CA2146551A1 - Magnetorheological materials based on alloy particles - Google Patents
Magnetorheological materials based on alloy particlesInfo
- Publication number
- CA2146551A1 CA2146551A1 CA002146551A CA2146551A CA2146551A1 CA 2146551 A1 CA2146551 A1 CA 2146551A1 CA 002146551 A CA002146551 A CA 002146551A CA 2146551 A CA2146551 A CA 2146551A CA 2146551 A1 CA2146551 A1 CA 2146551A1
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- Canada
- Prior art keywords
- material according
- iron
- magnetorheological material
- magnetorheological
- carrier fluid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/44—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids
- H01F1/447—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids characterised by magnetoviscosity, e.g. magnetorheological, magnetothixotropic, magnetodilatant liquids
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/44—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids
- H01F1/442—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids the magnetic component being a metal or alloy, e.g. Fe
Abstract
A magnetortheological material containing a carrier fluid and an iron alloy particle component. The particle component can be either an iron-cobalt alloy or an iron-nickel alloy. The iron-cobalt alloy has an iron:cobalt ratio ranging from about 30:70 to 95:5 while the iron-nickel alloy has an iron:nickel ratio ranging from about 90:10 to 99:1. The iron alloy particle components are capable of imparting high yield stress capability to magnetorheological materials.
Description
:) 94/10691 PCI~/US93/09517 21~61~ 1 ~ption MAGNE~ORE~OLOGICAL M~'I~RT~IS
R~'S~l- ONALLOYPART~CLES
c Technical E'ield 6 The present invention relates to fluid materials which exhibit subst~nt;~l increases in flow resistance when exposed to magnetic fields. More specific~lly~ the present invention relates to magneto-rheological materials that exhibit an enh~nced yield stress due to the use of certain iron alloy particles.
P~.~oundArt Fluid compositions which undergo a change in apparent vixcosity in the presence of a m~n~tiC field are commrnly larell~d to as Bingh~m magnetic fluids or magnetorheological materials.
Magnetorheological materials normally are comprised of ferro-15 magnetic or par~m~gnetic particles, typically greater than 0.1micrometers in diameter, dispersed within a carrier fluid and in the presence of a m~qgnetic field, the particles become polarized and are thereby organized into chains of particles within the fluid. The chains of particles act to increase the apparent viscosity or flow resistance of ~) the overall material and in the absence of a m~gnetic field, the particles return to an unorganized or free state and the apparent viscosity or flow resistance of the overall material is correspondingly reduced. These Bingh~m magnetic fluid compositions e2chibit controllable behavior .simil~r to that commonly observed for 25 electrorheological materials, which are responsive to an electric field instead of a m~netic field.
Both electrorheoloEic~l and m~gnetorheological materials are useful in providing valyillg tl~mping forces within devices, such as dampers, shock absorbers and elastomeric mounts, as well as in 30 controlling torque and or pressure levels in various clutch, brake and valve devices. M~gnetorheological materials inherently offer several advantages over electrorheological materials in these applications.
R~'S~l- ONALLOYPART~CLES
c Technical E'ield 6 The present invention relates to fluid materials which exhibit subst~nt;~l increases in flow resistance when exposed to magnetic fields. More specific~lly~ the present invention relates to magneto-rheological materials that exhibit an enh~nced yield stress due to the use of certain iron alloy particles.
P~.~oundArt Fluid compositions which undergo a change in apparent vixcosity in the presence of a m~n~tiC field are commrnly larell~d to as Bingh~m magnetic fluids or magnetorheological materials.
Magnetorheological materials normally are comprised of ferro-15 magnetic or par~m~gnetic particles, typically greater than 0.1micrometers in diameter, dispersed within a carrier fluid and in the presence of a m~qgnetic field, the particles become polarized and are thereby organized into chains of particles within the fluid. The chains of particles act to increase the apparent viscosity or flow resistance of ~) the overall material and in the absence of a m~gnetic field, the particles return to an unorganized or free state and the apparent viscosity or flow resistance of the overall material is correspondingly reduced. These Bingh~m magnetic fluid compositions e2chibit controllable behavior .simil~r to that commonly observed for 25 electrorheological materials, which are responsive to an electric field instead of a m~netic field.
Both electrorheoloEic~l and m~gnetorheological materials are useful in providing valyillg tl~mping forces within devices, such as dampers, shock absorbers and elastomeric mounts, as well as in 30 controlling torque and or pressure levels in various clutch, brake and valve devices. M~gnetorheological materials inherently offer several advantages over electrorheological materials in these applications.
2 ~ 2 ~, .
Magnetorheological fluids e2~hibit higher yield strengths than electrorheological materials and are, thelefule, capable of generating greater damping forces. Furthermore, m~gnetorheological materials are activated by m~netic fields which are easily produced by simple, 5 low voltage electrom~gnetic coils as compared to the expensive high voltage power supplies required to effectively operate electrorheological materials. A more specific description of the type of devices in which m~g7letorheologic~l materials can be effectively utilized is provided in co-per (ling U.S. Patent Application Serial Nos. 07/900,571 and 10 07/900,567 entitled "Magnetorheological Fluid Dampers" and "M~gnetorheological Fluid Devices," respectively, both filedL on June 18, 1992, the entire contents of which are incorporated herein by reference.
Magnetorheological or Bingham magnetic fluids are 15 disting~ h~ble from colloidal magnetic fluids or ferrofluids. In colloidal m~gnetiC fluids the particles are typically 5 to 10 n~nclmeters in diameter. Upon the application of a magnetic field, a colloidal ferrofluid does not exhibit particle structuring or the development of a resistance to flow. Instead, colloidal m~gnetic fluids experience a 20 body force on the entire material that is proportional to the m~gnetiC
field gr~-lient. This force causes the entire colloidal ferrofluid to be attracted to regions of high m~netiC field strength.
Magnetorheological fluids and corresponding devices have been discussed in various patents and pllhlic~tion~ For e~r~mrle~ U.S.
2~ Pat. No. 2,575,360 provides a description of an electromechanically controllable torque-applying device that uses a m~gnetorheological material to provide a drive connection between two independently rotating components, such as those found in clutches and brakes. A
fluid composition satisfactory for this application is stated to consist of 30 50~o by volume of a soft iron dust, commonly .efe.led to as "carbonyl iron powder", dispersed in a suitable liquid medium such as a light lubricating oil.
Another apparatus capable of controlling the slippage between moving parts through the use of m~netic or electric fields is disclosed 36 in U.S. Pat. No. 2,661,825. The space between the moveable parts is o 94/10691 Pcr/uss3/o95l7 filled with a field responsive medium. The development of a m~gnetic or electric field flux through this medium results in control of resulting slippage. A fluid responsive to the apFlic~tion of a m~netic field is described to coI-t~in carbonyl iron powder and light weight 5 _ineral oil.
U.S. Pat. No. 2,886,151 describes force trans_itting devices, such as clutches and brakes, that utilize a fluid film coupling respon-sive to either electric or m~gnetic fields. An ~Y~mple of a m~gnetiC
field responsive fluid is disdosed to COI t~in reduced iron oxide powder 10 and a lubricant grade oil having a viscosity of from 2 to 20 centipoises at 25C.
The construction of valves useful for controlling the flow of m~netorheologic~l fluids is described in U.S. Pat. Nos. 2,670,749 and 3,010,471. The m~gnetic fluids applicable for lt.ili~tion in the dis-~5 closed valve designs include ferrom~gnetic, par~m~gnetic and dia-m~gnetiC materials. A specific m~gnetic fluid composition specified in U.S. Pat. No. 3,010,471 consists of a suspension of carbonyl iron in a light weight hydrocarbon oil. ~gnetic fluid ~i~,ules useful in U.S.
Pat. No. 2,670,749 are described to consist of a carbonyl iron powder 20 dispersed in either a silicone oil or a chlorinated or fluorinated suspension fluid.
Various m~netorheological material l~ Lules are disclosed in U.S. Patent No. 2,667,237. The ...i~ e is defined as a dispersion of small par~m~netic or ferromagnetic particles in either a liquid, 25 coolant, antio~irl~nt gas or a semi-solid grease. A preferred com-position for a m~gnetorheqlogic~l material con~ictc of iron powder and light m~chine oil. A spe~ific~lly ~le~lled m~gnetiC powder is stated to be carbonyl iron powder wit~ an average particle size of 8 micrometers. Other possible carrier components include kerosene, 30 grease, and silicone oil.
U.S. Pat. No. 4,992,190 discloses a rheolo~ic~l material that is respons*e to a m~gnetic field. The composition of this material is disclosed to be magnetizable particles and silica gel dispersed in a liquid carrier vehicle. The magnetizable particles can be powdered W0 94/10691 2 1 ~ 6~ ~ ~ PCI/US93/09510 magnetite or carbonyl *on powders with insulated reduced carbonyl iron powder, such as that manufactured by GAF Corporation, being specificP.11y preferred. The liquid carrier vehicle is described as having a viscosity in the range of 1 to 1000 centipoises at 100F.
5 Specific e~r~mples of suitable vehicles include Conoco LVT oil, kerosene, light paraffin oil, mineral oil, and silicone oil. A ~lefel,ed ca~Tier ve-h-icle is silicone oil having a viscosity in the range of about 10 to 1000 cenl;poi.qe at 100F.
In many demanding applications for magnetorheological 10 materials, such as dampers or brakes for automobiles or trucks, it is desirable for the m~netorheological material to exhibit a high yield stress so as to be capable of tolerating the large forces experienced in these types of applications. It has been found that only a nomin~1 increase in yield stress of a given m~gnetorheological material can be L~ obtained by selecting among the dirre,~llt iron particles traditionally utilized in m~gnetorheological materials. In order to increase the yield stress of a given m~q~netorheological material, it is typically necessary to increase the volume fraction of magnetorheological particles or to increase the strength of the applied m~netic field.
20 Neither of these terhniques is desirable since a high volume fraction of the particle component can add si~nificant weight to a m~neto-rheologic~1 device, as well as increase the overall off-state viscosity of the material, thereby restricting the size and geometry of a m~gneto-rheological device capable of utili~ing that material, and high 25 m~gnetic fields significantly increase the power re4ui~e~ ents oiE a m~grletorheological device.
A need therefore e2~ists for a m~gr~etorheological particle component that will independently increase the yield stress of a magnetorheological material without the need for an increased 30 particle volume fraction or increased m~netiC field.
~isclosure of I~ ion The present invention is a m~gn~torheological material that utilizes a particle component which is capable of independently increasing the yield stress of the overall m~gnetorheological material.
~ 94/10691 ;~ PCI/US93/09517 5 21~6~
Specifically, the invention is a m~gnetorheological material com-prising a carrier fluid and a particle component wherein the particle -; component is comprised of an iron alloy selected from the group consisting of iron-cobalt alloys having an iron:cobalt ratio r~3nEing ~ 5 from about 30:70 to 95:5 and iron-nickel alloys having an iroIl nirkel ratio r~nEin~ from about 90:10 to 99:1. It has presently been discovered that iron-cobalt and iron-nickel alloys having the specific ratios disclosed herein are unusually effective when utilized as the particle component of a magnetorheological material. A m~qEnetorheological 10 material prepared with the present iron alloys exhibits a significantly improved yield stress as compared to a magnetorheological material prepared with traditional iron particles.
Brief De~iEltion of 1 he D~w~g Figure 1 is a plot of dynamic yield stress at 25C as a function 15 of m~gnetic field strength for m~netorheological materials prepared in accordance with h~r~mple 1 and Comparat*e h~J~r~mple 2.
Be~t Mode for C~ ;,r~ ~ Out the I~tion The prese~t invention relates to a m~netorheological mater-ial comprising a carrier fluid and an iron-cobalt or iron-nickel alloy 20 particle component. The iron-cobalt alloys of the invention have an iron:cobalt ratio r~ng-ng from about 30:70 to 95:5, ~lar~ldbly r~nging from about 50:50 to 85:15, while the iron-nickel alloys have an iroI7 nilkel ratio r~nging from about 90:10 to 99:1, preferably r:~nging from about 94:6 to 97:3. The iron alloys may cont~qin a small amount of 25 other elements, such as vanadium, chromium, etc, in order to improve the ductility and mechanical properties of the alloys. These other elements are typically present in an amount that is less than about 3.0% by weight. The di~meter of the particles utilized herein can range from about 0.1 to 500 ,um, l,lafelably from about 0.5 to 100 ~lm, 30 with about 1.0 to 50 ,um being especially preferred. Due to their ability to generate somewhat higher yield stresses, the iron-cobalt alloys are presently ~lafelled over the iron-nickel alloys for utilization as the particle component in a magnetorheological material. Examples of the lJre~l ed iron-cobalt alloys can be commercially obtained under wo 94/10691 2 1 ~ 1 PCr/US93/0951--; ~ 6 the tr~q-len~mes HYPERCO (Carpenter Technology), HYPERM (F.
Krupp Widiafabrik), SUPERMENDUR (Arnold Eng.) and 2V-P~ .~DUR (Western Electric).
The iron alloys of the invention are typically in the form of a 5 metal powder which can be prepared by processes well known to those skilled in the art. Typical methods for the preparation of metal powders include the reduction of metal oxides, grinrlinF or attrition, electrolytic deposition, metal carbonyl decomposition, rapid solidifi-cation, or smelt proces.sin~. Many of the iron alloy particle com-10 ponents of the present invention are commercially available in theform of powders. For ~mple~ [489'o]Fe/[50~o]Co/~2~o]V powder can be obtained from UltraE`ine Powder Terhnologies.
The iron alloy particlè component typically comprises from about 5 to 50, l,ler~ldbly about 10 to 45, with about 20 to 35 percent by 15 volume of the total m~netorheological material being especially l,lafel-led depen-lin~ on the desired m~netic activity and viscosity of the overall material. This corresponds to about 31.0 to 89.5, ~erelably about 48.6 to 87.5, with about 68.1 to 82.1 percent by weight being especially lJlefelled when the carrier fluid and the particle component 20 of the m~gnetorheological material have a specific gravity of about 0.95 and 8.10, respectively.
The carrier fluid of the m~gnetorheological material of the present invention can be any carrier fluid or vehicle previously flosed for use in m~gnetorheological materials such as the mineral 25 oils, silicor~e oils, and paraffin oils described in the patents set forth above. Adtlit,jon~l carrier fluids appropriate to the present invention include silicone copolymers, white oils, hydraulic oils, chlorinated hydrocarbons, transformer oils, halogenated aromatic liquids, halogenated paraffins, diester~, polyoxyalkylenes, perfluorinated 30 polyethers, fluorinated hydrocarbons, fluorinated silicones, and lules thereof. As known to those f~qmili~r with such compounds, transformer oils refer to those liquids having characteristic properties of both electrical and thermal insulation. Naturally occurring transfor_er oils include refined mineral oils that have low viscosity 35 and high chemical stability. Synthetic transformer oils generally ~ 94/10691 PC~r/US93/09517 7 21~B~5~
comprise chlorinated arom~tiCs (chlorinated biphenyls and trichloro-benzene), which are known collect*ely as "askarels", silicone oils, .~ and esteric liquids such as dibutyl seb~c~tes.
Additional carrier fluids suitable for use in the present 5 invention include the silicoI-e copolymers, hindered ester compounds and cyanoalkylsiloxane homopolymers disclosed in co-p~n(linE U.S.
Patent Application Serial No. 07/942,549 filed September 9, 1992, and entitled "High Strength, Low Conductivity Electrorheological Materials," the entire disclosure of which is incorporated herein by 10 lefele-lce. The carrier fluid of the invention may also be a modified carrier fluid which has been modified by e~rten~cive purification or by the formation of a miscible solution with a low conductivity carrier fluid so as to cause the modified carrier fluid to have a conductivity less than about 1 ~ 10-7 S/m. A detailed description of these modified 15 carrier fluids can be found in the U.S. Patent Application entitled "Modified Electrorheological Materials Having Minimum Conductivity," filed October 16, 1992, by Applicants B. C. Munoz, S. R. Wasserman, J. D. Carlson, and K. D. Weiss, and also assigned to the present ~.~signee, the entire disclosure of which is incorporated 20 herein by reference.
Polysil-~nes. and perfluorinated polyethers having a viscosity between about 3 and 200 centipoise at 25C are also appropriate for utilization in the magnetorheological material of the present invention. A detailed description of these low viscosity poly.~ilo~r~nes 25 and perfluorinated polyethers is given in the U.S. patent application entitled "Low Viscosity Magnetorheological Materials," filed concurrently herewith by ~pplicants K. D. Weiss, J. D. Carlson, and T. G. Duclos, and also ~.csiFned to the present ~signee~ the entire disclosure of which is incorporated herein by lerelal,ce. The plerelled 30 carrier fluids of the present invention include mineral oils, paraffin oils, silicone oils, silicone copolymers and perfluorinated polyethers, with silicone oils and mineral oils being especially ~refelled.
The carrier fluid of the magnetorheological material of the present invention should have a viscosity at 25C that is between about 35 2 and 1000 centipoise, ~lef~llably between about 3 and 200 centipoise, W O 94/10691 P~r/US93/0951 -;6 ~ ~ ~ 8 with a viscosity between about 5 and 100 centipoise being especially preferred. The carrier fluid of the present invention is typically utilized in an amount r~nEing from about 50 to 95, preferably from about 55 to 90, with from about 65 to 80 percent by volume of the total 6 magnetorheological material being especially preferred. This corresponds to about 10.5 to 69.0, ~.~,ably about 12.5 to 51.4, with about 17.9 to 31.9 percent by weight being especially preferred when the carrier fluid and particle component of the magnetorheological material have a specific gravity of about 0.95 and 8.10, respectively.
A surf~ct~nt to disperse the particle component may also be optionally utilized in the present invention Such surfactants include known surfactants or dispersing agents such as ferrous oleate and naphthenate, metallic soaps (e.g., aluminum tristearate and distearate), ~lk~line soaps (e.g., lithium and sodium stearate), 15 sulfonates, phosphate esters, stearic acid, glycerol monooleate, sorbitan sesquioleate, stearates, laurates, fatty acids, fatty alcohols, and the other surface active agents discussed in U.S. Patent No.
3,047,507 (incorporated herein by leîelellce). In addition, the optional surfactant may be comprised of steric st~hili7.ing molecules, including ao fluoroaliphatic polymeric esters, such as FC-430 (3M Corporation), and titanate, al-lmin~te or zirconate coupling agents, such as KEN-REACT (Kenrich Petrochemic~l.e, Inc.) coupling agents. The optional surf~ct~nt may also be hydrophobic metal oxide powders, such as AEROSIL R972, R974, EPR 976, R~705 and R812 (Degussa Corporation) 25 and CABOSIL TS-530 and TS-610 (Cabot Corporation) surface-treated hydrophobic fumed silica. Finally, a precipitated silica gel, such as that disclosed in U.S. Patent No. 4,992,190 (incorporated herein by le~lallce), can be used to disperse the particle component. In order to reduce the presence of moisture in the m~netorheological material, it 30 is l,lefelled that the precipitated silica gel, if utilized, be dlried in a convection oven at a temperature of from about 110C to 150C for a period of time from about 3 to 24 hours.
The surf~ct~nt7 if utilized, is preferably a hydrophobic filmed silica, a "dried" precipitated silica gel, a phosphate ester, a 3~ fluoro~liph~tic polyllleric ester, or a coupling agent. The optional 0 94/10691 Pcr/uss3/o95l7 9 2 1 4 ~
surfactant may be employed in an amount r~nging from about 0.1 to 20 percent by weight relative to the weight of the particle component.
Particle settling may be minimi~ed in the m~netorheological materials of the invention by forming a thixotropic network. A
thixotropic network is rlafinetl as a suspension of particles that at low shear rates form a loose network or structure, sometimes lafelled to as clusters or flocculates. The presence of this three-tlimen~ional structure imparts a small degree of rigidity to the m~gnetorheological material, thereby, reducing particle settling. However, when a 10 shearing force is applied through mild agitation this structure is easily disrupted or dispersed. When the shearing force is removed this loose nelwolk is lafoll"ed over a period of time.
A thixotropic network or structure is formed through the llt.ili~:~tion of a hydrogen-bonding thixotropic agent and/or a polymer-L~ modified metal oxide. Colloidal additives may also be llt;li~erl to assistin the formation of the thixotropic network. The formation of a thixotropic network ut.ili~ing hydrogen-bontling thixotropic agents, polymer-modified metal oxides and colloidal additives is further described in the U.S. Patent application entitled "Thixotropic ao Mf~gnetorheological Materials," filed concurrently herewith by applicants K. D. Weiss, D. A. Nixon, J. D. Carlson and A. J. Margida and also ~signed to the present ~signee~ the entire disclosure of which is incorporated herein by reference.
The formation of a thixotropic nelwolL in the invention can be 25 assisted by the addition of low molecular weight hydrogen-bonding molecules, such as water and other molecules cont~ining hydlvl~yl, carboxyl or amine functionality. Typical low molecular weight hydrogen-bonding molecules other than water include methyl, ethyl, propyl, isopropyl, butyl and hexyl alcohols; ethylene glycol; diethylene 30 glycol; propylene glycol; glycerol; aliph~t,ic, aromatic and heterocyclic amines, induding primary, secondary and tertiary a_ino alcohols and ~mino esters that have from 1-16 atoms of carbon in the molecule;
methyl, butyl, octyl, dodecyl, hexadecyl, diethyl, diisopropyl and dibutyl ~mines; ethanolamine; propanolamine; ethoxyethyl~mine;
35 dioctyl~mine; triethyl~mine; trimethyl~mina; tributyl~mine; ethylene-WO 94/10691 , ~ PCI`/US93/0951 rli~mine; propylene~ mine; triethanol~mine; triethylenetetramine;pyridine; morpholine; imidazole; and mi2~tures thereof. The low molecular weight hydrogen-bonding molecules, if utilized, are typically employed in an amount r~nFing from about 0.1 to 10.0, 5 ~le~lably from about 0.5 to 5.0, percent by weight relative to the weight of the particle component.
The m~gnetorheological materials of the present invention can be prepared by initially mi~ing the ingredients together by hand (low shear) with a spatula or the like and then subsequently more 10 thoroughly mi~ing (high shear) with a homogenizer, mechanical mixer or shaker or dispersing with an appropriate milling device ~uch as a ball mill, sand mill, attritor mill, colloid mill, paint mill, or the like, in order to create a more stable suspen.~ion Evaluation of the me~h~nic~l properties and characteristics of 1~ the m~netorheological materials of the present invention, as well as other m~gnetorheological materials, can be obtained through the use of parallel plate andlor concentric cylinder couette rheometry. The theories which provide the basis for these techniques are adequately described by S. Oka in Rheology, Theory and Applicnti~ns (volume 3, ~) F. R. Eirich, ed., Academic Press- New York, 1960) the entire conterlt~
of which are incorporated herein by lefe~ ce. The information that can be obtained from a rheometer includes data relating mer-h~nica shear stress as a function of shear strain rate. For m~gneto-rheological materials, the shear stress versus shear strain rate data 25 can be modeled after a BinFh~m plastic in order to determine the dynamic yield stress and viscosity. Within the co~fines of this model the dynamic yield stress for the magnetorheological material corresponds to the zero-rate intercept of a linear regression curve fit to the measured data. The magnetorheologic31 effect at a particular 30 m~gnetiC field can be further defined as the difference between the dynamic yield stress measured at that magnetic field and the dynamic yield stress measured when no magnetic field is present. The viscosity for the m~Fnetorheological material corresponds to the slope of a linear regression curve fit to the measured data.
2 1~
In a concentric cylinder cell configuration the m~gnetorheological material is placed in the annular gap formed r between an inner cylinder of radius R1 and an outer cylinder of radius R2, while in a simple parallel plate configuration the material is 5 placed in the planar gap formed between upper and lower plates both with a radius, R3. In these techniques either one of the plates or cylinders is then rotated with an angular velocity ~ while the other plate or cylinder is held mot;onle.s.s. A magnatic field can be applied to these cell configurations across the fluid-filled gap, either radially for 10 the concentric cylinder configuration, or axially for the parallel plate configuration. The relationship between the shear stress and the shear strain rate is then derived from this angular velocity and the torque, T, applied to m~int~in or resist it.
The following e~amples are given to illustrate the invention 15 and should not be construed to limit the scope of the invention.
E~ample 1 A m~netorheological material is prepared by initi~lly mi~ring together 112.00 grams of an iron-cobalt alloy powder consisting of [48%]Fe/[50%]Co/~2%]V obtained from UltraFine Powder Techno-20 logies, 2.24 grams of stearic acid (Aldrich Chemical Comp~ny) as a dispersant and 30.00 grams of 200 centistoke silic-~ne oil (L-45, Union Carbide Ch~mic~ & Plastics Comr~ny, Inc.). The weight amount of iron-cobalt alloy particles in this magnetorheological material corresponds to a volume fraction of 0.30. The m~Enetorheological 25 material is made homo~eneous by dispersing on an attritor mill for a period of 24 hours. The m~gnetorheological material is stored in a polyethylene cor t~iner until utilized.
Com~aL~Lv~ )le 2 A m~gnetorheological material is prepared according to the 30 procedure described in ~ mple 1. In this case the particle com-ponent consists of 117.90 grams of an insulated reduced carbonyl iron powder (MICROPOWDER R-252 1, GAF Chemical Corporation, simil~r to old GQ4 and GS6 powder notation). An a~l lvl~iate amount WO 94/10691 PCI'/US93/09Sl~
of stearic acid and silicone oil is utilized in order to m~int~in the volume fraction of the particle component at 0.30. This m~neto-rheological material is stored in a polyethylene container until utilized.
Ma~etorheolo{~ical Activit y The magnetorheological materials prepared in ~J~mples 1 and 2 are evaluated through the use of parallel plate rheometry. A
sllmm~ry of the dynamic yield stress values obtained for these m~gnetorheolgical materials at 25C is provided in Figure 1 as a 10 function of m~gnetic field. ~igh~r yield stress values are obtained for the magnetorheological material utili~in~ the iron-cobalt alloy particles (~ mple 1) as compared to the insulated reduced carbonyl *on powder (~ mple 2). At a m~gn~stic field strength of 6000 Oersted the yield stress exhibited by the magnetorheological material 1~ cont~ining the *on-cobalt alloy particles is about 70% greater than that exhibited by the reduced *on-based m~netorheological material.
As can be seen from the data in Figure 1, the iron alloy particles of the present invention provide for m~gnetorheological materials which exhibit substantially higher yield stresses than 20 m~gnetorheological materials based on traditional *on particles.
Magnetorheological fluids e2~hibit higher yield strengths than electrorheological materials and are, thelefule, capable of generating greater damping forces. Furthermore, m~gnetorheological materials are activated by m~netic fields which are easily produced by simple, 5 low voltage electrom~gnetic coils as compared to the expensive high voltage power supplies required to effectively operate electrorheological materials. A more specific description of the type of devices in which m~g7letorheologic~l materials can be effectively utilized is provided in co-per (ling U.S. Patent Application Serial Nos. 07/900,571 and 10 07/900,567 entitled "Magnetorheological Fluid Dampers" and "M~gnetorheological Fluid Devices," respectively, both filedL on June 18, 1992, the entire contents of which are incorporated herein by reference.
Magnetorheological or Bingham magnetic fluids are 15 disting~ h~ble from colloidal magnetic fluids or ferrofluids. In colloidal m~gnetiC fluids the particles are typically 5 to 10 n~nclmeters in diameter. Upon the application of a magnetic field, a colloidal ferrofluid does not exhibit particle structuring or the development of a resistance to flow. Instead, colloidal m~gnetic fluids experience a 20 body force on the entire material that is proportional to the m~gnetiC
field gr~-lient. This force causes the entire colloidal ferrofluid to be attracted to regions of high m~netiC field strength.
Magnetorheological fluids and corresponding devices have been discussed in various patents and pllhlic~tion~ For e~r~mrle~ U.S.
2~ Pat. No. 2,575,360 provides a description of an electromechanically controllable torque-applying device that uses a m~gnetorheological material to provide a drive connection between two independently rotating components, such as those found in clutches and brakes. A
fluid composition satisfactory for this application is stated to consist of 30 50~o by volume of a soft iron dust, commonly .efe.led to as "carbonyl iron powder", dispersed in a suitable liquid medium such as a light lubricating oil.
Another apparatus capable of controlling the slippage between moving parts through the use of m~netic or electric fields is disclosed 36 in U.S. Pat. No. 2,661,825. The space between the moveable parts is o 94/10691 Pcr/uss3/o95l7 filled with a field responsive medium. The development of a m~gnetic or electric field flux through this medium results in control of resulting slippage. A fluid responsive to the apFlic~tion of a m~netic field is described to coI-t~in carbonyl iron powder and light weight 5 _ineral oil.
U.S. Pat. No. 2,886,151 describes force trans_itting devices, such as clutches and brakes, that utilize a fluid film coupling respon-sive to either electric or m~gnetic fields. An ~Y~mple of a m~gnetiC
field responsive fluid is disdosed to COI t~in reduced iron oxide powder 10 and a lubricant grade oil having a viscosity of from 2 to 20 centipoises at 25C.
The construction of valves useful for controlling the flow of m~netorheologic~l fluids is described in U.S. Pat. Nos. 2,670,749 and 3,010,471. The m~gnetic fluids applicable for lt.ili~tion in the dis-~5 closed valve designs include ferrom~gnetic, par~m~gnetic and dia-m~gnetiC materials. A specific m~gnetic fluid composition specified in U.S. Pat. No. 3,010,471 consists of a suspension of carbonyl iron in a light weight hydrocarbon oil. ~gnetic fluid ~i~,ules useful in U.S.
Pat. No. 2,670,749 are described to consist of a carbonyl iron powder 20 dispersed in either a silicone oil or a chlorinated or fluorinated suspension fluid.
Various m~netorheological material l~ Lules are disclosed in U.S. Patent No. 2,667,237. The ...i~ e is defined as a dispersion of small par~m~netic or ferromagnetic particles in either a liquid, 25 coolant, antio~irl~nt gas or a semi-solid grease. A preferred com-position for a m~gnetorheqlogic~l material con~ictc of iron powder and light m~chine oil. A spe~ific~lly ~le~lled m~gnetiC powder is stated to be carbonyl iron powder wit~ an average particle size of 8 micrometers. Other possible carrier components include kerosene, 30 grease, and silicone oil.
U.S. Pat. No. 4,992,190 discloses a rheolo~ic~l material that is respons*e to a m~gnetic field. The composition of this material is disclosed to be magnetizable particles and silica gel dispersed in a liquid carrier vehicle. The magnetizable particles can be powdered W0 94/10691 2 1 ~ 6~ ~ ~ PCI/US93/09510 magnetite or carbonyl *on powders with insulated reduced carbonyl iron powder, such as that manufactured by GAF Corporation, being specificP.11y preferred. The liquid carrier vehicle is described as having a viscosity in the range of 1 to 1000 centipoises at 100F.
5 Specific e~r~mples of suitable vehicles include Conoco LVT oil, kerosene, light paraffin oil, mineral oil, and silicone oil. A ~lefel,ed ca~Tier ve-h-icle is silicone oil having a viscosity in the range of about 10 to 1000 cenl;poi.qe at 100F.
In many demanding applications for magnetorheological 10 materials, such as dampers or brakes for automobiles or trucks, it is desirable for the m~netorheological material to exhibit a high yield stress so as to be capable of tolerating the large forces experienced in these types of applications. It has been found that only a nomin~1 increase in yield stress of a given m~gnetorheological material can be L~ obtained by selecting among the dirre,~llt iron particles traditionally utilized in m~gnetorheological materials. In order to increase the yield stress of a given m~q~netorheological material, it is typically necessary to increase the volume fraction of magnetorheological particles or to increase the strength of the applied m~netic field.
20 Neither of these terhniques is desirable since a high volume fraction of the particle component can add si~nificant weight to a m~neto-rheologic~1 device, as well as increase the overall off-state viscosity of the material, thereby restricting the size and geometry of a m~gneto-rheological device capable of utili~ing that material, and high 25 m~gnetic fields significantly increase the power re4ui~e~ ents oiE a m~grletorheological device.
A need therefore e2~ists for a m~gr~etorheological particle component that will independently increase the yield stress of a magnetorheological material without the need for an increased 30 particle volume fraction or increased m~netiC field.
~isclosure of I~ ion The present invention is a m~gn~torheological material that utilizes a particle component which is capable of independently increasing the yield stress of the overall m~gnetorheological material.
~ 94/10691 ;~ PCI/US93/09517 5 21~6~
Specifically, the invention is a m~gnetorheological material com-prising a carrier fluid and a particle component wherein the particle -; component is comprised of an iron alloy selected from the group consisting of iron-cobalt alloys having an iron:cobalt ratio r~3nEing ~ 5 from about 30:70 to 95:5 and iron-nickel alloys having an iroIl nirkel ratio r~nEin~ from about 90:10 to 99:1. It has presently been discovered that iron-cobalt and iron-nickel alloys having the specific ratios disclosed herein are unusually effective when utilized as the particle component of a magnetorheological material. A m~qEnetorheological 10 material prepared with the present iron alloys exhibits a significantly improved yield stress as compared to a magnetorheological material prepared with traditional iron particles.
Brief De~iEltion of 1 he D~w~g Figure 1 is a plot of dynamic yield stress at 25C as a function 15 of m~gnetic field strength for m~netorheological materials prepared in accordance with h~r~mple 1 and Comparat*e h~J~r~mple 2.
Be~t Mode for C~ ;,r~ ~ Out the I~tion The prese~t invention relates to a m~netorheological mater-ial comprising a carrier fluid and an iron-cobalt or iron-nickel alloy 20 particle component. The iron-cobalt alloys of the invention have an iron:cobalt ratio r~ng-ng from about 30:70 to 95:5, ~lar~ldbly r~nging from about 50:50 to 85:15, while the iron-nickel alloys have an iroI7 nilkel ratio r~nging from about 90:10 to 99:1, preferably r:~nging from about 94:6 to 97:3. The iron alloys may cont~qin a small amount of 25 other elements, such as vanadium, chromium, etc, in order to improve the ductility and mechanical properties of the alloys. These other elements are typically present in an amount that is less than about 3.0% by weight. The di~meter of the particles utilized herein can range from about 0.1 to 500 ,um, l,lafelably from about 0.5 to 100 ~lm, 30 with about 1.0 to 50 ,um being especially preferred. Due to their ability to generate somewhat higher yield stresses, the iron-cobalt alloys are presently ~lafelled over the iron-nickel alloys for utilization as the particle component in a magnetorheological material. Examples of the lJre~l ed iron-cobalt alloys can be commercially obtained under wo 94/10691 2 1 ~ 1 PCr/US93/0951--; ~ 6 the tr~q-len~mes HYPERCO (Carpenter Technology), HYPERM (F.
Krupp Widiafabrik), SUPERMENDUR (Arnold Eng.) and 2V-P~ .~DUR (Western Electric).
The iron alloys of the invention are typically in the form of a 5 metal powder which can be prepared by processes well known to those skilled in the art. Typical methods for the preparation of metal powders include the reduction of metal oxides, grinrlinF or attrition, electrolytic deposition, metal carbonyl decomposition, rapid solidifi-cation, or smelt proces.sin~. Many of the iron alloy particle com-10 ponents of the present invention are commercially available in theform of powders. For ~mple~ [489'o]Fe/[50~o]Co/~2~o]V powder can be obtained from UltraE`ine Powder Terhnologies.
The iron alloy particlè component typically comprises from about 5 to 50, l,ler~ldbly about 10 to 45, with about 20 to 35 percent by 15 volume of the total m~netorheological material being especially l,lafel-led depen-lin~ on the desired m~netic activity and viscosity of the overall material. This corresponds to about 31.0 to 89.5, ~erelably about 48.6 to 87.5, with about 68.1 to 82.1 percent by weight being especially lJlefelled when the carrier fluid and the particle component 20 of the m~gnetorheological material have a specific gravity of about 0.95 and 8.10, respectively.
The carrier fluid of the m~gnetorheological material of the present invention can be any carrier fluid or vehicle previously flosed for use in m~gnetorheological materials such as the mineral 25 oils, silicor~e oils, and paraffin oils described in the patents set forth above. Adtlit,jon~l carrier fluids appropriate to the present invention include silicone copolymers, white oils, hydraulic oils, chlorinated hydrocarbons, transformer oils, halogenated aromatic liquids, halogenated paraffins, diester~, polyoxyalkylenes, perfluorinated 30 polyethers, fluorinated hydrocarbons, fluorinated silicones, and lules thereof. As known to those f~qmili~r with such compounds, transformer oils refer to those liquids having characteristic properties of both electrical and thermal insulation. Naturally occurring transfor_er oils include refined mineral oils that have low viscosity 35 and high chemical stability. Synthetic transformer oils generally ~ 94/10691 PC~r/US93/09517 7 21~B~5~
comprise chlorinated arom~tiCs (chlorinated biphenyls and trichloro-benzene), which are known collect*ely as "askarels", silicone oils, .~ and esteric liquids such as dibutyl seb~c~tes.
Additional carrier fluids suitable for use in the present 5 invention include the silicoI-e copolymers, hindered ester compounds and cyanoalkylsiloxane homopolymers disclosed in co-p~n(linE U.S.
Patent Application Serial No. 07/942,549 filed September 9, 1992, and entitled "High Strength, Low Conductivity Electrorheological Materials," the entire disclosure of which is incorporated herein by 10 lefele-lce. The carrier fluid of the invention may also be a modified carrier fluid which has been modified by e~rten~cive purification or by the formation of a miscible solution with a low conductivity carrier fluid so as to cause the modified carrier fluid to have a conductivity less than about 1 ~ 10-7 S/m. A detailed description of these modified 15 carrier fluids can be found in the U.S. Patent Application entitled "Modified Electrorheological Materials Having Minimum Conductivity," filed October 16, 1992, by Applicants B. C. Munoz, S. R. Wasserman, J. D. Carlson, and K. D. Weiss, and also assigned to the present ~.~signee, the entire disclosure of which is incorporated 20 herein by reference.
Polysil-~nes. and perfluorinated polyethers having a viscosity between about 3 and 200 centipoise at 25C are also appropriate for utilization in the magnetorheological material of the present invention. A detailed description of these low viscosity poly.~ilo~r~nes 25 and perfluorinated polyethers is given in the U.S. patent application entitled "Low Viscosity Magnetorheological Materials," filed concurrently herewith by ~pplicants K. D. Weiss, J. D. Carlson, and T. G. Duclos, and also ~.csiFned to the present ~signee~ the entire disclosure of which is incorporated herein by lerelal,ce. The plerelled 30 carrier fluids of the present invention include mineral oils, paraffin oils, silicone oils, silicone copolymers and perfluorinated polyethers, with silicone oils and mineral oils being especially ~refelled.
The carrier fluid of the magnetorheological material of the present invention should have a viscosity at 25C that is between about 35 2 and 1000 centipoise, ~lef~llably between about 3 and 200 centipoise, W O 94/10691 P~r/US93/0951 -;6 ~ ~ ~ 8 with a viscosity between about 5 and 100 centipoise being especially preferred. The carrier fluid of the present invention is typically utilized in an amount r~nEing from about 50 to 95, preferably from about 55 to 90, with from about 65 to 80 percent by volume of the total 6 magnetorheological material being especially preferred. This corresponds to about 10.5 to 69.0, ~.~,ably about 12.5 to 51.4, with about 17.9 to 31.9 percent by weight being especially preferred when the carrier fluid and particle component of the magnetorheological material have a specific gravity of about 0.95 and 8.10, respectively.
A surf~ct~nt to disperse the particle component may also be optionally utilized in the present invention Such surfactants include known surfactants or dispersing agents such as ferrous oleate and naphthenate, metallic soaps (e.g., aluminum tristearate and distearate), ~lk~line soaps (e.g., lithium and sodium stearate), 15 sulfonates, phosphate esters, stearic acid, glycerol monooleate, sorbitan sesquioleate, stearates, laurates, fatty acids, fatty alcohols, and the other surface active agents discussed in U.S. Patent No.
3,047,507 (incorporated herein by leîelellce). In addition, the optional surfactant may be comprised of steric st~hili7.ing molecules, including ao fluoroaliphatic polymeric esters, such as FC-430 (3M Corporation), and titanate, al-lmin~te or zirconate coupling agents, such as KEN-REACT (Kenrich Petrochemic~l.e, Inc.) coupling agents. The optional surf~ct~nt may also be hydrophobic metal oxide powders, such as AEROSIL R972, R974, EPR 976, R~705 and R812 (Degussa Corporation) 25 and CABOSIL TS-530 and TS-610 (Cabot Corporation) surface-treated hydrophobic fumed silica. Finally, a precipitated silica gel, such as that disclosed in U.S. Patent No. 4,992,190 (incorporated herein by le~lallce), can be used to disperse the particle component. In order to reduce the presence of moisture in the m~netorheological material, it 30 is l,lefelled that the precipitated silica gel, if utilized, be dlried in a convection oven at a temperature of from about 110C to 150C for a period of time from about 3 to 24 hours.
The surf~ct~nt7 if utilized, is preferably a hydrophobic filmed silica, a "dried" precipitated silica gel, a phosphate ester, a 3~ fluoro~liph~tic polyllleric ester, or a coupling agent. The optional 0 94/10691 Pcr/uss3/o95l7 9 2 1 4 ~
surfactant may be employed in an amount r~nging from about 0.1 to 20 percent by weight relative to the weight of the particle component.
Particle settling may be minimi~ed in the m~netorheological materials of the invention by forming a thixotropic network. A
thixotropic network is rlafinetl as a suspension of particles that at low shear rates form a loose network or structure, sometimes lafelled to as clusters or flocculates. The presence of this three-tlimen~ional structure imparts a small degree of rigidity to the m~gnetorheological material, thereby, reducing particle settling. However, when a 10 shearing force is applied through mild agitation this structure is easily disrupted or dispersed. When the shearing force is removed this loose nelwolk is lafoll"ed over a period of time.
A thixotropic network or structure is formed through the llt.ili~:~tion of a hydrogen-bonding thixotropic agent and/or a polymer-L~ modified metal oxide. Colloidal additives may also be llt;li~erl to assistin the formation of the thixotropic network. The formation of a thixotropic network ut.ili~ing hydrogen-bontling thixotropic agents, polymer-modified metal oxides and colloidal additives is further described in the U.S. Patent application entitled "Thixotropic ao Mf~gnetorheological Materials," filed concurrently herewith by applicants K. D. Weiss, D. A. Nixon, J. D. Carlson and A. J. Margida and also ~signed to the present ~signee~ the entire disclosure of which is incorporated herein by reference.
The formation of a thixotropic nelwolL in the invention can be 25 assisted by the addition of low molecular weight hydrogen-bonding molecules, such as water and other molecules cont~ining hydlvl~yl, carboxyl or amine functionality. Typical low molecular weight hydrogen-bonding molecules other than water include methyl, ethyl, propyl, isopropyl, butyl and hexyl alcohols; ethylene glycol; diethylene 30 glycol; propylene glycol; glycerol; aliph~t,ic, aromatic and heterocyclic amines, induding primary, secondary and tertiary a_ino alcohols and ~mino esters that have from 1-16 atoms of carbon in the molecule;
methyl, butyl, octyl, dodecyl, hexadecyl, diethyl, diisopropyl and dibutyl ~mines; ethanolamine; propanolamine; ethoxyethyl~mine;
35 dioctyl~mine; triethyl~mine; trimethyl~mina; tributyl~mine; ethylene-WO 94/10691 , ~ PCI`/US93/0951 rli~mine; propylene~ mine; triethanol~mine; triethylenetetramine;pyridine; morpholine; imidazole; and mi2~tures thereof. The low molecular weight hydrogen-bonding molecules, if utilized, are typically employed in an amount r~nFing from about 0.1 to 10.0, 5 ~le~lably from about 0.5 to 5.0, percent by weight relative to the weight of the particle component.
The m~gnetorheological materials of the present invention can be prepared by initially mi~ing the ingredients together by hand (low shear) with a spatula or the like and then subsequently more 10 thoroughly mi~ing (high shear) with a homogenizer, mechanical mixer or shaker or dispersing with an appropriate milling device ~uch as a ball mill, sand mill, attritor mill, colloid mill, paint mill, or the like, in order to create a more stable suspen.~ion Evaluation of the me~h~nic~l properties and characteristics of 1~ the m~netorheological materials of the present invention, as well as other m~gnetorheological materials, can be obtained through the use of parallel plate andlor concentric cylinder couette rheometry. The theories which provide the basis for these techniques are adequately described by S. Oka in Rheology, Theory and Applicnti~ns (volume 3, ~) F. R. Eirich, ed., Academic Press- New York, 1960) the entire conterlt~
of which are incorporated herein by lefe~ ce. The information that can be obtained from a rheometer includes data relating mer-h~nica shear stress as a function of shear strain rate. For m~gneto-rheological materials, the shear stress versus shear strain rate data 25 can be modeled after a BinFh~m plastic in order to determine the dynamic yield stress and viscosity. Within the co~fines of this model the dynamic yield stress for the magnetorheological material corresponds to the zero-rate intercept of a linear regression curve fit to the measured data. The magnetorheologic31 effect at a particular 30 m~gnetiC field can be further defined as the difference between the dynamic yield stress measured at that magnetic field and the dynamic yield stress measured when no magnetic field is present. The viscosity for the m~Fnetorheological material corresponds to the slope of a linear regression curve fit to the measured data.
2 1~
In a concentric cylinder cell configuration the m~gnetorheological material is placed in the annular gap formed r between an inner cylinder of radius R1 and an outer cylinder of radius R2, while in a simple parallel plate configuration the material is 5 placed in the planar gap formed between upper and lower plates both with a radius, R3. In these techniques either one of the plates or cylinders is then rotated with an angular velocity ~ while the other plate or cylinder is held mot;onle.s.s. A magnatic field can be applied to these cell configurations across the fluid-filled gap, either radially for 10 the concentric cylinder configuration, or axially for the parallel plate configuration. The relationship between the shear stress and the shear strain rate is then derived from this angular velocity and the torque, T, applied to m~int~in or resist it.
The following e~amples are given to illustrate the invention 15 and should not be construed to limit the scope of the invention.
E~ample 1 A m~netorheological material is prepared by initi~lly mi~ring together 112.00 grams of an iron-cobalt alloy powder consisting of [48%]Fe/[50%]Co/~2%]V obtained from UltraFine Powder Techno-20 logies, 2.24 grams of stearic acid (Aldrich Chemical Comp~ny) as a dispersant and 30.00 grams of 200 centistoke silic-~ne oil (L-45, Union Carbide Ch~mic~ & Plastics Comr~ny, Inc.). The weight amount of iron-cobalt alloy particles in this magnetorheological material corresponds to a volume fraction of 0.30. The m~Enetorheological 25 material is made homo~eneous by dispersing on an attritor mill for a period of 24 hours. The m~gnetorheological material is stored in a polyethylene cor t~iner until utilized.
Com~aL~Lv~ )le 2 A m~gnetorheological material is prepared according to the 30 procedure described in ~ mple 1. In this case the particle com-ponent consists of 117.90 grams of an insulated reduced carbonyl iron powder (MICROPOWDER R-252 1, GAF Chemical Corporation, simil~r to old GQ4 and GS6 powder notation). An a~l lvl~iate amount WO 94/10691 PCI'/US93/09Sl~
of stearic acid and silicone oil is utilized in order to m~int~in the volume fraction of the particle component at 0.30. This m~neto-rheological material is stored in a polyethylene container until utilized.
Ma~etorheolo{~ical Activit y The magnetorheological materials prepared in ~J~mples 1 and 2 are evaluated through the use of parallel plate rheometry. A
sllmm~ry of the dynamic yield stress values obtained for these m~gnetorheolgical materials at 25C is provided in Figure 1 as a 10 function of m~gnetic field. ~igh~r yield stress values are obtained for the magnetorheological material utili~in~ the iron-cobalt alloy particles (~ mple 1) as compared to the insulated reduced carbonyl *on powder (~ mple 2). At a m~gn~stic field strength of 6000 Oersted the yield stress exhibited by the magnetorheological material 1~ cont~ining the *on-cobalt alloy particles is about 70% greater than that exhibited by the reduced *on-based m~netorheological material.
As can be seen from the data in Figure 1, the iron alloy particles of the present invention provide for m~gnetorheological materials which exhibit substantially higher yield stresses than 20 m~gnetorheological materials based on traditional *on particles.
Claims
What is claimed is:
1. A magnetorheological material comprising a carrier fluid; a particle component having a diameter ranging from about 1.0 to 500 µm and being comprised of an iron alloy selected from the group consisting of iron-cobalt alloys having an iron:cobalt ratio ranging from about 50:50 to 85:15 and iron-nickel alloys having an iron:nickel ratio ranging from about 90:10 to 99:1, the iron alloy particle component being present in an amount from about 20 to 35 percent by volume and the carrier fluid being present in an amount from about 65 to 80 percent by volume; a surfactant; and a thixotropic agent.
3. A magnetorheological material according to Claim 1 wherein the iron alloys contain less than about 3 percent by weight of vanadium or chromium.
5. A magnetorheological material according to Claim 1 wherein the diameter ranges from about 1.0 to 100 µm.
6. A magnetorheological material according to Claim 5 wherein the diameter ranges from about 1 to 50 µm.
7. A magnetorheological material according to Claim 1 wherein the carrier fluid is selected from the group consisting of mineral oils, silicone oils, halogenated aromatic liquids, halogenated paraffins, diesters, polyoxyalkylenes, perfluorinated polyethers, fluorinated silicones, and mixtures thereof.
8. A magnetorheological material according to Claim 7 wherein the carrier fluid has a viscosity at 25°C of between about 2 and 1000 centipoise.
9, A magnetorheological material according to Claim 8 wherein the viscosity at 25°C is between about 3 and 200 centipoise.
10. A magnetorheological material according to Claim 9 wherein the viscosity at 25°C is between about 5 and 100 centipoise.
11. A magnetorheological material according to Claim 7 wherein the carrier fluid is selected from the group consisting of mineral oils, silicone oils, and perfluorinated polyethers.
12. A magnetorheological material according to Claim 11 wherein the carrier fluid is a silicone oil or a mineral oil.
14. A magnetorheological material according to Claim 13 wherein the surfactant is selected from the group consisting of ferrous oleate and naphthenate, aluminum soaps, alkaline soaps, sulfonates, phosphate esters, glycerol monooleate, sorbitan sesquioleate, fatty acids, fatty alcohols, fluoroaliphatic polymeric esters, hydrophobic fumed silica, precipitated silica gel, and titanate, aluminate and zirconate coupling agents.
15. A magnetorheological material according to Claim 14 wherein the surfactant is hydrophobic fumed silica, precipitated silica gel, a phosphate ester, a fluoroaliphatic polymeric ester or a titanate, aluminate or zirconate coupling agent.
16. A magnetorheological material according to Claim 15 wherein the precipitated silica gel is a dried precipitated silica gel obtained by drying the silica gel in a convection oven at a temperature of from about 110°C
to 150°C for a period of time from about 3 hours to about 24 hours.
17. A magnetorheological material according to Claim 13 wherein the surfactant is present in an amount ranging from about 0.1 to 20 percent by weight relative to the weight of the particle component.
19. A magnetorheological material according to Claim 1 wherein the thixotropic agent comprises a low molecular weight hydrogen-bonding molecule containing hydroxyl, carboxyl, or amine functionality.
20. A magnetorheological material according to Claim 19 wherein the low molecular weight hydrogen-bonding molecule is selected from the group consisting of water;
methyl, ethyl, propyl, isopropyl, butyl and hexyl alcohols; ethylene glycol; diethylene glycol; propylene glycol; glycerol; aliphatic, aromatic and heterocyclic amines; primary, secondary and tertiary amino alcohols and amino esters that have from 1-16 atoms of carbon in the molecule; and mixtures thereof.
1. A magnetorheological material comprising a carrier fluid; a particle component having a diameter ranging from about 1.0 to 500 µm and being comprised of an iron alloy selected from the group consisting of iron-cobalt alloys having an iron:cobalt ratio ranging from about 50:50 to 85:15 and iron-nickel alloys having an iron:nickel ratio ranging from about 90:10 to 99:1, the iron alloy particle component being present in an amount from about 20 to 35 percent by volume and the carrier fluid being present in an amount from about 65 to 80 percent by volume; a surfactant; and a thixotropic agent.
3. A magnetorheological material according to Claim 1 wherein the iron alloys contain less than about 3 percent by weight of vanadium or chromium.
5. A magnetorheological material according to Claim 1 wherein the diameter ranges from about 1.0 to 100 µm.
6. A magnetorheological material according to Claim 5 wherein the diameter ranges from about 1 to 50 µm.
7. A magnetorheological material according to Claim 1 wherein the carrier fluid is selected from the group consisting of mineral oils, silicone oils, halogenated aromatic liquids, halogenated paraffins, diesters, polyoxyalkylenes, perfluorinated polyethers, fluorinated silicones, and mixtures thereof.
8. A magnetorheological material according to Claim 7 wherein the carrier fluid has a viscosity at 25°C of between about 2 and 1000 centipoise.
9, A magnetorheological material according to Claim 8 wherein the viscosity at 25°C is between about 3 and 200 centipoise.
10. A magnetorheological material according to Claim 9 wherein the viscosity at 25°C is between about 5 and 100 centipoise.
11. A magnetorheological material according to Claim 7 wherein the carrier fluid is selected from the group consisting of mineral oils, silicone oils, and perfluorinated polyethers.
12. A magnetorheological material according to Claim 11 wherein the carrier fluid is a silicone oil or a mineral oil.
14. A magnetorheological material according to Claim 13 wherein the surfactant is selected from the group consisting of ferrous oleate and naphthenate, aluminum soaps, alkaline soaps, sulfonates, phosphate esters, glycerol monooleate, sorbitan sesquioleate, fatty acids, fatty alcohols, fluoroaliphatic polymeric esters, hydrophobic fumed silica, precipitated silica gel, and titanate, aluminate and zirconate coupling agents.
15. A magnetorheological material according to Claim 14 wherein the surfactant is hydrophobic fumed silica, precipitated silica gel, a phosphate ester, a fluoroaliphatic polymeric ester or a titanate, aluminate or zirconate coupling agent.
16. A magnetorheological material according to Claim 15 wherein the precipitated silica gel is a dried precipitated silica gel obtained by drying the silica gel in a convection oven at a temperature of from about 110°C
to 150°C for a period of time from about 3 hours to about 24 hours.
17. A magnetorheological material according to Claim 13 wherein the surfactant is present in an amount ranging from about 0.1 to 20 percent by weight relative to the weight of the particle component.
19. A magnetorheological material according to Claim 1 wherein the thixotropic agent comprises a low molecular weight hydrogen-bonding molecule containing hydroxyl, carboxyl, or amine functionality.
20. A magnetorheological material according to Claim 19 wherein the low molecular weight hydrogen-bonding molecule is selected from the group consisting of water;
methyl, ethyl, propyl, isopropyl, butyl and hexyl alcohols; ethylene glycol; diethylene glycol; propylene glycol; glycerol; aliphatic, aromatic and heterocyclic amines; primary, secondary and tertiary amino alcohols and amino esters that have from 1-16 atoms of carbon in the molecule; and mixtures thereof.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US968,734 | 1992-10-30 | ||
| US07/968,734 US5382373A (en) | 1992-10-30 | 1992-10-30 | Magnetorheological materials based on alloy particles |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2146551A1 true CA2146551A1 (en) | 1994-05-11 |
Family
ID=25514689
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002146551A Abandoned CA2146551A1 (en) | 1992-10-30 | 1993-10-06 | Magnetorheological materials based on alloy particles |
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| Country | Link |
|---|---|
| US (1) | US5382373A (en) |
| EP (1) | EP0667028A1 (en) |
| JP (1) | JPH08502779A (en) |
| CN (1) | CN1092460A (en) |
| CA (1) | CA2146551A1 (en) |
| LV (1) | LV11391B (en) |
| RU (1) | RU95109902A (en) |
| WO (1) | WO1994010691A1 (en) |
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|---|---|---|---|---|
| US6503414B1 (en) * | 1992-04-14 | 2003-01-07 | Byelocorp Scientific, Inc. | Magnetorheological polishing devices and methods |
| US5578238A (en) * | 1992-10-30 | 1996-11-26 | Lord Corporation | Magnetorheological materials utilizing surface-modified particles |
| WO1994010693A1 (en) * | 1992-10-30 | 1994-05-11 | Lord Corporation | Thixotropic magnetorheological materials |
| RU2106710C1 (en) * | 1992-10-30 | 1998-03-10 | Лорд Корпорейшн | Magnetorheological material |
| JPH0790290A (en) * | 1993-09-21 | 1995-04-04 | Nippon Oil Co Ltd | Dispersing particle having effects of both magnetic and electric viscosity and fluid by using the same |
| US5462685A (en) * | 1993-12-14 | 1995-10-31 | Ferrofluidics Corporation | Ferrofluid-cooled electromagnetic device and improved cooling method |
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- 1993-10-06 JP JP6511078A patent/JPH08502779A/en active Pending
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| RU95109902A (en) | 1997-04-10 |
| US5382373A (en) | 1995-01-17 |
| LV11391B (en) | 1996-10-20 |
| WO1994010691A1 (en) | 1994-05-11 |
| CN1092460A (en) | 1994-09-21 |
| LV11391A (en) | 1996-06-20 |
| EP0667028A4 (en) | 1995-05-23 |
| EP0667028A1 (en) | 1995-08-16 |
| JPH08502779A (en) | 1996-03-26 |
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