JPS6311109B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a welded can body made of stain-free steel (electrolytic chromic acid treated steel plate). Most of the thin metal sheet materials used for food cans, aerosol cans, 18 cans, and other miscellaneous cans are tinplate, which is tin plated steel sheet, and tainfree steel, which is electrolytic chromic acid treated steel sheet. Tinplate has excellent workability and corrosion resistance, and is currently mainly used as soldering cans, welding cans, and DI cans (drawn and ironed cans), but the tin used is quite expensive and rare. Since it is a highly valuable metal, the tin cans it manufactures must also be expensive. On the other hand, stain-free steel is a low-carbon thin steel plate coated with an extremely thin film mainly composed of chromium, i.e., a surface film consisting mainly of a metallic chromium layer and a chromium oxide layer (hereinafter referred to as the surface film). means. Although this stain-free steel is inferior to tinplate in terms of workability, it has better paint adhesion than tinplate, and depending on the contents, it also has better corrosion resistance, so it is suitable for paint cans. , moreover, it uses cheaper chrome, so it costs less than tinplate. Conventionally, adhesive cans, DR cans (squeezed cans), and welded cans have been known as cans made from stain-free steel. Bonded cans made of stain-free steel are usually produced by forming a single blank into a tubular shape to create an overlapping section, then inserting an organic material into the overlapping section and joining the can body, and a can body with two tubes attached to both ends of the can body. It is a three-piece can consisting of a pair of lids that are joined together with heavy seams. In this case, generally on the inner side of the adhesive can, the side edge of the original blank, which is the exposed iron surface, exists as the end surface of the overlapping part, so that end surface is covered with an organic material so that the exposed iron surface can be directly It has been repaired so that it is not exposed to the inside of the can. If the inner iron surface of such adhesive cans can be sufficiently repaired with an organic material, it will have sufficient corrosion resistance when combined with the electrolytic chromic acid treated surface that is usually painted. It has the following problems. First, since the can body is bonded to an organic material, damage or deterioration of the organic material may occur during can manufacturing processes such as flanging, netting, or beading, or during heating to sterilize the can. Similar concerns may remain when high-pressure contents are packed into cans. Second, the joint of the can body is 2
The thickness is the sum of two thin metal plates and the organic material used for joining, and when the lid is double-sealed, the seaming conditions between the joint and other parts are different, so the seaming conditions near the joint are different. Advanced technology is required to completely eliminate leakage of contents from the seaming area. Tein-free steel DR cans are usually composed of a draw cup with a bottom made by drawing and forming a blank of ten-free steel, and a lid double-sealed to the end of the cup, and are classified as so-called two-piece cans. There is. In this case, the electrolytic chromic acid treated layer (surface film) of stain-free steel has poor workability, so in the drawn cup, cracks occur in the surface film and the steel surface is locally exposed. , corrosion resistance and paint adhesion are lower than that of the unprocessed stain-free steel. After the drawing process, the inside surface of such drawing cups is usually painted, but since the chrome coating on the stain-free steel was damaged during the drawing process, it was necessary to completely apply the paint over the entire surface. It is not easy to apply. In addition, 2
DR cans, which are piece cans, are subject to the following restrictions as containers compared to other three-piece cans. That is,
First, the height of the body of the drawing cup of a DR can is limited by the drawing process, and it is difficult to manufacture one that is too high, which limits the can shapes that can actually be applied to DR cans. Second, with the squeeze cup of a DR can, it is theoretically impossible to freely control the thickness distribution of the body or bottom. In particular, the thickness of the boundary between the bottom and the body, or the bottom, which is important for the strength of the can, must be thinner than other parts.
If the thickness of the plate at the boundary between the bottom and the body or the bottom is increased, the thickness of the plate particularly near the open end of the drawing cup becomes extremely thick, which is not economical. On the other hand, 3
For piece cans, generally, by using a lid that is thicker than the can body, it is possible to prevent the lid from buckling and deforming due to pressure or vacuum pressure inside the can. The double seaming significantly increases the strength of the can itself, for example, the resistance to deformation of the can due to impact forces. As mentioned above, three-piece cans generally have many advantages over two-piece cans in terms of structure and strength. On the other hand, welded cans usually consist of a single blank formed into a tubular shape to create an overlapping part, a can body with the overlapping part welded together, and a lid double-sealed on both sides of the can body. It is a 3-piece can. In this case, the method of crushing and welding the entire overlapped part,
There is a so-called pine welding method and a method in which only a part of the overlapped part is welded, but the former has no gaps in the overlapped part, and the difference in level of the welded part is smaller, and the organic material of the welded part is used more effectively. Currently, the former method is mainly used because it facilitates correction. In a welded can body, the welded part is generally stronger than other parts, so there is no concern about the strength of the welded part like in a bonded can, and since it is a three-piece can. You can freely choose the size and lid of the can. moreover,
The thickness of the welded part using the Matsushi welding method is usually 1.0 to 1.8 times the original plate thickness, making double seaming between the welded can body and lid more stable than with other three-piece cans. It has the advantage of being able to Currently, the most common method for manufacturing the welded can bodies described above is by lap resistance seam welding. This lap resistance seam welding method usually involves stacking metal plates, successively pressurizing and crushing the stacked parts with a pair of electrodes, and applying alternating current between the electrodes to perform continuous resistance welding. Two rotating roll-shaped electrodes are generally used as the electrodes. A particular problem with welded can bodies manufactured by the above-mentioned lap resistance seam welding method using pine welding, that is, the pine seam welding method, is the generation of molten metal splash from the welded area, so-called splash. be. In other words, in the pine seam welding method, welding is performed over the entire overlapping part of metal plates, so if the metal melts excessively at the welded joint surface, the molten metal easily becomes a splash from the end of the overlapping part. is scattered. The presence of such splashes at and near the welds in the welded can body becomes an obstacle when the welds are corrected using organic materials, and is often not sufficiently corrected, which is unfavorable in terms of corrosion resistance. When welding stain-free steel by traditional lap resistance seam welding using two rotating roll electrodes, welding usually results in significant splashing or localized weld strength, making it difficult to achieve a complete seal. Welding performance is not guaranteed and a state of welding occurs, making it difficult to obtain a perfect welding condition. This situation is attributable to the electrolytic chromic acid treatment film on the surface of stain-free steel, especially the presence of a chromium oxide layer, which reduces electrical conductivity and increases the amount of heat generated during welding or reduces bondability. Therefore, in reality, the surface film of the stain-free steel at the welded part and its vicinity is removed in advance by a cutting method using a milling cutter, etc., as disclosed in Japanese Patent Publication No. 51-14189, and the steel surface is then removed. A welded can body made of stain-free steel is manufactured by exposing the exposed iron surface and pine seam welding the iron surface using two rotating roll-shaped electrodes. As the steel surface is exposed over the entire welded part of the welded can body of the above-mentioned stain-free steel can body and its vicinity, the adhesion and corrosion resistance of the welded steel can body to paints, plastic films, etc. It has the disadvantage that it is significantly inferior to areas where the surface film of stain-free steel exists. The present invention attempts to eliminate these drawbacks. An object of the present invention is to provide a welded can body made of stain-free steel that has excellent adhesion to a correction material and excellent corrosion resistance. Another object of the present invention is to provide a welded can body having a welded portion that can be easily corrected. The present invention provides a welded can body made of stain-free steel having a surface coating consisting of a metallic chromium layer and a chromium oxide layer, which has a pine seam welded portion having a thickness of 1.0 to 1.8 times the plate thickness of the stain-free steel. and the pine seam welded portion is covered with the surface film at least on the inner surface of the can body in contact with the welding electrode,
The present invention provides a welded can body made of stain-free steel, characterized in that the coverage of the chromium oxide layer is about 30% or more in terms of area ratio. The present invention will be explained in detail below. The stain-free steel used in the present invention is normally used as a thin plate material for cans, and is usually
A metallic chromium layer of ~200 mg/m ² , preferably 40-160 mg/m ² and an amount of chromium thereon of 5-30 mg/m ² ,
It refers to a low carbon thin steel sheet coated with a surface film preferably having a chromium oxide layer of 9 to 25 mg/m ² . Here, the chromium oxide layer is mainly composed of an amorphous hydrated chromium oxide layer in the manufactured state, but it is heated for baking paint or is exposed to the parts of the welded can body of the present invention that are in contact with the electrode. When it undergoes a thermal history as seen, the degree of hydration, the coordination state of chromium atoms, oxygen atoms, etc. change, and the degree of crystallinity progresses. The chromium oxide layer referred to in the present invention includes not only a completely amorphous layer but also a layer with a certain degree of crystallinity as shown in the transmission electron micrographs of FIGS. 9 and 10. This includes those in which a continuous coating is formed except for the cracked portions, as shown in FIG. The thickness of stain-free steel is the same as that of ordinary can sheet material, i.e. about 0.12-0.6 mm, especially about
It is preferably 0.15 to 0.4 mm. When manufacturing welded can bodies made of stain-free steel, the stain-free steel is usually painted.
It is processed into blanks cut to predetermined dimensions.
In this case, it is desirable that both sides of the blank to be welded be left unpainted by a so-called margin painting method. The painted blank is formed into a can body molded body having a circular or square cross section with overlapping parts on the sides by a known method, such as a roll form method or an inverted form method. By performing pine seam resistance welding on the overlapping portions of the body molded bodies, a welded can body having a side seam weld where the entire overlapping portion is crushed is produced. As a result of research on the pine seam resistance welding method for stain-free steel, the present inventors found that the reason why it is difficult to weld stain-free steel using the conventional pine seam resistance welding method using two rotating roll electrodes is as follows. , it is thought that this is due to the short instantaneous contact length during welding in the direction of the seam weld between the welding electrode and the overlapping part of the can body molded body, and a method that can increase the above contact length, that is, for example, When welding stain-free steel using the pine seam resistance welding method, which combines a straight electrode with infinite curvature and a rolled electrode with large curvature, welding of stain-free steel, which had been considered difficult, was successful. It has been found that this is possible with no splash and with sufficient strength of the welded part. What is even more surprising is that the chromium oxide layer that contributes to the adhesion of the correction material on the surface of the welded part in contact with the welding electrode, which was thought to be significantly destroyed or deteriorated due to heating or pressure during conventional welding, is considerably reduced. It was found that some parts remained. As mentioned above, in the conventional pine seam welding method using two rotating roll-shaped electrodes, the instantaneous contact length between the welding electrode and the overlapping part of the can body is limited. This is because the diameter of the rolled electrode inside the can body molded body is limited by the size of the molded body, and if the welding electrode inside the can body molded body is made straight, the contact between the welding electrode and the overlapping part will be reduced. The length can be increased as the radius of curvature of the external rolled electrode increases. The reason why stain-free steel can be welded due to the increase in contact length described above is considered to be as follows. In other words, pine seam welding of stain-free steel requires more heat at the joint surface than when welding clean steel surfaces, while the contact surface between the electrode and stain-free steel requires more heat due to the presence of a surface film. As the electrical resistance increases, the amount of heat generated increases, so heat accumulates in the welding area, and the welding area tends to be overheated to the extent that splash occurs. By increasing the instantaneous contact length, heat conduction from the weld to the electrode is significantly promoted, and it can be expected to prevent the weld from becoming significantly overheated, that is, to prevent splash. In addition, in seam resistance welding, alternating current is normally used as the welding current, but if the instantaneous contact length between the welding electrode and the welding part is short, the waveform of the alternating current, that is, the amount of current, will respond directly to the change. The distribution of heat generation at the welded joint surface is such that the joint tends to become weaker at the point corresponding to the zero value of the AC current waveform, but as the contact length is increased, the It is thought that alternating current of more frequencies will pass through, and the amount of heat generated at the welded joint surface will become uniform, making it possible to weld stain-free steel. An example of a method for manufacturing a welded can body according to the present invention will be described below with reference to the drawings. FIG. 1 shows a specific example of an apparatus for manufacturing a welded can body according to the present invention, and FIG. 2 is a partially cutaway side view taken along the - line in FIG. 1. Reference numeral 1 designates a can body molded body, which is molded by a can body molding machine (not shown) on the left side of FIG. 2 so that the overlapping portion 2 is directed downward. A can body forming machine is attached to the left end of the mandrel 3 and is configured to be welded at the right end, and the can body formed body 1 is transferred over the mandrel 3 from the left to the right. A can body molded body feed rod 4 is inserted into the long groove at the top of the mandrel 3, and claws 5 are attached to the feed rod 4 at regular intervals. When the feed rod 4 moves to the right, the upper rear end of the can body molded body 1 engages with the claw 5, thereby being conveyed. The claw 5 is configured to move downward when pressure is applied from above, and return to its original position by a spring when the pressure is released.
A linear electrode 6 is placed in the groove at the bottom of the tip of the mandrel 3.
is installed inside. The linear electrode 6 is made of elongated copper or copper alloy, and at least the electrode surface 7 is longer than the overlapping portion 2 (can height of the molded can body). The electrode surface 7 is a flat surface corresponding to the shape of the overlapping portion, or has a convex curved surface in the width direction. The width of the electrode surface 7 is larger than the width of the overlapping portion 2. The linear electrode 6 is also connected by a feeder (not shown) to a welding power source (eg, commercial frequency or about 100-500 Hz for high-speed can making). A pair of presser wings 9 are disposed on both sides of the electrode portion of the mandrel 3, and a support 10 is disposed on the upper part, and the mandrel 3 is horizontally moved by a cam mechanism (not shown) synchronized with the drive mechanism of the feed rod 4. It is configured to be movable in the vertical and vertical directions, and to be able to press the molded can body 1 against the mandrel 3 prior to welding. A rotating electrode 11 is arranged below the linear electrode 6. The rotating electrode 11 is disk-shaped, and the electrode surface 12 is a short cylindrical surface, the width of which is the same as the overlapping portion 2.
larger than the width of The rotating electrode 11 is supported by a bearing stand 13 via a bearing, and is also supported by a feeder 14.
connected to the welding power source by A support rod 15 is fixed to the lower part of the bearing stand 13.
The lower part of the bearing base 13 is fitted into a through hole in the sliding plate 16, and the bearing stand 13 can move up and down with respect to the sliding plate 16. A pressing spring 17 is provided surrounding the support rod 15 between the lower surface of the bearing stand 13 and the upper surface of the sliding plate 16, and pressurizing force is applied to the overlapping portion 2 during welding by the pressing spring 17. Both sides of the sliding plate 16 slide in the longitudinal direction of the mandrel 3 along the guide surfaces 20 of the guides 19 provided horizontally on both inner surfaces of the support frame 18, and the rotating electrodes 11 are overlapped accordingly. Rotate on part 2. Sliding of the rotating electrode 11 is performed via a connecting rod 21 and a pin 22 by a constant velocity cam movement mechanism (not shown). A protrusion (engaging part) 23 is provided at the upper end of the inner surface of both side plates of the support frame 18, and when the upper surface 13a of the bearing base bottom plate engages with the lower surface of the protrusion 23, the rotating electrode 11 is rotated. The gap between the top surface of the rotating electrode 11 and the electrode surface of the linear electrode 6 becomes larger than the thickness of the overlapped portion or the welded portion, and as a result, the electrode portion of the molded can body 1 is pushed down. The can body that has been fed and welded is delivered to the rotating electrode 1.
1. Welding is performed using the above apparatus as follows. The rotating electrode 11 is located on the left end side of the support frame 18, the protrusion 23a and the upper surface 13a of the bearing base bottom plate are engaged, and the distance between the top surface of the rotating electrode 11 and the electrode surface 7 of the linear electrode 6 overlaps. In a state where the thickness is larger than the thickness of the mating part, the can body molded body 1 is fed by the feed rod 4 to a predetermined position of the linear electrode part and is stopped. At the same time, a pair of presser wings 9 advance toward the mandrel 3 from the left and right, and a support 10 advances toward the mandrel 3 from above to press and fix the can body molded body 1 onto the mandrel 3. In this fixed state, it is important that the entire width of the overlapping portion 2 is in contact with the electrode surfaces 7 and 12, as shown in FIG. This is to crush the entire overlapping portion 2 and uniformly reduce the thickness of the entire welded portion. In other words, if there is a part in the width direction of the overlapping part 2 that does not contact the electrode surface, the non-contact part will not be crushed and a step almost equal to the thickness of the board will remain, and this step will be completely covered and the contents of the can will be removed. In order to protect objects from corrosion, a large amount of protective paint is required, which is extremely difficult. Next, the sliding plate 16 moves to the right, and the engagement between the upper surface 13a of the bearing base bottom plate and the protrusion 23a is released, and the electrode surface 12 of the rotating electrode rotates on the electrode surface 7 of the linear electrode, and is overlapped. Spring 17 pressing part 2
The electrode is pressurized by the electrode and moved to the right, during which time current passes between the rotating electrode, the overlapping portion, and the linear electrode to perform welding. FIG. 3 shows an example of a stain-free steel welded can body 25 of the present invention obtained by the above-described welding method, and includes a pine welded portion 24. FIGS. 4 and 5 are perspective views of a weld including a cross section perpendicular to the weld line of a typical pine weld of a stain-free steel welded can body according to an embodiment of the present invention, Figure 4 shows a case where the amount of crushing is small and there is a step, and Figure 5 shows a case where the amount of crushing is large and there is almost no step at the weld. In both cases, the upper side is the inner surface of the can body. (linear electrode side) is shown. As is clear from these figures, in the welded can body of the present invention, the weld surface along the weld line changes due to the change in heat generation according to the alternating current waveform of the welding current used during pine seam welding. There are almost no irregularities and it is crushed evenly. In addition, since the shape of the welding electrode is different between the inner and outer surfaces of the can body, the shape and surface condition of the welded part are different on the inner and outer surfaces of the can body, but generally the inner surface of the can body (linear electrode side) is different. Since the instantaneous contact length between the welding part and the welding electrode during welding is longer than that on the outer surface side (rotating electrode side), heat generation on the surface is suppressed to a low level, resulting in a more preferable surface condition of the welded part. Since the side seam welds on the inner surface of the can are particularly important in terms of corrosion resistance of the can body when filled with contents, the above-mentioned difference in the welds on the inner and outer surfaces of the can can be said to be favorable. The width of the mash welded part of the welded can body of the present invention is preferably 2 mm or less, and its thickness is 1t to 1.8t, which is the thickness (t) of the tubular body other than the welded part. It is preferable for the width of the above-mentioned pine weld to be narrow, from the viewpoint of correction by the organic material and also from the aesthetic point of view, but if the width is less than about 0.3 mm, it becomes difficult to actually manufacture the can body. The surface of the stain-free steel welded can body of the present invention can generally be classified into five areas depending on the condition. That is, in the surface part of the matash weld shown in Figs. 4 and 5, A is the surface part that is completely unaffected by welding heat and has a complete surface film, and B is the part that is in direct contact with the welding electrode and is welded. C is the completely exposed iron surface that was extruded during welding, and D is the exposed iron surface that remains as a step due to the remaining cut edge of the overlapping part of the can body molded body. In E, the surface film is significantly destroyed due to heating during welding or deformation of the overlapped part, or the amorphous chromium oxide is almost transformed into crystalline chromium oxide (Cr ₂ O ₃ ), and the base material is damaged. Indicates the surface area where the adhesion to iron has significantly decreased.
In the welded part with a relatively large step shown in FIG. 4, the region E mentioned above is usually limited to an extremely narrow range. The present inventors collected the surface film of the welded part and observed it with an electron microscope. As a result, the surface film was stretched in the direction of the extruded iron exposed surface C or the step D on the contact surface B with the electrode. Cracks occur perpendicular to the direction in which the surface film is stretched, and a considerable amount of chromium oxide remains in the surface film despite the heating during welding. It was confirmed that there was no significant deterioration in quality, and the adhesion to the base steel remained almost unchanged, and therefore the adhesion of the correction material remained without deterioration. The amount of cracks in the surface film at the contact surface B of the welded part on the inner surface of the can body with the electrode is usually:
The area ratio ranges from about 0 to 70%, while the coverage of chromium oxide ranges from about 30 to 100% in area ratio. In this case, the amount of cracks in the surface film tends to increase as the amount of crushing of the welded part or the amount of current applied during welding increases, and also increases as the area approaches the exposed surface C of the extruded iron. There is a tendency. When the amount of crushing of the welded part is increased, the stepped part D
The height L ₃ decreases, but on the other hand, the width L ₂ of the extruded iron exposed surface C and the width L ₄ of the altered part E of the surface film decrease.
tends to increase, and when the amount of crushing of the welded portion is reduced, the height _L3 of the stepped portion D increases. In this case, the width L ₂ of the extruded iron exposed surface C
is usually about 0 to 0.25 mm, and the height of the step D is L ₃
is in the range of 0 to 0.8t of the plate thickness (t) other than the welded part. In addition, the width L ₄ of the altered part E of the surface film is usually 0.
~0.3mm range. Even in the above-mentioned welded steel can body, there are completely exposed iron surfaces such as parts C and D at the welded part, but since the area is small, the parts near these parts, In particular, tests have shown that when the contact surface B with the electrode is corrected with an organic material, if the adhesion with the correction material is sufficiently guaranteed, satisfactory corrosion resistance performance can be obtained. In that case, the adhesion between the contact surface B with the electrode and the correction material depends on the amount of cracks in the surface film or the coverage of the chromium oxide layer, especially if the remaining area ratio of the chromium oxide layer is 30% or more. It has been confirmed that adhesion with the correction material is ensured. The stain-free steel welded can body of the present invention is
The pine seam welded portion is covered with a surface film consisting of a metallic chromium layer and a chromium oxide layer at least on the inner surface of the can body, on the surface in contact with the welding electrode, and the coverage of the chromium oxide layer is the area ratio. It is about 30% or more, so at least the inner side of the welded part has excellent adhesion with the correction material, and since pine welding is performed,
There are no voids in the welded area. Therefore, when filled with contents as a can, the corrosion resistance of the welded part is almost the same as that of the non-welded part, as shown in the following example, by appropriately selecting the corrective material. It has excellent features not found in steel welded can bodies. The effects of the present invention will be further clarified by Examples below. Example 1 A plate having a thickness of 99 mg/ ^m2 of chromium and a chromium oxide layer of 11 mg/ ^m2 of chromium.
We applied epoxy/phenol-based paint to the 0.23 mm thin stainless steel plate on the surface that should become the inner surface of the can body, leaving the area near the welded part of the can body as an unpainted area, so-called margin painting, and also painted the surface that should become the outer surface. After margin painting and printing, it was cut into blanks. Next, this stain-free steel blank was formed into a cylindrical shape with an inner diameter of 65.3 mm and a body length of 125.4 mm by the means shown in Figs. A welded can body was obtained by welding. At that time, a 50-cycle AC welding power source was used, the overlapping width of the cylindrical blanks was 0.4 mm, the diameter of the rotating electrode was 300 mm, the welding speed was 12 m/min, and the applied force and welding current amount were varied. I did some welding. On the inner surface of the resulting welded can body, the shape of the welded part, especially the width L ₁ of the contact surface B with the welding electrode, the width L ₂ of the extruded iron exposed surface C, and the amount of step of the welded part.
L ₃ and the width L ₄ of the altered part E of the chromium film were investigated.
Furthermore, a small piece of the welded part was cut out, carbon was vacuum-deposited on the inner surface of the can body, the base steel of the small piece was dissolved in a 5% nitric acid alcohol solution, and the metallic chromium film was further dissolved and removed with concentrated hydrochloric acid. , a thin film sample of the chromium oxide layer on the inner surface of the can body was prepared,
The sample was observed with an electron microscope to determine the remaining area ratio of the chromium oxide layer remaining on the contact surface B with the welding electrode. In this case, the contact surface B with the welding electrode is divided into three parts: the extruded iron exposed surface C side, the original stain-free steel surface A side, and the central part.
5 points on each site (each point is approximately 75μ in size)
×65 μ) was selected, the area ratio of the remaining chromium oxide layer was calculated, and the average value of these values was calculated to determine the coverage area ratio of the chromium oxide layer on the electrode contact surface B. Microscopic microstructure photograph of a cross section perpendicular to the welding direction of the welded part of the welded can body obtained when the pressurizing force was 80 kg and the welding current (effective value of sine wave current) was 3.5 kA (magnification 60, 4% nital) Fig. 6 shows a similar photomicrograph when the pressure was 100 kg and the welding current was 4.8 kA. Further, FIG. 8 shows an enlarged photograph (magnification: 340) of the vicinity of the welded part surface on the inner surface of the can in the photograph of FIG. 7. As is clear from these photographs, the metal structure near the top surface (inner side of the can) and bottom surface (outer side of the can) of the weld zone is largely the same as the ferrite structure of the base metal, which is not affected by welding. This indicates that there was little heat influence during welding in these parts. In addition, Figure 9 shows a transmission electron micrograph (magnification: 1200) of the chromium oxide layer at the center of the electrode contact surface B at the welded part on the inner surface of the can using the same sample as the photograph in Figure 6. A similar transmission electron micrograph of the same sample as the photograph in the figure is shown in FIG. In Figure 9, the chromium oxide layer almost completely remains, while in Figure 10, where the pressure is high and the amount of mashing is large, cracks (white visible parts) in the chromium oxide layer occur. I can see that it is.
Reference photo A shows an electron diffraction image of a part of the chromium oxide layer shown in FIG. An image photograph is shown in Reference Photograph B, and these photographs are very similar, indicating that the chromium oxide is amorphous. Next, apply epoxy/phenol paint as a correction material over a width of about 7 mm to the welded part on the inner surface of the welded welded can body of the above-mentioned stain-free steel can, so that the thickness of the coating after drying is 10 to 20 μm. , I created a printed version. Furthermore, as another correction material, a polyester film with a thickness of 30 μm and a width of 8 mm was bonded by thermocompression to the welded part on the inner surface of the welded can body. The welded can body with the above-mentioned welded parts corrected was flanged, and a stain-free steel lid whose inner surface was coated with epoxy/phenol paint was double-sealed using a conventional method to create an empty can. The above empty can was filled with 1.5% saline solution, double-sealed with the same stain-free steel lid as above, sterilized in a retort, stored at 50℃ for one month, opened, and welded the inside of the can. The corrosion state of the welded parts and the damage or separation of the compensation material from the welded parts were investigated.
Table 1 shows the results. As a comparative example, a welded can body was created using the same welding method using a blank in which the surface film near the welded part of the above-mentioned stain-free steel was previously removed to expose the iron locally. The test was also conducted under the same conditions as above. At this time, the width of the exposed iron surface of the welded can body was approximately 2 mm. As is clear from Table 1, the welded can body of the present invention has excellent characteristics, and in particular, as the proportion of the remaining area of the chromium oxide layer on the contact surface B of the welding electrode increases, the welded can body has excellent properties. The adhesion between the surface and the correction material is improved, and as a result, the corrosion resistance of the welded part is improved.

[Table] Example 2 Same as Example 1 from a 0.23 mm thick stain-free steel thin plate having a metallic chromium layer with a chromium content of 102 mg/m ² and a chromium oxide layer with a chromium content of 15 mg/m ² Welded can body (inner diameter 65.3 mm,
The body length was 125.4mm). At that time, the overlapping width of the cylindrical blanks is
0.4mm, the diameter of the rotating electrode is 300mm, the pressure is 100Kg,
Welding was performed at a welding speed of 9 m/sec and by varying the amount of welding current. The amount of welding current was adjusted by changing the voltage on the primary side of the welding AC power source (using a 50-cycle commercial frequency power source), and the amount of welding current was measured during welding. As a result, the stain-free steel has sufficient welding strength and sealing performance when the amount of welding current (effective value of sine wave current) is in the range of 3.7kA to 4.5kA, and has welded parts with no molten iron splash. I was able to get a can body. If the current amount is less than 3.7kA, welding strength or sealing performance will decrease, while if the current amount is 4.5kA
When it was larger than , molten iron splash tended to occur from the welded part. On the inner surface of the resulting welded can body, the shape of the welded part, especially the width L ₁ of the contact surface B with the welding electrode, the width L ₂ of the extruded iron exposed surface C, and the amount of step of the welded part.
Examine L ₃ and the width L ₄ of the altered part E of the chrome film,
Furthermore, the weld surface was observed using an electron microscope, and
The ratio of the area where the chromium oxide layer remained on the contact surface B with the welding electrode was examined using the same method as in Example 1. Next, epoxy/phenol paint is applied and baked on the welded parts of the inner and outer surfaces of the welded can body so that the thickness of the coating after drying is 20 to 30 μm, and then the can bodies are flanged and the inner surface Epoxy
An empty can was prepared by double-sealing a lid made of stain-free steel coated with a phenolic paint using a conventional method. The above empty can was filled with water boiled in water, double-sealed with the same stain-free steel lid as above, sterilized in a retort, stored at 50℃ for 6 months, and then opened. and the state of occurrence of black sulfide discoloration was investigated. Furthermore, the number of perforated cans that occurred within 6 months was investigated (the number of actual can tests above was 100 for each test).
can). Table 2 shows the results. In this case, as a comparative example, a welded can body was created using the same welding method using a blank in which the welded parts and the surface film in the vicinity of the stain-free steel were previously removed to expose the iron locally. However, the can body was also tested under the same conditions as above. At this time, the width of the exposed iron surface of the welded can body was approximately 2 mm. The results are shown in Table 2. As is clear from Table 2, the welded can body of the present invention has excellent properties.

[Table] Example 3 This was carried out using a 0.17 mm thick stain-free steel thin plate having a metallic chromium layer with a chromium content of 105 mg/m ² and a chromium oxide layer with a chromium content of 22 mg/m ² . Welded can body (202 diameter,
200ml) was created. On the inner surface of the resulting welded can body, the width L ₁ of the contact surface B with the welding electrode, the extruded iron exposed surface C
The width L ₂ of the weld, the amount of step L ₃ of the weld, and the width L ₄ of the altered part E of the chromium film were examined, and the weld surface was further observed with an electron microscope to determine whether chromium oxidation was detected on the contact surface B with the welding electrode. The coverage area ratio of the material layer was investigated. Next, a polyester film with a thickness of 20 μm and a width of 8 mm was bonded under heat to the welded part of the inner surface of the welded can body, and then multi-bead processing, net-in processing and flange processing were performed, and vinyl chloride resin paint was applied. Double-seal an aluminum easy-open lid, fill with orange juice at 90℃, double-seal a stain-free steel lid coated with epoxy phenol paint on the inside, and store at 50℃ for 6 months. The cans were opened and the corrosion state of the can inner welds, the amount of iron eluted, the discoloration of the contents, and the flavor evaluation were examined. In this case, as a comparative example, a welded can body was created using the same welding method using a blank in which the welded parts and the surface film in the vicinity of the stain-free steel were previously removed to expose the iron locally. However, the can body was also tested under the same conditions as above. At this time, the width of the exposed iron surface of the welded can body was approximately 2 mm. Table 3 shows the results. As is clear from the table, it can be seen that the can body of the present invention has excellent properties.

[Table] Example 4 The inner surface of a can body was made of a 0.23 mm thick stain-free steel plate having a metallic chromium layer with a chromium content of 53 mg/m ² and a chromium oxide layer with a chromium content of 11 mg/m 2 ^. After painting the margin with epoxy/urea paint on the surface that was to become the outer surface and performing margin painting and printing on the surface that was to become the outer surface, it was cut into blanks. Next, this stain-free steel blank was welded and can-formed using the same method as in Example 1 to produce a welded can body (inner diameter 65.3 mm, body length 125.4 mm). At that time, the overlapping width of the cylindrical blanks is
Welding was carried out at a welding speed of 0.6 mm and a welding speed of 12 m/min, with varying pressure and welding current. The shape of the welded portion on the inner surface side of the obtained welded can body and the coverage area ratio of the chromium oxide layer on the contact surface B with the welding electrode were investigated. Next, welded the welded part on the inner surface of the welded can body with a width of approximately 7 mm.
Epoxy/urea paint was applied, baked, and blanked to a thickness of 20 to 30 μm after drying. The welded can body is double-sealed with a tin eye lid and a tin bottom lid whose inner surfaces are coated with epoxy/urea paint, a mounting cup with a valve is attached, and a water-soluble glass cleaner is applied. Filled. After storing this aerosol can at 50°C for 6 months, the can was opened and the state of corrosion of the welded part on the inner surface of the can was examined. Furthermore, the number of perforated cans that occurred within six months was investigated (the number of actual cans tested above was 60 cans each). Table 4 shows the results. As a comparative example, a welded can body was created using the same welding method using a blank in which the electrolytic chromic acid treatment film near the welded part of the above-mentioned stain-free steel was previously removed to expose iron locally. The can body was also tested under the same conditions as above. At this time, the width of the exposed iron surface of the welded can body was approximately 2 mm. As is clear from Table 4, the can body of the present invention has excellent properties.

[Table] Example 5 Example 4 was made from a 0.23 mm thick stain-free steel sheet having a metallic chromium layer with a chromium content of 161 mg/m ² and a chromium oxide layer with a chromium content of 11 mg/m ² . A welded can body was created using the same method. At this time, the overlapping width of the cylindrical blanks was set to 0.4 mm.
And so. The welded part of the inner surface of the welded can body was painted with epoxy/urea paint in the same manner as in Example 4, baked, flanged, and a tin metal lid, tin bottom lid, and mounting cup were attached to the aerosol can. It was created. Fill this can body with laundry starch,
After storage at 50°C for 6 months, the cans were opened and the corrosion state of the welded parts inside the cans and changes in the color tone of the contents were examined. Furthermore, the number of perforated cans that occurred within six months was investigated (the number of actual can tests above was 60 cans each). Table 5 shows the results. As a comparative example, a welded can body was created using the same welding method using a blank in which the electrolytic chromic acid treatment film near the welded part of the above-mentioned stain-free steel was previously removed to expose iron locally. The can body was also tested under the same conditions as above. As is clear from Table 5, the can body of the present invention has excellent properties.

[Table] Example 6 A can body was coated on a 0.22 mm thick stain-free steel thin plate having a metallic chromium layer with a chromium content of 100 mg/m ² and a chromium oxide layer with a chromium content of 15 mg/m 2 ^. Apply epoxy/phenol paint to the surface that should be the inner surface, and leave the area near the welded part of the can body as an unpainted area, so-called margin painting.
After applying margin coating to the surface that would become the outer surface, this thin plate was cut into blanks. Next, this stain-free steel blank was processed using the equipment shown in Fig. 11 and Fig. 12 without removing the surface treatment film (metallic chromium layer and chromium oxide layer) from the part to be welded. A square can body preform 101 having a cross section of 132 mm x 77.4 mm, a body length of 185.7 mm, and an overlapping part located at the center of the short side was manufactured by pine seam welding the overlapping part. 11 and 12, 101 is a rectangular can body preform, and a can body forming machine (not shown) attached to the left end of the mandrel 104 in FIG. It is formed from a blank in the following manner. At the right end of the mandrel 104, an inner roll electrode 106 and an outer roll electrode 111 for welding the overlapping portion 102 to form the welded can body 100 are arranged. The can body preform 101 is transferred from the left side to the right side of the mandrel 104 by a chain conveyor (not shown) having feeding claws, and during the transfer, a plurality of roller groups 120, 121, 12
2, 123, 124, 125 and 126 ensure the square shape and a predetermined overlapping width of the overlapping portion 102. The inner roll electrode 106 has a rotating shaft 106a extending in the vertical direction, and the rotating shaft 106a is arranged to be perpendicular to the rotating shaft 111a of the outer roll electrode 111. 110 and 112 are each
The inner wire electrode and the outer wire electrode are supported by the inner roll electrode 106 and the outer roll electrode 111 during welding, and have a rectangular cross section with an arcuate side surface. The inner wire electrode 110 is moved in the direction of the arrow through guide rolls 127 and 128, and its bottom surface is connected to the disc-shaped main portion 10 of the inner roll electrode 106.
7 and its side surface contacts the side circumferential portion 108a of the disc-shaped upper projection 108, and then is guided in the direction of the arrow by guide rolls 129 and 130. The inner wire electrode 110 is substantially linear between the guide rolls 128 and 130, and the inner wire electrode 110 and the outer wire electrode 112 are opposed to each other at the portion where the inner roll electrode 106 and the outer roll electrode 111 face each other. are doing. The overlapping portion 102 of the can body preform 101 has inner and outer wire electrodes 110,1
12, is pressed and energized by the inner roll electrode 106 and the outer roll electrode 111 to perform electrical resistance pine seam welding, and the welded portion 1
Formed in 03. The outer roll electrode 111 is rotationally driven by a drive mechanism (not shown), and moves the can body preform 101 being welded from left to right in FIG. 11 to continuously perform pine seam welding.
Note that 131 is a conductive liquid for electricity supply, 132 is a cooling medium for cooling the disc-shaped main portion 107, and 1
33 is an O-ring. During welding, although the diameter of the inner roll electrode 106 is relatively small, the inner roll electrode 1
By using the disc-shaped main part 107, which is the flat part of 06, as the welding pressure surface, the instantaneous contact length during welding in the seam welding direction between the welding electrode and the overlapping part 102 of the can body preform 101 can be reduced. , it becomes possible to lengthen the stain-free steel to the extent that it can be welded without removing the surface treatment film. In the above device, the diameter of the outer roll electrode 111 is 140 mm, and the diameter of the inner roll electrode 106 is 32 mm.
mm, and a commercially available tin-plated annealed copper wire (diameter 1.5 mm, tin-plating amount 4 g/m ² ) was used as a wire electrode with a width of 2.1 mm.
A 0.85 mm thick rectangular cross-section with arcuate sides is rolled first into the outer roll electrode 111 and then into the inner roll electrode 106.
I used a single wire stretched out so that it was pointing towards. The width of the overlapping part 102 of the can body preform is
0.35mm, electrode pressure 70Kg, welding speed 7m/
min, and a 50Hz AC power source was used as the welding power source. As a result, the welding area 103 has sufficient welding strength and sealing performance when the amount of welding current (effective value of sine wave current) is in the range of 3.5 kA to 3.7 kA, and there is no molten iron splash. I was able to obtain a steel can body. Welded portion 1 on the inner surface of the obtained welded can body 100
In 02, the ratio of the area covered with the chromium oxide layer on the contact surface B with the inner line electrode 110 was investigated using the same method as in Example 1, and found to be approximately 60%.
It was hot. Next, epoxy/phenol paint is applied to the inner welded part of the welded can body 100 so that the thickness after drying is 30 to 40 μm and the width is about 8 mm, and then baked. An empty can was created by flanging the body and double-sealing the lid with a stain-free steel lid coated with epoxy/phenol paint on the inside using the usual method. The above empty can was filled with soy sauce, double-sealed with the same stain-free steel lid as above, stored at 50℃ for 6 months, then opened, and the corrosion state of the welded part on the inside of the can was examined. It wasn't happening at all. (The number of tests in the above actual can tests was 50 cans each.) As a comparative example, a blank was prepared in which the above-mentioned stain-free steel welds and the surface treatment film in the vicinity were removed in advance to expose iron locally. A welded can body was created using the same welding method. The can body was also tested under the same conditions as above, and as a result, significant rust had occurred at the weld on the inner surface of the can body, which was made of steel coated with epoxy/phenol paint. At this time, the width of the exposed iron surface of the welded can body was approximately 2 mm.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway side view of a device that is a specific example of manufacturing a welded can body of the present invention, FIG. 2 is a cross-sectional view taken along the line - in FIG. 1, and FIG. A perspective view of a welded can body, which is an example of
6, 7 and 8 are perspective views of a cross section taken along the line - in FIG.
The figure shows a cross-sectional microscopic structure of the welded part of the present invention, Figures 9 and 10 are transmission electron micrographs of the chromium oxide layer in the welded part of the present invention, and Figure 11 shows the welded can body of the present invention manufactured. FIG. 12 is a longitudinal cross-sectional view taken along the line XII-XII of FIG. 11. 24...Masushi welding part, 25...Tein-free steel can body, B...Contact surface with welding electrode in welding part, 100...Welding can body, 103...
…welded part.

Claims (1)

[Claims] 1. In a welded can body made of stain-free steel that has a surface film consisting of a metallic chromium layer and a chromium oxide layer, the plate thickness of the stain-free steel
It has a pine seam welded part with a thickness of 1.0 to 1.8 times, and the pine seam welded part, at least on the inner surface of the can body, is covered with the surface film in contact with the welding electrode, and is covered with the chromium oxide. A welded can body made of stain-free steel, characterized in that the coverage rate of the material layer is approximately 30% or more in terms of area ratio.