JPS6335719B2 - - Google Patents

Description

[Detailed Description of the Invention] In recent years, welded cans, which are formed by continuously joining the copper parts of the can by resistance welding, have been increasingly used as containers for foods, juices, carbonated drinks, etc., instead of soldered cans. .

In the case of conventional solder cans, a high degree of skill is required to form and solder the copper can soldering parts, and expensive solder (especially high in tin content) is used, and many materials are used in the soldering parts. In addition, since the plate thickness of the soldered part is thick when tightening the can lid, there are drawbacks such as uneven tightening in the circumferential direction, which tends to cause "leakage". Furthermore, the use of solder is not necessarily desirable for food or beverage cans from a food hygiene standpoint.

On the other hand, in the case of welded cans, the weld lap margin (the length of two pieces overlapping each other) is less than 1 mm, which reduces material costs, and the plate thickness after welding is approximately 1.4 times that of the raw material, making it easy to tighten. It is characterized by requiring relatively little skill on the part of the operator, and has come to be used for many types of contents.

Traditionally, tinplate and TFS (tein-free steel) have been widely used as steel products for food containers. Tinplate was used for solder cans and DI cans formed by drawing and ironing, and TFS was used for adhesive cans. When manufacturing welded cans using these materials, tin plated with tin has a low melting point and low contact resistance and exhibits excellent welding performance.
In the case of TFS, it has a two-layer structure of metallic chromium and hydrated chromium oxide, and has poor weldability because the upper layer hydrated chromium oxide film is thick and metallic chromium is a high melting point metal and has poor heat conduction. There were some drawbacks that made it unusable for practical use. That is, a small welding current will result in insufficient welding strength, and a large welding current will cause the strength to scatter, which in extreme cases may result in damage to the welding electrode.

To improve such poor weldability, reduce the amount of hydrated chromium oxide and metallic chromium deposited.
It is possible to improve weldability by reducing contact resistance, improving the melting of both metals at the welded joint surface, and reducing the occurrence of "splash". In order to satisfy properties such as rust resistance, paintability, and paint adhesion, the amount of hydrated chromium oxide or metallic chromium deposited is 40 mg/m2 ^or more for metallic chromium, and 10 mg/m2 for hydrated chromium oxide. ² or more is required, and to improve weldability, metallic chromium is 20 mg/m ² or less, and hydrated chromium oxide is 10 mg/m ²
The following are good.

Therefore, there is no chromium coating amount range that satisfies both weldability and corrosion resistance (rust resistance, paintability, etc.), and it is difficult to practically use TFS in welded cans.
In order to use such TFS as a material for welded cans, the chromium present on the welded joint surface of TFS, which maintains sufficient corrosion resistance, must be removed by polishing.
The method used is to expose the steel surface of the base material and then weld it. Polishing methods either prevent dust generated (which poses a hygiene problem) or expose the iron surface, which does not provide sufficient corrosion resistance even if a subsequent repaint is applied, leading to the problem of iron leaching into the contents of the can.

The inventors of the present invention have arrived at the present invention as a result of various studies on a method for producing a welded can made of stain-free steel that satisfies both weldability and corrosion resistance, and the content of the present invention will be described in detail below.

The basic idea of the present invention is to reduce local heat generation by lowering electrical resistance at the welded joint interface and to crimp the joint interface by plating Ni, Sn, or their alloys on a steel plate containing metallic chromium and chromium hydrated oxide. This is expected to improve sexual performance. In the case of stain-free steel, chromium hydrated oxide exists on the outermost surface, and it is not necessarily easy to apply metal plating on top of it, but the chromium hydrated oxide itself is very thin (about 100 to 300 Å). Also, since it has electrical conductivity, it is quite possible to apply metal plating on it.

When applying metal plating, it is possible to plate the entire surface of the steel plate, but stain-free steel itself has excellent corrosion resistance and paintability, and those properties should be effectively utilized in areas other than welded areas. There is a need. In addition, Ni is applied to the entire surface of the stain-free steel.
Plating expensive metals such as Sn is itself inappropriate from an economic point of view. Therefore, the present invention attempts to improve weldability by applying metal plating to at least the portion corresponding to the weld joint (including the cut end where iron is exposed).

The reason why we limited the types of metal plating to Ni, Sn, or their alloys is that they have a lower melting point than iron and have superior crimp properties. Considering that metals with easier alloying ratios with chromium are more advantageous in improving welding performance, it can be said that Ni or its alloys are more desirable in terms of performance than Sn or its alloys. The thickness of the metal chromium and hydrated chromium oxide present in the underlying layer is approximately 100 to 500 Å, and the coating must be sufficiently thicker than that to eliminate its influence. Therefore, 0.02 to 2.0 g/ ^m2 , more preferably 0.2 to 1.0 g/m2
^m2 .

Next, a method of applying the present invention will be described. The stain-free steel according to the present invention may be one currently produced commercially, but in order to expect further improvement in weldability, a material with a small amount of chromium deposited is desirable. Therefore, the amount of chromium deposited on the chromic acid-treated steel sheet that is the subject of the present invention is 5 to 200 mg/m ² as metallic chromium, and the amount of chromium hydrated oxide is 5 to 50 mg/m ² as chromium. These steel plates are coated with paint on the inside of the can and printing on the outside of the can, leaving only the portions corresponding to welding, and then slit into predetermined dimensions. The lap allowance (overlap allowance of the plates to be welded) during welding is usually about 0.3 to 2.0 mm, and the unpainted part should just be slightly larger than that. The metal plating method involves immersing the entire large plate before slitting in plating liquid and performing it at once, or the blank after slitting (cut plate per can).
It is also possible to plate the surface corresponding to the welded part.

When plating the entire large plate, there are problems such as damage to the coating film by the plating solution and the need for a large plating tank.However, when plating the blank after slitting, it is possible to simultaneously plate the cut section. , which is effective in improving the corrosion resistance of spot-welded cans by eliminating exposure of iron at the cut end. There is no particular reason to limit the plating bath, and ordinary Ni plating, Sn
All plating baths or alloy plating baths such as Ni and Sn can be used. After baking the paint, the surface of the chromic acid-treated steel sheet has organic oils and fats (surface oil) decomposed and removed by heating during the baking process, and it has excellent electrical conductivity and can be plated by directly immersing it in a plating bath.
In order to expect even more effective performance, more uniform plating can be expected by rubbing the surface with a soft substance such as a sponge to destroy the hydrated chromium oxide film present on the outermost surface. By going one step further and plating both the metallic chromium and hydrated chromium oxide films after polishing them off, weldability can be significantly improved. As for the surfaces to be plated, an effect of improving weldability can be expected by applying plating only to one or both of the surfaces where steel plates come into contact with each other, but if plating is also applied to the surfaces that come into contact with electrodes, weldability will be extremely excellent.

Comparative Example 1 A chromic acid-treated steel plate (thickness 0.21 mm) with a metallic chromium deposit of 70 mg/m ² and a hydrated chromium oxide deposit of 15 mg/m ² (as chromium) was applied to the inner and outer surfaces of the can, leaving only the welded portion. I painted it. After that 30m/
Sudronic welding (a type of resistance welding) with a weld lap width of 0.6 mm was performed at a welding speed of min. In the low current range, welding strength was insufficient, and in the high current range, ``spatter'' occurred and satisfactory welding could not be performed.

Example 1 A Ni plating solution consisting of nickel sulfate, nickel chloride, and boric acid was used on the welding portion of a chromic acid-treated steel plate having a chromium film similar to that in Comparative Example 1 at a bath temperature of 50°C.
Electroplating was carried out at a temperature of 10 A/dm ² at a current density of 400 mg/m ² . In this case, a method was used that allowed Ni plating on both sides of the steel plate blank (front and back of the plate) and on the cut edges. 30m after Ni plating/
Continuous welding was carried out with a welding speed of 0.6 mm and a lap width of 0.6 mm. As a result, it was possible to perform welding with excellent welding strength in a low current range and without the occurrence of "splashing".

Example 2 After polishing off the metallic chromium and hydrated chromium oxide films on the welded surface of the steel plate end of the painted steel plate of Comparative Example 1, the following two types of plating were performed.

0.1μSn plating 0.06μNi plating These materials exhibited extremely excellent weldability over a wide welding current range.

Claims (1)

[Claims] 1. When manufacturing a welded can using a chromic acid treated steel plate having a metallic chromium and/or chromium oxide coating on the surface of the steel plate, at least one surface corresponding to a welded joint or that surface A method for manufacturing a welded can using stain-free steel, which comprises plating a sheared cross section of a steel plate with nickel, tin, or an alloy thereof, and then resistance welding it. 2. When manufacturing welded cans using chromic acid-treated steel plates that have metallic chromium and/or chromium oxide coatings on the surface of the steel plates, wet or dry polishing of the surface corresponding to the weld joint may be performed to destroy the chromium oxide coating or remove the metal. A stain-free method characterized in that chromium and chromium oxide are removed, and then at least one surface corresponding to the weld joint or that surface and the sheared cross section of the steel plate are plated with nickel, tin, or an alloy thereof, and then resistance welded. Method of manufacturing welded cans using steel.