JP7698992B2 - Rotating equipment for machining - Google Patents

Description

The technology disclosed relates to rotating equipment for machining, such as a turntable that supports the workpiece, and in particular, to a technology that achieves both heat suppression in the sealed area and prevention of the intrusion of foreign matter.

During machining, cutting chips and cutting water are scattered around, so this type of rotating equipment rotates in a harsh environment. If foreign matter gets into the rotating parts, it can cause malfunctions. For this reason, the rotating parts are usually sealed with a sealant to prevent foreign matter from getting in.

Related to the technology being disclosed is a rotating device previously proposed by the present inventor (Patent Document 1).

The rotating device of Patent Document 1 is equipped with a spindle having a circular table, and a pair of annular seals are arranged across a predetermined annular gap to seal the gap between the table and a housing that rotatably houses the spindle.

Air is supplied to the annular gap from multiple positions spaced apart in the circumferential direction to prevent localized loss of sealing performance due to pressure differences.

JP 2020-151823 A

By applying the technology of Patent Document 1 to conventional rotating equipment, it has become possible to adequately suppress heat generation at the sealed area while preventing the intrusion of foreign matter.

However, in recent years, there has been a demand for rotating devices that can rotate at even higher speeds than before. The inventors have therefore been studying ways to increase the speed of rotation, and in the process have found that there is room for improvement in the technology of Patent Document 1 in terms of suppressing heat generation when the speed is increased.

In addition, even if this type of rotating equipment has excellent functionality, it is difficult to put it to practical use unless it is inexpensive.

Therefore, the main objective of the disclosed technology is to realize an inexpensive rotating machine tool that can more appropriately combine heat suppression at the sealed area with prevention of intrusion of foreign matter, and can handle higher speeds.

The disclosed technology relates to a rotating device for machining. The rotating device includes a spindle having a table, a housing that rotatably houses the spindle with the table exposed, a pair of annular seals consisting of an annular inner seal and an annular outer seal arranged to separate the inside and outside in the radial or axial direction across a predetermined annular gap so as to close the gap between the table and the housing, and a first air supply passage that supplies air to the annular gap.

The system further includes a second air supply passage that supplies air to the annular inner gap located inside the annular gap across the annular inner seal material, and a fine pressure difference adjustment mechanism that adjusts the air pressure in the annular inner gap so that it is higher than the annular gap by a predetermined fine pressure difference.

Preferably, the second air supply passage is formed in a structure that reduces the pressure loss of the air flowing through the passage compared to the first air supply passage, and the fine pressure differential adjustment mechanism is configured using the structure of the first air supply passage and the second air supply passage.

Preferably, the fine pressure differential adjustment mechanism is configured using a pressure adjustment exhaust passage that is connected to the inside of the housing and is capable of adjusting the air pressure inside the housing, and the pressure adjustment exhaust passage is capable of maintaining the inside of the housing at a pressure higher than atmospheric pressure.

Preferably, the fine pressure differential adjustment mechanism is configured using a pressure reduction and exhaust passage that communicates with the inside of the housing and reduces the pressure by the pressure loss of the air flowing therein, and the pressure reduction and exhaust passage allows the inside of the housing to be kept higher than atmospheric pressure.

Preferably, a chamber that houses a motor that rotates the spindle is provided inside the housing, and the second air supply passage supplies air to the annular inner gap through the chamber.

The technology disclosed here allows for a simple structure that can be implemented at low cost, while more appropriately suppressing heat generation at the sealed area and preventing the intrusion of foreign matter, making it possible to accommodate the increasing speeds of rotating machinery used in machining.

FIG. 1 is a schematic perspective view showing an NC circular table (rotating device) according to an embodiment of the present invention. 2 is a schematic cross-sectional view taken along the line XX of the arrow in FIG. 1. FIG. 1 is a schematic cross-sectional view of an NC circular table on which annular seal members are arranged in the radial direction. 6A to 6C are diagrams for explaining the operation of the annular sealing material. FIG. 11 is a schematic cross-sectional view of an NC circular table according to another embodiment. FIG. 11 is a schematic cross-sectional view of an NC circular table according to another embodiment.

The following describes an embodiment of the disclosed technology. However, the following description is essentially merely an example.

Unless otherwise specified, the "axial direction" used in the description means the direction in which the rotation axis J extends. Similarly, the "circumferential direction" means the circumferential direction centered on the rotation axis J, and the "radial direction" means the radial or diametric direction centered on the rotation axis J. "Front" means the side used during machining, and "rear" means the side not used during machining.

First Embodiment
1 and 2 show an NC circular table 1 (an example of a rotating device) to which the disclosed technology is applied. The NC circular table 1 is roughly composed of a housing 2, a box 3, a spindle 4, and a motor 5. The NC circular table 1 is used during machining, and a table 42 on the front side thereof rotates at high speed.

That is, a chuck or the like is attached to the table 42 to support the workpiece (object to be machined). In this state, the spindle 4 is rotated at high speed. The workpiece is machined by pressing a cutting tool or the like against it while supplying cooling oil or water to the rotating workpiece.

In recent years, particularly, there are cases where higher speed rotations than before are required during machining. Therefore, if it is possible to appropriately handle such high speed rotations, it will be very convenient. The technology disclosed here is based on such circumstances.

The housing 2 is composed of a main body 21, a front cover 22, a rear cover 23, etc. A cylindrical storage space that penetrates the main body 21 in the front-to-rear direction is formed. The rear cover 23 is attached to the rear side of the main body 21 and closes the rear opening of the storage space.

The front cover 22 is made of a cylindrical member. The front cover 22 is fitted into a circular recess formed on the front side of the main body 21. The front cover 22 is attached to the front side of the main body 21 so as to cover the front side of the storage space of the main body 21. This blocks the front and rear of the storage space of the main body 21, forming a substantially sealed storage chamber 21a inside the housing 2.

A circular opening 22a is formed in the front cover 22. The center line of the opening 22a and the center line of the storage chamber 21a are approximately aligned. An annular bearing 7 is disposed in front of the storage chamber 21a. The bearing 7 has an outer ring portion 7a and an inner ring portion 7b that rotate freely relative to each other. The bearing 7 is assembled to the housing 2 by sandwiching the outer ring portion 7a between the main body 21 and the front cover 22.

The box 3 is a box-shaped container that is attached to one side of the housing 2. Inside the box 3, various cables and electrical devices used to drive and control the NC circular table 1 are arranged. Power is supplied to the NC circular table 1 through a cable (not shown) extending from the box 3.

The spindle 4 of this embodiment has a shaft 41 and a table 42. The shaft 41 is made of a multi-stage cylindrical member and is housed in the housing chamber 21a. The shaft 41 has a small diameter portion 41a and a large diameter portion 41b whose outer diameter is larger than that of the small diameter portion 41a.

The table 42 is made of a disk-shaped member with an outer diameter slightly smaller than the inner diameter of the opening 22a, and is attached to the front surface of the shaft 41 (large diameter portion 41b). When the shaft 41 and table 42 are assembled, the inner ring portion 7b of the bearing 7 is sandwiched between the shaft 41 and the table 42. As a result, the spindle 4 is supported by the housing 2 via the bearing 7, and is freely rotatable around the rotation axis J.

As described above, the table 42 is the portion of the spindle 4 on which the workpiece is attached via a chuck or jig, and the circular front surface of the table 42 is exposed to the front surface of the housing 2 through the opening 22a. The spindle 4 may be configured by combining multiple parts, as in this embodiment, or may be configured as a single unit.

The motor 5 has a rotor 51 and a stator 52, and is housed in the housing chamber 21a. The rotor 51 is made of an annular member and is fixed to the small diameter portion 41a. The stator 52 is made of an annular member larger than the rotor 51, and is fixed to the main body portion 21 in a state where it faces the rotor 51 in the radial direction with a small gap between them.

By supplying a predetermined control current to the stator 52, a rotating magnetic field is formed between the stator 52 and the rotor 51. This directly drives the spindle 4, which rotates at a predetermined high speed (for example, the peripheral speed of the rotor 51 is 10 m/s or more) (so-called direct drive type).

In addition, the faster the spindle rotation speed, the more heat the motor generates when it is running. Therefore, when increasing the rotation speed, it is also important to deal with heat generation from the motor.

(Sealing gaps)
There is a gap between the table 42, which is a rotating body, and the housing 2, which is a non-rotating body. In the case of the NC circular table 1, since the front surface thereof is exposed to cutting chips and cutting water, it is necessary to prevent these foreign objects from entering the accommodation chamber 21a through the gap.

Sealing with a high contact pressure oil seal or face seal can effectively prevent the intrusion of foreign matter, but the high contact pressure creates the problem of heat generation due to friction at the contact points. At high speeds, excessive heat is generated, leading to deformation and deterioration of the sealing material. There is also the risk of the spindle 4 and table 42 expanding thermally, resulting in a deterioration in machining accuracy. The higher the rotation speed, the more pronounced this tendency becomes.

On the other hand, if sealing is done with a low contact pressure sealing material (such as a springless oil seal or a V-ring), the contact pressure is low, so heat generation at the contact points can be reduced. However, this reduces the sealing performance, making it easier for foreign matter to enter. In other words, it is not possible to suppress heat generation and prevent the intrusion of foreign matter at the same time.

The inventors therefore made efforts to use a low-contact pressure sealant and air pressure to simultaneously suppress heat generation and prevent the intrusion of foreign matter (see Patent Document 1). This NC circular table 1 is based on this idea.

(Annular seal material)
In this embodiment, a pair of annular seals 8, 8 (also referred to as an annular inner seal 81 and an annular outer seal 82) are arranged in the axial direction to seal the gap between the table 42 and the housing 2, separating the inside from the outside with a predetermined annular gap 100 between them. Each annular seal 8 is press-fitted into a step 30 formed on the inner peripheral edge of the opening 22a of the front cover 22.

All of these annular seals 8 are low-contact pressure seals (e.g., spring-less oil seals). Each annular seal 8 has an elastically deformable lip 8a and an annular base 8b that is attached to the step 30.

Each lip 8a is inclined. Each annular seal 8 is arranged so that the inner diameter of the lip 8a becomes smaller toward the outside of the gap. Each annular seal 8 is arranged in the gap between the table 42 and the housing 2. The tip portion of the lip 8a is in contact with the outer circumferential surface of the table 42. Note that, to increase the contact pressure of each lip 8a, for example, a spring may be added instead of a springless one.

(First air supply passage)
A first air supply passage 60 that communicates with the annular gap 100 and supplies air to the annular gap 100 is formed in the housing 2 .

As shown in FIG. 2, the first air supply passage 60 in this embodiment is composed of one main passage 60a, one annular space 60b, and multiple communication passages 60c.

The main passage 60a is a thin hole formed in the housing 2, and is formed in an L-shaped bend in the main body 21. The upstream end of the main passage 60a opens to the outer surface of the main body 21, and the downstream end of the main passage 60a opens to the joint surface of the main body 21 with the front cover 22.

A first throttle valve 9 capable of adjusting the flow rate of air is attached to the upstream end of the main passage 60a. An air supply pipe 11 connected to an air supply source (not shown), such as a compressor, is connected to the first throttle valve 9. During machining, air is introduced into the main passage 60a at a predetermined flow rate through the air supply pipe 11 and the first throttle valve 9. The main passage 60a is connected to the annular space 60b.

The annular space 60b is an annular space extending in the circumferential direction, and is provided in the housing 2 so as to go around the periphery of the spindle 4. Specifically, a recess is formed in the outer peripheral edge of the rear surface of the front cover 22, and the annular space 60b is formed by assembling the front cover 22 to the main body 21. Gaskets 12 are attached to both sides of the annular space 60b to ensure airtightness.

Each communication passage 60c is formed in the front cover portion 22. Each communication passage 60c is made of a thin hole and is formed in a shape that is bent in a substantially L shape. Each communication passage 60c is formed in multiple locations spaced apart from each other in the circumferential direction. The annular space 60b and the annular gap 100 communicate with each other via these multiple communication passages 60c.

Therefore, the air introduced from the air supply pipe 11 is supplied to the annular gap 100 through the main passage 60a, the annular space 60b, and each of the multiple communication passages 60c after the flow rate is adjusted by the first throttle valve 9. At that time, the occurrence of local air pressure differences at specific points in the circumferential direction of the annular gap 100 is suppressed, so that a well-balanced seal can be achieved around the entire circumference.

(Second air supply passage)
A second air supply passage 70 that supplies air through the accommodation chamber 21a to a gap (annular inner gap 101) located on the inside of the annular gap 100 is formed in the housing 2. The annular inner gap 101 is a gap located on the inside of the annular gap 100, separated by an annular inner seal material 81. In other words, the annular gap 100 and the annular inner gap 101 are partitioned from the inside and the outside by the annular inner seal material 81.

As shown in FIG. 2, the second air supply passage 70 in this embodiment is composed of a single vertical hole formed in the housing 2. Specifically, the second air supply passage 70 is formed by cutting the main body 21 to penetrate into the storage chamber 21a, with the upstream end of the second air supply passage 70 opening to the outer surface of the main body 21 and the downstream end of the second air supply passage 70 opening to the inner surface of the main body 21.

A second throttle valve 10, similar to that of the first air supply passage 60, is attached to the upstream end of the second air supply passage 70. The second throttle valve 10 is also connected to the air supply pipe 11. During machining, air is introduced into the storage chamber 21a at a predetermined flow rate through the air supply pipe 11, the second throttle valve 10, and the second air supply passage 70.

The storage chamber 21a is connected to the annular inner gap 101 through the gap of the bearing 7. Therefore, the air introduced into the storage chamber 21a from the air supply pipe 11 also flows into the annular inner gap 101.

(Pressure adjustment exhaust passage, pressure reduction exhaust passage)
The housing 2 is provided with an exhaust passage 90 that connects the accommodation chamber 21a to the environment outside the housing 2. In this embodiment, the exhaust passage 90 is formed in the rear lid portion 23, penetrating its plate surface. The exhaust passage 90 may also be formed in the main body portion 21 or the front lid portion 22. The exhaust passage 90 may be any passage that can exhaust air from inside the housing 2.

A pressure adjustment valve 91 is provided at the downstream end of the exhaust passage 90, i.e., on the outer surface side of the rear cover portion 23. The pressure adjustment valve 91 automatically exhausts air when the air pressure in the storage chamber 21a reaches a set predetermined pressure (pressure higher than atmospheric pressure). As a result, the exhaust passage 90 in this embodiment is configured to be able to adjust the air pressure in the storage chamber 21a (pressure adjustment exhaust passage 90A).

This pressure adjustment exhaust passage 90A makes it possible to maintain the inside of the housing 2, including the storage chamber 21a, at a pressure higher than atmospheric pressure. Therefore, by supplying air from the second air supply passage 70, the inside of the housing 2 can be maintained at an air pressure higher than atmospheric pressure.

Instead of the pressure regulation exhaust passage 90A, a reduced pressure exhaust passage 90B may be provided. The reduced pressure exhaust passage 90B is an exhaust passage 90 with a structure in which the pressure loss of the air flowing through the passage is large. For example, the reduced pressure exhaust passage 90B can be formed by lengthening the length of the exhaust passage 90, narrowing the passage by reducing the cross section of part or all of the passage 90, or bending the passage.

In FIG. 2, an example of such a pressure reduction exhaust passage 90B is shown by a two-dot chain line. This pressure reduction exhaust passage 90B is formed as a long, thin, curved flow path in the main body 21. By providing such a pressure reduction exhaust passage 90B and supplying air from the second air supply passage 70, the inside of the housing 2 can be dynamically maintained at an air pressure higher than atmospheric pressure.

In either case of the pressure-adjusting exhaust passage 90A or the reduced-pressure exhaust passage 90B, the air pressure inside the housing 2 can be adjusted by adjusting the air flow rate with the second throttle valve 10. In either case of the pressure-adjusting exhaust passage 90A or the reduced-pressure exhaust passage 90B, it can be implemented with extremely simple modifications to the existing structure, and is therefore inexpensive.

(Radial arrangement of annular seal material)
The pair of annular seal members 8, 8 may be disposed in a radial direction, not in an axial direction, to separate the inside and the outside with an annular gap 100 therebetween.

Figure 3 shows an NC circular table (NC circular table 1') in which a pair of annular seals 8, 8 are arranged in this way. The basic structure is the same as that of the NC circular table 1 shown in Figure 2.

In this NC circular table 1', the table 42 has a flange portion 42a that protrudes forward of the front cover portion 22. As a result, the front surface of the table 42 of this NC circular table 1' is larger than that of the above-mentioned NC circular table 1, and the size can be freely designed.

A pair of annular seals 8, 8 are arranged in the gap between the flange portion 42a and the front surface of the front cover portion 22, separating the inside and the outside by an annular gap 100 in the radial direction. For these annular seals 8, for example, V-rings can be used.

The V-ring is also a low contact pressure sealing material, similar to a springless oil seal. That is, each annular seal 8 (V-ring) has an elastically deformable lip 8a and an annular base 8b. Each lip 8a is inclined, and each annular seal 8 is formed so that the inner diameter of the tip of each lip 8a is larger than the inner diameter of the base of the lip 8a.

The base 8b is attached to a cylindrical receiving surface formed on the rear surface of the flange portion 42a. As a result, the tip portion of the lip 8a is in contact with the front surface of the front cover portion 22.

The downstream end of each communication passage 60c is bent and extends forward. The bent end is connected to the rear surface of the annular gap 100.

(Micro-differential pressure adjustment mechanism)
These NC circular tables 1 and 1' are provided with a minute pressure difference adjustment mechanism that adjusts the air pressure in the annular inner gap 101 to be higher than that in the annular gap 100 by a predetermined minute pressure difference.

In this embodiment, the fine differential pressure adjustment mechanism is configured using the first air supply passage 60 and the second air supply passage 70. That is, as described above, the first air supply passage 60 is long and is formed as a flow path with large air resistance. In contrast, the second air supply passage 70 is shorter than the first air supply passage 60 and is formed as a flow path with small air resistance. Therefore, the second air supply passage 70 has a smaller pressure loss of air flowing through the flow path than the first air supply passage 60.

Therefore, the air pressure can be dynamically adjusted to be higher in the second air supply passage 70 than in the first air supply passage 60. As a result, it is possible to easily generate a predetermined minute pressure difference between the annular gap 100 and the annular inner gap 101. Since it utilizes an existing structure and the new structure is simple, it can be implemented at low cost. Therefore, it is preferable to configure the minute pressure difference adjustment mechanism using the structure of the first air supply passage 60 and the second air supply passage 70.

The "micro-differential pressure" referred to here depends on the type and performance of the annular seal material 8, but is preferably 0.05 MPa or less, for example. 0.01 MPa or less is more preferable. When a general annular seal material 8 is used, an appropriate effect can be obtained within this range.

The fine pressure differential adjustment mechanism is preferably constructed using the pressure adjustment exhaust passage 90A or the reduced pressure exhaust passage 90B described above. That is, by providing these specific exhaust passages 90, it becomes possible to adjust the air pressure inside the housing 2, including the storage chamber 21a and the annular inner gap 101, to a predetermined pressure higher than atmospheric pressure. The structure is simple, so it can be implemented at low cost. Therefore, it is preferable to construct the fine pressure differential adjustment mechanism using these specific exhaust passages 90.

The fine pressure difference adjustment mechanism can also be constructed by individually controlling the air pressure supplied to each of the annular gap 100 and the annular inner gap 101, without using a specific structure for the first air supply passage 60 and the second air supply passage 70 and/or a specific exhaust passage 90.

In that case, however, it is necessary to provide a control device and a solenoid valve capable of controlling the air flow rate. This increases the number of parts and the implementation costs. In contrast, the micro-differential pressure adjustment mechanism of this embodiment requires fewer parts and fewer implementation costs, and can be implemented inexpensively. Furthermore, once the air pressure is adjusted to an appropriate state, it is unlikely that the air pressure will change significantly as long as the pressure of the air supply source is stable. Therefore, it can function in a state that is necessary and sufficient for practical use.

(Operation of the annular seal)
The operation of the annular seal 8 will be described taking as an example a configuration in which a pair of annular seals 81, 82 are arranged in the radial direction. Note that the operation is similar even in a configuration in which they are arranged in the axial direction.

First, we will explain the operation of the annular seal when air is supplied only from the first air supply passage 60 (the same as in the conventional configuration). The upper diagram (z) of Figure 4 shows a schematic diagram of the operation of the annular seals 81 and 82.

As shown by the arrows, each of the annular seals 81, 82 is in contact with the housing 2 with a predetermined pressing force F. Then, as shown by the dashed arrow, when air is supplied to the annular gap 100 through the first air supply passage 60, each of the annular seals 81, 82 is pressurized.

As a result, air pressure P1 acts on the annular outer seal 82 in a direction that pushes up the lip 8a (direction that opens the annular gap 100) against the pressing force F, as shown by the arrows. Air pressure P1 acts on the annular inner seal 81 in a direction that pushes the lip 8a (direction that closes the annular gap 100) together with the pressing force F, as shown by the arrows.

Therefore, even if the contact pressure of the annular seals 81, 82 is low and some gaps may occur, air can be supplied to the annular gap 100 to ensure sealing. Furthermore, when the air pressure reaches a certain level, the annular outer seal 82 is pushed up and air is blown out, further preventing the intrusion of foreign matter. Therefore, the intrusion of foreign matter from the gap between the table 42 and the front cover 22 (housing 2) can be reliably prevented.

The contact pressure of each annular seal material 81, 82 can be low, so heat generation at the contact points can be effectively reduced. This also reduces heat generation. It also reduces power consumption, inhibits deterioration of the seal material, and improves durability.

However, in this case, it was found that there is room for improvement in terms of heat generation suppression when the rotation speed is increased. That is, the air pressure P1 in the annular gap 100 acts on the annular inner seal material 81 in a direction pressing the lip 8a together with the pressing force F, so when the air pressure P1 in the annular gap 100 increases, the contact pressure of the tip portion of the lip 8a against the front cover portion 22 also increases accordingly.

Since the annular seals 81 and 82 are low-contact pressure seals, at normal rotational speeds, even if the air pressure in the annular gap 100 increases somewhat, the amount of heat generated by friction is small. Therefore, due to the balance with heat dissipation, there was no risk of heat generation becoming a problem. However, it was found that when the rotational speed was increased further, heat was generated even at such an air pressure, and that it was necessary to suppress this heat generation.

It was also found that this is especially necessary when the annular seals 81, 82 are arranged in the radial direction. That is, when the annular seals 81, 82 are arranged in the radial direction, the lip 8a of each annular seal 8 is more likely to open due to the action of centrifugal force during rotation. The annular outer seal 82, which is located on the radial outside, is more likely to open than the annular inner seal 81, which is located on the radial inside.

The higher the rotation speed, the greater the effect, so increasing the rotation speed may cause the annular outer seal 82 to open too much. In order to prevent the annular outer seal 82 from opening too much, it becomes necessary to make the pressing force F of the annular seals 81, 82 stronger than before. This increases the contact pressure of the annular inner seal 81.

Therefore, in the NC circular table 1, 1' of this embodiment, a second air supply passage 70 is provided to pressurize the annular inner gap 101 with air pressure, and a fine pressure difference adjustment mechanism is provided to adjust the air pressure in the annular inner gap 101 to be higher than that in the annular gap 100 by a predetermined fine pressure difference.

Specifically, in addition to supplying air to the annular gap 100 through the first air supply passage 60 as shown in the upper diagram (z) of Figure 4, air is supplied to the annular inner gap 101 through the second air supply passage 70 as shown by the dashed line in the lower diagram (a) of Figure 4. As a result, the annular inner seal material 81 is pressurized, but the annular outer seal material 82 is not pressurized.

Air pressure P2 acts on the annular inner seal material 81 in a direction that pushes up its lip 8a, as shown by the arrow. As a result, the lip 8a of the annular inner seal material 81 is pressed down by the combined force of the pressing force F of the annular inner seal material 81 and the air pressure P1 in the annular gap 100, and is also pushed up by the air pressure P2 in the annular inner gap 101.

In other words, the actual contact pressure of the lip 8a is the difference between the pressing force and the upward force (F+P1-P2). The air pressure P2 in the annular inner gap 101 is adjusted to be higher than the air pressure P1 in the annular gap 100 by a predetermined differential pressure (P2>P1) by the differential pressure adjustment mechanism, so that the pressing force F of the lip 8a of the annular inner seal material 81 itself can be reduced.

Then, as shown in the lower diagram (b) of Figure 4, when the air pressure in the annular gap 100 becomes higher than the pressing force (P1>F), the lip 8a of the annular outer seal material 82 opens. This causes the air in the annular gap 100 to be released to the outside.

At this time, it is preferable to set the air pressure P1 in the annular gap 100 and the air pressure P2 in the annular gap 101 so that the lip 8a of the annular inner seal material 81 does not open. Specifically, the air pressure P2 in the annular inner gap 101 is set to be smaller than the force (F+P1) pressing the lip 8a of the annular inner seal material 81 (F+P1>P2).

In this case, the air pressure P2 in the annular inner gap 101 is maintained higher than the air pressure P1 in the annular gap 100 by a predetermined slight pressure difference (P2>P1). This ensures that the lip 8a of the annular inner seal 81 does not open when the lip 8a of the annular outer seal 82 opens, ensuring a tight seal.

The air pressure P1 in the annular gap 100 may decrease due to the release of air. In that case, the air pressure P2 in the annular gap 101 becomes greater than the force (F+P1) pressing against the lip 8a of the annular inner seal material 81, causing the lip 8a of the annular inner seal material 81 to open, as shown in (c) of the lower diagram in Figure 4. This causes the air in the annular inner gap 101 to be replenished to the annular gap 100. The air pressure P1 in the annular gap 100 returns to an appropriate state.

In this way, the NC circular table 1, 1' to which the disclosed technology is applied can effectively reduce the contact pressure of the annular inner seal material 81. As a result, even if the rotation speed is increased, heat generation at the sealing portion of the lip 8a can be suppressed. Wear of the lip 8a can be suppressed. Power consumption can also be reduced by suppressing contact resistance.

Air flows into the sealing area from both the inside and outside of the annular inner seal material 81, so the lip 8a can be cooled effectively. Even if the air pressure in the annular gap 100 drops due to the release of air, it can be quickly replenished.

By supplying air to the annular inner gap 101 through the housing chamber 21a, the bearings 7 and motor 5 can be cooled. Heat generation by the motor 5 can also be suppressed. High-temperature air that accumulates inside the housing 2 can be expelled.

<Other embodiments>
In the above-described embodiment of the NC circular tables 1, 1', the second air supply passage 70 is formed in the main body 21 of the housing 2. However, the second air supply passage 70 can be changed as appropriate depending on the specifications.

Examples of such NC circular tables (NC circular table 1A and NC circular table 1B) are shown below. The basic structure of these NC circular tables 1A and 1B is the same as that of the NC circular tables 1, 1' described above. Therefore, only the different configurations will be described, and the same components will be designated by the same reference numerals and their description will be omitted.

The NC circular table 1A is shown in Figure 5. In this NC circular table 1A, the second air supply passage 70 is made up of one second main passage 201, one second annular space 202, multiple second communication passages 203, etc., similar to the first air supply passage 60.

These passages 201, 202, and 203 are formed in both the main body 21 and the front cover 22. As a result, air is supplied to the vicinity of the annular inner gap 101, bypassing the storage chamber 21a.

The NC circular table 1B is shown in Figure 6. In this NC circular table 1B, the second air supply passage 70 is formed by branching off from the first air supply passage 60.

Specifically, as shown in an enlarged view in FIG. 6, a branch flow passage 210 that branches in two directions toward both the annular gap 100 and the annular inner gap 101 is formed at the downstream end of each communication passage 60c of the first air supply passage 60. The second air supply passage 70 is formed by the branch flow passage 210 that branches toward the annular inner gap 101.

In this case, in order to distribute the air appropriately to both the annular gap 100 and the annular inner gap 101, it is preferable to provide a throttle port 211 with a reduced flow path cross section at each of the inflow points to the annular gap 100 and the annular inner gap 101.

The disclosed technology is not limited to the above-described embodiments, but also includes various other configurations.

For example, a low contact pressure seal is preferred for the annular seal, but a normal contact pressure seal may also be used. The actual contact pressure of each annular seal can be adjusted by adjusting the air pressure in the first and second air supply passages.

1, 1', 1A, 1B NC circular table (rotating equipment)
2 Housing 60 First air supply passage 70 Second air supply passage 81 Annular inner seal material 82 Annular outer seal material 100 Annular gap 101 Annular inner gap

Claims (4)

A rotating machine for machining,
a spindle having a table;
a housing that rotatably houses the spindle with the table exposed;
a pair of annular seals, each consisting of an annular inner seal and an annular outer seal, arranged to separate an inside from an outside in a radial or axial direction across a predetermined annular gap so as to close a gap between the table and the housing;
a first air supply passage for supplying air to the annular gap;
Equipped with
a second air supply passage that supplies air to an annular inner gap located inside the annular gap, across the annular inner seal;
a minute pressure difference adjustment mechanism that adjusts the air pressure in the annular inner gap to be higher than the air pressure in the annular gap by a predetermined minute pressure difference of 0.05 MPa or less;
Further comprising:
a rotating device for machining, wherein the micro-differential pressure adjustment mechanism is configured using a specific structure of the first air supply passage and the second air supply passage, such that a pressure loss of air flowing through the second air supply passage is smaller than that of the first air supply passage. 2. The rotating device for machining according to claim 1,
the fine differential pressure adjustment mechanism is configured using a pressure adjustment exhaust passage that communicates with the inside of the housing and is capable of adjusting the air pressure inside the housing,
The pressure adjusting exhaust passage enables the inside of the housing to be maintained higher than atmospheric pressure. The rotating device for machining according to claim 1 or 2,
the fine differential pressure adjustment mechanism is configured using a pressure reduction and exhaust passage that communicates with the inside of the housing and reduces pressure by a pressure loss of the air flowing therein,
The rotary machine for machining, wherein the pressure inside the housing can be maintained higher than atmospheric pressure by the pressure reduction exhaust passage. The rotating device for machining according to claim 2 or 3,
a housing that houses a motor that rotates the spindle is provided inside the housing;
The second air supply passage supplies air to the annular inner gap through the accommodation chamber.