Metallization or Thermal Coating Application – A Process Performed by “Orao” Bijeljina within Overhaul Operations
At the company “Orao”, within the Overhaul Division, experts perform, among other activities, a specialized process known as metallization. This process involves the application of protective coatings for the repair and overhaul of aircraft engine components, stated Saša Golubović, Head of the Engine Repair Division.
Golubović explains that metallization in the overhaul of turbojet aircraft engines is applied to various components and serves multiple purposes.
During the metallization process, wear-resistant coatings are applied to contact surfaces, thermal barrier coatings are used for protection against high temperatures, as well as anti-corrosion coatings. Additionally, we perform the repair of superalloy components using coatings with similar chemical compositions. These are just some examples of how the metallization process is utilized – said Golubović.
He further noted that coatings are applied through specialized systems in which molten material, in spray form, is propelled at high velocity onto a clean and properly prepared component surface.
At “Orao,” we employ three different coating application methods. High Velocity Oxygen Fuel (HVOF) is a relatively new process in metallization, as it utilizes a supersonic jet, distinguishing it from conventional flame spraying. The impact velocity of the molten powder is significantly higher, resulting in improved coating properties. The second method is Atmospheric Plasma Spraying (APS), where the coating material in powder form is injected externally into the plasma plume, which reaches temperatures above 10,000 degrees Celsius. The material melts and is then propelled onto the prepared component surface by process gases – Golubović emphasized.
The third method, according to him, is wire combustion spraying, where the wire is fed concentrically into a flame.
The wire melts and is atomized by compressed air, after which it is directed toward the surface of the component – Golubović added.
Regarding its application in production, he pointed out that metallization is used for repair during the overhaul of aircraft engine components, in order to restore their original dimensions.
Coatings applied in this manner can be machined and ground to the final required dimensions. However, speaking more broadly about industrial applications, metallization can be used for various types of shafts, for example in the mining and automotive industries, as well as for different types of axles, pistons, brake rings, and other components according to customer requirements. It is important to emphasize that the entire system, as well as coating quality, is controlled by our Laboratory, which also calibrates equipment in accordance with applicable standards. For turbojet engines, “Orao” applies Rolls-Royce and SNECMA quality standards – stated Saša Golubović.
The company “Orao” a.d. Bijeljina specializes in the overhaul of aircraft engines and today represents a highly organized system equipped with state-of-the-art technology and strong human resources for the production and overhaul of all types of turbojet engines.
