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Application of disc machines for testing the shock loading capability of hypoid and industrial gear oils
Application of disc machines for testing the shock loading capability of hypoid and industrial gear oils V. K. Jain, V.P. Sharma*
and A. Sethuramiah+
Hypoid rear axle oils are normally evaluated for performance on full-scale test benches under shock loading and high torque low-speed conditions. Shock load tests have rather poor repeatability and are expensive and time consuming. The present work describes a method to rate the relative shock load capabilities of reference oils and commercial additive systems on the Amsler disc machine. The technique effectively distinguishes the relative shock loading tendency as a function of additive concentration. The same technique is also useful in predicting the present day requirement of industrial gear oils with regard to their shock loading capability. Keywords:
oil performance
testing, shock loading capability
Automotive gear lubricants which meet the specification requirements of MIL-L-2105B are expected to continue for some time at the present level of performance. The specification prescribes L-42 high-speed shock load rear axle’ and L-37 high torque low-speed rear axle tests2. Experience with the L-42 test3 has indicated the need for improvements in test repeatability and differentiation. In order to eliminate the effect of some variables, a simpler method4 known as the variable severity scoring test (VSST) was developed. Besides this, various other laboratories576 are also working on different axles. The major difficulties with these tests are the procurement of required axles and quality control of materials as large variations have been observed between batches of test gears. Secondly, these tests are not capable of differentiating the entire range of RGO reference oils. Recently, Seitzinger’,’ reported successful differentiation of RGO oils by a modified FZG procedure, but again this test method is not capable of differentiating the entire range of RGO oils. It is, therefore, desirable to develop a simple test method in order to eliminate the many variables and overcome the difficulties. Recently, the authors’ laboratory ‘-12 had made a successful attempt to differentiate the entire range of RGO reference oils as a function of scuffing load under intermittent loading conditions with the Amsler disc machine. However, this method failed to match the performance of the current additives used by various oil companies at their recommended concentrations with that of RGO-110 oil. On the other hand, these additives attained the level of RGO-110 at higher concentrations. The additives recommended to meet the RGO-105 level performance at the recommended percentage, however, matched well. Furthermore, it was suggested that the scuff load level of 40 kg”>‘* for RGO-105 oil is to be improved. In order to meet these requirements, modification of the simpler test method was undertaken. This paper describes the complete study undertaken on the modified test condition with RGO oils and commercial additives. *Indian Institute of Petroleum, Dehradun 248005,
India.
findustrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMEC), Indian Institute of Technology, New Delhi-l 10016, India
92
0301-679X/86/010092-0.5
$03.00
0 1986
Experimental
details
Equipment
An Amsler type A 135 disc described elsewhere’?” was used The lower EN 3 1 steel disc was 40 mm in diameter and the upper disc was 35 mm in diameter. Both the discs were 10 mm wide and form the test pair. The tests were conducted under opposite peripheral velocities at a relative sliding velocity of 74.9 cm/s and oil temperature of 135 f 5°C. Normal load was applied by tension from a spring and intermittent loading between test discs was achieved by an eccentric wheel that rotates by means of a worm gear provided in the machine. The displacement between loading and unloading of testpieces was adjusted in such a way that the discs were loaded for one-third of a revolution of the eccentric wheel in each revolution. The arrangement results in a loading cycle of 4 revolutions per 12 revolutions of the lower disc. Surface
preparation
The test discs, hardness 62 f 1 Rc, were ground on the machine itself by emery paper and kerosene in order to achieve proper conformity at a load of 10 kg and rotational speed of 60 r/min. This procedure ensures proper surface roughness and adjustment (0.6 f 0.05 pm CLA). Each pair of discs was numbered and thoroughly cleaned in benzene.
Materials
used
Table 1 shows reference oils and additives at the recommended concentration to meet MIL-L-2105 and MIL-L2105B specifications. For making blends with commercial additives, RGO-100 was used as the base oil. Test procedure The discs are mounted in such a way that they can be offset between 1-3 mm as required. The lower disc was partially dipped in the lubricant bath (capacity 100 ml) maintained at a temperature of 135 f 5°C and carries the lubricant into the contact zone. The discs were first run-in at a load of 10 kg and sliding speed of 74.9 cm/s. A series of tests were conducted at different run-in times, ranging from 15 to 60 min. Also different offsets were given for obtaining
Butterworth
&Co (Publishers)
Ltd
April
86 Vol 19 No 2
Jain et al - shock loading capability of hypoid and industrial gear oils Table 1 Samples used in testing Sample number
Sample
Properties
1 2
RGO-100 oil RGO-100 oil
3
Additive A
4
Additive B
5
Additive C
SAE-90 grade base oil SAE-90 base oil containing 10% additive by weight Commercial additive recommended at 6.5% weight to meet MI L - L - 2 1 0 5 B , at 3.5% weight to meet M I L - L-2105 Commercial additive meeting 2105B specification at 6.5% weight, at 3.5% weight to meet 2105 specification Commercial additive meeting 2105B specification at 7% weight, at 3.5% to meet 2105 specification Commercial additive meeting 2105B specification at 7.5% weight, at 3.5% to meet 2105 specification Commercial additive meeting 2105 specification at 5% weight Reference oil meeting M I L - L - 2 1 0 5 specification Reference oil meeting M I L - L - 2 1 0 5 B specification
6
Additive D
7
Additive E
8
RGO-105 oil
9
RGO-110 oil
variation in pressure. It has been observed that the R G O 110 oil did not fail within the load capacity of the machine with zero offset position of the disc, while the large offset resulted in lower scuffing values and less differentiation. For good differentiation between RGO-100 to RGO-110 level oils, various combinations of offsets and run-in times were tried and it was observed that a condition of 2.25 mm offset of discs and 30 rain run-in time at 10 kg load offer the best solution for the test requirements. During the course of these trials, it was observed that both high run-in load and time improved the scuffing values significantly. At given conditions, a load of 20 kg was applied under a loading-unloading cycle. If no visible scoring of the discs was observed, a new pair of run-in discs was subjected to a 40 kg load in a similar manner. Subsequent tests were conducted in steps of 20 kg until failure occurred. For more accurate observation of scuffing, a 10 kg step can be used. The test duration of each loading was 1 rain. The load at which the scuffing occurs was referred to as scuffing load for characterization of lubricants.
(5)
Run the lower disc at 200 r/min under double sliding conditions in order to obtain a sliding speed of 74.9 cm/s. (6) Run-in the discs at 10 kg load with test oil for 30 min. (7) Adjust the machine for loading-unloading cycle as previously described. (8) Adjust load to 20 kg. (9) Start the machine and observe whether scuffing occurs within one minute. (10) Subsequently increase the load in steps of 20 kg/10 kg as per requirement by employing a new pair of run-in discs during each load stage until scuffing is observed. (11) Duplicate test results should not differ by more than a value of + 10 kg. If more, a third test is required. Test results and discussion Evaluation o f c o m m e r c i a l additives and reference oils Reference off RGO-105 was prepared by blending R G O 103 and R G O - I l 0 oils in suitable proportion by weight. Reference oils RGO-105 and RGO-110 are expected to meet M I L - L - 2 1 0 5 and M I L - L - 2 1 0 5 B specifications respectively and have shown a scuffing load of 60 and 180 kg by the proposed method. Hence, there is a clear differentiation between two specifications with very good repeatability. Reference oils above the RGO-110 level could not be evaluated within the toad capacity of the machine.
The utility of the technique was judged further by differentiating RGO-108 and RGO-110 oils, which is one of the general requirements for differentiation. These oils show a scuffing load of 130 and 180 kg, respectively, which can be considered a good differentiation. Commercial additives A, B, C and D were blended into RGO-100 base oil at the recommended percentage to meet M I L - L - 2 1 0 5 B specification (Table 1). As shown in Fig 1, additives C and D fail at 120 kg, whereas additives A and B fail at loads of 150 and 140 kg respectively, at a concentration of 6.5 %. None of them, however, match the performance level of RGO-110. It is interesting to observe that additives C and D tend to match the RGO-108 level oil (130 kg), while A at 150 kg and B at 140 kg proved to be higher than the RGO-108 level oils. However, the manufacturer of these additives, observes that additives C and D
The steps in the final test method adopted are: (1) (2) (3) (4)
Grind the discs properly on the machine at 60 r/rain, 10 kg load and number them. Clean the discs with benzene and allow them to air dry. Mount the discs in their respective shafts in such a way that they are offset by 2.25 mm. Heat 100 ml test oil to a temperature of 135°C and maintain within + 5°C.
TR I BO LOGY international
- L - 2 1 0 5 level
~
03
MIL
- L - 2105B
level
180 160
140 o ~=
Description o f f i n a l test m e t h o d
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120 100
80 60 40 20
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Fig l Commercial additives and reference oils for MIL L 2105 and 2105B specification
93
Jain et al - shock loading capability of hypoid and industrial gear oils
Add - B Add - A v'
180
/ /
160
Z DBDS
x J
140
/
x /
120 ,-
•
/ O
100
-
/
E / 80-
/
/
/
///
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/
f
/
/
Add - C
/
/
f
P
/
/ /
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i
/ t
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7'
Add - D
f
mC~/J
/
Add - E
/'2 X
/
//
60-
/
//
,"
40 ....
-Zk TCP
ZnDP
0
1
2
3
I 4
1 5
I 6
I 7
I 8
I 9
I 10
Concentration, %
Fig 2 Scuffing level as function of additive concentration are inferior to additive B with regard to shock loading tendency so that differentiation within the 2105B level is not altogether satisfactory. On the other hand, additives A, B, C, D and E, which meet the M1L L - 2 1 0 5 level oils at the recommended percentage, fail at around a load of 60 kg and match the performance level of R G O - 1 0 5 oil. Therefore, there is no doubt that the technique is capable of differentiating between M I L - L - 2 1 0 5 and M I L L 2105B level oils very well. E f f e c t o f additive c o n c e n t r a t i o n
the effect of additive concentration beyond 6.5% is not pronounced but below this, it is very effective. Additives A and B, which are current versions being used in automative gear lubricants, have shown better performance than others. Additive A seems to be better than B beyond a level of 6.5% but both additives differ markedly in their action although the scuff load level at the recommended concentration, ie 6.5% is more or less the same. However, the performance of additive A matches that of R G O - 1 1 0 at a concentration of 7.8% instead of the recommended 6.5%, while additive B produces a match at 9.5%.
The i m p o r t a n c e o f the technique was f u r t h e r v e r i f i e d b y
studying the scuff load level at various additive concentrations. The re'sults are plotted in Fig 2 and it is interesting to observe that these additives differ markedly from each other with respect to their action as a function of concentration. For example, additive E matches the M 1 L - L - 2 1 0 5 level oils at 5% and its concentration effect beyond 5% is less than the other oils. At 1% concentration, the scuff load value is 20 kg, the minimum load level of this method. It is, therefore, felt that additive E has the capability to improve shock loading tendency but only up to the level of R G O 105 oil. With increasing concentration the scuffing load of additive C appears to be unchanged beyond a level of 7.5%, at which the scuff level is 140 kg. Similarly, with additive D,
94
S t u d y o f DBDS and ZnDP Dibenzyl disulphide (DBDS) which is known to be good as an antiseizure additive and is used in many gear lubricant formulations was evaluated at different concentrations. As expected, the scuff load improves significantly with increasing concentration, while ZnDP has shown little or no effect on scuffing load. Similarly, other phosphate compounds, such as TCP, show the same effect. It can be said that phosphorous compounds do not perform well as antiscuff additives, while sulphur compounds have good antiseizure properties.
A p r i l 86 V o l 19 No 2
Jain et al - shock loading capability o f h y p o i d and industrial gear oils
Discussion The problem with existing rear axle tests is the differentiation ability of the entire range of RGO oils from R G O - 1 0 0 to R G O - 1 1 0 with a single set of test conditions. Different rear axles are required to study the range of RGO oils but, besides this, axle tests are expensive. As a result, it is difficult to know the actual level of additive performance relative to others. The main object of this work was to modify the test conditions of an earlier method H for better differentiation, while maintaining a single set of conditions. This would enable grading of the additive system on individual merit and would facilitate the selection of a proper additive system not only for automotive gear oils but for industrial gear oils also. In the earlier method the scuff level of 40 kg with R G O 105 was too small for differentiation amongst oils having a performance level below that of R G O - 1 0 5 . This range could be useful for determining the shock loading tendency of industrial types of gear lubricants, an important requirement for current lubricants in many applications where shock load operations are involved. Hence, there is a need to rationalize the test method in order to grade the additive system with respect to shock loading tendency. The proposed modified test method for evaluating hypoid gear oils under l o a d i n g - u n l o a d i n g conditions at a sliding speed of 74.9 cm/s and temperature of 135 + 5°C differentiates the RGO oils from R G O - 1 0 1 to R G O - 1 1 0 on the basis of scuffing load which varied from 20 to 180 kg. The R G O - 1 0 5 oil scuffed at a load of 60 kg. However, the range below this level is sufficient to determine the relative behaviour required for industrial gear lubricants. As a result, even R G O - 1 0 1 which scuffed at a load of 20 kg, could be evaluated. With various commercial additives the scuffing load differs significantly with concentration. Interesting trends were observed with the plot of scuff load level against concentration. The scuffing values are not improved noticeably beyond a particular concentration with additives C, D and E, although the scuffing values are different. Additive B, very widely used today, seems to be more active beyond a level of 3.5% and its effectiveness decreases in this test above 6.5% concentration. The scuffing load of additive A increases linearly from 1 to 7.5% concentration. Beyond this concentration no other studies were carried out. Sulphur compounds like DBDS seem to be effective in improving antiscuffing properties while phosphorous compounds like ZnDP have little or no influence on it. The interesting feature of this technique is its ability to differentiate the entire range of RGO oil series and commercial additives with one set of conditions not available with other test benches. The analysis of results in terms of application of the test method shows that the method is useful in evaluating the hypoid gear oils matching R G O - 1 0 5 or M I L - L - 2 1 0 5 performance levels. Regarding the use of this method as a substitute for shock loading tendency test as per L ~ 2 test specified in the M I L - L - 2 1 0 5 B specification, a compromise approach is needed. This is due to the fact that the current additives A and B did not match exactly the performance level with R G O - 1 1 0 at the recommended dosage of 6.5%. However, they meet at concentrations of 7 . 5 - 7 . 8 and 9.5% respectively. The efficiency of additives A and B at 6.5% is little higher than the R G O - 108 oil and well below the level of R G O - 1 1 0 . However, the difference between R G O - 1 0 8 and R G O - 1 1 0 is not large in the rear axle test. As such, it can be assumed that one
TRIBOLOGY international
may get a reasonable idea about the performance of oils in the absence of the rear axle test. Based on current additive performance at 6.5% by this procedure, a scuff load of 140 kg can be considered safe, to avoid the danger of premature failure. The technique can be used as an effective simple screening technique in additive development programmes. AlsQ in the absence of rear axle tests the prescribed seizure load provides a good alternative to specify performance. Further, the technique differentiates well between R G O - 1 0 1 and R G O - 1 0 5 oils which can be considered a requirement for shock loading tendency o f industrial type gear lubricants. In spite of reasonable correlation and the utility of the method, no clear scientific reasoning for correlation could be advanced, as the conditions between the two methods vary so widely. Basically, the method tests the ability of the ep lubricant to react fast enough at the new fresh metal contacts being generated when a sudden load is applied, thus protecting the surface from scuffing. This is directionally at least similar to what happens in a shock load test.
Conclusions (1) A laboratory test method has been developed on a disc machine to evaluate the shock loading tendency of gear oils. (2) The technique is useful for evaluating hypoid gear oils and can be used as a substitute for the L - 1 9 test specified in the M I L - L - 2 1 0 5 specification. A load of 60 kg can be considered for this level. (3) In the absence of L - 4 2 test facilities specified in the M I L - L - 2 1 0 5 B specification, the technique is useful for predicting the performance level of oils equivalent to RGO 110 oil and a minimum load of 140 kg may be considered for this level. (4) The technique is also useful for predicting the shock loading behaviour of oils required for industrial gear oils. This may be included in the specification of industrial gear oils as a means of evaluating the shock loading tendency of industrial gear oil, which is becoming important for today's lubricants.
Acknowledgements The authors are grateful to Dr I.B. Gulati, Director, Indian Institute of Petroleum, for permission to publish this work.
References 1 2
CRCRep. No. 330, April 1958 CRCRep. No. 308, February 1957
3
White R.B. Automotive gear lubricant test method development, Proc. Symp., 1P, Switzerland, April 1973 Schenk A.E., Powell D.L. and Barton H.R. Development of variable-severity scoring test for hypoid gear lubricants, SAE pap. 720152, January 1972, 10-74 Morris P.R. A progress report on the development of a high torque test procedure using a modern axle system, Proc. Syrup., IP, Switzerland, April 1973 Morris P.R. Development of a high speed shock test rig for the qualification of gear oils to ministry of defence specification of CS 3000 B, Proc. Symp., 1P, Switzerland, April 1973 Seitzinger K. Limitations and possibihties of the FZG gear testing of hypoid gear oils, Schmiertechnik und Tribologie, 19(1) February 1972, 22-29 Seitzinger K. Limitation and possibilities of application of the FZG gear test rig, particularly for the testing of hypoid gear oils, Schmiertechnik und Tribologie, October 1972, 19(5), 145-148
95
Jain et al - shock loading capability o f h y p o i d and industrial gear oils 9
Sethuramiah A. and Jain V.K. Evaluation of rear axle EP lubricant by a disc machine, Wear, 52, 1979, 4 9 - 5 6
10
Jain V.K. and Sethuramiah A. Detailed investigation of hypoid gear oils by a disc machine, Proc. Nat. Conf. lnd. Trib., DelhL
1979
96
11
Jain V.K., Sharma V.P. and Sethuramiah A. Evaluation of rear axle extreme pressure (EP) lubricants by a disc machine, CEC
lnt. Symp., Rome, June 1981 12
Jain V.K. Investigation of hypoid gear oils by disc machine,
Tribology Year Book, Springer- Verlag, Berlin, 1981
April 86 Vol 19 No 2
and A. Sethuramiah+
Hypoid rear axle oils are normally evaluated for performance on full-scale test benches under shock loading and high torque low-speed conditions. Shock load tests have rather poor repeatability and are expensive and time consuming. The present work describes a method to rate the relative shock load capabilities of reference oils and commercial additive systems on the Amsler disc machine. The technique effectively distinguishes the relative shock loading tendency as a function of additive concentration. The same technique is also useful in predicting the present day requirement of industrial gear oils with regard to their shock loading capability. Keywords:
oil performance
testing, shock loading capability
Automotive gear lubricants which meet the specification requirements of MIL-L-2105B are expected to continue for some time at the present level of performance. The specification prescribes L-42 high-speed shock load rear axle’ and L-37 high torque low-speed rear axle tests2. Experience with the L-42 test3 has indicated the need for improvements in test repeatability and differentiation. In order to eliminate the effect of some variables, a simpler method4 known as the variable severity scoring test (VSST) was developed. Besides this, various other laboratories576 are also working on different axles. The major difficulties with these tests are the procurement of required axles and quality control of materials as large variations have been observed between batches of test gears. Secondly, these tests are not capable of differentiating the entire range of RGO reference oils. Recently, Seitzinger’,’ reported successful differentiation of RGO oils by a modified FZG procedure, but again this test method is not capable of differentiating the entire range of RGO oils. It is, therefore, desirable to develop a simple test method in order to eliminate the many variables and overcome the difficulties. Recently, the authors’ laboratory ‘-12 had made a successful attempt to differentiate the entire range of RGO reference oils as a function of scuffing load under intermittent loading conditions with the Amsler disc machine. However, this method failed to match the performance of the current additives used by various oil companies at their recommended concentrations with that of RGO-110 oil. On the other hand, these additives attained the level of RGO-110 at higher concentrations. The additives recommended to meet the RGO-105 level performance at the recommended percentage, however, matched well. Furthermore, it was suggested that the scuff load level of 40 kg”>‘* for RGO-105 oil is to be improved. In order to meet these requirements, modification of the simpler test method was undertaken. This paper describes the complete study undertaken on the modified test condition with RGO oils and commercial additives. *Indian Institute of Petroleum, Dehradun 248005,
India.
findustrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMEC), Indian Institute of Technology, New Delhi-l 10016, India
92
0301-679X/86/010092-0.5
$03.00
0 1986
Experimental
details
Equipment
An Amsler type A 135 disc described elsewhere’?” was used The lower EN 3 1 steel disc was 40 mm in diameter and the upper disc was 35 mm in diameter. Both the discs were 10 mm wide and form the test pair. The tests were conducted under opposite peripheral velocities at a relative sliding velocity of 74.9 cm/s and oil temperature of 135 f 5°C. Normal load was applied by tension from a spring and intermittent loading between test discs was achieved by an eccentric wheel that rotates by means of a worm gear provided in the machine. The displacement between loading and unloading of testpieces was adjusted in such a way that the discs were loaded for one-third of a revolution of the eccentric wheel in each revolution. The arrangement results in a loading cycle of 4 revolutions per 12 revolutions of the lower disc. Surface
preparation
The test discs, hardness 62 f 1 Rc, were ground on the machine itself by emery paper and kerosene in order to achieve proper conformity at a load of 10 kg and rotational speed of 60 r/min. This procedure ensures proper surface roughness and adjustment (0.6 f 0.05 pm CLA). Each pair of discs was numbered and thoroughly cleaned in benzene.
Materials
used
Table 1 shows reference oils and additives at the recommended concentration to meet MIL-L-2105 and MIL-L2105B specifications. For making blends with commercial additives, RGO-100 was used as the base oil. Test procedure The discs are mounted in such a way that they can be offset between 1-3 mm as required. The lower disc was partially dipped in the lubricant bath (capacity 100 ml) maintained at a temperature of 135 f 5°C and carries the lubricant into the contact zone. The discs were first run-in at a load of 10 kg and sliding speed of 74.9 cm/s. A series of tests were conducted at different run-in times, ranging from 15 to 60 min. Also different offsets were given for obtaining
Butterworth
&Co (Publishers)
Ltd
April
86 Vol 19 No 2
Jain et al - shock loading capability of hypoid and industrial gear oils Table 1 Samples used in testing Sample number
Sample
Properties
1 2
RGO-100 oil RGO-100 oil
3
Additive A
4
Additive B
5
Additive C
SAE-90 grade base oil SAE-90 base oil containing 10% additive by weight Commercial additive recommended at 6.5% weight to meet MI L - L - 2 1 0 5 B , at 3.5% weight to meet M I L - L-2105 Commercial additive meeting 2105B specification at 6.5% weight, at 3.5% weight to meet 2105 specification Commercial additive meeting 2105B specification at 7% weight, at 3.5% to meet 2105 specification Commercial additive meeting 2105B specification at 7.5% weight, at 3.5% to meet 2105 specification Commercial additive meeting 2105 specification at 5% weight Reference oil meeting M I L - L - 2 1 0 5 specification Reference oil meeting M I L - L - 2 1 0 5 B specification
6
Additive D
7
Additive E
8
RGO-105 oil
9
RGO-110 oil
variation in pressure. It has been observed that the R G O 110 oil did not fail within the load capacity of the machine with zero offset position of the disc, while the large offset resulted in lower scuffing values and less differentiation. For good differentiation between RGO-100 to RGO-110 level oils, various combinations of offsets and run-in times were tried and it was observed that a condition of 2.25 mm offset of discs and 30 rain run-in time at 10 kg load offer the best solution for the test requirements. During the course of these trials, it was observed that both high run-in load and time improved the scuffing values significantly. At given conditions, a load of 20 kg was applied under a loading-unloading cycle. If no visible scoring of the discs was observed, a new pair of run-in discs was subjected to a 40 kg load in a similar manner. Subsequent tests were conducted in steps of 20 kg until failure occurred. For more accurate observation of scuffing, a 10 kg step can be used. The test duration of each loading was 1 rain. The load at which the scuffing occurs was referred to as scuffing load for characterization of lubricants.
(5)
Run the lower disc at 200 r/min under double sliding conditions in order to obtain a sliding speed of 74.9 cm/s. (6) Run-in the discs at 10 kg load with test oil for 30 min. (7) Adjust the machine for loading-unloading cycle as previously described. (8) Adjust load to 20 kg. (9) Start the machine and observe whether scuffing occurs within one minute. (10) Subsequently increase the load in steps of 20 kg/10 kg as per requirement by employing a new pair of run-in discs during each load stage until scuffing is observed. (11) Duplicate test results should not differ by more than a value of + 10 kg. If more, a third test is required. Test results and discussion Evaluation o f c o m m e r c i a l additives and reference oils Reference off RGO-105 was prepared by blending R G O 103 and R G O - I l 0 oils in suitable proportion by weight. Reference oils RGO-105 and RGO-110 are expected to meet M I L - L - 2 1 0 5 and M I L - L - 2 1 0 5 B specifications respectively and have shown a scuffing load of 60 and 180 kg by the proposed method. Hence, there is a clear differentiation between two specifications with very good repeatability. Reference oils above the RGO-110 level could not be evaluated within the toad capacity of the machine.
The utility of the technique was judged further by differentiating RGO-108 and RGO-110 oils, which is one of the general requirements for differentiation. These oils show a scuffing load of 130 and 180 kg, respectively, which can be considered a good differentiation. Commercial additives A, B, C and D were blended into RGO-100 base oil at the recommended percentage to meet M I L - L - 2 1 0 5 B specification (Table 1). As shown in Fig 1, additives C and D fail at 120 kg, whereas additives A and B fail at loads of 150 and 140 kg respectively, at a concentration of 6.5 %. None of them, however, match the performance level of RGO-110. It is interesting to observe that additives C and D tend to match the RGO-108 level oil (130 kg), while A at 150 kg and B at 140 kg proved to be higher than the RGO-108 level oils. However, the manufacturer of these additives, observes that additives C and D
The steps in the final test method adopted are: (1) (2) (3) (4)
Grind the discs properly on the machine at 60 r/rain, 10 kg load and number them. Clean the discs with benzene and allow them to air dry. Mount the discs in their respective shafts in such a way that they are offset by 2.25 mm. Heat 100 ml test oil to a temperature of 135°C and maintain within + 5°C.
TR I BO LOGY international
- L - 2 1 0 5 level
~
03
MIL
- L - 2105B
level
180 160
140 o ~=
Description o f f i n a l test m e t h o d
MIL
200
~,
120 100
80 60 40 20
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.-
O
'
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Fig l Commercial additives and reference oils for MIL L 2105 and 2105B specification
93
Jain et al - shock loading capability of hypoid and industrial gear oils
Add - B Add - A v'
180
/ /
160
Z DBDS
x J
140
/
x /
120 ,-
•
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100
-
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E / 80-
/
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-Zk TCP
ZnDP
0
1
2
3
I 4
1 5
I 6
I 7
I 8
I 9
I 10
Concentration, %
Fig 2 Scuffing level as function of additive concentration are inferior to additive B with regard to shock loading tendency so that differentiation within the 2105B level is not altogether satisfactory. On the other hand, additives A, B, C, D and E, which meet the M1L L - 2 1 0 5 level oils at the recommended percentage, fail at around a load of 60 kg and match the performance level of R G O - 1 0 5 oil. Therefore, there is no doubt that the technique is capable of differentiating between M I L - L - 2 1 0 5 and M I L L 2105B level oils very well. E f f e c t o f additive c o n c e n t r a t i o n
the effect of additive concentration beyond 6.5% is not pronounced but below this, it is very effective. Additives A and B, which are current versions being used in automative gear lubricants, have shown better performance than others. Additive A seems to be better than B beyond a level of 6.5% but both additives differ markedly in their action although the scuff load level at the recommended concentration, ie 6.5% is more or less the same. However, the performance of additive A matches that of R G O - 1 1 0 at a concentration of 7.8% instead of the recommended 6.5%, while additive B produces a match at 9.5%.
The i m p o r t a n c e o f the technique was f u r t h e r v e r i f i e d b y
studying the scuff load level at various additive concentrations. The re'sults are plotted in Fig 2 and it is interesting to observe that these additives differ markedly from each other with respect to their action as a function of concentration. For example, additive E matches the M 1 L - L - 2 1 0 5 level oils at 5% and its concentration effect beyond 5% is less than the other oils. At 1% concentration, the scuff load value is 20 kg, the minimum load level of this method. It is, therefore, felt that additive E has the capability to improve shock loading tendency but only up to the level of R G O 105 oil. With increasing concentration the scuffing load of additive C appears to be unchanged beyond a level of 7.5%, at which the scuff level is 140 kg. Similarly, with additive D,
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S t u d y o f DBDS and ZnDP Dibenzyl disulphide (DBDS) which is known to be good as an antiseizure additive and is used in many gear lubricant formulations was evaluated at different concentrations. As expected, the scuff load improves significantly with increasing concentration, while ZnDP has shown little or no effect on scuffing load. Similarly, other phosphate compounds, such as TCP, show the same effect. It can be said that phosphorous compounds do not perform well as antiscuff additives, while sulphur compounds have good antiseizure properties.
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Discussion The problem with existing rear axle tests is the differentiation ability of the entire range of RGO oils from R G O - 1 0 0 to R G O - 1 1 0 with a single set of test conditions. Different rear axles are required to study the range of RGO oils but, besides this, axle tests are expensive. As a result, it is difficult to know the actual level of additive performance relative to others. The main object of this work was to modify the test conditions of an earlier method H for better differentiation, while maintaining a single set of conditions. This would enable grading of the additive system on individual merit and would facilitate the selection of a proper additive system not only for automotive gear oils but for industrial gear oils also. In the earlier method the scuff level of 40 kg with R G O 105 was too small for differentiation amongst oils having a performance level below that of R G O - 1 0 5 . This range could be useful for determining the shock loading tendency of industrial types of gear lubricants, an important requirement for current lubricants in many applications where shock load operations are involved. Hence, there is a need to rationalize the test method in order to grade the additive system with respect to shock loading tendency. The proposed modified test method for evaluating hypoid gear oils under l o a d i n g - u n l o a d i n g conditions at a sliding speed of 74.9 cm/s and temperature of 135 + 5°C differentiates the RGO oils from R G O - 1 0 1 to R G O - 1 1 0 on the basis of scuffing load which varied from 20 to 180 kg. The R G O - 1 0 5 oil scuffed at a load of 60 kg. However, the range below this level is sufficient to determine the relative behaviour required for industrial gear lubricants. As a result, even R G O - 1 0 1 which scuffed at a load of 20 kg, could be evaluated. With various commercial additives the scuffing load differs significantly with concentration. Interesting trends were observed with the plot of scuff load level against concentration. The scuffing values are not improved noticeably beyond a particular concentration with additives C, D and E, although the scuffing values are different. Additive B, very widely used today, seems to be more active beyond a level of 3.5% and its effectiveness decreases in this test above 6.5% concentration. The scuffing load of additive A increases linearly from 1 to 7.5% concentration. Beyond this concentration no other studies were carried out. Sulphur compounds like DBDS seem to be effective in improving antiscuffing properties while phosphorous compounds like ZnDP have little or no influence on it. The interesting feature of this technique is its ability to differentiate the entire range of RGO oil series and commercial additives with one set of conditions not available with other test benches. The analysis of results in terms of application of the test method shows that the method is useful in evaluating the hypoid gear oils matching R G O - 1 0 5 or M I L - L - 2 1 0 5 performance levels. Regarding the use of this method as a substitute for shock loading tendency test as per L ~ 2 test specified in the M I L - L - 2 1 0 5 B specification, a compromise approach is needed. This is due to the fact that the current additives A and B did not match exactly the performance level with R G O - 1 1 0 at the recommended dosage of 6.5%. However, they meet at concentrations of 7 . 5 - 7 . 8 and 9.5% respectively. The efficiency of additives A and B at 6.5% is little higher than the R G O - 108 oil and well below the level of R G O - 1 1 0 . However, the difference between R G O - 1 0 8 and R G O - 1 1 0 is not large in the rear axle test. As such, it can be assumed that one
TRIBOLOGY international
may get a reasonable idea about the performance of oils in the absence of the rear axle test. Based on current additive performance at 6.5% by this procedure, a scuff load of 140 kg can be considered safe, to avoid the danger of premature failure. The technique can be used as an effective simple screening technique in additive development programmes. AlsQ in the absence of rear axle tests the prescribed seizure load provides a good alternative to specify performance. Further, the technique differentiates well between R G O - 1 0 1 and R G O - 1 0 5 oils which can be considered a requirement for shock loading tendency o f industrial type gear lubricants. In spite of reasonable correlation and the utility of the method, no clear scientific reasoning for correlation could be advanced, as the conditions between the two methods vary so widely. Basically, the method tests the ability of the ep lubricant to react fast enough at the new fresh metal contacts being generated when a sudden load is applied, thus protecting the surface from scuffing. This is directionally at least similar to what happens in a shock load test.
Conclusions (1) A laboratory test method has been developed on a disc machine to evaluate the shock loading tendency of gear oils. (2) The technique is useful for evaluating hypoid gear oils and can be used as a substitute for the L - 1 9 test specified in the M I L - L - 2 1 0 5 specification. A load of 60 kg can be considered for this level. (3) In the absence of L - 4 2 test facilities specified in the M I L - L - 2 1 0 5 B specification, the technique is useful for predicting the performance level of oils equivalent to RGO 110 oil and a minimum load of 140 kg may be considered for this level. (4) The technique is also useful for predicting the shock loading behaviour of oils required for industrial gear oils. This may be included in the specification of industrial gear oils as a means of evaluating the shock loading tendency of industrial gear oil, which is becoming important for today's lubricants.
Acknowledgements The authors are grateful to Dr I.B. Gulati, Director, Indian Institute of Petroleum, for permission to publish this work.
References 1 2
CRCRep. No. 330, April 1958 CRCRep. No. 308, February 1957
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White R.B. Automotive gear lubricant test method development, Proc. Symp., 1P, Switzerland, April 1973 Schenk A.E., Powell D.L. and Barton H.R. Development of variable-severity scoring test for hypoid gear lubricants, SAE pap. 720152, January 1972, 10-74 Morris P.R. A progress report on the development of a high torque test procedure using a modern axle system, Proc. Syrup., IP, Switzerland, April 1973 Morris P.R. Development of a high speed shock test rig for the qualification of gear oils to ministry of defence specification of CS 3000 B, Proc. Symp., 1P, Switzerland, April 1973 Seitzinger K. Limitations and possibihties of the FZG gear testing of hypoid gear oils, Schmiertechnik und Tribologie, 19(1) February 1972, 22-29 Seitzinger K. Limitation and possibilities of application of the FZG gear test rig, particularly for the testing of hypoid gear oils, Schmiertechnik und Tribologie, October 1972, 19(5), 145-148
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Sethuramiah A. and Jain V.K. Evaluation of rear axle EP lubricant by a disc machine, Wear, 52, 1979, 4 9 - 5 6
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Jain V.K. and Sethuramiah A. Detailed investigation of hypoid gear oils by a disc machine, Proc. Nat. Conf. lnd. Trib., DelhL
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Tribology Year Book, Springer- Verlag, Berlin, 1981
April 86 Vol 19 No 2