Chain wheel for scraper conveyor

Abstract

The utility model relates to a chain wheel for a scraper conveyor, which belongs to the technical field of scraper conveyors and comprises a rotary fixing cylinder, the rotary fixing cylinder is of a cylindrical structure with openings at the front end and the rear end, and a convenient-to-replace mechanism is mounted on the rotary fixing cylinder. The convenient-to-replace mechanism comprises four hollow rectangular connecting frames and a connecting shaft assembly, wherein the four hollow rectangular connecting frames are fixedly installed on the inner side of the rotary fixing cylinder and distributed circumferentially, and the connecting shaft assembly is connected into the rotary fixing cylinder and connected with the hollow rectangular connecting frames. According to the chain wheel for the scraper conveyor, the wear resistance, corrosion resistance, heat resistance, oxidation resistance and other performance of the chain nest of the chain wheel can be effectively improved through the cladding manufacturing technology, and therefore the adaptability of the chain wheel to the severe environment of an underground coal mine is remarkably improved; a function of enabling the chain wheel unit to be replaced more simply, conveniently and quickly is additionally arranged, and when a chain nest of the chain wheel is locally damaged, the whole chain wheel does not need to be replaced, and only the damaged chain wheel unit needs to be independently replaced.

Description

Technical Field

[0001] The utility model relates to the technical field of scraper conveyors, in particular to a sprocket wheel used for scraper conveyors. Background Art

[0002] Scraper conveyor is an important transportation equipment in coal mines. Its stable operation is of vital importance to the high production and efficiency of coal mines. As one of the core components of the scraper conveyor, the sprocket is mainly responsible for transmitting the power of the motor to the scraper chain, thereby realizing the transportation of coal.

[0003] During the operation of the scraper conveyor, complex contact and friction will occur between the sprocket chain socket and the ring chain, which will bear huge alternating loads and additional impact loads. These loads will cause wear on the sprocket tooth surface, fatigue cracks, and even serious faults such as sprocket breakage, thus affecting the normal operation of the scraper conveyor. In order to improve the service life and reliability of the sprocket, researchers have carried out a lot of research work. Among them, some studies have reduced the load of the sprocket and improved its wear resistance by optimizing the structural design and material selection of the sprocket. For example, high-strength, wear-resistant steel is used to manufacture the sprocket, or hardening treatment is performed on the sprocket tooth surface.

[0004] In addition, some studies focus on improving the manufacturing process and quality control level of sprockets. For example, advanced casting, forging and processing technologies are used to ensure the dimensional accuracy and surface quality of sprockets; or strict quality inspection and testing methods are used to ensure that the quality of sprockets meets the design requirements.

[0005] In addition, there are some studies dedicated to exploring new sprocket repair and strengthening technologies to extend the service life of the sprocket. For example, laser cladding, surfacing and other technologies are used to clad a layer of high-performance wear-resistant material on the sprocket tooth surface to improve the wear resistance of the sprocket; or cold spraying, hot spraying and other technologies are used to form a protective film on the sprocket surface to reduce corrosion and wear of the sprocket.

[0006] Although the existing sprocket chain sockets have undergone quenching and tempering processes, their adaptability to the harsh environment in coal mines is still insufficient in terms of wear resistance, corrosion resistance, heat resistance, and oxidation resistance. This is because although the quenching and tempering processes can improve the hardness and strength of the sprocket chain sockets, their performance will still be affected to a certain extent when facing the harsh conditions such as high humidity, high corrosiveness, and high temperature in coal mines. In addition, in order to increase the wear resistance of the surface of the existing sprocket body chain sockets, a wear-resistant layer is surfacing welded, but the surfacing welded wear-resistant layer cannot be metallurgically combined with the sprocket and is prone to falling off. This is because during the surfacing welding process, the bonding force between the wear-resistant layer and the sprocket is weak and cannot form a firm metallurgical bond. During the use of the sprocket, due to the large impact force and friction force, the wear-resistant layer is prone to falling off, thus affecting the service life of the sprocket. At the same time, when the current sprocket chain sockets are in use, tooth breakage often occurs after long-term use. This is because during the working process of the sprocket, the teeth have to bear a large impact force and friction force, and at the same time, they also have to bear repeated bending stresses. If the material of the sprocket is subjected to excessive impact or overload during use, it is easy to cause tooth breakage. Moreover, once a tooth breaks, the entire sprocket cannot be used and needs to be replaced as a whole to continue working. This is because the teeth on the sprocket are matched with each other. If one tooth breaks, it will affect the transmission accuracy and efficiency of the entire sprocket, thus unable to meet the working requirements.

[0007] In summary, the existing sprocket chain sockets have problems such as insufficient wear resistance, corrosion resistance, heat resistance, and oxidation resistance when facing the harsh environment in coal mines. At the same time, the surfacing welded wear-resistant layer is prone to falling off, and the teeth are prone to breakage. These problems seriously affect the service life and working efficiency of the sprocket. Therefore, it is necessary to further improve and optimize the existing sprocket chain sockets to improve their performance and reliability. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the present invention provides a sprocket for a scraper conveyor, which has the advantages of long service life, the ability to replace the sprocket unit separately to minimize the replacement cost and reduce the equipment downtime, etc., and solves the problems of insufficient wear resistance, corrosion resistance, heat resistance, and oxidation resistance of the existing sprocket chain sockets in the harsh environment of coal mines, the easy falling off of the surfacing welded wear-resistant layer, the easy breakage of the teeth, and the need to replace the entire sprocket when damaged, high cost, and long downtime.

[0009] In summary, the present invention provides the following technical solution: A sprocket for a scraper conveyor, including a rotating fixed cylinder, the rotating fixed cylinder is a cylindrical structure with openings at both the front and rear ends, and a replacement facilitating mechanism is installed on the rotating fixed cylinder;

[0010] The easy replacement mechanism includes four hollow rectangular connecting frames fixedly installed inside the rotating fixed cylinder and distributed in a circular pattern, as well as a connecting shaft assembly connected inside the rotating fixed cylinder and connected to the hollow rectangular connecting frames. Four insertion blocks are installed on one side of the connecting shaft assembly;

[0011] A mutually communicating first threaded hole is provided between one side of the insertion block and one side of the hollow rectangular connecting frame. A limit bolt for fixing the insertion block and the hollow rectangular connecting frame is threadedly connected in the first threaded hole;

[0012] The easy replacement mechanism further includes four fixed insertion plates fixedly connected to the outside of the rotating fixed cylinder and evenly distributed in a circular pattern. A sprocket body is fixedly connected to the outside of the fixed insertion plate by bolts;

[0013] A second threaded hole for bolt fixation is provided between the sprocket body and one side of the fixed insertion plate;

[0014] The easy replacement mechanism further includes an auxiliary installation component installed on one side of the sprocket body.

[0015] Furthermore, the connecting shaft assembly includes a limit plate and a driving shaft; the center of one side of the limit plate is fixedly connected to one end of the driving shaft.

[0016] By adopting the above technical solution, it is convenient to disassemble the driving shaft under the combined action of the limit plate and the driving shaft.

[0017] Furthermore, one side of the insertion block is fixedly connected to the side of the limit plate away from the limit plate. The outside of the insertion block is in sliding connection and fits snugly with the inside of the hollow rectangular connecting frame.

[0018] By adopting the above technical solution, it is to be able to fix the driving shaft more stably.

[0019] Furthermore, the auxiliary installation component includes a sliding block and a clamping block; one side of the sliding block is fixedly connected to one side of the sprocket body. The clamping block is fixedly connected to the side of the sprocket body close to the rotating fixed cylinder, and the number of clamping blocks is two and they are symmetrically distributed in a mirror image;

[0020] A chute for another sliding block to fit and slide is provided on the opposite side of the sprocket body. A clamping groove for the clamping block to fit and engage is provided on the outside of the rotating fixed cylinder.

[0021] By adopting the above technical solution, it is to facilitate disassembly, assembly and positioning.

[0022] Furthermore, a slot for the fixed insertion plate to fit and insert is provided on the side of the sprocket body close to the rotating fixed cylinder.

[0023] By adopting the above technical solution, it is to further improve the positioning effect and enhance the stability after fixation.

[0024] Furthermore, the sprocket body includes a matrix layer, a wear-resistant layer, a corrosion-resistant layer, a heat-resistant layer, and an antioxidant layer; the wear-resistant layer, the corrosion-resistant layer, the heat-resistant layer, and the antioxidant layer are all coated on the surface of the matrix layer by means of coating.

[0025] By adopting the above technical solution, it is to improve the wear resistance, corrosion resistance, heat resistance, and antioxidant properties of the sprocket chain socket, thereby effectively improving the performance and service life of the scraper conveyor.

[0026] Furthermore, the wear-resistant layer is composed of a tungsten carbide layer and a chromium carbide layer, and is coated on the surface of the chain socket by means of cladding. The thickness of the tungsten carbide layer is 0.5 mm, and the thickness of the chromium carbide layer is 0.6 mm.

[0027] By adopting the above technical solution, the wear resistance of the sprocket chain socket can be effectively improved, and its service life can be extended.

[0028] Furthermore, the corrosion-resistant layer is composed of a nickel-based alloy layer and a stainless steel layer, and is coated on the surface of the wear-resistant layer by means of cladding. The thickness of the nickel-based alloy layer is 0.3 mm, and the thickness of the stainless steel layer is 0.4 mm.

[0029] By adopting the above technical solution, the corrosion resistance of the sprocket chain socket can be effectively improved, and it can be prevented from being corroded in the harsh environment of the coal mine underground.

[0030] Furthermore, the heat-resistant layer is composed of a cobalt-based alloy layer and a ceramic layer, and is coated on the surface of the corrosion-resistant layer by means of cladding. The thickness of the cobalt-based alloy layer is 0.2 mm, and the thickness of the ceramic layer is 0.3 mm.

[0031] By adopting the above technical solution, the heat resistance of the sprocket chain socket can be effectively improved, and it can be prevented from deforming in a high-temperature environment.

[0032] Furthermore, the antioxidant layer is composed of an alumina layer and a chromium oxide layer, and is coated on the surface of the heat-resistant layer by means of cladding. The thickness of the alumina layer is 0.1 mm, and the thickness of the chromium oxide layer is 0.2 mm.

[0033] By adopting the above technical solution, the antioxidant property of the sprocket chain socket can be effectively improved, and it can be prevented from surface oxidation after long-term use.

[0034] Compared with the prior art, the present utility model provides a sprocket for a scraper conveyor, which has the following beneficial effects:

[0035] The sprocket for a scraper conveyor can, through the mutual cooperation of the convenient replacement mechanisms on the rotating fixed cylinder, effectively improve the wear resistance, corrosion resistance, heat resistance, oxidation resistance and other aspects of the sprocket chain socket through the cladding manufacturing technique. Thus, its adaptability to the harsh environment underground in coal mines is significantly enhanced, and the sprocket chain socket can operate stably and durably under severe working conditions, greatly extending its service life. At the same time, a function that makes the replacement of the sprocket unit more convenient and fast is added. When the sprocket chain socket is partially damaged, there is no need to replace the entire sprocket. Just replace the damaged sprocket unit alone, and the equipment can resume normal operation. This not only greatly reduces the replacement cost, but also significantly reduces the downtime of the equipment and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic structural diagram of the present utility model;

[0037] Figure 2 is Figure 1 the rear view schematic diagram of

[0038] Figure 3 is Figure 1 the schematic diagram of the layered structure of the sprocket body in

[0039] DESCRIPTION OF THE REFERENCE NUMERALS:

[0040] 1, rotating fixed cylinder; 200, convenient replacement mechanism; 201, hollow rectangular connecting frame; 2021, limiting plate; 2022, driving shaft; 203, inserting block; 204, limiting bolt; 205, first threaded hole; 206, fixed inserting plate; 207, sprocket body; 2071, matrix layer; 2072, wear-resistant layer; 2073, corrosion-resistant layer; 2074, heat-resistant layer; 2075, antioxidant layer; 2081, sliding block; 2082, clamping block; 209, sliding groove; 210, clamping groove; 211, second threaded hole; 212, inserting slot. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present utility model.

[0042] Please refer to Figures 1 to 3 , the present utility model provides a technical solution: a sprocket for a scraper conveyor, including a rotating fixed cylinder 1. The rotating fixed cylinder 1 is a cylindrical structure with openings at both the front and rear ends, and a convenient replacement mechanism 200 is installed on the rotating fixed cylinder 1;

[0043] By the mutual cooperation of the easy replacement mechanism 200 on the rotating fixed cylinder 1, the performance of the sprocket chain socket in terms of wear resistance, corrosion resistance, heat resistance, and oxidation resistance can be extremely effectively improved through the cladding manufacturing technique, thereby significantly enhancing its adaptability to the harsh environment in coal mines. The sprocket chain socket can operate stably for a long time under harsh working conditions, greatly extending its service life. At the same time, a function that makes the replacement of the sprocket unit more convenient and fast is added. When a local damage occurs to the sprocket chain socket, there is no need to replace the entire sprocket. Only the damaged sprocket unit needs to be replaced separately to make the equipment resume normal operation. This not only greatly reduces the replacement cost but also significantly reduces the downtime of the equipment and improves production efficiency.

[0044] In this embodiment, the easy replacement mechanism 200 is a structure for enhancing its adaptability to the harsh environment in coal mines and making the replacement of the sprocket unit more convenient and fast.

[0045] As Figure 1 、 Figure 2 and Figure 3 shown, the easy replacement mechanism 200 includes four hollow rectangular connecting frames 201 that are respectively fixedly installed on the inner side of the rotating fixed cylinder 1 and are circumferentially distributed, and a connecting shaft assembly that is connected inside the rotating fixed cylinder 1 and is connected to the hollow rectangular connecting frame 201. One side of the connecting shaft assembly is provided with four insertion blocks 203;

[0046] A mutually communicating first threaded hole 205 is provided between one side of the insertion block 203 and one side of the hollow rectangular connecting frame 201. A limit bolt 204 for fixing the insertion block 203 and the hollow rectangular connecting frame 201 is threadedly connected in the first threaded hole 205;

[0047] The easy replacement mechanism 200 further includes four fixed insertion plates 206 that are respectively fixedly connected to the outer side of the rotating fixed cylinder 1 and are circumferentially and evenly distributed. The outer side of the fixed insertion plate 206 is fixedly connected to a sprocket body 207 through bolts;

[0048] A second threaded hole 211 for bolt fixation is provided between one side of the sprocket body 207 and one side of the fixed insertion plate 206;

[0049] The easy replacement mechanism 200 further includes an auxiliary installation component installed on one side of the sprocket body 207.

[0050] It should be noted that the connecting shaft assembly includes a limit plate 2021 and a driving shaft 2022; the center of one side of the limit plate 2021 is fixedly connected to one end of the driving shaft 2022 to facilitate the disassembly of the driving shaft 2022.

[0051] It can be understood that one side of the insertion block 203 is fixedly connected to the side of the limiting plate 2021 away from the limiting plate 2021, and the outer side of the insertion block 203 is slidably connected and fits with the inner side of the hollow rectangular connection frame 201, in order to fix the drive shaft 2022 more stably.

[0052] In addition, the auxiliary installation component includes a sliding block 2081 and a clamping block 2082; one side of the sliding block 2081 is fixedly connected to one side of the sprocket body 207, the clamping block 2082 is fixedly connected to the side of the sprocket body 207 close to the rotating fixing cylinder 1, and the number of the clamping blocks 2082 is two and they are symmetrically distributed in a mirror image;

[0053] On the opposite side of the sprocket body 207, there is a chute 209 for another sliding block 2081 to fit and slide, and on the outer side of the rotating fixing cylinder 1, there is a clamping groove 210 for the clamping block 2082 to fit and engage, in order to facilitate disassembly and positioning.

[0054] In this embodiment, on the side of the sprocket body 207 close to the rotating fixing cylinder 1, there is a slot 212 for the fixing insertion plate 206 to fit and insert, in order to further improve the positioning effect and enhance the stability after fixation.

[0055] It should also be noted that the sprocket body 207 includes a base layer 2071, a wear-resistant layer 2072, a corrosion-resistant layer 2073, a heat-resistant layer 2074, and an antioxidant layer 2075; the wear-resistant layer 2072, the corrosion-resistant layer 2073, the heat-resistant layer 2074, and the antioxidant layer 2075 are all coated on the surface of the base layer 2071 by means of coating, in order to improve the wear resistance, corrosion resistance, heat resistance, and antioxidant properties of the sprocket chain socket, thereby effectively improving the performance and service life of the scraper conveyor.

[0056] It should be further noted that the wear-resistant layer 2072 is composed of a tungsten carbide layer and a chromium carbide layer, and is coated on the surface of the chain socket by means of cladding. The thickness of the tungsten carbide layer is 0.5 mm, and the thickness of the chromium carbide layer is 0.6 mm, which can effectively improve the wear resistance of the sprocket chain socket and extend its service life.

[0057] In addition, it should be noted that the corrosion-resistant layer 2073 is composed of a nickel-based alloy layer and a stainless steel layer, and is coated on the surface of the wear-resistant layer by means of cladding. The thickness of the nickel-based alloy layer is 0.3 mm, and the thickness of the stainless steel layer is 0.4 mm, which can effectively improve the corrosion resistance of the sprocket chain socket and prevent it from being corroded in the harsh environment of the coal mine underground.

[0058] Furthermore, the heat-resistant layer 2074 is composed of a cobalt-based alloy layer and a ceramic layer, and is coated on the surface of the corrosion-resistant layer by means of cladding. The thickness of the cobalt-based alloy layer is 0.2 mm, and the thickness of the ceramic layer is 0.3 mm, which can effectively improve the heat resistance of the sprocket chain socket and prevent it from deforming in a high-temperature environment.

[0059] In addition, it should be noted that the antioxidant layer 2075 is composed of an alumina layer and a chromium oxide layer, which is coated on the surface of the heat-resistant layer by a cladding method. The thickness of the alumina layer is 0.1 mm, and the thickness of the chromium oxide layer is 0.2 mm, which can effectively improve the antioxidant performance of the sprocket chain socket and prevent its surface from oxidizing after long-term use.

[0060] The working principle of the above embodiment is as follows:

[0061] When it needs to be disassembled and replaced in the later stage, first screw off the limit bolts 204 one by one, then pull out the plug 203 from the hollow rectangular connecting frame 201, then pull out the drive shaft 2022. Immediately afterwards, unscrew the bolts fixing the fixed plug plate 206 and the sprocket body 207, and pull the sprocket body 207 away from the rotating fixed cylinder 1. Under the sliding connection of the sliding block 2081 and another chute 209, it stably moves away from the rotating fixed cylinder 1. At this time, when the latch 2082 is separated from the card slot 210 and the fixed plug plate 206 is removed from the slot 212, the damaged sprocket body 207 can be removed. Then, the new sprocket body 207 can be installed by reverse operation according to the above principle to complete the replacement work.

[0062] Compared with the prior art: For the sprocket used in the scraper conveyor, through the mutual cooperation of the easy replacement mechanism 200 on the rotating fixed cylinder 1, the wear resistance, corrosion resistance, heat resistance and antioxidant properties of the sprocket chain socket can be extremely effectively improved by the cladding manufacturing technique, thus significantly enhancing its adaptability to the harsh environment in the coal mine. The sprocket chain socket can operate stably for a long time under harsh working conditions, greatly extending its service life. At the same time, a function that makes the replacement of the sprocket unit more simple and fast is added. When the sprocket chain socket is partially damaged, there is no need to replace the entire sprocket. Only the damaged sprocket unit needs to be replaced separately to make the equipment return to normal operation. This not only greatly reduces the replacement cost, but also significantly reduces the downtime of the equipment, improves the production efficiency, and solves the problems of insufficient wear resistance, corrosion resistance, heat resistance and antioxidant properties of the existing sprocket chain socket in the harsh environment of the coal mine, easy peeling of the surfacing wear-resistant layer, easy fracture of the teeth, and the need to replace the entire sprocket when damaged, high cost and long downtime.

Claims

1. A sprocket for a scraper conveyor, comprising a rotating fixed cylinder (1), wherein the rotating fixed cylinder (1) is a cylindrical structure with openings at both ends, and wherein: The rotating fixed cylinder (1) is provided with a replacement-facilitating mechanism (200); The easy-to-change mechanism (200) comprises four hollow rectangular connection frames (201) respectively fixedly mounted on the inner side of the rotating fixed cylinder (1) and distributed in a circumferential manner, and a connection shaft assembly connected to the rotating fixed cylinder (1) and connected to the hollow rectangular connection frames (201), wherein four insert blocks (203) are mounted on one side of the connection shaft assembly; A No. 1 threaded hole (205) is provided between the insert block (203) and one side of the hollow rectangular connection frame (201), and the No. 1 threaded hole (205) is internally threadedly connected to a limiting bolt (204) for fixing the insert block (203) and the hollow rectangular connection frame (201); The easy-to-change mechanism (200) further comprises four fixed plug plates (206) respectively fixedly connected to the outside of the rotating fixed cylinder (1) and evenly distributed around the circumference, and the outside of the fixed plug plates (206) is fixedly connected to a sprocket body (207) via bolts; A second threaded hole (211) for bolt fixing is provided between the sprocket body (207) and one side of the fixing plug plate (206); The easy-to-change mechanism (200) further comprises an auxiliary mounting assembly mounted on one side of the sprocket body (207).

2. The sprocket for a scraper conveyor according to claim 1, characterized in that: The connecting shaft assembly comprises a limit plate (2021) and a driving shaft (2022); the center of one side of the limit plate (2021) is fixedly connected to one end of the driving shaft (2022).

3. The sprocket for a scraper conveyor according to claim 2, characterized in that: One side of the insert block (203) is fixedly connected to a side of the limit plate (2021) away from the limit plate (2021), and the outer side of the insert block (203) is slidably connected to the inner side of the hollow rectangular connection frame (201) and slides in close contact.

4. The sprocket for a scraper conveyor according to claim 1, characterized in that: The auxiliary installation assembly comprises a sliding block (2081) and a clamping block (2082); one side of the sliding block (2081) is fixedly connected to one side of the sprocket body (207), and the clamping block (2082) is fixedly connected to one side of the sprocket body (207) close to the rotating fixed cylinder (1), and there are two clamping blocks (2082) which are distributed in a mirror-symmetrical manner; The other side opposite to the sprocket body (207) is provided with a sliding groove (209) for another sliding block (2081) to slide in, and the outer side of the rotating fixed cylinder (1) is provided with a clamping groove (210) for the clamping block (2082) to clamp in.

5. The sprocket for a scraper conveyor according to claim 1, characterized in that: A slot (212) for the fixed plug plate (206) to be fitted and plugged into is provided on one side of the sprocket body (207) close to the rotating fixed cylinder (1).

6. The sprocket for a scraper conveyor according to claim 1, characterized in that: The sprocket body (207) comprises a base layer (2071), a wear-resistant layer (2072), a corrosion-resistant layer (2073), a heat-resistant layer (2074) and an anti-oxidation layer (2075); the wear-resistant layer (2072), the corrosion-resistant layer (2073), the heat-resistant layer (2074) and the anti-oxidation layer (2075) are all coated on the surface of the base layer (2071) by means of a coating.

7. The sprocket for a scraper conveyor according to claim 6, characterized in that: The wear-resistant layer (2072) consists of a tungsten carbide layer and a chromium carbide layer, and is coated on the surface of the chain nest by cladding. The thickness of the tungsten carbide layer is 0.5 mm, and the thickness of the chromium carbide layer is 0.6 mm.

8. The sprocket for a scraper conveyor according to claim 6, characterized in that: The corrosion-resistant layer (2073) consists of a nickel-based alloy layer and a stainless steel layer, and is coated on the surface of the wear-resistant layer by cladding. The thickness of the nickel-based alloy layer is 0.3 mm, and the thickness of the stainless steel layer is 0.4 mm.

9. The sprocket for a scraper conveyor according to claim 6, characterized in that: The heat-resistant layer (2074) consists of a cobalt-based alloy layer and a ceramic layer, and is coated on the surface of the corrosion-resistant layer by cladding. The thickness of the cobalt-based alloy layer is 0.2 mm, and the thickness of the ceramic layer is 0.3 mm.

10. The sprocket for a scraper conveyor according to claim 6, characterized in that: The anti-oxidation layer (2075) consists of an aluminum oxide layer and a chromium oxide layer, and is coated on the surface of the heat-resistant layer by cladding. The thickness of the aluminum oxide layer is 0.1 mm, and that of the chromium oxide layer is 0.2 mm.

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