What are the operation skills and precautions of single-sided welding and double-sided welding?

CO2 gas shielded welding requires strict groove form and assembly. The groove form and size of butt weld include angle, blunt edge and assembly clearance. The groove angle mainly affects whether the arc can penetrate the root of the weld, so that the root can penetrate, and then better weld formation and welding quality can be obtained. On the premise of ensuring that the arc can penetrate deep into the root of the weld, the groove angle should be reduced as much as possible. The size of the blunt edge can directly affect the penetration depth of the root, and the larger the blunt edge, the less likely it is to penetrate. It is easy to weld through when the blunt edge is small or not, and it is easy to burn through when the assembly gap is large. Assembly clearance is the key parameter of back welding forming, which is easy to burn through if it is too large; The gap is too small to weld through. H08Mn2 Si welding wire with diameter of 1. Use 2 mm The droplet transfer form of one-sided welding and double-sided back cover welding is short-circuit transfer, and usually a smaller blunt edge can be selected, or even no blunt edge can be left. The assembly gap is 2 ~ 4 mm, and the groove form requires a V-groove with a groove angle of 60 5, which plays a very good role in improving the groove accuracy and welding quality. Pay attention to the influence of weather when welding, especially the windproof measures must be in place.

2.2 Selection of welding current

Welding current is the main factor to determine the penetration depth. When the welding current is too large, the back of the weld is easy to burn through, undercut, burr, and even serious splash and porosity. When the current is too small, defects such as incomplete fusion, incomplete penetration, slag inclusion and poor forming are easy to occur. The test shows that when the diameter of welding wire is 1. Choosing 2 mm, the welding current of the cover formed by one side welding and two sides is 85 ~ 100 a, so the welding current directly affects the formation of weld and the generation of welding defects.

2.3 Selection of welding voltage:

In the case of short circuit transition, the arc length increases with the increase of arc voltage. When the arc voltage is too low, the welding wire will be inserted into the molten pool and the arc will become unstable. Therefore, the arc voltage must be selected correctly. Generally, if the welding current is small, the arc voltage will be low. When the current is large, the arc voltage is high.

2.4 Selection of welding speed

When the welding wire diameter, welding current and voltage are constant, the penetration depth, width and residual height decrease with the increase of welding speed. If the welding speed is too fast, the protective effect of gas will be easily destroyed, and the weld will be cooled too fast, resulting in poor weld formation; If the welding speed is too slow, the weld width will increase obviously, and the heat in the molten pool will be too concentrated, which is easy to burn through or produce flash.

3 operation method:

CO2 gas shielded welding of welded pipe is an open arc operation, which has good visibility of weld pool, is easy to master the change of weld pool, can directly observe the weld hole broken by arc, and can control the size and consistency of weld hole, and is much superior to manual arc welding in this respect. In addition, there are few joints when welding, which is not easy to produce defects, but improper operation is also easy to produce defects. Therefore, special attention should be paid to the operation.

3. Control the dry extension length as 1

The length of dry drawing has a great influence on the stability of welding process. When the dry drawing length is long, the resistance of welding wire increases, and the welding wire is overheated and melted in sections, which leads to unstable welding process, serious metal spatter, poor weld formation and poor gas protection of molten pool. If the dry elongation is too short, the welding current will increase, the distance between the nozzle and the workpiece will be shortened, and the welding line of sight will be unclear, which will easily lead to poor weld formation and overheating of the nozzle, causing spatter to stick or block the nozzle, thus affecting the gas circulation. Therefore, ten times the diameter of welding wire is generally selected as the best dry elongation length.

3.2 Angle selection of welding wire and welded pipe

The longitudinal and transverse included angle between welding wire and welded pipe is the key to ensure the welding quality of single-sided welding and double-sided forming backing weld. Special attention should be paid to the angle between welding wire and welded pipe when back welding is carried out at various welding positions. When the welded pipe is butt welded horizontally, the axis of the welding wire and the welded pipe is inclined downward 10 ~ 20, and the circumferential tangent is 70 ~ 80; When the welded pipe is butt welded in all positions, the welding wire forms 90 degrees with the axis of the welded pipe and 60 ~ 80 degrees with the circumferential tangent.

3.3 backing weld welded joint

In backing weld, the number of joints should be reduced as much as possible. If joints are needed, the arc pit should be polished into a gentle slope shape with a grinding wheel. When grinding, be careful not to destroy the edge of the groove, which will enlarge the local gap of welded pipe and bring difficulties to backing weld. When jointing, align the dry joints and weld slowly. When the arc burns to the thinnest part of the gentle slope, it will swing normally. The welding method of CO2 gas shielded arc welding is completely different from manual arc welding. When welding the joint manually, when the arc burns to the molten hole, put down the arc and pause for a while before connecting; However, CO2 gas shielded welding only needs normal welding, and the joint can be connected with it through penetration.

3.4 Base weld

The backing weld is the key to the quality of welded joint of welded pipe. Only by paying attention to the method of welding joints can welding defects be avoided. The welding current should be properly adjusted according to the size of the groove angle. When the slot angle is large, the heat dissipation area is small, so the current should be reduced, otherwise it is easy to cause defects such as edge collapse and reverse undercut. When backing weld is used, the short tooth profile will swing. Because the spacing of the short tooth profile is not well grasped, the welding wire passes through the middle of the assembly gap. This is allowed if a small amount of welding wire passes through the whole weld. If there are many welding wires, it is not allowed. In order to prevent the welding wire from coming out, the welding torch should be held firmly when backing weld is in operation. You can hold the welding torch with both hands, the back of the welding torch with your right hand, the start switch with your index finger and the gooseneck of the welding handle with your left hand. This can reduce the welding leakage or not, and ensure the smooth progress of backing weld and the internal quality of backing weld.

It should be noted that before backing weld, it is necessary to check the welding specifications to avoid problems in the welding process, check whether the inner diameter of the conductive resistor is appropriate, and pay attention to whether the splash inside the nozzle blocks the nozzle. Don't leave the arc pit immediately after the arc stops or backing weld ends, so as to avoid shrinkage cavity and blowhole.

Needless to say, after filling in the bottom cover! Ha ha!