Overview of Carbon Arc Cutting

Carbon arc cutting, one of the steel cutting options is a cutting method that cuts metal by melting it from the heat of an air carbon arc. Molten metal is removed by a blast of air, a high velocity jet of compressed air. The external air jet is a consumable carbon-graphite electrode. The electrode strikes immediately behind the arc. This is different from plasma arc cutting in that it uses an un-constricted arc, independent of the gas jet.

Equipment required

Conventional welding machines with constant (extremely high) current are used for carbon arc cutting. Constant voltage can be used. A CV power source requires operation precautions. It must be operated within its rated output of current and duty cycle. Special applications may be able to use alternating current power sources with conventional drooping characteristics. AC type (large size) carbon electrodes must be used. Special heavy duty high current machines have been designed with the air carbon arc process in mind.

A carbon arc cutting electrode holder includes a small circular grip head to contain air jets and direct air to the electrode. A groove grips the electrode and the head can be rotated to allow angle variation. A valve on the holder controls air. The duty cycle of the work performed, welding current, and carbon electrode size all determine holder type. Water cooled holders are also available. Electrodes may be carbon graphite. Plain, uncoated electrodes are less pricy and start more easily, but carry less current. Copper-coated electrodes offer better conductivity and are better for maintaining original diameter. It lasts longer and carries higher current. The composition of carbon and graphite varies between the AC and DC types. DC is common. AC has additives to stabilize the arc. AC is used for direct current electrode negative when cutting cast iron. The electrode is usually operated with a positive charge. Electrode size ranges from 5/32 to one inch. Lengths may be six or 12 inches. Copper coated electrodes with tapered socket joints allow automatic, continuous operation.

Air pressure should be between 80-100psi. Volume should be between 5-50 cubic feet per minute (for large carbon electrodes). A small, one-horse compressor will work for small electrodes, but you’ll need ten horsepower for larger electrodes.

Uses

Carbon arc cutting can be used to cut metal, remove defective metal or welds, root gouging, and welding groove preparation. Common metal applications include aluminum, copper, iron, magnesium, stainless steel, and carbon. Cleaning via grinder to remove all surface carbonized material near the cut makes it feasible to work on stainless steel, titanium, and zirconium. Carbon arc cutting will not leave a perfect finish, the area of the cut is small, and the surrounding area will not reach high temperatures. There is little risk of distortion or cracking with carbon arc cutting. Cutting and gouging is done manually. A travel carriage can be used. An automatic cutting device can be made by doing cylindrical work on a lathe-like device and rotating under the air carbon arc torch. Carbon arc cutting can be done in all positions, although overhead requires a high level of skill.

Application

For cutting or gouging the user will strike an arc and the air flow. The electrode should point in the direction of travel. Push angle should be about 45 degrees, with the axis of the groove. Groove depth is determined by the speed of travel, electrode angle, electrode size, and current. Electrode diameter will determine groove width.

Safety Measures

Similar to carbon arc welding and shielded metal arc welding, precautions must be taken. Additionally, keep in mind that the air blast will cause the molten metal to travel a long distance. Place metal deflection plates in front of the gouging operation. No combustibles should be in the work area. Removed molten metal is a fire hazard if not contained. When using high currents and high air pressure, noise will be at a high level. Ear protection must be worn.


Written by Terra L. Fletcher