A high melting point alloy liquid-lifting pipe for counter-gravity casting and a preparation method thereof

Abstract

The application discloses a high-melting-point alloy counter-gravity casting liquid-lifting pipe and a preparation method thereof. The structure of the liquid-lifting pipe is characterized in that a quartz glass pipe is embedded in a silicon oxide ceramic matrix, and a protective coating is coated on the inner and outer surfaces. The manufacturing process is that the quartz glass pipe is prepositioned in a mold, the silicon oxide ceramic matrix is formed by hot-press injection molding, the protective coating is formed by coating an alumina powder and zirconium powder slurry on the inner and outer layers, and the liquid-lifting pipe is delivered after sintering. The liquid-lifting pipe has the advantages of high-temperature resistance, chemical stability, good airtightness, low cost and the like, and can be used for high-temperature alloy counter-gravity casting, and is also suitable for counter-gravity casting of metal materials such as cast steel and cast iron.

Description

Technical Field

[0001] This invention relates to the field of antigravity casting technology, specifically providing a riser pipe for antigravity casting of high-melting-point alloys such as high-temperature alloys, cast steel, and cast iron, and its preparation method. Background Technology

[0002] Anti-gravity casting, including low-pressure casting, vacuum casting, pressure-regulating casting, and differential pressure casting, is a casting technology in which molten metal fills the mold from bottom to top along a riser pipe under the drive of electromagnetic force or gas pressure. It has advantages such as good filling and feeding capabilities and high molten metal utilization, and has been widely used both domestically and internationally, producing a large number of high-quality alloy castings of aluminum alloys, magnesium alloys, cast iron, cast steel, and high-temperature alloys. In China, the application of anti-gravity casting technology in the field of low-melting-point light metals such as aluminum alloys and magnesium alloys is relatively mature, but its application in the field of high-melting-point alloys such as cast iron, cast steel, and high-temperature alloys is still in the exploratory stage. The riser pipe plays the role of guiding and feeding channels during casting formation and is a key component of anti-gravity casting equipment, requiring high levels of airtightness, high-temperature chemical stability, high-temperature strength, and thermal shock resistance.

[0003] Refractory materials possess good chemical stability and certain high-temperature strength, but a single refractory material cannot simultaneously possess both thermal shock resistance and airtightness. Therefore, riser pipes used in anti-gravity casting for cast steel, cast iron, and high-temperature alloys are mostly composite structures. Patent CN1039984A discloses an integrally cast composite riser pipe, which uses a steel pipe as a skeleton and is filled with high-alumina vanadium refractory material inside and out, suitable for ferrous metals such as cast iron and cast steel. Patent CN109940152A discloses an anti-gravity casting riser pipe for high-temperature alloys and its manufacturing method. This riser pipe uses a heat-resistant steel pipe as a skeleton, and ceramic liners are prepared inside and out by ramming or grouting. A rare earth oxide coating is then applied to the surface of the ceramic lining. The riser pipe prepared by this method has advantages such as high temperature resistance, no contamination of high-temperature alloy liquid, and good thermal shock resistance. However, the structure is relatively thick and large, and it absorbs heat severely after being inserted into the molten metal. It is generally used for sand casting of large cast steel parts. Hot-pressed silica-based ceramics are widely used as ceramic cores in investment casting processes for high-melting-point alloys such as cast steel, cast iron, and high-temperature alloys. They do not react with many alloying elements, exhibiting good chemical stability. Furthermore, due to their inherent porosity, they also exhibit good thermal shock resistance. However, when used as riser pipes in high-melting-point alloy reverse casting, they suffer from problems such as insufficient airtightness. In addition, when silica-based ceramics are immersed in molten metal for a long time, elements such as iron and chromium react with the silica matrix, resulting in severe corrosion. Summary of the Invention

[0004] This invention overcomes the drawback of insufficient airtightness in hot-press casting of ceramics, and provides a riser pipe for anti-gravity casting of high-melting-point alloys such as cast steel, cast iron, and high-temperature alloys, as well as its preparation method. This riser pipe has advantages such as high temperature resistance, non-contamination of high-temperature alloy molten metal, good thermal shock resistance, and low manufacturing cost.

[0005] The technical solution of this invention is as follows:

[0006] like Figure 1 As shown, a riser pipe for anti-gravity casting of high-melting-point alloys is characterized by:

[0007] The riser tube includes a protective coating, a silicon oxide-based ceramic matrix, and a quartz glass tube; wherein the quartz glass tube is embedded in the silicon oxide-based ceramic matrix, and the inner and outer surfaces of the silicon oxide-based ceramic matrix are provided with a protective coating.

[0008] The flange thickness of the silica ceramic matrix is ​​greater than 8 mm, and the wall thickness of the pipe wall is greater than 6 mm.

[0009] The quartz glass tube has good airtightness and its coefficient of thermal expansion is close to that of the silicon oxide-based ceramic matrix.

[0010] The quartz glass tube has holes in its circular wall, which improves the molding ability and structural strength of the silicon oxide-based ceramic matrix of the riser tube without significantly affecting its airtightness.

[0011] This invention achieves better airtightness by pre-placing a quartz glass tube in a mold during hot-press molding of a silicon oxide-based ceramic matrix. A protective coating of 0.5–1.5 mm thickness is applied to the inner and outer surfaces of the silicon oxide-based ceramic matrix using a brushing method to improve the chemical stability of the riser tube. The protective coating consists of: 50–60 wt.% high-purity alumina powder (purity ≥99.9%), 5–25 wt.% zircon powder, and 25–35 wt.% silica sol.

[0012] As a preferred technical solution:

[0013] The quartz glass tube wall is perforated by laser drilling, with a hole diameter of not less than 5mm; the holes are evenly distributed, with an axial spacing of not less than 30mm and a radial distribution of not less than 2 holes.

[0014] The silica-based ceramic matrix uses quartz glass powder as the base material and zircon powder and analytical grade alumina powder as mineralizers. The zircon powder has a particle size of 250-500 mesh, and the analytical grade alumina powder has a particle size of 250-500 mesh. By weight percentage, the base material is 75%-95%, and the mineralizer is 5%-25%.

[0015] The quartz glass powder is made from high-purity quartz glass tubes, which are crushed, shaped, and sieved into powders with particle sizes of 200 mesh, 325 mesh, and 500 mesh. The SiO2 content in the powder is ≥99.9 wt.%.

[0016] The content of the base material and mineralizer, by weight percentage, is as follows: 75-95% quartz glass powder, 4-20% zircon powder, and 1-5% analytical grade alumina powder; wherein, in the quartz glass powder, 200 mesh powder accounts for 8-12%, 325 mesh powder accounts for 59-71%, and 500 mesh powder accounts for 8-12%.

[0017] The silica-based ceramic matrix uses paraffin wax, beeswax, polyethylene, and polyethylene glycol as plasticizers for hot-press molding. The plasticizers contain 90-95% paraffin wax, 3-5% beeswax, 1-3% polyethylene, and 1-2% polyethylene glycol by weight percentage.

[0018] The high-temperature strengthening liquid for the silicon oxide-based ceramic matrix is ​​silica sol, with an immersion time of 0.5 hours, natural air drying for 4 to 6 hours, and drying at 110 to 150°C for 1 to 3 hours, and the strengthening is performed 1 to 3 times.

[0019] The method for preparing the riser tube for anti-gravity casting of high-melting-point alloys according to the present invention is characterized by the following specific process steps:

[0020] 1) Drilling holes in quartz glass tubes: Laser drilling is used to drill holes in the wall of quartz glass tubes; the holes are evenly distributed, with an axial spacing of not less than 30mm and a radial distribution of not less than 2 holes; the hole diameter is not less than 5mm.

[0021] 2) Slurry preparation: First, weigh out a certain amount of quartz glass powder, zircon powder, and analytical grade alumina powder and place them in a ball mill jar. Add 0.1-0.5% oleic acid by weight of the powder and add alumina ceramic balls at a ball-to-powder ratio of 2:1. Mix for 4-10 hours to obtain a mixed powder. Next, add 15-20% plasticizer by weight of the mixed powder to a core material mixer and heat to melt at a melting temperature of 90-110°C. The plasticizer composition by weight percentage is 90-95% paraffin wax, 3-5% beeswax, 1-3% polyethylene, and 1-2% polyethylene glycol. Finally, add the uniformly mixed powder to the core material mixer and continue mixing for 6-10 hours to ensure that the plasticizer and the mixed powder are evenly mixed.

[0022] 3) Pre-placed quartz glass tube: The quartz glass tube is preheated to 35-45℃ and pre-placed in the silicon oxide-based ceramic matrix mold of the riser tube;

[0023] 4) Hot press molding: Using a ceramic hot press molding machine, the uniformly mixed core material is pressed into the riser tube silica-based ceramic matrix mold to make the riser tube silica-based ceramic matrix blank;

[0024] 5) Trimming and Shaping: After trimming and shaping, the silicon oxide-based ceramic substrate blank of the riser tube is placed in a sagger and buried with industrial alumina filler. The industrial alumina filler is pre-calcined at 1450℃ for 8-12 hours and then passed through a 250-mesh sieve.

[0025] 6) Firing: The sagger containing the silicon oxide-based ceramic substrate blank with the riser tube and the industrial alumina filler is placed in a box-type resistance furnace for firing, and then cooled to room temperature with the furnace.

[0026] 7) High-temperature strengthening: The silicon oxide-based ceramic matrix of the riser tube is strengthened by using silica sol as the strengthening liquid. The soaking time is 0.5h, the natural air drying time is 4-6h, and the drying time is 1-3h at 110-150℃. After drying, the strengthening is repeated for the next time. The strengthening is repeated 1-3 times.

[0027] 8) Coating preparation: Mix 50-60 wt.% of 100-400 mesh high-purity alumina powder, 5-25 wt.% of 100-400 mesh zircon powder, and 25-35 wt.% of silica sol, and stir evenly for no less than 12 hours to prepare a coating. Apply a 0.5-1.5 mm thick coating to the inner and outer surfaces of the silica ceramic substrate by brushing.

[0028] 9) Coating Calcination: The coating is prepared by brushing and dried naturally for 8-12 hours. It is then used after calcination. The calcination process is as follows: the temperature is increased to 400-500℃ at a rate of 2-4℃ / min and held for 1-2 hours; the temperature is increased to 900-1100℃ at a rate of 3-5℃ / min and held for 4-8 hours before being cooled in the furnace.

[0029] As a preferred technical solution:

[0030] In step 4), the hot press injection molding process parameters are: injection temperature 95~105℃, mold temperature 35~45℃, injection pressure 2~6MPa, flow rate 100~300cc / s, injection time 20~30s, and holding time 100~200s.

[0031] In step 6), the calcination process is as follows: the temperature is increased to 400-500℃ at a heating rate of 2-6℃ / min and held for 4-6 hours; the temperature is increased to 700-900℃ at a heating rate of 3-7℃ / min and held for 2-4 hours; the temperature is increased to 1100-1200℃ at a heating rate of 4-8℃ / min and held for 8-12 hours, and then cooled to room temperature in the furnace.

[0032] The advantages of this invention are:

[0033] (1) The silica-based ceramic matrix formed by hot pressing has good thermal shock resistance and high high temperature strength;

[0034] (2) The shrinkage rate of quartz glass tubes is similar to that of silicon oxide-based ceramic matrix, which can avoid the generation of sintering cracks;

[0035] (3) The embedded dense quartz glass tube improves the airtightness of the hot-pressed silicon oxide ceramic matrix;

[0036] (4) The protective coating has good chemical stability and can prevent the riser pipe from contaminating the molten metal;

[0037] (5) The riser tube is lightweight, has a simple manufacturing process, is easy to manufacture and use, and has low cost. Attached Figure Description

[0038] Figure 1 Schematic diagram of a silicon oxide-based ceramic riser pipe.

[0039] Figure 2 Schematic diagram of the axial distribution of openings in the wall of a quartz glass tube.

[0040] Figure 3 Schematic diagram of the calcination process of silicon oxide-based ceramic riser tube substrate.

[0041] Figure 4 Protective coating baking process.

[0042] Figure 5 The specimen was formed by vacuum low-pressure casting using this riser tube. Detailed Implementation

[0043] In this embodiment, the silica-based ceramic matrix uses quartz glass powder as the base material. The quartz glass powder is made from high-purity quartz glass tubes, which are crushed, shaped, and sieved into powders with particle sizes of 200 mesh, 325 mesh, and 500 mesh. After acid washing and drying, the SiO2 content in the treated quartz glass powder is ≥99.9 wt.%. The carrier uses paraffin wax, beeswax, polyethylene, and polyethylene glycol as plasticizers for hot-press molding.

[0044] Example 1

[0045] A method for preparing a riser tube for anti-gravity casting of a high-melting-point alloy includes the following process steps:

[0046] 1. Drilling holes in quartz glass tubes: Laser drilling is used to drill holes in the wall of the quartz glass tubes; the holes are evenly distributed with an axial spacing of 30mm and two radially distributed holes; the hole diameter is 5mm.

[0047] 2. Slurry Preparation: First, weigh 8% by weight of 200-mesh quartz glass powder, 59% by weight of 325-mesh quartz glass powder, 8% by weight of 500-mesh quartz glass powder, 20% by weight of zircon powder, and 5% by weight of analytical grade alumina powder and place them in a ball mill jar. Add 0.1% by weight of oleic acid to the powder and add alumina ceramic balls at a ball-to-powder ratio of 2:1. Mix for 4 hours to obtain a mixed powder. Next, add 15% by weight of plasticizer to a core material mixer and heat to melt at a melting temperature of 90°C. The plasticizer consists of 90 wt.% paraffin wax, 5 wt.% beeswax, 3 wt.% polyethylene, and 2 wt.% polyethylene glycol. Finally, add the uniformly mixed powder to the core material mixer and continue mixing for 6 hours to ensure that the plasticizer and the mixed powder are evenly mixed.

[0048] 3. Pre-placed quartz glass tube: The quartz glass tube is preheated to 35°C and pre-placed in the silicon oxide-based ceramic matrix mold of the riser tube;

[0049] 4. Hot press injection molding: Using a ceramic hot press injection machine, the injection temperature is controlled at 95℃, the mold temperature at 35℃, the injection pressure at 2MPa, the flow rate at 100cc / s, the injection time at 20s, and the holding time at 100s. The uniformly mixed core material is then injected into the riser mold to form a ceramic riser substrate blank.

[0050] 5. Trimming and Shaping: After trimming and shaping, the riser tube blank is placed in a sagger and buried with industrial alumina filler. The industrial alumina filler is pre-calcined at 1450℃ for 8 hours and then passed through a 250-mesh sieve.

[0051] 6. Firing: Place the sagger containing the riser tube blank and industrial alumina filler into a box-type resistance furnace for firing. The firing regime is as follows: heat up to 400℃ at a heating rate of 2℃ / min and hold for 4 hours; heat up to 700℃ at a heating rate of 3℃ / min and hold for 2 hours; heat up to 1100℃ at a heating rate of 4℃ / min and hold for 8 hours; and then cool to room temperature with the furnace.

[0052] 7. High-temperature strengthening: The silicon oxide-based ceramic matrix of the riser tube is strengthened by using silica sol as the strengthening liquid. The substrate is soaked for 0.5 hours, air-dried naturally for 4 hours, and dried at 110℃ for 1 hour. The strengthening is repeated once.

[0053] 8. Coating preparation: 60wt.% of 325-mesh high-purity alumina powder, 5wt.% of 325-mesh zircon powder, and 35wt.% of silica sol were stirred evenly for 12 hours to prepare a coating. A 0.5mm thick coating was then applied to the inner and outer surfaces of the silica ceramic substrate by brushing.

[0054] 9. Coating Firing: The coating is prepared by brushing and naturally dried for 8 hours before firing. The firing regime is as follows: heat up to 400℃ at a heating rate of 2℃ / min and hold for 1 hour; heat up to 900℃ at a heating rate of 3℃ / min and hold for 4 hours. After cooling in the furnace, the coating is put into use.

[0055] 10. Seal the upper and lower ends of the prepared riser tube and test it using the water immersion method. Pressurize it to 3 Bar and there is no obvious bubble phenomenon. Immerse it in 1500℃ K4169 molten metal for 0.5 hours and there is no corrosion.

[0056] Example 2

[0057] A method for preparing a riser tube for anti-gravity casting of a high-melting-point alloy includes the following process steps:

[0058] 1. Drilling holes in quartz glass tubes: Laser drilling is used to drill holes in the wall of the quartz glass tubes; the holes are evenly distributed with an axial spacing of 50mm and a radial distribution of 3 holes; the hole diameter is 7mm.

[0059] 2. Slurry Preparation: First, weigh 10% by weight of 200-mesh quartz glass powder, 65% by weight of 325-mesh quartz glass powder, 10% by weight of 500-mesh quartz glass powder, 12% by weight of zircon powder, and 3% by weight of analytical grade alumina powder and place them in a ball mill jar. Add 0.3% by weight of oleic acid to the powder and add alumina ceramic balls at a ball-to-powder ratio of 2:1. Mix for 6 hours to obtain a mixed powder. Next, add 17% by weight of plasticizer to a core material mixer and heat to melt at a melting temperature of 100°C. The plasticizer consists of 93 wt.% paraffin wax, 4 wt.% beeswax, 2 wt.% polyethylene, and 1 wt.% polyethylene glycol. Finally, add the uniformly mixed powder to the core material mixer and continue mixing for 8 hours to ensure that the plasticizer and the mixed powder are evenly mixed.

[0060] 3. Pre-placed quartz glass tube: The quartz glass tube is preheated to 40°C and pre-placed in the silicon oxide-based ceramic matrix mold of the riser tube;

[0061] 4. Hot press injection molding: Using a ceramic hot press injection machine, the injection temperature is controlled at 100℃, the mold temperature at 40℃, the injection pressure at 4MPa, the flow rate at 200cc / s, the injection time at 25s, and the holding time at 150s. The uniformly mixed core material is then injected into the riser mold to form a ceramic riser substrate blank.

[0062] 5. Trimming and Shaping: After trimming and shaping, the riser tube blank is placed in a sagger and buried with industrial alumina filler. The industrial alumina filler is pre-calcined at 1450℃ for 10 hours and then passed through a 250-mesh sieve.

[0063] 6. Firing: Place the sagger containing the riser tube blank and industrial alumina filler into a box-type resistance furnace for firing. The firing regime is as follows: heat up to 450℃ at a heating rate of 4℃ / min, hold for 5h, heat up to 800℃ at a heating rate of 5℃ / min, hold for 3h, heat up to 1150℃ at a heating rate of 6℃ / min, hold for 10h, and then cool to room temperature with the furnace.

[0064] 7. High-temperature strengthening: The silicon oxide-based ceramic matrix of the riser tube is strengthened by using silica sol as the strengthening liquid. It is soaked for 0.5 hours, naturally air-dried for 5 hours, and then dried at 130℃ for 2 hours before being strengthened a second time. A total of two strengthening processes are performed.

[0065] 8. Coating preparation: Mix 55wt.% of 325-mesh high-purity alumina powder, 15wt.% of 325-mesh zircon powder, and 30wt.% of silica sol evenly for 12 hours to prepare a coating. Apply a 1mm thick coating to the inner and outer surfaces of the silica ceramic substrate by brushing.

[0066] 9. Coating Firing: The coating is prepared by brushing and then naturally dried for 10 hours before firing. The firing regime for the coating is as follows: heat up to 450℃ at a heating rate of 3℃ / min and hold for 1.5 hours; heat up to 1000℃ at a heating rate of 4℃ / min and hold for 6 hours. After cooling in the furnace, the coating is put into use.

[0067] 10. Seal the upper and lower ends of the prepared riser tube and test it using the water immersion method. Pressurize it to 3 Bar and there is no obvious bubble phenomenon. Immerse it in 1500℃ K4169 molten metal for 0.5 hours and there is no corrosion.

[0068] Comparative Example 1

[0069] Compared with Example 2, the comparative example does not have a quartz glass tube embedded in the silica ceramic matrix of the riser tube.

[0070] 1. Slurry Preparation: First, weigh 10% by weight of 200-mesh quartz glass powder, 65% by weight of 325-mesh quartz glass powder, 10% by weight of 500-mesh quartz glass powder, 12% by weight of zircon powder, and 3% by weight of analytical grade alumina powder and place them in a ball mill jar. Add 0.3% by weight of oleic acid to the powder and add alumina ceramic balls at a ball-to-powder ratio of 2:1. Mix for 6 hours to obtain a mixed powder. Next, add 17% by weight of plasticizer to a core material mixer and heat to melt at a melting temperature of 100℃. The plasticizer consists of 93 wt.% paraffin wax, 4 wt.% beeswax, 2 wt.% polyethylene, and 1 wt.% polyethylene glycol. Finally, add the uniformly mixed powder to the core material mixer and continue mixing for 8 hours to ensure that the plasticizer and the mixed powder are evenly mixed.

[0071] 2. Mold preheating: Preheat the silicon oxide-based ceramic substrate mold of the riser pipe to 40℃;

[0072] 3. Hot press injection molding: Using a ceramic hot press injection machine, the injection temperature is controlled at 100℃, the mold temperature at 40℃, the injection pressure at 4MPa, the flow rate at 200cc / s, the injection time at 25s, and the holding time at 150s. The uniformly mixed core material is then injected into the riser mold to form a ceramic riser substrate blank.

[0073] 4. Trimming and Shaping: After trimming and shaping, the riser tube blank is placed in a sagger and buried with industrial alumina filler. The industrial alumina filler is pre-calcined at 1450℃ for 10 hours and then passed through a 250-mesh sieve.

[0074] 5. Firing: Place the sagger containing the riser tube blank and industrial alumina filler into a box-type resistance furnace for firing. The firing regime is as follows: heat up to 450℃ at a heating rate of 4℃ / min, hold for 5 hours, heat up to 800℃ at a heating rate of 5℃ / min, hold for 3 hours, heat up to 1150℃ at a heating rate of 6℃ / min, hold for 10 hours, and then cool to room temperature with the furnace.

[0075] 6. High-temperature strengthening: The silicon oxide-based ceramic matrix of the riser tube is strengthened by using silica sol as the strengthening liquid. It is soaked for 0.5 hours, naturally air-dried for 5 hours, and then dried at 130℃ for 2 hours before being strengthened a second time. A total of two strengthening processes are performed.

[0076] 7. Coating preparation: Mix 55wt.% of 325-mesh high-purity alumina powder, 15wt.% of 325-mesh zircon powder, and 30wt.% of silica sol evenly for 12 hours to prepare a coating. Apply a 1mm thick coating to the inner and outer surfaces of the silica ceramic substrate by brushing.

[0077] 8. Coating Firing: The coating is prepared by brushing and then naturally dried for 10 hours before firing. The firing regime for the coating is as follows: the temperature is increased to 450℃ at a heating rate of 3℃ / min and held for 1.5 hours; the temperature is increased to 1000℃ at a heating rate of 4℃ / min and held for 6 hours. After cooling in the furnace, the coating is put into use.

[0078] 9. Seal the upper and lower ends of the prepared riser tube and test it using the water immersion method. Pressurize the tube to 3 Bar and a large number of bubbles will emerge from the side wall of the riser tube. Immerse it in 1500℃ K4169 molten metal for 0.5 hours and there will be no corrosion.

[0079] Comparative Example 2

[0080] Compared with Example 2, no protective coating was prepared in this comparative example.

[0081] 1. Drilling holes in quartz glass tubes: Laser drilling is used to drill holes in the wall of the quartz glass tubes; the holes are evenly distributed with an axial spacing of 50mm and a radial distribution of 3 holes; the hole diameter is 7mm.

[0082] 2. Slurry Preparation: First, weigh 10% by weight of 200-mesh quartz glass powder, 65% by weight of 325-mesh quartz glass powder, 10% by weight of 500-mesh quartz glass powder, 12% by weight of zircon powder, and 3% by weight of analytical grade alumina powder and place them in a ball mill jar. Add 0.3% by weight of oleic acid to the powder and add alumina ceramic balls at a ball-to-powder ratio of 2:1. Mix for 6 hours to obtain a mixed powder. Next, add 17% by weight of plasticizer to a core material mixer and heat to melt at a melting temperature of 100°C. The plasticizer consists of 93 wt.% paraffin wax, 4 wt.% beeswax, 2 wt.% polyethylene, and 1 wt.% polyethylene glycol. Finally, add the uniformly mixed powder to the core material mixer and continue mixing for 8 hours to ensure that the plasticizer and the mixed powder are evenly mixed.

[0083] 3. Pre-placed quartz glass tube: The quartz glass tube is preheated to 40°C and pre-placed in the silicon oxide-based ceramic matrix mold of the riser tube;

[0084] 4. Hot press injection molding: Using a ceramic hot press injection machine, the injection temperature is controlled at 100℃, the mold temperature at 40℃, the injection pressure at 4MPa, the flow rate at 200cc / s, the injection time at 25s, and the holding time at 150s. The uniformly mixed core material is then injected into the riser mold to form a ceramic riser substrate blank.

[0085] 5. Trimming and Shaping: After trimming and shaping, the riser tube blank is placed in a sagger and buried with industrial alumina filler. The industrial alumina filler is pre-calcined at 1450℃ for 10 hours and then passed through a 250-mesh sieve.

[0086] 6. Firing: Place the sagger containing the riser tube blank and industrial alumina filler into a box-type resistance furnace for firing. The firing regime is as follows: heat up to 450℃ at a heating rate of 4℃ / min, hold for 5h, heat up to 800℃ at a heating rate of 5℃ / min, hold for 3h, heat up to 1150℃ at a heating rate of 6℃ / min, hold for 10h, and then cool to room temperature with the furnace.

[0087] 7. High-temperature strengthening: The silicon oxide-based ceramic matrix of the riser tube is strengthened by using silica sol as the strengthening liquid. It is soaked for 0.5 hours, naturally air-dried for 5 hours, and then dried at 130℃ for 2 hours before being strengthened a second time. A total of two strengthening processes are performed.

[0088] 8. The upper and lower ends of the riser tube prepared by this method were sealed, and the riser tube was tested by water immersion method. The pressure was increased to 3 Bar, and no bubbles emerged from the side wall of the riser tube; after immersion in 1500℃ K4169 molten metal for 0.5h, severe corrosion was observed.

[0089] Example 3

[0090] A method for preparing a riser tube for anti-gravity casting of a high-melting-point alloy includes the following process steps:

[0091] 1. Drilling holes in quartz glass tubes: Laser drilling is used to drill holes in the wall of the quartz glass tubes; the holes are evenly distributed with an axial spacing of 80mm and a radial distribution of 4 holes; the hole diameter is 9mm.

[0092] 2. Slurry Preparation: First, weigh 12% by weight of 200-mesh quartz glass powder, 71% by weight of 325-mesh quartz glass powder, 12% by weight of 500-mesh quartz glass powder, 4% by weight of zircon powder, and 1% by weight of analytical grade alumina powder and place them in a ball mill jar. Add 0.5% by weight of oleic acid to the powder and add alumina ceramic balls at a ball-to-powder ratio of 2:1. Mix for 8 hours to obtain a mixed powder. Next, add 19% by weight of plasticizer to a core material mixer and heat to melt at a melting temperature of 110°C. The plasticizer consists of 95 wt.% paraffin wax, 3 wt.% beeswax, 1 wt.% polyethylene, and 1 wt.% polyethylene glycol. Finally, add the uniformly mixed powder to the core material mixer and continue mixing for 10 hours to ensure that the plasticizer and the mixed powder are evenly mixed.

[0093] 3. Pre-placed quartz glass tube: The quartz glass tube is preheated to 45°C and pre-placed in the silicon oxide-based ceramic matrix mold of the riser tube;

[0094] 4. Hot press injection molding: Using a ceramic hot press injection machine, the injection temperature is controlled at 105℃, the mold temperature at 45℃, the injection pressure at 6MPa, the flow rate at 300cc / s, the injection time at 30s, and the holding time at 200s. The uniformly mixed core material is then injected into the riser mold to form a ceramic riser substrate blank.

[0095] 5. Trimming and Shaping: After trimming and shaping, the riser tube blank is placed in a sagger and buried with industrial alumina filler. The industrial alumina filler is pre-calcined at 1450℃ for 12 hours and then passed through a 250-mesh sieve.

[0096] 6. Firing: Place the sagger containing the riser tube blank and industrial alumina filler into a box-type resistance furnace for firing. The firing regime is as follows: heat up to 500℃ at a heating rate of 6℃ / min and hold for 6 hours; heat up to 900℃ at a heating rate of 7℃ / min and hold for 4 hours; heat up to 1200℃ at a heating rate of 8℃ / min and hold for 10 hours; and then cool to room temperature with the furnace.

[0097] 7. High-temperature strengthening: The silicon oxide-based ceramic substrate of the riser tube is strengthened by using silica sol as the strengthening liquid. The substrate is soaked for 0.5 hours, air-dried naturally for 6 hours, and dried at 150℃ for 3 hours. The strengthening process is repeated for a total of three times.

[0098] 8. Coating preparation: Mix 50wt.% of 325-mesh high-purity alumina powder, 25wt.% of 325-mesh zircon powder, and 25wt.% of silica sol evenly for 12 hours to prepare a coating. Apply a 1.5mm thick coating to the inner and outer surfaces of the silica ceramic substrate by brushing.

[0099] 9. Coating Firing: The coating is prepared by brushing and then naturally dried for 12 hours before firing. The firing regime for the coating is as follows: heat up to 500℃ at a heating rate of 4℃ / min and hold for 2 hours; heat up to 1100℃ at a heating rate of 5℃ / min and hold for 8 hours. After cooling in the furnace, the coating is put into use.

[0100] 10. Seal the upper and lower ends of the prepared riser tube and test it using the water immersion method. Pressurize it to 3 Bar and there is no obvious bubble phenomenon. Immerse it in 1500℃ K4169 molten metal for 0.5 hours and there is no corrosion.

[0101] Matters not covered in this invention are common knowledge.

[0102] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A riser pipe for anti-gravity casting of high-melting-point alloys, characterized in that: The riser tube includes a protective coating (1), a silica-based ceramic matrix (2), and a quartz glass tube (3); wherein the quartz glass tube (3) is embedded in the silica-based ceramic matrix (2), and the inner and outer surfaces of the silica-based ceramic matrix (2) are provided with a protective coating (1); the quartz glass tube (3) is laser-drilled on its wall, with a hole diameter of not less than 5 mm, the holes are evenly distributed, the axial spacing is not less than 30 mm, and the radial distribution number is not less than 2; the silica-based ceramic matrix (2) uses quartz glass powder as the base material, and zircon powder and analytical grade alumina powder as mineralizers, wherein the zircon powder has a particle size of 250-500 mesh, the analytical grade alumina powder has a particle size of 250-500 mesh, and by weight percentage, the base material is 75%-95%, and the mineralizer is 5%-25%; the silica-based ceramic matrix (2) is obtained by hot pressing molding, and its preparation process includes: mixing the base material and mineralizer, and adding 0.1% of the powder weight. Oleic acid (approximately 0.5%) is added to alumina ceramic balls at a ball-to-powder ratio of 2:1 and ball-milled for 4-10 hours to obtain a mixed powder. Then, a plasticizer, comprising 15-20% by weight of the mixed powder, is heated and melted at a melting temperature of 90-110°C. The plasticizer consists of 90-95 wt.% paraffin wax, 3-5 wt.% beeswax, 1-3 wt.% polyethylene, and 1-2 wt.% polyethylene glycol. The mixed powder is then added to the melted plasticizer and kneaded for 6-15 minutes. 0h, core material is obtained; after preheating the quartz glass tube, it is placed in the mold of the riser tube silicon oxide ceramic matrix, and then the core material is formed into a blank by hot pressing; the protective coating (1) is applied to the inner and outer surfaces of the silicon oxide ceramic matrix (2) by brushing with a thickness of 0.5 to 1.5 mm. The composition of the protective coating (1) is: 50 to 60 wt.% high-purity alumina powder, 5 to 25 wt.% zircon powder, and 25 to 35 wt.% silica sol.

2. The riser pipe for anti-gravity casting of high-melting-point alloys according to claim 1, characterized in that: The content of the base material and mineralizer by weight percentage is as follows: 75-95% quartz glass powder, 4-20% zircon powder, and 1-5% analytical grade alumina powder; wherein, in the quartz glass powder, 200 mesh powder accounts for 8-12%, 325 mesh powder accounts for 59-71%, and 500 mesh powder accounts for 8-12%.

3. The riser pipe for anti-gravity casting of high-melting-point alloys according to claim 1, characterized in that: The high-temperature strengthening liquid of the silicon oxide-based ceramic matrix (2) is silica sol, soaking time is 0.5h, natural air drying is 4-6h, drying at 110-150℃ is 1-3h, and strengthening is performed 1-3 times.

4. A method for preparing a riser pipe for anti-gravity casting of high-melting-point alloys according to any one of claims 1 to 3, characterized in that, The specific process steps are as follows: 1) Drilling holes in quartz glass tubes: Laser drilling is used to drill holes in the wall of quartz glass tubes; the holes are evenly distributed, with an axial spacing of not less than 30mm, a radial distribution of not less than 2 holes, and a hole diameter of not less than 5mm. 2) Slurry preparation: First, weigh out a certain amount of quartz glass powder, zircon powder, and analytical grade alumina powder and place them in a ball mill jar. Add 0.1-0.5% oleic acid by weight of the powder and add alumina ceramic balls at a ball-to-powder ratio of 2:

1. Mix for 4-10 hours to obtain a mixed powder. Next, add 15-20% plasticizer by weight of the mixed powder to a core material mixer and heat to melt at a melting temperature of 90-110℃. The plasticizer consists of 90-95 wt.% paraffin wax, 3-5 wt.% beeswax, 1-3 wt.% polyethylene, and 1-2 wt.% polyethylene glycol. Finally, add the uniformly mixed powder to the core material mixer and continue mixing for 6-10 hours to ensure that the plasticizer and the mixed powder are evenly mixed. 3) Pre-placed quartz glass tube: The quartz glass tube is preheated to 35-45℃ and pre-placed in the silicon oxide-based ceramic matrix mold of the riser tube; 4) Hot press molding: Using a ceramic hot press molding machine, the uniformly mixed core material is pressed into the mold of the riser tube silica-based ceramic matrix to make the riser tube silica-based ceramic matrix green body; 5) Trimming and Shaping: After trimming and shaping, the silicon oxide-based ceramic substrate blank of the riser tube is placed in a sagger and buried with industrial alumina filler. The industrial alumina filler is pre-calcined at 1450℃ for 8-12 hours and then passed through a 250-mesh sieve. 6) Firing: The sagger containing the silicon oxide-based ceramic substrate blank with the riser tube and the industrial alumina filler is placed in a box-type resistance furnace for firing, and then cooled to room temperature with the furnace. 7) High-temperature strengthening: The silicon oxide-based ceramic matrix of the riser tube is strengthened with silica sol as the strengthening liquid. The strengthening is carried out 1 to 3 times. Each time, the substrate is soaked for 0.5 hours, air-dried for 4 to 6 hours, and then dried at 110-150℃ for 1 to 3 hours before the next strengthening is carried out. 8) Coating preparation: Mix 50-60 wt.% of 100-400 mesh high-purity alumina powder, 5-25 wt.% of 100-400 mesh zircon powder, and 25-35 wt.% of silica sol evenly for no less than 12 hours to prepare a coating. Apply a 0.5-1.5 mm thick coating to the inner and outer surfaces of the silica ceramic substrate by brushing. 9) Coating Firing: The coating is prepared by brushing and naturally dried for 8-12 hours. It is then used after firing. The firing regime is as follows: heat up to 400-500℃ at a heating rate of 2-4℃ / min and hold for 1-2 hours; or heat up to 900-1100℃ at a heating rate of 3-5℃ / min and hold for 4-8 hours before use.

5. The method for preparing the riser pipe for anti-gravity casting of high-melting-point alloys according to claim 4, characterized in that: In step 4), the hot press injection molding process parameters are: injection temperature 95~105℃, mold temperature 35~45℃, injection pressure 2~6MPa, flow rate 100~300cc / s, injection time 20~30s, and holding time 100~200s. In step 6), the calcination process is as follows: the temperature is increased to 400-500℃ at a heating rate of 2-6℃ / min and held for 4-6 hours; the temperature is increased to 700-900℃ at a heating rate of 3-7℃ / min and held for 2-4 hours; the temperature is increased to 1100-1200℃ at a heating rate of 4-8℃ / min and held for 8-12 hours, and then cooled to room temperature in the furnace.

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