Aluminum coating coating method for aerospace titanium alloy internal thread fastener

Abstract

The invention discloses an aerospace titanium alloy internal thread fastener aluminum coating coating method which comprises the following steps that S1, a to-be-treated fastener is pretreated, phosphate fluoride is used for treatment, and cleaning and drying are conducted; s2, after dip-coating drying, pre-curing is conducted, secondary dip-coating drying is conducted, and secondary pre-curing is conducted; and S3, front face spraying, pre-curing, back face spraying and curing are carried out. The internal thread fastener aluminum coating machined through the method is smooth in appearance and free of accumulated burls and foreign matter, the thickness of the coating is uniform and consistent and meets the requirement of 5-20 microns, the machined internal thread fastener is excellent in adhesive force, and the locking torque, the loosening torque and other performance of a locking test meet the technical condition requirements.

Description

Technical Field

[0001] The present invention belongs to the field of internal threads made of titanium alloy materials, and in particular relates to a method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener. Background Art

[0002] As one of the surface treatment methods for fasteners used in aerospace, the aluminum coating is commonly used for external thread fasteners, and functions to reduce the friction coefficient of the thread pair, the pressing force of the bare rod during interference fit installation, and prevent contact corrosion. The common materials for internal thread fasteners include titanium alloy, corrosion-resistant steel, carbon steel, alloy steel, etc. The main surface treatment methods include molybdenum disulfide, electroplating, anodization, etc., which mainly function to reduce the friction resistance of the thread pair. In recent years, with the increasing requirement for lightweight of internal thread fasteners, titanium alloy materials have been widely used in internal thread products. Due to its excellent lubrication performance and anti-contact corrosion function, the aluminum coating is also increasingly widely used in internal thread products. The range and uniformity of the coating thickness at the thread of the internal thread fastener have a great influence on the performance such as the locking torque and loosening torque of the product. Generally, it is required that the thickness at the thread should meet the requirement of (5-15) μm.

[0003] Internal thread fasteners are generally processed by dip coating. Due to the high viscosity of the aluminum coating, it is difficult for the parts to be separated from each other during the drying process after dip coating, and there are many quality problems such as poor appearance of the bonding surface and uneven thickness, which affect the processing efficiency and quality stability of the product in the actual engineering application process. Summary of the Invention

[0004] In view of this, the present invention aims to propose a method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener to solve at least one technical problem in the background art.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows: A method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener includes the following steps: S1: Pretreat the fastener to be processed, use phosphate fluoride treatment, and clean and dry it; S2: After dip coating and drying, pre-cure, perform secondary dip coating and drying, and secondary pre-cure; S3: Spray on the front side, pre-cure, spray on the back side, and cure.

[0006] Further, the pretreatment of the fastener to be processed in step S1 includes roughening the surface of the fastener by dry sandblasting, and then performing ultrasonic water washing; The sand used for dry sandblasting roughening is corundum sand, with a size of 200 mesh, a sandblasting pressure of 0.5-0.6 MPa, a distance of 300-500 mm, and a time of 10-15 min; The time for ultrasonic water washing is 8 - 12 min.

[0007] Further, the bath solution for phosphate fluoride treatment in step S1 includes trisodium phosphate, potassium fluoride, and hydrofluoric acid; The concentration of trisodium phosphate is 49 - 51.5 g / L; The concentration of potassium fluoride is 17.5 - 24 g / L; The mass fraction of hydrofluoric acid is 70%, and the concentration is 14 - 24 ml / L; In step S1, the temperature for phosphate fluoride treatment is 21 - 33 °C, and the treatment time is 2 - 4 min.

[0008] Further, the cleaning and drying in step S1 include deionized water washing at room temperature for 2 - 3 min, first blowing dry the moisture on the surface of the parts with cold air, and then drying; The drying temperature is 50 ± 10 °C, and the time is at least 10 min.

[0009] Further, the preparation of the coating in dip coating in step S2 includes stirring the coating stock solution until there is no precipitation or solidification phenomenon, and then adding a diluent until the solid content of the coating is 20% - 25%, and filtering the prepared coating through a 180 - 220 mesh filter screen into a clean and oil - free stainless steel bucket; The diluent includes one or more of methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate; Preferably, the diluent is methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate, and the mass ratio of methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate is 1:0.8 - 1.2:0.8 - 1.2.

[0010] Further, the dip coating in dip coating drying and secondary dip coating drying in step S2 both include loading the parts into a gauze net or a stainless steel frame and completely immersing them in a stainless steel bucket filled with the coating, ensuring that the parts can shake evenly up and down; Then place it in an oven for preheating, take it out and immerse the parts for 30 - 60 seconds, and continuously shake the gauze net during this period to make the parts fully immersed in the coating; The temperature of the oven is 80 ± 10 °C, and the preheating time is at least 30 min.

[0011] Further, the drying in both the dip coating drying and the secondary dip coating drying in step S2 includes taking out the parts from the stainless steel barrel, staying above the stainless steel barrel, and continuously shaking to drain the paint adhering to the surface of the parts until no paint drips; then putting the parts into a rotating drum with an inclination angle of 55 - 65 °C, and at the same time putting in a diameter larger than the inner thread part hole diameter, the inner thread part hole diameter is 2 - 3 mm, the clockwise rotation speed of the rotating drum is 7 - 11 r / min, and at the same time introducing hot air at 80 - 100 °C, after rotating for 30 - 40 seconds, adjusting the rotation direction of the drum to counterclockwise and continuing to rotate for 30 - 40 seconds, repeating this 3 - 5 times, and then the aluminum coating on the surface of the parts is completely dried.

[0012] Further, the drying temperature for pre - curing and secondary pre - curing is 150 ± 10 °C, and the time is at least 30 min; After pre - curing, take out the parts from the oven and cool them to room temperature, and then carry out secondary dip coating drying; The coating thickness of the threaded part after secondary pre - curing in step S2 is 5 - 20 μm.

[0013] Further, the preparation of the paint for spraying in step S3 includes stirring the purchased paint stock solution until there is no precipitation or solidification phenomenon, and then adding a diluent to make the solid content of the paint 30 - 40%; finally, filtering the prepared paint through a 180 - 220 - mesh filter screen into a clean and oil - free stainless steel barrel; The diluent includes one or more of methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate; Preferably, the diluent is methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate, and the mass ratio of methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate is 1:0.8 - 1.2:0.8 - 1.2.

[0014] Further, both the front spraying and the back spraying in step S3 include selecting a square - shaped perforated tooling according to the part size, and the square - shaped perforated tooling ensures that 1 / 6 of the height of the part is placed into the hole, and the distance between parts is half of the total height of the parts. The front spraying includes placing the parts one by one with the support surface facing up into the holes in the perforated tooling, putting the parts together with the tooling into an oven at 150 ± 10 °C for at least 30 min, taking them out and putting them into the spraying station, adjusting the spray gun and then spraying, the spraying distance is 100 - 150 mm, the spraying pressure is 0.2 - 0.4 MPa, so that a 5 - 15 - μm aluminum coating covers the surface of the parts; Back spraying: Place the part with the sprayed support surface facing down on a flat tooling fixture. Put the part together with the tooling into an oven at 150 ± 10°C for at least 30 minutes. After taking it out, place it at the spraying station. Adjust the spray gun and then spray. The spraying distance is 100 - 150 mm, and the spraying pressure is 0.2 - 0.4 MPa, so that a 5 - 15 μm aluminum coating is covered on the part surface; In step S3, pre - curing includes putting the part into an oven at 150 ± 10°C for pre - curing for at least 30 minutes; In step S3, curing after back spraying includes putting the part together with the perforated tooling into an oven at 150 ± 10°C for pre - curing for at least 30 minutes, and then putting it into an oven at 200 ± 10°C for heat preservation for 60 - 120 minutes to complete the coating.

[0015] Compared with the prior art, the aluminum coating application method for aerospace titanium alloy internal - thread fasteners of the present invention has the following advantages: 1. In view of the actual problems existing in the application of aluminum coatings to internal - thread products, the present invention optimizes and designs from aspects such as the pretreatment method, dip - coating process parameters, drying method and parameters, spray - coating tooling design and parameters, etc. The aluminum coating of the internal - thread fasteners processed by the method of this invention patent has a smooth appearance, no build - up, no foreign objects, the coating thickness is uniform, meeting 5 - 20 μm. The adhesion of the processed internal - thread fasteners is excellent, and the performance such as the locking torque and loosening torque in the locking test meets the technical condition requirements.

[0016] 2. This coating method can effectively improve the appearance quality of the aluminum coating of internal - thread titanium alloy fasteners, without problems such as adhesion, build - up, and foreign objects. At the same time, it can greatly improve the uniformity of the coating thickness, meeting the standard requirements of (5 - 20) μm. The adhesion of the aluminum coating is greatly enhanced, and it can withstand the mutual extrusion deformation force between the mandrel thread pairs during the locking test, and the locking test meets the standard requirements. Specific embodiments

[0017] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0018] The present invention will be described in detail with combined embodiments.

[0019] The main process of the method is as follows: Step 1: Dry - sandblast and roughen the surface of the fastener. The sand used is corundum sand, with a size of 200 mesh, the sand - blasting pressure is (0.5 - 0.6) MPa, the distance is (300 - 500) mm, and the time is (10 - 15) minutes.

[0020] Work step 2: Ultrasonic water washing. The purpose of this step is to remove the corundum sand adhering to the surface of the parts during sandblasting, especially the sand remaining in the threaded parts. Add deionized water to a cleaning tank with ultrasonic function (power 9 kW), completely immerse the sandblasted parts in the ultrasonic wave for cleaning for (8 - 12) min, and shake and turn the parts during this period to ensure thorough cleaning.

[0021] Work step 3: Phosphate fluoride treatment. This work step can form a phosphating film on the surface of the parts in the sandblasted state, further improving the adhesion of the aluminum coating. The bath composition is: trisodium phosphate (Na 3 PO 4 ·12H 2 O), with a concentration of 49 - 51.5 g / L. Potassium fluoride (KF·2H 2 O), with a concentration of 17.5 - 24 g / L. Hydrofluoric acid (HF), with a mass fraction of 70% and a concentration of 14 - 24 ml / L. Treat at a temperature of 21 - 33 °C for 2 - 4 min. When only hydrofluoric acid is used, it reacts with the titanium alloy to form TiF 4 , which is easily soluble in water and cannot form a porous and loose film layer on the surface of the titanium alloy. When only hydrofluoric acid and potassium fluoride are used, the reaction rate is faster than when only hydrofluoric acid is used, and TiF 4 is formed, but still cannot form a porous and loose film layer. When only hydrofluoric acid and trisodium phosphate are used, the reaction rate is slow and a porous and loose film layer cannot be formed quickly. When only potassium fluoride and trisodium phosphate are used, the solution is alkaline and cannot corrode the titanium alloy to form a film layer. When all three substances are used simultaneously, hydrofluoric acid can corrode the titanium alloy and react with trisodium phosphate to form titanium phosphate. This film layer is insoluble in water, has a porous and loose characteristic, can adhere to the surface of the titanium alloy, and improve the adhesion of the aluminum coating. Potassium fluoride can provide fluoride ions to promote the continuous formation of the film layer.

[0022] Work step 4: Clean with deionized water at room temperature for 2 - 3 min.

[0023] Work step 5: Drying. First, blow dry the moisture on the surface of the parts with cold air. Then dry in an oven at a temperature of 50 ± 10 °C for at least 10 min.

[0024] Process Step 6: Preparation of Dip-Coating Paint. First, stir the purchased paint (the paint uses existing technology and can be used as long as it is available on the market, only need to meet the subsequent requirements. For example, the paint model is HD-04) stock solution until there are no precipitation, solidification and other phenomena. Then add diluent to it until the solid content of the paint is between 20% and 25%. Diluent can be selected from methyl ethyl ketone, alcohol, ethylene glycol monoethyl ether acetate, and the mixing ratio of the three is 1:1:1. Among them, methyl ethyl ketone and alcohol are organic solvents with relatively fast volatilization rates, which are beneficial to the rapid drying of parts after dip-coating and prevent the parts from sticking together due to slow drying rate, affecting the appearance and thickness uniformity of the coating. Ethylene glycol monoethyl ether acetate is an organic solvent with relatively slow volatilization. The purpose of adding it to the paint is to adjust the volatilization rate of organic solvents with relatively fast volatilization rates such as methyl ethyl ketone and alcohol, and prevent poor leveling of the paint due to too fast volatilization, affecting the appearance and thickness uniformity. Finally, filter the prepared paint through a 200-mesh filter screen into a clean and oil-free stainless steel bucket.

[0025] Process Step 7: Dip-Coating. Place the parts in a gauze net or stainless steel frame and completely immerse them in the stainless steel bucket filled with paint, ensuring that the parts can be evenly jolted up and down. Then place them in an oven at 80±10°C for at least 30 minutes of preheating. After taking them out, immerse the parts for 30 to 60 seconds, and continuously jolt the gauze net during this period to ensure that the parts are fully immersed in the paint.

[0026] Process Step 8: Drying. Take the parts out of the stainless steel bucket and stay above the stainless steel bucket, continuously jolt to drain the paint adhering to the surface of the parts until no paint drips. Then place the parts in a rotating drum with an inclination angle of about 60°C, and at the same time put circular balls with a diameter 2 to 3 mm larger than the inner thread part aperture. Set the clockwise rotation speed of the rotating drum to about 9 r / min, and at the same time pass hot air at 80 to 100°C into it. After rotating for 30 to 40 seconds, adjust the rotation direction of the drum to counterclockwise and continue to rotate for 30 to 40 seconds. Repeat this 3 to 5 times, and then the aluminum coating on the surface of the parts is completely dry. This method and process parameters can ensure that the parts will not stick during the drying process.

[0027] Process Step 9: Pre-Curing. Place the parts in an oven at 150±10°C for at least 30 minutes of pre-curing.

[0028] After the pre-curing in Process Step 10, take the parts out of the oven and cool them to room temperature. Then execute Process Step 7, Process Step 8, and Process Step 9 again. For internal thread products, when dip-coated once, the coating thickness at the thread part is thin and cannot meet the requirement of at least 5 μm. When dip-coated twice, the coating thickness at the thread part can meet 5 to 20 μm. When the dip-coating times are more than 5 times, the coating thickness will be >20 μm, not meeting the standard requirements.

[0029] Process step 11: Preparation of spraying coating. First, stir the purchased coating stock solution until there are no phenomena such as precipitation and solidification, and then add a diluent to it until the solid content of the coating is between 30% and 40%. Finally, filter the prepared coating through a 200-mesh filter screen into a clean and oil-free stainless steel bucket.

[0030] Process step 12: Spraying. According to the part size, select a suitable square perforated tooling (ensure that 1 / 6 of the height of the part is placed into the hole, and the spacing between parts is about half of the total height of the part). Place the parts one by one with the support surface facing up into the holes in the perforated tooling, and then put the parts together with the tooling into an oven at 150 ± 10°C for at least 30 minutes. The purpose of using the perforated tooling is to ensure that each part will not come into contact or overlap with each other during the placement process, so as to prevent problems such as defective appearance and uneven thickness of the sprayed coating. After taking out, place it in the spraying station, adjust the spray gun and then spray. The spraying distance is 100 - 150 mm, and the spraying pressure is 0.2 - 0.4 MPa, so that a layer of aluminum coating about 5 - 15 μm thick covers the surface of the parts.

[0031] Process step 13: Pre-curing. Place the parts into an oven at 150 ± 10°C for pre-curing for at least 30 minutes.

[0032] Process step 14: Spraying. Place the parts with the sprayed support surface facing down one by one on a flat tooling. The spacing between parts is about half of the total height of the part. If the spacing between parts is too small, there will be a phenomenon of mutual shielding, which may cause problems such as defective coating appearance and uneven thickness. After adjusting the spray gun, spray. The spraying distance is 100 - 150 mm, and the spraying pressure is 0.2 - 0.4 MPa, so that a layer of aluminum coating about 5 - 15 μm thick covers the surface of the parts.

[0033] Process step 15: Curing. Place the parts together with the perforated tooling into an oven at 150 ± 10°C for pre-curing for at least 30 minutes, and finally place them into an oven at 200 ± 10°C for heat preservation for 60 - 120 minutes to complete the coating.

[0034] In order to solve the problems of poor appearance quality, uneven coating thickness, poor bonding force and poor lubrication performance of the aluminum coating on the internal thread titanium alloy fasteners, the present invention has developed a coating device and method. The internal thread fasteners processed by using this device and method have excellent appearance, improved production efficiency, controllable coating thickness, and the locking torque and other temperatures meet the requirements of the standard technical conditions.

[0035] Example 1 A certain type of self-locking nut, with a material of TC4, a specification of MJ6, a quantity of 5000 pieces, requires an aluminum coating on the surface. The appearance should be smooth, uniform, without defects such as build-up and foreign objects. The support surface and thread thickness should meet 5 - 20μm. Conduct 15 locking performance tests according to the requirements of HB7596 standard. The maximum screwing-in torque ≤ 2.7 N·m, and the minimum screwing-out torque ≥ 0.35 N·m.

[0036] Process according to the following operation flow: sandblasting → ultrasonic water washing → phosphate fluoride treatment → water washing → drying → dip coating of aluminum coating → pre-curing → spraying of aluminum coating → curing. The specific process parameters are mainly as follows: Sandblasting: Corundum sand, size 200 mesh, sandblasting pressure 0.5 - 0.6 MPa, distance 300 - 500 mm, time 15 min; Ultrasonic water washing: Deionized water, time 8 - 10 min.

[0037] Phosphate fluoride treatment: Trisodium phosphate (Na 3 PO 4 ·12H 2 O), concentration 50 g / L. Potassium fluoride (KF·2H 2 O), concentration 20 g / L. Hydrofluoric acid (HF), mass fraction 70%, concentration 20 ml / L. Treat at 30℃ for 3 min.

[0038] Water washing: Deionized water, room temperature, time 2 - 3 min. Drying: First, blow dry the moisture on the surface of the parts with cold air. Then dry in an oven at a temperature of 50 ± 10℃ for at least 10 min; Preparation of dip coating paint. First, stir the purchased paint stock solution until there are no phenomena such as precipitation and solidification. Then add 2 kg of methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate to it. The mass ratio of methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate is 1:1:1. After detection, the solid content of the paint is about 23%. Finally, filter the prepared paint through a 200 - mesh filter into a clean and oil-free stainless steel bucket.

[0039] Dip coating. Load 2500 parts into a gauze net, preheat in an 80℃ oven for 45 min, and completely immerse them in a stainless steel bucket filled with paint, ensuring that the parts can shake evenly up and down. Immerse for 45 seconds, and continuously shake the gauze net during this period to make the parts fully immersed in the paint.

[0040] Drying. Take out the parts from the stainless-steel barrel and stay above the barrel, constantly jiggling to drain the paint adhering to the surface of the parts until no paint drips. Then put the parts into a rotating cylinder with an inclination angle of about 60°C. The clockwise rotation speed of the rotating cylinder is about 9 r / min. At the same time, hot air at 100°C is introduced into it. After rotating for 30 seconds, adjust the rotation direction of the cylinder to counterclockwise and continue to rotate for 30 seconds. After repeating this 3 times, the aluminum coating on the surface of the parts is completely dried, and there is no bonding phenomenon between the parts.

[0041] Pre-curing. Put the parts into an oven at 150 ± 10°C for at least 30 min for pre-curing.

[0042] After the pre-curing is completed, take out the parts from the oven and cool them to room temperature. Then perform the dipping, drying, and pre-curing steps again.

[0043] Preparation of spraying paint. First, stir the purchased paint stock solution until there are no phenomena such as precipitation and solidification. Then add 1.5 kg of methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate to it. The mass ratio of methyl ethyl ketone, alcohol, and ethylene glycol monoethyl ether acetate is 1:1:1. After testing, the solid content of the paint is about 35%. Finally, filter the prepared paint through a 200-mesh filter into a clean and oil-free stainless-steel barrel.

[0044] Spraying. According to the part size, select a suitable perforated tooling. Place the parts one by one with the support surface facing up into the perforated tooling, and put the parts together with the tooling into an oven at 150 ± 10°C for at least 30 min. After taking them out, put them into the spraying station. After adjusting the spray gun, spray. The spraying distance is 130 mm, and the spraying pressure is 0.3 MPa, so that a layer of aluminum coating about 5 - 15 μm thick covers the surface of the parts.

[0045] Pre-curing. Put the parts into an oven at 150 ± 10°C for at least 30 min for pre-curing.

[0046] Spraying. Take out the parts from the perforated tooling and place them face down on a flat tooling with a spacing maintained at half of the total height of the parts. After adjusting the spray gun, spray. The spraying distance is 130 mm, and the spraying pressure is 0.3 MPa, so that a layer of aluminum coating about 5 - 15 μm thick covers the surface of the parts.

[0047] Curing. Put the parts together with the tooling into an oven at 150 ± 10°C for at least 30 min for pre-curing, and finally put them into an oven at 200 ± 10°C for heat preservation for 60 min to complete the coating.

[0048] Randomly select 5 pieces from the products and use the metallographic method to detect the thickness of the threaded part. The results are shown in Table 1 and Table 2.

[0049] Table 1 Results of thickness detection by metallographic method (support surface) Table 2 Results of Metallographic Method for Thickness Detection (Thread) Randomly select 5 products from the products and conduct a locking test according to HB7595. No excessive locking torque occurs, and it meets the standard requirements. The results are shown in Table 3.

[0050] Table 3 Results of Locking Torque Test Comparative Example 1 The difference from Example 1 is that in the phosphate fluoride treatment, only trisodium phosphate (Na 3 PO 4 ·12H 2 O) is used, with a concentration of 50 g / L. Hydrofluoric acid (HF), with a mass fraction of 70% and a concentration of 40 ml / L. Treat at a temperature of 30 °C for 3 min.

[0051] Randomly select 3 products from the products and detect the thickness of the thread part by the metallographic method. The results are shown in Tables 4 and 5.

[0052] Table 4 Results of Metallographic Method for Thickness Detection (Support Surface) Table 5 Results of Metallographic Method for Thickness Detection (Thread) Comparative Example 2 The difference from Example 1 is that in the phosphate fluoride treatment, only potassium fluoride (KF·2H 2 O) is used, with a concentration of 70 g / L. Hydrofluoric acid (HF), with a mass fraction of 70% and a concentration of 20 ml / L. Treat at a temperature of 30 °C for 3 min.

[0053] Randomly select 3 products from the products and detect the thickness of the thread part by the metallographic method. The results are shown in Tables 6 and 7.

[0054] Table 6 Results of Metallographic Method for Thickness Detection (Support Surface) Table 7 Results of Metallographic Method for Thickness Detection (Thread) Comparative Example 3 The difference from Example 1 is that in the phosphate fluoride treatment, only trisodium phosphate (Na 3 PO 4 ·12H 2 O) is used, with a concentration of 90 g / L.

[0055] Randomly select 3 pieces from the products and detect the thickness of the threaded part by metallographic method. The results are shown in Tables 8 and 9.

[0056] Table 8 Results of thickness detection by metallographic method (support surface) Table 9 Results of thickness detection by metallographic method (thread) Comparative Example 4 The difference from Example 1 is that only hydrofluoric acid (HF) with a mass fraction of 70% and a concentration of 90 ml / L is used in the phosphate fluoride treatment.

[0057] Randomly select 3 pieces from the products and detect the thickness of the threaded part by metallographic method. The results are shown in Tables 10 and 11.

[0058] Table 10 Results of thickness detection by metallographic method (support surface) Table 11 Results of thickness detection by metallographic method (thread) Comparative Example 5 The difference from Example 1 is that only 2 kg of methyl ethyl ketone and alcohol are added to the dip coating formulation; the ratio of methyl ethyl ketone to alcohol is 1:1; Only 1.5 kg of methyl ethyl ketone and alcohol are added to the spray coating formulation; the ratio of methyl ethyl ketone to alcohol is 1:1.

[0059] Randomly select 3 pieces from the products and detect the thickness of the threaded part by metallographic method. The results are shown in Tables 12 and 13.

[0060] Table 12 Results of thickness detection by metallographic method (support surface) Table 13 Results of thickness detection by metallographic method (thread) Comparative Example 6 The difference from Example 1 is that only 2 kg of alcohol and ethylene glycol monoethyl ether acetate are added to the dip coating formulation; the ratio of alcohol to ethylene glycol monoethyl ether acetate is 1:1; Only 1.5 kg of alcohol and ethylene glycol monoethyl ether acetate are added to the spray coating formulation; the ratio of alcohol to ethylene glycol monoethyl ether acetate is 1:1.

[0061] Randomly select 3 pieces from the products and detect the thickness of the threaded part by metallographic method. The results are shown in Tables 14 and 15.

[0062] Table 14 Results of thickness detection by metallographic method (support surface) Table 15 Results of Thickness Detection by Metallographic Method (Thread) Comparative Example 7 The difference from Example 1 is that only 2 kg of methyl ethyl ketone and ethylene glycol monoethyl ether acetate are added in the preparation of the dip coating; the ratio of alcohol to ethylene glycol monoethyl ether acetate is 1:1 1.5 kg of methyl ethyl ketone and ethylene glycol monoethyl ether acetate are added in the preparation of the spray coating; the ratio of alcohol to ethylene glycol monoethyl ether acetate is 1:1.

[0063] Randomly select 3 pieces from the products and detect the thickness of the thread part by metallographic method. The results are shown in Table 16 and Table 17.

[0064] Table 16 Results of Thickness Detection by Metallographic Method (Support Surface) Table 17 Results of Thickness Detection by Metallographic Method (Thread) The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener, characterized in that: The steps include: S1: Pre-treat the fasteners to be treated, use phosphate fluoride treatment, clean and dry; S2: After dipping and drying, pre-curing, secondary dipping and drying, and secondary pre-curing; S3: Front spraying, pre-curing, back spraying, curing.

2. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 1, characterized in that: In step S1, pre-treating the fastener to be treated includes roughening the surface of the fastener by dry sandblasting, and then ultrasonic washing; The sand used for dry sandblasting is corundum sand with a size of 200 mesh, a sandblasting pressure of 0.5-0.6 MPa, a distance of 300-500 mm, and a time of 10-15 min. The ultrasonic washing time is 8 to 12 minutes.

3. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 1, characterized in that: The bath solution for phosphate fluoride treatment in step S1 includes trisodium phosphate, potassium fluoride and hydrofluoric acid; The concentration of trisodium phosphate is 49-51.5 g / L; The concentration of potassium fluoride is 17.5-24 g / L; The mass fraction of hydrofluoric acid is 70% and the concentration is 14-24 ml / L; In step S1, the temperature of the phosphate fluoride treatment is 21-33° C., and the treatment time is 2-4 minutes.

4. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 1, characterized in that: The cleaning and drying in step S1 includes cleaning with deionized water at room temperature for 2 to 3 minutes, first drying the surface of the parts with cold air, and then drying; The drying temperature is 50±10℃ and the drying time is at least 10 minutes.

5. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 1, characterized in that: The preparation of the coating in the dip coating in step S2 includes stirring the coating stock solution until there is no precipitation or coagulation, then adding a diluent thereto until the solid content of the coating is 20% to 25%, and filtering the prepared coating with a 180-220 mesh filter into a clean, oil-free stainless steel barrel; The diluent includes one or more of butanone, alcohol, and ethylene glycol ethyl ether acetate; Preferably, the diluent is butanone, alcohol and ethylene glycol ethyl ether acetate, and the mass ratio of butanone, alcohol and ethylene glycol ethyl ether acetate is 1:0.8-1.2:0.8-1.

2.

6. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 5, characterized in that: The dip-drying in step S2 and the dip-drying in the secondary dip-drying both include placing the parts into a gauze net or a stainless steel frame and completely immersing them in a stainless steel barrel filled with paint, ensuring that the parts can be shaken evenly up and down; Then place it in the oven to preheat, take it out and immerse the part for 30 to 60 seconds, shaking the gauze mesh constantly during this period to make the part fully immersed in the paint; The temperature of the oven is 80±10℃ and the preheating time is at least 30 minutes.

7. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 6, characterized in that: The drying in the dip-drying in step S2 and the drying in the secondary dip-drying both include taking the parts out of the stainless steel barrel, staying above the stainless steel barrel, and continuously shaking to drain the paint adhering to the surface of the parts until no paint drips; then placing the parts in a rotating drum with an inclination angle of 55-65°C, and at the same time placing a part with a diameter larger than the aperture of the internal threaded part, the aperture of the internal threaded part is 2-3mm, the rotating drum rotates clockwise at a speed of 7-11r / min, and hot air at 80-100°C is introduced into it. After rotating for 30-40 seconds, adjust the rotation direction of the drum to counterclockwise and continue to rotate for 30-40 seconds. After repeating this 3-5 times, the aluminum coating on the surface of the parts is completely dry.

8. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 1, characterized in that: The drying temperature for pre-curing and secondary pre-curing is 150±10℃, and the time is at least 30min; After the pre-curing is completed, the parts are taken out of the oven and cooled to room temperature before a second dip coating and drying; The coating thickness at the threaded portion after the secondary pre-curing in step S2 is 5 to 20 μm.

9. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 1, characterized in that: The preparation of the coating for spraying in step S3 includes stirring the purchased coating stock solution until there is no precipitation or coagulation, and then adding a diluent thereto until the solid content of the coating is 30-40%; finally, filtering the prepared coating with a 180-220 mesh filter into a clean, oil-free stainless steel barrel; The diluent includes one or more of butanone, alcohol, and ethylene glycol ethyl ether acetate; Preferably, the diluent is butanone, alcohol and ethylene glycol ethyl ether acetate, and the mass ratio of butanone, alcohol and ethylene glycol ethyl ether acetate is 1:0.8-1.2:0.8-1.

2.

10. The method for coating an aluminum coating on an aerospace titanium alloy internal thread fastener according to claim 1, characterized in that: In step S3, both the front spraying and the back spraying include selecting a square tool with holes according to the size of the parts. The square tool with holes ensures that 1 / 6 of the height of the parts is placed in the hole, and the spacing between the parts is half of the total height of the parts. Front spraying includes placing the part with the support surface facing upward into the hole in the perforated tooling, placing the part together with the tooling in a 150±10℃ oven for at least 30 minutes, taking it out and placing it in the spraying station, adjusting the spray gun and spraying, the spraying distance is 100~150mm, the spraying pressure is 0.2~0.4MPa, so that the surface of the part is covered with a 5~15μm aluminum coating; Back spraying includes spraying the supporting surface of the parts. The supporting surface of the parts is placed on a flat tooling, and the parts and the tooling are placed in a 150±10℃ oven for at least 30 minutes. After taking them out, they are placed in the spraying station, and the spray gun is adjusted and sprayed. The spraying distance is 100-150mm, and the spraying pressure is 0.2-0.4MPa, so that the surface of the parts is covered with a layer of 5-15μm aluminum coating; The pre-curing in step S3 includes placing the parts in a 150±10°C oven for pre-curing for at least 30 minutes; The curing after back spraying in step S3 includes placing the part together with the perforated tooling in a 150±10°C oven for pre-curing for at least 30 minutes, and placing it in a 200±10°C oven for 60 to 120 minutes to complete the coating.

Images