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Plasma Spraying Process Flow
Release time:
2019-12-23 16:20
Source:
Plasma Spraying Process Flow
In the plasma spraying process, many process parameters influence coating quality, the main ones being:
① Plasma Gases: The selection of gases is primarily guided by availability and cost-effectiveness. Nitrogen (N2) is inexpensive and features a high enthalpy of ionization, enabling rapid heat transfer that facilitates the heating and melting of powders. However, it should not be used for powders or substrates that are prone to nitriding reactions. Argon (Ar), on the other hand, has a lower ionization potential, resulting in a stable plasma arc that is easy to ignite. Its arc flame is relatively short, making it well-suited for spraying small or thin components. Additionally, Ar provides excellent shielding protection. Nevertheless, Ar has a lower enthalpy and is more expensive.
The magnitude of gas flow directly affects the enthalpy and velocity of the plasma jet, thereby influencing spray coating efficiency, porosity of the coating, and bonding strength. If the flow rate is too high, the gas will carry away useful thermal energy from the plasma jet and increase the velocity of the sprayed particles, reducing their “residence time” within the plasma flame. As a result, the particles fail to reach the semi-molten or plastic state necessary for deformation, leading to poor adhesion strength, reduced density, and lower hardness of the coating, as well as a significant decrease in deposition rate. Conversely, if the flow rate is too low, it will lead to an inappropriate arc voltage and substantially reduce the velocity of the sprayed particles. In extreme cases, this can cause overheating of the spraying material, resulting in excessive melting or vaporization of the material. This, in turn, causes molten powder particles to aggregate at the nozzle or powder outlet and then deposit onto the coating in large spherical shapes, forming substantial voids.
② Arc power:
When the arc power is too high, the arc temperature rises, causing more gas to ionize into plasma. Under conditions of high power and low working gas flow rate, nearly all of the working gas is converted into an active plasma jet. The plasma flame temperature also becomes extremely high, which may cause some spray materials to vaporize and lead to changes in the coating composition. The vaporized spray materials can condense between the substrate and the coating or between coating layers, resulting in poor adhesion. Furthermore, this can also cause erosion of the nozzle and electrodes.
However, if the arc power is too low, the plasma flame will contain a partial amount of ionized gas and have a lower temperature, which in turn leads to insufficient particle heating, resulting in lower bonding strength, hardness, and deposition efficiency of the coating.
③ Powder supply
The powder feed rate must be matched to the input power. If it’s too high, unmelted (raw) powder will appear, reducing spraying efficiency; if it’s too low, the powder will oxidize severely and cause excessive heating of the substrate.
The feed position also affects the coating structure and spraying efficiency. Generally speaking, the powder must be fed into the flame core to ensure it receives adequate heating and achieves the optimal velocity.
④ Spray distance and spray angle
The distance between the spray gun and the workpiece affects the velocity and temperature of the spray particles upon impact with the substrate. The characteristics of the coating and the spray material are highly sensitive to the spray distance.
If the spray distance is too large, both the temperature and velocity of the powder particles will decrease, leading to a significant decline in bonding strength, porosity, and spraying efficiency. Conversely, if the spray distance is too small, the substrate temperature may rise excessively, causing oxidation of both the substrate and the coating and adversely affecting the bonding between them. Provided that the machine’s temperature rise is within acceptable limits, it’s best to keep the spray distance relatively short.
Spraying angle: refers to the angle between the axis of the flame jet and the surface of the workpiece being coated. When this angle is less than 45 degrees, the coating structure deteriorates due to the "shadow effect," resulting in voids and a loose coating.
⑤ Relative movement speed between the spray gun and the workpiece
The spray gun’s moving speed should ensure a smooth coating without leaving visible traces of overlapping spray strokes. In other words, the width of each pass should overlap sufficiently. Under the condition of meeting the above requirements, it is generally advisable to use a relatively high spray gun moving speed during spraying operations, as this can help prevent the formation of localized hot spots and surface oxidation.
⑥ Substrate Temperature Control
The ideal approach is to preheat the workpiece to the temperature required for the spraying process before spraying begins, and then employ jet-air cooling during the spraying process to maintain the workpiece at its original temperature.
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The complete set of plasma-sprayed equipment has been shipped to the customer’s site in Thailand.
Core spraying equipment: SX-80 plasma spray main unit, with a 15,000℃ flame suitable for multiple materials including zirconia and silicon carbide; powder feeding accuracy of ±1%, and coating thickness tolerance ≤ ±5 μm. Environmental protection support system: Customized soundproof booth + pulse dust collector—effectively addressing spray noise pollution while achieving highly efficient dust recovery, compliant with Thai environmental standards. Automated equipment: 6-axis industrial robot + intelligent spray cart, enabling precise spraying of complex workpieces and automated loading/unloading, boosting production efficiency by 40%.
On-site engineers provide hands-on training, focusing on the core operations of plasma spraying equipment such as the SX-80. Sanxin has customized a complete solution for its customers, including an automated spraying robotic arm, a soundproof booth, and a dust removal system—ensuring both high spraying efficiency and compliance with environmental standards.
Guangzhou Sanxin Thermal Spraying Turntable Shipment
Guangzhou Sanxin Company manufactures single-station and multi-station thermal spray turntables, which can be paired with plasma equipment, supersonic equipment, and arc equipment. We offer rapid, customized production tailored to customer requirements and product dimensions. A thermal spray turntable is a high-precision rotary worktable specifically designed for thermal spraying processes—including flame spraying, plasma spraying, and arc spraying. By providing controllable rotational speed and exceptional stability, it ensures uniform coating thickness on the workpiece surface, thereby enhancing spraying efficiency and quality.
SX-80 plasma equipment is being used at a customer site in Russia.
SX-80 plasma equipment is being used at a customer site in Russia.
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