Steel shell with straight-edge bottom cover plate
By using a straight-edged bottom cover plate that fits into the inner cavity of the stainless steel casing and providing a reserved space, the problems of difficult stamping and welding of the bottom cover plate are solved, achieving more efficient welding and greater utilization of battery cell space.
Patent Information
- Application Number
- CN202423230994.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-26
- Publication Date
- 2025-12-19
- Estimated Expiration
- 2034-12-26
AI Technical Summary
The existing stainless steel shell bottom cover plate is difficult to stamp and form, has a small range of thickness selection, is prone to sharp corners, is difficult to weld, and has many welding defects.
The design features a straight-edge bottom cover plate that fits into the inner cavity of the shell, with a space between them to hold molten welding material. A smooth weld is formed through laser composite welding or filler wire welding.
It improves the convenience of stamping and forming and the life of the mold, expands the range of bottom cover thickness selection, increases the utilization rate of battery cell space, prevents sharp corners from piercing the blue film of the battery cell, and makes the welding more robust.
Smart Images
Figure CN223693226U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to power battery technical field especially a steel shell with straight edge bottom cover plate. BACKGROUND
[0002] The stainless steel shell is the square shell with both ends open by welding stainless steel material, and the bottom cover plate is welded at one end port to form the shell of secondary battery. In order to facilitate the assembly and welding with the shell, the flange step is formed on the edge of the bottom cover plate by stamping, but the process will cause the sharp angle to be formed on the top of the cover plate flange, which is easy to pierce the blue film of the battery cell. At the same time, the small area of the top flange is not conducive to the overall stress of the bottom of the battery cell. The R angle in the step is also convenient to clear the angle. When the bottom cover plate is used in this way, the thickness of the bottom cover plate cannot be too thick, otherwise it is difficult to stamp into shape. Therefore, the thickness selection range of the bottom cover plate is small, stamping is difficult, and the service life of the die is short. The efficiency is low and the cost is high when the CNC milling step is used, which is not conducive to mass production. Since the wall thickness of the shell is usually thin, it is usually made of sheet material with a thickness of 0.15mm to 0.25mm. Therefore, during welding, it is often easy to deviate, resulting in welding defects such as welding hole, virtual welding, welding through and welding bead. SUMMARY
[0003] Therefore, the utility model aims at providing a steel shell with straight edge bottom cover plate to solve the problems of stamping difficulty, small thickness selection range, easy to form sharp angle and difficult to weld the shell and the bottom cover plate in the prior art.
[0004] To achieve the above-mentioned purpose, the utility model provides a steel shell with straight edge bottom cover plate, which comprises at least one open shell and a bottom cover plate for sealing the open end of the shell. The periphery of the bottom cover plate is matched with the inner cavity of the shell. The position between the periphery of the bottom cover plate and the shell is provided with a storage space for containing molten welding material.
[0005] In the above-mentioned scheme, the bottom cover plate for sealing the open end of the shell is a straight edge plate, without the need for stamping or milling flange step features. Therefore, stamping is convenient and simple, the service life of the stamping die is longer, the thickness selection range of the bottom cover plate is wide, the bottom cover plate has no boss and sharp angle features, which is conducive to increasing the space utilization rate of the battery cell in the shell and preventing the sharp angle from piercing the blue film of the battery cell. The welding material storage space is provided between the bottom cover plate and the shell, the welding seam is smooth, and the welding is firm.
[0006] Further, the upper surface of the bottom cover plate is 0.2mm to 0.4mm higher than the upper end surface of the shell. The upper end surface of the shell and the outer periphery of the bottom cover plate form the storage space.
[0007] Further, a first chamfer is arranged on the periphery of the upper surface of the bottom cover plate, and the first chamfer of the bottom cover plate and the inner wall of the upper end of the shell form the storage space.
[0008] Further, the first chamfer is a straight chamfer, the vertical distance of the straight chamfer is 0.15mm-0.3mm, and the horizontal distance of the straight chamfer is 0.1mm-0.2mm.
[0009] Further, the first chamfer is a first circular chamfer, and the radius R1 of the first circular chamfer is 0.15mm-0.3mm.
[0010] Further, the shell comprises a square, circular or polygonal thin-walled cylinder.
[0011] Further, the shell is a thin-walled cylinder made of stainless steel plate with a thickness of 0.15mm-0.3mm.
[0012] Further, the shell is a rectangular thin-walled cylinder made of stainless steel plate with a thickness of 0.2mm.
[0013] Further, the bottom cover plate is made of stainless steel plate with a thickness of 0.4mm-2.0mm, and the periphery of the lower surface of the bottom cover plate is provided with a second chamfer.
[0014] Further, the second chamfer is a second circular chamfer, and the radius R2 of the second circular chamfer is 0.1mm-0.15mm.
[0015] Compared with the steel shell formed by stamping or milling a bottom cover plate with a flange step and welding with a thin-walled shell, the bottom cover plate for plugging the open end of the shell of the utility model is a straight edge plate, and does not need to be punched or milled with a flange step, so that the stamping forming is convenient and simple, the cost is lower, the service life of the stamping die is longer, the thickness selection range of the bottom cover plate is wide, the bottom cover plate has no boss and sharp corner features, which is beneficial to increase the space utilization rate of the battery cell in the shell and prevent the sharp corner from piercing the blue film of the battery cell, the welding material storage space is arranged between the bottom cover plate and the shell, the welding seam is smooth and full, and the welding is more firm. BRIEF DESCRIPTION OF DRAWINGS
[0016] Figure 1 It is an exploded view of the steel shell with a straight edge bottom cover plate of the utility model.
[0017] Figure 2 It is a top view of the steel shell with a straight edge bottom cover plate of the utility model.
[0018] Figure 3 It is Figure 2 A-A sectional view.
[0019] Figure 4 It is an embodiment oneFigure 3 Enlarged view of A in FIG. 1.
[0020] Figure 5 For Figure 4 Structure after welding Structure schematic diagram.
[0021] Figure 6 For Figure 3 Enlarged view of A in FIG. 2.
[0022] Figure 7 For Figure 6 Structure after welding Structure schematic diagram.
[0023] Figure 8 For Figure 3 Enlarged view of A in FIG. 3.
[0024] Figure 9 For Figure 8 Structure after welding Structure schematic diagram.
[0025] The description of the drawings is as follows:
[0026] Housing - 10;
[0027] Bottom cover plate - 20; Straight chamfer - 201; First round chamfer - 202; Second round chamfer 203;
[0028] Residence space - 301a, 301b, 301c;
[0029] Melt pool - 401a, 401b, 401c. DETAILED DESCRIPTION
[0030] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme of the present application will be described clearly and completely below in combination with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.
[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is only for the purpose of describing specific embodiments and is not intended to limit the present application.
[0032] Embodiment one
[0033] The steel shell with straight edge bottom cover plate 20 disclosed in this embodiment is as follows: Figures 1-4As shown, the shell 10 includes at least one open end and a bottom cover plate 20 sealing the open end of the shell 10, the periphery of the bottom cover plate 20 is adapted to the inner cavity of the shell 10, and a storage space for storing molten welding material is provided at the position between the periphery of the bottom cover plate 20 and the shell 10.
[0034] The shell 10 in the embodiment is a cylindrical body with both upper and lower ends open, and the bottom cover plate 20 is arranged on one open end of the shell 10 to seal the open end. In this arrangement, after the electric core is installed in the shell 10 and the other open end of the shell 10 is sealed with an electrode cover plate, a power battery or battery pack is formed. Understandably, the shell 10 can also be closed at one end and open at the other end, and the bottom cover plate 20 is arranged on the open end to seal the open end. In the embodiment, the shell 10 is made of stainless steel sheet material with a thickness of 0.15mm-0.3mm, and the bottom cover plate 20 is fixedly connected to the shell 10 by welding. Figures 1-3 As shown, the shell 10 in the embodiment is a long rectangular thin-walled cylindrical body with both upper and lower ends open, including two oppositely arranged wide side walls and two oppositely arranged narrow side walls, and the bottom cover plate 20 is a long rectangular plate body that is adapted to the opening of the long rectangular cylindrical shell 10. Understandably, in other feasible embodiments, the shell 10 can also be a square, circular or other polygonal thin-walled cylindrical body, and correspondingly, the shape of the bottom cover plate 20 is adapted to the shape of the open end of the shell 10. After the shell 10 is made, the bottom cover plate 20 is fixedly connected to the shell 10 by welding. After being fixedly connected to the shell 10, the bottom cover plate 20 seals the open end of the shell 10 at this position. In the embodiment, the shell 10 is placed vertically, and the bottom cover plate 20 is arranged at the upper open end of the shell 10.
[0035] In combination with Figures 1-5As shown, the bottom cover plate 20 is a rectangular straight edge plate body matched with the opening of the shell 10, and in the embodiment, the bottom cover plate 20 is made of a stainless steel plate or an aluminum plate with a thickness of 0.4mm-2.0mm. In a feasible embodiment, according to the design strength of the steel shell, the bottom cover plate 20 is preferably made of a 0.6mm-thick stainless steel plate. Specifically, the bottom cover plate 20 can be made by punching and cutting or laser cutting. In this embodiment, the shell 10 is preferably made of a 0.2mm-thick stainless steel plate. Since the thickness of the shell 10 is relatively thin, the shell 10 cannot be made by punching. The shell 10 is made by punching and cutting, bending, and welding. When the bottom cover plate 20 is placed in the port of the shell 10 to block the opening end of the shell 10, the outer wall of the bottom cover plate 20 is matched with the inner wall of the shell 10, and the upper surface of the bottom cover plate 20 is 0.3mm higher than the upper end surface of the shell 10. In this way, a welding step is formed between the upper end surface of the shell 10 and the outer peripheral surface of the bottom cover plate 20, and the welding step forms a storage space 301a for accommodating molten welding material. At this time, the shell-in depth of the bottom cover plate 20 is 0.3mm (the shell-in depth of the bottom cover plate 20 is defined as the distance between the lower surface of the bottom cover plate 20 and the upper end surface of the shell 10 in the height direction of the shell 10). When the bottom cover plate 20 and the shell 10 are welded and connected by using a laser composite welding process, the laser beam is irradiated from the horizontal direction to the bottom cover plate 20 at the storage space 301a. The molten welding wire and the upper end surface layer of the shell 10 and the outer peripheral surface layer of the bottom cover plate 20 are melted and filled in the storage space 301a to form a molten pool 401a. Under the blowing of the welding protective gas during welding, the storage space 301a is finally naturally formed into a round-cornered molten pool 401a to fill the storage space 301a, so that a smooth and full welding scar is obtained. In this way, the contact area of the bottom cover plate 20, the shell 10, and the molten pool 401a is increased, and the welding of the bottom cover plate 20 and the shell 10 is firm and reliable.For the convenience of placing the lower plate body of the bottom cover plate 20 into the shell 10, a second circular chamfer 203 is arranged on the periphery of the lower surface of the bottom cover plate 20. In this embodiment, the radius R2 of the second circular chamfer 203 is 0.15 mm. At this time, R2 is smaller than the shell-in depth of the bottom cover plate 20, which is 0.3 mm. Therefore, part of the outer peripheral surface of the bottom cover plate 20 is in contact with the inner wall surface of the shell 10, and the positioning is stable. In another feasible embodiment, according to the design strength of the steel shell, the bottom cover plate 20 is preferably made of a 0.4 mm thick stainless steel plate. Specifically, the bottom cover plate 20 can be made by punching and cutting or laser cutting. In this embodiment, the shell 10 is preferably made of a 0.15 mm thick stainless steel plate. When the bottom cover plate 20 is placed in the port of the shell 10 to block the open end of the shell 10, the outer wall of the bottom cover plate 20 is adapted to the inner wall of the shell 10, and the upper surface of the bottom cover plate 20 is 0.2 mm higher than the upper end surface of the shell 10. In this way, a relatively small welding step is formed between the upper end surface of the shell 10 and the outer peripheral surface of the bottom cover plate 20, and the formed storage space 301a is also relatively reduced. At this time, the shell-in depth of the bottom cover plate 20 is 0.2 mm (the shell-in depth of the bottom cover plate 20 is defined as the distance between the lower surface of the bottom cover plate 20 and the upper end surface of the shell 10 in the height direction of the shell 10). Since the thickness of the bottom cover plate 20 is reduced at this time, in this embodiment, the radius R2 of the second circular chamfer 203 is set to 0.1 mm. Therefore, part of the outer peripheral surface of the bottom cover plate 20 is in contact with the inner wall surface of the shell 10, and the positioning is stable. In another feasible embodiment, according to the design strength of the steel shell, the bottom cover plate 20 is preferably made of a 2 mm thick stainless steel plate. Specifically, the bottom cover plate 20 can be made by punching and cutting or laser cutting. In this embodiment, the shell 10 is preferably made of a 0.3 mm thick stainless steel plate. When the bottom cover plate 20 is placed in the port of the shell 10 to block the open end of the shell 10, the outer wall of the bottom cover plate 20 is adapted to the inner wall of the shell 10, and the upper surface of the bottom cover plate 20 is 0.4 mm higher than the upper end surface of the shell 10. In this way, a relatively high welding step is formed between the upper end surface of the shell 10 and the outer peripheral surface of the bottom cover plate 20, and the formed storage space 301a is also relatively increased. At this time, the shell-in depth of the bottom cover plate 20 is 1.6 mm (the shell-in depth of the bottom cover plate 20 is defined as the distance between the lower surface of the bottom cover plate 20 and the upper end surface of the shell 10 in the height direction of the shell 10). In this embodiment, the radius R2 of the second circular chamfer 203 is set to 0.5 mm. Therefore, part of the outer peripheral surface of the bottom cover plate 20 is in contact with the inner wall surface of the shell 10, and the positioning is stable. Of course, the thickness of the shell 10, the thickness of the bottom cover plate 20, the distance between the upper surface of the bottom cover plate 20 and the upper end surface of the shell 10, and the radius R2 of the second circular chamfer 203 on the periphery of the lower surface of the bottom cover plate 20 can be flexibly selected according to the specific design requirements of the steel shell.It can be understood that when the bottom cover plate 20 is made of a stainless steel plate with a small thickness, such as a stainless steel sheet with a thickness of 0.4 mm, since the thickness of the bottom cover plate 20 is thin, the anti-explosion notch for relieving the pressure inside the shell 10 when the pressure inside the shell 10 increases can be directly punched on the upper surface or the lower surface of the bottom cover plate 20, and then the integrated anti-explosion valve is formed on the bottom cover plate 20. In the above scheme, since the bottom cover plate 20 is a straight edge plate, no upward or downward protruding step or flange is formed at the edge of the bottom cover plate 20, and therefore, when the straight edge bottom cover plate 20 is sealingly welded with the open end of the shell 10, the internal space of the shell 10 is relatively large and has a higher utilization rate. It should be noted that the welding material in the present application not only includes the welding wire used when the bottom cover plate is welded with the shell by laser composite welding, but also includes the welding material in other feasible embodiments, that is, the molten welding body in the molten pool formed by filling the molten welding body in the preset space after the welding body (such as the shell and the bottom cover plate in the present scheme) is melted under the irradiation of the laser.
[0036] Example two
[0037] In this example, the combination of Figure 3 , Figure 6 , Figure 7As shown, the upper surface of the bottom cover plate 20 is flush with the upper end surface of the shell 10, and a first circular chamfer 202 is arranged on the peripheral edge of the bottom cover plate 20, which, together with the inner wall of the upper end of the shell 10, forms a storage space 301b. When the bottom cover plate 20 is welded to the shell 10 by using the filler wire welding method, the molten filler wire is filled in the storage space 301b formed by the first circular chamfer 202 and the inner wall of the upper end of the shell 10 to form a molten pool 401b. Under the blowing state of the protective gas during welding, the surface of the molten pool 401b is smooth and flat. Since the storage space 301b forms the molten pool 401b, the contact area between the bottom cover plate 20, the shell 10 and the molten pool 401b is increased, and thus the bottom cover plate 20 is firmly and reliably welded to the shell 10. In a feasible embodiment, when the thickness of the cover plate is set to be 0.4 mm according to the design strength of the steel shell, the shell 10 can be made of a 0.15 mm stainless steel plate. At this time, the radius R1 of the first circular chamfer 202 can be set to be 0.15 mm, and the storage space 301b formed is relatively small. The radius R2 of the second circular chamfer 203 on the peripheral edge of the lower surface of the bottom cover plate 20 can be set to be 0.1 mm to 0.3 mm, and preferably the radius R2 of the second circular chamfer 203 is set to be 0.1 mm. Thus, part of the outer peripheral surface of the bottom cover plate 20 is in surface contact with the inner wall of the shell 10, the positioning between the bottom cover plate 20 and the shell 10 is stable, and the welding is facilitated. When the thickness of the cover plate is set to be 0.6 mm according to the design strength of the steel shell, the shell 10 can be made of a 0.2 mm stainless steel plate. At this time, the radius R1 of the first circular chamfer 202 can be set to be 0.2 mm, and the radius R2 of the second circular chamfer 203 on the peripheral edge of the lower surface of the bottom cover plate 20 can be set to be 0.1 mm to 0.3 mm, and preferably the radius R2 of the second circular chamfer 203 is set to be 0.2 mm. Thus, part of the outer peripheral surface of the bottom cover plate 20 is in surface contact with the inner wall of the shell 10, the positioning between the bottom cover plate 20 and the shell 10 is stable, and the welding is facilitated. When the strength of the steel shell needs to be higher, for example, the thickness of the bottom cover plate 20 is set to be 2 mm, the shell 10 can be made of a 0.3 mm stainless steel plate. At this time, the radius R1 of the first circular chamfer 202 can be set to be 0.5 mm, and the radius R2 of the second circular chamfer 203 on the peripheral edge of the lower surface of the bottom cover plate 20 can be set to be 0.3 mm. Thus, part of the outer peripheral surface of the bottom cover plate 20 is in surface contact with the inner wall of the shell 10, the positioning between the bottom cover plate 20 and the shell 10 is stable, and the welding is facilitated.
[0038] Example Three
[0039] In this embodiment, the bottom cover plate 20 is combined with the shell 10. Figure 3 , Figure 8 , Figure 9As shown, the upper surface of the bottom cover plate 20 is flush with the upper end surface of the shell 10, and a straight chamfer 201 is arranged on each of the four peripheral edges of the bottom cover plate 20, which, together with the inner wall of the upper end of the shell 10, forms a storage space 301c. When the bottom cover plate 20 is welded to the shell 10 by using a filler wire welding method, the molten filler wire is filled in the storage space 301c formed by the straight chamfer 201 and the inner wall of the upper end of the shell 10 to form a molten pool 401c. Under the blowing state of the protective gas during welding, the surface of the molten pool 401c is smooth and flat. Since the storage space 301c forms the molten pool 401c, the contact area between the bottom cover plate 20, the shell 10 and the molten pool 401c is increased, and thus the welding between the bottom cover plate 20 and the shell 10 is firm and reliable. In a feasible embodiment, when the thickness of the cover plate is set to be thin according to the design strength of the steel shell, for example, the thickness of the cover plate is 0.4 mm, the shell 10 can be made of a 0.15 mm stainless steel plate. At this time, the vertical chamfer distance of the straight chamfer 201 can be set to 0.15 mm, and the horizontal chamfer distance can be set to 0.1 mm. At this time, the storage space 301c formed is also relatively small. The radius R2 of the second circular chamfer 203 on the peripheral edge of the lower surface of the bottom cover plate 20 can be set to 0.1 mm-0.3 mm, and preferably the radius R2 of the second circular chamfer 203 is set to 0.1 mm. Thus, part of the outer peripheral surface of the bottom cover plate 20 is in surface contact with the inner wall of the shell 10, the positioning between the bottom cover plate 20 and the shell 10 is stable, and the welding is facilitated. When the thickness of the cover plate is set to 0.6 mm according to the design strength of the steel shell, the shell 10 can be made of a 0.2 mm stainless steel plate. At this time, the vertical chamfer distance of the straight chamfer 201 can be set to 0.2 mm, and the horizontal chamfer distance can be set to 0.15 mm. The radius R2 of the second circular chamfer 203 on the peripheral edge of the lower surface of the bottom cover plate 20 can be set to 0.1 mm-0.3 mm, and preferably the radius R2 of the second circular chamfer 203 is set to 0.2 mm. Thus, part of the outer peripheral surface of the bottom cover plate 20 is in surface contact with the inner wall of the shell 10, the positioning between the bottom cover plate 20 and the shell 10 is stable, and the welding is facilitated. When the strength of the steel shell needs to be higher, for example, the thickness of the bottom cover plate 20 is set to 2 mm, the shell 10 can be made of a 0.3 mm stainless steel plate. At this time, the vertical chamfer distance of the straight chamfer 201 can be set to 0.3 mm, and the horizontal chamfer distance can be set to 0.2 mm. The storage space 301c formed is also relatively large. The radius R2 of the second circular chamfer 203 on the peripheral edge of the lower surface of the bottom cover plate 20 can be set to 0.5 mm. Thus, part of the outer peripheral surface of the bottom cover plate 20 is in surface contact with the inner wall of the shell 10, the positioning between the bottom cover plate 20 and the shell 10 is stable, and the welding is facilitated.
[0040] Compared with the steel shell formed by stamping or milling the bottom cover plate 20 with a flange step and welding with the thin-walled shell 10, in the steel shell of the utility model, the bottom cover plate 20 for plugging the open end of the shell 10 is a straight edge plate, without the features such as stamping or milling flange steps, so that the stamping forming is convenient and simple, the cost is lower, the service life of the stamping die is longer, the thickness selection range of the bottom cover plate 20 is wide, the bottom cover plate 20 has no boss and sharp corner features, which is beneficial to increase the space utilization rate of the battery cell in the shell 10 and prevent the sharp corner from piercing the battery cell blue film, the molten welding material is arranged between the bottom cover plate 20 and the shell 10 to form a molten pool, under the blowing of the welding protective gas, the molten pool is smooth and full, and the welding is more firm.
[0041] The above embodiments only express the preferred embodiments of the utility model, and the description is more specific and detailed, but it cannot be understood as the limitation of the scope of the utility model patent. It should be pointed out that for ordinary skilled persons in the art, without departing from the concept of the utility model, a number of modifications and improvements can be made, which belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent should be subject to the appended claims.
Claims
1. A steel enclosure having a straight-sided bottom cover plate, comprising a housing having at least one open end and a bottom cover plate closing the open end of the housing, the periphery of the bottom cover plate fitting the interior cavity of the housing, characterized in that: A retaining space for retaining the molten welding material is arranged at a position between the peripheral edge of the bottom cover plate and the shell.
2. A steel enclosure having a straight-sided bottom cover plate according to claim 1, characterized in that: The upper surface of the bottom cover plate is 0.2mm-0.4mm higher than the upper end surface of the shell, and the upper end surface of the shell and the outer peripheral surface of the bottom cover plate enclose the retaining space.
3. The steel enclosure having a straight-sided bottom cover plate of claim 1, wherein: The peripheral edge of the upper surface of the bottom cover plate is provided with a first chamfer, and the first chamfer of the bottom cover plate and the inner wall of the upper end of the shell enclose the retaining space.
4. A steel enclosure having a straight-sided bottom cover plate according to claim 3, wherein: The first chamfer is a straight chamfer, the vertical distance of the straight chamfer is 0.15mm-0.3mm, and the horizontal distance of the straight chamfer is 0.1mm-0.2mm.
5. A steel enclosure having a straight-sided bottom cover plate as defined in claim 3 wherein: The first chamfer is a first circular chamfer, and the radius R1 of the first circular chamfer is 0.15mm-0.3mm.
6. The steel enclosure having a straight-sided bottom cover plate of claim 1, wherein: The shell comprises a square, circular or polygonal thin-walled cylinder.
7. The steel enclosure having a straight-sided bottom cover plate of claim 1, wherein: The shell is a thin-walled cylinder made of stainless steel plate with a thickness of 0.15mm-0.3mm.
8. The steel enclosure having a straight-sided bottom cover plate of claim 1, wherein: The shell is a rectangular thin-walled cylinder made of stainless steel plate with a thickness of 0.2mm.
9. The steel enclosure having a straight-sided bottom cover plate of claim 1, wherein: The bottom cover plate is made of stainless steel plate with a thickness of 0.4mm-2.0mm, and the peripheral edge of the lower surface of the bottom cover plate is provided with a second chamfer.
10. A steel enclosure having a straight-sided bottom cover plate according to claim 9, wherein: The second chamfer is a second circular chamfer, and the radius R2 of the second circular chamfer is 0.1mm-0.5mm.