Effects of oxygen on grease

Abstract

Effects of Oxygen on grease or another organic paste product can be evaluated with a modified version of the ASTM D942 test methodology for oxidation stability of lubricating greases or other organic paste products by employment of an oxidation pressure vessel, in which at least one of (A) a very small sample of the grease or other organic paste product is deployed for testing within the oxidation pressure vessel such that the sample has an enhanced surface area to mass ratio, and (B) a temperature other than about 99° C. is employed during the testing. In general, the testing is carried out under oxidation pressure conditions. The sample may be evaluated with respect to Oxygen uptake. Additional technique(s) directed to oxidation and/or other properties of the sample may be carried out before to after any Oxygen uptake evaluation, for example, FTIR analysis and/or ATR-FTIR analysis.

Claims

1. A method for evaluating effects of Oxygen on grease or another organic paste product, which comprises the following steps, which are not necessarily conducted in series: providing a bomb vessel capable of being pressurized, heated, and supplied with Oxygen and a sample of the grease or other organic paste product; providing the sample of the grease or other organic paste product to the bomb vessel; providing the Oxygen, under pressure, to the bomb vessel to expose the sample of the grease or other organic paste product to the Oxygen; heating the bomb vessel containing the sample of the grease or other organic paste and the Oxygen, under pressure, to a predetermined temperature for a predetermined time; and evaluating the sample of the grease or other organic paste product— wherein at least one of the following (A, B) is employed: (A) a very small sample of the grease or other organic paste product is employed within within the bomb vessel such that the sample has a greater surface area to mass ratio than that provided by employing a 20-g sample divided into five individual sample dishes, each containing 4 g of sample; and (B) the heating is at a heating temperature of other than about 99° C.

2. The method of claim 1, wherein evaluating the sample of the grease or other organic paste product includes evaluation for oxidation.

3. The method of claim 1, wherein the evaluation for oxidation includes ascertaining any Oxygen uptake of the sample by loss of pressure in the bomb vessel.

4. The method of claim 1, wherein the sample of the grease or another organic paste product is evenly distributed in a plurality of individual sample dishes such that the very small sample of the grease or other organic paste product is substantially less than 1 g per individual sample dish.

5. The method of claim 2, wherein the sample of the grease or another organic paste product is evenly distributed in a plurality of individual sample dishes such that the very small sample of the grease or other organic paste product is substantially less than 1 g per individual sample dish.

6. The method of claim 3, wherein the sample of the grease or another organic paste product is evenly distributed in a plurality of individual sample dishes such that the very small sample of the grease or other organic paste product is substantially less than 1 g per individual sample dish.

7. The method of claim 1, wherein the heating temperature is at least about 120° C.

8. The method of claim 2, wherein the heating temperature is at least about 120° C.

9. The method of claim 3, wherein the heating temperature is at least about 120° C.

10. The method of claim 4, wherein the heating temperature is at least about 120° C.

11. The method of claim 5, wherein the heating temperature is at least about 120° C.

12. The method of claim 6, wherein the heating temperature is at least about 120° C.

13. The method of claim 1, wherein at least one of FTIR analysis and ATR-FTIR analysis is employed in evaluating the sample of the grease or other organic paste product.

14. The method of claim 2, wherein at least one of FTIR analysis and ATR-FTIR analysis is employed in evaluating the sample of the grease or other organic paste product.

15. The method of claim 3, wherein at least one of FTIR analysis and ATR-FTIR analysis is employed in evaluating the sample of the grease or other organic paste product.

16. The method of claim 4, wherein at least one of FTIR analysis and ATR-FTIR analysis is employed in evaluating the sample of the grease or other organic paste product.

17. The method of claim 5, wherein at least one of FTIR analysis and ATR-FTIR analysis is employed in evaluating the sample of the grease or other organic paste product.

18. The method of claim 6, wherein at least one of FTIR analysis and ATR-FTIR analysis is employed in evaluating the sample of the grease or other organic paste product.

19. The method of claim 7, wherein at least one of FTIR analysis and ATR-FTIR analysis is employed in evaluating the sample of the grease or other organic paste product.

20. The method of claim 8, wherein at least one of FTIR analysis and ATR-FTIR analysis is employed in evaluating the sample of the grease or other organic paste product.

21. The method of claim 1, wherein the sample of the grease or another organic paste product is evenly distributed in a plurality of individual sample dishes such that the very small sample of the grease or other organic paste product is at most about 0.5 g per individual sample dish; the heating temperature is about 130° C.; and evaluating the sample of the grease or other organic paste product includes at least one of ascertainment of any Oxygen uptake of the sample by loss of pressure in the bomb vessel, and employment of at least one of FTIR analysis and ATR-FTIR analysis.

Description

[0019] The drawings form part of the specification hereof With respect to the drawings, which are not necessarily drawn to scale, the following is briefly noted:

[0020] FIG. 1 is a perspective view of a Quantum® instrument positioned upright for ASTM D942 type testing, and testing according to the present methodology.

[0021] FIG. 2 is a graph of Grease A, ASTM D942 oxidation testing at 99° C. and 130° C.

[0022] FIG. 3 is graph of Greases B and C, standard ASTM D942 oxidation testing at 99° C.

[0023] FIG. 4 is a graph of Greases A-F, ASTM D942 Oxidation Testing at 130° C.

[0024] FIG. 5 is a graph of ATR-FTIR spectra as a combined plot of a sample of Grease A.

[0025] FIG. 6 is a graph of ATR-FTIR spectra comparing samples of Grease A with Grease B, taken in conjunction with another test protocol, a modified falex pin and vee block testing of the greases with present methodology.

[0026] The invention can be further understood by the additional detail set forth below. As with the foregoing, the following, which also may be read in view of the drawings, is to be taken in an illustrative, and not necessarily limiting, sense.

[0027] Oxidation testing is exemplary of the invention.

OXIDATION TESTING

[0028] Oxidative resistance of six greases was initially evaluated by the ASTM D942-15 test method, which requires exposure of a 20-g grease sample to be tested distributed evenly in five glass dishes (4-g grease per dish) with an approximately 25-cm.sup.2 exposed surface area per dish and, thus, 125-cm.sup.2 surface area per 20-g sample per test. The dishes are stacked on a metal rack with an approximately 5-mm gap between the top of each stacked glass dish and the shelf above. The combined stack of grease-filled dishes is then inserted into a cylindrical pressure chamber and exposed to Oxygen of not less than 99.5% purity at an initial 100-psi (690-kPa) pressure and room temperature which is then increased to 99±0.5° C. Under this increased temperature, the Oxygen pressure is carefully released to maintain no more than 110±2 psi (758±14 kPa). The test is normally continued for a chosen period of one hundred to five hundred hours, and the resultant decrease in Oxygen pressure as a result of grease oxidation is taken as the test result.

[0029] As disclosed in the parent, the bath-free Quantum® instrument, modified as shown in FIG. 1 and operated under isothermal conditions, was used to perform the ASTM D942 grease oxidation testing. Compare with Selby, T., et al., “Comparative Study of Grease Oxidation Using an Advanced Bench Test Technique,” Proceedings of the 19.sup.th International Colloquium Tribology—Lubricants, Materials and Lubrication, Technische Akademie Esslingen, Esslingen, Germany, Jan. 22, 2014; Azad, S., et al., “An advanced Technique for Grease Oxidation Measurement,” NLGI Spokesman, 2015m 78(6), 30-40.

[0030] Applying the modified Quantum® instrument, normal 20-g grease test samples were run in ASTM D942 for 100-hour periods, additionally, in some cases, 200-hour periods, depending upon the response at one hundred hours. Results on five of the six greases tested are shown in the Table below. For each test, pressure change with time was continuously recorded. As seen in FIG. 2, Grease A, a bio-based soy grease with an aluminium-compound thickener, was subjected to a 100-hour oxidation exposure under ASTM D942 methodology and temperature-modified methodology (130° C.). Interestingly, final pressures in the chamber showed almost total Oxygen uptake by the grease during testing from the test chamber pressure dropping to about 20-psi atmospheric pressures. As would be expected, when Grease A was exposed to ASTM D942 oxidation conditions at an elevated temperature of 130° C. for the 100-hour period, the rate of oxidation was significantly faster as shown in FIG. 2. The fact that there was more Oxygen left after the pressure reached equilibrium suggested that the oxidation at the higher temperature was more efficient.

[0031] In contrast, as also shown in the Table, Grease B, another bio-based soy grease with an aluminium-additive thickener, and Grease C, a biodegradable synthetic ester grease with a lithium-additive thickener, were both found to be highly resistant to oxidation in this standard ASTM D942 test method. FIG. 3 shows the associated pressure-loss curves.

[0032] Greases B and C were found to have similar oxidative resistance to those of Greases E and F. Greases E and F samples were both mineral-based lithium-additive thickened grease found on the market with a similarly indicated application to automotive needs.

[0033] As also shown in the Table, the oxidative resistance of the greases at an elevated temperature of 130° C. was evaluated. As indicated by the Oxygen pressure drop, the oxidation response increased from that at a lower temperature, as expected. However, the effect of the increased temperature of test was interestingly quite different among the greases, except for Grease A, which was already essentially fully oxidized at 100° C. The effect of an increase in test temperature from 100° C. to 130° C. is shown in FIG. 4. As shown, decreases in Oxygen pressure—and presumably concomitant increases in the degree of grease oxidation—range from 13.8 psi for Grease B to 83.4 psi for Grease C for the five greases tested at both temperatures. The two mineral oil-based greases, Greases E and F, show Oxygen pressure changes of 71.3 psi and 35.8 psi, respectively. Such results indicate that some greases are more susceptible to temperature change than others, irrespective of base oil source. This leads to the question of the appropriate temperature of test for a grease application as well as the question of the oxidation response of a grease over a reasonable temperature range.

TABLE-US-00001 TABLE Oxidation Testing—Standard ASTM D942 and Modified ASTM D942 Testing psi Drop psi Drop (Temp. (Temp. Recommended psi Drop 99° C., 99° C., Base Operating psi Drop (Temp. 100-hour 200-hour Stock/ Temperature (Temp. 99° C., 130° C., data, data, Thickener Use Range for 100-hour test, 100-hour test, 2.5-g 2.5-g Grease Additive Grease 20-g Sample) 20-g Sample) Sample) Sample) A Bio (soy)/   0° C.-215° C. 97.0 87.9.sup.A 51.6 Not Aluminum performed B Bio (soy)/ −30° C. 149° C. 2.5 16.3  1.0 2.5 Aluminum C Synthetic ester/ −40° C.-120° C. 4.8 88.2.sup.A 2.5 4.9 Lithium D Bio (canola)/ −23° C.-188° C. Not performed 21.8  1.7 3.0 Aluminum E Mineral (Lithium −23° C.-204° C. 2.5 73.8.sup.A 2.5 2.7 Complex) F Mineral −12° C.-163° C. 5.7 41.5  1.9 3.7 (Lithium Complex) .sup.AVarying degree of melting observed

[0034] Some limitations of the ASTM D942 method include its 20-g grease sample size, and the manner of exposure of the sample to a fixed volume of Oxygen during the test. In consideration of this, the effect of using 2.5 g of grease samples in this test (a thin layer of 0.5 g of grease in each of the five dishes) for either a 100-hour or a 200-hour time was conceived and explored.

[0035] This data is also shown in the Table. For example, Grease A showed a 51.6-psi drop in Oxygen pressure when the 2.5-g sample distributed evenly in five dishes (0.5-g sample per dish) was exposed to otherwise standard ASTM D942 conditions for a 100-hour test. Considering that the 2.5-g mass of grease employed with the present methodology is only one-eighth of that used in the ASTM D942 test, and the surface areas were substantially identical, the surface area to mass ratio was enhanced eight times, and the pressure drop as a percentage of test sample mass for the 2.5-g sample (20.6 psi/gram) was considerably greater than that obtained for the 20-g sample (4.9 psi/gram). This implies a greater extent of oxidation for the 2.5-g sample versus the 20-g sample for the same exposure duration, engendered through the enhanced, increased surface area to mass ratio of the sample.

[0036] In another effort to improve the information gathered, ATR-FTIR analysis was employed. Comparison of the ATR-FTIR spectrograms of the 20-g and 2.5-g samples as in ASTM D942 tests on Grease A is shown in FIG. 5. For the 2.5-g sample, it is evident that at the wavenumbers between approximately 1700-1750 cm.sup.−1, which are associated with carbonyl oxidation products such as those of carboxylic acids, ketones, aldehydes, and so forth, there is, as would be expected, a substantial increase as a consequence of more extensive oxidation.

[0037] As a result of this test comparison of Grease A, all other greases, which were found to exhibit good Oxygen resistance under standard ASTM D942 testing over a 100-hour period but appeared more unstable at 130° C. testing, were evaluated at a 2.5-g sample size, at 99° C. for a 200-hour duration, as shown in the Table. Under these test conditions, Greases B, C, E and F were found to respond somewhat similarly to the response of Grease A. That is, they show a somewhat greater pressure drop as a percentage of sample size for the 2.5-g samples relative to the standard 20-g samples, although the pressure drop for all five greases tested is quite small.

[0038] One of the perceived limitations of the ASTM D942 test method is the time it takes to evaluate very oxidation-resistant greases. Based on information obtained from members of ASTM Work Group #51938 at a Dec. 8, 2015 Work Group Meeting of ASTM D02 Petroleum Products and Lubricants in Austin, Tex., U.S.A., several users of ASTM D942 test methodology have reported running samples for one thousand hours and longer in cases of highly Oxygen resistant greases. Based on the present findings, however, a 2.5-g test sample could dramatically reduce the time required to assess the oxidative resistance of such greases.

ADDITIONAL WORK

[0039] A new method employing a modified falex pin and vee block test unit was used to test Grease A and Grease B for wear resistance. The present methodology was employed to test a 2.5-g sample of each grease with 0.5-g in each sample dish. ATR-FTIR spectra were taken of the grease samples, Grease A at 99° C. for a 100-hour period, and Grease B at 99° C. for a 200-hour period. The spectra arc displayed in FIG. 6.

EPILOGUE

[0040] On the basis of the present discoveries, the ASTM D942 method could be extended to include other operational temperatures and a different test sample size, or a completely new method for assessing the oxidative resistance of a grease should be considered employing essential feature(s) hereof. Simple elevation of the test temperature resulted in accelerating the rate of oxidation, thus reducing one of the drawbacks of the ASTM D942 test method—testing duration—but depending upon the oxidative resistance the 20-g sample, it still may not fully oxidize in a reasonable test time owing to the fixed volume of Oxygen-to-sample ratio. On the other hand, reducing the test sample size and maintaining the same fixed volume of Oxygen, while heating at 99° C. as per ASTM D942, or at an elevated temperature, would reduce the overall test duration and provide greater insight into the oxidative stability of highly oxidative resistance grease formulations. The reduction in both sample size and test time would be beneficial in assessment of new additives and new grease formulations.

[0041] Thus, there is presented a significant new area of discovery or invention based on a fundamental experimental findings, i.e., the finding that a smaller grease sample, for example, a 2.5-g sample distributed equally into five test dishes and spread evenly and completely therein, oxidizes efficiently to a more complete extent in the Quantum® instrument with an ASTM D942 method, modified according to considerations of the smaller sample size, than a 20-g sample oxidizes per the standard ASTM D942 test method; and the finding that changing temperature from the 99° C. standard used in the ASTM D942 method can be beneficial and provide useful insight. Compare with the parent, noting the grease testing per ASTM D942 with the metal sleeve insert and the rack to hold the five glass dishes.

CONCLUSION TO THE INVENTION

[0042] The present invention is thus provided. Various feature(s), part(s), step(s), subcombination(s) and/or combination(s) can be employed with or without reference to or order of other feature(s), part(s), step(s), subcombination(s) and/or combination(s) in the practice of the invention, and numerous and sundry adaptations can be effected within its spirit, the literal claim scope of which is particularly pointed out by the following claims: