JP4770084B2 - Sealed can - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sealed container in which a beat is not generated by the influence of contents or a container body when the internal pressure of the sealed container is inspected by a percussion method.
[0002]
[Prior art]
Conventionally, the percussion method has been widely adopted as a method for nondestructively inspecting the internal pressure of a sealed container, particularly canned food or the like filled with foods and beverages that are susceptible to corruption. The percussion method is a test method that converts the percussion sound generated when electromagnetic shock is applied to the lid of the can (can bottom of a two-piece can) into an electrical signal using a microphone, thereby judging whether the internal pressure of the can is good or bad. It is.
[0003]
For example, in the case of canned low-acid beverages such as milk-containing beverages, negative pressure canned products are cooled to room temperature, but when rotted and fermented, gas is generated in the cans and the pressure rises, resulting in low positive pressure canned products. In addition, when the negative pressure can is sealed imperfectly, outside air enters the can and the pressure rises.
Therefore, impact is applied to a portion of the can, and the internal pressure of the can is detected by analyzing the echo vibration of the can to determine whether the contents are corrupt or the seal of the can is good, thereby eliminating defective cans. . Regarding the relationship between pressure and vibration, the larger the difference between the pressure inside the can and the outside air pressure, the more the can wall is stretched, and the natural vibration of the can becomes higher, resulting in a high sound. That is, if the material of the can, the size, the thickness, and the shape of the can, such as a two-piece can or a three-piece can, are the same, the echo vibration depends mainly on the internal pressure of the can.
[0004]
In the percussion detection method, a reverberation vibration sound generated when an impact is applied by an exciter coil is detected by a microphone. It is the natural vibration of the can that shows the peak value in the frequency distribution of the detected vibration sound. The quality of the can is judged by checking whether this value is in the frequency band corresponding to the appropriate pressure inside the can. Canned products are removed by a rejector etc. in the post-inspection process.
Negative pressure cans have a degree of vacuum in the range of 27 to 80 kPa, have little pressure variation, and have a large change in natural frequency due to fluctuations in internal pressure. There is an advantage in that it is possible to accurately detect corruption of contents. However, in the case of negative pressure canning, a rigid can body that can withstand negative pressure is required, and the side walls are thicker than positive pressure cans, and in the case of a three-piece can, the manufacturing cost is high. Yes.
[0005]
On the other hand, in order to solve the problems of the three-piece can described above, the can body is thinned by squeezing-scoring, drawing-stretching-scoring, etc., and the bottom and side walls are integrally formed. Cans are used. Furthermore, in order to reduce the manufacturing cost of the above two-piece can, an inert (liquefied / misted / solidified) gas such as liquid nitrogen is filled at the time of sealing so It has been proposed to make the side wall of the two-piece can thinner by compressing and imparting rigidity with the pressure inside the can.
[0006]
This can with low positive pressure has a positive pressure inside the can, so it is difficult to dent against the external pressure, and the thickness of the can body can be reduced, but the bottom part of the two-piece can is continuous with the body part. Because of this, and because the side walls are further thinned, the internal pressure inspection suitability by punching was lacking.
That is, in the case of a three-piece can, since the bottom lid is wound around the end of the body portion, the presence of the tightened portion causes a relatively simple vibration mainly composed of natural vibration such as drum vibration. It becomes. On the other hand, in the case of a two-piece can, since the trunk and the bottom are continuous, the location that becomes the end in vibration is not clear, and as a result, the percussion sound includes a plurality of vibration mode components. This is a complex vibration that causes a so-called “beat”.
[0007]
In addition, the material of the bottom part, which is a vibrating body, is a thin plate of tinned steel plate, tin-free steel, aluminum, etc., so it strongly affects the resonance of the can body and head space and the influence of the contents rather than the vibration itself. In particular, as the time passes from the impact, the vibration becomes a percussion sound including more complicated “beat” because elements other than the internal pressure of the can are superimposed. These phenomena are particularly prominent in a two-piece can filled with an inert (liquefied / misted / solidified) gas such as liquid nitrogen at the time of sealing to reduce the positive pressure.
[0008]
By the way, in the current percussion method, spectrum analysis is performed using the Fast Fourier Transform (FFT) method, and the frequency indicating the maximum value is specified as corresponding to the pressure in the can, and it is within the range of the determination standard. The quality of canned foods is judged based on whether or not However, when this FFT method is applied to a two-piece can inspection, the obtained frequency spectrum has low resolution accuracy and becomes a dull waveform when expressed in a graph, which is not satisfactory. This is because the frequency resolution by this method depends on the observation time. In other words, if the observation time is increased in order to increase the frequency resolution in the two-piece can percussion, the percussion reverberation will be complicated by noise superimposed on the time, so that the S / N ratio of the detection signal itself is increased. It will be lower. For this reason, there is a problem that a highly accurate inspection result cannot be expected for canned two-piece cans.
[0009]
As a result of intensive research in view of the above circumstances, the present inventors have obtained a frequency spectrum using the linear prediction coefficient method, and are therefore suitable for inspection of sealed containers, particularly cans consisting of two-piece cans. Invented the percussion device and filed a patent application earlier.
As a result of further research, the present inventors have processed the sealed container, particularly the two-piece can body itself, so that the frequency of the percussion sound generated during percussion does not cause a so-called “beat”. If the frequency band is set, it has been found that canned inspections consisting of two-piece cans can be performed with high accuracy by the percussion method, and the present invention has been completed.
[0010]
Therefore, the present invention provides a sealed container in which the initial shape of the bottom of the sealed container (the shape when the internal pressure of the can is 0) is curved so that the frequency of the percussion sound is in a frequency band that does not cause “beat”. With the goal.
JP-A-2000-128165 discloses a can having a shape in which the bottom of the can can be easily hit and the internal pressure of the can can be easily inspected. By forming an annular recess on the inner side and forming an annular protrusion inside the annular recess, it is easy to return to the original state when the internal pressure is unloaded, and the tension is reduced when the internal pressure is unloaded. There is no disclosure about the initial shape of the can bottom being a curved surface shape.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and by changing the rising point (rising frequency) and / or the slope of the frequency curve in the can internal pressure-frequency characteristics at the time of percussion, the frequency of the percussion sound is “ This is characterized by avoiding a frequency band in which a “beat” occurs.
FIG. 1 is a diagram for explaining the principle of the present invention, and curve 1 shows a percussion frequency characteristic when the bottom panel is flat, and shows a state in which a “beat” occurs when the internal pressure of the can is around 80 kPa. ing.
[0012]
In FIG. 1, curves 2 to 4 show the percussion frequency characteristics of the sealed can of the present invention. In the case of curve 2, the rising frequency of the percussion frequency characteristics is increased to avoid the frequency that causes “beat”. In the case of curve 3, the inclination of the tap frequency characteristic is relaxed to avoid the frequency that causes “beat”, and in the case of curve 4, the rising point of the tap frequency characteristic is increased. In addition, the state is shown in which the inclination is relaxed to avoid the frequency band in which the “beat” occurs.
The sealed can having the punching frequency characteristics of curves 1 to 4 in FIG. 1 has the same other conditions (for example, material, diameter, etc.) except only the shape of the bottom.
[0013]
[Means for Solving the Problems]
The sealed can of the present invention has the following configuration in order to have the inspection frequency characteristics as shown by the curves 2 to 4.
That is, according to the first aspect of the present invention, in the sealed can having the bottom panel portion inside the circumferential grounding portion formed on the outer periphery of the bottom portion, the shape of the bottom panel portion is 0 when the internal pressure of the can is 50 kPa. It is set as the structure made into the curved surface shape so that the difference of the punching frequency of 100-2000Hz.
[0014]
The invention according to claim 2 is a sealed can having a bottom panel portion inside a circumferential grounding portion formed on the outer periphery of the bottom portion,
The bottom panel part is a flat shaped sealed can,
The inspection frequency when the internal pressure of the can is 0 is f ₀ ,
The inspection frequency when the internal pressure of the can is 50 kPa is f ₅₀ ,
f ₅₀ −f ₀ = f _d ,
Bottom panel portion cans internal pressure of the sealed cans having a curved surface and the droplet detection frequency when 0 and f _R,
Furthermore, when f _R −f ₀ = Δf,
The curved surface shape is set such that Δf is in the range of 0.15 to 1.5 times f _d .
[0015]
When the sealed can is configured as described above, it is possible to obtain a sealed can having an inspection frequency characteristic that does not cause “beat”.
[0016]
In the sealed can, preferably, the bottom panel portion swells from a higher pressure inside or outside the can to a lower pressure.
In the can where the inside and outside pressure of the bottom panel bulges from the low side to the high side, when the internal pressure of the can is changed from 0 to positive pressure or negative pressure, the percussion frequency once decreases. It shows a rising characteristic and cannot obtain accurate percussion results. However, according to the present invention, there is no problem as described above, and an accurate percussion can be performed.
[0017]
The curved shape of the bottom panel portion can be a spherical shape having a certain radius of curvature. In this case, it is preferable that the diameter of the sealed can is 40 to 160 mm and the curvature radius of the bottom panel portion is 200 to 2000 mm.
In this way, it is possible to obtain a sealed can having a percussion frequency characteristic that does not cause “beat”.
The curved surface shape may be an aspherical shape in which the radius of curvature at the center of the bottom panel portion is increased and the radius of curvature of the end portion is decreased. Even in this case, the same effect as that of the spherical shape can be obtained.
[0018]
In the sealed can, it is preferable to form one or a plurality of convex portions and / or concave portions at an arbitrary position of the bottom surface panel portion having the curved shape.
Here, the convex portion and / or the concave portion are preferably formed in a dot shape or a streak shape, and the dotted convex portion and / or the concave portion is formed in the center of the bottom panel portion and / or the same circle. It can be formed at equal intervals on the circumference, or the streak-like convex portions and / or concave portions can be formed radially on the bottom panel portion. Further, the dot-like and streak-like convex portions and / or concave portions can be formed on the bottom panel portion so as to represent an arbitrary figure.
[0019]
If it does in this way, while being able to enlarge the bending rigidity of a bottom face panel part, the rising point of the inspection frequency characteristic and the inclination of a frequency characteristic can be adjusted.
[0020]
The present invention can be applied to both a two-piece can and a three-piece can. However, the present invention is effective when applied to a two-piece can (seamless can) that does not have a winding portion between a bottom portion and a trunk portion.
[0021]
Further, the sealed can preferably has a bead portion formed on the bottom panel portion.
When the bead portion is formed in this way, the pressure resistance strength of the bottom portion increases, so that even if the can internal pressure temporarily changes (for example, even if the can internal pressure increases during the retort process), the bottom portion does not deform. , Enabling accurate percussion.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a sealed can according to an embodiment of the present invention will be described with reference to the drawings.
[0023]
[First embodiment]
FIG. 2 is a bottom sectional view showing the first embodiment of the present invention.
The sealed can 1 of the first embodiment shown in FIG. 2 has a configuration in which a curved bottom panel portion 3 bulging outside the can is formed on the inner side of the ground contact portion 2 formed on the outer periphery of the bottom portion. It has become. The curvature of the curved surface shape is as follows when the internal pressure of the can is 0.
That is, as shown in FIG. 3, a striking test frequency _{f R} when the can internal pressure 0, and such curvature difference between the hit test frequency _{f S} when the cans pressure and 50kPa is 100~2000Hz . Here, when f _S −f _R <100 Hz, the inclination of the percussion frequency characteristic becomes too loose, and the resolution with respect to pressure is lowered. On the other hand, when f _S −f _R > 2000 Hz, the percussion frequency becomes too high, making measurement difficult and impractical.
[0024]
Moreover, you may make it the curvature of the curved surface shape of the bottom face panel part 3 become in the range set as follows.
That is, the shape of the bottom panel portion 3 is a plane,
The inspection frequency when the internal pressure of the can is 0 is f ₀ ,
The inspection frequency when the internal pressure of the can is 50 kPa is f ₅₀ ,
f ₅₀ −f ₀ = f _d ,
In addition, the shape of the bottom panel 3 is a radius of curvature R,
Let f _R be the percussion frequency when the internal pressure of the can is 0,
Furthermore, when f _R −f ₀ = Δf,
Δf is in the range of 0.15 to 1.5 times f _d (Δf = k · f _d 0.15 <k <1.5)
It can also be made to be.
[0025]
Here, when the magnification k is k <0.15, the radius of curvature of the bottom panel portion 3 is too large, and “bottom” occurs in the same frequency band as the bottom panel portion having a planar shape. On the other hand, if k> 1.5, the inspection frequency becomes too high, making measurement difficult and impractical.
[0026]
The curvature of the curved surface shape of the bottom panel portion 3 in the sealed can 1 is determined as described above. More specifically, when the diameter of the can is 40 to 160 mm, the curvature is preferably 200 to 2000 mm. Within this range, the frequency of the percussion sound is not too high and measurement is easy, and the frequency band is also in a range in which “beat” is unlikely to occur.
[0027]
Here, it is preferable that the curved surface shape of the bottom panel portion 3 bulges from the higher pressure side to the lower side inside and outside the can. Therefore, it is preferable that the positive pressure can be formed so as to bulge from the inside toward the outside, and the negative pressure can be formed so as to bulge from the outside to the inside.
If the curved surface shape of the bottom panel portion 3 is a curved surface shape bulging from the lower pressure to the higher pressure inside and outside the can, the percussion frequency once decreases when the pressure inside and outside the can is changed. Since it becomes higher again, the accuracy of the percussion test results is lacking.
[0028]
The present invention can be applied to both a two-piece can (seamless can) and a three-piece can as long as it is a sealed can. However, the present invention is effective when applied to a two-piece can that tends to “beat” in the inspection frequency.
Moreover, if the material of the sealing can is a metal can, it can be applied to cans of various materials using aluminum or steel. Depending on the material, the punching frequency differs, and the frequency at which the “beat” occurs and the internal pressure of the can also differ. However, according to the present invention, by changing the radius of curvature of the bottom panel 3 according to the material, a convex concave portion described later is formed. Thus, it is possible to set the percussion frequency to a frequency band in which no “beat” occurs.
[0029]
In the case of a two-piece can, a bead portion 4 may be formed between the grounding portion 2 and the bottom panel portion 3 as shown in FIG. When the bead portion 4 is formed, the pressure resistance strength of the bottom portion increases, so even if the can internal pressure temporarily changes (for example, even if the can internal pressure increases during the retort process), the bottom portion does not deform and is accurate. It enables a simple checkup.
[0030]
[Second Embodiment]
5-7 has shown the perspective view which shows each aspect of 2nd embodiment which formed the recessed part in the bottom face panel part made into the curved surface shape.
FIG. 5 shows a form in which one point-like recess 5 is formed in the center of the curved bottom panel portion 3, and FIG. 6 shows that the recess 5 is formed in the center of the curved bottom panel portion 3. In addition, there is shown a form in which four dot-like recesses 5a are formed at equal intervals around the periphery.
[0031]
FIG. 7 shows a form in which streak-like concave portions 6 are radially formed on the curved bottom surface panel portion 3 at intervals of 120 degrees from the center.
Further, FIG. 8 shows the bottom panel portion 3 having a curved shape in which the dot-like recesses 5a and the stripe-like recesses 6 are alternately formed, and each of the dot-like recesses is provided between the stripe-like recesses 6 shown in FIG. The form which formed 5a is shown.
[0032]
In each form described above, a convex portion may be formed instead of the concave portion, or the concave portion and the convex portion may be mixed and formed. Moreover, the shape of a recessed part and a convex part can also be made into shapes other than a dot shape or a streak shape, Furthermore, the magnitude | size and arrangement | positioning of these recessed parts and a convex part can be made arbitrary.
[0033]
As described above, when the concave and / or convex portions are formed on the bottom surface panel portion 3 having a curved shape, the rigidity of the bottom portion of the sealing can 1 can be increased, and the number and size of the concave and / or convex portions can be increased. By changing the position and the like, it is possible to change the start point of the percussion frequency and the degree of frequency change (inclination of frequency characteristics).
Therefore, it becomes easy to manufacture a sealed can having a percussion frequency that does not cause “beat” for each type of can.
[0034]
〔Example〕
Example 1
When the can diameter was 52 mm and the bottom panel portion was a planar can, and the sealed cans were 200 mm and 2000 mm in radius of curvature of the bottom panel portion, the results shown in FIG. 9 were obtained. It became.
From the analysis results, the planar sealed can with a can diameter of 52 mm has a frequency f ₀ of 1400 Hz when the internal pressure of the can is _{0 and} a frequency f ₅₀ of 2600 Hz when the internal pressure of the can is 50 kPa, and the frequency difference f _d (= f _50). -f ₀₎ was 1200Hz. In addition, a curved sealed can with a diameter of 52 mm has a radius of curvature of 3600 Hz and 3200 Hz when the internal pressure of the can is 50 kPa and 0 when the radius of curvature is 200 mm, and the difference between the frequencies is 400 Hz. When the inner pressure is 2000 mm, the inspection frequencies when the internal pressure of the can is 50 kPa and 0 are 2650 Hz and 1600 Hz, respectively, and the difference between the frequencies is 1050 Hz.
That is, regardless of whether the radius of curvature is 200 mm or 2000 mm, the difference in the inspection frequency when the internal pressure of the can is 50 kPa and 0 is in the range of 100 to 2000 Hz, and Δf (f _R −f ₀ ) is also the curvature. When the radius is 200 mm, it is 1800 Hz, and when the radius of curvature is 2000 mm, it is 200 Hz, and k of Δf = k · f _d is 1.5 to 0.17, and is within the range of 0.15 to 1.5. Met.
[0035]
When the curvature radius of the bottom panel is 2000 mm, the percussion frequency is changed to 1600 to 3150 Hz (can internal pressure 0 to 100 kPa), and a “beat” occurs near 1800 Hz (can internal pressure 10 kPa) (FIG. 9). Curve 3).
However, in the actual percussion, the internal pressure of the can is not changed in the range of 0 to 100 kPa, and it is usually performed in the range of the internal pressure of the can of 20 to 80 kPa, at most within the range of 15 to 90 kPa. Therefore, at the time of actual percussion inspection, even a can having a radius of curvature of the bottom panel portion of 2000 mm can be inspected in a state where a frequency band causing “beat” is avoided.
[0036]
(Example 2)
When a can with a diameter of 40 mm and a bottom panel with a flat bottom panel was punched, the punching frequency changed to 1900-3100 Hz (can internal pressure of 0-100 kPa), and a “beat” occurred near 2900 Hz ( Curve 1 in FIG.
Except for setting the radius of curvature of the bottom panel portion to 200 mm, when a sealed can under the same conditions as the sealed can was punched, the punching frequency changed to 2900-3700 Hz (can internal pressure 0-100 kPa). No “beat” occurred (curve 2 in FIG. 10).
[0037]
(Example 3)
When a can with a can diameter of 52 mm and a bottom panel portion having a flat shape was punched, the punching frequency changed to 1400 to 3100 Hz (can internal pressure of 0 to 100 kPa), and a “beat” occurred around 1800 Hz ( Curve 1) in FIG.
Except for setting the radius of curvature of the bottom panel portion to 400 mm, when a sealed can under the same conditions as the sealed can was punched, the punching frequency changed to 2200 to 3400 Hz (can internal pressure 0 to 100 kPa). No “beat” occurred (curve 2 in FIG. 11).
[0038]
Example 4
A sealed can of the same condition as the sealed can of Example 3 except that the radius of curvature of the bottom panel is 300 mm, and one point-like recess is formed at the center of the bottom and at six locations on the circumference. When the punching was performed, the punching frequency changed to 1900-3200 Hz (can internal pressure 0-100 kPa). No “beat” occurred (curve 3 in FIG. 11).
[0039]
(Example 5)
When the radius of curvature of the bottom panel portion is set to 300 mm, and a sealed can under the same conditions as the sealed can of Example 3 is performed except that six streaky concave portions are formed radially from the center of the bottom, The punching frequency changed to 2000 to 3100 Hz (can internal pressure 0 to 100 kPa). No “beat” occurred (curve 4 in FIG. 11).
[0040]
【The invention's effect】
According to the present invention having the above-described configuration, the frequency of the percussion sound generated during percussion can be set to a frequency band in which a so-called “beat” does not occur. This inspection can be performed with high accuracy by the percussion method.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the principle of the present invention.
FIG. 2 is a bottom cross-sectional view showing a first embodiment of the present invention.
FIG. 3 is an explanatory diagram for defining a radius of curvature of a bottom panel portion.
FIG. 4 is a bottom cross-sectional view of an embodiment in which a bead portion of the present invention is formed.
FIG. 5 is a bottom perspective view of a second embodiment of the present invention formed around a point-like recess.
FIG. 6 is a bottom perspective view of a second embodiment of the present invention in which a dot-like recess is formed on the same circumference as the center.
FIG. 7 is a bottom perspective view of a second embodiment of the present invention in which streak-like recesses are formed radially.
FIG. 8 is a bottom perspective view of a second embodiment of the present invention in which radial streak-like recesses and dot-like recesses are alternately formed.
FIG. 9 is a diagram showing the tapping frequency characteristics in the first example.
FIG. 10 is a diagram showing a tapping frequency characteristic in the second embodiment.
FIG. 11 is a diagram showing the tapping frequency characteristics in Examples 3 to 5;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sealing can 2 Grounding part 3 Bottom panel part 4 Bead part 5, 5a Dot-shaped recessed part 6 Streaky recessed part

Claims (9)

In a seamless sealed can having a diameter of the can of 40 to 160 mm, a radius of curvature of the bottom panel portion of 200 to 2000 mm, and having a bottom panel portion inside a circumferential grounding portion formed on the outer periphery of the bottom portion,
The bottom panel part is a flat shaped sealed can,
The inspection frequency when the internal pressure of the can is 0 is f ₀ ,
The inspection frequency when the internal pressure of the can is 50 kPa is f ₅₀ ,
f ₅₀ −f ₀ = f _d ,
When the inner pressure of the sealed can whose bottom panel is curved is 0, the punching frequency is f _R ,
Furthermore, when f _R −f ₀ = Δf,
A sealed can having a curved shape such that Δf is in a range of 0.15 to 1.5 times f _d . The sealed can according to claim 1 , wherein the bottom panel portion having the curved surface bulges from a higher pressure inside or outside the can to a lower pressure. The sealed can according to claim 1, wherein the curved shape of the bottom panel portion is a spherical shape. The sealed can according to any one of claims 1 to 3 , wherein one or a plurality of convex portions and / or concave portions are formed at an arbitrary position of the bottom surface panel portion having the curved shape. The sealed can according to claim 4, wherein the convex portion and / or the concave portion are formed in a dot shape or a streak shape. The sealed can according to claim 4, wherein the dot-like convex portions and / or concave portions are formed at equal intervals on the center and / or the same circumference of the bottom panel portion. The sealed can according to claim 5, wherein the line-like convex portions and / or concave portions are formed radially on the bottom panel portion. 6. The sealed can according to claim 5, wherein the dot-like and streak-like convex portions and / or concave portions are formed on the bottom panel portion so as to represent an arbitrary figure. The sealed can according to claim 1 , wherein a bead portion is formed on the bottom panel portion.

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