For applications such as low-speed heavily-loaded bearings and gear-boxes, or heavy-duty machining on tough metals, a 4 Ball Weld Load Test provides an insight on a lubricant’s load-carrying capability. A lubricant or grease is sandwiched between 3 bottom steel balls, and a rotating steel ball from the top. Load is gradually increased in the test-rig until such time that the lubricant film is not sufficient anymore to prevent welding of the 3 bottom balls and the top ball.
The load applied (in kgs) at weld point is recorded, and comparisons between different lubricants’ load carrying capability can be derived. Conventional gears oils, as example, normally record 200-250 kg weld load, and values exceeding such may be considered as excellent results. The test rig can apply a highest load of 800 kgs.
The 4-ball Weld Load Test rig uses three steel balls held in a cup with the lubricant. A forth ball is rotated against the three ball at a given speed. A starting load is applied and increased at pre-determined intervals until the rotating ball seizes and welds to the stationary balls.