Heat dissipation device for aircraft battery

Abstract

The invention discloses a heat dissipation device for an aircraft battery, and belongs to the technical field of aircraft batteries. Battery cells are distributed in a box body, air cooling parts are distributed on the outer side of the box body, the battery cells are connected with a phase change vapor chamber, the phase change vapor chamber is connected with the box body, and the box body is composed of an upper shell, a lower shell and a limiting female die; the upper shell and the lower shell are connected and fixed through a fastener, the limiting female die is installed at the bottom of the lower shell, the air cooling piece is composed of heat conduction fins and reinforcing ribs, the heat conduction fins and the reinforcing ribs are arranged on the outer surface of the lower shell, the battery cell makes contact with the surface of the phase change vapor chamber, the phase change vapor chamber and the battery cell are bent in a matched mode, and the surface of the battery cell and the surface of the phase change vapor chamber are attached to each other. The box body comprises a heat conduction interface material and a heat conduction block, the heat conduction block is embedded into the inner surface of the lower shell, and the two ends of the phase change soaking plate are fixedly connected with the heat conduction block through the heat conduction interface material.

Description

Technical Field

[0001] The invention relates to a heat dissipation device for aircraft batteries, belonging to the technical field of aircraft batteries. Background Art

[0002] In recent years, the development prospects of electric vertical take-off and landing vehicles (eVTOL) have been widely optimistic.

[0003] For example, an electric vertical take-off aircraft disclosed in publication number: CN218113004U includes a fuselage and at least two power components, arms are arranged on both sides of the fuselage, and the at least two power components are respectively installed on the arms on both sides of the fuselage to provide power for the electric vertical take-off aircraft to fly, each power component includes at least one heat generating device, and the electric vertical take-off aircraft also includes: at least one heat dissipation system for cooling the heat generating device; the heat dissipation system includes: an equipment cabin and an air cooling channel, the equipment cabin is arranged in the arm, and the air cooling channel is arranged on the arm, wherein the arm is provided with an air inlet connected to the air cooling channel, and the cooling air flow enters the air cooling channel from the air inlet during the flight of the electric vertical take-off aircraft, directly or indirectly provides cooling for the heat generating device in the equipment cabin, which can improve the problem of poor heat dissipation of the fuselage of the electric vertical take-off aircraft in the prior art and the heavy weight of the fuselage that is completely liquid cooled.

[0004] Electric aircraft can not only provide three-dimensional and convenient urban air travel services and alleviate traffic congestion, but also reduce pollution and promote the prosperity of the low-altitude economy. However, the potential high risk of aerial operations makes the safety assessment standards for electric aircraft very strict. The safety of electric aircraft batteries is the core of the safety of the entire machine. During the takeoff and landing process of electric aircraft, the extremely high power demand requires the battery to discharge at an ultra-high rate of 10C or above, which in turn generates huge heat. If the heat cannot be discharged in time, it will pose a serious threat to the battery cycle life and even flight safety.

[0005] Based on the above-mentioned deficiencies, therefore, there is a need for a heat dissipation device for aircraft batteries to improve the above-mentioned deficiencies. Summary of the invention

[0006] The main purpose of the present invention is to provide a heat dissipation device for aircraft batteries.

[0007] The purpose of the present invention can be achieved by adopting the following technical solutions:

[0008] A heat dissipation device for aircraft batteries, comprising a box for placing the batteries;

[0009] Battery cells are distributed in the box, air cooling parts are distributed on the outside of the box, the battery cells are connected to the phase change heat spreader, and the phase change heat spreader is connected to the box.

[0010] Preferably, the box body is composed of an upper shell, a lower shell and a limiting female die;

[0011] The upper shell and the lower shell are fixedly connected by fasteners, and the limiting female die is installed at the bottom of the lower shell.

[0012] Preferably, the air-cooling component is composed of heat-conducting fins and reinforcing ribs;

[0013] The heat-conducting fins and the reinforcing ribs are arranged on the outer surface of the lower shell.

[0014] Preferably, the battery cell and the phase-change heat spreader are in surface contact, the phase-change heat spreader is bent in cooperation with the battery cell, and the surfaces of the battery cell and the phase-change heat spreader are mutually attached.

[0015] Preferably, the box body includes a thermal interface material and a heat-conducting block;

[0016] The heat-conducting block is embedded in the inner surface of the lower shell, and the thermal interface materials at both ends of the phase-change heat spreader are fixedly connected to the heat-conducting block.

[0017] Preferably, the box body includes a buffer gasket, and the buffer gasket is placed between the lower shell and the limiting female die.

[0018] Preferably, the lower ends of the battery cell and the phase-change heat spreader are placed in the groove of the limiting female die.

[0019] Preferably, the shapes of the flow guiding fins and the reinforcing ribs include rectangle, circle, spiral, corrugation, serration or needle shape, and the materials of the flow guiding fins and the reinforcing ribs include aluminum alloy, stainless steel or titanium alloy.

[0020] Preferably, the phase-change heat spreader is either in single-sided or double-sided contact with the battery cell, and the phase-change heat spreader is either arranged between every two battery cells or arranged between battery packs composed of two or more battery cells.

[0021] Preferably, the heat-conducting block includes a high heat-conducting metal, a phase-change material, a heat spreader or a heat pipe, the shape of the heat-conducting block includes I-shaped, L-shaped or U-shaped, the heat-conducting block is simultaneously embedded in at least two adjacent inner surfaces of the lower shell, the battery cell includes a soft-pack battery, a cylindrical battery or a square-shell battery, and the material of the phase-change heat spreader includes copper, aluminum and its alloys, stainless steel or polymer.

[0022] The beneficial technical effects of the present invention:

[0023] A heat dissipation device for an aircraft battery provided by the present invention,

[0024] 1) When the electric aircraft battery is working, the phase-change heat spreader quickly transfers the heat generated by the battery cell to both sides, and the heat is transferred to the outer shell of the box body through the thermal interface material and the heat-conducting block. The heat-conducting block with high thermal conductivity can quickly diffuse the heat and guide it to the flow guiding fins and the reinforcing ribs on the outer shell, forming a heat path with high heat conduction efficiency;

[0025] 2) The diversion fins and the reinforcing ribs both increase the heat exchange area of the housing. The diversion fins can better guide the airflow to fully contact the housing, thereby improving the convective heat exchange efficiency between the housing and the air and achieving efficient heat dissipation.

[0026] At the same time, the diversion fins and the reinforcing ribs can also improve the strength and rigidity of the housing to a certain extent, providing effective protection for the battery cells against puncture.

[0027] 3) The heat conduction block can not only accelerate the diffusion of heat inside the housing but also build a high - heat - conduction channel to enhance the heat conduction efficiency on different surfaces of the housing, enabling the heat to be quickly evenly distributed throughout the housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 FIG. 14 is an external structure diagram of Embodiment 1 of a preferred embodiment of a heat dissipation device for an aircraft battery according to the present invention;

[0029] Figure 2 FIG. 18 is a partial detailed view of Embodiment 1 of a preferred embodiment of a heat dissipation device for an aircraft battery according to the present invention;

[0030] Figure 3 FIG. 22 is a top - view sectional view of Embodiment 1 of a preferred embodiment of a heat dissipation device for an aircraft battery according to the present invention;

[0031] Figure 4 FIG. 26 is a side - view sectional view of Embodiment 1 of a preferred embodiment of a heat dissipation device for an aircraft battery according to the present invention;

[0032] Figure 5 FIG. 30 is a front - view sectional view of Embodiment 2 of a preferred embodiment of a heat dissipation device for an aircraft battery according to the present invention;

[0033] Figure 6 FIG. 34 is an external structure diagram of Embodiment 2 of a preferred embodiment of a heat dissipation device for an aircraft battery according to the present invention.

[0034] In the figures: 1, box body; 2, air - cooling component; 3, battery cell; 4, phase - change heat - spreading plate; 5, thermal interface material; 6, heat conduction block; 7, buffer gasket; 11, upper housing; 12, lower housing; 13, limiting concave die; 21, diversion fin; 22, reinforcing rib. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the technical solutions of the present invention clearer and more definite for those skilled in the art, the present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings. However, the embodiments of the present invention are not limited thereto.

[0036] AsFigure 1 - Figure 6 As shown in Figure 6 , a heat dissipation device for an aircraft battery provided in this embodiment includes a box body 1 for placing the battery;

[0037] The battery cells 3 are distributed inside the box body 1, the air-cooling component 2 is distributed outside the box body 1, the battery cells 3 are connected to the phase change heat spreader 4, and the phase change heat spreader 4 is connected to the box body 1.

[0038] The box body 1 is composed of an upper shell 11, a lower shell 12 and a limiting die 13;

[0039] The upper shell 11 and the lower shell 12 are fixedly connected by fasteners, and the limiting die 13 is installed at the bottom of the lower shell 12.

[0040] The air-cooling component 2 is composed of heat-conducting fins 21 and reinforcing ribs 22;

[0041] The heat-conducting fins 21 and the reinforcing ribs 22 are arranged on the outer surface of the lower shell 12.

[0042] The surfaces of the battery cells 3 and the phase change heat spreader 4 are in surface contact, the phase change heat spreader 4 is bent in cooperation with the battery cells 3, and the surfaces of the battery cells 3 and the phase change heat spreader 4 are mutually attached.

[0043] The box body 1 includes a thermal interface material 5 and a heat-conducting block 6;

[0044] The heat-conducting block 6 is embedded in the inner surface of the lower shell 12, and the thermal interface materials 5 at both ends of the phase change heat spreader 4 are fixedly connected to the heat-conducting block 6.

[0045] The box body 1 includes a buffer gasket 7, and the buffer gasket 7 is placed between the lower shell 12 and the limiting die 13.

[0046] The lower ends of the battery cells 3 and the phase change heat spreader 4 are placed in the groove of the limiting die 13.

[0047] The shapes of the heat-conducting fins 21 and the reinforcing ribs 22 include rectangle, circle, spiral, corrugation, serration or needle shape, and the materials of the heat-conducting fins 21 and the reinforcing ribs 22 include aluminum alloy, stainless steel or titanium alloy.

[0048] The phase change heat spreader 4 is either in single-sided or double-sided contact with the battery cells 3, and the phase change heat spreader 4 is either arranged between every two battery cells 3 or arranged between battery packs composed of two or more battery cells 3.

[0049] The heat-conducting block 23 includes high-thermal-conductivity metal, phase change material, heat spreader or heat pipe, the shape of the heat-conducting block 23 includes I-shaped, L-shaped or U-shaped, the heat-conducting block 23 is simultaneously embedded in at least two adjacent inner surfaces of the lower shell 2, the battery cells 3 include soft-pack batteries, cylindrical batteries or square-shell batteries, and the material of the phase change heat spreader 4 includes copper, aluminum and its alloys, stainless steel or polymer.

[0050] As Figure 1 - Figure 6 shown, the working process of a heat dissipation device for an aircraft battery provided in this embodiment is as follows:

[0051] Step 1: By means of machining, heat conduction grooves are formed on the inner surface around the lower housing 2. The heat conduction blocks 6 are embedded in the heat conduction grooves of the lower housing 12 by welding. Each heat conduction block 6 communicates with a group of adjacent mutually perpendicular wall surfaces. The heat conduction block 6 refers to a material or device with super heat conduction performance, which can be graphene, metal, phase change material, heat pipe, etc. In this embodiment, please refer to Figure 2 and Figure 3 . Four L-shaped heat conduction blocks 6 are arranged in the heat dissipation device to construct four high heat conduction paths, so as to realize the rapid transfer of heat from the front and rear wall surfaces of the lower housing in contact with both ends of the heat pipe to the left and right wall surfaces, and then make full use of each wall surface of the box body for heat dissipation;

[0052] Step 2: The inside of the box body also includes a battery cell 3, a phase change heat pipe 4, a thermal interface material 5 and a buffer gasket 7. The surface of the battery cell 3 is in contact with the surface of the phase change heat pipe 4, and the lower ends of both are inserted into the limit concave die 13, so that the two are closely attached and fixed to each other. The battery cell 3 can be a cylindrical battery cell, a soft-pack battery cell, a square shell battery cell, etc. The shape of the phase change heat pipe 4 matches the shape of the battery cell 4. When a soft-pack battery cell or a square shell battery cell is adopted, the phase change heat pipe 4 is designed into a flat plate shape to fit with the battery cell 3. At this time, the ratio of the surface area of the phase change heat pipe 4 to the surface area of the battery cell 3 is 0.8-1.2;

[0053] Step 3: The battery cell 3 is a cylindrical battery cell, the thermal interface material 5 is a thermal double-sided adhesive, and the phase change heat pipe 4 is designed into an S shape to closely fit with the side surface of the cylindrical battery. The contact area between the S-shaped heat pipe and the cylindrical battery accounts for 20%-50% of the side surface area of the cylindrical battery. The two sides of the phase change heat pipe 4 are bent 90 degrees to be fixedly bonded to the heat conduction block 6 through the thermal double-sided adhesive, and the remaining gaps are filled with thermal adhesive to reduce the contact thermal resistance. The contact area between the phase change heat pipe 4 and the heat conduction block 6 accounts for 10%-50% of the surface area of the heat conduction block 6. The bottom of the limit concave die 13 is adhered with a buffer gasket 7, and the buffer gasket 7 is fixed on the inner wall surface of the bottom of the lower housing, which can reduce the vibration impact on the battery cell during flight bumps;

[0054] Step 4: The heat generated by the battery cell 3 is transferred to the wall surfaces around the lower housing 12 through the phase change heat pipe 4, the thermal double-sided adhesive and the heat conduction block 6. The box body 1 can fully receive the strong air flow generated during the flight of the aircraft, and export the heat through convective heat transfer with the air. At the same time, the convective heat transfer effect is enhanced by means of the guide fins 21 and the reinforcing ribs 22 structure, so as to improve the overall heat transfer efficiency on the premise of ensuring good sealing and good mechanical strength of the box body, so as to realize the efficient thermal management of the aircraft battery cell;

[0055] Step 5: The heat conduction block 6 is an aluminum heat pipe, and it is integrated into the lower housing 12, that is, the aluminum heat pipe is directly used as a component material of the lower housing 12, greatly improving the thermal conductivity of the housing, so that the lower housing 12 not only has the functions of support, protection and sealing, but also has strong heat conduction performance. A number of reinforcing ribs 22 are arranged at equal intervals on the surface of the lower housing 12 to improve the mechanical strength of the housing. At the same time, staggered prism fins are used as the flow guiding fins 21 to improve the convective heat transfer capacity of the housing;

[0056] The battery cells 3 and the phase change heat pipe 4 used in this device are a soft-pack battery cell and an L-shaped heat pipe respectively. The two main surfaces of each soft-pack battery cell are closely attached to the larger surfaces of two L-shaped heat pipes to form a small battery cell module.

[0057] Embodiment 1

[0058] As Figure 1 - Figure 4 shown, the present invention provides a heat dissipation device for an aircraft battery. This device can use the phase change heat pipe, the heat conduction block, the flow guiding fins and the reinforcing ribs to build multiple high heat conduction channels, and quickly export the heat generated by the battery cells to the outside;

[0059] The heat dissipation device includes a box body 1, an air cooling component 2, battery cells 3, a phase change heat pipe 4, a thermal interface material 5, a heat conduction block 6 and a buffer gasket 7;

[0060] The box body 1 includes an upper housing 11, a lower housing 12 and a limit die 13. The upper housing 1 is fixedly connected to the lower housing 2 by bolts to form a box body. The air cooling component 2 includes flow guiding fins 21 and reinforcing ribs 22;

[0061] By means of machining, the flow guiding fins 21 and the reinforcing ribs 22 are formed on the outer surface around the lower housing 2 in an alternating distribution;

[0062] The main function of the flow guiding fins 21 is to increase the specific surface area of the box body so as to increase the heat dissipation area, and a flow guiding structure is designed according to the actual working conditions to guide the air flow to fully contact with the box body. At the same time, it can also improve the mechanical strength of the box body to a certain extent. The main function of the reinforcing ribs 22 is to improve the mechanical strength of the box body, and it can also increase the heat dissipation area;

[0063] Therefore, the functions of the flow guiding fins 21 and the reinforcing ribs 22 have some overlap. When designing the structure, it is not necessary to strictly distinguish between the two. A structure can be designed to take into account both the functions of enhancing heat dissipation and improving strength. The shapes of the flow guiding fins 21 and the reinforcing ribs 22 can be rectangular, circular, spiral, corrugated, serrated and needle-shaped;

[0064] The processing methods of the flow guiding fins 21 and the reinforcing ribs 22 can be stamping, extrusion, forging and rolling, etc.;

[0065] The width ratio of the flow guiding fin 21 to the reinforcing rib 22 is 1 to 10; the surface area ratio of the flow guiding fin 21 to the surface area of the box body is 2 to 10;

[0066] In this embodiment, please refer to Figure 1 , the triangular flow guiding fins and the prismatic reinforcing ribs are prepared by stamping;

[0067] In addition, heat conduction grooves are formed on the inner surface around the lower shell 2 by machining, and the heat conduction blocks 6 are embedded in the heat conduction grooves of the lower shell 12 by welding. Each heat conduction block 6 communicates with a group of adjacent perpendicular wall surfaces. The heat conduction block 6 refers to a material or device with super heat conduction performance, which can be graphene, metal, phase change material, heat pipe and heat pipe. In this embodiment, please refer to Figure 2 and Figure 3 , four L-shaped heat conduction blocks 6 are arranged in the heat dissipation device to construct four high heat conduction paths, so as to realize the rapid transfer of heat from the front and rear wall surfaces of the lower shell in contact with both ends of the heat pipe to the left and right wall surfaces, and then make full use of each wall surface of the box body for heat dissipation;

[0068] The inside of the box body also includes a battery cell 3, a phase change heat pipe 4, a thermal interface material 5 and a buffer gasket 7. The surface of the battery cell 3 is in contact with the surface of the phase change heat pipe 4, and the lower ends of the two are inserted into the limiting concave die 13, so that the two are closely attached and fixed to each other. The battery cell 3 can be a cylindrical battery cell, a soft package battery cell, a square shell battery cell, etc. The shape of the phase change heat pipe 4 matches the shape of the battery cell 4. When a soft package battery cell or a square shell battery cell is adopted, the phase change heat pipe 4 is designed into a flat shape to fit with the battery cell 3. At this time, the surface area ratio of the phase change heat pipe 4 to the surface area of the battery cell 3 is 0.8 to 1.2;

[0069] In this embodiment, please refer to Figure 3 and Figure 4 , the battery cell 3 is a cylindrical battery cell, the thermal interface material 5 is a thermal double-sided adhesive, the phase change heat pipe 4 is designed into an S shape to closely fit with the side surface of the cylindrical battery. The contact area between the S-shaped heat pipe and the cylindrical battery accounts for 20% to 50% of the side surface area of the cylindrical battery. The two sides of the phase change heat pipe 4 are bent 90 degrees to be fixedly bonded with the heat conduction block 6 through the thermal double-sided adhesive, and the remaining gaps are filled with thermal adhesive, so as to reduce the contact thermal resistance;

[0070] The contact area between the phase change heat pipe 4 and the heat conduction block 6 accounts for 10% to 50% of the surface area of the heat conduction block 6. The bottom of the limiting concave die 13 is adhered with a buffer gasket 7, and the buffer gasket 7 is fixed on the inner wall surface of the bottom of the lower shell, which can reduce the vibration impact on the battery cell during flight bumps;

[0071] The heat generated by the battery cell 3 is transferred to the wall surface around the lower housing 12 via the phase change heat spreader 4, the thermally conductive double-sided tape, and the heat conducting block 6. The box body 1 can fully receive the strong airflow generated during the flight of the aircraft, and export the heat through convective heat exchange with the air. At the same time, the convective heat exchange effect is enhanced by means of the flow guiding fins 21 and the reinforcing ribs 22. Thus, on the premise of ensuring good sealing and mechanical strength of the box body, the overall heat exchange efficiency is improved, so as to realize the efficient thermal management of the aircraft battery cells.

[0072] Embodiment 2

[0073] As Figure 5 - Figure 6 As shown, the heat conducting block 6 in this embodiment is an aluminum heat spreader, which is integrated into the lower housing 12, that is, an aluminum heat spreader is directly used as the component material of the lower housing 12, greatly improving the thermal conductivity of the housing. The lower housing 12 not only has the functions of support, protection and sealing, but also has strong heat conducting performance. A number of reinforcing ribs 22 are arranged at equal intervals on the surface of the lower housing 12 to enhance the mechanical strength of the housing. At the same time, staggered prism fins are used as the flow guiding fins 21 to improve the convective heat exchange capacity of the housing;

[0074] The battery cell 3 and the phase change heat spreader 4 used in this device are a soft-pack battery cell and an L-shaped heat spreader respectively. The two main surfaces of each soft-pack battery cell are closely attached to the larger surfaces of two L-shaped heat spreaders to form a small battery cell module;

[0075] In this embodiment, EVA foam is used as the limiting female die 13 to separate each small battery cell module. The EVA foam is arranged between every two small battery cell modules, and its main functions are heat insulation, buffering and shock absorption;

[0076] In this embodiment, the thermal interface material 5 is thermal grease. The smaller surface of the L-shaped heat spreader is connected to the lower housing 12 with high thermal conductivity through thermal grease, forming a low thermal resistance heat conduction path, which is conducive to quickly exporting the heat to the external environment.

[0077] The above are only further embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, all belong to the protection scope of the present invention.

Claims

1. A heat dissipation device for aircraft batteries, characterized in that: It comprises a box (1) for placing batteries; The battery core (3) is distributed in the box (1), the air cooling component (2) is distributed outside the box (1), the battery core (3) is connected to the phase change heat spreader (4), and the phase change heat spreader (4) is connected to the box (1).

2. A heat dissipation device for aircraft batteries according to claim 1, characterized in that: The box body (1) is composed of an upper shell (11), a lower shell (12) and a limiting die (13); The upper shell (11) and the lower shell (12) are connected and fixed by fasteners, and the limiting die (13) is installed on the bottom of the lower shell (12).

3. A heat dissipation device for aircraft batteries according to claim 2, characterized in that: The air cooling part (2) is composed of heat-conducting fins (21) and reinforcing ribs (22); The heat-conducting fins (21) and the reinforcing ribs (22) are arranged on the outer surface of the lower shell (12).

4. A heat dissipation device for aircraft batteries according to claim 3, characterized in that: The battery core (3) and the phase change heat spreader (4) are in contact with each other on the surface, the phase change heat spreader (4) and the battery core (3) are bent in coordination, and the surfaces of the battery core (3) and the phase change heat spreader (4) are bonded to each other.

5. A heat dissipation device for aircraft batteries according to claim 4, characterized in that: The box body (1) comprises a thermal interface material (5) and a thermal conductive block (6); The heat conducting block (6) is embedded in the inner surface of the lower shell (12), and the heat conducting interface material (5) at both ends of the phase change heat spreader (4) and the heat conducting block (6) are fixedly connected to each other.

6. A heat dissipation device for aircraft batteries according to claim 5, characterized in that: The box body (1) comprises a buffer gasket (7), and the buffer gasket (7) is placed between the lower shell body (12) and the limiting concave mold (13).

7. A heat dissipation device for aircraft batteries according to claim 6, characterized in that: The lower ends of the battery core (3) and the phase change heat spreader (4) are placed in the groove of the limiting concave mold (13).

8. The heat dissipation device for aircraft batteries according to claim 7, characterized in that: The shapes of the guide fins (21) and the reinforcing ribs (22) include rectangular, circular, spiral, corrugated, sawtooth or needle-shaped shapes, and the materials of the guide fins (21) and the reinforcing ribs (22) include aluminum alloy, stainless steel or titanium alloy.

9. A heat dissipation device for aircraft batteries according to claim 8, characterized in that: The phase change heat spreader (4) is laminated to one side or both sides of the battery cell (3), and the phase change heat spreader (4) is arranged between every two battery cells (3) or between battery packs consisting of two or more battery cells (3).

10. A heat dissipation device for aircraft batteries according to claim 9, characterized in that: The heat conducting block (23) comprises a high heat conducting metal, a phase change material, a heat spreader or a heat pipe. The shape of the heat conducting block (23) comprises an I-type, an L-type or a U-type. The heat conducting block (23) is embedded in at least two adjacent inner surfaces of the lower shell (2) at the same time. The battery cell (3) comprises a soft-pack battery, a cylindrical battery or a square-shell battery. The material of the phase change heat spreader (4) comprises copper, aluminum and its alloy, stainless steel or a high molecular polymer.

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