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The conventional designs for the four-ball friction-and-wear tester that have been in use for more than 50 years allow us to measure friction and wear of lubricants under boundary condition at relatively low cost and with a good degree of repeatability. The Ann Arbor Testing & Development Model 201 Four-Ball Friction & Wear Tester uses an innovative, simplified design that offers superior reliability and repeatability of test data and makes lubricant testing and formulating procedures far less work intensive.

• The Model 201's mechanism to apply the load relies on simple gravity. It uses no levers that require periodic readjustment and no air cylinders that require a constant supply of dry air.
• The load is the combined weight of the motor, the frame and any additional weights -- all of which can be accurately weighed and which provide the same load, test after test, without requiring any adjustment.
• Some conventional designs rely on a ball-bearing thrust bearing under the test cup, which can trap dirt and can therefore degrade the friction measurement. But the unique design of the Model 201 requires no thrust bearing and can provide highly accurate and repeatable results.
• Other four-ball designs rely on air bearings that can change the load or tilt the test cup, but the Model 201 Four-Ball Friction & Wear Tester measures the friction force from the free-moving motor and not from the test cup. Its test cup is stationary and, because of this arrangement, the need for the thrust bearing is eliminated entirely. This unique design enables us to attach several different kinds of sensors directly to the test cup without affecting or limiting the friction readings in any way. For example, we can attach thermocouples and other sensors to measure characteristics of the oil being tested, and we can attach special tubing to circulate the test oil through the test cup.
• The Model 201's unique ability to have test lubricant flowing through the test cup while the machine is already running and collecting data opens exciting new possibilities for extracting more useful friction and wear data -- faster, more accurately, and with less investment of operator time.
• The Model 201's unique flow-through cup gives us the ability to make formulation changes after the run-in period. This enhances the formulation process by eliminating the test variable and leaving only one variable -- the formulation change itself. The formulation process is quicker because we no longer need to repeat the run-in period for each trial formulation.
• The test cup has also been simplified. It consists of just two pieces, a top and a bottom. In addition, the finer threads in the cup and the knurled top and bottom pieces allow the cup to be tightened by hand without using special wrenches.
• The chuck holding the rotating top ball has been simplified for quicker loading, faster and easier cleaning, and truer running.