Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
1998-04-22
2001-05-08
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C501S012000, C501S095100, C501S127000, C428S373000, C428S378000, C264S623000, C264S172150, C264S173120, C264S173160
Reexamination Certificate
active
06228134
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns alumina-based abrasive grits; methods of preparing such abrasive grits; and products incorporating the abrasive grits. In general, abrasive material as described herein have an internal core structure circumscribed by an external sheath structure. 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, this typically leads to decreased abrading performance.
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 an internal core structure continuously and contiguously circumscribed by an external sheath structure. The abrasive grit having internal and external sheath structures, in preferred constructions, results from co-extrusion processes.
The internal core structure may comprise a single material, two different materials, alternating layers of two different materials, or multiple layers of more than two types of materials. Likewise, the external sheath structure may comprise a single material, two different materials, alternating layers of two different materials, or multiple layers of more than two types of materials. Preferably the internal core structure and the external sheath structure comprise different materials. In some applications it may be desired to co-extrude two materials, which although prepared differently, may result in essentially the same microstructure and chemical structure. Additionally, advantages may be seen from co-extruding two identical materials, although in the final product no difference can be observed between the two structures.
General techniques of processing according to the present invention comprise co-extruding to form a co-extrudate. The co-extrudate is generally dried and fired to form a ceramic product. Typically, during processing, the co-extrudate can be crushed, broken or cut to form either a randonly shaped or a shaped particle. In some instances grading will be involved in order to obtain a preferred grade of abrasive grit.
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3M Innovative Properties Company
Busse Paul W.
Marcheschi Michael
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