© COPYRIGHT 1998 THE ESAB GROUP, INC. LESSON II
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Lesson 1
The Basics of Arc Welding
Lesson 2
Common Electric
Arc Welding Processes
Lesson 3
Covered Electrodes for Welding
Mild Steels
Lesson 4
Covered Electrodes for Welding Low Alloy Steels
Lesson 5
Welding Filler Metals for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc Electrodes Carbon Low Alloy Steels
Lesson 8
Hardsurfacing Electrodes
Lesson 9
Estimating & Comparing Weld Metal Costs
Lesson 10
Reliability of Welding Filler Metals
inch or 7 inch lengths.  Torches may be either air or water-cooled.  The air-cooled types actu- ally are cooled to a degree by the shielding gas that is fed to the torch head through a compos- ite cable.  The gas actually surrounds the copper welding cable, affording some degree of cooling.  Water-cooled torches are usually used for applications where the welding current exceeds 200 amperes.  The water inlet hose is connected to the torch head.  Circulating around the torch head, the water leaves the torch via the current-in hose and cable assembly. Cooling the welding cable in this manner allows the use of a smaller diameter cable that is more flexible and lighter in weight. 2.3.3.1 The gas nozzles are made of ceramic materials and are available in various sizes and shapes.  In some heavy duty, high current applications, metal water-cooled nozzles are used. 2.3.3.2 A switch on the torch is used to energize the electrode with welding current and start the shielding gas flow.  High frequency current and water flow are also initiated by this switch if the power source is so equipped.  In many installations, these functions are initiated by a foot control that also is capable of controlling the welding current.  This method gives the operator full control of the arc.  The usual welding method is to start the arc at a low current, gradually increase the current until a molten pool is achieved, and welding begins.  At the end of the weld, current is slowly decreases and the arc extinguished, preventing the crater that forms at the end of the weld when the arc is broken abruptly. 2.3.4 Shielding Gases - Argon and helium are the major shielding gases used in gas tungsten arc welding.  In some applications, mixtures of the two gases prove advantageous. To a lesser extent, hydrogen is mixed with argon or helium for special applications. 2.3.4.1 Argon and helium are colorless, odorless, tasteless and nontoxic gases.  Both are inert gases, which means that they do not readily combine with other elements.  They will not burn nor support combustion.  Commercial grades used for welding are 99.99% pure.  Argon is .38% heavier than air and about 10 times heavier than helium.  Both gases ionize when present in an electric arc.  This means that the gas atoms lose some of their electrons that have a negative charge.  These unbalanced gas atoms, properly called positive ions, now have a positive charge and are attracted to the negative pole in the arc.  When the arc is positive and the work is negative, these positive ions impinge upon the work and remove surface oxides or scale in the weld area. 2.3.4.2 Argon is most commonly used of the shielding gases.  Excellent arc starting and ease of use make it most desirable for manual welding.  Argon produces a better cleaning action when welding aluminum and magnesium with alternating current.  The arc produced is