Flame spraying uses the heat from the combustion of a fuel gas, usually acetylene or propane with oxygen, to melt the coating material. Here, too, metal powder is used which is sprayed on the surface. Virtually any material can be used, but mainly zinc, stainless steel, copper and bronze.
The temperature is rarely higher than 500° C.
There are several reasons for choosing flame spraying:
Flame spraying is generally used when a cost-effective coating is desired and where a slightly lower quality can be tolerated. Common uses for flame spraying are recycling of worn axles, in particular of bearing areas with materials such as stainless steel or bronze alloys.
It is also common when coating bonding layers before plasma spraying of gas turbines, for example. Common coating materials are aluminium, zinc, stainless steel, bronze, low carbon steel, nickel-based materials and molybdenum.
With acetylene being burned, the flame temperature reaches 3,100 ° C. The melting temperature of the powder limits the capacity to 2-16 kg / hour.
With a particle velocity of 35-75 m / sec, the layers get a relatively porous and lamellar structure. The layers can be sealed with wax, oil, grease or other special sealants.
Additives of wire or rods (ceramics) are fed through an oxygen / fuel gas flame and melt continuously. The molten material is atomized and transported to the surface to be coated by a jet of gas, which is usually compressed air.
Depending on the melting temperature of the additive, the capacity is limited to 1.8-24 kg / h. With a particle velocity of 120-140 m / sec, the layer becomes relatively dense.