CN211578865U

CN211578865U - Button cell pole shell and electrode lug seamless welding structure

Info

Publication number: CN211578865U
Application number: CN202020638498.5U
Authority: CN
Inventors: 常海涛; 苏盛; 叶永锋; 张志明
Original assignee: Nanfu New Energy Technology Co ltd Yanping District Nanping Fujian
Current assignee: Nanfu New Energy Technology Co ltd Yanping District Nanping Fujian
Priority date: 2020-04-24
Filing date: 2020-04-24
Publication date: 2020-09-25
Anticipated expiration: 2030-04-24

Abstract

The utility model provides a button cell polar shell does not have trace welded structure with electrode tab, welded structure includes polar shell and electrode tab, electric core mainly by positive plate, negative pole piece, diaphragm laminarization stack or convolute and form, positive, negative pole piece equally divide and do not be connected with an electrode tab electricity, a sheetmetal is fixed to be set up on the internal surface of arbitrary polar shell through first solder joint, be provided with the insulating piece between sheetmetal and the polar shell, the width of insulating piece is less than the width of sheetmetal, the quantity of first solder joint is more than or equal to 1 pair, can overlap between the first solder joint of different pairs, two first solder joints of the same pair dislocation set, all first solder joints all are located the sheetmetal outside the insulating piece coverage area; and the electrode lug corresponding to any one of the electrode shells is fixedly connected with the outer surface of the metal sheet through a second welding point, and the second welding point is positioned on the metal sheet in the coverage area of the insulating sheet. The utility model discloses a welding method and adopt this welded structure's button cell homoenergetic to keep utmost point shell surface intact harmless.

Description

Button cell pole shell and electrode lug seamless welding structure

Technical Field

The utility model relates to a button cell polar shell does not have trace welded structure with electrode tab.

Background

Button cells (button cells) are also called button cells, and refer to cells with the overall dimensions like a small button, generally speaking, the button cells have a larger diameter and a thinner thickness (compared with cylindrical cells such as a cell with a size of 5 AA on the market), the button cells are classified from the aspect of the appearance, and the equivalent corresponding cells are classified into cylindrical cells, square cells, special-shaped cells and the like.

Button cells include both laminate and wound. The basic structure of the winding type button cell is as follows: the button battery comprises a first pole shell, a second pole shell, an insulating seal ring and a battery cell, wherein the upper openings and the lower openings of the first pole shell and the second pole shell are oppositely buckled to form a cylindrical button battery shell; a gap is reserved between the first pole shell and the second pole shell, the gap is filled with an insulating sealing ring to electrically isolate the first pole shell from the second pole shell, and an accommodating cavity is formed among the first pole shell, the second pole shell and the insulating sealing ring; the electric core is located the holding intracavity, electric core include first pole piece, second pole piece and diaphragm, through the diaphragm interval between first pole piece and the second pole piece, first pole piece, second pole piece and diaphragm are convoluteed and are made electric core, and the center of electric core is formed with the axial cavity, is equipped with first output conductor on the first pole piece, and first output conductor stretches out and welds with first polar shell from electric core, is equipped with second output conductor on the second pole piece, and second output conductor stretches out and welds with second polar shell from electric core. When the conventional coiled button battery is manufactured, a first output conductor of a battery core is bent to enable the first output conductor to be tightly attached to the lower surface of the battery core, and the first output conductor extends to the position right below an axial cavity; then vertically arranging the battery cell into the first pole shell; then, the welding needle is vertically inserted downwards into the axial cavity, the first output conductor is tightly pressed on the first shell, and the first output conductor and the first polar shell are welded together in an electric resistance welding mode, or the first polar shell and the first output conductor are welded together in a laser welding mode by emitting laser from the lower part of the first polar shell opposite to the area of the first polar shell, which is vertically overlapped with the first output conductor; welding a second output conductor of the battery cell on a second pole shell, wherein an insulating sealing ring is sleeved outside the second pole shell; and finally, covering the opening at the upper end of the first polar shell together with the second polar shell and the insulating sealing ring, and sealing. One of them polar shell and the output conductor that corresponds and the battery negative pole return circuit that the electric core pole piece that corresponds in first polar shell and the second polar shell constitutes the battery of battery, another polar shell and the output conductor that corresponds and the battery negative pole return circuit that the electric core pole piece that corresponds constitutes the battery, because first output conductor when welding with first polar shell, the electric current of resistance welding and the laser beam of laser welding all can pierce through first polar shell, the solder joint of connecting first polar shell and first output conductor is run through first polar shell setting, the surface smoothness and the stability of first polar shell have been destroyed, in the battery use, electrolyte's weeping and surface swell phenomenons appear easily in the solder joint position of first polar shell.

Disclosure of Invention

An object of the utility model is to provide a button cell utmost point shell and electrode utmost point ear do not have trace welded structure, and this welded structure can keep the utmost point shell surface to level and smooth intact, and then avoids on the utmost point shell solder joint electrolyte weeping and the phenomenon such as surface swell that the brought of breaking.

A button battery pole shell and electrode lug seamless welding structure comprises a pole shell and an electrode lug, wherein the pole shell is cup-shaped, a battery cell is installed in the pole shell, the battery cell is mainly formed by laminating or winding a positive plate, a negative plate and a diaphragm, the positive plate and the negative plate are respectively and electrically connected with the electrode lug, a metal sheet is fixedly arranged on the inner surface of any pole shell through first welding spots, an insulating sheet is arranged between the metal sheet and the pole shell, the width of the insulating sheet is smaller than that of the metal sheet, the number of the first welding spots is not less than 1 pair, the first welding spots of different pairs can be overlapped, the two first welding spots of the same pair are arranged in a staggered manner, and all the first welding spots are positioned on the metal sheet outside a covering area of the insulating sheet; and the electrode lug corresponding to any one of the electrode shells is fixedly connected with the outer surface of the metal sheet through a second welding point, and the second welding point is positioned on the metal sheet in the coverage area of the insulating sheet.

The utility model discloses a button cell utmost point shell and electrode utmost point ear seamless welded structure in first solder joint and the second solder joint all are located the inboard of utmost point shell, the surface of utmost point shell keeps leveling intact, and, form 1 at least right first solder joint between sheetmetal and the utmost point shell, connection stability between sheetmetal and the utmost point shell is better, and simultaneously, solder joint is in large quantity between sheetmetal and the utmost point shell, the internal resistance of welding position is usually less than the internal resistance of physics contact position between utmost point shell and the sheetmetal in view of between utmost point shell and the sheetmetal, consequently, the whole contact internal resistance between utmost point shell and the sheetmetal is littleer, and the contact internal resistance is littleer, it is more favourable to battery discharge.

Preferably, all the first welding points are uniformly distributed around the circumference by taking the center of the polar shell as a circle center. The connection of the metal sheet and the pole shell is the most firm. More preferably, the first welding points of each pair are symmetrically distributed, so that the welding efficiency is higher, and the automatic welding is more facilitated.

Preferably, the battery cell is mainly formed by winding a first pole piece, a second pole piece and a diaphragm, and an axial cavity is formed in the center of the battery cell. Further preferably, the second welding point is located in a vertical projection area of the axial cavity of the battery core on the metal sheet. At the moment, after the battery core is placed in the pole shell, the second welding electrode is inserted into the axial cavity of the battery core to enable the electrode lug to be pressed against the metal sheet for welding, the operation is more convenient, at the moment, the length of the electrode lug does not need to be too long, and the cost is saved. Furthermore, the insulating sheet is located in the end face area of the axial cavity of the battery cell, so that after the battery cell is placed in the electrode shell, when the second welding electrode is inserted into the axial cavity of the battery cell to perform welding operation between the electrode lug and the metal sheet, the second welding point is only located in the insulating sheet covering area of the metal sheet.

Preferably, the insulating sheet is fixedly arranged on the polar shell side of the metal sheet, so that the insulating sheet is better prevented from shifting.

Drawings

Fig. 1 is a schematic view of a welding structure between a pole case and a metal sheet in embodiment 1, wherein the pole case, the metal sheet and an insulating sheet are cross-sectional views;

fig. 2 is a schematic view of a welding structure between an electrode tab and a metal sheet in embodiment 1, wherein a pole shell, the metal sheet and an insulation sheet are cross-sectional views;

FIG. 3 is a top view structural view of a pole case in embodiment 1;

FIG. 4 is a schematic sectional view of a button cell in example 1;

FIG. 5 is a top view structural view of a pole case in embodiment 2;

FIG. 6 is a top view structural view of a pole case in embodiment 3;

FIG. 7 is a schematic sectional view showing a button cell according to example 4;

wherein the reference numeral 50' in fig. 3, 5, 6 indicates the point of the first welding point.

Detailed Description

The embodiments of the present invention will now be described in detail with reference to the accompanying drawings:

example 1

With reference to fig. 1 to 3, a button battery electrode shell and electrode tab seamless welding structure includes an electrode shell 10 and an electrode tab 20, the electrode shell 10 is cup-shaped, an electrical core 30 is installed in the electrode shell 10, the electrical core 30 is mainly formed by laminating or winding a positive plate 31, a negative plate 32 and a diaphragm 33, the positive plate 31 and the negative plate 32 are respectively electrically connected to the electrode tab 20, a metal sheet 40 is fixedly disposed on an inner surface of any one of the electrode shells 10 through a first welding spot 50, an insulating sheet 80 is disposed between the metal sheet 40 and the electrode shell 10, the width of the insulating sheet 80 is smaller than the width of the metal sheet 40, the number of the first welding spots 50 is 1 pair, different pairs of first welding spots 50 can be overlapped, two first welding spots 50 of the same pair are disposed in a staggered manner, and all the first welding spots 50 are located on the metal sheet 40 outside a coverage area of the insulating sheet 80; the electrode tab 20 corresponding to any one of the electrode cases 10 is fixedly connected to the outer surface of the metal sheet 40 by a second welding point 60, and the second welding point 60 is located on the metal sheet 40 in the coverage area of the insulation sheet 80.

The utility model only forms a molten pool and a welding spot at the inner side of the pole shell 10, thereby keeping the complete appearance of the pole shell 10 and avoiding the risk of battery leakage caused by the rupture of the welding spot; and, 1 pair of first solder joints is formed between the metal sheet 40 and the polar shell 10, the connection stability between the metal sheet 40 and the polar shell 10 is better, and meanwhile, the number of the solder joints between the metal sheet 40 and the polar shell 10 is large, so that the contact internal resistance between the metal sheet 40 and the polar shell 10 can be reduced, and the improvement of the discharge performance of the battery is facilitated.

In the button cell electrode shell and electrode tab seamless welding structure of embodiment 1, the electrode shell 10 is a negative electrode shell 12, and the electrode tab 20 electrically connected with the electrode shell correspondingly is a negative electrode tab 22 electrically connected with a negative electrode sheet 32; of course, if the button cell electrode shell and the electrode tab are seamless welding method and welding structure, when the electrode shell 10 is the positive electrode shell 11, the electrode tab 20 electrically connected with the electrode shell correspondingly is the positive electrode tab 21 electrically connected with the positive electrode sheet 31.

As shown in fig. 4, embodiment 1 further provides a button battery, which includes a positive electrode case 11, a negative electrode case 12, an insulating seal ring 70, and a battery cell 30, where the positive electrode case 11 and the negative electrode case 12 are both cup-shaped, and the upper and lower openings of the positive electrode case 11 and the negative electrode case 12 are oppositely buckled to form a cylindrical button battery case; a gap is reserved between the positive electrode shell 11 and the negative electrode shell 12, the insulating sealing ring 70 is filled in the gap to electrically isolate the positive electrode shell 11 from the negative electrode shell 12, and an accommodating cavity is formed among the positive electrode shell 11, the negative electrode shell 12 and the insulating sealing ring 70; the battery cell 30 is arranged in the accommodating cavity, the battery cell 30 is mainly formed by laminating or winding a positive plate 31, a negative plate 32 and a diaphragm 33, the positive plate 31 is electrically connected with a positive pole tab 21, the positive pole tab 21 is electrically connected with the positive shell 11, the negative plate 32 is electrically connected with a negative pole tab 22, and the negative pole tab 22 is electrically connected with the negative shell 12; in the connection structure between the negative electrode shell 12 and the negative electrode tab 22 and the connection structure between the positive electrode shell 11 and the positive electrode tab 21, only the connection structure between the negative electrode shell 12 and the negative electrode tab 22 adopts the button battery electrode shell and electrode tab seamless welding structure of embodiment 1, which is specifically as follows:

the connection structure between the negative electrode shell 12 and the negative electrode tab 22 is as follows: a negative electrode metal sheet 42 is fixedly arranged on the inner surface of the negative electrode shell 12 through a negative electrode first welding point 52, a negative electrode insulation sheet 82 is arranged between the negative electrode metal sheet 42 and the electrode shell 12, the width of the negative electrode insulation sheet 82 is smaller than that of the negative electrode metal sheet 42, the number of the negative electrode first welding points 52 is 1 pair, different pairs of negative electrode first welding points 52 can be overlapped, two negative electrode first welding points 52 of the same pair are arranged in a staggered mode, and all the negative electrode first welding points 52 are positioned on the negative electrode metal sheet 42 outside the coverage area of the negative electrode insulation sheet 82; the negative electrode tab 22 is fixedly connected with the outer surface of the negative electrode metal sheet 42 through a negative electrode second welding point 62, and the negative electrode second welding point 62 is positioned on the negative electrode metal sheet 42 in the coverage area of the negative electrode insulation sheet 82;

the connection structure between the positive electrode shell 11 and the positive electrode tab 21 is as follows: in the inboard of positive pole shell 11, through the resistance welding mode of parallel welding with anodal utmost point ear 21 welding on the internal surface of positive pole shell 11, realize fixed connection through third solder joint 90 between the internal surface of positive pole shell 11 and anodal utmost point ear 21 promptly, the quantity of third solder joint 90 is 1 to, and adjacent third solder joint 90 dislocation set.

Example 2

As shown in fig. 5, embodiment 2 provides a seamless welding structure of a button battery pole shell and an electrode tab, which is different from the welding structure of embodiment 1 in that: the number of the first pads 50 is 2 pairs, and two of the first pads 50 of different pairs overlap, and the rest of the structure is the same as that of embodiment 1.

Example 3

As shown in fig. 6, embodiment 3 provides a seamless welding structure of a button battery pole shell and an electrode tab, which is different from the welding structure of embodiment 1 in that: the number of the first welding points 50 is 3 pairs, and the first welding points 50 of different pairs are not overlapped, and the rest of the structure is the same as that of the embodiment 1.

Example 4

As shown in fig. 7, embodiment 4 provides a button battery, which is different from the button battery of embodiment 1 in that: the connection structure between the negative electrode shell 12 and the negative electrode tab 22 and the connection structure between the positive electrode shell 11 and the positive electrode tab 21 both adopt the button cell pole shell and electrode tab traceless welding structure of embodiment 1, the connection structure between the positive electrode shell 11 and the positive electrode tab 21 is as follows:

the connection structure between the positive electrode shell 11 and the positive electrode tab 21 is as follows: a positive electrode metal sheet 41 is fixedly arranged on the inner surface of the positive electrode shell 11 through a positive electrode first welding point 51, a positive electrode insulation sheet 81 is fixedly arranged on the inner surface of the positive electrode metal sheet 41, the width of the positive electrode insulation sheet 81 is smaller than that of the positive electrode metal sheet 41, the number of the positive electrode first welding points 51 is 1 pair, different pairs of positive electrode first welding points 51 can be overlapped, two positive electrode first welding points 51 of the same pair are arranged in a staggered mode, and all the positive electrode first welding points 51 are positioned outside the coverage area of the positive electrode insulation sheet 81 on the positive electrode metal sheet 41; the positive electrode tab 21 is fixedly connected with the outer surface of the positive electrode metal sheet 81 through a positive electrode second welding point 61, and the positive electrode second welding point 61 is located in the coverage area of the positive electrode insulation sheet 81 on the positive electrode metal sheet 41.

The button cell pole shell and electrode tab traceless welding structure of embodiments 1-3 can be improved as follows:

(1) as shown in fig. 2, 5 and 6, all the first welding points 50 are uniformly distributed around the center of the pole shell 10, and the metal sheet 40 is most firmly connected to the pole shell 10. More preferably, the first welding points 50 of each pair are symmetrically distributed, so that the welding efficiency is higher, and the automatic welding is more facilitated;

(2) as shown in fig. 3, the battery cell 30 is formed by winding a first pole piece 31, a second pole piece 32 and a diaphragm 33, and an axial cavity 34 is formed in the center of the battery cell 30. Further preferably, as shown in fig. 3, the second welding point 60 is located in a vertical projection area of the cell axial cavity 34 on the metal sheet 40. At this time, after the battery cell 30 is placed in the electrode shell 10, the second welding electrode 300 is inserted into the axial cavity 34 of the battery cell to press the electrode tab 20 against the metal sheet 40 for welding, so that the operation is more convenient, and at this time, the length of the electrode tab 20 does not need to be too long, thereby saving the cost. Of course, the second welding spot 60 may also be located on the metal sheet 40 outside the vertical projection area of the cell axial cavity 34, and at this time, it is necessary to weld the electrode tab 20 on the metal sheet 40 before the cell 30 is installed in the pole casing 10, and then turn the cell 30 into the pole casing 10. Further, as shown in fig. 3, the insulation sheet 80 is located in the end surface area of the axial cavity 34 of the battery cell, so as to ensure that the second welding point 60 is only within the coverage area of the insulation sheet 80 on the metal sheet 40 when the electrode tab 20 is pressed against the metal sheet 40 for welding by inserting the second welding electrode 300 into the axial cavity 34 of the battery cell after the battery cell 30 is placed in the electrode shell 10.

The button cells of example 1 and example 4 were modified as follows: as shown in fig. 4 and 7, the connecting structure between the negative casing and the negative electrode tab adopts the button battery electrode casing and electrode tab traceless welding structure. Because the negative electrode shell 12 is mostly used as a bottom shell and the positive electrode shell 11 is mostly used as a top shell in the existing manufacturing process of the button battery, the battery cell 30 is firstly installed in the bottom shell, and then the top shell is arranged corresponding to the cover to assemble the battery, so that the operability is stronger by adopting the seamless welding structure of the button battery pole shell and the electrode pole ear between the negative electrode shell 12 and the negative pole ear 22.

The button cell of example 1 can be further modified as follows: as shown in fig. 4, the battery cell 30 is mainly formed by winding the first pole piece 31, the second pole piece 32 and the diaphragm 33, an axial cavity 34 is formed in the center of the battery cell 30, and the third welding point 90 is located outside a coverage area of the axial cavity 34 of the battery cell of the pole casing 11.

With reference to fig. 1 to 3, the present invention provides a button battery electrode shell and electrode tab seamless welding structure of embodiments 1 to 3, which comprises the following steps:

s1: firstly, laying a metal sheet 40 on the inner surface of a cup-shaped pole shell 10, arranging an insulating sheet 80 between the metal sheet 40 and the pole shell, wherein the width D of the insulating sheet 80 is less than the width D' of the metal sheet 40;

s2: then preparing a first resistance welding device, wherein the first resistance welding device comprises two first welding electrodes (100 and 200), the two first welding electrodes (100 and 200) are respectively pressed against different positions on the outer surface of the metal sheet 40, the contact positions of the two first welding electrodes (100 and 200) and the metal sheet 40 are both positioned on the metal sheet 40 outside the coverage area of the insulating sheet 80, then the two first welding electrodes (100 and 200) are electrified to realize the welding and fixing connection of the pole shell 10 and the metal sheet 40, the welding of the step S2 is continuously carried out for more than 1 time, at least 1 pair of first welding points 50 can be formed between the pole shell 10 and the metal sheet 40, and the welding positions of the metal sheet 40 and the pole shell 10 can be overlapped in the step S2 in different times;

s3: then pressing the electrode tab 20 on the outer surface of the metal sheet 10, and preparing a second resistance welding device, wherein the second resistance welding device comprises two second welding electrodes (300, 400), one second welding electrode 400 is a cylindrical electrode, the opening of the electrode shell 10 is upwards placed on the cylindrical electrode 400, the cylindrical electrode 400 is in surface contact with the outer surface of the electrode shell 10, the outer contour line 400 'of the coverage area of the cylindrical electrode 400 on the metal sheet 40 is positioned outside the outer contour line 80' of the coverage area of the cylindrical electrode 80, the other second welding electrode 300 is pressed on the outer surface of the electrode tab 20 on the inner side of the electrode shell, and the pressing position of the second welding electrode 300 is positioned on the metal sheet in the coverage area of the insulating sheet 80; the two second welding electrodes (300, 400) are then energized to form a second weld point 60 between the electrode tab 20 and the metal sheet 40. The outer contour line 400' of the coverage area of the columnar electrode 400 on the metal sheet 40 refers to the outer contour line of the vertical projection area of the columnar electrode 400 on the metal sheet 40; the outer contour line 80' of the area covered by the insulating sheet 80 on the metal sheet 40 refers to the outer contour line of the perpendicular projected area of the insulating sheet 80 on the metal sheet 40.

The utility model discloses a lay the sheetmetal at the polar shell internal surface, and through with these two first welding electrodes roof pressure respectively in the different positions on the surface of sheetmetal, through the resistance welding mode of parallel welding, realize the welded fastening between sheetmetal and the polar shell, because can form the annular welding electric current channel between two first welding electrodes, make welding electric current can not run through the polar shell, only can form solder joint molten bath and first solder joint in the polar shell inboard; meanwhile, the insulating sheet is arranged between the metal sheet and the electrode shell, so that annular welding current is formed on the metal sheet side of the insulating sheet by the two second welding electrodes, a second welding point is formed on the outer side of the metal sheet corresponding to the covering area of the insulating sheet, or the welding current of the second resistance welding equipment bypasses the insulating sheet and penetrates through the first welding point to realize current connection between the electrode shell and the metal sheet, and at the moment, because the resistance at the first welding point is lower, resistance heat is not easy to generate and a new molten pool is not easy to form, and resistance heat can be generated at the connecting position of the electrode lug and the metal sheet and a new molten pool and a welding point (namely, the second welding point) are formed; therefore, the utility model discloses a welding method can keep the utmost point shell outward appearance complete, stops to lead to the fact the risk of battery weeping because of the welding point breaks.

It should be noted that, when one of the connection structure between the positive electrode shell 11 and the positive electrode tab 21 and the connection structure between the negative electrode shell 12 and the negative electrode tab 22 adopts the button cell electrode shell and electrode tab seamless welding structure, the other connection structure may be that the electrode tab is welded on the metal sheet first, and then the metal sheet is fixed on the inner surface of the corresponding electrode shell by the parallel welding resistance welding method or the conductive adhesive coating method, or the electrode tab is directly fixed on the inner surface of the corresponding electrode shell by the parallel welding resistance welding method or the conductive adhesive coating method, and the like. The structure of the battery cell 30 of the present invention is not limited to the specific structure shown in the drawings, and may be any battery cell structure.

Claims

1. Button cell polar shell and electrode utmost point ear no trace welded structure, including polar shell and electrode utmost point ear, the polar shell is the cup, installs electric core in the polar shell, electric core mainly stacks or convolutes by positive plate, negative pole piece, diaphragm laminarity and forms, just, the negative pole piece is equallyd divide and is do not connected its characterized in that with an electrode utmost point ear electricity: the metal sheet is fixedly arranged on the inner surface of any one polar shell through first welding spots, an insulating sheet is arranged between the metal sheet and the polar shell, the width of the insulating sheet is smaller than that of the metal sheet, the number of the first welding spots is more than or equal to 1 pair, the first welding spots of different pairs can be overlapped, the two first welding spots of the same pair are arranged in a staggered manner, and all the first welding spots are positioned on the metal sheet outside the covering area of the insulating sheet; and the electrode lug corresponding to any one of the electrode shells is fixedly connected with the outer surface of the metal sheet through a second welding point, and the second welding point is positioned on the metal sheet in the coverage area of the insulating sheet.

2. The button cell pole shell and electrode tab seamless welding structure of claim 1, characterized in that: all the first welding points are uniformly distributed around the circumference by taking the center of the polar shell as a circle center.

3. The button cell pole shell and electrode tab seamless welding structure of claim 2, characterized in that: the first welding points of each pair are symmetrically distributed.

4. The button cell pole shell and electrode tab seamless welding structure of claim 1, characterized in that: the battery cell is mainly formed by winding a first pole piece, a second pole piece and a diaphragm, and an axial cavity is formed in the center of the battery cell.

5. The button cell pole shell and electrode tab seamless welding structure of claim 4, characterized in that: the second welding spot is positioned in the vertical projection area of the axial cavity of the battery core on the metal sheet.

6. The button cell pole shell and electrode tab seamless welding structure of claim 5, characterized in that: the insulating sheet is located in the end face area of the axial cavity of the battery core.

7. The button cell pole shell and electrode tab seamless welding structure of claim 1, characterized in that: the insulating sheet is fixedly arranged on the polar shell side of the metal sheet.