BOLT 1D5976 - Caterpillar

Fundamentals of the Process
Definition
Shielded Metal Arc Welding is an arc welding process wherein coalescence is produced by heating with an electric arc between a covered metal electrode and the work. Shielding is obtained from decomposition of the electrode covering. Pressure is not used and filler metal is obtained from the electrode.Slang Names
1. Stick/manual metal arc.Process Principles
1. Heat source - heat of the arc.2. Shielding gas - slag formed by the decomposition of the flux.3. Filler metal - comes from core wire.4. Flux - contains deoxidizers/slag formed/ionizing elements to stabilize the arc/iron powder for higher deposition.
Figure 1Methods of Application
1. Manual - most widely used - approximately 90%2. Semiautomatic - not used3. Machine4. Automatic - gravity/massive/firecrackerElectrical Requirements
Welding Circuit
Figure 2Welding Current types
1. A.C.2. D.C.E.N. (straight) polarity.3. D.C.E.P. (reverse) polarity.Power Source Types and Characteristics
1. Generator (DC)2. Transformer (AC)3. Rectifier (DC)4. Transformer Rectifier (AC/DC)5. Alternators (AC)Other Electrical Requirements
1. Multiple OperatorsOther Equipment Requirements
Additional Equipment Necessary
1. Helmet/gloves/leathers2. Chipping hammer/wire brush3. Grinder for repairSetup of Equipment
The manner in which equipment is set up in preparation for welding is an important consideration, both from the safety standpoint and for the speed and ease with which the weld can be made.Welding should be done in a specially prepared welding area if at all possible. It is usually quicker and easier and always safer and more convenient to carry the work to the welder rather than carry the welder to the work. If welding must be done in places other than the regular welding areas, extra attention should be given to safety precautions, and other workmen in the area should be notified that welding will be going on.Adequate ventilation and lighting and a source of sufficient power must be provided. The welding machine should be located close enough to the work to assure free and easy manipulation of the electrode holder and cable. Cable connections must be made soundly and the ground cable clamp must be attached securely to the work to assure an uninterrupted flow of current. The ground clamp should always be placed on the piece being welded; current must never be allowed to flow through bearings, hydraulic cylinders or other precision surfaces. If this occurs, minute pits will form at the points of contact and cause excessive wear.Whenever possible, the work should be positioned so the face of the weld being made and the axis of the weld will be within 10° of horizontal. In this position, higher amperages and deposition rates can be used, the puddle of molten metal is easier to control, and the welder is in a more comfortable position. In addition, more welding skill is generally required for welding in positions other than flat and horizontal.Striking an Arc
An arc is struck by momentarily touching the work with the electrode. When the arc is struck, there is a tendency for the electrode to stick to the work because of the sudden rush of current caused by the short-circuiting of the welding machine. To avoid this sticking or freezing of the electrode, a motion