B Stud-Type and Yoke-Type Track Rollers MOUNTING The surface of the hole in the machine element, which supports the stud or the mounting shaft, must not deform under the expected load, and the support should be suffi ciently rigid to resist bending loads. Deformation and bending will cause uneven loading of the outer ring. In mounting the stud-type track roller, the retaining washer must be fi rmly backed up by a fl at shoulder which is square with the stud center line. The shoulder diameter must be no smaller than the minimum clamping diameter (da) listed in the bearing tables. The maximum inherent strength of the stud is obtained when the unit is supported, as close as possible, to the retaining washer – which minimizes the bending moment. For this reason, the edge of the housing, which supports the stud shank, should be kept as sharp as possible, but free from burrs. To minimize defl ection in mounted stud-type track rollers, the stud shank should be housed with the fi t (db) shown in the bearing tables. The clamping nut should not be tightened with a torque value higher than the maximum listed. A screwdriver slot, or hexagonal socket in the end of the stud, is provided for a tool to prevent the stud from turning when the nut is being tightened. Because the bottom of the screwdriver slot is not fl at, it is helpful to put a radius on the tip of the screwdriver being used to hold the stud more securely. When the stud shank is housed with an interference fi t, installation force should be applied only to the center portion of the fl anged end of the stud, preferably with an arbor press. When the loads are high, the yoke-type track rollers should be mounted on a high strength bolt or shaft with the tight transition fi t listed in the bearing tables. The bearing should be clamped between fl at and parallel faces, at right angles, to the axis to prevent the retaining washers from coming off under load. If the bearing cannot be clamped, a close axial fi t in the yoke is required. When the applied loads are light to moderate, the inner ring of a yoke-type track roller may be mounted on an unhardened shaft, or a bolt with the loose transition fi t listed in the bearing tables. Again, the retaining washers should be backed up axially to prevent their coming off under load. LOAD RATINGS DYNAMIC LOADING AS A TRACK ROLLER When the outer ring of a stud-type or yoke-type track roller runs on a track, the contact under a radial load causes elastic (oval) deformation of the outer ring. As a result, a smaller zone of the raceway is loaded and the load is distributed on fewer needle rollers. This, in turn, affects the track roller’s dynamic and static load ratings. Also, this deformation generates bending stress in the outer ring, which must not exceed the maximum permitted for the material of the outer ring. The maximum permissible dynamic (Fr perm) radial load condition is determined by this requirement. The rating life of a stud-type or yoke-type track roller should be calculated using the dynamic load ratings, Cw, shown in the tables. The tables also show the maximum permissible radial load, Fr perm, that can be dynamically applied on the stud-type or yoke-type track rollers. However, to calculate the L10 life of a track roller, the applied radial load must not be greater than Cw/4 – based on ideal operating conditions of alignment, lubrication, temperature, speed and accelerations. STATIC LOADING In addition to the basic static load rating C0, the tables also list the maximum permissible static radial load, F0r perm, that may be applied to a stud-type or yoke-type track roller. The values of F0r perm result in a minimum static factor fs of 0.7, for the worst condition of internal load distribution in inch series track roller operation. The F0r perm values must not be exceeded. Exceeding F0r perm may cause permanent damage to the track roller. A damaged track roller could cause the equipment in which the track roller is installed to malfunction. The static factor fs can be calculated using the following formula: fs ≥ 0.7 ( F0r perm ) Where: F0r perm = Maximum permissible static radial load P0r = Equivalent static load (F0r for yoke-type track rollers) F0r = Static radial load fs = Static factor whose values should not be smaller than those suggested in Table B5-12. Table B5-12. Suggested values for static factors fs for inch series track rollers Requirements for yoke – type track rollers and stud – type track rollers Suggested fs values Max. Min. High shock-type loads – Quiet running 1.5 2.5 Normal loading – Normal quietness of running 1 1.5 Minor impact loads and rotary motion particularly quiet running not required 0.7 1 P0r NEEDLE ROLLER BEARINGS B-5-31