Preparation method for producing umbrella-leaf-free rod porcelain by dry method

Abstract

The invention belongs to the technical field of porcelain insulator preparation, and particularly relates to a preparation method for producing umbrella-leaf-free rod porcelain by a dry method. The preparation method for producing the umbrella-leaf-free rod porcelain by the dry method comprises the following steps: mixing and ball-milling green body raw materials, and uniformly mixing the green body raw materials with old slurry to obtain green body slurry; carrying out spray drying and aging on the green body slurry to obtain green body powder; filling a mold with the green body powder, placing corrugated boards on the lower surface and the upper surface of the green body powder in the mold, and performing compression molding by a cold isostatic press in a multi-step pressure boosting and reducing mode to obtain a rod porcelain green body; the method comprises the following steps of: fettling a rod porcelain green body, brushing insulating paint at two ends of the rod porcelain green body, blasting sand, spraying sand-consolidating glaze, drying, and firing in a kiln by adopting a layered kiln loading manner to obtain the umbrella-leaf-free rod porcelain, the green body formed by the method is uniform in density, low in internal stress, high in product strength, small in strength dispersity and free of hanging burning head and base parts, the production energy consumption is reduced, and the turning and cutting time is shortened.

Description

Technical Field

[0001] The invention belongs to the technical field of porcelain insulator preparation, and particularly relates to a preparation method for producing leaf-free porcelain rods by a dry process. Background Art

[0002] Rod porcelain is an oversized, high-strength, non-breakdown, aluminum or silicon porcelain insulation component. It is an important basic component in the power and electrical industries. Rod porcelain insulators are primarily used in outdoor power stations, substations, distribution equipment, and electrical equipment with power frequency AC voltages from 40.5 to 1100 kV to insulate and support live parts.

[0003] The rod porcelain is a solid structure, and the adhesive bonding part adopts a columnar sand-on structure. The element is made of porcelain parts and upper and lower flanges bonded with cement adhesive, and the porcelain components are fastened together by flanges. The umbrella shape can adopt a large umbrella, a medium umbrella, a small umbrella structure, or a large umbrella and two small umbrella structures. Depending on the pollution resistance level requirements, the umbrella can be a pollution-resistant bare umbrella structure with or without edges, or the surface can be sprayed with PRTV coating.

[0004] As power market demands evolve, outdoor power stations and substations are placing increasingly stringent demands on insulating support components. This has necessitated the development of a new type of porcelain-core composite insulator. This insulator features a porcelain core composed of a non-bladed porcelain rod and flanges bonded together with a cement adhesive. The insulator is then coated with a high-temperature vulcanized silicone rubber sheath and shed skirts. Combining the advantages of both porcelain and silicone rubber composite outer layers, it has become a crucial component in high-voltage power transmission and transformation projects.

[0005] At present, the key steps in the industrial production of umbrella-less leaf rod porcelain are molding and firing. Among them, the main molding methods are wet clay extrusion molding and dry powder wet bag cold isostatic pressing molding. Among them, wet clay extrusion molding has a high molding qualification rate, but has high requirements on equipment and high energy consumption; dry powder wet bag cold isostatic pressing molding has relatively low equipment cost and energy consumption, and the process flow is simpler, but there is a large internal stress in the green body during the dry molding process, which can easily cause the green body to explode and shatter after demolding, and the molding qualification rate is low.

[0006] The firing method mainly adopts the "seat first, hang later" method, that is, a base is left at the lower end of the blank and a hanging head is left at the upper end, so that the blank can sit in the sagger on the kiln car or on the refractory wool after loading, and ensure that the blank can be hung on the beam when it leaves the seat due to shrinkage during the firing process, so as to ensure the verticality and coaxiality of the porcelain piece. This is the most mature firing method in the production of umbrella-less stick porcelain. However, after firing is completed, the hanging head and base need to be removed by cutting, which produces a large amount of waste porcelain, which not only increases manufacturing costs and energy consumption, but also this firing method can cause quality problems such as cracking of the hanging head or cracking of the main body due to inappropriate coordination of the high-temperature viscosity of the formula, design scale, firing curve, etc.

[0007] Therefore, it is necessary to improve the process of dry-process production of umbrella-less rod porcelain to solve the above-mentioned problems of low dry-process molding qualification rate and firing method. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a dry method for producing umbrella-less leaf rod porcelain, which has strong versatility, uniform density of the formed body, low internal stress, high product strength and small strength dispersion, no hanging burning head and base part, reduces production energy consumption, and shortens turning and cutting time.

[0009] The dry process for producing non-umbrella-leaf rod porcelain of the present invention comprises the following steps: (1) Slurry mixing: The green body raw materials are mixed and ball-milled to obtain new slurry, the new slurry and the old slurry are mixed evenly, and iron is removed by sieving to obtain green body slurry; (2) Powdering: The green body slurry is spray-dried to obtain powder, and then aged to obtain green body powder; (3) Molding: The green body powder is filled into a mold, and corrugated cardboard is placed below and above the green body powder in the mold, and then pressed into shape by a cold isostatic press to obtain a rod porcelain green body; (4) Firing: After the rod porcelain body is trimmed, the two ends of the rod porcelain body are brushed with insulating paint, sandblasted, and sprayed with solid sand glaze, and then dried and fired in a kiln to obtain umbrella-free rod porcelain; In step (3), when the cold isostatic press is pressed and formed, a multi-step pressure increase and decrease mode is adopted, and the method is as follows: The pressure is increased at a rate of 1-1.2 MPa / s, and when the pressure reaches 30-40 MPa, 50-60 MPa, 70-80 MPa, and 90-100 MPa, the pressure is maintained for 30-50 seconds, and the pressure is continued to be increased, and finally the pressure is increased to 110-120 MPa, and the pressure is maintained for 120-150 seconds; then the pressure is reduced at a rate of 0.5-0.6 MPa / s, and when the pressure is reduced to 95-90 MPa, 85-80 MPa, 75-70 MPa, 60-55 MPa, 45-40 MPa, and 30-25 MPa, the pressure is maintained for 30-50 seconds, and the pressure is continued to be reduced, and finally the pressure is reduced to normal pressure to complete the cold isostatic pressing molding; In step (4), when loading the kiln for firing, a layered loading method is adopted, and the method is as follows: Place several silicon carbide columns at the bottom of the kiln, then spread a layer of alumina powder at the bottom of the kiln, then place a layer of alumina balls on the alumina powder layer, and place the dried rod porcelain body on the alumina ball layer; then place silicon carbide plates on the silicon carbide columns, and then follow the above operations to place silicon carbide columns, spread a layer of alumina powder, place a layer of alumina balls, place rod porcelain body, and place silicon carbide plates in sequence; continue to repeat the above operations until the kiln loading is completed.

[0010] In step (1), the green body raw materials include alumina raw materials, solvent raw materials, fired clay raw materials, soft clay raw materials, water reducing agent, and water, but are not limited to the above raw materials. The preparation method of the present invention has no restrictions on the raw material formula system of the rod porcelain green body, and is applicable to almost all raw material formula systems of the rod porcelain green body on the market, and has strong versatility.

[0011] In step (1), the ball milling time is 7-15 hours. During ball milling, alumina balls and alumina ball liners are preferably used to prevent the rubber ball liners from abrading and entering the slurry, which affects the firing density and product quality. During the ball milling process, a laser particle size tester is used to measure the particle size. The median particle size is maintained at 5.7±0.5µm, which is considered qualified. After the slurry is qualified, it is sieved and milled and enters the slurry tank.

[0012] In step (1), the old slurry is the slurry formed by mixing the leftover materials and broken green bodies left during the molding and repairing process of the leafless rod porcelain, which are crushed and then added with water and a water reducing agent.

[0013] The used pulp accounts for 0-60% by weight of the green body slurry; preferably, the mass ratio of new pulp to used pulp is 1:(0.8-1.5). Adding a certain amount of used pulp to the green body slurry not only allows for waste recycling, is simple and effective, and can significantly reduce production costs. Furthermore, due to repeated recycling, the used pulp's agglomeration and bonding properties deteriorate, making it relatively more dispersible. Therefore, compared to new pulp, its performance is more uniform and has better flowability, significantly improving the uniformity and flowability of the slurry in the use tank. Furthermore, after repeated soaking, drying, and polishing, the organic components of the used pulp expand and crack, causing them to leach out or become smaller. This reduces the decomposition time and the temperature at which organic matter begins to decompose during the product firing process. The overall particle size of the used pulp is smaller than that of the new pulp, which can also reduce the maximum firing temperature of the product to a certain extent. However, since the used pulp is mostly recycled pulp, it may introduce some unforeseen substances during processing. Therefore, the amount of used pulp added should be controlled and not too high.

[0014] In step (1), the number of times of sieving and removing iron should be no less than 3 times. Iron spots or other magnetic substances in the slurry will not only cause the partial insulation performance of the insulating part to fail, but also make it impossible to melt or synthesize other phases during the firing process, and will also cause quality defects inside the porcelain body, becoming a weak point affecting the strength of the porcelain part.

[0015] Preferably, the method for detecting the number of iron spots or other magnetic substances in the slurry is as follows: weigh 5 kg of slurry, stir it with a handheld magnetic rod, and each stirring time is not less than 5 minutes, then place the magnetic rod in a bucket of clean water, rinse off the adhering slurry with water by hand, observe the number of iron spots or other magnetic substances on the magnetic rod, and do this operation for 6 consecutive times. The cumulative number is calculated. The number of iron spots or other magnetic substances with a diameter greater than 1 mm shall not exceed 2, and the number of iron spots or other magnetic substances with a diameter greater than 0.5 mm shall not exceed 6; if it exceeds the process standard, the screening and iron removal work should be repeated, and then the iron spots or other magnetic substances should be detected until the process use standard is met before the slurry can be released into the use pool.

[0016] In step (2), the moisture content of the powder obtained by spray drying is 1-2 wt.%. When the moisture content of the powder is higher than 2 wt.%, it will increase the difficulty of trimming the blank after forming, and the blank may break.

[0017] In step (2), the aging time is not less than 24 hours. During the aging process, the moisture content of the powder will be more evenly dispersed, avoiding uneven surface or breakage of the blanks caused by uneven moisture content during trimming after molding. Aging can also increase the fluidity of the powder, allowing it to achieve optimal particle accumulation during the molding process and increase its packing density.

[0018] In step (3), the mold is preferably a silicone rubber mold. Using a hard silicone rubber mold instead of a soft rubber bag can ensure that the rod porcelain body is formed to near net size and reduce the turning allowance.

[0019] In step (3), preferably 3-5 layers of corrugated cardboard are placed below and above the green body powder in the mold. The corrugated cardboard is circular and its diameter is 1-2 mm smaller than the inner diameter of the mold.

[0020] By placing corrugated cardboard, the internal stress of the blank after molding can be reduced. When the mold is under pressure, the pressure around the mold penetrates normally, and the upper and lower surfaces with corrugated cardboard can slow down the penetration speed of the upper and lower pressures due to the special structure of the corrugated cardboard itself. This is more conducive to the exhaust of powder before molding, thereby improving the molding rate and density uniformity of the blank and reducing the internal stress after molding. In addition, when the blank is unloaded after molding, the corrugated cardboard has good softness and elasticity due to the certain space left in the structure, thereby dispersing the impact force during the mold recovery process and reducing vibration damage to the blank.

[0021] Preferably, the corrugated cardboard can be placed in the following manner: Before putting the green body powder into the mold, put 3-5 layers of corrugated cardboard at the bottom of the mold, and then put the green body powder into the mold. At the same time, the mold can maintain a uniform vibration to make the green body powder filled more compactly. When the green body powder is filled to 35-45mm from the upper edge of the mold, cover it with 3-5 layers of corrugated cardboard, and finally cover the top cover of the mold tightly, put it into the cold isostatic press, and press it into shape.

[0022] In step (3), a multi-step pressure increase and decrease mode is used for cold isostatic pressing, which can greatly reduce the stress in the rod porcelain blank, avoid the rod porcelain blank from bursting and breaking after demolding after dry forming, and significantly improve the pass rate of dry forming.

[0023] In step (4), it is preferred to use a CNC blanking machine to perform blanking treatment on the rod porcelain blank. When blanking, an industrial scouring pad is first used for rough polishing, and then a white cotton cloth is used for fine polishing to remove scratches on the surface of the main body of the rod porcelain blank to the greatest extent. After the surface treatment is completed, the rod porcelain blank is transferred from the CNC blanking machine to the blank transfer rack, and an electric grinder with a scouring pad is used to polish the two ends of the rod porcelain blank respectively until there are no bumps, cracks, etc., and the end faces are flat and smooth. Finally, compressed air is used to remove dust on the surface of the rod porcelain blank.

[0024] In step (4), after the rod porcelain body is trimmed, a circle of insulating paint is first brushed on both ends of the rod porcelain body with a brush, and then sandblasted immediately with a sandblasting instrument, and then a layer of sand-fixing glaze of the corresponding color is sprayed, and then transferred to the drying area for drying.

[0025] In step (4), the drying temperature is 35-45°C and the drying time is 24-36 hours.

[0026] In step (4), the firing conditions are: room temperature-120°C, 360-480 min; 120°C, 100-120 min; 120-640°C, 380-410 min; 640-830°C, 280-340 min; 830-950°C, 120-220 min; 950-980°C, 840-900 min; 980-1190°C, 300-330 min; 1190-1240°C, 180-230 min; 1240-1245°C, 20-30 min.

[0027] In step (4), the alumina powder layer is spread to a thickness of 6-11 mm, and the median particle size D50 of the alumina powder used is 55±5 µm. The alumina sphere layer is a single layer, and the diameter of the alumina spheres used is 10-15 mm, with the gap between adjacent alumina spheres maintained at 3-6 mm. Preferably, the purity of the alumina powder and alumina spheres is ≥99%.

[0028] The present invention can realize the rolling firing of the rod porcelain body by spreading an alumina powder layer and placing an alumina ball layer. The rod porcelain body has a porous structure before sintering. During the firing process, the high temperature will cause a low eutectic phenomenon to appear in the rod porcelain body, thereby causing a glass liquid phase to appear in the rod porcelain body. Due to the fluidity and surface tension of the liquid phase, the original pores are filled one by one, thereby causing a shrinkage phenomenon. The alumina balls can roll with the shrinkage of the rod porcelain at high temperature, preventing the ceramic product from directly contacting the bottom of the kiln to generate friction and cause cracking.

[0029] In step (4), the role of the silicon carbide columns and silicon carbide plates is to divide the interior of the kiln into a multi-layer structure, which is convenient for placing the rod porcelain blanks in layers. Therefore, the number and position of the silicon carbide columns can be set according to the bottom area of ​​the kiln, and their height can be set according to the placement height of the rod porcelain blanks; the area and shape of the silicon carbide plates should be adapted to the kiln. When placing the rod porcelain blanks, the gap between adjacent rod porcelain blanks is adjusted according to the specifications of the rod porcelain, and they do not contact each other during the firing process. The gap between the top of the rod porcelain blank and the bottom of the silicon carbide plate should be no less than 5mm to prevent the rod porcelain blanks from contacting the silicon carbide plate during the firing process.

[0030] In the existing technology, the firing method of "seating first and hanging later" is generally adopted, that is, a base is left at the lower end of the rod porcelain body and a hanging firing head is left at the upper end, so that the rod porcelain body can be placed in the sagger or on the refractory wool on the kiln car after loading, and it is ensured that the body can be hung on the beam when it shrinks and leaves the seat during the firing process, so as to ensure the verticality and coaxiality of the rod porcelain. This firing method not only has a low kiln space utilization rate of only 50-65%, but also the upper part of the kiln is empty, while the bottom is filled with rod porcelain blanks. When hot air blows, the air flow is uneven. The same rod porcelain blank (the height of the rod porcelain blank ranges from 500-2700mm) will have a large difference in body density and porosity between the upper, middle and lower parts, and the shrinkage uniformity of the entire body is also poor. In addition, the presence of the hanging firing head and base will increase the weight of the product itself, causing the center of gravity of the rod porcelain blank to change, which may easily lead to cracking of the main body at 1 / 3 of the rod porcelain blank, and will also increase the preparation difficulty, firing energy consumption and the amount of waste.

[0031] The present invention adopts a layered firing method instead of the "first seating and then hanging" firing method. On the one hand, it can increase the number of porcelain rod bodies that can be fired, maximize the use of kiln space, and increase the kiln space utilization rate to 85-90%; on the other hand, it changes the sintering position, and there is no need to add a hanging firing head and a base, saving raw materials and energy; at the same time, each layer of the product is kept on the same plane, the body density becomes relatively uniform, and the uniformity of the main body shrinkage is also significantly improved.

[0032] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention places corrugated cardboard above and below the material mold and adopts a multi-step pressure increase and decrease mode for cold isostatic pressing, thereby reducing the internal stress of the green body after forming, avoiding the cracking and breaking of the dry-formed porcelain green body after demolding, and greatly improving the pass rate of dry-formed green body; (2) The present invention adopts a layered firing method instead of the "first seating and then hanging" firing method, which can increase the number of rod porcelain blanks that can be fired and increase the kiln space utilization rate from 50-65% to 85-90%, thereby maximizing the use of the kiln space. In addition, there is no need to leave hanging firing heads and base parts at the upper and lower ends of the rod porcelain blanks, which reduces the weight of the product and the difficulty of manufacturing, thereby saving raw materials and energy consumption, and improving the body density and shrinkage uniformity of the upper, middle and lower parts of the porcelain body. (3) The preparation method of the present invention has strong versatility, the density of the formed green body is uniform, the internal stress is low, the product strength is high and the strength dispersion is small, there is no hanging burning head and base part, the production energy consumption is reduced, and the turning and cutting time are shortened. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the following examples. The raw materials used in the examples, unless otherwise specified, are all commercially available conventional raw materials; the process methods used in the examples, unless otherwise specified, are all conventional methods in the art.

[0034] For the convenience of comparison, the following green body raw material composition is used in both the examples and the comparative examples: 47 wt.% of alumina, 10 wt.% of feldspar, 11 wt.% of zhangcun clay, 14 wt.% of kaolin, and 18 wt.% of clay; and 0.23 wt.% of a polycarboxylic acid water reducer and 32 wt.% of water are additionally added.

[0035] The old slurry used in the embodiment is the residual material and broken green body left during the molding and repairing process of the leafless rod porcelain preparation process. After being crushed, 0.23wt.% of polycarboxylic acid water reducer and 32wt.% of water are added and mixed to form a slurry.

[0036] Example 1 A dry process for producing leaf-free porcelain rods comprises the following steps: (1) Slurry mixing: Weigh the green body raw materials in proportion and put them into a ball mill with alumina balls and alumina ball lining. After ball milling for 15 hours, use a laser particle size tester to detect the particle size. The median particle size is 5.69 μm, which is qualified. Sieve and mill to obtain new slurry; mix the new slurry and the old slurry in a mass ratio of 1:0.8, sieve and remove iron three times to obtain green body slurry; (2) Powdering: The green body slurry is spray-dried to obtain a powder with a water content of 1.1 wt.%, and aged at room temperature for 24 h to obtain green body powder; (3) Molding: Place 3 layers of circular corrugated paper at the bottom of the silicone rubber mold. The diameter of the corrugated paperboard is 1 mm smaller than the inner diameter of the silicone rubber mold. Then, fill the green body powder into the silicone rubber mold through a vibrating screen. When the green body powder is filled to 35 mm from the upper edge of the silicone rubber mold, place another 3 layers of circular corrugated paper. Cover the top cover of the silicone rubber mold tightly and place it in a cold isostatic press. Use a multi-step pressure increase and decrease mode for pressing and molding. The method is as follows: The pressure was increased at a rate of 1 MPa / s, and maintained for 30 seconds when the pressure was increased to 33 MPa, for 30 seconds when the pressure was increased to 55 MPa, for 45 seconds when the pressure was increased to 77 MPa, for 35 seconds when the pressure was increased to 90 MPa, and finally increased to 112 MPa and maintained for 130 seconds; the pressure was then reduced at a rate of 0.58 MPa / s, and maintained for 45 seconds when the pressure was reduced to 90 MPa, for 50 seconds when the pressure was reduced to 82 MPa, for 50 seconds when the pressure was reduced to 72 MPa, for 50 seconds when the pressure was reduced to 60 MPa, for 45 seconds when the pressure was reduced to 42 MPa, for 30 seconds when the pressure was reduced to 27 MPa, and finally reduced to normal pressure and demolded to obtain a rod porcelain green body; (4) Firing: Use a CNC blanking machine to perform blanking treatment on the rod porcelain blank. When blanking, first use an industrial scouring pad to roughly polish it, and then use a white cotton cloth to polish it finely to remove the scratches on the surface of the main body of the rod porcelain blank to the greatest extent. After the surface treatment is completed, the rod porcelain blank is transferred from the CNC blanking machine to the blank transfer rack. Use an electric grinder with a scouring pad to polish the two ends of the rod porcelain blank respectively until there are no bumps, cracks, etc., and the end surface is flat and smooth. Finally, use compressed air to remove the dust on the surface of the rod porcelain blank to complete the blanking; After the blank is trimmed, a circle of insulating paint is applied to both ends of the rod porcelain blank with a brush, and then sandblasted immediately with a sandblasting machine, followed by a layer of solid sand glaze of the corresponding color, and then transferred to the drying area and dried at 40℃ for 30 hours. Finally, it is loaded into the kiln and fired to obtain umbrella-free rod porcelain; When loading the kiln for firing, the layered loading method is adopted, and the method is as follows: Place several silicon carbide columns at the bottom of the kiln, then spread a 6mm thick layer of alumina powder (the median particle size D50 of alumina powder is 55±5µm, and the purity is ≥99%) at the bottom of the kiln, and then place a layer of alumina balls (the diameter of alumina balls is 10mm, and the purity is ≥99%) on the alumina powder layer. The gap between adjacent alumina balls is kept at 3mm. The dried rod porcelain blanks are evenly arranged on the alumina ball layer by a crane; then place silicon carbide plates on the silicon carbide columns, and the gap between the top of the rod porcelain blank and the bottom of the silicon carbide plates is not less than 5mm. Then, follow the above operations to place silicon carbide columns, spread the alumina powder layer, place the alumina ball layer, place the rod porcelain blank, and place the silicon carbide plates in sequence; continue to repeat the above operations until the kiln is loaded; The firing conditions are: room temperature-120℃, 480min; 120℃, 120min; 120-640℃, 410min; 640-830℃, 340min; 830-950℃, 220min; 950-980℃, 900min; 980-1190℃, 330min; 1190-1240℃, 230min; 1240-1245℃, 30min.

[0037] Example 2 A dry process for producing leaf-free porcelain rods comprises the following steps: (1) Slurry mixing: Weigh the green body raw materials in proportion and put them into a ball mill with alumina balls and alumina ball lining. After ball milling for 7 hours, use a laser particle size tester to detect the particle size. The median particle size is 6.21μm, which is qualified. Sieve and put it out of the mill to obtain new slurry; mix the new slurry and the old slurry in a mass ratio of 1:1.5, sieve and remove iron three times to obtain green body slurry; (2) Powdering: The green body slurry is spray-dried to obtain a powder with a water content of 2.0 wt.%, and aged at room temperature for 24 h to obtain green body powder; (3) Molding: Place 4 layers of circular corrugated paper at the bottom of the silicone rubber mold. The diameter of the corrugated paperboard is 2 mm smaller than the inner diameter of the silicone rubber mold. Then, fill the green body powder into the silicone rubber mold through a vibrating screen. When the green body powder is filled to 40 mm from the upper edge of the silicone rubber mold, place another 4 layers of circular corrugated paper. Cover the top cover of the silicone rubber mold tightly and place it in a cold isostatic press. Use a multi-step pressure increase and decrease mode for pressing and molding. The method is as follows: The pressure was increased at a rate of 1.2 MPa / s, and the pressure was maintained for 35 seconds when the pressure was increased to 30 MPa, for 35 seconds when the pressure was increased to 50 MPa, for 40 seconds when the pressure was increased to 70 MPa, for 30 seconds when the pressure was increased to 95 MPa, and finally the pressure was increased to 110 MPa and maintained for 150 seconds; the pressure was then reduced at a rate of 0.6 MPa / s, and the pressure was maintained for 45 seconds when the pressure was reduced to 92 MPa, for 55 seconds when the pressure was reduced to 80 MPa, for 50 seconds when the pressure was reduced to 70 MPa, for 40 seconds when the pressure was reduced to 55 MPa, for 35 seconds when the pressure was reduced to 40 MPa, and for 30 seconds when the pressure was reduced to 25 MPa, and finally the pressure was reduced to normal pressure and demolded to obtain a rod porcelain green body; (4) Firing: Use a CNC blanking machine to perform blanking treatment on the rod porcelain blank. When blanking, first use an industrial scouring pad to roughly polish it, and then use a white cotton cloth to polish it finely to remove the scratches on the surface of the main body of the rod porcelain blank to the greatest extent. After the surface treatment is completed, the rod porcelain blank is transferred from the CNC blanking machine to the blank transfer rack. Use an electric grinder with a scouring pad to polish the two ends of the rod porcelain blank respectively until there are no bumps, cracks, etc., and the end surface is flat and smooth. Finally, use compressed air to remove the dust on the surface of the rod porcelain blank to complete the blanking; After the blank is trimmed, a circle of insulating paint is applied to both ends of the rod porcelain blank with a brush, and then sandblasted immediately with a sandblasting machine, followed by a layer of solid sand glaze of the corresponding color, and then transferred to the drying area and dried at 35°C for 36 hours. Finally, it is loaded into the kiln and fired to obtain umbrella-free rod porcelain; When loading the kiln for firing, the layered loading method is adopted, and the method is as follows: Place several silicon carbide columns at the bottom of the kiln, then spread an 11mm thick layer of alumina powder (the median particle size D50 of alumina powder is 55±5µm, and the purity is ≥99%) at the bottom of the kiln, and then place a layer of alumina balls (the diameter of alumina balls is 15mm, and the purity is ≥99%) on the alumina powder layer. The gap between adjacent alumina balls is kept at 6mm. The dried rod porcelain blanks are evenly arranged on the alumina ball layer by a crane; then place silicon carbide plates on the silicon carbide columns, and the gap between the top of the rod porcelain blank and the bottom of the silicon carbide plates is not less than 5mm. Then, follow the above operations to place silicon carbide columns, spread the alumina powder layer, place the alumina ball layer, place the rod porcelain blank, and place the silicon carbide plates in sequence; continue to repeat the above operations until the kiln is loaded; The firing conditions are: room temperature-120℃, 360min; 120℃, 100min; 120-640℃, 380min; 640-830℃, 280min; 830-950℃, 120min; 950-980℃, 840min; 980-1190℃, 300min; 1190-1240℃, 180min; 1240-1245℃, 20min.

[0038] Example 3 A dry process for producing leaf-free porcelain rods comprises the following steps: (1) Slurry mixing: Weigh the green body raw materials in proportion and put them into a ball mill with alumina balls and alumina ball lining. After ball milling for 12 hours, use a laser particle size tester to detect the particle size. The median particle size is 5.93 μm, which is qualified. Sieve and put it out of the mill to obtain new slurry; mix the new slurry and the old slurry in a mass ratio of 1:1.2, sieve and remove iron three times to obtain green body slurry; (2) Powdering: The green body slurry is spray-dried to obtain a powder with a water content of 1.0 wt.%, and then aged at room temperature for 24 h to obtain green body powder; (3) Molding: Place 5 layers of circular corrugated paper at the bottom of the silicone rubber mold. The diameter of the corrugated paperboard is 1.5 mm smaller than the inner diameter of the silicone rubber mold. Then, fill the green body powder into the silicone rubber mold through a vibrating screen. When the green body powder is filled to 45 mm from the upper edge of the silicone rubber mold, place another 5 layers of circular corrugated paper. Cover the top cover of the silicone rubber mold tightly and place it in a cold isostatic press. Use a multi-step pressure increase and decrease mode for pressing and molding. The method is as follows: The pressure was increased at a rate of 1.1 MPa / s, and the pressure was maintained for 30 seconds when the pressure was increased to 40 MPa, for 30 seconds when the pressure was increased to 60 MPa, for 45 seconds when the pressure was increased to 80 MPa, for 35 seconds when the pressure was increased to 100 MPa, and finally the pressure was increased to 120 MPa and maintained for 120 seconds; the pressure was then reduced at a rate of 0.5 MPa / s, and the pressure was maintained for 40 seconds when the pressure was reduced to 95 MPa, for 50 seconds when the pressure was reduced to 85 MPa, for 45 seconds when the pressure was reduced to 75 MPa, for 45 seconds when the pressure was reduced to 58 MPa, for 40 seconds when the pressure was reduced to 45 MPa, for 35 seconds when the pressure was reduced to 30 MPa, and finally the pressure was reduced to normal pressure and demolded to obtain a rod porcelain green body; (4) Firing: Use a CNC blanking machine to perform blanking treatment on the rod porcelain blank. When blanking, first use an industrial scouring pad to roughly polish it, and then use a white cotton cloth to polish it finely to remove the scratches on the surface of the main body of the rod porcelain blank to the greatest extent. After the surface treatment is completed, the rod porcelain blank is transferred from the CNC blanking machine to the blank transfer rack. Use an electric grinder with a scouring pad to polish the two ends of the rod porcelain blank respectively until there are no bumps, cracks, etc., and the end surface is flat and smooth. Finally, use compressed air to remove the dust on the surface of the rod porcelain blank to complete the blanking; After the blank is trimmed, a circle of insulating paint is applied to both ends of the rod porcelain blank with a brush, and then sandblasted immediately with a sandblasting machine, followed by a layer of solid sand glaze of the corresponding color, and then transferred to the drying area and dried at 45°C for 24 hours. Finally, it is loaded into the kiln and fired to obtain umbrella-free rod porcelain; When loading the kiln for firing, the layered loading method is adopted, and the method is as follows: Place several silicon carbide columns at the bottom of the kiln, then spread a 9mm thick layer of alumina powder (the median particle size D50 of alumina powder is 55±5µm, and the purity is ≥99%) at the bottom of the kiln, and then place a layer of alumina balls (the diameter of alumina balls is 13mm, and the purity is ≥99%) on the alumina powder layer. The gap between adjacent alumina balls is kept at 4mm. The dried rod porcelain blanks are evenly arranged on the alumina ball layer by a crane; then place silicon carbide plates on the silicon carbide columns, and the gap between the top of the rod porcelain blank and the bottom of the silicon carbide plates is not less than 5mm. Then, follow the above operations to place the silicon carbide columns, spread the alumina powder layer, place the alumina ball layer, place the rod porcelain blank, and place the silicon carbide plates in sequence; continue to repeat the above operations until the kiln is loaded; The firing conditions are: room temperature-120℃, 420min; 120℃, 110min; 120-640℃, 395min; 640-830℃, 310min; 830-950℃, 170min; 950-980℃, 870min; 980-1190℃, 315min; 1190-1240℃, 220min; 1240-1245℃, 25min.

[0039] Example 4 The only difference between this embodiment and comparative example 1 is that no old pulp is added during the slurry mixing in step (1), and all new pulp is used.

[0040] Comparative Example 1 The only difference between this comparative example and Example 1 is that, during the molding process in step (3), no corrugated paper is placed at the bottom and top of the silicone rubber mold. Instead, the green body powder is directly loaded into the silicone rubber mold and then placed in a cold isostatic press, where it is molded using a multi-step pressure increase and decrease mode.

[0041] When this method was used for demolding, most of the porcelain rod blanks cracked, and the qualified rate of porcelain rod blanks was only 39%. This was because the hard silicone rubber mold did not play an effective buffering role during the pressurization and decompression process, resulting in greater internal stress in the blank.

[0042] Comparative Example 2 The only difference between this comparative example and Example 1 is that the conventional cold isostatic pressing mode is used in step (3) molding, and the method is as follows: the pressure is increased to 112 MPa at a pressure increase rate of 0.6 MPa / s, the pressure is maintained for 150 seconds, and then the pressure is reduced to normal pressure at a pressure reduction rate of 0.5 MPa / s.

[0043] When this method is used for demolding, a small number of porcelain rod blanks appear irregularly shaped or cracked, and the qualified rate of porcelain rod blanks is only 71%. This is because for hard silicone rubber molds, continuous pressure increase and decrease will cause the blank to undergo large deformation. It is necessary to increase and maintain the pressure in stages, and reduce and maintain the pressure in stages to reduce the internal stress of the blank and prevent the formed blank from exploding and breaking after demolding.

[0044] Comparative Example 3 The difference between this comparative example and Example 1 is that the base and the hanging head portion are added to the rod porcelain blank obtained during molding in step (3), and the conventional "seat first and hang later" kiln loading method is adopted during firing in step (4), that is, the rod porcelain blank with the base and the hanging head is seated on the rock wool on the kiln car. When loading the kiln, the blank is transferred to the sagger on the kiln car or seated on the refractory wool by the crane, and then fixed at the upper end of the neck with a silicon nitride column and a chuck. After reaching a certain temperature during the firing process, the blank leaves the seat due to shrinkage and is hung on the beam.

[0045] This method requires the addition of a base and a hanging firing head. Compared with the near-net-size forming method of the present invention, the size of the rod porcelain blank is about 10% larger, more waste is generated, and the difficulty of blank repair is also increased.

[0046] In order to compare the uniformity of bulk density, porosity and shrinkage of the non-umbrella-leaf rod porcelain prepared in each embodiment and comparative example, the upper, middle and lower parts of the qualified non-umbrella-leaf rod porcelain of the same type prepared in each embodiment and comparative example were respectively taken for bulk density, porosity and shrinkage testing. The results are shown in Table 1.

[0047] Table 1 Performance test results of non-umbrella-leaf rod porcelain As can be seen from Table 1, the bulk density, porosity and shrinkage of the upper, middle and lower parts of the umbrella-leaf-free rod porcelain bodies prepared in Examples 1-4 of the present invention are relatively consistent, indicating that the umbrella-leaf-free rod porcelain prepared by the preparation method of the present invention has good uniformity; compared with Examples 1-3, Example 4 does not add old slurry, and its bulk density is slightly decreased and its porosity is slightly increased. This is mainly because the old slurry is all recycled slurry, which is more difficult to melt under the same firing system, but does not affect the uniformity of the product, and all performance indicators are within the qualified range; the umbrella-leaf-free rod porcelain prepared in Comparative Examples 1 and 2 also have good uniformity, but the qualified rate of rod porcelain body molding is low; Comparative Example 3 adopts the conventional "first seating and then hanging" kiln loading method for firing. Due to the uneven temperature and atmosphere in the kiln, the bulk density, porosity and shrinkage of the upper, middle and lower parts of the product are significantly different, and the uniformity is poor.

Claims

1. A dry process for producing leafless rod porcelain, characterized in that: The following steps are involved: (1) Slurry mixing: The green body raw materials are mixed and ball-milled to obtain new slurry, the new slurry and the old slurry are mixed evenly, and iron is removed by sieving to obtain green body slurry; (2) Powdering: The green body slurry is spray-dried to obtain powder, and then aged to obtain green body powder; (3) Molding: The green body powder is filled into a mold, and corrugated cardboard is placed below and above the green body powder in the mold, and then pressed into shape by a cold isostatic press to obtain a rod porcelain green body; (4) Firing: After the rod porcelain body is trimmed, the two ends of the rod porcelain body are brushed with insulating paint, sandblasted, and sprayed with solid sand glaze, and then dried and fired in a kiln to obtain umbrella-free rod porcelain; In step (3), when the cold isostatic press is pressed and formed, a multi-step pressure increase and decrease mode is adopted, and the method is as follows: The pressure is increased at a rate of 1-1.2 MPa / s, and when the pressure reaches 30-40 MPa, 50-60 MPa, 70-80 MPa, and 90-100 MPa, the pressure is maintained for 30-50 seconds, and the pressure is continued to be increased, and finally the pressure is increased to 110-120 MPa, and the pressure is maintained for 120-150 seconds; then the pressure is reduced at a rate of 0.5-0.6 MPa / s, and when the pressure is reduced to 95-90 MPa, 85-80 MPa, 75-70 MPa, 60-55 MPa, 45-40 MPa, and 30-25 MPa, the pressure is maintained for 30-50 seconds, and the pressure is continued to be reduced, and finally the pressure is reduced to normal pressure to complete the cold isostatic pressing molding; In step (4), when loading the kiln for firing, a layered loading method is adopted, and the method is as follows: Place several silicon carbide columns at the bottom of the kiln, then spread a layer of alumina powder at the bottom of the kiln, then place a layer of alumina balls on the alumina powder layer, and place the dried rod porcelain body on the alumina ball layer; then place silicon carbide plates on the silicon carbide columns, and then follow the above operations to place silicon carbide columns, spread a layer of alumina powder, place a layer of alumina balls, place rod porcelain body, and place silicon carbide plates in sequence; continue to repeat the above operations until the kiln loading is completed.

2. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: In step (1), the old slurry is the slurry formed by mixing the leftover materials and broken green bodies left during the molding and repairing process of the leafless rod porcelain, which are crushed and then added with water and a water reducing agent.

3. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: In step (1), the old slurry accounts for 0-60wt.% of the green body slurry.

4. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: In step (2), the moisture content of the powder obtained by spray drying is 1-2 wt.%.

5. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: In step (2), the aging time is not less than 24 hours.

6. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: In step (3), 3-5 layers of corrugated cardboard are placed below and above the green body powder in the mold; the corrugated cardboard is circular, and its diameter is 1-2 mm smaller than the inner diameter of the mold; the mold is a silicone rubber mold.

7. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: In step (4), the drying temperature is 35-45°C and the drying time is 24-36 hours.

8. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: In step (4), the firing conditions are: room temperature-120°C, 360-480 min; 120°C, 100-120 min; 120-640°C, 380-410 min; 640-830°C, 280-340 min; 830-950°C, 120-220 min; 950-980°C, 840-900 min; 980-1190°C, 300-330 min; 1190-1240°C, 180-230 min; 1240-1245°C, 20-30 min.

9. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: In step (4), the spreading thickness of the alumina powder layer is 6-11 mm, and the median particle size D50 of the alumina powder used is 55±5µm.

10. The dry process for producing non-umbrella-leaf rod porcelain according to claim 1, characterized in that: The alumina ball layer is a single layer, the diameter of the alumina balls used is 10-15 mm, and the gap between adjacent alumina balls is maintained at 3-6 mm.

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