Aerial welding
Welding Features:
Molten metal falls naturally due to gravity, and the shape and size of the molten pool cannot be controlled.
Transporting the strip can be challenging and it may not be necessary to obtain a flat welding surface.
Defects such as slag inclusion, incomplete penetration, weld bead and poor weld formation are common problems.
Molten weld metal can splash and spread, which poses a risk of burn accidents.
Aerial welding tends to be less efficient than welding in other positions.
Aerial Welding Tips:
When performing aerial butt welding and the welding thickness is less than or equal to 4 mm, type I groove should be used. An electrode of φ3.2 mm should be selected and the welding current should be moderate. For welding thicknesses greater than or equal to 5 mm, multilayer and multipass welding must be used.
For overhead welding of T-joint welds, single-layer welding should be used when the weld leg is less than 8mm. However, when the weld leg is greater than 8 mm, multi-layer and multi-pass welding should be adopted.
When considering the specific situation, the appropriate strip transportation method should be adopted.
(1) For small sizes of welding legs, linear or linear alternative strip transportation should be used to complete single-layer welding. For larger sizes of welding legs, multi-layer welding or multi-layer, multi-pass welding strip conveying can be adopted. The first layer should use linear strip conveying, while inclined triangular strip or inclined ring conveying can be used for subsequent layers.
(2) Regardless of the strip transportation method used, the amount of weld metal added to the molten pool each time should not be excessive.
Flat welding
Welding Features:
Fusion welding relies primarily on its own weight to transition to the weld pool.
The shape and composition of the molten pool are easily maintained and controllable.
When welding metal with the same plate thickness, the welding current required for flat welding positions is greater than that for other welding positions, resulting in higher production efficiency.
The mixing of slag with the molten pool is common, especially when welding flat weld beads, which can lead to the inclusion of slag.
It is difficult to distinguish between the slag and the molten pool of acidic electrodes; Alkaline electrodes offer more clarity. According to HG20581, acid electrodes are not suitable for use in class II and III vessels.
Revised version:
Incorrect welding parameters and operations can lead to the formation of defects such as weld bead irregularities, undercuts and welding deformation.
During single-side welding, where the backside is left free, the first weld can easily result in uneven penetration and poor backside formation.
Flat Welding Tips:
Depending on the plate thickness, welding rods with larger diameters and higher welding currents can be selected for welding.
During welding, the electrode and welding must form an inclusive angle of 60 to 80 degrees, and the separation of slag and liquid metal must be controlled to prevent slag from entering the weld.
For plates with a thickness of ≤ 6 mm, a type I groove is generally used for flat butt welding. For frontal welding, short arc welding of φ3.2 to 4 electrodes must be used, and the penetration must reach 2/3 of the plate thickness. Before further sealing, the root does not need to be cleaned (except important structures), but the slag must be cleaned and the current can be greater.
In case of unclear mixture of slag and molten pool metal in flat butt welding, lengthen the arc, tilt the welding rod forward and push the slag behind the molten pool to avoid slag inclusion.
When welding horizontal and inclined welds, upward welding should be used to avoid slag inclusion and prevent the weld pool from advancing.
When using multi-layer and multi-pass welding, pay attention to the number of welding passes and the welding sequence, and ensure that each layer does not exceed 4 to 5 mm.
For overlapping T-type, fillet, and flat-angle welded joints, if the thickness of the two plates is different, the electrode angle should be adjusted to divert the arc to one side of the thicker plate to ensure that both plates are heated evenly .
Correct selection of strip transport method
(1) For butt and flat I-slot welding with welding thickness less than or equal to 6 mm, straight strip transportation is recommended for butt welding when double-sided welding is used, which may have a slightly slower speed. The back welding should also adopt linear strip transportation, but with slightly higher welding current and faster speed.
(2) When the plate thickness is ≤ 6mm and other groove shapes are opened, multi-layer welding or multi-layer multi-pass welding can be used. For the first backing welding layer, a low current electrode with linear or serrated electrode welding method is recommended.
When welding the filler layer, an electrode with a larger diameter and a short arc welding with a larger welding current can be selected.
(3) When the leg size of T-joint flat fillet welding is less than 6mm, single-layer welding is recommended. Linear, oblique ring or sawtooth strip conveying method can be used. For large sizes of welding legs, multilayer welding or multilayer multipass welding should be adopted.
For backing welding, the linear strip conveying method is recommended, and for the filler layer, the inclined sawtooth and inclined ring strip conveying methods can be selected.
(4) For multi-layer and multi-pass welding, it is generally recommended to use the linear strip welding method.
Vertical welding
Welding Features:
Molten metal and slag can easily separate as they fall under their own weight.
If the molten pool temperature is too high, molten metal can flow downward and cause defects such as weld beads, undercuts, and slag inclusions, resulting in uneven welding.
Incomplete penetration is a common problem that can occur at the root of T-joint welds.
The degree of penetration can be easily controlled.
Welding productivity is lower for T-joint welding compared to flat welding.
Vertical Welding Tips:
Ensure correct electrode angle:
Vertical upward welding is commonly used in production, and for vertical downward welding, special welding rods must be used to ensure the quality of the weld. The welding current for vertical upward welding should be 10-15% lower than that for flat welding, and for smaller electrode diameters (<0.05), a diameter of φ4mm should be selected.
Short arc welding should be adopted to reduce the distance between the droplet transition and the weld pool.
Adopt the correct method of transporting the strips.
(1) When vertically welding the T-slot butt joint (commonly used for thin plates), the linear, serrated and crescent strip conveying method is commonly used, and the maximum arc length should not exceed 6mm.
(2) For other forms of vertical groove butt welding, the first layer of the weld generally uses broken welding, a crescent type with a small overhang, or triangular strip welding. Subsequent layers can be conveyed in a crescent or sawtooth shape.
(3) During vertical welding of a T-joint, the electrode must remain on both sides and upper corners of the weld for an appropriate dwell time. The oscillation amplitude of the electrode must not be greater than the width of the weld. The electrode transport operation is similar to vertical welding of other groove shapes.
(4) When welding the cover layer, the shape of the welding surface depends on the strip transportation method used. For slightly larger weld surface requirements, a half-moon shaped strip can be used. For a flat surface, sawtooth strip transport can be used (the medium concave shape is related to the pause time).
Transverse welding
Welding Features:
The molten metal has a tendency to fall into the groove due to its weight, which can result in undercut defects on the upper side and teardrop weld beads or incomplete penetration defects on the lower side. Furthermore, the molten metal and slag tend to separate easily, similar to vertical welding.
Cross Welding Tips:
The groove for horizontal butt welding is generally V-shaped or K-shaped, and for butt joints with a plate thickness of 3~4mm, the I-type groove can be used on both sides.
Select a small diameter electrode and use a lower welding current than that used for flat welding. Short arc operation can better control the flow of molten metal.
When welding thick plates, multilayer and multipass welding should be adopted in addition to backing welds.
During multilayer and multipass welding, special attention must be paid to controlling the overlap distance between welding passes.
For each overlapping welding pass, start welding at 1/3 of the previous weld to avoid irregularities.
To obtain the best results, it is important to maintain a proper electrode angle and use a slightly blocked and uniform welding speed depending on the specific situation.
It is also essential to adopt the correct method of transporting the strips. Here are some guidelines:
(1) For type I horizontal butt welding, it is recommended to use the alternative linear strip conveying method for the face weld. For thicker parts, a linear or small inclined annular strip and a linear strip for the back should be used. You can also increase the welding current accordingly.
(2) For other horizontal groove butt welds with a small gap, straight strip transportation is suitable for butt welding. However, when the gap is large, you must adopt alternative transportation of linear strips to the supporting layer. Inclined annular strip transportation is recommended for multilayer welding of other layers, while linear strip transportation is suitable for multilayer and multipass welding.
