JPH0249809B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a tool for forming rivets on can lids, and more specifically, the present invention relates to a tool for forming rivets on can lids, and more specifically, it crushes a cup-shaped convex portion of a can lid, into which a knob tab is inserted, to form a rivet. The present invention relates to a can lid rivet forming tool comprising a male die and an anvil for fixing a can lid to a can lid. (Prior Art) In the process of manufacturing an easy-to-open lid, fixing a tab to a can lid with rivets is usually performed as follows. First, as shown in FIG. 1, there is a cup-shaped protrusion 2 (usually called a button) that protrudes outward on the can lid 1.
After forming this by stretching, the knob tab 3 having the hole 3a is inserted into the base of the convex portion 2. Next, the male mold 4 is inserted into the inside of the convex part 2, and as shown in FIG. The knob tab 3 is fixed by forming the rivet 6 so that d is larger than the inner diameter of the hole 3a. An anti-corrosion organic coating 7 is formed on the inner surface of the can lid 1, and the outer surface is also usually coated with a coating film, although not shown. The organic film 7 is usually a coating film such as an epoxy/phenol paint or a vinyl organosol paint (with a thickness of about 3 to 10 μm), or a polyethylene terephthalate film (with a thickness of about 20 μm, for example), and an adhesive (not shown). ) etc. are used. During the above crushing, as shown in Figure 2,
The head end 2a of the convex portion 2 is compressed by the bottom surface 4a of the male mold 4 and the anvil 5, and undergoes relatively large compression deformation. Conventionally, the male die 4 and the anvil 5 were made of tool steel or cemented carbide, but in that case, it is presumed that this is due to the frictional force accompanying the compression deformation. As the number of processes increases, radial linear flaws develop on the bottom surface 4a of the male die 4, and these linear flaws cause scratches on the organic coating 7 on the inner surface of the rivet 6 that is in contact with the bottom surface 4a, resulting in metal exposure. There was a problem that this resulted in a decrease in internal corrosion resistance. This tendency is particularly noticeable in the case of tool steel. In the case of cemented carbide, as shown in Table 1 below, no linear flaws are observed when observed at a magnification of 30, but as the degree of metal exposure increases, that is, a decrease in corrosion resistance is observed. It is thought that extremely microscopic linear flaws that are observed under high magnification develop. When the organic film 7 is made of polyethylene terephthalate film, the film 7 is relatively thick and soft, so it is thought that the above-mentioned linear flaws are unlikely to occur, but the linear flaws are more likely to develop than when it is made of a paint film. Therefore, it was found that the portion of the coating 7 that came into contact with the bottom surface 4a was easily damaged. This is presumed to be due to the ultrafine silica coated on the film surface to improve slip resistance during handling. (Problems to be Solved by the Invention) An object of the present invention is to provide a rivet forming tool for can lids in which the anticorrosive organic coating on the inner surface of the rivet is not easily damaged during forming. (Means for Solving the Problems) The can lid rivet forming tool of the present invention crushes the cup-shaped convex portion of the can lid, into which the knob tab is inserted, to form a rivet. It is equipped with a male mold and an anvil for fixing to the can lid, and at least the male mold is made of zirconia ceramic, and the surface of the male mold that comes into contact with the can lid is mirror-finished. do. Partially stabilized zirconia (PSZ) is preferably used as the zirconia ceramic. It is preferable that the material has a water absorption rate of 0%, a bending strength of 120 Kg/mm ² or more, and a mechanical strength of hardness (Hv) of 1200 Kg/mm ² or more. (Function) Zirconia ceramics have high hardness,
Moreover, the mirror-finished surface has a very small coefficient of friction. This may be because of this, even when the surface of the organic coating 7 is coated with ultrafine silica powder, micro radial linear flaws are difficult to develop on the bottom surface 4a of the male die 4, and a decrease in internal corrosion resistance is difficult to occur. . (Example) A 3 μm thick epoxy/urea coating was formed on the outer surface, a 20 μm thick polyethylene terephthalate film was adhered to the inner surface (the adhesive was an epoxy phenol paint), and a 0.30 mm thick A cup-shaped (circular cross-section) convex portion 2 was formed on an aluminum (5052-H38) can lid blank by stretching process. The height of the convex part 2 is 1.5mm,
The inner diameter of the base 2b was 4.2 mm, the outer diameter was 4.8 mm, and the thickness of the head end 2a was 0.25 mm. After applying a paraffin-based lubricant to the surface of the protrusion 2, the knob 3 was inserted onto the protrusion 2 with the protrusion facing downward as shown in FIG. The protruding part 4b of the male mold 4 has a protruding part 4b and a shoulder part 4c with a height of 1.2 mm and an outer diameter of 4.1 mm, and the surfaces of the protruding part 4b and shoulder part 4c are polished to a mirror finish by diamond paste polishing. As shown in Figure 1, after inserting and fixing into the convex part 2, the upper surface 5a
The anvil 5 (connected to the crankshaft via a connecting rod (not shown)), which has a mirror finish, is raised, and as shown in FIG. A rivet 6 was formed by compressing the head end 2a of the rivet. The number of rivets formed per minute is 300. The male mold 4 and anvil 5 have a water absorption rate of 0.
%, bending strength 150Kg/mm ² , hardness (Hv) 1300Kg/mm ²
A material made of partially stabilized zirconium (PSZ) was used. In this case, the diameter d of the head portion 6a of the rivet 6 is 5.2 mm, and the thickness t (thickness of the metal portion) of the central portion 6a' of the head portion 6a that is in contact with the protrusion 4b is
It was 0.15mm. For comparison, the same PSZ as above (maximum surface roughness of protrusions 4b etc.) was used except that it was not mirror finished.
A rivet 6 was molded using a male mold 4 and anvil 5 made of 1.6 μm). Furthermore, for comparison, the materials are tool steel (SKD11) surface-treated by TiN ion plating, and cemented carbide (JIS
Male type 4, same as above except that it is standard D20)
Then, a rivet 6 was formed using the anvil 5. In these cases, the diameter d of the head portion 6a is PSZ
The height of the anvil 5 was adjusted to obtain the same value (5.2 mm) as when using a tool made of 5.2 mm. Table 1 shows the degree of radial linear flaws developed on the bottom surface 4a of the male mold and the degree of metal exposure on the inner surface of the can lid after 20,000 pieces were produced.

【table】

[Table] If the male mold 4 is made of PSZ and the anvil 5 is made of tool steel or cemented carbide, this is probably because the coefficient of friction on the anvil 5 side increases, but the diameter d of the head portion 6a of the rivet 6 It tends to get bigger.
So that the diameter d is the same value as above (5.2 mm),
When molding is carried out by adjusting the height of the anvil 5, the thickness of the central part 6a' is greater than that when the anvil 5 is made of PSZ.
It became thinner by 0.02mm. This increases the riveting force, although not as much as when both the male die 4 and anvil 5 are made of tool steel or cemented carbide.
This may lead to a decrease in tool life and an adverse effect on the degree of metal exposure. (Effects of the Invention) The can lid rivet forming tool of the present invention has the effect that the anticorrosion organic coating on the inner surface of the rivet is not easily damaged during forming.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the state immediately before the rivet is formed, and FIG. 2 is a longitudinal sectional view showing the state immediately after the rivet is formed. 1... Can lid, 2... Convex portion, 3... Knob tab, 4... Male mold, 5... Anvil, 6... Rivet.

Claims (1)

[Claims] 1. A molding tool comprising a male die and an anvil for crushing and forming a cup-shaped convex portion of a can lid into which a knob tab is inserted into a rivet and fixing the knob tab to the can lid, comprising at least A can lid rivet forming tool, wherein the male mold is made of zirconia ceramic, and the surface of the male mold that comes into contact with the can lid is mirror-finished.