SKF NJ 311 ECP Cylindrical Roller Bearing, 55 mm Bore

A cylindrical roller bearing that also locates the shaft in one direction

The SKF NJ 311 ECP is a single row cylindrical roller bearing of the NJ design, with a 55 mm bore, 120 mm outside diameter and 29 mm width. The outer ring carries two integral flanges and the inner ring carries one, so the bearing carries heavy radial loads and can also take modest axial load in one direction. Compared with an NU bearing it can serve as the semi-locating position in a shaft arrangement, while still allowing axial displacement in the other direction.

It is typical for gearbox shafts, pump and compressor drives and large motors where one bearing must guide the shaft in one axial direction without a separate thrust bearing. The rings and the roller and cage assembly are separable, which eases fitting with interference fits.

Technical specifications

Choosing NJ rather than NU or N

The designation letters describe the flanges: NU has two on the outer ring and none on the inner; NJ adds a flange on one side of the inner ring; N has flanges on the inner ring and none on the outer. In an NJ the loose flange side lets the shaft move one way, so the bearing is placed where the axial load is directed against the inner ring flange. SKF lists the accessory angle ring HJ 311 EC as an associated product for arrangements that must locate the shaft axially in both directions with an NJ bearing.

In a shaft that carries axial load only occasionally, one NJ and one NU bearing are a common combination. Keep a minimum radial load on cylindrical roller bearings to avoid roller skidding; SKF gives a minimum load factor kr of 0.15 for this size, and the limiting value e of 0.2 and factor Y of 0.6 for combined loads.

Fitting guidance and ordering

Maintain a spacer sleeve diameter between 65 mm and 68 mm on the shaft side, a shaft abutment of at least 80 mm and a housing abutment of no more than 109.2 mm, with fillet radii up to 2 mm. The table lists a permissible axial displacement of up to 2 mm. Always check the flange direction against the load direction before assembly, and apply a light film of oil on the roller path when sliding the inner ring into the outer ring.

Confirm clearance class, cage and angle ring when ordering. See Electric Motors for related bearings on this site, and the SKF TLMR automatic lubricant dispenser as a lubrication accessory for bearing housings.

Documents and quotation

The attached SKF leaflet describes the Explorer single row cylindrical roller bearing features, such as the optimised internal geometry, the finish of the rollers and the dimensional stability up to 150 degrees C. The table figures come from the SKF product page for the NJ 311 ECP. Send the designation and quantity to Seven Star LLC, an independent supplier in Muscat.