JP2009293452A - Lubricating oil for oil cooled screw compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize lubricating oil having sufficient wear resistance and provided at low cost in relation to lubricating oil used for a screw compressor and containing silicone oil as primary ingredient. <P>SOLUTION: This lubricating oil is retained in the oil cooled screw compressor comprising a pair of mutually meshing rotors 2a, 2b, and lubricates and cools meshing parts of both of the rotors 2a, 2b and each of the bearing. Such lubricating oil contains silicone oil as the primary ingredient, is mixed with three or more kinds of mineral oil having different viscosity. In the concrete, mineral oil having kinematic viscosity at 40°C equivalent to VG220 in ISO viscosity grade, mineral oil equivalent to VG 32-68, and mineral oil equivalent to VG 10 are contained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement in lubricating oil that circulates in the oil-cooled screw compressor in order to ensure the durability of the screw compressor that sends out various gases while compressing them. Specifically, it aims at improving the durability of this oil-cooled screw compressor by improving the wear resistance.

  As a screw compressor that compresses various gases including air, for example, oil-cooled screw compressors as described in Patent Documents 1 to 3 are widely known. FIG. 1 shows an example of a conventionally known oil-cooled screw compressor. In the casing 1, a pair of (male and female) rotors 2a and 2b are arranged in parallel to each other. The rotors 2a and 2b are respectively provided with rotor portions 4a and 4b in the portion having a large diameter at the intermediate portion between the shaft portions 3a and 3b. Concave and convex strips inclined in opposite directions are formed on the outer peripheral surfaces of the rotor portions 4a and 4b, and the concave portions and the convex portions are engaged in a helical gear shape. Also, one of the shaft portions 3a and 3b (upper side in FIG. 1) is a driving side driven by an electric motor or the like, and the other (lower side in FIG. 1) is the shaft portion 3b. At the time of rotation of one shaft portion 3a, the driven side is driven based on the meshing of the rotor portions 4a and 4b. Further, both end portions of the shaft portions 3a and 3b are rotatably supported by bearings 5a, 5b, 5c and 5d, respectively. In the illustrated example, the bearings 5a and 5b for supporting both ends of the drive-side shaft portion 3a are cylindrical roller bearings and double-row ball bearings, and the bearings for supporting both ends of the driven-side shaft portion 3b. 5c and 5d are a sliding bearing and a double row ball bearing.

  During the operation of the screw compressor as described above, the shaft portion 3a is rotationally driven by a drive source such as an electric motor (not shown). Then, in a part of the casing 1, the gas sucked from the suction port provided in one of the portions aligned with the rotor parts 4a and 4b corresponding to the front and back directions in FIG. It discharges from the provided outlet. Further, during operation, lubricating oil is fed into the casing 1 from the supply port 6. This lubricating oil flows through the casing in the order of arrows (1) → (2) → (3) → (4) → (5) → (6) in FIG. Discharged. During this time, the lubricating oil lubricates the meshing portions of the rotor portions 4a and 4b and the bearings 5a, 5b, 5c and 5d. Further, the lubricating oil discharged to the outside of the casing 1 together with the gas is recovered by a separately provided recovery device and sent into the casing 1 from the supply port 6 again.

  In order to ensure the durability of the screw compressor as described above, it is necessary to use the lubricating oil having excellent lubricity. In addition, as a problem peculiar to the screw compressor, it is required that the viscosity change based on the temperature change is small, and that it is incombustible so as not to be ignited even when it is mixed and discharged into the gas. For this reason, conventionally, a silicone oil having a high viscosity index, a low driving torque at a low temperature, and flame retardancy has been used. However, since mere silicone oil does not necessarily have sufficient wear resistance, the requirements cannot be sufficiently satisfied from the viewpoint of improving the durability of the screw compressor. On the other hand, Patent Document 4 describes a silicone in which a plurality of types of polysiloxanes having different viscosities are mixed and wear resistance is improved by adding di-2-ethylhexyl chlorendate, which is an antiwear agent. Inventions relating to oil are described. Such a silicone oil described in Patent Document 4 cannot be said to have a sufficient performance improvement effect in terms of wear resistance.

JP 2006-214309 A JP 2007-113495 A JP 2007-146718 A Japanese Patent Laid-Open No. 10-87992

  In view of the circumstances as described above, the present invention realizes a lubricating oil that has sufficient wear resistance and can be obtained at a low cost with respect to a lubricating oil mainly composed of silicone oil used in a screw compressor. Invented as much as possible.

  The lubricating oil for an oil-cooled screw compressor according to the present invention is a pair in which concave and convex strips that are arranged in parallel to each other and are rotatably supported by bearings on respective outer peripheral surfaces and inclined with respect to the axial direction are formed on the outer peripheral surfaces. These rotors are held in an oil-cooled screw compressor formed by meshing with each other to lubricate and cool the meshing portions of the two rotors and the bearings described above, and are mainly composed of silicone oil.

In particular, in the oil-cooled screw compressor lubricating oil of the present invention, three or more mineral oils having different viscosities are mixed.
When the lubricating oil for an oil-cooled screw compressor of the present invention is implemented, the kinematic viscosity at 40 ° C. is an ISO viscosity grade equivalent to VG220 (at 40 ° C.), for example, as in the invention described in claim 2. the kinematic viscosity, 198 mm ² / s or more, mineral oil is a 242 mm ² / s or less), also it has a kinematic viscosity at VG32~68 corresponding ^{{VG32 (40 ℃, 28.8mm 2} / s or more, 35.2 mm ² VG46 (kinematic viscosity at 40 ° C. is 41.4 mm ² / s or more and 50.6 mm ² / s or less), VG68 (kinematic viscosity at 40 ° C. is 61.2 mm ² / s or more, 74.8 mm ² / s or less)} and a mineral oil equivalent to VG10 (kinematic viscosity at 40 ° C. of 9 mm ² / s or more and 11 mm ² / s or less).

  Since the lubricating oil for oil-cooled screw compressors of the present invention as described above is mixed with three or more mineral oils having different kinematic viscosities in silicone oil, each part regardless of temperature change during operation. An oil film having sufficient strength can be formed, exhibit sufficient wear resistance, and improve the durability of the screw compressor. Moreover, since what is mixed with silicone oil for improving wear resistance is mineral oil obtained at low cost, the cost of the entire lubricating oil can be suppressed.

  The feature of the present invention is to improve the durability of the oil-cooled screw compressor by improving the lubricating oil. Regarding the structure of the oil-cooled screw compressor itself, the structures of various oil-cooled screw compressors that have been conventionally known, such as the structure shown in FIG. Can be used. Therefore, description of the structure and operation of the oil-cooled screw compressor will be omitted, and an experiment conducted to confirm the effect of the present invention will be described.

  The lubricating oil for oil-cooled screw compressors according to the present invention improves wear resistance by adding three or more mineral oils to silicone oil. In order to ensure the performance required for the lubricating oil including this wear resistance, it is necessary that the mixed oils do not separate from each other as a premise, as well as having excellent wear resistance. Therefore, a phase oil compatibility test (room temperature 25 ° C.) of silicone oil and a plurality of types of mineral oils was conducted, and those that passed this phase oil compatibility test {not precipitated (separated by two layers)}, as shown in FIG. The abrasion resistance was evaluated using an experimental machine. The experimental machine shown in FIG. 2 applies a radial load to the outer ring 9 of the cylindrical roller bearing 7 in a state where only a part of the cylindrical roller bearing 7 is immersed (oil bath) in the lubricating oil 8 to be evaluated. Similarly, the inner ring 10 is rotated. The amount of the lubricating oil 8 is small (about 40 cc), which is a severe lubricating condition as compared with a circulating oil supply system of an actual oil-cooled screw compressor having an oil storage tank of several tens of liters.

[Compatibility test]
A predetermined amount of silicone oil and mineral oil were added to a 100 cc glass bottle and shaken. And after leaving still for 30 minutes in the thermostat kept at about 60 degreeC, the condition of the mixed oil in the state left still for 24 hours was observed. The combination after two-layer separation after standing for 24 hours was considered inappropriate as a lubricating oil and excluded from the wear resistance evaluation test described below.

[Abrasion resistance evaluation test]
This test was performed using the evaluation tester shown in FIG. The cylindrical roller bearing 7 used was NU308 with a steel plate cage (outer diameter: 90 mm, inner diameter: 40 mm, width: 23 mm), and only the lower end was immersed in the lubricating oil 8. The inner ring 10 is externally fixed to the rotary shaft 11 by an interference fit while being positioned by a flange 12 provided on the outer peripheral surface of the rotary shaft 11. The outer ring 9 was fitted in the bearing housing 13 with a gap fit, and was fixed in the bearing housing 13 by a pair of lids 14 and 14 fixed to the bearing housing 13 with screws. The amount of the lubricating oil 8 is 40 cc, and the oil level is at the pitch circle position of the rollers 15 and 15 (the lower half of the lowermost roller 15 is immersed in the lubricating oil 8 in a stationary state). I did it. This state is the amount of oil corresponding to micro lubrication. As shown in FIG. 2, the space in which the lubricating oil 8 can exist is a space surrounded by the lid bodies 14 and 14 and the cylindrical roller bearing 7 and a static space of the cylindrical roller bearing 7. is there. Further, a radial load Fr can be added to the outer ring 9 by a hydraulic ram. Further, the vibration generated with the operation of the cylindrical roller bearing 7 can be measured by a magnet type vibration sensor 17 installed on the outer peripheral surface of the bearing box 13. Further, the temperature of the outer ring 9 can be measured by a thermocouple 18.

When the lubricating oil 8 is evaluated using such an evaluation test machine, the rotary shaft 11 is rotationally driven by the induction motor while a radial load Fr of 4300 N is applied to the outer ring 9 in accordance with the maximum load of the actual machine. did. When the inner ring 10 rotates together with the rotating shaft 11, the rollers 15 and 15 revolve, and the retainer 16 rotates accordingly. Then, the lubricating oil in the vicinity of each of the rollers 15 and 15 and the cage 16 is pushed away and pressed against the inner wall surfaces of the lid bodies 14 and 14. As a result, the lubrication state of the rolling contact portion (friction portion) between the rolling surfaces of the rollers 15, 15 and the outer ring raceway on the inner peripheral surface of the outer ring 9 and the inner ring raceway on the outer peripheral surface of the inner ring 10 is very small. Oil lubrication is achieved. During the test, after operating 2 hours the rotating shaft 11 at 2000 min ^-1, 2 hours at 4000 min ^-1, 2 hours at 6000 min ^-1, and after operating for 2 hours at 8000min ^-1, stops the rotation shaft 11 The test was completed.

In this process, the maximum temperature and the maximum vibration value (effective value) were measured while operating at 8000 min ⁻¹ for 2 hours. Further, after the test is completed, the cylindrical roller bearing 7 is disassembled, the weight change (decrease amount) of the cage 16 is measured, and an indicator of the wear status of the components of the cylindrical roller bearing 7 including the cage 16 did. Such an evaluation test was conducted twice for the same type of lubricating oil 8. The maximum value (8000 min ⁻¹ ) of the rotational speed of the rotating shaft 11 is a value corresponding to the maximum rotational speed of the rotors 2a and 2b (see FIG. 1) of the oil-cooled screw compressor used as an air compressor. is there. The results of the tests conducted in this manner are shown in the following Table 1 and its margins, together with evaluation criteria and specific examples of each oil used.

The kinematic viscosity of each of the lubricating oils 8 (mixed oil) is 21 mm ² / s / 40 ° C., which is the kinematic viscosity of silicone oils currently commonly used as lubricating oils for oil-cooled screw compressors. The blending ratio of mineral oil was adjusted so that the values were close. Mineral oil that can be mixed with silicone oil has a limit depending on the ISO viscosity grade of the mineral oil. A combination (type and ratio) that separates into two layers is not preferable because the required lubricating performance cannot be obtained immediately after the start of operation. The limit amount (maximum mixing amount) of the mineral oil that can be mixed with the silicone oil tends to be lower as the high viscosity mineral oil. VG220 mineral oil with ISO viscosity grade used was separated into two layers at a mixing amount of 0.8% by mass, and also separated into two layers at 10% by mass for VG68 and VG32, while 15% by mass for VG10. However, the two layers were not separated (see Comparative Examples 2 to 4). Accordingly, the mixing amount of each mineral oil is 0.3 to 0.7 mass% for VG220, 3 to 9 mass% for VG32 to 68, and 5 to 15 mass% for VG10. Things are appropriate.

  When practicing the present invention, as in the invention described in claim 2, ISO viscosity grades VG220, VG68, and VG10 may be selected as three types of mineral oil to be added to the low kinematic viscosity silicone oil. preferable. This is shown in Table 1 as Example 2. The mixed oil of Example 2 is VG10, which is a low viscosity mineral oil that is easy to flow into the friction part and has a high oil film repairability, and a high viscosity mineral oil that is easy to maintain a thick lubricating oil film and hardly cause metal contact. It is considered that an excellent wear suppression effect was obtained by the existence of a certain VG 220 and VG 68 having intermediate characteristics. In the case of the cylindrical roller bearing 7, the pair of rotors 2 a and 2 b, which behave like a sliding contact portion between the rollers 15 and 15, the cage 16 and the bearing ring collar portion, are connected to each other. Excellent lubricating resistance can be obtained by blending three or more mineral oils with different ISO viscosity grades as lubricating oil 8 that rubs frictional parts with large slips, such as oil-cooled screw compressors that are meshed. It is done. This is apparent from the test results of the evaluation items of Examples 1, 2, and 3 and Comparative Examples 5, 6, 7, and 8 in Table 1.

  The mineral oil used in the evaluation test was paraffinic. However, synthetic hydrocarbon oil (poly-alpha olefin oil) and naphthenic mineral oil must be separated into two layers when mixed with silicone oil. Can be used. In any case, the lower the pour point of mineral oil, the better.

Sectional drawing which shows an example of the oil-cooled screw compressor in which the lubricating oil of this invention is used. Sectional drawing of the experimental apparatus used for the experiment conducted in order to confirm the effect of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Casing 2a, 2b Rotor 3a, 3b Shaft part 4a, 4b Rotor part 5a, 5b, 5c, 5d Bearing 6 Supply port 7 Cylindrical roller bearing 8 Lubricating oil 9 Outer ring 10 Inner ring 11 Rotating shaft 12 Ridge part 13 Bearing box 14 Lid 15 Rollers 16 Cage 17 Vibration sensor 18 Thermocouple

Claims (2)

  Oil-cooled screw compression, which is formed by engaging a pair of rotors that are arranged parallel to each other and that are rotatably supported by bearings and that each have an uneven surface that is inclined with respect to the axial direction. Three types of lubricating oils for oil-cooled screw compressors, mainly composed of silicone oil, that are held in the machine to lubricate and cool the meshing parts of these two rotors and the above bearings. Lubricating oil for oil-cooled screw compressors, characterized by mixing the above mineral oils.   2. The oil-cooled screw compressor according to claim 1, comprising a mineral oil having a kinematic viscosity at 40 ° C. of ISO viscosity grade corresponding to VG220, a mineral oil corresponding to VG32 to 68, and a mineral oil also corresponding to VG10. Lubricating oil.

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