Vacuum pump shell surface treatment method

Abstract

The invention relates to the technical field of vacuum pumps, and particularly discloses a vacuum pump shell surface treatment method which comprises the following steps: S10, pretreatment: sequentially carrying out plasma activation oil removal, gradient pickling and weak base neutralization passivation treatment, and completely blocking a pin hole in a shell through a first plug in the pretreatment process, the inner wall of the pin hole is completely isolated from the orifice; s20, oxidation treatment is conducted, specifically, the first plug in the shell subjected to pretreatment is pulled out, a second plug is plugged in, the second plug incompletely plugs the pin hole, part of the inner wall of the pin hole communicates with the hole opening, and then the shell is placed in an electrolytic bath to be subjected to oxidation coating; and S30, post-treatment is conducted, specifically, after the shell subjected to oxidation treatment is cleaned, the second plug is dismounted. The thermal expansion coefficient of the shell is reduced, the matching degree with the thermal expansion coefficient of a cast iron rotor is remarkably improved, and meanwhile the surface hardness, abrasion resistance and corrosion resistance of the shell are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of vacuum pump technology, specifically to a method for surface treatment of a vacuum pump housing. Background Technology

[0002] Vacuum pumps used in the semiconductor industry require the gap between the rotor and the housing to change stably within a certain range during high-speed operation, thereby ensuring a vacuum level of around 1 Pa during operation. However, vacuum pumps with aluminum alloy housings currently have three main problems during operation: 1. Temperature rises during operation, causing significant changes in the gap between the rotor and the housing: When the rotor rotates at high speed, it compresses air for air transfer, generating a significant amount of heat. This causes the rotor and housing to expand due to heat. The thermal expansion coefficient of the aluminum alloy housing is approximately 1.6–2.4 × 10E⁻⁵ / ℃. Due to the different materials used for the rotor and housing (the rotor is made of cast iron with a thermal expansion coefficient of approximately 0.8–1.1 × 10E⁻⁵ / ℃), at temperatures of 40–60℃, the difference in thermal expansion coefficients between the rotor and housing after expansion is too large (the housing's expansion coefficient is approximately twice that of the rotor). Therefore, the gap changes significantly, resulting in a larger discrepancy from the gap controlled during assembly, making it difficult to control the gap changes during operation.

[0003] 2. Poor vacuum: Due to the high speed of the rotor in the housing, the gap between the rotor and the housing changes too much, which causes the vacuum to gradually deteriorate after a period of operation.

[0004] 3. Defects in surface hardness, wear resistance, and weather corrosion resistance of aluminum alloy: Due to the material properties of aluminum housings, their surface hardness and wear resistance are relatively poor. With prolonged use, significant wear will occur, leading to an irreversible increase in the gap between the rotor and the housing. This can damage both the vacuum pump housing and the rotor, increasing the overall failure rate of parts. Summary of the Invention

[0005] The purpose of this invention is to provide a method for surface treatment of a vacuum pump housing to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: a method for surface treatment of a vacuum pump housing, comprising the following steps: S10, Pretreatment, the pretreatment includes sequential plasma activation degreasing, gradient acid washing, weak alkali neutralization passivation treatment, and during the pretreatment process, the pin hole on the shell is completely blocked by the first plug to ensure that the inner wall of the pin hole is completely isolated from the orifice. S20, oxidation treatment: the first plug in the pretreated shell is pulled out and the second plug is inserted. The second plug partially blocks the pin hole, and the inner wall of the pin hole is connected to the opening. Then the shell is placed in the electrolytic cell for oxidation coating. S30, post-processing: After cleaning the oxidized shell, the second plug is removed.

[0007] Furthermore, the plasma activation oil removal uses an argon-oxygen mixed gas source with a volume ratio of 4:1, a power of 300~400W, and a processing time of 8~12min.

[0008] Furthermore, the gradient acid washing first involves treating with sulfuric acid solution at room temperature for 2-3 minutes, followed by treatment with a mixed acid of phosphoric acid and sulfuric acid at a volume ratio of 1:3 at room temperature for 1-2 minutes.

[0009] Furthermore, the weak alkali neutralization and passivation uses a sodium bicarbonate-sodium silicate mixed solution with a mass ratio of 3:1 and a treatment time of 5-8 minutes.

[0010] Furthermore, in the oxidation process, a sulfuric acid-oxalic acid mixed electrolyte is used, and the electrolysis parameters are controlled in two stages. In the first stage, the current density is adjusted to 12~15A / dm² for 15~20min, and in the second stage, the current density is adjusted to 8~10A / dm² for 25~35min. The electrolyte temperature is controlled at 18~22℃ throughout the process to form an oxide film with a thickness of 0.01~0.02mm.

[0011] Furthermore, both the first plug and the second plug include an inner layer and an outer layer, wherein the inner layer is a soft rubber containing polytetrafluoroethylene micropowder, and the outer layer is a hard rubber containing nano-silica.

[0012] The present invention has the following beneficial effects: This invention forms a controllable thickness oxide film on the surface of an aluminum casing through a pretreatment, segmented anodizing, and post-treatment process. This oxide film reduces the thermal expansion coefficient of the casing, significantly improving its matching with that of the cast iron rotor, while also greatly enhancing the surface hardness, wear resistance, and corrosion resistance of the casing.

[0013] After applying this technology, the vacuum pump can operate stably for four hours with a vacuum rebound of no more than 0.2 Pa, the damage rate of parts is reduced by more than 60%, and the maintenance cycle is extended to more than twice the original cycle. This effectively solves the defects of existing technologies and meets the high-precision operation requirements of the semiconductor industry for vacuum pumps. Attached Figure Description

[0014] The accompanying drawings described herein are for illustrative purposes only and do not represent all possible implementations, nor should they be considered as limiting the scope of the invention.

[0015] Figure 1 The overall structure of the first plug of Embodiment 1 is shown schematically. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 The surface treatment method for the vacuum pump housing in this embodiment mainly includes pretreatment, oxidation treatment and posttreatment.

[0018] Specifically, the pretreatment includes sequential plasma activation degreasing, gradient pickling, and weak alkali neutralization passivation. During the pretreatment process, the pin holes on the shell need to be completely plugged with a first plug to ensure that the inner wall of the pin hole is completely isolated from the orifice, so as to avoid affecting the inner wall of the pin hole and avoid changes in porosity.

[0019] Among them, plasma-activated oil removal uses an argon-oxygen mixed gas source with a volume ratio of 4:1, a power of 300~400W, and a processing time of 8~12min. On the one hand, it directly breaks the chemical bonds of oil molecules to achieve efficient desorption of oil. On the other hand, it forms a micro-nano-scale rough structure on the aluminum surface and introduces active groups such as hydroxyl and carboxyl groups, which greatly enhances the adhesion of the subsequent oxide film.

[0020] Furthermore, the gradient pickling process first involves treating the aluminum surface with a 10-12% sulfuric acid solution at room temperature for 2-3 minutes, followed by a 5-8% phosphoric acid-sulfuric acid mixture (volume ratio 1:3) at room temperature for 1-2 minutes. This utilizes the corrosion-inhibiting effect of phosphoric acid to form a uniform micro-uneven structure on the aluminum surface, avoiding over-corrosion or uneven corrosion caused by single pickling. This provides a uniform substrate for oxide film growth. Simultaneously, the corrosion-inhibiting properties of phosphoric acid can form a temporary adsorption layer on the aluminum surface, slowing down the erosion of active groups by the acid solution. The resulting uniform microstructure can compensate for surface losses and ensure the adhesion of the oxide film.

[0021] Furthermore, the weak alkali neutralization passivation uses a 3-5% sodium bicarbonate-sodium silicate mixed solution with a mass ratio of 3:1 and a treatment time of 5-8 minutes. While neutralizing the residual acid, the sodium silicate forms a thin and dense silane passivation film on the surface, which can not only prevent secondary oxidation after pretreatment and before anodizing, but also further enhance the adhesion between the oxide film and the substrate.

[0022] In the oxidation process, a sulfuric acid-oxalic acid mixed electrolyte is used, with a sulfuric acid concentration of 180~220g / L and an oxalic acid concentration of 15~25g / L. Citric acid is added as a stabilizer, which can form a complex with aluminum ions, reduce the porosity of the oxide film, and improve the film density.

[0023] The electrolysis parameters are controlled in two stages. In the first stage, the electrolysis is carried out at a current density of 12~15A / dm² for 15~20min to quickly form a dense oxide film substrate, which provides a foundation for subsequent film growth.

[0024] In the second stage, the current density is adjusted to 8~10A / dm² and electrolysis is performed for 25~35 minutes. The electrolyte temperature is controlled at 18~22℃ throughout the process to slowly grow the oxide film and control the thickness uniformity, so as to form an oxide film with a thickness of 0.01~0.02mm.

[0025] It should be noted that before the oxidation treatment, the first plug in the pre-treated housing needs to be removed and a second plug inserted. The second plug partially blocks the pin hole, leaving the inner wall of the pin hole connected to the opening. The housing is then placed in an electrolytic tank for oxidation coating. This forms an oxide film of a certain thickness on the inner wall of the pin hole end. Because it has not undergone pretreatment, the thickness and wear resistance of this oxide film are lower than those of the oxide film formed on the housing surface. Therefore, during assembly, under the application of a certain external force, the pin can be pushed through the oxide film at its end and inserted into the other half of the housing, achieving an interference fit and thus preventing separation due to vibration during use.

[0026] Finally, after cleaning the oxidized shell with deionized water, the second plug is removed to obtain the finished product.

[0027] like Figure 1 As shown, it should be noted that both the first plug and the second plug include an inner layer 11 and an outer layer 12. The two have the same structure and material. The only difference is that the length of the first plug is greater than that of the second plug. The inner layer 11 is a soft rubber containing polytetrafluoroethylene micro powder, and the outer layer 12 is a hard rubber containing nano-silica. This facilitates insertion into the pin hole and avoids damage during pretreatment and oxidation treatment, so as to prevent leakage from the inner wall of the pin hole.

[0028] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for surface treatment of a vacuum pump housing, characterized in that, Includes the following steps: S10, Pretreatment, the pretreatment includes sequential plasma activation degreasing, gradient acid washing, weak alkali neutralization passivation treatment, and during the pretreatment process, the pin hole on the shell is completely blocked by the first plug to ensure that the inner wall of the pin hole is completely isolated from the orifice. S20, oxidation treatment: the first plug in the pretreated shell is pulled out and the second plug is inserted. The second plug partially blocks the pin hole, and the inner wall of the pin hole is connected to the opening. Then the shell is placed in the electrolytic cell for oxidation coating. S30, post-processing: After cleaning the oxidized shell, the second plug is removed.

2. The surface treatment method for a vacuum pump housing according to claim 1, characterized in that: The plasma activation oil removal uses an argon-oxygen mixed gas source with a volume ratio of 4:1, a power of 300~400W, and a processing time of 8~12min.

3. The surface treatment method for a vacuum pump housing according to claim 1, characterized in that: The gradient acid washing process first involves treating with sulfuric acid solution at room temperature for 2-3 minutes, followed by treatment with a mixed acid of phosphoric acid and sulfuric acid at a volume ratio of 1:3 at room temperature for 1-2 minutes.

4. The surface treatment method for a vacuum pump housing according to claim 1, characterized in that: The weak alkali neutralization and passivation uses a sodium bicarbonate-sodium silicate mixed solution with a mass ratio of 3:1 and a treatment time of 5-8 minutes.

5. The surface treatment method for a vacuum pump housing according to claim 1, characterized in that: During the oxidation process, a sulfuric acid-oxalic acid mixed electrolyte is used, and the electrolysis parameters are controlled in two stages. In the first stage, the current density is adjusted to 12~15A / dm² for 15~20min, and in the second stage, the current density is adjusted to 8~10A / dm² for 25~35min. The electrolyte temperature is controlled at 18~22℃ throughout the process to form an oxide film with a thickness of 0.01~0.02mm.

6. The surface treatment method for a vacuum pump housing according to claim 1, characterized in that: Both the first plug and the second plug include an inner layer and an outer layer. The inner layer is a soft rubber containing polytetrafluoroethylene micropowder, and the outer layer is a hard rubber containing nano-silica.

Images