Carbon Arc Cutting (CAC) Process & Guide

Carbon Arc Cutting (CAC ), is referred to as metal arc gouging, also previously as air arc cutting, is a metal cutting method, which uses the high temperature of carbon electrode arc to heat the metal locally to the melting state, and at the same time blows off the molten metal with the airflow of compressed air.

Figure 1 Carbon Arc Cutting Model

Brief of  Carbon Arc Cutting

Carbon arc cutting (CAC ) is “an arc cutting process that removes molten metal with a jet of air”. It is also used for gouging. Carbon arc cutting works by sending electrical current through an electrode made of solid carbon.  The heat of the arc at the end of the electrode liquefies the metal. A high-velocity air jet parallel to the carbon electrode strikes the molten metal puddle just behind the arc and blows the molten metal out of the immediate area. Figure 2 shows the arc between the carbon electrode and the work and the air stream parallel to the electrode from the special electrode holder.

Figure 2 Process diagram for Carbon Arc Welding or Gouping

Carbon arc cutting (CAC) process is used to cut metal, to gouge out defective metal, to remove inferior welds for root gouging, and to prepare grooves for welding. Carbon arc cutting is used when slightly ragged edges are not objectionable. The cutting area is small, and, since the metal is melted and removed quickly, the surrounding area does not reach high temperatures. This reduces the tendency towards distortion and cracking.

The carbon arc process is more likely to be used for gouging operations than cutting. Carbon arc gouging is used to remove unwanted weld beads. Carbon arc cutting also leaves a unique radius groove when it is used for edge preparation on plate stock. J-groove and U-groove joints are prepared by CAC operations. A variety of materials can be cut and gouged with the carbon- arc process including carbon steels, stainless steel, aluminum, cast iron, copper-based alloys,  nickle alloys, and magnesium. Since the electrode is made from solid carbon, a small amount of carbon will be transferred to the base metal.

After gouging metals such as aluminum, brass, and even steel, the gouge will need to be sanded out to remove any carbon residue before welding.

The carbon electrodes come in a variety of diameters. The larger the diameter, the more amperage output is required. The diameter of the electrode will also determine the depth and radius of a gouge it can make. Deeper gouges can be made with smaller electrodes by making multiple passes. The copper foil around the outside helps conduct electricity to the cutting arc.

Carbon arc cutting is extremely loud. Hearing protection is a must with this process. Unlike gas cutting and plasma arc cutting, the carbon arc cutting removes far more metal, creating a high volume of sparks and a large amount of hot dross. A welding helmet with a No. 10 shade lens will need to be worn. Darker lenses may need to be used for higher amperages.

Operation Process  of Carbon Arc Cutting

1. Cutting preparation: ①According to the type and thickness of the planed metal material, choose the polarity of the power supply, the diameter of the carbon rod and the planing current. ②Adjust the extension length of the carbon rod, 80 ～ 100mm, ③Adjust the air outlet so that it is aligned with the groove.

2. Cutting: ① In order to avoid carbon trapping defects during planing, the gas valve should be opened first, and then the arc is ignited; when gouging in a vertical position, the gouging direction should be from top to bottom, so that the slag is easily discharged. ②The inclination angle of the carbon rod depends on the depth of the groove, which is generally 45 degrees. ③ The center line of the carbon rod should coincide with the center line of the groove, otherwise the shape of the groove is asymmetrical. ④ During the planing operation, the arc should be stable and the planing speed should be uniform. When connecting each segment, the arc should be drawn on the arc pit. ⑤ In actual work, the compressed air is usually blown slightly, turning part of the slag to the outside of the tank (opposite to the operator).

3. Arc closing: In order to cool the carbon rod, the arc should be cut off at the end of each planing, and then the gas should be cut off after a few seconds. Take care not to allow molten molten iron to remain in the planing tank.

Figure 3  Carbon Arc Cutting Process

Application

1. Used to plan the roots (clear roots) on the opposite side of the weld before welding the bottom weld on both sides.

2. Used to remove defects in unqualified welding seams, planing layer by layer until there are no defects.

3. Used for opening bevels, especially U-shaped bevels.

4. Used to clean the burrs, burrs, casting ports and casting defects of castings.