Techno Linear Motion Catalog23Technical InformationRoller Bearingsare also widely used in linear / rotary motion applications. There are several principaltypes of roller bearings. In general, they have higher load capacities than ball bearings of the same sizedue to the increased area of contact and, except for the cylindrical type, lower speed capabilities. They arecommonly used in heavy-duty moderate-speed applications; and, as with ball bearings, there are manydifferent styles to choose from. Because of the geometry, roller bearings are not tolerant of shaftmisalignment.Cylindrical Roller Bearingshave the highest radial load capacity for a given cross section, and the highestspeed capability for any given roller bearing type. A common problem encountered is roller skidding, whichcauses premature failure. Solutions include a slightly concave raceway that pinches the ends of the rollers,or the use of hollow preloaded rollers to hold position.Needle Roller Bearingsare similar in appearance to cylindrical roller bearings, but typically have a muchsmaller diameter to length ratio. They typically exhibit higher load capacities than single row ball bearingsof comparable OD, and can nearly fit into the same space as a plain bearing. In most instances, a hardenedshaft acts as the bearings inner race, although an inner race can be supplied when the shaft cannot behardened.Crossed Roller Bearingsare very common in heavy-duty precise applications; however, they are extremelysensitive to contaminants. The principle is similar to that of cylindrical bearings; however, the roller diametermust be equal to the roller height. The rollers take on an alternating pattern, with their orientations beingcrossed at 90 degrees. This arangement allows very smooth motion, and large load capabilities in alldirections normal to travel. A further benefit of crossed roller bearings is very high straight line accuracy.Selecting and Sizing Bearing SystemsWhen selecting and sizing bearings for an application, there are several considerations. Most bearingapplications can be practically analyzed by sizing load and speed requirements. This section is intended toprovide a basic understanding of the bearing selection process, and should not used as an only source.Plain Bearing Selection: A plain bearings load capacity is generally expressed as pounds per square inch(psi) of projected bearing area. The size and material of the bearing determine most of the load carryingability, and there are several rules of thumb to use as a guide.Maximum load capacity for static or very low-speed applications is 1/3 the bearingmaterials compressive limit. The compressive limit is the lowest pressure that results inplastic (permanent) deformation.Most plain bearings carry less than 400 psi.Cylindrical Roller BearingNeedle Bearing CagedCrossed Roller Bearing