CN113210566A - Heat-conducting core material for forming cavity structure of precision casting and preparation method thereof - Google Patents
Heat-conducting core material for forming cavity structure of precision casting and preparation method thereof Download PDFInfo
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- CN113210566A CN113210566A CN202110380020.6A CN202110380020A CN113210566A CN 113210566 A CN113210566 A CN 113210566A CN 202110380020 A CN202110380020 A CN 202110380020A CN 113210566 A CN113210566 A CN 113210566A
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- forming
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
- B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/02—Sand moulds or like moulds for shaped castings
- B22C9/04—Use of lost patterns
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/10—Cores; Manufacture or installation of cores
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- Engineering & Computer Science (AREA)
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- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Molds, Cores, And Manufacturing Methods Thereof (AREA)
- Mold Materials And Core Materials (AREA)
Abstract
A heat-conducting core material for forming a cavity structure of a precision casting and a preparation method thereof are disclosed. The invention has the advantages of no exothermic reaction in the curing and forming process, higher high-temperature strength, good collapsibility and low cost, and simultaneously, the core material is the chromite powder with higher heat conductivity coefficient, so that the formation of heat nodes at the cavity of the casting is avoided, the generation of loose defects is inhibited, and the investment casting and forming requirements of hollow castings made of various metal materials can be met.
Description
Technical Field
The invention relates to a technology in the field of investment casting, in particular to a heat-conducting core material for forming a cavity structure of a precision casting and a preparation method thereof.
Background
The requirement of complex castings with cavity structures in the high-tech fields of aviation, aerospace and the like is increasing day by day, and the complete and accurate forming of the cavity structures is one of the manufacturing problems. In the traditional investment precision casting process, a hot-pressing injection ceramic core is usually adopted to form a casting cavity structure, but the prefabricated core is limited by a mold, the preparation difficulty is high, the cost is high, and the loose defect of the cavity structure is easily caused because the heat conductivity coefficient is lower, so that the casting is scrapped. Meanwhile, the prefabricated core is subjected to sintering treatment, so that the strength is high, and the cleaning difficulty is high. The ceramic slurry is poured into the cavity coated with a plurality of layers of shell molds, and then the slurry is solidified to form the mold core, which is a very simple and practical mold core in-situ forming process. In the prior art, a ceramic core is cast by taking ammonium dihydrogen phosphate, quartz and magnesium oxide as main components or ceramic powder such as fused quartz, ammonium chloride and silica sol are adopted to prepare core slurry, but the core slurry can generate heat during curing and is very likely to cause deformation of an internal wax mold, so that the core slurry is limited in use, and the ammonium chloride can change the pH value of the silica sol to cause gelation of the silica sol and form a three-dimensional network, so that the ceramic powder is bonded together and cured into the ceramic core. Because the ceramic core formed by casting and solidifying generally adopts ceramic powder with low heat conductivity coefficient such as fused quartz and the like as refractory filler, the core is slow in heat dissipation in the subsequent casting process, and easily causes the formation of thermal junctions at the cavity structure of the casting to cause the generation of loose defects.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides the heat-conducting core material for forming the cavity structure of the precision casting and the preparation method thereof, the heat-conducting core material has no exothermic reaction in the curing and forming process, has higher high-temperature strength, good collapsibility and low cost, and simultaneously, the core material is the chromite powder with higher heat conductivity coefficient, so that the formation of heat junctions at the cavity of the casting is avoided, the generation of loose defects is inhibited, and the requirement of investment casting and forming of hollow castings made of various metal materials can be met.
The invention is realized by the following technical scheme:
the invention relates to a preparation method of a heat-conducting core material for forming a cavity structure of a precision casting.
The dry mixing is preferably carried out by adopting a V-shaped mixer for 10min to 30 min.
Preferably, the stirring is carried out by adopting a powerful stirrer, and the stirring time is controlled to be less than or equal to 2 min.
The standing solidification refers to that: standing for 3-15 min after the cavity is filled with the mixed slurry.
The ferrochromium mineral powder specifically comprises the following components: cr (chromium) component2O3The mass percentage content is more than 44 percent, Fe2O3Less than 25 percent of SiO2The mass percentage of the ferrochromium ore powder is less than 3 percent.
The ferrochromium ore powder preferably has two particle sizes of 200-325 meshes and 70-140 meshes.
The mixed slurry comprises the following components in percentage by weight: 200-mesh 325-mesh ferrochromium ore powder: 30-40% of ferrochromium ore powder of 70-140 meshes: 30-40%, ammonium chloride: 0.5-2%, silica sol: 19.5 to 38 percent.
The purity of the ammonium chloride is analytical grade.
The silica sol has a mass percent purity of 29-31% and a pH of 9.7-10.5.
The heat-conducting core material with optimized collapsibility prepared based on the method has the following physical and chemical properties: the bending strength after drying is 6.0-8.5MPa, the high-temperature bending strength at 1000 ℃ is 4.0-6.4MPa, and the residual bending strength is 0.6-1.0MPa after roasting at 1500 ℃ for 2h and cooling to room temperature.
The invention relates to application of the heat-conducting core material, which is used for preparing a cavity structure of a precision casting, and specifically comprises the following steps: the method comprises the following steps of forming a hollow support plate of a high-temperature alloy turbine rear casing, forming a V-shaped annular narrow groove of a high-temperature alloy transition section support, forming an intermediate casing hollow support plate and the like.
Technical effects
The invention integrally solves the problems of in-situ pouring, curing and forming of the core forming the casting cavity structure and cleaning of the core from the interior of the casting cavity after casting. Compared with the prior art, the method consumes Na ions in the colloidal particles of the silica sol by adding ammonium chloride, so that the colloidal particles of the silica sol tend to aggregate, gel and solidify due to the consumption of the Na ions. The chromite powder selected by the invention has excellent chilling characteristic, and the heat conductivity is 4 times higher than that of zircon powder, so that a core formed by solidification in a closed or semi-open cavity has good heat dissipation performance, and the loose defect at the cavity of a casting can be avoided; the linear expansion coefficient of the ferrochromium mineral powder is small, so that the ferrochromium mineral powder cannot generate large size change in the roasting and pouring processes, can be well matched with most of shells, cannot generate the problem of shell expansion and cracking, and avoids the defect of molten steel leakage at the cavity of a casting. The high-heat-conductivity chromite core disclosed by the invention takes silica sol as a binder, has low residual strength, and is easy to remove from a casting cavity structure by adopting a mode of combining hydraulic sand removal and alkaline boiling. The prior art does not use chromite powder as a core material for casting.
Drawings
FIG. 1 is a schematic diagram of the ammonium chloride-promoted silica sol curing principle of the present invention;
FIG. 2 is a schematic view of an embodiment of a heat conducting core in use for forming an annular slot in a casting;
in the figure: a is an annular narrow groove on the fusible pattern of the embodiment; b is a heat conducting core of chromite powder; and c is an annular narrow groove on the casting.
Detailed Description
Example 1
As shown in fig. 1, the present embodiment includes the following steps:
step 1) weighing 3000g of 200-mesh 325-mesh ferrochromium mineral powder, 3000g of 70-140-mesh ferrochromium mineral powder and 200g of ammonium chloride, placing the weighed materials in a V-shaped mixer, and performing forced stirring dry mixing for 30min to obtain a premix for later use.
Step 2) weighing 620g of premix, pouring into a container filled with 380g of silica sol, and mixing for 2min by adopting a strong stirrer to obtain the core slurry.
And 3) directly pouring the mixed slurry or filling the mixed slurry into a cavity of the shell coated with the surface layer and the at least one back layer by using a tool such as a syringe and the like, standing for 15 minutes after the cavity is filled with the slurry, and curing the slurry. And then, the next layer of shell can be prepared continuously until the shell making process is finished.
In the ceramic core prepared by the formula, the bending strength after drying is 6.0MPa, the high-temperature bending strength at 1000 ℃ is 4.0MPa, and the residual bending strength after baking at 1500 ℃ for 2h and cooling to room temperature is 0.6MPa, which indicates that the ceramic core has good collapsibility.
The hollow support plate of the K4169 high-temperature alloy turbine rear casing with the contour diameter of 1130mm is molded by adopting the embodiment, and the result shows that the thickness of two side walls of the hollow support plate with the length of nearly 300mm is uniform, no fire running defect occurs, the metallurgical quality of the support plate is good, the support plate is composed of fine isometric crystals, and no loose defect occurs.
Example 2
The embodiment comprises the following steps:
step 1), weighing 3500g of 200-mesh 325-mesh ferrochromium ore powder, 3500g of 70-140-mesh ferrochromium ore powder and 100g of ammonium chloride, placing the weighed materials in a V-shaped mixer, and performing forced stirring dry mixing for 30min to obtain a premix for later use.
Step 2), weighing 710g of premix, pouring into a container filled with 290g of silica sol, and mixing for 2min by adopting a strong stirrer to obtain the core slurry.
And 3) directly pouring the mixed slurry or filling the mixed slurry into a cavity of the shell coated with the surface layer and the at least one back layer by using a tool such as a syringe and the like, standing for 7 minutes after the cavity is filled with the slurry, and curing the slurry. And then, the next layer of shell can be prepared continuously until the shell making process is finished.
In the ceramic core prepared by the formula, the bending strength after drying is 8.5MPa, the high-temperature bending strength at 1000 ℃ is 6.4MPa, and the residual bending strength after baking at 1500 ℃ for 2h and cooling to room temperature is 1.0MPa, which indicates that the ceramic core has good collapsibility.
As shown in FIG. 2, the K447A superalloy transition section support annular narrow groove with the profile diameter of 360mm is formed by adopting the embodiment, and the result shows that no spark-out defect occurs in the annular narrow groove with the depth of nearly 150mm, and the thin wall of the narrow groove is formed by fine isometric crystals and has no loose defect.
Example 3
The embodiment comprises the following steps:
step 1), 4000g of 200-mesh 325-mesh ferrochromium mineral powder, 4000g of 70-140-mesh ferrochromium mineral powder and 50g of ammonium chloride are weighed and placed in a V-shaped mixer for forced stirring and dry mixing for 30min to obtain a premix for later use.
Step 2) weighing 805g of premix, pouring into a container filled with 195g of silica sol, and mixing for 2min by adopting a strong stirrer to obtain the core slurry.
And 3) directly pouring the mixed slurry or filling the mixed slurry into a cavity of the shell coated with the surface layer and the at least one back layer by using a tool such as a syringe and the like, standing for 5 minutes after the cavity is filled with the slurry, and curing the slurry. And then, the next layer of shell can be prepared continuously until the shell making process is finished.
In the ceramic core prepared by the formula, the bending strength after drying is 7.4MPa, the high-temperature bending strength at 1000 ℃ is 5.8MPa, and the residual bending strength after baking at 1500 ℃ for 2h and cooling to room temperature is 0.8MPa, which indicates that the ceramic core has good collapsibility.
The hollow support plate of the TC4 titanium alloy intermediate casing, with the outline diameter of 1200mm, is molded by adopting the embodiment, and the result shows that the hollow support plate with the length of nearly 200mm has uniform thickness on two side walls, no fire running defect, good metallurgical quality, fine isometric crystal and no loose defect.
Compared with the prior art, the easy-collapsibility ceramic core for precision casting, which is prepared by the invention, has the bending strength of 6.0-8.5MPa after being dried and the high-temperature bending strength of 4.0-6.4MPa at 1000 ℃, and has the residual bending strength of 0.6-1.0MPa after being roasted for 2 hours at 1500 ℃ and cooled to room temperature after being solidified, thereby showing that the core has good collapsibility and is easy to remove from the interior of a casting cavity. The thermal conductivity of the traditional fused silica solidified core is only 1.951W/m2K, the heat conductivity of the chromite powder ceramic core reaches 8.376W/m2K, therefore, the application of the alloy can obviously improve the heat dissipation speed of the cavity structure of the casting and improve the metallurgical quality of the casting.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (10)
1. A preparation method of a heat-conducting core material for forming a cavity structure of a precision casting is characterized in that ferrochrome mineral powder and ammonium chloride are prepared, dry-mixed, added with silica sol, stirred to obtain mixed slurry, injected into a cavity of a shell coated with a surface layer and at least one back layer, and subjected to standing and curing;
the mixed slurry comprises the following components in percentage by weight: 200-mesh 325-mesh ferrochromium ore powder: 30-40% of ferrochromium ore powder of 70-140 meshes: 30-40%, ammonium chloride: 0.5-2%, silica sol: 19.5 to 38 percent.
2. The method for preparing the heat-conducting core material for forming the precision casting cavity structure according to claim 1, wherein the chromite powder specifically comprises: cr (chromium) component2O3The mass percentage content is more than 44 percent, Fe2O3Less than 25 percent of SiO2The mass percentage of the ferrochromium ore powder is less than 3 percent.
3. The method for preparing the heat-conducting core material for forming the cavity structure of the precision casting as claimed in claim 1, wherein the ferrochrome ore powder has two particle sizes of 200 meshes 325 and 70 meshes 140.
4. The method of claim 1, wherein the ammonium chloride is of analytical grade.
5. The method for preparing a heat conduction core material for forming a precision casting cavity structure according to claim 1, wherein the silica sol has a purity of 29 to 31 mass% and a pH of 9.7 to 10.5.
6. The method for preparing the heat-conducting core material for forming the cavity structure of the precision casting according to any one of claims 1 to 5, wherein the dry mixing is carried out by adopting a V-shaped mixer for mixing for 10min to 30 min.
7. The method for preparing the heat conduction core material for forming the cavity structure of the precision casting according to any one of claims 1 to 5, wherein the stirring is performed by using a powerful stirrer for a stirring time of 2min or less.
8. The method for preparing a heat conducting core material for forming a precision casting cavity structure according to claim 1, wherein the standing solidification is as follows: standing for 3-15 min after the cavity is filled with the mixed slurry.
9. A heat conducting core material with optimized collapsibility prepared by the method of any one of the preceding claims, wherein the bending strength after drying is 6.0-8.5MPa, the high temperature bending strength at 1000 ℃ is 4.0-6.4MPa, and the residual bending strength after baking at 1500 ℃ for 2h and cooling to room temperature is 0.6-1.0 MPa.
10. The use of the core material with optimized collapsibility and thermal conductivity as claimed in claim 9, in the preparation of a precision casting cavity structure, comprising: the method comprises the following steps of forming a hollow support plate of the high-temperature alloy turbine rear casing, forming a V-shaped annular narrow groove of a high-temperature alloy transition section support, and forming an intermediate casing hollow support plate.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202110380020.6A CN113210566A (en) | 2021-04-09 | 2021-04-09 | Heat-conducting core material for forming cavity structure of precision casting and preparation method thereof |
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| CN202110380020.6A CN113210566A (en) | 2021-04-09 | 2021-04-09 | Heat-conducting core material for forming cavity structure of precision casting and preparation method thereof |
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Application publication date: 20210806 |