The application research on series of ashless P‐containing EP and AW additives

In order to formulate ashless GL‐5 gear oils and high‐pressure antiwear hydraulic oils, the performances of extreme‐pressure (EP) and antiwear (AW), and the thermal and hydrolytic stability of series ashless P‐containing additives with different chemical structures are investigated by four‐ball EP test, high‐temperature oxidation test and hydrolytic stability test.Design/methodology/approach – Series ashless P‐containing EP and AW additives with different chemical structures were designed and selected, their EP and AW performances, high‐temperature oxidation, hydrolytic stability compared with the traditional zinc dialkyldithiophosphate (ZDDP) additive were investigated according to relative testing standards, and their applied performances compared with the traditional ZDDP additive were investigated using the CRC L‐37 gear oil rear axle test, Deniso T‐5D Vane Pump test and Deniso P‐46 Piston Pump test.Findings – The results indicate that two ashless neutral thiophosphate esters exhibit excellent EP and AW performances, high‐temperature oxidation and hydrolytic stability. The application performance of these P‐containing additives is also examined by CRC L‐37 rear axle test. The results show that only the oil samples with the addition of neutral thiophosphate esters correspondingly to API GL‐5 automotive gear oil can pass the CRC L‐37 gear oil rear axle test successfully. The results of further Deniso T‐5D Vane Pump and Deniso P‐46 Piston Pump tests prove that the ashless neutral thiophosphate ester is a very effective EP/AW additive for high‐pressure antiwear hydraulic oil. In one sentence, the neutral thiophosphate ester is the excellent ashless EP/AW additive and the useful substitute for ZDDP.Research limitations/implications – From the results, the neutral thiophosphate ester is the excellent ashless EP/AW additive and the useful substitute for ZDDP, however, their tribological mechanicsm and their synergic effect with the other additives used in the test base oil for the applied performance tests may be done in the future works.Practical implications – These results may be useful for the researchers to formulate some ashless high EP/AW industrial oils.Originality/value – This paper proves that the two ashless neutral thiophosphate esters exhibit excellent EP and AW performances, high‐temperature oxidation and hydrolytic stability, and is the useful substitute for ZDDP for formulating ashless GL‐5 gear oils and high‐pressure AW hydraulic oils.