A fuel cell bipolar plate structure

Abstract

The application provides a fuel cell bipolar plate structure, which comprises an anode plate and a cathode plate arranged in close contact; a plurality of anode recesses are arranged in the middle part of the anode plate, a plurality of cathode recesses are arranged in the middle part of the cathode plate, the cross-sectional area of the anode recesses is smaller than that of the cathode recesses; the cross-sectional shape of the anode recesses and the cross-sectional shape of the cathode recesses are both trapezoidal or wavy; the anode recesses and the cathode recesses are connected one by one and enclose a cooling water flow channel; hydrogen gas flow channels are formed between two adjacent anode recesses; oxygen gas flow channels are formed between two adjacent cathode recesses; and the cross-sectional area of the hydrogen gas flow channels is smaller than that of the oxygen gas flow channels. The cross-sectional area of the hydrogen gas flow channels is smaller than that of the oxygen gas flow channels, so that the electrochemical reaction is more sufficient under the premise of ensuring the uniform flow of the gas, and the performance of the fuel cell is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cells, in particular to a fuel cell bipolar plate structure. BACKGROUND

[0002] Hydrogen energy has many advantages such as clean and high efficiency, and is paid more and more attention by more and more people, and has been commercialized in many technical fields. The polar plate plays a role in distributing fuel gas, collecting current, supporting and other functions in the hydrogen fuel cell, and is one of the important components that determine the volume / weight power density, life and other performances of the fuel cell.

[0003] At present, in the field of fuel cell metal polar plate design, some enterprises and scholars have put forward some novel ideas. For example, Chinese patent CN2019207979251 proposes a bipolar plate with a partition plate, which can greatly improve the uniformity of cooling water distribution; Chinese patent application CN2018116115696 proposes a metal bipolar plate with good sealing performance, which can greatly improve the sealing performance of the polar plate. However, although the bipolar plates in the above prior art have different structures, the flow channel structure of the anode plate and the flow channel structure of the cathode plate have the same size, so that the hydrogen gas and oxygen gas have the same inlet amount, which is difficult to meet the requirements of the amount of oxygen and hydrogen in the electrochemical reaction. The required amount of hydrogen and the required amount of oxygen in the electrochemical reaction process are different, and the electrochemical reaction of the bipolar plate is insufficient due to the same inlet amount of hydrogen and oxygen, which reduces the utilization rate of hydrogen and oxygen and leads to the performance decline of the fuel cell. SUMMARY

[0004] Therefore, the present application provides a fuel cell bipolar plate structure, which aims to solve the problem that the flow channel structure of the anode plate and the flow channel structure of the cathode plate in the existing bipolar plate have the same size, so that the hydrogen gas and oxygen gas have the same inlet amount, which leads to insufficient electrochemical reaction of the bipolar plate, reduces the utilization rate of hydrogen and oxygen, and leads to performance decline of the fuel cell.

[0005] To achieve the above purpose, the present application provides the following technical scheme:

[0006] A fuel cell bipolar plate structure, comprising an anode plate and a cathode plate arranged in close contact.

[0007] The middle part of the anode plate is provided with a plurality of anode recesses; the middle part of the cathode plate is provided with a plurality of cathode recesses, and the cross-sectional area of the anode recess is smaller than the cross-sectional area of the cathode recess; the cross-sectional shape of the anode recess and the cross-sectional shape of the cathode recess are both trapezoidal or wavy.

[0008] The anode recesses and the cathode recesses are connected one by one and form a cooling water flow channel; a hydrogen gas flow channel is formed between two adjacent anode recesses; an oxygen gas flow channel is formed between two adjacent cathode recesses; the cross-sectional area of the hydrogen gas flow channel is smaller than that of the oxygen gas flow channel.

[0009] Further, the adjacent anode recesses and hydrogen gas flow channels, and the adjacent cathode recesses and oxygen gas flow channels form a concave-convex structure; the anode recesses and the cathode recesses are recesses formed by pressing.

[0010] Further, the width of the bottom of the hydrogen gas flow channel is equal to that of the oxygen gas flow channel; the depth of the hydrogen gas flow channel is smaller than that of the oxygen gas flow channel.

[0011] Further, when the cross sections of the anode recesses and the cathode recesses are both trapezoidal, the ratio of the depth of the hydrogen gas flow channel to that of the oxygen gas flow channel is 1:(1.5-2).

[0012] Further, the depth of the hydrogen gas flow channel is 0.2mm-0.4mm; the depth of the oxygen gas flow channel is 0.3mm-0.8mm.

[0013] Further, when the cross sections of the anode recesses and the cathode recesses are both wavy, the ratio of the depth of the hydrogen gas flow channel to that of the oxygen gas flow channel is 1:2.

[0014] Further, the depth of the hydrogen gas flow channel is 0.25mm-0.45mm; the depth of the oxygen gas flow channel is 0.5mm-0.9mm.

[0015] Further, the anode plate is provided with an anode sealing groove around the periphery; the cathode plate is provided with a cathode sealing groove corresponding to the anode sealing groove.

[0016] Further, the thickness of the anode plate and the cathode plate is 0.1mm-0.2mm.

[0017] Further, the anode plate and the cathode plate are plates formed by stamping or die forming a metal base material.

[0018] Further, the metal base material is a stainless steel plate or a titanium plate.

[0019] The application provides a fuel cell bipolar plate structure, which is characterized in that anode recesses and cathode recesses are arranged, hydrogen flow channels are formed between adjacent anode recesses, oxygen flow channels are formed between adjacent cathode recesses, the anode recesses and the hydrogen flow channels, and the cathode recesses and the oxygen flow channels are all formed in a concave-convex structure, so that the bipolar plate forms a two-plate three-field structure, and the performance of the fuel cell is effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some of the embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from the structures shown in the drawings without creative labor.

[0021] Figure 1 FIG. 1 is a front view of a fuel cell bipolar plate structure according to Embodiment 1 of the present application;

[0022] Figure 2 FIG. 2 is a front view of a fuel cell bipolar plate structure according to Embodiment 2 of the present application;

[0023] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but 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 the present application.

[0025] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, top, bottom, etc.), the directional indications are only used to explain the relative position relationship, movement condition, etc. between the components in a certain specific posture (as shown in the drawings), and if the specific posture changes, the directional indications will also change accordingly.

[0026] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship of two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0027] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on another element or there can be a mediating element. When an element is considered to be "connected" to another element, it can be directly connected to another element or a mediating element can exist at the same time.

[0028] In addition, if the present application embodiments involve "first", "second" and the like, the "first", "second" and the like are only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the scope of protection claimed by the present application.

[0029] The existing metal bipolar plate has the same flow channel structure size of the anode plate and the flow channel structure of the cathode plate, so that the hydrogen gas and oxygen gas have the same gas inlet amount; and in the process of electrochemical reaction, the required hydrogen gas and the required oxygen gas have different usage requirements, thereby causing insufficient electrochemical reaction of the bipolar plate, reducing the utilization rate of hydrogen gas and oxygen gas, and causing the performance of the fuel cell to decrease. In order to solve the above technical problems, the present application provides a fuel cell bipolar plate structure.

[0030] In the present application, the performance of the fuel cell (stack) can be evaluated by the voltage data corresponding to the three current densities of low current density, medium current density and high current density in the polarization curve. In the embodiments of the present application, the low current density is 0.6A / cm 2 , the medium current density is 1.4A / cm 2 , and the high current density is 2.0A / cm 2 .

[0031] Embodiment 1

[0032] As Figure 1As shown, the fuel cell bipolar plate structure provided by the embodiment of the present application comprises an anode plate 1 and a cathode plate 2 which are arranged in abutment;

[0033] The middle part of the anode plate 1 is provided with a plurality of anode recesses 11; the middle part of the cathode plate 2 is provided with a plurality of cathode recesses 21, and the cross-sectional area of the anode recess 11 is smaller than that of the cathode recess 21; the cross-sectional shape of the anode recess 11 and that of the cathode recess 21 are both trapezoidal;

[0034] The anode recess 11 and the cathode recess 21 are connected in one-to-one correspondence and enclose a cooling water flow channel 3; two adjacent anode recesses 11 form a hydrogen gas flow channel 4; two adjacent cathode recesses 21 form an oxygen gas flow channel 5; the cross-sectional area of the hydrogen gas flow channel 4 is smaller than that of the oxygen gas flow channel 5.

[0035] It can be understood that, in the embodiment of the present application, the side of the anode plate 1 away from the cathode plate 2 and the side of the cathode plate 2 away from the anode plate 1 are arranged in abutment with the membrane electrode 6, so as to cover the top of the hydrogen gas flow channel 4 and the top of the oxygen gas flow channel 5, and make the hydrogen gas flow channel 4 and the oxygen gas flow channel 5 form a closed flow channel, and the inlet and outlet are reserved at both ends of the flow channel. In this way, the bipolar plate of the present application forms a two-plate three-field structure, which effectively improves the performance of the fuel cell.

[0036] In the embodiment, the adjacent anode recess 11 and the hydrogen gas flow channel 4, and the adjacent cathode recess 21 and the oxygen gas flow channel 5 all form a concave-convex structure; the anode recess 11 and the cathode recess 21 are both recesses obtained by press forming. In this way, the bipolar plate of the present application forms a two-plate three-field structure, which effectively improves the performance of the fuel cell.

[0037] In the embodiment, the width of the bottom of the hydrogen gas flow channel 4 is equal to that of the bottom of the oxygen gas flow channel 5; the depth of the hydrogen gas flow channel 4 is smaller than that of the oxygen gas flow channel 5.

[0038] Specifically, the width of the bottom of the hydrogen gas flow channel 4 is equal to that of the bottom of the oxygen gas flow channel 5, which makes the bottom of the hydrogen gas flow channel 4 and the bottom of the oxygen gas flow channel 5 correspond completely, which is conducive to the electrochemical reaction; and the distance between two adjacent hydrogen gas flow channels 4 and the distance between two adjacent oxygen gas flow channels 5 are both 1.5 mm, which further improves the rate and efficiency of the electrochemical reaction.

[0039] In the embodiment, the ratio of the depth of the hydrogen gas flow channel 4 to that of the oxygen gas flow channel 5 is 1:1.5.

[0040] Specifically, the depth of the hydrogen flow channel 4 is 0.2 mm; the depth of the oxygen flow channel 5 is 0.3 mm. In this way, the ratio of the cross-sectional area of the hydrogen flow channel 4 to the cross-sectional area of the oxygen flow channel 5 meets the requirement of the amount of oxygen and hydrogen in the electrochemical reaction process on the bipolar plate, and under the premise of ensuring uniform gas flow, the electrochemical reaction is more sufficient, effectively improving the performance of the fuel cell.

[0041] In the embodiment, the anode plate 1 is provided with an anode sealing groove (not shown in the figure) around the periphery; the cathode plate 2 is provided with a cathode sealing groove (not shown in the figure) corresponding to the anode sealing groove around the periphery. It can be understood that the anode sealing groove and the cathode sealing groove are both used for glue sealing to ensure the sealing performance of the anode plate 1 and the cathode plate 2 after being attached.

[0042] In the embodiment, the thickness of the anode plate 1 and the cathode plate 2 is both 0.1 mm.

[0043] In the embodiment, the anode plate 1 and the cathode plate 2 are both plates formed by stamping or die forming a metal base material.

[0044] In the embodiment, the metal base material is a stainless steel plate or a titanium plate.

[0045] Through the performance test of the fuel cell, it is found that by setting the cross-sectional area of the hydrogen flow channel to be smaller than the cross-sectional area of the oxygen flow channel, the flow rate of hydrogen and the flow rate of oxygen on the bipolar plate can meet the requirement of the amount of oxygen and hydrogen in the electrochemical reaction process, and under the premise of ensuring uniform gas flow, the electrochemical reaction is more sufficient, effectively improving the performance of the fuel cell, and the structure is more energy-saving and has higher energy conversion efficiency. Specifically, in the embodiment, for the polarization performance curve, when the current density is 0.6 A / cm 2 , the average voltage of the fuel cell stack is 0.78 V-0.81 V, when the current density is 1.4 A / cm 2 , the average voltage of the fuel cell stack is 0.71 V-0.74 V, and when the current density is 2.0 A / cm 2 , the average voltage of the fuel cell stack is 0.60 V-0.62 V.

[0046] Embodiment 2

[0047] The difference between Example 2 and Example 1 is that the ratio of the depth of the hydrogen flow channel 4 to the depth of the oxygen flow channel 5 is 1:2; specifically, the depth of the hydrogen flow channel 4 is 0.2 mm; the depth of the oxygen flow channel 5 is 0.4 mm; the thickness of the anode plate 1 and the cathode plate 2 is 0.2 mm; the width of the bottom of the hydrogen flow channel 4 and the width of the bottom of the oxygen flow channel 5 are both 0.6 mm; and the distance between two adjacent hydrogen flow channels 4 and the distance between two adjacent oxygen flow channels 5 are both 1.8 mm.

[0048] Performance testing of the fuel cell revealed that, in this embodiment, by setting the cross-sectional area of ​​the hydrogen flow channel to be smaller than that of the oxygen flow channel, the flow rates of hydrogen and oxygen on the bipolar plates can meet the requirements for oxygen and hydrogen usage during the electrochemical reaction. While ensuring uniform gas flow, the electrochemical reaction is more complete, effectively improving the performance of the fuel cell. Its structure is more energy-efficient and has a higher energy conversion efficiency. Specifically, in this embodiment, for the polarization performance curve, at an electrical density of 0.6 A / cm... 2 At that time, the average voltage of its fuel cell stack was 0.77V to 0.79V, and the electrical density was 1.4A / cm. 2 At that time, the average voltage of its fuel cell stack was 0.71V to 0.73V, with an electrical density of 2.0A / cm. 2 At that time, the average voltage of its fuel cell stack was 0.59V to 0.62V.

[0049] Example 3

[0050] like Figure 2 As shown, the difference between Example 3 and Example 1 is that the cross-sectional shape of the anode recess 11 and the cross-sectional shape of the cathode recess 21 are both wavy; the ratio of the depth of the hydrogen flow channel 4 to the depth of the oxygen flow channel 5 is 1:2; the depth of the hydrogen flow channel 4 is 0.25 mm; the depth of the oxygen flow channel 5 is 0.5 mm; and the thickness of the anode plate 1 and the cathode plate 2 is 0.2 mm.

[0051] Performance testing of the fuel cell revealed that, in this embodiment, by setting the cross-sectional area of ​​the hydrogen flow channel to be smaller than that of the oxygen flow channel, the flow rates of hydrogen and oxygen on the bipolar plates can meet the requirements for oxygen and hydrogen usage during the electrochemical reaction. While ensuring uniform gas flow, the electrochemical reaction is more complete, effectively improving the performance of the fuel cell. Its structure is more energy-efficient and has a higher energy conversion efficiency. Specifically, in this embodiment, for the polarization performance curve, at an electrical density of 0.6 A / cm... 2 At that time, the average voltage of its fuel cell stack was 0.79V to 0.82V, and the electrical density was 1.4A / cm. 2When the current density is 0.6 A / cm2, the average voltage of the fuel cell stack is 0.78V-0.82V. 2 When the current density is 2.0 A / cm2, the average voltage of the fuel cell stack is 0.70V-0.75V.

[0052] Example 4

[0053] The difference between Example 4 and Example 3 is that the depth of the hydrogen flow channel 4 is 0.3mm; the depth of the oxygen flow channel 5 is 0.6mm; the width of the bottom of the hydrogen flow channel 4 and the width of the bottom of the oxygen flow channel 5 are both 0.6mm, and the distance between adjacent two hydrogen flow channels 4 and the distance between adjacent two oxygen flow channels 5 are both 1.8mm.

[0054] Through the performance test of the fuel cell, it is found that by setting the cross-sectional area of the hydrogen flow channel to be smaller than the cross-sectional area of the oxygen flow channel, the flow rate of hydrogen and the flow rate of oxygen on the bipolar plate can meet the requirement of the amount of oxygen and hydrogen in the electrochemical reaction process, and the electrochemical reaction is more sufficient under the premise of ensuring uniform gas flow, which effectively improves the performance of the fuel cell, and the structure is more energy-saving and the energy conversion efficiency is higher. Specifically, in this example, for the polarization performance curve, when the current density is 0.6 A / cm2, the average voltage of the fuel cell stack is 0.78V-0.82V, when the current density is 1.4 A / cm2, the average voltage of the fuel cell stack is 0.70V-0.75V, and when the current density is 2.0 A / cm2, the average voltage of the fuel cell stack is 0.60V-0.62V. 2 2 2

[0055] Comparative Example 1

[0056] The difference between the comparative example and Example 1 is that the ratio of the depth of the hydrogen flow channel 4 to the depth of the oxygen flow channel 5 is 1:1; specifically, the depth of the hydrogen flow channel 4 is 0.2mm; the depth of the oxygen flow channel 5 is 0.2mm.

[0057] Through the performance test of the fuel cell, it is found that by setting the cross-sectional area of the hydrogen flow channel to be smaller than the cross-sectional area of the oxygen flow channel, the flow rate of hydrogen and the flow rate of oxygen on the bipolar plate can meet the requirement of the amount of oxygen and hydrogen in the electrochemical reaction process, and the electrochemical reaction is more sufficient under the premise of ensuring uniform gas flow, which effectively improves the performance of the fuel cell, and the structure is more energy-saving and the energy conversion efficiency is higher. Specifically, in this example, for the polarization performance curve, when the current density is 0.6 A / cm2, the average voltage of the fuel cell stack is 0.78V-0.82V, when the current density is 1.4 A / cm2, the average voltage of the fuel cell stack is 0.70V-0.75V, and when the current density is 2.0 A / cm2, the average voltage of the fuel cell stack is 0.60V-0.62V. 2 2 ​​​​When the current density is 0.6 A / cm 2 When the current density is 1.4 A / cm

[0058] Comparative Example 2

[0059] Comparative Example 2 and Example 3 differ in that the ratio of the depth of the hydrogen flow channel 4 to the depth of the oxygen flow channel 5 is 1:1; specifically, the depth of the hydrogen flow channel 4 is 0.3 mm; and the depth of the oxygen flow channel 5 is 0.3 mm.

[0060] Through performance testing of the fuel cell, it was found that, when the ratio of the depth of the hydrogen flow channel 4 to the depth of the oxygen flow channel 5 is 1:1, the flow rate of hydrogen and the flow rate of oxygen on the bipolar plate do not meet the requirements for the amounts of oxygen and hydrogen in the electrochemical reaction process, the electrochemical reaction on the bipolar plate is insufficient, the utilization rates of hydrogen and oxygen are low, and the performance of the fuel cell is also low. Specifically, in this example, for the polarization performance curve, when the current density is 0.6 A / cm 2 When the current density is 1.4 A / cm 2 When the current density is 2.0 A / cm 2 When the current density is 1.4 A / cm

[0061] From the above experimental data, it can be seen that, whether the current density is low, medium or high, the average voltage of the fuel cell (stack) using the bipolar plate structure of the present application is higher than that of the fuel cell (stack) in the comparative example, which also shows that the bipolar plate structure of the present application can make the electrochemical reaction of hydrogen and oxygen more sufficient, and effectively improve the performance of the fuel cell (stack).

[0062] The bipolar plate structure of the fuel cell disclosed in the present application forms a two-plate three-field structure by setting the anode recesses 11 and the cathode recesses 21, forming hydrogen flow channels 4 between adjacent anode recesses 11, forming oxygen flow channels 5 between adjacent cathode recesses 21, and forming a concave-convex structure for the adjacent anode recesses 11 and the hydrogen flow channels 4 and the adjacent cathode recesses 21 and the oxygen flow channels 5, which effectively improves the performance of the fuel cell. By setting the cross-sectional area of the hydrogen flow channel 4 to be smaller than the cross-sectional area of the oxygen flow channel 5, the flow rate of hydrogen and the flow rate of oxygen on the bipolar plate meet the requirements for the amounts of oxygen and hydrogen in the electrochemical reaction process, the electrochemical reaction is more sufficient under the premise of ensuring uniform gas flow, and the performance of the fuel cell is effectively improved. Compared with the existing bipolar plate structure, the present application is more energy-saving and has a higher energy conversion efficiency.

[0063] The above merely provides the preferred embodiments of the present application, and is not intended to limit the patent scope of the present application. Any equivalent structure variations made according to the present application description and drawings, or direct / indirect application in other related technical fields, shall be included in the patent protection scope of the present application.

Claims

1. A fuel cell bipolar plate structure, characterized by, The anode plate and the cathode plate are arranged in abutment; The middle part of the anode plate is provided with a plurality of anode recesses, the middle part of the cathode plate is provided with a plurality of cathode recesses, and the cross-sectional area of the anode recess is smaller than that of the cathode recess; the cross-sectional shape of the anode recess and the cross-sectional shape of the cathode recess are both trapezoidal or wavy; The anode recess and the cathode recess are connected one by one and enclose a cooling water flow channel; two adjacent anode recesses form a hydrogen gas flow channel; two adjacent cathode recesses form an oxygen gas flow channel; the cross-sectional area of the hydrogen gas flow channel is smaller than that of the oxygen gas flow channel; The width of the bottom of the hydrogen gas flow channel is equal to that of the oxygen gas flow channel; the depth of the hydrogen gas flow channel is smaller than that of the oxygen gas flow channel; When the cross-section of the anode recess and the cross-section of the cathode recess are both trapezoidal, the ratio of the depth of the hydrogen gas flow channel to the depth of the oxygen gas flow channel is 1:(1.5-2); When the cross-section of the anode recess and the cross-section of the cathode recess are both wavy, the ratio of the depth of the hydrogen gas flow channel to the depth of the oxygen gas flow channel is 1:

2.

2. The fuel cell bipolar plate structure of claim 1, wherein When the cross-section of the anode recess and the cross-section of the cathode recess are both trapezoidal, the depth of the hydrogen gas flow channel is 0.2mm-0.4mm; the depth of the oxygen gas flow channel is 0.3mm-0.8mm.

3. The fuel cell bipolar plate structure of claim 1, wherein When the cross-section of the anode recess and the cross-section of the cathode recess are both wavy, the depth of the hydrogen gas flow channel is 0.25mm-0.45mm; the depth of the oxygen gas flow channel is 0.5mm-0.9mm.

4. The fuel cell bipolar plate structure of claim 1, wherein The adjacent anode recess and hydrogen gas flow channel, and the adjacent cathode recess and oxygen gas flow channel form a concave-convex structure; the anode recess and the cathode recess are recesses obtained by press forming.

5. The fuel cell bipolar plate structure of claim 1, wherein The thickness of the anode plate and the cathode plate is 0.1mm-0.2mm.

6. The fuel cell bipolar plate structure of claim 1, wherein The periphery of the anode plate is provided with an anode sealing groove; the periphery of the cathode plate is provided with a cathode sealing groove corresponding to the anode sealing groove.

7. The fuel cell bipolar plate structure of claim 1, wherein The anode plate and the cathode plate are both plates formed by stamping or molding a metal base material; The metal base material is a stainless steel plate or a titanium plate.

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