JP5432985B2 - Surface treatment method for members constituting mechanical booster pump, turbo molecular pump or dry pump, and mechanical booster pump, turbo molecular pump or dry pump treated by this surface treatment method - Google Patents

Description

  The present invention relates to a mechanical booster pump composed of aluminum or aluminum alloy exposed in a gas flow path, a surface treatment method for parts of a turbo molecular pump or a dry pump, and a mechanical booster composed of parts treated by this surface treatment method The present invention relates to a pump, a turbo molecular pump, or a dry pump.

As a conventional dry pump structure, for example, as shown in FIG. 1, the rotor chamber 4 in the flow path connecting the intake port 2 and the exhaust port 3 arranged to face the side surface of the housing 1. In this rotor chamber 4, a screw type is known that is configured by providing rotors 7 to 12 supported by a rotating shaft 6 driven by a motor 5. In the illustrated example, a gas ballast 14 for introducing air heated by the heating means 13, dry nitrogen, or the like is connected to the rotor chamber 4, and a shaft seal gas is introduced around the rotary shaft 6. A shaft seal gas introduction path 15 is formed for this purpose.
In the above structure, the gas sucked from the vacuum chamber passes through the rotor chamber 4 from the intake port 2 and is exhausted from the exhaust port 3. In the meantime, the gas is in the intake port 2, the rotors 7 to 12, When the gas sucked in contact with the surfaces of the rotor chamber 4 and the exhaust port 3 is corrosive, the surface of each component is normally subjected to anodizing (for example, see Patent Document 1). ).
However, in the case of alumite treatment, since a porous oxide film is formed on the surface of the member, there is a problem that the amount of gas released from the film is large and the exhaust efficiency of the vacuum pump is lowered. In addition, when the alumite-treated member is heated to about 120 ° C., there is a problem that the coating may crack and the corrosion resistance may be lowered. Further, there is a problem that the member is corroded in a short period of time when a gas containing chlorine is sucked.
On the other hand, GaN, which is a wide bandgap compound semiconductor, is manufactured by MBE or MOCVD as a light emitting diode (LED) or power device, and with mass production, metal Ga, which is an MBE raw material, or MOCVD raw material organic metal. Some trimethylgallium (TMG) and triethylgallium (TEG) are consumed in large quantities. However, since highly reactive Ga melts into an amalgam state when it comes into contact with Al, there is a problem that aluminum and aluminum alloys cannot be used for pipes and components through which raw materials and unreacted Ga flow.

JP 2006-257908 A

  In view of the above, the present invention provides a mechanical booster pump, a turbo molecular pump or a dry pump with a surface treatment method for a member constituting a mechanical booster pump which has excellent corrosion resistance and a low release gas, and a mechanical booster pump which has been treated by this surface treatment method. An object is to provide a turbo molecular pump or a dry pump.

In order to solve the above-mentioned problems, the present inventors have found a solving means as follows as a result of intensive studies.
That is, the first solving means of the surface treatment method of the members constituting the mechanical booster pump, turbo molecular pump or dry pump of the present invention is to replace the members constituting the mechanical booster pump, turbo molecular pump or dry pump with aluminum or aluminum. It is composed of an alloy, and the surface of the member is immersed in an alkaline solution and subjected to micro-arc oxidation treatment, and the thickness of the oxide film formed on the surface of the member by the treatment is set to 12 μm to 15 μm. .
The second solution is that the alkaline solution is disodium hydrogen phosphate, sodium tripolyphosphate, sodium dihydrogen phosphate, sodium ultrapolyphosphate, sodium silicate, potassium hydroxide, sodium diphosphate, trisodium phosphate, sodium aluminate, one kind or a mixture of of these in the sodium metasilicate and sodium hydroxide were dissolved in water, that it has a concentration of 0.1 mass% to 5 mass% Features.
The third solving means is characterized in that the applied voltage in the micro arc treatment is in the range of 300 V to 600 V, and the current density is 3.0 A / dm ^{2 to} 10 A / dm ² .
Moreover, the 4th solution means makes the temperature of the said alkaline solution 5 to 90 degreeC, It is characterized by the above-mentioned.
The fifth solving means is characterized in that the film thickness of the oxide film formed on the surface of the member by the treatment is 12 μm to 15 μm.
Moreover, the mechanical booster pump, the turbo molecular pump or the dry pump of the present invention is constituted by a member treated by the surface treatment method.

  According to the present invention, the surface of a member constituting a mechanical booster pump, a turbo molecular pump or a dry pump is made of aluminum or an aluminum alloy and subjected to a micro arc oxidation treatment, thereby exhausting corrosive gas. A dry pump having excellent corrosion resistance and a small amount of released gas can be obtained. And according to this mechanical booster pump, a turbo-molecular pump, or a dry pump, efficient suction becomes possible. Moreover, it becomes the thing with the excellent corrosion resistance with respect to the gas containing Ga.

Schematic configuration diagram of a conventional dry pump Schematic configuration diagram of mechanical booster pump The graph which measured the gas-release characteristic of Example 1 and Comparative Example 1 Surface SEM images after heating in Example 1 and Comparative Example 1 The graph which measured the corrosion resistance with respect to hydrochloric acid of Example 1 and Comparative Example 1 The graph which shows the time change of the pressure in a chamber when the 1 m < ³ > chamber is exhausted using the dry pump of Example 2 and Comparative Example 2. FIG. Surface SEM images before and after the test of Comparative Test 4 of Example 3 and Comparative Example 3

  Examples of the alkaline solution electrolyte used in the present invention include disodium hydrogen phosphate, sodium tripolyphosphate, sodium dihydrogen phosphate, sodium ultrapolyphosphate, sodium silicate, potassium hydroxide, sodium diphosphate. A solution obtained by dissolving one kind of trisodium phosphate, sodium aluminate, sodium metasilicate, sodium hydroxide, or the like or a mixture thereof in an electrolytic solution can be used. The concentration is preferably in the range of 0.1% to 5%.

Further, aluminum or an aluminum alloy is used as the base material. Aluminum alloy casting materials and die-casting materials, typically silicon, contain many elements in general, and it is said that it is difficult to form a porous anodic oxide film.
According to the present invention, it is possible to form a coating film with good corrosion resistance even in such a casting or die-casting with a lot of silicon. Further, among the wrought materials, the No. 4000 series treatment of the Al—Si alloy has a poor corrosion resistance due to the same reason, but according to the present invention, a good oxide film can be formed. The wrought material, in which silicon is not precipitated, and aluminum alloys in the 1000th to 3000th, 5000th to 7000th range, are also effective in the case of a complicated shape or a high temperature of 100 ° C. or higher.

In the present invention, the above-described base material is immersed in an alkaline solution as a constituent member of a mechanical booster pump, a turbo molecular pump or a dry pump to perform micro-arc oxidation treatment. Is not particularly limited, but is preferably in a range where the solution does not freeze or boil (about 5 ° C. to 90 ° C.). Moreover, it is preferable that the applied voltage shall be 300V-600V. If it is less than 300 V, dielectric breakdown does not occur, and if it exceeds 600 V, the voids of the film increase. The current density is preferably 3.0 A / dm ^{2 to} 10 A / dm ² . This is because if it is 3.0 A / dm ² , the film cannot be thickened, and if it exceeds 10 A / dm ² , the voltage increases and voids increase. In addition, the current may be any of direct current, alternating current, and orthogonal superimposition.

  Moreover, there is no restriction | limiting in particular about the film thickness of the oxide film formed in a base material surface, However, It is preferable to set it as the range of 12 micrometers-15 micrometers. This is because the function as an oxide film is exhibited within a range that does not hinder the operation of the pump.

The dry pump used in the present invention is not particularly limited to the structure shown in FIG. 1 as long as it does not use oil in the gas passage inside the pump. Depending on the shape, a root type, a claw type, a screw type, a turbo type, a scroll type, a multistage type, a diaphragm type, and the like can be given.
Moreover, although it does not restrict | limit especially regarding the structure of a mechanical booster pump, an example is demonstrated with reference to FIG. Reference numeral 21 in the drawing is a casing, and the casing 21 has a configuration in which an upper casing 21a constituting an upstream portion and a lower casing 21b constituting a downstream portion are integrated. The casing 21 is provided with an intake port 22 and an exhaust port 23, and a stationary blade 25 is fixedly provided inside the upper casing 21 a side where the intake port 22 is provided. The positions of these stationary blades 25 are fixed by spacers 28, respectively.
A rotating body 31 is installed in the casing 21 so as to be rotatable at a high speed with respect to the stationary side including the casing 21 and the stationary blade 25. The rotating body 31 includes a plurality of rotor blades 32 and a thread groove portion 33 provided in a rotor portion 35 integrally connected to a rotating shaft 34. Accordingly, the rotor 31 includes two axial flow stages and a thread groove stage. It has a stage compression structure. The moving blades 32 on the rotating body 31 side are alternately arranged in the axial direction of the stationary blade 25 and the rotating shaft 34 described above.
The rotating shaft 34 of the rotating body 31 includes a magnetic bearing 29a as an upper bearing, a magnetic bearing 29b as a lower bearing, and an axial bearing that are attached to the inner peripheral surface of the stator 26 fixed to the lower casing 21b. The magnetic bearing 29c is capable of rotating at high speed. In addition, the code | symbol M in a figure is the motor for a rotor drive provided between the internal peripheral surface of the stator 26 and the rotating shaft 34. FIG.
With such a configuration, the gas sucked from the intake port 22 passes between the stationary blade 25 and the moving blade 32 and is compressed by the axial flow stage, and then between the screw groove portion 33 and the heat radiating plate 41. It flows through the main flow of the gas flow path that passes through and receives compression by the thread groove step and flows out from the exhaust port 23.
In the above structure, the rotor blade 32 of the rotating body 31, the casing 21b, the stationary blade 25 fixed by the spacer 28, and the thread groove portion 33 of the rotating body 31 are made of aluminum or an aluminum alloy.

Example 1
Hereinafter, examples of the present invention will be described together with comparative examples.
A disc-shaped aluminum alloy casting (AC4A) material having a diameter of 40 mm and a length of 3 mm is made at room temperature with potassium hydroxide 1 g / L, sodium metasilicate 2 g / L and trisodium phosphate 3 g / L (0.1% hydroxide). (Potassium, 0.1% sodium metasilicate, 0.3% trisodium phosphate) in an electrolytic solution and microarc oxidation treatment was performed in a 50 Hz AC / DC superimposed waveform constant current mode to grow an oxide film with a thickness of about 15 μm on the surface of the member. .

(Example 2)
A rotor 8 to 12 made of cast aluminum alloy, a rotor chamber 4, a casing 1, and an intake air, which constitute the dry pump having the structure of FIG. 1 (maximum exhaust speed is 1.72 × 10 ⁻² m ³ / s (50 Hz)). The surface of the port 2 and the exhaust port 3 was subjected to micro-arc oxidation treatment in the same manner as in Example 1 to grow an oxide film having a thickness of about 12 μm on the surface of the member. In addition, the part which does not process, ie, the rotor shaft part 6 and knock pin part of an iron core, was masked by the silicon sealer and the silicon rubber stopper, respectively.
A dry pump was assembled from each member after the above treatment.

(Comparative Example 1)
The same aluminum alloy casting member as in Example 1 was subjected to an alumite treatment using a 20% by mass sulfuric acid solution to grow an alumite film having a thickness of about 20 μm on the surface of the member. Then, the sealing process was performed by immersing in boiling water for 20 minutes.

(Comparative Example 2)
The same treatment as in Comparative Example 1 was performed on the same aluminum alloy casting member as in Example 2.

(Comparative test 1)
FIG. 3 is a graph showing the results of measuring the gas release characteristics of the members of Example 1 and Comparative Example 1 at room temperature. The vertical axis of the graph represents the amount of gas released per unit area (Pa · m · s ⁻¹ ), and the horizontal axis represents time (hours).
From this graph, it was found that in Example 1, the amount of gas released per unit area was about 1/100 compared to Comparative Example 1.

(Comparative test 2)
Each of the members of Example 1 and Comparative Example 1 was subjected to heating for 30 minutes in an atmosphere of 120 ° C. three times, and then a surface SEM image of each member is shown in FIG.
From FIG. 4, it was found that Example 1 showed no change in film form before and after heating, and Comparative Example 2 showed that cracks occurred after heating.

(Comparative test 3)
The results of measuring the time until each of the members of Example 1 and Comparative Example 1 was immersed in 35 to 38 mass% concentrated hydrochloric acid and foamed vigorously are shown in the graph of FIG. The vertical axis of the graph is time (minutes), and the horizontal axis is the film thickness (μm).
From the graph, it was found that Example 1 has a corrosion resistance of about 2.5 times that of Comparative Example 1. Moreover, after atmospheric heating (same as the comparative test 2), the corrosion resistance of Example 1 hardly changed, and Comparative Example 1 had no corrosion resistance. In Comparative Example 1, it is considered that cracks occurred in the film and the surface of the base material was exposed.

(Comparative test 4)
FIG. 6 shows the time change of the pressure in the chamber when the 1 m ³ chamber was evacuated using the dry pumps of Example 2 and Comparative Example 2.
From the graph, when the dry pumps of Example 2 and Comparative Example 2 were used and the pressure in the chamber was 10 ² Pa or higher, there was not much difference between both cases, but when the pressure was less than 10 ² Pa, the air was exhausted by the dry pump of Example 2 However, the amount of pressure change over time increased. In addition, the ultimate pressure was increased about 2.5 times.

(Example 3)
A disc-shaped aluminum material having a diameter of 40 mm and a length of 3 mm is placed in an electrolytic solution of potassium hydroxide 1 g / L, sodium metasilicate 2 g / L and trisodium phosphate 3 g / L at room temperature, and a 50 Hz AC / DC superimposed waveform setting is performed. Micro-arc oxidation treatment was performed in the current mode, and an oxide film having a thickness of about 15 μm was grown on the surface of the member.

(Comparative Example 3)
The member used in Example 3 was not subjected to treatment on the member surface.

(Comparative test 5)
In order to compare the corrosion resistance of the members of Example 3 and Comparative Example 3 against Ga, it is difficult to obtain a Ga atmosphere (gas). Therefore, in a state where the temperature of each member is heated to about 100 ° C., the liquid state FIG. 7 shows a surface SEM image of each member after the Ga was rubbed against each member and pressed with a slide glass from the top for 60 hours to be adhered. No corrosion or the like is observed on the surface of the member of Example 3, and it is considered that Ga is in contact with the member of Comparative Example 3 and corrodes Al.

  INDUSTRIAL APPLICABILITY The present invention has industrial applicability in imparting corrosion resistance to components constituting a mechanical booster pump, a turbo molecular pump, or a dry pump using aluminum or an aluminum alloy as a base material.

DESCRIPTION OF SYMBOLS 1 Case 2 Intake port 3 Exhaust port 4 Rotor chamber 5 Motor 6 Rotating shaft 7-12 Rotor 13 Heating means 14 Gas ballast 15 Shaft seal gas introduction path 21 Casing 21a Upper casing (upstream part)
21b Lower casing (downstream part)
22 Intake Port 23 Exhaust Port 24 Stationary Body 25 Stator Blade 26 Stator 28 Spacer 29c Magnetic Bearing 30 Pump Mechanism 31 Rotating Body 32 Rotor Blade 33 Screw Groove 34 Rotating Shaft 41 Heat Dissipation Plate HI Heat Insulation Member Ht Heater T Trap Member

Claims (5)

A member constituting a mechanical booster pump, a turbo molecular pump or a dry pump is made of aluminum or an aluminum alloy, the surface of the member is immersed in an alkaline solution, subjected to micro arc oxidation treatment, and the member surface is subjected to the treatment. A surface treatment method for parts constituting a mechanical booster pump, a turbo molecular pump, or a dry pump , wherein a film thickness of an oxide film to be formed is 12 μm to 15 μm . The alkaline solution is disodium hydrogen phosphate, sodium tripolyphosphate, sodium dihydrogen phosphate, sodium ultrapolyphosphate, sodium silicate, potassium hydroxide, sodium diphosphate, trisodium phosphate, sodium aluminate, one kind or a mixture of of these in the sodium metasilicate and sodium hydroxide were dissolved in water, the surface according to claim 1, characterized in that its concentration of 0.1% to 5% by weight Processing method. 3. The surface treatment method according to claim 1, wherein an applied voltage in the micro arc treatment is in a range of 300 V to 600 V, and a current density is 3.0 A / dm ^{2 to} 10 A / dm ² .   The surface treatment method according to any one of claims 1 to 3, wherein a temperature of the alkaline solution is set to 5 to 90 ° C. A mechanical booster pump, a turbo molecular pump, or a dry pump, characterized by comprising a member treated by the surface treatment method according to any one of claims 1 to 4 .

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