6.4 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Detonation spraying | 1/3 | https://en.wikipedia.org/wiki/Detonation_spraying | reference | science, encyclopedia | 2026-05-05T10:47:14.991060+00:00 | kb-cron |
Detonation spraying is one of the many forms of thermal spraying techniques that are used to apply a protective coating at supersonic velocities to a material in order to change its surface characteristics. This is primarily to improve the durability of a component. It was first invented in 1955 by H.B. Sargent, R.M. Poorman and H. Lamprey and is applied to a component using a specifically designed detonation gun (D-gun). The component being sprayed must be prepared correctly by removing all surface oils, greases, debris and roughing up the surface in order to achieve a strongly bonded detonation spray coating. This process involves the highest velocities (≈3500 m/s shockwave that propels the coating materials) and temperatures (≈4000 °C) of coating materials compared to all other forms of thermal spraying techniques. Because of these characteristics, detonation spraying is able to apply low porous (below 1%) and low oxygen content (between 0.1 and 0.5%) protective coatings that protect against corrosion, abrasion and adhesion under low load. This process allows the application of very hard and dense surface coatings which are useful as wear resistant coatings. For this reason, detonation spraying is commonly used for protective coatings in aircraft engines, plug and ring gauges, cutting edges (skiving knives), tubular drills, rotor and stator blades, guide rails or any other metallic material that is subject to high wear and tear. Commonly the materials that are sprayed onto components during detonation spraying are powders of metals, metal alloys and cermets; as well as their oxides (aluminum, copper, iron, etc.). Detonation spraying is an industrial process that can be dangerous if not performed correctly and in a safe environment. As such there are many safety precautions that must be adhered to when using this thermal spraying technique.
== History == The process of detonation spraying was first developed in 1955 by H.B. Sargent, R.M. Poorman and H. Lamprey and was subsequently patented. It was first made commercially available as the 'D-Gun Process' by Union Carbide in the same year. It was further developed in the 1960s by the Paton Institute in Kiev (Ukraine), into a technology that is still currently commercially available in the US by Demeton Technologies (West Babylon).
== D-Gun == Detonation spray coatings are applied using a detonation gun (D-gun) which is composed of a long-water-cooled metal barrel containing inlet valves for introducing gases and powders into the chamber. A preselected amount of the desired protective coating material known as feedstock (in powder form of particle size 5–60μm) is introduced into the chamber (at common powder flow rates of 16–40 g/min). Here oxygen and fuel (generally acetylene) are ignited by a spark plug to create a supersonic shock wave that propels the mixture of melted and/or partially-melted and/or solid feedstock (depending on the type of material used) out of the barrel and onto the subject being sprayed. The barrel is then cleared using a short burst of nitrogen before the D-gun is ready to be fired again. This is an important step because the heat from the residual gases can cause the new fuel mixture to combust which would in turn cause an uncontrollable reaction. Also a small amount of inert nitrogen gas inserted between the two mixtures of fuel and feedstock prior to firing, helps to prevent backfiring. D-guns typically operate at firing rates of between 1–10 Hz. Many different mixtures of coating powders and D-gun settings can be used during detonation gun spraying of a material, all of which influence the final surface characteristics of the sprayed coating. Common powder materials used include but are not limited to: alumina-titania, alumina, tungsten carbide-tungsten-chromium carbide mixture with nickel-chromium alloy binder, chromium carbide, tungsten carbide with cobalt binder. Metallurgists consider the measurements of surface oxygen content, macro and micro-hardness, porosity, bond strength and surface roughness when determining the quality of a thermally sprayed coating.
=== Components ===
Spark plug Water cooled barrel Nitrogen inlet valve Fuel inlet valve Oxygen inlet valve Powder feedstock inlet valve
=== Cycle of operation overview === Mixture of fuel and oxygen is injected into the combustion chamber. Powder feedstock is introduced into the chamber. Nitrogen gas is added between the fuel-oxygen mixture and powder feedstock in order to prevent backfiring. Mixture is ignited, and heated powder is ejected from the barrel onto the target material. Barrel is then purged by nitrogen gas ready for firing again. This process is repeated at a rate of between 1–10 Hz until desired thickness of coating is achieved.
== Surface Preparation == Detonation sprayed coatings are primarily mechanically bonded. This means that the surface of the component being sprayed, must be properly prepared so as to maximise the bond strength between the sprayed coating and the substrate. To successfully prepare the surface it must be cleaned of all greases, oils, dirt and other contaminants and sufficiently roughened to provide enough of a surface irregularity for the coating to cling to. Chemical processes are generally the most suitable methods used to clean the substrate surface. After which care must be taken not to touch and/or dirty the surface prior to spraying. The three methods used to roughen up the substrate surface are abrasive blasting, machining and bond coating. Cleaning occurs only after the roughening of the surface except for when a bond coating is used; the surface must be cleaned before and possibly after this process too. Application of the detonation spray coating should be performed as soon as possible after a substrates surface has been prepared.
=== Abrasive Blasting === Abrasive blasting also known as sandblasting, involves using compressed air to fire a steam of clean, sharp, crushed steel grit or aluminum oxide onto the surface of the component. Aluminum is a good option as it is relatively cheap. The fired grit breaks off small chucks of the substrate surface creating an evenly rough surface for good mechanical bonds to form. The substrate needs to be cleaned of any debris and residual grit from blasting prior to spraying.
=== Machining ===