Ball bearings are used in twin screw compressors, either as main thrust bearings , or as reverse thrust bearings, or backup bearings to control axial clearance or preload in a set of bearings Angular contact

ball bearings with large contact angles are well suited as main thrust bearings because of their higher axial load capacity, compared to bearings with smaller contact angles Angular contact ball bearings can also be used as backup bearings Deep groove ball bearings are also a good choice as spring loaded reverse thrust bearings If the loads are light, deep groove ball bearings can also be used to take radial loads .

Deep groove ball bearings

Deep groove ball bearings have deep uninterrupted raceway groves with close osculation (conformity) with the balls This design enables the bearing to take radial and axial loads in both directions In order to make

bearing assembly possible, there are fewer balls compared to the same size angular contact ball bearing.

Deep groove ball bearings have limited radial and axial load capacity compared to angular contact ball bearings and cylindrical roller bearings When high load capacity is not needed, deep groove ball bearings can be a good and economical alternative.

The main application is as reverse thrust bearings, but deep groove ball bearings can also be used as the suction end radial bearing, if the radial load is light Bearings with steel or polyamide cages can be used in most cases The bearing internal clearance depends on the application but is typically greater than Normal (C3 sufix) lists the values of unmounted radial clearance The initial clearance in a bearing is

reduced by interference its and if the shaft and inner ring operate with a higher temperature than the outer ring and housing.

The bearing must support at least a minimum radial or axial load for satisfactory operation The recommended minimum radial load can be determined according to the  catalogue Rolling bearings An axial load can be provided by a spring .

Hybrid deep groove ball bearings

Deep groove ball bearings are also available as hybrid bearings, with ceramic balls made of bearing grade silicon nitride (Si3N4) See chapter Hybrid angular contact ball bearings.

Single row angular contact ball bearings

Single-row angular contact ball bearings are the most commonly used ball bearings in twin screw compressors They support pure axial loads or combined radial and axial loads The most important features of this bearing type are its high axial load capacity combined with a high speed rating Singlerow angular contact ball bearings operating with a small clearance or a light preload provide good axial positioning accuracy of the rotor For oil injected screw compressors, the most commonly used SKF single row angular contact ball bearings are of the 72 BE and 73 BE series which have 40° contact angle Also used are series 72 AC and 73 AC with 25° contact angle .

For dry air compressors, which operate at ndm speeds over 800 000, bearings of 70 and 72 series with 15° and 25° contact angles are used, 70 ACD, 70 CD, 72 ACD, 72 CD .

Universally matchable single row angular contact ball bearings

Bearings for universal matching are intended to be used in double and triple arrangements in screw compressors Single row angular contact bearings are usually mounted in face-to-face arrangements to

facilitate easy adjustment of the rotor end clearance and for easy dismounting.

The standoff between the rings is manufactured to close tolerances When two bearings are mounted immediately adjacent to each other, a given speciied internal clearance or preload, for example CB or GA, will be produced without shimming

Bearings mounted in tandem will distribute the load equally between the bearings.

Universally matchable bearings can also be used as single bearings Most bearings belong to the design and as such have smaller dimensional and geometrical tolerances, increased load carrying capacity and speed capability.

Universally matchable bearings in the 72 B(E) and 73 B(E) series are identiied by the sufix CA, CB or CC for internal clearance or GA, GB or GC for preload.

Arrangements of universally matchable bearings used to support axial loads, provide accurate axial positioning of the rotor Bearing sets made for preload (e g : GA sufix) provide axial positioning on both directions without clearance Angular contact ball bearings  combined with a spring loaded reverse

thrust bearing also provide accurate axial positioning, but the reverse axial force capability is limited by the spring force If the axial load of the compressor is heavy, two axial load carrying bearings can be arranged in tandem, with a third bearing as a backup bearing.

The standard  bearings available for universial matching have the CB or GA sufix, e g 7310 BECB or 7310 BEGA The CB sufix denotes that the bearing is universally matchable and that a pair of these bearings

will have a certain axial clearance when mounted in the arrangements .

 The GA sufix denotes that the bearing is universally matchable, but a pair of these bearings will have a light preload when mounted in any of the arrangements,

The initial bearing clearance or preload is only assured when the bearing rings are axially clamped together The initial clearance in a bearing pair is reduced or initial preload is increased by interference its and if the shaft and inner ring operate with a higher temperature than the outer ring and housing.

Universally matchable bearings are produced with P6 precision class dimensional tolerances and P5 precision class geometrical tolerances as standard