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Enhancing High Temperature Life Performance of Lithium-Complex
5. Anti-corrosion properties.
As a general rule, it is desirable to determine the corrosion and rust prevention properties of the rail curve grease to ensure the additive compositions are not causing undue rusting or corrosion on the rail surfaces.
6. Testing for conductivity
As a general rule, it is desirable to determine the electrical properties of the rail curve grease to ensure their long term use in the same location does not interfere with switching signals and other electrical systems. The following properties are proposed for consideration and possible inclusion in the specification:
7. Thin film strength - base oil
Thin film property can be tested on the base oil to be used in the manufacture of the grease. The following tests are proposed for evaluating this property:
Corrosion Preventions ASTM D1743 Standard Test Method for Determining Corrosion Preventive Properties of Lubricating Greases
Dielectric Constant and Dissipation ASTM D150 /IEC 60250 May need to be modified for grease Dielectric Breakdown Voltage and Dielectric Strength ASTM D149 Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies Volume Resistivity of Conductive ASTM D2739 Standard Test Method for Volume Resistivity of Conductive Adhesives
Falex Pin and Vee Block ASTM D3233 Standard Test Methods for Measurement of Extreme Pressure Properties of Fluid Lubricants Falex Four Ball Wear Test ASTM D4172 Standard Test Method for Wear Preventive Characteristics of Lubricating Fluid Fretting Wear Protection ASTM D4170 Standard Test Method for Fretting Wear Protection by Lubricating Greases
8. Flash and Fire Points of base oil - ASTM D92 and D93 Flash and Fire Points of base oil 9. Pour Point of base oil - ASTM D97 10. Viscosity Index of base oil - ASTM D2270 11. Other possible properties could include Spreadability, and Thermal Resistance.
Twelve commercially available mineral oil based and biobased greases were identified and acquired for testing. These greases were known to be commercially available and in use by US railroads. By performing the tests in the same laboratory, the side by side results provide an insight into the performance of these existing products. Table 1 presents the results to-date for this on-going comparative laboratory testing. The time table for this research activity requires all activities to be completed by September, 2013. A white paper will be published to report the results of the completed study in its entirety.
Table 1: test results from an on-going study of 12 greases including summer, winter, biobased and mineral based greases
Biobased 2 Winter Grease Biobased 2Summer Grease Mineral Based 2 Winter Grease Mineral Based 2 Summer Grease Mineral Based 1 Winter Grease Mineral Based 1 Summer Grease Mineral Based 1 Cold Temp Grease Mineral Based 3 Winter Grease Biobased 1 Summer Grease Biobased 1 Winter Grease Biobased 3 Winter Grease
Regular Testing Standard 12-012 12-013 12-014 12-015 12-045 12-046 12-053 12-061 12-065 12-066 12-067 12-068
Cone Penetration Unworked
Cone Penetration 60X Worked ASTM D 217
ASTM D 217
Dropping Point ASTM D 2265 290 279 316 316 323 266 303 325 317 293 325 287
294 285 332 314 305 281 297 256 314 281 318 279
303.3 274.6 212.3 200.6 205.3 204.7 260 249.17 201.34 196.33 200.67 195.98
Grease Mobility -15°C (g/ sec:g/min) US Steel 0.5 : 30.00 No Flow 0.42 : 25.41 0.39 : 23.54 0.98 : 58.65 0.212 : 12.72 0.145 : 8.68 Fail- no grease output 8.15 : 489.0 In Progress In Progress
Grease Mobility -8°C (g/ sec:g/min) Grease Mobility 0°C (g/ sec:g/min) Water Washout, 100°F
Timken Load Test US Steel 1.02 : 61.20 1.08 : 64.84 1.20 : 72.00 0.95 : 57.08 3.51 : 210.63 0.44 : 26.59 0.69 : 41.46 0.775 : 46.47 8.51: 510.6 In Progress In Progress
US Steel 6.49 : 389.40 6.67 : 400.38 6.88 : 413.02 3.11 : 187.17 8.04 : 482.16 0.82 : 49.27 2.54 : 152.54 11.23 : 673.8 16.59 : 995.4 In Progress In Progress
ASTM D1264 2.03% 1.75% 14.19% 16.90% 4.90% 28.50% 3.99% 11.23% 9.80% 0.00% 21.95% 12.20%
ASTM D 2509 40 lbs 50 lbs 40 lbs 35 lbs 45 lbs 35 lbs 45 lbs 45 lbs In Progress In Progress In Progress
Four Ball Extreme Pressure Test ASTM D 2596 400 400 400 400 400 400 400 250 500 620 500 500
Four Ball Wear D 2266 0.73 0.69 0.56 0.64 0.46 0.418 0.66 0.365 0.45 0.453 0.489 0.4053
Oil Separation D 1742 0.22% 0.16% 4.03% 7.18% 10.87% 5.16% 5.84% 7.03% In Progress 1.57% 5.06% 3.14%
Other tests including biodegradability, aquatic toxicity and terrestrial plant growth tests are in progress.
Testing in Environmental Chamber and Results
The same two OEM lubricators are also being used in an environmental chamber where the temperature of the equipment and grease is changed from about 65 °C (149 °F) down to -23 °C (-9.4 °F). The performance of the grease in the equipment at various temperatures is documented. The summer and winter versions of petroleum and biobased greases are tested. Figure 4 shows the two lubricators in the environment chamber.
The comparative tests performed in the above environmental chamber and in the field are being compared with the tests performed in the laboratory. The test involved, simulating the passing of 50 twenty-five car trains with 60 ft truck centers running at 5 mph. After each train there was a 1 minute delay before the next one starts. Also,
a. Through experimentation it was determined that the one unit (unit 1) lubricator should be set to pump for 0.35 seconds every 5 axles outputs 0.3778 pounds of grease at 100°F during one train pass using the simulator. The second unit (unit 2) was set to pump for 3.5 seconds on every axle in order to match the output of the other lubricator. The settings on this unit are such because a relay is used to simulate a wheel count every time the unit 1 pump engages. It is also determined that these settings on the unit 2 output 0.3908 lbs at the same conditions above. The output for each lubricator is similar in like conditions and is close to a desirable 0.8 pound grease per 100 wheels (figuring one bar system should be half of that).
b. After each simulation, the environmental chamber was cooled to the next lower temperature and the grease allowed to acclimate to the new temperature for a minimum of 24 hrs. The same simulation was run at each temperature. Figure 5 shows the reservoir of each lubricator before the start of the test. The grease in each reservoir was leveled and the height of the grease in the tank was recorded.
Figure 6 shows the grease dispensing bar from each manufacturer and the collection drum to collect and determine the weight of the grease after each test.
Figure 4: Environmental chamber with grease dispensing equipment from two manufacturers are used for testing petroleum based grease and biobased grease at different temperatures Figure 5: The lubricators from the two OEMs are filled with the same quantity of grease to test at the same temperatures
Figure 6: A train simulator is used to generate signals to actuate the pumps to pump grease through dispensing bars and collect the grease for weight measurement
In addition to determining the volume of grease pumped by each lubricator other visual monitoring included the shape of the grease in the reservoir and a measurement of the level of the grease at the center and at side wall of reservoir.
Field Testing and Results
Field testing begun in early February at two different sites in Cedar Rapids and in Cedar Falls, Iowa with two dispensers/lubricators at each site. One dispenser was set to pump petroleum grease to one track and the other was set to pump biobased grease to the other track. The tack in this location is almost S shape with curves on both sides of lubricator. Each site has lubricators from a different manufacturer. A petroleum grease was selected as reference because it is the most commonly known used grease by US railroads and this grease was considered reference test grease. Testing included taking tribometer readings for the measurements of friction at one mile intervals up to five miles on each side of the lubricators. The results will show how grease can handle the very cold Iowa temperatures and how far each of the test greases are carried down the track in a revenue service railroad. Figures 2 and 3 show the lubricators in the Cedar Rapids test site and Figure 3 shows the location of the wheel sensor at that site.
Figure 7: left and right: Two Lubricators from one OEM; one track receives the conventional grease and the other the biobased grease
Figure 8: Location of the wheel sensor and track (left); and site 2 two lubricators from a second OEM
The results of this testing are still pending. Due to time limitations only one set of winter greases were tested and the testing for the summer versions of those greases are just starting. The measurement of coefficient of friction is performed by using a handheld tribometer (Figure 9). The tribometer is pushed along the track and measure the coefficient of friction on the gage face of the rail. Coefficient of friction of lower than 0.3 is desirable for the gage face. Since, each track receive either the petroleum based grease or the biobased grease, the tribometer measurements are taken on both directions at different mile markers from the lubricator.
Figure 9: Handheld tribometer is used for measuring coefficient of friction
Since rain and snow impact the coefficient of friction the measurements are taken over several weeks. The following is an example of the measurement readings taken in one day of data collection. The east readings are for biobased grease and the west readings are for the mineral based grease. Mile posts (MP) are one mile apart and the measurements are repeated at each mile post over several weeks.
Figure 10: An example of a chart showing coefficient of friction reading at mile posts from the lubricator
Test of tackiness
Tackiness in rail curve grease formulation is an important and critical feature. Rail curve greases would need to have certain level of cohesiveness in order to flow into the inlet of the pump. An example of cohesiveness would be chewing gum that could be pulled into a long string. When a portion of the grease is pulled into the pump due to vacuum at its inlet, the rest of the grease should follow. Without this cohesion, especially when the grease level in the reservoir is low the pump could cavitate. At the same time the grease should have a certain level of adhesiveness so it can attach to the flange of the rail wheel and carried down to grease the gage face of the track. If the grease is too cohesive then, especially, at higher speeds of the wheel, it could stretch into a string and swing around the wheel and build up under the railcars. The adhesiveness and cohesiveness properties are often varied as the temperature changes which makes formulating a rail curve grease even more complex. The tests described above would help to determine how the grease pumps at different temperatures and in the field how far down the track it can be carried due to the adhesion to the gage face of the track.
The UNI-NABL Center has been experimenting with the use of a modified centrifuge for the purpose of comparing the adhesiveness and cohesiveness of different greases. This test method is proposed for discussion only. If the method can show a good differentiation between more and less tack and or the degree of cohesion then it can be proposed as a new standard method.
In the UNI-NABL proposed test method, a centrifuge is fitted with an 18-inch (45.72-cm) balanced aluminum disk. Grease samples are placed at different points on the radius of this disk and the disk is rotated at a given RPM for a certain period of time. An example would be to place a sample of 3 grams of grease at 4 inches (10.16 cm) from the center of the disk and runn the disk at 500 RPM for 10 seconds. The amount of grease sprayed on the walls of centrifuge can be collected and weighed. Also, the pattern of the grease on the disk can be compared with a reference grease. Table 2 illustrates the test variable as used in this study.
Table 2: Test variable including distance from the center of rotating disk, rpm and time Grease Quantity (grams) Distance from Center of Disk Grease Quantity after Test (grams) Distance from Center of Disk Grease Quantity after Test (grams) Distance from Center of Disk “ Grease Quantity after Test (grams)
2.5” 2.5” 2.5”
2.5 +/- .3 500 rpm 10 sec 750 rpm 10 sec 1000 rpm 10 sec
2.5 +/- .3 500 rpm 10 sec 750 rpm 10 sec 1000 rpm 10 sec
2.5 +/- .3 500 rpm 10 sec 750rpm 10 sec 1000 rpm 10 sec
Figure 11 shows the results of tests on the biobased 2 summer grease when the disk was run at three different speeds when the grease was placed three different distances from the center. The grease that remained on the disk after the test would indicate the degree of adhesion. Obviously, at higher speed less grease was left on the disk; and the farther away from the center (higher centrifugal force) also results in more grease spray off from the disk.
Figure 11: An example of test results for a biobased grease after 10 seconds in the centrifuge test
Figure 12 shows the results of tests for the same grease when the centrifuge was run for 20 seconds. The goal is to compile the results of these tests and identify the optimum time for performing this test. Figure 13 shows the grease patterns on the disk and the grease spray off on the inside bowl of the centrifuge. Table 3 present the numerical results of one of these tests.
Figure 12: An example of test grease samples before and after running on the centrifuge test plate
Figure 13: An example of test results for a biobased grease after 20 seconds in the centrifuge test
Figure 14: An example of grease patterns and grease spray off in the centrifuge Table 3: An example of a table with data on grease quantities after the centrifuge test RPM 500 Trial 1 Trial 2 Trial 3 Biobased 2 Grease Winter 20 Sec Average
Distance 2.5 2.693 2.708 2.658 500 RPM 2.5 in 2.686 4 2.633 2.556 2.591 500 RPM 4 in 2.593 8 0.821 0.742 0.811 500 RPM 8 in 0.791
Summary and Conclusions
Rail curve greases are complex products because the environments in which they are used are variable and demanding. The grease dispensers are placed within the elements and are expected to perform with different greases and adjust to different train speeds. With an understanding of the desired properties it is possible to formulate greases that meet a majority of performance requirements. The main objective of this study has been to compare commercial biobased and mineral based rail curve greases. The greater part of the rail curve greases used in the United States is for revenue service freight railroads employing wayside lubricant dispensers. As a result, the performance criteria selected are based on extreme pressure performance and ability to pump and carry down the track through a balanced level of adhesion and cohesion.
The selected test greases were put through an array of laboratory tests to determine their physiochemical, tribological and environmental properties. Then, a selected number of the test greases were evaluated in an environmental chamber using grease dispensers from two known original equipment manufacturers. While the grease and the equipment were exposed to varied temperatures, a train simulator was used to operate the pumps and measure the amount of grease pumped at each temperature.
Finally, one of the mineral based greases was selected as a reference grease and was tested against biobased greases in a revenue service railroad. Two lubricators from each original equipment manufacturer were placed before curves in two different sites in Iowa. One lubricator was used to grease one track with mineral based grease while the second lubricator at the same site greased the other track. Using a handheld tribometer the coefficient of friction was measured for nearly five miles at mile intervals on each side of the lubricator. The field testing is ongoing.
The results to date indicate that biobased greases perform side by side with mineral based greases at extreme hot and cold temperatures, which are typical of various geographic locations in the United States. At the end of this research project, the result of the environmental properties of these greases along with overall performances will be published as a reference for those engaged in friction management of railroad rolling stock.
Reference:
X. Lua,*, K.C. Wong b, P.C. Wong b, K.A.R. Mitchell b, J. Cotter a, D.T. Eadie (2005) “Surface characterization of polytetrafluoroethylene (PTFE) transfer films during rolling–sliding tribology tests using X-ray photoelectron spectroscopy”. Elsevier Wear publications:
http://www.ewp.rpi.edu/hartford/ users/papers/engr/ernesto/lessam/ FWM/Project/Research%20Materials/ Surface%20characterization%20 of%20polytetrafluoroethylene%20 (PTFE)%20transfer%20films%20 during%20rolling%3Fsliding%20 tribology%20tests%20using%20X-ray%20photoelectron%20 spectroscopy.pdf
Acknowledgement
The author would like to acknowledge the efforts of several individuals for performing tests in the laboratory and the field in support of this project. They include student assistants: Ashley Miles, Timothy Rusch, Greg Moklestad, Brendon Goode; consultant Mike Cook, and UNI-NABL Associate Director Wes James.
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