The Importance of Weld Load

The Load Wear Index (LWI) is a measure of a lubricant’s wear protection ability. It indicates how effectively a lubricant can minimize wear under applied loads. Additionally, the four ball weld load indicates the extreme pressure property of a lubricant. A higher weld load signifies that the lubricant can withstand more pressure without causing metal-to-metal contact.
The weld load is reported in kilograms (kg) or Newtons (N), with higher values indicating better performance in extreme pressure applications. The LWI is calculated using the wear scar data of 10 loads applied just before the weld occurs.
The weld load test is conducted according to ASTM D 2783 / DIN 51320-2 for lubricating fluids and ASTM D 2596 / DIN 51320 – 4 for greases.

The 4 Ball Test Method in Brief

The test begins by first placing one steel ball under load against three steel balls held stationary in a nut assembly. The top ball rotates at high specified RPM’s for suggested time. If the resulting scar on the ball is below the specified average scar diameter as per the standards then the weights are increased and runs repeated until welding or seizure occurs.
This usually means that the lubricant film can no longer separate the surfaces, allowing metal-to-metal contact.