What makes the perfect Flange Lubricant?
A high performing rail curve grease must have very distinct characteristics to ensure it meets challenging operational needs. These include extending the life of assets, reducing maintenance costs and time spent on track for corrective maintenance.
RS Clare have been formulating and developing specialist rail curve greases for over 50 years, and using this experience we have developed a list of 12 key characteristics that are essential.
1. Low coefficient of friction
The lubricant should ensure low coefficient of friction (CoF) at the wheel/rail interface, typically less than 0.15. The lower the value, the lower the friction which helps minimise wheel and rail wear.
2. Wide operating temperature
It is essential to maximise the temperature range over which a lubricant’s performance remains consistent. High-end products have a wide enough temperature range to allow a single product to be used all year round (instead of summer and winter grades) which has obvious logistical benefits and is important in environments with wide seasonal temperature variations. Consistent viscosity at extremes of temperature is essential to ensure adequate slumping within trackside applicator tanks to avoid pump cavitation and ensure consistent application on demand. Furthermore, it ensures consistent and stable beading from the applicator equipment.
3. Carry down
Generally speaking, the further a lubricant remains detectable and effective from the point of application (“carry down”), the better. From a customer’s perspective this is a key performance criteria as better carry down reduces the number of trackside dispenser systems needed along with their associated maintenance and replenishment costs, and reduces the application rate of grease required. It must be noted that this characteristic is heavily influenced by factors such as track condition, vehicle axle loading and number of axles over a given period.
4. G0od adhesion & cohesion
Adhesion in this context means the ability of the lubricant to stick to a wheel or track, not physical adhesion between rolling stock wheels and track. Cohesion refers to the ability of a lubricant to stick to itself. These are important as they relate to the amount of “splash-off” when a train initially picks up lubricant, and “fling-off” from the trains rotating wheels during the carry-down phase. Good cohesion also affects a lubricant’s elastic properties and helps minimise the amount of lubricant “squeezed” out of a contact patch under pressure, this particularly becomes a problem if the grease migrates to the top of the rail. Better Adhesion and Cohesion means more of the lubricant stays where it is needed leading to better performance, better carry down, less environmental contamination and less waste.
5. Oil Separation
A key characteristic here is stability in storage both pre-use and in dispenser tanks to minimise oil separation across the full operational and storage temperature ranges. Although a degree of oil separation is normal and essential from a performance perspective, excessive oil bleed is a problem as the grease left behind can become too thick and cause issues with pumpability and blockages in the lubricator.
6. Extreme pressure (EP & anti-wear (AW)
Good EP and AW characteristics indicated by both 4 ball weld and scar testing are essential in curved rail grease applications. Axel loads can be anything up to 40 tonnes which creates enormous pressures at the wheel/rail interface, and the grease film needs to be strong enough to prevent the metal to metal contact which then leads to increased wear and reduces track and wheel life.
7. Corrosion protection
The lubricant’s ability to offer corrosion protection to the steel rails and wheels is essential, particularly in adverse and wet conditions.
8. Wash off
A further desirable characteristic for flange lubricants is good resistance to water wash-off to ensure that the lubricant film is maintained in wet conditions over the claimed carry-down distances. It’s no use having great carry down characteristics if when it rains the grease is washed off and the rails and wheels are left unprotected.
9. Compatability
Products should be designed to be compatible with as many other rail lubricant and friction modifier technologies as possible. On some networks this is safety critical due to the risk of product “build up” neutralising track circuits and therefore train detection. In addition, the ability to replace existing Flange Grease in dispenser equipment without cleaning out the old product is a distinct advantage.
10. Consistency
Grease consistency is measured on a scale called the NLGI classification. For trackside rail curve lubricants, if the grease is too thick it can cause a problem with pumpability and cause clogging in the grease tank-pump inlet, outlets, pipes and GDU ports. If the grease is not thick enough it will not form stable beading on the GDU and will cause increased “splash-off” and “fling off”, meaning less of the grease gets to where it’ required in the contact interface between wheel and rail. A too thin grease can also increase the undesirable grease migrations to the top of the rail. Grease consistency has to match the application method, which is very different for trackside lubrication than it is for onboard lubrication.
11. Mechanical stability
The grease structure needs to be stable enough to withstand mechanical working without it breaking down and losing its consistency and other attributes.
12. Environmental factors
The fact that rail curve lubrication is a ‘total loss’ system where all the lubricant enters the environment means “Eco Credentials” are becoming increasingly important for many users. For a grease to excel in this category, it should be readily biodegradable, non bio accumulative, have low aquatic toxicity and have a large proportion of its raw materials be from renewable sources. Accreditations such as the European Ecolabel ensure that a product meets very strict environmental criteria and contributes to a network’s broader sustainability initiatives.
