Definition - What does Detonation mean?
Detonation is a form of improper combustion that is initiated suddenly and propagates rapidly producing a shock wave. A detonation gun (D-gun) is device that can deposit a variety of materials and ceramic coating at supersonic speeds onto a workpiece by controlled detonation of oxygen and acetylene. It is used in the thermal spraying process for providing hard, wear-resistant and dense-microstructured coatings.
The D-gun coating process, invented in 1948, is still the leading thermal spray process when extraordinary wear and mechanical properties are needed. This process generates outstanding bond strength and density. Typical applications include:
- Fan blade midspans in aviation engines
- Turbine blade z-notches
- Knife-edge seals in power generation
- Steel-sheet roller guides
Petropedia explains Detonation
The detonation gun is considered to be the first high-velocity thermal spray process. It gives an extremely good adhesive strength, low porosity and coating surface with compressive residual stresses. The detonation gun consists of a long water-cooled barrel with inlet valves for gases and powder. Oxygen and fuel (acetylene most common) is fed into the barrel along with a charge of powder. A spark is used to ignite the gas mixture and the resulting detonation heats and accelerates the powder to supersonic velocity through the barrel. A pulse of nitrogen is used to purge the barrel after each detonation. This process is repeated many times in a second. The high kinetic energy of the hot powder particles on impact with the substrate results in a buildup of a very dense and strong coating.
D-gun coating provides extended life to parts. It gives dependable wear and corrosion-resistant surface on machine parts under difficult service conditions. For example, detonation-gun spray coating of 437H boiler steel can be used to enhance its high-temperature corrosion resistance.
The resultant deposits porosity is low (below 1 %) and its oxygen content is between 0.1-0.5%. The deposition efficiency is about 90% for powder flow rates of 1 to 2 kg/hour. The sprayed materials are mainly powders of metals, alloys and cermets. The main applications are coatings against abrasion and adhesion (friction) under low load as well as coatings against corrosion.
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