High-strength hot-press sintered large-sized aluminum nitride ceramic jig

Abstract

This invention discloses a high-strength hot-pressing sintering fixture for large aluminum nitride ceramics. The fixture includes an upper pressure plate, a pressure block, a lower tray, a carbon-carbon composite outer jacket, an isostatically pressed graphite inner liner, and an inner liner second composed of three-lobed fan-shaped modules. The inner liner first and inner liner second have mutually cooperating tapered surfaces. Within the inner liner second, spacers first, second, and a lower pad are arranged sequentially from top to bottom, with material layers placed between adjacent components. During sintering, axial pressure is transmitted to the material layer through the pressure block and spacers. The tapered surfaces convert part of the axial force into radial clamping force, achieving three-dimensional densification. After sintering, the individual lobes of the inner liner second can be vertically extracted, allowing for frictionless removal of the complete ceramic plate. This invention solves the problems of difficult demolding and easy cracking of large aluminum nitride ceramic plates during hot-pressing sintering, and has the advantages of high density, high yield, and long fixture life.

Description

Technical Field

[0001] This invention relates to the field of ceramic material sintering, and specifically to a high-strength hot-pressed sintered large aluminum nitride ceramic fixture. Background Technology

[0002] Aluminum nitride ceramics possess high thermal conductivity, good electrical insulation, and a coefficient of thermal expansion that matches that of silicon, making them important for applications in high-power electronic packaging, high thermal conductivity substrates, and heat sinks. Hot pressing sintering is a common process for preparing high-performance large-scale aluminum nitride ceramic plates. This process applies axial pressure to the green body during high-temperature sintering, which effectively promotes particle rearrangement, pore closure, and grain boundary migration, significantly improving the density and mechanical properties of the ceramic.

[0003] In the hot pressing sintering process, the mold structure design has a decisive impact on product quality and process stability. Existing large-scale aluminum nitride ceramic hot pressing sintering fixtures typically employ a one-piece cylindrical graphite inner mold with an outer mold. During use, aluminum nitride powder is loaded into the mold cavity, and after sintering under pressure, the sintered ceramic plate needs to be removed from the mold. However, due to the tendency for the ceramic to adhere to the mold's inner wall under high temperature and pressure, and the significant contact pressure and friction between the ceramic plate and the mold after sintering, demolding is extremely difficult. Traditional demolding methods usually require a hydraulic press to apply a large ejection force to eject the ceramic plate. During this process, the edges of the ceramic plate are prone to chipping, cracking, or even complete breakage, significantly reducing the yield rate. Simultaneously, the large ejection force also causes severe wear on the mold's inner wall, significantly shortening the mold's lifespan.

[0004] Furthermore, existing hot-pressing sintering fixtures have shortcomings in pressure transmission. When the ceramic plate is large (diameter ≥ 200 mm), unidirectional pressurization can easily lead to uneven pressure distribution within the green body, causing density differences and warping deformation. Traditional multi-layer gasket arrangements lack effective positioning and clamping structures, and material layers may shift during pressurization, affecting product dimensional accuracy. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the technical problem to be solved by this invention is to provide a high-strength hot-pressed sintering large aluminum nitride ceramic fixture, which can improve demolding performance, ensure uniform pressure transmission, increase the yield of large aluminum nitride ceramic plates and the service life of the fixture.

[0006] To achieve the above objectives, the present invention provides a high-strength hot-pressed sintered large aluminum nitride ceramic fixture, comprising: The upper pressure plate has a top that is connected to the upper hydraulic column of the hot pressing sintering furnace, and a circular groove is provided at the bottom of the upper pressure plate. The pressure block has its top end embedded in the circular groove at the bottom of the upper pressure plate; The lower tray has a bottom that can be connected to the lower hydraulic column of the hot press sintering furnace, and the upper surface of the lower tray is provided with an annular groove. The outer casing is a cylindrical body made of carbon-carbon composite material. The bottom end of the outer casing can be inserted into the annular groove of the lower tray, and the side wall of the outer casing is provided with lifting holes along the circumference. The inner liner is a cylindrical body made of isostatically pressed graphite. The outer wall of the inner liner is fitted with the inner wall of the outer jacket, and the inner wall has a tapered surface that tapers inward from top to bottom. The second liner is composed of three equally divided fan-shaped isostatically pressed graphite modules. The outer wall of each fan-shaped isostatically pressed graphite module has a tapered surface that matches the tapered surface of the first liner. Each fan-shaped module has a lifting hole at its top. The inner wall of the second liner is a vertical plane. Gasket 1, Gasket 2, and Lower Gasket Block are arranged sequentially from top to bottom within the inner liner 2, with material layers placed between adjacent components.

[0007] Furthermore, it also includes an upper guide centering mechanism, wherein the diameter of the circular groove of the upper pressure plate is larger than the top diameter of the pressure block; the upper pressure plate is also connected to the frame of the hot pressing sintering furnace through the upper guide centering mechanism, and the upper guide centering mechanism is used to constrain the pressure direction of the upper pressure plate.

[0008] Furthermore, the upper guide centering mechanism includes a guide sleeve fixed to the frame and a sliding centering pressure head seat fitted inside the guide sleeve; the upper end of the sliding centering pressure head seat is rigidly connected to the upper hydraulic column, the lower end of the sliding centering pressure head seat is provided with a hemispherical self-aligning contact surface, the top of the upper pressure plate is hemispherical, and the hemispherical self-aligning contact surface abuts against the top of the upper pressure plate; the inner wall of the guide sleeve is provided with a vertical guide groove, and the outer side of the sliding centering pressure head seat is provided with a guide key that slides with the vertical guide groove.

[0009] Furthermore, it also includes a lower guide centering mechanism, through which the lower tray is connected to the lower hydraulic column of the hot-pressing sintering furnace, and the lower guide centering mechanism is used to center and fix the lower tray.

[0010] Furthermore, the lower guide centering mechanism includes a connecting plate, a fixed ring, a drive ring, a push rod, a slider, and a locking fastener. The connecting plate is sleeved and fixed to the top of the lower hydraulic column of the hot-pressing sintering furnace. The fixed ring is fixed to the connecting plate and is coaxially arranged with the circular groove. The upper surface of the fixed ring is circumferentially spaced with slots extending radially. Each slot can accommodate one push rod. The top of each push rod is fixed with a slider. The drive ring is coaxial with the fixed ring and rotatably connected. The drive ring is circumferentially spaced with multiple arc-shaped grooves. The top of the slider can slide into the corresponding arc-shaped groove. By rotating the drive ring, through the slider and the arc-shaped groove, all the push rods can be simultaneously driven to move towards the center along the slots to clamp and fix the outer sleeve or move outward simultaneously. The locking fastener is a set screw. The set screw is threadedly connected to the drive ring. By rotating the set screw, the end of the set screw can abut against the fixed ring, thereby locking and fixing the drive ring.

[0011] Furthermore, it also includes a liner demolding mechanism, which can be connected to the three liners II for assisting the liners II in demolding.

[0012] Furthermore, the liner demolding mechanism includes: A lifting ring is located above the guide sleeve and is coaxially arranged with the guide sleeve. The lifting ring can move vertically up and down. A guide rod is provided on the side wall of the lifting ring. A vertically extending guide groove is provided on the frame. The guide rod can slide up and down with the frame. A height adjusting screw is vertically fixed to the lifting ring and threadedly connected to the frame. Rotating the height adjusting screw drives the lifting ring to rise and fall vertically. Three hooks are mounted on the lifting ring in an isosceles triangle configuration, and the hooks can be connected to the lifting holes on the three inner linings.

[0013] Furthermore, the lining demolding mechanism also includes a fine-tuning knob, and the three hooks are connected to the lifting ring through the three fine-tuning knobs. Rotating the fine-tuning knobs drives the hooks to rise and fall vertically.

[0014] Furthermore, the inner diameter of the annular groove on the upper surface of the lower tray is larger than the outer diameter of the outer sleeve.

[0015] Furthermore, the wall thickness of the outer jacket is half the diameter of the pressed aluminum nitride ceramic plate.

[0016] The beneficial effects of this invention are: The aforementioned high-strength hot-pressed sintered large aluminum nitride ceramic fixture has at least the following advantages: 1. The inner liner II is a segmented structure composed of three equally divided fan-shaped modules, with each segment having a tapered surface on its outer wall that mates with the tapered surface of the inner liner I. During hot-pressing sintering, axial pressure is transmitted to the material layer through the pressure column, while the tapered surface converts part of the axial force into radial compaction force, causing each segment to contract inward and enhancing the compaction effect on the powder. After sintering, because the tapered surface has a one-way locking structure, simply lifting each segment of the inner liner II upwards immediately disengages the tapered surface, eliminating frictional resistance. Combined with the lifting holes on the top of each segment, the three segments can be vertically extracted, thus completely releasing the radial constraint on the sintered ceramic plate. At this point, there is no longer any contact pressure between the ceramic plate and the fixture, allowing operators to directly remove the complete ceramic plate without the need for a hydraulic press or hammering.

[0017] 2. The outer casing is a cylindrical body made of carbon-carbon composite material, possessing extremely high compressive strength and high-temperature resistance. It can withstand the enormous radial pressure generated during the hot-pressing and sintering of large ceramic plates, preventing radial expansion or cracking of the inner lining. Inner linings one and two are made of isostatically pressed graphite, exhibiting good self-lubrication and high thermal conductivity, ensuring a uniform temperature field within the mold cavity. When the upper pressure block and lower tray apply pressure from the upper and lower directions respectively, the pressure is sequentially transmitted to the two material layers via gasket one, gasket two, and the lower gasket block, achieving bidirectional reciprocating pressurization. Combined with the radial clamping force generated by the tapered surface of inner lining two, the material layers are simultaneously compressed in three dimensions, significantly improving the powder densification efficiency.

[0018] 3. Traditional one-piece inner liner molds require significant ejection force during demolding, resulting in severe wear on the inner wall. This fixture employs a segmented inner liner II, where each segment is pulled out vertically during demolding, generating almost no sliding friction with inner liners I and II, greatly reducing wear. Simultaneously, the outer jacket and inner liner I do not directly bear the demolding impact during normal use, allowing for reuse hundreds of times. Due to the significantly extended fixture lifespan, the mold cost per ceramic plate is significantly reduced, making it suitable for large-scale industrial production.

[0019] 4. Gasket 1, Gasket 2, and the lower gasket block are arranged sequentially from top to bottom within the inner liner 2, with material layers placed between adjacent components. This structure allows for the simultaneous filling of multiple layers of material, enabling the production of two ceramic plates in a single sintering process, or the composite sintering of material layers with different formulations, thus improving production efficiency. Simultaneously, the graphite paper acts as an isolation layer, effectively preventing adhesion between material layers and between material layers and gaskets, ensuring the independent integrity of each product layer. Lifting holes on the outer sleeve sidewall facilitate mechanical lifting and are suitable for the handling and assembly of large and heavy fixtures. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly described below. In all the drawings, the elements or parts are not necessarily drawn to scale.

[0021] Figure 1 This is a schematic diagram of a high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to an embodiment of the present invention; Figure 2 for Figure 1 A schematic diagram of a large aluminum nitride ceramic fixture with high strength hot-pressed sintering from another angle; Figure 3 for Figure 1 The diagram shown is a schematic of the assembly of the upper pressure plate, pressure block, gasket 1, gasket 2, lower pad, lower tray, outer jacket, inner liner 1, and inner liner 2 in a large high-strength hot-pressed sintered aluminum nitride ceramic fixture. Figure 4 for Figure 1 A schematic diagram at point A in the middle; Figure 5 for Figure 1 A schematic diagram at point B in the middle; Figure 6 for Figure 2 A schematic diagram at point C in the middle; Figure label: 11. Upper pressure plate; 12. Pressure block; 13. Gasket 1; 14. Gasket 2; 15. Lower pad block; 16. Lower tray; 17. Outer jacket; 18. Inner liner 1; 19. Inner liner 2; 2. Upper guide centering mechanism; 21. Guide sleeve; 22. Sliding centering pressure head seat; 23. Vertical guide groove; 3. Lower guide centering mechanism; 31. Connecting plate; 32. Fixing ring; 33. Drive ring; 34. Push rod; 35. Slider; 36. Locking fastener; 4. Inner liner demolding mechanism; 41. Lifting ring; 42. Guide rod; 43. Height adjusting screw; 44. Lifting hook; 45. Fine adjustment knob; 5. Upper hydraulic column; 6. Lower hydraulic column. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention; therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Please see Figures 1 to 6 This invention provides a high-strength hot-pressed sintered large aluminum nitride ceramic fixture, specifically designed for preparing large-size (e.g., diameter ≥ 200 mm, thickness ≥ 10 mm) high-density aluminum nitride ceramic plates.

[0024] The upper pressure plate 11 is cylindrical and is used to connect with the upper hydraulic column 5 of the hot-pressing sintering furnace. A circular groove is provided at the center of its lower part. The pressure block 12 is a cylindrical rod, and its top end is embedded in the circular groove. The top end of the pressure block 12 is embedded in the circular groove at the bottom of the upper pressure plate 11. The bottom of the lower tray 16 can be connected to the lower hydraulic column 6 of the hot-pressing sintering furnace, and an annular groove is provided on the upper surface of the lower tray 16. The outer casing 17 is a cylindrical body made of carbon-carbon composite material, possessing extremely high compressive strength and high-temperature resistance. The bottom end of the outer casing 17 is embedded in an annular groove on the upper surface of the lower tray 16. Multiple lifting holes are evenly distributed along the circumference of the side wall of the outer casing 17 for mechanical lifting.

[0025] The inner liner 18 is a cylindrical body made of isostatically pressed graphite, and its outer wall is tightly fitted with the inner wall of the outer jacket 17. The inner wall of the inner liner 18 is not a vertical plane, but has a tapered surface that tapers inward from top to bottom.

[0026] Liner 2 19 is composed of three perfectly equal fan-shaped isostatically pressed graphite modules, which, when assembled, form a complete cylinder. The outer wall of each module has a tapered surface that matches the tapered surface of Liner 1 18, while the inner wall of Liner 2 19 is a vertical plane. Each module has a lifting hole at its top.

[0027] When the three-lobed inner liner 19 is inserted into the inner liner 18, it automatically locks itself inward due to the wedge action of the tapered surface, forming a cavity that is larger at the top and smaller at the bottom. During the hot-pressing sintering process, the axial pressure is transmitted to the material layer through the pressure block 12. At the same time, the tapered surface converts part of the axial force into radial clamping force, causing each lobe of the inner liner 19 to contract inward, further compacting the powder in the cavity. After sintering, since the tapered surface is unidirectionally locked, as long as the lobes of the inner liner 19 are lifted upward, the tapered surface immediately disengages, with no frictional resistance.

[0028] Gasket 13, gasket 2 14, and lower gasket 15 are arranged sequentially from top to bottom within liner 2 19. Material layers are arranged sequentially and alternately above lower gasket 15 and between gasket 2 14 and gasket 13. Specifically, lower gasket 15 is placed at the bottom of liner 2 19. After graphite paper is laid on the upper surface of lower gasket 15, the first material layer (aluminum nitride powder) is placed. After graphite paper is laid on the upper surface of the first material layer, gasket 2 14 is placed. After graphite paper is laid on the upper surface of gasket 2 14, the second material layer is placed. After graphite paper is laid on the upper surface of the second material layer, gasket 13 is placed.

[0029] The alternating arrangement of multiple layers of gaskets and graphite paper serves two purposes: firstly, it isolates the interdiffusion between different powder layers; secondly, the rigid plane of the gaskets transmits pressure, ensuring uniform pressure distribution within the powder layers. At high temperatures, the graphite paper acts as a lubricant and separator, preventing the powder from sintering and sticking to the gaskets.

[0030] In a preferred embodiment, the fixture also includes an upper guide centering mechanism 2 to solve the problem of pressure eccentricity in large fixtures during hot pressing and sintering.

[0031] Specifically, the diameter of the circular groove in the upper pressure plate 11 is larger than the top diameter of the pressure block 12. The upper pressure plate 11 is connected to the frame of the hot-pressing sintering furnace via the upper guide centering mechanism 2, which constrains the pressure direction of the upper pressure plate 11 to keep it perpendicular. The upper guide centering mechanism 2 specifically includes a guide sleeve 21 fixed to the upper frame of the hot-pressing sintering furnace and a sliding centering pressure head seat 22 fitted inside the guide sleeve 21. The top of the upper pressure plate 11 is hemispherical. The upper end of the sliding centering pressure head seat 22 is rigidly connected to the upper hydraulic column 5 via threads or a flange, and its lower end is provided with a hemispherical self-aligning contact surface, which abuts against the top of the upper pressure plate 11. The inner wall of the guide sleeve 21 is provided with a vertical guide groove 23 along the axial direction, and the outer side of the sliding centering pressure head seat 22 is provided with a guide key that slides with the guide groove.

[0032] When the upper hydraulic column 5 applies downward pressure, the sliding centering pressure head seat 22 is constrained by the guide key and guide groove, and can only move in the vertical direction, unable to rotate or deviate radially, thus ensuring the perpendicularity of the pressure line of action. Simultaneously, the hemispherical self-aligning contact surface allows the upper pressure plate 11 to swing freely within the hemisphere. If there is a slight angle between the axis of the upper hydraulic column 5 and the center of the mold cavity, the upper pressure plate 11 will automatically tilt until its lower surface is completely parallel to the upper end face of the pressure block 12, so that the pressure acts perpendicularly on the center of the pressure block 12. This mechanism combines "rigid guidance" with "flexible self-alignment," preventing pressure head deflection and compensating for installation errors, ensuring that pressure is always transmitted in a centered manner, and avoiding uneven density or warping and cracking of the ceramic plate due to off-center loading.

[0033] As another preferred embodiment, the fixture also includes a lower guide centering mechanism 3. The lower tray 16 is connected to the lower hydraulic column 6 of the hot pressing sintering furnace through the lower guide centering mechanism 3. The lower guide centering mechanism 3 is used to center and fix the lower tray 16.

[0034] Specifically, the lower guide centering mechanism 3 includes a connecting plate 31, a fixing ring 32, a driving ring 33, a push rod 34, a slider 35, and a locking fastener. The connecting plate 31 is sleeved and fixed on the top of the lower hydraulic column 6 of the hot-pressing sintering furnace. The fixing ring 32 is fixed on the connecting plate 31 and is coaxially arranged with the circular groove. The upper surface of the fixing ring 32 is circumferentially spaced with slots extending radially. A push rod 34 is inserted into each slot, and a slider 35 is fixed to the top of each push rod 34. The driving ring 33 is coaxial with the fixing ring 32. The shaft is rotatably connected. The drive ring 33 has multiple arc-shaped grooves spaced circumferentially. The top of the slider 35 can slide into the corresponding arc-shaped groove. By rotating the drive ring 33, through the slider 35 and the arc-shaped grooves, all the push rods 34 can be driven to move towards the center along the slot to clamp and fix the outer sleeve 17 or move outward at the same time. The locking and fixing component is a set screw, which is threadedly connected to the drive ring 33. By rotating the set screw, the end of the set screw can abut against the fixing ring 32, thereby locking and fixing the drive ring 33.

[0035] In use, first position all the push rods 34 in the retracted position. Then, place the lower pad 16 on the connecting plate 31 and rotate the drive ring 33 to drive the three push rods 34 to move synchronously towards the center until they abut against the outer wall of the lower pallet 16, completing the centering. Subsequently, rotate the locking fastener to lock and fix the drive ring 33, completing the centering and fixing of the lower pallet 16. Using this method, the lower pallet 16 can be quickly fixed, thus preventing displacement during bidirectional reciprocating pressure.

[0036] In a more preferred embodiment, the fixture further includes an inner liner demolding mechanism 4, which can be connected to three inner liners 19 for demolding the auxiliary inner liners 19.

[0037] The demolding mechanism comprises a lifting ring 41, a height adjusting screw 43, and lifting hooks 44. The lifting ring 41 is located above and coaxially mounted with the guide sleeve 21. The lifting ring 41 can move vertically up and down. A guide rod 42 is provided on the side wall of the lifting ring 41, and a vertically extending guide groove is provided on the frame. The guide rod 42 is slidably connected to the frame. The height adjusting screw 43 is vertically fixed to the lifting ring 41 and threadedly connected to the frame. Rotating the height adjusting screw 43 drives the lifting ring 41 to rise and fall vertically. There are three lifting hooks 44, arranged in an isosceles triangle on the lifting ring 41. The hooks 44 can connect to the three lifting holes on the inner lining 19.

[0038] After sintering, connect the hook 44 to the three inner liners 19, then rotate the height adjusting screw 43 to drive the lifting ring 41 upward, thus completing the demolding of the three inner liners 19. The use of a threaded rod allows for stopping at any position, preventing the lifting beam from accidentally sliding down.

[0039] Furthermore, since the inner lining 19 and the inner lining 18 have a conical fit, theoretically, the three segments should rise simultaneously without friction. However, during the actual sintering process, the segments may experience slight height differences due to thermal deformation. Therefore, as a preferred embodiment, the inner lining demolding mechanism 4 also includes a fine-tuning knob 45. The three hooks 44 are connected to the lifting ring 41 via the three fine-tuning knobs 45. Manually rotating the fine-tuning knobs 45 can drive the hooks 44 to rise and fall vertically. When the segments may experience slight height differences due to thermal deformation, the operator can adjust the lifting height of a single segment individually using the independent fine-tuning knobs 45, ensuring that the lifting actions of the three segments are strictly synchronized, thus avoiding segment jamming or damage to the ceramic body due to asynchrony.

[0040] In practical implementation, the inner diameter of the annular groove on the upper surface of the lower tray 16 can be larger than the outer diameter of the outer sleeve 17. Preferably, this gap can be 0.3~0.6mm. This gap allows the outer sleeve 17 to easily fit into the annular groove at room temperature, while the gap is absorbed when the outer sleeve 17 expands due to heat at high temperatures, forming a tight fit and preventing radial movement of the outer sleeve 17. A gap that is too small will lead to assembly difficulties, while a gap that is too large will cause the outer sleeve 17 to wobble, affecting the alignment accuracy.

[0041] Alternatively, the wall thickness of the outer jacket 17 can be set to half the diameter of the pressed aluminum nitride ceramic plate. For example, when pressing a ceramic plate with a diameter of 300 mm, the wall thickness of the outer jacket 17 is 150 mm. This wall thickness can withstand the radial pressure transmitted by the lining during hot pressing and sintering (typically up to 50~100 MPa) without being too bulky. Too thin a wall thickness may cause the outer jacket 17 to crack under high pressure, while too thick a wall thickness increases manufacturing costs and lifting difficulty.

[0042] The specific method for using the above-mentioned fixture for high-strength hot-pressing sintering of large aluminum nitride ceramic plates is as follows: Step 1: Install the centering mechanism First, fix the guide sleeve 21 of the upper guide centering mechanism 2 to the upper frame of the hot-press sintering furnace, and rigidly connect the sliding centering pressure head seat 22 to the upper hydraulic column 5. Then, fix the lower guide centering mechanism 3 to the lower hydraulic column 6 of the hot-press sintering furnace, place the lower tray 16, and manually rotate the drive ring 33 to lock and fix the lower tray 16. Step 2: Mold Installation and Filling Insert the bottom end of the outer jacket 17 into the annular groove on the upper surface of the lower tray 16, insert the inner liner 18 into the outer jacket 17 so that its outer wall fits against the inner wall of the outer jacket 17, and then insert the three-part inner liner 19 into the inner liner 18, locking them together by the tapered surfaces.

[0043] A layer of graphite paper is attached to the inner wall of the inner liner 19 as an isolation layer. The lower pad 15 is placed in the liner, and graphite paper is laid on the upper surface of the lower pad 15. Then, the following materials are laid in sequence: first material layer (aluminum nitride powder, containing sintering aid, evenly spread and leveled), graphite paper, pad 14, graphite paper, second material layer, graphite paper, and pad 13. Finally, the lower end of the pressure block 12 is placed on the pad 13, the upper pressure plate 11 is placed on top of the pressure block 12, and the top of the pressure block 12 is embedded in the groove of the upper pressure plate 11. At the same time, the top of the upper pressure plate 11 abuts against the hemispherical self-aligning contact surface at the lower end of the sliding centering pressure head seat 22.

[0044] Start the hot-press sintering furnace and set the sintering temperature (usually 1800~1950℃), pressure (30~50MPa), and holding time (2~6 hours). Apply bidirectional pressure to the upper pressure plate 11 and the lower tray 16 through the upper hydraulic column 5 and the lower hydraulic column 6, respectively.

[0045] In this method, during the pressurization process, the pressure from the upper hydraulic column 5 is transmitted to the second material layer through the upper pressure plate 11, pressure block 12, and gasket 13, then to the first material layer through gasket 14, and finally to the lower tray 16 through the lower pad 15. The lower hydraulic column 6 simultaneously applies upward pressure, forming bidirectional counter-pressure. This counter-pressure method minimizes the pressure gradient within the material layer, significantly improving density uniformity. At the same time, the tapered surface of the inner liner 19 converts some of the axial force into radial force, further compacting the powder.

[0046] Step 3: Demolding After sintering, the furnace is cooled to room temperature. First, the hydraulic pressure is released, and the upper pressure plate 11 and pressure block 12 on the upper part of the furnace body are removed. Then, the inner lining 19 is removed using the inner lining demolding mechanism 4. Connect the three hooks 44 to the lifting holes at the top of the three segments of the inner lining 19, respectively. Manually rotate the height adjusting screw 43 to slowly raise the lifting ring 41 vertically. Observe the disengagement of each segment: due to the conical fit, under normal circumstances, the three segments should rise synchronously and without resistance. If a segment becomes slightly stuck due to sintering thermal stress deformation, the operator can rotate the corresponding fine-tuning knob 45 to adjust the lifting height of that segment individually, and the sticking will be released. Continue to adjust the height adjusting screw 43 until the three segments are completely and vertically pulled out of the mold cavity.

[0047] Finally, by hand or with a tool, remove gasket 13 and gasket 2 14 in sequence, and the complete aluminum nitride ceramic plate can be easily removed. Since the inner lining 2 19 has been removed, there are no constraints around the ceramic body, so it can be taken out directly without pushing or knocking.

[0048] This high-strength hot-pressed sintered large aluminum nitride ceramic fixture completely avoids problems such as ceramic body cracking and edge chipping caused by high friction or ejection force in traditional molds. This improves the yield rate. Furthermore, because the demolding process causes no impact or wear on the fixture, its service life is significantly extended, resulting in a substantial reduction in production costs.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A high-strength hot-pressed sintered large aluminum nitride ceramic fixture, characterized in that, include: The upper pressure plate has a top that is connected to the upper hydraulic column of the hot pressing sintering furnace, and a circular groove is provided at the bottom of the upper pressure plate. The pressure block has its top end embedded in the circular groove at the bottom of the upper pressure plate; The lower tray has a bottom that can be connected to the lower hydraulic column of the hot press sintering furnace, and the upper surface of the lower tray is provided with an annular groove. The outer casing is a cylindrical body made of carbon-carbon composite material. The bottom end of the outer casing can be inserted into the annular groove of the lower tray, and the side wall of the outer casing is provided with lifting holes along the circumference. The inner liner is a cylindrical body made of isostatically pressed graphite. The outer wall of the inner liner is fitted with the inner wall of the outer jacket, and the inner wall has a tapered surface that tapers inward from top to bottom. The second liner is composed of three equally divided fan-shaped isostatically pressed graphite modules. The outer wall of each fan-shaped isostatically pressed graphite module has a tapered surface that matches the tapered surface of the first liner. Each fan-shaped module has a lifting hole at its top. The inner wall of the second liner is a vertical plane. Gasket 1, Gasket 2, and Lower Gasket Block are arranged sequentially from top to bottom within the inner liner 2, with material layers placed between adjacent components.

2. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 1, characterized in that: It also includes an upper guide centering mechanism, wherein the diameter of the circular groove of the upper pressure plate is larger than the top diameter of the pressure block; the upper pressure plate is also connected to the frame of the hot pressing sintering furnace through the upper guide centering mechanism, and the upper guide centering mechanism is used to constrain the pressure direction of the upper pressure plate.

3. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 2, characterized in that: The upper guide centering mechanism includes a guide sleeve fixed to the frame and a sliding centering pressure head seat fitted inside the guide sleeve; the upper end of the sliding centering pressure head seat is rigidly connected to the upper hydraulic column, and the lower end of the sliding centering pressure head seat is provided with a hemispherical self-aligning contact surface. The top of the upper pressure plate is hemispherical, and the hemispherical self-aligning contact surface abuts against the top of the upper pressure plate; the inner wall of the guide sleeve is provided with a vertical guide groove, and the outer side of the sliding centering pressure head seat is provided with a guide key that slides with the vertical guide groove.

4. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 1, characterized in that: It also includes a lower guide centering mechanism, through which the lower tray is connected to the lower hydraulic column of the hot pressing sintering furnace. The lower guide centering mechanism is used to center and fix the lower tray.

5. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 4, characterized in that: The lower guide centering mechanism includes a connecting plate, a fixed ring, a drive ring, a push rod, a slider, and a locking fastener. The connecting plate is sleeved and fixed to the top of the lower hydraulic column of the hot-pressing sintering furnace. The fixed ring is fixed to the connecting plate and is coaxially arranged with the circular groove. The upper surface of the fixed ring is circumferentially spaced with slots extending radially. Each slot can accommodate one push rod. The top of each push rod is fixed with a slider. The drive ring is coaxial with the fixed ring and rotatably connected. The drive ring is circumferentially spaced with multiple arc-shaped grooves. The top of the slider can slide into the corresponding arc-shaped groove. By rotating the drive ring, through the slider and the arc-shaped groove, all the push rods can be simultaneously driven to move towards the center along the slots to clamp and fix the outer sleeve or move outward simultaneously. The locking fastener is a set screw. The set screw is threadedly connected to the drive ring. By rotating the set screw, the end of the set screw can abut against the fixed ring, thereby locking and fixing the drive ring.

6. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 3, characterized in that, It also includes a liner demolding mechanism, which can be connected to the three liners II for assisting the liner II in demolding.

7. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 6, characterized in that, The lining demolding mechanism includes: A lifting ring is located above the guide sleeve and is coaxially arranged with the guide sleeve. The lifting ring can move vertically up and down. A guide rod is provided on the side wall of the lifting ring. A vertically extending guide groove is provided on the frame. The guide rod can slide up and down with the frame. A height adjusting screw is vertically fixed to the lifting ring and threadedly connected to the frame. Rotating the height adjusting screw drives the lifting ring to rise and fall vertically. Three hooks are mounted on the lifting ring in an isosceles triangle configuration, and the hooks can be connected to the lifting holes on the three inner linings.

8. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 7, characterized in that: The lining demolding mechanism also includes a fine-tuning knob. The three hooks are connected to the lifting ring through the three fine-tuning knobs. Rotating the fine-tuning knobs drives the hooks to rise and fall vertically.

9. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 1, characterized in that: The inner diameter of the annular groove on the upper surface of the lower tray is larger than the outer diameter of the outer sleeve.

10. The high-strength hot-pressed sintered large aluminum nitride ceramic fixture according to claim 1, characterized in that: The wall thickness of the outer jacket is half the diameter of the pressed aluminum nitride ceramic plate.

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