When galvanized steel is welded, cracks are most likely to occur. These have been encountered in your production. The reason for the cracking is that the zinc that remains in the nugget and spreads to the heat affected zone makes the joint embrittlement and is caused by the stress. The method to prevent cracking is to choose the correct process parameters. Tests have shown that the smaller the penetration rate (10-26%), the fewer crack defects. When the seam welding speed is high, the heat dissipation conditions are poor, the surface is overheated, and the penetration depth is large, so cracks are easily generated. Generally, in the condition of ensuring the diameter of the nugget and the strength of the joint, a small current, a low welding speed, and a strong external water cooling should be selected as far as possible.
First, the theoretical welding conditions for seam welding of low carbon steel plate and galvanized steel plate
1 〠Welding conditions for seam welding of low carbon steel plates
Thickness mm
Wheel size
Mm
Electrode pressure
KN
Edge width
Mm
High speed welding
Minimum b
Standard b
Maximum B
Minimal
standard
Minimum b
Standard b
Welding current (KA)
Welding speed cm/min
Welding time week
Retired time week
0.6
4.2
5.9
12
2.2
2.8
8
11
13.5
270
2
2
0.8
4.7
6.5
13
2.5
3.3
9
12
15.5
260
3
2
1.0
5.1
7.1
14
2.8
4.0
10
13
18.0
250
3
3
1.2
5.4
7.7
14
3.0
4.7
11
14
19.0
240
4
3
1.6
6.0
8.8
16
3.6
6.0
12
16
21.0
230
5
4
Note: b is the width of the contact surface between the welding wheel and the steel plate, and B is the thickness of the welding wheel during seam welding.
2. Hot-dip galvanized steel ( 15~20 μm ) welding conditions during seam welding
Thickness (mm)
Welding wheel width (mm)
Electrode pressure (KN)
Time (week)
Welding current (KA)
Welding speed cm/min
welding
Stop
0.6
4.5
3.7
3
2
16
250
0.8
5.0
4.0
3
2
17
250
1.0
5.0
4.3
3
2
18
250
1.2
5.5
4.5
4
2
19
230
1.6
6.5
5.0
4
1
twenty one
200
In order to ensure the size of the nugget and the strength of the solder joint, the welding time and the welding current can complement each other within a certain range. In order to obtain a certain strength of the solder joints, large currents and short durations (strong conditions, also known as strong specifications) can be used, and small currents and long periods (weak conditions, also called weak specifications) can also be used. For example, for low-carbon steel plates, which are commonly referred to as cold-rolled steel sheets, strong and weak specifications can be used; however, for hot-dip galvanized steel sheets, weak or weak cracks must be used during seam welding. specification.
Second, the actual welding conditions of low carbon steel and galvanized steel seam welding
The theoretical welding conditions for seam welding of cold-rolled steel sheet and hot-dip galvanized steel sheet have been discussed. The following are some specific parameters in actual production for your reference. The seam welding machine we use is the equipment of the Shanghai Electric Welding Machine Factory. After the welding machine is refitted, the welding drum plate body is welded with a dimension of 4 mm and the width of the welding wheel is 20 mm. Since we use a semi-automatic welding machine, we have a little welding process, but The purpose of spot welding is positioning, which is superfluous for imported automatic welding machines. Here we mainly look at seam welding parameters.
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Material manufacturer
Material thickness mm
Welding current KA
Electrode pressure KN
Welding speed cm/min
Front section
Middle section
Afterwards
Wuxi Changjiang Iron and Steel Group
1.0 (Level A)
12.7
15.5
15.0
2.4
340
Tianjin Cold Rolling Mill
1.0 (Level A)
12.5
16.5
15.0
2.6
330
Shanghai Baoshan Iron and Steel Group
1.0 (Level B)
12.9
16.9
14.8
2.8
335
?
Wuxi Changjiang Iron and Steel Group
1.2 (Level A)
13.0
15.9
15.2
2.5
351
Tianjin Cold Rolling Mill
1.2 (Level A)
12.9
17.0
14.5
2.8
355
Shanghai Baoshan Iron and Steel Group
1.2 (Class B)
13.2
17.3
15.0
3.0
348
Note: The above parameters are the process parameters when seam welding cold rolled low carbon steel
Panzhihua Iron and Steel Group
1.2 hot dip galvanized
12.5
16.5
14.0
3.0
258
Wuhan Iron and Steel Group
1.2 hot dip galvanized
13.2
16.2
14.2
3.0
260
Shanghai Baoshan Iron and Steel Group
1.2 hot dip galvanized
13.6
17.3
13.8
3.0
258
Note: The zinc layer thickness of hot dip galvanized sheet is 175g/cm2.
The above parameters are some of the data that I summarized in the production practice. Due to different equipment, the same equipment with different accuracy will produce different results, which must be adjusted according to specific circumstances in production. We use two seam welders here for normal production. The process parameters of the two seam welders are also different, and the difference is larger. This is mainly due to the difference in precision and control box accuracy of the two welders.
Although the welding machine is different, welding parameters are different, but according to production experience, under normal circumstances, the welding of hot-dip galvanized steel, the need to use a small current, long-term weak welding specifications. If the same current is used to weld the same thickness of cold-rolled steel sheet and hot-dip galvanized steel sheet, then the electrode pressure of the hot-dip galvanizing sheet should be correspondingly larger (2.5~2.8KN cold plate; hot galvanized sheet should be Achieve 2.8~3.0KN). The welding speed hot dip galvanized sheet should be 2/3~3/5 times of the cold sheet. Therefore, for full-automatic welding machines, welding cold plate drums of 720/hour, hot-dip galvanizing plates can only reach 430 to 480/hour, which is generally 450/hour.
I don't know whether your company's barrel production line is equipped with an edge grinding machine, because I once mentioned in the article “Process Method of Zinc-plated Tank Seam Welding†that when welding galvanized steel plates, it is necessary to polish the welded parts. The top is to remove the surface zinc layer. Since the melting point of zinc is low, a copper-zinc alloy is formed with the brazing wheel during welding, which increases the surface resistance of the welding wheel and further exacerbates the heat dissipation. Adhesion becomes more severe; overheating of the surface layer further enhances the diffusion of zinc into the heat affected zone, increasing the chance of crack formation. These "galvanized barrel seam welding process method," a detailed introduction, I will not talk about here. If your company has a edging machine, it is best to polish the ends of the barrel material. We usually grind (polished) twice. We have also tried it without edging, but there are more leaks and can reach about 20%. However, if you increase the electrode pressure and welding current, it may also be solved, but further tests are needed.
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