JPS6143106B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for repairing a welded part, and more particularly to a method for repairing a side welded part of a welded can body using a liquid paint. While moving in the axial direction a can body formed body having side overlapped parts formed from blanks of metal plates such as electro-tinned steel plates and stain-free steel,
A method of manufacturing a welded can body having a welded portion by electrical resistance seam welding (preferably pine seam welding) of overlapping side portions has been put into practice. In this case, liquid paint is applied to the inner and outer surfaces of the welded part and the exposed metal parts in the vicinity, and then dried.
It is also widely practiced to prevent rust and corrosion of these parts. Note that in this specification, the liquid paint refers to a paint that is dissolved or dispersed using a solvent or water as a medium. In this case, the paint applicator is usually installed downstream of the welding roll, and welding, coating, and drying are performed on the same line, but in order to make the equipment more compact, the applicator can be placed within the range that is possible for the welding roll. It is preferable that they be provided close to each other. Recently, with the advancement of technology, the speed of the above-mentioned line has increased (e.g. 40 m/min), but in this case, there are phenomena in which the applied paint escapes from the welding part in the circumferential direction, and conversely, it does not flow in. In some cases, bubbling phenomena tend to cause the problem that the welds are not completely covered with a paint film. A specific example of this phenomenon is as follows. In Figures 1 and 2, 1 is a welded can body; 2 is a welded can body;
is the pine seam weld (hereinafter referred to as the weld),
3 is a protective baked coating film (for example, made of epoxy/phenol paint) formed on the blank before welding, and the welded part 2 and its vicinity 4 are exposed metal and become exposed metal parts 5. There is. The figure shows that a planar spray paint film 8 is sprayed from a spray nozzle 6 attached to a nozzle holder 7 by the method previously proposed in Japanese Patent Application No. 56-143908 by one of the present inventors. This figure shows a state in which the welding part 2 and its vicinity 4, that is, the exposed metal part 5, are being coated as the coating progresses in the direction. As shown in the figure, the paint film 8 hits the exposed metal portion 5 to form a paint film 8', but the paint film 8' moves outward in the circumferential direction, that is, in the direction of arrow B and the direction of arrow C. In other words, it tends to escape or not flow in, leaving uncoated areas 9 in the exposed metal parts 5, especially in the welded parts 2. This phenomenon occurs more easily as the temperature of the welded part 2 during application is higher, and as the boiling point of the solvent in the paint or the viscosity of the paint is lower. In order to prevent discoloration (to blue or yellowish brown, etc.) due to oxidation of the welded part 2,
On the exit side of the welding roll, nitrogen gas may be sprayed onto the welded part 2. In this case, the surface temperature of the welded part 2 is approximately 750 to 1450°C, a temperature that does not cause discoloration due to iron oxidation in the air. However, even in this case, if the transfer speed of the weld 2, that is, the line speed, is high, the above-mentioned phenomenon of escape of the coating film 8' occurs, causing the weld 2 and/or A problem arises in that the corrosion resistance of the adjacent portion 4 is likely to be impaired. The above phenomenon occurs when the paint is sprayed in the atomized area with a spray gun, or when it is applied by a roll method as proposed in Japanese Patent Publication No. 58-6542, or as proposed in Japanese Patent Publication No. 58-27668. This problem is also likely to occur when coating is carried out by flowing down a filamentous stream of paint such as slurry paint, as has been proposed. Although the reason for this phenomenon is not necessarily clear, it is presumed that boiling of the paint in contact with the relatively high temperature welding part 2, or a decrease in viscosity or surface tension due to the rise in temperature, etc. are involved. It is an object of the present invention to solve the problems of the prior art described above. In order to achieve the above object, the present invention moves a can body molded body having side overlapped portions in the axial direction and performs electric resistance seam welding on the side overlapped portions to form a welded can body having a welded portion. Immediately after that, a liquid mainly consisting of water is sprayed onto the outer surface of the weld to rapidly cool the weld, and then the liquid remaining on the outer surface is removed by gas spraying, and then the outer surface of the weld and This invention provides a method for repairing a welded part of a welded can body, characterized by applying a liquid paint to the inner surface. The present invention will be described below with reference to the drawings. In FIG. 3, parts having the same reference numerals as those in FIGS. 1 and 2 indicate similar parts. 10 is an internal welding roll, 11 is an external welding roll, and the internal welding roll 10 is attached to a mandrel 12. The can body formed body 21, which is fed at a high speed (for example, 40 m/min) in the direction of arrow D, has its side overlapped portion 22 connected to the internal and external welding rolls 10, 11, electrical resistance pine seam welding is performed to form a welded can body 1 having a welded portion 2. Immediately after the welding part 2 leaves between the welding rolls 10 and 11, an inert gas 13 (usually nitrogen gas) is sprayed on the inner and outer surfaces to prevent oxidation. At this time, the welded part 2 is usually cooled to approximately 300 to 550°C.
Immediately thereafter, the welded part 2 is sprayed with a spray water 15 made of a liquid mainly composed of water from the water spray nozzle 14 on the outer surface side, and then the droplets or liquid film remaining on the outer surface of the welded part 2 are removed with gas. It is removed by blowing it away by blowing gas 17 (usually air) from a nozzle 16. After the welding part 2 is rapidly cooled to an appropriate temperature (T) of preferably 200°C or less, more preferably 100°C or less by the latent heat of vaporization of this sprayed liquid, the welding part 2 and the exposed metal part 5 in the vicinity Apply liquid paint to the inside and outside surfaces. In this specification, a liquid mainly composed of water means
A liquid consisting only of pure water (e.g. ion exchange water),
and a liquid consisting of water (including pure water) and a small amount (approximately 1 to 20% by weight) of a water-soluble solvent such as ethyl alcohol. Tap water or the like may leave traces of water droplets scattered on the outer surface of the can body after they evaporate, but it is preferable to use pure water because such defects can be prevented. Further, it is preferable to use pure water containing a small amount of ethyl alcohol because the above-mentioned defects can be prevented, the cooling effect is promoted, and there is less danger in terms of explosion-proofness and hygiene. The inner surface of the welding part 2 can be painted by applying a planar paint film 8 formed by a spray nozzle 6 to the inner surface (including the inner surface of the welding area 4) to form a coating film 8'. It is carried out with The coating on the outer surface of the welded part 2 has a circumferential surface with a width almost equal to the width of the exposed metal part 5, and there is no step difference in the welded part along the circumferential surface, as disclosed in Japanese Patent Publication No. 58-6542, for example. This is done by forming a coating film 8'' using an applicator roll 23 having a groove deeper than the height of the welded part 2a. Since the liquid film is removed by the gas 17 injected from the nozzle 16, there is no risk of defects such as discontinuities occurring in the coating film 8'' due to the liquid film or the like. As described above, when coating the welded part 2 by forcedly cooling it to an appropriate temperature (T), preferably 200°C or less, the uncoated area 9 due to the escape of the coating film as shown in FIG. The exposed metal parts 5, including the welds 2, are covered with a coating 8', 8'' over the entire surface without any formation of welds.The coatings 8', 8'' are subsequently dried by heated air (not shown). . The above temperature (T) is determined by tests or experience, preferably within a temperature range lower than 200° C., depending on the boiling point of the paint solvent, the amount of coating, etc. The present invention is not limited to the above examples; for example, the water spray nozzle 14 and the gas nozzle 1
6 may be provided in the direction of travel to promote the cooling effect and the blowing effect. According to the present invention, the welded part is rapidly cooled with spray water before applying the liquid paint, so the applied paint does not escape or flow in, and the exposed metal part is completely covered with the paint film. It has the effect of being covered. Furthermore, since the liquid film remaining on the outer surface in the vicinity of the welded part is removed by gas spraying, there is an advantage that there is no risk of discontinuities in the outer coating film due to the liquid film or the like. Examples will be described below. Example A can body formed body 21 made of tin plate with a plate thickness of 0.21 mm and a plating amount of #25/#25 and having a diameter of 52.3 mm, a height of 133 mm, and a width of 0.4 mm at the overlapped side portion is welded as shown in Fig. 3. The welded can body 1 having the welded part 2 (thickness 0.3 mm, width of the exposed metal part 5 4 mm) is formed by welding the pine seam while moving at a speed of 40 m/min using the rolls 10 and 11, and is immediately heated with nitrogen gas. No. 13 was sprayed onto the inner and outer surfaces of the welded portion 2. The temperature of the welded part 2 after the nitrogen gas spraying was 509°C. This temperature measurement was performed as follows. Surface thermometer (model HR-4F (R) D-Anritsu Meter
During the continuous production of welded can bodies using a welded can body manufactured by INC. Co., Ltd., the welded can body is temporarily stopped, the measuring terminal of the surface thermometer is brought into contact with the welded part 2 instantly, and the maximum peak temperature is read. This was repeated at least 10 times and the average value was taken as the representative value of the weld surface temperature under the conditions. Subsequently, spray water 15 made of ion-exchanged water is sprayed onto the welded part 2 from the outside at a rate of 10 ml per minute.
After that, air 17 is sprayed to completely remove the collected water film, and then a planar paint film 8 is applied from a spray gun 6 mainly to the inner surface of the welded part 2 and its vicinity 4, and also applied to the outer surface. Coating was carried out using roll 23. The time from the end of nitrogen gas 13 spraying to the spray water 15 spraying is 0.45 seconds, and the time from the spray water 15 spraying to the air 17 spraying is 0.45 seconds.
The time it takes to spray the paint film 8 is 0.3 seconds, the time it takes to apply the paint film 8 is 1.4 seconds, and the temperature of the welding part 2 just before the paint film 8 is applied (the measurement method is the same as above).
It was 97℃. The composition of the paint forming the paint film 8 is as follows, the paint temperature immediately before the spray nozzle is 40° C., and the coating amount is 40 milliliters per minute.

[Table] * indicates boiling point.
After the above coating, hot air at 300°C was applied for 30 seconds to dry the coating film. The amount of exposed metal (current display) on the inner surface of the welded part 2 and its vicinity 4 obtained as described above was measured by the constant voltage electrolysis method described later, and it was 0 to 0.1 mA.
It was found that the inner surface of the welded part 2 and its vicinity 4 was substantially completely covered with the coating film 8' (thickness: 20 μm). On the other hand, for comparison, the amount of metal exposure in the welded part 2 and its vicinity 4 of the welded can body formed in the same manner as described above, except that the spray water 15 and air 17 were not sprayed, was 35 to 87 mA. The area of the exposed metal portion 5 was so large as to be impractical. Measuring the amount of metal exposure using constant voltage electrolysis method: After applying the specified paint and baking hardening it, cut out the welded area and its vicinity over a width of 2cm, and cut out a 5mm wide piece in the direction perpendicular to the welded area and 100mm in the parallel direction. Seal the remaining parts with vinyl tape and use them as test pieces. After immersing this test piece in an electrolyte of 3% saline at 25°C for 3 minutes, a carbon rod was used as a counter electrode.
Perform constant voltage electrolysis at a voltage of 100V for 10 seconds, and measure the average current flowing at that time. For each sample, the arithmetic mean value of the measurements of 5 specimens is taken as the result. The composition of the paint applied by the application roll 23 is as follows, and its average coating thickness (after drying)
was 20 μm.

[Table] * indicates boiling point.
In this case as well, as a result of measuring the amount of exposed metal using the constant voltage electrolysis method, it was found that the outer surface of the welded part 2 and its vicinity 4 was substantially completely covered with the coating film 8'', as in the case of the inner surface. It has been found.

[Brief explanation of the drawing]

Fig. 1 is a plan view of the main part showing the state when a planar paint film is applied to the welded part and its vicinity by the conventional method, Fig. 2 is a longitudinal sectional view taken along the - line in Fig. 1, and Fig. FIG. 3 is an explanatory front view showing an example of an embodiment of the method of the present invention. DESCRIPTION OF SYMBOLS 1... Welding can body, 2... Welding part, 8... Planar paint film, 8', 8''... Paint film, 10... Internal welding roll, 11... External welding roll, 15... Spray water , 17... gas, 21... can body molded body, 22...
...Side overlapping part.

Claims (1)

[Claims] 1. After forming a welded can body having a welded portion by electric resistance seam welding the side overlapped portion while moving the can body molded body having the side overlapped portion in the axial direction, immediately remove the outer surface of the welded portion. quenching the weld by spraying a water-based liquid on the weld, then removing the liquid remaining on the outer surface by blowing gas, and then applying a liquid paint to the outer and inner surfaces of the weld. Features: A method for repairing welds on the body of a welded can.