Axial/radial bearing YRT 

Axial/radial bearings YRT are designed, by means of the full complement radial roller bearing component for high rigidity, for rapid positioning and operating at low speed. Low speeds are normally required for multiple-axis simultaneous machining.

The limit value nG stated in the dimension tables relates to the maximum swivel speed and a maximum speed applied for a short period.

Axial radial bearings YRTC, YRTS and ZKLDF axial angular contact ball bearings

The limiting speeds nG stated for these bearing series were determined on test rigs.

During the test, the following conditions apply:

■ grease distribution cycle according to the defined data,

■ maximum increase in bearing temperature of 40 K in the areaof the raceway

■ operating duration ED = 100%, which means continuous operation at the limiting speed nG

■ bearing fully screw mounted on solid fixtures

■ no external load, only preload and mass of the fixtures.

Temperature distribution in the rotary axis system

Rotary axes with a main spindle function, such as those used for combined milling and turning and with direct drive by a torque motor, are systems with complex thermal characteristics.

The temperature distribution in the rotary axis system must be considered in greater detail during the design process:

■ Asymmetrical rotary axis housings can undergo asymmetrical deformation due to heating.

■ In turn, out-of-round bearing seats lead to additional bearing load, reduced life and a negative influence on running behaviour and running accuracy.

■ Temperature management of the rotary axis in the form of targeted cooling and heating is generally necessary for high performance rotary axes.

Where there is non-uniform temperature distribution between the inner and outer ring, rotary axis bearings with ball contact (ZKLDF) show more tolerant behaviour than rotary axis bearings with line contact (such as axial/radial cylindrical roller bearings or crossed roller bearings).

The stated bearing characteristics only apply if the bearing preload remains unchanged. The bearing preload can be altered by mechanical stresses, such as those which can be caused by temperature differences or adjacent machine elements (such as force-locking clamping connections for example).

Design regulations

Proven design regulations based on practical experiences,

■ The contact face between the stator of the torque motor and the rotary table housing should be as small as possible, in order to minimise the flow of heat between stator and rotary table housing.

■ Where possible, do not connect the casing of the stator cooling system to the rotary table housing.

■ In preference, flange mount the rotor of the torque motor on the rotary table plate rather than on the bearing, to keep the flow of heat through the bearing to a minimum.

■ The distance between the motor and the bearing should be as large as possible. A large distance reduces the transfer of heat from the rotor to the bearing. The stresses occurring between the components as a result of varying thermal expansion are reduced by the increased elasticity of the system.

■ The rotary table plate bearing must be centered with sufficient rigidity to allow the overall system to attain a high level of rigidity.

The risk of deformation to the bearing seat due to the increase in the temperature of the rotor is also reduced.

■ Use torque motors which are suitable for the requirements only, with low loss of power and a high motor constant. We recommend using IDAM torque motors.

Regulated cooling of the stationary and rotating components may be required in order to limit the temperature variations between the bearing inner and outer ring.