JPH0893670A - Oil-free screw compressor - Google Patents

Abstract

PURPOSE: To prevent seizure and scuffing phenomena, even if the surface of a rotor contacts with each other in gas of high temperature, by providing films having different performances from the suction side to the discharge side of the rotor of an oil-free screw compressor. CONSTITUTION: A film unnecessary of high lubrication performance and abrasion resistance is adopted for a suction side where atmospheric temperature is comparatively low compared with a surface film of a rotor so as to have less thermal expansion rate between rotors and less scuffing. On the other hand, a film in the discharge side of the rotor which directly contacts with high discharge air, has highest possibility of contacting with each other and considerably deteriorate its performances in the case of abrasion and damage so that the film of this part is made to have high adhesion property to a material metal, lubrication performance, and abrasion resistance. Sometimes adhesion property, lubrication performance, and abrasion resistance does not reach sufficient values in the suction side where atmospheric temperature does not rise, so that the rotor treated by a film on its surface is heated to a temperature equivalent to the intermediate degree before incorporated in a compressor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film provided on the surface of a rotor of an oil-free screw compressor, and more particularly to an oil-free screw compressor having a film with high reliability and long life.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Patent Laid-Open No. 2-201072, it has been known to provide a rotor of an oil-free screw compressor with a film mainly containing a material such as molybdenum disulfide.

[0003]

Since the oil-free screw compressor does not use lubricating oil or the like for lubrication or cooling during its compression, the discharge gas temperature during operation is 300 to 400 in a single-stage machine. 200 for a two-stage machine at ℃
It becomes high temperature above ℃. The coating on the surface of the rotor should prevent the phenomenon such as seizure or galling even if the surface of the rotor may come into contact with the surface due to complicated thermal expansion or machining error during operation. The purpose was to reduce the gap between the rotors.

However, it is difficult for these films to continuously exhibit their initial purpose over a long period of time, because it is difficult to stabilize the quality because variations occur depending on the use environment such as temperature and corrosive components. Due to the decrease or peeling of the film, problems such as deterioration of performance and rise of discharge gas temperature may occur.

Particularly, in the case of a single-stage machine, the discharge gas temperature is 30
Because of the high temperature of 0 to 400 ° C., it is difficult to achieve the initial purpose for a long period of time both as the performance of the solid lubricant and as the performance of the binder holding them.

[0006]

[Means for Solving the Problems] As the performance of the film provided on the rotor surface of the oil-free screw compressor,
The following items can be mentioned: (1) Heat resistance (2) Abrasion resistance (3) Lubricity (4) Corrosion resistance (5) Adhesion The above items are not independent but exert close performance. Yes, it is very difficult to produce a good film in all of these items.

Therefore, the present inventors have found that the characteristics required for the coating provided on the rotor surface are not uniform over the entire surface, and the coating having different properties from the suction side to the discharge side of the rotor. The above problem can be solved by providing.

[0008] Further, by providing a film whose properties change depending on the heating temperature on the rotor surface rather than forming a film having different properties in advance, the temperature distribution to which the film on the rotor surface is exposed by the operation of the compressor, or The characteristics are gradually changed from the suction side to the discharge side of the screw rotor according to the temperature gradient.

[0009]

[Function] A film in which a solid lubricant is uniformly dispersed is provided on the surface of the rotor of an oil-free screw compressor. The coating is provided with a property that it is dense in the temperature range from room temperature to about 200 ° C. and can surely prevent invasion of moisture and contact of corrosive components with the base metal of the rotor. In addition, the strength of this coating gradually increases at temperatures of 200 to 400 ° C, its adhesion to the base metal increases, and the solid lubricant is firmly held to prevent its oxidation. Keep it. However, the property as a corrosion resistant film required on the suction side may be lost to some extent. By doing so, the optimum properties required for the surface of the rotor of the oil-free screw compressor in operation are achieved.

Next, the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of the main body of an oil-free screw compressor. The compression of the suction gas is reduced by the meshing of the screw rotors 1 and 2 having a pair of twisted tooth grooves, the volume thereof is increased, and the pressure is discharged. Since no lubricating oil for cooling, lubrication and sealing purposes is injected between the rotors 1 and 2 in the compression process during this period, the gas to be discharged is, for example, air from atmospheric pressure to 7 kgf / cm ² g.
If it is compressed in a single stage up to 300 ° C., it will be a high temperature.
In general, a film containing a solid lubricant is provided on the surface of these screw rotors to minimize the clearance between the rotors and prevent the rotors from seizing even when they come into contact with each other.

Conventionally, this coating is applied to the surface of the rotor metal and is formed by baking. However, the solid lubricant is oxidized and retained and adheres to the surface of the rotor metal at the portion on the discharge side that comes into contact with the high temperature gas. Binding agent
The phenomenon that the film gradually thins or peels easily occurs.

Generally, the film provided on the rotor surface is
An organic resin binder in which a solid lubricant is dispersed is often used because of the ease of work for producing a uniform film thickness. Means such as making the resin an inorganic type and making the type of the solid lubricant have a higher oxidation start temperature are conceivable if only to increase the heat resistant strength of the film. In terms of wear resistance and workability (for uniformly forming a film), it is extremely difficult to find one that meets all requirements.

Therefore, in the present invention, the coating on the surface of the rotor is provided with the characteristics as shown in FIG. 2 in the axial direction. That is, a coating that does not require high lubricity or wear resistance is provided on the suction side where the temperature of the gas is relatively low, and therefore the degree of thermal expansion between the rotors is small and there is little risk of contact and galling. However, the corrosive components present in the suction gas on the suction side, and especially when used in the high pressure stage of the two-stage compressor, condensed water is generated in the intercooler, and the relative humidity of the suction gas becomes 100%. In consideration of such a case, the film is a dense film having high corrosion resistance or a film having water repellency.

On the other hand, in the case of the coating on the discharge side of the rotor, which is in direct contact with the high-temperature discharge gas, the possibility of contact between the coatings is highest, and the deterioration of the performance is remarkable when the coating is worn or damaged. The coating has high adhesion to the base metal, lubricity, and wear resistance. However, in this region, since the temperature becomes high, condensed water is not generated, and therefore the corrosion resistance required on the suction side is not provided.

However, according to this method, the adhesion, lubricity, and wear resistance may not be sufficient on the suction side where the temperature of the gas does not rise. Therefore, before the rotor with the film is assembled into the compressor, It is heated up to the temperature corresponding to the part (suction side and discharge side). As a result, the characteristics can be further improved as shown by the dotted line in FIG.

By this, only one kind of film is applied,
It is possible to heat-treat the rotor at a constant temperature before assembling, and further improve its properties by the temperature to which the coating on the rotor surface is actually exposed after assembly and operation of the actual machine.

Next, examples of the present invention will be described.

[0018]

【Example】

<Example 1> MoS ₂ 6.0 parts of graphite 1.5 to 17 parts by weight of polyamide-imide resin (hereinafter referred to simply as "parts")
Parts and 2.5 parts of other solid additives were uniformly mixed.

Next, 73 parts of 1-4 dioxane solution, a mixture of the above resin and the above solid content were mixed, the polyamideimide resin was dissolved in a solvent, and a uniform solid lubricant solution was prepared.

After that, the lubricity is measured by actually measuring the total number of revolutions until the friction coefficient reaches 0.3 with a pin-on-disk tester for the test pieces heat-treated at each temperature between 100 and 360 ° C. did.

The results are shown in FIG. 3, and it can be seen that the product of the present invention has improved lubricity as the heating temperature rises. Especially, when the temperature exceeds about 300 ° C., the rising tendency is dramatic.

FIG. 4 shows a comparison by the heating temperature, the wear resistance of the lubricating coating and the wear start time in the Amsla wear tester.

As a result, in the conventional product, the wear start time becomes shorter as the heating temperature rises, that is, the wear resistance decreases, whereas in the product of the present invention, the wear resistance rapidly improves as the heating temperature rises. Comparing the two cases when heated to 300 ° C., the time until abrasion powder is generated in the product of the present invention is about 180 times that of the conventional product, and the product of the present invention exhibits extremely good wear characteristics.

FIG. 5 shows the results obtained by measuring the time until rust was generated on the surface of the coating film by the salt spray test on the test piece with the heating temperature changed. It can be seen that at a heating temperature of 200 ° C. or lower, extremely good corrosion resistance is exhibited, but in a temperature range above that, the corrosion resistance gradually decreases.

As described above, in the present invention, the corrosion resistance is somewhat sacrificed at the disadvantage that the important properties required for the solid lubricant such as lubricity and wear resistance deteriorate as the coating film is heated by high temperature. By doing so, it was able to be greatly improved.

Further, the coating on the discharge side of the rotor, which is required to have high lubricity and wear resistance due to these characteristics, is generated by the operation of the compressor, especially the single-stage oil-free screw compressor in which the temperature of the gas rises up to about 360 ° C. By the high temperature, it is possible to change the film formed by coating into a film having extremely high durability.

This shows that the use conditions can naturally change the film to the optimum state, and can be said to be a "self-reinforcing" solid lubricant.

On the other hand, in that case, after forming a film on the rotor, 3
It may be considered that the rotor is heated to a temperature of 00 ° C. or higher to keep the entire rotor in a state of excellent wear resistance and lubricity, but as shown in FIG. 5, the corrosion resistance decreases at a temperature of 250 ° C. or higher.

Further, when heated to 250 ° C. or higher, surface oxidation of the metal base portion of the rotor on which the lubricating film is not formed starts, and the corrosion resistance of this portion is significantly reduced.

Therefore, after forming the lubricating coating of the present invention, the rotor is heated at a temperature of about 200 to 250 ° C. to improve the characteristics of the entire coating to a certain level within the range where corrosion resistance is not deteriorated. It is preferable that the discharge side region having a temperature condition higher than that has its characteristics improved by the operating temperature after being incorporated as a compressor. The characteristics of the lubricating coating in the axial direction of the rotor thus obtained are as shown in FIG.

Therefore, application examples will be described in Examples 2 and 3 below.

<Example 2> Polyamideimide resin and Mo
A solid lubricant such as S ₂ is uniformly mixed in a ratio of 1: 1. Next, 70 parts by weight of a solution of dimethylformamide (hereinafter abbreviated as "part") and a mixture of the above resin and the above solid content are mixed, the polyamideimide resin is dissolved in a solvent, and a uniform solid lubricant solution is prepared. .

Next, this solid lubricant solution (hereinafter abbreviated as "solid lubricant") was uniformly applied to the tooth profile and the end surface of the rotor for a single-stage oil-free screw compressor to a thickness of about 20 μm. After that, it was heated at about 250 ° C for about 2H to form a solid lubricant film layer on the surface of the tooth profile of the rotor, and then a compressor incorporating this one set of rotor was subjected to an ON-OFF test for 100,000 times, which is equivalent to driving for about 4 years After a short while, the operation continued smoothly under high performance.

After the actual operation, the main body block was disassembled and the surface layer coated with the solid lubricant was observed. The discoloration layer (heat resistance) on the discharge side at high temperature, which was observed in the conventional solid lubricant,
No wear phenomenon or rusting phenomenon on the suction side was observed at all. The lubricity and adhesion were also good.

Therefore, the technical excellence of the present invention was proved in this example.

Example 3 To 17 parts by weight of polyimide resin powder, 6.0 parts of MoS ₂ powder, 1.5 parts of graphite and 2.5 parts of other additives are uniformly mixed.

Next, this solid lubricant solution was uniformly applied to the tooth profile of the F (male) and M (female) rotors for the two-stage oil-free screw compressor and its end face to a thickness of about 20 μm.

After that, it was heated at about 250 ° C. for about 3 hours to form a strong coating on the tooth profile and the end face of the rotor. A solid lubricant film was formed on the tooth profile and end face of both rotors F and M of the screw compressor, and then the compressor incorporating the two rotor sets was driven for one year. Continued.

After the actual operation, the main body block was disassembled and the surface layer coated with the solid lubricant was observed. As a result, the wear phenomenon at high temperature on the discharge side and the suction side observed on the conventional solid lubricant were observed. No rusting phenomenon was observed.

In other words, the technical excellence of the present invention was proved also in this embodiment.

[0041]

According to the present invention, the optimum properties of the film provided on the rotor of the oil-free screw compressor are made of an inexpensive material, an easy production method, and have a long life and high reliability. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a compressor body according to the present invention.

FIG. 2 is a characteristic diagram of a coating on a compressor rotor according to the present invention.

FIG. 3 is a lubrication characteristic diagram of an example of a film on a compressor rotor according to the present invention.

FIG. 4 is a wear resistance characteristic diagram of an example of a coating on a compressor rotor according to the present invention.

FIG. 5 is a diagram showing the time until rusting related to the heating temperature.

FIG. 6 is a diagram showing characteristics of a lubricating film in the rotor axial direction.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Male rotor 2 ... Female rotor 3 ... Casing 4 ... Radial bearing 5 ... Thrust bearing 6 ... Timing gear 7 ... Pinion gear

Claims (3)

[Claims] 1. A rotor of an oil-free screw compressor having a pair of metal rotors, wherein (1) a film in which a solid lubricant is dispersed in a binder is formed on the surface of the rotor, (2) The coating on the rotor surface is made of the same material from the suction side to the discharge side of the rotor, and its characteristics change depending on the ambient temperature, (3) the characteristics of the coating on the rotor surface are: An oil-free screw compressor having corrosion resistance for protecting a metal rotor on a suction side and adhesion and wear resistance to a metal rotor on a discharge side. 2. The oil-free screw compression characterized in that the characteristic of the coating of the rotor is a characteristic which changes steplessly from the suction side to the discharge side of the rotor according to the ambient temperature. Machine. 3. The oil-free screw compressor, wherein the rotor having the film formed thereon is heated at a constant temperature before being incorporated into the compressor.