CN112719216A - Method for improving strength of oversized shell and controlling size of casting in precision investment casting process - Google Patents
Method for improving strength of oversized shell and controlling size of casting in precision investment casting process Download PDFInfo
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- CN112719216A CN112719216A CN202011451853.9A CN202011451853A CN112719216A CN 112719216 A CN112719216 A CN 112719216A CN 202011451853 A CN202011451853 A CN 202011451853A CN 112719216 A CN112719216 A CN 112719216A
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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
- B22C9/22—Moulds for peculiarly-shaped castings
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Abstract
The invention discloses a method for improving the strength of an oversized shell and controlling the size of a casting in the precision investment casting process, and belongs to the technical field of precision investment casting. The method comprises the following steps: preparing a ceramic rod with the required length and the diameter of 3-5 mm, and cleaning the surface of the ceramic rod. And when the shell preparation is finished at the 4 th layer, one end of the ceramic rod is bonded at the position of the shell, which is easy to expand, of the shell, the other end of the ceramic rod is bonded on the shell bearing structure, and the contact point of the ceramic rod and the shell is connected by using hot wax. And coating the ceramic rod with the surface layer coating which is the same as that of the shell, and spraying surface layer molding sand. And after the coating on the ceramic rod is completely dried, continuously executing the conventional shell making process, and wrapping the outer surface of the ceramic rod by the shell to form a whole with the shell. The ceramic rod supporting shell designed by the invention shows extremely high-temperature creep resistance in the process of pouring the oversized blade, and the size of the allowance-free precision casting is well controlled. The method has reasonable structure design, simple operation and high process stability.
Description
Technical Field
The invention relates to the technical field of investment precision casting, in particular to a method for improving the strength of an oversized shell and controlling the size of a casting in the investment precision casting process, which is suitable for preparing the shell for an oversized isometric crystal blade for a gas turbine and other fields relating to the preparation of the oversized shell by non-allowance investment precision casting.
Background
Turbine blades are the primary core components of advanced gas turbines. With the continuous improvement of the power of an advanced gas turbine, the size of a turbine blade is increased continuously, if the radial height of a last-stage moving blade and a last-stage static blade of a 300 MW-stage gas turbine reaches the magnitude of more than 700mm, the blade is difficult to prepare.
One of the key technical difficulties which cause difficulty in producing the oversized turbine blade is that a high-quality oversized shell for allowance-free precision casting is difficult to prepare. Because the super-large blade has large self weight and larger master alloy weight for single pouring, the ceramic shell bears extremely high pressure in the high-temperature pouring process, creep deformation is easy to occur, and the shell is induced to bulge, so that the profile size of the blade is seriously out of tolerance. Generally, increasing the number of the shell layers can effectively improve the strength of the shell and inhibit the shell from bulging. However, the increase of the number of the shell layers can slow down the solidification and heat dissipation of the casting, and is very unfavorable for controlling crystal grains and metallurgical shrinkage porosity on the surface of the casting. Therefore, it is more desirable to increase the strength of the shell while controlling the number of layers of the shell. Another key technical difficulty that makes oversized turbine blades difficult to produce is the dimensional control of the blades. Because the size of the blade is extremely large and the thickness difference of each part is large, the great thermal stress difference can be induced in the solidification process of the blade, so that the blade is seriously deformed, and the qualification rate of the blade is extremely low. Therefore, how to control the deformation of the casting during the solidification process is also an urgent problem to be solved.
Disclosure of Invention
The invention aims to provide a method for improving the strength of an oversized shell and controlling the size of a casting in the precision investment casting process, so as to meet the requirements of the preparation of an oversized blade of a gas turbine on the strength of a ceramic shell and the size control of the casting.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for improving the strength of an oversized shell and controlling the size of a casting in the precision investment casting process comprises the following steps:
(1) preparing a plurality of ceramic rods with required lengths and diameters of 3-5 mm, and cleaning the surfaces of the ceramic rods;
(2) preparing a ceramic shell of a casting by adopting a precision casting process, after the layer 4 is coated on the shell, bonding one end of a ceramic rod to the position of the shell where shell expansion is easy to generate, bonding the other end of the ceramic rod to a shell bearing structure, and connecting the ceramic rod with the shell contact point by using hot wax;
(3) after the ceramic rod is bonded, coating the ceramic rod with a surface layer coating which is the same as that of the shell, and spraying surface layer molding sand; and after the coating on the ceramic rod is completely dried, continuing to perform the shell making process after the 4 th layer, and wrapping the outer surface of the ceramic rod by the shell to form a whole with the shell.
In the step (1), the ceramic rod is an alumina ceramic rod, the cross sections of two ends of the ceramic rod are kept smooth, and a sharp cross section cannot exist.
In the step (2), in the preparation process of the ceramic shell, a surface layer, a transition layer, a reinforcing layer and a sealing slurry layer are sequentially coated on the wax pattern (taking 11 layers of the shell as an example, wherein the 1 st layer is the surface layer, the 2 nd, 3 rd and 4 th layers are the transition layers, the 5 th to 10 th layers are the reinforcing layers, and the 11 th layer is the sealing slurry layer).
In the step (2), after the fourth layer of sand scattering is finished, the shell is dried for 4-6 hours, then the whole shell is immersed in silica sol, taken out and dried for 4-6 hours, so that the ceramic rod is prevented from falling off due to insufficient adhesive force of the sand on the 4 th layer; and drying the shell, and then bonding the ceramic rod.
In the step (2), the wax material for bonding the ceramic rod and the shell is high-temperature wax material, and the wax material of the bonding point is as little as possible on the premise of ensuring firmness, so that the shell is prevented from generating larger hollow space after dewaxing, and the strength of the shell is reduced; after the hot wax connection, the coating operation is carried out after the standing for more than 10 minutes.
In the step (2), the ceramic rod is adhered to the surface of the shell as perpendicularly as possible to prevent the generation of hot spots during casting.
When the casting is a blade, in the step (2), ceramic rods are arranged on the blade basin and the blade back of the shell, and the number of the ceramic rods has no specific requirement so as to achieve the purposes of improving the strength of the shell and controlling the deformation of the casting.
The invention has the advantages and beneficial effects that:
the invention provides a method for improving the strength of an oversized shell for investment precision casting and controlling the size of a casting. Meanwhile, the ceramic rod shell supports the blade, so that the deformation of the blade caused by thermal stress in the solidification process is effectively inhibited. In addition, the method has small influence on the metallurgical quality of the casting, is not easy to generate defects such as shrinkage porosity, surface holes and the like, does not need to be polished during subsequent treatment, and greatly improves the production efficiency and the product percent of pass of the allowance-free precision casting blank.
Drawings
FIG. 1 is a diagram of a ceramic rod-supported shell-making shell of an oversized blade; wherein (a) is panoramic; (b) a close shot is obtained; (c) and (5) arranging a ceramic rod for supporting and then continuing to manufacture the shell.
FIG. 2 shows the three-coordinate detection results of the casting blade profile with or without ceramic rod support shell: wherein (a) there is no ceramic rod supporting shell; (b) the ceramic rod supports the shell.
FIG. 3 shows a scheme of directly connecting a ceramic rod with a wax piece; wherein (a) the ceramic rod is connected with the wax piece; (b) and (4) macroscopic shrinkage porosity at the blade support joint after casting.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.
Example 1:
in the embodiment, a ceramic rod with the diameter of 3mm is adopted to support and shell the blade shell (as shown in figure 1), and the profile size of a non-allowance precision casting obtained after shell making and pouring is compared with the profile size of a non-allowance precision casting obtained by pouring of an unsupported shell. The ceramic rod supporting and shell making process comprises the following steps:
step S1: preparing a blade shell by adopting a traditional allowance-free precision casting process, completing sand spraying of a 4 th transition layer, drying the shell for 5 hours, immersing the whole shell into silica sol, and drying for 5 hours for later use;
step S2: cutting a ceramic rod with the diameter of 3mm and the required length, processing the cross sections of two ends smoothly, and processing the surface of the ceramic rod cleanly;
step S3: one end of a ceramic rod is bonded to the middle position of the 4 th layer of the molded shell in the chord length direction after gum dipping, the other end of the ceramic rod is bonded and supported on the molded shell of the bearing structure of the molded shell, the ceramic rod is kept perpendicular to the surface of the molded shell as much as possible, the bonding positions at the two ends are coated by high-temperature wax, and the wax amount is controlled as little as possible. According to the steps, ceramic rods are bonded on the leaf basin and the leaf back type shell, and the distance between the ceramic rods is about 15 cm. After the hot wax connection, standing for 10 minutes and then carrying out subsequent operation;
step S4: and coating the ceramic rod with the surface layer coating which is the same as that of the shell, and spraying surface layer molding sand. And after the coating on the ceramic rod is completely dried, continuously executing a subsequent conventional shell making process.
The problems of the expansion shell of the ceramic rod support shell and the size of the blade profile of the allowance-free precision casting obtained by using the shell made by the ceramic rod support of the embodiment and the shell without the ceramic rod support in the same casting process are solved, and the comparison result of the three-coordinate detection of the blade is shown in figure 2.
Therefore, the shell prepared by the ceramic rod supporting structure is used for conventional casting, the high-temperature creep resistance of the blade body shell is obviously improved due to the support of the ceramic rod shell, the strength of the shell is improved, and the problem of shell expansion of the shell is thoroughly solved. Meanwhile, under the effect of the ceramic rod shell support, thermal stress deformation generated in the solidification process of the blade is inhibited.
Comparative example 1:
the ceramic rod supporting method for preparing the shell is a preferred scheme accumulated in a large amount of processes. The process schemes for preparing the shell by adding the ceramic rod support at the early stage are three. According to the scheme I, a ceramic rod is directly arranged on a wax piece; in the second scheme, the ceramic rod is arranged in the shell manufacturing process; and in the third scheme, the ceramic rod is arranged after the shell is sealed with slurry. The second scheme is the content of embodiment 1 of the present invention, and is not repeated in this embodiment. The first and third ceramic rod placement steps will now be briefly described as follows:
the first scheme is as follows:
step S1: cutting a ceramic rod with the diameter of 3mm and required by the length, processing the cross sections of two ends smoothly, and processing the surface of the ceramic rod cleanly;
step S2: connecting the two ends of a ceramic rod with wax rods with the length of 3mm and the diameter of 5mm respectively, connecting one end of the ceramic rod stuck with the wax rods to the middle position in the chord length direction of the blade body, connecting the other end of the ceramic rod to a wax piece bearing structure, keeping the ceramic rod vertical to the surface of the wax piece of the blade body as far as possible, and smearing high-temperature wax at the contact points of the two ends for connection. According to the steps, ceramic rods are bonded on the leaf basin and the leaf back type shell, and the distance between the ceramic rods is about 15 cm. After the hot wax connection, the subsequent operation is carried out after 10 minutes of standing;
step S3: and after the ceramic rod supporting structures are connected, carrying out a subsequent conventional shell manufacturing process.
Scheme II:
step S1: preparing a shell by using a conventional allowance-free precision casting shell-making process to obtain an 11-layer ceramic shell;
step S2: cutting a ceramic rod with the diameter of 5mm and the required length, processing the cross sections of two ends smoothly, and processing the surface of the ceramic rod cleanly;
step S3: and (3) arranging one direct end of the ceramic rod at the middle position of the 11 layers of ceramic shell blade chord length direction, connecting the other end of the ceramic rod on a shell bearing structure, smearing the joint by using a binder formed by mixing corundum powder and silica sol, drying for 6 hours after smearing, then carrying out secondary adhesion and drying, repeating the process for 4-8 times, finishing the preparation of the shell, and preparing for subsequent pouring.
The solution is a process where the ceramic rod support is directly connected to the wax piece (see fig. 3 a). According to the scheme, the purposes of improving the strength of the shell and controlling the solidification deformation of the casting can be achieved, however, the ceramic rod is connected with the wax piece through the wax rod, continuous vortex scouring is generated in the cavity position of the wax rod by high-temperature alloy liquid in the pouring and filling process, so that a thermal section is formed at the connecting position of the ceramic rod and the wax piece, and severe shrinkage porosity (shown in figure 3b) is easily generated in the area, and the blade is scrapped. In addition, the wax rod connected with the ceramic rod is thin and has insufficient strength, so that the wax rod is very easy to break in the shell manufacturing process, needs to be repaired repeatedly, and seriously influences the normal shell manufacturing progress. Therefore, the scheme is abandoned.
The third scheme is a process for connecting the ceramic rod support and the prepared ceramic shell. According to the scheme, the shell is prepared, the joint of the ceramic rod and the shell is weak, and the ceramic rod and the shell fall off in the pouring process, so that the supporting effect of the ceramic rod shell on the shell in the whole casting solidification process cannot be realized. If the number of times of coating the adhesive is increased, the shell thickness at the joint of the ceramic rod and the shell is obviously increased, and further, the local heat dissipation of the shell is difficult to induce, so that shrinkage porosity is formed. In addition, the scheme consumes more time besides the conventional shell manufacturing time, and the time cost is higher. Therefore, the scheme is abandoned for three times.
In summary, the second solution is a preferred process solution determined based on a large process accumulation. The ceramic shell prepared by the method of the invention obviously improves the shell strength in the processes of pouring and subsequent solidification, and thoroughly solves the problem of shell expansion caused by insufficient high-temperature strength of the oversized ceramic shell. Meanwhile, the deformation problem of the casting in the solidification process is also greatly solved, and the product percent of pass of the oversized blade blank is greatly improved. The method has the advantages of reasonable structural design, simple operation, high process stability and strong practicability, and is very suitable for industrial popularization.
Claims (7)
1. A method for improving the strength of an oversized shell and controlling the size of a casting in the precision investment casting process is characterized by comprising the following steps: the method comprises the following steps:
(1) preparing a plurality of ceramic rods with required lengths and diameters of 3-5 mm, and cleaning the surfaces of the ceramic rods;
(2) preparing a ceramic shell of a casting by adopting a precision casting process, after the layer 4 is coated on the shell, bonding one end of a ceramic rod to the position of the shell where shell expansion is easy to generate, bonding the other end of the ceramic rod to a shell bearing structure, and connecting the ceramic rod with the shell contact point by using hot wax;
(3) after the ceramic rod is bonded, coating the ceramic rod with a surface layer coating which is the same as that of the shell, and spraying surface layer molding sand; and after the coating on the ceramic rod is completely dried, continuing to perform the shell making process after the 4 th layer, and wrapping the outer surface of the ceramic rod by the shell to form a whole with the shell.
2. The method of improving the strength of oversized shells and controlling the size of castings during investment precision casting according to claim 1, wherein: in the step (1), the ceramic rod is an alumina ceramic rod, the cross sections of two ends of the ceramic rod are kept smooth, and a sharp cross section cannot exist.
3. The method of improving the strength of oversized shells and controlling the size of castings during investment precision casting according to claim 1, wherein: in the step (2), in the preparation process of the ceramic shell, a surface layer, a transition layer, a reinforcing layer and a sealing slurry layer are sequentially coated on the wax pattern.
4. The method of improving the strength of oversized shells and controlling the size of castings during investment precision casting according to claim 1, wherein: in the step (2), after the fourth layer of sand scattering is finished, the shell is dried for 4-6 hours, then the whole shell is immersed in silica sol, taken out and dried for 4-6 hours, so that the ceramic rod is prevented from falling off due to insufficient adhesive force of the sand on the 4 th layer; and drying the shell, and then bonding the ceramic rod.
5. The method of improving the strength of oversized shells and controlling the size of castings during investment precision casting according to claim 1, wherein: in the step (2), the wax material for bonding the ceramic rod and the shell is high-temperature wax material, and the wax material of the bonding point is as little as possible on the premise of ensuring firmness, so that the shell is prevented from generating larger hollow space after dewaxing, and the strength of the shell is reduced; after the hot wax connection, the coating operation is carried out after the standing for more than 10 minutes.
6. The method of improving the strength of oversized shells and controlling the size of castings during investment precision casting according to claim 1, wherein: in the step (2), the ceramic rod is adhered to the surface of the shell as perpendicularly as possible to prevent the generation of hot spots during casting.
7. The method of improving the strength of oversized shells and controlling the size of castings during investment precision casting according to claim 1, wherein: when the casting is a blade, in the step (2), ceramic rods are arranged on the blade basin and the blade back of the shell, and the number of the ceramic rods has no specific requirement so as to achieve the purposes of improving the strength of the shell and controlling the deformation of the casting.
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| CN202011451853.9A CN112719216A (en) | 2020-12-10 | 2020-12-10 | Method for improving strength of oversized shell and controlling size of casting in precision investment casting process |
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| CN202011451853.9A CN112719216A (en) | 2020-12-10 | 2020-12-10 | Method for improving strength of oversized shell and controlling size of casting in precision investment casting process |
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| JPS60121060A (en) * | 1983-12-05 | 1985-06-28 | Tokyo Tekko Kk | Production of nut for coupling screw threaded steel bar |
| JPS62230453A (en) * | 1986-03-31 | 1987-10-09 | Mitsubishi Metal Corp | Production of wax pattern |
| JP2007010261A (en) * | 2005-07-01 | 2007-01-18 | Noritz Corp | Tubular heat exchanger, and its manufacturing method |
| CN201921995U (en) * | 2010-12-01 | 2011-08-10 | 四川简阳海特有限公司 | Box expansion prevention device for casting sand box |
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| CN207119766U (en) * | 2017-07-31 | 2018-03-20 | 山东龙马重科有限公司 | The anti-swell support meanss of large-scale wind driven generator base casting |
| CN108127082A (en) * | 2017-12-22 | 2018-06-08 | 株洲九方铸造有限责任公司 | A kind of shell anti-deformation process |
| CN109940131A (en) * | 2019-03-26 | 2019-06-28 | 中国科学院金属研究所 | A method of reducing the formation of single crystal super alloy blade tenon internal defect defect |
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2020
- 2020-12-10 CN CN202011451853.9A patent/CN112719216A/en active Pending
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60121060A (en) * | 1983-12-05 | 1985-06-28 | Tokyo Tekko Kk | Production of nut for coupling screw threaded steel bar |
| JPS62230453A (en) * | 1986-03-31 | 1987-10-09 | Mitsubishi Metal Corp | Production of wax pattern |
| JP2007010261A (en) * | 2005-07-01 | 2007-01-18 | Noritz Corp | Tubular heat exchanger, and its manufacturing method |
| CN201921995U (en) * | 2010-12-01 | 2011-08-10 | 四川简阳海特有限公司 | Box expansion prevention device for casting sand box |
| CN104722706A (en) * | 2013-12-23 | 2015-06-24 | 东营市海河机械有限责任公司 | Open-type wide-plane casting anti-swelling method and wax mold |
| CN105855468A (en) * | 2016-04-13 | 2016-08-17 | 东方电气集团东方汽轮机有限公司 | Ceramic shell manufacturing method and method for manufacturing ceramic shell of turbine blade |
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