roller bearings.

To achieve optimized damping parameters, Hyprostatik Schönfeld works with proprietary software.

The spindle bearings are very finely balanced, with a balancing quality of G 0.1. The lowest balancing quality according to DIN ISO 1940 is G 0.4.

In addition, as the spindle suspension is not damped, the radial flexibility is very low, which means the optimal damping of the hydrostatic bearings has maximum effect.

Laminar-flow controlled capillaries control the oil flows in the pockets of the hydrostatic components. This reduces the oil flow in an increasingly stressed pocket, which leads to low rigidity of hydrostatic components with capillaries.

To correct this problem, Hyprostatik Schönfeld developed a progressive flow controller (PM flow controller), which is used instead of capillaries. The controller provides a progressive increase in oil flow with increasing gap stiffness of the pockets.

As the pockets are de-stressed, the oil flow is reduced accordingly. Compared with capillaries, the controller achieves rigidities that are 3 to 6 times higher.

In addition, the pumping and friction outputs from hydrostatic bearings under static and dynamic loads are lower than is possible with comparable spindles with capillaries as the control elements.

The PM flow controller prevents heat-related geometry faults, as the bearings heat up only slightly even at very high speeds.

The most significant benefit of Hyprostatik spindles is that these can be placed under unlimited stress even at very high speeds. Hyprostatik spindle bearings stand out very clearly from alternative hydrostatic spindle bearings, owing to their load capacity, rigidity, damping, and possible maximum speeds.

The difference between capillaries and PV controllers becomes obvious with spindle bearings rotating at high speeds. With the capillary solution, the oil in the stressed pocket is heated as the speed increases and the viscosity of the oil becomes significantly less. The gap in the stressed pocket becomes smaller, whereas the friction output rises. This frequently results in failures of conventional spindle bearings and a sceptical attitude towards hydrostatic products in general.

Hydrostatic bearings from Hyprostatik avoid this problem: With increasingly stressed pockets, the oil flow in these pockets increases, which significantly reduces the gap and in turn the increase in friction output. Accordingly, with an appropriate design, the heating of the oil in the stressed pocket remains constant or even falls. Thermally-related failure of the bearing at high speeds is not possible.

Spindle bearings from Hyprostatik can therefore be stressed without restriction even at very high speeds.

Learn more at www.hyprostatik.de