Effects of Dispersant and ZDDP Additives on Fretting Wear

Abstract

This paper examines the effect of dispersant and anti-wear additives on fretting wear in lubricated bearing steel contacts. Reciprocating sliding ball-on-flat fretting tests with a stroke length of 50 μm have been carried out on steel-to-steel contacts in both dry and lubricated conditions. Wear and friction coefficient have been measured, and surface characterisation has been carried out using optical techniques to investigate fretting wear. The presence of base oil reduces fretting wear markedly compared to dry conditions, but fretting damage is still observed at low reciprocation frequencies. As frequency is increased, there is a transition from oxidative to adhesive/scuffing damage. The anti-wear additive ZDDP is effective in forming a tribofilm on the surfaces and reducing visible oxidation and wear. A succinimide dispersant also reduces the accumulation of solid debris but does not alleviate wear damage. The combination of both ZDDP anti-wear additive and dispersant in base oil appears to provide significant protection against fretting wear.

Mitigation of False Brinelling in A Roller Bearing: A Case Study of 4 Types of Greases

“…The present nding is different from the observations in oil lubrications, where ZDDP reaction layers grow quickly and easily on the rubbing surface, in as little time as 75 minutes and around 60 µm thick [43,44]. Additionally, a general observation of tribo lm formation under oil lubricants in the EHL regime occurs when a combination of temperature increase and shear of the lubricant takes place [8,23,25].…”

“…This is because the ZDDP-containing greases were tested at the lower range of parameters compared to other grease studies (i.e. frequency > 20 Hz, pressure > 1GPa) [8,17,23]. As a result, low frequencies (low sliding speeds, below 0.1 m/s for 2-6 Hz) and the shear stress within the contacts are considered very low (due to low contact pressure).…”

“…with very little research available on AW additive performance in grease for false brinelling mitigation. Zinc dialkyl dithiophosphates (ZDDP) is the most popular AW agent [24,25] and has shown promising results in reducing fretting wear in oil lubricated conditions [8,21,22]. Given that all research into AW additives in grease focuses on tribo lm formation mechanisms during operating service conditions [24,[26][27][28], this paper sets out to explore the possibility of ZDDP tribo lm formation under false brinelling conditions (i.e.…”

“…If the false brinelling wear is left unaddressed, service failure of the bearing will arise due to excessive running vibration, production of oxide particles and subsequent fatigue damage to the bearing surface during service [4][5][6]. The de nition of false brinelling and fretting corrosion in the literature is inconsistent [7,8] and it can be a challenge to distinguish between these two terms because they can occur simultaneously, depending on the operating conditions [9]. For example, false brinelling can escalate to fretting corrosion when the number of cyclic vibrations increases, resulting in a lubricant being squeezed out of the contact zones [4,6,10,11].…”

Synergistic Enhancement of the Lubrication Performance of Zinc Dialkyldithiophosphate by Coexistence with Ionic Liquid

“…ZDDP also forms rough, patchy, and pad-like films with a thickness of about 100-150 nm and a width of about 2-6 µm [7,8,13]. The ZDDP tribofilms are composed of three layers: a bottom layer of iron and zinc sulfide, a middle layer of zinc and iron phosphates/polyphosphate, and a top layer of mixed oxide/zinc sulfide layer [7,14]. In the initial formation of tribofilm, iron and zinc sulfides are produced on the rubbing steel surface [15], and this has a protective effect at extreme pressure [16].…”