In the case of wire flame spraying, the spray filler material is continuously melted in the centre of an acetylene-oxygen flame. With the aid of an atomising gas, e.g. compressed air or nitrogen, the droplet-shaped spray particles are released from the melting area and thrown onto the prepared workpiece surface. Flame spraying with wire is a widespread method with a very high spray coating quality. In the automotive industry, this method is used to spray several hundred tonnes a year of molybdenum onto shift forks, synchroniser rings and piston rings.
In the case of wire flame spraying, the spray filler material is continuously melted in the centre of an acetylene-oxygen flame. With the aid of an atomising gas, e.g. compressed air or nitrogen, the droplet-shaped spray particles are released from the melting area and thrown onto the prepared workpiece surface. Flame spraying with wire is a widespread method with a very high spray coating quality. In the automotive industry, this method is used to spray several hundred tonnes a year of molybdenum onto shift forks, synchroniser rings and piston rings.
In the case of powder flame spraying, the powdered spray material is melted on or fused in an acetylene-oxygen flame and thrown onto the prepared workpiece surface with the help of the expanding combustion gas.
If necessary, an additional gas (e.g. argon or nitrogen) can also be used to accelerate the powder particles. The variety of spray materials is very wide when it comes to powders with well over 100 types.
When it comes to powders, a discrepancy is made between self-fluxing and self-adhesive powders. The self-fluxing powders usually also need a thermal follow-up treatment. This fusing process predominantly takes place with the acetylene-oxygen burners, which are ideally suited for the job. Thanks to the thermal process, the adhesion of the spray coating on the base material is significantly increased; the spray coating becomes impervious to gases and liquids.
Application areas are e.g. shaft bushings, rollers, bearing seats, fans, rotors on extruder screws etc.
In the case of plasma spraying, the powdered spray material is melted by a plasma jet in or outside the spray gun and thrown onto the workpiece surface. The plasma is generated by an arc, which burns concentrated in argon, helium, nitrogen, hydrogen or mixtures thereof. Here the gases are dissociated and ionised, reach high exhaust speeds and give off their heat energy to the spray particles during the recombination process.
The arc is not transmitting, i.e. it burns inside the spray gun between a centrally arranged electrode (cathode) and the water-cooled spray nozzle that forms the anode. The method is applied in a normal atmosphere, in an inert gas flow, i.e. inert atmosphere (e.g. argon), in a vacuum and under water. A specially shaped nozzle attachment is also used to generate a high-velocity plasma.
Areas of use include aerospace (e.g. turbine blades and run-in areas), medical technology (implants) and heat insulation coatings.
In high-speed flame spraying, continuous gas combustion takes place at high pressures within a combustion chamber, in the central axis of which the powdered spray material is supplied. The high pressure of the fuel gas-oxygen mixture generated in the combustion chamber and the usually downstream expansion nozzle generates the desired high flow velocity in the gas jet. As a result, the spray particles are accelerated to the high particle speeds, which lead to enormously dense spray coats with excellent adhesion properties.
Due to the sufficient but moderate temperature input, the spray material is only slightly metallurgically changed by the spraying process, e.g. minimal formation of mixed carbides. This method produces extremely thin coatings with high dimensional accuracy. Propane, propene, ethylene, acetylene and hydrogen can be used as fuel gases.
Areas of application are sliding surfaces of steam irons, rollers for the photo industry, parts for petrochemical and chemical machines, e.g. pumps, sliders, ball valves, mechanical seals, etc.
In the case of laser spraying, a powdered spray material is introduced into the laser beam via a suitable powder nozzle. By means of laser radiation, both the powder and a minimal part of the base material surface (micro range) are melted and the fed spray material is metallurgically bonded to the base material. An inert gas is used to protect the molten bath. The area of application of laser spraying is, for example, the partial coating of punching, bending or cutting tools.