Increasing the lifespan of rail fastening systems in sandy environments with nano-coating
Colleagues from the Islamic Republic of Iran Railways (RAI), Milad Alizadeh Galdiani, Navid Sabet and Mohamad Ali Mohit, explore how the lifespan of rail fastening systems in sandy environments can be increased by nano-coating the components, making them more resistant to the harsh operating environment.
The railway is one of the most important modes of transportation, able to pass through varying topography with ease. In many countries – such as China, United States, Australia and Iran – rail networks pass through desert areas. One of the main problems in these areas is the movement of sand causing various damage to ballasted railway track, such as corrosion to railway fastening systems. The soil composition of some desert areas, such as Fahraj in Iran, consists of sand and salt. Due to the movement of sand and the corrosive ions of salt, railway fastening systems can corrode which, in turn, reduces the thickness of the components and their lifespan.
Materials and methods
During research, nano-coating for fastening systems of ballasted track was introduced as a solution to prevent corrosion in rail clips and screw spikes, which is due to effects of sand dunes, and performance of that is evaluated in laboratory and field tests on the railway track. Corrosion as an electrochemical reaction which causes the metal to be converted to metal ion. In sandy regions, the accumulation of sand on the track causes the rail foot, the sleeper and the fastening systems to corrode. Nano-coating for fastening systems in ballasted track (rail clips and screw spikes) is composed of upgraded zinc-rich and epoxy, an additive which is produced by nano-technology and polyurethane. Its chemical formula is TiO2 PPY/Sn-doped + Zinc-Rich. Based on the amount and composition of the ingredients and the final cost of the product, nano-coating is classified in three categories (10–12). This classification of coatings, based on the amount of ingredients (grams) for covering a fastening system of railway track, is shown in Table 1. The three aforementioned nano‑coatings are economically affordable – the cost of implementing them is less than five per cent of the cost to manufacture a set of ballasted track fastening systems, and the first and third class has the highest and lowest prices, respectively. During the research, all three products were used in the field tests but, for the laboratory test, the third class was used, which has the lowest price in comparison with the other products.