Abrasive grain, abrasive articles, and methods of making and...

Details Abrasive grain, abrasive articles, and methods of making and... Abrasive grain, abrasive articles, and methods of making and...

1999-09-28

2001-08-21

Marcheschi, Michael (Department: 1755)

Abrasive tool making process, material, or composition

With inorganic material

Metal or metal oxide

C051S295000, C051S308000, C501S128000, C451S028000

Reexamination Certificate

active

06277161

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to abrasive grain and a method of making abrasive grain. The abrasive grain can be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.
DESCRIPTION OF RELATED ART
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. This new type of alpha alumina abrasive grain had a microstructure made up of very fine alpha alumina crystallites. The grinding performance of the new abrasive grain on metal, as measured, for example, by life of abrasive products made with the grain was dramatically longer than such products made from conventional, fused alumina abrasive grain.
In general, sol gel abrasive grain are typically made by preparing a dispersion or sol comprising water, alumina monohydrate (boehmite), and optionally peptizing agent (e.g., an acid such as nitric acid), 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 (e.g., CeO
2
, Cr
2
O
3
, CoO, Dy
2
O
3
, Er
2
O
3
, Eu
2
O
3
, Fe
2
O
3
, Gd
2
O
3
, HfO
2
, La
2
O
3
, Li
2
O, MgO, MnO, Na
2
O, Nd
2
O
3
, NiO, Pr
2
O
3
, Sm
2
O
3
, SiO
2
, SnO
2
, TiO
2
, Y
2
O
3
, Yb
2
O
3
, ZnO, and ZrO
2
), nucleating agents (e.g., &agr;-Al
2
O
3
, &agr;-Cr
2
O
3
, and &agr;-Fe
2
O
3
) and/or precursors thereof. Such additions are typically made to alter or otherwise modify the physical properties and/or microstructure of the sintered abrasive grain. In addition, or alternatively, such oxide modifiers, nucleating agents, and/or precursors thereof may be impregnated into the dried or calcined material (typically calcined particles). 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. 4,960,441 (Pellow 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. 5,547,479 (Conwell et al.), U.S. Pat. No. 5,498,269 (Larmie), U.S. Pat. No. 5,551,963 (Larmie), U.S. Pat. No. 5,725,162 (Garg et al.), and U.S. Pat. No. 5,776,214 (Wood).
Over the past fifteen years sintered alumina abrasive grain, in particular sol gel-derived alpha alumina-based sintered abrasive grain, have been used in a wide variety of abrasive products (e.g., bonded abrasives, coated abrasives, and abrasive brushes) and abrading applications, including both low and high pressure grinding applications. For example sol gel-derived abrasive grain have been incorporated into resin bonded grinding wheels, and have been found to be particularly useful in high pressure, high stock removal grinding applications. Such abrasive grain have been used in vitrified grinding wheels for the precision grinding of camshafts. Sol gel-derived abrasive grain have also been incorporated into medium grade coated abrasive products that are used to sand wood cabinet panels. In addition, coated abrasive discs that include sol gel-derived abrasive grain are used under relatively light pressure to abrade painted automotive parts.
For some higher pressure grinding applications, it is preferred that the sintered alumina abrasive grain be relatively tough to withstand the high grinding forces. Such increased toughness may be achieved through the addition of various metal oxides to the alumina crystal structure. Alternatively, in some lower pressure grinding applications, it is preferred that the sintered alumina abrasive grain be more friable so that the abrasive grain can “breakdown” during grinding. In order to achieve the optimum grinding performance under these wide ranges of grinding conditions, a variety of sintered alpha alumina abrasive grains have been developed and commercialized.
Although there are a number of commercially available sintered alumina abrasive grains, sintered alumina abrasive grain that can provide desirable grinding or abrading characteristics (e.g., long life, high metal removal rates, and desired finish) under certain grinding conditions (e.g., under relatively high grinding pressure or relatively low grinding pressures) what is desired is an abrasive grain that has desirable grinding or abrading characteristics under a relatively wide range of grinding pressure (e.g., both high and low grinding pressures). The availability of such an abrasive grain is advantageous, for example, because it reduces, or perhaps in some cases, eliminates the need for multiple inventories of abrasive grain or abrasive products. Further, for example, the availability of abrasive products incorporating such an abrasive grain reduces or eliminates the need for the end user to change the abrasive product because of a change in grinding conditions.
SUMMARY OF THE INVENTION
In one aspect, the present invention surprisingly provides sintered alpha alumina-based abrasive grain comprising SiO
2
and ZrO
2
(typically at least 0.1 percent (preferably, at least 0.2, 0.25, 0.3, or even 0.5 percent) by weight of each of SiO
2
and ZrO
2
, based on the total metal oxide content of the abrasive grain), wherein the alpha alumina of the abrasive grain has an average crystallite size of less than 1 (preferably, less than 0.8, 0.7 0.6, 0.5, 0.4, or even 0.3) micrometer, and wherein the ZrO
2
that is present as crystalline zirconia has an average crystallite size of less than 0.25 micrometer. Typically, at least a majority of the alpha alumina was nucleated with a nucleating agent. Preferably the average crystallite size of the alpha alumina is less than 0.75 micrometer, more preferably, less than 0.5 micrometer, and even more preferably, less than 0.3 micrometer.
One preferred sintered alpha alumina-based abrasive grain according to the present invention comprises at least 0.1 percent (preferably, at least 0.2, 0.25, 0.3, or even 0.5 percent; more preferably at least 1 percent; even more preferably in the range from 1 to 3 percent) by weight SiO
2
and at least 0.1 percent (preferably, at least 0.2, 0.25, 0.3, or even 0.5 percent; more preferably at least 1 percent; even more preferably in the range from 1 to 14 percent, or even from 4 to 14 percent) by weight ZrO
2
, based on the total metal oxide content of the abrasive grain), wherein the alpha alumina of the abrasive grain has an average crystallite size of less than 1 micrometer, and wherein the ZrO
2
that is present as crystalline zirconia has an average crystallite size of less than 0.25 micrometer.
In another aspect, the present invention provides a method of abrading a surface, the method comprising:
contacting a plurality of abrasive grain with a surface (e.g., a surface of a substrate (e.g., a titanium substrate or a steel substrate such as carbon steel (e.g., a 1018 mild steel substrate), a stainless steel (e.g., 304 stainless steel) substrate, or a tool steel (e.g., 4140 steel and 4150 steel) substrate) at a contact pressure of at least 1 kg/cm
2
, in some cases, preferably, 2 kg/cm
2
, 3.5 kg/cm
2
, 5 kg/cm
2
, 7 kg/cm
2
, 10 kg/cm
2
, 15 kg/cm
2
, and 20 kg/cm
2
, wherein at least a portion of the abrasive grain is alpha alumina-based abrasive grain according to the present invention; and
moving at least of one the plurality of abrasive grain or the surface relative to the other to abrade at least a portion of the surface with the abrasive grain. Preferably, at least 75 percent (or even 100 percent) by weight of the abra

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