Casting method of gas turbine strut

Abstract

The invention discloses a gas turbine strut casting method and relates to the technical field of gas turbine part casting. The problems that due to the fact that the diameter of a bent angle in a cavity of a traditional casting mold is small, stress of a cast supporting column workpiece is concentrated, and then cracks are generated on the cast supporting column are solved. By increasing the diameter of the internal corner of the cavity of the upper die and the lower die and matching the smooth transition connection between the internal corner of the cavity and the air outlet edge of the blade body, the stress concentration at the internal corner of the cavity in the mold filling process of molten metal is reduced, and meanwhile, the surface roughness of the corner is reduced, so that the molten metal flows more smoothly at the corner, and the service life of the blade body is prolonged. And the stress is further reduced, so that the phenomenon that cracks appear at the bent corner of the cast support column is effectively avoided, and the quality and the yield of the cast support column are improved. The method is suitable for the technical field of gas turbine pillar casting.

Description

Technical Field

[0001] The invention relates to the technical field of gas turbine component casting, and in particular to a method for casting a gas turbine strut. Background Art

[0002] The gas turbine pillar is a load-bearing part of the QD280 unit. It provides stable physical support for the core casing, combustion chamber, turbine blades and other components of the gas turbine, bears axial, radial and torque loads, and has the characteristics of high temperature resistance. In the investment casting production process, cracks often appear at the corners of the casting pillars, which not only affects the appearance quality of the casting, but also may cause the mechanical properties of the casting to deteriorate or even be scrapped. The diameter of the internal corner of the traditional casting mold cavity is small, which leads to stress concentration of the cast pillar workpiece, which in turn leads to cracks in the casting pillar. Summary of the invention

[0003] The present invention provides a method for casting a gas turbine strut to solve the problem that the inner bend angle diameter of a conventional casting mold cavity is small, which leads to stress concentration in the cast strut workpiece and further causes cracks in the cast strut.

[0004] A method for casting a gas turbine prop of the present invention is as follows:

[0005] Step 1: Change the diameter of the inner corner 5 of the cavity 3 of the upper mold 1 and the lower mold 2 from the original 3mm to 40mm; and select the medium-temperature wax material with the grade of 6226;

[0006] Step 2: Make the shell. Apply a layer of slurry prepared by silica sol and cobalt aluminate on the surface. Use 80 / 100 mesh corundum sand as the sand material. Dry naturally for more than 17 hours.

[0007] Apply two layers of slurry made of silica sol and corundum powder, and use 80 / 100 mesh corundum sand as the sand material, and dry it naturally for more than 17 hours;

[0008] The transition layer uses a slurry made of silica sol and mullite powder, and the sand material is 30 / 60 mesh mullite powder. It is air-dried for 0.5 to 1 hour and air-dried for 3.5 to 4 hours.

[0009] The back layer uses a slurry made of silica sol and mullite powder, and the sand material is 16 / 30 mesh mullite powder. Apply 2 layers a day and air dry them with an interval of more than 4 hours.

[0010] The sealing slurry layer uses a slurry made of silica sol and mullite powder, which is air-dried for more than 17 hours;

[0011] Step 3: Dewaxing is carried out by steam. The dewaxing temperature is 140 - 160 °C, the pressure is 0.4 - 0.6 MPa, and the heat preservation time is 10 - 15 minutes; the shell roasting temperature is 850 °C ± 10 °C, and the heat preservation time is 1 - 1.5 hours;

[0012] Step 4: Pouring is carried out using a three-chamber equiaxed crystal vacuum casting furnace. The shell of the gating system is wrapped with heat preservation felt. After the furnace charge is melted and cleared, the shell is taken out from the roasting furnace and added to the mold shell chamber of the three-chamber equiaxed crystal vacuum casting furnace. The time used for this process should be minimized, not exceeding 1.5 minutes at most. The shell roasting temperature is 900 °C ± 10 °C, and the heat preservation time is more than 1 hour. The melted steel liquid is refined at a temperature of 1560 °C ± 10 °C for 3 - 4 minutes. After the steel liquid temperature drops to 1450 °C ± 10 °C, pouring is completed within 2 - 3 seconds. The shell can be broken 5 hours after pouring is completed;

[0013] Step 5: Clean the shell on the surface of the casting. There should be no knocking scars and no deformation caused by knocking on the casting surface. The casting should not be damaged during shell shaking. After shell cleaning, use a cutting disc to cut the riser and runner. The residual riser is ≤ 3 mm. The inner gate should not be polished lower than the original surface of the casting. After polishing, sandblasting treatment is carried out;

[0014] Step 6: Fluorescent penetrant inspection;

[0015] Furthermore, in Step 1, the surface roughness Ra value of the internal bend 5 of the cavity 3 is 0.4 μm, the surface roughness Ra value of the parting surface is 0.8 μm, and the gap of the parting surface is not greater than 0.05 mm;

[0016] Furthermore, the internal bend 5 of the cavity 3 is connected to the trailing edge of the blade body in a smooth transition manner;

[0017] Furthermore, in Step 2, for the first coating of the intermediate layer, the slurry prepared by adding cobalt aluminate to silica sol has a flow cup viscosity of 35 - 40 S;

[0018] Furthermore, in Step 2, for the second coating of the intermediate layer, the slurry prepared by adding corundum powder to silica sol has a flow cup viscosity of 8 - 13 S;

[0019] Furthermore, in Step 2, for the transition layer, the slurry prepared by adding mullite powder to silica sol has a flow cup viscosity of 8 - 13 S;

[0020] Furthermore, in Step 2, for the backing layer, the slurry prepared by adding mullite powder to silica sol has a flow cup viscosity of 8 - 13 S;

[0021] Furthermore, in Step 2, the working room temperature of the intermediate layer is 18 - 21 °C, the humidity is 45% - 70%, the working room temperature of the backing layer is 22 - 25 °C, and the humidity is 40% - 60%;

[0022] Further, in Step 6, water-washable penetrant inspection is used, with a sensitivity level of Class III, and the type of developer used is dry powder developer.

[0023] The present invention has the following beneficial effects compared with the prior art:

[0024] The present invention overcomes the shortcomings of the prior art. By increasing the diameter of the internal bend angle of the cavities of the upper die and the lower die, and then cooperating with the smooth transition connection between the internal bend angle of the cavity and the air outlet edge of the blade body, the stress concentration at the internal bend angle of the cavity during the filling process of the molten metal is reduced. At the same time, the surface roughness of the bend angle is reduced, making the flow of the molten metal at the bend angle smoother, further reducing the generation of stress, thereby effectively avoiding the phenomenon of cracks appearing at the bend angle of the casting strut, and improving the quality and yield rate of the casting strut. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a three-dimensional structural schematic diagram of the mold in a casting method of a gas turbine strut according to the present invention;

[0026] Figure 2 is the front view of the internal bend angle of the cavity of the existing casting mold;

[0027] Figure 3 is the front view of the internal bend angle of the cavity of the casting mold in a casting method of a gas turbine strut according to the present invention;

[0028] Figure 4 is the effect diagram of fluorescence penetrant inspection on the strut cast using the existing mold;

[0029] Figure 5 is the effect diagram of fluorescence penetrant inspection on the strut cast by a casting method of a gas turbine strut according to the present invention;

[0030] In the figure, upper die 1, lower die 2, cavity 3, bend angle 4 inside the cavity of the original casting mold, bend angle 5. DETAILED DESCRIPTION OF THE INVENTION

[0031] Detailed Description of Embodiment 1: In combination with Figure 1 , Figure 3 and Figure 5 to illustrate this embodiment, a casting method of a gas turbine strut according to this embodiment is as follows:

[0032] Step 1: Change the diameter of the internal bend angle 5 of the cavity 3 of the upper die 1 and the lower die 2 from the original 3 mm to 40 mm; and select medium-temperature wax material with the grade number 6226;

[0033] Step 2: Perform shell making. For the surface layer, apply a layer of slurry prepared from silica sol and cobalt aluminate, select corundum sand with a mesh size of 80 / 100 for the sand material, and air dry for more than 17 hours;

[0034] Apply two layers of slurry prepared from silica sol and corundum powder, select corundum sand with a mesh size of 80 / 100 for the sand material, and air dry for more than 17 hours;

[0035] For the transition layer, use a slurry prepared from silica sol and mullite powder, select mullite powder with a mesh size of 30 / 60 for the sand material, air dry for 0.5 - 1 hour, and air dry for 3.5 - 4 hours;

[0036] For the back layer, use a slurry prepared from silica sol and mullite powder, select mullite powder with a mesh size of 16 / 30 for the sand material, apply 2 layers per day, air dry, and the interval is greater than 4 hours;

[0037] For the sealant layer, use a slurry prepared from silica sol and mullite powder, and air dry for more than 17 hours;

[0038] Step 3: Dewaxing is carried out by steam dewaxing. The dewaxing temperature is 140 - 160 °C, the pressure is 0.4 - 0.6 MPa, and the heat preservation time is 10 - 15 minutes; the shell baking temperature is 850 °C ± 10 °C, and the heat preservation time is 1 - 1.5 hours;

[0039] Step 4: Pour using a three-chamber equiaxed crystal vacuum casting furnace. The shell of the gating system is wrapped with heat preservation felt. After the furnace charge is melted, take out the shell from the baking furnace and add it to the mold shell chamber of the three-chamber equiaxed crystal vacuum casting furnace. Try to shorten the time used in this process, and it should not exceed 1.5 minutes at most. The shell baking temperature is 900 °C ± 10 °C, and the heat preservation time is more than 1 hour. The molten steel is refined at a temperature of 1560 °C ± 10 °C for 3 - 4 minutes. After the temperature of the molten steel drops to 1450 °C ± 10 °C, pouring is completed within 2 - 3 seconds. It is allowed to break the shell 5 hours after pouring is completed;

[0040] Step 5: Clean the shell on the surface of the casting. There should be no bumps or scratches on the surface of the casting, nor any deformation caused by knocking on the casting. The casting should not be damaged during shell shaking. After shell cleaning, use a cutting disc to cut the riser and runner. The residual riser ≤ 3 mm. The inner gate should not be polished lower than the original surface of the casting. After polishing, perform sandblasting treatment;

[0041] Step 6: Fluorescent penetrant inspection;

[0042] In this specific implementation, by increasing the diameter of the internal bend angle of the cavities of the upper and lower dies and, in combination with a smooth transition connection between the internal bend angle of the cavity and the trailing edge of the blade body, the stress concentration at the internal bend angle of the cavity during the filling process of the molten metal is reduced. At the same time, the surface roughness of the bend angle is decreased, enabling the molten metal to flow more smoothly at the bend angle, further reducing the generation of stress, thus effectively avoiding the phenomenon of cracks appearing at the bend angle of the cast strut and improving the quality and yield rate of the cast strut.

[0043] Specific implementation method two: In combination with Figure 1 , Figure 3 and Figure 5 to illustrate this implementation method. This implementation method is a further limitation on the casting method described in the first specific implementation method. For a casting method of a gas turbine strut described in this implementation method, the Ra value of the surface roughness of the internal bend angle 5 of the cavity 3 in step one is 0.4 μm, the Ra value of the surface roughness of the parting surface is 0.8 μm, and the gap of the parting surface is not greater than 0.05 mm.

[0044] In this specific implementation method, by reducing the surface roughness of the bend angle 5, the molten metal flows more smoothly at the bend angle.

[0045] Specific implementation method three: In combination with Figure 1 , Figure 3 and Figure 5 to illustrate this implementation method. This implementation method is a further limitation on the casting method described in the second specific implementation method. For a casting method of a gas turbine strut described in this implementation method, a smooth transition connection is adopted between the internal bend angle 5 of the cavity 3 and the trailing edge of the blade body.

[0046] Specific implementation method four: In combination with Figure 1 , Figure 3 and Figure 5 to illustrate this implementation method. This implementation method is a further limitation on the casting method described in the first specific implementation method. For a casting method of a gas turbine strut described in this implementation method, in step two, a layer of slurry prepared by mixing silica sol and cobalt aluminate is applied to the surface layer, and the flow cup viscosity of the slurry is 35 - 40 S.

[0047] Specific implementation method five: In combination with Figure 1 , Figure 3 and Figure 5 to illustrate this implementation method. This implementation method is a further limitation on the casting method described in the first specific implementation method. For a casting method of a gas turbine strut described in this implementation method, in step two, two layers of slurry prepared by mixing silica sol and corundum powder are applied to the surface layer, and the flow cup viscosity of the slurry is 8 - 13 S.

[0048] Specific implementation method six: In combination with Figure 1 ,Figure 3 and Figure 5 To illustrate this embodiment, this embodiment is a further limitation on the casting method described in the first specific embodiment. For a casting method of a gas turbine strut described in this embodiment, in step 2, the cup viscosity of the slurry prepared with silica sol and mullite powder for the transition layer is 8 - 13S.

[0049] Specific embodiment seven: In combination with Figure 1 、 Figure 3 and Figure 5 To illustrate this embodiment, this embodiment is a further limitation on the casting method described in the first specific embodiment. For a casting method of a gas turbine strut described in this embodiment, in step 2, the cup viscosity of the slurry prepared with silica sol and mullite powder for the backing layer is 8 - 13S.

[0050] Specific embodiment eight: In combination with Figure 1 、 Figure 3 and Figure 5 To illustrate this embodiment, this embodiment is a further limitation on the casting method described in the first specific embodiment. For a casting method of a gas turbine strut described in this embodiment, in step 2, the working room temperature of the facing layer is 18 - 21°C and the humidity is 45% - 70%, and the working room temperature of the backing layer is 22 - 25°C and the humidity is 40% - 60%.

[0051] Specific embodiment nine: In combination with Figure 1 、 Figure 3 and Figure 5 To illustrate this embodiment, this embodiment is a further limitation on the casting method described in the first specific embodiment. For a casting method of a gas turbine strut described in this embodiment, in step 6, a water-washable penetrant inspection is used, the sensitivity level is level three, and the type of developer used is dry powder developer.

Claims

1. A method for casting a gas turbine strut, characterized in that: The casting method is as follows: Step 1: Change the diameter of the inner corner (5) of the cavity (3) of the upper mold (1) and the lower mold (2) from 3 mm to 40 mm; and select medium-temperature wax material with a grade of 6226; Step 2: Make the shell. Apply a layer of slurry prepared by silica sol and cobalt aluminate on the surface. Use 80 / 100 mesh corundum sand as the sand material. Dry naturally for more than 17 hours. Apply two layers of slurry made of silica sol and corundum powder, and use 80 / 100 mesh corundum sand as the sand material, and dry it naturally for more than 17 hours; The transition layer uses a slurry made of silica sol and mullite powder, and the sand material is 30 / 60 mesh mullite powder. It is air-dried for 0.5 to 1 hour and air-dried for 3.5 to 4 hours. The back layer uses a slurry made of silica sol and mullite powder, and the sand material is 16 / 30 mesh mullite powder. Apply 2 layers a day and air dry them with an interval of more than 4 hours. The sealing slurry layer uses a slurry made of silica sol and mullite powder, which is air-dried for more than 17 hours; Step 3: Dewaxing: steam dewaxing is adopted, the dewaxing temperature is 140-160℃, the pressure is 0.4-0.6MPa, and the holding time is 10-15 minutes; the shell baking temperature is 850℃±10℃, and the holding time is 1-1.5 hours; Step 4: Use a three-chamber equiaxed crystal vacuum casting furnace for pouring. The mold shell of the pouring system is wrapped with insulation felt. After the charge is cleared, the mold shell is taken out of the roasting furnace and added to the mold shell chamber of the three-chamber equiaxed crystal vacuum casting furnace. The time used for this process should be shortened as much as possible, not exceeding 1.5 minutes at most. The mold shell roasting temperature is 900℃±10℃, and the insulation time is more than 1 hour. The molten steel is refined at a temperature of 1560℃±10℃ for 3-4 minutes. After the temperature of the molten steel drops to 1450℃±10℃, the pouring is completed in 2-3 seconds. The shell is allowed to break 5 hours after the pouring is completed; Step 5. Clean the mold shell on the surface of the casting. There should be no scratches on the surface of the casting, and no deformation caused by knocking the casting. The casting should not be damaged when the shell is shaken. After the shell is cleaned, use a cutting disc to cut the pouring riser and runner. The residual gate should be ≤3mm. The grinding of the inner gate should not be lower than the original mold surface of the casting. After grinding, sandblasting is performed; Step 6: Fluorescent penetrant inspection.

2. A method for casting a gas turbine strut according to claim 1, characterized in that: In the step 1, the surface roughness Ra value of the inner bend (5) of the cavity (3) is 0.4 μm, the roughness Ra value of the parting surface is 0.8 μm, and the gap of the parting surface is no greater than 0.05 mm.

3. A method for casting a gas turbine strut according to claim 2, characterized in that: The inner bend (5) of the cavity (3) is connected to the air outlet edge of the blade body in a smooth transition manner.

4. The method for casting a gas turbine strut according to claim 1, characterized in that: In the step 2, the coating layer of the surface layer is made of a slurry prepared with silica sol and cobalt aluminate and has a flow cup viscosity of 35-40S.

5. The method for casting a gas turbine strut according to claim 1, characterized in that: The second coating layer in the surface layer in the step 2 uses a slurry prepared with silica sol and corundum powder, and the flow cup viscosity is 8-13S.

6. The method for casting a gas turbine strut according to claim 1, characterized in that: In the step 2, the transition layer is made of a slurry prepared by adding silica sol and mullite powder, and the flow cup viscosity is 8-13S.

7. The method for casting a gas turbine strut according to claim 1, characterized in that: In the step 2, the back layer is made of silica sol and mullite powder, and the flow cup viscosity of the slurry is 8-13S.

8. The method for casting a gas turbine strut according to claim 1, characterized in that: In the step 2, the surface layer workshop has a temperature of 18-21° C. and a humidity of 45%-70%, and the back layer workshop has a temperature of 22-25° C. and a humidity of 40%-60%.

9. The method for casting a gas turbine strut according to claim 1, characterized in that: In step six, a water-washing penetrant test is used, the sensitivity level is level three, and the type of developer used is a dry powder developer.

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