Abrading – Flexible-member tool – per se – Laminate
Reexamination Certificate
1999-07-09
2001-11-20
Banks, Derris H. (Department: 3723)
Abrading
Flexible-member tool, per se
Laminate
C451S526000, C451S539000
Reexamination Certificate
active
06319108
ABSTRACT:
FIELD
This invention pertains to a metal bond abrasive article comprising a backing having affixed thereto a plurality of porous ceramic abrasive composites and to methods of using same to abrade a workpiece.
BACKGROUND
The use of electrodeposited metals to secure abrasive particles to a substrate is a well established practice in the abrasive industry. Conventional electroplating of abrasives involves depositing metal onto a substrate until a desired thickness is achieved. Abrasive particles such as diamond or cubic boron nitride are then introduced into the plating bath and are deposited on the plated metal. Further electrodeposition of metal affixes the abrasive particles to the substrate. As a result of this electrodeposition process a single layer of abrasive particles are affixed to the substrate by the electrodeposited metal coating.
One disadvantage associated with such abrasive articles is that the single layer of abrasive particles may be dulled, clogged with swarf and/or dislodged from the metal bond coat during an abrading process. As a result, the cutting efficiency of the abrasive article may be substantially deteriorated. A second disadvantage associated with such abrasive articles relates to the range of abrasive particles that can be utilized in this type of an abrasive article. Specifically, deposition of metal is not favored for affixing very fine grade abrasive particles (e.g., less than about 6 &mgr;m) to a substrate because the metal thickness would substantially engulf the very fine grade abrasive particles. In such instances, the metal coating itself may contact the workpiece during the abrading process which may result in uncontrolled scratching of the workpiece.
One potential application for metal bond abrasive articles is in the finishing of magnetic memory disc substrates, for example, ceramics or glass ceramic substrates. In order to produce an acceptable magnetic memory disc, the memory disc substrate must have precisely controlled dimensions and a precisely controlled surface finish. Typically, dimensioning and imparting the desired surface finish to memory disc substrates has involved a multi-step process using loose abrasive slurries. In the first step of the process, the memory disc substrates are dimensioned such that they have the desired thickness and thickness uniformity. After dimensioning, the discs may then be textured to provide the desired surface finish.
Although loose abrasive slurries are widely used in these process, loose abrasive slurries have many disadvantages associated with them. These disadvantages include, for example, the inconvenience of handling the required large volumes of the slurry, the required agitation to prevent settling of the abrasive particles and to assure a uniform concentration of abrasive particles at the polishing interface, and the need for additional equipment to prepare, handle, and dispose of (or recover and recycle) the loose abrasive slurry. Additionally, the slurry itself must be periodically analyzed to assure its quality and dispersion stability. Furthermore, pump heads, valves, feed lines, grinding laps, and other parts of the slurry supply equipment which contact the loose abrasive slurry eventually show undesirable wear. Further, the processes which use the slurry are usually very untidy because the loose abrasive slurry, which is a viscous liquid, splatters easily and is difficult to contain.
In view of the foregoing, there is a need for an abrasive article having an increased useful life over conventional metal bond abrasive articles. Preferably, such an abrasive article will be suitable in a wide range of abrasive particle grades including very fine grades and may be suitable as a replacement for loose abrasive slurries to dimension and/or texture glass ceramic memory discs.
SUMMARY
The present invention provides a metal bond abrasive article that provides a consistent, high cut rate on various workpieces, for example, memory disc substrates, while providing a very fine surface finish (e.g., 25 Å or less). The abrasive article comprises a rigid backing having a first major surface and a second major surface and a plurality of ceramic abrasive composites affixed to at least one major surface of the backing by at least one metal coating.
The ceramic abrasive composites each comprise a plurality of abrasive particles distributed throughout a porous ceramic matrix. The ceramic abrasive composites preferably erode during the abrading process thereby releasing used or dull abrasive particles from the abrasive composite and presenting fresh abrasive particles to the workpiece. In a preferred embodiment the abrasive composites comprise about 10-90 parts be weight abrasive particles, 90-10 parts by weight ceramic matrix and have a pore volume ranging from about 4%-70%. Preferably, the abrasive particles have a size ranging from about 0.05-100 &mgr;m and include diamond, cubic boron nitride, fused aluminum oxide, ceramic aluminum oxide, heated treated aluminum oxide, silicon carbide, boron carbide, alumina zirconia, iron oxide, ceria, garnet, and mixtures thereof Most preferably, the abrasive particles comprise diamond.
The ceramic abrasive composites are affixed to the backing by at least one metal coating, preferably a series of metal coatings. The metal coating(s) are preferably applied to the backing using metal electrodeposition techniques. Preferred metals for the metal coating(s) include, for example, nickel, copper, brass, bronze, steel and alloys thereof. In a preferred embodiment, the metal coating(s) have a combined thickness ranging from about 5%-50%, more preferably 10%-30% of the height of the ceramic abrasive composites in the abrasive article. Optionally, an organic size coating may be applied over the metal coating(s) and the ceramic abrasive composites. Preferred organic size coatings comprise phenolic resins, epoxy resins, aminoplast resins, urethane resins, acrylate resins isocyanurate resins, acrylated isocyanurate resins, urea-formaldehyde resins, acrylated epoxy resins, acrylated urethane resins or combinations thereof and may be dried, thermally cured or cured by exposure to radiation, for example, ultraviolet light.
Preferred backing materials for abrasive articles of the present invention are rigid and smooth and are suitable for electrodeposition (i.e., electroplating) of a metal coating. Preferred rigid backings have a modulus of rigidity of about 1×10
6
lb/in
2
(7×10
4
kg/cm
2
) or greater, more preferably about 10×10
6
lb/in
2
(7×10
5
kg/cm
2
) or greater. Examples of backing materials include, for example, metals, metal alloys, metal-matrix composites, metalized plastics or polymer matrix reinforced composites. More preferably, the backing is a bronze sheet, most preferably having a thickness ranging from about 0.3-10 mm.
The present invention also provides a method of abrading a workpiece using an abrasive article of the present invention, the method comprising the steps of:
(a) contacting a surface of a workpiece with an abrasive article of the present invention such that the ceramic abrasive composites of the abrasive article contact the surface of the workpiece;
(b) applying a liquid at an interface between the workpiece and the abrasive article; and
(c) moving the workpiece and the abrasive article relative to one another such that the abrasive article abrades the surface of the workpiece to provide a surface roughness.
Preferred lubricants to be applied at the interface between the abrasive article and the workpiece include, for example, mixtures of glycerol and water, more preferably a 20% weight solution of glycerol in water. In a preferred method, the abrasive article and the workpiece are contacted at a pressure ranging from about 0.5-45 g/mm
2
.
In another preferred method, the abrasive article is in the form of a disc having an imaginary center axis perpendicular to the backing of the abrasive article. In this method, step (c) is conducted by spinning the disc around the center axis. Optionally, the workpiece may also mo
Adefris Negus B.
Erickson Carl P.
3M Innovative Properties Company
Banks Derris H.
Pribnow Scott R.
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