JPS6221586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to coating the inner surface of a welded can body joint of metal cans.

BACKGROUND OF THE INVENTION In general can manufacturing, various methods are used to cover seam welded seams with a synthetic resin film or the like. The purpose of this coating is to prevent leakage and rust from the welded joints of metal container can bodies, and to prevent metal elution into the contents of the can, thereby protecting the contents.

When coating a welded can body seam with a thermosetting resin and baking it to form a coating, methods such as spraying, roller coating, and brush coating are used. Although this resin has excellent adhesion and barrier properties between the resin and metal, it has problems such as cracking and peeling during bead, flange, and seaming processes, and it cannot be expected to have a sufficient film thickness to achieve the purpose of coating.

On the other hand, a method in which resin powder is adhered to the joints of the metal container body and melted to cover it, for example,
As shown in Publication No. 4428, this resin powder is applied using an electrostatic coating method in which powder particles are ejected through a nozzle and adhered by heating the can body, or electrostatically charged on the powder particles. However, a popping phenomenon occurs when coating the can body, making it impossible to obtain a satisfactory coating width.

There is also a so-called slurry coating method in which resin powder is mixed with a thermosetting resin, but this method requires advanced techniques such as foaming during melting and baking. Furthermore, both of these coating methods require expensive equipment such as electrostatic coating equipment or induction heating equipment, and high running costs.

Problems to be Solved by the Invention The present invention aims to prevent rusting, leakage, and metal elution into the contents of the can body by welding the joint part of the can body to an exact desired width and thickness. coating,
The purpose of this project is to provide a new coating method and its equipment that can be obtained at lower equipment costs and lower running costs than conventional methods without requiring major changes to existing equipment. The invention will be explained in detail with reference to the drawings.

Means for Solving the Problems Figures 1 and 2 are schematic explanatory diagrams in which the present device is incorporated into a normal can manufacturing process line. A body maker that molds the can body 5, 2 denotes both side edges 6 of the can body 5,
This is a seam welding machine that welds the overlapping part of the body 6', in which a metal plate is formed into a cylindrical or square tube shape by the body maker 1, and then the overlapping body joint part 7 of the side edges 6 and 6' is welded in a straight line. It is designed to be seam welded into a shape and sent out.

Reference numeral 3 denotes a reformer for shaping the welded can body 5 into a regular shape. The can body 5 passes through the reformer 3 according to the shape of the body, is adjusted to a desired size and shape, and is coated by a coating conveyor 4 disposed in front of the reformer. Figure 1,
They are sent out sequentially in the directions of the respective arrows in FIG.

Reference numeral 10 denotes an airless spray device installed on the starting end side of the coating conveyor 4 that transfers the can body 5 so as to apply a thermosetting resin onto the inner surface of the weld seam of the can body 5, and an airless spray device installed outside the transfer line. The thermosetting resin is connected to a spray gun 10' to a desired width centering on the inner surface 8 of the weld seam to a thickness of 3 to 5 μm.

To bake this coating film, induction heating of the can body, infrared heating, direct flame, oven, etc. are used, but these devices are used as a preheater 12 as shown in Figures 1 and 2. It may be installed before or after the device 10, or before and after the device 10.

Reference numeral 13 denotes a dry resin powder quantitative applicator installed at a distance from the airless spray device 10 in the traveling direction of the can body, and is located within the cross section of the can body of the can body transfer line, and is installed outside the line for powder quantitative supply. A cyclone separator 16 introduces dry resin powder in the form of granules, flakes, powder, etc. by compressed air transport from the machine 14 through a metal pipe (mainly a copper pipe) 15, and the dry resin powder separated from the air is dropped into the lower part of the separator. It is comprised of an inverted ladder-shaped trough 17 which is held close to the inner surface of the weld seam with one end of its bottom slanted low so as to align the weld seam.

Furthermore, a ground wire is appropriately attached to the metal tube 15 to remove static electricity generated during transportation, and a static electricity eliminating bar 18 for preventing static electricity is attached to the inside of the trough 17 to further remove static electricity remaining in the powder. At the same time, an air vibrator 19 is attached to the cyclone separator 16 to prevent powder from adhering and growing inside the cyclone separator 16 and on the trough 17 and to ensure smooth outflow.

Reference numeral 20 indicates a collecting device installed to collect the dry resin powder falling from between the can bodies 5 and 5 which are successively transferred below the trough 17, and 21 indicates two left and right strips installed following the coating conveyor 4. This is a baking conveyor having a belt, and a heating device 22 such as a baking burner is installed linearly between the belts along the traveling direction of the can bodies.

23 is a cooling conveyor having two belts on the left and right, which is installed following the baking conveyor 21, and 24 and 25 are a cooling device using an air-cooled blower and a water-cooling spray installed between the conveyors.

Function As in the normal can manufacturing process, the body maker 1
The can body 5 is formed into a cylindrical or rectangular tube shape from a metal plate, and the can body 5 is welded through a seam welding machine 2 by welding the body joint in which both side edges 6 and 6' overlap at the center of the lower surface. 3
The coating conveyor 4 disposed in front of the coating conveyor 4 sequentially transports the coating material in the direction of the arrows in FIGS. 1 and 2 while maintaining the welding posture. On this coating conveyor 4, a spray gun 10' of an airless spray device 10 connected to a spray pump 11 outside the line is applied to the inner surface 8 of the weld seam at the center of the lower surface of these can bodies 5 by a predetermined width at the center of the weld seam. A thermosetting resin is applied to a thickness of 3 to 5 μm, and this coating film is cured by the heat of the heated can body 5 that passes over the preheater 12, and is baked onto the inner surface of the welded seam of the can body to form a coating film. is created. However, depending on the purpose of the can and the type of resin powder described below, the step of forming the coating film may be omitted.

Next, a dry resin powder 9' in the form of granules, flakes, or powder is directly applied to the upper surface of the coating film of the can body 5 or the inner surface 8 of the weld seam of the can body 5 using a trough 17 of a dry resin powder metering applicator 13. In other words, the powder is applied by a powder quantitative feeder 1 installed outside the line.
4, the dried resin powder is introduced into the cyclone separator 16 by compressed air transport through the metal tube 15 which is connected to earth to suppress the generation of static electricity.
The dry resin powder is dropped and aligned on the trough 17 by separating the air to lose its dynamic energy, and the residual static electricity of the powder generated during air transport is removed by the static eliminating bar 18 provided in the trough 17.
Combined with slight vibrations by the air vibrator 19, the flow of the powder is smoothed, and the dry resin powder is freely fallen from the trough 17 by gravity, and a fixed amount of dry resin powder is applied in a band shape to the inner surface of the seam of the can body being transferred by the width of the trough 17. Ru. In this case, the coating width is defined by the width of the trough, and the coating thickness is adjusted by the powder feed rate of the powder quantitative feeder 14.

Next, the can body 5 with the dry resin powder 9' placed on the inner surface 8 of the welding seam to a predetermined thickness and width is successively transferred by a baking conveyor 21, and high-frequency induction heating and infrared heating are installed between the conveyors. When the can body 5 is heated by a heating device 22 such as a direct flame baking burner, the powder applied to the inner surface of the seam is melted and fixed to the can body 5, and the smooth surface of the resin coating film 9 is formed. It is formed. After passing through the heating device 22, the can body 5 is cooled by an air cooling device 24 and a water cooling spray device 25 while being transferred by a continuous cooling conveyor 23, and the resin is rapidly cooled to below the crystallization temperature to complete the inner coating of the weld seam. Then, it is sent to the next process, the flange → seaming process.

Effects of the Invention As explained above, according to the present invention, when melting and covering the weld seam of a metal can body sent out by welding the body with dry resin powder, the metal can body is held in a welding position. Dry resin powder in the form of granules, flakes, or powder is placed on the inner surface of the weld seam at the center of the lower surface of the resin powder, and is passed through a grounded metal pipe from a powder quantitative feeder to suppress the generation of static electricity in the powder, and then compressed air is passed through it. During transportation, it is introduced into a cyclone separator to separate it from the air, lose its dynamic energy, fall onto a trough and align itself, and then fall freely from the trough due to gravity to coat a uniform layer of dry resin powder, which is then fused by post-heating. Compared to the conventional electrostatic coating method in which the resin powder adheres by electrostatic charge, the powder does not pop when applied to the can body, and the welded seam can be made to the desired specified width. Accurate and clean resin coating can be easily achieved, and the desired thickness and width of the resin powder coating can be easily obtained by adjusting the powder metering feeder and changing the width of the trough. To fuse the applied resin powder to the welding joint, the purpose can be achieved by direct flame heating, and there is no need to make major changes to existing equipment, allowing welding at low equipment costs and running costs. The joints of the can can be coated with a sufficient film thickness and the desired width, and depending on the content and purpose of the can, cans coated with thermosetting resin alone, cans coated with resin alone, Cans coated with thermosetting resin and resin,
Both have the characteristics that they can be manufactured on the same production line.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing the configuration of the device of the present invention;
Fig. 2 is an explanatory view as seen from the front, Fig. 3 is an enlarged detailed view showing the main parts of the device, Fig. 4 is a side view of Fig. 3, and Fig. 5 is a coating film applied according to the present invention. FIG. 6 is an enlarged sectional view of the joint portion of the welded can, and FIG. 6 is a perspective view of the welded can with the joint covered. 5... Metal can body, 7... Welded seam, 8... Seam inner surface, 9'... Dry resin powder, 9... Resin coating,
13... Dry resin powder quantitative applicator, 14... Powder quantitative feeder, 15... Metal tube, 16... Cyclone separator, 17... Inverted ladder-shaped trough, 22
...Heating device.

Claims (1)

[Claims] 1. A metal can body is transported in a welding position by a conveyor, and dry resin powder in the form of granules, flakes, or powder is placed on the inner surface of the weld seam at the center of the lower surface of the can body by a metal tube from a powder quantitative feeder. The resin powder is pneumatically transported through a cyclone installed in the transfer path of the can body, separated from the air, and dropped onto a trough with an inclined bottom to be aligned.The dry resin powder is then freely fallen from the trough due to gravity. A fixed amount of the powder is applied to a predetermined width after removing static electricity, and then the joint part of the can body is heated to melt the applied dry resin powder, and then rapidly cooled and fused to form a smooth surface and a predetermined thickness. A method for coating a welded seam of a welded can, the method comprising forming a resin coating film having a width of . 2. A dry resin powder metering applicator that applies dry resin powder in a free fall manner over a predetermined width while suppressing the generation of static electricity onto the inner surface of the weld seam at the center of the lower part of a metal can body that is sent out in a welding position by a conveyor; It is equipped with a can body heating device for fusing the resin powder placed on the inner surface of the weld seam by the device, and a rapid cooling device for the part, and the dry resin powder metering device is installed on the can body cross section of the can body transfer line. located within
A cyclone separator introduces dry resin powder by pneumatic transport through a metal tube equipped with a ground to remove static electricity from a powder quantitative feeder outside the line, and the dry resin powder separated from the air is dropped at the bottom of the separator. A covering for a welded seam of a welded can, comprising an inverted ladder-shaped trough of a predetermined width, one side of which is held at a low slope on the inner surface of the seam so as to align the trough, and a static electricity eliminator is provided inside. Device.