An electric arc spraying system is a popular coating method as it is comparatively more efficient and cheaper than other processes.
This process is accomplished by melting the filler metal at a high temperature obtained from an electric arc between two wires installed on the surface of the workpiece, and spraying it onto the workpiece by means of an air jet.
Concept of Electric Arc Spraying
In an electric arc spraying system,
An electric arc is maintained between the two wires which need to be deposited on the surface of the workpiece. Filler metal is melted by arc heat and then driven or sprayed onto the job surface using an air jet directed to spray across the arc and onto the workpiece surface.
Electric Arc Spraying Equipment
- wire reels
- Switchgear and control console
- Air supply input
- spray gun
Switchgear and control
Switchgear and control console are used to adjust current, voltage, air pressure, and rate of wire feed as required.
A spray gun is a case containing wire guides and wire feed parts and gearing, main electrical conducting parts, power controls, and atomizing air passages.
The power supply used in Electric arc spraying
A motor-generator or a solid-state power source (50-650) amp, is required for the arc spray system. Motor generator sets may have either constant voltage or constant current regulation depending on the application.
Working operation of Electrical arc spraying
- Although a very low roughness is required for electric arc spraying, the surface to be sprayed first is cleaned and roughened,
- The two metal wires are advanced under a small point-like contact surface by a feed mechanism. Due to the high density of the current and the excessive heat of the contact surfaces, an arc strikes immediately.
- The arc creates a molten state at the ends of the electrode wires and the molten particle is swept away at high velocities(about 100 particles/second)by an air jet or a gas such as nitrogen.
- The wire’s vibrations cease as they make and break contact, affecting the spraying action. Thus, the molten particle is sprayed onto the surface of the workpiece, As a result, a deposition of high-quality coating is formed.
Advantages and limitations of Electrical arc spraying
Advantages of Electrical arc spraying
- Arc spraying is less expensive than flame spraying.
- The electric arc spraying system has a high rate of white metal spraying from steel, copper, and copper alloys, zinc, lead aluminum, and wire.
- Since no combustion gases are required in this process, thus there is no problem associated with these gases.
- The arc spraying process can be interrupted and resumed at any time by removing and reassembling the wire feed mechanism.
- Arc spraying provides a high degree of thermal efficiency. In this process, the two-wire ends the short circuit and heat the resistance between 40-50% of the energy produced in the electric arc between the contact points.
- Arc spraying requires less surface preparation than flame spraying
- Arc spread particles and coating layers are 50-70% less oxidized than flame spread particles, resulting in higher resistance to tensile, compressive, and bending stresses.
- The arc can be struck between two wires of different materials such as stainless steel and aluminum bronze. In this situation, these two materials will mingle and deposit on the base metal, resulting in a desirable bearing surface with a longer wear surface.
Disadvantages of Electrical arc spraying
- Due to the burning of a significant amount of carbon from steel wires, losses of Mn and Si can be expected as a protective gas is not employed.
- The volatility of arc spraying is lower than that of flame spraying.
- Coatings generally do not resist applied loads due to high temperatures or great surface pressure or their limited adhesion over small areas. Nor can they resist the tension.
- Sufficient resistance to wear can be achieved but the performance cannot be compared to the surface produced by welding.
- The process produces smoke, dust, and odors around the work.