Chemical vibro‐descaling

This report describes a new system for descaling turbine blades which, by a combination of chemical and mechanical action, produces a clean smooth surface, suitable for penetrant inspection. Its development provides a solution to the problem of chemical attack on intermetallics in precipitation hardened nickel and cobalt base alloys by the conventional descaling sequences. The project study leading to the selection of the process is summarised, the development of the method, which is based on the use of a vibrated insoluble particulate burnishing medium used in conjunction with a hot chemical chelating solution, is described and typical results are given. Before proceeding to works trials of a new process, its technical effectiveness and any adverse effects on the substrate or the environment must be evaluated, in order that some estimate of its commercial viability can be made. It has been confirmed that the process cleans effectively and produces a satisfactory conditions for penetrant inspection. No adverse effects on surface profile or dimensions, for example, on the firtree roots of typical turbine blade, on alloys or protective catings, have been found. It has been verified that particles of the medium which may inadvertently remain in blade cooling passages after processing will not lead to local high temperature corrosion during subsequent operation. Chemical vibro‐descaling is also a suitable process to prepare components with oxide films for subsequent operations such as welding, heat treatment or surface treatment. Thus, the process, which is environmentally relatively benign, achieves its objective economically and without deleterious effect on the workpiece.