Spindle Bearings with adjustable preload

The preload of Spindle Bearings determines the running characteristic of a Working Spindle and the Work Piece quality thereof. Heavy preload raises stiffness, lower preload enables to work with higher speed of the bearing.

Advanced design of Machine Tools often meets a wider range of speeds. At one hand a sufficient stiffness of the bearings for higher working forces is necessary, at the other hand higher speed for efficient cutting operations.

Only a bearing design qualified to adapt the preload whilst operating will achieve best possible results.

The UKF System VARIORING makes it possible by oil pressure to vary the preload of a bearing from „light" via „middle" to „heavy" in order to adapt the bearing to given operation with highest possible speed and stiffness. This begins as „light" preload. The Outer Ring of a Double Row Spindle Bearing (design USO) gets a circumferential groove with O-Ring seals at both sides. Under oil pressure into the groove the Outer Ring will be compressed centrically by a few micron which rise the inner preload of the bearing.

Advantages:

• Range of possible operations on the machine enlarged
• During idle run preload can be taken back, so inside the bearings friction is reduced
• No additional mechanical parts inside the spindle
• No hydraulic aggregate necessary
• No axial displacement of the shaft
• Components are customary available

The configuration VARIO-D requires a hydraulic aggregate.

The configuration VARIO-E (Utility Model Admiss. No. 20 2013 100 940.7) is a closed hydraulic system without drains entering of flowing off. No additional hydraulic aggregate is needed. The oil pressure is generated by a cylinder with electrically driven piston.
The necessary oil pressure is a given value and can be reached by setting the piston to a determined position ("position controlled"). An option is to check the pressure by a sensor and to transmit this to the controller. So the electro cylinder can be controlled to maintain a demanded pressure("pressure controlled").
Customary pressure transmitter give for ex. values between 0...20 mA or 0...10 V to the controller. The electro cylinder with its electronic expects the same kind of values which are common in modern machine controlling.
Furthermore even the speed of the spindle (by speed encoder or CNC) and the admissible preload can be connected to a closed loop control.