Graphite kiln furniture for sintering high-straightness and high-roundness silicon carbide roller and batch sintering method

Abstract

The invention relates to graphite kiln furniture for sintering a high-straightness and high-roundness silicon carbide roller and a batch sintering method, and belongs to the technical field of engineering ceramic material preparation. The graphite kiln furniture comprises a graphite outer pipe and a graphite inner pipe; hollow holes are uniformly distributed in the graphite outer pipe in a plurality of axial directions; the hole diameter of the hollow holes of the graphite outer pipe is less than or equal to 2 of the inner diameter of the graphite outer pipe, and the product of the hole diameter of the hollow holes and the number of the hollow holes uniformly distributed on the same circumference is equal to 2 * the inner diameter of the graphite outer pipe; the axial center distance of the adjacent hollowed-out holes of the graphite outer pipe in the axial direction is larger than or equal to 2 * the hole diameter of the hollowed-out holes; hollow holes are uniformly distributed in the graphite inner pipe in a plurality of axial directions; the hole diameter of the hollow holes of the graphite inner pipe is less than or equal to 2 of the outer diameter of the graphite inner pipe, and the product of the hole diameter of the hollow holes and the number of the hollow holes uniformly distributed on the same circumference is 2 * the outer diameter of the graphite inner pipe; wherein the axial center distance of the adjacent hollow holes of the graphite inner pipe in the axial direction is larger than or equal to 2 * the hole diameter of the hollow holes. The problems of deformation, distortion, warping and the like possibly generated in the sintering process of the silicon carbide roller rod are solved.

Description

Technical Field

[0001] The invention relates to a graphite kiln for sintering silicon carbide rollers with high straightness and high roundness and a batch sintering method, in particular to batch sintering equipment for silicon carbide tubes with high straightness and high roundness, belonging to the technical field of engineering ceramic material preparation. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in mobile phones, computers, cars, power stations and other equipment due to their high energy density, small volume and mass, and high charge and discharge, and have become an inseparable part of people's daily life. Lithium battery materials are at the upstream of the entire lithium battery industry chain, and are mainly composed of positive electrode materials, negative electrode materials, diaphragms and electrolytes. Among them, the positive electrode material directly determines the energy density and safety of the battery, which in turn affects the overall performance of the battery. Since the positive electrode material accounts for as much as 30% to 40% of the cost of lithium battery materials, the positive electrode material occupies a pivotal position in lithium batteries and directly leads the development of the lithium battery industry. At present, the mainstream positive electrode materials in the market are lithium iron phosphate and ternary lithium materials, and their synthesis is mainly achieved by high-temperature solid-phase reaction in a roller kiln. Since the high-temperature solid-phase reaction process of the positive electrode material has high temperature and corrosiveness, the rollers in the roller kiln must have high temperature resistance, corrosion resistance, high strength, high thermal conductivity and other properties. At the same time, the rollers carry the sagger containing raw materials to roll and advance, and their straightness requirements are not less than 0.8‰, and the out-of-roundness shall not exceed 0.5mm.

[0003] Silicon carbide ceramics have become the preferred material for rollers in roller kilns due to their excellent high temperature resistance, corrosion resistance, high strength, and high thermal conductivity. At present, silicon carbide rollers are mainly divided into reaction-sintered silicon carbide rollers and pressure-solid-phase sintered silicon carbide rollers. Reaction-sintered silicon carbide rollers usually contain 10 to 20 vol% of free silicon, which is easily corroded by lithium sources at high temperatures, causing scaling on the roller surface and reduced mechanical strength, interfering with the normal movement of the sagger containing materials in the kiln, and thus affecting the service life and safety of the kiln. Pressure-solid-phase sintered silicon carbide uses submicron α-SiC powder as raw material and BC system sintering aids, and is sintered in an inert atmosphere at a high temperature of 2100 to 2200°C. The silicon carbide content of the solid-phase sintered silicon carbide product is more than 98wt%. Due to its strong covalent bond, it can withstand the corrosion of strong acids and alkalis such as hydrochloric acid, sulfuric acid, phosphoric acid, lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. It is also the only ceramic material that can withstand hydrofluoric acid corrosion, and has better mechanical and thermal properties than reaction-sintered silicon carbide. With the continuous expansion of the production capacity of positive electrode materials, the requirements for the high-temperature mechanical properties and high-temperature chemical stability of rollers in roller kilns are increasing. Therefore, atmospheric pressure solid-phase sintered silicon carbide rollers with better comprehensive performance are recognized as more promising and potential.

[0004] Unlike the reaction-sintered silicon carbide, which has almost no volume shrinkage during the sintering process, the pressure-sintered silicon carbide will produce a linear shrinkage rate of nearly 20% during the sintering process. The superposition of factors such as size effect, temperature field effect, and structural effect makes it very easy for large-sized pressure-sintered silicon carbide parts to deform and crack during the sintering process. For the mass production of silicon carbide rollers, V-shaped graphite sintering kiln furniture is currently commonly used, which is stacked in multiple layers in the height direction and connected by bolts or mortise and tenon joints in the length direction.

[0005] Chinese patent CN112179147B discloses a graphite groove for sintering silicon carbide ceramic tubes, high-performance silicon carbide ceramic tubes and preparation methods thereof. The graphite groove is a V-shaped graphite groove with a circular arc vertex angle, wherein: the diameter of the circular arc portion of the circular arc vertex angle = the outer diameter of the required silicon carbide ceramic tube + (0.1-0.3) mm, the angle α of the V-shaped graphite groove = 2×arcsin(m / M)-x, wherein 0≤x≤2, m is the maximum unit length mass of the silicon carbide ceramic tube blank corresponding to the outer diameter roundness of the silicon carbide ceramic tube obtained after placing the silicon carbide ceramic tube blank on a flat graphite plate for degreasing and sintering and can be maintained at ±0.1 mm; M is the unit length mass of the silicon carbide ceramic tube blank to be degreased and sintered, m<M≤8.0g / cm; the length of the graphite groove is ≥4m. For the pressure-solid-phase sintered silicon carbide ceramic tube with an outer diameter of 30 mm, a wall thickness of 5 mm, and a length of 10 mm after sintering (density is 3.10 g / cm 3 Calculated), its mass is about 12.17g; before degreasing and sintering, it contains a variety of organic additives and water, and its mass exceeds 12.17g. This exceeds the applicable scope of the graphite tank for sintering silicon carbide ceramic tubes described in Chinese patent CN112179147B.

[0006] In summary, the current graphite kiln tools for sintering silicon carbide rollers have the following main shortcomings: 1) It is only suitable for silicon carbide rollers with small size and self-weight (tube diameter not exceeding 30mm, wall thickness not exceeding 5mm). For the size and self-weight of silicon carbide rods with a tube diameter of 30-60mm and a wall thickness of up to 10mm, the V-groove is not enough to provide sufficient shape-preserving support during high-temperature sintering, and it is easy to become elliptical. 2) Bolts or mortise and tenon joints are used to connect the front and back of the same layer of graphite plates in the length direction. The connection parts repeatedly experience the process of temperature increase expansion and temperature decrease contraction, which is prone to fracture, dislocation, etc., resulting in deformation and distortion of the product at the splicing of the graphite plates, and it is impossible to obtain products with high straightness. 3) Production sintering furnaces generally have a large furnace cavity space and mainly rely on radiation heat transfer at high temperatures. The heating elements of the sintering furnace are usually arranged around the furnace, and the actual temperature at different positions inside the furnace itself has a certain degree of deviation, which affects the consistency of product performance. The stacking of multiple layers of graphite kiln furniture will aggravate the temperature unevenness between the center and the peripheral areas of the furnace, affecting the sintering density of products at different positions in the furnace chamber. Summary of the invention

[0007] In view of the above problems, the purpose of the present invention is to provide a graphite kiln tool for sintering silicon carbide rollers with high straightness and roundness and a batch sintering method. The present invention effectively solves the problems of deformation, distortion, warping and other problems that may occur during the sintering process of silicon carbide rollers, improves the uniformity of the temperature field in the furnace during the batch roller sintering process, and can obtain dense silicon carbide rollers with high straightness and roundness in batches.

[0008] In a first aspect, the present invention provides a graphite kiln tool for sintering silicon carbide rollers with high straightness and roundness. The graphite kiln tool comprises a graphite outer tube and a graphite inner tube; The graphite outer tube has hollow holes evenly distributed in multiple axial directions; the diameter of the hollow holes of the graphite outer tube is ≤ the inner diameter of the graphite outer tube / 2, and the diameter of the hollow holes × the number of hollow holes evenly distributed on the same circumference = 2 × the inner diameter of the graphite outer tube; wherein the axial center distance of the adjacent hollow holes of the graphite outer tube in the axial direction is ≥ 2 × the diameter of the hollow holes; The graphite inner tube has hollow holes evenly distributed in multiple axial directions; the diameter of the hollow holes of the graphite inner tube is ≤ the outer diameter of the graphite inner tube / 2, and the diameter of the hollow holes × the number of hollow holes evenly distributed on the same circumference = 2 × the outer diameter of the graphite inner tube; wherein the axial center distance of the adjacent hollow holes of the graphite inner tube in the axial direction is ≥ 2 × the diameter of the hollow holes.

[0009] The invention designs graphite inner and outer tubes that match the inner and outer diameters of the silicon carbide roller blank, thereby realizing and ensuring high roundness during the sintering process of the silicon carbide roller.

[0010] Preferably, the graphite outer tube or the graphite inner tube is integrally formed.

[0011] Preferably, the graphite outer tube or graphite inner tube is formed in sections, and the sections are connected by threads. The graphite outer tube or graphite inner tube is connected by threads, which effectively avoids the deformation and distortion of the product caused by the connection of the front and rear graphite layers with bolts or mortise and tenon joints, and realizes and ensures the high straightness of the silicon carbide roller sintering process.

[0012] Preferably, the inner diameter of the graphite outer tube is the outer diameter of the silicon carbide roller blank to be sintered + (0.3-1.0) mm; the wall thickness of the graphite outer tube is ≤5 mm, the straightness is ≤0.8‰, and the out-of-roundness is ≤0.5 mm.

[0013] Preferably, the outer diameter of the graphite inner tube is the inner diameter of the sintered silicon carbide roller minus (0.2 to 1.0 mm); the wall thickness of the graphite inner tube is ≤5 mm, the straightness is ≤0.8‰, and the out-of-roundness is ≤0.5 mm.

[0014] In a second aspect, the present invention provides a method for batch sintering of high-straightness and high-roundness silicon carbide rollers. The method comprises: (1) Assembling the graphite kiln furniture and the silicon carbide roller blank to be sintered: inserting the silicon carbide roller blank to be sintered into the graphite outer tube to form a first assembly, and then inserting the graphite inner tube into the first assembly to form a second assembly; (2) Debonding and sintering integration of batch silicon carbide roller blanks: The second assembly of the silicon carbide roller blanks to be sintered and the graphite kiln tool is naturally and tightly stacked in the graphite muffle box. The silicon carbide roller blanks to be sintered are debonded and sintered to obtain silicon carbide rollers with high straightness and high roundness.

[0015] Preferably, the graphite muffle box has a closed structure except for an air inlet channel arranged at a lower front end portion and an exhaust channel arranged at an upper rear end portion thereof.

[0016] Preferably, the gas inlet of the graphite muffle box is kept filled with argon during the sintering process; preferably, the argon flow rate is 5-20L / min. The use of high-temperature flowing argon to protect the sintering of the silicon carbide roller can effectively ensure the densification of the silicon carbide roller and realize the preparation of high-performance silicon carbide rollers.

[0017] Preferably, the hollow holes of the graphite outer tube and the graphite inner tube and the gaps formed by the natural and tight stacking of the graphite kiln furniture (the second assembly) together constitute a through-going gas flow and radiation heat transfer channel. In the present invention, the hollow holes of the graphite outer tube and the graphite inner tube and the gaps formed by the natural and tight stacking of the tubular kiln furniture together constitute a through-going gas flow and radiation heat transfer channel. This not only ensures the timely discharge of volatile decomposition products in the debonding stage of the silicon carbide roller blank and the protection of the silicon carbide roller sintering densification by the inert gas in the high-temperature sintering stage; and in the furnace of the same size, compared with the traditional layered V-shaped graphite groove stacking structure, it reduces thermal resistance, enhances the effective permeability of radiation heat transfer, and effectively improves the uniformity of the temperature field in the furnace cavity.

[0018] Preferably, debonding is carried out in a vacuum atmosphere, the debonding temperature is 1100-1500°C, and the debonding holding time is 0.5-2 hours; sintering is carried out in a normal pressure argon atmosphere, the sintering temperature is 2100-2250°C, and the sintering holding time is 0.5-2 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of silicon carbide roller blank.

[0020] Figure 2 Schematic diagram of graphite outer tube / graphite inner tube.

[0021] Figure 3 It is a schematic diagram of the assembly of the silicon carbide roller blank and the graphite inner and outer tubes into a whole.

[0022] Figure 4This is a schematic diagram of the natural and tight stacking of the silicon carbide roller blank and the graphite inner and outer tubes after being assembled into a whole.

[0023] Figure 5 Schematic diagram of the silicon carbide roller that is assembled into a whole with graphite inner and outer tubes and then sintered.

[0024] Figure 6 Schematic diagram of the silicon carbide roller that is naturally and tightly stacked and sintered after being assembled into a whole with graphite inner and outer tubes. DETAILED DESCRIPTION

[0025] The present invention is further described by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0026] The graphite kiln furniture of the present invention comprises a graphite outer tube and a graphite inner tube.

[0027] The graphite outer tube has (multiple) hollow holes evenly distributed in multiple axial directions. Preferably, each axial direction is parallel to each other. That is, the hollow holes of the graphite outer tube are evenly distributed around the central axis of the graphite outer tube. The design principles of the hollow holes are as follows:

[0028] (1) For the debonding sintering of a single roller, the design of the hollow hole facilitates the escape of decomposed volatiles during the debonding process of the roller blank. The content of organic additives in the extruded silicon carbide ceramic blank is usually more than 10%. The substances produced by the decomposition and volatilization of organic matter during the debonding process need to be discharged in time, otherwise it will affect the sintering densification of silicon carbide ceramics and form defects such as pores, inclusions, and cracks. If the silicon carbide roller blank is wrapped by inner and outer graphite tubes, due to its long length (the blank size is close to 4m), high organic content (under the premise of a certain organic content ratio, the roller has a large weight and a high absolute content), and narrow escape channel for decomposed volatiles (the roller is almost wrapped by the inner and outer graphite tubes. If there is no hollow hole, it can only be discharged from the gap between the roller blank and the inner and outer graphite tubes), the decomposed volatiles produced during the debonding process are difficult to be discharged in a timely and effective manner.

[0029] (2) For the debonding sintering process of the whole furnace roller, the hollow hole design improves the high-temperature thermal field uniformity of the large-size furnace batch sintering of silicon carbide rollers: When using traditional layered V-shaped graphite trough kiln to batch sinter silicon carbide tubes, because they are tightly stacked in layers in the heating chamber surrounded by the heating element in the high-temperature sintering furnace, the high-temperature heating process is mainly radiation. The radiation needs to penetrate multiple layers of graphite to heat the tube, resulting in a large temperature difference between the center and the surrounding of the graphite kiln, and the tube often appears "cooked outside and raw inside" or "burnt outside and cooked inside". The hollow hole design allows the heat to reach the tube in the center of the heating chamber more easily during the high-temperature sintering process of the roller, with a small temperature difference between the center and the surroundings and a high temperature field uniformity, so that the roller can use a larger furnace chamber for batch sintering.

[0030] (3) Reduce heat load, save energy and reduce consumption: During the debonding and sintering process, the silicon carbide roller needs kiln furniture to ensure its high straightness and roundness. However, the use of kiln furniture will reduce the roller loading rate in the sintering furnace chamber and increase heat consumption. The design of hollow graphite outer tube and graphite inner tube can reduce the heat load during the debonding and sintering process, save energy and reduce losses while ensuring the high straightness and roundness of the roller and smooth debonding and sintering.

[0031] The diameter of the hollow holes of the graphite outer tube is ≤ the inner diameter of the graphite outer tube / 2, and the diameter of the hollow holes × the number of hollow holes evenly distributed on the same circumference = 2 × the inner diameter of the graphite outer tube. The main purpose is to maintain the rigidity of the graphite outer tube so that it can meet the mechanical strength requirements of the silicon carbide blank. There is a certain inverse correlation between the diameter and number of hollow holes evenly distributed on the same circumference. That is, when the diameter of the hollow holes is large, the number is small; when the diameter of the hollow holes is small, the number is large. In this way, it can be ensured that there is enough cross-sectional area of ​​the hollow holes on the same circumference to meet the needs of the debonding sintering process.

[0032] The axial center distance between adjacent hollow holes of the graphite outer tube in the axial direction is ≥ 2× the diameter of the hollow holes. Ensure that the hollow holes of the graphite outer tube in the axial direction maintain a certain spacing to avoid being too dense, resulting in low overall mechanical strength of the graphite outer tube, and to avoid being too sparse, thereby reducing the cross-sectional area of ​​the hollow holes required for the tube for the debonding sintering process.

[0033] Preferably, the number of hollow holes distributed in each axial direction of the graphite outer tube is the same.

[0034] The hollow holes of the graphite outer tube are also evenly distributed in the circumferential direction. As an example, the graphite outer tube has M circumferences evenly spaced in its axial direction, and N hollow holes are evenly distributed on each circumference. Therefore, the total number of hollow holes in the graphite outer tube is M×N. That is, the graphite outer tube has M hollow holes evenly spaced in each axial direction, and N hollow holes are evenly distributed in each circumferential direction. Therefore, the total number of hollow holes in the graphite outer tube is M×N.

[0035] The graphite outer tube can be formed as a whole. The graphite outer tube can also be formed by splicing in sections. The splicing method is, for example, threaded connection. Threads are processed at the ends of the graphite outer tube sections, and the graphite outer tube sections are spirally connected in sequence to form a whole. For example, the thread length can be ≥80mm.

[0036] The outer diameter of the silicon carbide roller blank has a certain degree of non-roundness. At the same time, in order to facilitate the insertion of the silicon carbide roller blank, the inner diameter of the graphite outer tube is preferably slightly larger than the outer diameter of the silicon carbide roller. But it cannot be too large, otherwise it will not play the role of maintaining roundness. The inner diameter of the graphite outer tube is the outer diameter of the silicon carbide roller blank to be sintered + (0.3-1.0) mm. As an example, the inner diameter of the graphite outer tube = the outer diameter of the silicon carbide roller blank to be sintered + 0.5 mm.

[0037] The wall thickness of the graphite outer tube is ≤5mm. The wall thickness of the graphite outer tube cannot be too thick, otherwise it will increase the heat load in the sintering furnace cavity and reduce the effective loading rate of the roller. As an example, the wall thickness of the graphite outer tube is ≤4mm.

[0038] Straightness is an item that limits the variation of the actual straight line from the ideal straight line. It is used to limit the shape deviation of a straight line in a plane, the shape deviation of a spatial straight line in a certain direction, and the shape deviation of a spatial straight line in any direction. The straightness of the graphite outer tube is ≤0.8‰. That is, the bending and warping of the graphite outer tube in the length direction within any length of 1000mm cannot exceed 0.8mm. As an example, the straightness of the graphite outer tube is ≤0.5‰, preferably ≤0.3‰.

[0039] Out-of-roundness is the difference between the maximum and minimum diameters on the cross section of a circular tube, also known as ellipticity or out-of-roundness. The out-of-roundness of the graphite outer tube is ≤0.5 mm. As an example, the out-of-roundness of the graphite outer tube is ≤0.3 mm.

[0040] The finished length of silicon carbide rollers is generally more than 3000mm, and the length of green billets is usually at least 3800mm. In order to completely cover the silicon carbide roller green billet, the length of the graphite outer tube is not less than 4000mm.

[0041] The graphite inner tube has (multiple) hollow holes evenly distributed in multiple axial directions. Preferably, each axial direction is parallel to each other. That is, the hollow holes of the graphite inner tube are evenly distributed around the central axis of the graphite inner tube. The design principle of the hollow holes of the graphite inner tube is basically the same as that of the graphite outer tube.

[0042] The diameter of the hollow holes of the graphite inner tube is ≤ the outer diameter of the graphite inner tube / 2, and the diameter of the hollow holes of the graphite inner tube×the number of hollow holes uniformly distributed on the same circumference=2×the outer diameter of the graphite inner tube.

[0043] The axial center distance between adjacent hollow holes of the graphite inner tube in the axial direction is ≥ 2×the diameter of the hollow hole.

[0044] Preferably, the number of hollow holes distributed in each axial direction of the graphite inner tube is the same.

[0045] The hollow holes of the graphite inner tube are also evenly distributed in the circumferential direction. As an example, the graphite inner tube has M circumferences evenly spaced in its axial direction, and N hollow holes are evenly distributed on each circumference. Therefore, the total number of hollow holes in the graphite inner tube is M×N. That is, the graphite inner tube has M hollow holes evenly spaced in each axial direction, and N hollow holes are evenly distributed in each circumferential direction. Therefore, the total number of hollow holes in the graphite outer tube is M×N.

[0046] The graphite inner tube can be formed as a whole. The graphite inner tube can also be spliced ​​in sections. The splicing method is, for example, threaded connection. Threads are processed at the ends of the graphite inner tube sections, and the graphite inner tube sections are spirally connected in sequence to form a whole. For example, the thread length can be ≥80mm.

[0047] The sintered silicon carbide roller has a certain degree of non-roundness. In order to prevent the silicon carbide roller from squeezing or even crushing the graphite inner tube during the sintering shrinkage process, the outer diameter of the graphite inner tube is slightly smaller than the inner diameter of the sintered silicon carbide roller. The outer diameter of the graphite inner tube is the inner diameter of the sintered silicon carbide roller - (0.2 to 1.0 mm). As an example, the outer diameter of the graphite inner tube = the inner diameter of the sintered silicon carbide roller - 0.5 mm.

[0048] The wall thickness of the graphite inner tube is ≤5 mm. The wall thickness of the graphite inner tube cannot be too thick, otherwise the heat load in the sintering furnace chamber will be increased. As an example, the wall thickness of the graphite inner tube is ≤4 mm.

[0049] The straightness of the graphite inner tube is ≤0.8‰. As an example, the straightness of the graphite inner tube is ≤0.5‰, preferably ≤0.3‰.

[0050] The out-of-roundness of the graphite inner tube is ≤0.5 mm. As an example, the out-of-roundness of the graphite inner tube is ≤0.2 mm.

[0051] The finished product length of silicon carbide roller is usually more than 3000mm, and the blank length is usually more than 3800mm. In order to completely cover the silicon carbide roller blank, the length of the graphite inner tube is required to be no less than 4000mm.

[0052] The present invention uniformly radiates and heats the silicon carbide roller rod blank by designing a graphite outer tube that is approximately in line with the outer diameter of the silicon carbide roller rod blank, and at the same time, designs a graphite inner tube that is approximately in line with the inner diameter of the sintered silicon carbide roller rod to maintain roundness. The high straightness of the graphite inner and outer tubes also limits the deformation of the tube during the sintering process to the greatest extent, ensuring its high straightness. Therefore, the present invention can avoid the change from surface contact between the tube and the graphite groove to line contact, and fully ensure the straightness and roundness of the tube after sintering.

[0053] The present invention also provides a method for batch sintering of silicon carbide rollers with high straightness and roundness. The method designs the assembly of kiln tools for debonding and sintering of silicon carbide rollers, and controls the debonding and sintering processes, thereby finally realizing batch preparation of silicon carbide rollers with high straightness and roundness.

[0054] Assembly of silicon carbide roller blank and graphite kiln furniture. Silicon carbide roller blank can be prepared by extrusion molding and drying and curing. The silicon carbide roller blank is inserted into the graphite outer tube to form a first assembly, and then the graphite inner tube is inserted into the silicon carbide stick blank of the first assembly to form a second assembly. Although the graphite inner tube can also be inserted into the silicon carbide roller blank to form the first assembly, and then the first assembly is inserted into the graphite outer tube, due to the poor rigidity and long length of the silicon carbide roller blank, a certain degree of deflection and bending will occur during the process of placing it into the graphite outer tube. If the graphite inner tube is inserted into the silicon carbide roller blank first, it is easy to break due to the bending of the blank due to its thin wall and limited graphite strength.

[0055] No fixed connection is required between the graphite outer tube and the graphite inner tube.

[0056] Debonding and sintering integration of batch silicon carbide roller blanks. The second assembly is naturally and tightly stacked (stacked) in a graphite muffle box for debonding and sintering. Preferably, a plurality of second assemblies are naturally and tightly stacked in a graphite muffle box. There is no requirement for the number of stacking layers and the number of assemblies placed in each stacking layer. Stack as much as possible within the strength that the graphite outer tube can withstand.

[0057] The graphite muffle box is a graphite crucible installed in the debonding and sintering integrated furnace. The graphite muffle box is a conventional setting and is not the innovation of the present invention. Existing commercial graphite muffle boxes can be used. The difference is that the present invention is provided with a gas inlet channel and a discharge channel on the graphite muffle box. The design of the gas inlet and outlet channels should ensure that the products of volatile decomposition in the roller blank debonding stage are discharged in a timely and uniform manner, and the inert gas flows evenly through each second assembly in the high-temperature sintering stage. Preferably, the front lower part of the graphite muffle box is provided with an air inlet channel and the rear upper part is provided with an exhaust channel. In addition to these two channels, the graphite muffle box is a closed structure. The graphite muffle box can be a square structure. Existing graphite muffle furnace boxes need to use a negative pressure fan to generate a pressure difference at both ends of the sintering mechanism, thereby guiding the flow of airflow inside the sintering mechanism. The present invention can take out the decomposed volatiles of the inert gas by setting a gas inlet channel and a discharge channel, and taking in air from the inlet channel and exhausting air from the discharge channel.

[0058] Debonding (also known as degreasing) is carried out in a vacuum atmosphere, with a debonding temperature of 1100-1500°C and a debonding time of 0.5-2 hours. The debonding can be carried out under the condition of a vacuum degree of not less than 100Pa. Preferably, the debonding temperature is 1200-1500°C, and the debonding insulation time is 1-2 hours. Organic additives can usually be decomposed at 600-900°C. Increasing the debonding temperature allows the organic decomposition volatiles adsorbed in the insulation layer in the furnace to be removed under high temperature and high vacuum conditions, which is beneficial to the high temperature sintering of silicon carbide ceramics.

[0059] Sintering is carried out in an argon atmosphere at normal pressure. The sintering temperature is 2100-2250°C and the sintering time is 0.5-2 hours. The argon gas is kept flowing. The argon gas pressure can be 1 atmosphere + (20-50 kPa). Preferably, the sintering temperature is 2100-2200°C and the sintering holding time is 1-2 hours.

[0060] Preferably, during the sintering process, the gas inlet of the graphite muffle box is filled with argon at a low flow rate, for example, the argon flow rate is 5-20 L / min.

[0061] The silicon carbide roller prepared by the method of the present invention has excellent straightness and out-of-roundness (straightness ≤ 0.8‰, out-of-roundness ≤ 0.5mm), high density, excellent mechanical and thermal properties, high corrosion resistance, and a roller kiln assembled with the roller kiln can realize smooth and linear transportation of the sagger containing the positive electrode material raw materials in the kiln, and has a higher service life and safety.

[0062] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, without limiting the specific values ​​​​exemplified below.

[0063] The straightness, out-of-roundness and density of silicon carbide rollers are tested in accordance with JC / T 2212-2014 "Silicon carbide ceramic heat exchange tubes sintered at normal pressure solid phase".

[0064] Example 1

[0065] (1) Configure graphite kiln furniture

[0066] The inner diameter of the graphite outer tube is 37.4mm, the wall thickness is 4mm, the length is 4000mm, the straightness is 0.3‰, and the out-of-roundness is 0.3mm. The graphite outer tube is formed by threading 4 sections of graphite tubes with a length of 1000mm, and the threaded connection length at each location is 80mm. The hollow hole diameter of the graphite outer tube is 18.7mm, and there are 4 hollow holes evenly distributed on the same circumference. The axial center distance between adjacent hollow holes in the axial direction is 37.4mm.

[0067] The outer diameter of the graphite inner tube is 21.7mm, the wall thickness is 4mm, the length is 4000mm, the straightness is 0.3‰, and the out-of-roundness is 0.3mm. The graphite inner tube is formed by threading 4 sections of graphite tubes with a length of 1000mm, and the threaded connection length at each location is 80mm. The hollow hole diameter of the graphite inner tube is 10.85mm, and there are 4 hollow holes evenly distributed on the same circumference. The axial center distance between adjacent hollow holes in the axial direction is 21.7mm.

[0068] (2) Assembly of silicon carbide roller blank and graphite kiln furniture

[0069] The outer diameter of the silicon carbide roller blank is 37.1 mm, the wall thickness is 5 mm, and the length is 4000 mm. The silicon carbide roller blank after extrusion molding and drying and curing is inserted into the graphite outer tube to form a first assembly. Then the graphite inner tube is inserted into the silicon carbide rod blank of the first assembly to form a second assembly.

[0070] (3) Debonding and sintering integration of batch silicon carbide roller blanks

[0071] The second assembly after assembling the silicon carbide roller blank and the graphite kiln furniture is naturally and tightly stacked in a square graphite muffle box to achieve debonding and sintering integration. The front short lower part of the graphite muffle box is provided with an air inlet channel and the upper part of the rear end is provided with an exhaust channel. Except for this channel, the graphite muffle box is a closed structure. Debonding is carried out in a vacuum atmosphere, the debonding temperature is 1200℃, the vacuum degree is not less than 80Pa, and the debonding is kept warm for 1 hour. Sintering is carried out in an argon atmosphere at normal pressure, the sintering temperature is 2150℃, and the sintering insulation time is 1 hour. During the sintering process, the air inlet channel of the graphite muffle box is kept filled with argon gas at a flow rate of 10L / min.

[0072] After testing, the silicon carbide roller obtained in Example 1 has a length of 3300 mm, an outer diameter of 30±0.2 mm, an inner diameter of 21.9±0.2 mm, a straightness of 0.4‰, an out-of-roundness of 0.4 mm, and a density of 99.0% TD.

[0073] Example 2

[0074] (1) Configure graphite kiln furniture

[0075] The inner diameter of the graphite outer tube is 50mm, the wall thickness is 5mm, the length is 4500mm, the straightness is 0.5‰, and the out-of-roundness is 0.4mm. The graphite outer tube is formed by threading three sections of graphite tubes with a length of 1500mm, and the threaded connection length at each location is 100mm. The hollow hole diameter of the graphite outer tube is 25mm, and there are 4 hollow holes evenly distributed on the same circumference, and the axial center distance between adjacent hollow holes is 60mm.

[0076] The outer diameter of the graphite inner tube is 29.8mm, the wall thickness is 5mm, the length is 4500mm, the straightness is 0.5‰, and the out-of-roundness is 0.4mm. The graphite inner tube is formed by threading three sections of graphite tubes with a length of 1500mm, and the threaded connection length at each location is 80mm. The hollow hole diameter of the graphite inner tube is 14.9mm, and there are 4 hollow holes evenly distributed on the same circumference. The axial center distance between adjacent hollow holes in the axial direction is 29.8mm.

[0077] (2) Assembly of silicon carbide roller blank and graphite kiln furniture

[0078] The outer diameter of the silicon carbide roller blank is 49.5 mm, the wall thickness is 6 mm, and the length is 4500 mm. The silicon carbide roller blank that has been extruded, dried, and solidified is inserted into the graphite outer tube to form a first assembly. Then the graphite inner tube is inserted into the silicon carbide roller blank of the first assembly to form a second assembly.

[0079] (3) Debonding and sintering integration of batch silicon carbide roller blanks

[0080] The second assembly after assembling the silicon carbide roller blank and the graphite kiln furniture is naturally and tightly stacked in a circular graphite muffle box for debonding and sintering integration. The front lower part of the graphite muffle box is provided with an air inlet channel and the rear upper part is provided with an exhaust channel. Except for this channel, the graphite muffle box is a closed structure. Debonding is carried out in a vacuum atmosphere, the debonding temperature is 1100℃, the vacuum degree is not less than 70Pa, and the debonding is kept warm for 2 hours. Sintering is carried out in an argon atmosphere at normal pressure, the sintering temperature is 2100℃, and the sintering insulation time is 0.5 hours. During the sintering process, the air inlet channels of the graphite muffle box are kept filled with argon gas at a flow rate of 5L / min.

[0081] After testing, the silicon carbide roller obtained in Example 2 has a length of 3700 mm, an outer diameter of 40±0.3 mm, an inner diameter of 30.3±0.3 mm, a straightness of 0.5‰, an out-of-roundness of 0.5 mm, and a density of 99.0% TD.

[0082] Example 3

[0083] (1) Preparation of graphite kiln furniture

[0084] The inner diameter of the graphite outer tube is 62.8mm, the wall thickness is 5mm, the length is 4000mm, the straightness is 0.8‰, and the out-of-roundness is 0.5mm. The graphite outer tube is an integrally formed graphite tube. The hollow hole diameter of the graphite outer tube is 20.93mm, and the number of hollow holes is evenly distributed on the same circumference is 6, and the axial center distance between adjacent hollow holes in the axial direction is 41.86mm.

[0085] The outer diameter of the graphite inner tube is 32.8mm, the wall thickness is 5mm, the length is 4000mm, the straightness is 0.8‰, and the out-of-roundness is 0.5mm. The graphite inner tube is an integrally formed graphite tube. The hollow hole diameter of the graphite inner tube is 10.93mm, and the number of hollow holes is evenly distributed on the same circumference is 6, and the axial center distance between adjacent hollow holes in the axial direction is 21.86mm.

[0086] (2) Assembly of silicon carbide roller blank and graphite kiln furniture

[0087] The outer diameter of the silicon carbide roller blank is 61.8 mm, the wall thickness is 10 mm, and the length is 4000 mm. The silicon carbide roller blank after extrusion molding and drying and curing is inserted into the graphite outer tube to form a first assembly. Then the graphite inner tube is inserted into the silicon carbide roller blank of the first assembly to form a second assembly.

[0088] (3) Debonding and sintering integration of batch silicon carbide roller blanks

[0089] The second assembly after assembling the silicon carbide roller blank and the graphite kiln furniture is naturally and tightly stacked in a square graphite muffle box for debonding and sintering integration. The front lower part of the graphite muffle box is provided with an air inlet channel and the rear upper part is provided with an exhaust channel. Except for this channel, the graphite muffle box is a closed structure. Debonding is carried out in a vacuum atmosphere, the debonding temperature is 1500℃, the vacuum degree is not less than 100Pa, and the debonding is kept warm for 0.5 hours. Sintering is carried out in an argon atmosphere at normal pressure, the sintering temperature is 2250℃, and the sintering insulation time is 2 hours. During the sintering process, the air inlet channels of the graphite muffle box are kept filled with argon gas at a flow rate of 20L / min.

[0090] After testing, the silicon carbide roller obtained in Example 3 has a length of 3300 mm, an outer diameter of 50±0.4 mm, an inner diameter of 33.8±0.4 mm, a straightness of 0.8‰, an out-of-roundness of 0.5 mm, and a density of 98.8% TD.

[0091] Comparative Example 1

[0092] The inner diameter of the graphite outer tube is 38.2 mm, the outer diameter of the graphite inner tube is 20.8 mm, and the rest is the same as in Example 1.

[0093] After testing, the silicon carbide roller obtained in Comparative Example 1 has a length of 3300 mm, an outer diameter of 30±0.5 mm, an inner diameter of 21.9±0.5 mm, a straightness of 1‰, an out-of-roundness of 0.8 mm, and a density of 99.0% TD.

[0094] Comparative Example 2

[0095] The straightness of the graphite outer tube is 1.5‰, the straightness of the graphite inner tube is 1.5‰, and the rest is the same as in Example 1.

[0096] After testing, the silicon carbide roller obtained in Comparative Example 2 has a length of 3300 mm, an outer diameter of 30±0.2 mm, an inner diameter of 21.9±0.2 mm, a straightness of 1.5‰, an out-of-roundness of 0.5 mm, and a density of 99.0% TD.

[0097] Comparative Example 3

[0098] The out-of-roundness of the graphite outer tube is 0.6 mm, the straightness of the graphite inner tube is 0.6‰, and the rest is the same as in Example 1.

[0099] After testing, the silicon carbide roller obtained in Comparative Example 3 has a length of 3300 mm, an outer diameter of 30±0.4 mm, an inner diameter of 21.9±0.4 mm, a straightness of 0.5‰, an out-of-roundness of 1.0 mm, and a density of 99.0% TD.

[0100] Comparative Example 4

[0101] The threaded connection length of the graphite outer tube and the graphite inner tube is 50 mm, and the rest is the same as in Example 1. After being connected, the graphite outer tube and the graphite inner tube have poor strength and break.

[0102] Comparative Example 5

[0103] The graphite muffle box is provided with exhaust holes but no air inlet holes, and the rest is the same as in Example 1.

[0104] After testing, the density of the silicon carbide roller obtained in Comparative Example 5 is 97.0% TD.

[0105] Comparative Example 6

[0106] The debonding temperature is 1000° C., the process is carried out in a vacuum atmosphere with a vacuum degree not higher than 200 Pa, the debonding holding time is 0.5 hour, and the rest is the same as in Example 1.

[0107] After testing, the density of the silicon carbide roller obtained in Comparative Example 6 is 95.0% TD.

[0108] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A graphite kiln tool for sintering silicon carbide rollers with high straightness and roundness, characterized in that: The graphite kiln furniture comprises a graphite outer tube and a graphite inner tube; The graphite outer tube has hollow holes evenly distributed in multiple axial directions; the diameter of the hollow holes of the graphite outer tube is ≤ the inner diameter of the graphite outer tube / 2, and the diameter of the hollow holes × the number of hollow holes evenly distributed on the same circumference = 2 × the inner diameter of the graphite outer tube; wherein the axial center distance of the adjacent hollow holes of the graphite outer tube in the axial direction is ≥ 2 × the diameter of the hollow holes; The graphite inner tube has hollow holes evenly distributed in multiple axial directions; the diameter of the hollow holes of the graphite inner tube is ≤ the outer diameter of the graphite inner tube / 2, and the diameter of the hollow holes × the number of hollow holes evenly distributed on the same circumference = 2 × the outer diameter of the graphite inner tube; wherein the axial center distance of the adjacent hollow holes of the graphite inner tube in the axial direction is ≥ 2 × the diameter of the hollow holes.

2. The graphite kiln tool for sintering silicon carbide rollers according to claim 1, characterized in that: The graphite outer tube or the graphite inner tube is integrally formed.

3. The graphite kiln tool for sintering silicon carbide rollers according to claim 1, characterized in that: The graphite outer tube or the graphite inner tube is formed in sections, and the sections are connected by threads.

4. The graphite kiln furniture for sintering silicon carbide rollers according to any one of claims 1 to 3, characterized in that: The inner diameter of the graphite outer tube is the outer diameter of the silicon carbide roller blank to be sintered + (0.3-1.0) mm; the wall thickness of the graphite outer tube is ≤5 mm, the straightness is ≤0.8‰, and the out-of-roundness is ≤0.5 mm.

5. The graphite kiln tool for sintering silicon carbide rollers according to any one of claims 1 to 4, characterized in that: The outer diameter of the graphite inner tube is the inner diameter of the sintered silicon carbide roller - (0.2 to 1.0 mm); the wall thickness of the graphite inner tube is ≤5 mm, the straightness is ≤0.8‰, and the out-of-roundness is ≤0.5 mm.

6. The method for batch sintering high straightness and high roundness silicon carbide rollers according to any one of claims 1 to 5, characterized in that: The method comprises: (1) Assembling the graphite kiln furniture and the silicon carbide roller blank to be sintered: inserting the silicon carbide roller blank to be sintered into the graphite outer tube to form a first assembly, and then inserting the graphite inner tube into the first assembly to form a second assembly; (2) Debonding and sintering integration of batch silicon carbide roller blanks: The second assembly of the silicon carbide roller blanks to be sintered and the graphite kiln tool is naturally and tightly stacked in the graphite muffle box. The silicon carbide roller blanks to be sintered are debonded and sintered to obtain silicon carbide rollers with high straightness and high roundness.

7. The batch sintering method according to claim 6, characterized in that: The graphite muffle box has a closed structure except for an air inlet channel arranged at a lower front end portion and an exhaust channel arranged at an upper rear end portion.

8. The batch sintering method according to claim 7, characterized in that: During the sintering process, the gas inlet of the graphite muffle box is kept filled with argon; preferably, the argon flow rate is 5-20 L / min.

9. The batch sintering method according to any one of claims 6 to 8, characterized in that: The hollow holes of the graphite outer tube and the graphite inner tube and the gaps formed by the natural and tight stacking of graphite kiln tools together constitute a through-going gas flow and radiation heat transfer channel.

10. The batch sintering method according to any one of claims 6 to 9, characterized in that: Debonding is carried out in a vacuum atmosphere, the debonding temperature is 1100-1500°C, and the debonding holding time is 0.5-2 hours; sintering is carried out in a normal pressure argon atmosphere, the sintering temperature is 2100-2250°C, and the sintering holding time is 0.5-2 hours.

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