POLYALKYLENE GLYCOL FOR REDUCING WHITE ETCHING CRACKS

Abstract

The invention relates to a use of a lubricant comprising a polyalkylene glycol for reducing white etching cracks in lubricated metal surfaces; and to a method for reducing white etching cracks in lubricated metal surfaces comprising the steps of lubricating the metal surfaces with a lubricant comprising the polyalkylene glycol.

Claims

1.-14. (canceled)

15. A method comprising providing a lubricant comprising a polyalkylene glycol and reducing white etching cracks in lubricated metal surfaces.

16. The method according to claim 15, wherein the lubricant comprises at least 50 wt % of the polyalkylene glycol.

17. The method according to claim 15, wherein the polyalkylene glycol comprises ethylene oxide units in randomly polymerized form.

18. The method according to claim 15, wherein the polyalkylene glycol comprises ethylene oxide units and C.sub.3-C.sub.18 alkylene oxide units in randomly polymerized form.

19. The method according to claim 15, wherein the polyalkylene glycol comprises ethylene oxide units and propylene oxide units in randomly polymerized form.

20. The method according to claim 15, wherein the polyalkylene glycol comprises at least 25 wt % ethylene oxide units and at least 25 wt % propylene oxide units.

21. The method according to claim 15, wherein the polyalkylene glycol comprises 35 to 65 wt % ethylene oxide units in polymerized form.

22. The method according to claim 15, wherein the polyalkylene glycol comprises 35 to 65 wt % propylene oxide units.

23. The method according to claim 15, wherein the lubricant has a viscosity at 40° C. of 150 to 500 cSt.

24. The method according to claim 15, wherein the polyalkylene glycol has a solubility in water at 20° C. of at least 5 g/l.

25. The method according to claim 15, wherein the polyalkylene glycol has a molecular weight of 700 to 10 000 g/mol.

26. The method according to claim 15, wherein the concentration of hydrogen deposited in the metal surface is reduced.

27. The method according to claim 15, wherein the metal surface is the surface of a gear.

28. The method according to claim 15, wherein the metal surface is the surface of a wind turbine gear.

29. A method for reducing white etching cracks in lubricated metal surfaces comprising the steps of lubricating the metal surfaces with a lubricant comprising a polyalkylene glycol.

Description

EXAMPLE 1—LUBRICANTS

[0055] The following lubricants were used: [0056] Lube PAG-A: commercial lubrianct formulation with polyalkylene glycol comprising a butanol iniated 50 wt % ethylene oxide and 50% propylene oxide in randomly polymerized form copolymer with a kinematic viscosity at 40° C. of about 50 cSt (mol weight approx. 1200 g/mol) and a diethyleneglycol iniated 60 wt % ethylene oxide and 40% propylene oxide in randomly polymerized form copolymer with a kinematic viscosity at 40 of about 1100 cSt (mol weight approx. 6400 g/mol); viscosity at 40° C. 230 mm.sup.2/s (ISO 3104); viscosity index about 235; pour point about −40° C.; the lubricant contains commercial additives (1.5-2.5% antiwear additive based on organophosphate and organothiophosphat, partially amineneutralized; 1-3% phenolic and aminic antioxidants; <0.3% further additives (corrosion inhibitors, defoamer)). [0057] Lube PAG-B: Pure polyalkylene glycol comprising 60 wt % ethylene oxide and 40 wt.-% proplylene oxide in randomly polymerized form; viscosity at 40° C. 225 mm.sup.2/s (ASTM D445); viscosity index about 230; pour point about −45° C.; water soluble, molecular weight approx. 2400 g/mol; contains no additives.

[0058] For comparison, the following lubricants were used: [0059] Lube PAO: Polyalphaolefin, viscosity at 40° C. 48 mm.sup.2/s, viscosity at 100° C. 8 mm.sup.2/s (ASTM D445); viscosity index about 140; insoluble in water. [0060] Lube COM: commercially available industrial gear oil “MobilGear® SHC XMP 320” from ExxonMobil; based on polyalphaolefin base oil, contains 10-20 wt % isotridecyl adipate, 1-5 wt % methylene bis(dibutyldithiocarbamate), 0.1-1 wt % triphenyl phophorothionat.

EXAMPLE 2—BALL AND ROLLER TESTING MACHINE

[0061] The lubricants were tested on a ball and roller testing machine for testing axial cylindrical roller bearings. The test conditions were as follows: oil volume about 15 ml which was externally heated to 80-90° C., norm force 8 kN, rotation speed 700 min 1, duration 100 h, tested with 10 rolling bodies, maximum Hertz'sche pressure 1930 MPa, during each test Stribeck curves were made in 10 h intervals. The surface of the tested foiling bodies was analyzed under the light microscope and the results are summarized in Table 1 (middle column).

EXAMPLE 3—ANALYSIS OF MICROSTRUCTURE AND WHITE ETCHING CRACKS

[0062] In order to analyse the microstructure of the tested sample of Example 2 for each lubricant tested three cylindrical rollers were cross-section polished on the front surface. For the sectioning the cross-sections were made in 0.5 mm distance. Each cylinder roller was 4 mm broad. The polished cross-sections were etched with alcoholic picric acid before light microscopy to make the grain structure visible and to improve the assessment of the with etching cracks. The results are summarized in Table 1 (right column). The data demonstrated that lubricants based on polyalkylene glycol reduce the white etching cracks.

TABLE-US-00001 wTABLE 1 Surface Lubricant damages White etching cracks WEC Lube PAG-A No No WEC Lube PAG-B Pitting No WEC, only few fatigue regions (also called dark ething regions) Lube PAO Pitting WEC found, strong dark etching (comparative) regions Lube COM Micropitting WEC found. (comparative)

EXAMPLE 4—HYDROGEN DEPOSITION

[0063] The analysis of the hydrogen content in the roller bodies was achieved by thermal extraction with a carrier gas. The samples are molten and the liberated hydrogen analyzed. Calibration standards with 1.9 ppm±0.2 ppm hydrogen were used. Three roller bodies were analyzed for each lubricant after the test of Example 2 after washing them with n-hexane and acetone and drying under nitrogen atmosphere. As reference and initial hydrogen content three roller bodies were analyzed without testing them in Example 2. The increase in hydrogen concentration in the roller bodies tested in Example 2 is summarized in Table 2. The data showed that there is a reduced increase in hydrogen deposition in the roller bodies when polyalkylene glycol based lubricants were used.

TABLE-US-00002 TABLE 2 Increase of hydrogen in roller Lubricant body Lube PAG-A 0.33 ppm Lube PAG-B 0.37 ppm Lube PAO 0.49 ppm (comparative) Lube COM 0.52 ppm (comparative)