The flame-spray technology includes all thermal spray methods, where a coating material is wormed – and mostly molten – by a flame and sprayed to a previously treated (sand-blasted) surface. The coating material is mostly available as powder, wire, cord or stick.
You can differ between different methods of flamespray:
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method where the coating material is accelerated just by the flame
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method where additionally compressed air/gas is used to increase acceleration.
The properties of flamesprayed coatings differ very much due to the used method and spraying parameters. Besides Plasma- and Laserspray, Fa. Häuser uses as well the following flamespray methods:
Wire- flamespray:
Using wire-flamespray, the coating material comes as a wire, is molten by a flame and the molten particles are accelerated by compressed air/gas and are sprayed towards the substrate to be coated. Typical materials used for wire-flamespray are Aluminum, Aluminum-Zinc-alloys as atmospherical corrosion inhibitors.
Powder-flamespray:
Works very similar to wire-flamespray, but using coating-alloys in powder, which allows to work with coating-alloys that are not available as wire or cord.
High-Velocity-Oxigen-Fuel (HVOF) Flame-Spray
A derivate of the conventional powder-flamespray is the HVOF. The molten particles are accelerated by gas-stream and reach supersonic speed. HVOF coating-layers show high density and low porosity, which makes them more brittle and less ductil. Because of these characteristics HVOF is often used to apply coatings using Cr-oxide-alloys for abrasion-resistance. Depending on the spraygun-configuration HVOF can use flamable gas or liquides like Kerosin, Ethanol or petroleum.
Explosion / Detonation flamespray:
Another derivate is the detonation-flamespray, where coating material is introduced as powder into a chamber where a high-frequency electrical impuls triggers the induced gas to detonate. The detonation causes gas-expansion and creates a shockwave accelerating the molten particles to speed of up to ca. 600m/s. Today this method is still used to coat e.g. turbine-elements, but has been substituted in many cases by HVOF. The exotherm reaction of flamespray causes undesired heat-introduction into the workpiece, so that heat-sensitive workpieces or O2-affine coating-alloys can usually not be flamesprayed.
Cold-gas-flamespray:
This was reason to develop the cold-gas-spray, where gastemperatures remain a littler lower than melting point of the coating material. The injected particles are accelerated to such high speed, that they do not need to be molten to form a firm and adhesing layer when hitting the substrates surface. Typical applications are found in automotive and turbine applications.