Zinc dithiophosphate (ZnDTP) is widely used in hydraulic fluids. It is a multi-functional additive for lubricants providing benefit such as anti-wear, anti-corrosion, and anti-oxidation performance. It is thought that Zinc-containing hydraulic fluids had been inferior in sludge control and copper corrosion protection compared to non Zinc-containing fluids. The degradation of ZnDTP tends to generate sludge and sulfur compounds, which in turn, attack copper material in hydraulic pumps. Sludge and corrosion are detrimental to hydraulic circuit’s performance, with sludge causing filter blocking and valve sticking, and corrosion causing pump damage. However, it has recently been shown possible to reduce sludge and copper corrosion by combining low treatrate detergents with ZnDTP in hydraulic oil. This report shows the results of a study to understand how various detergents influence the control of sludge and the copper corrosion in the presence of ZnDTP. Furthermore, paying attention to the decomposition mechanism of ZnDTP, mentioned was made about the oxidation stability from a degradative intermediate. From these results, low treatrate particular type of metal detergents showed clearly to have controlled sludge generation and copper corrosion by contributing to the oxidization control from dithiophospate which carried out decomposition generation from ZnDTP.

The boundary lubrication properties of cobalt (Co), cerium (Ce), magnesium (Mg), nickel (Ni) and titanium (Ti)-containing hydrogen-free sputtered diamond-like carbon (DLC) films were investigated using a ball-on-disk tribometer and compared with those of diamond, FCVA (filtered cathodic vacuum arc) DLC, P-CVD (plasma chemical vapor deposition) DLC and sputtered DLC films. The friction coefficients of the Co, Ce, Mg and Ti-containing DLC films and diamond film are much lower than those of the metal-free sputter-, FCVA- and P-CVD DLC films under polyalphaolefin (PAO) lubricant with and without a glycerol monooleate (GMO) additive. Moreover, under boundary lubrication using PAO with GMO, DLC films containing an appropriate quantity of Co have the lowest friction coefficient of µ = 0.02 among all the tested films. Low-friction and low viscoelastic tribo products formed on the sliding surface of Co-containing DLC films were observed by atomic force microscopy (AFM) with a force modulation methods.

Running-in is a process that achieves smooth movement through low-speed operation of machine parts before the actual running of the machines. It plays an important role in improving the frictional characteristics, wear resistance, and seizure resistance of sliding surfaces. However, as running-in is conducted under mixed lubrication conditions, there exists a risk of incurring surface damage, such as wear and seizure under the wrong conditions. A surface design guide is needed to promptly complete the running-in process. However, such quantitative design guide has not been successfully proposed. This is because running-in occurs early in the operation stage, influenced by the load-applying process in the running-in period. However, not many researches have discussed this phenomenon. Especially, there are very few reports on the running-in process regarding DLC films.

In this study, we carried out friction tests by changing the loading rate and measured the number and size of the wear particles generated during the running-in process by using an online particle counter developed in our laboratory. In addition, we analyzed the running-in behavior of the DLC film through shape analysis by observing the wear particles with a scanning electron microscope (SEM).