A study to determine the effect of sand contamination on the wear protection properties of ClareTech EcoCurve Heavy Haul Flange Lubricant, and how this compares to using no lubricant at all.
In dry desert areas of the world, such as the Pilbara region of Australia and large parts of the Middle East, sand ingress onto the rails is a significant issue. Sand is blown onto the track by the wind, as well as by the air turbulence caused by the moving train, causing abrasive particles to get into the flange-wheel contact, increasing wear to the wheel and the rail.
Flange lubricants are often used on curved rails to reduce the noise, wear and the friction of the flange-wheel contact. The use of these lubricants improves efficiency and prolongs the lifetime of the wheels and the rails. It is sometimes assumed that by using a grease based flange lubricant in desert regions, the sand would become embedded in the tacky grease, increasing the volume of sand within the contact causing a greater amount of wear. The mixing of the sand and the grease would form an abrasive paste which is thought to grind the wheels and remain on the wheel for longer than if no lubricant was used.
This assumption however has not been proven. One report suggests that the use of a wayside gauge face lubricant containing a solid lubricant (such as Molybdenum disulphide) would reduce the wear on the wheels1. ClareTech EcoCurve Heavy Haul is an environmentally sensitive flange lubricant, containing a molybdenum-based friction modifier, which is used for reducing the wear in highly loaded rail applications in several locations around the world.
This study was run to determine the effect of sand contamination on the wear protection properties of ClareTech EcoCurve Heavy Haul flange lubricant.
Results and discussion
4-Ball Wear Scar
A 4-ball tester consists of 3 stationary balls at the base with a ball on top loaded with a known mass, as illustrated in Figure 1. The test pot is packed with grease covering the 3 areas of contact. The top ball is then rotated at a known speed for up to 1 hour. The balls are removed and cleaned before the wear scar diameter (WSD) of the 3 lower balls are measured and the average results are recorded.
These tests were run according to IP239. The 4-ball wear test was run at 1440 RPM with a load of 40kgf for up to 1 hour. The wear scars on the 3 stationary balls are measured and the average wear scar diameter is recorded.
This test represents the ability of a grease to protect the contact from wear and damage, such as those experienced over time on a wheel flange and the rail, which will eventually require the wheel and the rail to be replaced or reprofiled. The lower the wear scar diameter measured, the greater the level of protection provided to the surface.
When applied by the GDU (grease dispensing unit) the grease may be externally covered with sand blown in the wind or from the updraft caused by air turbulence of a passing train. The sand blown onto the tracks is thought to have a particle size of <300 μm to be light enough to be carried by turbulent air. The sand will stick onto the grease getting more and more concentrated over time as shown in Figure 2. The saturation of the thin layer of grease was found to be around 80wt% sand (4:1 sand to grease ratio) where no more sand could stick to the plate.
These ratios of different grease coverages were mixed together and are shown in Figure 3. At up to 50% sand concentration (1:1 sand to grease) the mixture still seemed tacky and grease-like but at 80% (sand saturation) the mixture had the consistency of a solid paste.
ClareTech EcoCurve Heavy Haul
ClareTech EcoCurve Heavy Haul with 20% sand
ClareTech EcoCurve Heavy Haul with 50% sand
ClareTech EcoCurve Heavy Haul with 80% sand
These greases were tested in the 4-ball tester comparing the results to that of a dry contact with residual sand present, with the results shown in Table 2. Surprisingly, the unlubricated contact with sand lasted longer than without sand. This is thought to be due to the contaminant acting as a third body within the contact reducing adhesive wear. After 150 seconds, loud squealing was heard indicating test failure. As expected, the results for the greased contact contaminated with sand show a significant increase in wear scar diameter compared to without sand, with the contaminant acting as an abrasive particle within the grease. For comparable results, the sand contaminated greases were tested for 150 seconds, despite the test being able to successfully run for at least 5 minutes without failing.
The greased samples all showed a smaller wear scar diameter compared to the dry sample, showing the grease provides better protection even when contaminated with sand. Interestingly, the WSD of 50% sand is larger than that of 80% sand. This could be caused by the solid paste assisting in carrying some of the contact load reducing the wear on the surface. This phenomenon would not be expected to be seen for a flange-rail contact.
These tests suggest that the application of ClareTech EcoCurve Heavy Haul would reduce the wear of the wheels and rails in sandy desert environments compared to not lubricating the contact at all.
Conclusions
These results suggest that the application of ClareTech EcoCurve Heavy Haul would reduce the wear of a flange-rail contact, even with the contamination from blown sand particles mixed into the grease. The grease was tested at different levels of sand contamination with all tests showing better wear protection than if no grease had been applied.
(1) Hewitt, T. Designing a Heavy Haul Desert Railway: Lessons Learned. IHHA 2015 Conf. 2015, June.
