A method for determining the load-carrying capacity of lubricants by four ball friction and wear tester

This method is suitable for evaluating the bearing capacity of lubricants on the four ball friction and wear tester, including the maximum no bite load PB, the sintering load PD, and the comprehensive wear value of ZMZ three indexes. In practical applications, different evaluation indexes can be selected according to various uses of lubricants.

1. Method summary

In the four ball machine, four steel balls are arranged in an equilateral tetrahedron. The ball is rotated at the 1400-1500 turn / sub. The next three balls are fixed together in oil tanks and load from bottom to top through a lever or hydraulic system. During the test, the contact points of four steel balls were immersed in the lubricant. The test time of each test was 10 seconds, and the wear mark of any steel ball in the oil box was measured after the test. Repeat the trial according to the prescribed procedure.

2. Test steps

2.1 the steel balls are respectively fixed on the upper ball seat and the oil box of the four ball friction machine. Pour the sample into the oil box and let the specimen cover through the steel ball to reach the joint between the pressure ring and the nut. If it is the test grease, put enough grease in the oil box first, put the ball into the grease, put the pressure ring, tighten the screw cap and tighten the oil box, smooth the grease on the surface and adjust it to the joint of the ring and the nut, and there can be no holes in the sample.

2.2 put the oil box with the sample and the ball in the middle of the upper seat, put the disc rack between the oil cup and the guide column, release the load lever and add the specified load to the ball. The load should be avoided when loading. Oil loaded four ball friction tester can be loaded according to the instructions.

2.3 after loading, start the motor and press the stopwatch at the same time. The test time from Startup to shutdown is 10 seconds.

2.4 after each test, measure the diameter of the grinding marks in the two directions of any steel ball in the oil box.

6.5 on the determination of the maximum non card load PB: the diameter of the grinding mark required under the maximum non card load PB when the PB is fixed is not greater than the grinding mark diameter of the corresponding compensation line (that is, the compensation diameter). If the diameter of the grinding mark under a load is measured to be larger than the grinding mark in the corresponding compensation line 5%., the next test will be done under a lower load and continue this operation until the maximum no bite load is determined.

To simplify the test program, this method provides a P-D compensation table (10 5%) to judge the PB point (Table 1). The D compensation in table I indicates the compensation diameter corresponding to the load P. For example, the diameter of the grinding mark of an oil at 80 kg load is 0.47 mm, and the table 1 knows that the D compensation (10 5%) at 80 kg (10 5%) is 0.44 mm, then the PB of the oil can be determined. The point is less than 80 kilograms.

The requirements for the determination of PB points are as follows: PB is below 40 kg, measured to 2 kg: PB in 41-80 kg, 3 kg; PB in 81-120 kg, to 5 kg; PB in 121-160 kg, to 7 kg, PB above 160 kg, to 10 kg.

6.6 on the side determination of sintering load PD: generally starting from 80 kilograms load, test according to the load level indicated in Table 2 until the sintering occurs. Repeat once, if two times are sintered, then the load used in the test is used as the sintering load. If the repeated test does not occur, it needs to be new with a larger load. Test and repeated test.

When sintering, the motor should be closed in time, otherwise serious wear and tear will be caused. The steel ball and the chuck are even sintered with the upper cone. The following images can help to determine whether the sintering is occurring.

A. frictional force records a sharp transverse movement of the pen tip.

The noise level of B motor is increased.

C oil box smoke;

The lever arm of the D is suddenly reduced.

Some very strong lubricating oil has not reached real sintering, the diameter of the steel ball grinding mark has reached the limit value, then the load that produces the maximum wear mark of 4 millimeters is used as the burning node, and some lubricants are not sintered under the high load, so the limit load of the machine is 800 kilograms.

Note: the experience of the test face shows that it is appropriate to tighten the oil box to the torque of 8.5 kilos when the burning load is loaded. The lower ball in the test does not roll, and the reproducibility of the PD point can be improved.

6.7 on the side determination of the comprehensive wear value ZMZ: first determine the PB point of the sample in Table 2, and then start from the load higher than the PB point, increase the load step by step until the sintering, check the compensation line correction load sum table (Table 3), and calculate the comprehensive wear value according to formula (3).