--A welding transformer uses the alternating current (AC) supplied to the welding shop at a high voltage to produce the low voltage welding power. As electrons flow through a wire they produce a magnetic field around the wire. If the wire is wound into a coil the weak magnetic field of each wire is concentrated to produce a much stronger central magnetic force. Because the current being used is alternating or reversing each 1/120 of a second, the magnetic field is constantly being built and allowed to collapse. By placing a second or secondary winding of wire in the magnetic field produced by the first or primary winding a current will be induced in the secondary winding. The placing of an iron core in the center of these coils will increase the concentration of the magnetic field.
-- A transformer welder is a step-down transformer. It takes the high line voltage (110V, 220V, 440V, etc..) and low amperage current (30A, 50A, 60A, etc.) and changes it into 17V to 45 V at 190 A to 590 A.
(Larry F. Jeffus, Welding: Principles and Applications 5th edition, page 53)
Cover Pass ( 12:43 pm 17.05 2011)
The final covering on a weld is referred to as the cover pass or cap. It may be a weave or stringer bead. The cover pass should not be too wide or have too much reinforcement. Cover passes that are excessively large will reduce the pipe's strength, not increase it.
(Larry F. Jeffus, Welding: Principles and Applications 5th edition, page 109)
Oxygen Lance Cutting (13:02 pm 07.05.2011)
--The oxygen lance cutting process uses a consumable carbon steel tube. The tip of the tube is heated to its kindling temperature. A high pressure oxygen flow is started through the lance. The oxygen reacts with the hot lance tip, releasing sufficient heat to sustain the reaction. Figure 9-25.
(Larry F. Jeffus, Welding: Principles and Applications 4th edition, page 199)Plasma Arc Gouging ( 13:19 pm 07.05.2011)
Plasma arc gouging is a recent itroduction to the PAC processes. The process is similar to that of air carbon arc gouging in that U-groove can be cut into the metal's surface. The removal of metal along a joint before the metal is welded or the removal of a defect for repairing can easily be done using this variation of PAC.
The torch is set up with a less concentrated plasma stream. This will allow the washing away the molten metal instead of thrusting it out to form a cut.
(Larry F. Jeffus, Welding: Principles and Applications 4th edition, page 178)
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