Method for Preheating a Gas Turbine Hollow Blade and Preparing a Coating with a Longitudinal Crack

Abstract

The invention discloses a method for preheating a hollow blade of a gas turbine and preparing a coating with longitudinal cracks, which includes: 1. Building a device for preheating the blade and preparing the coating; 2. Preheating the surface of the hollow blade of the gas turbine; 3. Spraying the hollow blade of the gas turbine. The method of the invention has simple steps. An air heater is used to preheat the rotating hollow blade of the gas turbine to improve the uniformity of the surface temperature distribution of the hollow blade of the gas turbine, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings for hollow blades of gas turbines, and particularly relates to a method for preheating hollow blades of gas turbines and preparing coatings with longitudinal cracks. Background Art

[0002] Gas turbines are one of the core power equipment in clean and efficient thermal power energy systems. The working environment of the hollow blades of gas turbines is harsh. Thermal barrier coatings are mainly applied to the blades of gas turbines, which not only have a thermal barrier effect but also can prevent damage to the blades caused by oxidation, corrosion, foreign object erosion, etc.

[0003] In order to improve the long-term service of thermal barrier coating materials, thermal barrier coatings with longitudinal crack structures have emerged. The existence of longitudinal cracks can increase the interfacial fracture resistance of the coating. The introduction of longitudinal cracks improves the strain tolerance of the coating, reduces the thermal stress accumulated in the coating due to the difference in thermal expansion coefficients between the ceramic layer and the bonding layer, and thus extends its service life.

[0004] At present, the preheating treatment of the substrate is usually achieved through a plasma spray gun. The thermal impulse that the plasma spray gun can provide in a short time is limited, which may lead to uneven temperature distribution on the blade. At the same time, when using a plasma spray gun for preheating, at the moment of contact between the plasma torch of the spray gun, the local temperature of the bonding layer will be too high, which will further cause oxidation of the bonding layer on the substrate. This oxidation reaction will change the physical and chemical properties of the bonding layer and may lead to early failure of the coating.

[0005] Therefore, a method for preheating hollow blades of gas turbines and preparing coatings with longitudinal cracks with reasonable design is needed. An air heater is used to preheat the rotating hollow blades of gas turbines to improve the uniformity of the surface temperature distribution of the hollow blades of gas turbines, so that the coating with longitudinal cracks can have a long service life while maintaining good performance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preheating hollow blades of gas turbines and preparing coatings with longitudinal cracks in view of the above-mentioned deficiencies in the prior art. The method steps are simple and reasonably designed. An air heater is used to preheat the rotating hollow blades of gas turbines to improve the uniformity of the surface temperature distribution of the hollow blades of gas turbines, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

[0007] To solve the above technical problem, the technical solution adopted by the present invention is: A method for preheating hollow blades of gas turbines and preparing coatings with longitudinal cracks, the method comprising the following steps:

[0008] Step 1. Set up a device for preheating blades and preparing coatings:

[0009] Step 101: Set up a blade preheating device; wherein, the blade preheating device includes a rotatable workbench and a preheating device arranged on the side of the rotatable workbench. The preheating device includes an air heater and an air outlet pipeline connected to the air heater, and the outlet of the air outlet pipeline is connected to the rotatable workbench.

[0010] Step 102: Set up an atmospheric plasma spraying device on the side of the rotatable workbench away from the air heater; wherein, the atmospheric plasma spraying device includes a base, a six-axis robotic arm arranged on the base, and a plasma spray gun arranged at the end of the six-axis robotic arm.

[0011] Step Two: Preheating the surface of the hollow blade of the gas turbine

[0012] The hollow blade of the gas turbine rotates with the rotatable workbench, and the air heater passes hot air into the hollow blade of the gas turbine for heating until the surface temperature of the hollow blade of the gas turbine reaches the set preheating temperature.

[0013] Step Three: Spraying the hollow blade of the gas turbine

[0014] Step 301: The air heater continuously passes hot air into the hollow blade of the gas turbine.

[0015] Step 302: Operate the plasma spray gun through the six-axis robotic arm to spray the surface of the hollow blade of the gas turbine to form a coating with longitudinal cracks.

[0016] Step 303: Obtain the cross-section of the hollow blade of the gas turbine with the coating having longitudinal cracks, and scan the cross-section of the hollow blade of the gas turbine with the coating having longitudinal cracks by using a scanning electron microscope to obtain the longitudinal crack density.

[0017] For the above method for preheating the hollow blade of the gas turbine and preparing the coating with longitudinal cracks, the rotatable workbench includes a bottom bracket, a workbench arranged on the bottom bracket, a turntable embedded in the workbench and flush with the workbench, and a motor driving member arranged at the bottom of the workbench and driving the turntable to rotate. The motor driving member includes an L-shaped bracket arranged at the bottom of the workbench, a hollow motor arranged on the L-shaped bracket, and an intermediate shaft passing through the hollow motor. The lower end of the intermediate shaft is connected to a rotary joint, the outlet of the air outlet pipeline is connected to the rotary joint, and a heat-resistant steel fixture for installing the hollow blade of the gas turbine is arranged on the turntable.

[0018] The above method for preheating a hollow blade of a gas turbine and preparing a coating with longitudinal cracks, wherein the intermediate shaft includes an outer shaft arranged coaxially and inner shafts extending from both ends of the outer shaft, the outer shaft is installed inside a hollow motor and is in driving connection, the upper end of the inner shaft extends into the turntable and is in driving connection, and the lower end of the inner shaft passes through the L-frame and is connected to a rotary joint;

[0019] Sealing plates are arranged between both ends of the outer shaft and the outer side wall of the inner shaft, and the cavity enclosed by the inner side wall of the outer shaft, the outer side wall of the inner shaft and the sealing plates is denoted as the outer cavity, and the inside of the inner shaft is hollow; the outlet of the inner shaft is located at the opening at the bottom of the blade root of the hollow blade of the gas turbine;

[0020] A lower end inlet pipe is arranged at the lower part of the outer shaft extending out of the L-frame, and an upper end inlet pipe is arranged at the upper part of the outer shaft close to the turntable, and both the lower end inlet pipe and the upper end inlet pipe are communicated with the outer cavity.

[0021] The above method for preheating a hollow blade of a gas turbine and preparing a coating with longitudinal cracks, step two, the specific process is as follows:

[0022] Step 201: Set a plurality of clamping frames on the workbench, and each clamping frame holds an infrared thermometer;

[0023] Step 202: Install the blade root of the hollow blade of the gas turbine on a heat-resistant steel fixture, the bottom surface of the blade root of the hollow blade of the gas turbine fits the surface of the turntable, and the blade tip of the hollow blade of the gas turbine faces upward;

[0024] Step 203: Operate the hollow motor to work, the turntable drives the hollow blade of the gas turbine to rotate, and at the same time, operate the air heater to work, the hot air output from the air outlet pipeline connected to the air heater passes through the inner shaft of the intermediate shaft, and the hot air output from the inner shaft outlet passes through the bottom of the blade root of the hollow blade of the gas turbine and enters the hollow blade of the gas turbine to heat the hollow blade of the gas turbine;

[0025] Step 204: During the rotation heating process of the hollow blade of the gas turbine, a plurality of infrared thermometers perform non-contact detection on the surface temperature of the hollow blade of the gas turbine according to the set sampling time until the surface temperature of the hollow blade of the gas turbine reaches the set preheating temperature.

[0026] The above method for preheating a hollow blade of a gas turbine and preparing a coating with longitudinal cracks, step 204, the specific process is as follows:

[0027] Step 2041: Process the multiple surface temperature values at any sampling time to obtain the average surface temperature and the standard deviation of the surface temperature;

[0028] Step 2042: If the standard deviation of the surface temperature at this sampling time is less than 10°C and the deviation between the average surface temperature and the set preheating temperature satisfies (-20°C, 20°C), then the preheating of the gas turbine hollow blade is stable and the surface temperature of the gas turbine hollow blade reaches the set preheating temperature.

[0029] For the above method for preheating the gas turbine hollow blade and preparing the coating with longitudinal cracks, after step three, the following process is executed:

[0030] Step A: Repeat step two and step three multiple times. At different set preheating temperatures, obtain the longitudinal crack density through a scanning electron microscope.

[0031] Step B: Use different set preheating temperatures as the abscissa and the longitudinal crack density corresponding to different set preheating temperatures as the ordinate to obtain a relationship diagram of the longitudinal crack density and the matrix preheating temperature.

[0032] For the above method for preheating the gas turbine hollow blade and preparing the coating with longitudinal cracks, during the process of hot air passing through the intermediate shaft in step 203, the lower inlet pipe is also connected to the inlet cooling water pipe, and the upper inlet pipe is connected to the return cooling water pipe to cool the outer cavity.

[0033] The present invention has the following advantages compared with the prior art:

[0034] 1. The method steps of the present invention are simple and reasonably designed, solving the problem of uneven preheating temperature distribution on the surface of the gas turbine hollow blade before spraying at present.

[0035] 2. The gas turbine hollow blade of the present invention is installed on a rotatable workbench and rotates with the rotatable workbench. During the rotation of the gas turbine hollow blade, it is preheated by an air heater. In this way, hot air is introduced while rotating to heat the gas turbine hollow blade, improving the uniformity of the surface temperature distribution of the gas turbine hollow blade.

[0036] 3. When the hot air output by the air heater of the present invention enters the gas turbine hollow blade through the bottom of the blade root of the gas turbine hollow blade for heating, the hot air overflows through the cooling holes on the hollow blade, forming a hot air film around the outer surface of the blade, reducing the heat exchange between the blade and the surrounding cold air during the blade preheating and coating preparation processes, and improving the preheating effect of the blade substrate; in addition, the hot air overflowing through the cooling holes on the hollow blade can also reduce the spraying thickness at the cooling holes when the plasma spray gun sprays the surface of the gas turbine hollow blade, reducing the subsequent treatment of the coating at the cooling holes.

[0037] 4. The present invention realizes preheating of the hollow blade of a gas turbine, reaches the set preheating temperature and the preheating is stable. Then, hot air is continuously introduced into the hollow blade of the gas turbine, and a plasma spray gun sprays the surface of the hollow blade of the gas turbine to form a coating with longitudinal cracks, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

[0038] In summary, the method steps of the present invention are simple and reasonably designed. An air heater is used to preheat the rotating hollow blade of the gas turbine to improve the uniformity of the surface temperature distribution of the hollow blade of the gas turbine, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

[0039] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0040] Figure 1 It is a schematic structural diagram of the blade preheating and coating preparation device of the present invention.

[0041] Figure 2 It is a schematic structural diagram of the rotatable workbench of the present invention.

[0042] Figure 3 It is a schematic structural diagram of the intermediate shaft of the present invention.

[0043] Figure 4 It is a flow chart of the method of the present invention.

[0044] 1 - air heater; 2 - outlet pipeline; 3 - bottom bracket;

[0045] 4 - hollow motor; 4-1 - turntable; 4-2 - L bracket;

[0046] 5 - six-axis robotic arm; 6 - intermediate shaft;

[0047] 6-1 - inner shaft; 6-2 - outer shaft; 6-3 - lower end inlet pipe;

[0048] 6-4 - upper end inlet pipe; 6-5 - limit connecting plate; 6-6 - sealing plate;

[0049] 6-7 - rotary joint; 7 - hollow blade of the gas turbine;

[0050] 8 - plasma spray gun; 9 - heat-resistant steel fixture; 10 - infrared thermometer;

[0051] 10-1 - clamping bracket; 11 - workbench; 12 - base. Detailed Embodiments

[0052] As Figures 1 to 4As shown, the method for preheating a hollow blade of a gas turbine and preparing a coating with longitudinal cracks includes the following steps:

[0053] The method includes the following steps:

[0054] Step 1: Set up the blade preheating and coating preparation device:

[0055] Step 101: Set up the blade preheating device; wherein, the blade preheating device includes a rotatable workbench and a preheating device arranged on the side of the rotatable workbench. The preheating device includes an air heater 1 and an air outlet pipeline 2 connected to the air heater 1, and the outlet of the air outlet pipeline 2 is connected to the rotatable workbench;

[0056] Step 102: Set up an atmospheric plasma spraying device on the side of the rotatable workbench away from the air heater 1; wherein, the atmospheric plasma spraying device includes a base 12, a six-axis robotic arm 5 arranged on the base 12, and a plasma spray gun 8 arranged at the end of the six-axis robotic arm 5;

[0057] Step 2: Preheat the surface of the hollow blade of the gas turbine:

[0058] The hollow blade 7 of the gas turbine rotates with the rotatable workbench, and the air heater 1 passes hot air into the hollow blade 7 of the gas turbine for heating until the surface temperature of the hollow blade 7 of the gas turbine reaches the set preheating temperature;

[0059] Step 3: Spray the hollow blade of the gas turbine:

[0060] Step 301: The air heater 1 continuously passes hot air into the hollow blade 7 of the gas turbine;

[0061] Step 302: Operate the plasma spray gun 8 through the six-axis robotic arm 5 to spray the surface of the hollow blade 7 of the gas turbine to form a coating with longitudinal cracks;

[0062] Step 303: Obtain the cross-section of the hollow blade of the gas turbine with the longitudinal crack coating, and scan the cross-section of the hollow blade of the gas turbine with the longitudinal crack coating using a scanning electron microscope to obtain the longitudinal crack density.

[0063] In this embodiment, the rotatable workbench includes a bottom bracket 3, a workbench 11 arranged on the bottom bracket 3, a turntable 4-1 embedded in the workbench 11 and flush with the workbench 11, and a motor driving member arranged at the bottom of the workbench 11 and driving the turntable 4-1 to rotate. The motor driving member includes an L-shaped bracket 4-2 arranged at the bottom of the workbench 11, a hollow motor 4 arranged on the L-shaped bracket 4-2, and an intermediate shaft 6 passing through the hollow motor 4. The lower end of the intermediate shaft 6 is connected to a rotary joint 6-7, and the outlet of the air outlet pipe 2 is connected to the rotary joint 6-7. A heat-resistant steel fixture 9 for installing the hollow blade 7 of the gas turbine is arranged on the turntable 4-1.

[0064] In this embodiment, the intermediate shaft 6 includes an outer shaft 6-2 arranged coaxially and inner shafts 6-1 extending from both ends of the outer shaft 6-2. The outer shaft 6-2 is installed in the hollow motor 4 and is in transmission connection. The upper end of the inner shaft 6-1 extends into the turntable 4-1 and is in transmission connection. The lower end of the inner shaft 6-1 passing through the L-shaped bracket 4-2 is connected to the rotary joint 6-7;

[0065] Sealing plates 6-6 are arranged between both ends of the outer shaft 6-2 and the outer side wall of the inner shaft 6-1. The cavity surrounded by the inner side wall of the outer shaft 6-2, the outer side wall of the inner shaft 6-1 and the sealing plates 6-6 is denoted as the outer cavity. The inside of the inner shaft 6-1 is hollow; the outlet of the inner shaft 6-1 is located at the bottom opening of the root of the hollow blade 7 of the gas turbine;

[0066] A lower end inlet pipe 6-3 is arranged at the lower part of the outer shaft 6-2 extending out of the L-shaped bracket 4-2, and an upper end inlet pipe 6-4 is arranged at the upper part of the outer shaft 6-2 close to the turntable 4-1. Both the lower end inlet pipe 6-3 and the upper end inlet pipe 6-4 are communicated with the outer cavity.

[0067] In this embodiment, step two is specifically as follows:

[0068] Step 201: Arrange a plurality of clamping brackets 10-1 on the workbench 11, and an infrared thermometer 10 is clamped on each clamping bracket 10-1;

[0069] Step 202: Install the root of the hollow blade 7 of the gas turbine on the heat-resistant steel fixture 9. The bottom surface of the root of the hollow blade 7 of the gas turbine is attached to the surface of the turntable 4-1, and the top of the hollow blade 7 of the gas turbine faces upward;

[0070] Step 203: Operate the hollow motor 4 to work, and the turntable 4-1 drives the hollow blade 7 of the gas turbine to rotate. At the same time, operate the air heater 1 to work. The hot air output from the air outlet pipe 2 connected to the air heater 1 passes through the inner shaft 6-1 of the intermediate shaft 6, and the hot air output from the outlet of the inner shaft 6-1 passes through the bottom of the root of the hollow blade 7 of the gas turbine and enters the hollow blade 7 of the gas turbine to heat the hollow blade 7 of the gas turbine;

[0071] Step 204: During the rotation and heating of the hollow blade 7 of the gas turbine, multiple infrared thermometers 10 perform non-contact detection on the surface temperature of the hollow blade 7 of the gas turbine according to the set sampling time until the surface temperature of the hollow blade 7 of the gas turbine reaches the set preheating temperature.

[0072] In this embodiment, step 204 is specifically as follows:

[0073] Step 2041: Process the multiple surface temperature values at any sampling time to obtain the average surface temperature and the standard deviation of the surface temperature.

[0074] Step 2042: If the standard deviation of the surface temperature at this sampling time is less than 10°C and the deviation between the average surface temperature and the set preheating temperature satisfies (-20°C, 20°C), then the preheating of the hollow blade 7 of the gas turbine is stable and the surface temperature of the hollow blade 7 of the gas turbine reaches the set preheating temperature.

[0075] In this embodiment, after step three, the following process is executed:

[0076] Step A: Repeat step two and step three multiple times. At different set preheating temperatures, obtain the longitudinal crack density through a scanning electron microscope.

[0077] Step B: Use the different set preheating temperatures as the abscissa and the longitudinal crack densities corresponding to the different set preheating temperatures as the ordinate to obtain a relationship diagram between the longitudinal crack density and the matrix preheating temperature.

[0078] In this embodiment, during the process of the hot air passing through the intermediate shaft 6 in step 203, the lower inlet pipe 6-3 is also connected to the inlet cooling water pipe, and the upper inlet pipe 6-4 is connected to the return cooling water pipe to cool the outer cavity.

[0079] In this embodiment, during actual use, the air heater 1 in step 301 continuously passes hot air into the hollow blade 7 of the gas turbine to maintain the surface temperature at the set preheating temperature during the spraying process.

[0080] In this embodiment, during actual use, a limit connecting plate 6-5 is provided at the top end of the inner shaft 6-1. A circular groove for the limit connecting plate 6-5 to be embedded is provided on the top surface of the turntable 4-1. The limit connecting plate 6-5 is embedded in the circular groove and connected to the turntable 4-1. The outer shaft 6-2 is located below the turntable 4-1. The limit connecting plate 6-5, the turntable 4-1, and the upper surface of the workbench 11 are flush.

[0081] In this embodiment, during actual use, the inner shaft 6-1 adopts a heat-insulated shaft to prevent the heat of the hot air conveyed in the inner shaft 6-1 from dissipating. Alternatively, the inlet cooling water pipe and the return cooling water pipe are connected to the cooling water tank. When hot air passes through the inner shaft 6-1, the outer cavity is cooled to prevent the temperature of the outer cavity from being too high and affecting the working performance of the hollow motor 4.

[0082] In this embodiment, during actual use, when the hot air output by the inner shaft 6-1 enters the root bottom of the hollow blade 7 of the gas turbine through the root bottom of the hollow blade 7 of the gas turbine and is heated, the hot air overflows through the cooling holes on the hollow blade, forming a hot air film around the outer surface of the blade, reducing the heat exchange between the blade and the surrounding cold air during the blade preheating and coating preparation processes, and improving the preheating effect of the blade substrate; in addition, the hot air overflows through the cooling holes on the hollow blade, which can also reduce the spraying thickness at the cooling holes when the plasma spray gun 8 sprays the surface of the hollow blade 7 of the gas turbine, reducing the subsequent treatment of the coating at the cooling holes.

[0083] In this embodiment, during actual use, the spraying of the surface of the hollow blade 7 of the gas turbine by the plasma spray gun 8 can refer to the preparation process parameters in the patent CN117072253B "Thermal Barrier Coating for High-Temperature Blades of Heavy Gas Turbines and Design, Manufacturing and Evaluation Methods".

[0084] In this embodiment, it should be noted that multiple infrared thermometers 10 are not shown in the figure; during actual use, multiple infrared thermometers 10 detect multiple parts on the surface of the hollow blade 7 of the gas turbine.

[0085] In this embodiment, during actual use, the sampling time set in step 204 is 1 s to 5 s.

[0086] In this embodiment, during actual use, the preheating temperature value range is set to 550 °C to 750 °C to generate a crack density of 0.5 cracks / mm to 6 cracks / mm, avoiding that too low a crack density will cause ineffective release of thermal stress, increasing the risk of coating spalling, and too high a crack density will weaken the mechanical strength of the coating and reduce the thermal shock resistance.

[0087] In this embodiment, it should be noted that the coating thickness on the surface of the hollow blade of the gas turbine is 300 microns to 1000 microns.

[0088] In this embodiment, it should be noted that the longitudinal cracks extend along the thickness direction of the coating on the surface of the hollow blade of the gas turbine.

[0089] In this embodiment, it should be noted that in this application, the coating relies on conventional atmospheric plasma, and the spraying process parameters are a power of 38 KW to 45 KW and a spraying distance of 60 mm to 100 mm. This is because by means of preheating measures, the temperature of the blade substrate is increased, effectively reducing the energy consumption in the first stage when the YSZ molten powder is sprayed onto the blade substrate instantaneously, and reserving sufficient energy for the subsequent second stage. Since the YSZ molten powder rapidly condenses in the first stage, generating a large number of microscopic reticular cracks, and further cools in the second stage, generating longitudinal cracks. When the spraying parameters are determined, the total energy of the YSZ molten powder is certain. Therefore, increasing the preheating temperature can effectively reduce the energy consumption in the first stage and reserve more energy for the initiation of longitudinal cracks in the second stage. Therefore, when preparing a coating with longitudinal cracks, it is necessary to control the preheating temperature of the substrate.

[0090] In summary, the method of the present invention has simple steps and reasonable design. An air heater is used to preheat the rotating hollow blades of a gas turbine to improve the uniformity of the surface temperature distribution of the hollow blades of the gas turbine, so that the coating with longitudinal cracks can have a long service life while maintaining good performance.

[0091] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent structural changes made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preheating a hollow gas turbine blade and preparing a coating with longitudinal cracks, characterized in that: The method comprises the following steps: Step 1: Build a blade preheating and coating preparation device: Step 101, constructing a blade preheating device; wherein the blade preheating device comprises a rotatable worktable and a preheating device arranged on the side of the rotatable worktable, the preheating device comprises an air heater (1) and an air outlet pipeline (2) connected to the air heater (1), and the outlet of the air outlet pipeline (2) is connected to the rotatable worktable; Step 102: Building an atmospheric plasma spraying device on the side of the rotatable worktable away from the air heater (1); wherein the atmospheric plasma spraying device comprises a base (12), a six-axis robot arm (5) disposed on the base (12), and a plasma spray gun (8) disposed at the end of the six-axis robot arm (5); Step 2: Preheating of the surface of the hollow gas turbine blades: The gas turbine hollow blade (7) rotates with the rotatable worktable, and the air heater (1) passes hot air into the gas turbine hollow blade (7) to heat it until the surface temperature of the gas turbine hollow blade (7) reaches a set preheating temperature; Step 3: Spraying of hollow gas turbine blades: Step 301: The air heater (1) continuously introduces hot air into the hollow blade (7) of the gas turbine; Step 302: using a six-axis robot arm (5) to operate a plasma spray gun (8) to spray the surface of the hollow blade (7) of the gas turbine to form a coating with longitudinal cracks; Step 303, obtaining a cross section of a gas turbine hollow blade with a longitudinal crack coating, and scanning the cross section of the gas turbine hollow blade with a longitudinal crack coating using a scanning electron microscope to obtain a longitudinal crack density; The rotatable workbench comprises a bottom bracket (3), a workbench (11) arranged on the bottom bracket (3), a turntable (4-1) embedded in the workbench (11) and flush with the workbench (11), and a motor drive component arranged at the bottom of the workbench (11) and driving the turntable (4-1) to rotate, the motor drive component comprising an L-frame (4-2) arranged at the bottom of the workbench (11), a hollow motor (4) arranged on the L-frame (4-2), and an intermediate shaft (6) passing through the hollow motor (4), the lower end of the intermediate shaft (6) being connected to a rotary joint (6-7), the outlet of the gas outlet pipeline (2) being connected to the rotary joint (6-7), and the turntable (4-1) being provided with a heat-resistant steel fixture (9) for mounting a hollow blade (7) of a gas turbine; The intermediate shaft (6) comprises a coaxially arranged outer shaft (6-2) and an inner shaft (6-1) extending from both ends of the outer shaft (6-2); the outer shaft (6-2) is installed in the hollow motor (4) and is transmission-connected thereto; the upper end of the inner shaft (6-1) extends into the turntable (4-1) and is transmission-connected thereto; the lower end of the inner shaft (6-1) passes through the L-frame (4-2) and is connected to a rotary joint (6-7); A sealing plate (6-6) is provided between the two ends of the outer shaft (6-2) and the outer side wall of the inner shaft (6-1); a cavity enclosed by the inner side wall of the outer shaft (6-2), the outer side wall of the inner shaft (6-1) and the sealing plate (6-6) is referred to as an outer cavity; the interior of the inner shaft (6-1) is hollow; the outlet of the inner shaft (6-1) is located at the bottom opening of the blade root of a hollow blade (7) of a gas turbine; A lower inlet pipe (6-3) is provided at the lower part of the outer shaft (6-2) extending out of the L frame (4-2), and an upper inlet pipe (6-4) is provided at the upper part of the outer shaft (6-2) close to the rotating disk (4-1), and both the lower inlet pipe (6-3) and the upper inlet pipe (6-4) are in communication with the outer cavity; Step 2: The specific process is as follows: Step 201, arranging a plurality of clamping frames (10-1) on a workbench (11), each clamping frame (10-1) clamping an infrared thermometer (10); Step 202, mounting the blade root of the gas turbine hollow blade (7) on the heat-resistant steel fixture (9), with the bottom surface of the blade root of the gas turbine hollow blade (7) in contact with the surface of the rotating disk (4-1), and the blade top of the gas turbine hollow blade (7) facing upwards; Step 203, operating the hollow motor (4) to drive the gas turbine hollow blade (7) to rotate, and at the same time, operating the air heater (1) to operate, and hot air output from the air outlet pipeline (2) connected to the air heater (1) passes through the inner shaft (6-1) of the intermediate shaft (6), and the hot air output from the outlet of the inner shaft (6-1) passes through the bottom of the blade root of the gas turbine hollow blade (7) and enters the gas turbine hollow blade (7), thereby heating the gas turbine hollow blade (7); Step 204: During the rotation and heating process of the gas turbine hollow blade (7), the plurality of infrared thermometers (10) perform non-contact detection of the surface temperature of the gas turbine hollow blade (7) according to a set sampling time until the surface temperature of the gas turbine hollow blade (7) reaches a set preheating temperature.

2. The method for preheating a hollow gas turbine blade and preparing a coating with longitudinal cracks according to claim 1, characterized in that: Step 204, the specific process is as follows: Step 2041, performing average and standard deviation processing on multiple surface temperature values ​​at any sampling time to obtain the surface temperature average and the surface temperature standard deviation; Step 2042: If the standard deviation of the surface temperature at the sampling time is less than 10°C, and the deviation between the average surface temperature and the set preheating temperature satisfies (-20°C, 20°C), the preheating of the gas turbine hollow blade (7) is stable, and the surface temperature of the gas turbine hollow blade (7) reaches the set preheating temperature.

3. The method for preheating a hollow gas turbine blade and preparing a coating with longitudinal cracks according to claim 1, characterized in that: After step 3, perform the following process: Step A, repeating step 2 and step 3 multiple times, obtaining the longitudinal crack density by scanning electron microscopy at different set preheating temperatures; Step B, using different set preheating temperatures as the horizontal coordinates and the longitudinal crack densities corresponding to the different set preheating temperatures as the vertical coordinates, to obtain a relationship diagram between the longitudinal crack density and the substrate preheating temperature.

4. The method for preheating a hollow gas turbine blade and preparing a coating with longitudinal cracks according to claim 1, characterized in that: In step 203, when the hot air passes through the intermediate shaft (6), the lower inlet pipe (6-3) is connected to the inlet cooling water pipe, and the upper inlet pipe (6-4) is connected to the return cooling water pipe, so as to cool the external cavity.

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