CA1195848A - Superior high sodium and calcium sol gel abrasive and process for its production - Google Patents
Superior high sodium and calcium sol gel abrasive and process for its productionInfo
- Publication number
- CA1195848A CA1195848A CA000403735A CA403735A CA1195848A CA 1195848 A CA1195848 A CA 1195848A CA 000403735 A CA000403735 A CA 000403735A CA 403735 A CA403735 A CA 403735A CA 1195848 A CA1195848 A CA 1195848A
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- Canada
- Prior art keywords
- grains
- dispersion
- weight percent
- calcium
- sintering
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
- B24D11/00—Constructional features of flexible abrasive materials; Special features in the manufacture of such materials
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
- B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
- B24D3/02—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent
- B24D3/04—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic
- B24D3/14—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic ceramic, i.e. vitrified bondings
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/021—After-treatment of oxides or hydroxides
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/44—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water
- C01F7/441—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water by calcination
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K3/00—Materials not provided for elsewhere
- C09K3/14—Anti-slip materials; Abrasives
- C09K3/1409—Abrasive particles per se
- C09K3/1418—Abrasive particles per se obtained by division of a mass agglomerated by sintering
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/21—Attrition-index or crushing strength of granulates
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Inorganic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Materials Engineering (AREA)
- Ceramic Engineering (AREA)
- Polishing Bodies And Polishing Tools (AREA)
Abstract
SUPERIOR HIGH SODIUM AND CALCIUM SOL GEL ABRASIVE
AND PROCESS FOR ITS PRODUCTION
ABSTRACT
A process for forming an abrasive grain from a sol gel which contains aluminum oxide monohydrate, a dissolved metal con-taining sintering aid and from above about .05 to about 1.8 weight percent sodium plus calcium, provided that the weight per-cent calcium is from 0 to about 1.8 and the weight percent sodium is from 0 to about .4. The high sodium and calcium is permitted due to rapid heating of the sol gel after drying through a tem-perature range of from below about 800°C to above about 1200°C, prior to sintering the dried gel at a temperature above 1200°C.
A grain made by the process and coated, bonded and non-woven abrasive articles comprising the grain.
AND PROCESS FOR ITS PRODUCTION
ABSTRACT
A process for forming an abrasive grain from a sol gel which contains aluminum oxide monohydrate, a dissolved metal con-taining sintering aid and from above about .05 to about 1.8 weight percent sodium plus calcium, provided that the weight per-cent calcium is from 0 to about 1.8 and the weight percent sodium is from 0 to about .4. The high sodium and calcium is permitted due to rapid heating of the sol gel after drying through a tem-perature range of from below about 800°C to above about 1200°C, prior to sintering the dried gel at a temperature above 1200°C.
A grain made by the process and coated, bonded and non-woven abrasive articles comprising the grain.
Description
~s~
1 SUPERIOR HIGH SODIUM ~ND C~LCIUM SOL GEL ABRA5IVE
AND PROCESS FOR ITS PRODUCTION
TECHNICAL FIELD
This invention relates o abrasive grains and mor@ par-ticularly relates to a sintered type of abrasive grain.
BACKGROUND ART
In the prior art, abrasive grains, especially abrasive grains comprising metal oxldes su~h as alumina, were tradi-tionally made by fusion of the oxide ~ollowed by eru~hing the cooled ~used oxide to ~orm the abrasive grain~
More recently, abrasive srains have been manufactured by sintering the metal oxide, such as alumina. Such grain~O
while wearin~ reasonably well, still do not wear as long as desirable and in addition, do not cut a~ rapidly as de~irable.
It is known that ceramic materials whieh may be in the for~ of ab~asive products can be prepared b~ binding cera~ic oxide particles together by using a mineral colloidal gel ~see U.S~ Patent 2,455,358). It is also known that cvlloidal disper-~9S~34~
1 sions can be gelled, dried and calcined to form porous ceramic materials tsee eOg., U.S. Patent 4,181,532~.
It has also been known that free flowing spheres of pure or mixed oxides could be made by dispersing an oxide hydrate followed by forming a gel in the shape of spheres followed by sintering (see "Application of Sol-Gel Processes ts Industrial Oxides", January 13, 1968, Chemistry and Industry3.
It has also been known by others in the United States, at least as early as lg71, that such particles in spherical or 1~ even angular shapes could be used as abrasives. Such prior knowledge by others in the United States is evidenced by a report from the United Ringdom Atomic Energy Authority at Harwell, England, to Carborundum Company, Ltd. and subsequently to several personnel at The Carborundum Company in the United States.
Recently, U.S. Patent No. 4,314,827 issued for a non-fused aluminum oxide-based abrasive mineral, a process for its production and abrasive products comprising the abrasive mineral.
U.S. Patent No. 4,314t827 generally discloses that an abrasive mineral having randomly oriented crystallites with diameters on the order of 3000 Angstroms or less can be made by gelling a colloidal dispersion or hydrosol of alumina and a modifying component, followed by firing the g21. The disclosure makes it clear that the mineral must be free (less than about 0.05 total weight percent) of calcium and alkali metal. Due to this requirement, complex purification processes must be used when calcium and alkali metal are present, as they often arel in the alumina or modifying component. Calcium, for example, is i ~s~
1 usually present in commercial water supplies and in magnesium containing modifying components unless costly and complicated purification steps are used to remove the calcium. Similarly, sodium i5 commonly present in many aluminas unless removed by additional purifica~ion steps. There is no suggestion in the U.S. patent of any process which would permit the presence of calcium or alkali metal and no process was actually used with high calcium or alkali metal which inherently permitted the presence of high calcium or alkali metal~
DISCLOSURE OF THE INVENTION
In accordance with the present invention, a process is provided for forming ceramic particles from a gelled dispersion ~sol gel~, by drying and sintering the gel. The particles of the invention may be used for any suitable purposeO Such particles may be used in any application where temperature resistance, strength, hardness~ wear resistance and inertness are desirable.
Such particles may, for example, be used as fillers, in aggregates, in distillation columns or due to the surface porosity of some of such particles t may be used as catalyst supports. The most common use for such particles is as abrasives. Such par~icles will therefore be referred to herein as abrasives, although it is to be understood that the term abrasive particle or abrasive grain is intended to include such particles regardless of their intended end use~
Even though the abrasive grain product obtained by the process of this invention usually contains greater than about 0.05 weight percent sodium plus calcium, it is greatly superior to traditional fused alumina abrasive. High sodium and calcium 3~
~ ~s~
1 in the grain is permitted due to rapid heating of the dried sol gel through a ~ritical temperature range of from below about 800C to above about 1200C. The grain is then sintered a~ a temperature above about 1200~C.
The preferred process comprises preparing a dispersion comprising from about 2 to about 60 weight percent aluminum o~ide monohydrate; a dissolved or dispersed metal containing sintering aid in an atomic ratio of metal to aluminum of from 1:2 to 1:35, preferably from 1:7 to 1:25; and from above about 0,05 to about lo 1.8 percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion.
The weight percent calcium plus the weight percent sodium is preferably less than 0.6, and more preferably less than 0.15. The weight percent calcium can range from 0 to about 1.8 and the weight percent sodium can range from about 0 to about 0.4. The weight percent calcium is preferably from 0 to about 0.6 and more preferably from 0 to about 0.15 and the weight percent sodium is preferably from 0 to about 0.25 and more preferably from 0 to about O~lo After the dispersion is prepared, it is gelled and dried at a temperature below the frothing temperature of the gel to remove free water. Any suitable drying method known to those skilled in the art may be used. "Drying" as used herein means dewatering by any method including solvent extraction. The dried solid is then crushed to form grains. The grains are then usually heated to between about 500 and 800C. The grains are then rapidly heated to above about 1200C in less than 10 and preferably less than 5 minutes. The grains then continue to be ~9x~
1 heated at a sintering temperature between about 1200C and about 1650C for a suficient sintering time to sinter the grains to a density above about 85% of theoretical density, at leas~ a por-tion of the heating at sintering temperature preferably occurring above 1300C.
The resulting grain is a sintered sol gel abrasive which has a combined sustained cutting rate and wear resistance against carbon steel which is substantially better than prior art fused alumina grain, and which is comparable to prior art sin-tered sol gel abrasive grains which require low sodium and lowcalcium (less than about 0.05 weight percent) as described in U.
SO Patent No~ 4,314,827. "Substantially better" means a relative cutting performance at least 1.5 times better and usually at least two times better.
The invention also includes bonded, coated and nonwoven abrasive articles comprising the novel grain. For example, not only do coated abrasives manufactured from the preferred abrasive grain of the invention continue to have a high cutting rate until the grain is worn from the backing~ but the total quantity of material cut by the abrasive article is superior to most prior art grains.
BEST MODE FOR CARRYING OUT THE lNv~ ION
In accordance with the process of the invention, the grain is prepared from a liquid (preferably water~ dispersion comprising from about 2 to about 60, usually from about 10 to about 40 weight percent aluminum oxide monohydrate (AlOOH~; a dissolved metal containing sintering aid at an a~omic ratio of metal in the sintering aid to aluminum of from 1:2 to 1:35; and ~L95~
1 up to about 1.8 and usually from above about 0.05 to about 1.8 percent combined alkali metal (espPcially sodium) and calcium by weight of dispersed and dissolved solids in ~he dispersion.
The weight percent calcium plus the weigh~ percent sodium is preferably less ~han 0.6, and more preferably less than .15. The weight percent calcium can range from 0 to about 1.8 and the weigh~ percent sodium can range from about 0 to about .4.
The weight percent calcium is preerably from 0 to about 0.6 and more preferably from 0 to about 0.1~ and the weight percent lo sodium is preferably from 0 to about .25 and more preferably from 0 to about .1~
The quantity of aluminum oxide monohydrate in the dispersion is usually from about 10 to about 40 and preferably from about 15 to about 35 percent by weight of the dispersion.
Aluminum oxide monohydrate as used herein is intended to include aluminum oxide hydrates having the stochiometric formula ~(A1203-XH20) where x is 0.5 to 3. Aluminum oxide monohydrate is also known as boehmite. Aluminum oxide monohydrate, as used herein, is also intended to include~ without limitation, pseudo boehmite.
In general, all solids in the dispersion are preferably dissolved or in colloidal form. The dispersion is formed by any suitable means which may simply be mixing of ~he aluminum oxide monohydrate with water. The liquid is almost always water but may be another liquid such as low molecular weight alcohoI. Any suitable mixing apparatus may be used including both high and low shear mixers. Dispersing aids such as acid are frequently employed. For example, from about 0~02 to 0.25 and preferably ~ 1~5~34~
1 0.05 to about 0.15 mole of HNO3 or other volatile mineral acid per mole of aluminum oxi~e monohydrate greatly aids dispersion.
"Volatile mineral acid" means an acid which will vaporize from the dispersion, gel or dried gel at a temperature below sintering temperature or all of whose residues will either so vaporize or form a part of an oxide within the finished grain. Examples of such acids are nitric, hydrochloric, acetic and formic acids.
The solids in the finished dispersion may comprise up to 50 weight percent of additional ingredients other than alumi-lo num oxide monohydrate, preferably compounds such as silica,magnesia, chromia and titanium dioxide in colloidal or dissolved form, or precursors of such compounds in colloidal or dissolved form.
The dissolved or dispersed mQtal containing sintering aid is added to the dispersion in an atomic ratio of metal to aluminum of from 1:2 to 1:35 and preferably at a ratio of rom 1:7 to 1-25. The sintering aid is a dispersible or scluble metal oxide or metal oxide precursor, i.e., a compound which will form a metal oxide during drying, calcining or sintering. In general, the sintering aid is usually a precursor of magnesium oxide, zinc oxide, cobalt oxide or nickel oxide and is therefore, when the liquid is water, a water soluble or dispersible compound of magnesium, zinc, nickel or cobaltc Specific examples of such precursors are the nitrates and chlorides of thos~ metals. The nitrates of those metals and especially of magnesium are par-ticularly preferred. The sintering aid may be prepared in situ, for example by adding magnesium oxide or hydroxide to an aqueous solution of inorganic acid such as hydrochloric or nitric acids 5~
to form a water soluble salt of magnesium. The sintering aid is usually a water soluble salt but may be a water soluble base.
The sodium and calcium in the dispersion usually results naturally from calcium impurities in other components of the dispersion. The usual source of sodium is from alumina. The usual source of calcium is from impuri~ies in magnesium con-taining sintering aid or water. "Calcium" and i'sodium", as used herein, mean chemically bound calcium and sodium, which due to the electropositive nature of calcium and sodium, are almost lo always calcium or sodium ion, i~e., free calcium or sodium ions or ionically bound sodium or calcium.
In accordance with the process of the invention, relatively high amounts of calcium and sodium can be tolerated in the dispersion, thus complicated and expensive purification steps are avoided. In accordance with the invention, up to about 1.8 percent combined sodium and calcium can be present in the disper-sion and a finished abrasive grain superior to traditional fused alumina grain will still be obtained. Preferably no more than ~.6 percent combined sodium and calcium is present~ The percent
1 SUPERIOR HIGH SODIUM ~ND C~LCIUM SOL GEL ABRA5IVE
AND PROCESS FOR ITS PRODUCTION
TECHNICAL FIELD
This invention relates o abrasive grains and mor@ par-ticularly relates to a sintered type of abrasive grain.
BACKGROUND ART
In the prior art, abrasive grains, especially abrasive grains comprising metal oxldes su~h as alumina, were tradi-tionally made by fusion of the oxide ~ollowed by eru~hing the cooled ~used oxide to ~orm the abrasive grain~
More recently, abrasive srains have been manufactured by sintering the metal oxide, such as alumina. Such grain~O
while wearin~ reasonably well, still do not wear as long as desirable and in addition, do not cut a~ rapidly as de~irable.
It is known that ceramic materials whieh may be in the for~ of ab~asive products can be prepared b~ binding cera~ic oxide particles together by using a mineral colloidal gel ~see U.S~ Patent 2,455,358). It is also known that cvlloidal disper-~9S~34~
1 sions can be gelled, dried and calcined to form porous ceramic materials tsee eOg., U.S. Patent 4,181,532~.
It has also been known that free flowing spheres of pure or mixed oxides could be made by dispersing an oxide hydrate followed by forming a gel in the shape of spheres followed by sintering (see "Application of Sol-Gel Processes ts Industrial Oxides", January 13, 1968, Chemistry and Industry3.
It has also been known by others in the United States, at least as early as lg71, that such particles in spherical or 1~ even angular shapes could be used as abrasives. Such prior knowledge by others in the United States is evidenced by a report from the United Ringdom Atomic Energy Authority at Harwell, England, to Carborundum Company, Ltd. and subsequently to several personnel at The Carborundum Company in the United States.
Recently, U.S. Patent No. 4,314,827 issued for a non-fused aluminum oxide-based abrasive mineral, a process for its production and abrasive products comprising the abrasive mineral.
U.S. Patent No. 4,314t827 generally discloses that an abrasive mineral having randomly oriented crystallites with diameters on the order of 3000 Angstroms or less can be made by gelling a colloidal dispersion or hydrosol of alumina and a modifying component, followed by firing the g21. The disclosure makes it clear that the mineral must be free (less than about 0.05 total weight percent) of calcium and alkali metal. Due to this requirement, complex purification processes must be used when calcium and alkali metal are present, as they often arel in the alumina or modifying component. Calcium, for example, is i ~s~
1 usually present in commercial water supplies and in magnesium containing modifying components unless costly and complicated purification steps are used to remove the calcium. Similarly, sodium i5 commonly present in many aluminas unless removed by additional purifica~ion steps. There is no suggestion in the U.S. patent of any process which would permit the presence of calcium or alkali metal and no process was actually used with high calcium or alkali metal which inherently permitted the presence of high calcium or alkali metal~
DISCLOSURE OF THE INVENTION
In accordance with the present invention, a process is provided for forming ceramic particles from a gelled dispersion ~sol gel~, by drying and sintering the gel. The particles of the invention may be used for any suitable purposeO Such particles may be used in any application where temperature resistance, strength, hardness~ wear resistance and inertness are desirable.
Such particles may, for example, be used as fillers, in aggregates, in distillation columns or due to the surface porosity of some of such particles t may be used as catalyst supports. The most common use for such particles is as abrasives. Such par~icles will therefore be referred to herein as abrasives, although it is to be understood that the term abrasive particle or abrasive grain is intended to include such particles regardless of their intended end use~
Even though the abrasive grain product obtained by the process of this invention usually contains greater than about 0.05 weight percent sodium plus calcium, it is greatly superior to traditional fused alumina abrasive. High sodium and calcium 3~
~ ~s~
1 in the grain is permitted due to rapid heating of the dried sol gel through a ~ritical temperature range of from below about 800C to above about 1200C. The grain is then sintered a~ a temperature above about 1200~C.
The preferred process comprises preparing a dispersion comprising from about 2 to about 60 weight percent aluminum o~ide monohydrate; a dissolved or dispersed metal containing sintering aid in an atomic ratio of metal to aluminum of from 1:2 to 1:35, preferably from 1:7 to 1:25; and from above about 0,05 to about lo 1.8 percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion.
The weight percent calcium plus the weight percent sodium is preferably less than 0.6, and more preferably less than 0.15. The weight percent calcium can range from 0 to about 1.8 and the weight percent sodium can range from about 0 to about 0.4. The weight percent calcium is preferably from 0 to about 0.6 and more preferably from 0 to about 0.15 and the weight percent sodium is preferably from 0 to about 0.25 and more preferably from 0 to about O~lo After the dispersion is prepared, it is gelled and dried at a temperature below the frothing temperature of the gel to remove free water. Any suitable drying method known to those skilled in the art may be used. "Drying" as used herein means dewatering by any method including solvent extraction. The dried solid is then crushed to form grains. The grains are then usually heated to between about 500 and 800C. The grains are then rapidly heated to above about 1200C in less than 10 and preferably less than 5 minutes. The grains then continue to be ~9x~
1 heated at a sintering temperature between about 1200C and about 1650C for a suficient sintering time to sinter the grains to a density above about 85% of theoretical density, at leas~ a por-tion of the heating at sintering temperature preferably occurring above 1300C.
The resulting grain is a sintered sol gel abrasive which has a combined sustained cutting rate and wear resistance against carbon steel which is substantially better than prior art fused alumina grain, and which is comparable to prior art sin-tered sol gel abrasive grains which require low sodium and lowcalcium (less than about 0.05 weight percent) as described in U.
SO Patent No~ 4,314,827. "Substantially better" means a relative cutting performance at least 1.5 times better and usually at least two times better.
The invention also includes bonded, coated and nonwoven abrasive articles comprising the novel grain. For example, not only do coated abrasives manufactured from the preferred abrasive grain of the invention continue to have a high cutting rate until the grain is worn from the backing~ but the total quantity of material cut by the abrasive article is superior to most prior art grains.
BEST MODE FOR CARRYING OUT THE lNv~ ION
In accordance with the process of the invention, the grain is prepared from a liquid (preferably water~ dispersion comprising from about 2 to about 60, usually from about 10 to about 40 weight percent aluminum oxide monohydrate (AlOOH~; a dissolved metal containing sintering aid at an a~omic ratio of metal in the sintering aid to aluminum of from 1:2 to 1:35; and ~L95~
1 up to about 1.8 and usually from above about 0.05 to about 1.8 percent combined alkali metal (espPcially sodium) and calcium by weight of dispersed and dissolved solids in ~he dispersion.
The weight percent calcium plus the weigh~ percent sodium is preferably less ~han 0.6, and more preferably less than .15. The weight percent calcium can range from 0 to about 1.8 and the weigh~ percent sodium can range from about 0 to about .4.
The weight percent calcium is preerably from 0 to about 0.6 and more preferably from 0 to about 0.1~ and the weight percent lo sodium is preferably from 0 to about .25 and more preferably from 0 to about .1~
The quantity of aluminum oxide monohydrate in the dispersion is usually from about 10 to about 40 and preferably from about 15 to about 35 percent by weight of the dispersion.
Aluminum oxide monohydrate as used herein is intended to include aluminum oxide hydrates having the stochiometric formula ~(A1203-XH20) where x is 0.5 to 3. Aluminum oxide monohydrate is also known as boehmite. Aluminum oxide monohydrate, as used herein, is also intended to include~ without limitation, pseudo boehmite.
In general, all solids in the dispersion are preferably dissolved or in colloidal form. The dispersion is formed by any suitable means which may simply be mixing of ~he aluminum oxide monohydrate with water. The liquid is almost always water but may be another liquid such as low molecular weight alcohoI. Any suitable mixing apparatus may be used including both high and low shear mixers. Dispersing aids such as acid are frequently employed. For example, from about 0~02 to 0.25 and preferably ~ 1~5~34~
1 0.05 to about 0.15 mole of HNO3 or other volatile mineral acid per mole of aluminum oxi~e monohydrate greatly aids dispersion.
"Volatile mineral acid" means an acid which will vaporize from the dispersion, gel or dried gel at a temperature below sintering temperature or all of whose residues will either so vaporize or form a part of an oxide within the finished grain. Examples of such acids are nitric, hydrochloric, acetic and formic acids.
The solids in the finished dispersion may comprise up to 50 weight percent of additional ingredients other than alumi-lo num oxide monohydrate, preferably compounds such as silica,magnesia, chromia and titanium dioxide in colloidal or dissolved form, or precursors of such compounds in colloidal or dissolved form.
The dissolved or dispersed mQtal containing sintering aid is added to the dispersion in an atomic ratio of metal to aluminum of from 1:2 to 1:35 and preferably at a ratio of rom 1:7 to 1-25. The sintering aid is a dispersible or scluble metal oxide or metal oxide precursor, i.e., a compound which will form a metal oxide during drying, calcining or sintering. In general, the sintering aid is usually a precursor of magnesium oxide, zinc oxide, cobalt oxide or nickel oxide and is therefore, when the liquid is water, a water soluble or dispersible compound of magnesium, zinc, nickel or cobaltc Specific examples of such precursors are the nitrates and chlorides of thos~ metals. The nitrates of those metals and especially of magnesium are par-ticularly preferred. The sintering aid may be prepared in situ, for example by adding magnesium oxide or hydroxide to an aqueous solution of inorganic acid such as hydrochloric or nitric acids 5~
to form a water soluble salt of magnesium. The sintering aid is usually a water soluble salt but may be a water soluble base.
The sodium and calcium in the dispersion usually results naturally from calcium impurities in other components of the dispersion. The usual source of sodium is from alumina. The usual source of calcium is from impuri~ies in magnesium con-taining sintering aid or water. "Calcium" and i'sodium", as used herein, mean chemically bound calcium and sodium, which due to the electropositive nature of calcium and sodium, are almost lo always calcium or sodium ion, i~e., free calcium or sodium ions or ionically bound sodium or calcium.
In accordance with the process of the invention, relatively high amounts of calcium and sodium can be tolerated in the dispersion, thus complicated and expensive purification steps are avoided. In accordance with the invention, up to about 1.8 percent combined sodium and calcium can be present in the disper-sion and a finished abrasive grain superior to traditional fused alumina grain will still be obtained. Preferably no more than ~.6 percent combined sodium and calcium is present~ The percent
2~ sodium and calcium as above described is by weight of dispersed and dissolved metal containiny solids in the dispersion. The percentages are essentially the same as the percentages in the finished abrasives.
After the di~persion is prepared, it is gelled. The addition of the dissolved or dispersed metal containing sintering aid, preferably magnesium nitrate, to the dispersion usually serves to gel the dispersion. If the solids content of the dispersion is quite low, the liquid may either have to be ~ ~58~8 1 vaporized in order for the dispersion to gel or another method of gelling may have to be employed, i.e , the addition of a gelling agent.
After the dispersion is gelled, it is dried at a tem-perature below the frothing temperature of the gel to vaporize free water. "Dried" or "drying", as used herein, means that at least 90~ of free (unbound) water is removed to form a solid.
The "frothing temperature" is the temperature at which the gel will foam or froth a~ the pressure applied to the gelO Drying lo may be accomplished by any means known to those skilled in the art. When heat is used, the drying temperature is usually from about 80 to about 120C. The drying time depends upon the quan-tity of water or other liquid present, upon drying pressure, and upon drying temperature. The drying time is usually from about 1 to about 72 hours at atmospheric pressure. The resulting dried gel i5 usually, but not necessarily, a translucent solid, i.e., a solid through which light will pass in diffused form.
After the solid is dry, it is crushed or broken by any suitable means such as a hammer or ball mill to form particles or grains. Any suitable method fvr comminuting the solid may be used and "crushing" is intended to include all such methods.
After crushing, the grains are usually heated to a tem-perature between about 500C and about 800C until essentially all water is removed and until all componen~s of the grains are either in the form of ceramics (usually metal oxides~ or else are vaporized. When the grains reach a tempera~ure between about 250C and about 300C, the acid residues are driven off. Between about 250C and about 300C, and usually between about 300C and _g ?
~9S~
1 600C, essentially all water is usually removed~ nEssentially all", as used in this context~ means that all free water and over 90 percent of bound water i5 removedO The calcining time to remove essentially all water is usually from about 5 to about 20 minutes.
After drying and after calcining, the grains are rapidly heated to above about 1200C. "Rapidly heated" means sufficiently fast to permit formation of an abrasive having a good cutting rate and good wear resistance. The rapid heating lo usually occurs in less than 10, preferably in less than 5 and most preferably in less than 1 minute. This rapid heating step permits the formation of a superior abras~ve grain from a gelled dispersion (sol gel) containing relatively high amounts of calcium and sodium. Any suitable means or method for rapidly heating the grains may be used such as injection of the grains in other than bulk form, i.e., separately, into a furnace preheated to above 1200~C and preferably to above 1300C.
It is possible to eliminate the calclning step and instead rapidly heat the grains to above ahout 1200C after drying. This particular procedure is particularly desirable for producing certain type abrasives.
After the grains are rapidly heated to above 1200C, they continue to be heated at a sintering temperature between about 1200C and about 1650C and preferakly between 1250C and 1500C for a sufficient sintering time to sinter the grains to a density above about 85% of~theoretical density. In the case where the abrasive is primarily aluminum oxide with about 6%
magnesium oxide by weight of aluminum oxideJ the desired densi~y 5~
1 is above about 3.3 grams per cubic centimeter. At least a por-tion of the heating usually occurs above 1300C~ The sufficient time to sinter the grain depends on sintering temperature and is usually from abou~ 5 to abou~ 30 minutes but may be less than about 5 minutes, e.g., from about 1 to about 5 minutes.
When looking at polished ~hin sec~ions of sintered grain manufactured in accordance with the process of the invention in a transmission optical microscope at about 500X or 700X with crossed polarizers, one observes the microstructure of lo material with a nominal composition of alumina-6~ magnesia to consist of areas of from about 5,000 up to about 200,000 Angstroms in nominal diameter which extinguish as a unit upon sample rotation. The extinction is believed to result, in this instance, from the birefringent alpha alumina phase which is pre-dominant~ In order for these areas to extinguish as a unit, it is believed that they have to be either continuous alpha alumina grains or areas of smaller non-randomly oriented alumina grains.
If the alpha alumina grains either have a diameter ranging from about 5,000 Angstroms to about 200,000 Angstroms or have much smaller diameters but are non-randomly orîented, the weight per-cent combined calcium plus sodium in the grains may be less than .05.
5~
1 The microstructure of the alumina grain of the inven-tion differs markedly from that o~ normal sintered or fused alu-mina grain of a similar composition in the degree of homogeneity of distribution of metal oxide sintering aid. On firing pre-viously calcined material, it is believed that a transformation from an atomistically homogeneous distribution of magnesia in gamma alumina transforms ~o a microscopically homogeneous inti-mate mixture of alumina and spinel.
Normal sintering of abrasive grains includes con-solidation by either a diffusional mechanism of preexistin~3 alpha alumina crystals or a liquid phase densification mechanism.
Sin~ering of sol sel abrasives may include a displasive poly-morphic transformation of gamma alumina to alpha alumina and spinel involving minimum di~fusion. This unique transformation normally results in a marked reduction in sintering temperature.
The invention fur~her includes bonded, coated and non-woven abrasive articles comprising the abrasive grain of the invention. In general, the abrasive grain of the invention may be described as a sintered abrasive grain comprising alumina, a metal oxide which aids sintering, and up to about 1.8 and usually ~`rom above about 0.05 to about 1.8, preferably to about 0.6 and -lla-9~
l most preferably ~o about 0.15 weight percent combined calcium plus sodium.
As previously discussed, the preferred sintered grains manu~actured in accordance with ~he process of the invention, have excellent wear characteristics and in addition, maintain a high cutting ra~e and remove larger quantities of carbon steel stock than most prior art grains. High sodium and calcium con-taining prior ar~ grains do not have a combination of cutting rate and wear resistance as high as the best abrasive grains lo manufactured in accordance with the present invention.
As previously discussed, ~he sintered sol gel abrasive of the invention has a relative cutting performance on coated discs against carbon steel which is better than fused alumina abrasive. The preferred sol gel abrasives of the invention have such a cutting rate which is at least two and usually at least three to four times better than traditional fused alumina abra-sive. Relative cutting performance is determined as defined and described in the following examples.
The following examples serve to illustrate and not limit the present invention.
EXAMPLE 1. Prior Art A high calcium sol gel abrasive grain was made essen~
tially in accordance with a process similar to the prior art, wherein a dried high calcium sol gel was heated slowly and essen-tially unifor~lly from ambient temperature to 1370C. In par-ticular, 10,199 grams of Condea Chemie Dispural~ boehmite was dispersed in 20.5 gallons of wa~er and 573 ml of concentrated ~9S~
1 nitric acid was then added to form a sol (colloidal solu~ion).
73.9 grams of titanium IV isopropoxide dispersed in 4150 ml of isopropyl alcohol and 36.5 grams of Nalco-Chemical Nalcoage~1034A
colloidal silica dispersion were then mixed into the sol.
3162 grams of magnesium nitrate was dissolved in 2 gallons of water and the resulting solution was added to the sol with stirring. Gelling occurred almost immediately. Stirring was continued for about 5 minutes.
The gel was then transferred to plastic trays at a depth or about 10 centimeters~ The trays were placed in a steam heated dryer to dry the gel which took about 60 hours.
The dry gel was passed through a roll crusher to reduce it to -28 mesh granules. A size fraction -28 to +48 mesh was separated by sieving.
The dry granules were placed in aluminum oxide coated saggers and placed into a kiln. Th~ kiln was heated to 1370C
over a period of six hours and held at 1370C for 30 minutes.
The kiln was turned of and allowed to cool. The resulting fired grains were porous and were analyzed as having a calcium content of 0.14 weight percent. The density was less than 85% of theore-tical.
The sintered granules were size classified on a conven-tional sifter to meet the ANSI 74.18-1977 specification for 50 grit.
A single coated abrasive material was made by electrostatically coating the 50 grit grain on a vulcanized fiber backing.
~1~5~
1 The fiber selected was abrasive grade 0.030 inch vulcanized fiber, having a nominal weight of 67 pounds per ream (480-9xll sheets~.
A maker adhesive mix, consisting of a commercial one-stage; liquid phenolic resin with a formaldehyde to phenol ratio of about 1:1 and ground limestone with an average particle size of between 17 and 25 microns, was made using a 1:1 net weight mix proportion.
The maker mix was then heated to 90F and roll coated lo on the fiber backing. About 14 pounds of adhesive per ream was applied.
Usin~ conven~ional sandpaper making equipment, the 50 grit abrasive was electrostatically projected onto the fiber carrying the maker mix with about 38 pounds per ream of grain bei~g applied.
The abrasive adhesive coated backing was then heated to 175F for one hour and 200F for two hours in the maker rack.
After drying, a size coat was then applied by standard roll coating methods with approximately 21 lbs/ream being applied.
The siæe mix consisted of the same 1:1 phenolic resin-filler ratio. However, a non-buffered synthetic cryolite with an average particle size of 25 microns was used as the filler.
Drying and curing was then accomplished by heating the coated material for one hour at 150F, four hours at 175F, and 16 hours at 22F.
After curing the material was humidified in the conven-tional manner to a moisture content of less than 8% by weight.
~s~
1 The material was then uniformly flexed and die cut into seven inch discs. These were then evaluated on a conventional pneuma-tic disc grinder using 1018 cold rolled steel as a workpiece and compared to a control disc made and handled in exactly the same manner except the abrasive grain was fused alumina. In ~his tes~, the abrasive disc was placed on the disc grinder in the standard manner and a 1 x 2 x 11 inch workpiece was positioned so that it engaged ~he disc on the 1 inch 1at side at a 10-15 angle~ ~he disc was passed back and forth along the workpiece.
lo The abrasive disc in this test was rotated at a nominal 5400 RPH's on a hard rubber type back-up pad 7" in diameter.
Eight pounds of dead weight in-feed force was exerted on the workpiece. Testing was for 30 seconds after which stock removed from the bar was measured (weight before grind-weight after grind) and recordedO This se~uence was continued until the measured stock removed was 5 grams or less per grinding interval.
Total stock removed in this manner for the test disc was compared to the total stock removed for the control disc. (Relative cutting performance) The high calcium (0.14 weight percent) slowly heated sol gel abrasive (substantially in accordance with the prior art) had only 97% o the cutting performance of standard and inexpen-sive fused alumina abrasive grain.
EXAMPLE 2.
Example 1. was substantially repeated except that instead of slowly heating the dried granules as in Example 1~, the granules were calcined at 550C for about 30 minutes and were then introduced into a rotary tube furnace a~ 1390C to rapidly ~ i 1 heat them to above 1200C in accordance with the present inven-tionO The granules (grains) were heated to 1390C in about 10 minu~es and retained at 1390C for about 30 minutes to sinter the grains, Any other differences from Example 1. were minor. The resulting sin~ered grains were analyzed as having a calcium con-tent of 0.11 weight percent and a specific gravity over 3.3 (greater than 85% of theoretical). Upon testing as described in Example 1., the discs were found to have a relative cutting per-formance which was 395 percent of the cutting performance of fused alumina abrasive grain. In other words, the grain of the invention had a cutting performance 3.95 times the cutting per-formance of fused alumina abrasive grain.
EXAMPLE 3.
Example ~. was substantially repeated except that the dried grains were calcined at 600C instead of 550C. The finished grain was found to have a calcium content of 0.12 weight percent and a density in excess o 85~ of theoretical. The rela-tive cutting performance was 4.39 times the performance of fused alumina abrasive grain.
EXAMPLE 4.
Example 20 was substantially repeat~d except that the magnesium nitrate used was prepared by dissolving 720 grams of magnesium hydroxide in 1.66 gallons of water containing 1660 ml of concentrated nitric acid. The resulting solution was added to ~he sol while stirring. As in Example 2., gelling occurred imme-diately and stirring was continued for 5 minutes.
The resul~ing grain had a calcium content of near 0~08 weight percent, a density in excess of 85% of theoretical, and s~
1 cutting performance about 4.5 times the cutting performance of fused alumina. In addition, the resulting grain had a cutting performance about 2.4 times the cutting performance of a commer-cial rapidly cooled fused alumina-zirconia grain and a cutting performance comparable to a commercial low calcium sintered sol gel alumina containing grain precoated on a commercial disc, which grain is similar to the low calcium and sodium grain described in U.S. Patent No. 4,314 r 827 .
EXAMPLE 5.
lo A high calcium and sodium sol gel abrasive grain was made essentially in accordance with Example 2. In particular, 20,559 grams of Conden Chemie ~ispural~ boehmite was dispersed in 33.5 gallons of water and 1250 ml of concentrated technical grade nitric acid dilu~ed with 2 gallons of water was then added to the dispersion to form a sol (colloidal solution).
6341 grams of magnesium nitrate was dissolved in 4 gallons of water and the resulting solution was added to the sol with stirring. Gelling occurred almost immediately. Stirring was continued for about 5 minutes.
The gel was then transferred to plastic trays at a depth of between 2.5 and 3.75 centimeters~ The trays were placed in an electrically heated dryer to dry the gel which took about 48 hours.
The dry gel was passed through a roll crusher to reduce it to -20 mesh granules. A size fraction ~20 to +48 mesh was ~eparated by sieving.
The granules were calcined at 550C for about 30 minutes and were then fast fired in a rotary tube furnace at 1.2 ~:~9513~
revolutions per minu~e at about 1395C to rapidly heat them to above 1200C in accordance with the invention. The granules (grains) were heated to 1390C for an additional 10 minutes. The resulting grain had a calcium content of about 0.07 weight percent and a sodium content of 0.015 weight percent. The density was in excess of 85~ of theoretical.
The sintered granules were size classified on a conventional sifter to meet the ~NSI 74.18-1977 specification for 36 grit.
lo A single coated abrasive material was ~ade by electrostatically coating the 36 grit grain on a vulcanized fiber backing.
The fiber selected was abrasive grade 0.030 inch vulcanized fiber, having a nominal weight of 67 pounds per ream (480-9xll sheets).
A maker adhesive mix, consisting of a commercial one-stage, liquid phenolic resin with a formaldehyde to phenol ratio of about 1:1 and ground limestone with an average particle size of between 17 and 25 microns, was made using a 1:1 nek weight mix proportion.
The maker mix was then heated to 90F and roll coated on the fiber backing. About 23 pounds of adhesive per ream was applied.
Using conventional sandpaper making equipment, the 36 grit abrasive was electrostatically projected onto the fiber carrying the maker mix with about 62 pounds per ream of grain being applied.
~ s~
1 The abrasive adhesive coated backing was then h~ated to 175F for one hour and 200F for two hours in the maker rack.
After drying, a size coat was then applied by standard roll coating methods with approximately 23 lbs/ream being applied.
The size mix consisted of the same 1:1 phenolic resin-filler ratio. Drying and curing was then accomplished by heating the coated material for one hour at 150F, four hours at 175F, and 16 hours at 225~F~
After curing the material was humidified in the conventional manner to a mois~ure conten~ of less than 8% by weight~ The material was then uniformly flexed and die cut into seven inch discs. Five of these discs were then evaluated on a conventional pneuma~ic disc grinder using quenched and tempered 4140 steel (hardness 285-320 BHN) as a workpiece and compared to a control disc made and handled in exactly the s~me manner except the abrasive grain was fused alumina. In this test, the abrasive disc was placed on the disc grinder in the standard manner and a 1 x 2 x 11 inch workpiece was positioned so that it engaged the disc on the 1 inch flat side at a 10-15 angle. The disc was 2~ passed back and forth along the workpiece.
The abrasive disc in this test was rotated at a nominal 5400 RPM's on a hard rubber type back-up pad 7" in diameter.
Eight pounds of dead weight in-feed force was exerted on the workpiece. Testing was for 30 seconds after which s~ock removed from the bar was measured (weight before grind-weight after grind) and recorded. This sequence was continued until the measured stock removed was 5 grams or less per grinding interval.
Total stock removed in this manner for the test disc was compared 3L~95~
1 to ~he total stock removed for the con~rol disc. (Relative cutting performance).
The high calcium and sodium (0.07 combined weight percent) rapidly heated sol gel abrasive had a mean cut of 612 grams (almost 7 times the cut of standard fused alumina). The results are shown in Table 1.
EXAMPLES 6. - 19.
The procedure of Example 5 was followed except that various known quantities of calcium and sodium were added to the dispersion prior to the addition of magnesium nitrate. The sodium and calcium were added as sodium and calcium nitrate solutions. The sodium nitrate solution contain~d 0.54 grams per ml of NaN03, equivalent to 0,2 grams/ml calculated as Na20, and the calcium nitrate solution contained 0.58 grams per ml of Ca(N03~2, equivalent to 0.2 grams/ml calculated as CaO. The results are set forth in Table 1. The calcium and sodium in the grain are analy~ed by emission spectroscopy. The slight variation between added calcium and actual calcium in the grain is believed due to additional calcium present in magnesium nitrate and in water and the slight variation between added sodium and actual sodium in the grain is ~elieved to be due to impurities in the components of the grain, especially water, and to some vaporization of sodium during calcining and sintering.
For comparison, the mean cut of traditional fused alumina grain is set forth in Table 1.
1~958~L~
,~
% Ca in % Na in Mean Cut EXAMPLE mls Ca~ mls Na+ Grain Grain Grams ~ -0~ .06 .01 612.0 6 24.9 -0- .0~ .02 644.8 7 -0- 83 ~06 .06 504.8 8 83 ~0- .13 ~01 494.6 9 -0- 166 .0~ .12 437.6 24~9 ~3 .08 .~7 424.0 lo 11 lÇ6 -0- ,1~ .~4 424.0 12 83 166 .13 - .13 383.2 `13 373.5 -0- .33 .02 369.8 14 166 166 .18 .12 326.4 166 270 .19 .21 275.4 16 -0- 270 .06 .18 270.0 17 83 27~ .13 .20 242.4 18 -0- 481.5 .06 .27 197.2 19 373.5 481.5 .36 .36 185.~
alumina 88.2 Examples 7, 11 and 15 were repeated except that the grain was slowly fired in a manner similar to prior art ~xample 1. In particular, the grain was slowly fired in a stationary kiln from ambient temperature to 1500C over a time period of 16 hours followed by 30 minutes at 1500C. The resulting abrasives were so poor that no cutting data could be obtained.
The foregoing examples clearly demonstrate the superiority of the cutting performance of high calcium and sodium sol gel abrasive grains manufactured in accordance with the pro-cess of the invention and show that when the step of rapidly heating dried high calcium and sodium sol gel to sintering tem-perature is omitted, as in the prior art, the resulting grain is an inferior grain.
After the di~persion is prepared, it is gelled. The addition of the dissolved or dispersed metal containing sintering aid, preferably magnesium nitrate, to the dispersion usually serves to gel the dispersion. If the solids content of the dispersion is quite low, the liquid may either have to be ~ ~58~8 1 vaporized in order for the dispersion to gel or another method of gelling may have to be employed, i.e , the addition of a gelling agent.
After the dispersion is gelled, it is dried at a tem-perature below the frothing temperature of the gel to vaporize free water. "Dried" or "drying", as used herein, means that at least 90~ of free (unbound) water is removed to form a solid.
The "frothing temperature" is the temperature at which the gel will foam or froth a~ the pressure applied to the gelO Drying lo may be accomplished by any means known to those skilled in the art. When heat is used, the drying temperature is usually from about 80 to about 120C. The drying time depends upon the quan-tity of water or other liquid present, upon drying pressure, and upon drying temperature. The drying time is usually from about 1 to about 72 hours at atmospheric pressure. The resulting dried gel i5 usually, but not necessarily, a translucent solid, i.e., a solid through which light will pass in diffused form.
After the solid is dry, it is crushed or broken by any suitable means such as a hammer or ball mill to form particles or grains. Any suitable method fvr comminuting the solid may be used and "crushing" is intended to include all such methods.
After crushing, the grains are usually heated to a tem-perature between about 500C and about 800C until essentially all water is removed and until all componen~s of the grains are either in the form of ceramics (usually metal oxides~ or else are vaporized. When the grains reach a tempera~ure between about 250C and about 300C, the acid residues are driven off. Between about 250C and about 300C, and usually between about 300C and _g ?
~9S~
1 600C, essentially all water is usually removed~ nEssentially all", as used in this context~ means that all free water and over 90 percent of bound water i5 removedO The calcining time to remove essentially all water is usually from about 5 to about 20 minutes.
After drying and after calcining, the grains are rapidly heated to above about 1200C. "Rapidly heated" means sufficiently fast to permit formation of an abrasive having a good cutting rate and good wear resistance. The rapid heating lo usually occurs in less than 10, preferably in less than 5 and most preferably in less than 1 minute. This rapid heating step permits the formation of a superior abras~ve grain from a gelled dispersion (sol gel) containing relatively high amounts of calcium and sodium. Any suitable means or method for rapidly heating the grains may be used such as injection of the grains in other than bulk form, i.e., separately, into a furnace preheated to above 1200~C and preferably to above 1300C.
It is possible to eliminate the calclning step and instead rapidly heat the grains to above ahout 1200C after drying. This particular procedure is particularly desirable for producing certain type abrasives.
After the grains are rapidly heated to above 1200C, they continue to be heated at a sintering temperature between about 1200C and about 1650C and preferakly between 1250C and 1500C for a sufficient sintering time to sinter the grains to a density above about 85% of~theoretical density. In the case where the abrasive is primarily aluminum oxide with about 6%
magnesium oxide by weight of aluminum oxideJ the desired densi~y 5~
1 is above about 3.3 grams per cubic centimeter. At least a por-tion of the heating usually occurs above 1300C~ The sufficient time to sinter the grain depends on sintering temperature and is usually from abou~ 5 to abou~ 30 minutes but may be less than about 5 minutes, e.g., from about 1 to about 5 minutes.
When looking at polished ~hin sec~ions of sintered grain manufactured in accordance with the process of the invention in a transmission optical microscope at about 500X or 700X with crossed polarizers, one observes the microstructure of lo material with a nominal composition of alumina-6~ magnesia to consist of areas of from about 5,000 up to about 200,000 Angstroms in nominal diameter which extinguish as a unit upon sample rotation. The extinction is believed to result, in this instance, from the birefringent alpha alumina phase which is pre-dominant~ In order for these areas to extinguish as a unit, it is believed that they have to be either continuous alpha alumina grains or areas of smaller non-randomly oriented alumina grains.
If the alpha alumina grains either have a diameter ranging from about 5,000 Angstroms to about 200,000 Angstroms or have much smaller diameters but are non-randomly orîented, the weight per-cent combined calcium plus sodium in the grains may be less than .05.
5~
1 The microstructure of the alumina grain of the inven-tion differs markedly from that o~ normal sintered or fused alu-mina grain of a similar composition in the degree of homogeneity of distribution of metal oxide sintering aid. On firing pre-viously calcined material, it is believed that a transformation from an atomistically homogeneous distribution of magnesia in gamma alumina transforms ~o a microscopically homogeneous inti-mate mixture of alumina and spinel.
Normal sintering of abrasive grains includes con-solidation by either a diffusional mechanism of preexistin~3 alpha alumina crystals or a liquid phase densification mechanism.
Sin~ering of sol sel abrasives may include a displasive poly-morphic transformation of gamma alumina to alpha alumina and spinel involving minimum di~fusion. This unique transformation normally results in a marked reduction in sintering temperature.
The invention fur~her includes bonded, coated and non-woven abrasive articles comprising the abrasive grain of the invention. In general, the abrasive grain of the invention may be described as a sintered abrasive grain comprising alumina, a metal oxide which aids sintering, and up to about 1.8 and usually ~`rom above about 0.05 to about 1.8, preferably to about 0.6 and -lla-9~
l most preferably ~o about 0.15 weight percent combined calcium plus sodium.
As previously discussed, the preferred sintered grains manu~actured in accordance with ~he process of the invention, have excellent wear characteristics and in addition, maintain a high cutting ra~e and remove larger quantities of carbon steel stock than most prior art grains. High sodium and calcium con-taining prior ar~ grains do not have a combination of cutting rate and wear resistance as high as the best abrasive grains lo manufactured in accordance with the present invention.
As previously discussed, ~he sintered sol gel abrasive of the invention has a relative cutting performance on coated discs against carbon steel which is better than fused alumina abrasive. The preferred sol gel abrasives of the invention have such a cutting rate which is at least two and usually at least three to four times better than traditional fused alumina abra-sive. Relative cutting performance is determined as defined and described in the following examples.
The following examples serve to illustrate and not limit the present invention.
EXAMPLE 1. Prior Art A high calcium sol gel abrasive grain was made essen~
tially in accordance with a process similar to the prior art, wherein a dried high calcium sol gel was heated slowly and essen-tially unifor~lly from ambient temperature to 1370C. In par-ticular, 10,199 grams of Condea Chemie Dispural~ boehmite was dispersed in 20.5 gallons of wa~er and 573 ml of concentrated ~9S~
1 nitric acid was then added to form a sol (colloidal solu~ion).
73.9 grams of titanium IV isopropoxide dispersed in 4150 ml of isopropyl alcohol and 36.5 grams of Nalco-Chemical Nalcoage~1034A
colloidal silica dispersion were then mixed into the sol.
3162 grams of magnesium nitrate was dissolved in 2 gallons of water and the resulting solution was added to the sol with stirring. Gelling occurred almost immediately. Stirring was continued for about 5 minutes.
The gel was then transferred to plastic trays at a depth or about 10 centimeters~ The trays were placed in a steam heated dryer to dry the gel which took about 60 hours.
The dry gel was passed through a roll crusher to reduce it to -28 mesh granules. A size fraction -28 to +48 mesh was separated by sieving.
The dry granules were placed in aluminum oxide coated saggers and placed into a kiln. Th~ kiln was heated to 1370C
over a period of six hours and held at 1370C for 30 minutes.
The kiln was turned of and allowed to cool. The resulting fired grains were porous and were analyzed as having a calcium content of 0.14 weight percent. The density was less than 85% of theore-tical.
The sintered granules were size classified on a conven-tional sifter to meet the ANSI 74.18-1977 specification for 50 grit.
A single coated abrasive material was made by electrostatically coating the 50 grit grain on a vulcanized fiber backing.
~1~5~
1 The fiber selected was abrasive grade 0.030 inch vulcanized fiber, having a nominal weight of 67 pounds per ream (480-9xll sheets~.
A maker adhesive mix, consisting of a commercial one-stage; liquid phenolic resin with a formaldehyde to phenol ratio of about 1:1 and ground limestone with an average particle size of between 17 and 25 microns, was made using a 1:1 net weight mix proportion.
The maker mix was then heated to 90F and roll coated lo on the fiber backing. About 14 pounds of adhesive per ream was applied.
Usin~ conven~ional sandpaper making equipment, the 50 grit abrasive was electrostatically projected onto the fiber carrying the maker mix with about 38 pounds per ream of grain bei~g applied.
The abrasive adhesive coated backing was then heated to 175F for one hour and 200F for two hours in the maker rack.
After drying, a size coat was then applied by standard roll coating methods with approximately 21 lbs/ream being applied.
The siæe mix consisted of the same 1:1 phenolic resin-filler ratio. However, a non-buffered synthetic cryolite with an average particle size of 25 microns was used as the filler.
Drying and curing was then accomplished by heating the coated material for one hour at 150F, four hours at 175F, and 16 hours at 22F.
After curing the material was humidified in the conven-tional manner to a moisture content of less than 8% by weight.
~s~
1 The material was then uniformly flexed and die cut into seven inch discs. These were then evaluated on a conventional pneuma-tic disc grinder using 1018 cold rolled steel as a workpiece and compared to a control disc made and handled in exactly the same manner except the abrasive grain was fused alumina. In ~his tes~, the abrasive disc was placed on the disc grinder in the standard manner and a 1 x 2 x 11 inch workpiece was positioned so that it engaged ~he disc on the 1 inch 1at side at a 10-15 angle~ ~he disc was passed back and forth along the workpiece.
lo The abrasive disc in this test was rotated at a nominal 5400 RPH's on a hard rubber type back-up pad 7" in diameter.
Eight pounds of dead weight in-feed force was exerted on the workpiece. Testing was for 30 seconds after which stock removed from the bar was measured (weight before grind-weight after grind) and recordedO This se~uence was continued until the measured stock removed was 5 grams or less per grinding interval.
Total stock removed in this manner for the test disc was compared to the total stock removed for the control disc. (Relative cutting performance) The high calcium (0.14 weight percent) slowly heated sol gel abrasive (substantially in accordance with the prior art) had only 97% o the cutting performance of standard and inexpen-sive fused alumina abrasive grain.
EXAMPLE 2.
Example 1. was substantially repeated except that instead of slowly heating the dried granules as in Example 1~, the granules were calcined at 550C for about 30 minutes and were then introduced into a rotary tube furnace a~ 1390C to rapidly ~ i 1 heat them to above 1200C in accordance with the present inven-tionO The granules (grains) were heated to 1390C in about 10 minu~es and retained at 1390C for about 30 minutes to sinter the grains, Any other differences from Example 1. were minor. The resulting sin~ered grains were analyzed as having a calcium con-tent of 0.11 weight percent and a specific gravity over 3.3 (greater than 85% of theoretical). Upon testing as described in Example 1., the discs were found to have a relative cutting per-formance which was 395 percent of the cutting performance of fused alumina abrasive grain. In other words, the grain of the invention had a cutting performance 3.95 times the cutting per-formance of fused alumina abrasive grain.
EXAMPLE 3.
Example ~. was substantially repeated except that the dried grains were calcined at 600C instead of 550C. The finished grain was found to have a calcium content of 0.12 weight percent and a density in excess o 85~ of theoretical. The rela-tive cutting performance was 4.39 times the performance of fused alumina abrasive grain.
EXAMPLE 4.
Example 20 was substantially repeat~d except that the magnesium nitrate used was prepared by dissolving 720 grams of magnesium hydroxide in 1.66 gallons of water containing 1660 ml of concentrated nitric acid. The resulting solution was added to ~he sol while stirring. As in Example 2., gelling occurred imme-diately and stirring was continued for 5 minutes.
The resul~ing grain had a calcium content of near 0~08 weight percent, a density in excess of 85% of theoretical, and s~
1 cutting performance about 4.5 times the cutting performance of fused alumina. In addition, the resulting grain had a cutting performance about 2.4 times the cutting performance of a commer-cial rapidly cooled fused alumina-zirconia grain and a cutting performance comparable to a commercial low calcium sintered sol gel alumina containing grain precoated on a commercial disc, which grain is similar to the low calcium and sodium grain described in U.S. Patent No. 4,314 r 827 .
EXAMPLE 5.
lo A high calcium and sodium sol gel abrasive grain was made essentially in accordance with Example 2. In particular, 20,559 grams of Conden Chemie ~ispural~ boehmite was dispersed in 33.5 gallons of water and 1250 ml of concentrated technical grade nitric acid dilu~ed with 2 gallons of water was then added to the dispersion to form a sol (colloidal solution).
6341 grams of magnesium nitrate was dissolved in 4 gallons of water and the resulting solution was added to the sol with stirring. Gelling occurred almost immediately. Stirring was continued for about 5 minutes.
The gel was then transferred to plastic trays at a depth of between 2.5 and 3.75 centimeters~ The trays were placed in an electrically heated dryer to dry the gel which took about 48 hours.
The dry gel was passed through a roll crusher to reduce it to -20 mesh granules. A size fraction ~20 to +48 mesh was ~eparated by sieving.
The granules were calcined at 550C for about 30 minutes and were then fast fired in a rotary tube furnace at 1.2 ~:~9513~
revolutions per minu~e at about 1395C to rapidly heat them to above 1200C in accordance with the invention. The granules (grains) were heated to 1390C for an additional 10 minutes. The resulting grain had a calcium content of about 0.07 weight percent and a sodium content of 0.015 weight percent. The density was in excess of 85~ of theoretical.
The sintered granules were size classified on a conventional sifter to meet the ~NSI 74.18-1977 specification for 36 grit.
lo A single coated abrasive material was ~ade by electrostatically coating the 36 grit grain on a vulcanized fiber backing.
The fiber selected was abrasive grade 0.030 inch vulcanized fiber, having a nominal weight of 67 pounds per ream (480-9xll sheets).
A maker adhesive mix, consisting of a commercial one-stage, liquid phenolic resin with a formaldehyde to phenol ratio of about 1:1 and ground limestone with an average particle size of between 17 and 25 microns, was made using a 1:1 nek weight mix proportion.
The maker mix was then heated to 90F and roll coated on the fiber backing. About 23 pounds of adhesive per ream was applied.
Using conventional sandpaper making equipment, the 36 grit abrasive was electrostatically projected onto the fiber carrying the maker mix with about 62 pounds per ream of grain being applied.
~ s~
1 The abrasive adhesive coated backing was then h~ated to 175F for one hour and 200F for two hours in the maker rack.
After drying, a size coat was then applied by standard roll coating methods with approximately 23 lbs/ream being applied.
The size mix consisted of the same 1:1 phenolic resin-filler ratio. Drying and curing was then accomplished by heating the coated material for one hour at 150F, four hours at 175F, and 16 hours at 225~F~
After curing the material was humidified in the conventional manner to a mois~ure conten~ of less than 8% by weight~ The material was then uniformly flexed and die cut into seven inch discs. Five of these discs were then evaluated on a conventional pneuma~ic disc grinder using quenched and tempered 4140 steel (hardness 285-320 BHN) as a workpiece and compared to a control disc made and handled in exactly the s~me manner except the abrasive grain was fused alumina. In this test, the abrasive disc was placed on the disc grinder in the standard manner and a 1 x 2 x 11 inch workpiece was positioned so that it engaged the disc on the 1 inch flat side at a 10-15 angle. The disc was 2~ passed back and forth along the workpiece.
The abrasive disc in this test was rotated at a nominal 5400 RPM's on a hard rubber type back-up pad 7" in diameter.
Eight pounds of dead weight in-feed force was exerted on the workpiece. Testing was for 30 seconds after which s~ock removed from the bar was measured (weight before grind-weight after grind) and recorded. This sequence was continued until the measured stock removed was 5 grams or less per grinding interval.
Total stock removed in this manner for the test disc was compared 3L~95~
1 to ~he total stock removed for the con~rol disc. (Relative cutting performance).
The high calcium and sodium (0.07 combined weight percent) rapidly heated sol gel abrasive had a mean cut of 612 grams (almost 7 times the cut of standard fused alumina). The results are shown in Table 1.
EXAMPLES 6. - 19.
The procedure of Example 5 was followed except that various known quantities of calcium and sodium were added to the dispersion prior to the addition of magnesium nitrate. The sodium and calcium were added as sodium and calcium nitrate solutions. The sodium nitrate solution contain~d 0.54 grams per ml of NaN03, equivalent to 0,2 grams/ml calculated as Na20, and the calcium nitrate solution contained 0.58 grams per ml of Ca(N03~2, equivalent to 0.2 grams/ml calculated as CaO. The results are set forth in Table 1. The calcium and sodium in the grain are analy~ed by emission spectroscopy. The slight variation between added calcium and actual calcium in the grain is believed due to additional calcium present in magnesium nitrate and in water and the slight variation between added sodium and actual sodium in the grain is ~elieved to be due to impurities in the components of the grain, especially water, and to some vaporization of sodium during calcining and sintering.
For comparison, the mean cut of traditional fused alumina grain is set forth in Table 1.
1~958~L~
,~
% Ca in % Na in Mean Cut EXAMPLE mls Ca~ mls Na+ Grain Grain Grams ~ -0~ .06 .01 612.0 6 24.9 -0- .0~ .02 644.8 7 -0- 83 ~06 .06 504.8 8 83 ~0- .13 ~01 494.6 9 -0- 166 .0~ .12 437.6 24~9 ~3 .08 .~7 424.0 lo 11 lÇ6 -0- ,1~ .~4 424.0 12 83 166 .13 - .13 383.2 `13 373.5 -0- .33 .02 369.8 14 166 166 .18 .12 326.4 166 270 .19 .21 275.4 16 -0- 270 .06 .18 270.0 17 83 27~ .13 .20 242.4 18 -0- 481.5 .06 .27 197.2 19 373.5 481.5 .36 .36 185.~
alumina 88.2 Examples 7, 11 and 15 were repeated except that the grain was slowly fired in a manner similar to prior art ~xample 1. In particular, the grain was slowly fired in a stationary kiln from ambient temperature to 1500C over a time period of 16 hours followed by 30 minutes at 1500C. The resulting abrasives were so poor that no cutting data could be obtained.
The foregoing examples clearly demonstrate the superiority of the cutting performance of high calcium and sodium sol gel abrasive grains manufactured in accordance with the pro-cess of the invention and show that when the step of rapidly heating dried high calcium and sodium sol gel to sintering tem-perature is omitted, as in the prior art, the resulting grain is an inferior grain.
Claims (11)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for forming abrasive grains which comprises:
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and from above about .05 to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight per-cent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) calcining the grains;
f) rapidly heating the grains to above about 1200°C in less than 10 minutes; and g) continuing to heat the grains at a sintering tem-perature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and from above about .05 to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight per-cent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) calcining the grains;
f) rapidly heating the grains to above about 1200°C in less than 10 minutes; and g) continuing to heat the grains at a sintering tem-perature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
2. A process for forming abrasive grains which comprises:
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and from above about .05 to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight per-cent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) rapidly heating the grains to above about 1200°C in less than 10 minutes; and f) continuing to heat the grains at a sintering temperature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and from above about .05 to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight per-cent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) rapidly heating the grains to above about 1200°C in less than 10 minutes; and f) continuing to heat the grains at a sintering temperature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
3. A process for forming abrasives having alpha-alumina grains with a diameter from about 5,000 Angstroms to about 200,000 Angstroms which comprises:
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and up to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight percent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) rapidly heating the grains to above about 1200°C in less than 10 minutes; and f) continuing to heat the grains at a sintering temperature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and up to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight percent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) rapidly heating the grains to above about 1200°C in less than 10 minutes; and f) continuing to heat the grains at a sintering temperature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
4. The process of claim 3 further including, prior to the rapidly heating step, the step of calcining the grains.
5. A process for forming abrasives having non-randomly oriented alpha-alumina grains which comprises:
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and up to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal contain-ing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight percent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) rapidly heating the grains to above about 1200°C in less than 10 minutes; and f) continuing to heat the grains at a sintering temperature between about 1200°C and about 1650°C for a suffi-cient sintering time to sinter the grains to a density above about 85% of theoretical density.
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and up to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal contain-ing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight percent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) rapidly heating the grains to above about 1200°C in less than 10 minutes; and f) continuing to heat the grains at a sintering temperature between about 1200°C and about 1650°C for a suffi-cient sintering time to sinter the grains to a density above about 85% of theoretical density.
6. The process of claim 5 further including, prior to the rapidly heating step, the step of calcining the grains.
7. The process of claims 1, 2 or 3 wherein the sintering aid is a water soluble compound of magnesium, zinc, nickel or cobalt.
8. The process of claims 4, 5 or 6 wherein the sintering aid is a water soluble compound of magnesium, zinc, nickel or cobalt.
9. A sintered abrasive grain composition manufactured in accordance with a process comprising:
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and from above about .05 to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight per-cent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) calcining the grains;
f) rapidly heating the grains to above about 1200°C in less than 10 minutes; and g) continuing to heat the grains at a sintering tem-perature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and from above about .05 to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight per-cent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) calcining the grains;
f) rapidly heating the grains to above about 1200°C in less than 10 minutes; and g) continuing to heat the grains at a sintering tem-perature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
10. A sintered abrasive grain composition manufactured in accordance with a process comprising:
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and from above about .05 to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight per-cent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) rapidly heating the grains to above about 1200°C in less than 10 minutes; and f) continuing to heat the grains at a sintering temperature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
a) preparing a dispersion comprising from about 2 to about 60 weight percent aluminum oxide monohydrate; a dissolved metal containing sintering aid in an atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate of from 1:2 to 1:35, and from above about .05 to about 1.8 weight percent sodium plus calcium by weight of dispersed and dissolved metal containing solids in the dispersion, provided that the weight percent calcium is from 0 to about 1.8 and the weight per-cent sodium is from 0 to about 0.4;
b) gelling said dispersion;
c) drying the gelled dispersion at a temperature below the frothing temperature of the gel to vaporize free water;
d) crushing the dried solid to form grains;
e) rapidly heating the grains to above about 1200°C in less than 10 minutes; and f) continuing to heat the grains at a sintering temperature between about 1200°C and about 1650°C for a sufficient sintering time to sinter the grains to a density above about 85%
of theoretical density.
11. An abrasive grain comprising alumina, a metal oxide, and up to about 1.8 weight percent sodium plus calcium, provided that the weight percent calcium is from 0 to about 1.8 and the weight percent sodium is from 0 to about 0.4.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US26749581A | 1981-05-27 | 1981-05-27 | |
| US267,495 | 1981-05-27 | ||
| US33012381A | 1981-12-14 | 1981-12-14 | |
| US330,123 | 1981-12-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1195848A true CA1195848A (en) | 1985-10-29 |
Family
ID=26952474
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000403735A Expired CA1195848A (en) | 1981-05-27 | 1982-05-26 | Superior high sodium and calcium sol gel abrasive and process for its production |
Country Status (6)
| Country | Link |
|---|---|
| BR (1) | BR8203073A (en) |
| CA (1) | CA1195848A (en) |
| DE (1) | DE3219607A1 (en) |
| FR (1) | FR2512828B1 (en) |
| GB (1) | GB2099012B (en) |
| MX (1) | MX156659A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5259147A (en) * | 1986-02-15 | 1993-11-09 | Vereinigte Schmirgel-Und Maschinenfabriken Aktiengesellschaft | Granular abrasive material |
| US5453104A (en) * | 1985-04-30 | 1995-09-26 | Minnesota Mining And Manufacturing Company | Process for durable sol-gel produced alumina-based ceramics and abrasive grain |
Families Citing this family (25)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4543107A (en) * | 1984-08-08 | 1985-09-24 | Norton Company | Vitrified bonded grinding wheels containing sintered gel aluminous abrasive grits |
| US5383945A (en) * | 1984-01-19 | 1995-01-24 | Norton Company | Abrasive material and method |
| US4623364A (en) * | 1984-03-23 | 1986-11-18 | Norton Company | Abrasive material and method for preparing the same |
| US5227104A (en) * | 1984-06-14 | 1993-07-13 | Norton Company | High solids content gels and a process for producing them |
| US4657754A (en) * | 1985-11-21 | 1987-04-14 | Norton Company | Aluminum oxide powders and process |
| DE3604848A1 (en) * | 1986-02-15 | 1987-08-20 | Ver Schmirgel & Maschf | ABRASIVE GRAIN AND METHOD FOR THE PRODUCTION THEREOF |
| AU604899B2 (en) * | 1987-05-27 | 1991-01-03 | Minnesota Mining And Manufacturing Company | Abrasive grits formed of ceramic, impregnation method of making the same and products made therewith |
| US5312789A (en) * | 1987-05-27 | 1994-05-17 | Minnesota Mining And Manufacturing Company | Abrasive grits formed of ceramic, impregnation method of making the same and products made therewith |
| JPH02263718A (en) * | 1988-09-09 | 1990-10-26 | Univ Simon Fraser | Preparation of transition alumina ground into ultrafine particle from porous alumina |
| US5076815A (en) * | 1989-07-07 | 1991-12-31 | Lonza Ltd. | Process for producing sintered material based on aluminum oxide and titanium oxide |
| JPH06104816B2 (en) * | 1990-02-09 | 1994-12-21 | 日本研磨材工業株式会社 | Sintered alumina abrasive grains and method for producing the same |
| US5219806A (en) * | 1990-07-16 | 1993-06-15 | Minnesota Mining And Manufacturing Company | Alpha phase seeding of transition alumina using chromium oxide-based nucleating agents |
| US5139978A (en) * | 1990-07-16 | 1992-08-18 | Minnesota Mining And Manufacturing Company | Impregnation method for transformation of transition alumina to a alpha alumina |
| CN1068092A (en) * | 1991-06-21 | 1993-01-20 | 瑞士隆萨股份公司 | Production is the agglomerated material method of abrasive material particularly of matrix with the Alpha-alumina |
| DE4124630A1 (en) * | 1991-07-25 | 1993-02-11 | Starck H C Gmbh Co Kg | COLORED COROD, METHOD FOR THE PRODUCTION AND USE THEREOF |
| CA2102656A1 (en) * | 1992-12-14 | 1994-06-15 | Dwight D. Erickson | Abrasive grain comprising calcium oxide and/or strontium oxide |
| DE19503854C2 (en) * | 1995-02-06 | 1997-02-20 | Starck H C Gmbh Co Kg | Process for the production of sintered alpha-Al¶2¶O¶3¶ bodies and their use |
| EP0817701B1 (en) * | 1995-03-21 | 1999-12-15 | Norton Company | Grinding wheel for flat glass beveling |
| US5516347A (en) * | 1995-04-05 | 1996-05-14 | Saint-Gobain/Norton Industrial Ceramics Corp. | Modified alpha alumina particles |
| US5611829A (en) * | 1995-06-20 | 1997-03-18 | Minnesota Mining And Manufacturing Company | Alpha alumina-based abrasive grain containing silica and iron oxide |
| US5645619A (en) * | 1995-06-20 | 1997-07-08 | Minnesota Mining And Manufacturing Company | Method of making alpha alumina-based abrasive grain containing silica and iron oxide |
| DE19629690C2 (en) * | 1996-07-23 | 1999-08-05 | Korund Laufenburg Gmbh | Process for the production of sintered alpha-AL¶2¶0¶3¶ bodies and their use |
| US20130337725A1 (en) * | 2012-06-13 | 2013-12-19 | 3M Innovative Property Company | Abrasive particles, abrasive articles, and methods of making and using the same |
| US10155892B2 (en) | 2014-02-27 | 2018-12-18 | 3M Innovative Properties Company | Abrasive particles, abrasive articles, and methods of making and using the same |
| BR102020017280A2 (en) | 2020-08-24 | 2022-03-03 | Mauro Tiecher | Machine and method for cleaning offal of slaughter birds |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3615308A (en) * | 1968-02-09 | 1971-10-26 | Norton Co | Crystalline abrasive alumina |
| FR2086972A5 (en) * | 1970-04-15 | 1971-12-31 | Pechiney | Abrasive grains by alpha alumina-in alumina zirconia eutectic - matrix |
| GB1392618A (en) * | 1971-06-03 | 1975-04-30 | Norton Co | Abrasive material |
| US4181532A (en) * | 1975-10-22 | 1980-01-01 | United Kingdom Atomic Energy Authority | Production of colloidal dispersions |
| US4314827A (en) * | 1979-06-29 | 1982-02-09 | Minnesota Mining And Manufacturing Company | Non-fused aluminum oxide-based abrasive mineral |
-
1982
- 1982-05-25 DE DE19823219607 patent/DE3219607A1/en active Granted
- 1982-05-26 GB GB8215424A patent/GB2099012B/en not_active Expired
- 1982-05-26 BR BR8203073A patent/BR8203073A/en not_active IP Right Cessation
- 1982-05-26 FR FR8209190A patent/FR2512828B1/en not_active Expired
- 1982-05-26 CA CA000403735A patent/CA1195848A/en not_active Expired
- 1982-05-27 MX MX192884A patent/MX156659A/en unknown
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5453104A (en) * | 1985-04-30 | 1995-09-26 | Minnesota Mining And Manufacturing Company | Process for durable sol-gel produced alumina-based ceramics and abrasive grain |
| US5259147A (en) * | 1986-02-15 | 1993-11-09 | Vereinigte Schmirgel-Und Maschinenfabriken Aktiengesellschaft | Granular abrasive material |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2099012A (en) | 1982-12-01 |
| FR2512828A1 (en) | 1983-03-18 |
| DE3219607A1 (en) | 1982-12-23 |
| MX156659A (en) | 1988-09-22 |
| DE3219607C2 (en) | 1990-04-19 |
| GB2099012B (en) | 1985-09-04 |
| BR8203073A (en) | 1983-05-10 |
| FR2512828B1 (en) | 1986-11-14 |
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