Alternative twin-disc assessment of solid stick flange lubricants

Lubrication between the gauge face of rail and the wheel flange is necessary to improve vehicle performance and protect both bodies from damage, reducing maintenance costs. Wayside application of grease in particular problem locations is well established, but lubrication applied to the wheel flange by a solid stick on-board the vehicle is gaining favour. On-board solid stick lubrication can potentially provide network wide coverage, whilst also reducing maintenance costs since the vehicles regularly visit depots. This paper details the twin-disc assessment of 8 available products according to the current standard, EN16028:2012, then details a new methodology to test the products in conditions more relevant to field contact conditions. Further work included encapsulation and microscopic analysis of the third body layer; this found evidence of a product layer, but further work is required to determine its constiuents. EN16028:2012 specifies conditions for a test involving application of the product during wheel-rail specimen contact. Once a specified time has elapsed, application of the product is ceased; product performance is assessed as the time the product continues to perform (coefficient of traction remains lower than a nominal dry value) after application ceases; this figure is known as "retentivity". The new methodology assesses the product's ability to protect the wheel and rail material rather than retentivity; the test is performed in conditions more typical of flanging contact. The product is applied whilst the wheel and rail are out of contact, to allow a layer of product to build up, then the specimens are put into contact, under conditions representing 150m of continuous, heavy flange contact; this process is repeated a set number of times, to allow comparison of results. Testing to the EN16028:2012 specification showed that only three of the eight products effectively lubricated the contact (coefficient of traction < 0.15), whilst two partially lubricated the contact (COT 0.15-0.4) and three did not lower the friction below levels considered to be a dry contact (COT > 0.4). The new wear methodology was performed on two lubricating products, and a non-lubricating product; the results show all products significantly reducing wear compared to a dry control test, with the non-lubricating product performing better than one of the lubricating products. However, confidence in the results needs to be built by increasing the number of repeats. To conclude, the testing specified in EN16028:2012, shows that many of the products available on the market do not perform their functions correctly; whereas wear testing under the new methodology shows they still successful protect the wheel and rail from wear. More work is required before the new methodology can be accepted as a replacement to the standard, but the results highlighted here show that there are significant improvements that could be made to the assessment of solid stick flange lubricants.