How to distinguish flat welding, vertical welding, horizontal welding and overhead welding
The film evaluators are familiar with the welding method (manual welding or automatic welding), welding type (single-sided welding or double-sided welding), welding position (flat welding, vertical welding, horizontal welding, overhead welding) and its image characteristics, which is very helpful for the correct judgment of defects, and this is also the content of the actual operation film evaluation examination, so this section makes a brief introduction.
Identification of welding method (manual welding or automatic welding)
The welding method (manual welding or automatic welding) is easy to identify. In most cases, automatic welding has no welding wave image. If the welding wave shown in the figure below appears, it also belongs to automatic welding.
Manual welding has all kinds of welding wave images (unless it has been polished smooth), as shown in the figure below.
The welding seam of liquefied gas cylinder is generally automatic welding. The butt girth welds of pipes with double wall single projection or double wall double projection transillumination are generally welded by hand.
Identification of welding type (single side welding or double side welding)
As shown in the figure on the left, the root of single side welding should be formed, with internal reinforcement or overhead welding to form concave. Therefore, the recognition of single side welding mainly depends on whether there is a narrow root image in the weld image, if there is one side welding.
Double side welding and double side welding, the reinforcement of both sides is wide, as shown in the figure below, there is no narrow root image.
Welding position (flat welding, vertical welding, horizontal welding, overhead welding)
① Flat welding: the position where the welding plate is placed horizontally and the welding rod (or welding wire) is welded vertically downward is called flat welding.
Most of automatic welding is flat welding without welding wave. The welding wave of manual flat welding is larger, similar to water ripple. Please refer to the weld appearance picture.
② Vertical welding: the welding plate is placed vertically on the ground, the weld bead runs vertically, and the welding rod (or welding wire) is roughly horizontally aligned with the weld bead. The welding position is called vertical welding. Vertical welding is mostly manual welding, from bottom to top welding, welding wave arc is small. When welding, the welding rod swings left and right, sometimes two welding waves are formed. See weld appearance picture.
③ Horizontal welding: the welding position where the welding plate is placed vertically on the ground, the weld bead moves horizontally, and the welding rod (or welding wire) is roughly horizontally aligned with the weld bead for welding is called horizontal welding. Horizontal welding is manual welding, from left to right or from right to left,
Especially when covering the surface, weld the lower weld bead first and weld the upper weld bead in turn, so as to form a weld groove along the longitudinal direction of the weld seam. The corresponding weld groove image will appear on the negative film. Please refer to the weld appearance diagram.
④ Overhead welding: the position where the welding plate is placed horizontally and the welding rod (or welding wire) is welded vertically upward is called overhead welding.
Overhead welding is manual welding, which is the most difficult position. If the fusion welding metal can’t be pushed up, it will stay. The arc of welding wave is also small, which is difficult to distinguish from vertical welding from image. Generally, the weld surface is sometimes uneven, and concave defects are easy to appear in single-sided welding, which can be judged with the help of judgment.
Brief introduction of overhead welding
- 1. The molten metal falls due to gravity, and the shape and size of the molten pool should not be controlled.
- 2. It is difficult to transport the strip, and the surface of the weldment should not be flat.
- 3. Defects such as slag inclusion, incomplete penetration, weld bead and poor weld formation are easy to appear.
- 4. Molten weld metal spatter diffusion, easy to cause scalding accident.
- 5. The efficiency of overhead welding is lower than that of other positions.
1. For overhead welding of butt weld, when the thickness of weldment is less than or equal to 4mm, type I groove shall be used, and φ The welding current of 3.2mm electrode should be moderate; When the welding thickness is greater than or equal to 5mm, multi-layer and multi pass welding shall be adopted.
2. For overhead welding of T-joint, when the welding leg is less than 8 mm, single layer welding shall be adopted, and when the welding leg is more than 8 mm, multi-layer and multi pass welding shall be adopted.
3. According to the specific situation, adopt the correct method of transporting the strip:
(1) When the welding leg size is small, the straight-line or linear reciprocating type is used to transport the strip, and the single-layer welding is completed; When the welding leg size is large, multi-layer welding or multi-layer and multi pass welding can be used to transport the strip. The first layer should be linear type, and the other layers can be inclined triangle type or inclined ring type.
(2) No matter which method is adopted, the weld metal should not be too much at each time.
Introduction of flat welding
1. The welding metal is mainly transferred to the molten pool by self weight.
2. The shape and metal of molten pool are easy to maintain and control.
3. When welding metal with the same thickness, the welding current of flat welding position is higher than that of other welding positions, and the production efficiency is higher.
4. Slag and molten pool are easy to mix, especially when welding flat fillet weld, slag is easy to lead and form slag inclusion.
*The slag and pool of acid electrode are not easy to distinguish; The basic electrode is clear; According to hg20581 standard, acid electrode can not be used for class II and III vessels.
5. When the welding parameters and operation are not appropriate, it is easy to form defects such as weld bead, undercut and welding deformation.
6. When the back of single side welding is free forming, the first weld is easy to produce images such as uneven penetration procedure and poor back forming.
1. According to the thickness of the plate, larger diameter electrode and larger welding current can be selected for welding.
2. When welding, the welding rod and weldment should be 60 ~ 80 ° The angle between slag and liquid metal should be controlled to prevent slag from leading.
3. When the plate thickness is less than or equal to 6 mm, type I groove is generally used for butt welding, and the front weld should be used φ 2 ~ 4 electrode short arc welding, the penetration can reach 2 / 3 of the plate thickness; Before back sealing, the root may not be cleaned (except for important structures), but the slag shall be cleaned, and the current may be higher.
4. In case of unclear mixing of slag and molten pool metal in butt welding, the arc can be lengthened, the electrode can be tilted forward, and the slag can be pushed to the back of molten pool to prevent slag inclusion.
5. When welding horizontal inclined weld, upslope welding should be adopted to prevent slag inclusion and molten pool from moving forward to avoid slag inclusion.
6. When multi-layer and multi pass welding is adopted, attention should be paid to the number of welding passes and welding sequence, and each layer should not exceed 4 ~ 5mm.
7. For T-type, corner joint and lap joint, if the thickness of two plates is different, the welding rod angle should be adjusted to deflect the arc to one side of the thick plate to make the two plates heated evenly.
8. Correct selection of strip transportation method.
- (1) When the welding thickness is less than or equal to 6 mm, type I groove butt flat welding is adopted. When double-sided welding is adopted, straight-line welding is adopted for the front weld, which is slightly slow; The back welding seam also adopts the linear type, the welding current is slightly larger, and the welding speed is faster.
- (2) When the plate thickness is less than or equal to 6 mm, multi-layer welding or multi-layer multi pass welding can be used for other forms of groove. The first layer of backing welding should use small current electrode, small standard current, straight-line or serrated welding. When welding filler layer, the welding rod with larger diameter and short arc welding with larger welding current can be selected.
- (3) When the leg size of flat fillet welding of T-joint is less than 6 mm, single-layer welding can be used, and straight-line, oblique ring or serrated welding method can be used; When the welding leg size is large, multi-layer welding or multi-layer multi pass welding should be adopted. The backing welding should adopt the straight-line strip transportation method, and the filling layer can choose the inclined serrated and inclined annular strip transportation method.
- (4) Multi layer and multi pass welding should be carried out by straight-line method.
Introduction of vertical welding
- 1. The metal and slag in molten pool are easy to separate due to self weight falling.
- 2. When the molten pool temperature is too high, the molten pool metal is easy to flow down, forming defects such as weld bead, undercut and slag inclusion, and the weld seam is not smooth.
- 3. The root of T-joint weld is easy to form incomplete penetration.
- 4. The degree of penetration is easy to master.
- 5. The productivity of welding is lower than that of flat welding.
1. Keep correct electrode angle;
2. Upward vertical welding is commonly used in production, and downward vertical welding needs special welding rod to ensure weld quality. The welding current of upward vertical welding is 10 ~ 15% less than that of flat welding, and the smaller electrode diameter (＜ 0 φ 4mm）
3. Short arc welding is adopted to shorten the distance from droplet transfer to molten pool.
4. Adopt the correct method of transportation.
- (1) When T-groove butt welding (commonly used for thin plate) is upward vertical welding, straight-line, zigzag and crescent welding methods are commonly used, and the maximum arc length is not more than 6 mm.
- (2) When other forms of groove butt welding are used, the first layer of weld is usually broken, crescent shaped and triangular welding with small swing. The following layers can be transported by crescent or zigzag method.
- (3) In the vertical welding of T-joint, the welding rod shall have proper residence time on both sides and top corner of the weld, the swing range of the welding rod shall not be greater than the width of the weld, and the operation of transporting the welding rod is similar to that of vertical welding of other groove forms.
- (4) When welding overlay, the shape of weld surface depends on the method of welding. If the surface requirement of weld is slightly higher, crescent shaped strip can be used; If the surface is flat, the serrated strip can be used (the concave shape in the middle is related to the pause time).
Brief introduction of horizontal welding
- 1. The molten metal is easy to fall on the groove due to its own weight, resulting in undercut defect on the upper side and tear bead or incomplete penetration defect on the lower side.
- 2. The molten metal and slag are easy to separate, which is slightly like vertical welding.
1. The groove of butt transverse welding is generally V-shaped or K-shaped, and the butt joint with plate thickness of 3 ~ 4mm can be double-sided welded with type I groove.
2. Select small diameter electrode, welding current is smaller than flat welding, short arc operation, can better control molten metal flow.
3. In addition to backing weld, multi-layer and multi pass welding should be used for thick plate welding.
4. When multi-layer and multi pass welding, special attention should be paid to control the overlapping distance between welding passes. For each overlap welding, the welding shall be started at 1 / 3 of the previous weld to prevent unevenness.
5. According to the specific situation, keep the appropriate electrode angle, and the welding speed should be slightly block and uniform.
6. Adopt the correct method of transportation.
- (1) For type I butt welding, it is better to use reciprocating straight-line welding method for front weld; For slightly thick parts, straight-line or small inclined annular strip should be used, and straight-line strip should be used at the back. The welding current can be increased appropriately.
- (2) When the gap is small, the backing welding can be carried out in a straight line; When the gap is large, the backing layer adopts reciprocating straight-line type. When the other layers are multi-layer welding, they can adopt inclined ring type. When multi-layer multi pass welding, they should adopt straight-line type.
Source: China Flange Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.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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