Spindle device, grinding device, and cutting machining device

Abstract

This spindle device is provided to a rotary shaft that can have a load mounted on the tip end thereof, a housing that supports the rotary shaft with a bearing therebetween, and the rotary shaft. The spindle device comprises: an impeller that draws outside air into the device from the rear end side of the device as the impeller rotates around the axial center of the rotary shaft and that discharges the drawn-in air from the device tip end side; and a seal device that is arranged between the housing and the rotary shaft on the device tip end side. The seal device seals a space between the housing and the rotary shaft on the device tip end side when the rotary shaft is stationary or in low-speed rotation, and allows discharge of the air from the device tip end side at at least a prescribed rotational speed at which the speed of the rotary shaft exceeds the speed during the low-speed rotation.

Description

Spindle devices, grinding devices, and cutting devices

[0001] The present invention relates to a spindle device, a grinding device, and a cutting device.

[0002] Conventionally, spindle devices in which tools are interchangeably attached to a rotatable spindle have been known as devices for rotating tools to perform machining. Specifically, spindle devices are used in machine tools for cutting and grinding to rotate tools such as end mills, grinding wheels, and dressers used to process workpieces, or to clamp and rotate the workpieces. Spindle devices generally include a rotating part supported by bearings and a fixed part other than the rotating part. Various machining tools (e.g., grinding wheels, cutting tools, etc.) are attached to the tip of the rotating shaft that constitutes the rotating part, and these machining tools are used to perform machining (polishing, cutting, etc.) on the workpieces.

[0003] This means that foreign matter such as machining fluid and chips may enter the spindle device through the gap between the rotating and fixed parts during machining, which may cause the rotating shaft to rotate impedimentally or may cause a large load to be applied, potentially damaging the spindle device.

[0004] Conventionally, compressed air is forcibly supplied into the device as the shaft (rotating part) rotates, and is then discharged outside the device through a gap formed between the rotating part and the fixed part (Patent Document 1).

[0005] By discharging the compressed air to the outside of the device in this manner, it is possible to effectively prevent machining fluid, chips, etc. from entering the device.

[0006] Japanese Patent Application Publication No. 11-277362

[0007] However, in the system described in Patent Document 1, compressed air must be continuously and forcibly supplied from the outside into the spindle device in order to constantly increase the pressure inside the spindle device regardless of the operating state of the spindle device, which poses a problem of increased power consumption due to the increased consumption of compressed air.

[0008] Installing a contact seal in the gap between the rotating and stationary parts of a spindle device can effectively prevent machining fluids, chips, and other contaminants from entering the device. In such cases, contact seals are typically installed in the stationary part of the spindle device when installed in devices with relatively high rotational speeds, such as spindle devices. A contact seal installed in the stationary part physically eliminates the gap, preventing machining fluids, chips, and other contaminants from entering the spindle device, eliminating the need for compressed air. However, the frictional resistance of the contact seal hinders smooth rotation of the rotating part and increases rotational torque, thereby increasing the power consumption required to rotate the spindle device. Furthermore, the frictional resistance of the contact seal generates heat between the rotating and stationary parts, shortening the lifespan of the contact seal due to abnormal wear. The heat then propagates to the bearings, causing an abnormal temperature rise in the bearings, leading to premature bearing failure.

[0009] Therefore, the present invention provides a spindle device, a grinding device, and a cutting processing device that can effectively prevent the intrusion of machining fluid, chips, etc. into the device, does not require the pressure inside the spindle device to be increased, effectively prevents an increase in power consumption, and effectively prevents a decrease in the lifespan of sealing members due to abnormal wear.

[0010] The spindle device of the present invention includes a rotating shaft to which an object can be attached at its tip, a housing that rotatably supports the rotating shaft via a bearing, an impeller attached to the rotating shaft that draws outside air into the device from the rear end as the rotating shaft rotates and discharges the drawn outside air from the tip end of the device, and a sealing device disposed between the rotating shaft at the tip end and the housing. The sealing device seals the gap between the rotating shaft at the tip end and the housing when the rotating shaft is stationary or rotating at a low speed, and allows air to be discharged from the tip end of the device when the rotating shaft is rotating at a predetermined rotation speed or higher. Here, the impeller is, for example, a propeller fan. Furthermore, when the rotation speed is higher than the predetermined speed, machining is performed by the object attached to the tip of the rotating shaft, generating chips and the like, while when the rotating shaft is stationary or rotating at a low speed, no chips and the like are generated.

[0011] In the spindle device of the present invention, by rotating the rotating shaft, outside air can be introduced into the device, and the introduced air is transported from the rear end to the front end of the device. When the rotating shaft is rotating at a predetermined rotational speed or higher, air is allowed to be discharged from the front end of the device. This effectively prevents machining fluid, chips, and the like from entering the device. Furthermore, when the rotating shaft is stationary or rotating at a low speed, a sealing device seals the gap between the rotating shaft at the front end of the device and the housing. Therefore, the rotating shaft is not driven to rotate except during machining, effectively preventing foreign matter and the like from entering the device.

[0012] Furthermore, when the rotating shaft rotates at a predetermined rotational speed or above, air is allowed to be discharged from the tip of the device, so the sealing device does not slide against the rotating side, or only slides against it at a slow rotational speed, preventing wear on the sealing device and extending its useful life.

[0013] The sealing device is configured with a seal lip that opens due to at least one of the centrifugal force generated by the rotation of the rotating shaft and the air pressure of the air compressed by the impeller. With this type of seal lip, a stable sealed state is formed when the rotating shaft is stationary or rotating at low speeds, and the seal lip remains stable at the rotation speed during processing. Therefore, foreign matter can be effectively prevented from entering the device, whether the rotating shaft is rotating or not.

[0014] It is preferable that a bearing be provided to rotatably support the rotating shaft relative to the housing, and that the bearing be a grease-lubricated angular contact ball bearing capable of receiving radial loads and axial loads.

[0015] Grease lubrication offers cost benefits due to simplified sealing structures and longer replacement cycles, as well as the benefit of reduced splashing and dripping. Angular contact ball bearings are designed so that the raceways of the inner and outer rings are slightly misaligned during use, creating a contact angle between the raceway and the balls, and the balls are mounted at an angle. This offset makes them suitable for bearing radial and axial loads. The main advantage of this angled arrangement is that the axial load capacity increases as the ball angle increases. This angled arrangement also extends the bearing's service life, improves operating speeds, and enhances durability. This allows them to be used in high-precision, high-speed applications where radial and axial loads exist.

[0016] The balls, which are the rolling elements of the bearing, are preferably made of ceramic. Ceramics are non-metallic, inorganic solid materials, and among solid materials, ceramics include materials made of non-metallic elements (e.g., silicon and diamond) and inorganic compound materials (oxides, carbides, nitrides, etc.) that are combinations of metallic and non-metallic elements. For this reason, ceramic balls have excellent chemical resistance and can be used in any environment, whether dry, wet, or chemical, and also have excellent insulation and heat resistance.

[0017] The housing may be configured as a cylindrical body having a peripheral wall, and a flow passage through which air drawn into the device by the rotation of the impeller flows from the rear side to the front side of the device may be formed in at least one of the rotary shaft and the peripheral wall of the housing. In this case, the air flow passage through which the air flows can be stably formed within the device without the need for additional piping or the like.

[0018] The grinding device according to the present invention is a grinding device equipped with the spindle device, in which the mounted object attached to the tip of the rotating shaft is a grinding wheel. In the grinding device according to the present invention, whether the rotating shaft is stopped or rotating, the inflow of foreign matter into the fluid passage can be prevented, and the inflow of foreign matter into the grinding device can be avoided.

[0019] The cutting apparatus according to the present invention is a cutting apparatus including the spindle device, and the load attached to the tip of the rotating shaft is a cutting tool. In the cutting apparatus according to the present invention, whether the rotating shaft is stopped or rotating, the inflow of foreign matter into the fluid passage can be prevented, and the inflow of foreign matter into the cutting apparatus can be avoided. The cutting tool includes a drill, a reamer, an end mill, a milling cutter, a turning tool, a tap, a die, etc.

[0020] The present invention can prevent foreign matter from entering the sealing device whether it is in processing or not, and can prevent the device's lifespan from being shortened due to the intrusion of foreign matter into the device. It can also effectively prevent wear on the sealing device, thereby extending the useful life of the sealing device. Furthermore, when the inflow of foreign matter is being prevented, the rotation of the rotating shaft is stopped or rotated at a low speed, thereby reducing power consumption.

[0021] Fig. 1 is a cross-sectional view of a spindle device according to the present invention; Fig. 2 is an enlarged cross-sectional view showing a main part of the spindle device when the rotating shaft is not rotating; Fig. 3 is an enlarged cross-sectional view showing a main part of the spindle device when the rotating shaft is rotating; Fig. 4 is an enlarged cross-sectional view showing a seal member of a seal device when the rotating shaft is not rotating; Fig. 5 is an enlarged cross-sectional view showing a seal member of a seal device when the rotating shaft is rotating

[0022] An embodiment of the present invention will be described below with reference to Figures 1 to 3B. Figure 1 is a cross-sectional view of a spindle device according to the present invention, Figures 2A and 2B are enlarged cross-sectional views thereof, and Figures 3A and 3B are enlarged cross-sectional views of a seal device.

[0023] The spindle device includes a rotating shaft 1 and a housing 5 that rotatably supports the rotating shaft 1 via front-end bearings 2 and 2 and rear-end bearings 3 and 3. The rotating shaft 1 receives the rotational driving force of a motor 4 installed inside the housing 5, and is driven to rotate around its axis. In this embodiment, the bearings 2 and 3 are grease-lubricated angular contact ball bearings that can withstand radial and axial loads. Angular contact ball bearings are designed so that the raceways of the inner and outer rings are slightly offset during use, creating a contact angle between the raceway and the balls, and the balls are mounted at an angle. This offset makes them suitable for bearing radial and axial loads.

[0024] The housing 5 has a cylindrical body 5a, a front cover member 5b that covers the front opening of the cylindrical body 5a, and a rear cover member 5c that covers the rear opening of the cylindrical body 5a, and the tip of the rotating shaft 1 protrudes forward beyond the front cover member 5b. The rear end of the rotating shaft 1 does not protrude rearward beyond the rear cover member 5c. An object T is attached to the tip side of the protruding portion 1a of the rotating shaft 1 that protrudes forward beyond the front cover member 5b. Here, the object T is a grinding wheel or the like.

[0025] The cylindrical body 5a of the housing 5 has a large-diameter main body portion 5a1 and a small-diameter portion 5a2 at the tip, and the front cover member 5b is attached to the rotary shaft 1 so that it rotates as the rotary shaft 1 rotates around its axis. The rear cover member 5c is integrated with the main body portion 5a1, so that it does not rotate as the rotary shaft 1 rotates.

[0026] The front cover member 5b has a disk-shaped main body 5b1 and a ring-shaped bulge 5b2 that bulges outward from the inner surface of the main body 5b1, and is loosely fitted into the recess 6a in the front end wall 6 of the main body 5a1. That is, as shown in Figures 2A and 2B, the recess 6a has an outer diameter inner circumferential surface 6a1 that faces the outer diameter surface 7 of the front cover member 5b, an outer diameter end face 9 that is outer diameter side of the bulge 5b2 and faces the inner end face 8 of the front cover member 5b, an inner diameter inner circumferential surface 11 that faces the outer diameter surface 10 of the bulge 5b2, and an inner diameter end face 13 that faces the end face 12 of the bulge 5b2.

[0027] A secondary member (inner ring nut) 15 is fitted to the front cover member 5b on the inner diameter side of the bulge portion 5b2. This secondary member 15 is threaded onto a threaded portion provided on the outer periphery of the rotating shaft 1 and is integrated with the rotating shaft 1 and the front cover member 5b. This secondary member 15 secures the inner ring of the front-row bearing 2. Spacers 17a1 and 17b1 are interposed between the inner ring and outer ring of the pair of bearings 2, 2. A ring-shaped receiving body 18A that receives the outer ring of the bearings 2, 2 is provided on the outer diameter side of the bearings 2, 2, and a spacer 19 is fitted to the axially inner end of the receiving body 18A. This spacer 19 supports the outer ring of the bearing 2 on the inner side of the housing 5.

[0028] In this case, gaps are formed between the inner diameter surface 16 of the front end wall 6 and the outer diameter surface 15a of the secondary material 15, and between the outer diameter surface 7 and the outer diameter inner circumferential surface 6a1 of the front cover member 5b, between the front end wall surface 8 and the outer diameter side end face 9, between the outer diameter surface 10 and the inner diameter side inner circumferential surface 11 of the bulging portion 5b2, and between the end face 12 and the inner diameter side end face 13 of the bulging portion 5b2, and these gaps are connected to form a tip side communicating passage 20 that connects the inside of the housing 5 to the outside of the housing. An external opening 20a of the tip side communicating passage 20 opens axially outward.

[0029] 1, the outer rings of the rear bearings 3, 3 are supported by a ring-shaped support body 18B, similar to the front bearings 2, 2, and spacers 17a2, 17b2 are interposed between the inner and outer rings of the pair of bearings 3, 3. An elastic member P is disposed between the support body 18B and the peripheral wall 30 of the housing 5 to apply a preload to the bearings 3, 3.

[0030] A seal device S that seals the tip-side communicating passage 20 is attached to the bulging portion 5b2 of the front cover member 5b. As shown in Figures 3A and 3B, the seal device S includes a seal member 22 made of an elastic material that fits into a fitting portion 21 provided in the bulging portion 5b2. The seal member 22 includes a ring-shaped main body portion 22a and a seal lip portion 22b. Therefore, the seal lip portion 22b is in pressure contact with the inner diameter side end face 13 of the front end wall 6 of the housing 5. Here, the inner diameter side of the inner diameter side end face 13 means the side of the rotary shaft 1 with respect to the outer circumferential surface of the housing 5.

[0031] An impeller 25 is attached to the rear end of the rotating shaft 1 and is housed within the housing 5. A through-hole 27 is provided in the axial center of the rear cover member 5c. In this case, the axis of the through-hole 27 coincides with the axis of the rotating shaft 1. When the rotating shaft 1 rotates about its axis, the impeller 25 also rotates about the axis of the rotating shaft 1, allowing outside air to be introduced into the housing 5 through the through-hole 27. The impeller 25 is formed, for example, by a propeller fan, but may also be a sirocco fan, turbo fan, mixed-flow fan, or the like.

[0032] The housing 5 is provided with a flow passage 30 that guides outside air introduced into the housing 5 to the tip side of the housing 5. In this case, the flow passage 30 is provided in a peripheral wall 31 of the housing 5. A plurality of flow passages 30 (e.g., six flow passages) may be formed at a predetermined pitch (e.g., 60° pitch) in the circumferential direction. A storage chamber 32 that stores the impeller 25 is provided at the rear end of the housing 5. An inlet 30a of the flow passage 30 opens into the storage chamber 32, and an outlet 30b of the flow passage 30 opens into the tip side communicating passage 20 that is radially outer than the seal device S. That is, the flow passage 30 has the inlet 30a that opens into the storage chamber 32, the outlet 30b that opens into the tip side communicating passage 20, and a flow passage main body 30c that communicates between the inlet 30a and the outlet 30b. Therefore, a plurality of inlets 30a and outlets 30b may be arranged at a predetermined pitch along the circumferential direction, and a plurality of flow passage main bodies 30c may be arranged at a predetermined pitch along the circumferential direction corresponding to the inlets 30a and outlets 30b, or the flow passage main body 30c may be formed from a single cylindrical body.

[0033] The impeller 25 is a so-called propeller fan impeller, and includes a shaft portion 25a connected to the rear end of the rotary shaft 1, and a blade portion 25b having a plurality of blades 26 that protrude radially outward in the radial direction of the shaft portion 25a.

[0034] Incidentally, when the rotating shaft 1 is not rotating, that is, in a free state, as shown in FIG. 3A , the seal lip portion 22 b of the seal member 22 of the seal device S is in pressure contact with the inner diameter side end face 13 of the front end wall 6 of the housing 5, so that intrusion of foreign matter from the outside into the front bearings 2, 2 on the inner diameter side of the seal member 22 in the tip side communicating passage 20 and into the internal space around the rotating shaft 1.

[0035] When the rotating shaft 1 rotates, the impeller 25 rotates, allowing outside air to be introduced into the housing 5 through the through-hole 27, as shown in FIG. 1 , as indicated by arrow A. The outside air introduced into the housing 5 flows into the tip-side communicating passage 20 via the flow passage 30, as indicated by arrow B, and is then discharged forward through the tip-side communicating passage 20 through the opening 20a of the tip-side communicating passage 20, as indicated by arrow C. At this time, air (compressed air) passes near the seal member 22, creating a pressure difference between the inner and outer diameter sides of the seal member 22. That is, the air flows faster on the outer diameter side of the seal member 22 than on the inner diameter side. As the fluid velocity increases, the pressure decreases, resulting in a higher pressure on the inner diameter side than on the outer diameter side. Therefore, as shown in FIG. 3B , a force acts on the seal member 22 in a direction that moves the seal lip portion 22b away from the inner diameter side end face 13 of the front end wall 6 of the housing 5. Moreover, at this time, the seal member 22 rotates around the axis of the rotating shaft 1, and centrifugal force acts in the outer diameter direction, which causes a force to act on the seal lip portion 22b in a direction separating it from the inner diameter side end face 13. Therefore, the centrifugal force and pressure difference cause the seal lip portion 22b to stably separate from the inner diameter side end face 13.

[0036] In this way, when the seal lip portion 22b separates from the inner diameter side end face 13, the tip side communication passage 20 is opened, and air inside the housing 5 can be discharged to the outside of the device.

[0037] By attaching a machining tool (e.g., a grinding wheel or cutting tool) as an object T to the tip of the rotating shaft 1 of the spindle device shown in Figure 1, a turning device or a cutting device can be configured. In this case, when the rotating shaft 1 is not rotating or is rotating at a low speed where the seal lip portion 22b does not separate from the inner diameter side end face 13, the seal lip portion 22b maintains a tight contact with the inner diameter side end face 13, preventing foreign matter from entering the device. Furthermore, when the rotating shaft 1 is rotating at a speed exceeding the low speed, air inside the housing 5 is discharged to the outside of the housing 5, preventing the intrusion of foreign matter. Cutting tools include drills, reamers, end mills, milling cutters, turning tools, taps, dies, etc.

[0038] Furthermore, by rotating the impeller 25 to such an extent that the seal lip portion 22b separates from the inner diameter side end face 13, the tip side communicating passage 20 is opened, and air within the housing 5 can be discharged to the outside of the device. Therefore, while the rotating shaft 1 is rotating, the fluid is sprayed outward, thereby preventing foreign matter from entering the device. Also in this case, at rotation speeds exceeding the low speed, the air within the housing 5 is discharged to the outside of the housing 5, preventing the intrusion of foreign matter.

[0039] In the spindle device of the present invention, by rotating the rotating shaft 1 about its axis, outside air can be introduced into the device, and the introduced air is transported from the rear end of the device to the front end of the device. When the rotating shaft 1 is rotating at a predetermined rotational speed or higher, air is allowed to be discharged from the front end of the device. This effectively prevents machining fluid, chips, and the like from entering the device. Furthermore, when the rotating shaft 1 is stationary or rotating at a low speed, a sealing device seals the gap between the rotating shaft at the front end of the device and the housing. Therefore, the rotating shaft 1 is not driven to rotate except during machining, effectively preventing foreign matter and the like from entering the device.

[0040] Furthermore, when the rotating shaft 1 is rotating at a predetermined rotational speed or higher, air is allowed to be discharged from the tip of the device, so the sealing device S does not slide against the rotating side, or only slides against it at a slow rotational speed, preventing wear on the sealing device S and extending the service life of the sealing device S.

[0041] The present invention can prevent foreign matter from entering the sealing device, whether during machining or not, and can prevent a shortened device life due to the intrusion of foreign matter. It also effectively prevents wear on the sealing device S, extending the useful life of the sealing device S. Moreover, in this state, the rotating shaft 1 is stopped or rotates at a low speed, thereby reducing power consumption. The sealing device S is configured with a seal lip portion 22b that opens due to the centrifugal force generated by the rotation of the rotating shaft and the air pressure of the air compressed by the impeller 25. With this seal lip portion 22b, a stable sealed state is formed when the rotating shaft 1 is stationary or rotating at a low speed, and the seal lip portion 22b remains stable at the rotational speed during machining. Therefore, the intrusion of foreign matter into the device can be effectively prevented whether the rotating shaft 1 is stopped or rotating.

[0042] Grease lubrication of bearings 2 and 3 has the advantages of simplifying the bearing lubrication structure and reducing the amount of lubricating oil used compared to oil mist lubrication, as well as cost benefits such as less oil scattering and dripping. Bearings 2 and 3 are angular contact ball bearings, which have the advantages of longer bearing life, improved operating speed, and improved durability.

[0043] By using ceramic balls, which are the rolling elements of the bearings 2 and 3, they have excellent chemical resistance and can be used in any environment, whether dry, wet, or chemical, and they also have excellent insulation and heat resistance.

[0044] By forming the flow path 30, an air flow path through which air flows can be stably formed within the device without the need to install additional piping or the like.

[0045] The grinding device of the present invention can prevent foreign matter from entering the fluid passage even when rotating, thereby avoiding the inflow of foreign matter into the grinding device, and the cutting device of the present invention can also prevent foreign matter from entering the fluid passage whether the rotating shaft 1 is stopped or rotating, thereby avoiding the inflow of foreign matter into the cutting device.

[0046] Incidentally, a passage for circulating the air drawn into the device by the rotation of the impeller from the rear side to the front side of the device may be provided in the rotary shaft 1. In this case, the passage may be provided only in the housing 5, only in the rotary shaft 1, or in both.

[0047] Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. In the above embodiment, the seal lip is separated from the press-contact portion that is in press-contact with the housing by centrifugal force and air pressure, but the seal lip may be separated by only centrifugal force or air pressure. That is, there are three cases: a case where both centrifugal force and air force are used, a case where centrifugal force only is used, and a case where air force only is used.

[0048] In the embodiment, the motor 4, which is the drive source for rotating the rotating shaft 1, is provided inside the housing 5. However, it may be provided outside the housing 5. When a motor is provided as a drive source, a transmission means (e.g., a gear mechanism, a belt mechanism, etc.) is required to transmit the driving force of the motor to the rotating shaft 1. In this case, the transmission means may be provided on the rotating shaft 1 side. The motor may be a DC (direct current) motor such as a brushed DC motor, a brushless DC motor, or a stepping motor, or an AC (alternating current) motor such as an induction motor or a synchronous motor. Any of these may be used in the spindle device according to the present invention. In the embodiment, the impeller 25 rotates in conjunction with the rotation of the rotating shaft 1. However, the impeller 25 itself may be driven to rotate by a power source different from that of the rotating shaft 1. In this case, it is preferable to synchronize the rotation of the rotating shaft 1 with that of the impeller 25.

[0049] Although a so-called V-ring is used as the sealing member, it is not limited to this and any other sealing member having a sealing lip that opens due to the centrifugal force generated by the rotation of the rotary shaft and the air pressure of the air compressed by the impeller may be used. The material may be nitrile rubber (NBR), fluororubber (FPM), chloroprene rubber (CR), ethylene propylene rubber (EPDM), ethylene acrylic rubber (EACM), silicone rubber (Q), etc. That is, the sealing member is opened at a predetermined rotation speed (for example, 5000 min). -1It is preferable to select such a state that the seal lip portion 22b is in the open state.

[0050] The bearings 2 and 3 are not limited to those lubricated with grease but may be lubricated with oil, and are not limited to angular bearings but may be various other ball bearings or roller bearings.

[0051] This spindle device has a rotating part supported by bearings and a fixed part other than the rotating part. Various processing tools (e.g., grinding wheels, cutting tools, etc.) are attached to the tip of the rotating shaft that makes up the rotating part, and these processing tools are used to process (polish, cut, etc.) the workpiece. Cutting tools include drills, reamers, end mills, milling cutters, turning tools, taps, and dies.

[0052] REFERENCE SIGNS LIST 1 Rotating shaft 2, 3 Bearing 5 Housing 22 Seal member 22b Seal lip portion 25 Impeller 30 Flow passage S Sealing device T Mounted object

Claims

1. A spindle device comprising: a rotating shaft capable of mounting an object at its tip; a housing that rotatably supports the rotating shaft via a bearing; an impeller attached to the rotating shaft that draws outside air into the device from the rear end side of the device as the rotating shaft rotates and discharges the drawn outside air from the tip side of the device; and a sealing device disposed between the rotating shaft on the tip side of the device and the housing, wherein the sealing device seals the gap between the rotating shaft on the tip side of the device and the housing when the rotating shaft is stationary or rotating at a low speed, and allows air to be discharged from the tip side of the device when the rotating shaft rotates at a predetermined speed or higher that exceeds the low speed.

2. A spindle device as described in claim 1, characterized in that the sealing device has a seal lip that opens due to at least one of the centrifugal force generated by the rotation of the rotating shaft and the air pressure of the air compressed by the impeller.

3. A spindle device as described in claim 1, characterized in that it is provided with a bearing that supports the rotating shaft rotatably relative to the housing, the bearing being a grease-lubricated angular contact ball bearing that can withstand radial loads and axial loads.

4. A spindle device according to claim 3, wherein the balls serving as rolling elements of said bearing are made of ceramics.

5. A spindle device as described in claim 1, characterized in that the housing is composed of a cylindrical body having a peripheral wall, and a circulation passage is formed in at least one of the rotating shaft and the peripheral wall of the housing, through which air sucked into the device by the rotation of the impeller flows from the rear side of the device to the front side of the device.

6. A grinding machine equipped with the spindle device according to any one of claims 1 to 5, characterized in that the mounted object attached to the tip of the rotating shaft is a grinding wheel.

7. A cutting processing device equipped with the spindle device according to any one of claims 1 to 5, characterized in that the load attached to the tip of the rotating shaft is a cutting tool.

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