As discussed earlier, the spraying system is a process of coating the surface of the workpiece in various ways. In today’s era, different types of spraying systems are being used for coating the work surface. such as combustion flame spraying, Detonation gun spraying, , Electric arc spraying, and Plasma arc spraying,
Detonation gun spraying
The detonation gun spraying system differs from other spraying systems due to its use of a special type of gun. It consists of a chamber in which metered amounts of oxygen and acetylene are kept along with powder particles suspended in nitrogen. As we can see in the diagram, the gaseous powder mixture is ignited with the help of a spark plug.
Mode of operation
This gaseous powder mixture is ignited with the help of a spark plug. The resulting detonation produces a high-velocity shock front that travels the length of the barrel at ten times the speed of sound, accelerating the powder particles, which are heated to a plastic state by the detonation. The wavefront caused by the detonation forces the particles out of the barrel and onto the work surface.
Due to the above process, the high kinetic energy of each particle is converted into high heat upon impact with the surface of the base metal, leading to the formation of metallurgical and mechanical bonds.
Detonation spraying gun
Although the metalizing and plasma torches work continuously, the detonation gun fires four to eight times per second, creating a laminar coating on the work surface. It can build the maximum thickness of coating up to 0.7 mm, successively.
Working Process of Detonation Gun
Since the firing of the gun in this process produces a lot of noise, the process is generally operated in a fully automatic mode and is aimed and fired by remote control.
Some of the facts used in the working process of detonation gun are:-
- The process is usually carried out in sound-absorbing walls due to heavy noise.
- Usually, the distance from the detonation gun to the workpiece is kept 50-100 mm.
- An auxiliary cooling system is used to keep the temperature between 65 °C to 150°C.
Materials to be used
Various types of coating ingredients may be used by detonation gun spraying systems like aluminum oxide, tungsten carbide, chromium carbide, etc.
since the operation of detonation gun spraying is carried out with the high velocity of particles thus the substrate is only metallic. Non-metallic surfaces may be corded by the high velocity of particles.
Applications of Sprayed coatings
Sprayed coatings are applied on the work surface to get the desire properties. It can be defined as follows:
- Zink and aluminum are sprayed on the workpiece surface to obtain corrosion resistance.
- To obtain a conductive surface on a poor conductor Copper or Silver is sprayed on the glass plastics.
- Building up worn out the surface of machine components like armature shafts. etc.
- Hard-facing a component to achieve desired hardness, wear resistance, etc.
- Providing a thin coating of noble metals to a small area where conventional plating would not be economic.
- Obtain reflecting surfaces(e.g. Al is sprayed on the back of the glass.
- Mechanically size a component that has not been produced to correct specifications.
Provide decorative effects on architectural works
Spraying imparts –
Corrosion resistance by a coat of stainless steel, Heat resistance by a coat of zirconium oxide in the combustion chamber of a jet engine, and wear resistance by a coat of aluminum oxide in an extrusion die.
Advantages and limitations of Detonation spray spraying
- The porosity and oil-retention capacity of the sprayed metal are a great achievement of sprayed coatings.
- A metal of the right characteristics can be coated at a particular part only where needed.
- For corrosion-resistance purposes, zink and aluminum can be applied to any practical desired thickness.
Sprayed metals are brittle, therefore the use of sprayed materials on machine parts is limited, where it is not necessary for the coating to add strength.