⚙️ EP properties of lubricants — 4-ball test

Petrochemistry ASTM D2783

Overview

STATUS (as of 06.11.2026). The current edition in the ASTM store is ASTM D2783-25; ASTM D2783-21, given in this description until now, is a historical edition. The American standard has not been adopted into the PN collection. We did not have the full text — the scope and significance of the method come from the standard's page in the ASTM store, and the test conditions (speed, temperature, run duration, initial load) from a summary of four-ball test conditions in an article by a manufacturer of tribological equipment (Bruker Nano Surfaces and Metrology, AZoM, 2023).

SCOPE (ASTM D2783, Section 1). The method covers the determination of the load-carrying properties of lubricating fluids. Two determinations are made: load-wear index (formerly mean-Hertz load) and weld point, in the four-ball extreme-pressure tester. The properties of lubricating greases are tested according to a separate standard, ASTM D2596.

SIGNIFICANCE (ASTM D2783, Section 5). The method, used for specification purposes, differentiates between lubricating fluids having low, medium and high levels of extreme-pressure properties. The user should determine whether the results correlate with field performance or with results of other test machines.

TEST CONDITIONS (according to the Bruker summary). Rotational speed (1760 ± 40) rpm, temperature 18 °C to 35 °C, run duration 10 s at each load step, step load starting from 784 N, new balls for each step. The rotating top ball is pressed against three stationary balls immersed in the test fluid; the wear scar diameters are measured on the bottom balls, and the weld point is the load at which the balls weld together during a run.

WHAT WE DO NOT GIVE HERE. Without the text of the standard we do not give the requirements for the balls (material, size, grade, hardness), the table of load steps, the way of measuring scars, the formula of the load-wear index, the seizure criteria or the precision. We have removed figures and statements without a source or contradicting the sources: the formula "LWI = Σ(Fi × di)/n", the "last non-seizure load" as a result of this standard (the scope lists only two determinations), oil specification requirements (API GL-5, DIN 51524, ISO 6743-7) attributed to this method, manufacturers and prices of testers, step times and the description of EP additive chemistry.

Method principle

In the four-ball tester one ball, rotated in a chuck, is pressed against three stationary balls immersed in the lubricating fluid tested. The test is carried out as a series of short runs at stepwise increasing loads, each time with new balls. The wear scar diameters are measured on the stationary balls, and the load-wear index is calculated from the results at loads below welding. The weld point is the load at which the balls weld together during a run. According to the Bruker summary the conditions are (1760 ± 40) rpm, 18 °C to 35 °C and 10 s per load step, starting from 784 N.

Applications

• Specifications of lubricating fluids — differentiating low, medium and high levels of EP properties
• Determination of the load-wear index and weld point of lubricating fluids
• Comparison of lubricating fluids in laboratory tests (the user establishes the correlation with field performance)

Key parameters

Standard

Standard number

ASTM D2783-25

Title (PL)

Oznaczanie właściwości przeciwzatarciowych (EP) płynów smarowych — Metoda czterech kulek

Title (EN)

Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Four-Ball Method)

Step-by-step procedure

1. Preparation

   Fit new balls: three stationary ones in the cup, one in the rotating chuck; cover the stationary balls with the test fluid.

2. Run at a load step

   Apply the load and carry out a run; according to the Bruker summary (1760 ± 40) rpm, 10 s, at a temperature of 18 °C to 35 °C.

3. Scar measurement

   Measure the wear scar diameters on the stationary balls.

4. Further steps

   Repeat the runs with new balls at successively higher loads (according to the Bruker summary starting from 784 N) until the balls weld.

5. Results

   Report the weld point and calculate the load-wear index using the formula of the standard (the formula is not given here).

Required equipment and apparatus

Health and safety (OHS)

• The standard contains a general statement that it does not address all safety concerns and that establishing safety practices is the responsibility of the user

Frequently asked questions