Heihachiro Okabe

Lubrication performance of perfluoropolyalkylethers under high vacuum

Abstract The tribological properties of three types of commercially available perfluoropolyalkylethers (PFPEs) were measured under vacuum using a vacuum four-ball friction apparatus with 440C stainless steel balls as test specimens. A non-fluorinated polyalkylether was also used as a reference, and it showed high friction and wear at atmospheric pressure due to local seizure, while PFPEs did not. On the contrary, PFPEs showed high wear under vacuum at high load while maintaining low friction coefficients. Derivatives of PFPE, i.e. carboxylic acid, alcohol and phosphate, were also studied. The lubrication mechanism of PFPE can be explained using the analogy of ordinary EP additives, considering their reactivity with the surface.

Dynamic Behavior of Surface-Adsorbed Molecules Under Boundary Lubrication

Friction under boundary lubrication was measured using a pendulum-type friction machine. Long straight-chain fatty acids with even carbon numbers, amine, and alcohol were used as additives, and n-hexadecane was used as the base oil. Effect of the temperature, chain length of additives and additive concentration were investigated. The phenomena obtained under 373 K were as follows: 1) “Transition concentration” wherein a drastic change of friction coefficient appeared were observed. 2) “Transition concentration” of amine or alcohol solutions appeared at higher concentration than that of acid solution. 3) In “high concentration region,” the friction coefficient gradually increased with the decrease of the concentration. 4) Temperature raise caused a high friction coefficient. 5) Friction coefficient gradually decreased with an increase in chain length. 6) “Transition concentration” shifted toward low concentration with an increase in chain length. 7) No chain-matching effect was observed. These results are ...

A Kinetic Study on the Reaction of Labeled Sulfur Compounds with Steel Surfaces during Boundary Lubrication

The kinetic study of the reaction between steel surfaces and lubricants containing labeled sulfur compounds was carried out by using an NACA-type friction machine with line contact. When the line contact apparatus is used, a correction term should be added to the theoretical equation for a point contact to apply the empirical results. Apparently the effective surface concentration of sulfur compounds decreased markedly as the sliding velocity increased in speed. Elementary sulfur had less than good lubricating properties and readily made surface temperatures rise, but both dibenzyl disulfide and diphenyl disulfide behaved as effective lubricants over the whole range of sliding velocities. The increase of compressive pressure on frictional surface did not affect the chemical activity of the sulfur compounds, but did increase the reacting regions of frictional surface. The thickness of FeS film effective in the reduction of friction was calculated to be about 30–50 layers of FeS under dynamic conditions. Th...

Evaluation of anti-wear performance of PFPE-soluble additives under sliding contact in high vacuum

The anti-wear performances of perfluoropolyether (PFPE)-soluble additives were evaluated under vacuum using a vacuum four-ball tribometer with 440C stainless steel balls as test specimens. PFPE derivatives having the hydroxyl, carboxyl and phosphate groups at the end of the Type D-PFPE molecules were studied. The addition of either PFPE-soluble carboxylic acid or PFPE-soluble phosphates to the PFPE base oil remarkably reduced steady wear rates in a vacuum environment, whereas the addition of PFPE-soluble alcohol did not. Contrary to the performance in vacuum, an appreciable increase in wear rate was observed in the air atmosphere with all the types of additives used. The effect of moisture is studied in explaining the high wear rates obtained with the additives in the air environment. The mechanism of boundary lubrication with PFPE-soluble additives is discussed. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Lahaina, Hawaii, October 16–20, 1994

Anti-wear and friction reducing additives composed of ortho-phenylene phosphate-amine salts for polyether type base stocks

Lubrication properties of amine salts of diaryl phosphates in polyether type base oils were evaluated by means of the four-ball wear test. The unique cyclic phosphate, ortho-phenylene phosphate, prevented wear and reduced friction when combined with tertiary amines. Adsorptivity, solubility, and corrosivity of the additives were taken into account.

Behavior of Polar Compounds in Lubricating-Oil Films

The effect of oil films was investigated under comparatively mild conditions of boundary lubrication (up to 10 MPa) using electrical methods. For a dynamic investigation, a pin-on-disk-type friction apparatus was uses. The capability of oil films for preventing metal-metal contact was estimated by measuring the contact resistance of the mating surfaces. For a static investigation, the characteristics of oil films while being squeezed from a very narrow slit between mercury and steel surfaces was observed by measuring the capacitance and conductance of oil films. Squalane was used as a base oil. Saturated straight chain carboxylic acids (C6-C18), and methylesters and alcohols which had the corresponding chains to the acids were used as additives. The following were found for the capability of oil films for preventing metal contact: 1) Prevention depended on the concentration of the additives (5—20 mol·m-3), and increased with the increase of the concentration. 2) Prevention did not necessarily correspond t...

Critical temperatures in ep lubrication

Abstract This paper deals with EP lubrication failure as a temperature problem. In the Shell 4-ball machine using five sulfur compounds and two chlorine compounds two types of failure are recognized. Temperature calculations showed that the two failures occur at critical temperatures. To explain the constancy of the critical temperatures a different model for EP lubrication is proposed. Also under modified test conditions the possibility of EHD effects is recognized with some additives. An explanation for this effect is suggested. Electron probe micro analysis indicated the possibility of barrier films which may be responsible for the antiwear action of these additives leading to EHD effects.

An Apparatus to Investigate Sulfur Reactions on Nascent Steel Surfaces

A test rig has been designed to investigate of some of the kinetic aspects of EP lubrication. Results for sulfurization under very short reaction times by EP additives have been obtained. From these data, some information necessary for the development of a fundamental model to predict scoring in high-speed mechanisms lubricated by sulfur-containing EP oils has been found. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in San Diego, California, October 22–24, 1984

A Kinetic Study of the Reaction of Labeled Sulfur Compounds in Binary Additive Systems During Boundary Lubrication

A kinetic investigation of the reaction of steel surfaces and labeled sulfur compounds under boundary lubrication with line contact was carried out. The active sulfur compound was examined with an accompanying compound, such as a sulfur or chlorine compound, in a binary additive system in cetane solution. In the friction tests for the solutions containing two kinds of sulfur compounds, elementary sulfur showed the highest reactivity among the sulfur compounds used, didodecyl disulfide the lowest. Dibenzyl disulfide reduced the wear rate of the frictional surface, although it produced no disturbance of the reaction between the frictional surface and elementary sulfur, which is simultaneously used in the sample solution. It was suggested that a dynamic model rather than a static model be considered for the lubricant film functioning under boundary lubrication, and also that any deficiency of an additive could be made up by addition of the second compound used simultaneously in oil. In the friction tests usi...

Static and Dynamic Properties of Oil Films Containing Organic Polar Compounds on Metal Surfaces, Using Electric Measurements

Using electric measurements, an oil film of liquid paraffin solutions of some surface active compounds was investigated in static, transitional, and dynamic states. In the static state, the film strength for mechanical deformation depended on the surface active compound in the oil. The adsorbed molecules in the oil film formed a multilayered film causing a mesomorphic state in the oil film. The oil film thickness in the transitional state was reduced by about 30 percent, in comparison with that in the static state. This reduction depended on which surface active compound was added. The film thickness decreased depending on the sliding velocity when it was below 30 cm/sec. The structure of an oil film below 30 cm/sec sliding velocity was considered to be in a dynamic equilibrium between the destruction or disturbance by a mechanical force and the molecular rearrangement or recovery of the structure. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held...