With above rail maintenance costs accounting for at least 40% of a rail operator’s ongoing costs, any potential efficiency must be realised and implemented. Making up at least 2/3 of these costs is wagon or car wheelsets. Maintenance strategies for wheelsets can vary from running to a wear limit (19mm flange for example) to implementing a monitoring and testing program to ensure wheel life is maximised through managing flange wear. Excessive flange wear can seriously compromise the life of a wheelset and to restore the profile during machining, for every 1mm of flange wear 2.5mm of tread material must be removed.
What Causes Accelerated Wheel Flange Wear?
The causes for accelerated flange wear that have the potential to be managed by an above rail operator are as follows:
Excessive friction and the wagon or car top centre/centre bowl interface
Poor bogie condition – for example, spring condition
Unsuitable wheel profiles that do not allow for efficient contact with the rail
Of these factors outlined the leading cause of accelerated wheel flange wear for an above rail operator could be excessive friction at the top centre/centre bowl interface as this is often overlooked and not measured.
The Impact to an Above Rail Operator
Accelerated flange wear due to excessive friction at the top centre/centre bowl interface will reduce wheelset life. Above rail operators experiencing accelerated flange wear may be unable to plan their wheelset maintenance and therefore find they are reacting to wheelset measurement data rather than be able to predict wheelset life and proactively plan maintenance around this. Typical approaches to wheelset maintenance can vary from running to the operating limit to trigger a changeout too based on data obtained from a condition monitoring program, develop an approach which balances a flange wear threshold above the operating limit. This flange wear threshold will trigger a preventative maintenance changeout. By implementing this threshold and preventative maintenance approach for flange wear the quantity of material required to restore the wheelset profile during machining will be reduced. As stated above, for every 1mm of flange wear prevented, 2.5mm of tread material is saved during machining when restoring the wheelset profile.
Running to the Operating Limit
Running a wheelset until it reaches its allowed operating limit of 19mm of wheelset flange remaining will require a significant quantity of material to be removed during machining to restore the wheelset’s profile. With the wheelset wearing approximately 9mm of its flange to reach the condemning limit, approximately 23mm of tread will have to be removed to restore the profile, effectively halving the life of the wheelset. The figure below shows a thin flange in comparison with the new profile and provides an indication as to how much wheelset material will have to be removed to restore this profile should wheelsets reach flange wear operating limits prior to any preventative wheelset maintenance.
Implementing a Managed Wheelset Maintenance Approach
By managing friction at the top centre/centre bowl interface and monitoring flange wear will enable above rail operators to be proactive with wheelset maintenance. Accurate predictions can be made based on historical data as to when wheelsets will reach wear limits. However, this data provides an opportunity to implement wear limits above the condemning limit and result in far less material removed to restore the original profile prolonging the life of the wheelset and reducing the wagon or car’s life cycle cost model.
How to Control Friction at the Top Centre/Centre Bowl Interface
In order to control friction at the top centre/centre bowl interface the friction must initially be known. To achieve this knowledge a bogie rotational resistance test can be conducted to measure the friction for both loaded and unloaded wagons and cars. Different combinations of friction modifiers including grease and non-metallic liners placed in the centre bowl can be tested to ensure the most sustainable solution is implemented. Following the implementation of these tests, wheel wear can be monitored to ensure the solution is providing an ongoing reduction in wheelset flange wear. A sustainable solution to manage friction at the top centre/centre bowl interface combined with a proactive maintenance strategy can prolong wheelset life by 50%. This can be achieved by reducing flange wear to 1-2mm per 100,000km of wagon or car operation.
The Bogie Rotational Resistance Test
Some years ago Jon developed a method to measure friction at the top centre/centre bowl interface that is efficient, can be carried out within any maintenance facility with slab track and is independent of the wagon or car body. The test method is simple and can be carried out quickly enough to test every wagon or car at each maintenance interval without adding any time to the current maintenance duration.
This controlled test will reveal the friction at the top centre/centre bowl interface and enable above rail operators to make informed decisions as to the sustainable solution to be implemented to ensure maximum wheelset life through reduced flange wear.