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Bearing Types
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Needle Roller Bearings
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Needle Roller Bearings |
Physical Characteristics
Needle roller bearings contain precision needle rolling elements, which have multiple uses in a variety of industries including automotive, truck, farm and construction equipment, two-cycle engines, outboard engines and consumer durables. Needle rollers are mainly used as bearing rolling elements to transmit torque and reduce friction. They can also serve as precision shafts or as precision locating pins. Other uses for needle roller bearings include crank pins, precision shafts and as locating pins.
 Different
types of Needle roller bearings involved in general engineering are:
Drawn cup needle roller bearings, are needle roller bearings with a deep thin-walled outer ring with open or closed ends. They have a very low sectional height and high load carrying capacity. They are used when the housing bore cannot be used as a raceway and a very compact bearing arrangement is required. Drawn cup needle roller bearings are generally used directly on the shaft. Where the shaft cannot be hardened and ground, they can be combined with an inner ring. Drawn cup needle roller bearings with closed ends The drawn cup of hardened sheet steel and the needle roller and cage assembly forms a non-separable unit. The outside surface of the rollers is slightly relieved towards the roller ends giving a favorable load distribution in the bearing. The space available for lubricant is large. Usually they have a single row of rollers. Some may have two-needle roller and cage assemblies adjacent to each other with the lubrication hole in the outer ring. With and without inner rings For applications where a seal is not available, or cannot be used, bearings with integral seals may be used. These are rubbing seals of polyurethane or nitrile rubber (NBR). High quality lithium base grease is used in them. To utilize maximum load carrying capacity, the raceways on the shaft must have the hardness and surface finish normally found on bearing raceways. Recommendations will be found in the section. Needle Roller Bearings Specifications & Standards  Dimensions
- The boundary dimensions of the drawn cup needle roller
bearings are in accordance with ISO. Bore Size - Bore is a hollow, usually cylindrical chamber or barrel where the metal balls are to be placed. Its size is measured in millimeters. Outer Ring Width - It is the width of the outer ringmeasured in millimeters. Revolutions - Revolutions indicate the rotation speed of the bearing. Bearing Weight - It indicates the weight of the bearing, measured in pound. Tolerance - They are usually meant for normal tolerance but can be enhanced. Internal Clearance - SKF needle roller bearings with inner ring are supplied with Normal radial internal clearance as standard. For needle roller bearings without inner ring, a suitable internal clearance is achieved by selecting the appropriate tolerance. Misalignment - The line contact between the raceways and the rollers prevent damaging edge stresses from occurring and also allows bearings to accommodate very minor angular misalignments of the shaft relative to the housing. Cages - There are standard cages but some may have pressed steel cage, glass fiber reinforced, or machined brass cages. Minimum load - For satisfactory operation, the bearings must be subjected to the minimum load that is calculated by Frm = 0,02 C where Frm = minimum radial load, kN C = basic dynamic load rating
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