Multidirectional isostatic pressing die, isotropic material and forming method of isotropic material

Abstract

The invention discloses a multidirectional isostatic pressing die, an isotropic material and a forming method of the isotropic material. The multidirectional isostatic pressing die comprises a metal shell, a metal pressing plate, a pushing and pressing mechanism, a magnetic material blocking plate frame and a pressure sensor. The forming method comprises the following steps: assembling a mold and charging; pressure is equally applied in three directions; heating, curing and post-processing. According to the multidirectional isostatic pressing die, through the metal shell, the metal pressing plate, the pushing and pressing mechanism, the magnetic material blocking plate frame and the pressure sensor, equal pressure applying in the X direction, the Y direction and the Z direction can be achieved, and the die is simple in structure, easy to implement and low in cost; the material prepared by adopting the mold has isotropy, the layering phenomenon can be effectively avoided, the material performance is improved, and the industrial production and use requirements are met.

Description

Technical Field

[0001] The present invention relates to the technical field of pressurized thermal solidification of powder materials, in particular to a multi-directional isostatic pressing die, an isotropic material and a molding method thereof. Background Art

[0002] At present, the main pressurizing technologies for powder materials are uniaxial pressing and isostatic pressing.

[0003] Unidirectional pressing technology involves loading the mold cavity with powder to be pressed, and then moving the upper pressing plate downward to apply pressure, which compresses the powder into a compact. Unidirectional pressing only applies pressure in one direction, and the pressure in the up-down, left-right, and front-back directions is uneven. This causes stratification of the compact and significant anisotropy in the product. In the manufacturing of thermal insulation materials for the growth of single-crystal silicon and silicon carbide single crystals, the unidirectional pressing molding process is currently widely used. The resulting products exhibit significant stratification, and the thermal conductivity, resistivity, and compressive / flexural strength of the products vary significantly in the transverse and longitudinal directions, hindering the efficient application of thermal insulation materials.

[0004] Isostatic pressing technology involves wrapping the powder material to be pressed in a sheath and placing it in a high-pressure container with a hydraulic medium. Utilizing the incompressible and uniform pressure-transmitting properties of the liquid medium, the powder material to be pressed is evenly pressurized from all directions, ensuring uniform force and density distribution.

[0005] Pressurized heat curing and heat treatment processes for powder materials involve heat curing or heat treating the material under pressure in a high-temperature environment. However, due to the inability of the hydraulic oil used in cold isostatic pressing equipment to withstand heat, and the bulk of the cold isostatic pressing and auxiliary equipment, pressurized heat curing and heat treatment of powder materials are not feasible. While hot isostatic pressing technology exists, the equipment is bulky and expensive, making it costly to operate and unsuitable for the pressurized heat curing process used in the manufacture of thermal insulation materials. Summary of the Invention

[0006] The present invention provides a multi-directional isostatic pressing die, an isotropic material and a molding method thereof, which can apply pressure evenly from three directions and can be placed in a high-temperature oven for heat curing treatment, so as to solve the problems of product stratification, anisotropy and high cost of hot isostatic pressing equipment in the prior art.

[0007] In order to solve the above technical problems, the present invention provides a multi-directional isostatic pressing die, characterized in that it includes: A metal shell, the metal shell consisting of a bottom plate, a front plate, a rear plate, a left plate, a right plate and an upper cover plate; A metal pressing plate, the metal pressing plate correspondingly adheres to the inner wall surface of each plate of the metal shell, with a gap left at its edge; A pushing mechanism, the pushing mechanism passes through the bottom plate, front plate, rear plate, left plate, right plate and upper cover plate of the metal shell, contacts the corresponding metal pressing plates, and pushes the metal pressing plates to move parallel to the center of the mold; A magnetic baffle plate frame, wherein the magnetic baffle plate frame is arranged in the cavity formed by the metal pressure plates, and its outer surface is in contact with the inner wall surface of each metal pressure plate; the magnetic baffle plate frame is formed by overlapping and splicing a plurality of L-shaped magnetic plates along their edge portions, and the adjacent side edges of each L-shaped magnetic plate are tightly fitted together by magnetic attraction to form a retractable space; under the push of the metal pressure plates, the L-shaped magnetic plates slide relatively along the normal direction of the splicing boundary, so that the sealed space shrinks evenly toward the center of the mold, squeezing the powder material therein; under the push of the metal pressure plates, the sealed space shrinks by the overlapping sliding of the L-shaped magnetic plates, squeezing the powder material therein; A pressure sensor is built into the middle of the inner surface of the metal pressure plate and is connected to the push mechanism signal.

[0008] In a preferred embodiment of the present invention, the bottom plate, front plate, rear plate, left plate and right plate of the metal shell are an integrated structure, and the edge of the upper cover plate is detachably connected to the top ends of the front plate, rear plate, left plate and right plate.

[0009] In a preferred embodiment of the present invention, the magnetic baffle plate frame is a hexahedral hollow structure, which is composed of eight L-shaped magnetic plates with overlapping edges and magnetically spliced together; Each of the four side surfaces is formed by partially overlapping and magnetically splicing the folded edges of four L-shaped magnetic plates in the vertical and horizontal directions; The bottom surface and the top surface are respectively formed by the bottom pressing plate and the upper pressing plate of the metal pressing plate; The L-shaped magnetic plate is arranged at the corners of the hexahedron, and its two folded surfaces respectively cover the edge areas of two adjacent surfaces.

[0010] In a preferred embodiment of the present invention, on each side, the overlapping length in the vertical direction accounts for 4-50% of the vertical height of a single L-shaped magnetic plate; the overlapping length in the horizontal direction accounts for 4-50% of the folded surface length of a single L-shaped magnetic plate.

[0011] In a preferred embodiment of the present invention, the L-shaped magnetic plate is a metal plate coated with a NdFeB magnetic material layer or a magnetic composite plate formed by mixing and solidifying resin and NdFeB magnetic powder.

[0012] In a preferred embodiment of the present invention, the pushing mechanism includes a screw, a runner nut and a multi-claw connected push rod sleeve; For the bottom plate and the upper cover plate, the screw is vertically fixed to the middle of the outer side of the bottom plate and the upper cover plate; For the front plate, rear plate, left plate and right plate, the screw rods are respectively fixed vertically at the lower middle position thereof; The multi-claw conjoined ejector rod is sleeved on the screw rod, and its multiple claws penetrate the plates of the metal shell and contact the metal pressure plate; The runner nut is threadedly connected to the screw rod and can be rotated to push the multi-claw connected push rod sleeve to move.

[0013] In a preferred embodiment of the present invention, a program controller is further included, which is connected to the pressure sensor signal and dynamically adjusts the rotation angle of the wheel nut through real-time measurement data of the pressure sensor to make the six-sided pressure deviation ≤5%.

[0014] In a preferred embodiment of the present invention, the metal shell is further provided with holes or notches for heat conduction and gas escape during high-temperature thermal curing.

[0015] To solve the above technical problems, the present invention further provides a method for molding an isotropic material, using the above mold, comprising the following steps: (1) Mold assembly and material addition: The metal pressing plate and the magnetic baffle frame are placed in the metal shell in sequence, the powder material to be extruded is added to the magnetic baffle frame, the edge parts of the L-shaped magnetic plate are overlapped with each other by magnetic attraction to form a retractable space, the upper pressing plate of the metal pressing plate is placed on top of it, and finally the upper cover of the metal shell is covered and fixed; (2) Applying pressure equally in three directions: Under the real-time monitoring of the pressure sensor, the pushing mechanism applies pressure of the same magnitude to each metal pressure plate in the metal shell at the same time, so that each metal pressure plate moves parallel to the center of the mold, thereby causing the magnetic baffle frame to contract adaptively under pressure and compress the powder material therein; (3) Heating and curing: each of the pushing mechanisms is locked and fixed to ensure that the applied pressure remains constant, and the mold is pushed as a whole into the heating device to perform thermal curing under pressure; (4) Post-processing: After the curing is completed, the pushing mechanism is unlocked, the upper cover plate and the upper pressure plate are removed, and the solidified blank is taken out. After post-processing, an isotropic material is obtained.

[0016] In order to solve the above technical problems, the present invention also provides an isotropic material prepared using the above mold.

[0017] The beneficial effects of the present invention are as follows: a multi-directional isostatic pressing die of the present invention can achieve equal pressure in the X, Y and Z directions through a metal shell, a metal pressure plate, a pushing mechanism, a magnetic baffle plate frame and a pressure sensor. The die structure is simple, easy to implement and low in cost; the material prepared by the die of the present invention has isotropy, can effectively avoid stratification, improve material performance and meet the requirements of industrial production and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the three-dimensional structure of a preferred embodiment of a multi-directional isostatic pressing die of the present invention; Figure 2 : is a schematic diagram of the three-dimensional structure of the magnetic baffle plate frame shown; in the figure, H represents the height of the L-shaped magnetic plate in the vertical direction, and L represents the length of the folded surface of the L-shaped magnetic plate; Figure 3 This is an electron microscope photograph of the isotropic carbon fiber-carbon composite material prepared in a preferred embodiment 1 of the present invention; Figure 4 This is a microscopic photograph of the isotropic carbon fiber-carbon composite material prepared in a preferred embodiment 1 of the present invention at an optical magnification of 20 times; Figure 5 is an electron microscope photograph of the carbon fiber-carbon composite material prepared in Comparative Example 1 of the present invention; Figure 6 This is a micrograph of the carbon fiber-carbon composite material prepared in Comparative Example 1 of the present invention at an optical magnification of 20 times; The markings of the components in the accompanying drawings are as follows: 10. Metal casing, 11. Front panel, 12. Rear panel, 13. Left panel, 14. Right panel, 15. Upper cover, 16. Holes or notches; 20.Metal pressure plate; 30. Pushing mechanism, 31. Screw, 32. Multi-claw one-piece push rod sleeve, 33. Rotor nut; 40. Magnetic baffle frame. DETAILED DESCRIPTION

[0019] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0020] See also Figure 1-6 , embodiments of the present invention include: The present invention discloses a multi-directional isostatic pressing die, comprising: a metal shell 10, a metal pressing plate 20, a pushing mechanism 30, a magnetic baffle frame 40 and a pressure sensor.

[0021] The metal housing 10 is composed of a bottom plate, a front plate 11, a rear plate 12, a left plate 13, a right plate 14, and an upper cover plate 15. The bottom plate, front plate, rear plate, left plate, and right plate are welded together to form an integral structure, and the edge of the upper cover plate is detachably connected to the top ends of the front plate, rear plate, left plate, and right plate via screws.

[0022] There are 6 metal pressing plates, which are respectively attached to the inner wall of each plate of the metal shell 10, with gaps left at the edges to provide space for them to move toward the center of the mold. Regarding the size of each metal pressing plate 20, the preferred solution is: The bottom and upper pressure plates have the same size and are the largest, which is comparable to the inner size of the bottom plate of the metal housing 10; The size (width) of the front pressing plate and the rear pressing plate is the same and smaller than the size of the bottom pressing plate or the upper pressing plate; The left pressing plate and the right pressing plate have the same size (width) and are smaller than the size of the front pressing plate or the rear pressing plate.

[0023] The reserved gaps between the front and rear pressure plates and the left and right pressure plates are the largest, reserving space for subsequent movement during pressure.

[0024] The left pressing plate, the right pressing plate, the front pressing plate and the rear pressing plate have the same height, which is lower than the inner height of the metal shell 10 , so as to reserve space for the movement of the upper pressing plate and the bottom pressing plate.

[0025] In the above design, the dimensions of the front and rear pressure plates are interchangeable without affecting the effect. Other dimensional designs for the bottom, upper, front, rear, left, and right pressure plates, as long as they meet the requirements of the present invention, such as reserving sufficient space for the metal pressure plates to move and achieving the same three-directional pressure to achieve uniform extrusion of powder materials and isotropic compression, are equivalent improvements to the present invention.

[0026] The number of the pushing mechanism 30 is the same as the number of the plates of the metal shell 10 , and includes a screw 31 , a multi-claw connected push rod sleeve 32 and a wheel nut 33 .

[0027] Among them, on the bottom plate and the upper cover plate of the metal shell 10, the screw 31 is vertically fixed to the middle part of the outer side of the bottom plate and the upper cover plate; On the left plate, right plate, front plate and rear plate of the metal housing 10, screws 31 are vertically fixed at the lower middle portion of the corresponding plates, specifically at 2 / 5 of the height of each plate; The multi-claw conjoined push rod 32 is sleeved on the screw rod 31, and its four claws penetrate the through holes on the bottom plate, front plate, rear plate, left plate, right plate and upper cover plate of the metal shell and contact the corresponding metal pressure plate 20; The wheel nut 33 is threadedly connected to the screw 31 and can rotate to push the multi-claw connected push rod 32 to move, pushing the metal pressure plate to move parallel to the center of the mold.

[0028] The wheel nut 33 is rotated by manual, mechanical or motor drive to drive the multi-claw connecting rod push rod to move forward, and the multi-claws press and push the metal pressure plate to translate toward the center of the mold.

[0029] The magnetic baffle frame 40 is disposed in the cavity formed by the metal pressing plates 20, and its outer surface is in contact with the inner wall of each metal pressing plate 20. Since the metal pressing plates 20 are discontinuous spaces or cavities with reserved gaps, powder materials cannot be directly loaded. Therefore, the magnetic baffle frame 40 is disposed in the cavity formed by the metal pressing plates 20 to load the powder materials.

[0030] The magnetic baffle plate frame 40 is formed by overlapping and splicing 8 L-shaped magnetic plates along their edge portions. The adjacent sides of each L-shaped magnetic plate are tightly fitted together by magnetic attraction, and together with the upper pressure plate and the bottom pressure plate, a retractable sealed space is formed.

[0031] Specifically, the magnetic baffle frame 40 is a hexahedral structure, wherein: Each of the four side surfaces is composed of four L-shaped magnetic plates whose folded edge portions partially overlap and magnetically attract each other in the vertical and horizontal directions; on each side surface, the four L-shaped magnetic plates are divided into two groups, upper and lower, and the upper and lower groups partially overlap and magnetically attract each other in the vertical direction; the two L-shaped magnetic plates in each group partially overlap and magnetically attract each other in the horizontal direction; and the overlapping height in the vertical direction accounts for 4-50% of the vertical height of a single L-shaped magnetic plate, preferably 10%; the overlapping length in the horizontal direction accounts for 4-50% of the length of the folded surface of a single L-shaped magnetic plate, preferably 10%.

[0032] The L-shaped magnetic plate is arranged at the corners of the hexahedron, and its two folded surfaces respectively cover the edge areas of two adjacent surfaces.

[0033] The bottom and top of the magnetic baffle frame 40 are respectively formed with the bottom pressing plate and the upper pressing plate of the metal pressing plate 20, and the bottom pressing plate and the upper pressing plate are used to block the material. The structural design of the magnetic baffle frame 40 can not only meet the compression and contraction in three directions, but also facilitate the addition of materials.

[0034] In addition, the L-shaped magnetic plate is a metal plate coated with a NdFeB magnetic material layer on the surface or a magnetic composite plate formed by mixing and solidifying resin and NdFeB magnetic powder. The NdFeB magnetic material layer has a heat resistance temperature greater than or equal to 250°C and has strong high temperature stability.

[0035] Under the push of the metal pressing plate 20 , the L-shaped magnetic plate slides relatively along the normal direction of the splicing boundary, so that the magnetic baffle plate frame shrinks evenly toward the center of the mold, squeezing the powder material therein.

[0036] The pressure sensor is built into the middle of the inner surface of each pressure plate of the metal pressure plate 20 and is connected to the signal of the pushing mechanism 30. It can measure the pressure exerted on each metal pressure plate in real time, and then feedback-regulate the thrust of the pushing mechanism 30 to ensure that the pressure exerted on the six surfaces is the same, thereby achieving equal pressure in three directions.

[0037] The pressure sensor is of high temperature resistant type. The pressure sensor and its connecting cable can withstand high temperature of 250°C and can be used repeatedly, ensuring that they will not be damaged by high temperature in a high temperature oven or heating furnace, thereby extending the service life.

[0038] Preferably, it also includes a program controller, which is connected to the pressure sensor signal and dynamically adjusts the rotation angle of the runner nut through the real-time measurement data of the pressure sensor to make the six-sided pressure deviation ≤5%.

[0039] The tops of the front, rear, left and right plates of the metal shell 10 are further provided with holes or notches 16 for heat conduction and gas escape during high-temperature thermal curing.

[0040] The above mold can achieve equal pressure on six surfaces, that is, equal pressure in the X, Y and Z directions.

[0041] Example 1 Six 10mm-thick 304 stainless steel sheets were cut and welded together to form a 500*500*500 cubic metal enclosure with a bottom, front, back, left, and right panels. This served as the mold shell, with the top cover set aside for future use. Four 20mm-inner-diameter through-holes were symmetrically drilled in the center of the bottom and top panels. Four 20mm-inner-diameter through-holes were also drilled symmetrically in the sides of the front, back, left, and right panels, moving down from the center to 2 / 5 of the height. A screw with a 15mm outer diameter and a height of 150mm was vertically welded to the center of each of the four through-holes.

[0042] An aluminum plate with a size of 470mm*470mm and a thickness of 20mm is placed on the inner bottom of the metal shell as a bottom pressure plate.

[0043] Two aluminum plates of the same material and thickness are placed vertically against the inner walls of the front plate and the rear plate of the metal shell as the front pressure plate and the rear pressure plate. The width of the front pressure plate and the rear pressure plate is 470 mm and the height is 260 mm.

[0044] Two aluminum plates of the same material and thickness are placed vertically against the inner walls of the left and right plates of the metal shell as the left and right pressure plates. The width of the left and right pressure plates is 260 mm and the height is 260 mm.

[0045] Select eight L-shaped 201 stainless steel plates with a wall thickness of 2mm and two folded surfaces measuring 250mm*250mm. Evenly spray a 0.2mm NdFeB magnetic powder coating on their surfaces to make L-shaped magnetic plates. Adhere these eight L-shaped magnetic plates to each other and partially overlap to form a magnetic retaining plate frame with an outer length of 440mm, an outer width of 440mm, and a height of 470mm, which is the magnetic retaining plate frame 40. The specific splicing method is as follows: The four sides of the magnetic baffle frame are each formed by overlapping and attracting the edges of four L-shaped magnetic plates, with an overlap of 30 mm in the vertical direction and 60 mm in the horizontal direction.

[0046] The L-shaped magnetic plate is arranged at the corners of the hexahedron, and its two folded surfaces respectively cover the edge areas of two adjacent surfaces.

[0047] Place the magnetic baffle frame within the discontinuous space enclosed by the metal pressure plate. Add a uniformly mixed powder of chopped carbon fiber, phenolic resin, and additives to the frame. Once filled, add the upper pressure plate, which measures 470mm*470mm and is 20mm thick. Then, install the upper cover of the metal casing and screw the four corners together with the metal casing to form a single unit.

[0048] Attach six 304 stainless steel, four-jaw conjoined push rods 32 to the screws on the six exterior surfaces of the metal housing 10, inserting the four claws into the four through-holes. The claws are 120 mm long and 15 mm in outer diameter. Attach the hand-cranked turntable nut 33 to the screws. Tighten the hand-cranked turntable nut clockwise, pushing the four-jaw conjoined push rods forward. The four claws tighten, pushing the pressure plate toward the center of the mold.

[0049] The six metal pressure plates are then translated and tightened in this manner. Based on the pressure data from the high-temperature sensor located in the center of each platen's inner surface, the tightening state of the six surfaces is adjusted to ensure that the tightening pressure on all six surfaces is completely equal. Once the six pressure plates have been translated and brought together to form a 260mm*260mm*260mm cubic isostatic compression chamber, the hand-cranked turntable nut is tightened with a lock nut to ensure constant pressure.

[0050] The pressure sensor's gauge was removed, and the entire mold was placed in a high-temperature oven for heat curing at 180°C for 25 hours. 20mm*300mm notches were provided on the upper edges of the left, rear, left, and right plates of the mold's metal shell. This notches facilitate heat entry into the mold's pressure cavity and allow gases generated by the heated material to escape.

[0051] After curing is complete, remove the locking nut, remove the hand-crank turntable nut, remove the four-claw conjoined push rod, remove the upper cover plate, remove the upper pressure plate, and remove the cured carbon fiber resin composite body. This is then carbonized at 1300°C in a high-purity nitrogen (99.999%) atmosphere for 24 hours, graphitized at 1800°C in a vacuum of 200Pa for 20 hours, and purified in a vacuum of 2200°C in a vacuum of 20Pa for 30 hours to obtain the carbon fiber-carbon composite thermal insulation material.

[0052] The obtained carbon fiber-carbon composite thermal insulation material samples were observed by electron microscope and optical microscope. Figure 3 and Figure 4 As shown, there is no delamination phenomenon.

[0053] The resistivity of the sample was tested using the national standard GB / T24525-2009 "Test method for resistivity of carbon materials". The thermal conductivity was tested using the national standard GB / T10295-2008 "Heat flow meter method for determination of steady-state thermal resistance and related properties of thermal insulation materials". The compressive strength was tested using the national standard GB / T4740-1999 "Test method for compressive strength of ceramic materials". The flexural strength was tested using the national standard GB / T3074.1-2021 "Test method for flexural strength of carbon materials". As shown in Table 1: the transverse and longitudinal resistivities are almost the same; there is no obvious difference in the transverse and longitudinal thermal conductivity; the transverse and longitudinal compressive / flexural strengths are almost the same. This shows that the product prepared by the mold of the present invention has isotropy and can well meet the stringent technical requirements of thermal insulation materials in thermal fields.

[0054] Example 2 Using 10mm thick 304 stainless steel plate as raw material, it is cut and welded into a rectangular metal shell with outer dimensions of 600mm long * 500mm wide * 400mm high, including bottom plate, front plate, back plate, left plate and right plate. It is used as the mold shell, and its upper cover is placed aside for use.

[0055] A screw with an outer diameter of 15mm and a height of 150mm is welded 180mm below the center point of the four outer surfaces of the rectangular metal shell. Four through-holes with an inner diameter of 20mm are symmetrically opened around the screw. A screw with an outer diameter of 15mm and a height of 150mm is welded at the center point of the bottom of the shell and the upper cover. Four through-holes with an inner diameter of 20mm are symmetrically opened around the screw.

[0056] An aluminum plate with a size of 570mm*470mm and a thickness of 20mm is placed on the inner bottom of the metal shell as a bottom pressure plate.

[0057] Two aluminum plates of the same material and thickness are placed vertically against the inner walls of the front plate and the rear plate of the metal shell as the front pressure plate and the rear pressure plate. The width of the front pressure plate and the rear pressure plate is 570 mm and the height is 160 mm.

[0058] Two aluminum plates of the same material and thickness are placed vertically against the inner walls of the left and right plates of the metal shell as the left and right pressure plates. The width of the left and right pressure plates is 260 mm and the height is 160 mm.

[0059] Select eight L-shaped 202 stainless steel plates with a wall thickness of 2mm and two folding surfaces measuring 300mm*200mm and 250mm*200mm, respectively. The 200mm height is the vertical height. Then, evenly spray a 0.2mm coating of NdFeB magnetic powder material on the surface to form an L-shaped magnetic plate. These eight L-shaped magnetic plates are adhered to each other and partially overlapped to form a magnetic baffle frame with an outer length of 540mm, an outer width of 440mm, and a height of 370mm. This is the magnetic baffle frame 40. The specific splicing method is as follows: The four sides of the magnetic baffle frame are made of four L-shaped magnetic plates that overlap and attract each other. The vertical overlap is 30mm, and the 540mm long side of the baffle frame overlaps 60mm in the horizontal direction. The 440mm short side of the baffle frame overlaps 60mm in the horizontal direction.

[0060] The L-shaped magnetic plate is arranged at the corners of the hexahedron, and its two folded surfaces respectively cover the edge areas of two adjacent surfaces.

[0061] Place the magnetic baffle frame within the discontinuous space enclosed by the metal pressure plate. Add a uniformly mixed mixture of graphite powder, resin, and additives. Once filled, add the upper pressure plate, which measures 570mm*470mm and is 20mm thick. Then install the upper cover of the metal shell, and screw the four corners to the metal shell to form a single unit.

[0062] Attach six 304 stainless steel, four-jaw conjoined push rods 32 to the screws on the six exterior surfaces of the metal housing 10, inserting the four claws into the four through-holes. The claws are 120 mm long and 15 mm in outer diameter. Attach the hand-cranked turntable nut 33 to the screws. Tighten the hand-cranked turntable nut clockwise, pushing the four-jaw conjoined push rods forward. The four claws tighten, pushing the pressure plate toward the center of the mold.

[0063] The six metal pressure plates are then translated and tightened in this manner. Based on the pressure data from the high-temperature sensor located in the center of each platen's inner surface, the tightening state of the six surfaces is adjusted to ensure equal tightening pressure. Once the six platens have been translated and brought together to form a rectangular, quasi-isostatic compression chamber measuring 432mm x 342mm x 282mm, the hand-cranked turntable nut is tightened with a locknut to ensure constant pressure.

[0064] The pressure sensor's gauge was removed, and the entire mold was placed in a high-temperature oven for heat curing at 200°C for 10 hours. A row of 20mm-diameter exhaust ports were installed on the upper edges of the left, rear, left, and right plates of the mold's metal shell. These ports facilitate heat entry into the mold's pressure cavity and allow gases generated by the heated material to escape.

[0065] After curing is complete, remove the locking nut, remove the hand-crank turntable nut, remove the four-claw jointed ejector pin, remove the upper cover plate, remove the upper pressure plate, and remove the cured graphite resin composite body. This is then followed by high-temperature carbonization at 1000°C in a high-purity nitrogen (99.999%) atmosphere for 20 hours, high-temperature graphitization at 1800°C in a vacuum of 200 Pa for 25 hours, and high-temperature vacuum purification at 2300°C in a vacuum of 20 Pa for 30 hours to obtain a graphite-carbon composite thermal field composite material.

[0066] The obtained graphite-carbon composite thermal field composite material sample was observed by optical microscopy and electron microscopy at a magnification of 20 times, and no delamination phenomenon was found.

[0067] The resistivity of the sample was tested using the national standard GB / T24525-2009 "Test method for resistivity of carbon materials". The thermal conductivity was tested using the national standard GB / T10295-2008 "Heat flow meter method for determination of steady-state thermal resistance and related properties of thermal insulation materials". The compressive strength was tested using the national standard GB / T4740-1999 "Test method for compressive strength of ceramic materials". The flexural strength was tested using the national standard GB / T3074.1-2021 "Test method for flexural strength of carbon materials". The results are shown in Table 1: the transverse and longitudinal resistivity are almost the same; there is no obvious difference in transverse and longitudinal thermal conductivity; the transverse and longitudinal compressive / flexural strength are almost the same. This shows that the product prepared by the mold of the present invention has isotropy and can meet the quality requirements of high-quality graphite-carbon composite high-temperature materials.

[0068] Comparative Example 1 Prepare a one-way compression molding die.

[0069] Using 20mm thick 304 stainless steel plate as raw material, cut six pieces and weld them into a cubic metal shell with an outer size of 500*500*500 with a bottom plate, front plate, back plate, left plate and right plate, which is used as the mold shell. The upper cover plate is placed aside for use.

[0070] Add a uniformly mixed powder of chopped carbon fiber, phenolic resin, and additives to the prepared mold shell. Once filled, add an aluminum upper pressure plate measuring 458mm x 458mm and 20mm thick. Then, install the upper cover, screwing the four corners of the upper cover to the outer shell to form a single unit. The upper cover has four symmetrically distributed 15mm diameter internal thread screw holes. Four 200mm long, 15mm diameter external thread screws are screwed into each of these four screw holes. Tighten the upper pressure plate downward to compress the powder mixture.

[0071] After the four 200mm long external screws are fully screwed in, tighten them with locking nuts. Push the entire mold into a high-temperature oven at 180°C for thermal curing for 25 hours. After the curing is completed, remove the locking nut, upper cover plate and upper pressure plate, and take out the cured carbon fiber resin composite blank. Then, after the same high-temperature carbonization, high-temperature graphitization and high-temperature purification process as in Example 1, a carbon fiber-carbon composite thermal field insulation material is obtained.

[0072] The obtained carbon fiber-carbon composite thermal insulation material sample cut section has obvious transverse layered structure. The electron microscope and 20 times magnified optical microscope photos are shown as follows: Figure 5 and 6 shown.

[0073] Using the same testing methods as in Example 1, samples were taken and tested for resistivity, thermal conductivity, and compressive / flexural strength. The results are shown in Table 1: The longitudinal and transverse resistivity differed by nearly a factor of three; the transverse and longitudinal thermal conductivity varied significantly; and the transverse and longitudinal compressive / flexural strength also differed significantly. This indicates that the product exhibits significant anisotropy, making it difficult to meet the technical requirements for thermal insulation materials used in silicon carbide single crystal growth. Furthermore, it is difficult to process into a thermal cavity, resulting in thermal field instability.

[0074] Comparative Example 2 Prepare a one-way compression molding die.

[0075] Using 20mm thick 304 stainless steel plate as raw material, cut six pieces and weld them into a cubic metal shell with an outer dimension of 500*500*500 with a bottom plate, front plate, back plate, left plate and right plate, which is used as the mold shell. The upper cover plate is placed aside for use.

[0076] Add the uniformly mixed graphite powder, resin, and additive mixture. Once the mixture is filled, add the upper pressure plate, which measures 458mm x 458mm and is 20mm thick. Then, install the upper cover, screwing the four corners of the upper cover to the mold shell to form a single unit. The upper cover of the mold shell has four symmetrically spaced 15mm diameter internal thread screw holes. Four 200mm long, 15mm diameter external thread screws are screwed into each of these four holes. Tighten the upper pressure plate downward to compress the powder mixture.

[0077] After four 200mm long external threaded screws are screwed into 100mm, they are tightened with locking nuts. The entire mold is pushed into a high-temperature oven at 200°C for thermal curing for 10 hours. After the curing is completed, the locking nuts, upper cover plate and upper pressure plate are removed, and the cured graphite resin composite body is taken out. Then, after high-temperature carbonization, high-temperature graphitization and high-temperature purification, the same process as in Example 2 is used to obtain a graphite-carbon composite material.

[0078] Optical microscopic observation of the resulting graphite-carbon composite material samples revealed delamination. The test results, as shown in Table 1, show significant differences in resistivity between the transverse and longitudinal directions. Thermal conductivity also differed significantly between the transverse and longitudinal directions. Compressive strength / flexural strength also differed significantly between the transverse and longitudinal directions. This indicates that the prepared graphite-carbon composite material exhibits significant phase anisotropy and fails to meet the quality requirements for qualified high-temperature graphite-carbon composite materials.

[0079] Table 1 Sample performance test data Note: The horizontal direction refers to the x and y directions (in the horizontal plane) when manufacturing the product. The vertical direction refers to the z direction (height direction) when manufacturing the product.

[0080] The multi-directional isostatic pressing mold of the present invention can apply pressure evenly from three directions and can be placed in a high-temperature oven for high-temperature curing while maintaining constant pressure, thereby resolving product delamination and anisotropy. The material produced using the mold of the present invention is isotropic and meets application requirements.

[0081] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A multi-directional isostatic pressing die, characterized in that: include: A metal shell, the metal shell consisting of a bottom plate, a front plate, a rear plate, a left plate, a right plate and an upper cover plate; A metal pressing plate, the metal pressing plate correspondingly adheres to the inner wall surface of each plate of the metal shell, with a gap left at its edge; A pushing mechanism, the pushing mechanism passes through the bottom plate, front plate, rear plate, left plate, right plate and upper cover plate of the metal shell, contacts the corresponding metal pressing plates, and pushes the metal pressing plates to move parallel to the center of the mold; A magnetic baffle plate frame, wherein the magnetic baffle plate frame is arranged in the cavity formed by the metal pressure plates, and its outer surface is in contact with the inner wall surface of each metal pressure plate; the magnetic baffle plate frame is formed by overlapping and splicing a plurality of L-shaped magnetic plates along their edge portions, and the adjacent side edges of each L-shaped magnetic plate are tightly fitted together by magnetic attraction to form a retractable space; under the push of the metal pressure plates, the L-shaped magnetic plates slide relatively along the normal direction of the splicing boundary, so that the sealed space shrinks evenly toward the center of the mold, squeezing the powder material therein; under the push of the metal pressure plates, the sealed space shrinks by the overlapping sliding of the L-shaped magnetic plates, squeezing the powder material therein; A pressure sensor is built into the middle of the inner surface of the metal pressure plate and is connected to the push mechanism signal.

2. The mold according to claim 1, characterized in that The bottom plate, front plate, rear plate, left plate and right plate of the metal shell are an integrated structure, and the edge of the upper cover plate is detachably connected to the top ends of the front plate, rear plate, left plate and right plate.

3. The mold according to claim 1, characterized in that The magnetic baffle frame is a hexahedral hollow structure, consisting of eight L-shaped magnetic plates with overlapping edges that are magnetically attracted to each other. Each of the four side surfaces is formed by partially overlapping and magnetically splicing the folded edges of four L-shaped magnetic plates in the vertical and horizontal directions; The bottom surface and the top surface are respectively formed by the bottom pressing plate and the upper pressing plate of the metal pressing plate; The L-shaped magnetic plate is arranged at the corners of the hexahedron, and its two folded surfaces respectively cover the edge areas of two adjacent surfaces.

4. The mold according to claim 3, characterized in that On each side, the overlapping length in the vertical direction accounts for 4-50% of the vertical height of a single L-shaped magnetic plate; the overlapping length in the horizontal direction accounts for 4-50% of the folded surface length of a single L-shaped magnetic plate.

5. The mold according to claim 3, characterized in that The L-shaped magnetic plate is a metal plate with a NdFeB magnetic material layer coated on its surface or a magnetic composite plate formed by mixing and solidifying resin and NdFeB magnetic powder.

6. The mold according to claim 1, characterized in that The pushing mechanism includes a screw, a runner nut and a multi-claw connected push rod sleeve; For the bottom plate and the upper cover plate, the screw is vertically fixed to the middle of the outer side of the bottom plate and the upper cover plate; For the front plate, rear plate, left plate and right plate, the screw rods are respectively fixed vertically at the lower middle position thereof; The multi-claw conjoined ejector rod is sleeved on the screw rod, and its multiple claws penetrate the plates of the metal shell and contact the metal pressure plate; The runner nut is threadedly connected to the screw rod and can be rotated to push the multi-claw connected push rod sleeve to move.

7. The mold according to claim 6, characterized in that It also includes a program controller, which is connected to the pressure sensor signal and dynamically adjusts the rotation angle of the runner nut through real-time measurement data of the pressure sensor to make the six-sided pressure deviation ≤5%.

8. The mold according to claim 1, characterized in that The metal shell is also provided with holes or notches for heat conduction and gas escape during high-temperature thermal curing.

9. A method for forming an isotropic material, characterized in that: Using the mold according to any one of claims 1 to 8, comprising the following steps: (1) Mold assembly and material addition: The metal pressing plate and the magnetic baffle frame are placed in the metal shell in sequence, the powder material to be extruded is added to the magnetic baffle frame, the edge parts of the L-shaped magnetic plate are overlapped with each other by magnetic attraction to form a retractable space, the upper pressing plate of the metal pressing plate is placed on top of it, and finally the upper cover of the metal shell is covered and fixed; (2) Applying pressure equally in three directions: Under the real-time monitoring of the pressure sensor, the pushing mechanism applies pressure of the same magnitude to each metal pressure plate in the metal shell at the same time, so that each metal pressure plate moves parallel to the center of the mold, thereby causing the magnetic baffle frame to contract adaptively under pressure and compress the powder material therein; (3) Heating and curing: each of the pushing mechanisms is locked and fixed to ensure that the applied pressure remains constant, and the mold is pushed as a whole into the heating device to perform thermal curing under pressure; (4) Post-processing: After the curing is completed, the pushing mechanism is unlocked, the upper cover plate and the upper pressure plate are removed, and the solidified blank is taken out. After post-processing, an isotropic material is obtained.

10. An isotropic material, characterized in that The mold is prepared using any one of claims 1 to 8.

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