JP3553149B2 - Lightweight 2-piece DI can with excellent strength and uniform heating properties and electro-tin plating - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a steel container, particularly to a two-piece can (hereinafter referred to as a DI can) provided with electrotin plating in which a can bottom and a can body are integrally formed by drawing and ironing.
[0002]
[Prior art]
When metal containers are classified from the viewpoint of can bodies, they can be broadly classified into three-piece cans composed of a canopy, a canopy, and a trunk, and two-piece cans in which a can trunk and a canopy are integrated.
The process of forming a two-piece DI can is called DI process, which is formed by two drawing operations (Ironing) and two or three times of ironing operation. It is processed to about 3. For this reason, a high degree of workability is required for the material to be used, and an aluminum plate and tinplate tinned on a steel plate are currently used.
DI cans include beverage cans filled with beer, carbonated beverages, and the like, and aerosol cans filled with antiperspirants, shaving creams, and the like.
[0003]
Three-piece cans have been used mainly for vacuum-tightened (non-inner pressure) beverages other than carbonated beverages. There is a problem in that the weight of the can is heavy due to the thickness, and the competitiveness in terms of can cost is weak.
Therefore, contents that have been filled in three-piece cans in recent years tend to be gradually filled in two-piece cans.
[0004]
When the contents of a three-piece can are filled into a two-piece can, there are roughly two new problems.
The first problem is the problem of can strength. For non-inner pressure beverages or non-inner pressure foods (three-piece cans), the can strength was the strength of the can itself, but in the case of two-piece cans filled with beer, carbonated beverages, etc., the can strength is maintained by the can internal pressure. However, the strength of the can itself is very low. Therefore, it is necessary to take measures in terms of the strength of the can, and it is conceivable to increase the strength of the two-piece can, or to fill the contents with nitrogen gas or the like and apply a can internal pressure.
[0005]
The second problem is that, unlike beer and carbonated beverage cans, many heating and cooling steps are required. For example, when natural food is used as the content, heat sterilization treatment (usually called retort treatment) is required after filling the content, and the temperature is raised to nearly 130 ° C. at a high temperature.
When performing this retort treatment, it is important that the contents can be heated uniformly and in a short time (see, for example, Shohachiro Kamijima, published in 1986 by The Canning Technology Research Institute, pages 293-332).
In the case of a two-piece can, as described above, the thickness of the can body is extremely thin compared to the can bottom, and the thickness difference between the can bottom and the can body is large, which is suitable for uniform heating. There are no problems. In addition, there is a problem in rapid cooling.
[0006]
[Problems to be solved by the invention]
The present invention solves the problem of can strength and non-uniformity during heating / cooling that occur when filling non-inner pressure beverages or non-inner pressure foods into two-piece DI cans, and is an electric tin that ensures sufficient economic competitiveness. It is an object of the present invention to provide a plated two-piece DI can.
[0007]
[Means for Solving the Problems]
The present invention places the highest priority on economics, and proposes the most rational can in combination with a steel plate material and a can, and furthermore, a filling method.
(1) A high-purity steel sheet having a C and N content of (C + N) of 0.02% or less and a thickness of 0.22 mm or less is used as a material. A light-weight, two-piece DI can with excellent difference in strength and uniform heating, characterized in that the difference is 0.15 mm or less. and,
(2) The strength and uniform heating property as described in (1) above, wherein the steel plate at the bottom of the can has a hardness (HR30T conversion) of 74 or more and the ratio of the major axis to the minor axis of the crystal grains is 4.0 or more. It is a lightweight 2-piece DI can with excellent electrical tin plating .
[0008]
Hereinafter, the contents of the present invention will be described in detail.
In the case of a conventional two-piece can, a relatively thick material of 0.24 mm or more has been used to maintain the strength of the can. In the case of the present invention, the thickness of the raw material is 0.22 mm or less, preferably 0.14 to 0.20 mm for economical consideration. 0.14 mm is the lower limit in terms of the pressure resistance of the can bottom when filling with nitrogen, and the upper limit of 0.22 mm is a constraint in terms of economy.
[0009]
When performing vacuum winding, the pressure inside the can is reduced, so that the can strength itself is required. However, even in the case of natural foods or non-carbonated beverages, the can strength is exhibited by filling with nitrogen. Therefore, on the premise of nitrogen filling, it becomes possible to fill natural foods or non-carbonated beverages into thin two-piece cans.
The internal pressure level of the can expressed by nitrogen needs to be determined in view of the balance between the can itself and the internal pressure as well as having a resistance to an external force. If the internal pressure is 2 kg / cm ² , practical can strength can be obtained even with a plate thickness of about 0.14 mm to 0.16 mm.
[0010]
Next, the reason for setting the (C + N) content to 0.02% or less is to improve the workability of the steel sheet. Generally, the workability of a steel sheet tends to improve as the (C + N) content decreases, but significant improvement in workability can be expected by limiting the workability to 0.02% or less, preferably 0.01% or less. Furthermore, the condition under which this effect can be expected most is when the (C + N) content is 0.006% or less, whereby DI molding can be performed even with cold rolling.
Due to recent advances in steelmaking technology, it is relatively easy to obtain a steel sheet having a (C + N) content of 0.006% or less, and if the conventional annealing and pressure control steps can be omitted, the most economical material Can be obtained.
[0011]
When a steel having a low content of (C + N) is rolled at a rolling reduction of 70% or more after hot rolling, the hardness (HR30T conversion) is 74 or more, and the ratio of the major axis to the minor axis of the crystal grains is 4.0 or more. A high-strength steel plate can be obtained. This steel sheet has a tensile strength of 70 kg / mm ² or more, and can withstand a higher can internal pressure with a thinner sheet thickness. Therefore, it is possible to provide a more economical can.
[0012]
In addition, there is a problem of the shape of the can from the plate thickness side. The difference (t ₀ −t _min ) between the bottom plate thickness (t ₀ ) and the side wall thinnest portion plate thickness (t _min ) of the can is 0.15 mm. Hereafter, it is more preferable that the distance be in the range of 0.13 mm or less. When cooling in a refrigerator at home, it is possible to take a sufficient time to a certain extent and there are relatively few problems, but the retort treatment after filling the contents requires mass production on an industrial scale, and is uniform in a short time. Processing is required. Therefore, it is required that the thickness of the steel plate constituting the can be thin and uniform.
[0013]
If the thickness of the steel sheet constituting the can body is gradually reduced, it is naturally expected that the heating or cooling rate of the contents will increase, but the strength against the internal pressure of the can by nitrogen filling is insufficient. The coming point is as described above. Normally, the side wall has a circular cross section and exhibits excellent pressure resistance against the internal pressure of the can. However, the bottom of the can has a weak point that cannot easily withstand the internal pressure of the can and swells outward. Therefore, the bottom of the can requires a certain thickness, and a thicker plate than the side wall is required.
[0014]
If the thickness difference between the bottom of the can and the side wall is too large, a difference occurs in the heating or cooling rate of the contents. Results of the examination of its limitations, the bottom thickness (t ₀₎ the difference between the side wall thinnest portion thickness _{(t min) (t 0 -t} min) is 0.15mm or less, the may further its effect stably It has been found that if the thickness is desirably within the range of 0.13 mm or less, uniform heating can be practically performed.
This value is determined in consideration of the balance between can strength and uniform heating / cooling.
[0015]
【Example】
Hereinafter, the embodiment will be described in detail.
[Example 1]
A steel having a C content of 0.0010% and an N content of 0.0028% is melted and hot-rolled to a thickness of 2.5 mm, and the scale is removed by pickling to obtain a thickness of 0.26 mm. Cold rolled until After recrystallizing annealing at 720 ° C. and sufficiently softening, a second cold rolling was performed at a rolling reduction of 31% to obtain a steel sheet having a tensile strength of 52 kg / mm ² in C direction (width direction of sheet) (0 mm). .18 mm).
[0016]
After electric tin plating coating weight 2.8 g / m ² on both sides of the steel plate, starting from the blank dimensions 150 mm, and a cup of 85mmφ at the first stage of the drawing, by drawing in the second stage 65mmφ , And the thickness of the side wall was reduced to 0.065 mm by ironing three times in total. After ironing the side walls, the bottom of the can was processed into a shape as shown in FIG. 1 to withstand the internal pressure and to form a can body capable of stacking cans.
[0017]
After degreasing and chemical conversion treatment, the cans were subjected to an outer surface coating and an inner surface coating and subjected to a performance test for practical quality.
As a practical test, when the internal pressure resistance of the can body and the buckling strength in the vertical direction were measured, the internal pressure resistance showed a strength of 7.5 kg / cm ² or more, and the buckling strength was 100 kg or more. Buckling strength was confirmed.
[0018]
On the other hand, a can filled with tap water was placed in a heating furnace set at a temperature of 130 ° C., and the time-temperature curve was measured at the center of the can body and near the bottom of the can to find the maximum value of the temperature difference, It was a measure of heatability. In the can of this example, the maximum temperature difference was 6 ° C. or less, indicating good uniform heating.
[0019]
[Example 2]
A steel having a C content of 0.0006%, an N content of 0.0026%, and a B content of 0.0006% was melted, hot-rolled to a thickness of 2.3 mm, and scale was removed by pickling. And cold-rolled to a sheet thickness of 0.18 mm. This steel sheet has a hardness (HR30T conversion) of 77, and the ratio of the major axis to the minor axis of the crystal grains is difficult to measure accurately with a microscope, but is theoretically estimated to be about 160.
Moreover, the tensile strength was 78-80 kg / mm ² , which was a considerably high strength steel plate.
[0020]
After degreasing and pickling the steel sheet, the front and back sides were subjected to electrotin plating with an adhesion amount of 2.8 g / m ² , starting from a blank size of 150 mm, forming a 85 mmφ cup by the first stage drawing, and forming the second stage. After forming into a 65 mmφ cup by drawing, the thickness of the side wall was reduced to 0.065 mm by three times of ironing. After ironing the side walls, the bottom of the can was processed into a shape as shown in FIG. 1 to withstand the internal pressure and to form a can body capable of stacking cans.
[0021]
After degreasing and chemical conversion treatment, the cans were subjected to an outer surface coating and an inner surface coating and subjected to a performance test for practical quality.
As a practical test, when the internal pressure resistance of the can body and the buckling strength in the vertical direction were measured, the internal pressure resistance showed a strength of 8.0 kg / cm ² or more, and the buckling strength of the empty can was 100 kg or more. It was confirmed that it had sufficient practical strength.
When a uniform heating property test similar to that in Example 1 was performed, the maximum temperature difference was 6 ° C. or less in the can body of the present example, indicating good uniform heating property.
[0022]
[Comparative Example 1]
A steel having a C content of 0.056% and an N content of 0.0032% is melted and hot-rolled to a thickness of 2.5 mm, and the scale is removed by pickling to obtain a thickness of 0.26 mm. Cold rolled until After performing recrystallization annealing at 680 ° C. and sufficiently softening, temper rolling was performed at a rolling reduction of 1.3% to produce a steel sheet having a tensile strength in the C direction of 40 kg / mm ² .
[0023]
After performing electro-tin plating of 2.8 g / m ^{2 on} the front and back of the steel sheet, starting from a blank size of 139 mm, a cup of 85 mmφ was formed by the first stage drawing, and a 65 mmφ cup was formed by the second stage drawing. , And the thickness of the side wall was reduced to 0.080 mm by a total of three times of ironing. After ironing of the side wall, the can bottom was processed into a shape as shown in FIG. 1 to withstand the internal pressure and a can body capable of stacking cans was obtained.
[0024]
After degreasing and chemical conversion treatment, the can was subjected to an outer surface coating and an inner surface coating, and a performance test for practical quality was performed.
As a practical test, the internal pressure resistance of the can body and the buckling strength in the vertical direction were measured. The internal pressure resistance was 7.5 kg / cm ² or more, and the empty can buckling strength was 100 kg or more. It was confirmed that the resin had sufficient buckling strength.
In the uniformity test in the heating furnace, a temperature difference of 10 ° C. or more was generated between the center of the can body and the vicinity of the bottom of the can, and the uniform heating property was poor.
[0025]
[Comparative Example 2]
A steel having a C content of 0.063% and an N content of 0.0035% is melted, hot-rolled to a thickness of 2.3 mm, and scale is removed by pickling to obtain a thickness of 0.18 mm. Cold rolled until The tensile strength of this steel sheet was 93 to 96 kg / mm ² , which was a considerably high strength.
After degreasing and pickling the steel sheet, the front and back sides were subjected to electrotin plating with an adhesion amount of 2.8 g / m ² , starting from a blank size of 150 mm, forming a cup of 85 mmφ by the first stage drawing, and forming the second stage. After forming into a 65 mmφ cup by drawing, the thickness of the side wall was reduced to 0.065 mm by a total of three times of ironing.
After ironing of the side wall, the bottom of the can and the top of the can were flanged in the same manner as in Example 1. "Wrinkles" frequently occurred at the bottom of the can, and "cracks" frequently occurred at the flange, and a normal can was prepared. I could not do it.
[0026]
【The invention's effect】
The can body of the present invention uses an ultra-thin material to reduce the weight of the can body and pursue the limit of economic efficiency. Furthermore, by minimizing the difference in plate thickness in the can body, the problem of non-uniform heating in retort treatment and the like is eliminated, and a valuable effect that non-inner pressure foods including solid contents can be filled into lightweight two-piece cans. Demonstrate.
[Brief description of the drawings]
FIG. 1 is a view showing a bottom shape of a molded can.

Claims (2)

Using a high-purity steel sheet having a C and N content of (C + N) of 0.02% or less and a thickness of 0.22 mm or less, the difference between the bottom plate thickness of the can body and the side wall thinnest part plate thickness is zero. A lightweight two-piece DI can that has excellent strength and uniform heating characteristics and is electrotin-plated, characterized in that it is 15 mm or less. Steel at the can bottom, the hardness (HR30T basis) 74 or more, the crystal grains of the major axis to the excellent electrical tin strength and uniform heating of claim 1, wherein the ratio of the minor axis is 4.0 or more Lightweight 2-piece DI can with plating .

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