Research on the problem of steel barrel seam welding technology

Research on the problem of steel barrel seam welding technology

Chen Renbing Xin Qiaojuan

The quality of seam welding is the key factor affecting the quality of steel drums. Many steel drum manufacturers have controlled this process as a special process in quality management. Therefore, how to improve the quality of seam welding in steel drum production process is very important. In order to improve the quality of domestic steel drums, in the 1980s, the domestic steel drum industry adopted the method of going out, please come in, organize domestic experts and scholars to go abroad for inspection, and introduced several barrel production lines of the United States Calando Company. And several automatic seam welders.

At that time, the domestically produced seam welder welded the barrel with a width of 10-12 mm, while the imported automatic seam welder welded the steel barrel with a width of only 2-3 mm and after welding. Not only the appearance of the steel barrel is beautiful and beautiful, but also helps to ensure the quality of the steel drum, and saves the raw materials. The control panel adopts direct dialogue between people and machines, and the operation method is simple and easy to learn. Although this kind of welding machine has so many advantages, most of the barrel-making enterprises can only be sighed by the price because it is very expensive. At this time, people of insight in China are optimistic about this business opportunity, decided to develop and manufacture welding electric control box, installed on the domestic FN1-150-5 seam welder.

Through technical transformation, most steel barrel seam welders can achieve the desire of seam welding width of 4 mm without spending too much money. Jiangsu Jiangyin Wuxing Copper Co., Ltd. is one of them. Through the research of technicians, the steel box seam welder control box was quickly developed and manufactured, and the corresponding mechanical transmission part of the seam welder was modified. The FN1 produced by the company was matched. On the -150-5 seam welder, the desire to weld the narrow seam of the steel barrel is realized. This technology has been applied in many steel drum enterprises in China, but due to lack of technology and experience, as well as the unskilled operation of operators, the quality of steel drum welding has not achieved the expected results.

The following is a discussion of some practical problems in the actual welding process of the FN1-150-5 steel barrel seam welder.

problem:

1. There are sand holes in the weld and leakage occurs.

2. The welding wheel wears unevenly, and the groove appears in the middle of the welding wheel, which directly affects the welding quality.

3. When the barrel is seamed and welded, the ends of the barrel are cracked, and even a weld of 100 mm length leaks.

4. There is no damage to the flanges at both ends of the barrel, but the ring ribs are cracked after the expansion.

5. There are flying thorns after welding, which affects the appearance quality of the steel drum and the intrinsic quality of the fully open barrel.

The above five problems are problems that many steel drum enterprises often encounter in production practice. For this reason, on the basis of full practice, we have discussed from three aspects: welding theory, mechanical principle and practical operation.

First, the influence of welding current, electrode pressure and welding speed on the quality of barrel seam welding

The welding principle of the steel barrel body is resistance welding. Welding is to melt the steel sheet by welding heat and then press it together. Welding heat Q=I2Rt

Where: Q - heat generated; I - welding current; R - resistance between electrodes; t - power-on time

It can be seen from the formula that the factors affecting the welding quality of the barrel include the welding current, the resistance between the electrodes, and the energization time, and the resistance between the electrodes is determined by the magnitude of the electrode pressure, and the welding speed determines the energization time. Therefore, the main process parameters affecting the welding quality are: welding current, electrode pressure, welding speed

1, welding current

The source of heat required to form a nugget by seam welding is the heat generated by the current through the resistance of the weld zone. The magnitude of the welding current determines the penetration and overlap of the nugget, given other conditions. When welding the barrel of the steel drum, the average penetration rate of the nugget is 30-70% of the thickness of the steel plate, and 45-50% is the best. In order to obtain the weld overlap of the hermetic welded joint, the amount of overlap should be not less than 15-20%.

When the welding current exceeds a certain value, continuing to increase the current can only increase the penetration rate and the amount of overlap of the nugget without increasing the joint strength, which is uneconomical. If the current is too large, defects such as excessive barrel indentation and burnt through the barrel weld will occur. Therefore, the welding current should not be too large or too small, but should be controlled within a certain range.

2, electrode pressure

The electrode pressure during the seam welding of the barrel has a significant effect on the total resistance R between the two electrodes. As the electrode pressure increases, R decreases significantly, and decreases the electrode pressure, and R increases significantly. Therefore, the welding strength always decreases as the electrode pressure increases. Increasing the electrode pressure, increasing the welding current or prolonging the welding time can compensate for the effect of the resistance reduction, thereby keeping the welding strength constant. The use of such welding conditions is advantageous for improving the stability of the welding strength and avoiding cracking at both ends and the ring ribs after the barrel is welded. If the electrode pressure is too small, it will cause splashing and will also reduce the welding strength. At the same time, the electrode pressure is too high, which will make the barrel body indentation too deep, and accelerate the deformation and loss of the welding roller (welding wheel). Insufficient pressure is easy to produce flying thorns and a large number of sparks, and the contact resistance is too large, so that the welding roller burns and shortens its service life.

3, welding speed

The welding speed of the barrel body has a direct relationship with the thickness and material of the barrel material. The welding parameters of the steel drum special plates produced by different manufacturers are different when welding, and are not listed here. In short, the welding speed determines the contact area between the welding reel (welding wheel) of the barrel seam welder and the barrel body, and the contact time between the welding wheel and the heating part (the weld bead edge). When the welding speed increases, To get enough heat, you must increase the welding current. Excessive welding speed will cause the barrel surface to burn and the electrode to adhere. Therefore, even if the barrel seam welder has enough external cooling water, the welding speed should not be too large and should be limited.

The following is a set of process parameters in the production of a steel drum manufacturer, for reference only. Because of the accuracy of the welder itself, the modification method, the accuracy of the controller, the working environment during welding, the raw materials used, the proficiency of the operator, etc., the parameters of the barrel welding will be affected.

Comparison of different welding current and electrode pressure welding results (welding thickness is 1mm oil drum special steel plate)

Welding current welding speed electrode pressure welding quantity qualified barrel body qualification rate 11.5 kA 2.5m/min 0.21 MPa 450 415 90.22% 10.5 kA 2.5m/min 0.19 MPa 460 458 99.57% 9.5 kA 2.5m/ Min 0.17 MPa 445 413 92.81%

It can be seen from the table that the small fluctuations of the welding current and the electrode pressure have a great influence on the qualification rate of the semi-finished steel drum. Therefore, the process parameters that have been explored in the actual production process and meet the welding requirements are not changed when the steel material is not changed. ,unchangeable.

Second, the influence of the mechanical part of the welder and the spot welding process on the welding quality of the barrel

The first five phenomena are produced. In addition to the influence of the welding process parameters, the adjustment of the welding machine itself has a great relationship. Because in general, the electrode pressure and the welding speed are infrequently changed parameters when welding the barrel, and this parameter changes unless the material thickness of the welded barrel body changes greatly. When the material thickness of the welded barrel is 1.2 or 1.0, the electrode pressure and the welding speed are not changed, and the welding quality of the barrel is not affected. However, if the bucket holder is too high or too low, the electrode pressure during the barrel welding is directly changed. If the tray is too high, the electrode pressure is increased, and the welded barrel has a significant indentation. As we talked about earlier, as the electrode pressure increases, R decreases significantly. At this time, the welding heat generated by the welding will be reduced due to the decrease of the electrode resistance R, and the welding strength will also decrease as the electrode pressure increases, so that the leakage or the flange is broken; if the bracket is too low, the electrode pressure Decrease, the welded barrel will produce a distinct peach shape, that is, the barrel is too high outside the weld, not an arc. At this time, the electrode pressure decreases and R increases significantly. At this time, the welding heat generated by the welding will increase due to the increase of the electrode resistance R, which may cause burn-through or splashing, which may easily cause leakage or burring. Therefore, after checking the height of the barrel welding machine, the level should be adjusted first, and the parallelism of the bucket frame should be adjusted with the level to the level. If the height of the two ends is uneven, the welding strength of the welded end of the barrel may be different due to the difference in the electrode pressure, so that it leaks or ruptures. Secondly, it is to check whether the seam welder head is normal, sometimes there will be a lower head swing or the upper head will cause the lubricating oil to dry due to poor long-term lubrication, so that the upper head cannot be moved down to the position required by the process. These are the main factors affecting the barrel welding. Third, check the size and solder joints of the two sides of the barrel body spot welding. If the process stipulates that the barrel is welded with a mating degree of 4 mm and four solder joints, then there should be no excessive error at both ends, otherwise it will cause leakage at one end of the barrel after welding. Fourth, check whether the welding pressure is correct, and whether the air pipe or air valve has air leakage.

Third, pay attention to the following matters during the actual welding process

1. Select welding process parameters such as welding current, electrode pressure and welding speed. First cut about 20 pieces of cold-rolled sheet with a width of about 10 cm, then connect according to the process requirements, then seam welding. The welding speed is controlled at 2~3m/min, the welding current is adjusted, and the electrode pressure is not generated until the current is generated. Stinging fire, the steel plate traces are clear, the welding is uniform, the surface is free from scratches, the nugget penetration rate is 40-60%, and then the barrel is actually welded. After the plate is expanded, the rib is formed without leakage. At this time, the welding current is recorded. The data of electrode pressure and welding speed are used as welding process parameters. As long as the material and thickness of the steel plate do not change greatly, the adjusted welding current, electrode pressure and welding speed can be maintained.

2, often use anhydrous alcohol to clean the surface of the welding wheel slag to avoid the production of sand holes in the weld.

3. When the crack occurs in the front end of the barrel after welding, adjust the pre-pressing time to 000 or adjust the position of the photoelectric detection to make it detect in advance and weld in time.

4. Adjust and replace the welding wheel correction wheel in time to correct the surface of the welding wheel in time to avoid the groove. If there is a groove on the surface of the welding wheel and it is larger than 1mm, it should be smoothed or the lathe should be level. Otherwise, the welded barrel is prone to leakage after molding.

In short, seam welding quality is an important part of controlling the quality of steel drums. In the future, we should summarize on the basis of continuous practice, explore the best welding process and welding specifications for seam welding, and ensure that steel barrel welds do not leak.