Fred G. Rounds

Additive Interactions and Their Effect on the Performance of a Zinc Dialkyl Dithiophosphate

Four-ball wear studies have demonstrated that the antiwear performance of a commercial zinc dialkyl dithiophosphate (ZDP) antiwear agent can be adversely affected by the presence of some friction modifiers, EP agents, oxidation inhibitors, and detergent-dispersants. To explain these observations, ZDP decomposition studies were conducted with these other additives present. None of the measured ZDP decomposition characteristics completely explain the observed changes in ZDP antiwear performance. Complex formation in the bulk oil and competition for the surface seem to be involved. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Boston, Massachusetts, October 5–7, 1976

Some Factors Affecting the Decomposition of Three Commercial Zinc Organodithiophosphates

Despite the widespread use of zinc organodithiophosphates (ZDPs) as antiwear additives, how the ZDPs perform their antiwear function is still vague. Thermal decomposition of ZDPs and the formation of a protective antiwear coating by the decomposition products is one popular theory; but the correlation between thermal decomposition temperature and antiwear performance leaves something to be desired. To determine if other factors influence ZDP behavior, bench decomposition studies were conducted on three commercial ZDPs in which the effects of oxygen, water, other additives in the blend, and the base oil were investigated. For these studies, the bulk oil changes were followed by infrared spectroscopy, volatiles formation by pressure measurements, solids formation by centrifugation and subsequent elemental analysis and surface coating formation on steel balls by x-ray fluorescence spectroscopy. It was found that the decomposition of ZDPs is affected by oxygen availability, water, other additives in the ...

Some Effects of Amines on Zinc Dialkyldithiophosphate Antiwear Performance as Measured in 4-Ball Wear Tests

Adverse interactions of zinc dialkyldithiophosphate (ZDPs) with other required additives in an engine oil is one factor contributing to the high phosphorus content of some engine oils. Sine phosphorus poisons exhaust gas emission catalysts, ways to reduce the adverse interactions are being sought. The ZDP-amine interaction was investigated as a model of such an interaction. Above a critical concentration, amines can cancel the antiwear performance of ZDPs as measured in a 4-ball machine. At amine concentrations below the critical value, a synergistic antiwear effect was observed at higher loads. The tolerance of different ZDPs to the presence of amines was the same as the ranking of the ZDPs in terms of antiwear performance. A mechanism for the antiwear action of ZDPs involving the formation of an acid phosphate decomposition product has been proposed. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

Some Environmental Factors Affecting Surface Coating Formation with Lubricating Oil Additives

Dynamic friction and static immersion tests in which oil temperature was varied and dynamic friction tests in which load was varied have been run on steel balls with oil blends containing seven commercial additives. Analyses of the ball surfaces by X-ray fluorescence have shown that significant surface coating formation is initiated at calculated surface temperatures of from 250 to 350 F for most of the additives studied. Although the surface coating “thickness” generally increased with temperature, the rate of increase was generally different for the static and dynamic tests. Both surface temperature and mechanical shearing appear to influence the reactions responsible for the surface coatings. Used oil analyses showed that base oil oxidation, additive decomposition, and, in some cases, sludge formation became detectible at temperatures corresponding to the start of significant surface coating formation. The results suggest that in situ polymerization may be an important phenomenon occurring on rubbing s...

Effects of Base Oil Viscosity and Type on Bearing Ball Fatigue

Thirty-to-one differences in fatigue life have been observed during four-ball fatigue studies conducted on sixty base oils selected from eleven different chemical classes including mineral oils and most of the commonly used synthetic fluids. Among the lubricant factors that appear to control fatigue are: (a) lubricant viscosity, (b) molecular shape, (c) reactivity or polarity, and (d) anti-wear characteristics. Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Chicago, Illinois, October 1961.

Effects of Additives on the Friction of Steel on Steel I. Surface Topography and Film Composition Studies

Thrust ball bearing studies in which the surface topography of bearing races was examined with an electron microscope and in which additive elements were measured on ball surfaces by X-ray fluorescence have indicated that surface films of appreciable thickness are formed by oil additives and that the additive composition controls both surface topography and surface coating composition. Further, additive concentration, friction-time, and oil temperature studies have shown that the composition and/or thickness of the surface film is a function of the additive concentration, and suggest that most of the surface-active additives read in some manner rather than physically adsorb on surfaces. However, friction measurements correlate only to a limited degree with either the measured surface film composition or the observed topography. Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Rochester, New York, October 15–17, 1963.

SOOTS FROM USED DIESEL ENGINE OILS -- THEIR EFFECTS ON WEAR AS MEASURED IN 4-BALL WEAR TESTS

Diesel engine oil soot from different engines have the appearance of carbon black but contains significant concentrations of engine oil additive elements. Evaluation of the soot in 4-ball wear tests supported the theory that the soot reduces the antiwear additive effectiveness by preferentially adsorbing the active antiwear additive components before they can form the essential antiwear surface coating rather than removing the surface coatings by abrasion after they are formed. Engine load and exhaust gas recirculation have large effects on the soot prowear characteristics, whereas engine refinements, engine make and oil type have lesser effects. No antiwear additives were found more effective than the currently used zinc dialkyldithiophosphates. Several preferential adsorber additives were effective in simple blends but not in fully formulated engine oils.

Influence of Steel Composition on Additive Performance

Coatings formed by lubricants on rubbing surfaces are believed to control the friction, wear, and fatigue of rolling contact bearings, gears, cams and tappets, and other heavily loaded components. To investigate the influence of steel composition on the formation of these surface coatings, friction, fatigue, and static immersion studies were conducted with two case-hardened steels (1018 and 4118) and five through-hardened materials (51100, 52100, M-50, 440-C, and Stellite #3). More surface coating formed on the low alloy steels than on the high alloy steels, with the composition of the oxide layer apparently being the controlling factor. The magnitude of the steel effect depended on the additive and the oxygen available. Elemental analyses of the surface coatings obtained with representative additives indicated that all contained significant organic fractions. Decomposition of the additive in the bulk oil was a necessary prerequisite for surface coating formation. Additive decomposition was generally prom...

Effects of Hydroperoxides on Wear as Measured in Four-Ball Wear Tests

Four-ball wear studies have demonstrated that hydroperoxides formed by oil oxidation can greatly increase wear of rubbing steel parts. Peroxides, in contrast, have no effect on the wear of steel parts. Engine oil components, including the antiwear additive type, the detergent, the dispersant, and the base oil, as well as the type of steel, can all influence the magnitude of the prowear effect of hydroperoxides. Surface analyses by SEM, EDAX, and XRF showed hydroperoxides reduced the surface coating formed by antiwear additives. Wear tests on blends containing potential oil additive reaction products demonstrated that none caused the high wear observed with hydroperoxides. Presented at the 46th Annual Meeting in Montreal, Quebec, Canada April 29–May 2, 1991

Effects of Organic Molybdenum Compounds on the Friction and Wear Observed with ZDP-Containing Lubricant Blends

Combining an organic molybdenum compound with a zinc dialkyl dithiophosphate (ZDP) antiwear additive can significantly reduce kinetic friction at loads in the antiwear regime as determined in laboratory, 4-ball wear tests. Both molybdenum dithiophosphates and dithiocarbamates are effective. The friction and wear benefits are independent of the ZDP present. Adding a high total base number (TBN) metallic detergent can greatly enhance the high load antiwear behavior of the three component blend whereas lower TBN detergents do not. Unfortunately, ashless dispersants can destroy the observed benefits. The performance improvements obtained with organic additives could not be duplicated by adding specific inorganic solids, either singly or in combination. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October 16–19, 1989