Soldagem a arco de carbono – Vantagens e Desvantagens

Carbon arc welding – Advantages and Disadvantages

What is carbon arc welding process:

  • Carbon arc welding is one of the oldest welding techniques still in use today.
  • The carbon arc welding process uses low voltage, high amperage electricity to heat the metal once an arc is formed between a carbon electrode and the part being welded; if an arc is formed between two carbon electrodes, this technique is known as double carbon arc.
  • The single carbon arc welding technique uses a direct current power source which, if necessary, a filler rod can be used in carbon arc welding. The end of the rod is kept in the arch zone. Molten material from the rod is supplied to the weld pool.
  • Shields (neutral gas, flux) can be used to protect the weld pool, depending on the type of metal welded. is connected using a straight polarity.
carbon arc welding carbon arc welding

Principle and working of carbon arc welding

In carbon arc welding, the heat from the arc between the carbon electrode and the workpiece melts the base metal and, when necessary, also melts the filler rod. As the molten metal solidifies, a weld is produced. The non-consumable graphite electrode erodes rapidly and, as it disintegrates, produces a protective atmosphere of carbon monoxide and carbon dioxide gas. These gases partially displace air from the arc atmosphere and prohibit oxygen and nitrogen from contacting the molten metal. The filler metal, when used, has the same composition as the base metal. Bronze filler metal can be used for brazing and brazing.

Workpieces must be free from grease, oil, scale, paint and other foreign materials. The two pieces must be well attached, without opening the roots. They can be welded together.

1/8 to 5/16 inch carbon electrodes (3.2 to 7.9 mm) diameter can be used depending on the current required for welding. The end of the electrode should be prepared with a long cone at one end. The tip diameter should be about half the electrode diameter. For steel, the electrode should protrude about 4.0 to 5.0 in. (101.6 to 127.0 mm) from the electrode holder.

A carbon arc can be formed by placing the electrode tip in contact with the workpiece and immediately withdrawing it to the correct length for welding. In general, an arc length between 1/4 and 3/8 in. (6.4 and 9.5 mm) is best. If the arc length is too short, excessive carburization of the molten metal is likely, resulting in a brittle weld.

When the arc is interrupted for any reason, it must not be restarted directly on the hot weld metal. This can cause a hard spot in the solder at the point of contact. The arc should be started on the cold metal on one side of the joint and then quickly return to the point where welding will resume.

When the joint requires filler metal, the welding rod is fed into the weld pool with one hand while the arc is manipulated with the other. The arc is directed at the surface of the work and gradually moves along the joint, constantly maintaining a weld pool into which the welding rod is added in the same way as in gas tungsten arc welding. Progress along the weld joint and the addition of a welding rod must be synchronized to provide the desired weld bead size and shape. Vertical or overhead carbon arc welding is difficult because carbon arc welding is essentially a puddle process. The solder joint must be supported, especially in the case of thin sheets, to support molten pools and prevent excessive melting.

For outside corner welds on 14 to 18 gauge steel sheets, carbon arc can be used to weld the two sheets without filler metal. Such welds are generally hotter and more economical to make than shielded metal arc welds made under similar conditions.

Benefits:

  • Low cost of welding equipment and operation;
  • A high level of operator skill is not required;
  • The process is easily automated;
  • Low distortion of the workpiece.

Disadvantages:

  • Unstable weld quality (porosity);
  • The carbon from the electrode contaminates the welding material with carbides.

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