Impeller shell for precisely casting large-diameter narrow-air-outlet impeller and shell manufacturing method

Abstract

The invention discloses an impeller shell for precisely casting a large-diameter narrow-air-outlet impeller and a shell manufacturing method, and belongs to the technical field of casting. Comprising the following steps: 1) manufacturing a wax mold, assembling a tree and drying; 2) preparing zirconium powder slurry for a first layer; (3) a second layer is sealed after zirconium powder slurry placed for 20-25 h is air-dried; (4) a sand inclusion layer is prepared, specifically, the zirconium powder slurry, zircon sand and mullite sand which are placed for 20-25 h are evenly mixed to prepare mud, air outlets in the periphery of an impeller and holes in the bottom of the impeller are plugged with the mud, and after drying, the mullite sand is poured from the top of the impeller; 5) airing the third layer and the fourth layer by using mullite powder slurry; (6) mullite powder slurry is used for the fifth layer and the sixth layer, a shell cleaning agent is added, and air drying is conducted; (7) sealing the sixth layer to obtain a second sealing layer, and air-drying to obtain the precision casting large-diameter narrow-air-outlet impeller shell. According to the precision casting large-diameter narrow-air-outlet impeller shell, a double-layer sand inclusion process is adopted, the strength is improved, the casting yield is increased, and the casting defects of steel leakage, slag inclusion and insufficient pouring caused by insufficient strength of the shell or existence of gravel clusters and air holes in the shell are overcome.

Description

Technical Field

[0001] The present invention belongs to the field of casting technology, and particularly relates to an impeller housing for precision casting a large-diameter narrow air outlet impeller and a shell-making method therefor. Background Art

[0002] See Figure 1 , a large-diameter narrow air outlet impeller is a key component of a large fan, which is characterized by a diameter > 30mm, a narrow air outlet < 8mm, a large wall thickness difference, high strength and durability requirements, difficult casting, and prone to casting defects. Moreover, the impeller for a fan has high requirements for its surface quality and dynamic balance. Therefore, the casting is required to have a smooth surface, uniform texture, and no casting defects are allowed at the blade part.

[0003] During the traditional ceramic core pressing process, there are problems such as insufficient pressure holding time and unstable sintering temperature control, resulting in an increased risk of high-temperature creep or shell expansion of the shell, and it is difficult to meet the stability requirements of the narrow flow channel structure.

[0004] The existing shell-making method is layer-by-layer shell-making. Due to the presence of a narrow air outlet, the narrow groove is completely blocked by the third-layer shell during the shell-making process, and the subsequent shell layers cannot be effectively prepared. The shell strength is uneven, the thickness difference is large, and casting defects such as steel leakage and steel inclusion are likely to occur. Moreover, the texture at the blade part of the casting is uneven, the defective rate is high, and the defects at the narrow groove are not easy to be repaired by welding due to their deep position. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide an impeller housing for precision casting a large-diameter narrow air outlet impeller and a shell-making method therefor. The present application adopts a double-layer sand sandwich process, which improves the strength of the impeller housing for precision casting a large-diameter narrow air outlet and the finished product rate of the casting, and solves the casting defects such as steel leakage, slag inclusion, and insufficient pouring caused by insufficient strength of the shell or the presence of sand clusters and pores inside the shell.

[0006] A shell-making method for precision casting a large-diameter narrow air outlet impeller includes the following steps: (1) Making a wax pattern and assembling the trees, and removing the surface release agent; (2) Preparing the first layer, the first layer is in contact with the wax pattern, the first layer uses zircon powder slurry, the slurry viscosity is 40 - 45s, 100 - 120-mesh zircon sand is sprinkled, and it is dried; (3) Preparing the second layer, using the zircon powder slurry after being placed for 20 - 25h, 80 - 100-mesh mullite sand is sprinkled, after sprinkling the mullite sand and air-drying, the second layer is obtained, and the second layer is sealed to obtain the first seal layer, and the first seal layer uses the zircon powder slurry after being placed for 20 - 25h; (4)Preparation of the sand inclusion layer: After the zircon powder slurry has been placed for 20 - 25 hours, zircon sand with a mesh size of 80 - 100 and mullite sand with a mesh size of 60 - 80 are made into mud in a mass ratio of 1:1:3. The air outlets around the wax mold and the openings at the bottom are sealed with the mud. After drying, mullite sand is filled from the top. While filling, it is shaken and tamped, and then the opening at the top is sealed with mud and air-dried. The filled mullite sand is 80 - 100 mesh mullite sand; (5)Preparation of the third and fourth layers: Use mullite powder slurry with a viscosity of 24 - 30 s; sprinkle mullite sand; (6)Preparation of the fifth and sixth layers: Use mullite powder slurry and add a shell cleaning agent simultaneously. The viscosity of the mullite powder slurry is 12 - 16 s, and sprinkle mullite sand with a mesh size of 16 - 30; (7)Seal the sixth layer to obtain the second seal layer. The second seal layer uses the mullite powder slurry of the fifth layer and adds a shell cleaning agent simultaneously, air-dry it, and put it into a steam dewaxing kettle; The fifth layer, the sixth layer, and the second seal layer all use mullite powder slurry and add the same shell cleaning agent; The dewaxing method uses a steam dewaxing kettle.

[0007] After each layer is dipped in the slurry, the excess floating slurry needs to be blown off with an air gun. After the sand hanging is completed, the inside of the narrow groove needs to be cleaned with an iron sheet or wire to remove the floating sand and sand conglomerates; The shear force of the air flow of the air gun can break the surface tension of the slurry, remove the slurry agglomerates, improve the surface flatness; Remove the sand conglomerates to prevent the formation of pore defects during the roasting process; Especially the first layer and the second layer are more important.

[0008] In step (1), a medium-temperature wax is used to make the wax mold, which is cleaned with a cleaning agent to remove the release agent on the surface; In this application, the air-drying uses a blower for air-drying.

[0009] The zircon powder slurry described in step (2) is prepared from zircon powder, silica sol, wetting agent, and defoaming agent in a mass ratio of 200:950:1:1. The defoaming agent is composed of 50 wt% glycerol polyoxypropylene ether and 50 wt% polydimethylsiloxane; The wetting agent is composed of 50 wt% sodium dodecylbenzenesulfonate and 50 wt% polyethylene glycol. Silica sol and zircon powder are the main components of the slurry. The wetting agent optimizes the dispersion effect, and the defoaming agent ensures that there are no bubble defects in the slurry. The synergistic effect of the four can ensure the fluidity, coating property, shell strength, and surface quality of the slurry.

[0010] In the zircon powder slurry, the ratio of zircon powder to silica sol is mainly to adjust the viscosity of the zircon powder slurry. In the shell-making process of precision casting, as the number of layers increases, the viscosity of the slurry decreases. Excessive silica sol will cause the slurry viscosity to be too small, and excessive zircon powder will cause the slurry viscosity to be too large.

[0011] Excessive silica sol and too low slurry viscosity will result in uneven coating. When the slurry is too thin, its fluidity is too high, and it is prone to flow during coating, resulting in uneven coating thickness, local thinning or sagging, which affects the smoothness and density of the casting surface. The thin coating area may not be able to effectively protect the substrate, resulting in defects such as pores and sand holes on the casting surface. The coating formed with too low slurry viscosity has low density, loose structure after drying, and significant decline in tensile strength, wear resistance and thermal shock resistance. The casting will crack or deform at high temperature or under stress.

[0012] The ratio of wetting agent and defoamer in this slurry is the best ratio tested during the production process. Excessive wetting agent will reduce the surface tension of the slurry, resulting in too low viscosity and too strong fluidity, and it is prone to penetrate the substrate or form sag during coating. Excessive defoamer can cause local viscosity increase due to poor compatibility, exacerbating the uneven slurry flow. When the defoamer is excessive, its active ingredients can be solubilized by surfactants or compete for adsorption with wetting agents, instead weakening the defoaming ability. Excessive wetting agent causes the slurry to overly wet the substrate, the coating layer is too thin and the adhesion is insufficient, and it is prone to peel off due to shrinkage stress after drying. At the same time, it takes longer to remove the residual slurry during shell cleaning. Excessive defoamer leads to increased costs. When the defoamer is insufficient, the foam in the slurry cannot be eliminated in time, resulting in defects such as pores and sand holes in the coating, reducing density and mechanical strength. Insufficient wetting agent makes the surface tension of the slurry too high, with poor fluidity, and it is difficult to spread evenly during coating, resulting in uneven coating thickness or local missed coating.

[0013] The first layer contacts the wax pattern and determines the surface quality. The first layer is connected to the wax pattern, providing a stable base support for the transition layer and preventing the shell from delaminating or cracking due to insufficient adhesion. Since the first layer directly contacts the wax pattern, it is necessary to control the addition amount of the wetting agent to ensure that there is no residue of the wetting agent on the surface of the wax pattern after cleaning, enhance the adhesion of the coating, and reduce the risk of cracking during shell demolding.

[0014] The second layer, the second sealing layer and the third layer are transition layers. The transition layers can provide uniform support force, play a role in fixing and protecting the sand filling layer, and reduce the reduction of shell strength caused by too high local porosity.

[0015] All layers except the first layer are back layers. The back layers use large-grained sand and low-viscosity slurry, which improves the mechanical strength of the shell, enhances the overall strength and creep resistance of the shell, increases the filling pressure of the molten metal supported, and prevents the shell from deforming or cracking during pouring; thus improving the yield.

[0016] The sealing layer can promote the formation of a complete and unified whole inside, thereby enhancing the high-temperature performance of the shell and playing a supporting role in the shell structure. In addition, the sealing layer can also play a role in fixing and protecting the outermost layer, and can prevent the occurrence of sand dropping.

[0017] During the process of preparing the impeller casting by the original process, when the shell-making reached the third layer, the inside of the air outlet was blocked, resulting in the inability to effectively prepare the subsequent shell layers. The strength of this part was lower than that of other parts, and during the casting process, a "runaway fire" phenomenon would occur. To solve the problem of low strength in this part, in this application, after the second layer of the shell was made, a plugging and sand-filling process was adopted, filling the gap with mullite sand to improve the strength of this part.

[0018] The "runaway fire" phenomenon during the shell-making process refers to the accidental leakage of molten metal from the mold shell during the pouring or molding stage. The "runaway fire" phenomenon is mainly caused by insufficient strength of the mold shell. To avoid the "runaway fire" phenomenon, the fifth and sixth layers are added in this application.

[0019] In this application, the first layer, the second layer, and the sealing layer of the second layer are the inner layers. The inner layers mainly play the role of connecting the wax mold and improving the surface quality of the casting; the third layer, the fourth layer, the fifth layer, the sixth layer, and the sealing layer of the sixth layer are the outer layers. By using a low-viscosity slurry and large-grained sand in the outer layer, the overall strength of the mold shell is improved. Sand sandwich layer: By plugging with mud and filling with mullite sand, the strength inside the air outlet is improved. The sand sandwich layer treatment adopts the mud plugging process and fills with mullite sand, which can enhance the internal structure strength of the air outlet, thereby preventing the occurrence of the "runaway fire" phenomenon. This application adopts a double-layer sand sandwich process, improving the strength and casting yield of a shell-making method for precision casting a large-diameter narrow air outlet impeller, and solving the casting defects such as steel leakage, slag inclusion, and insufficient pouring caused by insufficient strength of the mold shell or the existence of sand conglomerates and air holes inside the mold shell.

[0020] This application adopts a shell-making process of mullite sand grouting. By adding a shell cleaning agent to the fifth and sixth layer mold shells, not only does it make the shell cleaning work easier, but also there is no need to purchase additional materials, which will not increase the overall process cost, and the operation is simple and easy.

[0021] Step (4): Mix the zirconium powder slurry placed for 20 - 25h, zircon sand with a mesh size of 80 - 100, and mullite sand with a mesh size of 60 - 80 in a mass ratio of 1:1:3 to make mud. Plug the air outlets around the impeller and the openings at the bottom with the mud. After drying, fill the top with mullite sand, shaking and tamping while filling, and then seal the opening at the top with mud and air-dry. The zirconium powder slurry placed for 20 - 25h, zircon sand with a mesh size of 80 - 100, and mullite sand with a mesh size of 60 - 80 are mixed in a mass ratio of 1:1:3 to make mud. Under the condition of this mass ratio, the zirconium powder slurry placed for 20 - 25h makes the prepared mud have a relatively high slurry viscosity, and there will be no leakage when plugging the air outlet. At the same time, ensure that the surface is the zirconium powder slurry placed for 20 - 25h before making the third layer of the shell, making the subsequent mold shell bond more evenly. The zircon sand with a mesh size of 80 - 100 can make the mud finer and denser, increasing the slurry viscosity. The mullite sand with a mesh size of 60 - 80 can improve the strength of the air-dried mud and enhance the connection with the third layer of the shell, avoiding delamination.

[0022] The mullite powder slurry described in step (5) is prepared from mullite powder and silica sol at a mass ratio of 3 - 5:1; preferably, the mass ratio of mullite powder to silica sol is 4:1. The ratio of mullite powder to silica sol is mainly to adjust the viscosity of the slurry. In the shell-making process of precision casting, as the number of layers increases, the viscosity of the slurry decreases. Excessive silica sol will cause the slurry viscosity to be too low, and excessive addition of mullite powder will cause the slurry viscosity to be too high.

[0023] The mullite powder slurry described in step (6) is prepared from mullite powder and silica sol at a mass ratio of 3 - 3.5:1; preferably, the mass ratio of mullite powder to silica sol is 3.2:1. The ratio of mullite powder to silica sol is mainly to adjust the viscosity of the slurry. In the shell-making process of precision casting, as the number of layers increases, the viscosity of the slurry decreases; excessive silica sol will cause the slurry viscosity to be too low, and excessive addition of mullite powder will cause the slurry viscosity to be too high.

[0024] The shell cleaning agent described in step (6) is composed of a disintegrant, magnesium oxide, and graphite powder; the disintegrant is composed of 30 - 50 wt% sodium carboxymethylcellulose, 10 - 20 wt% sodium carbonate, and 30 - 50 wt% calcium carbonate. The addition amount of the disintegrant is 1.5 wt% of 16 - 30 mesh mullite sand, the addition amount of magnesium oxide is 1 wt% of 16 - 30 mesh mullite sand, and the addition amount of graphite powder is 0.2 wt% of 16 - 30 mesh mullite sand. The synergistic effect of the disintegrant, magnesium oxide, and graphite powder in the shell cleaning agent improves the shell cleaning efficiency and performance. Through the penetration of the disintegrant in the shell cleaning agent, the structure becomes loose, the chemical decomposition of magnesium oxide, and the heat conduction and lubrication of graphite powder, the three work together to completely peel off the residue.

[0025] Adding the shell cleaning agent to the mold shell makes it have sufficient strength after hardening. After high-temperature pouring, the residual strength of the molding sand is greatly reduced, and it is easy to clean without affecting the use. The reduction of the residual strength of the molding sand refers to the phenomenon that the remaining strength after hardening of the molding sand decreases during or after high-temperature pouring. If the addition amount is too small, the disintegration effect is not obvious; if the addition amount is too large, it will affect the strength of the mold shell after roasting and cause steel leakage during pouring. The water-soluble polymer component in the shell cleaning agent maintains the structural stability of the mold shell at high temperature, absorbs water and swells after cooling, and destroys the internal adhesion of the mold shell; it reduces the adhesion strength between sand grains, forms more microcracks and pore structures, and makes the mold shell easier to break and peel after cooling. Adding a disintegrant during shell-making, its components will not reduce the adhesion of the slurry to the casting sand, and can ensure that the mold shell maintains sufficient strength during the casting process. By adjusting the powder-liquid ratio of the slurry, the process performance and subsequent disintegration requirements are balanced. The disintegrant makes the mold shell automatically disintegrate into fine particles after the casting cools, reducing the mechanical impact or chemical corrosion steps required for traditional sand cleaning.

[0026] Sodium carboxymethyl cellulose, as an organic dispersant, accelerates the disintegration of the material by forming a porous structure, and at the same time has a binding function to improve the initial formability; sodium carbonate and calcium carbonate reduce chemical corrosion by neutralizing the acidic environment and release gas to promote the loosening inside the material; sodium carbonate can adjust the pH and activate the reaction; calcium carbonate has the functions of filling and promoting decomposition; the generation of the porous structure of sodium carboxymethyl cellulose and the neutralization reaction of sodium carbonate and calcium carbonate act synergistically to balance the forming strength of the material and the subsequent decomposition efficiency.

[0027] Graphite powder can make the shell layer after pouring and cooling, improve the demoulding ability and is easy to clean the shell. Graphite powder has the function of lubrication and resistance reduction. Through its layered crystal structure, it reduces the friction coefficient between the residue and the metal shell and reduces the risk of secondary adhesion. As a high thermal conductivity material, graphite accelerates the heat transfer in the crust layer and promotes the thermal activation process of the disintegrant and magnesium oxide.

[0028] Too much graphite powder will block the pores of the shell, hinder the gas discharge during pouring, and can cause casting defects such as pores and slag inclusions; too much graphite powder will lead to insufficient high-temperature strength of the shell, resulting in cracking and damage during demoulding or pouring. Insufficient graphite powder will weaken the lubrication effect, increase the friction between the shell and the casting, and easily cause scratches on the surface of the casting during demoulding. At the same time, the delamination performance of the shell decreases, and the difficulty of cleaning the residual sand shell increases. When the graphite powder is insufficient, the pores on the surface of the shell are not effectively closed.

[0029] Magnesium oxide can improve the high-temperature strength of the shell, further improve the strength of the shell during pouring, and reduce the phenomenon of steel leakage. Magnesium oxide reacts with the acidic components in the residue to form magnesium salts that are easily soluble in water, reducing the stability of the crust; the volume expansion generated by the hydration reaction of magnesium oxide further intensifies the internal stress in the crust layer, assisting the disintegrant to complete the shell stripping.

[0030] Too much magnesium oxide will form too high high-temperature strength, but the difference in thermal expansion coefficient leads to stress concentration, which instead increases the brittleness and cracking risk of the shell and increases the probability of steel leakage. Too little magnesium oxide cannot effectively form a reinforcing phase and a dense gel structure, and the shell is prone to softening or deformation during high-temperature pouring, increasing the probability of steel leakage; too little magnesium oxide reduces the erosion resistance, and the chemical erosion resistance of the shell to molten metal or slag is weakened, which can accelerate the material peeling or penetration. Too little magnesium oxide will lead to an increase in porosity, reduce the structural density, and weaken the mechanical strength and stability.

[0031] During the shell-making process, after each layer is completed, it is dried for 8 to 12 hours. After the coating is completely cured and the moisture is fully volatilized, the next layer of shell-making operation is carried out; this can avoid the interlayer peeling caused by the vapor pressure during high-temperature roasting and prevent its structural defects. The high-temperature strength in this application refers to the strength of the shell mold baked to 1150 °C; the high temperature in this application refers to 1100 to 1200 °C. During the whole process of shell-making for the precision casting of a large-diameter narrow air outlet impeller in this application, the temperature needs to be kept constant at 20 °C and the humidity at 50%; floor-standing wall-mounted powerful fans are used for the fans, and Opuri dehumidifiers are used for the dehumidifiers, and an air cooler is used to keep the temperature constant.

[0032] In another aspect of this application, for the impeller shell obtained by the above preparation method, from the wax mold outwards, there are successively the first layer, the second layer, the first sealing layer, the third layer, the fourth layer, the fifth layer, the sixth layer, and the second sealing layer; the air outlets around the mold cavity of the impeller shell and the openings at the bottom are blocked with mud. The mud at the air outlet is arranged between the two first sealing layers and inside the third layer, and mullite sand is filled between the mold cavity and the mud. The sand inclusion layer adopts the mud plugging process and is filled with mullite sand to enhance the internal structural strength of the air outlet, thereby preventing the occurrence of the "blowout" phenomenon.

[0033] Compared with the prior art, the beneficial effects of the present invention are: 1. In this application, the first layer, the second layer, and the sealing layers of the second layer are the inner layers, and the inner layers mainly play the role of connecting the wax mold and improving the surface quality of the casting; the third layer, the fourth layer, the fifth layer, the sixth layer, and the sealing layers of the sixth layer are the outer layers. During the preparation of the outer layer, a low-viscosity slurry is selected and used in combination with large-grained sand, which can improve the overall strength of the shell mold. The sand inclusion layer adopts the mud plugging process and is filled with mullite sand to enhance the internal structural strength of the air outlet, thereby preventing the occurrence of the "blowout" phenomenon. This application adopts a double-layer sand inclusion process, which improves the strength and casting yield of the shell-making method for precision casting of a large-diameter narrow air outlet impeller, and solves the casting defects such as steel leakage, slag inclusion, and insufficient pouring caused by insufficient strength of the shell mold or the existence of sand and gravel clusters and pores inside the shell mold. The yield of this application reaches 92 to 95%, the hardness reaches 127 to 133 HB, the tensile strength reaches 574 to 587 MPa, the salt spray test reaches 96 to 122 h, and the weight difference before and after shell cleaning reaches 9500 to 9567 g.

[0034] 2. This application adopts a shell-making process of mullite sand grouting, and a shell cleaning agent is added to the fifth layer and the sixth layer. Through the penetration of the disintegrant, the structure becomes loose, the chemical decomposition of magnesium oxide, and the heat conduction and lubrication of graphite powder, the three work together to completely peel the residue, improving the shell mold performance and shell cleaning efficiency. Moreover, there is no need to purchase additional materials, which will not increase the overall process cost, and the operation is simple and easy. Description of the Drawings

[0035] Figure 1Schematic diagram of the side of the impeller with a large diameter and a narrow air outlet.

[0036] Figure 2 Schematic diagram of the local shell-making structure of the impeller with a large diameter and a narrow air outlet.

[0037] Wherein: 1. Casting body; 2. First layer; 3. Second layer; 4. First sealing layer; 5. Third layer; 6. Fourth layer; 7. Fifth layer; 8. Sixth layer; 9. Second sealing layer; 10. Sand inclusion layer; 11. Filling mullite sand; 12. Mud. Specific implementation manner

[0038] Example 1 is the best example of the present invention. The present invention will be further described below in conjunction with specific examples and comparative examples.

[0039] The chemical additives used in the examples and comparative examples of the present invention are all commercially available. The specific information is as follows: Zircon powder: The zircon powder is zirconium powder, industrial grade, purchased from Weifang Huazhong New Composite Materials Co., Ltd.; Silica sol: Specification GS-830; industrial grade, HB5346-1986, purchased from Yancheng Haixin Foundry Materials Co., Ltd.; Defoamer: Industrial grade, the defoamer is composed of 50wt% glycerol polyoxypropylene ether and 50wt% polydimethylsiloxane; purchased from Zibo Kulun Foundry Materials Co., Ltd.; Wetting agent: Industrial grade, the wetting agent is composed of 50wt% sodium dodecylbenzenesulfonate and 50wt% polyethylene glycol; purchased from Zibo Kulun Foundry Materials Co., Ltd.; Collapsing agent: Industrial grade, the collapsing agent is composed of 30-50wt% sodium carboxymethyl cellulose, 10-20wt% sodium carbonate and 30-50wt% calcium carbonate; purchased from Xuzhou Rekar Foundry Materials Co., Ltd.; Cleaning agent: Model 7620, industrial grade, purchased from Xuzhou Rekar Foundry Materials Co., Ltd.; Magnesium oxide: Industrial grade, purchased from Shandong Haihui Chemical Co., Ltd.; Graphite powder: Industrial grade, purchased from Qingdao Huashichuang Precision Materials Co., Ltd.; Zircon sand of 100-120 mesh is zircon, industrial grade, purchased from Shandong Yuechi New Materials Co., Ltd.; Zircon sand of 80-100 mesh is zircon, industrial grade, purchased from Shandong Yuechi New Materials Co., Ltd.; Mullite sand of 80-100 mesh is foundry sand: Industrial grade, purchased from Zibo Huasheng Mining Co., Ltd.; Mullite sand of 60-80 mesh is foundry sand: Industrial grade, purchased from Zibo Huasheng Mining Co., Ltd.; Mullite sand of 30-60 mesh is foundry sand: Industrial grade, purchased from Zibo Huasheng Mining Co., Ltd.; The mullite sand with a mesh size of 40 - 60 is used as foundry sand: industrial grade, purchased from Zibo Huasheng Mining Co., Ltd.; The mullite sand with a mesh size of 16 - 30 is used as foundry sand: industrial grade, purchased from Zibo Huasheng Mining Co., Ltd.; The blower: The blower is a floor - mounted wall - mounted powerful blower, model FS - 75, purchased from Foshan Karnas Electric Appliance Co., Ltd.; The dehumidifier: The dehumidifier is an Aopurui dehumidifier, model H - 8480C, purchased from Shandong Aopurui Electric Appliance Co., Ltd.; The air cooler: The model is SDD, purchased from Zhejiang Shengzhou Zhong'ai Refrigerator Parts Factory; The smoke machine: The model is YWX - 150, purchased from Nanjing Huanke Experimental Equipment Co., Ltd.

[0040] Example 1 A method for making the shell of a precision - cast large - diameter narrow - air - outlet impeller, comprising the following steps: (1) Make a wax pattern with medium - temperature wax and group the trees, clean it with a cleaning agent to remove the mold release agent on the surface, and transfer it to the shell - making process after drying; (2) Prepare the first layer 2. The first layer 2 is in contact with the wax pattern. The first layer 2 uses zircon powder slurry, which is prepared from zircon powder, silica sol, wetting agent and defoaming agent in a mass ratio of 200:950:1:1; sprinkle zircon sand with a mesh size of 100 - 120, the viscosity of the slurry is 45 s; dry for 12 h; (3) Prepare the second layer 3. Use the zircon powder slurry after standing for 24 h, sprinkle mullite sand with a mesh size of 100, air - dry for 12 h to obtain the second layer 3, and seal the second layer 3 to get the first seal layer 4. The first seal layer uses the zircon powder slurry after standing for 24 h; After each layer is dipped in the slurry, use an air gun to blow off the excess floating slurry. After hanging the sand, use an iron sheet or wire to clean the inside of the narrow groove, and clean off the floating sand and sand gravel clusters; (4) Prepare the sandwich layer 10: Make a mud 12 from the zircon powder slurry after standing for 24 h, zircon sand with a mesh size of 80 - 100 and mullite sand with a mesh size of 60 - 80 in a mass ratio of 1:1:3. Seal the air outlets around the wax pattern and the openings at the bottom with the mud 12. After drying for 2 h, pour 80 - 100 - mesh mullite sand 11 from the top, shake and tamp while pouring, and then seal the opening at the top with the mud 12, air - dry for 12 h. The filled mullite sand 11 is 80 - 100 - mesh mullite sand; (5) Prepare the third layer 5 and the fourth layer 6. Use mullite powder slurry, sprinkle mullite sand with a mesh size of 40 - 60, and the viscosity of the slurry is 30 s; air - dry each layer for 12 h; (6) Prepare the fifth layer 7 and the sixth layer 8 using mullite powder slurry, and add a shell cleaning agent to each layer. The viscosity of the mullite powder slurry is 12 - 16 s, and sprinkle mullite sand with a mesh size of 16 - 30; the shell cleaning agent is composed of a collapsible agent, magnesium oxide, and graphite powder; the addition amount of the collapsible agent is 1.5 wt% of the mullite sand with a mesh size of 16 - 30, the addition amount of magnesium oxide is 1 wt% of the mullite sand with a mesh size of 16 - 30, and the addition amount of graphite powder is 0.2 wt% of the mullite sand with a mesh size of 16 - 30; air dry each layer for 12 h; (7) Seal the sixth layer 8 to obtain the second seal layer 9. The second seal layer 9 uses the mullite powder slurry of the fifth layer and the same shell cleaning agent as the fifth layer 7, and air dry for 12 hours; finally, dewax to obtain a precision-cast large-diameter narrow air outlet impeller housing.

[0041] See Figure 2 , this embodiment also provides an impeller housing obtained by the above shell-making method, including a first layer 2, a second layer 3, a first seal layer 4, a third layer 5, a fourth layer 6, a fifth layer 7, a sixth layer 8, and a second seal layer 9 arranged in sequence from the inside to the outside, and the first layer 2, the second layer 3, and the first seal layer 4 are respectively arranged on both sides of the air outlet of the wax mold. The two first seal layers 4 are spaced apart to form a sandwiched sand layer 10. The layer of the sand layer 10 close to the third layer 5 is blocked with mud 12, and mullite sand 11 is filled between the mold cavity and the mud 12.

[0042] Example 2 A shell-making method for precision-casting a large-diameter narrow air outlet impeller, including the following steps: (1) Make a wax mold with medium-temperature wax and group the trees, clean it with a cleaning agent to remove the mold release agent on the surface, and transfer it to the shell-making process after drying; (2) Prepare the first layer 2. The first layer 2 is in contact with the wax mold. The first layer 2 uses zircon powder slurry, which is prepared by mixing zircon powder, silica sol, wetting agent, and defoaming agent in a mass ratio of 200:950:1:1; sprinkle zircon sand with a mesh size of 100 - 120, and the slurry viscosity is 40 s; dry for 8 h; (3) Prepare the second layer 3. Use the zircon powder slurry after standing for 20 h, sprinkle mullite sand with a mesh size of 80, and obtain the second layer 3 after air drying for 8 h. Seal the second layer 3 to obtain the first seal layer 4. The first seal layer uses the zircon powder slurry after standing for 20 h; After each layer is dipped in the slurry, use an air gun to blow off the excess floating slurry. After hanging the sand, use an iron sheet or wire to clean the inside of the narrow groove, and clean off the floating sand and sand conglomerates; (4)Fabricating the sand inclusion layer 10: Prepare a mud 12 by mixing zircon powder slurry that has been placed for 20 h, zircon sand with a mesh size of 80 - 100, and mullite sand with a mesh size of 60 - 80 in a mass ratio of 1:1:3. Seal the air outlets around the wax mold and the openings at the bottom with the mud 12. After drying for 2 h, pour and fill mullite sand 11 from the top, shaking and tamping it while pouring. Then seal the top opening with the mud 12 and air-dry for 8 h. The filled mullite sand 11 is 80 - 100 mesh mullite sand. (5)Fabricating the third layer 5 and the fourth layer 6, using mullite powder slurry and sprinkling 60 - mesh mullite sand, with the slurry viscosity being 24 s; air-dry each layer for 12 h. (6)Fabricating the fifth layer 7 and the sixth layer 8, using mullite powder slurry and adding a shell cleaning agent to each layer simultaneously. The viscosity of the mullite powder slurry is 12 - 16 s, and 16 - 30 - mesh mullite sand is sprinkled; the shell cleaning agent is composed of a disintegrating agent, magnesium oxide, and graphite powder; the addition amount of the disintegrating agent is 1.5 wt% of the 16 - 30 - mesh mullite sand, the addition amount of magnesium oxide is 1 wt% of the 16 - 30 - mesh mullite sand, and the addition amount of graphite powder is 0.2 wt% of the 16 - 30 - mesh mullite sand; air-dry each layer for 8 h. (7)Sealing the sixth layer 8 to obtain the second sealing layer 9. The second sealing layer 9 uses the mullite powder slurry of the fifth layer and the same shell cleaning agent as the fifth layer 7, and air-dry for 8 hours; finally, dewax to obtain a precision-cast large-diameter narrow air outlet impeller housing.

[0043] See Figure 2 This embodiment also provides an impeller housing obtained by the above shell-making method, including a first layer 2, a second layer 3, a first sealing layer 4, a third layer 5, a fourth layer 6, a fifth layer 7, a sixth layer 8, and a second sealing layer 9 arranged in sequence from the inside to the outside. The first layer 2, the second layer 3, and the first sealing layer 4 are respectively arranged on both sides of the air outlet of the wax mold. The two first sealing layers 4 are spaced apart to form a sand inclusion layer 10. The layer of the sand layer 10 close to the third layer 5 is sealed with the mud 12, and mullite sand 11 is filled between the mold cavity and the mud 12.

[0044] Example 3 A shell-making method for precision-casting a large-diameter narrow air outlet impeller, comprising the following steps: (1)Make a wax mold with medium-temperature wax and group the trees, clean it with a cleaning agent to remove the release agent on the surface, and transfer it to the shell-making process after drying. (2)Fabricate the first layer 2. The first layer 2 is in contact with the wax mold. The first layer 2 uses zircon powder slurry, which is prepared by mixing zircon powder, silica sol, a wetting agent, and an antifoaming agent in a mass ratio of 200:950:1:1; sprinkle 100 - 120 - mesh zircon sand, with the slurry viscosity being 45 s; dry for 12 h. (3) Preparation of the second layer 3: Use the zircon powder slurry after standing for 25 h, sprinkle mullite sand with a mesh size of 100, and obtain the second layer 3 after air drying for 12 h. Seal the second layer 3 to obtain the first seal layer 4, and the first seal layer uses the zircon powder slurry after standing for 25 h. After each layer is dipped in slurry, the excess floating slurry needs to be blown off with an air gun. After sand hanging is completed, the inside of the narrow groove needs to be cleaned with an iron sheet or wire to remove the floating sand and sand conglomerates. (4) Preparation of the sandwich layer 10: Prepare a mud 12 by mixing the zircon powder slurry after standing for 25 h, zircon sand with a mesh size of 100, and mullite sand with a mesh size of 80 in a mass ratio of 1:1:3. Seal the air outlets around the wax mold and the openings at the bottom with the mud 12. After drying for 3 h, fill with mullite sand 11 from the top, shake and tamp while filling, then seal the opening at the top with the mud 12 and air dry for 10 h. The filled mullite sand 11 is 100-mesh mullite sand. (5) Preparation of the third layer 5 and the fourth layer 6: Use mullite powder slurry, sprinkle mullite sand with a mesh size of 60, and the slurry viscosity is 24 s; air dry each layer for 8 h. (6) Preparation of the fifth layer 7 and the sixth layer 8: Use mullite powder slurry, and add a shell cleaning agent to each layer at the same time. The viscosity of the mullite powder slurry is 12 s, and sprinkle mullite sand with a mesh size of 16 - 30; the shell cleaning agent is composed of a disintegrant, magnesium oxide, and graphite powder; the addition amount of the disintegrant is 1.5 wt% of the mullite sand with a mesh size of 16 - 30, the addition amount of magnesium oxide is 1 wt% of the mullite sand with a mesh size of 16 - 30, and the addition amount of graphite powder is 0.2 wt% of the mullite sand with a mesh size of 16 - 30; air dry each layer for 8 h. (7) Seal the sixth layer 8 to obtain the second seal layer 9. The second seal layer 9 uses the mullite powder slurry of the fifth layer and the same shell cleaning agent as the fifth layer 7, and air dry for 8 hours; finally, dewax to obtain a precision casting large-diameter narrow air outlet impeller housing.

[0045] See Figure 2 This embodiment also provides an impeller housing obtained by the above shell-making method, including a first layer 2, a second layer 3, a first seal layer 4, a third layer 5, a fourth layer 6, a fifth layer 7, a sixth layer 8, and a second seal layer 9 arranged in sequence from the inside to the outside. And the first layer 2, the second layer 3, and the first seal layer 4 are respectively provided on both sides of the air outlet of the wax mold. The two first seal layers 4 are spaced apart to form a sandwich layer 10. The layer of the sand layer 10 close to the third layer 5 is sealed with the mud 12, and mullite sand 11 is filled between the mold cavity and the mud 12.

[0046] Comparative Example 1 The shell-making method described in this comparative example includes the following steps: For the first layer, dip in zirconium-containing slurry and hang zircon sand. Use zircon powder slurry, which is prepared by mixing zircon powder, silica sol, wetting agent, and defoaming agent in a mass ratio of 230:50:0.24:0.27, sprinkle zircon sand with a mesh size of 100 - 120, and the slurry viscosity is 45 s. The second and third layers are dipped in the mixed slurry and coated with mullite sand; the slurry is prepared from mullite powder and zircon powder in a mass ratio of 1:1; the viscosity of the slurry is 24 - 30 s, and the mullite sand is 30 - 60 mesh; The fourth and fifth layers are dipped in mullite slurry and coated with mullite sand; the slurry is prepared from silica sol and mullite powder in a mass ratio of 1:3.2; the viscosity of the slurry is 13 s, and the particle size of the mullite sand is 16 - 30 mesh; The fifth layer is sealed with the slurry of the fifth layer; after each layer of shell making is completed, it is air-dried for 8 h, and finally dewaxed to obtain a precision casting large-diameter narrow air outlet impeller shell.

[0047] Comparative Example 2 The shell making method described in this comparative example includes the following steps: The first layer is dipped in zircon slurry and coated with zircon sand. The zircon powder slurry is used, which is prepared from zircon powder, silica sol, wetting agent and defoaming agent in a mass ratio of 230:50:0.24:0.27. The viscosity of the slurry is 40 s, and the zircon sand is 80 - 120 mesh; The second and third layers are dipped in zircon slurry and coated with mullite sand. The slurry of the first layer after being prepared for 24 h is used, and the viscosity of the slurry is 24 s; the mullite sand is 30 - 60 mesh; For the fourth and fifth layers, they are dipped in mullite slurry and coated with mullite sand. The slurry is prepared from silica sol and mullite powder in a mass ratio of 1:3.2; the viscosity of the slurry is 13 s, and the mullite sand is 16 - 30 mesh; The fifth layer is sealed with the slurry of the fifth layer; after each layer of shell making is completed, it is air-dried for 8 h, and finally dewaxed to obtain a precision casting large-diameter narrow air outlet impeller shell.

[0048] Comparative Example 3 The shell making method described in this comparative example includes the following steps: The first layer is dipped in zircon slurry and coated with zircon sand. The zircon powder slurry is used, which is prepared from zircon powder, silica sol, wetting agent and defoaming agent in a mass ratio of 230:50:0.24:0.27. 80 - 120 mesh zircon sand is sprinkled, and the viscosity of the slurry is 40 s; For the second and third layers, the slurry of the first layer after being prepared for 24 h is used, the viscosity of the slurry is 24 s, and the mullite sand is 30 - 60 mesh; The fourth and fifth layers are dipped in mullite slurry and coated with mullite sand; the slurry is prepared from silica sol and mullite powder in a mass ratio of 1:3.2; the viscosity of the slurry is 13 s, and the particle size of the mullite sand is 16 - 30 mesh; The fifth layer is sealed with the slurry of the fifth layer; after each layer of shell making is completed, it is air-dried for 8 h, and finally dewaxed to obtain a precision casting large-diameter narrow air outlet impeller shell.

[0049] Comparative Example 4 The shell-making method described in this comparative example is the same as that in Example 1, except that in step (6), a collapsible agent and magnesium oxide are added to each furnace simultaneously. The addition amount of the collapsible agent is 1.5 wt% of mullite sand with a particle size of 16 - 30 mesh, and the addition amount of magnesium oxide is 1 wt% of mullite sand with a particle size of 6 - 30 mesh.

[0050] Comparative Example 5 The shell-making method described in this comparative example is the same as that in Example 1, except that in step (6), a collapsible agent and graphite powder are added to each furnace simultaneously; the addition amount of the collapsible agent is 1.5 wt% of mullite sand with a particle size of 16 - 30 mesh, and the addition amount of graphite powder is 0.2 wt% of mullite sand with a particle size of 6 - 30 mesh.

[0051] Comparative Example 6 The shell-making method described in this comparative example is the same as that in Example 1, except that in step (6), magnesium oxide and graphite powder are added to each furnace simultaneously; the addition amount of magnesium oxide is 1 wt% of mullite sand with a particle size of 6 - 30 mesh, and the addition amount of graphite powder is 0.2 wt% of mullite sand with a particle size of 6 - 30 mesh.

[0052] Comparative Example 7 The shell-making method described in this comparative example is the same as that in Example 1, except that in step (6), a collapsible agent is added to each furnace simultaneously, and the addition amount of the collapsible agent is 2.7 wt% of mullite sand with a particle size of 16 - 30 mesh.

[0053] Performance Test Perform performance tests on the precision-cast large-diameter narrow air outlet impeller shells prepared in the examples and comparative examples. The specific test results are shown in Table 1.

[0054] Calculation formula for the qualified product rate: Qualified product rate = (Number of qualified products / Total number of products produced) × 100%; The hardness of the precision-cast large-diameter narrow air outlet impeller shell is tested with reference to GB / T 231.3 - 2019; The tensile strength of the precision-cast large-diameter narrow air outlet impeller shell is tested with reference to GB / T 15248 - 2008 "Test Method for Axial Equal-Amplitude Low-Cycle Fatigue of Metallic Materials"; The salt spray test of the precision-cast large-diameter narrow air outlet impeller shell is tested with reference to GB / T 10125 - 2021; Measure the weight difference of the precision-cast large-diameter narrow air outlet impeller shell before and after shell cleaning by the weighing method.

[0055] Table 1 Performance Test Results of Examples and Comparative Examples 。

[0056] As can be seen from Table 1, the present application adopts a double-layer sand inclusion process, which improves the strength and casting yield rate of the shell making method of precision casting large-diameter narrow air outlet impellers, and solves the casting defects of steel leakage, slag inclusion, and insufficient pouring caused by insufficient strength of the shell or the presence of gravel groups and pores inside the shell. The yield rate of the present application reaches 92~95%, the hardness reaches 127~133HB, the tensile strength reaches 574~587MPa, the salt spray test reaches 96~122h, and the weight difference before and after shell cleaning reaches 9500~9567g. Examples 1~3 achieve the optimized preparation of precision casting large-diameter narrow air outlet impeller shells through the reasonable selection and control of various process parameters; compared with the shell making methods of comparative examples 1~3, the present application improves the yield rate and optimizes the shell performance.

[0057] It can be seen from the results of Example 1 and Comparative Examples 4 to 7 that since Comparative Examples 4 to 7 contain only two or a single component, and the three components of the shell cleaning agent are not fully added, the residue stripping efficiency is reduced, the residue inside the shell is increased, and the yield and mechanical properties are affected; the disintegrator loosens the structure through penetration, magnesium oxide promotes chemical decomposition, and graphite powder improves thermal conductivity and lubricity. The three work together to achieve efficient residue stripping, and its performance is better than that of a single or two-component system, thereby comprehensively improving the comprehensive performance of the shell.

[0058] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for manufacturing a shell of a precision casting large diameter narrow outlet impeller, characterized in that: The following steps are involved: (1) Make wax molds and assemble trees, and remove surface release agents; (2) Prepare the first layer, the first layer contacts the wax model, use zirconium powder slurry for the first layer, the slurry viscosity is 40-45s, sprinkle zircon sand, and dry; (3) preparing the second layer, using zirconium powder slurry after being placed for 20 to 25 hours, adding molybdenum sand, and air-drying to obtain the second layer, and sealing the second layer to obtain the first sealing layer; (4) Preparation of sand layer: Mix the zircon powder slurry, zircon sand and mullite sand after 20-25 hours of storage to make mud. Use mud to seal the air outlets around the wax model and the bottom openings. After drying, fill the mullite sand from the top, shake and tamp it while filling, and then seal the top opening with mud and air dry. (5) Prepare the third and fourth layers using mullite powder slurry with a viscosity of 24-30s; sprinkle with mullite sand; (6) Prepare the fifth and sixth layers using mullite powder slurry and a shell cleaning agent. The viscosity of the mullite powder slurry is 12-16s and mullite sand is sprinkled. (7) The sixth layer is sealed to obtain a second sealing layer. The second sealing layer uses the mullite powder slurry of the fifth layer, and a shell cleaning agent is added at the same time, and air-dried.

2. The method for manufacturing a shell of a precision casting large-diameter narrow-outlet impeller according to claim 1, characterized in that: The zirconium powder slurry described in step (2) is prepared from zircon powder, silica sol, wetting agent and defoaming agent in a mass ratio of 200:950:1:

1.

3. The method for manufacturing a shell of a precision casting large-diameter narrow-outlet impeller according to claim 1, characterized in that: Step (4) The zirconium powder slurry after being placed for 20 to 25 hours, 80 to 100 mesh zircon sand and 60 to 80 mesh mullite sand are mixed in a mass ratio of 1:1:3 to form mud, and the air outlet around the impeller and the bottom opening are sealed with mud. After drying, mullite sand is filled from the top, and it is shaken and tamped while filling, and then the top opening is sealed with mud and air-dried.

4. The method for manufacturing a shell of a precision casting large-diameter narrow-outlet impeller according to claim 1, characterized in that: The mullite powder slurry described in step (5) is prepared by mixing mullite powder and silica sol in a mass ratio of 3 to 5:

1.

5. The method for manufacturing a shell of a precision casting large-diameter narrow-outlet impeller according to claim 1, characterized in that: The mullite powder slurry described in step (6) is prepared by mixing mullite powder and silica sol in a mass ratio of 3 to 3.5:

1.

6. The method for manufacturing a shell of a precision casting large-diameter narrow-outlet impeller according to claim 1, characterized in that: The shell cleaning agent described in step (6) is composed of a disintegrating agent, magnesium oxide and graphite powder.

7. The method for manufacturing a shell of a precision casting large-diameter narrow-air-outlet impeller according to claim 1, characterized in that: During the shell making process, each layer is dried for 8 to 12 hours after completion.

8. An impeller shell obtained by the method for manufacturing a shell of a precision casting large-diameter narrow-air-outlet impeller according to any one of claims 1 to 7, characterized in that: The air outlets around the mold cavity of the impeller shell and the bottom openings are sealed with mud, the mud at the air outlet is arranged between the two first sealing layers and inside the third layer, and mullite sand is filled between the mold cavity and the mud.

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