JPS5853950B2 - Manufacturing method for welded can bodies - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a can body in which side seams made of thin steel plates are electrically resistance welded.

In particular, the present invention relates to a method for producing the can body, which is characterized by a treatment step after painting the inner and outer surfaces of the side joints.

A thin metal plate piece such as a tin plate is rolled up to form a hollow cylindrical body, and the hollow cylindrical body is placed horizontally, and the side seam is formed by moving it in the axial direction of the cylinder with the side seam facing upward. A side seam is formed by joining the two ends of thin metal plates parallel to the axial direction using electrical resistance stitch welding, and after applying protective paint to the inner and outer surfaces of the side seam, the painted cylindrical body is assembled. A method of manufacturing a can body by feeding the can body into a heating furnace using a conveying means that includes at least a part of the process of rolling and conveying, and drying and baking both of the protective coatings has actually been adopted in the can manufacturing industry in recent years.

The can body used for canned food must not react with the contents and cause the contents to change in quality or become rotten.

Incidentally, the portions of the welded can body that become the side seams are heated and melted or softened by interfacial heat generation when electricity is passed through them, and at the same time are pressurized and forge-welded.

Both the inner and outer surfaces of the side joint formed by welding due to this heating are in a state where they are easily oxidized and will react with the contents if left as is, so to prevent this, immediately after welding, the inner and outer surfaces of the side joint Painted and coated with a suitable protective coating.

Therefore, as mentioned above, the above welding is performed with the part that will become the side seam located on the upper side of the hollow body, and after welding, when the side seam is at a fairly high temperature, a protective coating is applied to the side seam and its vicinity. In order for this to occur, a thick layer of highly viscous paint must be applied to the inner surface of the protective paint.

If the viscosity of the paint is low, when it is applied, it will be heated by the high temperature of the side seam and become more fluidized, and as a result, it will flow down and the residual paint will form a thin film, which will cause the side seam to flow. This is because the coating film swells due to the rapid drying of the coating film from the cylindrical body side at that location, and does not adhere firmly to the side seam location.

Furthermore, even with well-known high viscosity paints such as slurry paints, when applied thinly as a high viscosity paint, the applied paint is heated at high temperatures at the side seam, becoming more fluid and flowing down or dripping. Or, as mentioned above, it causes blistering.

Therefore, as mentioned above, a high viscosity paint is applied to the inner surface more than 10 times thicker than the normal inner surface protective coating of a can body, but it is difficult to apply a thick coating only to the side joints (1 to 2 mm wide). Therefore, generally centering on the side seam, 5~
It is applied to a width of 10 mrrt.

However, even with the above-mentioned commonly used coating, there is a risk that the paint in the center of the coating (at the side seam) will heat up and become fluidized, causing it to drip, or be attached to the cylindrical wall along with both sides of the coating. There is a risk of it flowing down.

The above-mentioned dripping or flowing starts soon after the paint is applied.

The protective coating effect of the paint film at the locations where this dripping or running down occurs will be severely reduced, and there is a risk that lumps of the dropped paint may be mixed with the contents of the can.

To avoid this, the can body should be painted and quickly rotated 180 degrees around the can body axis and immediately sent to a heating oven for drying. During or after the rotation, the paint may be rubbed off against a supporting object and wiped off, leaving the outer surface unprotected.Also, on a high-speed production line that produces hundreds of cans per minute, this rotation itself requires complicated equipment. can be considered, and
If you install a heating furnace long enough to dry and bake the paint by moving the cylindrical body horizontally with the side seam on the top, the problem of paint dripping and flowing down can be solved, but the drawbacks of this heating furnace are: The furnace would be an extremely long straight line furnace measuring several tens of meters long, which would be impractical for factory equipment layout, and as a result, it would not be an appropriate countermeasure.

The present invention is a method for manufacturing a welded can body, which includes a process that solves the above problems of paint dripping and flowing down using simple equipment.

While advancing the cylindrical body made of a thin metal plate which is placed horizontally and has the part that will become the side seam on the upper side, the part that will become the side seam is welded by electric resistance welding to form the side joint, and then the inside of the side seam is welded. In a method for producing a can body, in which a protective paint is applied to the outer surface, and then the coated cylinder is transported to a heating furnace by a transport means that includes at least a part of the step of rolling and transporting the paint, and the paint is dried and baked. After applying the protective coating, the cylindrical body is preheated with heated air while the coated cylindrical body is placed horizontally with the side seam facing upward. A welded can body characterized in that the surface of the inner coating film is rendered non-fluid, and then the surface of the outer coating film is made non-adhesion resistant by being cooled by blowing cooling air, and then transported by the transporting means. It is the manufacturing method.

Examples of the method of the present invention will be explained.

Fig. 1 is a line side view showing an embodiment of the method of the present invention;
The figure is a sectional view taken along the line ■-■ in FIG.

In FIG. 1, 1 is a guide component that guides the cylindrical body when painting the inner and outer surfaces of the electrical resistance welded side joints on the upper side of the horizontally placed thin metal plate cylindrical body A, and 10 is the guide. A horizontal chain conveyor 11 and 12 starting from the front of the tip 2 of the part 1 (on the left in the figure) is a sprocket for rotating the conveyor, 13 is an endless chain of the conveyor, and 14 runs parallel to the chain 13. 16 is a preheating tunnel provided covering the conveyor 10, and 36 is a preheating tunnel provided at a distance 30 from the preheating tunnel and in front of the tunnel (on the right side in the figure) and covering the conveyor 10. A cooling device 41 is provided following the front end of the conveyor 10 and is a drop chute for rolling the cylinder down.

The preheating tunnel 16 has vertical walls 22,23 and ceiling walls 2.
4, the inside of which is defined by a heated air chamber 18 divided by an upper partition wall 25, and an upper support plate 2 that defines an upper passage of the chino 13 of the conveyor 10 and receives the chino.
It is divided into three parts: a can body passage chamber 19 divided by 6, and a chamber 27 below the upper support plate 26.

The lower chamber 27 is provided with a lower support plate 28 that defines a return passage (lower passage) for the chino 13.

17 is a pipe that sends heated air into the heated air chamber 18, and 20 is the can entry side of the preheating tunnel (left side in the figure)
It is a pipe located near the end of the can body for sucking heated air inside the can body passage chamber.

Similarly to the preheating tunnel, the cooling device also has divided chambers.

That is, it has a can body passage chamber 39 and a lower chamber 47, and a cooling air chamber 38 is formed as an upper chamber.

37 is a pipe that blows cooling air into the cooling air chamber 38.

The can body A, which has a side seam on the upper side and whose inner and outer surfaces of the seam are painted, is moved from the guide part 1 to the conveyor 10's chain 13,
14 and proceed with Cheno to enter tunnel 16.

The can body passage chamber 19 of the preheating tunnel 16 is supplied with heated air from a heated air injection port 21 provided in the center of the upper partition wall 25 and provided in the longitudinal direction of the preheating tunnel 16 except for both ends of the preheating tunnel 16. , heated air is blown onto the side seam of the advancing can body and its vicinity.

Next, can body A exits the preheating tunnel pro and cools down to cooling device 3.
Enter 6.

Air from the cooling air chamber 38 is blown onto the side joint of the can body traveling through the can body passage chamber 39 of the cooling device and its vicinity.

The cooled can bodies leave the cooling chamber and are transferred from the conveyor 10 to the chute 41, where they roll down the chute and fall.

In this specific example, the length of the preheating tunnel is approximately 2.5 meters, and the length of the cooling device is approximately 1 meter.
A can body with a diameter of 02 and a can height of 100 mm was advanced at a speed of 500 cans per minute.

The inner surface of the side seam of the can body is coated with a dry coating of 30~80cm4d.
A high viscosity thermosetting paint was applied to the outer surface of the side wall joint so that the dry film thickness was within the range of 2 to 7 .mu./am.

The preheated air was controlled so that the average temperature of the air was 175° C., and the air velocity at the injection port was set to be 15 meters per second on average.

Air at a room temperature of about 18° C. was used as the cooling air, and the injection speed was set to an average of 10 meters per second.

The inner surface paint of the above-mentioned can that has passed through the preheating tunnel and cooling device of this example is still soft and feels a little sticky to the touch, but after leaving the can in various orientations indoors for 10 minutes. There was no paint running or dripping.

Furthermore, the exterior paint did not become sticky even when the surface was touched with the hand.

The preheated and cooled cylindrical body was sent to a heating furnace to dry and bake the paint on the inner and outer surfaces.

A clean coating film with no bubbles was created.

In this embodiment, since the suction pipe 20 is provided on the inlet side of the can body, hardly any heated air flows out from the can passage chamber toward the guide parts. When spilled, the viscosity of the paint for painting the inner and outer surfaces of the side joints provided along the guide component will not exceed a predetermined viscosity.

Furthermore, since the space 30 is provided between the preheating tunnel and the cooling device, heated air does not enter the can body passage chamber of the cooling device, resulting in better cooling efficiency than when both devices are connected.

When using the method of the present invention, after coating the protective coating on both the inner and outer surfaces of the side seam, the coating film is preheated and cooled while the coated cylindrical body is placed horizontally with the side seam facing upward. Therefore, there is no need for a device to rotate the cylindrical body 180° to bring the side seam to the lower side, and the equipment process is simplified.

Furthermore, since the preheating is carried out using heated air, the surface of a thick coating film can be made non-fluid, and even if the inside is fluid, the non-fluidization of the surface can prevent the paint from dripping or flowing down.

If the heating method, such as high-frequency induction heating, heats the cylindrical body itself and dries the paint that is in contact with the cylindrical body first and then reaches the surface, the paint on the surface side becomes non-fluid in the case of a thick coating. It is difficult to prevent the paint film from dripping or flowing down.

On the other hand, the gas infrared heating device is not installed inside the moving cylinder, but is installed on the outside of the cylinder, so the protective paint film on the outside becomes non-fluid, but As for the inner surface of the body, it is difficult to make the surface of the coating non-fluid while leaving fluid parts inside the inner protective coating, as in the case of high-frequency induction heating.

In addition, cooling air was blown onto the exterior paint, which had become non-fluid due to the preheating described above, but still had adhesion resistance. Even if a step of rolling the cylindrical body is included when conveying the body to the heating furnace, the outer coating film will not be damaged or peeled off during the rolling conveyance.

Therefore, rolling conveyance can be used without impairing the protective function of the outer surface protective coating, so it can be conveyed to any location using any conveyance path, and therefore the heating furnace can be installed at the desired location, making effective use of factory space. Can be done.

Furthermore, since the preheating is limited to making the surface of the coating film non-fluid, the solvent inside the coating film can be released during drying and baking in a heating oven, and the sagging of the coating film that occurs when the surface is cured first can be avoided. will not occur.

[Brief explanation of drawings]

FIG. 1 is a schematic side view showing an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the line ■--■ in FIG. A: Can body, 16: Preheating tunnel, 36: Cooling device.

Claims (1)

[Claims] 1. While advancing a cylindrical body made of a thin metal plate that is placed horizontally and has a portion on the upper side that will become a side seam, the portion that will become a side seam is welded by electric resistance welding to form a side seam. After applying a protective paint to the inner and outer surfaces of the side joint, the painted cylinder is transported to a heating furnace by a transport means that includes at least a part of the step of rolling and transporting the painted cylinder, and the paint is dried and baked. In the method for producing a can body, after applying the protective coating, the coated cylindrical body is placed horizontally with the side seam facing upward, and the cylindrical body is heated subsequent to the application of the protective coating. Preliminarily heating with air to make the surface of the inner coating film non-fluid, and then cooling by blowing cooling air to make the surface of the outer coating film non-adhesive, and then conveying to the heating furnace by the conveying means. A manufacturing method for welded can bodies characterized by: