What kind of bar carrying technique for welders to be correct
Boilers and pressure vessels and other important structures, requiring a safe weld through the joint, but due to the size and shape of the structure and other restrictions, sometimes can not be double-sided welding. Can only open a single-sided bevel special operation method single-sided welding double-sided formation technology, it is a difficult operation skills in hand arc welding.
When welding vertical welding, due to the high temperature of the molten pool, under the action of gravity, the molten droplets formed by the melting of the welding rod and the molten pool of iron is easy to flow down to form a weld tumor, the formation of both sides of the weld bite.
When the temperature is too low, it is easy to produce slag, the opposite side is easy to form defects such as failure to weld through, weld tumor, resulting in difficult welding seam formation.
The temperature of the melt pool is not easy to determine directly, but it is related to the shape and size of the melt pool, therefore, when welding, as long as you carefully observe and control the shape and size of the melt pool can achieve the purpose of controlling the temperature of the melt pool to ensure the quality of welding.
According to the teacher’s experience of more than a decade, with such a few words can summarize the law.
The angle of the welding rod is very important, welding specifications are indispensable.
Table of Contents
- 1 The angle of the welding rod is very important, welding specifications are indispensable.
- 2 Watch the molten pool, listen to the arc sound, melt hole shape in mind
- 3 The melt pool temperature control, the quality of the weld can be improved
- 4 The transport method to ensure correct, the weld can be shaped well
When standing welding, due to the melting of the electrode formed by the molten droplets and molten pool of iron is easy to flow down to form a weld tumor, the weld formed on both sides of the biting edge, so that the weld formation deteriorates. Master the correct welding specification and adjust the welding rod angle and speed according to the changes in welding conditions.
The angle between the welding rod and the surface of the welded part is 90° in the left and right direction, and the angle with the welding seam is 70°-80° at the start of welding, 45°-60° in the middle, and 20°-30° at the end. The assembly gap is 3-4㎜, smaller welding rod diameter Φ3.2㎜ and smaller welding current should be chosen, 110-115A for bottom welding, 115-120A for middle over layer and 105-110A for cover layer.
The current is generally 12%-15% smaller than flat welding to reduce the volume of the molten pool, so that it is less affected by gravity, which is conducive to excessive melt drops. The use of short arc welding, shorten the distance from the molten drop to the molten pool to form a short-circuit transition.
Watch the molten pool, listen to the arc sound, melt hole shape in mind
Bottom welding of the root of the weld is a key to ensure the quality of the weld. Using the arc extinguishing method of welding, vertical welding arc extinguishing rhythm than flat welding slightly slower than 30 to 40 times per minute, each point of welding when the arc burning slightly longer, so the weld meat of vertical welding than flat welding thick.
Welding from the lower end of the welding, bottoming the angle of the welding rod about 70 ° – 80 °, using two-point penetration welding, the bevel side of the ignition arc along the spot welding point to the root of the preheating melting, hear the arc penetrate the bevel and the “puff” sound, see the melt hole, the formation of molten pool seat, immediately lift the welding rod to extinguish the arc.
Then reignite the other side of the bevel, the second molten pool should be pressed into the first solidification pool 1/2 to 2/3, so that the use of left and right arc extinguishing penetration will get the whole weld. Extinguish the arc to use the flexibility of the wrist, each time cleanly extinguish the arc, so that the molten pool has the opportunity to instantaneously solidify.
When the arc is extinguished, it is obvious that the blunt edge of the fusion hole formed by the penetration, vertical welding fusion hole of about 0.8mm, the size of the fusion hole is closely related to the back molding, the fusion hole is too large back easily formed weld tumor, on the contrary, there is no fusion hole back often not welded through, the operation requires the maintenance of uniform fusion hole size, so as to ensure that the root of the bevel is evenly penetrated, the back of the weld channel is full, the width and height of uniform.
Bottoming for welding rod joints, each time the joint parts of the flux skin clean, in the bevel from a new ignition arc, along to form the weld about 10mm at the continuous welding change the angle of the welding rod, to 90 degrees when reaching into the center of the weld around a slight swing, and at the same time press down a little arc, hear the arc sound, the formation of molten hole, immediately extinguish the arc, so that the welding rod arc into the root of the weld, the formation of the melting hole immediately extinguish the arc.
Then the same as the first electrode bottoming welding method, left and right alternating cycle arc extinguishing penetration, each action should be concentrated, pay attention to the outline of the melt hole and both sides were melted gap, the bevel root melted gap, only when the arc moved to the other side can be seen, found blunt edge not fused well slightly downward generation point arc, in order to achieve a good fusion, each time the arc time control in the molten pool is still a third of the unconsolidated on a new arc.
When closing the arc, it should be noted that each welding rod only 80 – 100mm long, the welding rod due to overheating, melting accelerated, when the arc extinguishing time should grow, so that the molten pool has a momentary solidification, to prevent the high temperature molten pool to transport the bar down to form a weld tumor. When the welding rod only 30 – 40mm when ready to do arc extinguishing action, the melt pool on one side of two or three consecutive drops, so that its melt pool to achieve the purpose of slow cooling, which can prevent the front and back of the welding channel to produce shrinkage and arc pit cracking and other defects.
The melt pool temperature control, the quality of the weld can be improved
Requires the middle layer of the weld wave flat positive. The middle two layers according to the diameter of the welding rod φ3.2㎜, welding current is 115 – 120A, the welding rod angle is about 70 ° – 80 °, the use of sawtooth-shaped transport method, the use of welding rod angle, arc length, welding speed and bevel on both sides of the residence time to control the temperature of the molten pool. Make both sides good fusion, and to ensure the shape of the flat round molten pool.
The third layer of welding, do not destroy the edge of the bevel, leaving a depth of about 1mm, so that the entire filler welding channel flat. Depth above the bevel edge as the reference line, to cover the surface to lay the foundation, the use of left and right swing in general both sides of the bevel slightly more stop, so that the bevel edge melting 1 – 2㎜, and to ensure that the melt pool and the bevel on both sides of the temperature balance.
Mainly observe the shape of molten pool, control the molten pool into crescent type, stop less on the side with more molten pool and stop more on the side with less, calculate the height and width of weld seam while applying welding. Because the weld flesh of vertical welding is thicker than flat welding, pay attention to the shape of the melt pool and the thickness of the weld flesh, if the lower edge of the melt pool from the gentle side down convex, indicating that the temperature of the melt pool is too high, which should shorten the arc burning time, extend the arc extinguishing time to reduce the temperature of the melt pool. Before replacing the welding rod must fill the arc pit to prevent the emergence of arc pit cracks.
The transport method to ensure correct, the weld can be shaped well
Cover welding, welding can be used when the serrated or crescent-shaped transport method, the transport of the strip to be stable, in the middle of the welding channel speed to be slightly faster, in the bevel on both sides of the edge to stay a little. The process specification is φ3.2㎜ of welding rod diameter, welding current is 105-110A, the angle of welding rod should be kept about 80°, the welding rod is swung around so that the edge of bevel is melted 1-2㎜, and the sides are stopped with a slight up and down trembling.
However, when the welding rod goes from one side to the other, the arc in the middle is slightly lifted and the shape of the whole molten pool is observed. If the molten pool is flat and oval, it means the temperature of the molten pool is more suitable for normal welding and the surface of the weld is well formed. If the melt pool is found below the drum belly rounded, the melt pool temperature has been slightly higher, should immediately adjust the method of transport, that is, the welding rod in the bevel on both sides of the time to increase the stay, speed up the middle over speed, and try to shorten the arc length.
If the molten pool can not restore the flat elliptical state, and the drum belly has increased, it means that the temperature of the molten pool has been too high, should immediately extinguish the arc, give the molten pool cooling time, to continue welding after the molten pool temperature drops.
Cover to ensure that the edge of the weld is good, found biting edge welding rod slightly move, or more stay to make up for defects, the surface excess to round and smooth.
Covering the joint start welding, the temperature of the weld is low, prone to poor fusion and slag, joint disconnection, too high defects, so the cover is good or bad directly affect the surface of the weld forming. Therefore, the preheating method is applied to the joint, and the arc is ignited from top to bottom with the scratch method about 15mm above the starting end, and the arc is stretched by 3-6mm to preheat the starting point of the weld. Then lower the arc and swing 2-3 times at 2/3 of the original arc pit in order to achieve good dissolution and then transfer to normal welding.
Although the position of the weld is different, they also have a common law. Practice proves that by choosing the appropriate welding process parameters, maintaining the correct angle of the welding rod and mastering the three movements of the welding rod, and strictly controlling the temperature of the molten pool, excellent weld quality and beautiful weld formation can be obtained when welding standing welds.
Source: Network Arrangement – China Flange Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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