Operation of carbon arc welding
The CAW process is still used in certain application although it almost hasn’t been applied in the welding industry. Carbon or graphite in CAW electrodes can baked, however, it is most commonly used due to their durability and avalability
- In the single-electrode operation, the carbon electrode is prepared to a long tapered point that is one half the electrode diameter
- The arc is established by “scratch starting,” that is, by bringing the electrode into contact with the workpiece and immediately withdrawing it to the correct length for welding. The generally accepted arc length is maintained between 6.4 and 9.5 mm.
- Holding the length too short can result in carburization of the base metal, creating potentially brittle welds. This is particularly true when welding without filler metal.
- When the joint requires filler metal, the same technique that is used in GTAW or oxyfuel gas welding (OFW) should be employed.
- The arc welding rod in arc welding machine should be fed into the weld pool with one hand while manipulating the arc with the other. If the arc is broken for any reason, then restart should not occur directly at the hot metal where welding stopped, because a hard spot could result.
- Rather, a restart should occur in front or to one side of the weld, followed by a quick return to the point where welding stopped.
- Care should be taken to either incorporate the restart area into the weld or to grind the arc strike after welding is completed. The arc strike areas can be very hard and can cause cracking if they are not fused into the weld or ground out.
- In the twin-electrode operation, the workpiece is not part of the electrical circuit. The heat for welding is produced by creating an arc between the two electrodes.
- The electrode holder has two adjustable arms that grip the carbon electrodes at the proper length to maintain the arc.
- The operator maintains a constant distance between the carbon electrodes by adjusting them as they are consumed. An experienced welder can make these adjustments while still welding or brazing.
- Small arc welding machines are normally used in the twin-electrode process because the electrodes will wear at an equal rate.
- Direct current can be used as long as the positive-side electrode is one size larger than the negative electrode.
- The larger electrode compensates for the faster consumption rate on the positive side of the direct current. Electrodes range in size from 6.4 to 9.5 mm and are copper coated for better current flow.
- The heat must be maintained so that the copper does not melt more than 13 mm back from the electrode tip.
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