JP4138085B2 - Screw type vacuum pump - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a screw-type vacuum pump used for evacuating a reaction chamber in a semiconductor manufacturing apparatus or the like and discharging generated reaction by-products.
[0002]
[Prior art]
As a screw-type vacuum pump, for example, a structure shown in FIG. 4 is known. The screw type vacuum pump 300 is an example of a dry vacuum pump that does not use a sealing liquid in a pump working chamber used in a semiconductor manufacturing process or the like. Further, in order to maintain the cleanliness of the vacuum, the screw rotor is supported by a one-side shaft support structure having no bearing that requires oil lubrication or the like on the vacuum side.
[0003]
That is, in this screw type vacuum pump 300, a pair of screw rotors 304 and 305 are arranged in parallel in a vertically installed state in a pump working chamber 303 in which an intake port 301 and an exhaust port 302 are formed. A right screw 307 and a left screw 308 are formed with equal leads on the outer peripheral surfaces of the screw rotors 304 and 305 and mesh with each other. The lower ends of the screw rotors 304 and 305 protrude into the gear chamber 310 and are rotatably supported by bearings 311 and 312.
[0004]
The screw rotors 304 and 305 are connected to the motor 320 via timing gears 313 and 314, an idle gear 315, and a drive gear 316. When the pair of screw rotors 304 and 305 rotate relative to each other by the motor 320, a pumping action occurs in which the gas sucked from the intake port 301 is transferred while being compressed toward the exhaust side.
[0005]
Here, since a sealing liquid is not used in the pump working chamber 303 in order to form a clean vacuum space, the reverse flow rate of the suction gas through the gap between the screw rotors 304 and 305 and the pump casing 330 is large. . Therefore, in general, the number of turns of the screw is increased to increase the number of partitions.
[0006]
In addition, reaction by-products (powder, etc.) generated in each process such as etching and CVD, which are semiconductor manufacturing processes, accumulate in the screw vacuum pump 300 and stick to the screw rotors 304 and 305. In order to prevent this, the screw rotors 304 and 305 are placed vertically, so that the reaction by-products that have entered through the intake port 301 located at the upper end do not stick to the lower end of the rotor. A large gap is provided between the lower end of 305 and the inner end face of the pump casing 330 facing it.
[0007]
[Problems to be solved by the invention]
In order to increase the exhaust speed of the screw type vacuum pump having this configuration, a method of increasing the rotational speed of the screw rotor, a method of increasing the volume of the spiral groove defined by the screw, and the like can be considered.
[0008]
However, increasing the rotational speed of the screw rotor is not preferable because it causes problems such as a decrease in the life of the bearing mechanism.
[0009]
Further, as a method of increasing the volume of the spiral groove, methods such as increasing the lead angle of the screw, increasing the rotor diameter, and increasing the depth of the groove can be considered. However, an increase in the screw lead angle significantly increases the overall length of the screw rotor, and it is mechanically difficult to adopt the one-side shaft support structure of the screw rotor. In addition, an increase in the rotor diameter leads to an increase in thrust acting on the screw rotor.
[0010]
The method of deepening the groove has a limitation that the depth of the groove is limited when the outer diameter of the rotor is limited and the desired groove volume cannot be obtained. In addition to this, when an equal lead screw is formed as in the example shown in the figure, the volume of the groove on the exhaust side increases in the same manner, so that the required power also increases accordingly. There is. In order to avoid this problem, it is conceivable to increase the lead angle of the screw on the intake side and to make it an unequal lead that decreases toward the discharge side. However, unequal lead screws pose a problem of complicated and time-consuming processing.
[0011]
On the other hand, in order to increase the exhaust speed, a multistage vacuum pump as shown in FIG. 5 is used, and the suction volume of a roots rotor or the like is provided via the partition wall 401 at the tip side of the screw rotors 304 and 305, that is, the suction stage. It is conceivable to add pump elements 402 and 403 having a large rotor length and a short rotor length to the coaxial state.
[0012]
However, the multistage vacuum pump 400 having this structure has a problem that the structure becomes complicated by the multistage structure. Moreover, the problem that the reaction by-product tends to adhere to the partition wall 401 at the lower end of the pump elements 401 and 402 such as a roots rotor also occurs.
[0013]
In view of these points, an object of the present invention is to realize a small screw-type vacuum pump capable of increasing the exhaust speed without using a complicated structure.
[0014]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention includes a pair of screw rotors each having a right-hand screw and a left-hand screw that can be engaged with each other formed on the outer peripheral surface, and exhausting by rotating these screw rotors relative to each other. In a screw type vacuum pump that operates, a rotor extension is integrally formed on or attached to a shaft end on the suction side of each screw rotor. In addition, the rotor extension portion has a cross-sectional shape perpendicular to the axis substantially the same as the cross-sectional shape perpendicular to the axis at the shaft end on the suction side of the screw rotor. Further, the rotor extension portion and the shaft end on the suction side of the screw rotor are joined to each other in a state where both end face shapes coincide with each other.
[0015]
In the screw type vacuum pump of the present invention, since the rotor extension portion having a large suction capacity is formed on the suction side of the screw rotor, the exhaust speed can be increased. Further, the structure is not complicated. Furthermore, since the joint surface of the rotor extension portion and the screw rotor has the same end face shape, the gas sucked by the rotor extension portion is smoothly introduced into the screw groove side of the screw rotor. No adverse effects such as gas leakage will occur.
[0016]
In the present invention, in addition to the above configuration, when powder or the like adheres between the outer peripheral surface of each rotor extension portion located on the pump suction side and the inner peripheral surface of the pump casing, the sliding area between them for the smaller, the contour shape of the rotor extension as follows, in other words, it is characterized by defining its axis perpendicular cross-section.
[0017]
That is, the cross-sectional shape perpendicular to the axis of each of the rotor extension portions is a portion receding inward in the radial direction from the outer diameter line of the screw rotor defining the cross-sectional shape perpendicular to the axis at the shaft end on the suction side of the screw rotor. And a portion that protrudes outward in the radial direction from the screw rotor thread valley diameter line.
[0018]
Next, when the rotor extension portion is configured to be fastened and fixed to the shaft end on the suction side of the screw rotor by a fastener, the rotor extension portion and the shaft end on the suction side of the screw rotor By inserting a shim plate in between, the clearance between the suction end of the rotor extension and the pump casing can be easily adjusted. As a result, a desired assembled state can be formed without increasing the component accuracy of the screw rotor and the rotor extension.
[0019]
On the other hand, it is desirable to arrange the screw rotor in a vertically placed state so that the suction side is located on the upper side, and to support the shaft only by the portion on the exhaust side located on the lower side. When this configuration is adopted, there is no bearing that requires oil lubrication on the pump suction side, which is suitable for maintaining the cleanliness of the vacuum atmosphere on the side to be evacuated. In addition, since the screw rotor is installed vertically, the reaction by-product that has entered the pump is screwed into the pump when used in processes where powdery reaction by-products are generated, such as etching and CVD processes. It can be dropped to the lower end in the pump without being fixed to the rotor or the like. For this reason, it becomes possible to use stably for the use which attracts | sucks the gas containing a powdery reaction by-product.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Below, with reference to drawings, the example of the screw type vacuum pump to which the present invention is applied is described.
[0021]
FIG. 1A is a schematic longitudinal sectional view of the screw type vacuum pump of this example. The basic configuration of the screw-type vacuum pump 1 is the same as that of the screw-type vacuum pump 300 shown in FIG. 4, and has a pump casing 4 in which an intake port 2 and an exhaust port 3 are formed. Inside the pump casing 4, a pair of screw rotors 5, 6 are arranged in parallel in a vertically placed state.
[0022]
The screw rotors 5 and 6 include rotor main bodies 5a and 6a, rotor shafts 5b and 6b attached so as to penetrate the center thereof, and right and left screws 5c and 6c formed on the outer peripheral surfaces of the rotor main bodies 5a and 6a, respectively. It has. The right screw 5c and the left screw 6c are in a positional relationship in which they are engaged with each other with a slight gap. The right screw 5c and the left screw 6c in this example are equal lead square screws.
[0023]
Rotor extensions 7 and 8 are fastened and fixed by fastening bolts 9 to the shaft ends 5d and 6d on the suction side of the screw rotors 5 and 6 in a coaxial state. These rotor extensions 7 and 8 have a cross-sectional shape perpendicular to the axis obtained by extending the axially perpendicular sectional shape of the shaft ends 5d and 6d on the suction side of the screw rotors 5 and 6 substantially in the axial direction.
[0024]
In general, as shown in FIG. 1 (B), one is a large-diameter semicircle portion 7a, 8a, and the other is a small-diameter semicircle portion 7b, 8b. The outlines of the large-diameter semicircular portions 7a and 8a substantially coincide with the outer diameter lines of the screw rotors 5 and 6, and the outlines of the small-diameter semicircular parts 7b and 8b correspond to the screw valley diameter lines of the screw rotors 5 and 6. It is almost coincident.
[0025]
Here, FIG. 2 shows an example of a specific contour shape of each of the rotor extension portions 7 and 8. As shown in this figure, the large-diameter semicircular portions 7a and 8a are provided with portions slightly receding inward in the radial direction with respect to the screw rotor outer diameter line indicated by a one-dot chain line. On the other hand, the small-diameter semicircular portions 7b and 8b are provided with portions that slightly protrude outward in the radial direction with respect to the screw rotor screw valley diameter line indicated by a one-dot chain line. The reason for this is to reduce the sliding area between the powder and the like when adhering to the outer peripheral surface of the rotor extension or the inner peripheral surface of the pump casing facing it.
[0026]
Next, returning to FIG. 1 again, the shaft ends on the exhaust side of the shafts 5b and 6b of the screw rotors 5 and 6 are respectively connected to the bearing 11 and the pump casing bottom wall 4a in which the pump discharge port is formed. 12, and is rotatably supported by 12 and projects through the bottom wall 4 a into the gear box 10 attached to the bottom surface of the pump casing. The lower ends of the lower end protrusions 51 and 61 of these rotor shafts are also rotatably supported by bearings 13 and 14. Thus, the support structure of the screw rotors 5 and 6 is a one-side shaft support structure in which only the lower end portion on the exhaust side is rotatably supported.
[0027]
Inside the gear box 10 are timing gears 21 and 22 which are attached to the lower end protrusions 51 and 61 of the rotor shaft and mesh with each other, and a pinion gear 23 which is integrally formed with one timing gear 22 in a coaxial state, An idle gear 24 meshed with the pinion gear 23 and a drive gear 25 meshed with the idle gear are housed. The drive gear 25 is fixed to the output shaft 31 of the motor 30 that is vertically placed in a downward posture at a position adjacent to the pump casing 4.
[0028]
In the screw-type vacuum pump 1 having this configuration, screw rotors 5 and 6 having rotor extensions 7 and 8 attached to the upper ends are arranged inside the pump casing 4, and these rotor extensions, screw rotors, A pump working chamber is defined by the inner surface of the pump casing 4. When the motor 30 is driven, the motor rotation is transmitted to the screw rotors 5 and 6 through the gear train having the above-described configuration, and these are rotated in the opposite directions to perform the pump operation.
[0029]
FIG. 3 shows the exhaust principle of the rotor extensions 7 and 8 of the screw type vacuum pump 1 of this example. The rotor extension 8 on one side will be described. First, as shown in FIGS. 3A and 3B, a space formed between the small diameter portion 8 b of the rotor extension 8 and the inner peripheral surface of the pump casing 4. However, it increases with the rotation of the rotor extension 8 in the direction of the arrow, and gas is sucked from the intake port 2 with this increase.
[0030]
When the small-diameter portion 8b of the rotor extension 8 passes through the intake port 2 (FIG. 3C), the intake operation is finished.
[0031]
Next, as shown in FIG. 3 (d), when the leading portion in the rotational direction of the small diameter portion of the rotor extension portion 8 that sucked in the gas reaches a position facing the other rotor extension portion 7, the gas was sucked in. While the gas compression operation is started, the gas is transferred into the screw grooves of the screw rotors 5 and 6 while being compressed as the rotor extension rotates. When the rear end portion in the rotational direction of the small-diameter portion 8b of the rotor extension portion 8 rotates to a position facing the outer peripheral surface of the other rotor extension portion 7, the gas transfer into the screw grooves of the screw rotors 5 and 6 is completed. .
[0032]
In this way, the gas is sucked from the intake port 2 and transferred to the pair of screw rotors 5 and 6 while being compressed by the pair of rotor extensions 7 and 8.
[0033]
In the screw type vacuum pump 1 of the present example configured as described above, a rotor having a right-angle cross-sectional shape obtained by extending the axial right-angle cross-sectional shape of the shaft end as it is in the axial direction at the shaft end on the suction side of the screw rotors 5 and 6. The structure which attached the extension parts 7 and 8 is employ | adopted. Since the suction capacity of the rotor extensions 7 and 8 is larger than that of the screw rotors 5 and 6, the pumping speed of the pump can be increased.
[0034]
Here, in a constant pressure region where a screw type vacuum pump is normally used, the power required for the pump is substantially determined by a screw rotor that compresses gas to atmospheric pressure. Therefore, there is no problem that the required power increases even if the suction volume on the vacuum side is increased as in this example.
[0035]
Further, as described above, the gas discharged from the rotor extensions 7 and 8 flows directly into the screw grooves of the screw rotors 5 and 6. Therefore, it is not necessary to provide a partition between the rotor extensions 7 and 8 and the screw rotors 5 and 6 to form a flow path connecting the two. For this reason, the pump can be single-staged and the structure can be simplified. Further, there is no adverse effect such that the powdery reaction by-product contained in the suction gas is fixed to the partition wall or the like.
[0036]
Furthermore, the screw type vacuum pump 1 of this example employs a structure in which the screw rotors 5 and 6 having the rotor extensions 7 and 8 attached to the upper ends are vertically arranged, and only the lower end portion on the exhaust side is axially supported. ing. As a result, there is no bearing portion that requires oil lubrication on the suction side, so that there is no adverse effect that oil or the like enters the vacuum side space and the cleanliness is lowered. In addition, because it is placed vertically, the powdered reaction product that has entered from the air inlet located at the upper end tends to fall to the bottom wall of the pump casing, so that it adheres to the inner peripheral side surface of the screw rotor or pump casing. Accumulation is suppressed.
[0037]
The rotor extensions 7 and 8 of this example are fastened and fixed to the suction ends of the screw rotors 5 and 6 by fastening bolts. Instead, the rotor main bodies 5a and 6a of the screw rotors 5 and 6 are fixed. It is also possible to extend the tip of the first and integrally form a large diameter portion and a small diameter portion there.
[0038]
It is also possible to attach leads to the rotor extensions 7 and 8.
[0039]
【The invention's effect】
As described above, the screw-type vacuum pump of the present invention includes a rotor extension portion having a right-angle cross-sectional shape obtained by extending the right-angle cross-sectional shape of the shaft end as it is at the suction end of the pair of screw rotors. It is a formed configuration or an attached configuration.
[0040]
Since such a rotor extension portion has a larger gas suction capacity than a screw rotor, the pump exhaust speed can be increased. In addition, the rotor extension is a cross-sectional shape obtained by extending the right-angle cross-sectional shape of the shaft end on the suction side of the screw rotor as it is, so that the gas sucked by the rotor extension can be smoothly and without causing leakage etc. There is an advantage that it can be transferred to the rotor side. Furthermore, compared to a multistage vacuum pump equipped with a pump element partitioned by a partition wall, the structure can be simplified, and deposition and sticking of powdery reaction byproducts sucked together with gas can be suppressed. There is also an advantage.
[0041]
Further, in the present invention, since the split rotor having a structure in which the rotor extension is fastened and fixed by the fastening bolt is used at the shaft end on the suction side of the screw rotor, the screw rotor and the rotor extension are processed separately. Therefore, there is an advantage that processing is simplified. Further, since the axial length of the divided rotor can be adjusted by sandwiching shim plates or the like between these divided portions, there is an advantage that the component accuracy of each rotor does not need to be increased so much.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view of a screw-type vacuum pump to which the present invention is applied, and an end view of a rotor extension portion thereof.
2 is an explanatory view showing a shape of a rotor extension portion of the pump of FIG. 1;
3 is an operation explanatory diagram for explaining gas suction, compression, and transfer operations by a rotor extension portion of the pump of FIG. 1; FIG.
FIG. 4 is a schematic longitudinal sectional view of a general screw type vacuum pump and an end view of the screw rotor.
FIG. 5 is a schematic longitudinal sectional view of a multistage vacuum pump and an end view showing the shape of its roots rotor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Screw type vacuum pump 2 Intake port 3 Discharge port 4 Pump casing 4a Casing bottom wall 5, 6 Screw rotor 5a, 6a Rotor main body 5b, 6b Rotor shaft 5c, 6c Screw 5d, 6d The shaft end 51 at the suction side of a screw rotor, 61 Shaft end protruding portions 7, 8 Rotor extension portions 7a, 8a Large-diameter semicircular portions 7b, 8b Small-diameter semicircular portions 11-14 Bearing

Claims (3)

In a screw-type vacuum pump that includes a pair of screw rotors each having a right-hand screw and a left-hand screw that can be engaged with each other formed on the outer peripheral surface, and that performs an exhaust operation by relatively rotating these screw rotors,
At the shaft end on the suction side of each screw rotor, a rotor extension is integrally formed or attached in a coaxial state,
Each rotor extension has an axially perpendicular cross-sectional shape substantially the same as the axially perpendicular sectional shape at the shaft end on the suction side of the screw rotor,
Each rotor extension and the shaft end on the suction side of the screw rotor are connected to each other in a state in which both end face shapes are substantially matched ,
The cross-sectional shape perpendicular to the axis of each of the rotor extension portions is a portion recessed inward in the radial direction from the outer diameter line of the screw rotor that defines the cross-sectional shape perpendicular to the axis at the shaft end on the suction side of the screw rotor; The screw type vacuum pump characterized by including the part which protruded to the outward of radial direction rather than the said screw rotor thread valley diameter line . In claim 1,
The rotor extension is fastened and fixed by a fastener to the suction-side shaft end of the screw rotor,
A screw type characterized in that a clearance between the suction end of the rotor extension and the pump casing can be adjusted by inserting a shim plate between the rotor extension and the suction end of the screw rotor. Vacuum pump. In claim 1 or 2,
The screw-type vacuum pump is characterized in that the screw rotor is arranged in a vertical state so that the suction side is located on the upper side, and is supported only by the exhaust side part located on the lower side .

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