Ceramic coatings are very useful procedure used to protect machine parts. We will spend a good deal of time covering the aspects of ceramic coatings for metals including plasma spray, electric arc, and detonation spray methods of application.
Ceramic coating is a process in which a coating of ceramic material is applied to a metal surface to increase the strength of the machine part. It offers significant benefits in automotive applications because the coatings reduce heat loss in automobile engines, exhaust manifolds, headers, turbocharger casings, downpipes and tailpipes, etc. The typical application of this process can be found in places like high performance automobiles. They also provide thermal protection to several high end automobile engines.
Ceramic coatings are also used for protecting automobile parts from degradation of material composition due to friction that occurs during parts movement. It doesn’t stick to the surface of the metal like paint; the ceramic coating bonds with the material of the parts. Due to this, it’s a tough coating and doesn’t flake easily.
Applications of Ceramic Coatings
Ceramic coatings are used for increasing resistance to corrosion in metal surface by spraying Zinc and Aluminum.
- They are also used to repair surfaces of various machine parts like motor armature shafts.
- They can be used to achieve desired hardness on the surface of the metal components.
- The incorrect specification of any machine part may be compensated for by using ceramic coatings.
- They are also used to produce reflecting surfaces. For example, glass gets the property of reflection due to the ceramic coating on its back side.
- If the surface of any metal part has less conductivity this method can be used to increase the conductivity.
- The ceramic coatings on the exhaust manifold of the engine restrict heat loss and improve appearance.
The Plasma Spraying Method for Ceramic Coatings
The process involves generating a stream of high temperature ionized plasma gas. This gas then acts as a heat source. materials need to be prepared in powdered form and then the inert gas stream in the plasma jet is propelled towards the coating substance to heat it and cuase the bonding to occur.
- This method of coating can be used for almost every material composition.
- The bond strength provided by this coating is very high.
- High density can be achieved by this method of coating.
- The problem of heat distortion is very low in this method.
- The main disadvantage of this method is that it produces high noise level on the of order 100 decibles.
- It produces ultraviolet and infrared radiation that may harm the eyes of the worker.
- Its most valuable application is in rocket parts like nozzles. This method is widely used in aerospace.
- This method is used for coating seal ring grooves present in the compressor of aeroengines.
- The zirconia based coating in a turbine compressor chamber is also done by this method.
- It is used for spraying aluminum and chromium oxide ceramic on to printing rolls.
- This method is used for prosthesis for biocompatible hydroxyapatite coatings.
- The ceramic coatins for manifolds is done by this method.
Electric Arc Spraying Method
The process involves an electric arc that works between two wires of the ceramic. The whole system is then exposed to the metal where the coating is wanted. The ceramic material is heated and sprayed on to the metal surface using an air jet across the electric arc and the metal surface.
This method is basically applied for anti-corrosion coatings of Zinc and Aluminum on large machine components.
- The main advantage of this method is its lower cost. It is cheaper than any other method of ceramic coating.
- Combustion of gases is not required, and due to this, there is no any threat of fire.
- It has a wire fed mechanism, i.e., it provides flexibility to engage and disengage while performing the operation.
- The thermal efficiency of this method is very high.
- The velocity of spraying of this method is very low.
- Coatings provided by this method have less resistance to high temperature and surface pressure.
- This method may cause pollution, because it develops harmful fumes around the working area.
Detonation Gun Spray Method
This method involves use of a special type of gun in which measured amounts of oxygen, acetylene, and powder particles of coating can be stored. This mixture is then ignited using a spark plug. The whole process detonates, and thereby, a high speed shock front develops. This front is then used for coating the metal surface.
- It provides better resistance to wear in the surface.
- The coating speed is very high in this method.
- This method is very expensive compared to others.
- The firing of the gun produces extremely loud noise.
- The coating of tungsten carbide, aluminum oxide, and chromium carbide is performed by this method.
- This method works only for metals; non-metallic parts can not be coated by this material.
Ceramic coatings are directly applied to the metal parts like exhaust manifolds. Recently, new technologies to apply ceramic coatings have been introduced including plasma spray. This process is very beneficial in restricting heat loss and degradation of metal materials, though, the preparation of the surface for ceramic coating is very tough job.