October 12th, 2021
Plasma spraying is an energy-intensive thermal spray technique widely used to produce wear-resistant, high-quality, uniform functional coatings. Due to the extremely high temperatures of plasma arcs (5000--16000 deg. C), plasma spraying is mostly used to produce coatings based on ceramic-based composites and insoluble metals.
It uses complex integrated equipment that primarily includes two components: a plasma spray gun for generating an extremely hot plasma plume by ionizing an inert gas that passes between an anode and a cathode. Second, it has an injector system to inject the feedstock material into the plasma that accelerates the melt as a high-velocity stream onto a pre-treated substrate. The operating current and power in the plasma spray gun can be as high as 100 A and 200 kW, respectively.
Inefficient energy conversion and spraying processes can have dire consequences on the environment and the coating quality. Therefore, sustainable development and optimum utilization of plasma spray technology call for adequate energy consumption of plasma spray guns.
Key Processing Steps & Factors Affecting Coating Performance
One key measure of gauging the output efficiency of plasma spray guns is the coating quality and performance. Compared to the pre-treatment and post-treatment processes, the main spray cycle consumes most of the power. The critical processing parameters that characterize the main coating process and directly influence the coating performance are spraying power, spray distance, spray jet velocity, and powder feeding.
On the one hand, too low spray power leads to incomplete melting of powder and hence poor-quality coatings with porosity. On the other hand, too high spray power can cause undesired phase changes or vaporization of the material, and substrate temperature control issues. Hence, optimum performance requires a critical power of a plasma spray gun. Therefore, Saint-Gobain’s ProPlasma HP gun offers two power configurations - standard (30-40 kW) and high power (45-65 kW) – allowing better power control to achieve optimum performance & energy savings. The angle of powder injection also plays an important role in optimizing the output deposition efficiency. ProPlasma HP gun allows complete flexibility to set the angular position of powder injectors.
Sufficient melting power and high specific enthalpy of the plasma are crucial preconditions for refractory materials to obtain improved deposition efficiency and a homogeneous coating. Of all subprocesses, most of the power is consumed in this preparation stage of the coating. The formation of a stable plasma needed for the spray process requires around 30 seconds – the so-called ignition stage. The ProPlasma HP gun uses a self-aligned single cathode and single anode design that delivers high enthalpy and superb arc stability. It can also operate with up to four powder injectors, thus rendering a high deposition rate.
Compared to conventional guns, the ProPlasma HP gun has three to four times faster deposition rates with limited consumption of expensive gases like Helium, Argon, and Hydrogen. It is suitable to spray a wide range of materials like carbides, ceramics, and metals, thereby serving as a multipurpose coating solution. Our plasma spray gun also has a reduced overspray and generates fewer fumes during spraying leading to less waste.
The powder feeding rate of a plasma spray gun also influences the coating efficiency by reducing processing time per part. Saint-Gobain’s ProPlasma HP gun can operate under a range of feeding rates, making it an ideal solution for various applications.
The spray parameters of the ProPlasma HP gun are controllable using a PLC control. The user has complete control of critical process parameters affecting the plasma spray process, such as the gun power, powder feed rate and gas flow rate. Compared to the conventional plasma spray guns available in the market, the ProPlasma HP gun has a much lower power/deposited material ratio (e.g., 1/3 for chromium oxide coatings).
If you are interested in knowing more about our high-performance plasma spray gun technology, contact us today.