JPH10311288A - Screw type vacuum pump and screw finishing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw pump to further reduce the size of a blow hole and improve the degree of a reach vacuum by reducing the lead angle of a screw compared with a conventional type. SOLUTION: A screw type vacuum pump comprises a pair of make and female screws 1 and 2 engaged with each other for rotation; and a drive device to rotate the screws 1 and 2. In the screw type vacuum pump, the screws 1 and 2 machined by cutting or a generating method by grinding such that an orthogonal cross section is the same in any position of an axis and a lead angle α is adjusted to approximate 40 deg. are used. It is preferable that the lead angle α is an angle in a range of 6-25 deg.. Further, it is desirable that the lead angle α on the intake side is approximate 40 deg. and a screw machined by cutting or a generating method by grinding such that the lead angle is gradually decreased from the intake side to the exhaust side is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw vacuum pump and a screw machine for machining a screw used in the screw vacuum pump.

[0002]

2. Description of the Related Art A screw type vacuum pump is a volume transfer type pump similar to a roots type or a claw type vacuum pump, and has excellent characteristics in a high vacuum region from about atmospheric pressure to about 10 ^-4 Torr. . Therefore, it has been conventionally used for exhausting, for example, semiconductor manufacturing equipment. The structure of the screw-type vacuum pump will be schematically described with reference to FIG. 13. The screw-type vacuum pump accommodates a pair of male screws 50 and female screws 51 rotating while meshing with each other in a casing (not shown). A working chamber is formed by the gears 50a and 51a formed on the screw and the casing, and the suction gas confined in the working chamber is pressed out from a discharge port by rotation of the screws 50 and 51. ing.

A screw type vacuum pump having such a structure is generally low in vibration, low in noise, small in size,
Lubricating oil used like an oil rotary pump uses various gases used in the semiconductor manufacturing process (for example, arsenic, gallium,
(Chlorine, Poly-Si, Fluorine) to shorten the life of the lubricating oil, or to prevent oil molecules from being mixed into the semiconductor manufacturing equipment and contaminated, and various gases used in the semiconductor manufacturing process. Therefore, it is considered to be suitable for an exhaust pump of a semiconductor manufacturing apparatus because it has better durability and reliability with respect to a solid product generated in the pump.

However, in recent years, as the diameter of a semiconductor wafer has been increased, the vacuum pump for evacuation of a semiconductor manufacturing apparatus has been improved in evacuation speed and ultimate vacuum degree (ultimate pressure) (exhaust capacity is 10 ^-1).
Thousands of l / mi in a vacuum state of about 10 Torr
n. To tens of thousands l / min. , Ultimate vacuum 10 ^-2 to 10 ^-6
(Approximately Torr), and further improvement in the performance of the vacuum pump is desired.

[0005]

By the way, in such a screw type vacuum pump, in the vicinity of the meshing point on the pitch tangent line of the male and female screws, there is a processing error or an operating gap (between the screw outer circumference and the casing inner circumference). Air side (discharge side) not caused by the necessary operation gap)
There is a technical problem that a gap called a blow hole is formed that communicates with the vacuum side (suction side) and hinders achievement of a high degree of vacuum.

The inventor of the present application has conducted intensive studies on the problem of the blowhole, and has found that the lead angle of the screw can be made smaller than that of the conventional screw without changing the tooth profile of the screw itself. It has been found out that the blow hole can be made smaller and the ultimate vacuum degree can be improved.

Further, as described above, when the lead angle of the screw is reduced, a new problem arises in that the amount of exhaust per rotation of the screw is reduced. In order to solve this problem, it is conceivable to reduce the lead angle of the screw and increase the outer diameter of the screw to secure the displacement, but when the outer diameter of the screw is formed larger, The operating gap provided between the casing and the inner periphery of the casing must be made large in consideration of the thermal expansion of the exhaust-side screw portion.

However, if the operation gap provided between the outer periphery of the screw and the inner periphery of the casing is made large, the amount of blow-out from the operation gap increases, and the increase in the amount of blow-off reduces the lead angle. Therefore, the blow-off amount from the blow hole is reduced by a greater amount, and a high degree of vacuum cannot be obtained. That is, simply increasing the outer diameter of the screw not only causes a disadvantage that the device becomes large, but also causes a technical problem that a high vacuum degree and a large pumping speed of the screw type vacuum pump cannot be achieved. It is.

[0009] In this regard, the inventor of the present application has proposed that a screw having a fixed lead angle (hereinafter referred to as a “constant lead angle type”).
And a screw-type vacuum pump in which the lead angle of the screw gradually decreases from the suction side (vacuum side) toward the exhaust side (atmosphere side) (hereinafter referred to as "lead angle gradual type"). We worked hard on pumps. As a result, the inventor of the present application has found that when the gas transfer volume per rotation of the screw is the same, the lead angle gradually decreasing type can form a dense screw lead on the discharge side as compared with the constant lead angle type. It has been found that the blow hole on the exhaust side where the influence of the hole is large can be made smaller than that of the fixed lead angle type. That is, the inventor of the present application has found that a screw type vacuum pump with a gradually decreasing lead angle can obtain a higher degree of vacuum than a screw type vacuum pump with a fixed lead angle.

However, a screw with a gradually decreasing lead angle, that is, a screw in which the lead angle of the screw gradually decreases from the intake side (vacuum side) toward the exhaust side (atmosphere side), is economical in conventional machining. In addition, they cannot be machined with high accuracy, and have been manufactured on a trial basis by a casting method, an electric discharge machining method, etc., but those manufactured by these methods have not yet been put to practical use in terms of accuracy or economy. As a result of intensive studies on this problem, the inventor of the present application has devised a processing machine.

As is apparent from the above description, a first object of the present invention is to make the lead angle of a screw smaller than that of a conventional screw, so that the blow hole can be made smaller. It is an object of the present invention to provide a screw pump capable of improving the ultimate vacuum.

A second object of the present invention is to provide an economically and precisely machined screw whose lead angle changes so that the lead angle of the screw gradually decreases from the intake side to the exhaust side. Accordingly, it is an object of the present invention to provide a screw pump capable of increasing the displacement and improving the ultimate vacuum without increasing the size.

Further, a third object of the present invention is to achieve a large displacement and a high ultimate vacuum degree at the same time, with high precision machined so that the lead angle is small and the lead angle is constant. By combining the screw part with a high-precision screw part machined so that the lead angle is larger than the lead angle of the screw part and the lead angle is gradually reduced, the lead angle is simply reduced gradually. Another object of the present invention is to provide a screw pump capable of obtaining a higher degree of vacuum than that of a conventional type.

Still another object of the present invention is to provide a machine capable of machining a screw having a constant lead angle and a screw having a gradually decreasing lead angle. Is to provide a machine.

[0015]

SUMMARY OF THE INVENTION A screw-type vacuum pump according to the present invention, which has been made to solve the above technical problem, has a pair of male and female screws which rotate while meshing with each other, and a drive for rotating these screws. In the screw type vacuum pump provided with an apparatus, each of the screws is formed by cutting or grinding such that the cross section perpendicular to the axis is the same at any position of the axis and the lead angle is less than 40 degrees. The basic configuration is to use screws processed by the raw method. Here, the leak
The angle is preferably in the range of 6 to 25 degrees.

Further, a screw-type vacuum pump according to the present invention is a screw-type vacuum pump including a pair of male and female screws that rotate while meshing with each other, and a driving device that rotates these screws. Cutting is performed such that the cross section perpendicular to the axis is the same at any position along the axis, the lead angle on the intake side is less than 40 degrees, and the lead angle gradually decreases from the intake side to the exhaust side. The basic configuration is to use a screw processed by the creation method by grinding. Here, it is preferable that the lead angle on the exhaust side is in the range of 6 degrees to 25 degrees.

Further, a screw-type vacuum pump according to the present invention is a screw-type vacuum pump comprising a pair of male and female screws rotating in mesh with each other, and a driving device for rotating these screws. The lead angle changes so that the section perpendicular to the axis is the same at any position along the axis, and the lead angle on the intake side is less than 40 degrees and gradually decreases from the intake side to the exhaust side. However, the exhaust-side end has a basic configuration in which a screw processed by a creation method by cutting or grinding is used so that the lead angle does not change and remains constant. Here, it is preferable that the lead angle at the end on the exhaust side is in the range of 6 to 25 degrees.

Further, a screw-type vacuum pump according to the present invention is a screw-type vacuum pump comprising a pair of screws that mesh with each other and rotate, and a driving device that rotates these screws, wherein each of the screws is a shaft. The right-angled cross section is formed with a rotating disk-shaped cutting tool having a diameter of 250 mm or less so as to be the same at any position of the axis, and if the cutting tool is not a cutting tool having a diameter of 250 mm or less, the screw groove surface being processed by the cutting tool is not used. The basic configuration is that the groove surface that is obliquely adjacent to the cutting tool and the screw has a screw shape that causes interference.

In order to solve the above-mentioned technical problems, a screw processing machine according to the present invention is a machine for generating a screw such as a screw type vacuum pump, wherein the rotary blade is located at a position where the rotary blade can contact a screw lead. A tool axis for rotating the, a tool rest on which the tool axis is installed, and an ω axis for rotating a workpiece which is a screw generating material,
A y-axis for relatively moving the tool rest and the workpiece in the normal direction from the center of the workpiece, an x-axis for relatively moving the tool rest and the workpiece in the axial direction of the workpiece, Turn the tool post on which the tool axis is installed to change the screw lead angle θ
, And at least the ω axis and the x axis can be simultaneously controlled. Here, the rotary blade of the processing machine is preferably a relatively thin rotary blade or an end mill-shaped rotary blade.

According to the present invention, by setting the lead angle of the screw smaller than the conventional lead angle (about 40 degrees) as described above, the blow hole can be made smaller and the ultimate vacuum can be reduced. The degree can be improved. In addition, by providing a screw whose lead angle changes so that the lead angle of the screw gradually decreases from the intake side to the exhaust side, it is possible to increase the displacement and improve the ultimate vacuum degree without increasing the size. Can be. In addition,
Combine the screw part processed so that the lead angle is small and the lead angle is constant, and the screw part processed so that the lead angle is larger than that of the screw part and the lead angle is gradually reduced. Thus, it is possible to obtain a screw-type vacuum pump capable of obtaining a higher degree of vacuum than that of the type in which the lead angle is gradually reduced. Furthermore, according to the processing machine of the present invention, it is possible to machine both the constant lead angle type and the lead angle gradually decreasing type screws.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a screw type vacuum pump according to the present invention will be described below with reference to FIGS. FIG. 1 is a schematic sectional view of a screw type vacuum pump, and FIG. 2 (a) is a side view of a male and female screw used in the screw type vacuum pump of FIG.

As shown in the figure, a male screw-1 and a female screw-2 of this screw type vacuum pump are housed in a main casing 3 and attached to an end plate 4 which seals one end face of the main casing 3. Bearings 5, 6 and auxiliary casing 7
Are rotatably supported by bearings 8 and 9 attached to the shaft. The rotating shafts 10, 1 of the male and female screws-1, 2
1 is provided with timing gears 12, 13 housed in the sub-casing 7, and the gap between the two screws is adjusted so that the male and female screws 1, 2 do not contact each other. A motor M is attached to the rotating shaft 10 of the male screw 1 via a coupling or a speed increasing gear. The rotation of the motor M is transmitted to the male screw 1 and is transmitted through timing gears 12 and 13. It is configured to rotate the female screw-2.

Since lubrication of the bearings 8 and 9 is performed by lubricating lubrication, lubricating oil (not shown) accumulated in the sub-casing 7 is splashed by timing gears 12 and 13. Sealing members 14 and 15 are attached to the bearings 5, 6 and 8, 9, respectively.
The lubricating oils 2 and 13 are prevented from entering the working chamber. A suction port 16 is provided at one end of the main casing 3. A discharge port 17 for discharging the gas compressed by the male and female screws 1 and 2 to the outside is provided on the end plate 4 side of the main casing 3. The main casing 3
Since the temperature rises due to the compression of the gas, a cooling jacket 18 is provided, and cooling water is passed through the jacket to cool the casing 3 and the compressed gas.

When the male screw-1 is driven to rotate by the motor M, the female screw-2 is driven by the timing gears 12,13.
Is driven to rotate. Then, as the male and female screws 1 and 2 rotate, gas is sucked from the suction port 16 into the working chamber formed by the male screw 1, the female screw 2 and the casing 3. The sucked gas transfers the gas while the volume is kept constant at the beginning with the rotation of the male and female screws 1 and 2. However, when the screws 1 and 2 further rotate, the volume is reduced and the gas is compressed. And the compressed gas is
The ink is finally discharged from the discharge port 17 while being compressed.

Next, the male and female screws will be described with reference to FIG. The feature of this male and female screw is, for example, a screw that can be formed by a processing machine described below,
That is, the lead angle α is formed smaller than that of the conventional one. That is, the lead angle of the conventional male and female screws is 40
In contrast to the above degree, the present invention is characterized in that the lead angle of the screw is set to 6 to 25 degrees. Here, the lead angle is the angle formed by the helical curve of the screw thread and the plane perpendicular to the axis of the screw passing through one point on it.

As described above, when the lead angle α is reduced, the blow hole can be reduced. The blow hole is a blow-through hole formed between the inner periphery 3a of the casing 3 and the tooth tips 1a, 2a of the male and female screws 1, 2, and the shape of the hole (passage) is described in the Transactions of the Japan Society of Mechanical Engineers (B As shown in FIG. 7 of “Performance Analysis of Screw Compressor” of Vol. 50, No. 452, the shape is almost triangular, and in the embodiment of the present invention, this is shown in FIGS. 2 (b) and 2 (c). Show. FIG. 2 (b)
Represents the blowholes H ₀ in the lead L _0, 2
(C) shows the blowholes H ₁ in the lead _{L 1 (L 1 <L 0} ). Here, the area S of the blow holes H ₀ and H _1
0 and S ₁ are S ₀ : S ₁ ≒ L ₀ : L ₁ if the cross sections of the screws at right angles to the axis are the same. That is, the lead angle α
Becomes smaller, the lead L also becomes smaller, and the blow hole becomes smaller.

As described above, since the lead angle of the screw is formed smaller than that of the conventional screw, the screw hole can be made smaller, and the screw pump which can achieve the ultimate degree of vacuum can be improved. Obtainable.

Each of the screws has the same cross section perpendicular to the axis at any position along the axis, so that analysis and formation of the seal line can be easily performed.

Next, a first modified example of the screw will be described with reference to FIGS. FIG. 3A is a side view of the male screw, and FIG.
FIG. 4A is a side view of the female screw, and FIG. 4B is a cross-sectional view of the female screw taken along line IV-IV. The male and female screws are, for example, screws that can be machined economically and accurately by a processing machine described later. The male screw has a smaller lead angle than the conventional one, and the lead angle is smaller than that of the conventional screw. The point is that the lead angle is gradually reduced from the side to the exhaust side so that the helical curve of the thread becomes gradually denser.

That is, the lead angles of the male and female screws 1 and 2 on the intake side are 15 and 25 degrees, and the lead angles of the male and female screws 1 and 2 on the exhaust side are 6 and 12 degrees. Is configured. The rate of change of the lead angle is expressed by the following equation.

[0031]

(Equation 1)

Here, D is the diameter at the screw processing point, x is the axial length from the processing origin, and L ₀
Is the lead length as viewed at the processing origin, and c is a constant.

Although the size of the blow hole of the screw whose lead angle gradually decreases becomes larger on the vacuum side (intake side),
If it is small on the atmosphere side (exhaust side), this is not a problem in relation to the ultimate vacuum.

As described above, the screw in which the lead angle is changed from the intake side to the exhaust side so that the helical curve of the screw thread becomes gradually denser and the lead angle gradually decreases becomes smaller. When the gas transfer volume per rotation of the screw is the same, the blowhole can be made smaller than that of a screw vacuum pump having a constant lead angle. That is, a higher degree of vacuum can be obtained. In addition,
As described above, each of the screws has the same cross section perpendicular to the axis at any position along the axis.

Next, a second modification of the screw will be described with reference to FIGS. 5A is a side view of the male screw, FIG. 5B is a cross-sectional view taken along line VV, FIG. 6A is a side view of the female screw,
(B) is the VI-VI sectional view. The male and female screws are characterized in that the lead angle changes from the intake side to the exhaust side so that the helical curve of the thread becomes gradually denser and the lead angle gradually decreases, and The point is that the lead angle is constant without changing. Here, the lead angles on the intake side and the exhaust side and the lead angle change rate in the lead angle changing portion are the same as those in FIGS.

As described above, by combining the screw portion having a constant lead angle and the screw portion processed so that the lead angle becomes gradually smaller, a small and large displacement can be achieved.
A screw type vacuum pump with a high ultimate vacuum can be obtained.

Next, a machine for processing the screw of the above-described screw type vacuum pump will be described with reference to FIG. As shown in the drawing, a blade axis A for rotating the rotary blade 100 at a position where the rotary blade 100 can come into contact with the screw lead, and a workpiece W which is located above the rotary blade 100 and is a screw generating material, is rotated. ω axis and workpiece W
A y-axis for vertically moving the tool rest 102 with respect to the tool rest 102,
An x-axis for moving the workpiece W in the front-rear direction with respect to the tool rest 102, and a θ-axis for changing the screw lead angle by turning the tool rest 102 on which the tool axis A is installed. The axis and the x axis can be controlled simultaneously. The rotary blade 100 is a relatively thin rotary blade or an end mill-shaped rotary blade.

Here, the table 103 has a tool post 102
Is provided, and a tool rest 10 is provided.
2 is configured to be rotatable on the θ axis by the servo motor 105. A rotary grindstone (blade) 100 rotated by a motor 106 on a blade axis A orthogonal to the θ axis is detachably attached to the tool rest 102. The blade 100 can be adjusted so that a processing point (a contact portion between the blade 100 and the workpiece W (see FIG. 8)) substantially at the center of the thickness or in the thickness direction is positioned on the θ axis. .

The table 103 is provided on the table 103 so that it can slide in the x-axis direction perpendicular to the θ axis along the guide 107.
The column 108 is attached to the column 108 by a servomotor 109 via a well-known slide mechanism (not shown).
It is slidable in the axial direction.

The column 108 has x along the guide 115.
A work mount 110 is mounted so as to be slidable in the y-axis direction perpendicular to the axis, and the work mount is also provided with a servo motor 111 via a well-known slide mechanism (not shown).
Slidable in the y-axis direction.

The work mounting table 110 is provided with a well-known work chuck mechanism 112 and a centering mechanism 113, and the workpiece W is parallel to the x axis and orthogonal to the θ axis.
The shaft is rotated by a servomotor 114.

FIG. 2 shows the processing machine constructed as described above.
A case where the fixed lead angle type screw shown in (1) is processed using a rotary forming tool will be described. The screw shown in FIG. 2 has one or more torsion turns and is designed so that the cross section perpendicular to the axis is the same at any position of the axis, and the lead angle is larger than that of the conventional screw as described above. Designed small.

As shown in FIG. 8, a rotary forming tool (grinding stone) whose circumferential cross section is formed to have substantially the same shape as the desired screw groove cross section has its thickness substantially centered on the θ-axis line. To the blade axis A. At this time, the rotary blade 100 is located immediately below the workpiece W. Next, the lead angle θ of the fixed lead angle type screw
Is input to the servo motor 105 and θ
The shaft is rotated so that the plane of rotation of the cutting tool and the tooth trace of the screw (lead angle) are substantially coincident with each other. Next, the rotary blade is rotated at a high speed, and the x-axis and the y-axis are operated by the respective servo motors, so that the rotary blade is substantially brought into contact with one end (one end of the first line) of the work. Next, a predetermined cutting depth h is given by the y-axis, and while simultaneously controlling the ω-axis and the x-axis, that is, while moving the workpiece at a constant angular velocity and moving at a constant speed in the x-axis direction, a constant lead angle type is provided. A screw groove is formed from one end to the other end.

In this way, the first cutting step of the first row is performed, and then the second and third rows are similarly cut one after another. When the first cutting operation is completed for each strip, a second cutting operation is performed for each strip by further providing a cutting depth. In this way, several cutting operations are performed until the cumulative value of the cutting depth finally reaches the groove depth, thereby completing the processing of the fixed lead angle type screw.

As described above, the ω axis and the x axis are controlled at the same time, but the control is controlled with a fixed relationship. That is, the command signal generated based on the correlation between Ω and x as shown in FIG.
And the x-axis (servo motor 109) are controlled simultaneously. Here, FIG. 9 shows a developed view of the tooth trace helical winding at a predetermined groove depth of the fixed lead angle type screw, the horizontal axis Ω indicates the rotation angle of the screw, and the vertical axis x indicates the screw corresponding to the rotation angle Ω. Indicates the axial position. The screw formed in this manner has the same cross section perpendicular to the axis at any position along the axis.

Next, a description will be given of a case where the lead angle gradually decreasing type screw shown in FIGS. 3 and 4 is processed. Here, the screw shown in FIGS. 3 and 4 has one or more twist turns, and its lead angle gradually decreases in proportion to the rotation angle Ω of the screw from the intake side to the exhaust side, and The section perpendicular to the axis is designed to be the same at any position of the axis. In the case of such a lead angle decreasing type screw, rough processing is performed by using a general-purpose rotary blade (grinding stone) having substantially the same shape as the groove cross section of the exhaust portion that is the densest lead, and a rotary blade having a small thickness ( Finishing with a grindstone).

First, rough machining will be described. When machining a groove from the intake side to the exhaust side of the screw, the ω axis is rotated at a constant angular velocity, the moving speed of the x axis is gradually reduced, and The θ axis is gradually rotated so that the angle becomes gradually smaller. Other processing procedures are the same as in the above-described processing of the fixed lead angle type screw. FIG. 10 is a partial cross-sectional view of the screw after the rough processing. In the figure, a dotted line indicates a design profile, and a portion of the pressure between the dotted line and the solid line is a finishing margin. As can be seen from this figure, the rough machining in the present embodiment involves cutting the center of the groove width of the screw.

In this rough machining, the ω axis, the θ axis, and the x axis are controlled based on coordinate data obtained from a vine winding development view at a predetermined depth position in the center of the groove width of the screw as shown in FIG. I do. In FIG. 11, the horizontal axis Ω indicates the rotation angle of the screw, and the vertical axis x indicates the position in the screw axis direction.

In the finishing, the above-mentioned finishing margin is cut with a thin rotary knife. In the present embodiment, the processing starts with the processing of the helical winding passing through the point A shown in FIG. In this processing,
The ω-axis, θ-axis, and x-axis are simultaneously controlled based on coordinate data obtained from the vine winding development view shown in FIG. When the machining of the vine winding passing through the point A is completed, the vine winding is successively machined at points B and C at intervals such that the profile of the machining groove becomes smooth. The other processing procedures are the same as in the case of the fixed lead angle type screw described above.

Next, a description will be given of the case of processing a screw composed of a gradually decreasing lead angle type and a constant lead angle type shown in FIGS. This is the same as the case of processing the lead angle gradually decreasing screw except that the rotation of the screw is stopped and the moving speed of the x-axis is kept constant.

Also, in the case of processing the screw shown in FIGS. 3 to 6 by using a rotary blade having a diameter of 250 mm or less, when the lead angle is gradually reduced, the blade and the teeth which are diagonally adjacent to each other across the blade. It does not cause interference with the surface.

In the finishing of each screw described above, a certain radial position (for example, point A in FIG. 10)
The method has been described in which a cutting tool is positioned at a position, the position is used as a starting point, and continuous processing is performed along the tooth trace to the end, and this processing is sequentially performed in different radial directions. In such processing, as shown in FIG. When a cutting tool having a rough cross-sectional shape is used and the feed pitch is roughened, the cross section of the screw tooth at right angles to the axis becomes stepped as shown in FIG.

Therefore, as another finishing method, the finishing may be performed one after another along the profile of each section perpendicular to the axis of the screw. In other words, while simultaneously controlling the ω-axis and the y-axis while fixing the x-axis, the entire circumference of one cross section perpendicular to the axis is finished, and then the x-axis is slightly moved,
The process of similarly processing a cross section perpendicular to the axis slightly deviated in the axial direction from the finished cross section perpendicular to the axis is sequentially performed.

In this case, since the lead angle changes continuously at the position of the tooth space in the depth direction, in addition to the simultaneous control of the x-axis and the y-axis, the θ-axis is simultaneously controlled. By performing such processing, the section perpendicular to the axis of the tooth can be obtained as shown in FIG.
As shown in (b), the shape is slightly polygonal,
It can be much smoother than the cross-sectional shape of FIG. In this processing, since the processing is performed for each section perpendicular to the axis, the processing shape in the tooth trace direction is the same as that in FIG.
As shown in (c), it becomes wavy.
mm, the height h of the wave is at most about 1 micron, even if the feed pitch in the x-axis direction is 1 mm, and the meshing surface of the male and female screws and the functional surface of the vacuum pump This is not a practical problem.
12 (a), 12 (b) and 12 (c) show the blade 100,
The vertical position relationship between 100 ′ and the work W is shown in reverse.
Further, in the above two finishing methods, FIG.
As shown in (b), the right half of the tooth is finished using a blade 100 provided with a processing edge on the right side, and the left half is finished using a blade 100 'provided with a processing edge on the left side. ,preferable. Also in this case, FIGS.
The processing point is set on the θ-axis as shown in FIG. By doing so, even if the θ axis is rotated, the processing point is simply on the θ axis line, making it easy to create a processing program, and at the time of processing, interference between the blades 100, 100 ′ and the screw tooth surface. This makes it difficult for the screw to be formed. As a result, a screw having a small lead angle can be produced in combination with the blade diameter of 250 mm or less.

[0055]

According to the screw pump according to the present invention, the lead angle can be made smaller than that of the conventional pump, so that the blow hole can be made smaller and the ultimate vacuum can be improved. Can be. Further, according to the screw type pump according to the present invention, since the lead angle of the screw is provided with a screw whose lead angle changes so as to gradually decrease from the intake side toward the exhaust side, without increasing the size, It is possible to increase the displacement and improve the ultimate vacuum.

Further, according to the screw pump according to the present invention, the screw portion processed so that the lead angle is small and the lead angle is constant, and the screw processed so that the lead angle is gradually reduced are integrally formed. Because of the combination, a higher degree of vacuum can be obtained than that of the type in which the lead angle is simply reduced. Furthermore, according to the screw processing machine of the present invention, not only a screw with a constant lead angle but also a screw with a gradually decreasing lead angle, which cannot be processed with a conventional lathe or grinding machine, can be processed economically and accurately. .

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a screw-type vacuum pump according to an embodiment of the present invention.

FIG. 2A is a view showing the male and female screws shown in FIG. 1, and FIGS. 2B and 2C are schematic views showing the shape of a blowhole.

FIGS. 3A and 3B are diagrams showing a first modified example of the male screw, in which FIG. 3A is a side view, and FIG.
It is a III sectional view.

FIGS. 4A and 4B are views showing a first modification of the female screw, wherein FIG. 4A is a side view, and FIG.
It is IV sectional drawing.

FIGS. 5A and 5B are diagrams showing a second modification of the male screw, wherein FIG. 5A is a side view, and FIG.
It is sectional drawing.

FIGS. 6A and 6B are views showing a second modified example of the female screw, wherein FIG. 6A is a side view, and FIG. 6B is a view showing VI- of FIG.
It is VI sectional drawing.

FIG. 7 is a perspective view of a screw processing machine according to the present invention.

FIG. 8 is a diagram showing a processing state.

FIG. 9 is a development view of a tooth trace helical winding of a screw having a constant lead angle.

FIG. 10 is a partial cross-sectional view of the screw after rough processing.

FIG. 11 is a development view of a tooth vine winding of a lead-reducing screw.

FIG. 12 is a diagram showing a finishing process.

FIG. 13 is a perspective view showing a conventional screw.

[Explanation of symbols]

Reference Signs List 1 Male screw 1a Male screw tooth tip 2 Female screw 2a Male screw tooth tip 3 Casing 3a Inner circumference of casing α Lead angle H ₀ blow hole H ₁ blow Hall

Claims (9)

[Claims] 1. A screw-type vacuum pump comprising a pair of male and female screws rotating in mesh with each other, and a driving device for rotating these screws, wherein each of the screws has an axis perpendicular to any axis. And a screw type vacuum pump characterized in that a screw formed by cutting or grinding so as to have a lead angle of less than 40 degrees is used. 2. The screw type vacuum pump according to claim 1, wherein the lead angle is in the range of 6 degrees to 25 degrees. 3. The screw vacuum pump according to claim 1, wherein the lead angle is constant at any position in the axial direction. 4. A screw-type vacuum pump comprising a pair of male and female screws rotating in mesh with each other and a driving device for rotating these screws, wherein each of the screws has an axis perpendicular to any axis. And a screw formed by cutting or grinding so that the lead angle on the intake side is less than 40 degrees and the lead angle gradually decreases from the intake side to the exhaust side. Screw type vacuum pump characterized by using. 5. The screw type vacuum pump according to claim 4, wherein a lead angle on an exhaust side is an angle in a range of 6 degrees to 25 degrees. 6. A screw-type vacuum pump comprising a pair of male and female screws that rotate in mesh with each other and a driving device that rotates these screws, wherein each of the screws has a section perpendicular to the axis at any position on the axis. The lead angle changes so that the lead angle on the intake side is less than 40 degrees and gradually decreases from the intake side to the exhaust side, and the lead angle at the end on the exhaust side. A screw-type vacuum pump characterized by using a screw processed by a creation method by cutting or grinding so that a constant value does not change. 7. The screw-type vacuum pump according to claim 6, wherein a lead angle of the exhaust-side end is in a range of 6 degrees to 25 degrees. 8. A screw-type vacuum pump comprising a pair of screws meshing with each other and rotating, and a driving device for rotating these screws, wherein each of the screws has a cross section perpendicular to the axis at any position along the axis. A groove that is formed with a rotating disk-shaped cutting tool having a diameter of 250 mm or less so as to be the same, and that is not a cutting tool having a diameter of 250 mm or less, a groove that is obliquely adjacent to a screw groove surface being processed by the cutting tool and sandwiches the cutting tool. A screw-type vacuum pump having a screw shape that causes interference between the surface and the cutting tool. 9. A machine for creating a screw, such as a screw vacuum pump, comprising: a blade shaft for rotating the rotary blade at a position where the rotary blade can contact a screw lead; a tool rest on which the blade shaft is installed; An ω axis for rotating a workpiece as a generating material, a y axis for relatively moving the tool rest and the workpiece in a normal direction from the center of the workpiece, and a tool rest in an axial direction of the workpiece. And an x-axis for relatively moving the workpiece and the workpiece, and a θ-axis for changing the screw lead angle by turning the tool rest on which the tool axis is installed, wherein at least the ω-axis and the x-axis can be simultaneously controlled. And screw processing machine.