JP2006112389A - Gas compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain reduction in startability, when moisture remaining inside a housing freezes when stopping a compressor. <P>SOLUTION: In gas compression equipment, a thermal expansion coefficient of the housing 7 is set larger than a thermal expansion coefficient of a plurality of rotors 1 and 2. A pin 50 having a thermal expansion coefficient smaller than the housing 7 is arranged between two bearings 18 and 19 in the housing 7. A contraction quantity of inter-shaft pitch caused by a temperature drop, is reduced by this pin 50, and a reduction quantity of inter-rotor clearance is restrained in a low temperature environment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas compressor that compresses and discharges a sucked gas by rotating a plurality of rotors.

Conventionally, as a roots-type gas compressor, one that selects each material from the rotor temperature and the housing temperature during rotation has been proposed so that the clearance between the rotor and the housing does not change (see, for example, Patent Document 1). .
Japanese Patent Laid-Open No. 2003-166383

  However, the above-mentioned conventional roots-type gas compressor takes into consideration the difference between the rotor temperature and the housing temperature during operation, and does not take into account the change in clearance when the ambient temperature changes. When the low thermal expansion coefficient material and the housing are made of a high thermal expansion coefficient material and the ambient temperature becomes low (hereinafter referred to as a low temperature environment), the clearance between the rotors decreases.

  Therefore, when the moisture remaining inside the housing due to condensation is frozen in a low temperature environment when the compressor is stopped, a large torque is required when rotating the rotor. In other words, there arises a problem that startability in a low temperature environment is lowered.

  On the other hand, in a screw compressor that does not inject lubricating oil or the like into the compression chamber, since the clearance between the rotors has a great influence on the performance of the compressor, it is necessary to minimize this clearance. However, in a screw compressor, since it is common to use a low thermal expansion coefficient material for the rotor and a high thermal expansion coefficient material for the housing, the heat of the housing-side components and the rotor-side components that determine the inter-axis pitch is determined. Due to the difference in expansion rate, the clearance between the rotors is reduced in a low temperature environment. Therefore, when water is mixed in for some reason, freezing occurs in the reduced clearance, resulting in a problem that the startability is lowered.

  In view of the above-described points, an object of the present invention is to suppress a decrease in startability in a low-temperature environment in a gas compressor that compresses and discharges a sucked gas by rotating a plurality of rotors.

  In order to achieve the above object, according to the first aspect of the present invention, the housing member (7, 8) having the suction port (7a) and the discharge port (7b) is housed in the housing member (7, 8). , A plurality of rotors (1, 2) for compressing and discharging the gas sucked along with the rotation, and a plurality of rotors (1, 2) fixed to the housing members (7, 8) and rotatably holding the plurality of rotors (1, 2) In the gas compression device comprising the bearings (18 to 21), the thermal expansion coefficient of the housing members (7, 8) being larger than the thermal expansion coefficients of the plurality of rotors (1, 2). A first adjustment member (50) having a smaller coefficient of thermal expansion than the housing members (7, 8) is provided between the plurality of bearings (18-21).

  According to this, since the reduction amount of the inter-axis pitch accompanying the temperature drop becomes small, the reduction amount of the clearance between the rotors in the low temperature environment is suppressed, and the deterioration of the startability in the low temperature environment can be suppressed.

  According to a second aspect of the present invention, in the gas compressor according to the first aspect, the thermal expansion between the housing member (7, 8) and the bearing (18-21) is greater than that of the housing member (7, 8). A second adjustment member (51) having a small rate is provided.

  According to this, it is possible to prevent a decrease in the internal clearance of the bearing in a low temperature environment, and to maintain a smooth operation of the bearing.

  The invention according to claim 3 is the gas compressor according to claim 2, wherein the first adjustment member (50) and the second adjustment member (51) are integrated. According to this, the number of parts can be reduced by integration.

  According to a fourth aspect of the present invention, in the gas compressor according to the first or second aspect, the first adjustment member (50) has a cylindrical shape. According to this, since it is a simple shape, processing man-hours can be reduced.

  In invention of Claim 5, in the gas compressor as described in any one of Claim 1, 2, 4, a 1st adjustment member (50) is the center position between several bearings (18-21). It is characterized by being arranged in.

  According to this, since the housing thin part (the dimension between the first adjustment member and each bearing) can be made uniform, insufficient rigidity of the housing can be suppressed.

  According to a sixth aspect of the present invention, in the gas compressor according to the fourth or fifth aspect, each rotor (1, 2) includes a rotating shaft (1a, 2a) and an outer peripheral side of the rotating shaft (1a, 2a). The rotor body (1z, 2z) is disposed on the outer shaft portion (1b, 2b) and is held by the bearings (18-21). And the inner shaft portion (1c, 2c) covered by the rotor body (1z, 2z), the sum of the radii of the two inner shaft portions (1c, 2c) is R1, the inter-axis pitch is P, The sum of the radii of the outer peripheral portions of the bearings (18 to 21) is R2, the diameter of the first adjustment member (50) is D, the thermal expansion coefficient of the inner shaft portions (1c, 2c) is α1, and the rotor body (1z, 2z). Is α2, the housing member (7, 8) is α3, and the bearing (18-21) is thermally expanded. When the rate is α4 and the thermal expansion coefficient of the first adjusting member (50) is α5, R1 × α1 + (P−R1) × α2> R2 × α4 + (P−R2−D) × α3 + D × α5 It is characterized by.

  According to this, the amount of reduction in the pitch between the shafts due to the temperature drop is smaller than the amount of reduction in the rotor radius, and the clearance between the rotors in a low temperature environment increases, thus preventing a decrease in startability in a low temperature environment. be able to.

  As in the invention according to claim 7, in the gas compressor according to any one of claims 1 to 6, the plurality of rotors (1, 2) may be a screw-shaped male rotor and a female rotor. .

  According to an eighth aspect of the present invention, in the gas compressor according to the seventh aspect, the rotors (1, 2) are arranged on the rotary shaft (1a, 2a) and the outer peripheral side of the rotary shaft (1a, 2a). The screw-shaped rotor body (1z, 2z) includes a rotating shaft (1a, 2a), an outer shaft portion (1b, 2b) held by bearings (18-21), and a rotor body (1z, 2z). 2z) and the thermal expansion coefficient of the rotor body (1z, 2z) is larger than the thermal expansion coefficient of the inner shaft part (1c, 2c), and the inner shaft part (1c, 2c) The diameter (D) of 1c, 2c) is 70% or more of the diameter of the root (1x, 2x) of the rotor body (1z, 2z).

  By the way, the reason why the diameter of the inner shaft portion is set to 70% or more of the diameter of the tooth base of the rotor body is because it is necessary to thicken the inner shaft portion for speeding up. The overall coefficient of thermal expansion becomes smaller, the amount of decrease in the clearance between the rotors in the low temperature environment increases, and the startability in the low temperature environment decreases remarkably. Therefore, it is particularly effective for a gas compressor having such a thick inner shaft portion.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. 1 is a cross-sectional view of the gas compressor according to the first embodiment, FIG. 2 is a view showing the shape of the axial end face of the rotor of FIG. 1, and FIG. 3 is a cross-sectional view taken along line AA of FIG.

  As shown in FIG. 1, the gas compressor of this embodiment is a screw compressor, a screw-shaped male rotor 1 and a female rotor 2, and a rotation transmission mechanism 3 that rotationally drives the rotors 1 and 2 by the rotational force of a drive source. The casing 4 accommodates the pair of rotors 1 and 2 and the rotation transmission mechanism 3, the input shaft 5 that receives the rotational force of the drive source, and the like. In FIG. 1, the pair of rotors 1 and 2 are arranged side by side on the back side and the near side.

  The male rotor 1 and the female rotor 2 are rotationally driven by a rotation transmission mechanism 3 that obtains rotational force from a drive source such as an electric motor 100. In the first embodiment, the male rotor 1 is on the driving side and the female rotor 2 is on the driven side, and rotates about the rotation shafts 1a and 2a, respectively.

  As shown in FIGS. 1 and 2, the male rotor 1 and the female rotor 2 are formed in a male screw shape in which a spiral protrusion is formed so as to mesh with each other. Moreover, the male rotor 1 and the female rotor 2 are comprised from the rotating shaft 1a, 2a and the screw-shaped rotor body 1z, 2z arrange | positioned and integrated on the outer peripheral side of this rotating shaft 1a, 2a.

  The rotary shafts 1a and 2a are stepped and have outer shaft portions 1b and 2b held by bearings described later and inner shaft portions 1c and 2c covered by the rotor body. Incidentally, the inner shaft portions 1c and 2c have a larger diameter than the outer shaft portions 1b and 2b.

  On the other hand, the screw-shaped rotor bodies 1z and 2z are configured such that the tooth tip 1y of the male rotor 1 and the tooth root 2x of the female rotor 2 mesh with each other, and the tooth root 1x of the male rotor 1 and the tooth tip 2y of the female rotor 2 mesh with each other. The male rotor 1 is a large-diameter rotor and the female rotor 2 is a small-diameter rotor. The outer diameter of the male rotor 1 is larger than the outer diameter of the female rotor 2.

  The diameter of the inner shaft portion 1c in the rotating shaft 1a on the male rotor 1 side is 70% or more of the diameter of the tooth root 1x in the rotor body 1z on the male rotor 1 side, and the inner shaft portion 2c in the rotating shaft 2a on the female rotor 2 side. Is 70% or more of the diameter of the tooth root 2x in the rotor body 2z on the female rotor 2 side.

  Returning to FIG. 1, the casing 4 includes a lubrication box 6, a rotor housing 7, and a cover 8 in order from the motor 100 side. The rotor housing 7 and the cover 8 correspond to the housing member of the present invention.

  The lubrication box 6, the rotor housing 7, and the cover 8 are firmly coupled by fastening means such as bolts (not shown). The rotors 1 and 2 and the rotation transmission mechanism 3 are housed in the casing 4 in a state of being separated from each other, the pair of rotors 1 and 2 are housed in the rotor housing 7, and the rotation transmission mechanism 3 is housed in the circulation box 6. Has been.

  In the lubrication box 6, a lubricating oil space 9 in which the rotation transmission mechanism 3 and the lubricating oil supplied to the rotation transmission mechanism 3 are accommodated is formed. As the lubricating oil, for example, an oil having a viscosity comparable to that of engine oil can be used. Lubrication is carried out by splashing the lubricating oil in the lubricating oil space 9 on the gears and the like constituting the rotation transmission mechanism 3.

  The lubrication box 6 is provided with an input shaft 5 that receives a rotational force from the motor 100. The lubrication box 6 is provided with a first bearing 11 on the motor 100 side and a second bearing 12 on the lubricating oil space 9 side. The input shaft 5 is connected to the lubrication box 6 via these bearings 11 and 12. It is supported by. A first oil seal 13 for preventing the lubricating oil from flowing out of the casing 4 is mounted inside the insertion hole into which the input shaft 5 formed in the lubricating box 6 is inserted.

  A rotor chamber 10 in which a pair of rotors 1 and 2 are housed is formed in the rotor housing 7. In the rotor housing 7, a suction port 7 a for sucking gas into the rotor chamber 10 and a discharge port 7 b for discharging gas to the outside of the rotor chamber 10 are formed. The suction port 7 a is provided on the cover 8 side of the axial end portion of the rotor housing 7, and the discharge port 7 b is provided on the lubrication box 6 side of the axial end portion of the rotor housing 7.

  Further, a seal structure is formed in which a minute gap is formed between the outer peripheral tips of the rotors 1 and 2 and the inner wall of the rotor chamber 10. A compression chamber 10a for compressing the gas sucked from the suction port 7a is formed between the rotors 1 and 2 and the inner wall of the rotor chamber 10.

  As described above, the rotors 1 and 2 are rotationally driven by the rotation transmission mechanism 3. The rotation transmitting mechanism 3 is configured to transmit the rotation of the input shaft 5 to the male rotor rotating shaft 1a and the female rotor rotating shaft 2a and to rotate the pair of rotors 1 and 2 synchronously. The rotation transmission mechanism 3 is transmitted to the male rotor rotary shaft 1a from the first and second gears 14 and 15 that transmit the rotation of the input shaft 5 driven by the motor 100 to the male rotor rotary shaft 1a. The third and fourth gears 16 and 17 are configured to transmit the rotation to the female rotor rotating shaft 2a. The third and fourth gears 16 and 17 are timing gears for synchronously rotating the pair of rotors 1 and 2.

  One end side of the male rotor rotating shaft 1a and the female rotor rotating shaft 2a is rotatably supported by the rotor housing 7 via the third and fourth bearings 18 and 19, and the other end side is supported via the fifth and sixth bearings 20 and 21. The cover 8 is rotatably supported.

  Further, the lubricating oil supplied to the third and fourth bearings 18 and 19 is prevented from leaking into the rotor chamber 10 in the insertion holes formed in the rotor housing 7 into which the rotor rotary shafts 1a and 2a are inserted. For this purpose, second and third oil seals 22 and 23 are mounted. Further, the grease sealed in the fifth and sixth bearings 20 and 21 is prevented from leaking into the rotor chamber 10 through the insertion holes formed in the cover 8 into which the rotor rotation shafts 1a and 2a are inserted. The fourth and fifth oil seals 24 and 25 are attached.

  As shown in FIG. 3, a cylindrical pin 50 is press-fitted between the third bearing 18 and the fourth bearing 19 in the rotor housing 7. Further, the pin 50 is provided between the third and fourth bearings 18 and 19 so that the dimension between the third bearing 18 and the pin 50 and the dimension between the fourth bearing 19 and the pin 50 are uniform. Located in the center position. Similarly, a cylindrical pin (not shown) is press-fitted between the fifth bearing 20 and the sixth bearing 21 in the cover 8. The pins 50 correspond to the first adjustment member of the present invention.

  Here, the material of main components will be described. The rotor bodies 1z and 2z, the rotor housing 7 and the cover 8 are made of aluminum. The rotating shafts 1a and 2a, the third to sixth bearings 18 to 21, and the pin 50 are made of iron having a smaller thermal expansion coefficient than aluminum.

  Furthermore, in this embodiment, the reduction amount of the inter-axis pitch P (see FIG. 3) of the rotor housing 7 and the cover 8 due to the temperature drop is the sum of the reduction amount of the radius of the male rotor 1 and the reduction amount of the radius of the female rotor 2 ( The dimensions and thermal expansion coefficients of the main components are set as follows so as to be smaller than the amount of reduction in the pitch between the axes of the pair of rotors 1 and 2.

  First, the sum of the radius of the one inner shaft portion 1c and the radius of the other inner shaft portion 2c is R1, the sum of the radius of the outer peripheral portion of the third bearing 18 and the radius of the outer periphery of the fourth bearing 19 is R2, the fifth. The sum of the radius of the outer periphery of the bearing 20 and the radius of the outer periphery of the sixth bearing 21 is R2, and the diameter of the pin 50 is D.

  Further, the coefficient of thermal expansion of the inner shaft portions 1c, 2c is α1, the coefficient of thermal expansion of the rotor bodies 1z, 2z is α2, the coefficient of thermal expansion of the rotor housing 7 and the cover 8 is α3, and the third to sixth bearings 18-21. The thermal expansion coefficient is α4, and the thermal expansion coefficient of the pin 50 is α5.

  R1 × α1 + (P−R1) × α2> R2 × α4 + (P−R2−D) × α3 + D × α5 is satisfied. Incidentally, R1 × α1 + (P−R1) × α2 is the amount of dimensional change when the ambient temperature of the radius of the male rotor 1 changes by 1 ° C. and the amount of dimensional change when the ambient temperature of the radius of the female rotor 2 changes by 1 ° C. R2 × α4 + (P−R2−D) × α3 + D × α5 is a dimensional change when the atmospheric temperature of the inter-pitch pitch P of the rotor housing 7 and the cover 8 is changed by 1 ° C.

  Next, the operation of the screw compressor of this embodiment will be described.

  When the pair of rotors 1 and 2 are synchronously rotated by the rotation transmission mechanism 3, gas is sucked into the compression chamber 10a from the suction port 7a provided on the cover 8 side of the rotor casing 7. At this time, the volume of the compression chamber 10a is reduced while moving from the cover 8 side to the lubricating oil space 9 side with the rotation of the pair of rotors 1 and 2, so that the gas in the compression chamber 10a is gradually pressurized. It moves toward the lubricating oil space 9 while being compressed.

  When the rotation angle of the pair of rotors 1 and 2 reaches a predetermined angle, the compression chamber 10a reaches the discharge port 7b provided on the lubricating oil space 9 side of the rotor casing 7, and the compression that has been sealed until then. Since the chamber 10a is opened at the discharge port 7b, the compressed gas in the compression chamber 10a is discharged from the discharge port 7b.

  According to the present embodiment described above, the pin 50 having a smaller coefficient of thermal expansion than that of the rotor housing 7 is disposed between the third bearing 18 and the fourth bearing 19 in the rotor housing 7. Accordingly, the reduction amount of the inter-shaft pitch P is reduced, the reduction amount of the clearance between the rotors in the low temperature environment is suppressed, and the decrease in the startability in the low temperature environment can be suppressed. In addition, since a pin having a smaller coefficient of thermal expansion than the cover 8 is disposed between the fifth bearing 20 and the sixth bearing 21 in the cover 8, the startability in a low temperature environment is similarly reduced. Can be suppressed.

  Further, since the pin 50 has a simple cylindrical shape, the number of processing steps can be reduced.

  In addition, since the pin 50 is arranged at the center position between the third and fourth bearings 18 and 19 and the pin 50 is arranged at the center position between the fifth bearing 20 and the sixth bearing 21, the thin housing portion (pin and The dimension between each bearing) can be made uniform, and insufficient rigidity of the rotor housing 7 and the cover 8 can be suppressed.

  In addition, since the dimensions and thermal expansion coefficient of main components are set so as to satisfy R1 × α1 + (P−R1) × α2> R2 × α4 + (P−R2−D) × α3 + D × α5, the temperature The reduction amount of the pitch P between the shafts of the rotor housing 7 and the cover 8 due to the reduction becomes smaller than the sum of the reduction amount of the radius of the male rotor 1 and the reduction amount of the radius of the female rotor 2, and the clearance between the rotors in a low temperature environment is reduced. It can be expanded to prevent a decrease in startability in a low temperature environment.

  Further, when the inner shaft portions 1c and 2c are made thicker for speeding up, the overall thermal expansion coefficient of the rotors 1 and 2 becomes smaller, and the amount of reduction in the clearance between the rotors in a low temperature environment increases. The decrease in startability in a low temperature environment becomes significant. Therefore, the gas compressor having such thick inner shaft portions 1c and 2c is particularly effective as a means for suppressing a decrease in startability in a low temperature environment.

(Second Embodiment)
A second embodiment of the present invention will be described. FIG. 4 is a sectional view of a gas compressor according to the second embodiment. This embodiment is different from the first embodiment in that a ring to be described later is added, and other points are common to the first embodiment.

  As shown in FIG. 4, in this embodiment, a cylindrical ring 51 is provided between the rotor housing 7 and the outer peripheral surface of the third bearing 18 and between the rotor housing 7 and the outer peripheral surface of the fourth bearing 19. Is provided. Similarly, cylindrical rings (not shown) are also provided between the cover 8 and the fifth bearing 20 and between the cover 8 and the sixth bearing 21, respectively. These rings 51 are made of iron and have a smaller coefficient of thermal expansion than the rotor housing 7 and the cover 8. These rings 51 correspond to the second adjusting member of the present invention.

  In this embodiment, since the shrinkage of the rotor housing 7 and the cover 8 under a low temperature environment is suppressed by the ring 51, the bearing internal clearance under the low temperature environment is prevented from decreasing, and the bearings 18 to 21 are prevented from being reduced. Smooth operation can be maintained.

(Third embodiment)
A third embodiment of the present invention will be described. FIG. 5 is a sectional view of a gas compressor according to the third embodiment. In this embodiment, a plate 52 is provided in place of the pin 50 of the first embodiment, and the other points are common to the first embodiment.

  As shown in FIG. 5, the plate 52 has an oval shape, and a hole 52 a into which the third bearing 18 is inserted and a hole 52 b into which the fourth bearing 19 is inserted are formed. A plate having the same shape is also provided on the cover 8 side. These plates 52 are made of iron and have a smaller coefficient of thermal expansion than the rotor housing 7 and the cover 8.

  And between the two holes 52a and 52b in the plate 52 demonstrates the function of the pin 50 of 1st Embodiment, and the circumference | surroundings of each hole 52a and 52b in the plate 52 exhibits the function of the ring 51 of 2nd Embodiment. These plates 52 correspond to the first adjustment member and the second adjustment member of the present invention.

  According to the present embodiment, the amount of decrease in the clearance between the rotors in the low temperature environment is suppressed by the space between the two holes 52a and 52b in the plate 52, and the decrease in the startability in the low temperature environment can be suppressed.

  Further, the surroundings of the holes 52a and 52b in the plate 52 can prevent the bearing internal clearance from decreasing in a low temperature environment, and the smooth operation of the bearings 18 to 21 can be maintained.

  Moreover, since the part which exhibits the function of the pin 50 of 1st Embodiment and the part which exhibits the function of the ring 51 of 2nd Embodiment are integrated, the number of parts can be reduced.

(Other embodiments)
In each of the above embodiments, an example in which the present invention is applied to a screw compressor has been described, but the present invention can also be applied to a roots type compressor.

It is sectional drawing of the gas compressor which concerns on 1st Embodiment of this invention. It is a figure which shows the shape of the axial direction end surface of the rotor of FIG. It is sectional drawing which follows the AA line of FIG. It is sectional drawing of the gas compressor which concerns on 2nd Embodiment of this invention. It is sectional drawing of the gas compressor which concerns on 3rd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... Rotor, 7 ... Rotor housing (housing member), 7a ... Inlet port, 7b ... Discharge port, 8 ... Cover (housing member), 18-21 ... Bearing, 50 ... Pin (1st adjustment member).

Claims (8)

A housing member (7, 8) having a suction port (7a) and a discharge port (7b);
A plurality of rotors (1, 2) housed in the housing members (7, 8) and compressing and discharging the gas sucked with rotation;
A plurality of bearings (18-21) fixed to the housing members (7, 8) and rotatably holding the plurality of rotors (1, 2);
In the gas compression device, the thermal expansion coefficient of the housing members (7, 8) is larger than the thermal expansion coefficient of the plurality of rotors (1, 2)
A first adjustment member (50) having a smaller coefficient of thermal expansion than the housing member (7, 8) is provided between the plurality of bearings (18-21) in the housing member (7, 8). Gas compressor to do. A second adjusting member (51) having a smaller coefficient of thermal expansion than the housing member (7, 8) is provided between the housing member (7, 8) and the bearing (18-21). The gas compressor according to claim 1. The gas compressor according to claim 2, wherein the first adjustment member (50) and the second adjustment member (51) are integrated. The gas compressor according to claim 1 or 2, wherein the first adjustment member (50) has a cylindrical shape. The said 1st adjustment member (50) is arrange | positioned in the center position between these bearings (18-21), The gas compression as described in any one of Claim 1, 2, 4 characterized by the above-mentioned. Machine. Each of the rotors (1, 2) includes a rotating shaft (1a, 2a) and a rotor body (1z, 2z) disposed on the outer peripheral side of the rotating shaft (1a, 2a) to form a compression chamber (10a). Consists of
The rotating shaft (1a, 2a) includes an outer shaft portion (1b, 2b) held by the bearings (18-21) and an inner shaft portion (1c, 2c) covered by the rotor body (1z, 2z). And
The sum of the radii of the two inner shaft portions (1c, 2c) is R1, the pitch between the shafts is P, the sum of the radii of the outer peripheral portions of the two bearings (18 to 21) is R2, and the first adjusting member (50 ) Is D, the thermal expansion coefficient of the inner shaft portions (1c, 2c) is α1, the thermal expansion coefficient of the rotor body (1z, 2z) is α2, and the thermal expansion coefficient of the housing members (7, 8) is When α3, the coefficient of thermal expansion of the bearing (18-21) is α4, and the coefficient of thermal expansion of the first adjustment member (50) is α5,
The gas compressor according to claim 4, wherein R1 × α1 + (P−R1) × α2> R2 × α4 + (P−R2−D) × α3 + D × α5 is satisfied. The gas compressor according to any one of claims 1 to 6, wherein the plurality of rotors (1, 2) are a screw-shaped male rotor and a female rotor. Each of the rotors (1, 2) includes a rotating shaft (1a, 2a) and a screw-shaped rotor body (1z, 2z) disposed on the outer peripheral side of the rotating shaft (1a, 2a).
The rotating shaft (1a, 2a) includes an outer shaft portion (1b, 2b) held by the bearings (18-21) and an inner shaft portion (1c, 2c) covered by the rotor body (1z, 2z). And
The coefficient of thermal expansion of the rotor body (1z, 2z) is greater than the coefficient of thermal expansion of the inner shaft (1c, 2c);
The diameter (D) of the inner shaft portion (1c, 2c) is 70% or more of the diameter of a tooth root (1x, 2x) of the rotor body (1z, 2z). Gas compressor.

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