JPH0216792B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to abrasine grains, and more particularly to abrasine grains of the sintered type. This application is filed on December 14, 1981 and is entitled U.S. Patent Application No. 330123 entitled Superior High Sodium and Calcium Gel Abrasive and Method for Making the Same.
The above application was filed in May 1981.
This is a continuation-in-part of co-pending U.S. Patent Application No. 267,495, filed on the 27th, entitled Superior High Calcium Sol-Gel Abrasive and Method for Making the Same. In the prior art, abrasive grains, particularly abrasive grains containing metal oxides such as alumina, have traditionally been prepared by melting the oxide and subsequently crushing the cooled molten oxide to form abrasive grains. Manufactured with More recently, abrasive grains have been produced by sintering metal oxides such as alumina. Such abrasive grains are reasonably usable, but do not last as long as desired, and furthermore do not cut as fast as desired. Ceramic materials that may be in the form of abrasive products include inorganic colloidal gels (see U.S. Pat. No. 2,455,358).
It is known that ceramic oxide particles can be produced by bonding them to each other by using . It is also known to gel, dry, and calcinate colloidal dispersions to form porous ceramic materials (see, eg, US Pat. No. 4,181,532). Free-flowing spheres of pure or mixed oxides are also known to be produced by dispersing oxide hydrates, followed by shaping the gel into spheres, followed by sintering [industrial Application of Sol-Gel Processes to Oxides, January 13, 1968
“Industrial oxides”, January 13, 1968,
(See Chemistry and Industry). It is at least possible that such particles of spherical or angular shapes can be used as abrasives.
Also known by others in the United States as early as 1971. Such previous findings by others in the United States were confirmed by Harwell, UK.
United Kingdom Atomic Energy Agency (England)
This is evidenced by a report from Atomic Energy Autority to Carborundim Company, Ltd, and then to several people at Carbonundim Company, Ltd. in the United States. Recently, U.S. Pat. No. 4,314,827 was issued for a process for making an abrasive mineral based on non-fused aluminum oxide and an abrasive product containing the abrasive mineral. U.S. Pat. No. 4,314,827 discloses that an abrasive mineral having randomly oriented crystallites having diameters on the order of 3000 angstroms or less gels a colloidal dispersion or hydrosol of alumina and a modified component, and then It is generally disclosed in US Pat. No. 4,314,827 that the gel can be made by firing the gel. This disclosure makes clear that the mineral should not contain calcium and alkali metals (less than about 0.05% total weight). This requirement requires the use of complex purification methods when calcium and alkali metals are present in the alumina or modified components, as they often are. Calcium is present, for example, in common water supplies and in magnesium-containing modified components unless costly and complex purification methods are used to remove the calcium. Similarly, sodium is commonly present in many aluminas unless removed by additional purification steps. No methods that allow for the presence of calcium or alkali metals are suggested in the above US patents, and any methods that inherently allow for the presence of high calcium or alkali metals have not been used in practice with high calcium or alkali metals. Nakatsuta. In accordance with the present invention, a method is provided for forming ceramic particles from a gelled dispersion (sol-gel) by drying and sintering the gel. The particles of the present invention can be used for any suitable purpose. Such particles can be used in applications where temperature resistance, strength, hardness, abrasion resistance, and inertness are desired. Such particles can be used, for example, as aggregates, fillers in distillation columns, or as catalyst supports due to the superficial porosity of some of such particles. The most common use for such particles is as an abrasive. Such particles are therefore referred to herein as abrasives, but are also referred to as abrasive particles.
The term abrasive grains is intended to encompass such particles regardless of their intended end use. The abrasive product obtained by the method of the present invention is approximately 0.05
They are far superior to conventional fused alumina abrasives, even though they typically contain more sodium + calcium by weight. High sodium and calcium in the abrasive grains are tolerated by rapid heating of the dried sol-gel over a critical temperature range of less than about 800°C to greater than about 1200°C. The abrasive grains are then sintered at a temperature greater than about 1200°C. A preferred method is from about 2% to about 60% by weight aluminum oxide monohydrate, with a molten or dispersed metal having an atomic ratio of metal to aluminum of 1:2 to 1:35, preferably 1:7 to 1:25. preparing a dispersion comprising a sintering aid containing sintering aid, and greater than about 0.05% to about 1.8% sodium plus calcium by weight of the dispersed and dissolved metal-containing solids in the dispersion. . Calcium weight %+sodium weight % is preferably less than 0.6, more preferably less than 0.15. Calcium weight percentage can range from 0 to about 1.8, and sodium weight percentage can range from about 0 to about 0.4.
Calcium weight percentage is preferably from 0 to about 0.6
and more preferably from 0 to about 0.15, and the sodium weight percentage is preferably from 0 to about
0.25, more preferably 0 to about 0.1. After the dispersion is prepared, it is gelled and dried below the gel's freezing temperature to remove free water. Any suitable drying method known to those skilled in the art can be used.
As used herein, "drying" means dehydrating by any method including solvent extraction. The dried solids are then crushed to form grains. The grains are then heated, usually to about 500°C to 800°C. The grains are then rapidly heated to a temperature above about 1200° C. for less than 10 minutes, preferably less than 5 minutes. Then, 3.3g/
^cm3 or more (theoretical density of α-alumina 3.96g/ ^cm3
Continue heating at a sintering temperature of about 1200°C to about 1650°C for a period sufficient to sinter to a density (greater than about 85% of
Preferably it is carried out at a temperature higher than 1300°C. The resulting grains are substantially better than prior art fused alumina grains and are
4,134,827, which requires low sodium and calcium (less than about 0.05 wt%)
It is a sintered sol-gel abrasive with a combination of cutting rate) and wear resistance. “Substantially better” means at least 1.5 times better;
Usually means at least twice as good relative cutting performance. The present invention also encompasses bonded, coated, non-woven abrasive articles comprising the novel particles described above. For example, coated abrasives made from the preferred abrasive grains of the present invention continue to have high cutting speeds until the grains are suspended from the substrate, whereas the total amount of material cut by the abrasive article is lower than that of most prior art materials. Better than grains. According to the method of the invention, the particles are about 2% by weight.
From about 60% by weight, usually from about 10% to about 40% by weight
aluminum oxide monohydrate (AlOOH), a dissolved metal-containing sintering aid with an atomic ratio of metal to aluminum in the sintering aid of 1:2 to 1:35, and alkali metals (especially sodium) and calcium. The total amount of dispersed and dissolved solids in the dispersion is approximately
It is prepared from a liquid (preferably aqueous) dispersion comprising up to 1.8% by weight, and usually greater than about 0.05% to about 1.8% by weight, of alkali metals (particularly sodium) and calcium. Calcium weight percentage + sodium weight percentage is preferably less than 0.6, more preferably
Less than 0.15. Calcium weight percentage can range from 0 to about 1.8 and sodium percentage can range from 0 to about 0.4. The calcium weight percentage is preferably from 0 to about 0.6;
More preferably, it is from 0 to about 0.15, and the sodium weight percentage is preferably from 0 to 0.25, and even more preferably from 0 to about 0.1. The amount of aluminum oxide monohydrate in the dispersion is usually about 10 to about 40% by weight of the dispersion, preferably about 15% by weight of the dispersion.
to about 35% by weight. As used herein, aluminum oxide monohydrate has the stoichiometric formula 1/2
( _Al2O3.xH2O ), where x _is from 0.5 _to 3 ^, is intended to be included. Aluminum oxide monohydrate is also known as boehmite. As used herein, aluminum oxide monohydrate is also intended to include, but is not limited to, pseudo boehmite. Generally, all solids in the dispersion are preferably in dissolved or colloidal form. The dispersion is formed by any suitable means, which may be simply by mixing aluminum oxide monohydrate and water. This liquid is almost always water, but may also be other liquids such as low molecular weight alcohols. Any suitable mixing equipment can be used, including high shear and low shear mixers. Dispersing aids such as acids are often used. For example, about 0.02 mole to 0.25 mole, preferably 0.05 mole to about 0.15 mole of HNO ₃ or other volatile mineral acid per mole of aluminum oxide monohydrate greatly aids in dispersion. "Volatile mineral acid" means a mineral acid that evaporates from a dispersion, gel, or dried gel at a temperature below the sintering temperature, or that all of its residues are dissolved as such in the finished grain. means an acid that evaporates or forms part of an oxide.
Examples of such acids are nitric acid, hydrochloric acid, acetic acid and formic acid. The solids content in the final dispersion is up to 50% by weight of additional components other than aluminum oxide monohydrate, preferably compounds such as silica, magnesia, chromia and titanium dioxide in colloidal or dissolved form, or colloids. may contain precursors of such compounds in solid or dissolved form. The dissolved or dispersed metal-containing sintering aid is added to the dispersion in a metal to aluminum atomic ratio of 1:2 to 1:35, preferably 1:7 to 1:25. Sintering aids are dispersible or soluble metal oxides or metal oxide precursors, ie compounds that form metal oxides during drying, calcination or sintering.
In general, the sintering aid is usually a precursor of magnesium oxide, zinc oxide, cobalt oxide or nickel oxide, so that when the liquid is water, the magnesium, zinc, nickel or cobalt is soluble or dispersible in water. It is a chemical compound. Particular examples of such precursors are nitrates and chlorides of these metals. Nitrates of these metals, especially magnesium, are particularly preferred. Sintering aids can be prepared in situ, for example, by adding magnesium oxide or hydroxide to an aqueous solution of an inorganic acid such as hydrochloric acid or nitric acid to form a water-soluble salt of magnesium. The firing aid is usually a water-soluble salt, but may also be a water-soluble base. Sodium and calcium in the dispersion usually arise naturally from calcium impurities in other components in the dispersion. A common source of sodium is from alumina. Common sources of calcium are from magnesium-containing sintering aids or impurities in the water. As used herein, "calcium" and "sodium" almost always refer to calcium or sodium ions, due to the electropositive nature of calcium and sodium.
That is, it means chemically bound calcium and sodium, which is free calcium or sodium ions or ionically bound sodium or calcium. According to the method of the invention relatively high amounts of calcium and sodium can be tolerated in the dispersion, thus avoiding complex and expensive purification steps. According to the present invention, sodium and calcium together can be present in the dispersion up to about 1.8% and will still yield a final abrasive grain superior to conventional fused alumina grains. Preferably, sodium and calcium are present in a combined amount of no more than 0.6%. The percentages of sodium and calcium as noted above are based on the weight of dispersed and dissolved metal-containing solids in the dispersion. The percentage is essentially the same as the percentage in the final abrasive. After preparing the dispersion, it is gelled. Addition of a 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 very low, either the liquid must be evaporated or other gelling methods must be used in order for the dispersion to gel, i.e. the addition of a gelling agent. Sometimes. After the dispersion gels, it is dried at a temperature below the foaming temperature of the gel to evaporate free water. As used herein, "dry" or "dried" means that at least 90% of the free (unbound) water has been removed to form a solid. "Foaming temperature" is the temperature at which the gel foams or bubbles under the pressure applied to the gel. Drying can be accomplished by means known to those skilled in the art. If heat is used, the drying temperature is usually about 80°C to about 120°C. Drying time depends on the amount of water or other liquid present, drying pressure and drying temperature. Drying time is usually about 1 hour at atmospheric pressure.
It is 72 hours. The resulting dry gel is usually
But not necessarily a translucent solid,
That is, it is a solid body through which light rays pass in a diffused form. After the solid has dried, it is crushed or fractured to form particles or grains by suitable means such as a hammer or ball mill.
Any suitable means for comminuting the solids may be used, and "crushing" is intended to encompass all such methods. After crushing, the grains are typically heated at about 500°C until all water has been removed and all components of the grains are in the form of ceramics (usually metal oxides) or otherwise evaporated. It is usually heated to a temperature of about 800°C. When the grain reaches a temperature of about 250°C to about 300°C, acid residues are driven
off). About 250℃ to about 800℃, usually about 300℃ to 600℃
C. essentially all the water is usually removed. "Essentially all" as used in this context means that all free water and more than 90% of the feed water are removed. Calcination times to remove essentially all water are typically about 5 minutes to about 20 minutes. After drying and after calcination, the grains are rapidly heated to a temperature above about 1200°C. “Heats quickly”
By this we mean fast enough to allow the formation of an abrasive with good cutting rates and good wear resistance. 10 for quick heating
It is usually carried out for less than a minute, preferably for less than 5 minutes, and most preferably for less than 1 minute. This rapid heating step allows the formation of superior abrasive grains from gelled dispersions (sol-gels) containing relatively high amounts of calcium and sodium. For example, in a form other than in bulk, i.e. in pieces, above about 1200°C, preferably at 1300°C.
Any suitable means or method for rapidly heating the grains can be used, such as injection into a higher preheated furnace. Skip the calcination process and instead dry at approximately 1200℃
It is possible to quickly heat the grains to higher temperatures. This particular procedure is particularly desirable for producing certain abrasives. After rapidly heating the grains to a temperature higher than 1200℃,
They range from about 1200°C to about 1650°C, preferably 1250°C.
Continue heating for a sufficient sintering time to sinter the grains to a density greater than about 85% of the theoretical density at a sintering temperature of 1500°C to 1500°C. When the abrasive is primarily aluminum oxide with about 6% magnesium oxide by weight of aluminum oxide, the desired density is greater than about 3.3 grams per cubic centimeter. At least the heating portion typically occurs at temperatures above 1300°C. The sufficient time to sinter the grains depends on the sintering temperature and is typically from about 5 minutes to about 30 minutes, but may be less than about 5 minutes, such as from about 1 minute to about 5 minutes. It may be hot. With crossed polarizers, approx.
Transmission light microscope at 500X or 700X
When looking at polished thin sections of sintered grains produced according to the method of the invention under an optical microscope, the microstructure of the material with a nominal composition of alumina-6% magnesia disappears as a unit when the sample is rotated. Areas with a nominal diameter of approximately 5,000 angstroms to approximately 200,000 angstroms
It is observed that it consists of In this example, extinction is believed to result from the predominant birefringent α-alumina phase. For these areas to disappear as a unit, they must be either continuous alpha alumina grains or smaller non-randomly oriented (n+n-
It is thought that the area must be somewhere in the area of alumina grains (randomly oriented). If the alpha-alumina grains have a diameter in the range of about 5,000 angstroms to about 200,000 angstroms, or have a much smaller diameter but are non-randomly oriented, the combined weight percentage of calcium + sodium in the grains is May be smaller than 0.05. The microstructure of the alumina grains of the present invention differs significantly from that of conventionally sintered or fused alumina grains of similar composition in the uniformity of the distribution of metal oxide sintering aids. Upon firing of the previously calcined material, a phase transition from an atomically homogeneous distribution of magnesia in γ-alumina to a microscopically homogeneous intimate mixture of alumina and spinel occurs. It is thought that the Ordinary sintering of abrasive grains is achieved by a diffusion mechanism or a liquid phase densification mechanism of pre-existing α-alumina crystals.
phase densification mechanism). Sintering of sol-gel abrasives is a displasiul polymorphic trans-
formation). This unique phase transition usually results in a significant reduction in sintering temperature. The present invention provides a combination comprising the abrasive grains of the present invention,
Coated and nonwoven abrasive articles are further included.
Generally, the abrasive grains of the present invention contain up to about 1.8 weight percent, typically greater than about 0.05 weight percent, to about 1.8 weight percent of alumina, metal oxides that aid in sintering, and calcium and sodium. Preferably up to about 0.6% by weight, most preferably about 0.15% by weight
It can be said that the abrasive grains are sintered abrasive grains containing calcium and sodium. As previously stated, the preferred sintered grains produced according to the method of the present invention have excellent serviceability properties, furthermore, retain high cutting speeds and are superior to most prior art grains. Eliminate large amounts of carbon steel stock. High sodium and calcium containing prior art grains do not have as high a combined cutting speed and wear resistance as the best abrasive grains made in accordance with the present invention. As mentioned above, the sintered sol-gel abrasives of the present invention have better relative cutting performance with coated discs on carbon steel than fused alumina abrasives. Preferred sol-gel abrasives of the present invention are at least twice as effective as conventional fused alumina abrasives.
Typically, such cutting speeds are at least three to four times better. Relative cutting performance is determined as defined and described in the Examples below. The following examples illustrate the present invention, but are not intended to limit the invention. Example 1 Prior Art High calcium sol gel abrasive grains were prepared according to essentially the same method as the prior art, consisting of slowly and essentially uniformly heating a dry high calcium sol gel from ambient temperature to 1370°C. Manufactured.
In particular, the Condair Hemy Dispiral
(Condea Chemie Dispural) 10,199 grams of boemite were dispersed in 20.5 gallons of water and then 573 ml of concentrated nitric acid was added to form a sol (colloidal solution). Then 73.9 g of titanium isopropoxide dispersed in 4150 ml of isopropyl alcohol and Nalco-Chemical Nalcoage 1034A were added.
1034A) 36.5 g of colloidal silica dispersion were mixed into the above sol. 3162 grams of magnesium nitrate was dissolved in 2 gallons of water and the resulting solution was added to the sol with stirring. Gelation occurred almost instantaneously. Stirring was continued for approximately 5 minutes. The gel was then transferred to a plastic tray approximately 10 cm deep. The tray was placed in a steam heated dryer and the gel was dried for about 60 hours. Pass the dried gel through a roll crusher to reduce it to -28 mesh granules. Size fractions -28 to +48 mesh were separated by sieving. The dried granules were placed in aluminum oxide coated saggers and placed in the kiln.
Heat the kiln to 1370°C for 6 hours and
It was held at 1370°C for minutes. The kiln was switched off and allowed to cool. The resulting calcined grains were porous and analyzed to have a calcium content of 0.14% by weight. The density was 85% less than theory. Sintered granules to 50 grit
Particle size classification was performed using a conventional sieve meeting ANSI 74.18-1977 specifications. One coated abrasive material was prepared by electrostatic coating of 50 grain size particles onto a vulcanized fibrous matrix. The fibers chosen were abrasive grade 0.030 inch vulcanized fibers (480
-9 x 11 sheets). A manufacturer adhesive mixture consisting of a commercially available one-stage liquid phenolic resin having a formaldehyde to phenol ratio of approximately 1:1 and ground limestone having an average particle size of 17 microns to 25 microns.
Adhesive mix) was prepared using a 1:1 net weight mix ratio. The above manufacturer's mixture was then heated to 90°C and roll coated onto the fiber substrate. Approximately 14 pounds of adhesive was applied per ream. Using regular sandpaper making equipment, 50
A grain size abrasive was electrostatically projected onto the fibers supporting the above manufacturer's mixture at approximately 38 pounds of grain applied in a barrage. Then apply the abrasive adhesive coated substrate to 175〓 for 1 hour and 200〓 for 2 hours on maker rack.
It was heated at After drying, a size coating was then applied using standard roll coating techniques at approximately 21 pounds per coat. The sizing mixture consisted of the same 1:1 phenolic resin-filler. However, 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 1 hour at 150 degrees, 4 hours at 175 degrees, and 16 hours at 22 degrees. After curing, the material was conditioned in conventional manner to a moisture content of less than 8% by weight. The material was then uniformly bent and die cut into 7 inch discs. These were then evaluated in a conventional pneumatic disc grinder using 1018 cold rolled steel as the workpiece and made and handled in exactly the same manner except that the abrasive grain was molten alumina. compared to a control disc. In this test, an abrasive disc is placed on a disc grinder in a standard manner and a 1 x 2 x 11 inch workpiece is engaged to the disc with the 1 inch flat side at a 10-15 degree angle. It was positioned as such. The disk was passed back and forth along the work piece. The abrasive disc in this test was a hard rubber type with a diameter of 7". Nominal on the back-up pad.
Rotated at 5400 RPH′. The test was 30 seconds after which the stock removed from the bar was measured (weight before grinding - weight after grinding) and recorded. This sequence was continued until the measured stock removed was 5 grams per grinding interval or less. The total stock removed in this manner for the test disc was compared to the total stock removed for the control disc (relative cutting performance). High calcium (0.14% by weight) loose and heated sol-gel abrasive (substantially in accordance with the prior art)
had only 97% of the cutting performance of standard and inexpensive fused alumina abrasives. Example 2 Instead of slowly heating the dried granules as in Example 1, the granules were heated to 550° C. for approximately 30 minutes.
After calcining, they were heated in accordance with the invention above 1200°C by introduction into a rotary tube furnace at 1390°C. The granules were heated to 1390°C for about 10 minutes and held at 1390°C for about 30 minutes to sinter the grains. Other points were not much different from Example 1. Analysis of the resulting sintered grains revealed a calcium content of 0.11% by weight and a specific gravity exceeding 3.3 (theoretical).
>85%). When tested as described in Example 1, the disc was found to have a relative cutting performance that was 395% of the cutting performance of fused alumina abrasive. In other words, the grains of the present invention had a cutting performance 3.95 times that of the fused alumina abrasive grains. Example 3 Example 2 was substantially repeated except that the dried grains were calcined at 600°C instead of 550°C. The finished grain was found to have a calcium content of 0.12% by weight and a density of 85% over theory. The relative cutting performance was 4.39 times that of fused abrasive. Example 4 720 in 1.66 gallons of water containing 1660 ml of concentrated nitric acid
Example 2 was substantially repeated except that the magnesium nitrate used was prepared by dissolving grams of magnesium hydroxide. The resulting solution was added to the sol with stirring. As in Example 2, gelation occurred immediately and stirring was continued for 5 minutes. The resulting grains had a calcium content around 0.08% by weight, a density 85% over theoretical, and a cutting performance about 4.5 times that of fused alumina. Furthermore, the resulting grains have a cutting performance approximately 24 times that of commercially available quenched fused alumina-zirconia grains, and have a cutting performance that is approximately 24 times that of commercially available quenched fused alumina-zirconia grains.
It had comparable cutting performance to commercially available low calcium sintered sol-gel alumina-containing grains similar to the low calcium and sodium grains described in No. 4,314,827. Example 5 High calcium and sodium sol-gel abrasive grains were prepared essentially according to Example 2. In particular, 33.5 grams of condensed hemi-dispiral Boehmite (20,559 g)
Disperse in 1 gallon of water and then add 1250 ml of concentrated technical grade nitric acid diluted in 2 gallons of water 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. Gelation occurred almost instantaneously. Stirring was continued for approximately 5 minutes. The gel was then transferred to a 2.5 cm to 3.75 cm deep plastic tray. The tray was placed in an electrically heated dryer to dry the gel, which took approximately 48 hours. The dried gel was passed through a roll crusher to reduce it to -20 mesh granules. The particle size fraction -20 to +48 mesh was separated by sieving. The granules were calcined at 550℃ for about 30 minutes and then
They were rapidly heated in accordance with the present invention to temperatures above 1200°C by rapid firing at about 1395°C in a rotary tube furnace at 1.2 rpm. Granules (granules) for another 10 minutes
Heated to 1390°C. The resulting granules had a calcium content of approximately 0.07% by weight and a sodium content of 0.015% by weight. The density was 85% over theory. Sintered granules meet ANSI74.18− for 36 grain size
The grain size was classified using conventional sieves to meet the 1977 specifications. One coated abrasive material was produced by electrostatically coating 36 grain size particles onto a vulcanized fibrous matrix. The fiber chosen was an abrasive grade 0.030 inch vulcanized fiber (480-9 x 11 sheets) having a nominal weight of 67 pounds per ream. Using a 1:1 net weight mix ratio, a manufacturer's adhesive mixture consisting of a commercially available one-stage liquid phenolic resin having a formaldehyde to phenol ratio of approximately 1:1 and ground limestone having an average particle size of 17 microns to 25 microns was used. Manufactured by The above manufacturer's mixture was then heated to 90°C and roll coated onto the fiber substrate. Approximately 23 pounds of adhesive was applied per ream. Using regular sandpaper making equipment, 36
A particle size abrasive was electrostatically projected onto the fibers supporting the above manufacturer's mixture having approximately 62 pounds of grain applied in a barrage. The abrasive adhesive coated substrate was then heated on the manufacturer's shelf to 175° for 1 hour and 200° for 2 hours. After drying, a size coating was then applied using standard roll coating techniques at approximately 23 pounds per ream. The sizing mixture consisted of the same 1:1 phenolic resin-filler ratio. The coated material was then heated at 150° for 1 hour, 175° for 4 hours, and 225° for 1 hour.
Drying and curing was achieved by heating for 16 hours. After the material had been cured, it was conditioned to a moisture content of less than 8% by weight in a conventional manner. The material was then uniformly bent and die cut into 7 inch disks. Five of these discs were then evaluated in a conventional pneumatic disc grinder using rapidly cooled and tempered 4140 steel (hardness 285-320 BHN) as workpieces and were accurate except that the abrasive grains were fused alumina. compared to a control disk made and treated in the same manner. In this test, an abrasive disk is placed on a disk grinder in a standard manner and a 1 x 2 x 11 inch workpiece is positioned so that it engages the disk with the 1 inch flat side at a 10-15 degree angle. Ta. The disk was passed back and forth along the work piece. In this test, the abrasive disc was nominally mounted on a 7" diameter hard rubber type backup pad.
Rotated at 5400RPM. A dead weight in-feed force of 8 pounds was applied to the workpiece. The test was run for 30 seconds, after which the stock removed from the bar was measured (weight before grinding - weight after grinding) and recorded. This sequence was continued until the measured stock removed was 5 g per grinding interval or less. The 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 and sodium (0.07 combined weight percent) rapidly accelerated sol-gel abrasive had an average cut of 612 g (almost 7 times that of standard fused alumina). The results are shown in Table 1. Examples 6-19 The method of Example 5 was followed except that various known amounts of calcium and sodium were added to the dispersion prior to the addition of magnesium nitrate. Sodium and calcium were added as sodium and calcium nitrate solutions. Sodium nitrate solution is
Calculated as Na ₂ O, equivalent to 0.2 g/ml per ml
Contains 0.54g of NaNO ₃ , and the calcium nitrate solution has an equivalent of 0.2g/ml as CaO.
It contained 0.58 g of Ca(NO ₃ ) ₂ per ml. The results are listed in Table 1. Calcium and sodium in the grains are analyzed by optical emission spectroscopy. The slight variation between added and actual calcium in the granules is believed to be due to the magnesium nitrate and additional calcium present in the water, and the slight variation between added and actual sodium in the granules. is believed to be due to impurities in the grain components, especially water, and some evaporation of sodium during the calcination and sintering period. For comparison, the average cutting of conventional fused alumina grains is shown in Table 1.

Table: Example 20 Examples 7, 11 and 15 were repeated except that the grains were slowly calcined in a manner similar to Prior Art Example 1. Specifically, the grains were slowly heated in a stationary kiln from ambient temperature to 1500°C for 16 hours followed by 30 minutes at 1500°C. The quality of the resulting abrasive was so poor that no cutting data could be obtained. The above examples clearly demonstrate the superior cutting performance of high calcium and sodium sol-gel abrasive grains produced according to the method of the present invention, and the dry high calcium and sodium sol-gel is rapidly heated to sintering temperature. If this step is omitted as in the prior art, the grains obtained represent inferior grains.

Claims (1)

[Scope of Claims] 1 (a) from about 2% to about 60% by weight of aluminum oxide monohydrate, wherein the atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate is 1; 0.05% to about 1.8% by weight of the metal-containing solids dispersed and dissolved in the dispersion. preparing a dispersion having a calcium weight percent of 0 to about 1.8 and a sodium weight percent of 0 to about 0.4; (b) gelling the dispersion; drying at a temperature below the foaming temperature of the gel to evaporate free water; (d) crushing the dried solids to form granules; (e) calcining the granules; rapidly heated to a temperature above about 1200°C for less than 10 minutes, and (g) 3.3 g/g at a sintering temperature of about 1200°C to about 1650°C.
A method of forming abrasive particles comprising continuing to heat the particles for a sintering time sufficient to sinter the particles to a density greater than or equal to cm ³ . 2 (a) from about 2% to about 60% by weight of aluminum oxide monohydrate; the atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate is from 1:2 to 1:35; preparing a dispersion comprising a dissolved metal-containing sintering aid and from greater than about 0.05% to about 1.8% by weight of the dissolved metal-containing solids dispersed in the dispersion; provided that the calcium weight percentage is from 0 to about 1.8 and the sodium weight percentage is from 0 to about 0.4; (b) the dispersion is gelled; and (c) the gelled dispersion is heated above the foaming temperature of the gel. (d) crushing the dried solids to form granules; (e) rapidly heating the granules to a temperature greater than about 1200° C. for less than 10 minutes; , and (f) 3.3g/at a sintering temperature of about 1200°C to about 1650°C.
A method of forming abrasive particles comprising continuing to heat the particles for a sufficient sintering time to sinter the particles to a density of cm ³ or higher. 3 (a) from about 2% to about 60% by weight of aluminum oxide monohydrate; the atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate from 1:2 to 1:35; A dispersion was prepared comprising a dissolved metal-containing sintering aid and a dispersion of sodium plus calcium up to about 1.8% by weight of the dissolved metal-containing solids, with the exception that the calcium weight percentage was 0. to about 1.8,
(b) gelling the dispersion; (c) drying the gelled dispersion at a temperature below the foaming temperature of the gel to evaporate free water; (d) crushing the dry solids to form granules; (e) rapidly heating the granules to a temperature greater than about 1200°C for less than 10 minutes; 3.3g/at sintering temperature
continuing to heat the grains for a sufficient sintering time to sinter to a density of at least ³ cm3.
A method of forming an abrasive having alpha-alumina grains having a diameter of 5,000 angstroms to about 200,000 angstroms. 4. The method of claim 3, further comprising the step of calcining the grains before said rapid heating step. 5 (a) from about 2% to about 60% by weight of aluminum oxide monohydrate; the atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate from 1:2 to 1:35; A dispersion was prepared comprising a dissolved metal-containing sintering aid and up to about 1.8% by weight of the dispersion and dissolved metal-containing solids of sodium+calcium in the dispersion, where the calcium weight percentage was (b) gelling the dispersion; (c) drying the gelled dispersion at a temperature below the foaming temperature of the gel; (d) crushing the dried solids to form granules; (e) rapidly heating the granules to a temperature greater than about 1200°C for less than 10 minutes; (f) 3.3g/at sintering temperature of 1200℃ to approx. 1650℃
A method of forming an abrasive having non-randomly oriented alpha-alumina grains comprising continuing to heat the grains for a sufficient sintering time to sinter the grains to a density greater than or equal to ^cm3 . 6. The method of claim 5, further comprising the step of calcining the grains before said rapid heating step. 7. The method according to any one of claims 1 to 6, wherein the sintering aid is a water-soluble compound of magnesium, zinc, nickel, or cobalt. 8 (a) from about 2% to about 60% by weight of aluminum oxide monohydrate; the atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate is from 1:2 to 1:35. preparing a dispersion comprising a dissolved metal-containing sintering aid and from greater than about 0.05% to about 1.8% by weight of the dissolved metal-containing solids dispersed in the dispersion; provided that the calcium weight percentage is from 0 to about 1.8 and the sodium weight percentage is from 0 to about 0.4; (b) the dispersion is gelled; and (c) the gelled dispersion is heated above the foaming temperature of the gel. (d) crushing the dried solids to form granules; (e) calcining the granules; (f) drying the granules for a period of less than 10 minutes; (g) 3.3g/g at a sintering temperature of about 1200°C to about 1650°C;
A sintered abrasive particle composition made according to a method comprising continuing to heat the particles for a sufficient sintering time to sinter to a density of cm ³ or higher. 9 (a) from about 2% to about 60% by weight of aluminum oxide monohydrate; the atomic ratio of metal in the sintering aid to aluminum in the aluminum oxide monohydrate is from 1:2 to 1:35; preparing a dispersion comprising a dissolved metal-containing sintering aid and from greater than about 0.05% to about 1.8% by weight of the dissolved metal-containing solids dispersed in the dispersion; provided that the calcium weight percentage is from 0 to about 1.8 and the sodium weight percentage is from 0 to about 0.4; (b) the dispersion is gelled; and (c) the gelled dispersion is heated above the foaming temperature of the gel. drying at a low temperature to evaporate free water; (d) crushing the dried solids to form granules; and (e) rapidly heating the granules to a temperature above about 1200°C for a period of less than 10 minutes. and (f) 3.3g/at a sintering temperature of about 1200°C to about 1650°C.
A sintered abrasive particle composition made according to a method comprising continuing to heat the particles for a sufficient sintering time to sinter to a density of cm ³ or higher. 10 comprising alumina, metal oxides and up to about 1.8% by weight of sodium plus calcium, with the weight percentage of calcium being from 0 to about 1.8;
and an abrasive particle having a sodium weight percentage of 0 to about 0.4.