Linear ball bearing
Linear ball bearings or linear bearings for short, colloquially also called ball bush ings or also ball bushings, are special ball bearings with an unusual, because axial (instead of radial) ball circulation. The purpose of this bearing is not (as with all other rolling bearings) to support a rotating element, but to guide the translational, i.e. straight-line, motion of a machine element along a cylindrical shaft with as little friction as possible. This gives rise to one of several types of special linear guidance system, the so-called shaft guidance system. A distinction between locating and non-locating bearings, as is usual in rolling bearings, is therefore meaningless in the case of linear ball bearings.
In these linear systems without stroke limitation, there is point contact between the bearing balls of the bearing and the shaft. The permissible load of a linear ball bearing depends on the number of supporting rows of balls. Earlier linear ball bearings consisted of high-carbon rolling bearing steel that was ground internally and externally after hardening.
Instead of an outer ring, today’s linear bearings have several raceway plates on the outside diameter of the bearing (one per ball recirculation) on which the balls roll in the linear bearing. The raceway plates of modern linear bearings are located in a plastic housing that also serves as a ball cage and assumes the function of ball recirculation. Instead of running on an inner ring, the balls run directly on a shaft made of precision steel. This design has now almost completely replaced the previously common solid steel design.
Linear bearings are available both without and with sealing on one or both sides at the end faces.
During axial ball recirculation in the linear ball bearing, only the inner, load-bearing row of balls is ever loaded, while the outer, unloaded row of balls moves against the bearing movement direction through a ball deflection and the ball return back to the second ball deflection at the starting point of the load zone.
Similar to rolling bearings, linear ball bearings are offered in a standardised range of dimensions. Various ISO series (e.g. ISO series 1 or ISO series 3) define the exact inner and outer diameters as well as the lengths of these bearings.
Usually, linear ball bearing sizes are defined according to the inner diameter. (nominal diameter)
|Nominal diameter in mm|
DIN designation for linear bearings
In the list of DIN standards, linear rolling bearings can be found under DIN 636 and DIN 644, which according to the DIN definition include not only linear ball bearings, but also
- Profile rail ball guideways = Profile rail guideways with balls as rolling elements as well as
- Linear guideways without rolling element recirculation = cage rail guideways count.
However, the designation in accordance with DIN does not correspond to the designations commonly used on the market. For example, the designation linear ball bearing, also known as ball bush in older linguistic usage, is customary on the market.
Use of linear ball bearings
Linear ball bearings are used in many technical applications such as computers and peripherals (e.g. scanners), automatic recording systems, 3D measuring equipment (e.g. multi-spindle drilling machines and other precision machines), presses, machine tools and machining centres including their doors, automatic flame cutting machines, printing machines, card selection machines, food packaging machines.
Furthermore, linear ball bearings can be used for the construction of linear tables and other displacement units. For example, corresponding displacement units based on linear ball bearings can be found at the foot under the armchairs of the front rows in the plenary hall of the German Bundestag, enabling the members of parliament sitting there to move back and forth on their armchair.
Linear ball bearing manufacturer
Manufacturers of linear ball bearings include large industrial groups producing in Germany in the rolling bearing and mechanical engineering industries such as Bosch Rexroththe Schaeffler Group (INA, FAG) or Ewellix or Ewellixas well as various medium-sized and smaller companies from the European, American and Asian regions.
- Bosch Rexroth ball bushings(Memento of the Originals of 2 September 2014 in the Internet Archive) Info:The archive linkwas inserted automatically and has not yet been checked. Please check original and archive link according to instructions and then remove this note. , retrieved 19 June 2011.
- INA Linear ball bearings(Memento of the Originals january 7, 2017 on the Internet Archive) Info:The archive linkwas automatically inserted and not yet checked. Please check original and archive link according to instructions and then remove this note. , retrieved 19 June 2011.
- Ewellix Linear Ball Bearings, retrieved 2 July 2020
- Ball screw