Cylindrical ceramic sintering method

Abstract

The invention discloses a cylindrical ceramic sintering method in the technical field of ceramic material processing, which comprises the following steps: preparing an isolating agent for preventing a ceramic cylinder from being adhered to a limiting tool, coating the isolating agent on the inner wall and the outer wall of a position needing to be limited of the ceramic cylinder and the inner wall and the outer wall of the limiting tool, and then drying; assembling the porcelain cylinder after the separant is completely dried and the limiting tool into a sintering whole; a sliding shrinkage layer is laid on a sintering platform, and the assembled sintering whole is placed on the sliding shrinkage layer to be sintered; the limiting tool reduces the probability that after the ceramic cylinder is sintered, the upper size and the lower size are different, or the end opening position is oval or even cracked, the sliding shrinkage layer reduces the sintering shrinkage friction coefficient between the bottom limiting block and the sintering platform, sliding sintering is achieved, and an isolating agent is arranged between the limiting tool and the ceramic cylinder. The limiting tool and the porcelain barrel are prevented from being adhered in the sintering process, it is guaranteed that the porcelain barrel and the limiting tool can be conveniently detached after sintering, and therefore the quality of sintered products is comprehensively improved.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic material processing, in particular to a cylindrical ceramic sintering method. Background Art

[0002] Traditional oxide ceramics (alumina, zirconium oxide, beryllium oxide, etc.) are widely used in the fields of power electronics, electric vacuum, and mechanical parts because of their excellent electrical insulation, mechanical properties, and wear resistance. Ceramic sleeves and bushings made of cylindrical ceramics can be used as arc-extinguishing tube shells in the field of electric vacuum, power electronic insulation sleeves, and wear-resistant airtight valves of some vacuum devices and precision machinery. In recent years, with the development of the industry, related equipment has developed towards large-scale and high-power development, and the volume of ceramic cylinders has also been required to increase accordingly. The inner and outer diameters of the ceramic cylinders have developed from the traditional 100mm (wall thickness 5-20mm) to more than 200mm (wall thickness 3-20mm). The outer diameter of some products even reaches 300mm and the height reaches 500mm. This size specification has reached the limit size of the current domestic ceramic forming means. Although there is no major problem at the forming end, the problem at the sintering end will become very prominent.

[0003] Since oxide ceramics have 18-25% sintering shrinkage, when the outer diameter of the ceramic exceeds 200mm, the deformation of the ceramic after sintering reaches more than 35mm. Improper control of the shrinkage deformation during the sintering process will cause the ceramic tube to have problems such as upper and lower cross-section distortion and radial ellipse.

[0004] In order to overcome the shrinkage and deformation during sintering, the traditional sintering method adopts the method of co-firing with gaskets with the same shrinkage coefficient. That is, the porcelain tube is placed on a green gasket made of the same material (same shrinkage coefficient) for sintering. The porcelain tube and the gasket are isolated by isolation powder. However, when the mass of a single porcelain tube exceeds 1kg, due to the deadweight of the ceramic tube, the bottom pressure is large, resulting in large shrinkage resistance, resulting in inconsistent shrinkage of the upper and lower sections. Finally, after sintering, a conical porcelain tube with a small top and a large bottom is easily formed. This size difference can reach more than 3mm. At the same time, because the top is in a free shrinkage state and there is no restricted tooling, it is easy to cause the top to be elliptical or even cracked. Therefore, the traditional sintering method has the disadvantages of low sintering product qualification rate and poor product quality. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the technical problem to be solved by the present invention is: how to improve the problem of poor quality of the porcelain tube due to shrinkage during the sintering process.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A cylindrical ceramic sintering method comprises the following steps:

[0008] Prepare an isolating agent to prevent the porcelain cylinder and the limiting tool from sticking together, apply the isolating agent to the inner and outer walls of the position where the porcelain cylinder needs to be limited and the inner and outer walls of the limiting tool, and then dry;

[0009] Assemble the porcelain cylinder and the limit fixture after the isolation agent is completely dried into a sintered whole;

[0010] A sliding shrinkage layer is laid on the sintering platform, and the assembled sintering unit is placed on the sliding shrinkage layer for sintering.

[0011] Furthermore, the above-mentioned limiting tooling includes a first boss, a second boss and a limiting ring, and the above-mentioned first boss and the above-mentioned second boss both include a circular substrate and a protrusion, the outer diameter of the protrusion of the above-mentioned first boss is smaller than the inner diameter of the upper end of the porcelain tube, and the protrusion of the first boss extends downward into the above-mentioned porcelain tube; the outer diameter of the protrusion of the above-mentioned second boss is smaller than the inner diameter of the lower end of the porcelain tube, and the protrusion of the second boss extends upward into the porcelain tube; a limiting ring is arranged at the upper end of the substrate of the above-mentioned second boss, the inner diameter of the above-mentioned limiting ring is larger than the outer diameter of the porcelain tube, and the above-mentioned limiting ring is arranged around the outer wall of the lower end of the porcelain tube.

[0012] Furthermore, the difference between the outer diameter of the protrusion of the above-mentioned first boss and the inner diameter of the upper end of the porcelain tube is in the range of 0.2-0.4mm; the difference between the outer diameter of the protrusion of the above-mentioned second boss and the inner diameter of the lower end of the porcelain tube is in the range of 0.8-1mm; the difference between the inner diameter of the above-mentioned limit ring and the outer diameter of the lower end of the porcelain ring is in the range of 0.2-0.4mm.

[0013] Furthermore, the first boss is hollow.

[0014] Furthermore, the base plate diameter of the second boss is 20-40 mm larger than the outer diameter of the porcelain tube, and the outer diameter of the limit ring is equivalent to the base plate diameter of the second boss.

[0015] Furthermore, the difference between the inner and outer diameters of the above-mentioned limiting ring is 3-5 mm.

[0016] Furthermore, the preparation method of the above-mentioned isolation agent is: industrial alcohol and alumina isolation powder are mixed with each other and stirred evenly, with a mass ratio of 100:10-15.

[0017] Furthermore, the particle size of the alumina isolation powder is in the range of 3-15 μm.

[0018] Furthermore, the thickness of the sliding shrinkage layer is 3-5 cm.

[0019] Furthermore, the sliding shrinkage layer comprises aluminum oxide isolation powder with a particle size of 3-15 μm.

[0020] The beneficial effects of the present invention are:

[0021] (1) Through the limiting function of the limiting fixture, the shrinkage of the porcelain tube during the sintering process is reasonably suppressed, reducing the probability of the porcelain tube having different upper and lower sizes or an elliptical or even cracking port after sintering, thereby improving the quality of the porcelain tube product after sintering.

[0022] (2) A sliding shrinkage layer is set on the sintering platform to reduce the sintering shrinkage friction coefficient between the bottom limit block and the sintering platform, realize sliding sintering, and improve product quality.

[0023] (3) An isolating agent is provided between the limit fixture and the porcelain tube to prevent the limit fixture and the porcelain tube from sticking together during the sintering process, thereby ensuring that the porcelain tube and the limit fixture can be easily disassembled after sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the steps of the method of the present invention;

[0025] Figure 2 It is a schematic diagram of the sintered overall structure of the present invention;

[0026] Marked in the figure, 1-ceramic cylinder, 2-first boss, 3-second boss, 4-limiting ring, 5-sliding shrinkage layer, 6-through hole. DETAILED DESCRIPTION

[0027] Example 1

[0028] like Figure 1 As shown, the embodiment of the present application proposes a cylindrical ceramic sintering method, comprising the following steps:

[0029] Prepare an isolating agent to prevent the porcelain tube 1 from sticking to the limiting fixture, apply the above-mentioned isolating agent to the inner and outer walls of the position where the porcelain tube 1 needs to be limited and the inner and outer walls of the limiting fixture, and then dry; assemble the porcelain tube 1 and the limiting fixture after the isolating agent is completely dried into a sintered whole; lay a sliding shrinkage layer 5 on the sintering platform, and place the assembled sintered whole on the sliding shrinkage layer 5 for sintering.

[0030] First of all, it should be stated that the limiting effect of the limiting fixture can ensure that the shrinkage of the porcelain tube 1 during the sintering process is reasonably suppressed, reducing the probability of the porcelain tube 1 having different upper and lower sizes or an elliptical or even cracked port after sintering, thereby improving the product quality of the sintered porcelain tube 1. A sliding shrinkage layer 5 is set on the sintering platform to reduce the sintering shrinkage friction coefficient between the bottom limiting block and the sintering platform, achieve sliding sintering, and improve product quality. An isolation agent is set between the limiting fixture and the porcelain tube 1 to prevent the limiting fixture and the porcelain tube 1 from sticking during the sintering process, ensuring that the porcelain tube 1 and the limiting fixture can be easily disassembled after sintering.

[0031] Specifically, the above-mentioned limiting tooling mainly realizes the limiting effect on the contraction position of the upper and lower ends of the porcelain cylinder 1, such as Figure 2 As shown, the above-mentioned limiting tooling includes a first boss 2, a second boss 3 and a limiting ring 4. The above-mentioned first boss 2 and the above-mentioned second boss 3 both include a circular substrate and a protrusion. The outer diameter of the protrusion of the above-mentioned first boss 2 is smaller than the inner diameter of the upper end of the porcelain tube 1, and the protrusion of the first boss 2 extends downward into the above-mentioned porcelain tube 1; the outer diameter of the protrusion of the above-mentioned second boss 3 is smaller than the inner diameter of the lower end of the porcelain tube 1, and the protrusion of the second boss 3 extends upward into the porcelain tube 1; a limiting ring 4 is arranged on the upper end of the substrate of the above-mentioned second boss 3, the inner diameter of the above-mentioned limiting ring 4 is larger than the outer diameter of the porcelain tube 1, and the above-mentioned limiting ring 4 is arranged around the outer wall of the lower end of the porcelain tube 1.

[0032] The above-mentioned first boss 2 is made of the same material or material with the same shrinkage coefficient as the porcelain tube 1, the height of the boss is 3-5mm, the thickness of the substrate is 3-5mm, the boss of the first boss 2 can be embedded in the opening at the top of the porcelain tube 1, and the difference between the outer diameter of the boss of the above-mentioned first boss 2 and the inner diameter of the upper end of the porcelain tube 1 is in the range of 0.2-0.4mm. When the upper end of the porcelain tube 1 shrinks during the actual sintering process, the boss of the first boss 2 and the inner wall of the upper end of the porcelain tube 1 realize abutment and limiting effect, thereby improving the shrinkage condition of the upper end of the porcelain tube 1.

[0033] In actual work, if the mass of the first boss 2 is large, it may affect the shrinkage resistance at the bottom. Therefore, the first boss 2 is hollow. Specifically, the hollowness may be a through hole 6 set along the axis of the boss, or a hollow inner cavity is set in the first boss 2 to reduce the mass of the first boss 2 and reduce the shrinkage resistance to the bottom, thereby further improving the control effect of the shrinkage condition during the sintering process of the porcelain tube 1.

[0034] The above-mentioned second boss 3 is made of the same material or material with the same shrinkage coefficient as the porcelain tube 1, and the boss height is 5-15mm. The difference between the outer diameter of the boss of the above-mentioned second boss 3 and the inner diameter of the lower end of the porcelain tube 1 is in the range of 0.8-1mm. In order to withstand pressure deformation, the gap between the boss of the second boss 3 and the inner wall of the bottom of the porcelain tube 1 is larger than the gap between the boss of the first boss 2 and the inner wall of the top of the porcelain tube 1, ensuring that the inner diameter of the bottom end of the porcelain tube 1 has more shrinkage space, ensuring the good quality of the upper and lower ends of the porcelain tube 1 after shrinkage.

[0035] The above-mentioned limit ring 4 is made of the same material or material with the same shrinkage coefficient as the porcelain tube 1, with a substrate thickness of 3-5mm, a bump thickness of 3-5mm, an inner diameter slightly larger than the outer diameter of the sleeve green ring of the porcelain tube 1, and an outer diameter that should be 20-40mm larger than the outer diameter of the bottom of the porcelain tube 1. The limit ring 4 is a circular ring structure. To prevent sintering deformation, its thickness t2 is 10-15mm, and its outer diameter should be equivalent to the outer diameter of the substrate of the second boss 3. The difference between the inner diameter of the above-mentioned limit ring 4 and the outer diameter of the lower end of the porcelain ring is in the range of 0.2-0.4mm, which ensures that the outer diameter of the bottom of the porcelain tube 1 does not expand outward during the sintering process.

[0036] The above-mentioned isolation agent is prepared by mixing industrial alcohol and aluminum oxide isolation powder with a particle size of 3-15μm, with the mass ratio of industrial alcohol to isolation powder being 100:10-15. The mixture is stirred evenly to form an isolation agent, and the coating process is performed with a brush when the isolation powder is in a suspension state in the alcohol.

[0037] The sliding shrinkage layer 5 is made of alumina isolation powder with a particle size of 3-15 μm and a thickness of 3-5 cm, which reduces the sintering shrinkage friction coefficient between the bottom limit block and the sintering platform, realizes sliding sintering, and improves product quality.

[0038] In this embodiment, the green body size of the porcelain cylinder 1 is selected to be 145 mm in outer diameter, 130 mm in inner diameter and 70 mm in height.

[0039] The outer diameter of the substrate of the first boss 2 is 145 mm, and the thickness is 3 mm; the outer diameter of the bump is 129.6 mm, and the thickness is 5 mm; in order to reduce the mass of the first boss 2, the inner diameter of the through hole 6 is 119.6 mm.

[0040] The outer diameter of the substrate of the second boss 3 is 195 mm, and the thickness is 10 mm; the outer diameter of the bump is 129.2 mm, and the thickness is 10 mm.

[0041] The outer diameter of the limiting ring 4 is 195 mm, the inner diameter is 145.2 mm, and the thickness is 10 mm.

[0042] Industrial alcohol with a mass ratio of 100:10 and alumina isolation powder with a particle size of 3-15μm are mixed together and stirred evenly to form an isolation agent. In the suspension state, a layer of isolation agent is brushed on all the contact places between the sintering tooling and the product with a brush, and it is set aside after drying.

[0043] The small end of the green body of the porcelain tube 1 is placed on the second boss 3, and the convex block of the second boss 3 extends upward into the interior of the porcelain tube 1. Then the limit ring 4 is put on the porcelain tube 1, and the limit ring 4 contacts the upper end of the base plate of the second boss 3. Finally, the first boss 2 is placed on the top of the green body of the porcelain tube 1 to form a sintered whole.

[0044] A 3-cm thick alumina isolation powder layer of 3-15 μm is spread on the support plate, and the sintering unit is placed stably on the isolation powder layer for high-temperature sintering.

[0045] After sintering, the product appearance, upper and lower section outer diameters, upper and lower end inner diameters, and product roundness are inspected. The inspection structure is as follows:

[0046] The difference between the upper and lower outer diameters: 0.18mm;

[0047] The difference between the inner diameter of the upper and lower ends: 0.15mm;

[0048] Outer diameter roundness: 0.12mm;

[0049] Inner diameter roundness 0.10mm;

[0050] The sintered porcelain tube 1 sample is a qualified product.

[0051] Example 2

[0052] The difference from the above embodiment is that:

[0053] In this embodiment, the green body size of the porcelain cylinder 1 is selected to be 270 mm in outer diameter, 250 mm in inner diameter and 450 mm in height.

[0054] The outer diameter of the substrate of the first boss 2 is 270 mm, and the thickness is 5 mm; the outer diameter of the bump is 249.6 mm, and the thickness is 5 mm; in order to reduce the mass of the first boss 2, the inner diameter of the through hole 6 is 209.6 mm.

[0055] The outer diameter of the substrate of the second boss 3 is 320 mm, and the thickness is 10 mm; the outer diameter of the bump is 249 mm, and the thickness is 15 mm.

[0056] The outer diameter of the limiting ring 4 is 320 mm, the inner diameter is 270.4 mm, and the thickness is 15 mm.

[0057] Industrial alcohol with a mass ratio of 100:15 and alumina isolation powder with a particle size of 3-15μm are mixed together and stirred evenly to form an isolation agent. In the suspension state, a layer of isolation agent is brushed on all the contact places between the sintering tooling and the product with a brush, and it is set aside after drying.

[0058] The small end of the green body of the porcelain tube 1 is placed on the second boss 3, and the convex block of the second boss 3 extends upward into the interior of the porcelain tube 1. Then the limit ring 4 is put on the porcelain tube 1, and the limit ring 4 contacts the upper end of the base plate of the second boss 3. Finally, the first boss 2 is placed on the top of the green body of the porcelain tube 1 to form a sintered whole.

[0059] A 3-cm thick alumina isolation powder layer of 3-15 μm is spread on the support plate, and the sintering unit is placed stably on the isolation powder layer for high-temperature sintering.

[0060] After sintering, the product appearance, upper and lower section outer diameters, upper and lower end inner diameters, and product roundness are inspected. The inspection structure is as follows:

[0061] The difference between the upper and lower outer diameters: 0.21mm;

[0062] The difference between the inner diameter of the upper and lower ends: 0.30mm;

[0063] Outer diameter roundness: 0.24mm;

[0064] Inner diameter roundness 0.27mm;

[0065] The sintered porcelain tube 1 sample is a qualified product.

[0066] In summary, the present invention proposes a cylindrical ceramic sintering method, by first taper forming and processing the large-scale ceramic tube 1 green body, ensuring that the inner and outer diameters of the upper and lower ends of the ceramic tube 1 green body have a taper of 1-3mm; during the sintering process, improvements are made on the basis of the existing shrinkage sintering gasket, and a first boss 2 is added to the upper end, and a second boss 3 is set at the lower end. In order to prevent the outer diameter of the lower end from deforming, a limit ring 4 is added to the lower end simultaneously, and then the sliding isolation powder is spread under the bottom pad to reduce the sintering shrinkage friction coefficient between the bottom limit block and the sintering platform, so as to achieve sliding sintering. Through the offset taper design of the green body and the setting of various limit tooling components, the shrinkage deformation of the large-scale ceramic tube 1 during the sintering process is limited as a whole, and the inner and outer diameter size deviation of the upper and lower sections of the product after sintering does not exceed 0.3mm. The roundness deviation of the inner and outer diameters of the upper and lower end surfaces of the ceramic tube 1 does not exceed 0.5mm. The dimensional accuracy and processing performance of the large-scale ceramic tube 1 are guaranteed, and the product can be free of processing after sintering, thereby improving the overall qualification rate and product quality of the large-scale ceramic tube 1 product.

Claims

1. A method for sintering cylindrical ceramics, characterized in that: The following steps are included: Prepare an isolating agent to prevent the porcelain cylinder and the limiting tool from sticking together, apply the isolating agent to the inner and outer walls of the position where the porcelain cylinder needs to be limited and the inner and outer walls of the limiting tool, and then dry; Assemble the porcelain cylinder and the limit fixture after the isolation agent is completely dried into a sintered whole; A sliding shrinkage layer is laid on the sintering platform, and the assembled sintering unit is placed on the sliding shrinkage layer for sintering.

2. A cylindrical ceramic sintering method according to claim 1, characterized in that: The limiting tooling includes a first boss, a second boss and a limiting ring, the first boss and the second boss both include a circular substrate and a protrusion, the outer diameter of the protrusion of the first boss is smaller than the inner diameter of the upper end of the porcelain tube, and the protrusion of the first boss extends downward into the porcelain tube; the outer diameter of the protrusion of the second boss is smaller than the inner diameter of the lower end of the porcelain tube, and the protrusion of the second boss extends upward into the porcelain tube; a limiting ring is provided at the upper end of the substrate of the second boss, the inner diameter of the limiting ring is larger than the outer diameter of the porcelain tube, and the limiting ring is arranged around the outer wall of the lower end of the porcelain tube.

3. A cylindrical ceramic sintering method according to claim 2, characterized in that: The difference between the outer diameter of the first boss and the inner diameter of the upper end of the porcelain tube is in the range of 0.2-0.4mm; the difference between the outer diameter of the second boss and the inner diameter of the lower end of the porcelain tube is in the range of 0.8-1mm; the difference between the inner diameter of the limit ring and the outer diameter of the lower end of the porcelain ring is in the range of 0.2-0.4mm.

4. A cylindrical ceramic sintering method according to claim 2, characterized in that: The first boss is hollow.

5. A cylindrical ceramic sintering method according to claim 2, characterized in that: The base plate diameter of the second boss is 20-40 mm larger than the outer diameter of the porcelain tube, and the outer diameter of the limiting ring is equivalent to the base plate diameter of the second boss.

6. A cylindrical ceramic sintering method according to claim 2, characterized in that: The difference between the inner and outer diameters of the limiting ring is 3-5 mm.

7. A cylindrical ceramic sintering method according to claim 1, characterized in that: The preparation method of the isolation agent is as follows: industrial alcohol and alumina isolation powder are mixed with each other and stirred evenly, wherein the mass ratio of industrial alcohol to alumina isolation powder is 100:10-15.

8. A cylindrical ceramic sintering method according to claim 7, characterized in that: The particle size of the alumina isolation powder is in the range of 3-15 μm.

9. A cylindrical ceramic sintering method according to claim 1, characterized in that: The thickness of the sliding shrinkage layer is 3-5 cm.

10. A cylindrical ceramic sintering method according to claim 9, characterized in that: The sliding shrinkage layer comprises aluminum oxide isolation powder with a particle size of 3-15 μm.

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