Coating processes – Spraying
Patent
1998-10-16
1999-11-16
Mai, Ngoclan
Coating processes
Spraying
427427, 239 80, 239 81, 419 8, B05D 110
Patent
active
059853735
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the field of gas detonation coating apparatus for industrial use for applying protective coating to workpieces.
BACKGROUND ART
Many industrial applications exist where materials are exposed to severe environmental conditions of heat, wear and corrosion. Spray coating processes utilizing powder coating materials offer high quality protection in some of these applications. A common method of spray coating is the detonation gun process. This process uses kinetic energy from the detonation of combustible mixtures of gases to deposit powdered coating materials on workpieces.
Typical coating materials used in conjunction with detonation gun in the spray coating process include powder forms of metals, metal-ceramic, ceramic, erosion resistant, thermal protection, electrically insulating, electrically conductive, and other coating materials. In addition powder forms of other materials can be utilized in conjunction with the detonation gun process for parts cleaning, hole drilling, making powders, and other conceivable applications.
A typical detonation gun functions in the following manner. A certain amount of a combustible gas mixture, oxygen and acetylene for example, is fed into a tubular combustion chamber have a closed end and an open end where it is subsequently ignited by a spark plug. The ignition of the gas beings about detonation and the formation of a shock wave. The shock wave travels down the combustion chamber to the open end which is attached to a tubular barrel. A suitable coating powder is typically injected into the barrel in front of the propagating shock wave and is subsequently carried out the open end of the barrel and deposited onto a substrate positioned in front of the barrel. The impact of the powder onto the substrate produces a high density coating with good adhesive characteristics. The process is repeated in a rapid fashion until the workpiece is coated to satisfaction. Between successive ignitions an inert gas, such as nitrogen, may be fed into the combustion chamber after the ignition to halt combustion and prevent backfire into the fuel and oxygen supply and to purge the barrel of combustion products.
The mechanics of detonation are key to the operation of the detonation gun. Detonation produces shock waves that travel at supersonic velocities, as high as 4000 m/s, and elevated temperatures, as high as 3137.degree. C. Detonation is the detonation gun is controlled by the type of fuel used, such as propane, acetylene, butane, etc., the fuel and oxygen mixture ration, the initial pressure of the gases in the combustion chamber, and the geometry of the combustion chamber. After ignition of the fuel and oxygen mixture deflagration produces an initial detonation wave front that increases the temperature and pressure within the combustion chamber which in turn propagates ignition of the combustible mixture throughout the combustion chamber. Given the correct combination of parameters, the detonation continues to propagate until all available fuel and oxygen is consumed. The detonation front moves toward the open end of the combustion chamber and into the barrel. It is of particular importance that the combustion chamber be of sufficient length, for the specific detonable mixture in use, to complete the transition from deflagration to detonation before entering the barrel or the detonation wave front may not be sustained within the barrel. It is also important in the operation of a detonation gun to produce as strong a shock wave as possible and direct it to the barrel as efficiently as possible so that a large amount of the kinetic energy of the detonation wave goes directly to carrying the powder out of the barrel and onto the substrate.
At a fixed moment in time the detonation wave front is made up of a system of individual stationary detonation cells. The behavior of detonation at the cell level is an important attribute in the control and operation of a typical detonation gun. The detonation cell is a multidimensional structure which incl
REFERENCES:
patent: 5206059 (1993-04-01), Marantz
patent: 5542606 (1996-08-01), Kadyrov et al.
Aerostar Coatings, S.L.
Mai Ngoclan
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