Classifications

• • 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

Definitions

• the present invention relates to magneto-rheological materials with a high switching factor, in particular magnetorheological fluids (MRF) with a high switching factor, and their use.
• MRF magnetorheological fluids
• MRF are materials that change their flow behavior under the influence of an external magnetic field.
• electrorheological fluids are usually non-colloidal suspensions of particles which can be polarized in a magnetic or electric field in a carrier liquid which optionally contains further additives.
• MRFs are usually non-colloidal suspensions of magnetizable particles, from about one micron to one millimeter in size in a carrier liquid.
• the MRF can also contain additives, such as, for example, B. Dispergiertoskar and thickening additives contain.
• the particles are ideally homogeneous and isotropically distributed, so that the MRF in the magnet-free space has a low dynamic basis viscosity ⁇ 0 [measured in Pa * s].
• an external magnetic field H When an external magnetic field H is applied, the magnetizable particles arrange in chain-like structures parallel to the magnetic field lines. This restricts the fluidity of the suspension, which manifests itself macroscopically as an increase in viscosity.
• the field-dependent dynamic viscosity ⁇ H increases monotonically with the applied magnetic field strength H.
• the dynamic viscosity of an MRF is determined with a rotational viscometer.
• the shear stress ⁇ [measured in Pa] is measured at different magnetic field strengths and given shear rate D [in s "1 ], whereby the dynamic viscosity ⁇ [in Pa * s] is determined
• the changes in the flow behavior of the MRF depend on the concentration and nature of the magnetizable particles, their shape, size and size distribution; but also on the properties of the carrier liquid, the additional additives, the applied field, the temperature and other factors.
• the mutual interactions of all these parameters are extremely complex, so that individual improvements of an MRF with regard to a specific target variable have always been the subject of investigations and optimization efforts.
• the switching factor w D is defined at a fixed shear rate D as the ratio of the shear stress T H of the MRF in the external magnetic field H to the shear stress ⁇ 0 without magnetic field:
• the switching factor w D can thus be regarded as a measure of the convertibility of a magnetic excitation into a rheological state change of the MRF.
• a "high" switching factor means that a small change in the magnetic flux density B results in a large change in the shear stress ⁇ B / ⁇ 0 or the dynamic viscosity ⁇ B / ⁇ o in the MRF.
• spherical particles of carbonyl iron are used for MRF.
• MRF magnetizable substances and mixtures of substances known.
• WO 02/45102 A1 describes an MRF with a mixture of high-purity iron particles and ferrite particles in order to simultaneously optimize the properties of the MRF with and without a magnetic field. About the particle shape and size are given no information.
• US Pat. No. 5,667,715 discloses MRFs which contain spherical particles having a bimodal particle size distribution, the ratio of the average particle sizes of the two fractions being between 5 and 10. In addition, the width of the particle size distributions of the two individual fractions must not exceed the value of two-thirds of the respective average particle sizes.
• MRFs with bimodal particle size distributions are also described, the ratio of the average particle sizes of the two fractions being between 3 and 15.
• EP 1 283 530 A2 the concentration of the magnetisable particles, which in turn are in bimodal size distribution, is given as 86-90% by mass.
• US Pat. No. 6,610,404 B2 describes a magnetorheological material made of magnetic particles with defined geometric features, such as cylinder or prism shapes, among others. The production of such particles is very expensive. For strongly asymmetric particles, a high base viscosity of the MRF is also to be expected.
• US Pat. No. 6,395,193 B1 and WO 01/84568 A2 describe magnetorheological compositions with nonspherical magnetic particles, but these are not combined with spherical magnetic particles. All of these MRFs have in common that they are dependent on specific particle sizes or particle size distributions and / or defined particle geometries for achieving a high switching factor. As a result, their preparation becomes complicated and correspondingly expensive.
• magnetorheological materials in particular MRF, with two types of magnetizable particles are proposed, wherein the first particle fraction p consists of irregularly shaped non-spherical particles and the second fraction q consists of spherical particles.
• the combination of irregularly shaped non-spherical particles and spherical particles in the support medium surprisingly achieves both a low base viscosity without field and a high shear stress in the external magnetic field. That is, the magnetorheological materials according to the invention have an exceptionally high switching factor.
• the production of the irregular is shaped particle fraction p little expensive and so ⁇ extremely inexpensive.
• the average particle size of the fraction p is equal to or greater than that of the fraction q.
• the use of irregularly shaped, non-spherical particles thus entails a significant cost advantage compared to the production of known materials.
• An advantageous embodiment of the invention erfindungs ⁇ magne 'torhetreun materials provides that the mean particle size of the fraction p Trains t Credit ⁇ at least twice the value of the average of the fraction q Par ⁇ tikel seal has. Furthermore, it is favorable if the average particle sizes of the fractions p and q are between 0.01 ⁇ m and 1000 ⁇ m, preferably between 0.1 ⁇ m and 100 ⁇ m.
• a further advantageous embodiment of the magnetorheological materials according to the invention provides that the volume ratio of fractions p and q is between 1:99 and 99: 1, preferably between 10:90 and 90:10.
• the magnetizable Parti ⁇ angle of soft magnetic particles according to the state of the technique.
• the magnetizable particles both from the amount of soft magnetic metallic materials such as iron, cobalt, nickel (even in non-pure form) and alloys thereof such as iron-cobalt, iron-nickel / magne ⁇ tischer steel;
• Iron-silicon can be selected nen nen as well as from the amount of soft magnetic oxide ceramic materials such as the cubic ferrites, the perovskites and the garnets of the general formula
• metals from the group M Mn, Fe, Co, Ni, Cu, Zn, Ti, Cd or Mg.
• mixed ferrites such as MnZn, NiZn, NiCo, NiCuCo, NiMg or CuMg ferrites.
• the magnetizable particles can also consist of iron carbide or iron nitride particles and of alloys of vanadium, tungsten, copper and manganese, as well as mixtures of the mentioned particulate materials or of mixtures of different magnetizable types of solids.
• the soft magnetic materials may also be present all or partially in contaminated form.
• Carrier media in the context of the invention are carrier liquids and fats, gels or elastomers.
• the carrier liquids which may be used are the liquids known from the prior art, such as water, mineral oils, synthetic oils, such as polyalphaolefins, hydrocarbons, silicone oils, esters, polyethers, fluorinated polyethers, polyglycols, fluorinated carbonates. Hydrogens, halogenated hydrocarbons, fluorinated silicones, organically modified silicones and copolymers thereof or mixtures of these liquids can be used.
• inorganic particles such as SiO 2 TiO 2, iron oxides, layered silicates or organic additives and combinations thereof may be added to the suspension.
• a further advantageous embodiment of the magnetorheological materials according to the invention provides that the inorganic particles are at least partially organically modified.
• the suspension contains particle-shaped additives such as graphite, perfluoroethylene or molybdenum compounds such as molybdenum disulfite and combinations thereof in order to reduce abrasion phenomena. It is also possible for the suspension to be used for the surface treatment of workpieces special abrasives and / or chemically etching additives such. Ko ⁇ round, cerium oxides, silicon carbide or diamond contains.
• the proportion of magnetizable particles between 10 and 70 vol .-%, preferably between 20 and 60 vol .-%, is; the proportion of the carrier medium is between 20 and 90% by volume, preferably between 30 and 80% by volume, and the proportion of nonmagnetizable additives is between 0.001 and 20% by mass, preferably between 0.01 and 15 mass% (based on the magnetisable solids), is.
• the invention further relates to the use of the materials described in more detail above.
• magnetorheological materials according to the invention provides for their use in adaptive shock and vibration dampers, controllable brakes, clutches and in sports or training equipment. Special materials can also be used for the surface treatment of workpieces.
• the magnetorheological materials can also be used to generate and / or display haptic information such as characters, computer-simulated objects, sensor signals or images, in haptic form, to simulate viscous, elastic and / or viscoelastic properties or the consistency distribution of an object, in particular Training and / or research purposes and / or for medical applications.
• haptic information such as characters, computer-simulated objects, sensor signals or images, in haptic form, to simulate viscous, elastic and / or viscoelastic properties or the consistency distribution of an object, in particular Training and / or research purposes and / or for medical applications.
• MRF magnetorheological fluid
• Polyalphaolefin having a density of 0.83 g / cm 3 at 15 ° C. and a kinematic viscosity of 48.5 mm / s 2 at 40 ° C., Irregularly shaped iron particles (p) having an average particle size of 41 ⁇ m, measured in isopropanol by means of laser diffraction with the aid of a Mastersizer S from Malvern Instruments,
• spherical iron particles (q) with a mean particle size of 4.7 ⁇ m, measured in isopropanol by means of laser diffraction with the aid of a Mastersizer S from Malvern Instruments.
• the magnetorheological fluid MRF 3 thus prepared with the iron particle mixture (p) + (q) was subsequently evaluated for its properties characterized and compared with two other magnetorheological fluids prepared accordingly. It contained
• the rheological and magnetorheological measurements were carried out in a Searle Systems MCR 300 from Paar Physica.
• the rheological properties were carried out without applied magnetic field in a measuring system with coaxial cylindrical geometry, while the measurements in the magnetic field were made in a plate-plate arrangement perpendicular to the field lines.
• the shear stress ⁇ 0 as a function of the shear rate D for the MRF 3 according to the invention and the two comparative approaches MRF 1 and MRF 2 without an applied magnetic field. It can be seen that the flow curve of the MRF 3 according to the invention lies at all shear rates outside the quasistatic range (D> 1 s -1 ) below those of MRF 1 and MRF 2. This means that the MRF 3 according to the invention has a Magnetfeld ⁇ free space at a fixed shear rate D in comparison to the other approaches the lowest dynamic Ba ⁇ sisviskostician ⁇ 0 (see equation (1) of the description).
• the MRF 3 according to the invention has the highest shear stresses T B overall in the magnetic field in comparison with the lugs MRF 1 and MRF 2 without particle mixtures.
• MRF 3 in the entire measuring range exceeds those of MRF 1 and MRF 2.
• B 500 mT
• the MRF 3 according to the invention with the particle mixture consists of large, unclean gel-shaped iron particles and small ball-shaped iron particles both the lowest dynamic basic viscosity ⁇ o in the field-free space and the largest switching factor W D in the magnetic field in relation to the comparison approaches MRF 1 and MRF 2 auf ⁇ points.

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• 2004
  • 2004-08-27 DE DE102004041650A patent/DE102004041650B4/de not_active Expired - Fee Related
• 2005
  • 2005-08-25 EP EP05782479A patent/EP1782437B1/fr not_active Expired - Lifetime
  • 2005-08-25 US US11/574,395 patent/US7897060B2/en not_active Expired - Fee Related
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