A processing method for an aircraft coating corrosion monitoring probe

Abstract

The present invention belongs to the field of aircraft structural coating corrosion health monitoring, and relates to a method for processing an aircraft coating corrosion monitoring probe. The method comprises: processing two electrode holes on a shell; covering the electrode holes with masking paper, sealing the electrode holes with sealant, and removing the masking paper after the sealant is completely cured; drilling a hole from the center of the electrode hole on the outer surface of the shell so that the side wall of the electrode hole is covered with an insulating layer formed by a sealant; installing a circuit board with an electrode into the shell, the electrode extending out of the probe surface, using a temporary cover with a glue injection port to support the circuit board and fix it to the probe shell, and padding a layer of protective steel gasket on the probe surface; cutting off the excess electrode length and using a polishing pen to polish the electrode surface; removing the protective steel gasket; using a U-shaped clamp to support the probe, and pressing the electrode down to be flush with the probe surface; injecting sealant from the glue injection hole of the temporary cover, and after the glue is injected to fill the entire probe, using the probe cover to seal the probe, so that the sealant inside the probe is completely cured and then the probe surface is sprayed with paint.

Description

Technical Field

[0001] The present invention belongs to the field of aircraft structure coating corrosion health monitoring, and particularly relates to a processing method for aircraft coating corrosion monitoring probes. Background Art

[0002] In recent years, aircraft serving in coastal and maritime areas have been in high-temperature, high-humidity, and high-salt environments for a long time, and the corrosion problem has become increasingly serious. Therefore, higher requirements have been put forward for the inspection, maintenance, and repair of aircraft structure corrosion. Aircraft structure coating corrosion is a major damage form of aircraft corrosion. As the protective layer outside the aircraft structure, the corrosion of the coating often indicates the beginning of the matrix structure corrosion. Therefore, the monitoring and early warning of coating corrosion are of great significance for avoiding safety accidents caused by aircraft corrosion damage.

[0003] The electrochemical alternating current impedance method is a commonly used method for aircraft coating corrosion monitoring. It is based on electrochemical principles. A small-amplitude alternating sinusoidal potential wave with different frequencies is applied to the monitoring system. Through the response of the system, the ratio of the alternating potential to the current signal changes with the frequency of the sinusoidal wave, or the phase angle changes with the frequency. The complex impedance of the measuring electrode system is obtained by using relevant integral algorithms. As the coating continuously degrades or the metal corrosion intensifies, the impedance characteristics it exhibits will also change. This method has the advantages of fast measurement speed, small interference to the structure, easy operation, and online monitoring. However, engineering applications have proved that the electrode processing based on this method has the following two special functional and structural characteristics:

[0004] a) First, ensure that the electrode passes through the probe housing and does not contact the side wall of the aperture of the probe metal housing to form an electrical conduction path;

[0005] b) Ensure that the top surface of the electrode is flat and does not affect the flatness of the later coating.

[0006] At present, the processing of the electrodes of domestic aircraft coating corrosion detection probes is still in the initial stage. Basically, most of them are for theoretical research in universities or stay in the initial principle prototype stage, and few are truly applied to the aircraft engineering application field. The processing of the electrodes is relatively rough, and less consideration is given to the coating defects caused by the unqualified flatness of the electrodes.

[0007] However, the practice of engineering applications has proved that ensuring the processing technology for the electrodes to be reliably insulated and flat is the top priority for improving the measurement reliability and whether it can be truly applied to engineering practice. If high-precision processing special instruments are used under a microscope, it will not only increase time and effort but also greatly increase production costs. How to develop a reliable processing technology that meets the performance requirements of the electrodes under low-cost conditions is an urgent need in the field of aircraft coating corrosion detection probe electrode processing. Summary of the Invention

[0008] Objective of the Invention: To provide a processing method for an aircraft coating corrosion monitoring probe that ensures reliable insulation and flatness of the electrodes.

[0009] Technical Solution:

[0010] A processing method for an aircraft coating corrosion monitoring probe, comprising:

[0011] Step 1: Process the housing of the coating corrosion monitoring probe and machine two electrode holes on the housing.

[0012] Step 2: Stick masking paper on the outer surface of the probe housing, so that the masking paper covers the electrode holes. Use a sealant to block the electrode holes from the inner surface of the probe housing, and place it in an oven at 70 °C for 30 min to completely cure the sealant, and then remove the masking paper.

[0013] Step 3: Use a drill bit to drill a hole from the center of the electrode hole on the outer surface of the housing, so that an insulating layer formed by a layer of sealant covers the side wall of the electrode hole.

[0014] Step 4: Install the circuit board with electrodes inside the housing. The electrodes extend out of the outer surface of the probe housing. Use a temporary cover with a glue injection port to hold the circuit board against the probe housing and fix it, so that the electrodes and the circuit board are firm and stable. Place a protective steel gasket on the surface of the probe. The diameter of the probe hole of the steel gasket is the same as the diameter of the electrodes.

[0015] Step 5: Use diagonal cutters to cut off the excess electrode length and use a grinding pen to grind the surface of the electrodes. After grinding, the surface of the electrodes is flat and strictly flush with the surface of the protective steel gasket.

[0016] Step 6: Remove the protective steel gasket. At this time, the surface of the electrodes is flat.

[0017] Step 7: Use a U-shaped fixture to hold the probe and press down the electrodes to be flush with the outer surface of the probe housing. At this time, use bolts to fix the U-shaped fixture to the probe housing to prevent the electrodes from rebounding due to deformation.

[0018] Step 8: Pour sealant into the glue injection hole of the temporary cover. After filling the entire inside of the probe with glue, use the probe cover to seal it, and bake it at 70 °C for 2 h with a dryer to completely cure the sealant inside the probe.

[0019] Step 9: Spray paint on the surface of the probe.

[0020] Further, in Step 1, the diameter of the electrode holes on the housing surface is 1.5 mm, and the hole spacing is 7 mm.

[0021] Further, in Step 7, the thickness of the gasket is less than 0.5 mm.

[0022] Further, in Step 8, the amount of glue poured ensures that the sealant covers the solder joints of the electrodes and the circuit board.

[0023] Further, in step 3, the thickness of the insulating layer is 0.3 mm.

[0024] Further, in step 4, the thickness of the protective steel gasket is 0.3 mm.

[0025] Further, in step 7, the U-shaped fixture is a housing structure conforming to the probe housing.

[0026] Further, step 8 specifically includes:

[0027] Step 81: Pour sealant into the glue injection hole of the temporary cover. The best amount of glue injection for the first time can cover the solder joints of the electrode and the circuit board. Use a dryer to bake at 70 °C for 1 h to completely cure the sealant. After the first glue injection is completed and the glue is dried, remove the U-shaped fixture and the temporary cover with the glue injection hole. The circuit board is completely fixed inside the probe and the electrode will not rebound. The electrode remains flush with the probe surface. Use a multimeter to test whether the surface of the electrode and the probe surface are electrically connected. If they are not electrically connected, it is qualified. If it is unqualified, it can be adjusted or discarded.

[0028] Step 82: If it is unqualified, perform secondary glue injection inside the probe. The secondary glue injection fills the entire inside of the probe. Seal it with the probe cover and bake it at 70 °C for 2 h using a dryer to completely cure the sealant inside the probe.

[0029] Beneficial effects:

[0030] The electrode processing method determined by the present invention can not only be applied to the coating corrosion monitoring of the electrochemical impedance spectroscopy method, but also be applied to coating monitoring technologies based on electrochemical measurement principles such as the electrochemical noise method, the linear polarization method, and the DC method. These coating corrosion monitoring technologies all inevitably require two or more detection electrodes. The electrode processing method determined by the present invention has low cost, simple operation, stable and reliable performance, and can effectively ensure the requirements of electrode insulation and flatness. At present, this method has been used on a certain domestic aircraft model, which is of great significance for the engineering practical application of the current coating corrosion monitoring system prototype. Description of the Drawings

[0031] Figure 1a Schematic diagram of sealing holes of the probe sealant;

[0032] Figure 1b Schematic diagram of drilling and forming a sealant insulating layer;

[0033] Figure 1c Schematic diagram of fixing the electrode and installing the protective steel gasket;

[0034] Figure 1d Schematic diagram of using the protective steel gasket to assist in grinding to make the electrode flat;

[0035] Figure 1e Schematic diagram of the electrode being 0.3 mm higher

[0036] Figure 1f Schematic diagram of using a U-shaped fixture to flatten the electrode flush with the probe

[0037] Figure 1g Schematic diagram of the sealant keeping the electrode flush

[0038] Figure 1h Schematic diagram of the electrode after processing and painting on the surface Specific implementation manner

[0039] As a sensor probe for aircraft coating detection, the aperture through which the probe electrode passes through the housing should not be too large. If it is too large, it will affect the consistency of the coating in the detection area. Generally, the aperture size is not more than 1.5 mm. Therefore, the electrode and the housing are relatively close (generally less than 0.25 mm). In such a small aperture, it is necessary to ensure the insulation and flatness between the electrode and the housing, which poses very high requirements for the processing technology of the electrode.

[0040] There are the following difficulties in the processing of the coating corrosion monitoring probe electrode:

[0041] a) The electrode is relatively close to the side wall of the aperture. Once a path is formed between the electrode and the probe housing during the electrode processing, it will directly lead to false alarms of the electrical signal.

[0042] b) If the flatness of the electrode processing surface is unqualified, it will cause the coating on the surface to be detected to corrode rapidly in the electrode area, affecting the accuracy.

[0043] To solve the above problems, taking a coating corrosion monitoring probe using the electrochemical alternating current impedance method as an example, aiming at the function and structural characteristics of the probe electrode for aircraft coating corrosion detection, to solve the problems of uneven electrode surface and easy conduction between the electrode and the housing, a low-cost, high-efficiency and reliable electrode processing method based on small-aperture electrodes is developed.

[0044] The present invention has the following technical difficulties:

[0045] Difficulty 1: If the installed probe electrode is directly polished, it will seriously damage the surface treatment layer of the probe housing, not only inconsistent with the aircraft structure coating system, but also reduce the bonding force between the probe surface and the coating, affecting the accuracy of the monitoring results. At the same time, when the electrode is polished, due to the ductility of the copper electrode, the top of the electrode expands, and the expanded copper material is very easy to contact the electrode hole wall, forming a path, resulting in false alarms. The failure rate of the direct polishing method has been verified by experiments to be more than 60%.

[0046] Difficulty 2: If the grinding process is not adopted and the probe electrode is directly cut flush by processes such as wire cutting, due to the anti-collision strip structure (the influence of four anti-collision protrusions) on the edge of the upper surface of the probe, it will interfere with the cutting process, so wire cutting operation cannot be carried out.

[0047] Difficulty 3: Try to accurately calculate the circuit board size and electrode size so that the protruding end of the electrode is flush with the surface of the probe housing. First, finish-machine the electrode size according to the calculated size and ensure the surface is flat. After welding the finish-machined electrode to the circuit board and then putting it into the probe electrode hole, although it can avoid the surface unevenness caused by later cutting, due to the welding angle cannot be guaranteed and the solder volume at the pad solder joints cannot be completely consistent, the surface of the finish-machined electrode after installation cannot be completely flush with the probe surface. It has been verified that even a height error of 0.1 mm will have an adverse impact on the surface quality of the paint spraying.

[0048] Difficulty 4: If the method of automatically filling the sealant between the hole wall and the electrode during later potting is used to ensure insulation (after the circuit board and the electrode are installed in the probe housing, directly potting), it will cause the potting glue to overflow from the electrode hole wall along the protruding electrode before curing, and a hard mound-shaped bulge will be formed in the electrode hole after curing, affecting the later grinding operation, and the insulating glue cannot completely fill the edge between the electrode and the housing, and may shift left and right, resulting in partial contact between the side of the electrode and the probe housing during the potting process.

[0049] The electrode processing process steps of the present invention are as follows. Figure 1a to Figure 1b It is the key process to ensure the insulation between the electrode and the probe housing. Figure 1c to Figure 1d It is the key process to ensure the horizontal flatness of the electrode surface. Figure 1e to Figure 1h It is the key process to ensure the flushness of the electrode horizontal plane and the probe housing horizontal plane.

[0050] 1) Process the coating corrosion monitoring probe housing, with the diameter of the electrode hole on the housing surface being 1.5 mm and the hole pitch being 7 mm.

[0051] 2) Stick masking paper on the outer surface (the painted surface) of the probe housing, and the masking paper covers the electrode hole. Use the sealant YH-9621 to block the electrode hole from the inner surface of the probe housing. Put it into the oven and keep it at 70 °C for 30 min to make the sealant completely cured, and then remove the masking paper, as shown in Figure 1a .

[0052] 3) Use a 0.9 mm drill bit to drill a hole from the center of the electrode hole on the outer surface of the housing. At this time, an insulating layer formed by a layer of sealant covers the side wall of the electrode hole, and the thickness of the insulating layer is about 0.3 mm, as shown in Figure 1bThe above steps make the insulating layer between the electrode and the housing uniform. One is to fix the electrode and the other is to better insulate it from the probe housing. Compared with the method of pouring glue from the inside of the housing after installing the circuit board and the electrode into the probe housing to insulate the outer surface of the electrode from the probe housing, it avoids the situation where the insulating glue cannot completely fill the edges between the electrode and the housing, and may shift left and right, resulting in partial contact between the side surface of the electrode and the probe housing during the glue pouring process, and at the same time, it cannot well fix the end of the electrode.

[0053] 4) The circuit board with the electrode (diameter 0.9 mm) is installed inside the housing, and the electrode extends out of the probe surface. The probe opening is fixed with a temporary cover with a glue injection port against the circuit board and the probe housing to make the electrode and the circuit board firm and stable, preventing them from being unable to bear force during subsequent grinding. A protective steel gasket with a thickness of 0.3 mm is placed on the probe surface, and the diameter of the probe hole of the steel gasket is 0.9 mm (the same as the electrode diameter). See Figure 1c The thickness selection of the steel gasket is related to the electrode diameter. The larger the electrode diameter, the thinner the steel gasket thickness. Through experimental verification, when the electrode diameter is 0.9 mm, the steel gasket thickness ≤ 0.5 mm can ensure the smooth progress of the subsequent pressing process and does not affect the electrode solder joints and the circuit board. The diameter of the probe hole of the steel gasket is the same as the electrode diameter, both being 0.9 mm. This size ensures that the top extension of the electrode during subsequent grinding can be effectively avoided, resulting in electrical continuity. The function of using the steel gasket is that one is to avoid damaging the probe surface coating during direct grinding, affecting the sensitivity and accuracy of the probe; at the same time, the gasket should have good wear resistance to prevent the unevenness during the grinding process from affecting the electrode surface. In addition, the thinner the gasket thickness, the better. Being thin enough makes it easier to achieve during the subsequent pressing process and is not easy to damage the electrode and the coating on the probe surface.

[0054] 5) Use diagonal pliers to cut off the excess electrode length. After cutting, the electrode is slightly higher than the surface of the protective steel gasket, showing unevenness. Use a grinding pen to grind the electrode surface. After grinding, the electrode surface is flat and strictly flush with the surface of the protective steel gasket. Figure 1d 。

[0055] 6) Remove the protective steel gasket. At this time, the electrode surface is flat, and the height is slightly higher than the probe outer surface by 0.3 mm. Figure 1e 。

[0056] 7) Use a U-shaped fixture to hold the probe and press down the electrode until it is flush with the probe surface. At this time, use bolts to fix the U-shaped fixture to the probe housing to prevent the electrode from rebounding due to deformation. See Figure 1f The gasket thickness should be below 0.5 mm, and placing the gasket does not damage the probe housing coating.

[0057] 8) Pour the sealant XM-33 into the glue injection hole of the temporary cover, with the glue injection volume of 2 ml (when the probe size is different, the glue injection volume only needs to ensure that the sealant covers the solder joints of the electrode and the circuit board). The first glue injection volume is preferably able to cover the solder joints of the electrode and the circuit board, that is, cover the entire electrode to fix the electrode and the circuit board to prevent rebound. Use a dryer to bake at 70 °C for 1 h to completely cure the sealant. Due to the effect of the sealant, after the first glue injection is completed and the glue dries, remove the U-shaped fixture and the temporary cover with the glue injection hole. The circuit board is completely fixed inside the probe and the electrode will not rebound. The electrode remains flush with the probe surface. See Figure 1g . At this time, use a multimeter to test whether the surface of the electrode is conductive to the surface of the probe. If the two are not conductive, it is qualified and the next operation can be carried out. After the first glue injection is completed, the probe can be tested to judge in advance whether the probe is qualified. If it is qualified, continue the second glue injection. If it is unqualified, it can be adjusted or discarded;

[0058] 9) Secondary glue injection inside the probe, filling the entire inside of the probe, sealing with the probe cover, and using a dryer to bake at 70 °C for 2 h to completely cure the sealant inside the probe. The two curing processes can, first, discover problems in advance, and second, compared with the completion of the first glue injection, the drying time required is shorter, saving process time and cost. The two-stage glue injection is because the first glue injection can ensure that the circuit board and the electrode can be completely fixed to the probe, facilitating early testing; more importantly, the layered curing uses less glue and can be in full contact with the air, accelerating the curing time, avoiding the situation that the bottom curing state cannot be fully guaranteed and the electrode rebounds due to the one-time full filling method.

[0059] 10) Spray paint on the probe surface. At this time, the surface is flat after spraying, and there is no trace of electrode pores at all. See Figure 1h .

Claims

1. A processing method for an aircraft coating corrosion monitoring probe, characterized in that, Including: Step 1: Process the housing of the coating corrosion monitoring probe and machine two electrode holes on the housing; Step 2: Stick masking paper on the outer surface of the probe housing to cover the electrode holes. Use a sealant to plug the electrode holes from the inner surface of the probe housing, and place it in an oven at 70 °C for 30 min to completely cure the sealant, then remove the masking paper; Step 3: Use a drill bit to drill a hole from the center of the electrode hole on the outer surface of the housing, so that an insulating layer formed by a layer of sealant covers the side wall of the electrode hole; Step 4: Install the circuit board with electrodes inside the housing. The electrodes extend out of the outer surface of the probe housing. Use a temporary cover with a glue injection port to hold the circuit board against the probe housing and fix it, so that the electrodes and the circuit board are firm and stable. Pad a protective steel gasket on the probe surface. The diameter of the probe hole of the steel gasket is the same as the diameter of the electrode; Step 5: Use diagonal pliers to cut off the excess electrode length and use a grinding pen to grind the surface of the electrode. After grinding, the surface of the electrode is flat and strictly flush with the surface of the protective steel gasket; Step 6: Remove the protective steel gasket. At this time, the surface of the electrode is flat; Step 7: Use a U-shaped fixture to hold the probe and press down the electrode to be flush with the outer surface of the probe housing. At this time, use bolts to fix the U-shaped fixture to the probe housing to prevent the electrode from rebounding due to deformation; Step 8: Pour sealant into the glue injection hole of the temporary cover. After filling the entire inside of the probe with glue, use the probe cover to seal it, and bake it at 70 °C for 2 h with a dryer to completely cure the sealant inside the probe; Step 9: Spray paint on the probe surface.

2. The processing method of the aircraft coating corrosion monitoring probe according to claim 1, wherein In step 1, the diameter of the electrode hole on the housing surface is 1.5 mm, and the hole spacing is 7 mm.

3. The method for manufacturing an aircraft coating corrosion monitoring probe according to claim 1, characterized in that, In step 7, the thickness of the gasket is less than 0.5 mm.

4. The processing method of the aircraft coating corrosion monitoring probe according to claim 1, characterized in that, In step 8, the amount of glue injection should ensure that the sealant covers the solder joints of the electrodes and the circuit board.

5. The processing method of the aircraft coating corrosion monitoring probe according to claim 1, characterized in that, In step 3, the thickness of the insulating layer is 0.3 mm.

6. The processing method of the aircraft coating corrosion monitoring probe according to claim 1, wherein In step 4, the thickness of the protective steel gasket is 0.3 mm.

7. The processing method of the aircraft coating corrosion monitoring probe according to claim 1, characterized in that In step 7, the U-shaped fixture is a housing structure conforming to the probe housing.

8. The processing method of the aircraft coating corrosion monitoring probe according to claim 1, characterized in that, Step 8 specifically includes: Step 81: Pour sealant into the glue injection hole of the temporary cover. The best amount of glue injection for the first time can cover the solder joints of the electrodes and the circuit board. Use a dryer to bake at 70 °C for 1 h to completely cure the sealant. After the first glue injection is completed and the glue has dried, remove the U-shaped fixture and the temporary cover with the glue injection hole. The circuit board is completely fixed inside the probe and the electrodes will not rebound. The electrodes remain flush with the probe surface; Use a multimeter to test whether the surface of the electrode and the surface of the probe are conductive. If they are not conductive, it is qualified. If it is unqualified, it can be adjusted or discarded; Step 82: If it is unqualified, perform secondary glue injection on the inside of the probe. Fill the entire inside of the probe with secondary glue injection, use the probe cover to seal it, and bake it at 70 °C for 2 h with a dryer to completely cure the sealant inside the probe.

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