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Significance and Use
In service, there is a space between a shaft and a self-lubricating PM bearing that contains an oil film when the bearing is operating properly. In the event the oil film is disrupted or fails to form the bearing will exhibit increased wear and possibly fail. Therefore the ability for oil to flow through the porosity of a PM bearing is critical to the performance of the bearing.
The porosity of the bearing must be open to the surface and interconnected within the bearing. This allows the oil in a self-lubricating PM bearing to flow during operation to the space between the bearing and the shaft to form an oil film and protect the shaft from wear.
The ability of a gas to flow through the bearing reflects the openness and interconnected properties of the porosity in the bearing.
Data from this test can be used as an internal quality tool and can be reported to buyers of bearings.
A number of other factors also affect the performance of the bearing and the movement of oil; factors such as the oil viscosity, operating temperature, load, shaft speed, surface area, surface finishes and others. This test provides information on only one property and cannot be the sole consideration in the design and testing of a bearing application.
1.1 This test method covers the determination of the permeability of a PM bearing when subjected to pressurized nitrogen under controlled conditions.
1.2 The values stated in SI units are to be regarded as the standard with the exception of flow rate for which the cm3/min unit is the industry standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
B243 Terminology of Powder Metallurgy
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
ICS Number Code 21.100.01 (Bearings in general)