Preparation process of oxidation film on inner wall of precise aluminum pipe

Abstract

The invention discloses a preparation process of an oxidation film on the inner wall of a precise aluminum pipe, which comprises the following steps: step 1, oxidizing the aluminum pipe by adopting a semi-hard anodic oxidation electrolyte and a pulse current with the density of 1.5-2A / dm < 2 > in a bath solution temperature environment of 15-20 DEG C, the semi-hard anodic oxidation electrolyte comprises sulfuric acid with the concentration of 12%-15%, oxalic acid with the concentration of 2%-3% and glycolic acid with the concentration of 0.5%-1%. Step 2, carrying out hole sealing treatment on the oxide film on the inner wall of the aluminum pipe by using a nickel salt-containing medium-temperature hole sealing agent; 3, the aluminum pipe is soaked in methyl phenyl silicone resin, and meanwhile the permeability of the methyl phenyl silicone resin is improved through ultrasonic-assisted permeation; and 4, the aluminum pipe is baked, so that the methyl phenyl silicone resin permeates into the oxidation film on the inner wall of the aluminum pipe to form the composite coating. By adopting semi-hard anodic oxidation, the requirement of 3000 times of friction wear resistance of the selfie telescopic rod can be met, the cost is obviously lower than that of hard anodic oxidation, and mass production is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of precision aluminum tube surface treatment, and in particular to a preparation process for an oxide film on the inner wall of a precision aluminum tube. Background Art

[0002] Precision aluminum tubes can be used to make selfie telescopic rods. The selfie telescopic rods have high requirements for the wear resistance of the oxide films on the inner and outer walls of the aluminum tubes. The inner and outer walls of the telescopic rods need to be in close friction with POM materials to achieve locking. The number of telescopic times is required to reach more than 3000 times, and the locking force cannot decrease significantly. Generally, the weight of a selfie telescopic rod is more than one kilogram. The existing aluminum tube oxidation processes generally include ordinary anodic oxidation and hard anodic oxidation. Among them, ordinary anodic oxidation has low cost, but the thickness and hardness of the oxide film are small, and the wear resistance is poor, which is not suitable for processing precision aluminum tubes; although hard anodic oxidation can produce an oxide film with high hardness, large thickness and good wear resistance (HV 400-600, 30-50 μm), its electrolyte generally uses sulfuric acid with a concentration of 15%-25%, with high cost, and requires low temperature control (-5 to 0 °C), resulting in high energy consumption. Moreover, it is difficult to form an oxide film inside the aluminum tube by anodic oxidation. Especially when the length of the aluminum tube exceeds one meter, the oxide film on the inner wall is thinner. For a selfie rod that needs to be telescoped, abnormal noises are likely to occur during the stretching process and the friction plates made of POM material wear faster. Summary of the Invention

[0003] An object of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide a preparation process for an oxide film on the inner wall of a precision aluminum tube with low cost, low energy consumption and improved wear resistance of the inner wall of the aluminum tube.

[0004] The preparation process for an oxide film on the inner wall of a precision aluminum tube according to an embodiment of the present invention includes: Step 1, in a bath temperature environment of 15-20 °C, use a semi-hard anodic oxidation electrolyte and a pulsed current with a density of 1.5-2 A / dm 2 to oxidize the aluminum tube, and the semi-hard anodic oxidation electrolyte includes sulfuric acid with a concentration of 12-15%, oxalic acid with a concentration of 2-3%, and glycolic acid with a concentration of 0.5-1%;

[0005] Step 2, use a medium-temperature sealing agent containing nickel salt to seal the oxide film on the inner wall of the aluminum tube;

[0006] Step 3, immerse the aluminum tube in methylphenyl silicone resin, and at the same time, use ultrasonic wave to assist penetration to improve the permeability of the methylphenyl silicone resin;

[0007] Step 4, bake the aluminum tube so that the methylphenyl silicone resin penetrates into the oxide film on the inner wall of the aluminum tube to form a composite coating.

[0008] According to some embodiments of the present invention, in step 2, the cathode rod is driven to rotate simultaneously. The surface of the cathode rod is provided with diversion grooves distributed in a spiral manner. When the cathode rod rotates, the electrolyte forms a turbulent flow on the inner wall of the aluminum tube.

[0009] According to some embodiments of the present invention, the spiral angle of the diversion groove is 30 - 45°.

[0010] According to some embodiments of the present invention, before step 1, the aluminum tube is pre - treated. The pre - treatment includes cleaning the aluminum tube, removing the natural oxide film on the surface of the aluminum tube, neutralizing the surface of the aluminum tube, and chemically polishing the aluminum tube.

[0011] According to some embodiments of the present invention, an air pipe is installed in the oxidation tank. The air pipe is provided with openings at intervals. During oxidation, compressed air is introduced into the air pipe, and the compressed air flows through the openings, driving the electrolyte to form a vortex in the aluminum tube.

[0012] The preparation process of the oxide film on the inner wall of the precision aluminum tube according to the embodiments of the present invention has at least the following beneficial effects: 1. The concentration of sulfuric acid in the semi - hard anodic oxidation electrolyte is 12 - 15%. Compared with the concentration of sulfuric acid in the hard anodic oxidation solution (15% - 25%), the concentration of sulfuric acid is significantly reduced, and the consumption of sulfuric acid solution is reduced, which can reduce costs.

[0013] 2. 0.5 - 1% of glycolic acid is added to the semi - hard anodic oxidation electrolyte. Glycolic acid can form a stable complex with aluminum ions (Al 3 +), slowing down the dissolution rate of aluminum ions and promoting the growth of the oxide film to be denser. The dense and smooth oxide film can make the electric field distribution more uniform, reduce the electric field strength at the tip part, and thus inhibit the occurrence of tip discharge.

[0014] 3. The combination of semi-hard anodic oxidation and secondary special material sealing process has a synergistic effect. First, a porous alumina layer is formed on the inner wall of the aluminum tube through the semi-hard anodic oxidation process to provide basic wear resistance, and the porous structure of the oxide film (porosity about 10 - 30%) provides anchor points for subsequent sealing. Then, medium-temperature nickel salt is first used to partially seal the larger pores to enhance the adhesion of the subsequent secondary sealing material. Next, secondary sealing is carried out. Since the oxide film on the inner wall of the aluminum tube is porous, the low viscosity of methylphenyl silicone resin enables it to penetrate into the pores of the inner wall of the aluminum tube, so that methylphenyl silicone resin penetrates into the pores of the oxide film on the inner wall of the aluminum tube and covers the surface, forming a "ceramic matrix + organic resin" composite layer. Resin filling the pores can reduce stress concentration during friction, and at the same time, the lubricity of the resin itself can reduce the friction coefficient. Moreover, the -Si-OH groups in methylphenyl silicone resin and the -Al-OH on the surface of alumina form Si-O-Al covalent bonds through dehydration condensation reaction, which can enhance the interfacial bonding force. And during the curing process, methylphenyl silicone resin further crosslinks and undergoes thermal densification with alumina, improving the structural density. The organic component of methylphenyl silicone resin gives the surface a low friction coefficient, reduces abrasive wear, and has excellent wear resistance.

[0015] 4. Reduction in equipment investment: There is no need for a -5°C cryogenic system. Especially in southern regions where the environmental temperature is relatively high, the lower the temperature drop, the higher the cost. Semi-hard anodic oxidation can be operated at a bath temperature of 15 - 20°C, effectively reducing costs and facilitating mass production.

[0016] That is, through this solution, on the premise of ensuring product performance (3000 - time friction requirement), the process cost can be reduced. The long aluminum tube can be oxidized and then cut short, effectively reducing costs.

[0017] The additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. Detailed implementation mode

[0021] For the preparation process of the oxide film on the inner wall of a precision aluminum tube of the present invention, pretreatment is first carried out: cleaning the aluminum tube, removing the natural oxide film on the surface of the aluminum tube through alkali etching, and neutralizing the surface of the aluminum tube, and then the following steps are carried out:

[0022] Step 1, in a bath temperature environment of 15 - 20°C, use a semi-hard anodic oxidation electrolyte and a pulsed current with a density of 1.5 - 2 A / dm 2 to oxidize the aluminum tube. The semi-hard anodic oxidation electrolyte includes sulfuric acid with a concentration of 12 - 15%, oxalic acid with a concentration of 2 - 3%, and glycolic acid with a concentration of 0.5 - 1%;

[0023] Step 2, seal the oxide film on the inner wall of the aluminum tube with a medium-temperature sealing agent containing nickel salt;

[0024] Step 3: Immerse the aluminum tube in methylphenyl silicone resin, and at the same time, assist the penetration through ultrasonic waves to improve the permeability of methylphenyl silicone resin.

[0025] Step 4: Bake the aluminum tube so that the methylphenyl silicone resin penetrates into the oxide film on the inner wall of the aluminum tube to form a composite coating.

[0026] Furthermore, in Step 1, the cathode rod is driven to rotate simultaneously. The surface of the cathode rod is provided with diversion grooves distributed in a spiral manner. When the cathode rod rotates, the electrolyte forms a turbulent flow on the inner wall of the aluminum tube, making the formation of the oxide film more uniform and efficient.

[0027] Preferably, the spiral angle of the diversion groove is 30 - 45°, and at this time, the film formation uniformity of the oxide film is better.

[0028] In some embodiments, an air pipe is installed in the oxidation tank. The air pipe is provided with openings at intervals. When oxidizing, compressed air is passed into the air pipe, and the compressed air flows through the openings, driving the electrolyte to form a vortex in the aluminum tube, that is, replacing the rotating cathode rod by the air wave oscillation method, saving costs.

[0029] The specific advantages of the preparation process of the oxide film on the inner wall of the precision aluminum tube are as follows: 1. The sulfuric acid concentration in the semi-rigid anodic oxidation electrolyte is 12 - 15%. Compared with the sulfuric acid concentration (15% - 25%) in the hard anodic oxidation solution, the sulfuric acid concentration is significantly reduced, and the consumption of the sulfuric acid solution is reduced, which can reduce costs.

[0030] 2. 0.5 - 1% of glycolic acid is added to the semi-rigid anodic oxidation electrolyte. Glycolic acid can form a stable complex with aluminum ions (Al 3 +), slowing down the dissolution rate of aluminum ions and promoting the growth of the oxide film more densely. The dense and smooth oxide film can make the electric field distribution more uniform, reduce the electric field strength at the tip part, and thus inhibit the occurrence of tip discharge.

[0031] The combination of semi-hard anodizing and secondary special material sealing process has a synergistic effect. First, a porous alumina layer is formed on the inner wall of the aluminum tube through the semi-hard anodizing process to provide basic wear resistance, and the porous structure of the oxide film (porosity about 10-30%) provides anchor points for subsequent sealing; then, medium-temperature nickel salt is used to partially seal the larger pores first to enhance the adhesion of the subsequent secondary sealing material; then, secondary sealing is carried out. Since the oxide film on the inner wall of the aluminum tube is a porous structure, the low viscosity characteristic of methylphenyl silicone resin enables it to penetrate into the pores of the inner wall of the aluminum tube, so that the methylphenyl silicone resin penetrates into the pores of the oxide film on the inner wall of the aluminum tube and covers the surface, forming a "ceramic matrix + organic resin" composite layer. Resin filling the pores can reduce stress concentration during friction, and at the same time, the lubricity of the resin itself can reduce the friction coefficient. Moreover, the -Si-OH groups in methylphenyl silicone resin and the -Al-OH on the surface of alumina form Si-O-Al covalent bonds through dehydration condensation reaction, which can enhance the interfacial bonding force. And during the curing process, methylphenyl silicone resin is further cross-linked and undergoes thermal densification with alumina, improving the structural density. The organic component of methylphenyl silicone resin gives the surface a low friction coefficient, reduces abrasive wear, and has excellent wear resistance.

[0032] 4. Reduction in equipment investment: There is no need for a -5°C cryogenic system. Especially in southern regions where the environmental temperature is relatively high, the lower the temperature drop, the higher the cost. Semi-hard anodizing can be operated at a bath temperature of 15-20°C, effectively reducing costs and facilitating mass production.

[0033] That is, through this solution, while ensuring product performance (3000 times friction requirement), the process cost can be reduced. The long aluminum tube can be oxidized and then cut short, effectively reducing costs.

[0034] Taking the oxidation of Φ8×200mm aluminum tube as an example, the hard anodizing parameters, semi-hard anodizing parameters and the corresponding inner oxide film thickness data are shown in Table 1:

[0035] Table 1

[0036]

[0037] Next, wear resistance tests are carried out on Sample 2 (semi-hard anodized film), Sample 3 (hard anodized film) and Sample 4 (ordinary anodized film):

[0038] 1. Simulate the actual working conditions, reciprocally rub with a POM film under a pressure of 1 kg, and record the locking force attenuation after 3000 times. The locking force retention rate of Sample 2 (semi-hard anodized film) > 90%; the locking force retention rate of Sample 4 (ordinary anodized film) is about 80%.

[0039] 2. Dry friction test

[0040] 1) Test conditions

[0041] The counter - grinding material is a Si3N4 ball (diameter 6 mm)

[0042] The load is: 10 N

[0043] The sliding speed is: 0.3 m / s

[0044] The sliding distance / time is: 200 m / 40 min

[0045] 2) Performance comparison is shown in Table 2:

[0046] Table 2

[0047]

[0048] It can be clearly seen from Tables 1 and 2 that the thickness and performance of the semi - hard anodic oxidation film are both between those of the ordinary anodic oxidation film and the hard anodic oxidation film. Moreover, the thickness and performance of the semi - hard anodic oxidation film are both close to those of the hard anodic oxidation film, significantly better than those of the ordinary anodic oxidation film, and fully meet the requirements for the performance of the anodic oxidation film on the inner wall of the aluminum tube of the selfie telescopic rod.

[0049] 3. Wear resistance comparison is shown in Table 3

[0050] Table 3

[0051] Sample Number of frictions (to 1 kgf attenuation) <![CDATA[Energy consumption (kWh / m 2 )]]> Sample 2 (Semi-hard anodic oxidation film) 3,200 times 12.7 Sample 3 (Hard anodic oxidation film) 3,500 times 18.5

[0052] It can be seen from Table 3 that the number of friction times of the semi - hard anodic oxidation film is more than 3000 times, meeting the requirements for the wear resistance of the anodic oxidation film on the inner wall of the aluminum tube of the selfie telescopic rod, and the energy consumption is significantly lower than that of the hard anodic oxidation film.

[0053] Cost accounting is shown in Table 4:

[0054] Table 4

[0055] Item Sample 3 (Hard anodic oxidation film) Sample 2 (Semi-hard anodic oxidation film) Electricity cost 0.8 yuan / m 0.5 yuan / m Cost of chemical solution 0.6 yuan / m 0.3 yuan / m Cost of equipment transformation 50,000 yuan < 5,000 yuan

[0056] It can be seen from Table 4 that the cost of the semi - hard anodic oxidation film is significantly lower than that of the hard anodic oxidation film.

[0057] In summary, using semi - hard anodic oxidation can not only meet the requirement of 3000 - time friction wear resistance of the selfie telescopic rod, but also the cost is significantly lower than that of hard anodic oxidation, which is convenient for mass production.

[0058] It is easy for those skilled in the art to understand that, on the premise of no conflict, the above preferred modes can be freely combined and superimposed. The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural transformation made by using the content of the specification of the present invention under the inventive concept of the present invention, or directly or indirectly applied to other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A preparation process for an oxide film on the inner wall of a precision aluminum tube, characterized in that, It includes the following steps: Step 1, in a bath temperature environment of 15 - 20 °C, use a semi-hard anodic oxidation electrolyte and a pulsed current with a density of 1.5 - 2 A / dm 2 to oxidize the aluminum tube. The semi-hard anodic oxidation electrolyte includes sulfuric acid with a concentration of 12 - 15%, oxalic acid with a concentration of 2 - 3%, and glycolic acid with a concentration of 0.5 - 1%. Step 2: Seal the oxide film on the inner wall of the aluminum tube with a medium-temperature sealing agent containing nickel salt; Step 3: Immerse the aluminum tube in methylphenyl silicone resin, and at the same time, enhance the permeability of methylphenyl silicone resin through ultrasonic-assisted penetration; Step 4: Bake the aluminum tube so that the methylphenyl silicone resin penetrates into the oxide film on the inner wall of the aluminum tube to form a composite coating.

2. The preparation process of the oxide film on the inner wall of the precision aluminum tube according to claim 1, characterized in that: In Step 1, the cathode rod is driven to rotate simultaneously. The surface of the cathode rod is provided with spiral distribution of flow guiding grooves. When the cathode rod rotates, the electrolyte forms a turbulent flow on the inner wall of the aluminum tube.

3. The preparation process of the oxide film on the inner wall of the precision aluminum tube according to claim 2, characterized in that: The spiral angle of the flow guiding groove is 30-45°.

4. The preparation process of the oxide film on the inner wall of the precision aluminum tube according to claim 1, characterized in that: Before Step 1, the aluminum tube is pretreated. The pretreatment includes cleaning the aluminum tube, removing the natural oxide film on the surface of the aluminum tube by alkali etching, and neutralizing the surface of the aluminum tube.

5. The preparation process of the oxide film on the inner wall of the precision aluminum tube according to claim 1, characterized in that: An air pipe is arranged in the oxidation tank. The air pipe is provided with openings at intervals. During oxidation, compressed air is introduced into the air pipe. The compressed air generates bubbles through the openings, driving the electrolyte to form a vortex in the aluminum tube.

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