# US 2012/0074348 A1 · High durability magnetorheological fluids > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2012/0074348 A1 - Document ID: US20120074348A1 - Status: Published application - Kind: A1 - Application number: 13/263,763 - Filed: 2010-05-28 - Published: 2012-03-29 - Earliest claimed: 2009-06-01 - Assignees: Lord Corporation - Inventors: Teresa L. Forehand; Daniel E. Barber - Web page: https://patentgrep.com/patent/US20120074348A1 ## CPC - H01F 1/442: {the magnetic component being a metal or alloy, e.g. Fe (H01F1/447 takes precedence)} - H01F 1/445: {the magnetic component being a compound, e.g. Fe3O4 (H01F1/447 takes precedence)} - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES ## Abstract A magnetorheological fluid comprising a mixture of soft and hard iron particles, an organic based carrier fluid, and optional additives such as anti-friction, anti-wear, or surfactants unexpectedly have improved durability when used in devices for control vibration and/or noise, for example, shock absorbers, elastomeric mounts, dampers, and the like. ## Claims ### Claim 1 A magnetorheological fluid, comprising: a blend of two classes of magnetically responsive particles wherein one class is relatively hard and has a mean diameter particle range of about 1 micron to about 150 microns and the other class is relatively soft and has a mean diameter particle range of about 1 micron to about 100 microns, and wherein said fluid is free of fluorocarbons. ### Claim 2 (depends on 1) The magnetorheological fluid of claim 1, wherein the hard particles comprise an iron alloy particles, and wherein the hard particles are present in an amount of about 50 percent by weight or less based on the total weight of the two classes of magnetically responsive particles. ### Claim 3 (depends on 2) The magnetorheological fluid of claim 2, wherein the soft particles have a Vickers hardness of less than 400 Hv and wherein the hard particles have a Vickers hardness of at least 550 Hv. ### Claim 4 (depends on 3) The magnetorheological fluid of claim 3, wherein the magnetorheological fluid further comprises a hydrocarbon carrier fluid and optionally a suspension aid. ### Claim 5 (depends on 4) The magnetorheological fluid of claim 4, wherein the amount of said hard particles is from about 5% to about 30% by weight and the amount of said soft particles is from about 70% to about 95% by weight based upon the total weight of said hard and said soft particles. ### Claim 6 (depends on 5) The magnetorheological fluid of claim 5, wherein the amount of said hard particles is from about 10% to about 20% by weight and the amount of said soft particles is from about 80% to about 90% by weight based upon the total weight of said hard and soft particles; and wherein the total amount of said hard and soft iron particles is from about 50 parts to about 90 parts by weight per 100 total parts by weight of said carrier fluid. ### Claim 7 (depends on 6) The magnetorheological fluid of claim 6, wherein the total amount of said hard and soft iron particles is from about 60 parts by weight to about 89 parts by weight per 100 parts by weight of said carrier fluid; wherein the mean diameter of said hard particles is from about 2 to about 10 microns and wherein the mean diameter of said soft particles is from about 2 to about 8 microns. ### Claim 8 (depends on 1) The magnetorheological fluid of claim 1, wherein the composition further includes an organomolybdenum additive or an organothiophosphorus additive, or a combination thereof. ### Claim 9 (depends on 6) The magnetorheological fluid of claim 6, wherein the composition further includes an organomolybdenum additive or an organothiophosphorus additive, or a combination thereof; and wherein said magnetorheological fluid has a durability of at least 2.0 million cycles in an automotive linear damper. ### Claim 10 (depends on 3) The magnetorheological fluid of claim 3, wherein the soft particles have a Vickers hardness from about 50 to about 300 Hv, and when the hard particles have a Vickers hardness of about 600 to about 1050 Hv. ### Claim 11 A method for forming a magnetorheological fluid, comprising the step of: blending hard magnetically responsive particles and soft magnetically responsive particles with a carrier fluid, said magnetorheological fluid being free of fluorocarbons, wherein said hard particles have a mean diameter particle range of 1 micron to 150 microns and the soft particles have a mean diameter particle range of 1 micron to 100 microns. ### Claim 12 (depends on 11) The method according to claim 11, wherein the soft particles have a Vickers hardness of less than 400 Hv, and wherein the hard particles have a Vickers hardness of at least 550 Hv. ### Claim 13 (depends on 12) The method according to claim 12, wherein the amount of said hard particles is from about 5% to about 30% by weight and the amount of said soft particles is from about 70% to about 95% by weight based upon the total weight of said hard and said soft particles. ### Claim 14 (depends on 13) The method according to claim 13, wherein the amount of said hard particles is from about 10% to about 20% by weight and the amount of said soft particles is from about 80% to 90% by weight based upon the total weight of said hard and soft particles; and wherein the amount of said hard and soft iron particles is from about 50 parts to about 90 parts by weight per 100 total parts by weight of said carrier fluid. ### Claim 15 (depends on 14) The method according to claim 14, wherein the soft particles have a Vickers hardness from about 50 to about 300 Hv, and when the hard particles have a Vickers hardness of about 600 to about 1050 Hv. ### Claim 16 (depends on 15) The method according to claim 15, wherein the amount of said hard and soft iron particles is from about 60 parts by weight to about 89 parts by weight per 100 parts by weight of said carrier fluid; wherein the mean diameter of said hard particles is from about 2 to about 10 microns and wherein the mean diameter of said soft particles is from about 2 to about 8 microns. ### Claim 17 (depends on 16) The method according to claim 16, wherein the composition further includes an organomolybdenum additive or an organothiophosphorus additive, or a combination thereof.