Single-row cylindrical bearing ups spindle speeds

A completely new kind of high precision cylindrical roller bearing, developed by SKF, enables high-speed spindles to achieve very high rigidity without design compromise.

A completely new kind of high precision cylindrical roller bearing, developed by SKF, enables high-speed spindles to achieve very high rigidity without design compromise.

Without any doubt the best possible bearing arrangement for most machine tool spindles incorporates a cylindrical roller bearing on the drive side.

This component brings two advantages to the spindle design: the thermal expansion of the shaft is catered for by the bearing's internal design and at the same time the bearing can run radially preloaded.

In this way the spindle stiffness is maximised and the risk of vibration is reduced.

This arrangement can achieve speeds of around 1 million ndm (ndm = rotational speed in rpm x bearing mean diameter in mm), at point at which 'standard' high precision cylindrical roller bearings run the risk of overheating.

Until now the solution for higher speeds was to substitute the cylindrical roller bearing with a set of angular contact ball bearings.

In spite of the fact that it allows the spindle to run faster, this arrangement has two negative aspects.

First the spindle radial rigidity is affected by the presence of bearings of a different nature, resulting in negative affects on the machine's overall precision, especially in the case of high cutting loads.

Secondly, in order to allow the thermal expansion of the shaft, the set of bearings mounted on the drive side must be mounted with a clearance fit into the housing.

This gap is a very critical point in the spindle design.

It must be carefully evaluated and executed because if incorrectly set it could lead to vibration during operation.

The introduction of this new bearing has the potential to enhance the performance of every high-speed spindle by avoiding these compromises.

The new features of this bearing include a large number of small ceramic rolling elements and a 'high tech' engineered polymered cage.

Made of lightweight, glass fibre reinforced, poly-ether-ether-ketone (PEEK), the cage has excellent wear resistance, very low friction and good stability at high speeds.

The use of silicon nitride rollers reduces the centrifugal load and further improves the bearing kinematics.

This bearing can reach speeds of 2 million ndm with oil-air lubrication, which represents a 40 to 50% increase over conventional high precision cylindrical roller bearings.

The whole range is available with a taper bore inner ring.

This feature allows the best possible preload (or clearance) adjustment, depending on the specific needs of the application.

For example when fitted in the rear position of a motorised spindle, and combined with a set of angular contact ball bearings with ceramic balls in the front, they allow a smooth shaft thermal elongation.

This eliminates the need for complicated arrangements involving sliding brushes and avoids compromise on stiffness.

There is the option to further improve the lubricant flow by ordering bearings with special lubrication features on the outer ring.

The standard range covers sizes from 40 mm to 120 mm bore diameter, the most popular for machine centre spindles.

Back to top