This is a popular welding technique for thin sheets and sections. Tungsten electrodes create the arc. Inert gases like argon or helium or a mix of the two is used to protect the shield. Filler wires add molten material if needed.
Plasma arc welding PAW This arc welding technique uses ionized gases and electrodes that create hot plasma jets aimed at the welding area. As the jets are extremely hot, this method for narrow and deep welds.
PAW is also good for increasing welding speeds. The arc is generated when the coated electrode tip touches the welding area and is then withdrawn to maintain the arc. The heat melts the tip, coating, and metal, so that the weld is formed once that alloy solidifies. This technique is typically used in pipeline work, shipbuilding, and construction. Submerged arc welding SAW SAW works with a granular flux that creates a thick layer during welding, which completely covers the molten metal and prevents sparks and spatter.
The arc is generated when the coated electrode tip touches the welding area and is then withdrawn to maintain the arc. The heat melts the tip, coating, and metal, so that the weld is formed once that alloy solidifies. This technique is typically used in pipeline work, shipbuilding, and construction. SAW works with a granular flux that creates a thick layer during welding, which completely covers the molten metal and prevents sparks and spatter.
This method enables deeper heat penetration because it acts like a thermal insulator. SAW is sued for high-speed sheet or plate steel welding. It can be semiautomatic or automatic. However, it is limited to horizontal welds. Tags: arc welding electrode welding. Two of many examples include: Surface Tension Transfer — a drop of molten metal touches the molten metal pool and is drawn into it by surface tension. Spray Arc — the drop is ejected from the molten metal at the electrode tip by an electric pinch propelling it to the molten pool.
Electrodes In arc welding, an electrode is used to conduct current through a work-piece to fuse two pieces together. Electrodes need to be stored in a moisture free environment and carefully removed from any package Depending upon the process, the electrode is either consumable, in the case of gas metal arc welding or shielded metal arc welding, or non-consumable, such as in gas tungsten arc welding. Consumable Electrodes Consumable electrodes are those which melt away or consumed during the welding process.
Only the alloy or the metal wire. Light coated electrodes — These are electrodes having coating factor of 1. Medium coated electrodes — These have coating factor of about 1. Heavily coated electrode — Coating factor is between 1. Non Consumable Electrodes Non-consumable electrodes are those which do not melt away or consumed during the welding process.
Plasma Arc Welding PAW This arc welding technique uses ionized gases and electrodes that create hot plasma jets aimed at the welding area. Submerged Arc Welding SAW SAW works with a granular flux that creates a thick layer during welding, which completely covers the molten metal and prevents sparks and spatter. Search for:. Subscribe via Email Name.
A small depression is formed in the work and the molten metal is deposited around the edge of this depression, which is called the arc creator. The slag is cleaned after the joint has cooled.
They are, once started, should be advanced at a uniform speed along the desired line of welding. The melting should reach enough depth below the original surfaces of the metal pieces to be joined to obtain the desired weld. This is known as obtaining proper penetration. The direct or alternating current may be used for arc welding, but the direct current is preferred for most purposes. The straight polarity is more useful for some welds while for other welds reversed polarity should be utilized.
Essentially welding is not a hazardous occupation if proper precautionary measures are observed. This requires continuous awareness of possibilities of danger and habitual safety precautions by the welder.
One reason for the wide acceptance of the Arc welding process is the simplicity of the necessary equipment. The equipment consists of the following items. This welding uses either AC or DC, but in either case, the power source selected must be of the constant current type. This type of power source will deliver relatively constant amperage or welding current regardless of arc length variations by the operator. The electrode holder connects to the welding cable and turns the electrode on.
Insulated handles are used to guide the electrode to the welded joint. And feed the electrode above the weld joint and feed the electrode into the weld puddle.
Electrode holders are available in various sizes and are rated at their current carrying capacity. The ground clamp is used to connect the ground cable to the work he connected directly to the work or to the table or fixture upon which the work is positioned. Being a part of the welding circuit, the ground clamps able to conduct welding current without overheating due to electrical resistance.
Electrode cable and ground cable are essential parts of the welding circuit. They must be very flexible and have tough heat-resistant insulation. Connections in the electrode holder, ground clamp, and on the power source must be soldered or well crimped to assure low electrical resistance. Increasing the cable length requires increasing the cable diameter to reduce resistance and voltage drop.
Now most welders can agree that it is necessary to remove the slag from the weld metal. You may be wondering how to remove slag. The acceptability standard is satisfied when the exposed surfaces of each sample show complete penetration and fusion. The maximum size of porosity must not exceed 1. Slag inclusion must not exceed 0. Furthermore, there must be at least 12mm of sound metal between one inclusion and the other. The joint is prepared by making a bevel as indicated in the figures.
If the seam is uneven bevelled edge then rest the second pipe section on the and strongly convex, the current must be increased. If it spacing wire with the bevelled edge facing downwards.
In accordance with the ASME code, misalignment must not exceed 1. If in one of the spans the root 20mm long bead. If the gap at its widest point is too great to permit a third tack, first correct the gap by compressing the most open side.
Make the third and fourth tacks at right angles to the first and second. Then reposition the spacing wire and deposit a second tack. Use a light up and down swinging movement. To maintain a crater of the correct dimensions the movements must be rapid and precise.
Start the arc at the root of the joint never on the edge of the tack or the external pipe surface. Maintain an arc length double the electrode diameter and swing from one edge to the other, to and fro, to pre-heat the edges of the shoulders.
If the crater tends to close, mm of seam. Move back and forth on the crater to preheat the edges then reset the normal arc length.
In this way complete penetration is assured at restart. The travel speed and dwell time determine the result. If the arc is interrupted before the bead is complete, remove the crater slag, restart the arc starting on the last bead approximately 12mm in front of the crater then turn back until the crater is full and resume normal travel.
Finally, remove the slag from the weld ends and carry out the second half of the joint. After having carried out preparation and tacking, the The overlap on the joint edges must measure piece is marked for identification then welded in the 5G approximately 1. A visual examination of metal from 0. Proceed again in the vertical up position, by using the 3. Welding current should be lower than that used in the root and is determined by the pipe size.
Keep the electrode on the edges of the shoulder. If the electrode tip is pushed too far into the joint, undercuts form along the root and excessive penetration and defects occur.
If the electrode is not pushed deep enough into the joint, insufficient Use a perpendicular W motion, with pauses at the points penetration and undercuts on the beveled surfaces of the indicated in the figure to correctly fill the welding crater.
Keep the arc as short as possible. The bead must be flat or slightly convex with good fusion on the edges. The work angle varies, relevant quality assessment of the weld on a sample. A visual analysis of the weld is then carried out. The beads must overlap up to half of the previous one. Use the same swinging movement described for the second bead.
The finished joint must have a projecting machine allowance of 1. The tip of the electrode This type of joint and position is used to weld bends, should be kept on the edges of the shoulder but without flanges, fittings.
The following example shows the welding exerting pressure on them. If qualifies all the others. Execute both halves of the bead and remove the slag before laying the second bead. Then carry out the root bead with E electrodes of 3. Angles as per figure.
Use E electrodes of current. The filling pass should reach approximately 1. The filler metal is generated by the electrode, which through the arc starts mixing with the melted base metal.
In vertical down welding, the arc force tends to make the melted metal flow towards the rear part of the crater to form the seam, while the force of gravity tends to counterbalance that of the arc, making the fusion pool flow in feed direction.
On the contrary, in vertical up welding, the force of the arc and that of gravity push the melted metal back in the crater to form the seam. The movement of the melted metal towards the back of the crater and its form provide the operator with a means of continuous quality control, without interrupting the arc.
The essential variables by which the operator In this case, during welding the groove becomes too interprets the fusion bath on which he must intervene to wide and the weld pool control is difficult due to its size prevent welding defects are: electrode diameter, and fluidity.
To reduce penetration and eliminate this current, arc length, feed speed and electrode problem feed speed may be increased, possibly also positioning angles. If this is not sufficient, interrupt welding and reduce the current. One of the most important factors is penetration. There is correct penetration when the weld completely An excessive heat supply may cause shrinkage This crosses the joint thickness, leaving a small seam of makes the internal surface of the joint concave.
It is a continuous penetration well-fused at the back.
0コメント