Bogies are an essential part of a train as these constructions form its drive system and guidance mechanism on the railway track. Generally, a bogie consists of a steel frame containing the suspension, the wheels, brake equipment and in some cases also the transmission. Mounted underneath the locomotive and the carriages bogies are under severe mechanical impact and fulfill their task under harsh circumstances. However, as they are expensive, re-manufacturing them at the end of the life cycle often pays off. During the reman process there are several different cleaning challenges. Today we will have a closer look at a particularly demanding one: the removal of old paint systems from bogie frames.
Lots of dirt to be removed first
A used bogie is covered with thick layers of grime, grease, mud and rail dust. This crust is up to several centimeters thick and must be removed before the re-manufacturer can start removing the underlying paint system. Although it is best to have an individual alkaline cleaning step, some remanufacturers prefer a one step cleaning / paint stripping process because of limitations in available equipment or floor space.
There are several ways in which a paint system can be removed from its substrate and they all have their own benefits but also disadvantages:
- Mechanical methods as brushing and blasting: effective, but also very labor intensive;
- Thermal methods like cryogenic stripping: effective, but not on all paint technologies. Further energy consumption is high due to elevated temperatures needed;
- Chemical methods such as caustic or solvent stripping: effective but Health & Safety precautions must be taken.
Sometimes a combination of different technologies is necessary to get the paint off. Whatever the challenge is, there is no standard solution when it comes to paint stripping. Especially in re-manufacturing each application must be investigated and tested to come to the best solution.
Amongst railway operators in Europe it is quite common to re-manufacture their own rolling stock. In this specific case a large railway operator remanufactures bogies in their own remanufacturing plant. Most of the incoming bogies are coated with solvent based paint which must be removed. Until now the company had some issues in doing this. The first issue they were facing was that it took a long time and several attempts to remove the thick layer of contamination that covered the bogie frame, resulting in long waiting times in the plant. Secondly, the paint stripping process was not effective enough to strip off all paint. Besides a negative impact on efficiency, this also resulted in problems within the subsequent blasting process as the paint residues quickly contaminated the blast medium (in this case corundum).
In order to solve these problems and improve the plants efficiency Henkel was approached and asked to design a solution. The demand was to come to perfect degreasing & paint stripping within 2 hours in their existing closed paint stripping tank (A one-step cleaning / paint stripping process was thus mandatory).
As with every cleaning or paint stripping request the Henkel field technician started to investigate and collect information on the remanufacturing process, paint technologies & substrates. After several trials with different cleaner-paint strippers BONDERITE® S-ST 699 (1K technology) and BONDERITE® S-ST 600 (2K technology) turned out to perform best in this specific case. Both the thick layer of contamination and the paint system are now completely removed within two hours. The problem of paint contamination in the blast medium is solved with this too. Also, the provided solution offers a reduction in VOC’s and non-toxic labelling.
Altogether, both efficiency and effectiveness of the paint stripping process have been significantly improved while health & safety risks have been further reduced.