Thermal spraying method for gas turbine shell

Abstract

The invention discloses a thermal spraying method for a gas turbine shell, and belongs to the technical field of thermal spraying. The method comprises the following steps: S1, cleaning the inner surface of a shell, and keeping the inner surface of the shell dry; s2, the non-spraying surface of the shell is protected through a high-temperature-resistant adhesive tape and a protection tool; s3, the inner surface of the shell is subjected to sand blasting treatment, and the surface of the shell is roughened through the mechanical scouring effect of sand grains on the surface of the shell; s4, the shell is fixed to a rotating platform, and the shell is preheated to 70-90 DEG C; s5, a spraying material is manufactured, specifically, the spraying material is prepared according to the proportion, stirred to be uniform and dried for use; s6, spraying process parameters are set, and thermal spraying is conducted through cooperation of a rotating platform and a mechanical arm spraying gun; and S7, the high-temperature-resistant adhesive tape and the protection tool are removed, and the surface of the coating is trimmed. By means of the process, the coating which is high in bonding strength with the shell and high in compactness can be obtained, and the high temperature resistance and corrosion resistance of the shell are improved.

Description

Technical Field

[0001] The invention relates to the technical field of thermal spraying, and in particular to a thermal spraying method for a gas turbine casing. Background Art

[0002] With the rapid development of gas turbines at home and abroad, thermal spraying, such as supersonic spraying and plasma spraying, is required for various components inside gas turbines. As a core component of heavy-duty gas turbines, the casing needs to be coated with plasma spraying to improve the high temperature resistance and corrosion resistance of the casing.

[0003] At present, the coating obtained by plasma spraying process usually has insufficient bonding strength between the coating and the workpiece due to unreasonable coordination of the previous surface treatment, spraying method and spraying parameters. For example, the roughness of the surface treatment is too low, and even if the spraying parameters are appropriate, the bonding strength of the coating will be unqualified; and the roughness of the surface treatment is appropriate, but the spraying parameters of the spray gun are unreasonable, so the bonding strength of the sprayed coating does not meet the requirements. The above reasons can easily cause the internal coating of the gas turbine casing to fall off and fail early, and the coating metallographic structure has low density, high porosity, and impurities, resulting in low density of the coating, reduced corrosion resistance of the coating, and more prone to failure during subsequent use, and cannot achieve long-term protection. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a thermal spraying method for a gas turbine casing, which can obtain a coating with high bonding strength and high density with the casing, thereby improving the high temperature resistance and corrosion resistance of the casing.

[0005] The technical solution adopted by the present invention is: A thermal spraying method for a gas turbine casing comprises the steps of: S1. Clean the inner surface of the shell and blow it dry to keep it dry. S2. Use high temperature resistant tape and protective tooling to protect the non-sprayed surface of the shell; S3, sandblasting the inner surface of the shell to roughen the shell surface through the mechanical scouring effect of sand particles on the shell surface; S4. Fix the shell on the rotating platform and preheat the shell to 70~90℃; S5, prepare spraying materials, mix the spraying materials according to the proportion and stir them evenly, and dry them for later use; S6. Setting spraying process parameters, and using the rotating platform and the manipulator spray gun to perform plasma spraying; S7. Remove the high temperature resistant tape and protective tooling, and trim the coating surface; The spraying process parameters in step S6 include: the rotation speed of the rotating platform is 25~30rev / min, the stepping speed of the robot spray gun is 4~5mm / rev, the flow rate of the main gas argon is 100~120SCFH, the flow rate of the auxiliary gas helium is 30~35SCFH, the powder feeding rate is 17~20g / min, the rotation speed of the powder feeding plate is 1.0~1.3rpm, the flow rate of the powder feeding carrier gas argon is 5~6SCFH, the spraying current is 745~755A, and the spraying voltage is 31~32V.

[0006] Furthermore, during the cleaning in step S1, an alkaline solvent is first used for degreasing and cleaning, and then cleaned with clean water.

[0007] Furthermore, when protecting the gas turbine casing in step S2, a high temperature resistant tape is firstly pasted on the non-sprayed surface of the casing, and then protective tooling is used for protection.

[0008] Furthermore, the protective tooling includes an upper protective piece and a lower protective piece, and the upper protective piece and the lower protective piece protect the non-sprayed surfaces of the upper end portion and the lower end portion of the shell respectively.

[0009] Furthermore, in the step S3, 30-mesh brown corundum sand is used for the sandblasting treatment, and the roughness of the shell surface after sandblasting is Ra7-10 μm.

[0010] Furthermore, in step S4, a ventilation hole is provided at the center of the rotating platform, and during the spraying process, ventilation is conducted from bottom to top through the ventilation hole to cool the inner cavity of the shell.

[0011] Furthermore, the components of the spraying material in step S5 are: C 0.8~1.0wt%, Fe 3.0~5.0wt%, Cr16.0~18.0wt%, Si 3.9~4.9wt%, B 3.2~3.5wt%, and the balance is Ni.

[0012] Furthermore, during spraying in step S6, the distance between the nozzle of the robot spray gun and the shell surface is set to 100 mm±5 mm.

[0013] Furthermore, during spraying in step S6, the thickness of a layer of coating sprayed by the robot spray gun is 12-15 μm, and the total spraying thickness is 160-210 μm.

[0014] The beneficial effects of the present invention are: (1) The present invention controls the roughness of the inner surface of the shell after sandblasting to Ra 7-10 μm. Based on this surface roughness and combined with an optimized spraying process, not only the bonding strength between the subsequent coating and the shell is ensured, but also the peak tip is exposed due to excessive roughness, which causes subsequent peak tip corrosion of the coating; (2) The present invention utilizes a rotating platform and a manipulator spray gun to perform plasma spraying, which can prevent the manipulator spray gun from having insufficient coating thickness or being unable to spray in individual areas due to rotation angle, space limitation, etc.; and by controlling the rotation speed of the rotating platform and the moving speed of the manipulator spray gun, the sprayed coating can be made uniform; in addition, the rotation speed of the rotating platform and the moving speed of the manipulator spray gun are also coordinated with the powder feeding rate, the rotation speed of the powder feeding plate, and the powder feeding carrier gas argon to control the thickness of a single-layer coating. Under the single-layer thickness, the metallographic structure of the coating has a high density and a low porosity, thereby further ensuring the bonding strength between the coating and the shell; (3) The present invention also improves the bonding strength between the coating and the shell by controlling the preheating temperature of the shell; (4) The bonding strength between the coating and the shell prepared by the spraying method of the present invention can reach above 60 MPa, with high bonding strength and good density, thereby ensuring the high temperature resistance and corrosion resistance of the shell and improving the service life of the shell. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a flow chart of the spraying process of the present invention; Figure 2 It is a structural schematic diagram of the protective tooling of the present invention; Figure 3 This is a metallographic structure photograph of the coating of Example 1 of the present invention at 200 times magnification; Figure 4 This is a metallographic structure photograph of the coating of Example 1 of the present invention at 500 times magnification.

[0017] Labels in the figure: 1. Shell; 2. Upper protective part; 3. Lower protective part. DETAILED DESCRIPTION

[0018] The present invention provides a thermal spraying method for a gas turbine casing. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] The present invention provides a thermal spraying method for a gas turbine casing, comprising the following steps: S1. Clean the inner surface of the shell and blow it dry to keep it dry.

[0020] In a preferred embodiment of the present invention, during the cleaning step S1, an alkaline solvent is first used for degreasing and then rinsed with clean water to remove oil stains on the shell surface and reduce the salt content on the shell surface.

[0021] S2. Use high temperature resistant tape and protective tooling to protect the non-sprayed surface of the shell.

[0022] In a preferred embodiment of the present invention, when protecting the gas turbine casing in step S2, firstly, a high temperature resistant tape is pasted on the non-sprayed surface of the casing, i.e., the outer surface and the end face of the casing, to prevent the coating from breaking when the protective tooling is removed later, which may cause irreversible damage; then, protective tooling is used for protection, and the material of the protective tooling is aluminum. The tooling made of aluminum can be processed by machine tools without welding, and can meet the tooling size requirements. Specifically, the protective tooling includes an upper protective part and a lower protective part, and the upper protective part and the lower protective part respectively protect the non-sprayed surfaces of the upper end and the lower end of the casing; more specifically, the upper protective part and the lower protective part are annular structures matching the outer ring of the casing, and the upper protective part and the lower protective part are provided with mounting holes matching the threaded holes of the gas turbine casing, which are used to connect and fix with the casing.

[0023] S3. The inner surface of the shell is sandblasted to roughen the shell surface through the mechanical scouring effect of sand particles on the shell surface.

[0024] In a preferred embodiment of the present invention, the sandblasting treatment in step S3 uses 30 mesh brown corundum sand particles to roughen the surface. The brown corundum sand particles have a uniform sandblasting density and obvious peaks and valleys on the sand surface after sandblasting, which is more conducive to subsequent coating adhesion. The roughness of the shell surface after sandblasting is 7~10μm, and the roughness in this range is beneficial to coating adhesion.

[0025] S4. Fix the shell on the rotating platform and preheat the shell to 70~90℃.

[0026] In a preferred embodiment of the present invention, in step S4, a ventilation hole is also provided at the center of the rotating platform. During the spraying process, the inner cavity of the shell is continuously cooled by ventilation from bottom to top through the ventilation hole. The temperature of the air introduced is 24-28°C to prevent the shell temperature from being too high due to long-term spraying, causing deformation or discoloration of the workpiece, resulting in an unsightly appearance, and even possibly affecting the internal structure of the shell. In addition, in step S4, the shell is also preheated before spraying, which can ensure that the shell and the coating have better bonding strength during the subsequent spraying process.

[0027] S5. Prepare spraying materials, mix the spraying materials according to the proportions, stir them evenly, and dry them for later use.

[0028] In a preferred embodiment of the present invention, the components of the spraying material in step S5 are: C 0.8~1.0wt%, Fe 3.0~5.0wt%, Cr 16.0~18.0wt%, Si 3.9~4.9wt%, B 3.2~3.5wt%, and the balance is Ni.

[0029] S6. Set the spraying process parameters and use the rotating platform and the manipulator spray gun to perform plasma spraying.

[0030] In a preferred embodiment of the present invention, the spraying process parameters in step S6 include: the rotation speed of the rotating platform is 25~30rev / min, the stepping speed of the robot spray gun is 4~5mm / rev, which is converted into a moving speed of the robot spray gun of 740~888mm / s, the flow rate of the main gas argon is 100~120SCFH, the flow rate of the auxiliary gas helium is 30~35SCFH, the powder feeding rate is 17~20g / min, the rotation speed of the powder feeding plate is 1.0~1.3rpm, the flow rate of the powder feeding carrier gas argon is 5~6SCFH, the spraying current is 745~755A, and the spraying voltage is 31~32V; and during spraying, the distance between the robot spray gun nozzle and the shell surface is set to 100mm±5mm.

[0031] In a preferred embodiment of the present invention, during spraying in step S6, the thickness of a layer of coating sprayed by the manipulator spray gun is 12 to 15 μm, the total spraying thickness is 160 to 210 μm, and the number of spraying times is 13 to 15 times. The present invention controls the spraying parameters, mainly the rotating platform speed, the stepping speed of the manipulator spray gun, the powder feeding rate, the powder feeding disk speed, and the powder feeding carrier gas argon, to control the thickness of the single-layer coating to be neither too thin nor too thick, so as to ensure the internal structure of the coating, even if the coating is densely organized and has low porosity, thereby ensuring the bonding strength between the coating and the shell, and at the same time, no stripes are generated, thereby improving the appearance quality. If the turntable speed and the manipulator spray gun stepping speed are not well matched, the coating appearance is prone to obvious stripes.

[0032] S7. After spraying is completed, the high temperature resistant tape and protective tooling are removed, and the coating surface is trimmed to obtain a shell with a coating.

[0033] Example 1

[0034] Reference Figure 1 In this embodiment, plasma spraying is performed on the inner surface of the gas turbine casing. The casing is made of ASTM-A182-GR-F22-CL3 carbon steel. The specific spraying steps are as follows: S1. Use alkaline solvent to remove oil and clean the inner surface of the shell, then rinse it with clean water and blow it dry to keep the inner surface of the shell dry; S2. Use high temperature resistant tape and protective tooling to protect the non-sprayed surface of the shell. That is, first stick the high temperature resistant tape on the non-sprayed surface of the shell, that is, the outer surface of the shell, and then use protective tooling for protection, such as Figure 2 As shown, the protective tooling is made of aluminum, and includes an upper protective member 2 and a lower protective member 3. The upper protective member 2 and the lower protective member 3 are annular structures matching the outer ring of the housing 1, and the upper protective member 2 and the lower protective member 3 are provided with mounting holes matching the threaded holes of the housing 1, which are used to connect and fix with the housing, and the upper protective member 2 and the lower protective member 3 are used to protect the non-sprayed surfaces of the upper end and the lower end of the housing 1 respectively; S3, use 30 mesh brown corundum sand to sandblast the inner surface of the shell, and the shell surface is coarsened by the mechanical scouring effect of the sand on the shell surface. The roughness of the shell surface after sandblasting is 8μm; S4. Fix the shell on a rotating platform with a ventilation hole in the center, and preheat the shell to 80°C; S5. Prepare a spraying material. The components of the spraying material are: C 0.8wt%, Fe 3.2wt%, Cr 16.5wt%, Si4.0wt%, B 3.2wt%, and the balance is Ni. Mix the spraying material according to the proportion and stir evenly, and dry it for later use. S6. Setting spraying process parameters, and using the rotating platform and the manipulator spray gun to perform plasma spraying; Specifically, the spraying process parameters include: the rotating platform speed is 25rev / min, the stepping speed of the robot spray gun is 4mm / rev, which is converted into a moving speed of 740mm / s for the robot spray gun, the flow rate of the main gas argon is 100SCFH, the flow rate of the auxiliary gas helium is 30SCFH, the powder feeding rate is 20g / min, the powder feeding plate speed is 1.2rpm, the flow rate of the powder feeding carrier gas argon is 5SCFH, the spraying current is 750A, the spraying voltage is 31.5V, and the power of the robot spray gun is 23.69kW; and when spraying, the distance between the robot spray gun nozzle and the shell surface is set to 100mm; in addition, when spraying, the inner cavity of the shell is cooled by ventilation from bottom to top through the ventilation hole in the center of the rotating platform; Specifically, the above-mentioned plasma spraying using a rotating platform and a manipulator spray gun means that the shell is fixed to the rotating platform through a lower protective part and bolts, the rotating platform drives the shell to rotate, the manipulator spray gun extends into the inner cavity of the shell, and the manipulator spray gun moves up and down under the drive of the manipulator stepper motor. During the spraying process, the rotating movement of the rotating platform and the up and down movement of the manipulator spray gun are coordinated to achieve spraying of the entire inner surface of the shell, and by controlling the rotation speed of the rotating platform and the moving speed of the manipulator spray gun, the sprayed coating can be uniform and without stripes. If the speeds of the two are not well coordinated, obvious stripes are likely to appear on the appearance of the coating; in addition, the rotation speed of the rotating platform and the moving speed of the manipulator spray gun are also coordinated with the powder feeding rate, the powder feeding plate rotation speed, and the powder feeding carrier gas argon to control the thickness of the single-layer coating. The metallographic structure density of the coating under the single-layer thickness is high and the porosity is low, thereby further ensuring the bonding strength between the coating and the shell; S7. After spraying is completed, the high temperature resistant tape and protective tooling are removed, and the coating surface is trimmed to obtain a shell with a coating.

[0035] The gas turbine casing is sprayed by the above plasma spraying process to obtain a coating with a coating thickness of 160-190 μm, a single-layer coating thickness of 12-15 μm, and 14 spraying times.

[0036] After testing, the bonding strength (ie, tensile strength) between the coating and the shell obtained in this embodiment is 60 MPa.

[0037] In addition, the coating of this embodiment 1 was sampled and subjected to metallographic examination. Figure 3 and Figure 4 As shown, from Figure 3 It can be seen from the figure that the thickness of the coating in Example 1 is 160-190 μm. Figure 3 and Figure 4 It can be seen that the metallographic structure of the coating is dense, the porosity is low, and there is basically no inclusion at the interface, which meets the requirement of ≤10%.

[0038] Example 2

[0039] In this embodiment, plasma spraying is performed on the inner surface of the gas turbine casing. The casing is made of ASTM-A182-GR-F22-CL3 carbon steel. The specific spraying steps are as follows: S1. Use alkaline solvent to remove oil and clean the inner surface of the shell, then rinse it with clean water and blow it dry to keep the inner surface of the shell dry; S2. Use high temperature resistant tape and protective tooling to protect the non-sprayed surface of the shell. That is, first stick the high temperature resistant tape on the non-sprayed surface of the shell, that is, the outer surface of the shell, and then use protective tooling for protection, such as Figure 2As shown, the protective tooling is made of aluminum, and includes an upper protective member 2 and a lower protective member 3. The upper protective member 2 and the lower protective member 3 are annular structures matching the outer ring of the housing 1, and the upper protective member 2 and the lower protective member 3 are provided with mounting holes matching the threaded holes of the housing 1, which are used to connect and fix with the housing, and the upper protective member 2 and the lower protective member 3 are used to protect the non-sprayed surfaces of the upper end and the lower end of the housing 1 respectively; S3, use 30 mesh brown corundum sand to sandblast the inner surface of the shell, and the shell surface is coarsened by the mechanical scouring effect of the sand on the shell surface. The roughness of the shell surface after sandblasting is 7μm; S4. Fix the shell on a rotating platform with a ventilation hole in the center, and preheat the shell to 70°C; S5. Prepare spraying material. The components of the spraying material are: C 0.9wt%, Fe 4.0wt%, Cr 17.0wt%, Si4.5wt%, B 3.5wt%, and the balance is Ni. Mix the spraying material according to the proportion and stir evenly, and dry it for later use. S6. Set the spraying process parameters, and use the rotating platform and the manipulator spray gun to perform plasma spraying; specifically, the spraying process parameters include: the rotating platform speed is 28rev / min, the stepping speed of the manipulator spray gun is 4.5mm / rev, which is converted into a moving speed of 820mm / s for the manipulator spray gun, the flow rate of the main gas argon is 110SCFH, the flow rate of the auxiliary gas helium is 33SCFH, the powder feeding rate is 17g / min, the powder feeding plate speed is 1.2rpm, the flow rate of the powder feeding carrier gas argon is 5SCFH, the spraying current is 750A, the spraying voltage is 31.1V, and the manipulator spray gun power is 23.86kW; and when spraying, the distance between the manipulator spray gun nozzle and the shell surface is set to 95mm; in addition, when spraying, the inner cavity of the shell is cooled by ventilation from bottom to top through the ventilation hole in the center of the rotating platform; S7. After spraying is completed, the high temperature resistant tape and protective tooling are removed, and the coating surface is trimmed to obtain a shell with a coating.

[0040] The gas turbine casing is sprayed by the above plasma spraying process to obtain a coating with a coating thickness of 170-200 μm, a single-layer coating thickness of 12-15 μm, and 14 spraying times.

[0041] After testing, the bonding strength (ie, tensile strength) between the coating and the shell obtained in this embodiment is 63.7 MPa.

[0042] Example 3

[0043] In this embodiment, plasma spraying is performed on the inner surface of the gas turbine casing. The casing is made of ASTM-A182-GR-F22-CL3 carbon steel. The specific spraying steps are as follows: S1. Use alkaline solvent to remove oil and clean the inner surface of the shell, then rinse it with clean water and blow it dry to keep the inner surface of the shell dry; S2. Use high temperature resistant tape and protective tooling to protect the non-sprayed surface of the shell. That is, first stick the high temperature resistant tape on the non-sprayed surface of the shell, that is, the outer surface of the shell, and then use protective tooling for protection, such as Figure 2 As shown, the protective tooling is made of aluminum, and includes an upper protective member 2 and a lower protective member 3. The upper protective member 2 and the lower protective member 3 are annular structures matching the outer ring of the housing 1, and the upper protective member 2 and the lower protective member 3 are provided with mounting holes matching the threaded holes of the housing 1, which are used to connect and fix with the housing, and the upper protective member 2 and the lower protective member 3 are used to protect the non-sprayed surfaces of the upper end and the lower end of the housing 1 respectively; S3, use 30 mesh brown corundum sand to sandblast the inner surface of the shell, and the shell surface is coarsened by the mechanical scouring effect of the sand on the shell surface. The roughness of the shell surface after sandblasting is 10μm; S4. Fix the shell on a rotating platform with a ventilation hole in the center, and preheat the shell to 90°C; S5. Prepare a spraying material. The components of the spraying material are: C 0.98wt%, Fe 5.0wt%, Cr 18.0wt%, Si4.9wt%, B 3.3wt%, and the balance is Ni. Mix the spraying material according to the proportion and stir evenly, and dry it for later use. S6. Set the spraying process parameters, and use the rotating platform and the manipulator spray gun to perform plasma spraying; specifically, the spraying process parameters include: the rotating platform speed is 30rev / min, the stepping speed of the manipulator spray gun is 5mm / rev, which is converted into a moving speed of 888mm / s for the manipulator spray gun, the flow rate of the main gas argon is 120SCFH, the flow rate of the auxiliary gas helium is 35SCFH, the powder feeding rate is 20g / min, the powder feeding plate speed is 1.3rpm, the flow rate of the powder feeding carrier gas argon is 6SCFH, the spraying current is 745A, the spraying voltage is 32V, and the power of the manipulator spray gun is 23.88kW; and when spraying, the distance between the manipulator spray gun nozzle and the shell surface is set to 105mm; in addition, when spraying, the inner cavity of the shell is cooled by ventilation from bottom to top through the ventilation hole in the center of the rotating platform; S7. After spraying is completed, the high temperature resistant tape and protective tooling are removed, and the coating surface is trimmed to obtain a shell with a coating.

[0044] The gas turbine casing is sprayed by the above plasma spraying process to obtain a coating with a coating thickness of 160-190 μm, a single-layer coating thickness of 13-15 μm, and 14 spraying times.

[0045] After testing, the bonding strength (ie, tensile strength) between the coating and the shell obtained in this embodiment is 70.5 MPa.

[0046] In addition, the coating of Example 3 was sampled and subjected to metallographic examination. Figure 3 and Figure 4 As shown, the coating of Example 3 has a thickness of 160-190 μm, a dense metallographic structure, low porosity, and substantially no inclusions at the interface, meeting the requirements of interface contaminants and porosity ≤ 10%.

[0047] Comparative Example 1

[0048] This comparative example is used to verify the effect of roughness on the bonding strength between the shell and the coating. The spraying process follows the process parameters of Example 3, and only the surface roughness of the shell is adjusted. The test results are shown in Table 1 below.

[0049] Table 1 Test results of comparative example 1

[0050] It can be seen from Table 1 that when the roughness is small, the bonding strength between the shell and the coating is relatively low. When the roughness is between Ra7 and 10 μm, the bonding strength can reach more than 60 MPa. As the roughness increases, the bonding strength increases. However, the roughness cannot be too large. If the roughness is too large, spike corrosion will easily occur on the shell surface.

[0051] Comparative Example 2

[0052] This comparative example is used to verify the effect of preheating on the bonding strength between the shell and the coating. The spraying process follows the process parameters of Example 3, and only the shell preheating temperature is adjusted. The test results are shown in Table 2 below.

[0053] Table 2 Test results of comparative example 2

[0054] It can be seen from Table 2 that when the preheating temperature is low, the bonding strength between the shell and the coating is relatively low. When the preheating temperature is between 70 and 90 °C, the bonding strength can reach about 70 MPa. However, the preheating temperature cannot be too high, otherwise the shell may be deformed.

[0055] Comparative Example 3

[0056] The main factors affecting coating thickness are the powder feeding rate and the moving speed of the robot spray gun. When the powder feeding rate is high, the thickness of the single layer coating is large. When the spray gun moves slowly, the thickness of the single layer coating is large. Conversely, the thickness of the single layer is small. During the spraying process, the thickness of the single layer coating is mainly adjusted by controlling the powder feeding rate and the moving speed of the robot spray gun.

[0057] The spraying process of this comparative example follows the process of Example 3, and the movement speed of the robot spray gun is controlled by adjusting the rotation speed of the rotating platform and the stepping speed of the robot spray gun, thereby controlling the thickness of the single-layer coating. The test results are shown in Table 3 below.

[0058] Table 3 Test results of comparative example 3 at different robot spray gun moving speeds

[0059] This embodiment also controls the thickness of a single layer of coating by adjusting the powder feeding rate, and the test results are shown in Table 4 below.

[0060] Table 4 Test results of comparative example 3 at different powder feeding rates

[0061] It can be seen from Tables 3 and 4 above that when the thickness of a single-layer coating is too small or too large, the bonding strength will be affected. The reason for this is that: when the single-layer coating is too small, the porosity of the single-layer coating itself will increase, which will increase the porosity of the overall coating, resulting in a decrease in tensile strength. In addition, the coating may generate internal stress during the curing process. The internal stress of a coating that is too thin is more difficult to distribute and release evenly, which makes the coating more likely to break when stretched. When the single-layer coating is too large, due to the different thermal expansion coefficients of the coating and the substrate, the expansion of the coating and the substrate is inconsistent when the temperature changes. A coating that is too thick is prone to generate greater internal stress, thereby affecting the tensile strength.

[0062] It should be noted that some parts not described in the present invention can be implemented by adopting or drawing on existing technologies.

[0063] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A thermal spraying method for a gas turbine casing, characterized in that: Includes steps: S1. Clean the inner surface of the shell and blow it dry to keep it dry. S2. Use high temperature resistant tape and protective tooling to protect the non-sprayed surface of the shell; S3, sandblasting the inner surface of the shell to roughen the shell surface through the mechanical scouring effect of sand particles on the shell surface; S4. Fix the shell on the rotating platform and preheat the shell to 70~90℃; S5, prepare spraying materials, mix the spraying materials according to the proportion and stir them evenly, and dry them for later use; S6. Setting spraying process parameters, and using the rotating platform and the manipulator spray gun to perform plasma spraying; S7. After spraying is completed, remove the high temperature resistant tape and protective tooling, and trim the coating surface; The spraying process parameters in step S6 include: the rotation speed of the rotating platform is 25~30rev / min, the stepping speed of the robot spray gun is 4~5mm / rev, the flow rate of the main gas argon is 100~120SCFH, the flow rate of the auxiliary gas helium is 30~35SCFH, the powder feeding rate is 17~20g / min, the rotation speed of the powder feeding plate is 1.0~1.3rpm, the flow rate of the powder feeding carrier gas argon is 5~6SCFH, the spraying current is 745~755A, and the spraying voltage is 31~32V.

2. A thermal spraying method for a gas turbine casing according to claim 1, characterized in that: During the cleaning in step S1, an alkaline solvent is first used for degreasing and cleaning, and then cleaned with clean water.

3. A thermal spraying method for a gas turbine casing according to claim 1, characterized in that: In the step S2, when protecting the gas turbine casing, a high temperature resistant tape is firstly pasted on the non-sprayed surface of the casing, and then protective tooling is used for protection.

4. A thermal spraying method for a gas turbine casing according to claim 3, characterized in that: The protective tooling comprises an upper protective piece and a lower protective piece, and the upper protective piece and the lower protective piece respectively protect the non-sprayed surfaces of the upper end portion and the lower end portion of the shell.

5. A thermal spraying method for a gas turbine casing according to claim 1, characterized in that: In step S3, 30-mesh brown corundum sand is used for sandblasting, and the roughness of the shell surface after sandblasting is Ra 7-10 μm.

6. A thermal spraying method for a gas turbine casing according to claim 1, characterized in that: In step S4, a ventilation hole is provided at the center of the rotating platform. During the spraying process, the ventilation hole ventilates from bottom to top to cool the inner cavity of the shell.

7. A thermal spraying method for a gas turbine casing according to claim 1, characterized in that: The components of the spraying material in step S5 are: C 0.8-1.0wt%, Fe 3.0-5.0wt%, Cr 16.0-18.0wt%, Si 3.9-4.9wt%, B 3.2-3.5wt%, and the balance is Ni.

8. A thermal spraying method for a gas turbine casing according to claim 1, characterized in that: During spraying in step S6, the distance between the nozzle of the robot spray gun and the shell surface is set to 100 mm ± 5 mm.

9. A thermal spraying method for a gas turbine casing according to claim 1, characterized in that: During spraying in step S6, the thickness of a layer of coating sprayed by the robot spray gun is 12-15 μm, and the total spraying thickness is 160-210 μm.

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