PN-C-04362 Petroleum Products - Testing the Lubricating Properties of Oils and Greases

The standard “PN-C-04362 Petroleum products – Testing of the lubricating properties of oils and greases” developed by the Polish National Standards Organization (PKN) describes a procedure for testing the lubricating properties of oils and greases in a four-ball apparatus for:

• Determination of wear rate under welding load
• Determination of the diameter of defects in abrasion testing
• Determination of wear load limit

The wear scar characteristics and friction coefficient of a lubricating grease can be determined using a four-ball wear configuration. The purpose of this test is to determine the antiwear properties of a lubricant. In the four-ball wear test, a steel ball is rotated against three lubricated stationary steel balls under a specified load, speed, temperature and time. The better the lubricant prevents wear, the smaller the wear mark on the three retaining balls. At the end of the test, three wear marks are measured and the average is reported. The friction coefficient is also measured over the 60-minute test and its average is reported at the end of the test.

Quad-ball data is useful for distinguishing between lubricating greases with different levels of load carrying capacity, wear protection and friction reduction properties. Although these results do not necessarily correlate with real-life applications, this method has become an industry standard for comparing wear and friction functionality.

Lubrication is one of the most important factors determining bearing performance. The suitability of the lubricant and the lubrication method has a dominant influence on bearing life. The main functions of the lubrication process are:

• Lubricate every part of the bearing and reduce friction and wear
• To remove the heat generated inside the bearing due to friction and other reasons
• Coating the rolling contact surface with suitable oil film to extend the fatigue life of the bearing
• Prevent corrosion and contamination from dirt

Bearing lubrication is generally divided into two categories: grease lubrication and oil lubrication.

• Since there is no need to refill for a long time after the grease is filled, and a relatively simple structure can be sufficient for the lubricant sealing device, grease lubrication is widely applied. There are two methods of lubricating with grease. One of these is the closed lubrication method, in which grease is filled into pre-protected/sealed bearings. The other method is the feed method, in which the bearing is first filled with appropriate amounts of grease and refilled at regular intervals by renewal or replacement.
• Oil lubrication can be used even at high speed rotation and slightly high temperature, and is effective in reducing bearing vibration and noise. Therefore, oil lubrication is used in many cases where grease lubrication does not work.

The test method briefly described in standard PN-C-04362 is used to determine the relative anti-wear properties of lubricating fluids in sliding contact under prescribed test conditions. No attempt has been made to relate this test to rolling balls in contact. The user of this testing method must determine to his or her own satisfaction whether the results of this testing procedure correlate with field performance or other bench testing machines.

This test method covers the determination of the load carrying properties of lubricating greases and three types of determinations are made:

• Load-wear index (formerly called mean-Hertz load)
• Weld point via four-ball extreme pressure tester
• Last non-compressible load

This test method distinguishes between lubricating greases with low, medium and high extreme pressure properties.

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