Specific Characteristics of Ball Bearings
In the modern ball bearings the machine designer has available, also, many widely varying specific characteristics, according as different types are considered, over and above the general advantages commonly listed as attributes of anti-friction bearings as a whole.
In this way they are particularly adaptable to a great many specialized fields, slight variations here and there enabling them to meet satisfactorily those factors of operation or service requiring special consideration.
Ball bearings in various types and sizes are designed to carry either radial loads or thrust loads in nearly any practical magnitude. In general, they afford maximum load capacity in the smallest possible space. Most of them will have the ability, furthermore, to carry both radial and thrust loads at the same time,in various proportions and totals.
Requirements may demand that shafts be located positively under light thrust loads or it may be necessary to provide very positive location even under considerable thrust. Specific types of ball bearings offer these possibilities. For example, the standard Single Row Type is satisfactory for locating shafts end-wise in assemblies, where slight end-wise or axial deflection under load is not serious. On the other hand, if under load practically no movement of the shaft is permissible, and great rigidity must be assured, the Double Row Angular-Contact Bearing may be employed or perhaps a Duplex Unit. These qualities of definite axial location are procured with certain types of bearings without sacrificing their capacity for radial an d thrust loads as well.
Thrust in both directions — as experienced with reversing worm drives — can be carried by more than one type of bearing, but other designs are not suitable at all, and some discrimination must be exercised.
Where the speed factor is involved still other characteristics may be required, and these too can be obtained by proper selection, some bearings carry greater loads at higher speeds than others, due to their internal design.
Radial rigidity of shaft — as well as the end-wise rigidity mentioned — is offered by various types of assemblies, including preloaded bearing combinations, for the extreme rigidity of machine tool spindles, etc. Shafts must be adjusted end wise on initial assembly to compensate for certain demands which may be made in service.
Adjustable bearings are available to meet particular requirements, but on the whole, adjustment of bearings is a negative feature, since the principle of ball bearing design permits of virtually non-wearing operation. The majority of bearing types are non-adjustable, requiring no adjustment either in mounting or in service, even though their useful life may be extended over many years.
The extreme degree of precision which may be obtained with ball bearings is well known, and in many applications is the determining factor in their use.
The small amount of space along the shaft which ball bearings occupy in comparison to other bearing types is very often a deciding point in their favor, and appeals particularly to machine designers.
The foregoing constitutes a rough outline of the specific characteristics which to one degree or another are a feature of each ball bearing type and design, all of which must be considered in selecting the proper bearing in view of the service demands to be made upon it.
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