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introduction·
Thermal spraying technology is a process in which the coating material (powder or wire) is melted in a certain heat source (arc, combustion flame, plasma, etc.
), and sprayed onto the surface of the base material by high-speed airflow to form a coating.
.
Thermal spray coating has excellent properties such as wear resistance, corrosion resistance, high temperature resistance and heat insulation, and can repair the size reduction of parts caused by wear, corrosion or processing tolerances.
It is used in aerospace, machinery manufacturing, petrochemicals, etc.
Has been widely used in the field.
Thermal spraying technology first appeared in Switzerland in the early 20th century, and then it has been continuously developed in the former Soviet Union, Germany, Japan, the United States and other countries.
The development of various thermal spraying equipment, the development of new thermal spraying materials and the application of new technologies , So that the quality of thermal spray coatings has been continuously improved and opened up new application areas of com" href="http://">coatings online coatingol.
com .
The mainstream thermal spraying technology includes flame spraying technology, plasma spraying technology, supersonic flame spraying technology, arc spraying technology, supersonic arc spraying technology and cold spraying technology.
Plasma spraying is a material surface strengthening and surface modification technology, which can make the surface of the substrate have the properties of wear resistance, corrosion resistance, high temperature oxidation resistance, electrical insulation, heat insulation, radiation protection, wear reduction and sealing.
Plasma coating technology uses a plasma arc driven by a direct current as a heat source to heat ceramics, alloys, metals and other materials to a molten or semi-molten state, and spray them to the surface of the pretreated workpiece at a high speed to form a firm surface layer.
Plasma spraying technology is a new type of multi-purpose precision spraying method vigorously developed after flame spraying.
It has ultra-high temperature characteristics and is convenient for spraying high melting point materials.
The spraying speed of particles is high, the coating is dense, and the bonding strength is high.
At present, with the rapid development of thermal spraying technology, plasma spraying has obvious advantages in the world, and a variety of new technologies such as three-cathode plasma spraying, high-energy plasma spraying, micro-arc plasma spraying and suspension plasma spraying have been developed.
01
Three cathode plasma spraying
The three-cathode plasma spray gun consists of 3 cathodes and a nozzle composed of several insulated rings in series, and only the last ring relatively far away from the cathode works as the anode.
Since the lengths of the three independent arcs generated from the three cathodes to the same anode are stable and constant, the three plasma jets converge into a main plasma jet in the confluence chamber, forming a hollow tubular jet that is ejected from the nozzle, thereby producing a stable Plasma jet.
02
High-energy plasma spraying
High-energy plasma spraying is a high-energy, high-speed plasma spraying technology developed to meet the higher demands of ceramic materials for coating density, bonding strength and spraying efficiency.
Its characteristic is that the arc current is equivalent to ordinary atmospheric plasma spraying.
03
Micro plasma spraying
Micro-plasma spraying is characterized by laminar plasma jet, low power, low heating of the substrate, low noise, and can be sprayed on extremely thin substrates.
Although the power of this spraying method is low, the energy is concentrated, and its beam spot diameter is small, so it can still spray a variety of materials.
04
Suspended powder feeding plasma spraying
Suspended powder feeding plasma spraying is a new type of spraying technology that adopts liquid feeding method, which can spray nano powder directly and can form an ultra-thin nano coating.
Suspension plasma spraying uses liquid material as the medium, uses dispersing agent to disperse the particles in the liquid material to form a suspension, and sends the suspension into the plasma arc through the liquid material feeder.
05
Reactive plasma spraying
Reactive plasma spraying is the result of further improvement of vacuum plasma spraying.
In the process of vacuum plasma spraying, reactive gas (such as N2) is added to the plasma jet at the nozzle outlet, and the reactive gas interacts with the heated spray particles to obtain new。 The product.
06
Vacuum plasma spraying
Vacuum plasma spraying (also called low-pressure plasma spraying) is a technology for spraying in a controlled atmosphere and a vacuum sealed chamber.
After the working gas is plasmaized, it is sprayed while expanding its volume in a low-pressure atmosphere, so the jet velocity is supersonic, and it is very suitable for materials that are highly sensitive to oxidation.
07
Water-stable plasma spraying
The working medium of this method is not air but water.
It is a high-power or high-speed plasma spraying method.
Its working principle is: a high-pressure water flow is passed into the spray gun, and a vortex is formed on the inner wall of the gun barrel.
A DC arc is generated between the rear cathode and the rotating anode at the front of the gun body, which evaporates and decomposes a part of the inner wall surface of the gun barrel into a plasma state, generating a continuous plasma arc.
Due to the bunching effect of the swirling vortex water, the energy density is increased and the combustion is stable.
Therefore, high melting point materials, especially oxide ceramics, can be sprayed, and the spraying efficiency is very high.
08
Gas stabilized plasma spraying
The principle of gas-stable plasma spraying is that plasma spray gun (plasma arc generator) generates plasma jet (arc flame flow).
The electrode (cathode) and nozzle (anode) of the spray gun are respectively connected to the positive and negative electrodes of the rectifier power supply, and the working gas (Ar, N2, etc.
) is supplied to the spray gun, and the arc is ignited by high-frequency sparks.
The arc heats the gas to a very high temperature and ionizes the gas.
Under the action of the thermal contraction effect, the self-magnetic contraction effect and the mechanical effect, the arc is compressed to produce a non-transferred plasma arc.
After the high-temperature plasma gas is ejected from the nozzle, the volume expands rapidly to form a high-temperature high-speed plasma jet.
After the powder-feeding airflow pushes the powder into the plasma jet, it is quickly heated to a molten or semi-molten state, and the plasma jet is accelerated to form a sprayed ion beam of the flying substrate, which successively hits the surface of the pretreated substrate to form a coating.
Atmospheric plasma spraying uses argon, nitrogen, and hydrogen as plasma gas.
