JPS6160729B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an easy-open lid that has excellent can opening performance. BACKGROUND ART In recent years, easy-open lids that can be opened without the use of tools such as can openers or bottle openers have been widely used for the can lids of various food containers such as beer cans, carbonated beverage cans, and dry pack cans. As materials for such easy-open lids, aluminum alloys are mainly used for their ease of opening, except in the case of contents where corrosion resistance is a problem, and tinplate is also used in consideration of the corrosion resistance. Although aluminum alloy lids are easier to open than tinplate lids, they are considerably more expensive, and there is a strong desire for the development of an inexpensive and easy-to-open steel sheet easy-open lid to replace aluminum alloy. ing. The ease with which an easy-open lid can be opened, that is, the openability of the can, is determined by the remaining thickness after scoring, that is, the remaining score thickness t, and its material properties, as shown in Figure 1.
Decrease in score remaining thickness t or score remaining after machining 1
It is known from experience that can opening performance can be improved by softening No. 2. However, if the score is processed so that the remaining score thickness t becomes thinner, the score bottom 11
A crack 13 occurs, which reduces the fall strength and pressure strength, causing an accident. Note that the average score residual thickness t of the current easy-open lid made of tinplate is 70 μm, which is controlled within a variation range of ±15 μm from the viewpoint of manufacturing technology, but the lower limit of this control standard is:
This is set in consideration of the occurrence of cracks 13 at the bottom of the score 11, and if the cracks 13 do not occur, the remaining score thickness should be reduced to a range that does not pose a practical problem from the viewpoint of can strength. t
can be made thinner. In addition, in order to make the score machining residue 12 soft and have low strength, there are three methods: to make the material soft, to reduce the degree of score machining, or to reduce the degree of hardening due to score machining.
laws and combinations of these are contemplated. However, reducing the degree of scoring by making the material softer or thinner is undesirable because it lowers the compressive strength. Therefore, improving can opening performance is achieved by using materials that do not easily cause cracks 13 even when the degree of scoring is increased, or
From the viewpoint of can strength, it is preferable to use a material with less work hardening of the score remaining portion 12 even after score processing. Based on the above-mentioned circumstances, the present invention aims to reduce the residual thickness t of the score without causing the crack 13 at the bottom of the score, and to minimize work hardening due to score processing. Its feature is that it has an appropriate residual stress distribution in the thickness direction. The contents of the present invention will be explained in detail below. The present invention has an appropriate residual stress distribution in the plate thickness direction, that is, in a range of 1/4 from the steel plate surface to the plate thickness T, the maximum value of compressive residual stress is 5 to 40 kg/
mm ² , preferably 10 to 40 Kg/mm ² , and the maximum value of the tensile residual stress in the center of the remainder is 5 to 40 Kg/mm 2 .
By applying a load of Kg/mm ² , preferably 10 to 40 Kg/mm ² , the score remaining portion 12 is difficult to work harden even after score processing, and the score can be processed to a thinner thickness without causing clutch 13. This aims to improve can opening performance. In general, it is preferable that the residual stress mentioned above be as small as possible from the viewpoints of shape stability, magnetic properties, corrosion resistance, etc., and measures are taken to remove residual stress depending on the steel plate application. This is where we can see a glimpse of it. In addition, for the numerical limitations of compressive and tensile residual stresses in the patent claims, and their distribution limitations, the lower limit is set based on the opening force when the remaining score thickness is 70 μm and the limit score remaining thickness, and the upper limit is set based on the yield strength of the material. I was able to do it. When the residual stress distribution as described above is applied in the thickness direction,
Work hardening is reduced and cracks 13 are less likely to occur, and the possible reasons for this will be explained with reference to the drawings. In FIG. 2, the principal stresses acting on the unit cell 30 are σ ₁ , σ ₂ , σ ₃ , and their magnitudes are sequentially expressed as σ ₁
>σ ₂ >σ ₃ , according to Tresca's theory,
When the difference between the maximum principal stress and the minimum principal stress reaches the yield stress, that is, when σ ₁ −σ ₃ =Y (Formula 1), the material yields. However, the yield stress of the material is Y. Now, for a plate with residual stress distribution in the thickness direction,
Let us consider the yield condition of the material when score processing is performed in the state shown in FIG. 3 by applying Tresca's yield condition of Equation 1. Note that the principal stress σ acting on the material
₁ , σ ₂ , and σ ₃ are determined as follows. That is, the force acting in the plate thickness direction by the score tool 20 is defined as principal stress σ ₁ , the force acting in the direction perpendicular to the drawing is defined as σ ₂ , and the force acting in the direction perpendicular to σ ₁ and σ ₂ is defined as principal stress σ _3. shall be. Here, σ ₃ is the residual stress portion 31, 3 in the plate thickness direction, which is the focus of the present invention.
It is 2. Here, in the compressive stress section 32, the stress order is σ ₂ >σ ₃ >σ ₁ , and the yield condition |σ ₂ |−
Since σ ₂ ≒ 0 at (−|σ ₁ |)=Y, |
When σ ₁ |=Y, the material yields. On the other hand, in the tensile stress portion 31, the stress order is σ ₃ >σ ₂ >σ
₁ , and since |σ ₃ |−(−|σ ₁ |)=Y is the yield condition, yield occurs at |σ ₁ |=Y−|σ ₃ |. Also, if the plastic flow of the material in the direction perpendicular to the drawing is restrained, that is, if stress in the direction perpendicular to the drawing does not participate in deformation, the score line of the actual lid is closed in a plane, so this assumption is close to It is possible, but in this case, the stress rank in the compressive stress section 32 is 0>
σ ₃ > σ ₁ and −|σ ₃ |−(−|σ ₃ |)=Y
becomes the yield condition, and the material yields at |σ ₁ |=|σ ₃ |+Y. On the other hand, in the tensile stress part, the stress order is σ ₃ >0>σ ₁ , |σ ₃ |−(−|σ ₁ |)=
Y becomes the yield condition, and the material yields at |σ ₁ |=Y−|σ ₃ |. By substituting concrete numerical values for this point, the understanding of its magnitude will be made clearer. The yield strength of the material was set to 35Kg/ ^mm2 , which is the same as the current T-4CA material, and the compressive residual stress σ
₃ is -10Kg/mm ² and the tensile residual stress is +10Kg/mm ² . Assuming that there is no plastic flow in the direction perpendicular to the drawing, 45Kg/mm2 is required to yield the material in areas where compressive residual stress _σ3 exists, but 25Kg/ ^mm2 is required in areas where tensile residual stress exists. / ^mm2 is fine.
Therefore, so that the part that is scored has mainly tensile residual stress, and the part that remains after scoring has mainly compressive residual stress.
If a residual stress distribution is provided in the plate thickness direction, the portion remaining after score processing will be difficult to process due to compressive stress, the load strain will be small, and work hardening will be small. Therefore, even if the degree of score processing is increased, cracks 13 are less likely to occur. From the point of view of score machining force, the machining force is also smaller than when score machining is performed mainly on the tensile residual stress portion. The above is thought to be one of the reasons why work hardening is small, cracks 13 are less likely to occur, and processing force is small. Another reason is that the excess metal 16 that is removed by the score tool 20 remains. One example is the difference in the ease with which it is absorbed due to the difference in stress. It is thought that if the excess meat 16 is easily absorbed, the score processing force will also be reduced. In Figure 4, when the distance between scores is L, the compressive residual stress part of -10Kg/ ^mm2 is 10
In the compressed state proportional to Kg/mm ² , that is, at L, there is already a surplus of length (L x 10/E), and in the tensile residual stress part of 10 Kg/mm ² ,
Stretched state proportional to 10Kg/mm ² , i.e. L
has an ability to absorb excess thickness of length (L×10/E), and from the standpoint of absorption of excess thickness, tensile residual stress is considered to reduce processing force. However, E is the longitudinal elastic modulus of the material. Further, scoring is usually performed after painting, but since the processing force σ ₁ is small, the score processing has less influence on the back surface, less damage to the coating film, and is advantageous in terms of corrosion resistance. Naturally, a small σ ₁ is also advantageous with respect to tool wear. The steel plate of the present invention can be obtained by repeated bending using a roller leveler or the like, rolling, shot blasting, electrodeposition, or the like. However, the technical scope of the present invention was limited to the bending method because the bending method does not cause hardening due to processing and has the best effect on improving can opening properties. The reason why bending is performed after recrystallization is that even if it is performed before recrystallization annealing, the effect will be lost by recrystallization annealing. Here, the reason for determining the tension, sheet passing speed, bending angle, bending radius, and number of bending times in the bending process performed after the recrystallization annealing step will be explained. The lower limit of tension is set to 1Kg/ ^mm2 because in order to bend the material to a bending angle of 15 to 60 degrees and a bending radius of 2 to 10mm, it is necessary to apply a tension of at least 1Kg/ ^mm2 in the threading direction. The reason why the upper limit was set at 25 Kg/mm ² is that if a tension exceeding this is applied, the plate will break more easily. The lower limit of the plate threading speed was determined from the viewpoint of productivity, and the upper limit was determined in consideration of scratches on the plate due to rolls, etc. In addition, the lower limit of the bending angle is set at 15 degrees because it is necessary to bend at a minimum bending angle of 15 degrees in order to impart the desired residual stress. This is because the strain is insufficient and the desired residual stress cannot be obtained. On the other hand, set the upper limit to 60
The reason why the bending angle is set at 100 degrees is because the effect will not increase even if the bending angle is increased further, and also because the larger the bending angle, the larger the equipment will be.
Next, the smaller the bending radius, the better, and the effect becomes clear at 10 mm or less, so the upper limit should be set at 10 mm.
mm, and the lower limit bending radius was set to 2 mm since the work would be difficult below that. Moreover, the reason why the number of bending times is set to 2 to 50 is that at least 2 times are necessary to obtain the desired residual stress, and the reason why the upper limit is set at 50 times is from the point of view of economy. Examples will be described below. Example 1 A hot-rolled plate with a thickness of 2.0 mm made of an ordinary lid-making component system, which was melted, ingot-formed, and hot-rolled by a known method, was
After cold rolling to 0.235mm, cleaning and continuous annealing (680℃
(20 seconds), after temper rolling (elongation rate 1.5%), radius 5.5
Bending was carried out 5 times in succession with a roll of 1.5 mm, and then tinning was carried out in a normal ferrostane bath. The steel sheets produced in this way are scored at various depths to obtain the critical score residual thickness,
We also compared the initial can-opening force and score processing force, which is referred to as the pop value by can manufacturing companies. The critical score residual thickness was defined as the minimum score residual thickness among those in which the crack did not penetrate from the bottom of the score to the opposite side. A penetrating flaw detector was used to evaluate the residual thickness of the critical score. Comparison of can opening force is based on the current score remaining thickness of 70μ
Comparison was made using a score residual thickness that is 15 μm thicker than the critical score residual thickness due to manufacturing technology variations. In addition, the score machining force is as shown in Figure 4. A ring with a trapezoidal cross-sectional shape, which is the same as the score cross section of the actual lid, and a planar shape of 20 mm in diameter, is applied to a steel plate with a force of 2000 kg for 10 min.
They were stamped in seconds and their depths were compared. Example 2 The temper rolling process was carried out in the same manner as in Example 1, and then bending was performed repeatedly five times using rolls with a radius of 10 mm, and then tin plating was performed in a ferrostane bath in the same manner as in Example 1. The same evaluation test as in Example 1 was conducted. Comparative Example 1 The repeated bending process after temper rolling in Examples 1 and 2 was not performed, and the same manufacturing process as the current product was used. The above results are summarized in Table 1. As is clear from the results in Table 1, steel plates that have been given the desired residual stress distribution through repeated bending have less work hardening and lower opening force than conventional steel plates. In addition, the residual thickness of the critical score is thin, and the can opening force can be further reduced. Furthermore, although score processing performance was demonstrated, the score processing power was also small, and the score processing ability was small.

[Table] It is also advantageous against damage to the surface coating and tool wear.

[Brief explanation of the drawing]

In the drawings, Fig. 1 is a vertical cross-sectional view with respect to the score line, Fig. 2 is a unit cell model diagram for schematically showing the stress state, and Fig. 3 is a schematic diagram of an example of residual stress distribution in a vertical cross-section of a steel plate. What is shown and the stress state during score processing, Figure 4 shows the stress state during score processing,
FIG. 3 is a cross-sectional view illustrating material removed by the scoring tool, that is, surplus material generated. 10... Steel plate cross section, 11... Score bottom, 12
...Remaining score, 13...Crack, 16...Excess meat, 20...Score processing tool, 30...Unit cell,
31...Tensile residual stress part, 32...Compressive residual stress part, _σ1 ...Principal stress, _σ2 ...Principal stress, _σ3 ...
Principal stress, T...plate thickness, t...score residual thickness, L...
Distance between scores.

Claims (1)

[Claims] 1 After the recrystallization annealing process, which is an intermediate process in the production of cold-rolled steel sheets for easy-open lids that undergo score processing, the steel sheets are heated at a speed of 5 to 600 m/min while applying a tension of 1 to 25 kg/ ^mm2 in the sheet threading direction. When bending is repeated 2 to 50 times at a bending speed of 15 to 60 degrees and a bending radius of 2 to 10 mm, and the thickness of the plate is T, the cross-sectional residual stress parallel to the rolling direction is distribution,
The maximum value of compressive residual stress in the range of 0 to 1/4T of the surface layer is 5 to 40 Kg/ ^mm2 , and the maximum value of tensile residual stress in the range of the remaining center is 5 to 40 Kg/ ^mm2. A method for producing a steel plate for an easy-open lid, characterized by: