AWS C5.3:00R2011

This publication establishes a method of conveying to the welder/operator the proper setup and use of air carbon arc gouging and cutting. Instructions and procedures are supplied in detail so the welder/operator can establish the correct air pressure, amperage, voltage, and techniques.
Scope : 1.1 Scope. This publication presents the basic concepts of the air carbon arc cutting (CAC-A)1 process to provide a fundamental understanding of the process and its variables. In addition, specific technical data are presented as a guide in establishing optimum operation of this process. This standard makes use of the U.S. Customary Units. Approximate mathematical equivalents in the International System of Units (SI) are provided for comparison in parentheses ( ) or in appropriate columns in tables and figures. Annex A is included to identify metric equivalents if the reader requires precise conversion information. Safety and health issues and concerns are beyond the scope of this standard and, therefore, are not fully addressed herein. Some safety and health information can be found in Section 9. Safety and health information is available from other sources, including, but not limited to, ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes, and applicable federal and state regulations. 1.2 Description. CAC-A is a physical means of metal removal in contrast to the oxidation reaction in oxyfuel gas cutting (OFC). In the CAC-A, the intense heat of the arc between the carbon electrode and the workpiece melts a portion of the workpiece. Simultaneously, a jet of air is passed parallel to the arc and is of sufficient volume and velocity to blow away the molten material. The exposed solid metal is then melted by the heat of the arc, and the sequence continues. CAC-A does not depend on oxidation to maintain the cut, so it is capable of cutting metals that OFC will not cut. The process is used successfully on carbon steel, stainless steel, many copper alloys, and cast irons. The melting rate is a function of current. The metal removal rate is dependent upon the melting rate and the efficiency of the air jet in removing the molten metal. The air must be capable of lifting the molten metal out and clear of the arc region before resolidification. 1.3 History. CAC-A was developed in the 1940s as an extension of an existing processâ??carbon arc cutting. Faced with the removal, in the flat position, of several hundred feet of cracked stainless steel weld, a welding engineer developed CAC-A. Carbon arc cutting was used to remove defective welds and rivet heads, but only in the overhead and vertical positions. The carbon arc melted the metal and gravity moved the molten metal out of the area. It was reasoned that an air jet could provide the force to remove the metal in the flat position. A direct current electrode negative (DCEN) carbon arc was tried, and an air blast was provided by the second cutter with an air nozzle directed at the pool. This attempt was not very successful because the arc was not stable. Direct current electrode positive (DCEP) was tried, and the result made air carbon arc cutting practical. The basic principle remains the same today, but the equipment and applications have been improved and expanded. In 1948, the first air carbon arc torch was introduced to the welding industry. No longer were two cutters needed. The air was fed through the torch and out beneath the electrode at the correct location. This new tool was found to save time on back gouging of welds and removal of cracks and other weld defects on carbon, alloy, and stainless steels. Previously, this type of work had been done by grinding or chipping. As the use of the CAC-A expanded, torches were designed for more efficient and cleaner metal removal and for cutter comfort. 1.4 Applications. The CAC-A process is used throughout industry in a variety of applications, such as metal fabrication and casting finishing, chemical and petroleum technology, construction, mining, general repair, and maintenance. CAC-A torches and electrodes are used to create groove weld preparations in plates butted together. If the process is performed properly a minimal amount of additional cleaning and grinding is required. The CAC-A process can then be used to back gouge the joint to sound metal to ensure complete joint penetration. If during welding, a problem arises and an area of the weld does not meet specifications, the CAC-A process can be used to remove the defective weld metal without damaging or detrimentally affecting the base metal. The CAC-A process is used in the foundry industry to remove fins and risers from castings and then used to wash the contact areas smooth with the surface in preparation for shipment of the casting. The air carbon arc process presents great flexibility, efficiency, and cost effectiveness when applied to practically any type of metal. Carbon steel, stainless steel, gray, malleable, and ductile iron, aluminum, nickel, copper alloys, and other nonferrous metals can be worked on with CAC-A.