Abstract: A differential pressure sensor includes a ferrofluid sensing element, or slug, that changes position in a tapered magnetic field in response to a pressure differential. The ferrofluid slug is contained in a tube and moves within the tapered magnetic field, which is perpendicular to the longitudinal axis of the tube. The field has a maximum flux density at its center and tapers off in both axial directions from its center. In response to a pressure differential of zero, the slug is centered in the field. In response to a non-zero pressure differential, the slug moves to the position in the field where the net magnetic forces equal the pressure differential. The position of the slug is sensed by sensing elements which produce output signals that vary according to the position of the slug.

Abstract: A long-life, stacked pole-piece magnetic fluid seal for sealing between a housing and magnetically permeable shaft, in one embodiment is comprised of an annular magnet, having poles of opposite polarity on first and second end surfaces thereof, an annular, magnetically permeable primary pole-piece axially abutting the first end surface of the magnet, and one or more annular, magnetically permeable secondary pole-pieces stacked axially adjacent the primary pole-piece and separated therefrom and from each other by one or more annular spacers which define intermediate spaces between the pole-pieces. The pole-pieces are in a closely-spaced, non-contacting relationship with the shaft to define one or more radial gaps which, in conjunction with the intermediate spaces collectively form an annular ring in which a magnetic fluid is disposed and retained. In a second embodiment, the annular magnet is separated from the primary pole piece by a spacer which defines an intermediate space therebetween.

Abstract: In a ferrofluid seal which comprises a magnet and at least one pole piece, the pole piece is fabricated from a ferromagnetic material which directly bonds to the magnet face. Since the pole piece material directly bonds to the magnet, no additional adhesive is necessary. Thus, the conventional steps of applying an adhesive and mounting pole pieces on the magnet are eliminated. In addition, voids and bubbles in the adhesive are eliminated, thus, enhancing seal integrity.In one embodiment, the ferromagnetic material is a ferromagnetic epoxy compound comprising a mixture of conventional epoxy materials plus a fine powder of ferromagnetic material such as iron, cobalt, nickel or various metal alloys.

Abstract: A sealed, rolling element bearing includes an inner race attached to a shaft, an outer race attached to a housing, a plurality of rolling elements in an annular region and a pair of shields extending inwardly from the outer race toward the inner race so as to substantially enclose the annular region. The shields have a closely-spaced, noncontacting relationship with the inner race thereby defining gaps. The elements of the bearing are of magnetically permeable material, and the sealed bearing includes means for producing a magnetic field in the gaps and in the regions where the rolling elements contact the races. A ferrofluid is retained by the magnetic field in the gaps for sealing and in the regions of contact between the rolling elements and the races for lubrication. A reservoir of ferrofluid in the regions between the two seals replenishes ferrofluid lost at the sealing and lubrication areas.

Abstract: A ferrofluid seal wherin the amount of ferrofluid which may be used is increased by tapering the gap in which the ferrofluid is retained from one end of the gap to the other. One side of this gap is the magnet and, where used, pole pieces used to generate the magnetic field retaining the sealing ferrofluid, and the other side is a wall forming the opening to be sealed. The tapering of the gap width may be achieved by tapering either side forming the gap or by tapering both sides. The taper is preferably uniform from one end of the gap to the other.

Abstract: A multi-stage ferrofluid seal incorporates a ferrofluid reservoir for extending seal life. The reservoir is located between seal stages and contains a quantity of ferrofluid sufficient to replace ferrofluid in the seal stages which is lost due to evaporation or contamination. The seal is designed to withstand a pressure drop between a high pressure area and a low pressure area and the location of the reservoir is selected so that the pressure capacity of the seal stages between the low pressure area and the reservoir is sufficient to withstand the entire pressure drop. The pressure capacity of the seal stages between the high pressure area and the reservoir is less than the entire pressure drop. Failure of the seal stages between the reservoir and low pressure area causes failure of the seal stages between the reservoir and the high pressure area.

Abstract: A compact long-life magnetic fluid seal for sealing between a housing and a magnetically permeable rotating shaft includes an annular magnet having a closely-spaced, noncontacting relationship with the shaft to define a first gap and an annular pole piece axially abutting the magnet and having a closely-spaced, noncontacting relationship with the shaft to define a second gap. The first gap has a slightly larger radial dimension than the second gap, and the first and second gaps together define an elongated annular space for retention of a magnetic fluid. The outer edges of the pole piece and magnet inner surfaces can be rounded to limit splashing of the magnetic fliud. In another embodiment, a magnetic fluid seal includes first and second pole pieces axially abutting opposite ends of an annular magnet. The magnet has a slightly larger inside diameter than either of the pole pieces. The pole pieces and the magnet together define an elongated annular gap for retention of magnetic fluid.

Abstract: A bearing and magnetic fluid seal assembly includes a shaft mounted by axially spaced-apart bearings for rotation relative to a housing. A magnetic fluid seal includes an annular magnet axially positioned between the bearings in the space that is wasted and not utilized for any purpose, and a thin, disk-like annular polepiece positioned between one of the bearings and the environment to be protected by the seal. Magnetic flux from the magnet is conducted by a magnetically permeable housing or shaft to an annular gap between the outside diameter of the polepiece and the housing. A magnetic fluid is retained in the gap by the magnetic flux, thereby providing an exclusion seal. Embodiments utilizing radially and axially polarized magets are provided. A magnetic fluid seal can be provided at each end of the assembly. The bearings supporting the shaft can be magnetically permeable or nonmagnetic. The seal(s) can be electrically conducting or nonconducting depending upon the type of ferrofluid used.

Abstract: A sealed, rolling element bearing includes an inner race attached to a shaft, an outer race attached to a housing, a plurality of rolling elements in an annular region and a pair of shields extending inwardly from the outer race toward the inner race so as to substantially enclose the annular region. The shields have a closely-spaced, noncontacting relationship with the inner race thereby defining gaps. The elements of the bearing are of magnetically permeable material, and the sealed bearing includes means for producing a magnetic field in the gaps and in the regions where the rolling elements contact the races. A ferrofluid is retained by the magnetic field in the gaps for sealing and in the regions of contact between the rolling elements and the races for lubrication. A reservoir of ferrofluid in the regions between the two seals replenishes ferrofluid lost at the sealing and lubrication areas.

Abstract: A bearing and magnetic fluid seal assembly includes a shaft mounted by axially spaced-apart bearings for rotation relative to a housing. A magnetic fluid seal includes an annular magnet axially positioned between the bearings in the space that is wasted and not utilized for any purpose, and a thin, disk-like annular polepiece positioned between one of the bearings and the environment to be protected by the seal. Magnetic flux from the magnet is conducted by a magnetically permeable housing or shaft to an annular gap between the inside diameter of the polepiece and the shaft. A magnetic fluid is retained in the gap by the magnetic flux, thereby providing an exclusion seal. Embodiments utilizing radially and axially polarized magnets are provided. A magnetic fluid seal can be provided at each end of the assembly. The bearings supporting the shaft can be magnetically permeable or nonmagnetic. The seal(s) can be electrically conducting or nonconducting depending upon the type of ferrofluid used.

Abstract: A low viscosity, electrically conductive ferrofluid composition and method of making and using same, which composition comprises: a first polar liquid carrier; a second polar liquid carrier miscible in the first polar carrier and comprising a polyol, such as a tetraethylene glycol dimethyl ether; magnetic particles to impart magnetic characteristics to the ferrofluid composition; and a surfactant, particularly a cationic surfactant in an amount sufficient to stabilize and disperse the magnetic particles, the surfactant dissociated or ionized predominately by the second polar liquid carrier.

Abstract: A bearing assembly with an integrated single-stage ferrofluid seal incorporated therein, which assembly comprises: a bearing assembly having an inner and outer race to define a raceway and a plurality of rolling elements within the raceway to permit rotation of the inner and outer races relative to one another; and a single-stage ferrofluid seal within the raceway and positioned adjacent one side of the roller element, and which ferrofluid seal comprises a single pole piece having one end which extends into a close, noncontacting relationship with the surface of the inner and outer races to define a radial gap, ferrofluid in the radial gap to form a seal, an annular permanent magnet secured to and adjacent the single pole piece, and a nonmagnetic permeable housing extending about a portion of the pole piece and the permanent magnet, to divert magnetic flux toward the surfaces of the inner or outer race in which the ferrofluid seal is formed in the radial gap, thereby providing a compact, integrated bearing as

Abstract: A low viscosity, electrically conductive ferrofluid composition and method of making and using same, which composition comprises: a first polar liquid carrier; a second polar liquid carrier miscible in the first polar carrier and comprising a polyol, such as a tetraethylene glycol dimethyl ether; magnetic particles to impart magnetic characteristics to the ferrofluid composition; and a surfactant, particularly a cationic surfactant in an amount sufficient to stabilize and disperse the magnetic particles, the surfactant dissociated or ionized predominately by the second polar liquid carrier.

Abstract: An electrically conductive ferrofluid-film-bearing apparatus and seal apparatus for a shaft which employs a low-viscosity, electrically conductive ferrofluid composition, which composition comprises a liquid carrier, and contains in combination an electrically conductive amount of a cationic surfactant and dispersed carbon particles, to obtain a low-electrical-resistivity ferrofluid having a low viscosity and suitable for use in a ferrofluid bearing apparatus.

Abstract: A bearing assembly with an integrated single-stage ferrofluid seal apparatus incorporated therein, which assembly comprises a bearing assembly having an inner and outer race to define a raceway, a plurality of rolling elements retained within the raceway to permit rotation of the inner and outer races relative to one another, and a single-stage ferrofluid seal apparatus within the raceway and adjacent one side of the roller elements and which ferrofluid seal apparatus comprises a single-pole piece which extends into a close, noncontacting relationship with the surface of the inner or the outer race to define a radial gap, ferrofluid in the radial gap to form a ferrofluid seal, and an annular, permanent magnet secured to and adjacent the single-pole piece, the magnet having a generally-L sectional shape and in contact with one side and about one end of the pole piece to provide both a source of magnetic flux and as a magnetically insulating housing for the pole piece.

Abstract: An electrically conductive ferrofluid composition and a method of preparing and using the ferrofluid composition in a ferrofluid seal apparatus, and which ferrofluid composition comprises a liquid carrier having a colloidal dispersion of ferromagnetic particles in an amount sufficient to provide magnetic properties to the ferrofluid composition and carbon particles in an amount sufficient to provide electrical conductive properties to the ferrofluid composition, the ferromagnetic and carbon particles stabilized in the ferrofluid composition by a surface active dispersing agent. The electrically conductive ferrofluid composition is usefully employed in a ferrofluid exclusion seal apparatus to provide an electrically conductive seal apparatus particularly useful for computer disk drives and sputtering apparatus in the semiconductive industry.

Abstract: A stable ferrofluid composition and the method of preparing and using the ferrofluid composition, such as in a ferrofluid seal apparatus, and which ferrofluid composition comprises: a liquid carrier; ferromagnetic particles sufficient to provide magnetic properties to the ferrofluid dispersed in the liquid carrier; and a dispersing amount of a cationic surfactant to provide a stable ferrofluid composition. The stable ferrofluid compositions have improved electrical conductivity and are useful in sealing computer disc drives and in sputtering apparatus in the semiconductive industry.

Abstract: A compact, coaxial multiple-shaft ferrofluid seal apparatus which comprises: a housing; a central shaft and magnetically permeable coaxial shafts about the central shaft, the coaxial shafts having a pair of spaced apart nonmagnetically permeable insulator shaft sections; magnetically permeable bearings to support each shaft; pole piece elements to provide radial gaps within the inner or outer shaft surfaces; ferrofluid disposed in the radial gaps to provide a seal apparatus for the shafts of designed pressure capacity; and a single radially polarized permanent magnet to provide a source of magnetic flux for the seal apparatus.

Abstract: The compact ferrofluid seal and radial bearing assembly, particularly useful for the support and sealing of a shaft, such as a computer disk drive shaft, where space is at a premium, which assembly comprises a magnetically-permeable radial bearing apparatus having inner and outer race elements, moveable elements, and a cage element to retain the moveable elements, and a ferrofluid single-stage seal apparatus comprising a radially-polarized permanent magnet to retain a sealing amount of ferrofluid in a radial gap between the inner and outer race elements.

Abstract: A high-pressure rotary seal apparatus with a radially-polarized permanent magnet, which seal apparatus comprises: a housing; a magnetically-permeable shaft to be sealed extending through the housing, the shaft characterized by a plurality of separate grooves or stages on the shaft; a radially-polarized permanent magnet extending about the shaft, at least one pole piece adjacent to and in a magnetic flux relationship with the radially-polarized permanent magnet and extending about the shaft, one polarized end of the polarized magnet and one end of the pole piece extending into a close, noncontacting relationship with the grooves on the surface of the shaft to form a plurality of separate radial gaps; ferrofluid disposed in the radial gaps to define a plurality of separate, spaced-apart ferrofluid O-ring seals about the surface of the shaft; and a generally cylindrical, magnetically-permeable keeper element extending about the other polarized end of the magnet and the other end of the pole piece in order to pro