Plasma spraying preparation method of micro-nano double-layer PTFE coating on surface of flexible shaft steel wire

Abstract

The invention discloses a plasma spraying preparation method for a micro-nano double-layer PTFE coating on the surface of a flexible shaft steel wire, and particularly relates to the technical field of functional materials.The plasma spraying preparation method comprises the following steps that 1, a mandrel and a steel wire are installed on twisting equipment, and an inductive coupling plasma torch tube is installed on a driving guide rail parallel to the mandrel; 2, the pickling solution serves as a raw material, the pickling solution is atomized into micro-droplets through a feeding system and an air supply system, the micro-droplets are rapidly sprayed out of the torch pipe, and pickling spray is formed; 3, the twisting equipment is started, the steel wire is twisted around the mandrel, meanwhile, the driving guide rail is started, the twisted steel wire is subjected to acid pickling treatment through acid pickling spray sprayed out of the torch pipe, and the surface of the steel wire is roughened; 4, feeding of the pickling solution is stopped, high-flow gas is introduced into the torch pipe through the gas supply system to form high-speed gas flow, and the residual pickling solution on the surface of the flexible shaft is blow-dried; and 5, starting an inductively coupled plasma spraying system, injecting the PTFE emulsion serving as a raw material into plasma flame flow, driving a guide rail to move to enable the plasma flame flow to scan the steel wire on the surface of the flexible shaft, and depositing a PTFE coating on the surface of the steel wire. According to the method disclosed by the invention, the double-layered PTFE coating is deposited on the surface of the steel wire by using an inductive coupling plasma spraying process for the first time in the flexible shaft steel wire twisting process, so that one-step rapid preparation of the anti-corrosion coating is realized.

Description

Technical Field

[0001] The invention relates to the field of plasma spraying processing, and in particular to an inductively coupled plasma spraying method for preparing a micro-nano double-layer structure PTFE corrosion-resistant coating on the surface of a flexible shaft steel wire. Background Art

[0002] The flexible shaft is made by twisting multiple layers of steel wire around a core shaft. It has good strength and flexibility, and can realize the transmission of force and torque between non-straight lines and between different planes. It has significant advantages in working conditions that require flexible transmission or complex path transmission. Flexible shafts are widely used in key equipment such as automotive power systems and aircraft engines, and are key components for power transmission in actuator systems. The working environment medium of flexible shafts is mostly liquid fuels such as kerosene, hydraulic oil, and aviation fuel. Non-hydrocarbon substances in liquid fuels (sulfur, sulfur compounds, organic acids, moisture, microorganisms, etc.) will cause serious corrosion to metal flexible shafts that are immersed in them for a long time, especially the multiple layers of steel wire wrapped on the surface of the flexible shaft, which will seriously affect the performance of the flexible shaft and the safety of equipment operation.

[0003] Preparing a polymer coating with good chemical inertness on the surface of a workpiece is a common anti-corrosion method. Polymer materials hardly react with corrosive media, and can isolate the workpiece from the corrosive media to play an anti-corrosion function. In addition to using the inherent chemical inertness of the material to resist corrosion, preparing a super-hydrophobic coating is another effective emerging anti-corrosion method. The super-hydrophobic coating has a unique micron-nano double-layer surface structure, which is mainly composed of a micron-sized structure and a nano-sized structure covered thereon. According to the air layer theory of the super-hydrophobic surface, air can be trapped in the gap of the micron structure of the super-hydrophobic coating, which greatly reduces the contact area between the corrosive medium and the coating, and the corrosive medium is difficult to infiltrate the inside of the coating, thereby producing excellent anti-corrosion performance. Polytetrafluoroethylene (PTFE) material has excellent thermal stability, chemical stability, lubricity and hydrophobicity. Preparing a PTFE coating with a micro-nano double-layer structure on the surface of a flexible shaft can not only use the inherent chemical inertness of the PTFE material to resist the corrosion of non-hydrocarbon substances in the fuel, but also resist corrosion through the air layer trapped between the super-hydrophobic microstructures, which will greatly improve the corrosion resistance of the coating.

[0004] The preparation of PTFE coating mainly uses PTFE emulsion as raw material. Through air spraying, dipping, brushing and other processes, the PTFE emulsion is applied to the surface of the workpiece, and then the workpiece is cured (keep at 80°C for 10-20 minutes) and sintered (keep at 360-380°C for 15-30 minutes) in an oven to obtain a PTFE thin layer. The entire process has many steps and is time-consuming. The curing and sintering treatment in the oven limits the size of the workpiece. In addition, the surface of the PTFE thin layer prepared by the existing air spraying, dipping, brushing and other processes is flat and cannot form the micro-nano double-layer surface structure required for the super-hydrophobic surface. Summary of the invention

[0005] In view of the corrosion resistance requirements of the flexible shaft surface and the limitations of the existing double-layer PTFE coating preparation process, the present invention provides a method for preparing a micro-nano double-layer PTFE coating on the surface of a steel wire wound on a flexible shaft by inductively coupled plasma spraying. At the same time, the method proposed in the present invention also combines the four processes of "steel wire twisting, steel wire pickling and roughening, drying, and PTFE spraying". When using the same equipment and the same workstation, the complete process of "steel wire twisting-steel wire pickling and roughening-drying-PTFE coating preparation" can be achieved by only changing different raw materials and gases, which greatly improves the preparation efficiency.

[0006] The plasma spraying preparation method of the micro-nano double-layer PTFE coating on the surface of the flexible shaft steel wire proposed in the present invention comprises the following steps: Step 1: Install the mandrel on the rotating table fixture, install the steel wire on the stranding machine, and install the inductively coupled plasma torch on the driving rail parallel to the mandrel; in all processes, the axis direction of the torch is always perpendicular to the mandrel; Step 2: Without starting the inductively coupled plasma spraying system, use the pickling solution as the raw material, start the feeding system to inject the pickling solution into the torch tube, and start the gas supply system at the same time, use a large flow of gas to further atomize and accelerate the pickling solution, and quickly spray it out of the torch tube to form a pickling spray; Step 3: Steel wire twisting and steel wire pickling and roughening: Start the twisting equipment to twist the steel wire on the mandrel; at the same time, start the driving guide rail to move the torch tube along the shaft core, and pickle the twisted steel wire with the pickling spray sprayed from the torch tube to roughen its surface; Step 4: Blow dry: turn off the feeding system and stop feeding the pickling solution; introduce a large flow of gas into the torch through the gas delivery system to form a high-speed airflow, and at the same time start the drive guide to move the torch along the axis core, and use the high-speed airflow in the torch to blow dry the pickling solution remaining on the surface of the flexible shaft; Step 5: PTFE spraying: Start the inductively coupled plasma spraying system, use PTFE emulsion as raw material, inject it into the plasma flame flow in the torch tube through the feeding system, and start the driving guide rail at the same time to make the torch tube move along the axis core. The plasma flame flow in the torch tube scans the surface of the soft shaft steel wire to deposit the PTFE coating on the surface of the steel wire; through the reciprocating motion of the driving guide rail, multiple layers of coating are deposited on the surface of the soft shaft steel wire.

[0007] Inductively coupled plasma spraying is a process that generates a high-frequency electric field through a radio frequency power supply, thereby exciting a plasma gas (such as argon, nitrogen, etc.) to form a plasma, which is ejected from the outlet of the torch tube to form a high-temperature and high-speed flame flow. Compared with the traditional DC plasma spraying using powder as raw material, in the inductively coupled plasma spraying process, the raw material is directly transported to the center of the torch tube, the raw material is heated more evenly and fully, and the coating preparation can be completed under the premise of consuming very little raw material. The present invention proposes for the first time a method for preparing a double-layer structure PTFE coating on the surface of a soft shaft steel wire in one step through an inductively coupled plasma spraying process. During the inductively coupled plasma spraying process, a PTFE emulsion is transported to a high-temperature and high-speed plasma flame flow. PTFE is atomized into tiny droplets in the flame flow, and the solvent in the droplets evaporates rapidly to form tiny PTFE particles. The PTFE particles are heated in the flame flow and impact the workpiece surface in a molten / semi-molten state to form a PTFE coating. Compared with the traditional "spraying / dipping / brushing-curing-sintering" process, the PTFE emulsion in the inductively coupled plasma spraying process completes the "curing-sintering" process in the high-temperature flame flow, realizing the one-step preparation of the PTFE coating on the workpiece surface, without the need for curing and sintering after the spraying is completed. In addition, in the method described in the present invention, while preparing the PTFE coating in one step, the PTFE coating can be made to present a micro-nano double-layer structure, that is, a coating with a micro-nano double-layer structure is prepared in one step. Many existing technologies need to first prepare the PTFE coating through the traditional "spraying / dipping / brushing-curing-sintering" process, and then combine it with post-processing processes such as plasma etching and laser etching to prepare a microstructure on the PTFE coating. Compared with the existing technology, the method for preparing a micro-nano double-layer structure PTFE coating in one step described in the present invention greatly improves the preparation efficiency, saves equipment investment costs, and has important engineering significance for the corrosion resistance requirements of the flexible shaft surface. Furthermore, the four different processes of "steel wire twisting, steel wire pickling and roughening, blow drying, and PTFE spraying" in the steps are completed by the same equipment and the same work station.

[0008] Furthermore, the steel wire twisting process and the steel wire pickling and roughening process are carried out simultaneously, that is, the twisted steel wire is pickled during the steel wire twisting process.

[0009] Furthermore, the steel wire is made of stainless steel wire, alloy steel wire or nickel-based alloy wire, and the diameter of the steel wire is 0.2-1 mm.

[0010] Furthermore, the pickling solution used is 100-250 g / L of hydrochloric acid, sulfuric acid, nitric acid or a mixture thereof.

[0011] Furthermore, the concentration of the PTFE emulsion used is 20% to 60%.

[0012] Furthermore, the PTFE coating presents a micro-nano double-layer structure. The PTFE coating is prepared in one step without curing and sintering, and the coating presents a micro-nano double-layer structure after preparation without any post-processing process.

[0013] Furthermore, the micro-nano double-layer structure is a micron-sized convex hull structure formed on the surface of the PTFE coating, and there are obvious gaps between the convex hull structures, and the surface of the convex hull structure has submicron / nano-sized particles.

[0014] Compared with the prior art, the present invention has the following innovative features: (1) The present invention innovatively uses an inductively coupled plasma spraying process to prepare a PTFE coating on the surface of a steel wire wound around a flexible shaft in one step, without the need for a curing and sintering process, and is a one-step rapid preparation process; (2) The method described in the present invention combines the four processes of "steel wire twisting - steel wire pickling and roughening - blow drying - PTFE spraying" on the same equipment and the same workstation, greatly shortening the process flow and improving the preparation efficiency; (3) The present invention combines a liquid PTFE emulsion with a plasma spraying device, and the prepared PTFE coating can present a micro-nano double-layer structure after spraying, achieving super-hydrophobic properties, without the need for post-processing processes such as etching in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the process of pickling the steel wire using a torch during the steel wire winding process; Figure 2 This is a schematic diagram of the process of using a torch to dry the pickled steel wire; Figure 3 Schematic diagram of the process of depositing PTFE coating on the surface of flexible shaft steel wire by inductively coupled plasma spraying process; Figure 4 The surface microstructure of the PTFE coating on the flexible shaft surface in Example 1, wherein (a) is a low-magnification surface microstructure, and (b) is a high-magnification surface microstructure; Figure 5 is the water contact angle of the PTFE coating in Example 1; Figure 6 The surface microstructure of the PTFE coating on the flexible shaft surface in Example 2, wherein (a) is a low-magnification surface microstructure, and (b) is a high-magnification surface microstructure; Figure 7 is the water contact angle of the PTFE coating in Example 2.

[0016] In the figure: 1. Rotary table fixture; 2. Mandrel; 3. Steel wire; 4. Stranding machine; 5. High frequency generator; 6. Induction coil; 7. Gas supply system; 8. Torch; 9. Drive rail; 10. Pickling solution; 11. Peristaltic pump; 12. Atomizing air pump; 13. Atomizing nozzle; 14; Pickling spray; 15. Blow-drying air flow; 16. Plasma flame flow; 17. PTFE emulsion. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with the accompanying drawings and embodiments. In order to better illustrate the coating preparation process and method of the present invention, the flexible shaft steel wire twisting system, inductively coupled plasma spraying system, feeding system and other related devices used in the method of the present invention are described below. Figure 1-3 As shown, the flexible shaft steel wire twisting system mainly includes a rotating table fixture 1, a mandrel 2, a steel wire 3 and a stranding machine 4. During the steel wire twisting process, the mandrel 2 is installed in the rotating table fixture 1 to rotate, and the stranding machine 4 twists the steel wire 3 on the mandrel 2. The inductively coupled plasma spraying device mainly includes a high-frequency generator 5, an induction coil 6, a gas supply system 7, a torch 8, and a drive guide 9. Among them, the torch 8 is a standard Fassel type, which is composed of three layers of coaxial quartz tubes. The gas supply system 7 is connected to different layers of the torch 8 to transport gas therein, wherein the gas flow rate input to the middle layer of the torch 8 is small, and it is mainly ionized to generate a plasma flame flow, while the gas flow rate input to the outer layer of the torch 8 is large, and it is mainly used to cool the torch 8 to prevent it from overheating and ablation. When the high-frequency generator 5 is started, a high-frequency current is generated in the coil 6, thereby forming a high-frequency magnetic field, and the gas passed into the torch 8 is ionized into a high-temperature plasma. The torch tube 8 is installed on the driving guide rail 9, the driving guide rail 9 is parallel to the core shaft, and the axis of the torch tube 8 is kept perpendicular to the core shaft 2. The feeding system includes raw materials (acid washing solution 10 or PTFE emulsion 17), peristaltic pump 11, atomizing air pump 12 and atomizing nozzle 13. The feeding system can atomize the raw materials and transport them to the torch tube 8. Figure 1-3 The arrow shown represents the direction of movement of the torch 8 .

[0018] In the present invention, the above-mentioned flexible shaft steel wire twisting system, inductively coupled plasma spraying device and feeding system together constitute an integrated flexible shaft steel wire twisting and spraying equipment. The flexible shaft steel wire twisting system is used for twisting the flexible shaft steel wire, and is also used as a workpiece clamping device for plasma spraying. The inductively coupled plasma spraying device is used for plasma spraying, pickling, roughening and blow-drying. In this way, the four different processes of "steel wire twisting, steel wire pickling, roughening, blow-drying and PTFE spraying" are completed using the same equipment and the same workstation, which greatly improves the preparation efficiency.

[0019] In addition, in order to more clearly state the formation of the micro-nano double-layer structure in the present invention, the coating deposition principle in the method of the present invention is described. When the PTFE emulsion is injected into the plasma flame flow, it is atomized into a large number of tiny droplets under the action of the high-speed flame flow, and these droplets undergo processes such as solvent volatilization and internal particle agglomeration of the droplets to form extremely small molten or partially molten particles. When the plasma flame flow carrying a large number of particles contacts the substrate, the flame flow is blocked by the substrate and deflected, and a deflected flame flow parallel to the substrate surface is formed near the substrate. Since the size and mass of the particles carried in the flame flow are very small, they are easily affected by the deflected flame flow during the deposition process (i.e., when colliding with the substrate), forming an inclined deposition trajectory, and hitting the substrate surface at an inclined angle. As the spraying process proceeds, since the impact of the particles is inclined, the particles will only hit one side of the previously deposited coating, but cannot hit the other side, which causes the coating on one side to accumulate and increase continuously, while the other side forms a gap due to the lack of particle impact. Therefore, under this effect, a micron structure and gap are gradually formed. The above theory can also explain why traditional plasma spraying with powder as raw material cannot produce micro-nano double-layer structure. Traditional plasma spraying uses large-sized powder (particle size 20~100 microns) as raw material. Due to the large mass of large-sized powder, it will not be affected by the deflected flame flow when hitting the substrate, and all hit the substrate surface at a vertical angle, eventually forming a coating morphology with a flat surface.

[0020] Example 1 (1) A stainless steel wire with a diameter of 0.2 mm is used as a twisted steel wire, which is installed on a stranding machine 4, and a mandrel 2 is installed on a rotating table fixture 1. An inductively coupled plasma torch 8 is installed on a driving guide rail 9, and the axial direction of the torch 8 is kept perpendicular to the mandrel 2.

[0021] (2) Without starting the inductively coupled plasma spraying system, a mixed pickling solution 10 of 100 g / L sulfuric acid solution and 100 g / L hydrochloric acid solution is used as a raw material, and the peristaltic pump 11 and the atomizing gas pump 12 are started. The atomizing gas is argon gas with an argon flow rate of 0.5 standard liters per minute. The pickling solution 10 is injected into the torch tube 8 through the atomizing nozzle 13. At the same time, the gas supply system 7 is started to inject a large flow of argon gas into the torch tube 8 with an argon flow rate of 30 standard liters per minute. The large flow of argon gas further atomizes and accelerates the pickling solution injected into the torch tube 8, and the pickling solution is quickly ejected from the outlet of the torch tube 8 to form a pickling spray 14.

[0022] (3) Start the rotary table fixture 1 and the stranding machine 4, and twist the steel wire around the core shaft 2. During the twisting process, keep the rotary table fixture 1 rotating at a speed of 30 revolutions per minute, and the steel wire twisting speed is 10 mm per second. When the twisting length reaches 100 mm, start the drive guide rail 9, and spray the pickling spray 14 sprayed from the torch tube 8 onto the surface of the soft shaft that has been twisted, so as to pickle and roughen the twisted steel wire portion. During the pickling process, the moving speed of the torch tube 8 is maintained at 5 mm per second, so that the position of the torch tube 8 lags behind the part where the steel wire is being twisted, thereby ensuring that the pickling solution spray 14 is always sprayed on the twisted steel wire. When all the steel wires twisted on the surface of the soft shaft are pickled, the drive guide rail 9 stops moving. The pickling process is as follows Figure 1 shown.

[0023] (4) After the pickling process is completed, turn off the peristaltic pump 11 and the atomizing gas pump 12, and stop delivering the pickling solution; at the same time, close the end of the steel wire and gather it into a square so that the steel wire is fixed on the core shaft 2; start the gas supply system 7, and input a large flow of argon gas into the torch tube 8. The argon gas flow rate is 40-50 standard liters per minute. After the argon gas is sprayed out through the torch tube 8, a high-speed drying airflow 15 is formed. Start the drive guide rail 9 to make the torch tube 8 make a return motion to dry the pickling solution remaining on the surface of the soft shaft steel wire. During the drying process, the rotation speed of the rotary table fixture 1 is 20 revolutions per minute, and the movement speed of the torch tube 8 is 10 mm per second. When the return stroke is completed, the drive guide rail 9 stops moving. The drying process is as follows Figure 2 shown.

[0024] (5) After the drying process is completed, the inductively coupled plasma spraying system is started: the gas supply system 7 is started to input argon gas into the torch tube 8, wherein the gas flow rate of the outer layer of the torch tube 8 is 20 standard liters per minute, and the gas flow rate of the middle layer of the torch tube 8 is 1.5 standard liters per minute. The high-frequency generator 5 is started to ionize the gas in the torch tube to form a high-temperature and high-speed plasma flame flow 16, and the plasma power is adjusted to 1.5 kilowatts.

[0025] (6) Using 60% PTFE emulsion 17 as raw material, start the peristaltic pump 11 and the atomizing gas pump 12. The atomizing gas is argon gas with an argon flow rate of 0.5 standard liters per minute. Inject the PTFE emulsion 17 into the plasma flame flow 16 generated by the torch tube 8 through the atomizing nozzle 13. The PTFE emulsion delivery rate is 200 microliters per minute.

[0026] (7) After the PTFE liquid delivery and plasma flame flow reach a stable state, start the driving guide rail 9, so that the plasma flame flow 16 generated in the torch tube 8 scans the surface of the flexible shaft steel wire and deposits the PTFE coating on the surface of the steel wire. During the coating deposition process, the rotation speed of the rotating table fixture 1 is 30 revolutions per minute, and the moving speed of the torch tube 8 is 20 mm per second. By driving the reciprocating motion of the driving guide rail 9, 30 layers of coating are deposited on the surface of the flexible shaft steel wire. The PTFE coating deposition process is as follows Figure 3 shown.

[0027] According to the process described in Example 1, the microstructure of the PTFE coating after spraying is as follows: Figure 4 As shown in the low-magnification microstructure picture ( Figure 4 As shown in a), the coating surface presents obvious micron-sized convex structures, with a diameter of 10-25 μm, and obvious grooves between the convex structures; as shown in the high-magnification microstructure image ( Figure 4 As shown in Figure b), submicron / nano sized granular structures are distributed on the surface of the micron-sized convex structure. This micron-sized convex structure and submicron / nano sized granular structure are combined to form a double-layer structure. The sprayed PTFE coating exhibits super hydrophobic properties, and its water contact angle is 158°, as shown in Figure 2. Figure 5 shown.

[0028] Example 2 In Example 2, the process parameters of the "steel wire twisting-steel wire pickling and roughening-blow drying" process are kept consistent with those in Example 1, while the plasma power, air supply volume, PTFE emulsion concentration and liquid supply volume in the "PTFE spraying" process are changed, which ultimately leads to changes in the microstructure of the PTFE coating.

[0029] (1) A stainless steel wire with a diameter of 1 mm is used as a twisted wire and is installed on a stranding machine 4, and a mandrel 2 is installed on a rotating table fixture 1. An inductively coupled plasma torch 8 is installed on a driving guide rail 9, and the axial direction of the torch 8 is kept perpendicular to the mandrel 2.

[0030] (2) Without starting the inductively coupled plasma spraying system, a mixed pickling solution of 100 g / L sulfuric acid solution and 100 g / L hydrochloric acid solution is used as the raw material 10, and the peristaltic pump 11 and the atomizing gas pump 12 are started. The atomizing gas is argon gas with an argon flow rate of 0.5 standard liters per minute. The pickling solution 10 is injected into the torch tube 8 through the atomizing nozzle 13. At the same time, the gas supply system 7 is started to inject a large flow of argon gas into the torch tube 8 with an argon flow rate of 30 standard liters per minute. The large flow of argon gas further atomizes and accelerates the pickling solution injected into the torch tube 8, and the pickling solution is quickly ejected from the outlet of the torch tube 8 to form a pickling spray 14.

[0031] (3) Start the rotary table fixture 1 and the stranding machine 4, and twist the steel wire around the core shaft 2. During the twisting process, keep the rotary table fixture 1 rotating at a speed of 30 revolutions per minute, and the steel wire twisting speed is 10 mm per second. When the twisting length reaches 100 mm, start the drive guide rail 9, and spray the pickling spray 14 sprayed from the torch tube 8 onto the surface of the soft shaft that has been twisted, so as to pickle and roughen the twisted steel wire portion. During the pickling process, the moving speed of the torch tube 8 is maintained at 5 mm per second, so that the position of the torch tube 8 lags behind the part where the steel wire is being twisted, thereby ensuring that the pickling solution spray 14 is always sprayed on the twisted steel wire. When all the steel wires twisted on the surface of the soft shaft are pickled, the drive guide rail 9 stops moving. The pickling process is as follows Figure 1 shown.

[0032] (4) After the pickling process is completed, turn off the peristaltic pump 11 and the atomizing gas pump 12, and stop delivering the pickling solution; start the gas delivery system 7, and input a large flow of argon gas into the torch tube 8. The argon gas flow rate is 40-50 standard liters per minute. The argon gas is ejected through the torch tube 8 to form a high-speed drying airflow 15. Start the drive guide rail 9 to make the torch tube 8 make a return motion to dry the pickling solution remaining on the surface of the soft shaft wire. During the drying process, the rotation speed of the rotary table fixture 1 is 20 revolutions per minute, and the movement speed of the torch tube 8 is 10 mm per second. When the return stroke is completed, the drive guide rail 9 stops moving. The drying process is as follows Figure 2 shown.

[0033] (5) After the drying process is completed, the inductively coupled plasma spraying system is started: the gas supply system 7 is started to input argon gas into the torch tube 8, wherein the gas flow rate of the outer layer of the torch tube 8 is 20 standard liters per minute, and the gas flow rate of the middle layer of the torch tube 8 is 0.8 standard liters per minute. The high-frequency generator 5 is started to ionize the gas in the torch tube to form a high-temperature and high-speed plasma flame flow 16, and the plasma power is adjusted to 0.7 kilowatts.

[0034] (6) Using 20% ​​concentration PTFE emulsion 17 as raw material, start the peristaltic pump 11 and the atomizing gas pump 12. The atomizing gas is argon gas with an argon flow rate of 0.5 standard liters per minute. Inject the PTFE emulsion 10 into the plasma flame flow 16 generated by the torch tube 8 through the atomizing nozzle 13. The PTFE emulsion delivery rate is 400 microliters per minute.

[0035] (7) After the PTFE liquid delivery and plasma flame flow reach a stable state, start the driving guide rail 9, so that the plasma flame flow 16 generated in the torch tube 8 scans the surface of the flexible shaft steel wire and deposits the PTFE coating on the surface of the steel wire. During the coating deposition process, the rotation speed of the rotating table fixture 1 is 30 revolutions per minute, and the moving speed of the torch tube 8 is 20 mm per second. By driving the reciprocating motion of the driving guide rail 9, 30 layers of coating are deposited on the surface of the flexible shaft steel wire. The PTFE coating deposition process is as follows Figure 3 shown.

[0036] According to the process described in Example 2, the microstructure of the PTFE coating after spraying is as follows: Figure 6 As shown in the low-magnification microstructure picture ( Figure 6 As shown in a), the coating surface presents a micron-sized convex structure, and there are gaps between the convex structures; as shown in the high-magnification microstructure image ( Figure 6 As shown in Figure 2(b), submicron / nano sized granular structures are distributed on the surface of the micron-sized convex structure. The micron-sized convex structure and the submicron / nano sized granular structure together form a double-layer structure. The sprayed PTFE coating exhibits super hydrophobic properties, with a water contact angle of 156°. Figure 7 shown.

[0037] Finally, it should be noted that the parts not involved in the present invention are the same as the prior art or can be implemented by the prior art. The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention is described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that they can still modify or replace the technical solution of the present invention, and these modifications or replacements cannot make the modified technical solution deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A plasma spraying preparation method for a micro-nano double-layer PTFE coating on the surface of a flexible shaft steel wire, characterized in that The following steps are involved: Step 1: Install the mandrel and the steel wire on the twisting equipment, and install the inductively coupled plasma torch on the driving rail parallel to the mandrel, with the axis direction of the torch perpendicular to the mandrel; Step 2: Using the pickling solution as raw material, the pickling solution is injected into the torch tube through the feeding system, and the gas supply system is started at the same time. The pickling solution droplets are further atomized and accelerated by the large flow gas, and are quickly ejected from the torch tube to form a pickling spray; Step 3: Steel wire twisting and steel wire pickling and roughening: Start the twisting equipment to twist the steel wire around the mandrel; at the same time, start the driving guide rail to move the torch tube along the shaft core, and pickle the twisted steel wire with the pickling spray sprayed from the torch tube to roughen its surface; Step 4: Blow dry: turn off the feeding system, introduce a large flow of gas into the torch through the gas delivery system to form a high-speed airflow, and start the drive guide rail at the same time to make the torch move along the axis core, and use the high-speed airflow in the torch to blow dry the acid cleaning solution remaining on the surface of the flexible shaft; Step 5: PTFE spraying: Start the inductively coupled plasma spraying system, use PTFE emulsion as raw material, inject it into the plasma flame flow in the torch tube through the feeding system, and start the driving guide rail at the same time to make the torch tube move along the axis core. The plasma flame flow in the torch tube scans the surface of the soft shaft steel wire to deposit the PTFE coating on the surface of the steel wire; through the reciprocating motion of the driving guide rail, multiple layers of coating are deposited on the surface of the soft shaft steel wire.

2. The plasma spraying preparation method of the micro-nano double-layer PTFE coating on the surface of the flexible shaft steel wire according to claim 1 is characterized in that: The four different processes of "steel wire twisting, steel wire pickling and roughening, drying, and PTFE spraying" are completed using the same equipment and the same workstation.

3. The plasma spraying preparation method of the micro-nano double-layer PTFE coating on the surface of the flexible shaft steel wire according to claim 1 is characterized in that: The steel wire twisting process is carried out simultaneously with the steel wire pickling and roughening process, that is, the twisted steel wire is pickled during the steel wire twisting process.

4. The plasma spraying preparation method of the micro-nano double-layer PTFE coating on the surface of the flexible shaft steel wire according to claim 1 is characterized in that: The steel wire is made of stainless steel wire, alloy steel wire or nickel-based alloy wire, and the diameter of the steel wire is 0.2-1 mm.

5. The plasma spraying preparation method of the micro-nano double-layer PTFE coating on the surface of the flexible shaft steel wire according to claim 1 is characterized in that: The pickling solution used is 100-250 g / L of hydrochloric acid, sulfuric acid, nitric acid or a mixture thereof.

6. The plasma spraying preparation method of the micro-nano double-layer PTFE coating on the surface of the flexible shaft steel wire according to claim 1 is characterized in that: The concentration of the PTFE emulsion is 20% to 60%.

7. The plasma spraying preparation method of the micro-nano double-layer PTFE coating on the surface of the flexible shaft steel wire according to claim 1 is characterized in that: The PTFE coating prepared in step 5 exhibits a micro-nano double-layer structure.

8. The plasma spraying preparation method of the micro-nano double-layer PTFE coating on the surface of the flexible shaft steel wire according to claim 7, characterized in that: The micro-nano double-layer structure is a micron-sized convex hull structure formed on the surface of the PTFE coating, and there are obvious gaps between the convex hull structures, and the surface of the convex hull structure has submicron / nano-sized particles.

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