HVOF (high velocity oxygen fuel) is the abbreviation of HVOF (high velocity oxygen fuel). High speed flame spraying is a new thermal spraying technology developed on the basis of explosive spraying. It was first developed by browning company in the early 1980s, and a commercial spraying equipment named jet-kote was introduced. As soon as the technology of high-speed flame spraying came out, it showed obvious advantages in spraying metal carbide and metal alloy with its ultra-high flame velocity and relatively low temperature. With the active promotion of the world's major thermal spraying companies, this technology has developed rapidly. At present, high speed flame spraying technology has gradually replaced plasma spraying and other spraying processes in spraying metal carbides and metal alloys, and has become an important process method of thermal spraying.
1. Principle of high speed flame spraying
High speed flame spraying is a method of continuously burning combustion supporting gas and combustion gas in the combustion chamber. The combustion flame generates high pressure in the combustion chamber and generates high-speed flame flow through the expansion nozzle connected with the outlet of the combustion chamber. The spraying material is sent into the high-speed jet to be heated and accelerated to spray on the surface of the pretreated substrate to form a coating. Acetylene, propane, propylene and hydrogen can be used as fuel gas, and liquid fuels such as diesel or kerosene can also be used.
Kerosene and oxygen enter the combustion chamber through small holes and then mix, and burn stably and uniformly in the combustion chamber. A monitor is used to monitor the pressure in the combustion chamber to ensure stable combustion. The speed of spraying powder is proportional to the pressure in the combustion chamber. The exit design of the combustor accelerates the rapid expansion of high-speed airflow, forming supersonic and low-pressure regions. The powder is injected into the low pressure region at many points along the radial direction, and the powder is mixed uniformly and ejected rapidly in the air flow. The flame velocity of high speed flame spraying is as high as 1500m / s-2000m / s. generally, 5-8 obvious Mach cones can be observed, and the particle velocity is as high as 300-650m / s.
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