The resistance welding food cans refer to food cans made by resistance welding in the can seams. They were first produced in Switzerland in the 1970s and then used extensively in the world. In 1981, the Canzhou Cannery introduced the first VAAK production line. Until now, it has been able to produce resistance welding machines.
Food tank resistance welding is a new can making technology that has replaced the production of solder cans. There will be some technical issues in production that need further exploration. Welding quality is the question of whether or not the resistance welding machine is used properly. During the production process, problems such as spatters, perforations, missing welds, butterfly welding or irregular welding lines, overlapping lap angles, or unsatisfied widths may occur. Severely caused large quantities of cans to leak. Therefore, it is of great significance to study the factors of welding quality and find solutions to improve the quality of empty cans.
One, heat
Resistance welding is the use of electricity through the heat generated by the workpiece resistance, so that the contact surface of the metal melt to form solder joints. Only by controlling the proper heat production can a good solder joint be formed. The heat generation is determined by the welding current (I), the workpiece resistance (R) and the welding time. Heat is proportional to the square of the current and is also proportional to the resistance time. The formula is expressed as follows: Q=I2Rt
1, welding current
During welding, the current path in the workpiece is very short, and only two tinplate thicknesses (approximately 0.4-0.5 mm) can weld only one solder joint for only half a cycle (0.01 s). Therefore, the welding current has the greatest influence on the heat generation, so controlling the welding current is particularly important. If the current is too large, the welding is excessive and there is splashing, the current is too small, the solder joint is not firm or there is no solder joint. Current regulation is generally divided into coarse and fine adjustments. Coarseness is regulated by the tap changer of the transformer. Generally, the manufacturer has adjusted well and the fine tuning is adjusted by the current phase. During the production process, adjustments must be made according to the actual situation.
2, welding force
Welding force is the force exerted by the electrode on the solder joint. Its role is to make the two sheets in close contact, reduce the initial contact resistance between the interfaces, and finally compact the fusion. The initial resistance between the workpieces during welding has a great influence on the welding quality. If the surface is in poor contact, defects such as arcing and splashing are likely to occur, and the welding force affects the heat through the resistor R. Therefore, when the other conditions are constant, the welding current increases as the welding force increases.
3, the state of the welding surface
The state of the tinplate welding surface is very important for welding quality. When the welding surface is covered with non-uniform coating of oxides, rust, coating films, or other impurities, the interface contact resistance is changed, the heat generated by each welding spot is inconsistent, and the welding quality Unstable, it is possible to make the weld seam irregular. Leave empty iron and ferrite, because the surface is smooth and soft, and the change of the contact resistance of the lapped surface is small, the welding current should be larger. Although the coating iron is yellowed, the surface is not very smooth, and some steel substrates are also damaged. The contact resistance of the lapped surface is relatively large and the welding current is slightly smaller. Some of them are not clean or leaky when scraping yellow, and the resistance increases sharply during welding. The heat generation rate is too fast and too high, causing overheating and violent liquid metal splashing, causing serious flaws such as splashes and perforations in the weld to become waste products. , sometimes the heat is too high, the welding machine automatically jump stop.
4, electrode copper wire
The formed flat copper wire passes as an intermediate electrode in the welding roller groove, and the tin is deposited on the copper wire to be carried away without contaminating the welding wheel, thereby ensuring the cleaning of the wheel groove. As the middle electrode, the copper wire is in contact with the welding wheel and the tin plate. The resistance of the copper wire itself affects the welding quality. For example, the surface of the copper wire has oxide, oil, impurities, and the contact resistance between the copper wire and the tin plate changes. The heat generated by each solder joint is inconsistent, causing irregular weld quality defects in the weld. Therefore, it is required that copper wire, diameter tolerance is less than 0.02mm, purity is 99.9%, and the surface is smooth, clean, free from oxide film and coating pollution. In addition, the formed copper wire must work well with the wheel groove to reduce the contact resistance, otherwise the wheel groove should be repaired.
5, heat conduction
During resistance welding, part of the heat generated by the welding current is used to form solder joints, so that the center temperature of the solder joint reaches around 1200 to 1300°C, and part of the solder is diffused into the tinplate due to the conductive effect of the tin plate. The quality of welding is related to thermal diffusion. Faster diffusion, larger welding current, slower diffusion and lower current, otherwise, slow diffusion will cause excessive welding. Therefore, during the welding start and end of the two solder joints, due to slow air heat diffusion, the welding current To make weaker adjustments. The adjustment is performed by the time controller and the current controller, the former controlling the width of the weakened current across the weld, and the latter controlling the amount of current reduction at both ends. In addition, the domestic DODO-S welder adopts the shunting method to reduce the current, and the adjustment requirements are relatively high. Otherwise, it is difficult to ensure the smooth production.
Second, mechanical positioning
The overlap width of welding seams for resistance welding food cans is generally 0.4mm, 0.5mm for large cans, 0.5mm for manual welding machines, and the deviation range is not more than ±0.05mm. Therefore, the can body must be accurately positioned during welding. If the positioning is inaccurate, the two ends of the can body weld will have a wrong angle, and the weld laps will have inconsistent or inconsistent quality defects such as non-conformity, so the mechanical positioning is also an important factor affecting the welding quality.
1, can body transmission push rod system
The can body transmission push rod is a part that pushes the rounded can body to the front of the welding wheel. If the adjustment is incorrect, the two ends of the can body seam will have a wrong angle. The original VAAK-100 type uses a pawl to push in parallel. Due to the reasons of adjustment and wear, often the pawls on both sides are not parallel and the wrong angle occurs. The unstable operation of the push rod will also affect the stability of the pawl. The wear-resistant push system of Beijing Aopu Company can solve the problem of wear of the pawl. It basically overcomes the non-parallel phenomenon of the pawl, and the misalignment may be very small.
2, cans calibration ring
The can body calibration ring is the guiding and calibrating device for the can body during welding, which has a great influence on the overlapping width of the welding seam. The calibration of the calibration ring seriously affects the overlapping amount of the can body welding, and the inconsistency between width ends is likely to occur. Does not meet the requirements, and even the can body guide is not correct.
3, Z-shaped guide rod
The Z-bar is a Z-shaped cross-section rail. Each side has a V-shaped groove. The relative distance between the two bottoms of the groove determines the overlap of the can weld. Under the guidance and limitation of the calibration ring and Z-bar, ensure the amount of overlap. Under normal circumstances, the relative distance at the bottom of the Z-bar groove is 0.4mm for small cans and 0.5mm for manual and large cans. When the distance is less than 0.4mm, production will be difficult, and Z-bars made in China may have this possibility. The Z-bar will affect the welding quality under the following conditions.
A, wear
When the Z-bar wears, the relative distance at the bottom of the groove increases, and the amount of overlap increases. This has a greater influence on the front end of the weld, resulting in an excessively large lap width at the starting end, as well as insufficient welding, resulting in false welding.
B, Z position
The distance between the center of the Z-bar head and the center of the upper roller must be 17.0mm. The center of the front end should be at the same height as the edge of the copper wire, so that the can body will be horizontal when it is advanced from the Z-bar to the welding wheel. When the Z-bar is high or low, it will cause the tank body to warp or incline to affect the amount of overlap. , especially the front end, resulting in insufficient or excessive lap volume.
Third, other factors
1, the amount of travel beyond
Stroke overrunning refers to the amount of overrunning of the pusher when the can body cylinder is rounded and pushed by the pusher to the welding roller. If the can body is pushed to the welding roller and the pushing claw does not exceed the amount, the can body stops and cannot be carried away by the welding wheel. Therefore, there must be an excess of the trip. However, improper adjustment will affect the quality of welding. If the stroke is too large and the tank is sent too fast, the beginning of the weld will be missed and the can body will be damaged due to excessive thrust. If the stroke is too small, that is, the tank is too slow, the beginning of the weld will be excessively welded, resulting in perforation and even adhesion to the copper wire. The amount of travel exceeded is proportional to the height of the tank. The higher the can body, the greater the amount of overrun.
2, welding frequency and speed
In resistance welding, welding current generates one welding point per half cycle, and the higher the frequency is, the more welding spots are produced per unit time. The welding spot spacing=welding speed/(welding frequency×2), the larger the welding spot spacing, the welding strength The worse, the food tank joint must be a continuous airtight weld, therefore, the solder joint must have 15% to 20% overlap, when the distance exceeds a certain range, the solder joints do not overlap, the weld will Leakage failed. For example, the VAAK-100 type has a spot diameter of 2 mm and its maximum welding speed Vmax=2×0.85×200×60÷1000=20.4 m/min. If it is more than this speed, the welding quality will be affected. DODO-S machine adopts the adjustable frequency inverter, its frequency choice f(HZ) =1000×V/2×60×P P generally chooses between 0.8~1.2mm. Therefore, for the adjustable frequency resistance welding machine, the weld seams increase, the welding strength is uniform, and the quality is good. Generally high-speed welders use high-frequency welding.
The production technology of resistance welding machines only gradually explored in continuous production. With the development of canned beverage industry, the development prospects of the canning industry are broad. The canning industry in Ningbo has started early and is developing slowly. There is a big gap between Guangdong and the Pearl River Delta. . Therefore, the discussion of resistance welding technology has great significance for the development of can making industry.
Food tank resistance welding is a new can making technology that has replaced the production of solder cans. There will be some technical issues in production that need further exploration. Welding quality is the question of whether or not the resistance welding machine is used properly. During the production process, problems such as spatters, perforations, missing welds, butterfly welding or irregular welding lines, overlapping lap angles, or unsatisfied widths may occur. Severely caused large quantities of cans to leak. Therefore, it is of great significance to study the factors of welding quality and find solutions to improve the quality of empty cans.
One, heat
Resistance welding is the use of electricity through the heat generated by the workpiece resistance, so that the contact surface of the metal melt to form solder joints. Only by controlling the proper heat production can a good solder joint be formed. The heat generation is determined by the welding current (I), the workpiece resistance (R) and the welding time. Heat is proportional to the square of the current and is also proportional to the resistance time. The formula is expressed as follows: Q=I2Rt
1, welding current
During welding, the current path in the workpiece is very short, and only two tinplate thicknesses (approximately 0.4-0.5 mm) can weld only one solder joint for only half a cycle (0.01 s). Therefore, the welding current has the greatest influence on the heat generation, so controlling the welding current is particularly important. If the current is too large, the welding is excessive and there is splashing, the current is too small, the solder joint is not firm or there is no solder joint. Current regulation is generally divided into coarse and fine adjustments. Coarseness is regulated by the tap changer of the transformer. Generally, the manufacturer has adjusted well and the fine tuning is adjusted by the current phase. During the production process, adjustments must be made according to the actual situation.
2, welding force
Welding force is the force exerted by the electrode on the solder joint. Its role is to make the two sheets in close contact, reduce the initial contact resistance between the interfaces, and finally compact the fusion. The initial resistance between the workpieces during welding has a great influence on the welding quality. If the surface is in poor contact, defects such as arcing and splashing are likely to occur, and the welding force affects the heat through the resistor R. Therefore, when the other conditions are constant, the welding current increases as the welding force increases.
3, the state of the welding surface
The state of the tinplate welding surface is very important for welding quality. When the welding surface is covered with non-uniform coating of oxides, rust, coating films, or other impurities, the interface contact resistance is changed, the heat generated by each welding spot is inconsistent, and the welding quality Unstable, it is possible to make the weld seam irregular. Leave empty iron and ferrite, because the surface is smooth and soft, and the change of the contact resistance of the lapped surface is small, the welding current should be larger. Although the coating iron is yellowed, the surface is not very smooth, and some steel substrates are also damaged. The contact resistance of the lapped surface is relatively large and the welding current is slightly smaller. Some of them are not clean or leaky when scraping yellow, and the resistance increases sharply during welding. The heat generation rate is too fast and too high, causing overheating and violent liquid metal splashing, causing serious flaws such as splashes and perforations in the weld to become waste products. , sometimes the heat is too high, the welding machine automatically jump stop.
4, electrode copper wire
The formed flat copper wire passes as an intermediate electrode in the welding roller groove, and the tin is deposited on the copper wire to be carried away without contaminating the welding wheel, thereby ensuring the cleaning of the wheel groove. As the middle electrode, the copper wire is in contact with the welding wheel and the tin plate. The resistance of the copper wire itself affects the welding quality. For example, the surface of the copper wire has oxide, oil, impurities, and the contact resistance between the copper wire and the tin plate changes. The heat generated by each solder joint is inconsistent, causing irregular weld quality defects in the weld. Therefore, it is required that copper wire, diameter tolerance is less than 0.02mm, purity is 99.9%, and the surface is smooth, clean, free from oxide film and coating pollution. In addition, the formed copper wire must work well with the wheel groove to reduce the contact resistance, otherwise the wheel groove should be repaired.
5, heat conduction
During resistance welding, part of the heat generated by the welding current is used to form solder joints, so that the center temperature of the solder joint reaches around 1200 to 1300°C, and part of the solder is diffused into the tinplate due to the conductive effect of the tin plate. The quality of welding is related to thermal diffusion. Faster diffusion, larger welding current, slower diffusion and lower current, otherwise, slow diffusion will cause excessive welding. Therefore, during the welding start and end of the two solder joints, due to slow air heat diffusion, the welding current To make weaker adjustments. The adjustment is performed by the time controller and the current controller, the former controlling the width of the weakened current across the weld, and the latter controlling the amount of current reduction at both ends. In addition, the domestic DODO-S welder adopts the shunting method to reduce the current, and the adjustment requirements are relatively high. Otherwise, it is difficult to ensure the smooth production.
Second, mechanical positioning
The overlap width of welding seams for resistance welding food cans is generally 0.4mm, 0.5mm for large cans, 0.5mm for manual welding machines, and the deviation range is not more than ±0.05mm. Therefore, the can body must be accurately positioned during welding. If the positioning is inaccurate, the two ends of the can body weld will have a wrong angle, and the weld laps will have inconsistent or inconsistent quality defects such as non-conformity, so the mechanical positioning is also an important factor affecting the welding quality.
1, can body transmission push rod system
The can body transmission push rod is a part that pushes the rounded can body to the front of the welding wheel. If the adjustment is incorrect, the two ends of the can body seam will have a wrong angle. The original VAAK-100 type uses a pawl to push in parallel. Due to the reasons of adjustment and wear, often the pawls on both sides are not parallel and the wrong angle occurs. The unstable operation of the push rod will also affect the stability of the pawl. The wear-resistant push system of Beijing Aopu Company can solve the problem of wear of the pawl. It basically overcomes the non-parallel phenomenon of the pawl, and the misalignment may be very small.
2, cans calibration ring
The can body calibration ring is the guiding and calibrating device for the can body during welding, which has a great influence on the overlapping width of the welding seam. The calibration of the calibration ring seriously affects the overlapping amount of the can body welding, and the inconsistency between width ends is likely to occur. Does not meet the requirements, and even the can body guide is not correct.
3, Z-shaped guide rod
The Z-bar is a Z-shaped cross-section rail. Each side has a V-shaped groove. The relative distance between the two bottoms of the groove determines the overlap of the can weld. Under the guidance and limitation of the calibration ring and Z-bar, ensure the amount of overlap. Under normal circumstances, the relative distance at the bottom of the Z-bar groove is 0.4mm for small cans and 0.5mm for manual and large cans. When the distance is less than 0.4mm, production will be difficult, and Z-bars made in China may have this possibility. The Z-bar will affect the welding quality under the following conditions.
A, wear
When the Z-bar wears, the relative distance at the bottom of the groove increases, and the amount of overlap increases. This has a greater influence on the front end of the weld, resulting in an excessively large lap width at the starting end, as well as insufficient welding, resulting in false welding.
B, Z position
The distance between the center of the Z-bar head and the center of the upper roller must be 17.0mm. The center of the front end should be at the same height as the edge of the copper wire, so that the can body will be horizontal when it is advanced from the Z-bar to the welding wheel. When the Z-bar is high or low, it will cause the tank body to warp or incline to affect the amount of overlap. , especially the front end, resulting in insufficient or excessive lap volume.
Third, other factors
1, the amount of travel beyond
Stroke overrunning refers to the amount of overrunning of the pusher when the can body cylinder is rounded and pushed by the pusher to the welding roller. If the can body is pushed to the welding roller and the pushing claw does not exceed the amount, the can body stops and cannot be carried away by the welding wheel. Therefore, there must be an excess of the trip. However, improper adjustment will affect the quality of welding. If the stroke is too large and the tank is sent too fast, the beginning of the weld will be missed and the can body will be damaged due to excessive thrust. If the stroke is too small, that is, the tank is too slow, the beginning of the weld will be excessively welded, resulting in perforation and even adhesion to the copper wire. The amount of travel exceeded is proportional to the height of the tank. The higher the can body, the greater the amount of overrun.
2, welding frequency and speed
In resistance welding, welding current generates one welding point per half cycle, and the higher the frequency is, the more welding spots are produced per unit time. The welding spot spacing=welding speed/(welding frequency×2), the larger the welding spot spacing, the welding strength The worse, the food tank joint must be a continuous airtight weld, therefore, the solder joint must have 15% to 20% overlap, when the distance exceeds a certain range, the solder joints do not overlap, the weld will Leakage failed. For example, the VAAK-100 type has a spot diameter of 2 mm and its maximum welding speed Vmax=2×0.85×200×60÷1000=20.4 m/min. If it is more than this speed, the welding quality will be affected. DODO-S machine adopts the adjustable frequency inverter, its frequency choice f(HZ) =1000×V/2×60×P P generally chooses between 0.8~1.2mm. Therefore, for the adjustable frequency resistance welding machine, the weld seams increase, the welding strength is uniform, and the quality is good. Generally high-speed welders use high-frequency welding.
The production technology of resistance welding machines only gradually explored in continuous production. With the development of canned beverage industry, the development prospects of the canning industry are broad. The canning industry in Ningbo has started early and is developing slowly. There is a big gap between Guangdong and the Pearl River Delta. . Therefore, the discussion of resistance welding technology has great significance for the development of can making industry.
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