Usage:
Introduction
The Air-Arc process is most frequently used to gouge-out defective welds in preparation for repair welding, although the process can also be used to prep a joint prior to welding. The process is also referred to as the Arcair process, referring to the Arcair brand name. The arc-air process has no Caterpillar specification and is not called out on any print.
Process and Materials
The air-arc process uses a carbon-graphite electrode, usually copper-colored, that is gradually consumed by the arc. The arc melts the metal to be removed and compressed air is used to blow the molten metal off the part. An electrode holder is used to clamp the electrode and to direct the compressed air down the electrode.
Figure 30 - Electrode Holder
Figure 31 - Air and Power Connections
The electrode holder ids connected to compressed air using a quick-disconnect fitting. The electrical current is furnished by clamping the air-arc connector in the jaws of a stick-weld cable.
Although individual machines may have different switches that must be placed in proper position to enable air-arc gouging, air-arc is generally done with very few changes from the normal production welding processes.
Amperage is the variable that is set by the operator, depending on the electrode size. In order to set the amperage, control must be removed from the wire feeder boxes and given to the power source. This is usually done with a local/remote output switch on the front of the power source that is switched to the LOCAL position. Once LOCAL control is selected, the amperage can be controlled using the rheostat output dial.
A toggle switch is used to select the voltage parameters for the power source. This switch is put in the CC mode, setting up the power source for constant current. On power sources that do not have constant current capabilities, the mode switch, if present, is left in the normal position.
The third and last switch to be changed is the process switch. This switch can be an unmarked switch on the front of the power source. When this switch is placed in the air-arc or stick position, the power source will immediately supply an open-circuit voltage capable of creating an arc.
Figure 32 - Lincoln DC600 power source and switches for air-arc.
Unlike a stick electrode holder the air-arc holder has a rotating disk with air ports that direct air down the electrode, and a valve to turn the air on or off. The air ports are located behind the electrode to force the molten metal out in front of the electrode. This necessitates moving the disk or repositioning the electrode each time the direction of travel is changed.
The electrode is always "hot" once the proper machine settings have been selected.
To start the gouging process, the air valve is opened and the electrode is touched to the workpiece. The electrode is moved along the part to gouge a shallow channel in the part. Several passes may be required to complete the gouging.
Figure 33 - Proper position of air ports and electrode.
Figure 34 - New and used air-arc electrodes.
The dross or slag formed during the removal process must be removed before repair welding begins. The air-arc electrodes tend to leave carbon and copper deposits in the groove which will cause additional weld defects if not cleaned out prior to welding.
The only adjustable air-arc variables are the amperage and airflow. Airflow can be varied using the on-off valve. The air valve is normally used fully open, but can be partially closed to control airborne sparks and slag in tight areas. The air-arc process is very tolerant of amperage variations, and the operator can use this fact to control the speed of metal removal. This is very helpful in following defects in the joint. The following table shows ranges for various size electrodes.
