Surface Treatment Processes in Rail Vehicles and General Transportation

Railway vehicles, whether for freight or passenger trains, require thoroughly prepared surface preparation before coating. Since coatings that enhance corrosion resistance will be used, the profile depth on the surface must be at suitable depth for anticorrosive coatings. According to steel surface standards, the minimum level should be SA 2.5. This ensures that the coating adheres better, allowing railway vehicles to be used for extended periods without corrosion damage. For railway vehicles, considering both the steel surface preparation scale and profile depth, as well as operating time and costs, a blasting facility complying with environmental regulations and occupational health standards is required. This blasting facility contains many parameters. The first of these is a professional filtration system, which is the first step in creating an environmentally friendly facility. This filtration system both determines the quality of air released to the environment and ensures that blasting dust is drawn from the environment and discharged with a fan calculated for pressure. Second, the statically calculated blasting cabin operates under negative pressure with sealing as the priority. When blasting is carried out using abrasive material, the entire cabin is exposed to abrasive granules rather than merely withstanding negative pressure. For this reason, the cabin must achieve returning the abrasive—which is expensive per unit kilogram—with minimum loss, while also ensuring the cabin has a long service life. The recovery of the abrasive granule mentioned in the previous sentence is possible through several methods. These methods vary depending on the processing hours to be performed in the blasting chamber, the number of operators, and the abrasive tonnage. The first of these methods is the pneumatic conveying system. Through this system, abrasive can be recycled at up to ten tonnes per hour. The second is the mechanical recycling system.

Tonnages here can reach 60-70 tonnes per hour. The mechanical recycling system is divided into two categories. These are: conveyor system and floor sweeping system. This process directly affects operating profitability, surface processing speed, and facility lifespan.One of the important headings in the blasting process, which is the most critical aspect of pre-coating preparation, is granule-resistant lighting. Minimum shadowing is desired in the lighting. The lumen value is close to that of the coating process, though not quite the same.

Another subject we must address is blasting equipment. Blasting equipment must comply with occupational safety standards. This is achieved through remote control pendants. A blasting chamber with these processes has high-standard quality and can serve railways and transportation with low operating costs. Wagons or equipment prepared in this facility are ready for corrosion-resistant coating. To apply this coating, there must be a paint facility with the same dimensions as the blasting chamber, capable of application in all seasons and weather conditions, with minimized heat transfer, thereby reducing operating costs. Among the characteristics of the paint facility, climate control—which we can describe as the most important—must have adjustable humidity and temperature. The paint cabin will comply with environmental ministry standards and will have filtration that prevents solvent accumulation inside, and correspondingly, explosion-proof fans. We have briefly explained the facility characteristics for applying the relevant coatings. However, special spraying equipment is needed to apply these special coatings. This equipment operates with compressor air and increases the coating pressure to facilitate its adhesion to the surface, reduces overspray ratio, and makes coating more efficient. The two-component paint pump visible in the photo is new spraying technology. It is designed to achieve maximum surface quality and square metre coverage with minimum paint. Generally, surface treatment processes for railway or transportation products are as described. You can see details about the steel surface standards we mentioned in blasting facilities below: Swedish Standards SA (ISO 8501-1:1998) are used in the cleanliness grading of surfaces undergoing blasting. In grading, the lowest level begins with SA1 and ends with the highest level, SA3.  

SA1: Light Cleaning by Blasting

Loose mill scale, loose rust, and loose paint are roughly cleaned by the effect of abrasives sprayed from the blasting nozzle. Complete removal of mill scale, paint, and rust is not intended. For good paint adhesion, remaining mill scale, paint, and rust must be adhered to the surface. With light cleaning, the surface is cleaned of oil, grease, dirt, rust layer, loose mill scale, loose rust, loose paint, and coatings. However, adherent mill scale, rust, paint, and coating may remain.

SA2: Partial Cleaning by Blasting

Oil, grease, dirt, rust, and foreign matter are partially cleaned from the surface by the effect of abrasives sprayed from the blasting nozzle. With partial blasting cleaning, oil, grease, dirt, rust, mill scale, and foreign matter are completely cleaned from the surface. If the surface is pitted and contains light rust and paint residue, all rust, mill scale, and old paints are completely removed from the surface except for light shadows, lines, and colour changes resulting from this.

SA 2.5: Thorough Cleaning by Blasting

By the effect of abrasives sprayed from the blasting nozzle, all oil, grease, dirt, mill scale, rust, abrasive matter, oxides, paint, and other foreign matter are cleaned, except for very light shadows, very light lines, and light colour changes resulting from nearly all mill scale, rust stains, mill scale oxides, and light, persistent paint and coating residue. At least 95% of the surface area is cleaned of visible residue and the aforementioned colour changes.

SA3: Complete Cleaning by Blasting

Mill scale, rust, coatings, and contaminants are completely removed by the effect of abrasives sprayed from the blasting nozzle. With complete blasting cleaning, a grey-white, homogeneous metallic coloured surface suitably roughened for coating is obtained. The surface, when viewed with the naked eye, is cleaned of all oil, grease, dirt, visible mill scale, rust, abrasive materials, oxides, paint, and all other foreign matter. Tolga Zent Sales Coordinator Alfatechnic Makina San. ve Dış Tic. Ltd. Şti.