Ignition and maintain the arc.
Before ignition (excitation) of the arc should set the desired effect of welding current, which depends on the type of electrode, the spatial position of welding, weld type, etc. The Kindle arc in two ways. In one method, the electrode closer to the vertical surface of the product until it touches the metal and rapidly withdrawn up to the desired length of the arc. In another - passing electrode "strike sharply" over the surface of the metal. The use of a method of ignition of the arc depends on the welding conditions and the skill of the welder.
The arc length depends on the type and diameter of the electrode, the spatial position of welding, cutting edges and welded T-section normal length of the arc is within the ld = (0.5 - 1.1) * del (del - the diameter of the electrode). Increasing the length of the arc decreases the quality of the deposited weld metal because of its intense oxidizing and nitriding increases the loss of metal fumes and spatter, reduces the depth of penetration of the base metal. It also deteriorates the appearance of the seam.
During the process of the welder moves the electrode is usually at least two directions. First, it gives the electrode along its axis in an arc, keeping the required depending on the rate of melting of the electrode arc length. Second, the moves in the direction of welding electrode or welding to form a seam. In this case a narrow ridge, with a width equal to the surfacing of approximately (0.8 - 1.5) * del and depends on the welding current and speed of movement of the arc on the surface of the product. Narrow ridges are usually imposed at the root penetration weld, welding of thin sheets, and similar cases.
When properly chosen diameter of the electrode and the strength of the welding current velocity of the arc is of great importance for the quality of the seam. At higher speeds the arc melts the base metal at a shallow depth and formation of fusions. At low speeds due to excessive heat input of the arc in the base metal is often formed by burn-through, and the molten metal is derived from the weld pool. In some cases, such as welding on the descent, the formation of an arc of a liquid layer of molten electrode metal thickness increased, by contrast, can lead to poor penetration.
Sometimes, the welder has to move the electrode across the joint, thus regulating the distribution of the heat of the arc across the joint to obtain the required depth of penetration of the base metal and weld width. The depth of penetration of the base metal and weld formation is mainly dependent on the type of transverse oscillations of the electrode, which are usually committed with constant frequency and amplitude with respect to the axis of the joint. The trajectory of the electrode depends on the spatial position of the welding, cutting edge and skills of the welder. When welding with transverse vibrations of the roller are broadened, the width of which is typically (2 - 4) * del, and the form of penetration depends on the trajectory of the transverse oscillations of the electrode, ie, the conditions of the heat input of the arc in the base metal.
At the end of welding - arc is broken to properly weld crater. The crater is the zone with the most harmful substances in view of the high rate of crystallization of the metal, so it is most likely the formation of cracks. Upon completion of welding arc should not be cut short, abruptly assigning the electrode from the product. Must stop all movement of the electrode and slowly lengthen the arc to break, a refiner with the electrode metal to fill the crater. When welding mild steel crater sometimes derive from the side seam - on the base metal. When the random cliffs arc or by changing the arc electrodes excite the still molten base metal to the crater and then proplavlyayut metal in the crater.
The position of the electrode relative to the workpiece surface and the spatial position of the welding have a great influence on the shape of the weld and base metal proplavke not. When welding angle back from the improved conditions of marginalization of the arc of a liquid metal, the thickness of the layer is reduced. At the same time improve the conditions of heat transfer from the arc to the base metal and increases its depth of penetration. The same is observed in the welding seam on the rise on an inclined or vertical plane. When welding angle forward or descend the molten metal weld pool, smudges under the arch, affects the heat transfer from it to the base metal - the depth of penetration decreases and the width of the joint increases.
Other things being equal amount of molten electrode metal per unit length of weld, remains constant, but is distributed over a large width of the joint and therefore the height of the gain is reduced. When surfacing or welding sheet metal (thickness 3 mm) to reduce the depth of penetration and prevent burn-through is recommended for 15-20 "to carry out welding on the slope (the slope to 15 °) angle or forward without bending vibrations of the electrode. to build products for welding (software defined gap in the joint, the provisions of articles, etc.) can use special devices or short stitches - potholders. tack length is typically 20 - 120 mm (more on the thicker the metal) and the distance between 200-1200 mm (less for thicker metal for increase in stiffness). tack section shall not exceed the third section joints. When welding must be completely remelted tack.
See also:
Manual Arc Welding
Introduction to Arc Welding
Creating and maintaining an arc
Ways to improve performance
Technique of upper and horizontal joints
Technique of the lower seam
Pipe Welding Technique
The Method
Arc Welding in Protective Gases
Electrodes for Manual Arc Welding
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