Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
1997-01-09
2001-03-27
Jones, Deborah (Department: 1108)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S293000
Reexamination Certificate
active
06206942
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for making alpha alumna-based abrasive grain. The abrasive grain can be incorporated into abrasive products such as coated abrasives, bonded abrasives, and non-woven abrasives.
DESCRIPTION OF RELATED ART
Fused alumina abrasive grain have been utilized in abrasive applications for close to one hundred years. Such abrasive grain are made by heating an alumina source above its melting point, quenching, and then crushing to form alumina abrasive grain or particles.
In the early 1980's a new and substantially improved type of alumina abrasive grain, commonly referred to as “sol gel” or “sol gel-derived” abrasive grain, was commercialized. In general, sol gel abrasive grain are typically made by preparing a dispersion or sol comprising water and alumina monohydrate (boehmite), gelling the dispersion, drying the gelled dispersion, crushing the dried dispersion into particles, calcining the particles to remove volatiles, and sintering the calcined particles at a temperature below the melting point of alumina. Frequently, the dispersion also includes one or more oxide modifiers, nucleating agents, and/or precursors thereof. Further details regarding sol gel abrasive grain, including methods for making them, can be found, for example, in U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No. 5,011,508 (Wald et al.), U.S. Pat. No. 5,090,968 (Pellow), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,227,104 (Bauer), U.S. Pat. No. 5,366,523 (Rowenhorst et al.), U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat. No. 5,498,269 (Larmie), and U.S. Pat. No. 5,551,963 (Larmie).
Some methods for making sol gel alpha alumina-based abrasive grain utilize an impregnation step wherein the dried or calcined material (i.e., ceramic precursor material) is impregnated with a composition that includes metal oxide, metal oxide precursor, and/or combinations thereof, and a liquid medium, to provide an impregnated abrasive grain precursor. After the impregnation step, the impregnated ceramic precursor material is typically dried and then calcined (generally, this is a second calcining step) to form an impregnated, calcined ceramic precursor material, which is in turn sintered (see, e.g., U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No. 5,164,348 (Wood), U.S. Pat. No. 5,213,591 (Celikkaya et al.) and U.S. Pat. No. 5,011,508 (Wald et al.)).
Typically, conventional sol gel-derived alpha alumina-based precursor material does not split when impregnated by a liquid or solution. Although not wanting to be bound by theory, it is believed such cracking does not occur for one or more reasons. First, a conventional sol gel-derived alpha alumina-based abrasive grain precursor generally contains cracks generated during drying, crushing, and/or calcining steps. Such cracks are believed to provide a path of escape during impregnation for entrapped air, thereby preventing sufficient buildup of air pressure within the particle to cause cracking. Second, as the size of the abrasive grain precursor material is reduced, for example, by crushing, the volume of air which may be entrapped during impregnation is also reduced (i.e., smaller particles of the precursor material have proportionately smaller volumes of air therein), thereby not providing sufficient air, even if some or all of it were entrapped, to cause cracking or splitting of the abrasive grain precursor. However, larger abrasive grain precursor, if impregnated, may split when impregnated.
In another aspect, a common, optional step in conventional sol gel processes for making abrasive grain is crushing the dried gel (see, e.g., U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,881,951 (Wood et al.), and U.S. Pat. No. 5,139,978 (Wood)). Typically, the crushed material does not provide a single grade, or size range, of dried particles, but rather a large distribution of particle sizes. Particles less than about 60 micrometers in size are commonly referred to as “fines”. In some instances, these fines are too small to be economically further processed into sintered abrasive particles using the same techniques (typically rotary calcining and sintering) used to further process the larger sized dried particles (see, e.g., U.S. Pat. No. 5,489,204 (Conwell et al.)). In many instances, these fines are sent to landfills or stored until a use for them can be found.
In an effort to eliminate the dried fines, attempts have been made to incorporate them back into the sol gel process (i.e., to recycle them into new dried particles, and ultimately into sintered abrasive grain). For example, U.S. Pat. No. 4,314,827 (Leitheiser et al.), the disclosure of which is incorporated herein by reference, teaches redispersing the fines in a sol or dispersion. A drop in abrading performance and other properties (e.g., density and hardness), however is experienced when too many fines are recycled. Further, in general, recycled material from sols or dispersions containing alpha alumina seeds typically exhibits a significantly lower percent decrease in abrading performance than does recycled material from sols or dispersions free of alpha alumina or alpha ferric oxide seeds. One need in the art is a process wherein such recycled material can be used to make abrasive grain having good abrading performance characteristics.
SUMMARY OF THE INVENTION
The present invention provides a method for making alpha alumina-based ceramic abrasive grains, said method comprising the steps of:
(a) impregnating an impregnation composition comprising a liquid (preferably, water) into a porous, calcined, elongated particle (typically a plurality of particles) of alpha alumina-based precursor having a longitudinal axis and interconnected internal pores, the particle being capable of receiving the liquid and upon impregnation fracturing generally in the direction of the longitudinal axis into smaller elongate particles to cause conchoidal fracture of the elongated particle into the smaller elongate particles; and
(b) converting the smaller elongate particles to alpha alumina-based ceramic abrasive grain.
Optionally, the impregnation composition comprises a mixture comprising the liquid and at least one of a metal oxide(s) or a precursor(s) thereof; and is preparable by (and is typically prepared by) combining components comprising the liquid with at least one of a metal oxide(s) or a precursor(s) thereof.
The porous, calcined, elongated particle(s) is preferably provided by converting at least a portion of a dispersion comprising a mixture comprising liquid (preferably, water), peptizing agent (typically an acid), and boehmite into the porous, calcined, elongated particle(s); the dispersion being preparable by (and typically prepared by) combining components comprising liquid, peptizing agent, and boehmite. Optionally, the dispersion contains, on a theoretical metal oxide basis, less than 0.05 percent by weight of alpha alumina seeds or nucleating agent or nucleating material, based on the total theoretical metal oxide content of the dispersion, wherein it is understood that “less than 0.05 percent by weight of alpha alumina seeds or nucleating agent or nucleating material” includes zero percent by weight alpha alumina seeds, nucleating agent, or nucleating material, respectively.
Preferably, the dispersion is compacted (preferably, at a pressure of at least 3.5×10
4
kg/m
2
(50 lb/in
2
); more preferably, at least 1.05×10
5
kg/m
2
or even at least 1.4×10
5
kg/m
2
) prior to converting it to alpha alumina-based ceramic precursor material. Compacting the dispersion typically increases the density and significantly increases the abrading performance of the resulting abrasive grain in one or more abrading app
Allen Gregory D.
Jones Deborah
Minnesota & Mining Manufacturing Company
LandOfFree
Method for making abrasive grain using impregnation, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for making abrasive grain using impregnation, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for making abrasive grain using impregnation, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2439130