Air carbon arc cutting is a process of removing metal by means of heat generated from a carbon arc. This process employs a carbon/graphite electrode, compressed air and a standard power source. The intense heat arc created between the electrode and a metal workpiece cuts and melts the workpiece. At the same time, the molten metal is blown away by the compressed air. This process is commonly used for cutting stainless steel, carbon steel, and alloys of copper, brass, aluminum and magnesium.
The main purpose of this process is to remove defective or old welds in order to repair or dismantle equipment. Unlike oxy-fuel cutting, this process avoids the need for oxidation of the metal to be cut. The rate of metal removal is based on the efficiency of air jet in removing molten metal and the melting rate.
How Does Air Carbon Arc Cutting Work?
In this process, an intense arc is used to form a molten pool on a metal workpiece, and compressed air is used for blowing the molten metal thoroughly from the metal surface. It is important that the metal is only gouged or cut along the airflow direction. Moreover, appropriate arc length has to be maintained to completely remove the molten metal.
The components required for air carbon arc cutting are listed below:
Power source - Air carbon arc cutting requires a three-phase welding power source with high capacity. A voltage drop is created in the circuit only if the open-circuit voltage is greater than the required arc voltage. The arc voltage required to perform this process should be in the range of 35 to 56 V. Hence, the open-circuit voltage should be at least 60V. However, the actual arc voltage is set based on the type of gouging and an arc length.
Compressed Air - Compressed air with pressures in the range of 80 to 100 psi can be used. Higher pressures may not remove the molten metals properly.
Electrode - Three types of electrodes can be used for the air carbon arc cutting process. The most widely used electrodes are DC copper-coated electrodes that are formed by combining carbon-graphite mixture with a binder. These electrodes have groove uniformity, stable arc characteristics and prolonged service life. DC plain electrodes are another type of electrodes, which are formed similar to the coated electrodes with an exception of the copper coating. AC coated electrodes on the other hand are made using a special binder in addition to carbon and graphite. They include copper coating and rare- earth materials for stabilizing the arc while using alternating current.
Gouging Torch - A swivel head on the torch holds the electrode in one or more air holes. Usually, torches are air-cooled. Sometimes, water-cooled cables are used along with heavy-duty torches for high-current applications.
The electrodes are fixed to the swivel head of the torch various positions that include flat, vertical, horizontal and overhead positions. The air jet on the two sides of the electrode is turned on before it strikes the arc. During the process, the air jet in the electrode end sweeps all the molten metal. A slight contact of the electrode to the workpiece creates an arc. It should be noted that the electrodes are not drawn back after the ignition of the arc. However, the smoothness of the cut can be achieved by controlling the electrode movement.
Applications and Products of Air Carbon Arc Cutting
The major applications of air carbon arc cutting process include:
Chemical and petroleum technology
Metal fabrication and casting finishing
The air carbon arc process is inexpensive and efficient on all suitable metals. It is used for gouging and cutting magnesium, iron, copper, aluminum and stainless and carbon steels.
Benefits of Air Carbon Arc Cutting
Some of the advantages of air carbon arc cutting process are the following:
Besides being used for cutting metals and gouging defective metal, the air carbon arc cutting process is used for preparing welding grooves and removing old or damaged welds. One main advantage of this technique is that the temperature of the surrounding area of the cut material does not reach the maximum as the metal is quickly removed after melting.
The air carbon arc cutting process can be performed on the workpiece in all positions.
This process can gouge or cut almost all common metals.
Cleaning is important while performing carbon arc cutting process for the weld preparation of zirconium, titanium, stainless steel as most of the surface carbonized materials near the cut are removed during cleaning. These materials can be cut using carbon arc cutting process to form scraps that can be re-melted.