Machinery's Handbook, 31st Edition
PLAIN BEARINGS 2401 Fig. 5 is a general guide to the ranges required for bearing and journal surface finishes. Selecting a particular surface finish in each range can be simplified by observing the gen eral rule that smoother finishes are required for the harder materials, for high loads, and for high speeds.
63
Bearing
32
Bearing Journal
Journal
20 12 6
Bearing Journal Full Film
16 8
Complete Boundary
Mixed Film Type of Operation
Fig. 5. Recommended Ranges of Surface Finish for the Three Types of Sleeve Bearing Operations. Machining Bores.— The methods most commonly used in finishing journal bearing bores are boring, broaching, reaming, and burnishing. Broaching is a rapid finishing method providing good size and alignment control when adequate piloting is possible. Soft babbitt materials are particularly compatible with the broaching method. A third finishing method, reaming, facilitates good size and alignment control when piloting is utilized. Reaming can be accomplished both manually or by machine, the machine method being preferred. Burnishing is a fast sizing operation that gives good alignment control, but does not give as good size control as the cutting meth ods. It is not recommended for soft materials such as babbitt. Burnishing has an ironing effect that gives added seating of the bushing outside diameter in the housing bore; conse quently, it is often used for this purpose, especially on a 1 ∕ 32 -inch (0.794 mm) wall bushing, even if a further sizing operation is to be used subsequently. Boring of journal bearings provides the best concentricity, alignment, and size control and is the finishing method of choice when close tolerances and clearances are desirable. Methods of Lubrication.— There are numerous ways to supply lubricant to bearings. The more common of these are described in the following. Pressure lubrication, in which an abundance of oil is fed to the bearing from a central groove, single or multiple holes, or axial grooves, is effective and efficient. The moving oil assists in flushing dirt from the bearing and helps keep the bearing cool. In fact, it removes heat faster than other lubricating methods and, therefore, permits thinner oil films and unimpaired load capacities. The oil-supply pressure needed for bushings carrying the basic load is directly proportional to the shaft speed, but for most installations, 50 psi (345 kPa) will be adequate. Splash fed applies to a variety of intermittently lubricated bushings. It includes every thing from bearings spattered with oil from the action of other moving parts to bearings regularly dipped in oil. Like oil bath lubrication, splash feeding is practical when the hous ing can be made oiltight and when the moving parts do not churn the oil. The fluctuating
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