JPS6029630B2 - Cylindrical body with inner protective coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cylindrical body provided with a protective coating on its inner surface, particularly a cylindrical body in which plate materials are formed into a desired shape and joined together by welding or soldering at both green parts. , apply the necessary paint in advance to form a protective film on the inner surface of the cylindrical body, except for the required parts of both green parts that will be the joint, and after joining, apply synthetic resin powder to the unpainted part of the joint. This invention relates to round, square, and polygonal cylindrical bodies such as cans, pipes, and tubes that are electrostatically coated and then heated to form a resin coating.

Conventionally, when making round, square or polygonal cylindrical bodies such as can bodies, pipes, tubes, etc. from plate materials, both edges of the plate material are cut out by forming the plate material as required. They are usually joined by welding, soldering, resin adhesive, etc.

In such a cylindrical body, especially when applying a protective coating to the inner surface of the cylindrical body for rust prevention, etc., the inner surface of the cylindrical body must be coated with rust prevention, corrosion prevention, elution prevention, etc. before joining. A liquid surface treatment agent such as paint is applied to the intended purpose, but in the case of items that are joined by welding or soldering, rust prevention is applied to the joint and the surrounding area in consideration of the effects of heat during joining. A surface treatment agent such as a paint is not applied, and a liquid surface post-treatment is applied to the portion of the joint where the surface treatment layer is not provided. However, in the case of a cylindrical body with a joint made in this way, it is difficult to form a thick treated layer with good edge covering performance by liquid post-treatment due to the roughness of the surface and edges of the joint, and pinholes may occur. However, there are disadvantages such as not being able to obtain sufficient post-treatment effects. Therefore, in order to eliminate such drawbacks, the present invention involves forming a plate material into a desired shape without applying a liquid pretreatment agent such as anti-rust paint to the required portions of both green areas in advance, and then welding or soldering the plate material. After joining, synthetic resin powder is electrostatically coated on the parts that have not been coated with liquid pre-treatment, and a resin film is formed by heating the electrostatically powder coated parts. Our goal is to provide the following.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of an embodiment thereof, which is illustrated in the accompanying drawings.

The drawings show an embodiment in which the present invention is applied to a cylindrical body such as a pipe, and FIG. 1 is a schematic perspective view of the cylindrical body, and FIG. 2 is an enlarged partial cross-sectional view of the joint portion thereof.

The cylindrical body 1 is made by first forming a plate material 2 into a desired shape such as round, square, oval, etc. (in the illustrated embodiment, a round shape), and then forming both green portions 4.
, 4' are joined by, for example, welding. The plate material 2 is coated with a suitable pretreatment layer on the inner surface of the cylindrical body 1, except for the two green parts 4, 4' to be fitted and the necessary parts in their vicinity, thereby forming a protective coating 2'. is formed. Since both traverse portions 4 and 4' of the plate material 2 forming the joint portion 3 are affected by heat during joining by welding, soldering, etc., it is preferable that no pretreatment be performed on these portions. After joining, electrostatic powder is applied as shown in FIG. A synthetic resin powder P is applied by body coating, and by heating this by an appropriate means, it sufficiently covers the roughness, burrs, etc. of the joint part caused by the joining process.
A thick synthetic resin film with good edge covering performance is formed so as to overlap the joint and the edges of the pretreatment layer in the vicinity thereof. As shown in FIG. 2, the joint 3 of the cylindrical body 1
An electrostatic coating device 10 that electrostatically coats synthetic resin powder on
For example, Japanese Patent Publication No. 50-34582, Japanese Patent Publication No. 48-420
It is equipped with an electric field curtain type small electrostatic powder gun 11 as described in Japanese Patent No. 28. The small electrostatic powder 11 has parallel spiral electrodes 14, 14 installed on the inner surface of the insulating hollow body 12.
By applying an alternating current voltage from the alternating current power source 17 during this period, an unequal alternating electric field can be created that exerts a repulsive force on the charged powder particles existing near the inner surface of the gun and prevents them from adhering. A DC electric field is generated between the joint 3 of the cylindrical body 1 and the gun by the action of the DC voltage applied by the DC power source 18. This kind of electric field curtain type gun does not have synthetic resin powder attached to the inside, so the powder can be discharged from the gun using a very small amount of transport gas.In particular, it is possible to discharge the powder from the gun using a very small amount of transport gas. In some cases, it is possible to discharge only the powder internally, so the gun discharge port can be brought very close to the cylindrical object to be coated, making it possible to coat powder in an extremely narrow area with high efficiency. This makes it possible for the first time to industrially implement the post-treatment powder coating of joints as described above. For example, it is possible to form a thin strip-shaped post-treated powder layer of modified polyethylene, nylon, etc., which has a film thickness of 100 mm after dawning and has adhesive properties of medium 10%. For powder coating in small areas like this, conventional electrostatic powder guns use a large amount of conveying air to eject powdered resin, but the conveying air blows away the deposited powder layer. In addition, the method becomes too wide, making it impossible to apply it to the above-mentioned purpose. In an electric field curtain type powder electrostatic gun, for example, synthetic resin powder P to be coated is fed into a pre-charging section 15 from an inlet pipe 16 in a state suspended in a small amount of gas. The powder is charged in advance to the same polarity as the DC applied voltage in the small electrostatic powder gun 11. Therefore, the powder P pre-charged in the pre-charging section 15 then passes through the electric field curtain type small electrostatic powder gun 11 and is discharged toward the joint 3 of the cylindrical body 1 to be coated. painted on the part. Once the synthetic resin powder P is electrostatically applied to the joint 3 of the cylindrical body 1 in this way, it is then heated by an appropriate heating means such as a heating furnace to form a synthetic resin coating. , the inner surface of the cylindrical body 1 is completely covered and protected. It goes without saying that the formation of a protective film by such liquid pretreatment and electrostatic powder coating can be applied not only to the inner surface of the cylindrical object to be coated, but also to the outer surface, if necessary. As described above, according to the present invention, when forming a plate material into a desired shape and joining both edges to make a cylindrical body, and forming a protective coating on the inner surface of the cylindrical body, the joint part and its vicinity can be A protective film is formed by applying an inexpensive and high-performance liquid pre-treatment to the parts except for the necessary parts, and after bonding, synthetic resin powder is electrostatically applied to the parts. By heating the powder coating, a high-performance, thick coating made of synthetic resin with the necessary minimum width and good edge coverage that can sufficiently protect the joints is formed by powder coating, which completely covers the inner surface of the cylindrical body. can be protected and cost significantly less.

The cylindrical body having an inner surface protective coating manufactured in this way uses metal as a base material, and has end plates closely arranged at both ends that have similar anti-corrosion and anti-melt properties at least on the inner surface. A highly corrosion-resistant metal can can be constructed, which can be used in a wide range of applications as containers for foods, medicines, etc. due to its low cost.

Furthermore, it goes without saying that the cylindrical body according to the present invention can be used as a pipe for purposes such as highly corrosion-resistant transport ducts for gases, liquids, powders, etc. Further, similar treatment can be performed on the outside, and this is extremely effective for ducts used outdoors and for other purposes.

[Brief explanation of the drawing]

Fig. 1 is a schematic perspective view showing an embodiment in which the present invention is applied to a cylindrical body such as a tube, and Fig. 2 is an electrostatic powder for forming a protective film at the joint of the cylindrical body shown in Fig. 1. FIG. 3 is an enlarged partial view showing the state of body painting. In the figure, 1... cylindrical body, 2... plate material, 3
...Joint part, 4,4'...Green part, 10...
... Electrostatic powder coating device, 11 ... Small electrostatic powder gas, 15 ... Preliminary charging section. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. After joining plate materials whose surfaces other than the joint and the vicinity thereof are coated with anti-rust coating to form a desired shape, synthetic resin powder is applied to the areas where the anti-rust coating is not coated. What is claimed is: 1. A cylindrical body characterized in that a synthetic resin film is formed by partially electrostatically coating the powder and heating the electrostatically powder-coated portion. 2. After joining the plates that have been coated with anti-rust coating on surfaces other than the joints and their surrounding areas to form the desired shape, synthetic resin powder is partially applied electrostatically to the areas that are not coated with the anti-rust coating. A metal can comprising a bottom and a lid attached to a cylindrical body which is coated with electrostatic powder and heated to form a synthetic resin coating.