Energy-saving and environment-friendly magnesia-alumina-carbon brick

Abstract

The utility model relates to the technical field of refractory bricks, in particular to an energy-saving and environment-friendly magnesia-alumina-carbon brick which comprises a brick body, a top limiting groove is formed in the top of the brick body, a bottom limiting protrusion is integrally formed at the bottom of the brick body, a left side matching protrusion is integrally formed on the left side of the brick body, and a right side matching groove is formed in the right side of the brick body. The upper layer brick body and the lower layer brick body are fixed through a connecting device, the connecting device comprises a fixing pipe fixed in the middle of the brick bodies, a rotatable sliding column is slidably installed in the fixing pipe, a limiting sleeve is integrally formed in the fixing pipe, a screw joint column is integrally formed above the sliding column, and a screw joint sleeve is integrally formed below the sliding column. A bottom limiting groove is formed in the lower portion of the fixing pipe, and a top limiting protrusion is integrally formed on the sliding column. According to the utility model, gaps are not required to be filled among the brick bodies, and the brick bodies are provided with zigzag joint surfaces, so that further erosion of external high-temperature fluid can be effectively relieved, heat energy loss and frequent replacement are avoided, and the purposes of energy conservation and environmental protection are achieved.

Description

Technical Field

[0001] This utility model relates to the field of refractory brick technology, specifically to an energy-saving and environmentally friendly magnesium-aluminate-carbon brick. Background Technology

[0002] Alumina-magnesia-carbon bricks are refractory materials made primarily from high-alumina bauxite or corundum sand, magnesia, and flake graphite. They can be used as refractory bricks in the metallurgical field and also in regenerators, hot blast stoves, etc.

[0003] The utility model disclosed in CN221001627U provides a cost-effective, high-compressive-strength alumina-magnesia-carbon brick, which is easier to install and reduces material costs. However, the following problems affecting the performance of this alumina-magnesia-carbon brick may occur during use:

[0004] 1. When laying aluminum-magnesium-carbon bricks, there are many gaps between the bricks that need to be filled with joint filler. However, the joint filler and the bricks have different dimensions when subjected to thermal expansion and contraction, which will cause the gaps to gradually deteriorate. This will accelerate the deterioration of the bricks. After the bricks are damaged, the thermal insulation capacity will be greatly reduced, and heat will be easily lost, resulting in heat waste. Moreover, the bricks need to be replaced and cleaned in time after they are damaged, which not only increases the maintenance cost but also generates a lot of construction waste, thus being environmentally unfriendly.

[0005] 2. After the aluminum-magnesium-carbon bricks are laid, they cannot form tortuous joints at the interface. As a result, after the joints widen, external fluids can easily erode directly from the front end of the brick to the rear end along the joints, thereby further accelerating the damage to the bricks. Utility Model Content

[0006] The purpose of this invention is to provide an energy-saving and environmentally friendly magnesium-aluminum-carbon brick to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, this utility model provides the following technical solution: An energy-saving and environmentally friendly magnesium-aluminum-carbon brick includes a brick body for masonry. The top of the brick body has a top limiting groove, and the bottom of the brick body has an integrally formed bottom limiting protrusion corresponding to the top limiting groove. The left side of the brick body has an integrally formed left-side fitting protrusion, and the right side of the brick body has an integrally formed right-side fitting groove corresponding to the left-side fitting protrusion. The upper and lower layers of the brick body are fixed together by a connecting device. The connecting device includes a fixing tube fixed in the middle of the brick body. A rotatable sliding column is slidably installed inside the fixing tube, and a limiting sleeve for restricting the sliding position of the sliding column is integrally formed inside the fixing tube. A threaded column is integrally formed above the sliding column, and a threaded sleeve is integrally formed below the sliding column to be threaded and fixed to an adjacent threaded column. A bottom limiting groove is formed below the fixing tube, and a top limiting protrusion that engages with the bottom limiting groove is integrally formed on the sliding column.

[0008] Preferably, the top of the brick is integrally formed with a first top positioning protrusion and a second top positioning protrusion, and a top front positioning groove is provided between the first top positioning protrusion and the second top positioning protrusion. The bottom of the brick is provided with a first bottom positioning groove and a second bottom positioning groove corresponding to the first top positioning protrusion and the second top positioning protrusion, respectively, and the bottom of the brick is provided with a bottom front positioning protrusion corresponding to the top front positioning groove.

[0009] Preferably, the brick body forms a top slope behind the top limiting groove, and a bottom slope corresponding to the top slope is formed behind the bottom limiting protrusion. The brick body forms a left front slope and a left rear slope at the front and rear ends corresponding to the left side fitting protrusion, and a right front slope and a right rear slope at the front and rear ends corresponding to the right side fitting groove. The left front slope and left rear slope correspond to the right front slope and right rear slope, respectively.

[0010] Preferably, a top rear positioning groove is provided on the top slope, and a bottom rear positioning protrusion that matches the top rear positioning groove is integrally formed on the bottom slope.

[0011] Preferably, a left positioning block is integrally formed on the left mating protrusion, and a left positioning groove is formed on the left mating protrusion; a right positioning block corresponding to the left positioning groove is integrally formed on the right mating groove, and a right positioning groove corresponding to the left positioning block is formed on the right mating groove.

[0012] Preferably, half of a foolproof positioning post that can be fully assembled is provided on the left and right sides of the top limiting groove, and a foolproof positioning groove corresponding to the foolproof positioning post is provided in the middle of the bottom limiting protrusion. The foolproof positioning groove and the foolproof positioning post are used to make the left and right joints of the upper and lower bricks staggered.

[0013] Preferably, the brick body is provided with a connecting groove that extends through the top limiting groove and the bottom limiting protrusion, and the fixing pipe is fixedly installed in the connecting groove. A fixing bracket is fixedly installed on the fixing pipe, and the brick body is provided with an internal fixing groove for placing the fixing bracket. The top of the screw post is provided with a mating port for easy rotation of a screwdriver.

[0014] Preferably, the rear of the brick is provided with an arc-shaped weight-reduction hole for weight reduction, and the arc-shaped weight-reduction holes on adjacent bricks in the same layer are connected to each other and form a common heat-insulating air layer inside.

[0015] Preferably, the brick body is provided with a microporous filler layer for heat insulation at the middle position of the corresponding top limiting groove and bottom limiting protrusion. The microporous filler layer is formed by one or more of corundum powder, zirconia hollow spheres or foam ceramic.

[0016] Compared with existing technologies, the beneficial effects of the energy-saving and environmentally friendly magnesium-aluminum-carbon brick provided by this utility model are:

[0017] 1. This utility model, through customized model and size design of the brick body, combined with the mutual interlocking of the left side protrusion and the right side groove to form a locking fit, can apply pre-tightening force to eliminate gaps at the joint surface, thus eliminating the need for grouting material and eliminating the problems caused by grouting material;

[0018] 2. This utility model, through various special structural designs on the brick body, makes the joint surface tortuous, which can effectively alleviate further erosion by external high-temperature fluids, thereby maintaining a longer service life, avoiding heat loss and frequent replacement, and thus achieving the purpose of energy saving and environmental protection;

[0019] 3. This utility model, through the connecting device, enables bricks of different layers to fit together more tightly and apply prestress to each other to resist the erosion of external high-temperature fluids. Moreover, the brick surface is more likely to form staged local erosion rather than overall erosion, thus facilitating timely inspection and maintenance without the need for complete replacement.

[0020] 4. By setting arc-shaped weight-reducing holes and microporous filler layers, this utility model can not only reduce weight and material usage, but also utilize the air stored inside to reduce heat transfer efficiency, further avoiding heat loss and achieving energy-saving effects. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of this utility model;

[0022] Figure 2 This is a side view of the structure of this utility model;

[0023] Figure 3 This is a cross-sectional view of the structure of this utility model;

[0024] Figure 4 This is a cross-sectional view of the connecting device of this utility model.

[0025] In the diagram: 1. Brick body; 2. Connecting device; 201. Mating joint; 202. Threaded post; 203. Top limiting protrusion; 204. Sliding post; 205. Fixing pipe; 206. Limiting sleeve; 207. Fixing frame; 208. Threaded sleeve; 209. Bottom limiting groove; 3. Top limiting groove; 4. Foolproof positioning post; 5. Top ramp; 6. Top rear positioning groove; 7. First top positioning protrusion; 8. Top front positioning groove; 9. Left front ramp; 10. Microporous filler layer; 11. Bottom front positioning protrusion; 12. 13. First bottom positioning groove; 14. Arc-shaped weight reduction hole; 15. Left rear ramp; 16. Left mating protrusion; 17. Left positioning groove; 18. Left positioning block; 19. Bottom ramp; 20. Bottom limiting protrusion; 21. Foolproof positioning groove; 22. Bottom rear positioning protrusion; 23. Connecting groove; 24. Right front ramp; 25. Right positioning groove; 26. Right positioning block; 27. Right mating groove; 28. Right rear ramp; 29. ​​Second top positioning protrusion; 30. Internal fixing groove. Detailed Implementation

[0026] To clearly and completely describe the objectives and technical solutions of this utility model, and to more clearly illustrate its advantages, the embodiments of this utility model will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some, not all, embodiments of this utility model, and are merely used to explain the embodiments of this utility model. They are not intended to limit the embodiments of this utility model. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0027] Example 1: Please refer to Figures 1 to 3This utility model provides an energy-saving and environmentally friendly magnesium-aluminum-carbon brick, including a brick body 1 for masonry. The top of the brick body 1 is provided with a top limiting groove 3, and the bottom of the brick body 1 is integrally formed with a bottom limiting protrusion 20 corresponding to the top limiting groove 3. The left side of the brick body 1 is integrally formed with a left matching protrusion 16, and the right side of the brick body 1 is provided with a right matching groove 27 corresponding to the left matching protrusion 16. The top of the brick body 1 is integrally formed with a first top positioning protrusion 7 and a second top positioning protrusion 29, and a top front positioning groove 8 is provided between the first top positioning protrusion 7 and the second top positioning protrusion 29. The bottom of the brick body 1 is provided with a first bottom positioning groove 13 and a second bottom positioning groove 12 corresponding to the first top positioning protrusion 7 and the second top positioning protrusion 29, respectively, and the bottom of the brick body 1 is provided with a bottom front positioning protrusion 11 corresponding to the top front positioning groove 8. Through the interlocking of the aforementioned structures, not only can the bricks 1 be more tightly embedded and positioned using their own shape-locking ability, but also complex and interwoven bonding surfaces can be formed between adjacent bricks 1. This prevents the expansion and contraction of bricks 1 from proceeding along a straight line during thermal expansion and contraction. Consequently, during operation, high-temperature fluid cannot directly enter the rear end of bricks 1 from the front end along the gaps between them. This significantly reduces the corrosive effect of high-temperature fluid on the gaps between bricks 1, extending the service life of bricks 1. Furthermore, because the fluid cannot easily pass through the gaps between bricks 1, it also prevents the fluid from crossing the gaps between them. Since brick 1 is in contact with other external structures, it can effectively ensure safety and reduce the direct transfer of heat from high-temperature fluids to the outside, thereby achieving the purpose of energy saving. Moreover, since brick 1 is less prone to damage, it does not require frequent replacement and maintenance, reducing waste generation and making it more environmentally friendly. In addition, this staggered design also allows for more obvious staged damage when brick 1 is damaged, rather than damaging all at once from the front along the gap between the joint surfaces of brick 1 to the back. This makes it easier to repair the damaged areas of brick 1 with other materials in a timely manner, without having to replace the entire brick 1, thus making maintenance more convenient.

[0028] Please see Figures 1 to 3The brick 1 forms a top slope 5 behind the top limiting groove 3, and the brick 1 forms a bottom slope 19 behind the bottom limiting protrusion 20 that corresponds to the top slope 5. The brick 1 forms a left front slope 9 and a left rear slope 15 at the front and rear ends of the corresponding left side fitting protrusion 16, respectively. The brick 1 forms a right front slope 24 and a right rear slope 28 at the front and rear ends of the corresponding right side fitting groove 27, respectively. The left front slope 9 and the left rear slope 15 correspond to the right front slope 24 and the right rear slope 28, respectively. The aforementioned sloping structure is designed to extend the flow path of external high-temperature fluids as they erode into the bonding surface of brick 1. This allows the external high-temperature fluids to be cooled down during the long flow process, preventing them from continuing to flow behind brick 1. When these high-temperature fluids are heated by subsequent high-temperature fluids and can flow again, brick 1 itself has already been heated by the high-temperature fluids and will expand, thus squeezing the high-temperature fluids out of the gaps between bricks 1. Therefore, it can greatly reduce the further erosion of the gaps between bricks 1 by the high-temperature fluids, thereby extending the service life of brick 1.

[0029] A top rear positioning groove 6 is provided on the top slope 5, and a bottom rear positioning protrusion 22 matching the top rear positioning groove 6 is integrally formed on the bottom slope 19. Besides facilitating the positioning of the upper and lower brick layers 1 during installation and preventing lateral slippage of the bricks 1 after construction, the top rear positioning groove 6 and the bottom rear positioning protrusion 22 also allow for a certain deformation gap to reduce the stress on the middle of the bricks 1 due to thermal expansion, thereby mitigating damage caused by stress concentration. A left positioning block 18 is integrally formed on the left-side protrusion 16, and a left positioning groove 17 is provided on the left-side protrusion 16. A right-side recess... The groove 27 has an integrally formed right-side positioning block 26 that corresponds to and mates with the left-side positioning groove 17, and the right-side mating groove 27 has a right-side positioning groove 25 that corresponds to and mates with the left-side positioning block 18. By setting the left-side positioning groove 17, left-side positioning block 18, right-side positioning groove 25, and right-side positioning block 26, the bricks 1 in the same layer can restrict each other's vertical displacement. This avoids uncoordinated vertical movement of a single brick 1 during use, especially vertical displacement caused by high-temperature fluid intrusion into the gaps, thus maintaining a tight bond between the bricks 1. It should be noted that... Figures 1 to 3The left positioning groove 17, left positioning block 18, right positioning groove 25, and right positioning block 26 are depicted with exaggerated dimensions. In reality, the left positioning block 18 and right positioning block 26 protrude from the brick body 1 by less than two millimeters. Similarly, the left positioning groove 17 and right positioning groove 25 are recessed into the brick body 1 by less than two millimeters. When laying the brick body 1, it needs to be pre-frozen to allow the aforementioned structures between adjacent brick bodies 1 to interlock using the principle of thermal expansion and contraction. This method also ensures that the gaps between the brick bodies 1 are kept within two millimeters during construction. After construction, the brick body 1 expands upon heating, completely sealing the gaps between the brick bodies 1 and creating pre-stress compression, thus ensuring the joint surface is seamless. The gaps almost completely disappear. When the brick 1 is further heated by the external high-temperature fluid, the gaps are squeezed even tighter, thus completely preventing the high-temperature fluid from entering the gaps. On the other hand, the size of the brick 1 is customized as needed. The size of each type of brick 1 is precisely designed according to the diameter of the circular wall to be built. Therefore, no additional grouting material is needed during construction. The gaps at the joint surface can be completely sealed by the prestress between the bricks 1 after construction. This also avoids the gap size change caused by the different expansion coefficients of the grouting material and the brick 1 during use, or damage to the brick 1 caused by the grouting material. Therefore, it can better protect the gaps between the bricks 1 and extend the service life of the bricks 1.

[0030] Please see Figures 1 to 4The upper and lower brick layers 1 are fixed together by a connecting device 2. The connecting device 2 includes a fixing tube 205 fixed in the middle of the brick layer 1. A rotatable sliding column 204 is slidably installed inside the fixing tube 205. A limiting sleeve 206 for limiting the sliding position of the sliding column 204 is integrally formed inside the fixing tube 205. A screw-in column 202 is integrally formed above the sliding column 204, and a screw-in sleeve 208 that is screwed and fixed to the adjacent screw-in column 202 is integrally formed below the sliding column 204. A hole is opened at the bottom of the fixing tube 205. The brick body 1 has a bottom limiting groove 209 and a top limiting protrusion 203 integrally formed on the sliding column 204 that engages with the bottom limiting groove 209. The brick body 1 has a connecting groove 23 that passes through the top limiting groove 3 and the bottom limiting protrusion 20. The fixing tube 205 is fixedly installed in the connecting groove 23. The fixing tube 205 is fixedly installed with a fixing bracket 207. The brick body 1 has an internal fixing groove 30 for placing the fixing bracket 207. The top of the screw thread 202 has a mating port 201 for easy rotation of the screwdriver. During the use of the connecting device 2, first adjust the position of the top limiting protrusion 203 located on the lower layer so that after the brick 1 on the upper layer is correctly placed, the top limiting protrusion 203 between the two layers can be engaged in the bottom limiting groove 209. In this way, the fixed tube 205 on the upper layer can be used to restrict the rotation of the screw post 202 on the lower layer. At this time, the screw post 202 on the upper layer can be rotated by inserting a screwdriver into the mating port 201 of the screw post 202 on the upper layer. This will drive the screw sleeve 208 on the upper layer to engage with the screw on the lower layer. The connecting posts 202 are screwed together. As the screwing proceeds, the lower screw sleeve 208 will be locked below the limiting sleeve 206, while the top of the upper sliding post 204 will be locked above the fixing tube 205, thus ensuring that the two bricks 1 are correctly fixed. Continuing to rotate the screw post 202 can also apply a preload to prevent excessive dimensional changes in the gap between the upper and lower bricks 1 during thermal expansion and contraction, thereby making the bricks 1 more tightly bonded. In order to ensure the working performance in high-temperature environments, the connecting device 2 can be made of nickel-based alloy or ceramic material.

[0031] Example 2: Please refer to Figure 1 and Figure 2Based on Embodiment 1, half of the anti-foolproof positioning post 4, which can be completely spliced ​​together, is provided on the left and right sides of the top limiting groove 3, and an anti-foolproof positioning groove 21, which is inserted into the middle of the bottom limiting protrusion 20, is provided. The anti-foolproof positioning groove 21 and the anti-foolproof positioning post 4 are used to make the left and right joints of the upper and lower brick bodies 1 staggered. By adopting the above-mentioned anti-foolproof design, the left and right joints between the upper brick bodies 1 will be located in the middle position of the brick body 1 below it. This forms an staggered masonry layout between brick bodies 1 in different layers, avoiding the formation of a straight gap in the vertical direction. This can better prevent external high-temperature fluid from invading the gaps and continuing to infiltrate the gaps of other brick bodies 1, thereby effectively improving the service life.

[0032] Example 3: Please refer to Figures 1 to 3 Based on Embodiment 2, an arc-shaped weight-reducing hole 14 for weight reduction is provided at the rear of the brick body 1, and the arc-shaped weight-reducing holes 14 on adjacent brick bodies 1 in the same layer are connected to each other and form a common heat-insulating air layer inside. A microporous filler layer 10 for heat insulation is provided at the middle position of the corresponding top limiting groove 3 and bottom limiting protrusion 20 of the brick body 1. The microporous filler layer 10 is formed by filling one or more of corundum powder, zirconia hollow spheres or foam ceramics. Both the arc-shaped weight-reducing hole 14 and the microporous filler layer 10 can reduce the overall thermal conductivity of the brick body 1 by utilizing the internal air, thereby slowing down the heat loss of the internal high-temperature fluid through the brick body 1, effectively playing a role in energy saving. Moreover, the arc-shaped weight-reducing hole 14 itself can also achieve a weight reduction effect, so that the brick body 1 can maintain sufficient size to ensure functional effect while using less material.

[0033] Although the illustrative specific embodiments of this application have been described above to enable those skilled in the art to understand this application, this application is not limited to the scope of the specific embodiments. For those skilled in the art, all applications utilizing the concept of this application are protected as long as various variations are within the spirit and scope of this application as defined and determined by the appended claims.

Claims

1. An energy-saving and environmentally friendly magnesium-aluminum-carbon brick, comprising a brick body (1) for masonry, characterized in that: The top of the brick (1) is provided with a top limiting groove (3), and the bottom of the brick (1) is integrally formed with a bottom limiting protrusion (20) that corresponds to and cooperates with the top limiting groove (3). The left side of the brick (1) is integrally formed with a left side cooperating protrusion (16), and the right side of the brick (1) is provided with a right side cooperating groove (27) that corresponds to and cooperates with the left side cooperating protrusion (16). The upper and lower layers of the brick (1) are fixed together by a connecting device (2), and the connecting device (2) includes a fixing tube (205) fixed in the middle of the brick (1). The fixing tube (205) slides inside. A rotatable sliding column (204) is installed, and a limiting sleeve (206) for limiting the sliding position of the sliding column (204) is integrally formed inside the fixing tube (205). A screw post (202) is integrally formed above the sliding column (204), and a screw sleeve (208) for screwing and fixing to the adjacent screw post (202) is integrally formed below the sliding column (204). A bottom limiting groove (209) is opened below the fixing tube (205), and a top limiting protrusion (203) for engaging with the bottom limiting groove (209) is integrally formed on the sliding column (204).

2. The energy-saving and environmentally friendly magnesium-aluminate-carbon brick according to claim 1, characterized in that: The top of the brick body (1) is integrally formed with a first top positioning protrusion (7) and a second top positioning protrusion (29), and a top front positioning groove (8) is provided between the first top positioning protrusion (7) and the second top positioning protrusion (29). The bottom of the brick body (1) is provided with a first bottom positioning groove (13) and a second bottom positioning groove (12) corresponding to the first top positioning protrusion (7) and the second top positioning protrusion (29), respectively, and the bottom of the brick body (1) is provided with a bottom front positioning protrusion (11) corresponding to the top front positioning groove (8).

3. The energy-saving and environmentally friendly magnesium-aluminate-carbon brick according to claim 1, characterized in that: The brick (1) forms a top slope (5) behind the top limiting groove (3), and the brick (1) forms a bottom slope (19) behind the bottom limiting protrusion (20) that corresponds to the top slope (5). The brick (1) forms a left front slope (9) and a left rear slope (15) at the front and rear ends of the corresponding left side fitting protrusion (16), and forms a right front slope (24) and a right rear slope (28) at the front and rear ends of the corresponding right side fitting groove (27). The left front slope (9) and the left rear slope (15) correspond to the right front slope (24) and the right rear slope (28), respectively.

4. The energy-saving and environmentally friendly magnesium-aluminate-carbon brick according to claim 3, characterized in that: The top slope (5) is provided with a top rear positioning groove (6), and the bottom slope (19) is integrally formed with a bottom rear positioning protrusion (22) that matches the top rear positioning groove (6).

5. The energy-saving and environmentally friendly magnesium-aluminate-carbon brick according to claim 1, characterized in that: The left-side mating protrusion (16) is integrally formed with a left-side positioning block (18), and a left-side positioning groove (17) is provided on the left-side mating protrusion (16). The right-side mating groove (27) is integrally formed with a right-side positioning block (26) that corresponds to and mates with the left-side positioning groove (17), and a right-side positioning groove (25) that corresponds to and mates with the left-side positioning block (18) is provided on the right-side mating groove (27).

6. The energy-saving and environmentally friendly magnesium-aluminate-carbon brick according to claim 1, characterized in that: The top limiting groove (3) is provided with half of a foolproof positioning post (4) that can be fully assembled with each other on the left and right sides, and the bottom limiting protrusion (20) is provided with a foolproof positioning groove (21) that is inserted into the foolproof positioning post (4) in the middle. The foolproof positioning groove (21) and the foolproof positioning post (4) are used to make the left and right joints of the upper and lower brick bodies (1) staggered.

7. The energy-saving and environmentally friendly magnesium-aluminate-carbon brick according to claim 1, characterized in that: The brick body (1) is provided with a connecting groove (23) that passes through the top limiting groove (3) and the bottom limiting protrusion (20), and the fixing tube (205) is fixedly installed in the connecting groove (23). The fixing tube (205) is fixedly installed with a fixing bracket (207), and the brick body (1) is provided with an internal fixing groove (30) for placing the fixing bracket (207). The top of the screw thread (202) is provided with a mating port (201) for easy rotation of the screwdriver.

8. The energy-saving and environmentally friendly magnesium-aluminate-carbon brick according to claim 1, characterized in that: The rear of the brick (1) is provided with an arc-shaped weight-reducing hole (14) for weight reduction, and the arc-shaped weight-reducing holes (14) on adjacent bricks (1) in the same layer are connected to each other and form a common heat-insulating air layer inside.

9. The energy-saving and environmentally friendly magnesium-aluminate-carbon brick according to claim 1, characterized in that: The brick body (1) has a microporous filler layer (10) for heat insulation at the middle position of the corresponding top limiting groove (3) and bottom limiting protrusion (20). The microporous filler layer (10) is formed by filling one or more of corundum powder, zirconia hollow spheres or foam ceramics.

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