First, the principle of arc spraying
Arc spraying uses two continuously fed metals as consumable electrodes, generates an arc as a heat source at its ends, atomizes the melted wire with compressed air, and sprays it onto the surface of the workpiece at a high speed to form a coating. A thermal spray method. During spraying, the two filamentous metal spray materials are uniformly and continuously fed into the contact nozzles of the arc spray gun through the wire feeding device, and the contact nozzles are respectively connected to the positive and negative poles of the power source to ensure reliable reliability of the two wires before being contacted. insulation. When the ends of the two metal wires are brought into contact with each other due to feeding, a short circuit occurs to generate an arc, and the ends of the wires are instantaneously melted, and the compressed air melts the molten metal into micro-melts and is sprayed onto the surface of the workpiece at a high speed. An arc sprayed layer is formed.
Second, the characteristics of the arc spray process
Arc spray as a new type of thermal spray method has many significant advantages.
2.1 The coating has high bonding strength, high hardness and low porosity.
When the arc is sprayed, the droplet temperature can reach above 6000 °C, and the micro-melt heating temperature and ejection speed are higher than those in the flame spraying. Therefore, the kinetic energy and thermal energy of the particles are relatively high, thereby obtaining high bonding strength and coating strength. Tests have shown that the combined strength of arc spray is about 2.5 times that of the flame sprayed layer. The hardness of the coating formed by arc spraying is 30%-80% higher than that of the sprayed material. The porosity of the arc spray coating is less than 8%, which is lower than the porosity of the coating obtained by flame spraying.
2.2 High productivity, safe and reliable, the workpiece is not deformed
The productivity of arc spraying is proportional to the spray current, and its high efficiency is manifested by the large amount of metal sprayed per unit time. The test proves that when the spraying current is 300A, the spraying Zn efficiency can reach 30kg/h, and the spraying Al can reach 10 kg/h. The arc spraying technology uses only the power source and compressed air, and does not use flammable gas such as oxygen or acetylene. It has high safety and the workpiece is not deformed.
2.3 High energy efficiency and low spraying cost
The energy-saving effect of arc spraying is very prominent, the energy utilization rate is significantly higher than other spraying methods, and the energy cost is reduced by more than 50%. In addition to its high energy efficiency, the price of electricity is much lower than that of oxygen and acetylene. The cost is usually only 1/5 to 1/10 of the flame spray and 1/5 to 1/20 of the cost of plasma spraying. And its spraying efficiency has nearly doubled.
2.4 equipment cost is low, easy to use and maintain, easy to construct on site
The cost of arc spraying equipment is only 1/4 to 1/6 of that of plasma spraying equipment. Moreover, the arc spraying equipment is small in size, light in weight, convenient in movement, less wearing parts, convenient in maintenance, and easy on-site construction.
Third, arc spraying equipment and materials
3.1 Arc spraying equipment
The arc spraying equipment is composed of an arc spray gun, a control box, a power source, a wire feeding device, and a compressed air system.
(1) Arc spray power supply
In recent years, arc spray power sources have adopted flat volt-ampere characteristics. In the past, DC welding machine was used as the arc spraying power source. Because the electric welding machine has the characteristic of steep drop, the arc working voltage is above 40V, which causes the carbon burning loss during the spraying process to reduce the hardness of the coating. The flat volt-ampere characteristic arc spraying power supply can be sprayed at a lower voltage, so that the carbon loss in the coating is greatly reduced (about 50% reduction), the arc length self-regulation can be maintained, and the arc can be effectively controlled. Voltage. The flat characteristic power supply changes rapidly when the wire feed speed changes, maintaining a stable arc spraying process. According to the spraying wire, a certain no-load voltage is selected, and changing the wire feeding speed can automatically eliminate the arc spraying current, thereby controlling the productivity of the arc spraying.
(2) Arc spray gun
Arc spray guns are a key component of arc spray equipment. The function is to intersect the continuously fed wire at a certain angle at the front of the spray gun. Since the wires are connected to the two poles of the direct current power source to generate an arc, the compressed air flow ejected from the nozzle is blown against the molten metal to form a stable Atomized metal particle stream.
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