2.3 Clearances

As in all bearings, satisfactory operation of porous-metal bearings require suitable clearances between shaft and housing. While guidelines depend on the materials used and the nature of the application, a representative chart showing recommended bearing clearances for porous-bronze and porous-iron bearings is given in Figure 2-1.

We carry a full line of both thick and thin wall bushings. Please consult the tables in this section of the handbook for information on recommended shaft size and bore diameter to be used with various bushing sizes.

Table 2-1 General Guidelines for the PV Factor in Porous-Metal Bearings

Limiting conditions for operation of porous bearings can be expressed as a PV factor. Since P = load, psi; V = surface velocity, fpm; the PV value gives an index of frictional heat generated on a unit area of the bearing surface. A maximum value of 50000 is common for porous bearings. For long-time running with no additional lubrication, 20000 should be a limit in selecting loads for various speeds. For thrust bearings, a maximum PV of 10000 should be used.

Provision to replenish the oil supply is desirable when the PV factor approaches the maximum under continuous operation for extended periods of time, or for high temperatures. For such cases, oil can be applied to the OD or ends of the bearing. From there it is drawn, by capillary action, into the bearing and metered to the shaft. A reservoir of grease next to the bearing also can be helpful.

Under certain conditions these recommended values can be exceeded but with a sacrifice in service life.

Reprinted with the permission of Machine Design Magazine, Vol. 54, #14, June 17, 1982, p. 131.

Fig. 2-1 Recommended Bearing Clearances*
* Reprinted with the permission of Keystone Carbon Company, St. Mary’s, PA, from Keystone Porous Bronze and Porous Iron Bearings, Fig. B-34, p. 9.

SINTERED BEARINGS INSTALLATION DATA

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