Submerged Arc Welding (SAW)

Submerged arc welding is a process in which the joining of metals is produced by heating with an arc or arcs between a bare metal electrode or electrodes and the work.

The arc is shielded by a blanket of granular fusible material on the work.

Pressure is not used.

Filler metal is obtained from the electrode or from a supplementary welding rod.

b. Equipment.

(1) The equipment components required for submerged arc welding are shown by figure 10-59.

Equipment consists of a welding machine or power source, the wire feeder and control system, the welding torch for automatic welding or the welding gun and cable assembly for semiautomatic welding, the flux hopper and feeding mechanism, usually a flux recovery system, and a travel mechanism for automatic welding.

(2) The power source for submerged arc welding must be rated for a 100 percent duty cycle, since the submerged arc welding operations are continuous and the length of time for making a weld may exceed 10 minutes.

If a 60 percent duty cycle power source is used, it must be derated according to the duty cycle curve for 100 percent operation.

(3) When constant current is used, either ac or dc, the voltage sensing electrode wire feeder system must be used.

When constant voltage is used, the simpler fixed speed wire feeder system is used. The CV system is only used with direct current.

(4) Both generator and transformer-rectifier power sources are used, but the rectifier machines are more popular.

Welding machines for submerged arc welding range in size from 300 amperes to 1500 amperes.

They may be connected in parallel to provide extra power for high-current applications.

Direct current power is used for semiautomatic applications, but alternating current power is used primarily with the machine or the automatic method.

Multiple electrode systems require specialized types of circuits, especially when ac is employed.

(5) For semiautomatic application, a welding gun and cable assembly are used to carry the electrode and current and to provide the flux at the arc.

A small flux hopper is attached to the end of the cable assembly.

The electrode wire is fed through the bottom of this flux hopper through a current pickup tip to the arc.

The flux is fed from the hopper to the welding area by means of gravity.

The amount of flux fed depends on how high the gun is held above the work.

The hopper gun may include a start switch to initiate the weld or it may utilize a "hot" electrode so that when the electrode is touched to the work, feeding will begin automatically.

(6) For automatic welding, the torch is attached to the wire feed motor and includes current pickup tips for transmitting the welding current to the electrode wire.

The flux hopper is normally attached to the torch, and may have magnetically operated valves which can be opened or closed by the control system.

(7) Other pieces of equipment sometimes used may include a travel carriage, which can be a simple tractor or a complex moving specialized fixture. A flux recovery unit is normally provided to collect the unused submerged arc flux and return it to the supply hopper.

(8) Submerged arc welding system can become quite complex by incorporating additional devices such as seam followers, weavers, and work rovers.