High temperature ceramic hollow roller and preparation method

Abstract

The present invention provides a high-temperature ceramic hollow roller and a method for making it. The hollow roller comprises a rod body formed by a hollow portion and a rod wall. The rod wall is made from a base material consisting of 25-30% α-alumina powder, 10-15% zirconium silicate powder, 10-15% silicon nitride powder, 10-15% sericite powder, 10-15% feldspar powder, 10-15% ball clay powder, 15-20% soft kaolin powder, and 0.16-0.21% methyl cellulose powder, by mass percentage. A reinforcing structure made of polycrystalline mullite fiber is also provided within the rod wall, integrated with the rod wall. This invention improves the structural strength and fracture resistance of the high-temperature ceramic hollow roller without increasing its weight.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic production equipment manufacturing, and particularly relates to a high-temperature ceramic hollow roller and a preparation method thereof. Background Art

[0002] The high-temperature ceramic rollers used in ceramic kilns are mostly cylindrical rollers and columnar rollers in terms of their basic morphological characteristics (cylindrical rollers and cylindrical rollers can be collectively referred to as round rollers), and occasionally square tubular rollers and square columnar rollers (square tubular rollers and square columnar rollers can be collectively referred to as square rollers). Among them, cylindrical rollers and square tubular rollers are hollow rollers, and cylindrical rollers and square columnar rollers are solid rollers. As for arc rollers (along the length direction, the roller is partially enlarged, and the enlarged part has arc-shaped longitudinal sections on both sides), they are derived from cylindrical rollers or cylindrical rollers. Arc rollers derived from cylindrical rollers are hollow rollers, and arc rollers derived from cylindrical rollers are solid rollers.

[0003] Hollow rollers and solid rollers each have their own advantages and disadvantages. Specifically, when the material, shape and outer diameter are the same, solid rollers have higher structural strength. However, solid rollers are heavier and not very flexible to operate. Hollow rollers are relatively lighter and easier to operate, but their structural strength is correspondingly reduced.

[0004] Due to specific process requirements, the production of certain ceramic products requires the use of hollow rollers. Since hollow rollers have relatively low structural strength, they can break during use. To address this, some manufacturers have resorted to increasing the wall thickness of the hollow rollers to improve their strength. (For cylindrical rollers, the wall is also called the barrel wall; for square tubular rollers, the wall is also called the tube wall.) However, increasing the wall thickness of the hollow rollers also increases their weight, which in turn reduces the ease of manipulation that hollow rollers offer over solid rollers.

[0005] It should also be noted that the invention patent application with publication number CN 114180978 A (the applicant's prior invention patent application) discloses a high-temperature ceramic roller (a hollow roller) comprising a cylindrical roller body. The raw materials used to prepare the roller body are composed, by mass, of 25-30% α-alumina powder, 10-15% zirconium silicate powder, 10-15% silicon nitride powder, 10-15% sericite powder, 10-15% feldspar powder, 10-15% ball clay powder, 15-20% soft kaolin powder, and 0.16-0.21% methyl cellulose powder. Compared to several common high-temperature ceramic rollers (hollow) of the same basic size currently available on the market, the high-temperature ceramic roller disclosed in CN 114180978 A exhibits greater structural strength due to improved materials. However, when users particularly emphasize the maneuverability of the roller, the high-temperature ceramic roller disclosed in the invention patent application may also break during use due to the thinning of the rod wall. Summary of the Invention

[0006] The present invention aims to improve the structural strength of a high-temperature hollow ceramic roller without increasing its weight, thereby overcoming the above-mentioned shortcomings of the prior art. This object is achieved through the following technical solutions:

[0007] A high-temperature ceramic hollow roller includes a roller body composed of an internal hollow portion and a roller wall. The basic raw materials for preparing the roller wall are composed, by mass percentage, of 25-30% α-alumina powder, 10-15% zirconium silicate powder, 10-15% silicon nitride powder, 10-15% sericite powder, 10-15% feldspar powder, 10-15% ball clay powder, 15-20% soft kaolin powder, and 0.16-0.21% methyl cellulose dry powder. A reinforcing structure made of polycrystalline mullite fiber is also provided within the roller wall, and the reinforcing structure is integrated with the roller wall.

[0008] On the basis of the above technical solution, the present invention may add the following technical means:

[0009] The high-temperature ceramic hollow roller is a cylindrical roller, and the reinforcement structure is a cylindrical reinforcement mesh made of polycrystalline mullite fiber twisted wire. At least two layers of cylindrical reinforcement mesh made of polycrystalline mullite fiber twisted wire are arranged inside the rod wall.

[0010] Furthermore, the high-temperature ceramic hollow roller is a square tubular roller, the reinforcement structure is a square frame-shaped reinforcement mesh made of polycrystalline mullite fiber twisted wire, and at least two layers of square frame-shaped reinforcement mesh made of polycrystalline mullite fiber twisted wire are arranged inside the rod wall.

[0011] Furthermore, the high-temperature ceramic hollow roller is an arc-shaped roller, and the reinforcement structure is an arc-shaped reinforcement mesh made of polycrystalline mullite fiber twisted wire. At least two layers of arc-shaped reinforcement mesh made of polycrystalline mullite fiber twisted wire are arranged in the rod wall.

[0012] Furthermore, the reinforcement structure is a plurality of lines arranged in parallel along the length direction of the high-temperature ceramic hollow roller and twisted from polycrystalline mullite fibers.

[0013] Furthermore, a plurality of protrusions are provided on the surface of the wire twisted from polycrystalline mullite fibers.

[0014] Furthermore, a plurality of concave cavities are provided on the surface of the wire twisted from the polycrystalline mullite fibers.

[0015] Furthermore, the present invention also provides a method for preparing the high-temperature ceramic hollow roller, comprising the following steps:

[0016] Step 1-1, preparing basic raw materials, wherein the basic raw materials are composed of 25-30% α-alumina powder, 10-15% zirconium silicate powder, 10-15% silicon nitride powder, 10-15% sericite powder, 10-15% feldspar powder, 10-15% ball clay powder, 15-20% soft kaolin powder, and 0.16-0.21% methyl cellulose dry powder, by mass percentage;

[0017] Step 1-2, preparing a reinforcement structure, wherein the reinforcement structure is a plurality of parallel strands of polycrystalline mullite fibers twisted together, or a cylindrical reinforcement mesh, a square reinforcement mesh, or an arc-shaped reinforcement mesh made of polycrystalline mullite fibers twisted together; after the reinforcement structure is prepared, it is placed in the cavity between the inner lining and the outer lining of the mold for later use;

[0018] Step 2, ball milling the basic raw materials to prepare a slurry, wherein the α-alumina powder, zirconium silicate powder, silicon nitride powder, sericite powder, feldspar powder, ball clay powder, and soft kaolin powder in the basic raw materials are mixed and added to a ball mill, and a tartaric acid aqueous solution having a temperature of 85 to 90° C. and a concentration of 3 to 5% is added according to a material-water mass ratio of 1:1.25 to 1.35, and the slurry is prepared by milling for 3.5 to 4.5 hours; the liner in the ball mill is a ceramic liner having an alumina content of 88 to 92%, and the grinding balls in the ball mill are natural granite balls;

[0019] Step 3, slurrying and aging the basic raw materials; placing the slurry prepared in step 3 into a slurry pool, adding the methyl cellulose dry powder, stirring evenly and dehydrating with a plunger pump, and then using a vacuum slurry mixer to prepare a slurry powder with a moisture content of 15-16%, and placing the slurry powder in an aging device for 164-172 hours;

[0020] Step 4, preparation of a high-temperature ceramic hollow roller body; placing the clay powder prepared in step 3 into the cavity between the inner lining M1 and the outer lining M2 of the mold, allowing it to fuse with the reinforcement structure previously set in the cavity, and after compaction, forming a high-temperature ceramic hollow roller body;

[0021] Step 5: Place the high-temperature ceramic hollow roller body flat on an aluminum alloy bracket, cover the high-temperature ceramic hollow roller body with cotton cloth, and dry in the shade for 11 to 13 hours;

[0022] Step 6: Send the shade-dried high-temperature ceramic hollow roller body to a drying room, introduce hot air at 65-70°C, and dry for 22-26 hours until the moisture content of the high-temperature ceramic hollow roller body is less than 1%.

[0023] Step 7: Place the dried high-temperature ceramic hollow roller body into a pit kiln, cover the kiln, and fire it by alternating heating and cooling until the temperature reaches 1560-1565°C.

[0024] Furthermore, when implementing step 7, first raise the temperature in the pit kiln to 300°C and then stop heating; after the temperature in the pit kiln drops to 150°C, raise the temperature again until the temperature in the pit kiln reaches 600°C, and then stop heating; after the temperature in the pit kiln drops to 300°C, raise the temperature again until the temperature in the pit kiln reaches 900°C, and then stop heating; after the temperature in the pit kiln drops to 450°C, raise the temperature again until the temperature in the pit kiln reaches 1200°C, and then stop heating; after the temperature in the pit kiln drops to 600°C, raise the temperature again until the temperature in the pit kiln reaches 1560-1565°C, maintain the temperature at 1560-1565°C for 4 hours, and then stop heating and cool for 72 hours.

[0025] Compared with the existing high-temperature ceramic hollow roller, the present invention has the following beneficial effects:

[0026] First, compared to the basic raw materials commonly used to make high-temperature ceramic rollers (including hollow rollers), polycrystalline mullite fibers possess greater high-temperature resistance and toughness. Therefore, whether the present invention directly employs multiple strands of polycrystalline mullite fibers twisted parallel to the length of the roller as a reinforcement structure, or employs a reinforcing mesh of various shapes made from multiple strands of polycrystalline mullite fibers as a reinforcement structure, both provide a balanced combination of rigidity and flexibility, thereby improving the roller's resistance to fracture. Furthermore, compared to the basic raw materials used to make rollers, polycrystalline mullite fibers have a relatively low specific gravity. Therefore, the present invention is able to improve the fracture resistance of high-temperature ceramic hollow rollers without increasing their weight. In particular, by providing multiple protrusions or multiple cavities on the surface of the strands of polycrystalline mullite fibers, the present invention further strengthens the bonding between the reinforcing structure and the rod wall, thereby further enhancing the structural strength of the roller.

[0027] Second, the present invention employs a technique of alternating heating and cooling until the temperature reaches 1560-1565°C during the firing of the high-temperature ceramic hollow roller. This helps improve the microstructural fusion between the base material and the reinforcement structure. Specifically, the shrinkage rate of polycrystalline mullite fibers differs from that of the base material. If the high-temperature ceramic hollow roller is fired by continuously heating to 1560-1565°C (as in the prior art), numerous microcracks will form at the interface between the base material and the reinforcement structure (polycrystalline mullite fibers) within the roller after cooling, thereby reducing the microscopic fusion between the base material and the reinforcement structure. The present invention employs a technique of alternating heating and cooling until the temperature reaches 1560-1565°C. While microcracks will still form at the interface, their number is significantly reduced, significantly improving the fusion between the base material and the reinforcement structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic cross-sectional structural diagram of Example 1 of the present invention;

[0029] Figure 2 Schematic diagram of the structure of the outer reinforcement mesh in Example 1;

[0030] Figure 3 This is a schematic cross-sectional structural diagram of Example 2 of the present invention;

[0031] Figure 4 Schematic diagram of a partial longitudinal section of a wire twisted from polycrystalline mullite fibers in Example 2 of the present invention;

[0032] Figure 5Schematic diagram of a partial longitudinal section of a wire twisted from polycrystalline mullite fibers having another structure in Example 2 of the present invention;

[0033] Figure 6 Schematic diagram of a horizontal cross-section of the main body of the mold corresponding to Example 1 of the present invention;

[0034] Figure 7 Schematic diagram of a vertical cross-section of the main body of the mold corresponding to Example 1 of the present invention;

[0035] Figure 8 It is a schematic diagram of the vertical cross-sectional structure of the main part of the mold corresponding to Example 2 of the present invention. DETAILED DESCRIPTION

[0036] In order to more fully describe the technical solution of the present invention, two embodiments of the present invention are introduced below with reference to the accompanying drawings.

[0037] Example 1

[0038] like Figure 1 As shown, a cylindrical high-temperature ceramic hollow roller includes a roller body composed of an internal hollow portion 4 and a rod wall 1. The basic raw materials for preparing the rod wall 1 are composed of 25-30% α-alumina powder, 10-15% zirconium silicate powder, 10-15% silicon nitride powder, 10-15% sericite powder, 10-15% feldspar powder, 10-15% ball clay powder, 15-20% soft kaolin powder, and 0.16-0.21% methyl cellulose powder. Inside the rod wall 1, there are two layers of cylindrical reinforcement mesh made of polycrystalline mullite fiber twisted into wires, namely the outer reinforcement mesh 2 and the inner reinforcement mesh 3. The shape and structure of the outer reinforcement mesh 2 are as shown in FIG. Figure 2 As shown. The shape and structural features of the inner reinforcement mesh 3 are identical to those of the outer reinforcement mesh 2; both are cylindrical reinforcement meshes. The difference is that the inner reinforcement mesh 3, because it is located in the inner layer, is relatively smaller. Furthermore, depending on the overall size of the high-temperature ceramic hollow roller and actual needs, additional cylindrical reinforcement meshes made of twisted polycrystalline mullite fiber strands, such as a middle reinforcement mesh, may be placed within the roller wall 1. Furthermore, the diameter of the twisted polycrystalline mullite fiber strands is preferably 2 to 3 mm.

[0039] Example 2

[0040] like Figure 3As shown, a cylindrical high-temperature ceramic hollow roller includes a roller body composed of an internal hollow portion 4 and a rod wall 1. The basic raw materials for preparing the rod wall 1 are composed, by mass percentage, of 25-30% α-alumina powder, 10-15% zirconium silicate powder, 10-15% silicon nitride powder, 10-15% sericite powder, 10-15% feldspar powder, 10-15% ball clay powder, 15-20% soft kaolin powder, and 0.16-0.21% methyl cellulose dry powder. Within the rod wall 1, a plurality of parallel strands 5 of twisted polycrystalline mullite fibers are disposed along the length of the high-temperature ceramic hollow roller, constituting the reinforcement structure of this embodiment. (The specific number of strands 5 of twisted polycrystalline mullite fibers can be adjusted based on the specific dimensions of the high-temperature ceramic hollow roller and actual needs. For example, when the diameter of the strands 5 is 3 mm, the thickness of the rod wall 1 is 1 cm, and the diameter of the hollow portion 4 is 5 cm, if the bending strength of Example 2 at 1500°C is required to be no less than 60 MPa, then at least 60 strands 5 must be disposed within the rod wall 1.)

[0041] like Figure 4 As shown, in order to firmly bond the basic raw material for the rod wall 1 with the twisted string 5 of polycrystalline mullite fibers, in this embodiment, a plurality of protrusions 5a are provided on the surface of the twisted string 5 of polycrystalline mullite fibers. The plurality of protrusions 5a increase the contact surface between the twisted string 5 of polycrystalline mullite fibers and the basic raw material for the rod wall 1, thereby improving the structural strength of the rod wall 1.

[0042] In addition to the technical means of using multiple protrusions 5a, this embodiment can also use other technical means to expand the contact surface between the wire 5 twisted from polycrystalline mullite fibers and the basic raw material for preparing the rod wall 1. Figure 5 As shown, the surface of the wire 5 twisted from polycrystalline mullite fibers is provided with a plurality of concave cavities 5b. Through the plurality of concave cavities 5b, the contact surface between the wire 5 twisted from polycrystalline mullite fibers and the basic raw material for preparing the rod wall 1 can also be expanded, thereby improving the structural strength of the rod wall 1.

[0043] In this embodiment, the length of the wire 5 twisted from polycrystalline mullite fibers is the same as that of the high-temperature ceramic hollow roller, and its diameter is also 2 to 3 mm.

[0044] The structural features of the two embodiments of the present invention are described above in conjunction with the accompanying drawings. It should be emphasized that the technical means adopted in Example 2, which is to provide multiple protrusions 5a or multiple cavities 5b on the surface of the wire 5 twisted from polycrystalline mullite fibers, is also applicable to Example 1. In addition, Example 2 and the technical concept of Example 2 are also applicable to square tubular rollers and curved rollers. The slight difference is that when the technical concept of Example 1 is applied to square tubular rollers or curved rollers, the cylindrical reinforcement mesh needs to be replaced with a square frame reinforcement mesh or a curved reinforcement mesh.

[0045] It should be noted that the (production) molds corresponding to Example 1 and Example 2 are basically the same, and the main parts of both include the following Figures 6 to 8 The inner lining M1 and outer lining M2 shown (in these two embodiments, the inner lining M1 is cylindrical and the outer lining M2 is cylindrical. If the roller rod to be prepared is a square tubular roller rod or an arc-shaped roller rod, the shape of the inner lining and outer lining of the mold should be adjusted accordingly). During the production process, the basic raw materials used to prepare the roller rod and the reinforcing structure are fused in the cavity between the inner lining M1 and the outer lining M2. Slightly different, the main part of the production mold corresponding to Example 2 also includes a bracket M3. The crossbeam of the bracket M3 is arranged above the inner lining M1 and the outer lining M2. Its function is to suspend the wire twisted from the polycrystalline mullite fiber. During the production process, when the basic raw materials for preparing the roller rod and the wire twisted from the polycrystalline mullite fiber are fused into an embryo in the cavity between the inner lining M1 and the outer lining M2 to form an embryo, the wire exposed outside the embryo needs to be cut off. In the scheme of Example 1, the reinforcing structure can be directly placed in the cavity without the need for the bracket M3. In addition, whether it is Example 1 or Example 2, its preparation method includes the following steps:

[0046] Step 1-1, preparation of basic raw materials, in terms of mass percentage, the basic raw materials are composed of 25-30% α-alumina powder, 10-15% zirconium silicate powder, 10-15% silicon nitride powder, 10-15% sericite powder, 10-15% feldspar powder, 10-15% ball clay powder, 15-20% soft kaolin powder, and 0.16-0.21% methyl cellulose dry powder.

[0047] Step 1-2, preparation of a reinforcement structure, wherein the reinforcement structure is a plurality of parallel arranged, twisted polycrystalline mullite fiber wires, or a cylindrical reinforcement mesh, a square reinforcement mesh or an arc-shaped reinforcement mesh made of twisted polycrystalline mullite fiber wires; after the reinforcement structure is prepared, it is placed in the cavity between the inner lining M1 and the outer lining M2 of the mold for standby use.

[0048] Step 2, ball milling the basic raw materials to prepare a slurry, mixing the α-alumina powder, zirconium silicate powder, silicon nitride powder, sericite powder, feldspar powder, ball clay powder, and soft kaolin powder in the basic raw materials and adding them to a ball mill, adding a tartaric acid aqueous solution with a temperature of 85-90°C and a concentration of 3-5% according to a material-water mass ratio of 1:1.25-1.35, and grinding for 3.5-4.5 hours to form a slurry; the liner in the ball mill is a ceramic liner with an alumina content of 88-92%, and the grinding balls in the ball mill are natural granite balls.

[0049] Step 3, slurrying and aging the basic raw materials; placing the slurry prepared in step 3 into a slurry pool, adding the methyl cellulose dry powder, stirring evenly and dehydrating with a plunger pump, and then using a vacuum slurry machine to prepare the slurry into a mud powder with a water content of 15-16%, and placing the mud powder in an aging device for 164-172 hours.

[0050] Step 4, preparation of a high-temperature ceramic hollow roller rod embryo; placing the clay powder prepared in step 3 in the cavity between the inner lining M1 and the outer lining M2 of the mold, allowing it to fuse with the reinforcing structure previously set in the cavity, and after compaction, a high-temperature ceramic hollow roller rod embryo is made.

[0051] Step 5: Place the high-temperature ceramic hollow roller body flat on an aluminum alloy bracket, and then cover the high-temperature ceramic hollow roller body with cotton cloth to dry in the shade for 11 to 13 hours.

[0052] Step 6: Send the shade-dried high-temperature ceramic hollow roller body to a drying room, introduce hot air at 65-70° C., and dry for 22-26 hours to reduce the moisture content of the high-temperature ceramic hollow roller body to ≤1%.

[0053] Step 7: Place the dried high-temperature ceramic hollow roller blank into a pit kiln, cover the kiln, first raise the temperature in the pit kiln to 300°C and then stop heating; after the temperature in the pit kiln drops to 150°C, raise the temperature again until the temperature in the pit kiln reaches 600°C, then stop heating; after the temperature in the pit kiln drops to 300°C, raise the temperature again until the temperature in the pit kiln reaches 900°C, then stop heating; after the temperature in the pit kiln drops to 450°C, raise the temperature again until the temperature in the pit kiln reaches 1200°C, then stop heating; after the temperature in the pit kiln drops to 600°C, raise the temperature again until the temperature in the pit kiln reaches 1560-1565°C, maintain the temperature at 1560-1565°C for 4 hours, and then stop heating for 72 hours.

[0054] It should be noted that, when the reinforcing structure of the present invention is incorporated, even when firing the high-temperature ceramic hollow roller using a method of continuously increasing the temperature to 1560-1565°C (a technique known in the prior art), the fracture resistance of the high-temperature ceramic hollow roller can be enhanced. However, the method of alternately increasing and decreasing the temperature until the temperature reaches 1560-1565°C, as described in the present invention, is more effective. Microscopic observation shows that although microcracks are generated at the interface between the base material and the reinforcing structure (polycrystalline mullite fiber) within the high-temperature ceramic hollow roller when firing the high-temperature ceramic hollow roller using a method of alternating increasing and decreasing the temperature until the temperature reaches 1560-1565°C, the alternating increasing and decreasing temperature technique employed by the present invention significantly reduces the number of microcracks at the interface compared to the conventional method of continuously increasing the temperature. This means that this method can significantly improve the degree of integration between the base material and the reinforcing structure.

Claims

1. A method for preparing a high-temperature ceramic hollow roller, characterized in that: The steps include: Step 1-1, preparing basic raw materials, wherein the basic raw materials are composed of 25-30% α-alumina powder, 10-15% zirconium silicate powder, 10-15% silicon nitride powder, 10-15% sericite powder, 10-15% feldspar powder, 10-15% ball clay powder, 15-20% soft kaolin powder, and 0.16-0.21% methyl cellulose dry powder, by mass percentage; Step 1-2, preparing a reinforcement structure, wherein the reinforcement structure is a plurality of parallel strands of polycrystalline mullite fibers twisted together, or a cylindrical reinforcement mesh, a square reinforcement mesh, or an arc-shaped reinforcement mesh made of polycrystalline mullite fibers twisted together; after the reinforcement structure is prepared, it is placed in the cavity between the inner lining and the outer lining of the mold for later use; Step 2, ball milling the basic raw materials to prepare a slurry, wherein the α-alumina powder, zirconium silicate powder, silicon nitride powder, sericite powder, feldspar powder, ball clay powder, and soft kaolin powder in the basic raw materials are mixed and added to a ball mill, and a tartaric acid aqueous solution with a temperature of 85-90° C. and a concentration of 3-5% is added according to a material-water mass ratio of 1:1.25-1.35, and the slurry is prepared by milling for 3.5-4.5 hours; the liner in the ball mill is a ceramic liner with an alumina content of 88-92%, and the grinding balls in the ball mill are natural granite balls; Step 3, slurrying and aging the basic raw materials; placing the slurry prepared in step 2 into a slurry pool, adding the methyl cellulose dry powder, stirring evenly and dehydrating with a plunger pump, and then using a vacuum slurry mixer to prepare the slurry into a slurry powder with a moisture content of 15-16%, and placing the slurry powder in an aging device for 164-172 hours; Step 4, preparing a high-temperature ceramic hollow roller body; placing the clay powder prepared in step 3 into the cavity between the inner lining and the outer lining of the mold, allowing it to fuse with the reinforcement structure previously set in the cavity, and after compacting, forming a high-temperature ceramic hollow roller body; Step 5: Place the high-temperature ceramic hollow roller body flat on an aluminum alloy bracket, cover the high-temperature ceramic hollow roller body with cotton cloth, and dry in the shade for 11 to 13 hours; Step 6: Send the air-dried high-temperature ceramic hollow roller body to a drying room, introduce hot air at 65-70°C, and dry for 22-26 hours until the moisture content of the high-temperature ceramic hollow roller body is less than 1%. Step 7: Place the dried high-temperature ceramic hollow roller body into a pit kiln, cover the kiln, and fire it by alternating heating and cooling until the temperature reaches 1560-1565°C.

2. The method for preparing a high-temperature ceramic hollow roller according to claim 1, wherein: When implementing step 7, first raise the temperature in the pit kiln to 300°C and then stop heating; after the temperature in the pit kiln drops to 150°C, raise the temperature again until the temperature in the pit kiln reaches 600°C, and then stop heating; after the temperature in the pit kiln drops to 300°C, raise the temperature again until the temperature in the pit kiln reaches 900°C, and then stop heating; after the temperature in the pit kiln drops to 450°C, raise the temperature again until the temperature in the pit kiln reaches 1200°C, and then stop heating; after the temperature in the pit kiln drops to 600°C, raise the temperature again until the temperature in the pit kiln reaches 1560-1565°C, maintain the temperature at 1560-1565°C for 4 hours, and then stop heating and cool for 72 hours.

Images