Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
2000-05-05
2001-07-24
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C501S127000, C428S403000, C428S404000, C264S623000, C264S172140, C264S172150, C264S173120, C264S173160
Reexamination Certificate
active
06264710
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns alumina-based abrasive grit material; methods of preparing such abrasive grit material; and, products incorporating the abrasive grit material. In general, abrasive grits as described herein have internal stratified or layered structures. The abrasive grits can be made using sol-gel techniques.
BACKGROUND OF THE INVENTION
Abrasive grits or particles have long been employed in abrasive products. These abrasive products include bonded abrasives (e.g., grinding wheels), coated abrasives, and nonwoven abrasives. Preferred abrasive grit is typically tough, hard, and chemically resistant to the workpiece being abraded. A “tough” abrasive grit is generally strong and fracture resistant. A “hard” abrasive grit generally resists yielding or dulling from the forces of grinding. When the abrasive grit does yield or dull, decreased abrading performance typically results.
One common type of aggressive abrasive grit, known as fused alumina, is formed by heating a source of aluminum oxide to a molten state, rapidly cooling and then crushing. This type of abrasive grit is hard, tough, and chemically resistant.
A more recently developed type of abrasive grit is often referred to as alpha alumina-based ceramic abrasive grit. This type of abrasive grit can be made by a sol-gel process, wherein, for example, a dispersion comprising a liquid medium (typically water), alpha alumina monohydrate, and optional additives such as metal oxide precursors (e.g., magnesium nitrate), is dried, crushed, calcined, and then sintered. The resultant ceramic abrasive grit is typically tougher than the fused alumina grit, and typically exhibits superior performance in abrading operations.
Abrasive products containing sol-gel based alpha alumina grits or particles have been in commercial use for up to 15 years. During this time, there have been numerous improvements made to the alumina abrasive grits or particles. Some of these improvements concern modifications to the crystal structure (referred to as the microstructure) of the alpha alumina crystals which form the abrasive grits or particles. The abrasives industry has, in general, been seeking higher performing alumina abrasive particles to incorporate into abrasive articles.
SUMMARY OF THE INVENTION
According to the present invention there is provided alumina-based abrasive grit having internal stratified or layered structure. Generally, at least one internal layer is found in the abrasive grit. Techniques for preparing abrasive grits having multiple internal layers are provided.
The internal layering may comprise alternating layers of two different materials, or multiple layers of more than two types of materials. The layering, in preferred constructions, results from co-extrusion processes. The co-extrusion process can be combined with stratifying or mixing, to achieve still more layers.
In some applications it may be desired to co-extrude two materials, which although prepared differently, may result in somewhat the same microstructure and chemical structure. Additionally, in some instances, advantages may be seen from co-extruding two identical materials, even in situations wherein no difference can be observed between the two structures in the final produce.
General techniques of processing, according to the present invention, comprise co-extruding to form a co-extrudate, with or without a mixing step. The co-extrudate is generally dried and fired to form ceramic product. Typically, during processing, the co-extrudate can be crushed, broken or cut to form either a randomly shaped or a shaped particle, and in some instances sizing will be involved in order to obtain a preferred grade of abrasive grit.
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3M Innovative Properties Company
Allen Gregory D.
Marcheschi Michael
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