Abstract: Crowning is applied to a side surface of an inner ring which abuts against a side surface of a drive shaft in a radial direction. With this construction, when the two side surfaces abut against each other by a pressing operation of a threadedly-engaged nut at the time of connecting the drive shaft and an inner shaft, a contact pressure distribution of abutting surfaces is made generally uniform, thereby suppressing the occurrence of an edge load. By thus preventing a contact pressure from increasing at part of the abutting surfaces, energy released by a stick-slip phenomenon is reduced, and a sound pressure level of an abnormal sound generated at this time is reduced.

Abstract: The present invention provides a method for producing an ?-alumina particle. The method for producing an ?-alumina particle comprises steps of: (1) placing a powdery mixture containing an aluminum salt and a seed crystal under a circumstance at not less than pyrolysis temperature of the aluminum salt, and (2) calcining the resultant.

Abstract: A method for producing an ?-alumina powder is provided. T method for producing an ?-alumina powder comprising steps of: (1) pulverizing a metal compound having a full width at half maximum (Ho) of a main peak in XRD pattern to obtain a seed crystal having a full width at half maximum (H) of the main peak in XRD pattern in the presence of pulverizing agent, (2) mixing the obtained seed crystal with an aluminum salt, (3) calcining the mixture, and wherein a ratio of H/Ho is 1.06 or more.

Abstract: A coating composition, a method for producing the coating composition, a coating film and magnetic recording medium are described. The coating composition comprises a binder, a solvent, and an ?-alumina powder, wherein the ?-alumina powder satisfies the following (a) and (b): (a) when the ?-alumina powder is pressed to obtain a green body and the green body is sintered at 1250° C. under the atmospheric pressure, a relative density of the obtained sintered body is about 80% or more, and (b) a BET specific surface area of the ?-alumina powder is about 10 m2/g or more.

Abstract: Crowing is applied to a side surface of an inner ring which abuts against a side surface of a drive shaft in a radial direction. With this construction, when the two side surfaces abut against each other by a pressing operation of a threadedly-engaged nut at the time of connecting the drive shaft and an inner shaft, a contact pressure distribution of abutting surfaces is made generally uniform, thereby suppressing the occurrence of an edge load. By thus preventing a contact pressure from increasing at part of the abutting surfaces, energy released by a stick-slip phenomenon is reduced, and a sound pressure level of an abnormal sound generated at this time is reduced.

Abstract: A tapered roller bearing includes: an outer race including an outer raceway surface; an inner race including an inner raceway surface and a larger collar surface which is a concave curved surface; and tapered rollers provided between the outer and inner races, each of the tapered rollers including a tapered surface and a larger end surface which is a convex curved surface communicating with the tapered surface and corresponds to the larger collar surface.

Abstract: A method for producing ?-alumina powder is described. The method comprises the steps of removing water from a compound containing the following (1), (2), (3) and (4), and calcining the results: (1) ?-alumina precursor, (2) seed crystal, (3) water, (4) nitrate ion in an amount of from 2.8 to 3.3 mol per mol of aluminum (Al) contained in the ?-alumina precursor and the seed crystal.

Abstract: A method for producing an ?-alumina powder is provided. T method for producing an ?-alumina powder comprising steps of: (1) pulverizing a metal compound having a full width at half maximum (Ho) of a main peak in XRD pattern to obtain a seed crystal having a full width at half maximum (H) of the main peak in XRD pattern in the presence of pulverizing agent, (2) mixing the obtained seed crystal with an aluminum salt, (3) calcining the mixture, and wherein a ratio of H/Ho is 1.06 or more.

Abstract: The present invention provides a method for producing an ?-alumina particle. The method for producing an ?-alumina particle comprises steps of: (1) placing a powdery mixture containing an aluminum salt and a seed crystal under a circumstance at not less than pyrolysis temperature of the aluminum salt, and (2) calcining the resultant.

Abstract: A tapered roller bearing includes: an outer race including an outer raceway surface; an inner race including an inner raceway surface and a larger collar surface which is a concave curved surface; and tapered rollers provided between the outer and inner races, each of the tapered rollers including a tapered surface and a larger end surface which is a convex curved surface communicating with the tapered surface and corresponds to the larger collar surface.

Abstract: A coating composition, a method for producing the coating composition, a coating film and magnetic recording medium are described. The coating composition comprises a binder, a solvent, and an ?-alumina powder, wherein the ?-alumina powder satisfies the following (a) and (b): (a) when the ?-alumina powder is pressed to obtain a green body and the green body is sintered at 1250° C.

Abstract: A method for producing ?-alumina powder is described. The method comprises the steps of removing water from a compound containing the following (1), (2), (3) and (4), and calcining the results: (1) ?-alumina precursor, (2) seed crystal, (3) water, (4) nitrate ion in an amount of from 2.8 to 3.3 mol per mol of aluminum (Al) contained in the ?-alumina precursor and the seed crystal.

Abstract: An &agr;-alumina powder suitably used as an additive to a magnetic recording medium and a method of producing the same are described.

Abstract: A calcined alumina, its production method and fine a alumina powder obtained by using the calcined alumina are described. The calcined alumina has the SET specific surface area of 10 to 20 m2/g, the main crystal phase of &agr; phase, a &thgr; phase not substantially contained, and the average particle size of 0.5 &mgr;m or less. The method for producing the calcined alumina comprising calcining an aluminum-containing substance containing substantially no metal element other than aluminum in an atmosphere having a partial pressure of water vapor of 600 Pa or less. The fine &agr;-alumina powder having a purity of 99.99% or more and a BET specific surface area of 15 m2/g or more, containing substantially no transition alumina, and providing, when calcined at 1250° C. under normal pressure, a sintered body having a relative density of 95% or more.

Abstract: The present invention provide a boehmite in which (i) a crystallite diameter in the direction perpendicular to the plane (020) is about 65 angstrom or longer and (ii) a ratio of a crystallite diameter in the direction perpendicular to the plane (002) to a crystallite diameter in the direction perpendicular to the plane (200) is about 1.8 or more. By using the boehmite as a non-magnetic pigment, a base coat layer for magnetic recording medium having an excellent surface smoothness can be obtained.

Abstract: The present invention is intended to provide a pressed retainer which can meet requirements for operation at high temperature and high speed, can sufficiently retain lubricant, does not allow ceramic balls, if used, to cut away track surfaces and is superior in wear resistance, and also intended to provide a ball bearing comprising the pressed retainer.In order to solve problems, in the pressed retainer, wherein two ring-shaped retainer plates, having ball retaining portions and flat portions at predetermined intervals in the circumferential direction thereof, are combined to face with each other so as to form pockets for accommodating balls, a first spherical concave portion and a second spherical concave portion having a curvature radius smaller than that of the first spherical concave portion are formed at the ball retaining portions, and a nitrided layer is formed on the surfaces of the ring-shaped retainer plates. The ball bearing of the present invention uses the pressed retainer and ceramic balls.

Abstract: A bearing retainer having a body formed of steel has a nitride layer on the body surface. The average particle diameter of a nitride contained in the nitride layer is not more than 1 .mu.m. The surface of the retainer is subjected to fluoriding treatment, and is then subjected to nitriding treatment. The above-mentioned oxide is removed by replacing an oxide on the surface of the retainer with a metal fluoride film by the fluoriding treatment. In the nitriding treatment, a gaseous mixture of gas for nitriding, for example, ammonia gas and hydrogen gas for removing the metal fluoride film is brought into contact with the surface of the retainer. A precise and uniform nitride layer is obtained in a state where the oxide is reliably removed from the surface of the retainer.

Abstract: The present invention provides a dimethylaluminum hydride composition having a low viscosity at normal temperature, comprising dimethylaluminum hydride and at least one Lewis base in an amount of from about 0.001 to about 10% by weight based on dimethylaluminum hydride. The resulting dimethylaluminum hydride composition is superior in handling properties. The present invention also provides a method for reducing the viscosity of dimethylaluminum hydride.

Abstract: There is provided a bearing sealing device capable of substantially completely preventing a leak of grease. A taper end portion of an axial extension of the bearing sealing device has an opposite surface and a rake face that forms a specified rake angle with the opposite surface. The opposite surface forms a narrow passage between the opposite surface and an outer peripheral surface of an inner ring. The narrow passage allows air to pass easily, but it allows grease to hardly pass therethrough. Further, the axial extension includes part of a core metal that extends axially and has its foremost end located axially inside an axial outermost end of the outer peripheral surface of the inner ring. Grease moving axially outwardly on the outer peripheral surface is moved along the rake face of the taper end portion and then guided along a cover portion of the bearing sealing device to an outer ring. The part of the core metal prevents the axial extension from being bent radially outwardly by a centrifugal force.

Abstract: There is provided a bearing sealing device capable of substantially completely preventing a leak of grease. A taper end portion of an axial extension of the bearing sealing device has an opposite surface and a rake face that forms a specified rake angle with the opposite surface. The opposite surface forms a narrow passage between the opposite surface and an outer peripheral surface of an inner ring. The narrow passage allows air to pass easily, but it allows grease to hardly pass therethrough. Further, the axial extension includes part of a core metal that extends axially and has its foremost end located axially inside an axial outermost end of the outer peripheral surface of the inner ring. Grease moving axially outwardly on the outer peripheral surface is moved along the rake face of the taper end portion and then guided along a cover portion of the bearing sealing device to an outer ring. The part of the core metal prevents the axial extension from being bent radially outwardly by a centrifugal force.