Alloys or metallic compositions – Ferrous – Nine percent or more chromium containing
Reexamination Certificate
2000-05-19
2002-03-26
Yee, Deborah (Department: 1742)
Alloys or metallic compositions
Ferrous
Nine percent or more chromium containing
C420S073000, C420S074000, C148S325000, C148S337000
Reexamination Certificate
active
06361740
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composition of matter comprising an alloy having a high vibrational damping capacity and, in another aspect, to a disk drive actuator suspension arm comprised of the alloy.
2. Prior Art
At the present time, most computer systems store data on a disk drive. A disk drive includes inter alia a rotatable disk, and an actuator that moves a transducer over the surface of the disk. The transducer element is normally disposed within a small ceramic body affixed to a pivotally mounted load beam. In operation, in order for the transducer to sustain a transducing relationship with the disk, the transducer “flys” over the surface of the disk at an elevation of less than 0.001 mm. Electronic circuitry and servo-motor means enable the transducer to write data on, and read data from, a selected portion of the disk surface.
The high rotational speed of the disk creates fluid turbulence (or windage) in the volume of air adjacent thereto. This turbulence may impart a force upon the loadbeam, driving a resonant response. During operation, the loadbeam may be subjected to sudden acceleration due to actuator arm contact with travel-limiting “crash” stops. This contact may also initiate a resonant response in the loadbeam. In addition, the forces of acceleration, accompanying normal disk drive data-seeking operations, may generate a resonant response in the loadbeam. Non-repeatable runout (NRR) of the disk, coupled with the loadbeam's attempt to follow these eccentricities, may result in a resonant response. Disk drives sometimes operate in hazardous environments that may include being dropped from several inches. Such shock loads, when experienced during disk operation, may drive a resonant response in the loadbeam. Notwithstanding these excitations, the load beam, and the transducer attached thereto, must maintain the transducing relationship between the transducer and the surface of the disk at all times. If the resonant vibrations are not damped promptly and effectively, the elevational excursions of the load beam may cause damage to the surface of the disk, the transducer and/or the load beam, or the lateral excursions of the load beam may cause data track mis-registration and read-write errors. It is, therefore, desirable to provide a load beam, mounting arm and/or flexure having a high damping capacity.
Material damping occurs when repetitive deformation (vibration) of a material is dissipated through internal energy losses, usually in the form of heat. There are two basic types of damping behavior: inelastic and hysteretic. Inelastic damping occurs when there is a lag between the application of a stress and the resulting equilibrium value of the strain that is frequency and temperature dependent. Mechanisms that give rise to this type of damping, in metals, include the interaction of specific point defects with other point defects or dislocations, precipitation phenomena, and ordering effects.
Hysteretic damping, as used herein, is defined as frequency independent loss. Hysteretic damping materials exhibit a stress-strain behavior on loading that does not retrace the behavior on unloading. The area difference between the loading and unloading curves is then proportional to the energy loss for the material. While hysteretic damping is independent of frequency it is dependent on the applied stress (or strain amplitude). Materials that exhibit hysteretic damping are the preferred materials for applications where noise and vibration reduction are desired. Hysteretic damping occurs through boundary motion, for example, the motion of magnetic domains in ferromagnetic materials (magnetoelastic behavior) and the motion of twin boundaries (thermoelastic behavior).
The damping capacities of various metals are shown in FIG.
1
. Exemplary of materials having excellent damping capacity are “shape memory” alloys such as NiTi (Nitinols), cast Mn—Cu alloys (Sonotron), and polymer matrix composites. Fe-based materials, other than pure Fe, exhibiting the highest specific damping capacity are Fe—Cr alloys, cast irons, and ferritic stainless steels. Fe—Cr—Al, ferritic stainless alloys (known as “Silentalloy”) are reported to be high damping structural materials and were developed for use in corrosive environments. This type of alloy would would be ideal for fabricating a load beam for a disk drive actuator, meeting almost all requirements except for the fact that these materials are ferritic and thus, ferromagnetic. There is, therefore, a continuing need for a high damping, substantially non-magnetic material for use in disk drive actuator assemblies.
SUMMARY OF THE INVENTION
A high-damping, corrosion resistant and substantially non-magnetic material for a disk drive suspension arm and load beam having high damping properties is disclosed. A disk drive assembly includes a disk having a readable and writeable surface, a motor operable for rotating the disk, and an actuator assembly that includes a transducer mounted on a load beam. The actuator assembly is operable for positioning the transducer in transducing relationship with the surface of the disk.
The high rotational speed of the disk creates fluid turbulence (or windage) in the volume of air adjacent thereto. Such turbulence may impart a force upon the loadbeam, driving a resonant response. During operation, the loadbeam may be subjected to sudden acceleration due to actuator arm contact with travel- limiting “crash” stops. This contact may also initiate a resonant response in the loadbeam. The forces of acceleration resulting from normal disk drive data-seeking operations may generate a resonant response in the loadbeam. Non-repeatable runout (NRR) of the disk, coupled with the loadbeam's attempt to follow these eccentricities, may result in a resonant response within the loadbeam. Disk drives occasionally operate in hazardous environments that mayinclude being dropped from several inches. Such operating shock loads may drive a resonant response in the loadbeam. Notwithstanding these excitations, the load beam, and the transducer attached thereto, must maintain the transducing relationship between the transducer and the surface of the disk at all times. If the resonant vibrations are not damped promptly and effectively, the elevational excursions of the load beam may cause damage to the surface of the disk, the transducer and/or the load beam or result in data track mis-registration and read-write errors. It is, therefore, desirable to provide a load beam, or any similar flexure used in a disk drive, having a high damping capacity.
The present invention discloses alloy compositions of the form (14-20)Mn, (10-13)Cr, (0-6)Si, (4-10)Ni, (
0-6
)Co, and (
0-0.2
)N, the components being present in the range of percentages indicated with the balance being Fe. A preferred embodiment of the present invention is an alloy consisting essentially of Fe-15Mn-12Cr-3Co-3Ni-0.1N. The alloy has stainless steel-type properties and exhibits high damping characteristics. The alloy, which has both an austentitic and a ferrite phase, can be melted, cast and rolled into sheets. Disk drive load beams cut from the alloy sheet exhibit higher vibrational damping than materials currently used in the art.
It is an overall object of the invention to provide a composition of matter that is substantially non-magnetic and can be shaped to form a body characterized by, in combination, a high strength to weight ratio and a high vibrational damping capacity.
It is a particular object of the invention to provide an alloy which is suitable for fabricating a suspension mounting arm, loadbeam and/or flexure for a computer disk drive which meets the requirements demanded by the application. An exemplary list of typical specifications setting forth the requirements for a material suitable for use in manufacturing a suspension arm include:
1. be capable of being welded to 302/304 stainless steel;
2. have a high a strength to weight ratio;
3. be substantially non-magnetic;
4. be corrosion resistant;
Noebe Ronald
Zamanzadeh Mehrooz
Intri-Plex Technologies, Inc.
Petit Michael G.
Yee Deborah
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