Principles Of Shielded Metal Arc Welding (SMAW)

Posted by Florida Gas Welding power in a welding circuit is measured by the voltage and current. However, the voltage is governed by the arc length and in turn depends on the electrode diameter. Therefore, the practical measure of the power, or heat, is in terms of the current, generally measured in amperes. Obviously a small electrode requires less current than a large one. To simplify operations the scale on the front of the welding machine is marked off for the various current values. The exact current selected for a job depends upon the size of the pieces to be welded and the position of welding. Generally a lower current will be sufficient for welding on a small part than would be necessary to weld on a large piece of the same thickness. Similarly with a given size of electrode a lower current should be used on thin metals than on the heavier sections
welding smaw


While it is always a good policy to weld on work in the flat position, occasionally, when working on machines or other large units it will be necessary to weld in a vertical, horizontal or overhead position. As seen in the above illustrations. Generally, under these difficult conditions it is helpful to reduce the current from the value used on welding in the flat position.

Striking The Arc – Running Beads

welding smaw2

In learning to weld there are certain fundamental steps which must be mastered before one can attempt to weld on actual work. Preparatory to the actual striking of the arc, it is necessary to insert the electrode in the holder.

Scratching Technique – In this method the striking end of the electrode is dragged across the work in a manner much the same as striking a match. When the electrode touches the work, the welding current starts. If held in this position, the electrode would “freeze” or weld itself to the work and to overcome this, the electrode is withdrawn from the work immediately after contact has been made. The amount that the electrode is withdrawn is small and depend upon the diameter, this distance is known as the arc length. If in striking the arc, the electrode freezes, it may be freed by a quick twist of the wrist.

Another method of establishing the arc is available. It is known as the “tapping method”. In this the electrode in the holder is brought straight down on the work and immediately after contact, is withdrawn to the proper arc length. Practice striking the arc using both method. Generally the scratching method is preferred for AC welding. Determination of the correct arc length is difficult since there is no ready means of measuring it. As a preliminary guide, use about 1/16″ and 3/32″ electrode, for 1/8″ and 5/32″ electrodes use about 1/8″ arc length. When skill is acquired , the sound of the arc will be a good guide. A short arc with correct current will give a sharp, crackling sound. Examination of the deposited bead will give a further check.

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