Needle rollers

Needle rollers are an extension to normal roller bearings and a basic part of some manufacturers’ product range. They can be used either on their own as a bearing arrangement or in combi­nation with components such as cages, drawn outer cups, outer and inner rings and seals to give a wide range capable of meeting the technical and economic demands of many different applications. Whilst not common for fans they are used in cer­tain applications for high speeds and high radial loads.

Dimensions

Needle rollers may conform to DIN 5402-3, grade G2 or ISO 3096, type B, with flat ends. They are made as standard from through hardened rolling bearing steel in accordance with DIN 17230. They have a core hardness of at least 670 HV and a pre­cision machined surface. Standard diameters usually range from 1 to 6 mm, and the length is generally between 3 and 11 times the diameter.

Needle rollers are grouped in sorts corresponding to tolerance groups for the diameter measured at the centre of the needle roller length. The ends of the needle rollers are of a profiled form, with a curved transition from the longitudinal surface to the end face. This has the effect of reducing the edge stresses that would occur at the ends of the roller if it were not in com­pletely flat contact with the raceway. Needle rollers can be used for full complement needle roller arrangements, or alternatively as pins or axles.

Design options

Afull complement needle roller arrangement is one in which the entire available space between the inner and outer raceway is filled with needle rollers. This gives a particularly compact bear­ing arrangement with high load carrying capacity and high rigid­ity. When needle rollers are used in such an arrangement, they require a shaft and a housing bore as inner and outer raceways respectively, both of which must be hardened and ground in or­der to provide the necessary characteristics. If the raceways are of sufficient geometrical accuracy, a full complement bear­ing arrangement will have high runout accuracy and adjustable radial internal clearance. Such designs are preferably used for applications involving swivel type motion and high loads.

Needle rollers can be used not only in full complement arrange­ments but also in assemblies in which the rollers are separated and guided by a metal or plastic cage (see Figure 10.26). These are particularly suitable for applications involving high speeds, since separation of the needle rollers allows faster rotation with­out generating unacceptable levels of friction and heat. Due to the relatively narrow crosspieces of the cage, the cage can still accommodate a large number of needle rollers and these as­semblies therefore offer high load carrying capacity. As in the case of the full complement arrangements, a hardened and ground shaft and housing bore are required as raceways and high runout accuracy can be achieved if these are of sufficient geometrical accuracy. Depending on the needle roller sorts and the shaft and housing tolerances, adjustable radial internal clearance is possible. Needle roller and cage assemblies are available in single row design for shaft diameters from 3 to 265 mm and in double row design for shaft diameters from 24 to 95 mm.

Posted in Fans Ventilation A Practical Guide