Needle Roller Bearings with Machined Rings
Needle roller bearings with machined rings made of carbon chromium bearing steel have a low sectional height and a very high load carrying capacity for their size. They may be used with or without an inner ring, depending on the application.
Needle roller bearings without an inner ring are an excellent choice for compact bearing arrangements if the shaft can be hardened and ground. Eliminating the need for a separate inner ring enables a larger shaft diameter and a stiffer arrangement.
Needle roller bearing without an inner ring
Axial displacement of the shaft relative to the housing is only limited by the width of the raceway on the shaft. By machining the shaft raceways to the appropriate dimensional and form accuracy, it is possible to obtain bearing arrangements with heightened running accuracy. For additional information, refer to the section Raceways on shafts and in housings and to Internal clearance.
Needle roller bearings with an inner ring are used for arrangements where it is not possible or uneconomical to harden and grind the shaft. Bearings with an inner ring only permit axial displacement of the shaft relative to the housing within certain limits (demo). If the permissible axial displacement provided by a standard inner ring is insufficient, it is possible to use an extended inner ring. Extended inner rings can also provide an excellent counterface for the lips of external G or SD seals. For additional information, refer to the section Needle roller bearing inner rings.
Needle roller bearing with an inner ring
SKF supplies needle roller bearings with machined rings in several designs and sizes:
- with flanges (closure rings or integral flanges) on the outer ring, sealed or not sealed and with or without an inner ring
Needle roller bearing with inserted closure rings (for bearings with Fw = 10 mm)
Needle roller bearing with integral outer ring flanges (for bearings with Fw = 12 mm)
Needle roller bearing, sealed
- without flanges on the outer ring, not sealed and with or without an inner ring
Needle roller bearing without flanges on the outer ring
To accommodate combined radial and axial loads, needle roller bearings of certain sizes can be combined with needle roller thrust bearings with a centring spigot, AXW series
Needle roller bearing combined with a needle roller thrust bearing, AXW series
Bearings with flanges
SKF needle roller bearings with flanges on the outer ring and with an outside diameter up to and including 17 mm (Fw = 10 mm), are manufactured with inserted closure rings. These bearings do not have a lubrication hole or an annular groove.
Design with inserted closure rings, without a lubrication hole
Larger bearings have integral flanges on the outer ring, an annular groove and, depending on the bearing size, one or more lubrication holes in the outer ring.
Design with integral flanges, with a lubrication hole and an annular groove
Needle roller bearings with flanges are generally designed as single row bearings. Bearings in the RNA 69 and NA 69 series, with an outside diameter D= 52 mm, have two needle roller and cage assemblies.
Needle roller bearing, double row
The outer ring and cage assembly of a needle roller bearing with flanges form a non-separable unit.
Single row bearings, in the RNA 49 and NA 49 series, are also available with a contact seal on one or both sides. The seals are made of acrylonitrile-butadiene rubber (NBR) that efficiently protects the bearing against the entry of contaminants and retains the lubricant in the bearing.
Needle roller bearing, sealed on one side
Needle roller bearing, sealed on both sides
The operating temperature range for sealed needle roller bearings with machined rings, which is limited by the seal material and the grease fill, is -20 °C to +100 °C.
The inner ring of sealed bearings is 1 mm wider than the outer ring. This maintains the efficiency of the seals even when a small amount of axial displacement occurs.
Initial grease fill and relubrication
Sealed needle roller bearings with machined rings are filled at the factory with a high-quality grease with good rust inhibiting properties. The most important technical specifications for this grease are listed in the table. Because these bearings can hold a relatively large quantity of grease, they can be operated for long periods before relubrication is required. The lubrication groove and lubrication hole in the outer ring enable the lubricant to reach the bearing cavity during relubrication. The inner ring is also provided with a lubrication hole so that the bearing can be relubricated either via the outer or inner ring, depending on the application. SKF recommends 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
SKF supplies an assortment of radial shaft seals that can be used as external seals. Extended inner rings can be used if the inner ring raceway is to serve as a counterface for a seal adjacent to the bearing. Appropriate seals are listed in the product tables, when available. For additional information, refer to the sections Radial shaft seals with low cross sectional height
and to Radial shaft seals
Bearings without flanges
Needle roller bearings without flanges are completely separable, i.e. the outer ring, the needle roller and cage assembly and the inner ring can all be mounted separately. In many applications, this makes mounting a great deal easier. The needle roller and cage assembly can either be mounted together with the outer ring or with the shaft or inner ring, depending on the arrangement design. It can also be inserted between the outer ring and shaft or inner ring as the final step. However, needle roller and cage assemblies and bearing outer rings must always be kept together as supplied.
SKF needle roller bearings without flanges are available as single row or double row bearings. Double row bearings have two needle roller and cage assemblies arranged adjacent to each other. They have an annular groove and a lubrication hole in the outer ring to enable efficient lubrication.
Needle roller bearing, single row, with an inner ring
Needle roller bearing, double row, without an inner ring
To provide efficient lubrication for needle roller bearings with an inner ring, SKF supplies some bearings with one lubrication hole in the inner ring. These bearings are listed in the product table. The cage of needle roller bearings without flanges must be axially guided by fine turned and burr-free surfaces on adjacent machine components. Recommended dimensions for these surfaces are listed in the product tables.
The boundary dimensions of SKF needle roller bearings with machined rings in the RNA 48, RNA 49, RNA 69, NA 48, NA 49 and NA 69 series are in accordance with ISO 1206-2001. The dimensions of the other needle roller bearings do not adhere to any national or international standards, but are common in the market.
- NK, NKS, RNA
- NKI, NKIS, NA
SKF supplies needle roller bearings with machined rings to Normal tolerances in accordance with ISO 492:2002, as standard.
On request, needle roller bearings with higher accuracy to tolerance P6 or P5 specifications can be supplied. For bearing arrangements with higher accuracy, inner rings with a pre-ground raceway and a machining allowance can be supplied, but must be finish ground after mounting.
The inside diameter Fw of the needle roller and cage assembly, when the rollers are in contact with the outer ring raceway, lies within the limits of F6 tolerance class (table) before the bearings are mounted.
On request, SKF supplies needle roller bearings without an inner ring and with reduced inside diameter tolerances. These bearings are identified by the designation suffix H followed by a figure combination that gives the actual maximum and minimum values in µm for the deviation from the nominal inside diameter Fw, e.g. H+24+20.
SKF needle roller bearings with an inner ring have Normal radial internal clearance as standard. The clearance values are listed in the table and are in accordance with ISO 5753-1:2009. They are valid for unmounted bearings under zero measuring load.
For needle roller bearings without an inner ring, a suitable internal clearance is achieved by selecting the appropriate tolerance class for the raceway diameter. Recommended values are listed in the table. The recommendations apply, provided the housing bore is not tighter than a K7 tolerance class.
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. It also enables needle roller bearings with machined rings 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.
Depending on their size, SKF needle roller bearings with machined rings are fitted as standard with a machined steel (fig) or sheet steel cage (fig), no designation suffix. A number of bearing are fitted as standard with an injection moulded cage of glass fibre reinforced polyamide 66 (fig), designation suffix TN.
Machined steel cage
Sheet steel cage
Polyamide 66 cage
Needle roller bearings with a polyamide 66 cage that are not sealed 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 additional information about the temperature resistance and the applicability of cages, refer to the section Cage materials
Shaft and housing tolerances
The shaft tolerances for SKF needle roller bearings with machined rings should be in accordance with the fits that are listed in the table.
When needle roller bearings with an inner ring are used under conditions of point load and mounted with a loose fit, the inner ring seat should be machined to h6 or g6 tolerance class.
When the load rotates, the inner rings should have an interference fit. Sufficient interference can be obtained if the recommended shaft tolerance classes (table) are applied.
For information about housing tolerances for needle roller bearings with an inner ring, refer to the SKF General Catalogue, section Application of bearings/Recommended fits.
Recommendations for bearing fits for housings are listed in the tables (table and table).
Raceways on shafts
If the load carrying capacity of a needle roller bearing with machined rings, 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.
To achieve satisfactory operation, needle roller bearings with machined rings 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 needle roller bearings can be estimated using
Frm = 0,02 C
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 needle roller bearing must be subjected to an additional radial load.
Equivalent dynamic bearing load
Needle roller bearings with machined rings can only accommodate radial loads. Therefore, the equivalent dynamic bearing load is equal to the calculated radial bearing load:
P = Fr
P = equivalent dynamic bearing load [kN]
Fr = actual radial bearing load [kN]
Equivalent static bearing load
Needle roller bearings with machined rings can only accommodate radial loads. Therefore, the equivalent static bearing load is equal to the calculated radial bearing load:
P0 = Fr
P0 = equivalent static bearing load [kN]
Fr = actual radial bearing load [kN]
The designation suffixes used to identify certain features of SKF needle roller bearings with machined rings are explained in the following:
|C2||Bearing internal clearance smaller than Normal|
|C3||Radial internal clearance greater than Normal|
|C4||Radial internal clearance greater than C3|
|CN||Bearing internal clearance Normal, only used together with an additional letter (H,L,M,P) that identifies a reduced or displaced clearance range|
|H..||Needle roller bearing without an inner ring, with reduced inside diameter (under rollers) tolerance, followed by tolerance limits in µm, e.g. H+27+20|
|IS..||Needle roller bearing with one or more lubricating holes in the inner ring, a figure following indicates the number of holes|
|ISR..||Needle roller bearing with an annular groove and one or more lubricating holes in the inner ring, a figure following indicates the number of holes|
|P5||Dimensional and running accuracy to ISO tolerance class 5 specifications (better than P6)|
|P6||Dimensional and running accuracy to ISO tolerance class 6 specifications (better than Normal)|
|RS||Contact seal of acrylonitrile-butadiene rubber (NRB) with or without sheet steel reinforcement on one side of the bearing|
|.2RS||RS contact seal on both sides of the bearing|
|TN||Injection moulded cage of glass fibre reinforced polyamide 66, rolling element centred|
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