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Knowledge Center Gear Oils: Part 5 – FZG Scuffing Load Tests On Gear Oil Wear Protection Find out how scuffing load tests are used to qualify the wear protection of your industrial gear oils.

  • Most gear oil standards (CLP and AGMA) require a gear oil to pass a certain FZG scuffing load stage.
  • Numerous variations of scuffing tests can determine wear protection levels of gear oils.

With gear pair types that have a considerable profile offset, the tooth flanks to move at higher speeds relative to each other. This in turn increases the percentage of sliding movement on the flanks, which makes the teeth more susceptible to scuffing. How can you know the level of protection your gear oil provides against scuffing?

To determine the extent to which gear lubricants help to prevent scuffing on the tooth faces at the lubrication gaps, an FZG test rig is used. Scuffing occurs locally where:

  1. The gears are in mesh, i.e., where at roughness peaks in contact temperatures rise sharply (‘flash temperatures’), depending on the load, peripheral speed and oil sump temperature.
  2. At these contact points, the surfaces weld together briefly and are torn apart again as the gears revolve, which leads to partial destruction of the surfaces.

The scuffing load capacity of a lubricant depends primarily on the base oils and additives used and the consequent lubricant film thickness. In the FZG standard scuffing load test, a defined load is applied to a pair of spur wheels, which is increased after a certain run time. After each load stage, the gear wheels are inspected visually and wear is measured. If wear exceeds a certain limit, the test is terminated and the last load stage is documented as scuffing load step. However, there is a variety of different FZG scuffing load tests with different peripheral speeds, oil sump temperatures, gear pairs and senses of rotation. Different tests and, consequently, different scuffing load steps are listed for the various lubricants.

Would your lubricant pass these wear-protection tests?

Read part 4 on foaming characteristics.

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