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Drawn Cup Needle Roller Bearings

Drawn cup needle roller bearings, as the name suggests, are needle roller bearings with a deep drawn, thin-walled outer ring with either open ends or a closed end. They are characterized by a very low sectional height and high load carrying capacity. Drawn cup needle roller bearings are typically used in applications where the housing bore cannot be used as a raceway for a needle roller and cage assembly, but where a very compact and economical bearing arrangement is required.

Generally, drawn cup needle roller bearings have a recommended maximum operating temperature of 140 C, unless otherwise stated in the relevant sections in this chapter. The maximum operating temperature is limited by the seal and cage materials and the applied grease.

SKF supplies a wide assortment of drawn cup needle roller bearings. This includes:

  • drawn cup needle roller bearings with open ends
  • Drawn cup needle roller bearings with open ends

  • drawn cup needle roller bearings with a closed end
  • Drawn cup needle roller bearings with a closed end

  • full complement drawn cup needle roller bearings with open ends
  • Full complement drawn cup needle roller bearings with open ends

Drawn cup needle roller bearings with a closed end are suitable for bearing arrangements at the ends of shafts. The profiled design of the closed end accommodates small axial guidance forces. Drawn cup needle roller bearings generally run directly on the shaft. However, in cases where the shaft cannot be hardened and ground, they can be combined with an inner ring.

Drawn cup needle roller bearing combined with an inner ring and an external seal

The drawn cup of hardened steel and the needle roller and cage assembly of these bearings form a non-separable unit. The space available for lubricant is large enough to enable long relubrication intervals.

Typically, drawn cup needle roller bearings have a single row of rollers. However, wide sizes incorporate two needle roller and cage assemblies immediately adjacent to each other with a lubrication hole in the outer ring.

Wide size drawn cup needle roller bearing, double row, with a lubrication hole

On request, any single row drawn cup needle roller bearing for shaft diameters of 7 mm and above can be supplied with a lubrication hole in the outer ring.

Drawn cup needle roller bearing with a closed end and a lubrication hole

Drawn cup needle roller bearings are mounted with an interference fit in the housing bore. Therefore, shoulders or snap rings are not required to locate the bearing axially so the design of the housing bore is simple and can be produced economically.

To accommodate combined radial and axial loads, drawn cup needle roller bearings of certain sizes can be combined with a needle roller thrust bearing with a centring spigot, AXW series.

Drawn cup needle roller bearing combined with a needle roller thrust bearing, AXW series

Sealed drawn cup needle roller bearings

For applications where a sufficiently efficient seal is not available, or cannot be used for space reasons, drawn cup needle roller bearings can also be supplied with integral lip seals as follows:

  • Drawn cup needle roller bearings with open ends, sealed on one side, designation suffix RS (fig), available for shaft diameters ranging from 8 mm to 50 mm.
  • Drawn cup needle roller bearings with open ends, sealed on both sides, designation suffix .2RS (fig), available for shaft diameters ranging from 8 mm to 50 mm.
  • Sealed drawn cup needle roller bearings with a closed end, designation suffix RS (fig), available for shaft diameters ranging from 10 mm to 25 mm.

The integral seals are contact seals made of polyurethane (AU), fluoro rubber (FKM) or acrylonitrile-butadiene rubber (NBR). The use of a sealed drawn cup needle roller bearing is, under normal conditions, an extremely cost-effective solution to exclude solid contaminants and moisture and retain the lubricant in the bearing. The permissible operating temperature range for sealed bearings is 30 to +100 C.

Initial grease fill and relubricationSealed drawn cup needle roller bearings are initially filled with high-quality grease that has good corrosion inhibiting properties. The most important technical specifications for this grease are listed in the table. The relatively large quantity of grease in the bearings means they can be operated for long periods before relubrication is required. SKF recommends using SKF LGWA 2 grease for relubrication. Characteristics of this standard grease are listed in the table.

For additional information, refer to the section Grease lubrication.

Full complement drawn cup needle roller bearings

Full complement drawn cup needle roller bearings with open ends (fig) are suitable for very heavy radial loads at moderate speeds.

Initial grease fill and relubrication A special grease is used to secure the rollers during transportation, however, this grease does not provide sufficient long term lubrication. Therefore, relubrication after mounting may be necessary. The most important technical specifications for this grease are listed in the table. Depending on the required consistency class, SKF recommends SKF LGEP2 or SKF LGWM1 grease for lubrication. Characteristics of these standard greases are listed in the table.

For additional information, refer to the section Grease lubrication.

DimensionsThe boundary dimensions of drawn cup needle roller bearings are in accordance with ISO 3245:2007, as far as they have been standardized.

TolerancesThe dimensional accuracy of drawn cup needle roller bearings cannot be checked until they have been mounted, because the thin-walled outer ring may be slightly out-of-round. Only after the bearing has been pressed into a housing bore that is machined to the recommended tolerance classes can the outer ring obtain its correct form, which is crucial for bearing performance. To check the inside diameter Fw of the roller set, the bearing must first be pressed into a thick-walled gauge ring with a bore diameter as listed in the table. A measuring mandrel can then be used to check the inside diameter deviation. The permissible deviations are also listed in the table.

The tolerance values listed are in accordance with ISO 3245:2007, as far as they have been standardized.

The width tolerance is 0/0,3 mm for all drawn cup needle roller bearing sizes.

Paired mounting If drawn cup needle roller bearings are to be mounted immediately adjacent to each other, the deviations from the nominal internal diameter must be the same for both bearings if they are to share the load equally.

Operational clearanceWhen the recommended tolerance classes are applied, the inside diameter Fw (diameter under the rollers) will be approximately within F8 tolerance class. This, together with the recommended shaft tolerance class, which is also listed in the table, will reach a suitable (medium) operational clearance in the range of C2 to C3 radial internal clearance. The clearance value depends on the shaft diameter, the operating temperature, and on the raceway diameter when combined with an inner ring.

MisalignmentThe 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. It also enables single row drawn cup needle roller bearings to accommodate a small amount of misalignment, approximately 1 min of arc between the shaft and housing.

The detrimental effects of misalignment increase with increasing bearing width and load. For additional information, contact the SKF application engineering service.

CagesSKF drawn cup needle roller bearings are fitted, as standard, with a sheet steel cage (fig), except for those identified by the designation suffix TN. These have an injection moulded, glass fibre reinforced polyamide 66 cage (fig).

NoteDrawn cup needle roller bearings with a polyamide 66 cage can be operated 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 bearings with a steel cage.

For detailed information about the temperature resistance and the applicability of cages, refer to the section Cage materials.

Shaft and housing tolerancesDrawn cup needle roller bearings need a housing bore that has a good dimensional form and accuracy. For these bearings, to obtain the necessary interference fit in the housing, the tolerance classes listed in the table must be applied. The cylindricity of the housing bore should be within IT5/2 tolerance grade and the shaft raceway should be within IT3 tolerance grade.

Raceways on shaftsIf the load carrying capacity of a drawn cup needle roller bearing, mounted without an inner ring, in applications where the shaft is used as raceway is to be fully exploited, it 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.

Mounting instructionsDrawn cup needle roller bearings should be mounted with a heavy interference fit in the housing bore. Therefore, SKF recommends mounting them using a mounting dolly (fig). An O-ring provides a simple means of retaining the bearing on the mounting dolly. The stamped side face of drawn cup needle roller bearings should preferably abut the flange of the mounting dolly.

If grease lubrication is going to be used, the bearing should be lubricated before mounting.

NoteSpecial care should be taken to prevent the bearings from skewing or tilting when they are being pressed into the housing. Otherwise the rollers and raceways could easily be damaged.

Minimum loadTo achieve satisfactory operation, drawn cup needle 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 radial load to be applied to drawn cup needle roller bearings can be estimated using

Frm = 0,02 C

where

Frm = minimum radial load [kN]

C = basic dynamic 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 drawn cup needle roller bearing must be subjected to an additional radial load.

Equivalent dynamic bearing load

Drawn cup needle roller bearings can only accommodate radial loads. Therefore, the equivalent dynamic bearing load is equal to the calculated radial bearing load:

P = Fr

where

P = equivalent dynamic bearing load [kN]

Fr = actual radial bearing load [kN]


Equivalent static bearing loadDrawn cup needle roller bearings can only accommodate radial loads. Therefore, the equivalent static bearing load is equal to the calculated radial bearing load:

P0 = Fr

where

P0 = equivalent static bearing load [kN]

Fr = actual radial bearing load [kN]


Static safety factorSKF recommends applying a static safety factor of 3 or larger, i.e. s0 = C0/P0 = 3.Supplementary designationsThe designation suffixes used to identify certain features of SKF drawn cup needle roller bearings are explained in the following:

AS1 One lubrication hole in the outer ring

DesignationBearing Features
H..Needle roller bearing without an inner ring, with reduced inside diameter (under rollers) tolerance, followed by tolerance limits in m, e.g. H+27+20
RSContact seal on one side of the bearing
.2RSContact seal on both sides of a drawn cup needle roller bearing with open ends
TNInjection 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

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