JPH0782925B2 - Fluid sensitive to magnetic field - Google Patents

Description

FIELD OF THE INVENTION The invention of this application relates to rheological fluids that are sensitive to magnetic fields.

Prior Art Rheological fluids that are sensitive to magnetic fields are known.

Also known are rheological fluids that are sensitive to electric fields, such fluids being used in clutches, shock absorbers and other devices. However, the rheological fluid has a feature that when exposed to an appropriate energy field, the solid particles in the fluid are aligned and the fluidity is significantly reduced.

The fluid sensitive to an electric field and the fluid sensitive to a magnetic field include a dielectric medium such as mineral oil and silicone oil, and solid particles. Solid particles in a fluid that are sensitive to a magnetic field are magnetizable. Examples of solid particles proposed for use in magnetic field sensitive fluids include magnetite and carbonyl iron. The fluid may also contain a surfactant to suspend the solid particles in the vehicle.

The booklet entitled Code No. 1M-785 "Carbonyl Iron Powder" published by GAF Corporation of Wayne, NJ describes carbonyl iron powder commercially available from the company. Here, iron particles are classified into “straight powder”, “alloy”, “reducing powder” and “insulating reducing powder”. An example of “straight powder” is a powder known as carbonyl “E”. Get it.

This booklet gives a brief description of fluids that are sensitive to magnetic fields: "Spherical particles of carbonyl iron act like ball bearings in magnetic fluid coupling devices. Due to the smaller iron particles, the larger surface area and more contact than other powders, a better force transmission is achieved when engaged, in order to get the best results. Normally requires a lubricant and a dispersant. "However, this booklet does not mention the type of carbonyl iron or dispersant used in a magnetic field sensitive fluid.

In addition, AIEE Transactions JD Coolidge Jr. and RW Halberg in the publication entitled "Characteristics of Magnetic Fluids" (published February 1955), Article Nos. 55-170, 149-15.
Page 2 describes the use of different iron carbonyls in magnetic field sensitive fluids. Carbonyl iron disclosed herein includes carbonyl “E” and carbonyl “S” which are so-called straight powders.
F ", and reducing powders such as carbonyl" L ", carbonyl" HP "and carbonyl" C ". In this paper, which carbonyl iron is used in a magnetic field sensitive fluid. No mention is made of what is more desirable.

Also, NBS Technology, "Magnetic Fluid Clutch" by Jacob Rabinou (Rep. No. 1213-1948, and National Electric Engineering Institute Preprint 48-238-1948) in a paper with hydrogen-reduced iron,
And the use of carbonyl iron "SF" which is the straight particle.

In addition, a paper entitled "Magnetic Fluid Clutch" by SF Branden (Di Engineer, 191, 244-1951).
Et al.) Disclose the use of two different grades of carbonyl iron, “ME” and “MC”. Grade "M
It is said that E "is mechanically" hard "and grade" MC "is" soft. "However, this paper does not mention which carbonyl iron is preferable. Absent.

Also, NBS Technology News Bulletin 34.168 (1950), entitled "Further Development of NBS Magnetohydrodynamic Clutch," discloses the use of carbonyl "E" powder in a magnetic field and other compositions related to fluids. It also teaches information about.

U.S. Pat. No. 4,604,229 discloses combining a dispersant with a hydrocarbon carrier comprising 4-10 percent magnetite and 8-12 percent conductive carbon black. Particulate magnetite (Fe ₃ O ₄ ) is a magnetic oxide obtained by sufficiently oxidizing iron, carbonyl iron, or an alloy of iron and nickel. Note that similar disclosure is made in US Pat.
It is also done in the issue.

U.S. Pat. No. 3,006,656, on the other hand, discloses a magnetic particle buffer using a composition that may include carbonyl iron, a vehicle such as oil, and graphite. Here, carbonyl iron and magnetite are described as equivalent materials in the composition. However, there is no description about which carbonyl iron was used in this patent.

Further, US Pat. No. 2,519,449 discloses a combination of carbonyl E and solid particle graphite mixed in a ratio of 50:50. In the composition, the continuous phase or dielectric medium is air and the graphite acts as a lubricant.

Also, US Pat.No. 2,661,596 is 100 parts of carbonyl iron powder,
A magnetically sensitive fluid is disclosed which comprises 10 parts of dielectric oil and 2 parts of a dispersant such as iron oleate. On the other hand, U.S. Pat. Nos. 2,663,809 and 2,886,151 disclose the use of carbonyl iron in fluid coupling, but do not describe the type of carbonyl iron used.

In U.S. Pat.No. 2,772,761, plast-iron (p
A magnetically sensitive fluid consisting of iron powder with 80:20 mixture of last-iron) and carbonyl "E" and a dispersant consisting of 39% graphite, 46% naphtha and 15% alkyl resin was used. Teaches electromagnetic clutches.

In U.S. Pat. No. 4,737,886 an electrorheological fluid is disclosed, the fluid being sensitive to an electric field. Also described herein are fluids that are sensitive to magnetic fields. According to the patent, a relatively large amount of electric current and an essential electric circuit (for example, a large coil winding) are required to cause an appropriate reaction in a fluid by the above magnetic field.

5 of the 1986 summer issue of "Quest" magazine, published by TRW Corporation
Pages 5-63. A paper by Jack L. Blumenthol discloses the composition and properties of carbonaceous materials composed of fibrous carbon particles produced in a carbon disproportionation reaction.
Here, the carbon fibers of each particle are entangled to form a porous structure, and the particle can mix and suspend other fine powders in the fluid.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The object of the present application is to improve the rheology compared to the prior art, in which the speed of response to a magnetic field is high and the magnetic field is generated by a relatively low current flowing through a small number of coil windings. It is to provide a magnetic field sensitive fluid.

The fluid composition of the present invention comprises a vehicle and solid magnetizable particles suspended in the vehicle, preferably the fluid composition comprises a dispersant.

According to the invention, the magnetizable particles are reduced carbonyl iron particles with an insulating coating.

Further, the invention of the present application lies in the discovery of a novel dispersant used for a fluid which is sensitive to a magnetic field, and the dispersant is fibrous carbon particles, and each particle has a length-diameter ratio of 10: 1 to 1000: 1. Where the carbon fibers are intertwined. However,
The fibers preferably have a surface area of about 300 m ² per gram.

Means for Solving the Problems It is considered that the features of the present invention other than the above will be apparent to those skilled in the art by reading the specification according to the accompanying drawings.

The fluid composition of the present invention comprises a vehicle, such as mineral oil, silicone oil, or CONOCO LVT oil, and a reduced carbonyl iron having an insulating coating and a dispersant which is preferably entangled carbon fiber particles.

Carbonyl iron is made by decomposition of pentacarbonyl iron Fe (CO) ₅ . From this process, onion skin texture (Onion-
Spherical non-reducing particles called skin structure) are obtained. The carbon content is about 18%. Also, reduction or decarburization of non-reduced particles exposes the particles to a hydrogen atmosphere,
Then, it is compressed. By this treatment, the onion skin structure is destroyed and a structure in which fine iron particles are randomly arranged is formed.

The carbon content of the particles is about 0.075 percent.

In the present invention, the reduced particles are provided with an insulating coating in order to prevent contact between the particles. The particles are physically soft and compressible. The shape is spherical. Reduced particles with an insulating coating include "GQ-4" and "GS-6" commercially available from GAF Corporation. Table 1 below shows the physical and chemical properties of the insulating / reducing powder.

The data in Table 1 are those listed on page 4 of the above code number IM-785GAF catalog. For reference here
The disclosure items in the GAF catalog are described below.

The insulating coating may be any type of particle coating agent as long as it can insulate particles of carbonyl iron and prevent eddy currents or insulating leakage between particles. The insulating coating on the "GQ-4" and "GS-6" powders should be a discontinuous layer of silicon oxide, primarily silicon dioxide. Silicon is about the surface composition of carbonyl iron particles.
Constituting 6.9 atomic percent, silicon dioxide is also highly dielectric and also provides resistance.

It is believed that the reduced powder has iron particles arranged more randomly than the so-called "straight" powder, and therefore has a lower hysteresis effect than that for the straight powder.

Insulating the powder promotes the magnetohydrodynamic effect of reducing eddy currents around the particles. This eddy current adversely affects the magnetic field force in the fluid.

When the magnetic fluid composition of the present invention is used in a coupling device such as a clutch, a dispersant is not required because the movable part of the clutch effectively agitates the composition.

This is especially the case when using permanent magnets, so that the clutch is never demagnetized. In such cases,
The precipitation of iron particles does not pose any problem.

If a dispersant is required, then any of the dispersants or surfactants conventionally used in magnetic field sensitive fluids can be used in the compositions of the present invention.

Examples of surfactants used in the prior art include: dispersants such as ferrous oleate or ferrous naphthenate; aluminum such as aluminum tristearate or aluminum distearate. Soap; alkali stones such as lithium stearate or sodium stearate used for imparting thixotropic properties; surfactants such as fatty acids, ie oleic acid; sulfonates, ie petroleum sulfonates; phosphate esters, ie Alcohol esters of ethoxylated phosphate esters; and combinations of the above.

A more desirable dispersant material is fibrous carbon. Fibrous carbon is carbon fine particles in which each carbon particle is composed of many small carbon fibers. An example of such fibrous carbon is "TRW Carbon" (trademark) of TRW Corporation, which is disclosed in the above-mentioned "Quest" magazine. To refer to this disclosure,
I will write it here.

"TRW carbon" is made by catalytic carbon disproportionation reaction. In this reaction, a low heating value fuel gas or other carbon source is used as a reaction feed material. Each fiber of fibrous carbon has a diameter of 0.05 to 0.5 microns and a length up to several thousand times its thickness. According to the catalytic carbon disproportionation reaction, the preferable average length-to-diameter ratio is 10: 1 to 1000: 1, which is difficult to produce outside this range. Most of the fibers also contain single crystals of iron metal (iron, nickel, cobalt or alloys thereof) or iron metal carbide. Carbon fiber
It becomes longer during the disproportionation reaction from the opposite surfaces of the single crystal. Single crystals usually make up 1 to 10 weight percent of the material, but can be reduced to as low as 0.1 percent by acid extraction. Except for single crystals, the fibers consist of small amounts of hydrogen, such as 0.5 to 1 percent, and pure carbon and are either hollow or porous.

It is during the progress of the disproportionation reaction that the fibers become entangled and become aggregates of particles. The entanglement and formation of small voids in the carbon particles allows the fibrous carbon to mix micron-sized carbonyl iron particles and mechanically suspend the dispersed carbonyl iron particles in the fluid carrier. Fibrous carbon particles have a large surface area of 300 m ² per gram and a low bulk density of about 0.02 to 0.7 g per milliliter, and the pore volume is typically about 0.5 to 0.9 ml per gram. I can say.

Fibrous carbon particles have fluid-like characteristics and flow like a fluid similar to graphite.

If the particles are placed in a liquid vehicle in a dispersed amount,
Concentrate or gel the vehicle and prevent the precipitation of carbonyl iron particles. It also forms a thixotropic mixture with a highly fluid vehicle when subjected to shearing action. The viscosity of thixotropic mixtures is relatively temperature insensitive.

The vehicle used in the composition of the present invention may be any vehicle conventionally used for fluids sensitive to magnetic fields. Examples of substances suitable as vehicles are described in the above prior art. However, 100 ° F
It is desirable to use an oil having a viscosity of 1-1000 centipoise as the vehicle. Table 2 below shows specific examples of suitable vehicles and their viscosities.

The proportion of ingredients used in the composition of the invention varies over a wide range. For example, if the composition requires the use of a dispersant, the carbonyl iron particles will be dispersed and a sufficient amount of the dispersant will be used to suspend the particles in the vehicle.

The amount of vehicle used is that which is sufficient to function sufficiently as the continuous phase of the composition. Also, air pockets in the composition should be avoided. The balance of the composition is essentially carbonyl iron powder. Here, the weight ratio of carbonyl iron to dispersant is preferably in the range of about 90:10 to 99.5: 0.5. The weight of the vehicle is about 15 to 50 percent of the combined weight of iron carbonyl and dispersant.

The desired proportion should be determined according to the composition of the present invention. The proportion is preferably such that the composition of the present invention has thixotropy and is mechanically stable to such an extent that homogeneity can be maintained for a long period of time.

In the case of a composition consisting essentially of insulating / reduced carbonyl iron and vehicle, the amount of vehicle is such that it forms a continuous phase in the composition. The specific amount is determined according to the physical properties of the vehicle such as viscosity. The preferred weight ratio of vehicle to galbonyl iron is in the range of about 85 to 45 percent carbonyl iron to about 15 to 55 percent vehicle.

Example In this example, firstly 99% by weight of carbonyl iron and
1 weight percent TRW carbon was mixed. Then CONOCO
20 weight percent LVT oil and 80 weight percent mixture of carbonyl iron and TRW carbon mixed above were homogenized under vacuum for 12-24 hours in a homogenizer. The TRW carbon and carbonyl iron are thoroughly mixed by vigorous mixing with a homogenizer, and the carbonyl iron is trapped in the fibrous structure of TRW carbon. In addition, this mixing operation causes TRW
All carbon and carbonyl iron surfaces are fully wetted by LVT oil. Here, carbonyl "GS-6" (trademark) of GAF Corporation was used.

A test device was set up to characterize the coupling load characteristics of the composition under various conditions. The most desirable test device can be said to be a device that is structurally similar to the shock absorber disclosed in Application No. 339,126, filed April 14, 1989 (assigned to the assignee of the present application). In addition, this test apparatus is described in the drawings of the present application.

1 and 2, the test device 12 has a non-magnetic aluminum housing. The housing comprises first and second housing members 16, 18 (Fig. 2) which are engaged by bolts 20. Also, as shown, the housing members 16, 18 define a fluid chamber 22 at the right end 24 of the housing.

On the other hand, a shaft 26 extends from the left end 28 of the housing, and the shaft 26 has shaft end portions 30, 32 (Fig. 2).
There is a shaft central portion 34. The shaft 26 rotates within the bearing assemblies 36,38. At this time, seal 4
0, 42 prevents liquid leakage along the shaft 26.

The central portion 34 of the shaft 26 has a square shape, and
44 is fixed to the central portion 34 so as to rotate together with the shaft. The shape of the rotary blade is as shown in FIG. 3, and extends radially from the shaft central portion 34 toward the fluid chamber 22.

The right end 24 of the housing has openings 45 and 47,
A holder 46 for the electromagnet 54 is provided at 5, and the electromagnet 5 is provided at the opening 47.
6 holders 48 are located respectively. The holders 46 and 48 have chambers 50 and 52, respectively, in which the electromagnets 54 and 56 are located.

The holders 46, 48 are fixed to the housing members 16, 18 by brackets 58, 60, respectively.

Also, the coil holders 46 and 48 are brackets by screws 62 and 64.
It is fixed at 58,60. In addition, brackets 58 and 60 have screws 66
It is fixed to the housing members 16 and 18 by (Fig. 1). The electromagnets 54,56 can be chemically connected to the holders 46,48 or fixed to the holders with screws (not shown). Housing material 16, 18 and holder
The non-magnetic materials of 46 and 48 minimize the leakage of magnetic flux from the electromagnets 54 and 56.

The details of the electromagnets 54 and 56 are shown in FIGS. The electromagnets 54, 56 are composed of a soft iron core 70 around which an electric coil 72 is wound. The electric coil 72 is covered with an encapsulating material such as epoxy. The electromagnets 54 and 56 each have a pair of wire ends 74, and the outer soft iron pole 76 extends so as to surround the coil 72.

The electromagnets 54 and 56 are installed so that the electromagnet 54 faces the poles of the electromagnet 56. Rotor 44 and fluid chamber 22 are electromagnets
It is installed between 54 and 56, and the clearance between one electromagnet and the rotor is about 0.25 mm. In addition, the thickness of the rotor blade is about
It is 2 mm.

In this embodiment, the diameter of the center 70 of each electromagnet is 38 mm (1.5 mm
Inch), the outer diameter of the electromagnet is 76 mm (3 inches).
The thickness of the outer pole 76 is 4.8 mm (0.1875 inches), and the electrode coils 72 each have 894 wire turns. When the electromagnets 54 and 56 are excited, each electromagnet produces its own magnetic field, and a magnetic field line is formed between the two electromagnets. The lines of magnetic force pass through the fluid in the fluid chamber and the rotor blades 44. Further, the magnetic field lines act on the fluid in the fluid chamber 22 and change the resistance force to the movement of the rotor blades 44 in the fluid.

To test the coupling force of the magnetic fluid of the present invention when exposed to a magnetic field, shaft 26 was connected by an arm 78 (Fig. 2) to a torque motor (not shown). Further, the torque motor was connected to the torque measuring means. Electromagnet 5
Different currents were applied to 4,56 and the torque required to rotate the blades in the magnetic field in chamber 22 under the influence of the magnetic field was measured. The results are shown in FIG.

In Fig. 7, the magnetomotive force of the coil (unit: ampere turn)
Is shown on the X-axis. The applied current ranges from 0 to about 3.5 amps (3
129 ampere turns). On the other hand, the resistance against rotation of the rotary blade 44 is shown on the Y-axis in grams (g) per 645 mm ² (1 square inch). This value is the torque (gram) value required to rotate the rotor blade
It is calculated as the quotient by dividing by the surface area of the blade that is exposed to the magnetically sensitive fluid. Values at different frequencies from 0.5 to 5 hertz were also measured.

Effect of the Invention As can be seen from the fact that the resistance to rotation at zero current is close to zero, the composition of the present invention exhibits excellent lubricity. The resistance to rotation is 3129 ampere turns (about 3.
At 5 ampere), it rapidly increased with increasing current up to 26-34 g / mm ² . The values at different frequencies were also measured, but all showed almost the same curves, which shows that the composition of the present invention is relatively frequency independent.

In contrast, conventional magnetic field sensitive fluids require a significant amount of current to achieve a coupling force comparable to the above. That is, a conventional magnetic field sensitive rheological fluid is about 31
A magnetic field created by a current of 29 ampere turns can only provide coupling forces of less than 0.7 g / mm ² . Therefore, the rheological fluid of the present invention makes it possible to produce a very compact magnetic field sensitive fluid device having a relatively high coupling force.

From the above preferred embodiments, those skilled in the art should be able to find the improvements, differences from the conventional type, and the changes made by the present invention. In addition, these improvements / differences /
The changes will be described in the attached claims.

[Brief description of drawings]

FIG. 1 is a diagram of an apparatus using a rheological fluid according to the present invention. FIG. 2 is a sectional view taken along the line 2-2 in FIG. FIG. 3 is a plan view of the wing used in the apparatus of FIG. FIG. 4 is a perspective view of the electromagnet used in the apparatus of FIG. FIG. 5 is an enlarged sectional view taken along the line 5-5 in FIG. FIG. 6 is a plan view of the electromagnet of FIG. FIG. 7 is a graph showing the operational features of the apparatus of FIG.

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Claims (3)

[Claims] 1. A rheological fluid composition sensitive to a magnetic field, comprising a vehicle and solid magnetizable particulates suspended in the vehicle, the magnetizable particulates having an insulating coating. A rheological fluid composition, which is iron carbonyl. 2. The composition comprises a dispersant that disperses magnetizable microparticles throughout a vehicle, the vehicle being a compositionally continuous phase, and the dispersant comprising fibrous carbon particles, the carbon particles comprising: A fluid composition according to claim 1 wherein the fibers have a length to diameter ratio of 10: 1 to 1000: 1. 3. A rheological fluid composition sensitive to a magnetic field comprising a vehicle, solid magnetizable particulates suspended in the vehicle, and a dispersant, wherein the dispersant is length to diameter. A rheological fluid composition comprising fibrous carbon particles having a ratio of 10: 1 to 1000: 1.