Master the quick method of one-sided welding and two-sided forming

According to the operation method, the manual arc welding process of "single side welding and double side forming" can be divided

into continuous welding method and intermittent arc extinguishing method.

Intermittent arc welding is almost used for welding the first layer of low carbon steel and low alloy steel. This welding method can use

a large current, has a large penetration force, and can control the temperature and switch of the weld pool, and can achieve root

penetration. However, the continuous welding method, i.e. continuous welding with uninterrupted arc, must use a small welding current,

and the temperature is low at the time of welding. However, when the workpiece temperature rises after welding a section of weldment,

it is not easy to control the temperature and size of the weld pool, so it is difficult to ensure root penetration and no weld overlap.

Therefore, The first layer is rarely used, but used for welding after the second layer.

The intermittent arc extinguishing method is mainly used to control the temperature of the molten pool, the time of the molten pool, the

thickness of the molten pool switch and the liquid metal layer, etc. by controlling the time of arc burning and arc extinguishing, and by

using the reasonable strip handling action to obtain good reverse formation and internal quality. However, no matter which welding

method, the melting degree of the arc to the groove can be divided into penetration and filling of the gap. Seen from the surface, it is

formed at the root, but in essence, the root of the groove has not really penetrated, and can not pass the reverse bending test, so it

has not been used. Generally, the welding method of puncturing the root is used to realize single-sided welding and double-sided forming.

The operation method of single-sided welding and double-sided forming, whether for the welding of carbon steel, low alloy steel or stainless

steel, as well as the use of DC power or AC power supply, although the welding performance is very different, its operation essentials are

consistent, mainly controlling the following three aspects.

1. The assembly clearance of the root clearance should be appropriate.

When the groove angle is reasonable, there must be proper root clearance to ensure that the welding rod is sent to the root and that the arc

passes through the northern part and penetrates the root. In order to easily achieve uniform penetration, the size deviation of the root gap

should be about 1mm.

The root gap size should be equal to the diameter of the electrode used or about 0.5~1.0 mm larger than the diameter.

The size of root gap is related to many factors and should be comprehensively considered.

①The thickness of the workpiece, such as thinner weldment, slower heat dissipation, and heat loss of weldment, can reduce the root gap,

and thicker weldment should be appropriately larger to facilitate root penetration.

②Process parameters: when the welding current is small, the root gap should be slightly larger. When the welder is accustomed to using

large current operation, the root gap should be reduced accordingly.

③At the welding position, the root gap between the flat seam and the transverse seam can be smaller, while the upper seam and the

vertical seam need to be slightly larger.

④Blunt edge size: the blunt edge is large, and the root gap is also larger.

⑤In the welding sequence, those with small root gap should be welded first, and those with large root gap should be welded later. In

addition, factors such as thermal expansion should also be considered.

2. The groove angle should be appropriate, and there should be a certain size of blunt edge.

The groove angle must be determined according to the "rules" and the technical conditions of the relevant design. The groove angle

directly affects the joint quality and weld size. A reasonable angle must be selected, generally 60 °~70 ° for the "v" groove.

Blunt edge is the part of the end face that is not beveled along the thickness direction of the weldment. According to the thickness of

the workpiece, a blunt edge of 0.5~2.0 mm is generally reserved. If the wall thickness is 3 mm, the blunt edge should be 0.5 mm. If

the wall thickness is more than 12 mm, it should be 1.5 mm generally, and the maximum should not exceed 2 mm. If the blunt edge

is too thick, it is easy to cause root incomplete penetration. If it is too thin, it is easy to be broken down and large molten holes will appear.

With the blunt edge, the preheating time of the workpiece with the arc after arc striking can be longer, and the preheating range can be larger,

thus improving the welding process conditions, increasing the fluidity of the liquid metal, and easy to ensure the penetration.

With the blunt edge, it can withstand large welding current, and there will be no phenomenon that the root will be pierced by an induced arc.

It is easy to control the size of molten pool with blunt edges, which is conducive to root penetration. In particular, the overhead welding position

must be operated with a slightly higher current, otherwise it is difficult to form and overcome the process defects such as pores and slag inclusion.

Therefore, it is necessary to have a certain size of blunt edge.

3. The breakdown welding method is adopted.

The breakdown welding method is a kind of welding method that leads the penetration of the arc in the welding process, melts and penetrates

the root, and ensures the root penetration and formation.

The specific operation method is as follows: after striking the arc, lengthen the arc to preheat (the preheating time for flat welding is short and

not very obvious, and the position for overhead welding is very obvious), when the semi-melting state is reached (that is, when the "sweat"

appears on the edge of the preheated groove under the electric welding goggles for about 3 to 4 seconds), lower the arc, melt and break

through the blunt edge, making it appear a "molten hole" slightly larger than the gap between the two sides, So as to ensure that a part of

the deposited metal will transfer to the root and back of the weld and form a weld pool together with the melted base metal.

As the welding rod continues to melt, the penetrated weld hole is welded. At this time, appropriate arc extinguishing measures are taken to

cool it to form a weld. Then the blunt edge is penetrated and melted, and then the molten hole is formed, and then the back weld is formed

by welding.

The formation of fusion hole means that the root has been fully welded. The size of the weld hole is the size of the weld on the back of the

mark. Generally, the diameter of the fusion hole is controlled to be about 1.1~1.5 times of the butt gap. The specific size shall be adjusted

according to the workpiece thickness, welding position, specification parameters, root clearance, steel grade and other factors. Generally,

process test shall be carried out first, and then welding shall be carried out to ensure the welding quality.

The welding after the second layer adopts the continuous welding method. Attention should be paid to reducing the process defects and

the welding current should be moderate. For carbon steel and low alloy steel weldments, the slow cooling should be controlled after welding,

in order to obtain the joints with good structure and properties and create conditions for gas escape. For austenitic stainless steel weldments,

it is required to select a smaller welding process specification. After welding, the natural cooling or rapid cooling should be made to prevent

the tendency of intergranular corrosion due to overheating.

When welding the cover layer (reinforced welding layer), the "filling and leveling" shall be carried out first to make the weld meat consistent in

height and not exceed the groove surface, keep the groove contour, adjust the welding current, and cover the surface at one time to achieve

beautiful appearance.