The Combustion flame spraying process, also known as LVOF ( low velocity oxygen and fuel) is the spraying of molten material onto a surface substrate to provide a coating. The spray material, in powder form, is fed continuously into the middle of the flame via an inert carrier gas. The flame consists of oxygen and a fuel gas, either acetylene or hydrogen depending on the melting point of the material to be sprayed, and typically can achieve temperatures in excess of 3000 Celsius. When the spray stream is passed across the surface of the substrate material, the molten material rapidly cools forming a coating.
The combustion spraying process, compared with others, is relativity low energy and can be used to spray substrates that cannot be exposed to high temperatures. This can help when component distortion and structure damage is an issue.
There are two forms of combustion spraying. Either a powder or wire can be used, and both have there advantages. Raw materials are much easier to process into a powder form rather than a wire, and the only limit is the melting point of the powder. However, wire coatings such as molybdenum give excellent bond strength and are often used for bond coats .
Combustion spraying can be used to make repairs, improve efficiency, and restore dimensions. It is often a cost effective method when repairs are required to high cost components. It is most often used for applying coatings that have high oxide and porosity levels, and can be used to achieve rough coatings. They also provide very low stress coatings, therefore allowing very thick coatings to be applied.