ENGINEERING HOUSING DESIGNS BEARINGS WITH OUTER RINGS For bearings with outer rings, the function of the housing is to locate and support the outer ring. The following specifi cations must be met: 1. Strength – housings should be designed so that the radial loads placed on the bearings will cause a minimum of defl ection or distortion of the housing. 2. Variation of mean housing diameter (taper) – within the width of the outer ring, 13 μm or one-half the diameter tolerance (whichever is smaller) or less. 3. Deviation from circular form – the housing bore should be round within one-half the housing bore tolerance. 4. Parallelism – when possible, line bore housings that are common to one shaft to obtain parallelism of the housing bores and the shaft axis. 5. Surface fi nish – The surface fi nish should not exceed Ra 1.6 μm. 6. End chamfer – to permit easy introduction of the bearing into the housing, the end of the housing should have a generous chamfer. Only heavy-duty needle roller bearings can be installed into housings with a transition fi t or a clearance fi t. The outer ring should be a transition fi t in the housing when it rotates relative to the load. The outer ring may be a clearance fi t in the housing when it is stationary relative to the load. In either case, locate the bearings by shoulders, or other locating devices, to prevent axial movement. Since only the heavy-duty needle roller bearing does not require an interference fi t in the housing to round and size it properly, a split housing may be used if desired. Dowels should be used to maintain proper register of the housing sections. Drawn cup needle roller bearings have a thin case-hardened outer ring that is out-of-round from the hardening operation. For proper mounting it must always be pressed into the housing. Split housings will not round and size a drawn cup bearing. When split housings must be used, the bearing should fi rst be mounted in a cylindrical sleeve. The housing should be of suffi cient tensile strength and section to round and size the bearing. It must be designed for minimum distortion under load. Steel or cast iron housings are preferred. Housing bores in low tensile strength materials such as aluminum, magnesium, phenolics, etc., should be reduced to provide more interference fi t. Thin section cast iron and steel housings may also require reduced bores. Consult your representative for suggestions when working with these lower strength housings. The housing should be through-bored if possible. When shouldered housing bores are unavoidable, the bearing should be located far enough from the shoulder to avoid the danger of crushing the end of the drawn cup during installation. When the drawn cup bearing is mounted close to the housing face, care should be taken to mount the bearing at least 0.250 mm (0.0100 in) within the housing face to protect the bearing lip. BEARINGS WITHOUT OUTER RINGS In many cases, such as with gear bores, it is desirable to have the housing bore serve as the outer raceway for radial needle roller and cage assemblies or loose needle roller complements. In those instances, as for shafts used as raceways, the housing bore must have a hardness of 58 HRC or harder and a surface roughness Ra 0.2 μm so that the full load-carrying capacity of the bearing is realized. 1. Strength – the housing must be of suffi cient cross section to maintain proper roundness and running clearance under maximum load. 2. Metallurgical – material selection, hardness and case depth should be consistent with the requirements for inner raceways given in the shaft design. 3. Variation of mean housing raceway diameter (taper) – within the range of the bearing width, 5 μm or less per 25 mm or one- half the housing bore diameter tolerance or less (whichever is smaller). In addition, the bore diameter must never be smaller at both ends than in the center [sway-back]. 4. Deviation from circular form – the raceway out-of-roundness should not exceed one-half the bore tolerance. 5. Surface fi nish – In addition to a wave-free fi nish, the raceway surface roughness of Ra 0.2 μm must be maintained for the bearing to utilize its full load rating. The raceway area also must be free of nicks, burrs, scratches and dents. 6. Grind reliefs – care must be exercised to ensure that grind reliefs, fi llets, etc., do not extend to the raceway. Oil holes in the raceway area are permissible, but the edges must be blended smoothly with the raceway and, if possible, the hole should be located in the unloaded zone of the raceway. Table A-12. Housing designs summary Housing bore Raceway surface Fitting surface Out-of-roundness One-half of bore tolerance or less One-half of bore tolerance or less Variation of mean dia. (taper) 5 μm or less per 25 mm within the range of outer ring width, or one-half of bore tolerance or less (whichever is smaller) 13 μm or less within the range of outer ring width, or one-half of bore tolerance or less (whichever is smaller) Surface roughness 0.2a or less 1.6a or less Hardness 58 HRC or harder1) – 1) During the carburizing or induction-hardening of case hardened steel, not only must the surface hardness requirement of 58 HRC or higher be met, but the basic concept is that the case depth with a hardness of HV 550 (52.3 HRC) must be 0.4 mm or higher. However, if DW is smaller than 4 mm, a case depth of (0.1 × Dw) mm or higher is recommended. (Dw: roller dia.) A-14 NEEDLE ROLLER BEARINGS A