Induction graphite crucible and method of ramming and use thereof

Abstract

The application provides an induction graphite crucible and a ramming method and use thereof. The induction graphite crucible comprises: a graphite heat-conducting layer, which forms a crucible space for containing molten material; a sintering layer, which is tightly arranged on the outside of the graphite heat-conducting layer; a solidification layer, which is tightly arranged on the outside of the sintering layer; a loose layer, which is tightly arranged on the outside of the solidification layer; an induction coil, which is solidified on the outside of the loose layer for electric heating; and a sealing layer, which is in a ring structure, arranged above the induction graphite crucible and covers the graphite heat-conducting layer, the sintering layer, the solidification layer and the loose layer. The application adopts layered ramming, effectively solves the problems of looseness, holes, sand leakage and unfirm sintering in the ramming of the crucible.

Description

Technical Field

[0001] This invention relates to the field of crucible equipment technology, and in particular to an induction graphite crucible, its preparation method, and its applications. Background Technology

[0002] Currently, most production processes utilize medium-frequency vacuum induction crucible melting to produce ultra-high purity metal ingots, primarily to prevent environmental contamination of the materials. However, defects such as porosity, voids, sand leakage, and incomplete sintering can occur during crucible preparation. Poor crucible preparation results in low electrical power, difficulty in melting the metal raw material, uneven heat transfer, and partial oxidation on the crucible surface. Furthermore, poor crucible preparation increases the content of moisture and gaseous impurities, causing some material from the crucible surface to detach and float on the molten metal surface during melting. These floating substances can then enter the mold with the molten metal during casting, creating casting defects and inclusions on the ingot surface and inside the ingot.

[0003] Therefore, there is a need to manufacture induction graphite crucibles with better service life and performance. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides an induction graphite crucible, its tamping method and application. By adopting a layered tamping method, the present invention significantly improves the service life of the graphite crucible and avoids the situation where part of the crucible surface material falls off and floats on the surface of the molten metal, and can be better applied in the preparation process of ultra-high purity metal ingots.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides an induction graphite crucible, the induction graphite crucible comprising:

[0007] A graphite thermally conductive layer forms a crucible space for holding molten material;

[0008] A sintered layer is disposed in close contact with the outer side of the graphite thermally conductive layer;

[0009] A curing layer, wherein the curing layer is disposed in close contact with the outer side of the sintered layer;

[0010] A loose layer, wherein the loose layer is disposed in close contact with the outer side of the cured layer;

[0011] An induction coil, which is solidified on the outside of the porous layer for heating by electricity;

[0012] A sealing layer, which is a ring-shaped structure, is disposed above the induction graphite crucible and covers the graphite thermally conductive layer, sintered layer, cured layer and porous layer.

[0013] The present invention produces a crucible with a layered tamping method that eliminates defects such as looseness, holes, sand leakage, and weak sintering. The sintered layer fixes the graphite crucible, provides heat preservation and insulation, the solidified layer increases strength and hardness and prevents metal leakage, and the loose layer dissipates heat and allows for air permeability. By setting these different layers in close succession and using a layered tamping method, the solidification density of the tamping process is significantly improved, and the service life of the crucible is also significantly extended.

[0014] Preferably, the thickness of the sealing layer is 10 to 20 mm, for example, it can be 10 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm or 20 mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the sealing layer is made of refractory clay and sodium silicate.

[0016] Preferably, the refractory clay in the sealing layer is an aluminosilicate mineral.

[0017] Preferably, the Al2O3 content in the refractory clay of the sealing layer is greater than 30wt%, for example, it can be 31wt%, 32wt%, 35wt%, or 40wt%.

[0018] Preferably, the refractory clay in the sealing layer has a refractoriness greater than 1580℃, for example, it can be 1590℃, 1600℃, 1610℃, 1620℃ or 1650℃, etc.

[0019] Preferably, the refractory clay content in the sealing layer is 97-98.5 wt%, for example, it can be 97 wt%, 97.2 wt%, 97.5 wt%, 97.8 wt%, 98 wt%, 98.2 wt%, or 98.5 wt%.

[0020] Preferably, the sodium silicate content in the sealing layer is 1.5 to 3 wt%, for example, it can be 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.3%, 2.5%, 2.8%, or 3.0%.

[0021] Preferably, the porosity of the sealing layer is ≤1wt%, for example, it can be 1wt%, 0.9wt%, 0.8wt%, 0.7wt%, or 0.6wt%.

[0022] Preferably, the thickness of the cured layer is 10 to 20 mm, for example, it can be 10 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm or 20 mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the material of the cured layer includes quartz sand, magnesia sand, refractory clay, and sodium silicate.

[0024] Preferably, the mass ratio of quartz sand, magnesia, and refractory clay in the cured layer is 25-35:25-35:35-45, for example, it can be 25:25:35, 25:30:35, 25:35:35, 25:25:45, 28:25:36, 30:25:45, 30:30:35, or 30:30:40, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] The present invention preferably uses the above composition in the curing layer, which is more conducive to improving the hardness and refractoriness of the curing layer material. When the magnesia content is too low, there is a problem of reduced hardness and refractoriness of the curing layer material. When the magnesia content is too high, there is a problem of increased refractoriness but increased production cost. When the quartz sand content is too low, there is a problem of reduced strength. When the quartz sand content is too high, there is a problem of reduced refractoriness.

[0026] The refractory clay in the curing layer and the refractory clay in the sealing layer can be the same material.

[0027] Preferably, the sodium silicate content in the cured layer is 5-10% by mass, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc.

[0028] Preferably, the porosity of the cured layer is 5-10%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc.

[0029] Preferably, the induction coil is made of copper.

[0030] Preferably, the thickness of the sintered layer is 10 to 20 mm, for example, it can be 10 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm or 20 mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the sintered layer is made of magnesia, refractory clay, sodium silicate, and boric acid.

[0032] Preferably, the mass ratio of magnesia to refractory clay in the sintered layer is 5-7:3-5, for example, it can be 5:3, 5.5:3, 6:3, 6.5:3, 7:3, 5:4, 5:4.5, 5:5, 6:4 or 6:5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] The present invention preferably uses the above composition in the sintering layer, which is more conducive to sintering and forming, has high refractoriness, and fixes the graphite crucible. When the magnesia content is too low, there is a problem of reduced refractoriness. When the magnesia content is too high, there are problems such as high refractoriness and difficulty in forming.

[0034] Preferably, the refractory clay in the sintering layer can be made of the same material as the refractory clay in the sealing layer.

[0035] Preferably, the mass ratio of sodium silicate to boric acid in the sintered layer is 0.9 to 1.1:1, for example, it can be 0.9:1, 0.93:1, 0.95:1, 0.97:1, 0.99:1, 1.02:1, 1.04:1, 1.06:1, 1.08:1 or 1.1:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] The present invention preferably uses sodium silicate and boric acid in the above-mentioned mass ratio for tamping. When the boric acid content is too low, there is a problem of reduced hardness, and when the boric acid content is too high, there is a problem of increased cost.

[0037] Preferably, the sodium silicate content in the sintered layer is 5-10% by mass, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc.

[0038] Preferably, the porosity of the sintered layer is 5 to 10%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc.

[0039] Preferably, the thickness of the loose layer is 20 to 40 mm, for example, it can be 20 mm, 23 mm, 25 mm, 27 mm, 29 mm, 32 mm, 34 mm, 36 mm, 38 mm or 40 mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the material of the porous layer includes quartz sand.

[0041] Preferably, the porosity of the loose layer is 20-30%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%.

[0042] Preferably, the thickness of the graphite thermal conductive layer is 20 to 40 mm, for example, it can be 20 mm, 23 mm, 25 mm, 27 mm, 29 mm, 32 mm, 34 mm, 36 mm, 38 mm or 40 mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the diameter of the graphite thermal conductive layer is 500-700 mm, for example, it can be 500 mm, 523 mm, 545 mm, 567 mm, 589 mm, 612 mm, 634 mm, 656 mm, 678 mm or 700 mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the height of the graphite thermal conductive layer is 500-700mm, for example, it can be 500mm, 523mm, 545mm, 567mm, 589mm, 612mm, 634mm, 656mm, 678mm or 700mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In a second aspect, the present invention provides a method for preparing the induction graphite crucible described in the first aspect, the method comprising:

[0046] (1) Install insulating paper on the induction coil and set a heat insulation base plate at the bottom. Hang the steel mold core into the induction coil. Then, place the slurry of the loose layer, the solidified layer and the sintered layer in sequence at the bottom of the induction coil. Each layer is compacted until the distance between the upper surface of each layer and the furnace opening is the same as the height of the crucible.

[0047] (2) A sealing layer of slurry is placed on the upper part of the loose layer, the solidified layer and the sintered layer and compacted. Then, the furnace is baked under vacuum to form an induction graphite crucible.

[0048] Preferably, the moisture content of the slurry in the loose layer in step (1) is 2-5%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc.

[0049] It is worth noting that the viscosity of the slurry in the loose layer is controlled so that the slurry can be formed into a ball when squeezed by hand and then released.

[0050] Preferably, the moisture content of the slurry for the curing layer in step (1) is 10-20%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc.

[0051] It is worth noting that the viscosity of the slurry in the cured layer is controlled so that the slurry can clump together when squeezed by hand and then released.

[0052] Preferably, the moisture content of the slurry for the sintering layer in step (1) is 10-20%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc.

[0053] It is worth noting that the viscosity of the slurry in the sintering layer is controlled so that the slurry can be formed into a ball when squeezed by hand and then released.

[0054] Preferably, the moisture content of the slurry in the sealing layer in step (2) is 55% to 65%, for example, it can be 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64% or 65%, etc.

[0055] It is worth noting that the slurry of the sealing layer is in the form of mud.

[0056] Preferably, the vacuum level in step (2) is between atmospheric pressure and 6.7E-1Pa.

[0057] Preferably, the vacuum degree of the vacuum condition in step (2) is between 6.7E-1 Pa and 6.7E-2 Pa.

[0058] Preferably, the oven drying process includes: first drying the oven at a first low temperature for a first time, and then drying the oven at a second high temperature for a second time.

[0059] Preferably, the temperature range of the first low temperature is room temperature to 300°C, for example, it can be 25°C, 30°C, 100°C, 150°C, 180°C, 200°C or 300°C.

[0060] It is worth noting that the first low temperature refers to the first moment when the temperature rises from room temperature to 300℃ for oven baking, and the entire heating process is part of the oven baking process.

[0061] Preferably, the first time is 8 to 12 hours, for example, it can be 8 hours, 8.5 hours, 9.5 hours, 10 hours, 11 hours or 12 hours.

[0062] Preferably, the temperature range of the second high temperature is 300 to 1000°C, for example, it can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 800°C, 900°C or 1000°C.

[0063] Preferably, the second time includes heating the oven for 11 to 13 hours, such as 11 hours, 11.2 hours, 11.5 hours, 12 hours, 12.5 hours or 13 hours, and keeping it warm for 20 to 28 hours, such as 20 hours, 21 hours, 22 hours, 25 hours or 28 hours.

[0064] Preferably, the oven is cooled down slowly after baking.

[0065] Thirdly, the present invention provides an application of the induction graphite crucible described in the first aspect in smelting.

[0066] The induction graphite crucible prepared by this invention has a long service life and will not contaminate the raw materials.

[0067] Compared with the prior art, the present invention has at least the following beneficial effects:

[0068] (1) The induction graphite crucible provided by the present invention has a tamping layer containing a sintered layer, a solidified layer and a loose layer. By tamping in layers, the dimensional deviation is minimized, the sintered layer, the solidified layer and the loose layer are tamped smoothly, and defects such as pores and shrinkage cavities inside the sand and gravel are eliminated.

[0069] (2) The method of tamping the induction graphite crucible provided by the present invention adopts a layered tamping method, which significantly improves the service life of the induction graphite crucible. The graphite crucible can be used without pollution for more than 40 times, preferably more than 58 times. Attached Figure Description

[0070] Figure 1 This is a schematic diagram of the induction graphite crucible provided in Embodiment 1 of the present invention.

[0071] In the diagram: 1-Induction coil; 2-Sealing layer; 3-Loose layer; 4-Curing layer; 5-Sintered layer; 6-Graphite thermal conductive layer. Detailed Implementation

[0072] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0073] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0074] It should be understood that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0075] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0076] Example 1

[0077] This embodiment provides an induction graphite crucible, such as Figure 1 As shown, the induction graphite crucible includes: a graphite thermally conductive layer 6, a sintered layer 5, a solidified layer 4, a porous layer 3, an induction coil 1, and a sealing layer 2.

[0078] The graphite thermally conductive layer 6 forms a crucible space for holding molten material; the sintered layer 5 is closely attached to the outside of the graphite thermally conductive layer 6; the cured layer 4 is closely attached to the outside of the sintered layer 5; the loose layer 3 is closely attached to the outside of the cured layer 4; the induction coil 1 is cured on the outside of the loose layer 3 for heating; the sealing layer 2 has a ring structure, is disposed above the induction graphite crucible and covers the graphite thermally conductive layer 6, the sintered layer 5, the cured layer 4 and the loose layer 3.

[0079] The thickness of the sealing layer 2 is 15 mm; the material of the sealing layer 2 includes refractory clay and sodium silicate; the refractory clay in the sealing layer 2 is refractory mortar from Huatuo Metallurgy Co., Ltd.; the mass content of the refractory clay in the sealing layer 2 is 98%; the mass content of the sodium silicate in the sealing layer 2 is 2%; and the porosity of the sealing layer 2 is 0.9 wt%.

[0080] The thickness of the curing layer 4 is 15 mm; the material of the curing layer 4 includes quartz sand, magnesia sand, refractory clay and sodium silicate; the mass ratio of quartz sand, magnesia sand and refractory clay in the curing layer 4 is 30:30:40; the refractory clay in the curing layer 4 is the same as that in the sealing layer 2; the mass content of sodium silicate in the curing layer 4 is 8%; the porosity of the curing layer 4 is 6%; the material of the induction coil 1 is a copper coil.

[0081] The thickness of the sintered layer 5 is 15 mm; the material of the sintered layer 5 includes magnesia, refractory clay, sodium silicate, and boric acid; the mass ratio of magnesia to refractory clay in the sintered layer 5 is 6:4; the refractory clay in the sintered layer 5 is the same as that in the sealing layer 2; the mass ratio of sodium silicate to boric acid in the sintered layer 5 is 1:1; the mass content of sodium silicate in the sintered layer 5 is 6%; and the porosity of the sintered layer 5 is 6.5%.

[0082] The thickness of the loose layer 3 is 30 mm; the material of the loose layer 3 includes quartz sand; the porosity of the loose layer 3 is 22%.

[0083] The graphite thermal conductive layer 6 (high-purity thermally conductive graphite, with a graphite purity ≥ 98 wt%) has a thickness of 30 mm; the graphite thermal conductive layer 6 has a diameter of 600 mm; and the graphite thermal conductive layer 6 has a height of 600 mm.

[0084] This embodiment also provides a method for preparing the induction graphite crucible, the method comprising:

[0085] (1) Install insulating paper on the induction coil and set a heat insulation base plate at the bottom. Hang the steel mold core into the induction coil. Then, place the slurry of the loose layer, the solidified layer and the sintered layer in sequence at the bottom of the induction coil. Each layer is compacted until the distance between the upper surface of each layer and the furnace opening is the same as the height of the crucible.

[0086] The moisture content of the slurry in the loose layer is 2-5%, and the viscosity is controlled so that the slurry can clump together when squeezed by hand and then released. The moisture content of the slurry in the curing layer is 10-20%, and the viscosity is controlled so that the slurry can clump together when squeezed by hand and then released. The moisture content of the slurry in the sintering layer is 10-20%, and the viscosity is controlled so that the slurry can clump together when squeezed by hand and then released. The moisture content of the slurry in the sealing layer is 55-65%, and the slurry in the sealing layer is in the form of a mud slurry.

[0087] (2) A sealing layer of slurry is placed on top of the loose layer, the cured layer, and the sintered layer, and then compacted. The mixture is then baked in a vacuum oven. The baking process includes: heating from room temperature to 300°C for 8–12 hours, then heating from 300°C to 1000°C over 11–13 hours and holding at that temperature for 20–28 hours, followed by slow cooling to form an induction graphite crucible. Example 2

[0088] This embodiment provides an induction graphite crucible, which includes: a graphite thermally conductive layer, a sintered layer, a cured layer, a porous layer, an induction coil, and a sealing layer.

[0089] The graphite thermally conductive layer forms a crucible space for holding molten material; the sintered layer is closely attached to the outside of the graphite thermally conductive layer; the cured layer is closely attached to the outside of the sintered layer; the porous layer is closely attached to the outside of the cured layer; the induction coil is cured on the outside of the porous layer for heating; the sealing layer is a ring structure, located above the induction graphite crucible and covering the graphite thermally conductive layer, sintered layer, cured layer and porous layer.

[0090] The thickness of the sealing layer is 10 mm; the material of the sealing layer includes refractory clay and sodium silicate; the type of refractory clay in the sealing layer is refractory mortar from Huatuo Metallurgy Co., Ltd.; the mass content of the refractory clay in the sealing layer is 97.8%; the mass content of the sodium silicate in the sealing layer is 2.2%; and the porosity of the sealing layer is 0.9 wt%.

[0091] The thickness of the cured layer is 10 mm; the material of the cured layer includes quartz sand, magnesia sand, refractory clay and sodium silicate; the mass ratio of quartz sand, magnesia sand and refractory clay in the cured layer is 25:25:45; the refractory clay in the cured layer is the same as that in the sealing layer; the mass content of sodium silicate in the cured layer is 5%; the porosity of the cured layer is 5.2%; the material of the induction coil is a copper coil.

[0092] The thickness of the sintered layer is 10 mm; the material of the sintered layer includes magnesia, refractory clay, sodium silicate, and boric acid; the mass ratio of magnesia to refractory clay in the sintered layer is 7:3; the refractory clay in the sintered layer is the same as that in the sealing layer; the mass ratio of sodium silicate to boric acid in the sintered layer is 1.1:1; the mass content of sodium silicate in the sintered layer is 5.5%; and the porosity of the sintered layer is 8.2%.

[0093] The thickness of the loose layer is 40 mm; the material of the loose layer includes quartz sand; the porosity of the loose layer is 30%.

[0094] The thickness of the graphite thermal conductive layer (high-purity thermally conductive graphite, with a graphite purity ≥ 98%) is 20 mm; the diameter of the graphite thermal conductive layer is 700 mm; and the height of the graphite thermal conductive layer is 700 mm.

[0095] This embodiment also provides a method for preparing the induction graphite crucible, the method comprising:

[0096] (1) Install insulating paper on the induction coil and set a heat insulation base plate at the bottom. Hang the steel mold core into the induction coil. Then, place the slurry of the loose layer, the solidified layer and the sintered layer in sequence at the bottom of the induction coil. Each layer is compacted until the distance between the upper surface of each layer and the furnace opening is the same as the height of the crucible.

[0097] The moisture content of the slurry in the loose layer is 3%, and the viscosity of the slurry in the loose layer is controlled so that it can clump together when squeezed by hand and then released. The moisture content of the slurry in the curing layer is 15%, and the viscosity of the slurry in the curing layer is controlled so that it can clump together when squeezed by hand and then released. The moisture content of the slurry in the sintering layer is 15%, and the viscosity of the slurry in the sintering layer is controlled so that it can clump together when squeezed by hand and then released. The moisture content of the slurry in the sealing layer is 58%, and the slurry in the sealing layer is in the form of a mud slurry.

[0098] (2) A sealing layer of slurry is placed on the upper part of the loose layer, the solidified layer and the sintered layer and compacted. Then, the furnace is baked under vacuum conditions. The furnace baking includes: heating from room temperature to 300°C for 9 hours, then heating from 300°C to 1000°C within 12 hours and holding for 24 hours, and then slowly cooling down to form an induction graphite crucible.

[0099] Example 3

[0100] This embodiment provides an induction graphite crucible, which includes: a graphite thermally conductive layer, a sintered layer, a cured layer, a porous layer, an induction coil, and a sealing layer.

[0101] The graphite thermally conductive layer forms a crucible space for holding molten material; the sintered layer is closely attached to the outside of the graphite thermally conductive layer; the cured layer is closely attached to the outside of the sintered layer; the porous layer is closely attached to the outside of the cured layer; the induction coil is cured on the outside of the porous layer for heating; the sealing layer is a ring structure, located above the induction graphite crucible and covering the graphite thermally conductive layer, sintered layer, cured layer and porous layer.

[0102] The thickness of the sealing layer is 20 mm; the material of the sealing layer includes refractory clay and sodium silicate; the refractory clay in the sealing layer is refractory mortar from Huatuo Metallurgical Co., Ltd.; the mass content of the refractory clay in the sealing layer is 98.5%; the mass content of the sodium silicate in the sealing layer is 1.5%; and the porosity of the sealing layer is 0.8 wt%.

[0103] The thickness of the cured layer is 20 mm; the material of the cured layer includes quartz sand, magnesia sand, refractory clay and sodium silicate; the mass ratio of quartz sand, magnesia sand and refractory clay in the cured layer is 35:35:35; the refractory clay in the cured layer is the same as that in the sealing layer; the mass content of sodium silicate in the cured layer is 8%; the porosity of the cured layer is 7%; the material of the induction coil is copper coil.

[0104] The thickness of the sintered layer is 20 mm; the material of the sintered layer includes magnesia, refractory clay, sodium silicate, and boric acid; the mass ratio of magnesia to refractory clay in the sintered layer is 5:5; the refractory clay in the sintered layer is the same as that in the sealing layer; the mass ratio of sodium silicate to boric acid in the sintered layer is 0.9:1; the mass content of sodium silicate in the sintered layer is 5.5%; and the porosity of the sintered layer is 8.5%.

[0105] The thickness of the loose layer is 20 mm; the material of the loose layer includes quartz sand; the porosity of the loose layer is 22%.

[0106] The thickness of the graphite thermal conductive layer (high-purity thermally conductive graphite, with a graphite purity ≥ 98%) is 40 mm; the diameter of the graphite thermal conductive layer is 500 mm; and the height of the graphite thermal conductive layer is 500 mm.

[0107] This embodiment also provides a method for preparing the induction graphite crucible, the method comprising:

[0108] (1) Install insulating paper on the induction coil and set a heat insulation base plate at the bottom. Hang the steel mold core into the induction coil. Then, place the slurry of the loose layer, the solidified layer and the sintered layer in sequence at the bottom of the induction coil. Each layer is compacted until the distance between the upper surface of each layer and the furnace opening is the same as the height of the crucible.

[0109] The moisture content of the slurry in the loose layer is 2.5%, and the viscosity of the slurry in the loose layer is controlled so that it clumps together when squeezed by hand and then released. The moisture content of the slurry in the curing layer is 15%, and the viscosity of the slurry in the curing layer is controlled so that it clumps together when squeezed by hand and then released. The moisture content of the slurry in the sintering layer is 10%, and the viscosity of the slurry in the sintering layer is controlled so that it clumps together when squeezed by hand and then released. The moisture content of the slurry in the sealing layer is 5%, and the slurry in the sealing layer is in the form of a mud slurry.

[0110] (2) A sealing layer of slurry is placed on the upper part of the loose layer, the solidified layer and the sintered layer and compacted. Then, the furnace is baked under vacuum to form an induction graphite crucible.

[0111] Example 4

[0112] This embodiment provides an induction graphite crucible, which is the same as that in Embodiment 1 except that the cured layer does not contain quartz sand.

[0113] Example 5

[0114] This embodiment provides an induction graphite crucible, which is the same as that in Embodiment 1 except that the curing layer does not contain magnesia.

[0115] Example 6

[0116] This embodiment provides an induction graphite crucible, which is the same as in Embodiment 1 except that the mass ratio of sodium silicate to boric acid in the sintered layer is 0.8:1.

[0117] Example 7

[0118] This embodiment provides an induction graphite crucible, which is the same as in Embodiment 1 except that the mass ratio of sodium silicate to boric acid in the sintered layer is 1.3:1.

[0119] Comparative Example 1

[0120] This comparative example provides an induction graphite crucible, which is identical to that of Example 1 except that the positions of the curing layer and the sintering layer are interchanged.

[0121] In this comparative example, the positions of the curing layer and the sintering layer are interchanged, which will result in insufficient sintering temperature, incomplete molding, and reduced strength and hardness. Excessive curing temperature reduces the refractoriness, increases the coefficient of thermal expansion, and weakens the fixation of the graphite crucible, posing a significant safety hazard and leading to incomplete molding, potentially causing the graphite crucible to detach or leak.

[0122] Comparative Example 2

[0123] This comparative example provides an induction graphite crucible, which is identical to that of Example 1 except that it does not contain a sintered layer.

[0124] The sintered layer serves to secure the graphite crucible and possesses high strength, hardness, and refractoriness, as well as a low coefficient of thermal expansion. In this comparative example, due to the absence of a sintered layer, the strength, hardness, and refractoriness of the crucible are reduced, and the coefficient of thermal expansion increases, resulting in cracks and pores.

[0125] Comparative Example 3

[0126] This comparative example provides an induction graphite crucible, which is identical to that of Example 1 except that it does not contain a porous layer.

[0127] Because this comparative example does not contain a porous layer, the temperature of the crucible is easily lowered by the water-cooled induction coil during cooling, which reduces the service life of the graphite crucible.

[0128] Comparative Example 4

[0129] This comparative example provides an induction graphite crucible, which is identical to that of Example 1 except that it does not contain a curing layer.

[0130] Because this comparative example does not contain a solidification layer, the strength, hardness, and refractoriness of the tamping crucible are reduced. The temperature of the loose layer rises, causing damage to the induction coil. In addition, problems such as difficulty in heating up and prolonged melting time are likely to occur.

[0131] Comparative Example 5

[0132] This comparative example provides an induction graphite crucible, which is identical to that of Example 1 except that it does not have a sealing layer.

[0133] Because this comparative example does not have a sealing layer, the strength, hardness, and refractoriness of the upper part of the tamping crucible are reduced. During furnace drying, refractory clay, quartz, and other furnace materials will volatilize from the upper part and fall into the graphite crucible, causing contamination of the graphite crucible and increasing the impurity content. In addition, it is easy to cause problems such as temperature rise and damage to the induction coil.

[0134] Comparative Example 6

[0135] This comparative example provides an induction graphite crucible in which the loose layer, solidified layer and sintered layer are all replaced with a sintered layer, and except for the one-step tamping process, it is the same as in Example 1.

[0136] This comparative example, due to having only a sintered layer and being formed in one step, suffers from increased production costs, uneven molding and sintering, difficulty in replacing and cleaning the crucible, and a short service life for the graphite crucible.

[0137] Test method: After drying the furnace, the vacuum level was checked, and then the furnace was washed with metal material. Samples were taken to test the content of GDMS and gaseous impurities in the metal samples to determine whether the overall crucible preparation result was qualified. The crucible prepared in the above manner was then used in the production of 6N ultra-high purity copper to calculate the number of times the crucible could be used without contamination.

[0138] The standard for no pollution is that the content of metal impurities GDMS and gaseous impurities in the metal material is ≤0.001%, and the moisture content is zero.

[0139] The test results of the above embodiments and comparative examples are shown in Table 1.

[0140] Table 1

[0141]

[0142] The following points can be observed from Table 1:

[0143] (1) As can be seen from the comprehensive examples 1 to 3, the induction graphite crucible provided by the present invention significantly improves the life of the induction graphite crucible by setting the tamping layer in layers. The graphite crucible can be used more than 50 times without pollution, which can meet the technical standards for ultra-high purity metals used in semiconductor sputtering targets and provide customers with stable quality products.

[0144] (2) It can be seen from the combined examples 1 and 4-5 that example 1 contains both quartz sand and magnesia sand. Compared with examples 4-5, which do not contain quartz sand and magnesia sand respectively, the service life of the graphite crucible in example 1 is 58 times, while the service life of the graphite crucible in examples 4-5 is only 48 times and 42 times respectively. This shows that the selection of each component in the curing layer has a significant impact on the final service life of the graphite crucible. The present invention further improves the number of times the graphite crucible can be used by optimizing the composition in the curing layer.

[0145] (3) As can be seen from the combined examples 1 and 6-7, the mass ratio of sodium silicate to boric acid in the sintered layer in example 1 is 1:1, which is 0.8:1 and 1.3:1 in examples 6-7, respectively. Therefore, the graphite crucible in example 1 has a longer service life. This shows that the present invention improves the service life of the graphite crucible by controlling the mass ratio of sodium silicate to boric acid in the sintered layer.

[0146] (4) As can be seen from the combined examples 1 and 6, the present invention significantly improves the service life of graphite crucibles by layering and strictly controlling the order of each layer, and by the synergistic effect of each layer.

[0147] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An induction graphite crucible for casting ultra-high purity metal ingots, characterized in that, The induction graphite crucible includes: A graphite thermally conductive layer forms a crucible space for holding molten material; A sintered layer is disposed in close contact with the outer side of the graphite thermally conductive layer; A curing layer, wherein the curing layer is disposed in close contact with the outer side of the sintered layer; A loose layer, wherein the loose layer is disposed in close contact with the outer side of the cured layer; An induction coil, which is solidified on the outside of the porous layer for heating by electricity; A sealing layer, which is a ring-shaped structure, is disposed above the induction graphite crucible and covers the graphite thermally conductive layer, sintered layer, cured layer and porous layer; The materials of the cured layer include quartz sand, magnesia sand, refractory clay and sodium silicate; The sintered layer is made of magnesia sand, refractory clay, sodium silicate, and boric acid. The mass ratio of sodium silicate to boric acid in the sintered layer is 0.9~1.1:

1.

2. The induction graphite crucible according to claim 1, characterized in that, The thickness of the sealing layer is 10~20mm.

3. The induction graphite crucible according to claim 1, characterized in that, The sealing layer is made of refractory clay and sodium silicate.

4. The induction graphite crucible according to claim 3, characterized in that, The refractory clay content in the sealing layer is 97~98.5 wt%.

5. The induction graphite crucible according to claim 3, characterized in that, The sodium silicate content in the sealing layer is 1.5~3wt%.

6. The induction graphite crucible according to claim 1, characterized in that, The porosity of the sealing layer is ≤1wt%.

7. The induction graphite crucible according to claim 1, characterized in that, The thickness of the cured layer is 10~20mm.

8. The induction graphite crucible according to claim 1, characterized in that, The mass ratio of quartz sand, magnesia sand and refractory clay in the solidified layer is 25~35:25~35:35~45.

9. The induction graphite crucible according to claim 1, characterized in that, The sodium silicate content in the cured layer is 5-10% by mass.

10. The induction graphite crucible according to claim 1, characterized in that, The porosity of the cured layer is 5-10%.

11. The induction graphite crucible according to claim 1, characterized in that, The induction coil is made of copper.

12. The induction graphite crucible according to claim 1, characterized in that, The thickness of the sintered layer is 10~20mm.

13. The induction graphite crucible according to claim 1, characterized in that, The mass ratio of magnesia to refractory clay in the sintered layer is 5~7:3~5.

14. The induction graphite crucible according to claim 1, characterized in that, The sintered layer contains 5-10% sodium silicate by mass.

15. The induction graphite crucible according to claim 1, characterized in that, The porosity of the sintered layer is 5-10%.

16. The induction graphite crucible according to claim 1, characterized in that, The thickness of the loose layer is 20~40mm.

17. The induction graphite crucible according to claim 1, characterized in that, The porous layer is made of quartz sand.

18. The induction graphite crucible according to claim 1, characterized in that, The porosity of the loose layer is 20-30%.

19. The induction graphite crucible according to claim 1, characterized in that, The thickness of the graphite thermal conductive layer is 20~40mm.

20. The induction graphite crucible according to claim 1, characterized in that, The diameter of the graphite thermal conductive layer is 500~700mm.

21. The induction graphite crucible according to claim 1, characterized in that, The height of the graphite thermally conductive layer is 500~700mm.

22. The use of an induction graphite crucible according to any one of claims 1 to 21 in smelting.

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