IDEA OF THE PROCESS
THERMAL SPRAYING
The thermal spraying process - often referred to colloquially as metallization or sputtering - is carried out to apply a coating with specific properties most often to a metallic substrate in order to improve its resistance to abrasion, erosion, corrosion, temperature or other surface degradation factors. The coating material, depending on the technique chosen, is most often in the form of powder, wire or string. It is heated or fused and then fired towards the coated surface. No thermal changes are produced in the substrate material as a result of the process. The most important characteristics for assessing the quality of the coating include...
Adhesion to the substrate
This is the result of the thermal spraying technology used, the materials and the quality of the surface preparation. It is tested using pull-off tests. Low adhesion is responsible for the most failures of thermal sprayed coatings. The maximum adhesion values we are able to achieve are around 80 MPa. Larger values are only achieved with remelted coatings, where diffusion bonding to the substrate material occurs.
Coating porosity
Resulting from the thermal spraying technology used, in particular the speed at which the particles of the coating material leave the gun, but also their temperature. Porosity is examined using light microscopes with special software.
Hardness of the coating
It depends primarily on the coating materials used, the particle velocity (strengthening effect due to plastic deformation upon collision of the material with the substrate) and the temperature affecting the speed of crystallisation, degree of oxidation or distribution of the frequently used hard reinforcing phases. The supersonic spraying equipment we use allows the application of approximately 250 HV harder carbide coatings compared to the most commonly used equipment on the market.
One of the most important determinants affecting the parameters described is the thermal spraying technique. Four technologies are used in today's market. For each of them, we have dedicated equipment which, in our opinion, is one of the best solutions on the market. Robotisation of the process makes it possible to produce homogenous, repeatable layers in terms of properties and thickness on a series of components.
HVOF and HVAF supersonic spraying
The most advanced spraying technique to obtain layers with the highest adhesion to the substrate - about 80 MPa - and the highest hardness of 1550 HV 0.1. The materials used are cobalt-chromium or nickel-chromium matrix composites with tungsten carbide or chromium reinforcement. We recommend robotisation even for single parts.
Arc spraying
Technology based on welding solutions. Two wires of specific chemical compositions connected to a specially designed welding power supply meet in the gun of a metallization device, resulting in an electric arc. A compressed air forming nozzle sprays the liquid metal onto the surface to be coated. Advantages include the high performance and quality of the coatings. Dedicated coating materials are usually high-alloy steels with or without the addition of carbides, as well as zinc, aluminium and their alloys.
Cold Spray
A niche technology that enables thick coatings to be applied to plastic materials such as copper, copper-zinc alloys, nickel, aluminium. It is often used for spot-filling. Spraying on plastics is possible.
Flame spraying with remelting
A two-stage process involving the spraying of NiCrBSi-based self-fluxing coatings with or without carbide, followed by remelting of the layer to the substrate to achieve metallurgical bonding. A technology used most often when the component is subjected to complex impact and abrasion processes.