JPS583152B2 - Magnetic seal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotation transmission device having a magnetic seal device provided to prevent leakage of lubricating fluid.
To provide a bearing structure with low torque, less volatilization of lubricating fluid even after long-term use, and capable of maintaining good lubrication conditions for a long time.

For the purpose of preventing leakage of lubricating fluid, it has been conventional to use a magnetic seal that combines a magnetic fluid and a permanent magnet.

When a magnetic seal is used, lubricating oil can be kept in a sealed state in a non-contact state, so it is suitable for precision equipment etc. that require a high-precision rotation function that is sensitive to load fluctuations.

For example, a hydrodynamic bearing can be constructed using mineral oil or synthetic oil as a base oil and a magnetic lubricating fluid with lubricating properties.

For example, by applying fluid bearings that use magnetic fluid as lubricant and providing magnetic seals to high-precision rotating devices such as the cylinders of VTRs (video tape recorders), the characteristics of fluid lubrication can be achieved. It is possible to obtain an extremely high-precision rotation function.

Hereinafter, as one embodiment of the present invention, a case where the present invention is applied to a cylinder (head assembly) of a VTR will be described.

As VTR devices have recently become more portable, there have been demands for bearings to be more compact and highly precise, as well as for the following points.

1. Load torque is small and is not susceptible to changes in environmental temperature.

II. Lubricating performance is maintained over a long period of time even under adverse conditions (for example, under high temperatures).

The above item 1 is particularly required since portable VTRs with built-in batteries have been designed with emphasis on low power consumption.

Regarding 1i above, due to the nature of the product, portable VTRs are
Bearings may be left under adverse environmental conditions, so particularly demanding performance is required of bearings.In particular, when fluid-lubricated bearings are used in cylinders, the bearings must have a certain level of lubricating oil in them. Since it is a hydrodynamic bearing, there was a major challenge in keeping the lubricating oil sealed while it was left at high temperatures.

The properties of a magnetic fluid as a lubricating oil are largely influenced by the properties of its base oil.

For example, when synthetic oil such as ester or silicone oil and mineral oil such as turbine oil or mobil oil are used, the characteristics of magnetic fluid as a lubricating oil have mutually exclusive advantages and disadvantages, In order to construct a hydrodynamic bearing that satisfies the following, there are some difficulties as described below.

Among synthetic oils, ester-based lubricating oils have excellent boundary lubricity (oil-based) and volatility, and are suitable for lubrication of fluid bearings. Since the molecular weight of the obtained ester group is large, the dispersion of the magnetic fine particles becomes poor between the low-viscosity fat and oil and the base oil, making it difficult to reduce the viscosity of the magnetic fluid.

In the case of magnetic lubricating fluids that use silicone-based lubricating oil as a base oil, it is possible to reduce the viscosity, but since silicone oil inherently has poor boundary lubricity, the oil film on the fluid bearings runs out, and after long-term use, it may burn out. There were problems such as bumps occurring.

In the case of a magnetic fluid based on mineral oil, for example paraffin, the value (temperature Effects such as improved viscosity change characteristics can be obtained.

However, due to the nature of mineral oil, it easily volatizes, so when used under harsh conditions, particularly at high temperatures, there have been problems such as difficulty in sealing and retaining the lubricating oil for a long period of time.

In general, the higher the viscosity of a lubricating oil, whether it is synthetic oil or mineral oil, the lower its volatility.If it is made into a magnetic fluid, it is preferable in terms of long-term sealing, but there is an irreconcilable contradiction in that the viscous load increases. there were.

The present invention solves the above-mentioned problems regarding magnetic seals using magnetic fluid.

In other words, by using two types of magnetic fluids with different types or viscosity characteristics, the lower viscosity one is used as the lubricating oil for the fluid bearing, and the higher viscosity one is used as the magnetic seal, thereby improving the load characteristics of the device. It is possible to maintain good lubrication conditions by keeping the lubricating fluid sealed for a long period of time without damage.Hereinafter, the case where the present invention is applied to the cylinder structure of a VTR will be described using examples.

FIG. 1 explains the basic configuration of the present invention, in which a low-viscosity magnetic fluid is used to lubricate the fluid bearing, and a high-viscosity magnetic fluid is used to prevent leakage and volatilization, thereby reducing the torque of the fluid bearing. It has a magnetic seal structure that satisfies both aspects of long-term sealing performance.

1 is a fixed shaft, 2 is a lower base that supports the fixed shaft 1, 3 is a housing rotatably engaged with the fixed shaft 1, and 4 is a spherical pivot bearing formed at the tip of the fixed shaft 1.

Reference numeral 5 denotes a lubricating magnetic fluid, which is completely sealed in the gap formed between the fixed shaft 1 and the housing 3, and is prevented from leaking by the magnet 6.

Moreover, 7 is a storage cage for fixing the magnet 6 to the housing 3.

8 is a sealing magnetic fluid, and 9 and 10 are magnets, respectively.

A fixed sleeve 11 houses the magnets 9 and 10 and is fixed to the lower base 2.

Reference numeral 12 denotes a space formed between the magnets 9 and 10, the inner surface of the fixed sleeve 11, and the outside of the storage case 7, and the sealing magnetic fluid 8 is sealed in the gap 12.

Now, this device has three magnets 6, 9 . 10
The magnetic seal is made up of two types of magnetic fluids 5 and 8, and their individual functions will be explained as follows.

([) Action of the magnet 6 A fluid lubrication receiver is formed between the fixed shaft 1 and the housing 3, and the magnetic fluid 5 for lubrication is sealed as lubricating oil.
As a result, an oil film pressure is generated to balance the radial load applied to the housing 3.

Due to the oil film pressure, the magnetic fluid 5 serving as lubricating oil tries to flow out from the lower end opening of the housing 3, which is the only opening to the atmosphere, but is caught by the magnet 6 provided at the lower end opening. Spillage is prevented.

In this way, the lubricating fluid 5 can always be sealed and held between the fixed shaft 1 and the housing 3 due to the magnetic sealing effect of the magnet 6. The magnetic lubricating fluid used in this device has both the fluidity of a liquid and the properties of a magnetic material made from an alloy (solid) of iron, nickel, ferrite, etc.

In the embodiment of the present invention, about 100
A commercially available product was used, which was made into fine particles with a diameter of Å and dispersed in a solvent with the help of a surfactant.

Furthermore, in the examples, mineral oil (high vapor pressure) was used as the solvent for the magnetic fluid in order to reduce the viscosity.

(11) Actions and effects of magnets 9 and 10 Magnet 9
．． A sealing magnetic fluid 8 whose base oil is ester oil having a much higher viscosity than the lubricating magnetic fluid 5 is sealed in the gap 12 between the lubricating magnetic fluids 5 and 10 .

A gap 13 exists between the magnets 9 and 6, and neither of the magnetic fluids 5 and 8 exists in this gap.

The magnet 9 has the function of preventing the sealing magnetic fluid 8 from flowing out into the lower cavity 13, and the magnet 10 has the function of preventing the sealing magnetic fluid from leaking to the outside of the device. .

The gap between the storage case 7 and the fixed sleeve 11 (second
δ2) in the figure is the gap between the housing 3 and the fixed shaft 1:
It is formed much larger than δ1.

Therefore, it is possible to confine an amount of magnetic fluid in the gap 12 that is sufficient to compensate for the slight volatilization of the sealing magnetic fluid 8 after long-term use.

In addition, the gap δ1 is formed small in order to maintain the rigidity of the fluid bearing, but the gap δ2 is small even though the high viscosity sealing magnetic fluid 8 is sealed in the gap 12. Since it is sufficiently large, the viscous load is small.

In the examples, δ1≦15-25μ, δ2≦500
By forming the diameter to 600μ, it was possible to obtain sufficient rigidity as a fluid bearing despite low torque drive.

Now, as an example of an embodiment, the characteristics of two types of magnetic fluids 5 and 8 are compared as follows.

In Table 1, the amount of volatilization is calculated using a quantitative beaker (50cc.
) to 300CC. (7) Add magnetic fluids 5 and 6 and 80℃
The results are compared after being left for 200 hours at a temperature of

The lower the viscosity, the greater the volatility of lubricating oils, not just magnetic fluids, and the lower the flash point, the greater the amount of volatilization, and this trend can be seen from the results in Table 1.

It can be seen that when the lubricating magnetic fluid 5 with low viscosity is used as the lubricating oil of the hydrodynamic bearing, the viscous load is small, but the amount of volatilization is extremely large compared to the sealing magnetic fluid 8 with high viscosity.

For example, when a rotating device is configured using only the lubricating magnetic fluid 5 shown in Table 1 as a lubricating oil for a hydrodynamic bearing and left at high temperature (about 80° C.), it has been found that the following process occurs.

Magnetic fluids are usually composed of magnetic particles, fats and oils, and base oil. Initially, the base oil, which is the most volatile, evaporates from the openings of the fluid bearing that are in contact with the atmosphere, resulting in an apparent The viscosity of the magnetic fluid increases.

In other words, by leaving the rotating device under high temperatures, the load torque of the rotating device gradually increases, the amount of lubricating oil trapped decreases, and the lubrication conditions deteriorate.

For example, in a VTR cylinder, air gets mixed into the lubricating oil film, resulting in the occurrence of oil-whirl, which is an unstable phenomenon unique to hydrodynamic bearings.

Alternatively, various negative effects may occur, such as an increase in uneven rotation due to non-uniform torque and seizure of the bearing.

However, in this device, the highly volatile magnetic fluid 5 is isolated from the atmosphere outside the device by the “barrier” formed by the low-volatility sealing magnetic fluid 8, and the volatilization of the magnetic fluid 5 is prevented from occurring in the gap 13. can be kept within a small volume.

As a result, a constant amount of the lubricating magnetic fluid 5 can be maintained in the oil film portion of the fluid bearing even after being left for a long period of time.

Furthermore, the present device is characterized in that independent magnetic seals 6 and 9 are provided between the respective magnetic fluids 5 and 8.

The space between the lubricating magnetic fluid 5 and the sealing magnetic fluid 8 is sealed by two magnets 6 and 9, and since there is a gap 13 in between, the magnetic fluids 5 and 8 are not in contact with each other. ' will be prevented.

When two types of magnetic fluids made of different base oils are mixed, the dispersion of the magnetic particles in the solvent becomes poor, and phenomena such as precipitation and descent of the magnetic particles occur, resulting in an increase in the torque of the fluid bearing. However, in this device, such troubles are prevented.

For example, even if the device is subject to external disturbances or vibrations, such as a portable VTR, this device will not allow the magnetic fluids 5 and 8 to leak out and get mixed in, and will last for a long time. , it is possible to maintain good lubrication conditions.

Now, as mentioned above, the magnetic fluid (or magnetic lubricating fluid, magnetic lubricant) used in this device is a suspension of magnetic particles, and is normally used for sealing pressurized gas. .

In the present invention, a magnetic fluid having an arbitrary configuration can be applied.

For example, synthetic hydrocarbons, diesters, fluoroethers,
Any magnetic fluid consisting of petroleum or the like as a base liquid and magnetic particles of magnetic material such as ferrite or magnetite can be used in combination for lubricating the seal.

As listed in Table 1, in the examples, magnetic fluids with different types of lubricating oils as base oils were used;
A structure may be adopted in which the lower viscosity magnetic fluid made of the same base oil is used for lubrication, and the higher viscosity one is used for sealing.

Even in this case, the contamination of the sealing magnetic fluid with the lubricating magnetic fluid is prevented, so the increase in viscosity due to contamination will cause
Trouble such as increase in load torque can be prevented.

The permanent magnet used for the magnetic seal may be an alnico magnet, a ferrite magnet, a manganese aluminum magnet, a flexible magnet, or the like.

In an embodiment in which the present invention is applied to a VTR cylinder, the pressure generated in the fluid bearing oil film portion may be small, so it is sufficient to install only permanent magnet rings 6, 9, and 10 magnetized in the axial direction. I was able to obtain a good sealing effect.

In addition, in the structure shown in FIG. 2, if the magnetic force of the magnet 9 is strong enough, the fluidity of the sealing magnetic fluid 8 with high viscosity is poor, so even if the magnet 10 is omitted, the sealing magnetic fluid 8 can be applied to the gap 12. It can be contained and prevented from leaking outside the device.

When applying the present invention to devices that require high sealing pressure in other applications, for example, as is known in the art, a multi-stage edge that causes magnetic concentration may be provided to create a closed-loop magnetic field. The circuit can be configured positively.

Furthermore, although FIG. 1 shows a structure in which the housing 3 engaged with a fixed shaft 1 fixed to a substrate rotates, a structure in which a shaft housed in a fixed housing 3 rotates may also be used.
The present invention can be applied.

Furthermore, since one side of the housing in FIG. 1 has a sealed structure, the magnetic seal is provided only on the open side of the housing, but the present invention can be applied even when both ends are open.

In this case, two sets of magnetic seals of the present invention are required.

Now, another embodiment based on the present invention will be described.

In FIG. 2, a fixed sleeve 11 is provided to confine the sealing magnetic fluid 8, but as shown in FIG. I can do things.

Although the overall length of the housing is longer than the structure shown in Figure 2,
The outer diameter of the fixed shaft 1 near the support portion becomes smaller.

Now, in FIG. 3, 14 is a lubrication spiral group formed on the fluid bearing side of the fixed shaft 1, and 15 is a sealing spiral group formed on the seal side.

Spiral groups are normally formed to prevent instability phenomena in hydrodynamic bearings, but when used in the present device, magnetic seals become even more effective.

The lubrication spiral group 14 pumps the sealing magnetic fluid 5 by its pumping action (pumping action of lubricating fluid).
A force is applied to cause the fluid to flow toward the sealed side of the hydrodynamic bearing (the upper part of the fixed shaft 1).

By the trapping action of the magnet 6 on the magnetic fluid and the visco-sealing effect caused by the pumping action of the spiral group 14, leakage of the lubricating magnetic fluid 5 into the cavity 13 is prevented (that is, prevention of mixing of the two magnetic fluids is further prevented). strengthened.

The sealing spiral group 15 is also formed so as to receive the force of the magnetic fluid 8 flowing in the center of the gap 12.
A similar effect further strengthens the effect of preventing leakage to the cavity 13 and the outside.

In particular, the viscoseal effect of the lubricating spiral group 14 is effective only when rotating, but it is during rotating that lubricating fluid may leak due to the generation of high pressure, and when stationary, it is usually due to the surface tension. Because of the added effect, a weak magnet can prevent leakage of magnetic fluid.

Spiral groups 15 and 14 are formed in the parts where the sealing magnetic fluid 8 and the lubricating magnetic fluid 5 are sealed, respectively.
With this device, which is formed independently, the magnetic seal magnet may have a weak magnetic force, and as a result, the structure of the magnetic seal can be made sufficiently small and simple.

The method of this device, which forms spiral groups independently in the lubricating part and the seal part of the hydrodynamic bearing to strengthen prevention of leakage to the outside and prevention of mixing of the two magnetic fluids, is of course shown in Figure 2. It can also be applied to the structure of

In the case of the structure shown in Figure 2, the spiral groove for lubrication is
The sealing spiral group 15 may be formed on the inner wall of the storage case 7 or the fixed sleeve 11.

In the case where the spiral group is formed in a VTR cylinder, which is one of the embodiments, the shape and dimensions of the spiral group are listed in the table below as an example.

FIG. 4 shows a VTR cylinder, which is an embodiment of the present invention, for reference.

16 is an upper cylinder, 17 is a head attached to the upper cylinder 16, 18 is a lower cylinder, and a lower base 19
Fixed.

Reference numerals 20 and 21 denote rotary transformers for the rotating side and the fixed side, which transmit signals from the head 17 from the rotating side to the stationary side in a non-contact manner.

Reference numeral 22 denotes a housing, which is fixed to the upper cylinder 16 so as to be removably attached from above the apparatus, and constitutes a rotating part of the apparatus.

Reference numeral 23 denotes an upper lid, which is fixed to the rotating sleeve 22 via a gasket 24 for preventing leakage of lubricating fluid.

25 is a fixed shaft, 27 is a thrust support portion formed at the tip of the fixed shaft 25, and 28 is a spacer for the thrust bearing.

Reference numerals 29 and 30 denote a stator 29 and a rotor 30 of a direct drive motor for applying rotational driving force to the rotating part of this device.

31 is a magnet, which connects the fixed shaft 25 and the housing 22.
The lubricating magnetic fluid 5 sealed between the two has the effect of a magnetic seal.

Reference numeral 32 denotes an auxiliary sleeve, which is provided at the tip of the housing 22 for mounting the macnet 31 thereon.

33. 34 is a magnet, and the sealing magnetic fluid 8
It has the effect of sealing and holding.

This cylinder structure utilizes the basic structure shown in FIGS. 1 and 2, and has a direct connection with the lower end of the housing 22.
The magnetic seal effectively utilizes the space on the inner wall of the stator 29 of the drive motor, making it possible to achieve an extremely compact configuration.

By applying the present invention, which separates two types of magnetic fluids with different characteristics into one for lubrication and one for sealing to form independent magnetic seals, stable rotational performance can be achieved over a long period of time even under adverse environmental conditions at low torque. Portable V that provides
We were able to realize the TR cylinder.

The present invention can be applied and expanded to various devices.

For example, it can be used in a wide range of applications such as video disks, magnetic disks, electric motors, and gyro players that require high-precision rotational performance.

In addition, in the example, a low-viscosity magnetic fluid was used as a lubricant inside the device, and a high-viscosity magnetic fluid was used as a magnetic seal at the opening to the outside of the device, but even in the opposite case,
The present invention can be applied.

For example, the bearing part of a vacuum pump is constructed with a double sleeve, and the part that comes into contact with the low-pressure air inside the pump is sealed using a low-volatility, high-viscosity magnetic fluid, and the outer sleeve is used to seal the part that comes into contact with the low-pressure air inside the pump. A method such as constructing a fluid bearing using a low-viscosity magnetic fluid can be applied to the portion in contact with the magnetic fluid.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the basic configuration of the present invention, and FIG. 2 is a diagram explaining the basic configuration of the present invention.
A partially enlarged view thereof, FIG. 3 is a basic configuration diagram of an example in which the present invention is developed, and FIG. 4 is a front sectional view in which the present invention is applied to a V'TR cylinder. 1...Axis, 3...Housing, 5...
...Magnetic fluid A, 8...Magnetic fluid B, 6,
9,10... Magnet.

Claims (1)

[Claims] 1. A magnetic fluid A that is confined in a gap formed between the shaft and the housing and lubricates a bearing formed between the shaft and the housing, and a path leading from the gap to the outside of the device. The magnetic fluid B is sealed by providing a gap for the magnetic fluid A, the leakage of the magnetic fluid A into the gap, and the leakage of the magnetic fluid B to the gap and the outside of the device. 1. A magnetic sealing device comprising magnets each arranged so as to prevent the magnetic fluid A and the magnetic fluid B, the magnetic fluid A and the magnetic fluid B being of different types or having different viscosity characteristics. 2. The magnetic seal device according to claim 1, wherein the viscosity of the magnetic fluid B is higher than that of the magnetic fluid A. 3. The magnetic seal device according to claim 1, wherein the shaft and the housing are rotatably engaged by a fluid-lubricated bearing. 4. According to claim 1, a spiral groove is formed in a path leading from the gap to the outside of the device, so that the magnetic fluid A and the magnetic fluid B are pumped in a direction away from the gap. The magnetic seal device described.