Cutting with Electrodes
Aluminium
In addition to welding, the arc can be used for certain other operations such as cutting, piercing, chamfering and gouging of metals. There are two variations of the process:
- The use of conventional welding electrodes at high currents
- The oxy-arc process
Cutting with Conventional Electrodes
Whereas the gas cutting of steel is a burning action, the metal being oxidised by the oxygen stream and blown away as a molten stream. The arc cutting action depends entirely on the heat of the electric arc to melt the metal, and the force of arc to remove it from the face of the cut. For this reason the arc cutting process can be used on metals such as cast iron, stainless steel and non-ferrous metals, which are not readily oxidisable or which cannot be otherwise cut with the gas process unless the power cutting or plasma arc process is available.
Higher currents are used than are needed for ordinary welding purposes. The actual current value will depend on the thickness of metal to be cut. With the electrode held vertical the arc is struck on the edge of the plate and played up and down the face of the cut with a see-saw motion. A long arc is held, which is made possible by the high current, and this causes molten metal to run down the cut.
If properly used, no metal will be deposited from the electrode. To cut a section (e.g. a circle) from a plate, a hole is first pierced in it by concentrating the arc at one spot and pushing the electrode into the molten pool until it melts through to the other side. The hole can be enlarged or extended into a cut as required.
Back-gouging and grooving of weld joints can also be done with welding electrodes. As for cutting, a high current is needed. The electrode is inclined at about 50 to the plate surface and pointed in the direction in which the grooving is to be done. The molten metal is pushed ahead of the electrode tip, and periodically the electrode is run back along the groove to clean out slag. It is an advantage also if the job can be positioned so that the slope allows molten material to run ahead clear of the groove. PACWELD 800 electrodes are particularly suitable for grooving and clean, neat grooves can be made.
Piercing is best done, where possible, from beneath the job, the molten metal then falling clear of the hole. Chamfering is performed in a similar manner to cutting. Arc cutting is not as neat as gas cutting; it is intended for use where gas equipment is not available or where materials have to be cut for which the gas cutting process is not effective.
