Arc spraying equipment and process
Arc spraying equipment is key to achieving arc spraying technology, and its performance directly determines coating quality and production efficiency. A complete set of arc spraying equipment primarily consists of a power supply, spray gun, wire feed system, compressed air system, and control system. The power supply, serving as the core of energy supply, typically uses a DC power supply, with an output voltage typically ranging from 20-40V and an adjustable current between 100-500A. By varying the current, the arc power can be precisely controlled, thereby adjusting the melting rate of the wire. For example, when spraying high-melting-point alloy wire, the current needs to be increased to ensure sufficient melting of the material; whereas, when spraying low-melting-point metals (such as zinc and aluminum), a lower current can suffice.
The spray gun is the core executive component of arc spraying equipment, and its structural design directly affects arc stability and droplet atomization. The spray gun primarily consists of a conductive nozzle, a gas guide, and a gas flow device. The conductive nozzle is made of copper alloy, ensuring excellent conductivity while withstanding wear caused by wire friction. The gas guide directs compressed air to form a high-speed airflow, atomizing the molten metal droplets melted by the arc into fine particles. The wire feed system utilizes a dual-drive roller structure, capable of stably conveying two metal wires. The wire feed speed is adjustable within a range of 1-10 m/min, ensuring uniform wire feeding and avoiding arc fluctuations caused by unstable wire feeding. The compressed air system must provide dry, clean compressed air at a pressure controlled between 0.4 and 0.6 MPa. Filtered and dehydrated compressed air can reduce pores and impurities in the coating, improving coating density.
The arc spraying process requires strict process control, and pretreatment is crucial to the coating’s bonding strength. First, the surface is cleaned with solvents to remove oil and dirt. Sandblasting, typically using aluminum oxide or steel grit, removes scale and rust. The surface roughness reaches Ra 2.5-6.3μm, creating a rugged surface that enhances the mechanical bond between the coating and the substrate. For thicker workpieces, preheating is also required, maintaining a temperature between 80-150°C to reduce stress caused by thermal contraction during the spraying process and prevent coating cracking.
The parameter settings during the spraying process directly affect the coating performance and need to be precisely controlled according to the wire material and coating requirements. The spraying distance is usually set at 100-150mm. If it is too close, the substrate will overheat and deform, and if it is too far, the molten droplets will cool too quickly, reducing the bonding strength. The movement speed of the spray gun is maintained at 0.5-2m/min, and the wire feeding speed is coordinated to form a uniform coating thickness. The thickness of each spraying layer is controlled at 50-100μm, and the required total thickness is achieved by superimposing multiple layers. For example, when spraying anti-corrosion zinc-aluminum coating, the current is generally set to 200-300A and the wire feeding speed is 3-5m/min to ensure uniform coating coverage and thickness compliance. When spraying high-hardness wear-resistant alloys, the current needs to be increased to 300-500A, and the gas pressure needs to be appropriately increased to obtain finer atomized particles.
Post-processing is an important step in improving coating performance, and the corresponding treatment method should be selected according to different application scenarios. For anti-corrosion coatings, sealing treatment is required, and epoxy resin or polyurethane coating is used to fill the pores of the coating to isolate the intrusion of corrosive media; wear-resistant coatings need to be ground to reduce the surface roughness to below Ra1.6μm to meet mechanical fit requirements. In addition, for coatings that are subjected to impact loads, low-temperature annealing treatment at 200-300℃ can be performed to eliminate internal stress and improve coating toughness. In actual production, the process needs to be optimized in combination with the characteristics of the substrate material. For example, when spraying on an aluminum alloy substrate, the preheating temperature needs to be lowered and the spraying power needs to be controlled to avoid overheating and deformation of the substrate; for spraying on cast iron parts, the surface roughening needs to be strengthened to compensate for the lack of bonding caused by the loose material.
