SELF LUBRIFICATING DRY ELEMENTS DJA MOND
The purpose of this handbook is to provide comprehensive technical information regarding characteristics of Djamond bearings. The information given may assist designers to establish the correct size of required bearing as well as the expected life and performance. I.T.S. ITALIA research and revelopment services are available to assist with any unusual design problems.
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Dja mond is the quality brand for sliding bushings produced by ITS Italia.
The range of producs is composed by self lubricating bushings, relubricating
bushings, sintered bronze or iron bushings, dry lubricating elements, rolled bronze bushings and bimetallic bushings. The high quality standards of Dja monds products are synonymous of top class performance and long lasting in time
These products are manufactured according to International and National standards.
Metric and Imperial sizes
• Cylindrical Bushes
• Flanged Bushes
• Thrust Washers
• Flanged Washers
• Strip Material
The main parameters to determine the size or calculate the service life for a bearing are:
• Specific Load Limit
• PV Factor
• Mating surface roughness Ra
• Mating surface material
• Temperature T
• Other environmental factors e.g. Housing design,dirt, lubrication
Two design procedures are provided as follows:
• A bushing service life calculation based on thepermitted bearing dimensions
• A calculation of the bushing dimensions based on the required bushing service life
To evaluate the bearing performance the specific load P is defined as the working load divided by the projected area of the bearing and is expressed in N/mm2.
Specific Load Limit
The maximum load which can be applied to a bearing can be expressed in terms of the Specific Load Limit, which depends on the type of the loading. It is highest under steady loads. Conditions of dynamic load or oscillating movement which produce fatigue stress in the bearing result in a reduction in the permissible specific load limit.
In general the specific load on a bearing should not exceed the Specific Load Limits given in the related tables. The values of Specific Load Limit specified in the tables assume good alignment between the bearing and mating surface.
The useful operating life of a bearing is regulated by the PV factor, which is the product of the specific load P[N/mm2] and the sliding speed V [m/s].
For the thrust washers and the surface of flanged bushing is used the sliding speed on the mean diameter.
The following factors influence the bushing’s performance and must be considered to calculate the required dimension or to estimate the bearing life for a particular application.
The lifetime of a bearing depends on the operating temperature.
Under dry conditions the frictional heat generated on the sliding surface of the bearing depend on the PV factor. For a given PV factor the operating temperature of the bushing depends on the temperature of the surrounding environment and the heat dissipation properties of the housing. Intermittent operation helps the heat dissipation from the couple housing - bushing and reduce the operating temperature of the bushing.
Cutting and Machining
The modification of Djamond bearing components requires no special procedures. In general it is more satisfactory to perform machining or drilling
operations from the inside of the bushing to avoid burrs. When the cutting is made from outside, a minimum cutting pressure should be used to ensure
that any steel or bronze particles projecting on the remaining bearing surface, and all burrs, are removed.
Drilling Oil Holes
Bushes should be adequately supported during the drilling operation to ensure that no distortion is caused by the drilling pressure.
Cutting Strip Material
The strip material may be cut to desired size by any of the following methods. Take care to protect the bearing surface from any damage and to avoid any deformation of the strip:
• Using side and face cutter, or slitting saw, with the strip held flat and securely on a horizontal milling machine.
• Guillotine (For widths less than 90 mm only)
• Water-jet cutting
• Laser cutting (see Health Warning)