JP2009243281A - Surface treatment method of screw rotor for screw fluid machine and screw rotor for screw fluid machine - Google Patents

Abstract

An object of the present invention is to form a high-hardness coating useful for preventing corrosion, improving wear resistance and lubricity on the surface of a rotor portion of a screw rotor for a screw fluid machine.
Screw rotors 3 and 4 having a structure in which rotor parts 31 and 41 made of aluminum alloy having a Si content of 1 wt% or less are formed on the outer periphery of rotor shafts 32 and 42 are prepared. , 4 are immersed in an electrolyte containing zirconium salt, and spark discharge is performed by energization using the rotor portions 31 and 41 as anodes. By this spark discharge, a ceramic film having a composition of mainly ZrO ₂ —Al ₂ O ₃ —MgO having high hardness, excellent wear resistance, and lubricity is formed on the surfaces of the rotor portions 31 and 41. .
[Selection] Figure 2

Description

  The present invention relates to a surface treatment method for a screw rotor for a screw fluid machine, and a screw rotor for a screw fluid machine subjected to the surface treatment.

  A screw fluid machine such as a rotary pump or a blower, for example, a screw compressor 1, accommodates a pair of male and female screw rotors 3 and 4 in a cylinder 20 formed in a casing 10 in a rotatable manner. The compressed gas sucked from the suction port 11 by the rotation of the screw rotors 3 and 4 is compressed and discharged from the discharge port 12 (see FIGS. 1 and 2).

  As such a screw compressor 1, an oil-cooled screw compressor that introduces lubricating oil into the compression working space in order to lubricate, cool, and seal the compression working space is generally used. In this oil-cooled screw compressor, since the lubricating gas is contained in the compressed gas supplied to the consumer side, as a screw compressor used for applications that do not want to supply such compressed gas containing oil. A screw compressor has been proposed that can perform compression without supplying lubricating oil into the compression working space.

  Thus, as an example of a screw compressor capable of compressing compressed gas without supplying lubricating oil into the compression working space, a so-called “oil-free screw compressor” is known as a screw compressor. is there.

  As shown in FIG. 3, the oil-free screw compressor 1 includes timing gears on the rotor shafts 32 and 42 of a pair of male and female screw rotors 3 and 4 housed in a cylinder 20 formed in a casing 10. 51 and 52 are provided, and the rotation timings of the screw rotors 3 and 4 are regulated by the timing gears 51 and 52, so that the screw rotors 3 and 4 are rotated in a non-contact state with a slight interval. This makes it possible to compress the compressed gas without introducing lubricating oil into the compression working space. With this configuration, the compressed gas containing no oil or moisture is supplied to the consumer side. It is possible to do.

  In such an oil-free screw compressor 1, both screw rotors 3, 4 can be rotated in a non-contact state by regulating the rotation timing by the timing gears 51, 52 described above. When the compressed gas in the cylinder 20 becomes high temperature due to the compression heat, the rotor portions 31 and 41 of the screw rotors 3 and 4 are thermally expanded, and the rotor portions 31 and 41 are slightly in contact with each other, and seizure may occur. When the compressor is stopped, high-temperature compressed air cools and condenses, which may cause moisture to adhere to the rotor portions 31 and 41 of the screw rotors 3 and 4. By applying molybdenum sulfide to the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4, such seizure and rusting are prevented. See Patent Documents 1 and 2).

  Another example of the screw compressor 1 that can supply a compressed gas that does not contain oil is a so-called “water jet screw compressor”.

  In this water-injection screw compressor, the cooling space is cooled and sealed by injecting cooling water instead of the lubricating oil introduced into the compression space by the oil-cooled screw compressor described above. This makes it possible to supply compressed gas that does not contain oil.

  In such a water injection screw compressor, unlike the oil-free screw compressor described with reference to FIG. 3, timing gears 51 and 52 that regulate the rotation timing of both screw rotors 3 and 4 are not provided. , The screw rotors 3 and 4 apply the rotational driving force input to one screw rotor (female rotor 4 in the illustrated example) to the other screw rotor (male rotor 3 in the illustrated example) by contact rotation of the rotor portions 31 and 41. It has the same structure as the oil-cooled screw compressor described above in that it is transmitted and rotated, but it introduces cooling water with poor lubricity into the compression working space compared to lubricating oil. In general, in an oil-cooled screw compressor, the rotor portions 31 and 41 of the screw rotors 3 and 4 that come into contact with cooling water may be corroded or rusted. Instead of the steel screw rotors 3 and 4 used, a screw rotor in which rotor portions 31 and 41 formed of a synthetic resin having self-lubricating properties are attached to rotor shafts 32 and 42 made of metal such as stainless steel, for example. 3, 4 are used (see Patent Document 3).

  None of the following exists as a surface treatment technique for the screw rotors 3 and 4 of the screw compressor 1, but as an example, the following is given as a surface treatment technique for an aluminum material.

As a surface treatment technique widely used for an aluminum material, there is an alumite treatment in which a film of γ-Al ₂ O ₃ is formed on the surface of the aluminum material by anodic oxidation.

  In addition, as a surface treatment technology that replaces the alumite treatment, a method is used in which an aluminum material is energized in an electrolytic bath as an anode and a glassy protective film is formed on the surface of the aluminum material by spark discharge (hereinafter referred to as “anodic spark discharge treatment”). Is also proposed (see Patent Document 4).

  Furthermore, in order to solve the problem that the surface hardness of the glassy protective coating (ceramic coating) formed by the anode spark discharge treatment is low, the first electrolysis containing silicate and / or oxyacid salt is used. After the first film is formed by spark discharge in the bath, the ceramic particles are co-deposited by spark discharge in the second electrolytic bath containing the ceramic fine particles in a suspended state. It has also been proposed to increase the surface hardness of the coating film by forming the second coating film (claim 1, column "0004", column "0013", etc. of Patent Document 5).

Prior art document information of the present invention includes the following.
JP-A-2-201072 Japanese Patent No. 3267814 JP 2004-36586 A Japanese Patent Publication No.58-17278 JP-A-5-86485

1. Problems in Applying Solid Lubricant In the configuration of the screw compressor 1 described above, in an oil-free screw compressor in which neither lubricating oil nor cooling water is introduced into the compression working space, a pair of male and female screws as described above is used. In order to prevent the rotors 3 and 4 from being seized or rusted, solid lubrication is performed by applying a solid lubricant such as molybdenum disulfide to the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4. A coating of the agent is formed, and seizure is prevented by the lubricity of molybdenum disulfide, which is this solid lubricant.

  However, since the solid lubricant film formed in this manner easily peels off when rubbed strongly, it does not have the timing gears 51 and 52 as described above and is input to one screw rotor 4. Therefore, the present invention cannot be applied to a screw rotor for a water jet type screw compressor that transmits and drives the rotational driving force transmitted to the other screw rotor 3 by meshing the rotor portions 31 and 41.

  In addition, since molybdenum disulfide, which is a solid lubricant, does not adhere to the rotor portions 31 and 41 of the screw rotors 3 and 4 alone, the heat-resistant resin is mixed with the solvent together with molybdenum disulfide and applied as a binder. Thus, a solid lubricant film is formed.

  However, since the inside of the cylinder 20 of the oil-free screw compressor is heated to a high temperature of 200 ° C. to 300 ° C. due to the heat of compression, even if the solid lubricant is adhered using a heat resistant resin as a binder. When exposed to high temperatures for a long time, the heat-resistant resin may gradually deteriorate and peel off.

  Further, in the oil-free screw compressor, as described above, the cooling water or the lubricating oil having the sealing action of the compression working space is not injected into the cylinder 20, so that the rotor portions 31, 41 of both screw rotors 3, 4 are not used. The compressed gas can be compressed by minimizing the gap between the teeth. In order to realize this minimal gap, the rotor portions 31 of the screw rotors 3 and 4 of the oil-free screw compressor, First, a solid lubricant is applied to 41 so as to be thicker than the required thickness of the solid lubricant film, and then the male and female screw rotors 3 and 4 are slid together. In some cases, excessive film removal may be performed. At this time, the film is too thick to be formed, or when the film is rubbed too hard during adjustment, it may be difficult to process. It requires the skill to.

  In addition, since the screw rotors 3 and 4 are not fixed planes but are complicated shapes, it is difficult to apply the solid lubricant to a uniform film thickness. This is also a cause of variations in performance among the individual screw compressors manufactured by generating a portion where the four rotor portions 31 and 41 are in strong contact with each other and a portion having a large gap.

2. Problems in Synthetic Resin Rotor In the water jet screw compressor described above, the rotor portions 31 and 41 made of a self-lubricating synthetic resin are provided on the outer periphery of the rotor shafts 32 and 42 to form a screw rotor. This makes it possible to reduce the lubricity and prevent corrosion and rusting by introducing water having a lower lubricity than the lubricating oil into the compression working space.

  However, the temperature in the cylinder 20 of the water jet screw compressor is lowered (about 80 ° C.) from the temperature in the cylinder 20 of the oil-free screw compressor by cooling with the cooling water introduced into the cylinder 20. Although it is maintained, the synthetic resin constituting the rotor parts 31 and 41 of the screw rotors 3 and 4 is thermally expanded and swollen by the temperature in the cylinder 20 and the cooling water, and the rotor parts 31 and 41 of the screw rotors 3 and 4 There is a problem that the inner wall surface of the cylinder 20 may come into contact, and this contact may damage the rotor portions 31 and 41 of the screw rotors 3 and 4.

  Further, if the gas to be compressed (for example, air outside the machine) compressed by the water jet screw compressor contains a component that deteriorates the synthetic resin constituting the rotor portions 31 and 41, the strength of the resin is reduced. The rotor portions 31 and 41 of the screw screw rotors 3 and 4 may be damaged.

  Further, since the rotor portions 31 and 41 made of synthetic resin are formed by a mold, the processing accuracy is inferior to that of a metal screw rotor manufactured by cutting or grinding. There is a problem that the compression performance is low because a large gap is provided in advance so as not to be unable to rotate.

3. Problems in surface treatment technology of aluminum material (1) Problems in general surface treatment technology Forming a film of solid lubricant on the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4, and screw rotors 3 and 4 In order to solve the above-mentioned various problems caused by making the rotor parts 31 and 41 themselves made of synthetic resin, a hard film such as a ceramic film is formed on the surface of the metal rotor part by, for example, spraying or vapor deposition. However, it is difficult to form the coating film formed on the surface of the screw rotors 3 and 4 by thermal spraying or the like because it is necessary to control the film thickness with high accuracy. In addition, when a film is formed by vapor deposition or the like, a large initial investment is required such as an expensive vacuum device.

On the other hand, in order to apply the surface treatment technology to the aluminum material, the rotor portions 31 and 41 of the screw rotors 3 and 4 are formed of the aluminum material, and the surface thereof is coated with an alumite (γ-Al ₂ O ₃ ) by anodic oxidation. Can also be considered.

  However, since the alumite film formed in this way has a porous structure, for example, when it is applied to the screw rotors 3 and 4 of a water jet type screw compressor, it is compressed in the cylinder 20. Since the gas and cooling water flow vigorously from the suction side to the discharge side, the coating is eroded when such high pressure and high flow rate cooling water comes into contact with the porous alumite coating with low surface smoothness. There is a risk of being peeled off or peeling off, and because of the porous structure, pinholes are likely to occur, and if a pinhole occurs, the base material begins to corrode from this portion.

  In addition, although the alumite coating has a relatively high hardness, it does not have a strength sufficient to withstand the impact when the contact between the screw rotors 3 and 4 or the contact with the inner wall of the cylinder 20 occurs. The porous structure described above lacks surface smoothness, has low lubricity, and cannot exhibit slidability when in contact.

(2) Problems of anode spark discharge treatment Instead of the alumite coating having such a porous structure, according to the anode spark discharge treatment described in Patent Documents 4 and 5, the glassy ceramic coating is formed. Since it can be formed, it is conceivable to form a ceramic film by the anode spark discharge treatment on the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4.

  However, it has been pointed out that ceramic coatings formed by anodic spark discharge treatment are vulnerable to damage due to impact or abrasion due to the low surface hardness of the coatings (Patent Document 5 “0004” column above). However, it is not suitable for the surface treatment of the screw rotors 3 and 4 of the screw compressor.

  Further, in order to solve such a problem that the surface hardness is low, ceramic fine particles are contained in a suspended state after the spark discharge treatment by the first electrolytic bath as in the invention described in Patent Document 5 described above. If the method of forming a second coating with excellent strength, wear resistance, etc., in which ceramic fine particles are co-deposited by spark discharge in the second electrolytic bath, a two-step process is required for forming the ceramic coating. It is necessary, and the film forming operation is complicated, for example, it is necessary to perform the first electrolytic bath and the second electrolytic bath using two types of electrolytic solutions having different components.

  Further, the inventor of the present invention forms a ceramic coating on the surface of the screw rotors 3 and 4 of a screw compressor made of AC4C (JIS symbol: hereinafter the same), which is an aluminum alloy for casting, by the above-described anode spark discharge treatment. The test showed that, unlike alumite, a ceramic film without a porous structure could be formed, but the formed ceramic film had low hardness, and a lot of voids were formed in the formed ceramic film. It was confirmed that a hole was formed.

  The generation of such holes is not particularly problematic when a ceramic film is formed as an insulating film such as an electric wire as described in Patent Document 5, but the screw of the screw compressor 1 is not particularly problematic. If such vacancies occur in the protective coating on the surfaces of the rotors 3 and 4, the strength and hardness of the coating will decrease at the vacancy-generating portion, and if this is used particularly in a water jet screw compressor, Cavitation damage based on the hole generation point, erosion and separation due to contact with high-pressure and high-speed cooling water, destruction due to contact with the rotor portions 31 and 41 of the screw rotors 3 and 4 and the inner wall surface of the cylinder 20, etc. If the aluminum alloy as the base material of the rotor parts 31 and 41 of the screw rotors 3 and 4 comes into contact with the cooling water through the holes, the gold in the cooling water will be peeled off. Etc. eluting under the influence of ions, causing corrosion.

  In addition, when manufacturing the rotor parts 31 and 41 of the screw rotors 3 and 4 with an aluminum alloy, the rotor parts 31 and 41 manufactured by casting are further processed into a final shape by cutting or grinding. The aluminum alloy used for casting is represented by the above-mentioned AC4C, etc., which has high fluidity in the molten state and excellent castability, has little shrinkage and hot brittleness during solidification, and is relatively excellent in corrosion resistance. Al-Si based alloys are generally used.

  However, as a result of diligent research by the inventors of the present invention, in the ceramic film formed by anodic spark discharge treatment, the mechanical properties of the formed film decrease as the Si content in the aluminum alloy increases. In addition, the Si component in the aluminum alloy intervenes as an impurity in the formed film to reduce the hardness of the film, and the inclusion of Si as an impurity causes voids in the film. I found out.

  On the other hand, if all the alloy components that may adversely affect the ceramic film to be formed are eliminated, and the rotor parts 31 and 41 of the screw rotors 3 and 4 are made of pure aluminum, for example, the film that is formed Although it is possible to prevent impurities from interposing, the mechanical strength of the base metal itself is reduced.

4). SUMMARY OF THE INVENTION In view of the above disadvantages of the prior art, the present invention is such that the rotor part of a screw rotor of a screw fluid machine is manufactured from an aluminum alloy that is a metal, and the rotor part made of a synthetic resin is employed. While trying to solve the problem, a new problem arising from the adoption of the aluminum alloy rotor part, that is, the rotor part surface does not have a porous structure, no voids are generated, and the hardness A surface treatment method of a screw rotor that can prevent corrosion, seizure, and breakage by forming a ceramic film excellent in mechanical properties such as by a relatively simple method, and a screw fluid treated by the method It aims at providing the screw rotor for machines.

  In addition to the above-mentioned object, the present invention provides a coating film having excellent characteristics as described above for a screw fluid machine that can form without sacrificing mechanical properties such as strength and corrosion resistance of the base material itself. It is an object of the present invention to provide a screw rotor surface treatment method and a screw rotor for a screw fluid machine treated by the method.

In order to achieve the above object, the surface treatment method for the screw rotors 3 and 4 for the screw fluid machine according to the present invention is such that the screw rotors 32 and 42 of the screw fluid machine 1 are made of, for example, stainless steel. A structure in which rotor parts 31 and 41 made of aluminum alloy having a Si content of 1 wt% or less are formed on the outer periphery,
The rotor parts 31 and 41 are immersed in an electrolytic solution, and spark discharge is performed by energization using the rotor parts 31 and 41 as anodes, thereby including aluminum oxide in the surface of the rotor parts 31 and 41 in the composition. A ceramic film is deposited (claim 1).

In the above method, a zirconium salt may be included in the electrolytic solution, and a ceramic film mainly having a composition of ZrO ₂ —Al ₂ O ₃ may be deposited on the surfaces of the rotor portions 31 and 41 (Claim 2). .

  Furthermore, in the method, it is preferable that the aluminum alloy constituting the rotor portions 31 and 41 is an Al—Mg alloy (Claim 3).

As described above, the rotor parts 31 and 41 made of an Al—Mg-based alloy mainly include ZrO ₂ —Al _{2 on the} surfaces of the rotor parts 31 and 41 by performing the spark discharge including the zirconium salt in the electrolytic solution. A ceramic film having a composition of O ₃ —MgO may be deposited (claim 4).

  Further, the surface of the ceramic coating formed on the surfaces of the rotor portions 31 and 41 as described above is further provided with a solid lubricant coating such as a resin in which a solid lubricant such as fluororesin or molybdenum disulfide is dispersed. It can also be formed (Claim 5).

  In addition, the said surface treatment method is suitable for performing with respect to the screw rotors 3 and 4 of an oil-free screw compressor or a water-injection-type screw compressor (Claim 6).

  Further, the screw rotors 3 and 4 of the screw fluid machine according to the present invention are the same as those of the screw rotors 3 and 4 of the screw fluid machine 1 in which the rotor parts 31 and 41 are formed on the outer periphery of the rotor shafts 32 and 42. Is manufactured with an aluminum alloy having a Si content of 1 wt% or less, and the surface of the rotor portions 31 and 41 is formed of a ceramic film containing aluminum oxide deposited by spark discharge in the electrolyte in the composition. It is characterized by being coated (claim 7).

In the screw rotors 3 and 4 having the structure described above, the surface of the rotor portions 31 and 41 may be covered with a ceramic film mainly containing a composition of ZrO ₂ —Al ₂ O ₃ including a zirconium salt in the electrolytic solution ( Claim 8).

  Furthermore, the aluminum alloy constituting the rotor portions 31 and 41 of the screw rotors 3 and 4 is an Al-Mg alloy, for example, AC7A, ADC5, ADC6, A5000 series aluminum alloy (all are JIS symbols). (Claim 9).

Further, in the above-described configuration in which the rotor parts 31 and 41 are made of an Al—Mg alloy, the rotor part is made of a ceramic film containing a zirconium salt in the electrolyte and mainly having a composition of ZrO ₂ —Al ₂ O ₃ —MgO. The surface of 31,41 can also be covered (claim 10).

The screw rotors 3 and 4 may be formed by further coating the surface of the ceramic film with a solid lubricant film (Claim 11).
These screw rotors 3 and 4 are suitable for use as screw rotors 3 and 4 of an oil-free screw compressor or a water jet screw compressor.

  With the configuration of the present invention described above, the following remarkable effects can be obtained in the surface treatment method of the present invention and the screw rotor for a screw fluid machine to which the surface treatment method is applied.

(1) Formation of a coating on the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4 is performed by spark discharge using the rotor portions 31 and 41 as anodes in an electrolytic solution (hereinafter referred to as “anodic spark discharge treatment”). As a result, a ceramic film having no porous structure could be formed on the surfaces of the rotor portions 30 and 41.

  The ceramic coating formed in this way is superior in that it is harder than molybdenum disulfide coating coated with resin, has high adhesion strength to the base material, and has excellent heat resistance. It exhibited the characteristics.

  Moreover, the rotor parts 31 and 41 of the screw rotors 3 and 4 to be processed are made of an aluminum alloy having a Si content of 1 wt% or less, so that there are no Si and other impurities in the coating. Moreover, it was possible to form a ceramic film with almost no voids.

  Thus, a ceramic coating that does not have a porous structure and has no interstitial impurities or vacancies has excellent mechanical properties such as high hardness, and is also porous. The surface of the rotor portion is smooth because it does not have a quality structure, and lubricity is imparted to the rotor portion surface. The contact between the rotor portions 31 and 41 of the screw rotors 3 and 4 and the rotor portions 31 and 41 are connected to the inner wall surface of the casing 20. Even if it contacts, it does not easily break or peel off, and the coating film has a porous structure or various adverse effects caused by having pores, for example, the screw rotors 3 and 4 are water jet type screw compressors. Erosion and delamination of the coating that occurs when used in No. 1, cavitation damage based on the vacancy generation part, the base material comes into contact with cooling water through the vacancy, and is eluted under the influence of metal ions. Rot It was possible to eliminate the occurrence.

  In addition, a ceramic film with excellent mechanical properties could be formed, making it possible to reduce the film thickness. As a result, in general, as the film thickness increases, the film thickness becomes non-uniform or the surface smoothness is lost. However, such an adverse effect can be easily eliminated by making the film thinner.

  In addition, since such a surface treatment method is performed by immersing the rotor portions 31 and 41 in the electrolytic solution, the film thickness is uniform even with respect to the rotor portions 31 and 41 of the screw rotors 3 and 4 having complicated shapes. Can be formed, and the contact and spacing of the rotor portions 31 and 41 of the male and female rotors can be made uniform. Thus, the individual screw compressors 1 incorporating the screw rotors 3 and 4 can be separated. As well as reducing the variation in the performance of the film, it was also possible to prevent the occurrence of a thin film portion that becomes the starting point of corrosion and peeling.

(2) A ceramic film having a composition of high hardness ZrO ₂ —Al ₂ O ₃ is formed on the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4 by a relatively simple method of including a zirconium salt in the electrolytic solution. It could be precipitated.

  Moreover, since the zirconia-based ceramic coating formed in this way has high hardness and stickiness, it was applied to the rotor portions 31 and 41 of the screw rotors 3 and 4 using aluminum having a high thermal expansion coefficient as a base material. Even in this case, it was possible to prevent the coating from cracking due to the thermal expansion of the rotor portions 31 and 41.

(3) Since the rotor portions 31 and 41 of the screw rotors 3 and 4 are made of an Al—Mg alloy, Mg as an alloy component forms voids in a ceramic film formed like Si. Mg does not have an adverse effect, and Mg forms a hard film by oxidation, and does not adversely affect the formed ceramic film, such as a decrease in hardness or the generation of voids.

  On the other hand, aluminum alloy containing Mg component can improve the mechanical properties of the base metal itself, such as high strength and excellent corrosion resistance, and is compatible with the fact that the formed ceramic coating has high hardness and high corrosion resistance. Thus, the rotor portions 31 and 41 of the screw rotors 3 and 4 can be more suitably prevented from being damaged or corroded.

(4) Further, the rotor parts 31 and 41 of the screw rotors 3 and 4 formed of an Al-Mg alloy are subjected to an anodic spark discharge treatment in an electrolytic solution containing a zirconium salt, whereby the surfaces of the rotor parts 31 and 41 are formed on the surfaces described above. As a result, a high hardness, high corrosion resistance, and high heat resistance coating mainly composed of ZrO ₂ —Al ₂ O ₃ —MgO was formed, and it was possible to prevent the hardness of the coating from being lowered due to the influence of the alloy components.

  The ceramic coating formed in this way is applied to the screw rotors 3 and 4 of the screw compressor 1 using aluminum having a high thermal expansion coefficient as a base material because it has high hardness and stickiness as described above. Even in this case, it was possible to prevent the coating from cracking due to the thermal expansion of the screw rotor.

(5) The surface of the rotor portions 31 and 41 of the screw rotors 3 and 4 is formed by forming a solid lubricant film on the surface of the ceramic coating by applying a resin containing fluorine resin or molybdenum disulfide. The lubricity could be further improved.

  In addition, the solid lubricant film is formed thinner than the screw rotor of the conventional oil-free screw compressor in which the solid lubricant film is directly formed on the surface of the screw rotors 3 and 4. However, since sufficient corrosion resistance, wear resistance, etc. can be imparted, and the solid lubricant film can be made thin, it is necessary to adjust the film thickness by rubbing as described above. However, the operation was easy and it was possible to prevent the solid lubricant film from being peeled off during rubbing.

  Next, an embodiment of the present invention will be described below.

1. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended for processing a screw rotor of a screw fluid machine, and is particularly applicable to the screw rotors 3 and 4 of a water jet or oil-free screw compressor 1. Suitable for

  The screw compressor 1 houses a pair of male and female screw rotors 3 and 4 in a cylinder 20 formed in a casing 10, and sucks outside air into the cylinder 20 by the rotation of both screw rotors 3 and 4. The compressed air is discharged after being compressed.

  The screw rotors 3 and 4 to be processed in the present invention are formed by forming aluminum alloy rotor parts 31 and 41 around rotor shafts 32 and 42 made of stainless steel or the like, and cutting the rotor parts 31 and 41. Alternatively, the rotor parts 31 and 41 having a rough tooth profile formed by casting are first manufactured, for example, by casting, and the rotor part 31 having the final tooth profile is cut and polished. , 41, or a rotor part 31, 41 having a predetermined tooth shape by cutting and polishing a billet made of an aluminum alloy such as a bar. The processing method and the like are not particularly limited.

  The tooth shapes of the rotor portions 31 and 41 of the screw rotors 3 and 4 are regular tooth shapes during operation, that is, the clearance between the rotor portions 31 and 41 of the male and female screw rotors 3 and 4 and the screw rotor 3 during operation. , 4 and the inner wall surface of the cylinder 20 so as to have an appropriate value, a film formed by deformation due to thermal expansion accompanying compression heat generated during operation or an anode spark discharge process (to be described later) Is formed in accordance with a processing tooth profile obtained in advance in consideration of the film thickness of the solid lubricant film).

  When the treatment target is a screw rotor of a water jet screw compressor, the temperature in the cylinder 20 is kept lower than that in the case of an oil-free screw compressor. What is processed into a regular tooth profile without considering the deformation amount due to the above may be used as a processing target of the present invention.

(2) Range to be treated The surface treatment in the present invention is performed on the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4 described above, and the treatment range is the peripheral surface of the rotor portions 31 and 41 ( In addition to the portions where teeth, tooth gaps and the like are formed), both end surfaces 31a, 31b, 41a, 41b on the discharge side and the suction side are included.

  The surface treatment of the present invention is intended for both male and female screw rotors 3 and 4 for the anode spark discharge treatment described later, but for the formation of the solid lubricant film described later, either male or female. It is good also as what is performed only with respect to a screw rotor (3 or 4). However, it is preferable to form the solid lubricant film on both the male and female screw rotors 3 and 4.

(3) Material The rotor parts 31 and 41 of the screw rotors 3 and 4 to be treated by the surface treatment method of the present invention are manufactured from an aluminum alloy having a Si content of 1 wt% or less.

  When the rotor parts 31 and 41 of the screw rotors 3 and 4 are manufactured by casting, as described above, they have high fluidity in a molten state and excellent castability, and also have less shrinkage and hot brittleness during solidification, and are resistant to corrosion. Although the use of a relatively excellent Al-Si alloy is suitable, as described above, the Si component in the aluminum alloy is one that degrades the mechanical properties of the ceramic coating formed by the anodic spark discharge treatment. By suppressing the Si content to 1 wt% or less, it is possible to form a ceramic film of Hv600-1900 that is much harder than hard anodized up to about Hv500, and In the ceramic film formed as described above, almost no interposition of Si as an impurity or generation of vacancies was confirmed.

  On the other hand, since the Si component in the aluminum alloy is useful for improving the castability as described above, when the rotor parts 31 and 41 are formed by casting, they are 1 wt% or less, preferably An aluminum alloy containing Si at 0.2 wt% or less is used.

Further, as the aluminum alloy forming the rotor portions 31 and 41 of the screw rotors 3 and 4, preferably an Al-Mg alloy is used. Since the Al—Mg alloy is difficult to cast due to an oxide film formed on the surface of the molten metal when melted, considering the case where the rotor parts 31 and 41 of the screw rotors 3 and 4 are manufactured by casting, the rotor It can be said that it is preferable to use the above-described Al—Si based alloy as a forming material for the portions 31 and 41, but the alloy component Mg is a ceramic film that is formed like the above-described Si even after anodic spark discharge treatment. ZrO ₂ —Al ₂ O ₃ — containing magnesium oxide (MgO) by performing an anodic spark discharge with an electrolyte containing a zirconium salt as will be described later. It functions as a protective coating for protecting the surfaces of the rotor portions 31 and 41 by depositing a ceramic coating of MgO composition.

  Aluminum alloy containing Mg as an alloy component itself has excellent mechanical properties and high corrosion resistance, heat resistance, etc., so the use of Al-Mg alloy is based on the mechanical properties and corrosion resistance of the base metal itself. In combination with the formation of a high-hardness ceramic film, the surfaces of the rotor portions 31 and 41 can be protected from wear and corrosion.

  Here, the Mg content of the Al—Mg alloy used is in the range of 2 to 11 wt%, and if it exceeds 11 wt%, the castability is remarkably lowered, and the rotor portions 31 and 41 of the screw rotors 3 and 4 are cast. It becomes difficult to manufacture, and if it is less than 2 wt%, the mechanical properties of the base material cannot be improved. More preferably, the Mg content is 3.5 to 5.5 wt%.

  Examples of the Al—Mg alloy satisfying such conditions include AC7A, which is an aluminum alloy for casting, ADC5, ADC6, which is an aluminum alloy for die casting, and A5000 series aluminum alloy, which is a wrought material. Use of AC7A is suitable.

2. Anode spark discharge treatment The surface treatment according to the present invention for the surfaces of the rotor portions 31 and 41 provided on the screw rotors 3 and 4 of the screw compressor 1 is performed by the rotor portions 31 and 41 of the screw rotors 3 and 4 immersed in the electrolytic solution. It is performed by performing a spark discharge in the electrolyte by energization with the anode as the anode.

  The electrolysis apparatus used for the anode spark discharge treatment is not particularly limited, and various known electrolysis apparatuses can be used.

  In addition, as the electrolytic solution for immersing the rotor portions 31 and 41, various known electrolytic solutions used for the anodic spark discharge treatment can be used, but an electrolytic solution containing a zirconium salt is preferably used.

  As an electrolytic solution to be used, it is preferable to use an electrolytic solution containing at least one of water and a zirconium compound, and alkali metal ions, ammonium ions, and organic alkalis. As an example, water, a zirconium compound, and an alkaline solution are used. An electrolytic solution containing metal ions and / or ammonium ions can be preferably used.

  The zirconium compound included in the electrolytic solution is not particularly limited, but is preferably a water-soluble zirconium compound. By using such a water-soluble zirconium compound, a film having a dense structure can be formed.

  Further, the electrolytic solution to be used may contain two or more kinds of zirconium compounds. In this case, it is preferable that at least one of the zirconium compounds, more preferably all of them are water-soluble zirconium compounds.

  Examples of the water-soluble zirconium compounds include zirconium salts of organic acids such as zirconium acetate, zirconium formate, and zirconium lactate; Zirconium complex salts such as ammonium zirconium acid can be used, but usable water-soluble zirconium compounds are not limited to these.

In particular, the zirconium carbonate compound represented by the chemical formula M ₂ ZrO (CO ₃ ) ₂ (wherein M represents ammonium or an alkali metal) is dissolved in an alkaline electrolyte and is likely to remain stable. Preferably, examples of such a zirconium carbonate compound include zirconium ammonium carbonate and potassium zirconium carbonate.

  Moreover, zirconium hydroxide can also be suitably used as the zirconium compound.

  The content of the zirconium compound in the electrolytic solution is preferably 0.0001 to 5 mol / L, more preferably 0.001 to 0.5 mol / L in terms of zirconium.

The ceramic coating formed on the surfaces of the rotor portions 31 and 41 by the anode spark discharge treatment using such an electrolyte containing a zirconium salt is excellent in mechanical properties mainly composed of ZrO ₂ —Al ₂ O ₃ —MgO. A zirconia-based ceramic coating can be obtained.

  The temperature of the electrolytic solution is not particularly limited and can be performed at various temperatures, but the anode spark discharge treatment is economical and the anode rotor discharge portions 31 and 41 are prevented from being melted by the anode spark discharge treatment. It is preferable to carry out as the range of 10-60 degreeC by the point which can be performed, and in order to maintain at this temperature, it is good also as what cools an electrolytic bath.

  The electrolytic treatment method is not particularly limited, and various known methods such as a direct current electrolytic method, a bipolar electrolytic method, and a pulse electrolytic method can be applied. However, the direct current electrolytic method is excellent in economic efficiency because the electrolytic solution boils. The bipolar electrolysis method and the pulse electrolysis method performed at a relatively high voltage are preferable. In particular, in the bipolar electrolysis method, it is preferable to use a voltage waveform in which an AC component is superimposed on a DC component.

  In the pulse electrolysis method, it is preferable to use a voltage waveform in which at least one pulse wave selected from the group consisting of a rectangular wave, a sine wave and a triangular wave with a duty ratio of 0.5 or less is superimposed on a DC component or an AC component.

  The conditions for the electrolytic treatment can be appropriately selected according to the type of the electrolytic solution used, the material and size of the rotor portions 31 and 41 to be treated, the thickness of the coating film to be formed, etc. In the present invention in which the portions 31 and 41 are treated, it is necessary to apply a voltage of at least 200 V to the electrodes. When performing, the maximum value (peak voltage) of a voltage waveform becomes like this. Preferably it is 300-800V, More preferably, it is 400-800V.

  If the maximum value of the voltage waveform is 300 V or more, particularly 400 V or more, spark discharge is likely to occur. On the other hand, if the maximum value of the voltage waveform is 800 V or more, the surface roughness of the formed film becomes too large. It is.

  In this embodiment, as an example, a voltage of 600 V is applied at a frequency of 60 Hz.

The current density is preferably in the range of 1 to 250 A / dm ² at the positive peak, and more preferably in the range of ^{20 to} 150 A / dm ² . By setting the current density to 1 A / dm ² or more at the positive peak, not only the film formation speed is increased and the workability is improved, but also the oxidation of aluminum and the crystallization of zirconium oxide are facilitated. This is because if the current density is 250 A / dm ² or more at the positive peak, the surface roughness of the formed film increases, which is not preferable.

  During this electrolytic treatment, a clear light emission phenomenon may be observed on the surface. Luminescence can be easily confirmed visually. In this electrolytic treatment, it is preferable to carry out the treatment with this light emission. There are many unclear points about the light emission phenomenon that occurs in this liquid, and light emission is called glow discharge, arc discharge, micro arc discharge, plasma discharge, and the like. The temperature at which these light emission occurs is said to exceed 1000 ° C., and therefore, zirconium in the electrolytic solution can be crystallized and deposited.

  The electrolytic treatment time is not particularly limited and can be appropriately selected so as to obtain a desired film thickness. However, as an example, it is preferably 1 to 45 minutes, more preferably 5 to 30 minutes.

  The thickness of the film obtained by the method of the present invention is not particularly limited, and can be a desired thickness. Usually, the thickness is preferably 0.01 to 500 μm, and more preferably 0.5 to 50 μm. If it is within the above range, the impact resistance is excellent, and the time for the electrolytic treatment is too long, and the economic efficiency is not inferior. In the present embodiment, as an example, a ceramic coating of about 2 to 10 μm was formed with a processing time of 10 minutes.

By the above anode spark discharge treatment, the surfaces of the rotor portions 31 and 41 provided on the screw rotors 3 and 4 of the screw compressor 1 are made of ZrO ₂ − by Al, Mg in the base material, and zirconium in the electrolyte. A zirconium ceramic layer having an Al ₂ O ₃ —MgO composition is formed.

  This zirconium-containing ceramic is a high-hardness and tough material known as engineering ceramics, which can dramatically improve the wear resistance, heat resistance, and corrosion resistance of the rotor parts 31 and 41. It is.

  In this surface treatment method, the rotor portions 31 and 41 are immersed in the electrolytic solution to perform the surface treatment. Therefore, even with the rotor portions 31 and 41 having complicated tooth shapes, a film can be formed with a uniform film thickness. Therefore, it is possible to reduce the variation in performance of each compressor, and it is possible to prevent the occurrence of a thin film portion that tends to be a starting point of corrosion and peeling because of the uniformity of the film thickness.

3. Solid Lubricant Film Formation Treatment As described above, the solid lubricant film is applied to the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4 on which the ceramic film is formed by the anode spark discharge treatment as described above. (See FIG. 4).

  The formation of the solid lubricant film may be performed on one of the male and female screw rotors 3 and 4 as described above, but preferably both the male and female screw rotors 3 and 4 are solid. A lubricant film is formed.

  The solid lubricant film can be formed by various known methods, for example, by applying a fluororesin or by applying a solid lubricant powder such as molybdenum disulfide using a heat-resistant resin as a binder. Can do.

  The solid lubricant film may be formed to be thicker than the first required film thickness, and may be worn by rubbing described as the prior art to adjust the final film thickness.

  As an example, such balancing is performed by engaging a pair of male and female rotors 3 and 4 used by being incorporated in the same cylinder 20 on a substantially parallel axis so as to be rotatable, and both screw rotors. A synchronous gear having a backlash equivalent to the backlash to be applied to 3 and 4 is fixed to the rotor shafts 32 and 42 of both screw rotors 3 and 4, and in this state, a brake torque is applied to one screw rotor. By adjusting the distance between the cores of the two screw rotors while driving the other screw rotor forward and backward, the solid lubricant film on the screw rotor is abraded by dry friction during this drive. can do.

  As described above, when a solid lubricant film is further formed on the surface of the ceramic film, the lubricity of the surfaces of the rotor portions 31 and 41 can be further improved.

  Moreover, compared to the screw rotors 3 and 4 of the conventional oil-free screw compressor in which the solid lubricant film is directly formed on the surfaces of the rotor portions 31 and 41 of the screw rotors 3 and 4, the film of the solid lubricant film Even when the thickness is thin, sufficient corrosion resistance, wear resistance, etc. can be imparted, and the solid lubricant film can be made thin, making the above-mentioned combination easy. In addition, it was possible to prevent the solid lubricant film from being peeled off during rubbing.

  The results of a corrosion resistance test by salt spray are shown below.

(1) Examples As an example, AC7A (Si: 0.2% or less, Mg: 3.5 to 5.5%), which is an aluminum alloy, was used, and an anode spark discharge was performed using an electrolyte containing a zirconium salt. By carrying out the above, samples each having a ceramic film with a thickness of 30 μm (Example 1) and 10 μm (Example 2) were prepared.

(2) Comparative Example As a comparative example, AC4C (Si: 6.5 to 7.5%, Mg 0.2 to 0.4%), which is an aluminum alloy, is used, and an anode spark is formed by an electrolyte containing a zirconium salt. A hard alumite film with a thickness of 30 μm is formed on the surface of a sample (Comparative Example 1) on which a ceramic film with a thickness of 30 μm is formed by discharge and a similar aluminum alloy (AC4C) by a known method. The prepared samples (Comparative Example 2) were prepared.

(3) Test method Each sample (Examples 1 and 2, Comparative Examples 1 and 2) is sprayed with salt water having a salt water concentration of 5% and left at a temperature of 35 ° C. for 200 hours, 600 hours, and 1000 hours. The surface state after observation was observed.

(4) Test results The observation results are shown in Table 1.

(5) Consideration of test results In the sample of Comparative Example 2 in which a hard alumite film was formed, rust (corrosion) had already occurred at the elapse of 200 hours.

  Further, in the sample of Comparative Example 1 in which the ceramic film was formed by anode spark discharge, the generation of rust could not be confirmed after 200 hours and 600 hours, and a comparison was made in which a hard anodized film was formed. Although it was confirmed that the sample had higher corrosion resistance than the sample of Example 2, it was confirmed that rust was generated after 1000 hours.

  On the other hand, in the samples of Examples 1 and 2 in which the ceramic coating was formed by the method of the present invention, it was not possible to confirm the occurrence of rust after 1000 hours. It was confirmed that a drastic improvement in corrosion resistance can be obtained by appropriately adjusting the alloy components in the base metal.

  In particular, in the sample of Example 2, although the thickness of the formed ceramic film is 10 μm, which is 1/3 of the thickness of the ceramic film formed on the sample of Comparative Example 1, Since the sample of Comparative Example 2 also shows high corrosion resistance, the surface treatment method of the present invention can reduce the thickness of the coating, and the screw rotor for fluid machinery before coating is formed in the final shape of the product. It is also possible to make the shape close to.

Explanatory drawing of a screw compressor. II-II sectional view taken on the line of FIG. The cross-sectional top view of a screw compressor. The schematic diagram which shows the layer structure of the surface film in the case of forming a solid lubricant film.

Explanation of symbols

1 Screw compressor 3 Screw rotor (male rotor)
31 Rotor (male rotor)
31a discharge side end face (of the rotor part of the male rotor)
31b End surface of suction side (of rotor part of male rotor)
32 Rotor shaft (male rotor)
4 Screw rotor (female rotor)
41 Rotor (female rotor)
41a Discharge side end face (of the rotor part of the female rotor)
41b Inlet side end face (of rotor part of female rotor)
42 Rotor shaft (for female rotor)
10 Casing 11 Suction port 12 Discharge port 20 Cylinder 51, 52 Timing gear

Claims (12)

The screw rotor of the screw fluid machine has a structure in which a rotor part made of an aluminum alloy having a Si content of 1 wt% or less is formed on the outer periphery of the rotor shaft,
A ceramic coating containing aluminum oxide in the composition was deposited on the surface of the rotor portion by immersing the rotor portion in an electrolyte and performing a spark discharge by energization using the rotor portion as an anode. A surface treatment method for a screw rotor for a screw fluid machine. The electrolyte including a zirconium salt, the rotor section surface mainly ZrO ₂ -Al ₂ O ₃ according to claim 1 screw fluid surface of the machine for the screw rotor, wherein the precipitating a coating of ceramics having the composition Processing method.   The surface treatment method for a screw rotor for a screw fluid machine according to claim 1, wherein the aluminum alloy is an Al-Mg alloy. 4. A screw rotor for a screw fluid machine according to claim 3, wherein a zirconium salt is included in the electrolyte solution, and a ceramic film mainly having a composition of ZrO ₂ —Al ₂ O ₃ —MgO is deposited on the surface of the rotor portion. Surface treatment method.   The surface treatment method for a screw rotor for a screw fluid machine according to any one of claims 1 to 4, wherein a solid lubricant film is further formed on the surface of the ceramic film.   The surface treatment method for a screw rotor for a screw fluid machine according to any one of claims 1 to 5, wherein the treatment is performed on a screw rotor of an oil-free screw compressor or a water jet screw compressor. . In a screw rotor of a screw fluid machine having a rotor portion formed on the outer periphery of a rotor shaft
The rotor part is made of an aluminum alloy having a Si content of 1 wt% or less, and the surface of the rotor part is made of a ceramic film containing aluminum oxide deposited by spark discharge in the electrolyte in its composition. A screw rotor for a screw fluid machine, characterized by being coated. 8. The screw rotor for a screw fluid machine according to claim 7, wherein the surface of the rotor part is covered with a ceramic film mainly containing a composition of ZrO ₂ —Al ₂ O ₃ containing a zirconium salt in the electrolytic solution.   The screw rotor for a screw fluid machine according to claim 7, wherein the aluminum alloy is an Al-Mg alloy. The screw for a screw fluid machine according to claim 9, wherein the surface of the rotor part is covered with a ceramic film mainly containing a composition of ZrO ₂ --Al ₂ O ₃ --MgO, including a zirconium salt in the electrolyte. Rotor.   The screw rotor for a screw fluid machine according to any one of claims 7 to 10, wherein the surface of the ceramic coating is further coated with a solid lubricant coating.   The screw rotor for a screw fluid machine according to any one of claims 7 to 11, wherein the screw rotor is a screw rotor of an oil-free screw compressor or a water jet screw compressor.

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