Molding shell construction method for large-module casting molding

Abstract

The invention provides a shell construction method for large-module casting molding, which comprises the following steps: firstly, designing a large-module model and selecting a module assembling scheme, then preparing a split wax mold, and carrying out slurry dipping, sand spraying and drying to prepare a split shell; and the split shells are spliced into a large-module shell through shell bonding glue, and finally casting forming is conducted. The whole set of castings can be cast and formed at a time, the large-module shell preparation qualification rate and the casting qualification rate can be improved, the situation that the whole set of castings are scrapped due to the leakage problem of alloy liquid is prevented, the cost is low, the preparation method is simple, the manufacturing time is short, applicability is high, and the method has the obvious technical advantage in quality consistency.

Description

Technical Field

[0001] The present invention relates to the technical field of investment precision casting, in particular to a method for constructing a mold shell for large die casting. Background Art

[0002] The preparation of ceramic shells is an important part of the investment casting process. In the precision casting process, the quality of the shell is one of the key factors affecting the alloy casting. In order to improve the efficiency of casting preparation and reduce the cost of casting preparation, the metallurgical quantity of castings per batch can be increased by manufacturing large-module shells. Due to the large volume, heavy weight and complex structure of large-module shells, there are great difficulties in the shell preparation process, including low shell qualification rate and difficulty in manual preparation. Splitting the shell can effectively improve the shell preparation efficiency, increase the shell qualification rate, reduce the alloy leakage rate, and directly affect the production cost and production efficiency of large-module preparation of single crystal alloys. Based on this need, a split shell construction method is designed. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for constructing a mold shell for large-module casting in response to the deficiencies of the above-mentioned existing technologies. This method improves the mold shell preparation qualification rate and the metallurgical quantity of single-furnace castings through split mold shell construction, effectively reducing production costs and improving production efficiency.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for constructing a shell for large-module casting, characterized by comprising the following steps: S1. Module preparation: Connect the wax mold to the wax pressing device, inject liquid wax into the mold through the wax pressing device, cool it down to obtain the wax mold, and combine the wax molds to obtain the split module unit; S2. Slurry preparation: The powders of the surface layer, transition layer and back layer are mixed with silica sol, wetting agent and defoaming agent respectively, and stirred to form a uniformly mixed ceramic shell slurry; S3. Mold shell preparation: The split module units are immersed in the ceramic mold shell slurry respectively, and the slurry is sequentially formed into a surface layer, a transition layer, and a back layer. The number of back layers is greater than six. After each layer is slurried, the molding sand is evenly sprinkled on the split module. After each layer is slurried, the split module unit is placed in a ceramic mold shell drying room for drying. After multiple dryings, the ceramic mold shell is obtained; S4, shell dewaxing: the dried split ceramic shell is placed in a high-pressure steam dewaxing kettle for dewaxing; S5, shell firing: Place the dewaxed split ceramic shell in a firing furnace, set the firing furnace heating curve, and cool it with the furnace after firing; S6. Mold shell assembly: The split ceramic mold shells are bonded with a shell adhesive to form a combined module mold shell, which is then wrapped around the outer side of the combined module mold shell and fixed, and then placed in a baking furnace for secondary sintering and reinforcement; S7. Alloy casting: Casting is carried out in the combined mold shell according to the pouring process.

[0005] Preferably, the pouring system includes a large module model, in which a pouring cup, a sprue and an ingrown are arranged. The pouring cup is located at the top for receiving and introducing the molten alloy liquid. The sprue is a vertical channel, and the sprue connects the pouring cup and the ingrown. The ingrown is connected to the casting cavity of the combined module shell. The ingrowns are connected in a radial ring array around the sprue, and the angle between adjacent ingrowns is 30°. The large module model includes a chassis with a diameter of 400 mm, 4 center columns with a length of 345 mm, and 12 casting wax molds. The large module model is divided into four split models, and each split model includes 3 casting wax molds, a quarter chassis and a center column.

[0006] Preferably, the slurry ratio corresponding to the surface layer of S2 is: the powder-liquid ratio of 320# white corundum powder and silica sol is 3.8-4.2:1, the wetting agent content is 0.3%-0.5%, the defoaming agent content is 1%-2%, and the viscosity is 35s-45s; the slurry ratio of the transition layer is: the powder-liquid ratio of 320# white corundum powder and silica sol is 3.5-4.0:1, the wetting agent content is 0.3%-0.5%, the defoaming agent content is 1%-2%, and the viscosity is 15s-25s; the slurry ratio of the back layer is: the powder-liquid ratio of 320# white corundum powder and silica sol is 3.0-3.5:1, the wetting agent content is 0.3%-0.5%, the defoaming agent content is 1%-2%, and the viscosity is 10s-15s.

[0007] Preferably, when preparing the ingredients in S2, the silica sol is first weighed and placed in a slurry stirring barrel, and the stirring device is turned on, the stirring speed is set to 35r / min-40r / min, and the powder is slowly added in batches using a feeding spoon, and the wetting agent is gradually added during the stirring process. After continuous stirring for 20 minutes, the defoaming agent is added and the stirring is continued for more than 48 hours to complete the slurry preparation.

[0008] Preferably, the drying conditions for the surface layer are temperature 22±5°C, humidity 75±10%RH, and drying time ≥240min; the drying conditions for the back layer are temperature 22±5°C, humidity 75±10%RH, and drying time ≥180min; the drying time after slurry sealing is ≥48h, and slurry sealing is the last layer in the preparation of the shell, which only needs to be dipped in slurry without being sanded.

[0009] Preferably, the sand material for the surface layer of S3 after being dipped in slurry is 100# white corundum sand, the sand material for the transition layer after being dipped in slurry is 60# white corundum sand, and the sand material for the back layer after being dipped in slurry is 24# white corundum sand.

[0010] Preferably, the pressure during dewaxing is 8.2 bar ± 0.2 bar, and the temperature is 185 ° C ± 5 ° C; during roasting, the distance between the shells is greater than 10 cm, and the roasting furnace is set to heat up to 300 ° C at a rate of 5 ° C / min and then keep warm for 0.5 h, then heat up to 600 ° C at a rate of 5 ° C / min, keep warm for 0.5 h, and then heat up to 950 ° C ± 20 ° C at a rate of 6 ° C / min, and keep warm for 2 h.

[0011] Preferably, in S7, a high-temperature alloy liquid is poured into the combined mold shell. The combined mold shell is preheated to a temperature of 900-1000°C. After pouring, the shell is removed after cooling to obtain a casting. The pouring temperature of the high-temperature alloy liquid is 1520°C ± 10°C, the pouring time is 30-40 seconds, the refining temperature is 1550°C ± 10°C, the refining time is 5 minutes ± 1 minute, the vacuum degree during alloy casting is ≤ 7 Pa, and the crystal pulling rate is 3 mm / min-5 mm / min. After pouring, the casting is cut to obtain a single crystal high-temperature alloy casting. The high-temperature alloy liquid has the following components: C: 0.04-0.06%, Cr: 6.75-7.25%, Mo: 3.80-5.2%, Co: 7.0-8.0%, Al: 6.0-6.4%, W: 4.75-5.25%, Ta: 6.3-6.7%, Re: 2.75-3.25%, and the balance is Ni.

[0012] Preferably, the model of the wetting agent is Nalco 7667; the model of the defoaming agent is Nalco 2305.

[0013] Compared with the prior art, the present invention has the following advantages: 1. The present invention is scientifically and rationally designed. It improves construction accuracy and reduces construction difficulty by constructing a split shell, thereby increasing the mold shell preparation qualification rate and the metallurgical quantity of single-furnace castings, effectively reducing production costs and improving production efficiency.

[0014] 2. The surface slurry of the present invention is prepared using 320# white corundum powder as raw material. White corundum powder has excellent high temperature and corrosion resistance. Therefore, the white corundum coating can maintain its stability under high temperature conditions, is not easy to crack or fall off, and has good high temperature strength. Therefore, even if the alloy liquid is injected into the mold shell under high temperature conditions, it is unlikely to break through the mold shell and cause sparks, resulting in a high casting forming rate.

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural diagram of the large module model in the present invention.

[0017] Description of reference numerals: DETAILED DESCRIPTION

[0018] Example 1 This embodiment provides a method for constructing a shell for large-module casting, comprising the following steps: S1. Module preparation: Select a suitable mold based on the shape and size of the product, place the pouring system containing the embedded rods and metal tooling into it and close the mold. Then inject liquid wax into the mold and maintain pressure. After the mold material solidifies and forms, the split module unit is obtained and assembled according to the requirements of the combination plan; S2. Slurry preparation: The powders of the surface layer, transition layer and back layer are mixed with silica sol, wetting agent and defoaming agent respectively, and stirred to form a uniformly mixed ceramic shell slurry; the slurry ratio corresponding to the surface layer is: the mass ratio of silica sol, white corundum powder, wetting agent and defoaming agent is 1:4.0:0.003:0.01, and the viscosity range is 38s-42s; the slurry ratio of the transition layer is: the mass ratio of silica sol, white corundum powder, wetting agent and defoaming agent is 1:3.5:0.003:0.01, and the viscosity range is 25s-35s; the slurry ratio of the back layer is: silica sol, white corundum powder, wetting agent and defoaming agent The mass ratio of the agent is: 1:3.0:0.003:0.01, and the viscosity range is 10-15s; when preparing the ingredients, first weigh the silica sol and place it in the slurry stirring barrel, turn on the stirring device, set the stirring speed to 35r / min-40r / min, use a feeding spoon to slowly add the weighed white corundum powder in batches, gradually add the wetting agent during the stirring process, continue stirring for 20 minutes, then add the required defoaming agent, wait until the slurry is evenly mixed and there is no clumping or caking on the slurry surface, adjust the stirring speed to 30r / min-35r / min, and continue stirring for more than 48 hours to complete the slurry preparation.

[0019] S3. Mold shell preparation: The split modules are immersed in the ceramic mold shell slurry respectively. The slurry is applied in the order of surface layer, transition layer and back layer. The number of back layer layers is seven. After each layer is slurried, the molding sand is evenly sprinkled on the split module. After each layer of slurry and sand is sprinkled, the split module is placed in the ceramic mold shell drying room for drying. After multiple dryings, the ceramic mold shell is obtained; the drying conditions for the surface layer are temperature 22±5℃, humidity 75±10%RH, and drying time 240min; the drying conditions for the back layer are temperature 22±5℃, humidity 75±10%RH, and drying time 180min; the drying time after sealing is 48h.

[0020] S4. Dewaxing of mold shell: Place the dried split ceramic mold shell in a high-pressure steam dewaxing kettle for dewaxing; the pressure during dewaxing is 8.2 bar ± 0.2 bar, and the temperature is 185 ° C ± 5 ° C; during roasting, the distance between the mold shells is greater than 10 cm, and the roasting furnace is set to heat up to 300 ° C at a rate of 5 ° C / min and keep warm for 0.5 h, then heat up to 600 ° C at a rate of 5 ° C / min, keep warm for 0.5 h, and then heat up to 950 ° C ± 20 ° C at a rate of 6 ° C / min, and keep warm for 2 h.

[0021] S5, shell firing: Place the dewaxed split ceramic shell in a firing furnace, set the firing furnace heating curve, and cool it with the furnace after firing; S6. Mold shell assembly: The split ceramic mold shells are bonded with a shell adhesive to form a combined module mold shell, which is then wrapped around the outer side of the combined module mold shell and fixed, and then placed in a baking furnace for secondary sintering and reinforcement; S7. Alloy Casting: Cast the alloy in a modular shell using a pouring process. A high-temperature alloy liquid is poured into the modular shell, preheated to 900-1000°C. After cooling, the shell is removed to produce the casting. The pouring temperature of the high-temperature alloy liquid is 1520°C ± 10°C, the pouring time is 35 seconds, the refining temperature is 1550°C ± 10°C, the refining time is 5 minutes, the vacuum during alloy casting is 5 Pa, the crystal pulling rate is 4 mm / min, and the rest time is 5 minutes. After pouring, the casting is cut to produce a single crystal high-temperature alloy casting. The high-temperature alloy liquid has the following components: C: 0.04-0.06%, Cr: 6.75-7.25%, Mo: 3.80-5.2%, Co: 7.0-8.0%, Al: 6.0-6.4%, W: 4.75-5.25%, Ta: 6.3-6.7%, Re: 2.75-3.25%, and the balance is Ni.

[0022] In this embodiment, the pouring system includes a large module model, in which a pouring cup, a sprue and an ingrown are arranged. The pouring cup is located at the top for receiving and introducing the molten alloy liquid. The sprue is a vertical channel, and the sprue connects the pouring cup and the ingrown. The ingrown is connected to the casting cavity of the combined module shell. The ingrowns are connected in a radial ring array around the sprue, and the angle between adjacent ingrowns is 30°. The large module model includes a chassis 1 with a diameter of 400 mm, 4 center columns 2 with a length of 345 mm, and 12 casting wax molds 3. The large module model is divided into four split models, and each split model includes 3 casting wax molds 3 and a quarter chassis 1 and a center column 2.

[0023] In this embodiment, the sand material for the surface layer of S3 after being dipped in slurry is 100# white corundum sand, the sand material for the transition layer after being dipped in slurry is 60# white corundum sand, and the sand material for the back layer after being dipped in slurry is 24# white corundum sand.

[0024] Comparative Example 1 In this comparative example, a large-module ceramic shell is prepared, and the shell is used to pour high-temperature alloy liquid to prepare single-crystal high-temperature alloy blades.

[0025] The method for preparing the investment casting shell of this comparative example mainly includes the following steps: Slurry Preparation: Mix the powder with a high-polymer silica sol, a wetting agent, and a defoamer in a specific ratio and stir to form a uniformly mixed ceramic shell slurry. The surface layer slurry consists of silica sol, white corundum powder, a wetting agent, and a defoamer in a mass ratio of 1:4.0:0.003:0.01, with a viscosity range of 38s-42s. The transition layer slurry consists of silica sol, white corundum powder, a wetting agent, and a defoamer in a mass ratio of 1:3.5:0.003:0.01, with a viscosity range of 25s-35s. The backing slurry consists of silica sol, white corundum powder, a wetting agent, and a defoamer. The mass ratio of silica sol, white corundum powder, wetting agent, and defoamer is 1:3.0:0.003:0.01, and the viscosity range is 10-15s. To prepare the slurry, weigh the silica sol and place it in a slurry mixing bucket. Turn on the stirring mechanism and set the stirring speed to 35-40 rpm. Use a feeding spoon to slowly add the weighed zircon powder and cobalt aluminate powder in portions. Gradually add the wetting agent during stirring, and continue stirring for 20 minutes before adding the required defoamer. Once the slurry is evenly mixed and there are no lumps or agglomerates on the surface, adjust the stirring speed to 30-35 rpm and continue stirring for at least 48 hours. This completes the slurry preparation and is ready for mold shell preparation.

[0026] Preparation of wax mold module: Select a suitable mold according to the shape and size of the product, place the pouring system containing embedded rods and metal tooling into it and close the mold, then inject liquid wax into the mold and maintain pressure. After the mold material is condensed and formed, a wax mold is obtained, which is combined with the pouring system according to the requirements of the combination plan to obtain a wax mold module.

[0027] Mold Shell Preparation: A surface layer, transition layer, and backing layer are prepared on the wax mold to form a mold shell containing the wax pattern. The sand grades used for the surface layer, transition layer, and remaining backing layers are 100# white corundum, 60# white corundum, and 24# white corundum, respectively. During mold shell coating, the wax mold is immersed in the surface layer slurry for 5-10 seconds. After immersion, the wax mold is removed from the surface layer slurry and the slurry is evenly distributed. Sanding is then performed. Tilt the mold 30°-45° and rotate it at a constant speed to ensure even distribution of the sand.

[0028] The shell drying environment is as follows: Surface drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 240min Back layer drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 180min Before applying each next layer of coating, enter the drying room to check and confirm that there are no defects such as cracks, expansion, and falling off on the shell surface.

[0029] After sealing, the shell was dried for 48 hours, and the number of layers of the shell was 8.5.

[0030] Dewaxing and calcining treatment: dewaxing the shell containing the wax pattern to obtain a dewaxed shell; calcining the dewaxed shell to obtain a shell for investment casting.

[0031] When the mold shell is roasting, place the mold shell in the furnace, and keep the distance between the mold shells more than 10 cm. After closing the furnace door, set the gas furnace to heat up to 300℃ at a rate of 5℃ / min, keep warm for 0.5h, then heat up to 600℃ at a rate of 5℃ / min, keep warm for 0.5h, and then heat up to 950℃±20℃ at a rate of 6℃ / min, keep warm for 2h. After the mold shell is roasted, cool it to room temperature with the furnace, open the furnace door and take out the mold shell.

[0032] A high-temperature alloy liquid is poured into the cavity of the above-mentioned investment casting mold shell. When pouring the high-temperature alloy liquid, the temperature of the investment casting mold shell is a set temperature. After the investment casting mold shell is cooled, the shelling treatment is performed to obtain a casting; preferably, the set temperature is 900~1000℃.

[0033] The high-temperature alloy composition is: C: 0.04-0.06%, Cr: 6.75-7.25%, Mo: 3.80-5.2%, Co: 7.0-8.0%, Al: 6.0-6.4%, W: 4.75-5.25%, Ta: 6.3-6.7, Re: 2.75-3.25, and the balance is Ni.

[0034] Among them, the specific casting process parameters of the casting are: Refining temperature: 1520℃±10℃ Refining time: 5min Pouring temperature: 1520℃±10℃ Pouring time: 35s Vacuum degree after alloy melting: 5Pa Standing time: 10min The casting after pouring is subjected to shelling and cutting treatment to finally obtain a single crystal high-temperature alloy casting.

[0035] In this comparative example, sparking occurred during alloy pouring. The main reason was that the mold shell module was large and complex in structure, resulting in inconsistent inner and outer thicknesses during the mold shell preparation process, and the mold shell had local high-temperature strength defects. During the pouring process, the mold shell was impacted by the alloy liquid and ruptured. In addition, since the inner runner of the pouring system was connected to the casting, the alloy sparking caused by the mold shell rupture would lead to a low casting molding rate.

[0036] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for constructing a shell for large die casting, characterized in that: The following steps are involved: S1. Module preparation: placing a gating system in a mold, and injecting liquid wax into the mold through the gating system to obtain a split module unit including the gating system; S2. Slurry preparation: The powders of the surface layer, transition layer and back layer are mixed with silica sol, wetting agent and defoaming agent respectively, and stirred to form a uniformly mixed ceramic shell slurry; S3. Mold shell preparation: The split module units are immersed in the ceramic mold shell slurry respectively, and the slurry is sequentially formed into a surface layer, a transition layer, and a back layer. The number of back layers is greater than six. After each layer is slurried, the molding sand is evenly sprinkled on the split module. After each layer is slurried, the split module unit is placed in a ceramic mold shell drying room for drying. After multiple dryings, the ceramic mold shell is obtained; S4, shell dewaxing: the dried split ceramic shell is placed in a high-pressure steam dewaxing kettle for dewaxing; S5, shell firing: Place the dewaxed split ceramic shell in a firing furnace, set the firing furnace heating curve, and cool it with the furnace after firing; S6. Mold shell assembly: The split ceramic mold shells are bonded with a shell adhesive to form a combined module mold shell, which is then wrapped around the outer side of the combined module mold shell and fixed, and then placed in a baking furnace for secondary sintering and reinforcement; S7. Alloy casting: Casting is carried out in the combined mold shell according to the pouring process.

2. A method for constructing a shell for large die casting according to claim 1, characterized in that: The pouring system includes a large module model, wherein a pouring cup, a sprue and an ingrown are arranged in the large module model, the pouring cup is located at the top for receiving and introducing molten alloy liquid, the sprue is a vertical channel, the sprue connects the pouring cup and the ingrown, the ingrown is connected to the casting cavity of the combined module shell, the ingrown is in a radial annular array connected to the circumference of the sprue, and the angle between adjacent ingrowns is 30°, the large module model includes a chassis (1) with a diameter of 400 mm, 4 center columns (2) with a length of 345 mm, and 12 casting wax molds (3), and the large module model is divided into four split models, each split model includes 3 casting wax molds (3) and a quarter of the chassis (1) and a center column (2).

3. The method for constructing a shell for large die casting according to claim 1, characterized in that: The slurry ratio corresponding to the S2 middle surface layer is: the powder-liquid ratio of 320# white corundum powder and silica sol is 3.8-4.2:1, the wetting agent content is 0.3%-0.5%, the defoaming agent content is 1%-2%, and the viscosity is 35s-45s; the slurry ratio of the transition layer is: the powder-liquid ratio of 320# white corundum powder and silica sol is 3.5-4.0:1, the wetting agent content is 0.3%-0.5%, the defoaming agent content is 1%-2%, and the viscosity is 15s-25s; the slurry ratio of the back layer is: the powder-liquid ratio of 320# white corundum powder and silica sol is 3.0-3.5:1, the wetting agent content is 0.3%-0.5%, the defoaming agent content is 1%-2%, and the viscosity is 10s-15s.

4. The method for constructing a shell for large die casting according to claim 1, characterized in that: When preparing S2, first weigh the silica sol and place it in the slurry stirring barrel, turn on the stirring device, set the stirring speed to 35r / min-40r / min, use a feeding spoon to slowly add the powder in batches, and gradually add the wetting agent during the stirring process. After stirring for 20 minutes, add the defoaming agent and continue stirring for more than 48 hours to complete the slurry preparation.

5. The method for constructing a shell for large die casting according to claim 1, characterized in that: The drying conditions for the surface layer are temperature 22±5°C, humidity 75±10%RH, and drying time ≥240min; the drying conditions for the back layer are temperature 22±5°C, humidity 75±10%RH, and drying time ≥180min; the drying time after sealing is ≥48h.

6. The method for constructing a shell for large die casting according to claim 1, characterized in that: The sand material for the surface layer of S3 after being dipped in slurry is 100# white corundum sand, the sand material for the transition layer after being dipped in slurry is 60# white corundum sand, and the sand material for the back layer after being dipped in slurry is 24# white corundum sand.

7. The method for constructing a shell for large die casting according to claim 1, characterized in that: The pressure during dewaxing is 8.2 bar ± 0.2 bar, and the temperature is 185 ° C ± 5 ° C; during roasting, the distance between the shells is greater than 10 cm, and the roasting furnace is set to heat up to 300 ° C at a rate of 5 ° C / min and keep warm for 0.5 hours, then heat up to 600 ° C at a rate of 5 ° C / min, keep warm for 0.5 hours, and then heat up to 950 ° C ± 20 ° C at a rate of 6 ° C / min, and keep warm for 2 hours.

8. The method for constructing a shell for large die casting according to claim 1, characterized in that: In S7, a high-temperature alloy liquid is poured into the combined module shell, and the preheating temperature of the combined module shell is 900~1000℃. After the pouring is completed and the shell is cooled, the shell is removed to obtain a casting; the pouring temperature of the high-temperature alloy liquid is 1520℃±10℃, the pouring time is 30-40s, the refining temperature is 1550℃±10℃, the refining time is 5min±1min, the vacuum degree during alloy melting is ≤7Pa, the crystal pulling rate is 3mm / min-5mm / min, and the casting is cut after the pouring is completed to obtain a single crystal high-temperature alloy casting.

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