Needle Roller Thrust Bearings
SKF needle roller thrust bearings are fitted with a form-stable cage to reliably guide and retain a large number of needle rollers. The diameter deviations of the rollers within one assembly are within 2 Ám, enabling these bearings to accommodate heavy axial loads and shock loads. These bearings provide a high degree of stiffness within a minimum axial space. In applications where the faces of adjacent machine components can serve as raceways, needle roller thrust bearings will take up no more space than a conventional thrust washer. They can accommodate axial loads acting in one direction only.
SKF supplies needle roller thrust bearings in two designs:
- needle roller and cage thrust assemblies, AXK series (fig)
- needle roller thrust bearings with a centring spigot, AXW series (fig)
For applications where adjacent components cannot serve as raceways, the assemblies can also be combined with washers of various designs.
Needle roller and cage thrust assemblies, AXK series
SKF needle roller and cage thrust assemblies in the AXK series (fig) range from a 4 to 160 mm bore. If required, washers in the LS, AS, GS 811 or WS 811 series can be used with these assemblies.
Double direction bearings
A double direction needle roller thrust bearing can be created by combining two needle roller and cage thrust assemblies and bearing washers with an intermediate washer. Depending on the design of the intermediate washer, the bearing has internal centring (fig) or external centring (fig).
The intermediate washers must have the same surface finish and hardness as the bearing washers. SKF does not supply intermediate washers, but recommendations about suitable dimensions of the washers can be supplied on request.
Needle roller thrust bearings with a centring spigot, AXW series
SKF needle roller thrust bearings in the AXW series (fig) consist of a needle roller and cage thrust assembly and a thrust washer with a centring spigot. The spigot facilitates the mounting process of the thrust bearing and provides an accurate radial centring of the housing washer. Available bore sizes for the thrust assembly range from 10 to 50 mm.
Combination with radial needle roller bearings
To accommodate combined radial and axial loads, AXW series needle roller thrust bearings can be combined with the following radial needle roller bearings:
- drawn cup needle roller bearings with a closed end or with open ends (fig)
- needle roller bearings with machined rings (fig)
These arrangements provide an economical and compact solution for combined loads.
SKF bearing washers are required in cases where adjacent machine components cannot serve as raceways.
Available bore sizes for washers in the LS series range from 6 to 160 mm and in the AS series from 4 to 160 mm.
Washers in the LS and AS series can be used as a shaft washer (for AXK or AXW series needle roller thrust assemblies) or housing washer (for AXK series needle roller thrust assemblies).
Because of all the possible combinations, the appropriate washers must be ordered separately.
Raceway washers, LS series
Raceway washers in the LS series (fig) are made of carbon chromium (rolling bearing) steel and are hardened. The raceway is ground and the bore and outside diameter are turned. These washers are used for bearing arrangements where accurate centring of the washers is not necessary or where low speeds are involved. The side face with the smaller chamfers is the raceway, and should face the rollers.
Thrust washers, AS series
Thrust washers in the AS series (fig)are made of spring steel and are 1 mm thick. Both sides of these washers, which are hardened and polished, can be used as raceways. If adjacent machine components are not hardened but have adequate stiffness and the running accuracy requirements are moderate, washers in the AS series can be used to provide a cost-effective bearing arrangement.
Shaft and housing washers, WS 811 and GS 811 series
Shaft washers in the WS 811 series (fig) and housing washers in the GS 811 series (fig) are developed primarily for applications with cylindrical roller and cage thrust assemblies, but they can also be combined with needle roller and cage thrust assemblies. These washers, made of carbon chromium bearing steel are hardened and have precision machined raceways. Therefore, SKF recommends using these shaft and housing washers in high-speed applications where accurate centring of the bearing washers is required. WS 811 series shaft washers, which have a ground bore, are available in bore sizes ranging from 15 to 630 mm. When combined with needle roller and cage thrust assemblies, bore sizes up to 160 mm are used. GS 811 series housing washers, which have ground outside diameter, are available for housing bore diameters ranging from 28 to 750 mm. When combined with needle roller and cage thrust assemblies, outside diameter sizes up to 200 mm are used.
The dimensions of needle roller and cage thrust assemblies and thrust washers in the AS series are in accordance with ISO 3031:2000.
The bore and outside diameters of the other bearing washers are in accordance with ISO 104:2002 for Diameter Series 1 thrust bearings.
Needle roller and cage thrust assemblies, needle roller thrust bearings with a spigot and bearing washers are manufactured to the tolerance classes listed in the table. The values for the dimension deviations of the various ISO tolerance classes mentioned in the table are listed in the table.
Needle roller thrust bearings cannot tolerate any angular misalignment between the shaft and the housing, or any misalignment between the shaft and the axial support surfaces in the housing.
The ends of the needle rollers are relieved slightly to modify the line contact between the raceways and the rollers. This provides favourable load distribution in the bearing and minimizes damaging edge stresses.
SKF needle roller and cage thrust assemblies are fitted as standard with a form-stable, machined steel cage (fig) or a sheet steel cage (fig), except for those identified by the designation suffix TN. These assemblies have an injection moulded, glass fibre reinforced, polyamide 66 cage (fig).
The complete range of needle roller thrust bearings with a centring spigot in the AXW series are fitted exclusively with steel cages.
Assemblies with a polyamide 66 cage can be used at temperatures up to +120 ░C.
The lubricants generally used for rolling bearings do not have a detrimental effect on cage properties. Exceptions are a few synthetic oils and greases with a synthetic oil base and lubricants containing a high proportion of EP additives when used at high temperatures.
For bearing arrangements that operate at continuously high temperatures or under arduous conditions, SKF recommends using needle roller and cage thrust assemblies with a steel cage.
For detailed information about the temperature resistance and the applicability of cages, refer to the section Cage materials.
Design of associated components
The support surfaces in the housing and on the shaft must be at right angles to the shaft axis and should provide uninterrupted support for the bearing washers across the entire width of the raceways. When using thrust washers in the AS series, the dimensions Ea and Eb listed in the product table should be applied.
To provide satisfactory radial guidance for the individual thrust bearing components, suitable tolerance classes for shafts and housings are listed in the table. Radial space between the shaft and the bore is required for washers that are externally guided in the housing. For washers that are internally guided on the shaft, radial space in the housing bore is required.
When SKF needle roller and cage thrust assemblies in the AXW series are combined with drawn cup needle roller bearings (fig) or needle roller bearings, the same housing tolerance must be selected for the centring spigot as for the radial bearing.
Needle roller and cage thrust assemblies are generally guided radially on the shaft in order to obtain the lowest possible sliding speed against the guiding surfaces. At high speeds, radial guidance must be provided by the shaft and the guiding surface must be ground.
Raceways on shafts and in housings
If the load carrying capacity of a needle roller thrust bearing in applications where the shaft and the housing bore are used as raceways is to be fully exploited, both should have the same hardness and accuracy as a bearing raceway.
The running accuracy of the bearing arrangement also depends on the accuracy of the raceways. For additional information about accuracy, suitable materials, surface roughness and hardness, refer to the section Raceways on shafts and in housings.
Raceways machined on the shaft or in the housing should have the same axial runout as is common for shaft or housing washers. The values for the permissible axial runout for the shaft and housing washers of thrust bearings are listed in the table.
To achieve satisfactory operation, needle roller thrust bearings, like all ball and roller bearings, must always be subjected to a requisite minimum load. Applying a requisite minimum load is especially important for bearings that operate at high speeds or are subjected to high accelerations or rapid changes in the direction of load. Under these conditions, not applying the correct minimum load can result in damaging sliding movement between the rollers and raceways caused by the inertial forces of the needle roller and friction in the lubricant.
The requisite minimum axial load to be applied to needle roller thrust bearings can be estimated using
Fam = 0,0005 C0
Fam = minimum axial load [kN]
C0 = basic static load rating [kN]
When starting up at low temperatures or when the lubricant is highly viscous, an even greater minimum load may be required. However, the weight of the components supported by the bearing, together with the external forces, generally exceeds the requisite minimum load. If this is not the case, the needle roller thrust bearing must be subjected to an additional axial load.
Equivalent dynamic bearing load
Needle roller thrust bearings can only accommodate axial loads. Therefore, the equivalent dynamic bearing load is equal to the calculated axial bearing load:
P = Fa
P = equivalent dynamic bearing load [kN]
Fa = actual axial bearing load [kN]
Equivalent static bearing load
Needle roller thrust bearings can only accommodate axial loads. Therefore, the equivalent static bearing load is equal to the calculated axial bearing load:
P0 = Fa
P0 = equivalent static bearing load [kN]
Fa = actual axial bearing load [kN]
The designation suffixes used to identify certain features of SKF needle roller thrust bearings are explained in the following.
|TN||Injection moulded cage of glass fibre reinforced polyamide 66|
Needle roller bearings
Needle roller and cage assemblies
Drawn cup needle roller bearings
Needle roller bearings with machined rings
Alignment needle roller bearings
Needle roller bearing inner rings
Universal joint bearings
Deep groove ball bearings
Needle roller bearings
Combined cylindrical roller/taper roller bearings
Cylindrical roller bearings
Angular contact ball bearings
Combined needle roller bearings
Spherical roller bearings
Tapered roller bearings
Thrust ball bearings
CARB« toroidal roller bearings
Cylindrical roller thrust bearings
Angular contact thrust ball bearings
Tapered roller thrust bearings
Needle roller thrust bearings
Track runner bearings
Spherical roller thrust bearings
Indexing roller units
Backing bearings for cluster mills
Other SKF rolling bearings