arc spraying

　　

Arc spraying is to use two metal wires as consumable electrodes, use the arc generated at the end as a heat source to melt the front end of the wire, and compress the air flow to atomize the metal droplets and accelerate the atomized particles for spraying . The metal wire is short-circuited and discharged at the moment of contact. Under the action of high-speed airflow and wire feeding mechanism, the metal at the end undergoes the following process: melting into molten droplets → molten droplets are blown away from the matrix → molten droplets are blown away and atomized into particles → particles are further Acceleration → Atomized particles are deposited as a coating on the substrate, this process occurs continuously and continues to form the spray.
the
equipment composition
the
Arc spraying equipment is mainly composed of the following parts:
the
Spraying power supply: In order to ensure the stability of the arc, it is required that the power supply can be adjusted quickly when the arc length changes. When the arc length becomes smaller, the current should increase rapidly to accelerate the melting of the wire to restore the arc length; otherwise, it is required to decrease rapidly to reduce melting. The rate of current change is required to reach 104-105 A/s, so the power supply should have relatively flat external characteristics.
the
Arc spray gun:
the
The arc spray gun is one of the key equipment. The wire material meets at the end of the spray gun through the conductive tip. The two conductive tips with a certain relative angle, the compressed air nozzle, the insulating block and the air cap form the atomizing head of the spray gun. The new spray gun has a secondary atomizing airflow. The primary airflow is blown directly to the arc point, and the secondary airflow forms a secondary atomized airflow after passing through the specially designed airflow channel in the air cap. The secondary atomization can make the particle atomization more uniform, the beam more concentrated, the particle speed faster and the coating quality better. Modern arc spray guns have multiple monitoring points on the gun to obtain the voltage on the gun. Current, and even the compressed air pressure at the outlet of the spray gun and other technical parameters.
the
Wire feeding mechanism:

The wire-drawing spray gun is equipped with a wire-drawing mechanism on the gun. There is no wire push gun, and the wire is pushed into the gun by the wire feeder. The wire feeding mechanism is composed of a wire feeding motor, a deceleration device and a wire feeding roller. The process requires that the twin wires should be fed synchronously and the speed can be adjusted. In order to send the wire farther, some equipment has a push-pull compound wire feeding function. The wire feeder can be combined with the wire drawing device on the gun to feed the wire together, and the wire can be sent farther.
the
Control System:

The control system ensures the reliable operation of the equipment. Control the synchronous feeding of double wires, and control the wire feeding speed to be consistent with the set value. In the push-pull wire feeding, it is necessary to control the drawing speed to be synchronized with the pushing speed. Some advanced equipment also controls the pressure of compressed air on the "gun head" of the spray gun. So as to ensure the accurate and reliable operation of the equipment.
the
main feature
the
The main process characteristics of arc spraying are:
High utilization rate of heat energy. Most of the heat of flame spraying is dissipated into the atmosphere, and the utilization rate of heat energy is only about 5% to 15%. Arc spraying converts electrical energy directly into heat energy to melt metal, and the utilization rate of heat energy can reach 60% to 70%.
Lower cost and higher productivity. Since two wires are fed at the same time, the spraying efficiency is higher. If the same material is sprayed, arc spraying is more than three times that of combustion wire spraying.
High bonding strength of the coating. Since all particles are sprayed by droplet atomization, the particles are fully melted, and the bonding strength of the coating is much higher than that of flame spraying, and some are comparable to plasma coatings.
The adaptability of the process is good. Because the particles are fully melted, the requirements for the spraying distance are not strict during spraying, and can vary between 150 and 250 mm, which brings convenience to manual operation.
However, since the wire material is melted as an electrode, the burning loss of elements in the material is serious, and the burning loss of elements such as manganese, silicon, and carbon must reach about 20%. Therefore, the wire material has a larger difference in material composition than the coating.
the
Advanced Technology Characterization
the
Advanced arc spraying equipment should have some or all of the following functions:
Spray gun: high spraying rate; larger compressed air flow capacity; secondary atomization function; pull-type wire feeding mechanism is driven by servo motor; conductive tip has long service life, and the spray gun is easy to maintain; Accurate positioning, stable arc; a variety of spraying beam shapes can be selected; a number of parameter detection and feedback functions are provided. At present, the typical advanced arc spray gun in the world is 9935 of Praxair.
Power supply: relatively flat characteristic curve, continuous control; good output current stability; low noise level of the power supply; stable work at low arc voltage; easy control of electrical parameters, and convenient movement.
Control system: computer closed-loop control, user-friendly touch screen operation interface, making the operation simple and reproducible. The console monitors and automatically adjusts the voltage and air pressure to match the values preset on the console, and it also monitors the voltage and air pressure on the gun. An optional feature of the control system is direct control of the arc voltage at the gun, allowing more precise control of the supply voltage regardless of the length of the power cable. The console air supply system is designed to reduce pressure drop for better flow and control of the gun supply air. The pressure of the compressed air at the end of the spray gun can be controlled. This capability provides the operator with a tool to monitor gun performance during the spraying process. Combining the monitoring of the pressure at the end of the spray gun with the automatic control of the power supply current (spraying rate), the real closed-loop control of the spraying process is implemented, which is a revolutionary breakthrough in arc spraying and also ensures the stability and reproduction of coating quality. At present, the typical advanced arc spraying control system in the world is CoArc of Praxair.
Push wire feeder: Servo motor is used to make the wire feeding speed accurate, stable and continuously adjustable; it has closed-loop control function; remote control can be implemented.