Substrate Surface Preparation Handbook by Max Robertson download in ePub, pdf, iPad
Material in powder form is melted in a flame oxy-acetylene or hydrogen most common to form a fine spray. Solidification occurs rapidly so the as-sprayed deposit is ultra-fine grained. Electric wire Arc In the Arc Spray Process a pair of electrically conductive wires are melted by means of an electric arc. The hot material impacts on the substrate surface and rapidly cools forming a coating. Thermal Spraying Thermal spraying Thermal sprayed coatings are used extensively for a wide range of industrial applications.
Roughening is necessary for most of the thermal spray processes to ensure adequate bonding of the coating to the substrate. Material in the form of powder is injected into a very high temperature plasma flame, where it is rapidly heated and accelerated to a high velocity.
The most common method is grit blasting usually with alumina. The impacting molten particles on the substrate rapidly solidify to form a coating. The technique generally involves the spraying of molten powder or wire feedstock, the melting being achieved by oxy-fuel combustion or an electric arc plasma.
The molten material is atomised by compressed air and propelled towards the substrate surface. The main applications of the arc spray process are anti-corrosion coatings of zinc and aluminium and machine element work on large components. Disadvantages of the plasma spray process are relative high cost and complexity of process. Electric arc spray coatings are normally denser and stronger than their equivalent combustion spray coatings.
Plasma spray coatings probably account for the widest range of thermal spray coatings and applications and makes this process the most versatile. When the spray contacts the prepared surface of a substrate material, the fine molten droplets rapidly solidify forming a coating. The flame spray process is only limited by materials with higher melting temperatures than the flame can provide or if the material decomposes on heating.
The molten particles are accelerated by the flame and impact onto a properly prepared substrate, usually metallic. The materials which are sprayed include most metal alloys and ceramics. Plasma Arc The Plasma Spray Process is basically the spraying of molten or heat softened material onto a surface to provide a coating. Process The basic steps involved in any thermal coating process are substrate preparation, masking and fixturing, coating, finishing, inspection, and stripping when necessary.
Plasma spraying has the advantage that it can spray very high melting point materials such as refractory metals like tungsten and ceramics like zirconia unlike combustion processes. Low running costs, high spray rates and efficiency make it a good tool for spraying large areas and high production rates.
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