JPS60231462A - Abrasive material and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention is directed to the production of dense polycrystalline alumina or alumina abrasive grains or compacts containing such alumina and other additives.

BACKGROUND OF THE INVENTION Hard, high-strength abrasive grains for grinding wheels, flexible coated abrasive papers ("sandpaper"), or loose abrasive grains are commercially produced using alumina-containing raw materials, melted in electric furnaces or It is manufactured by firing a molded body containing finely pulverized alumina at a humidity sufficiently lower than the melting point of the raw material. This lower temperature treatment is called sintering, and the present invention relates to an alumina abrasive material made by the sintering method.

The first sintered abrasive produced commercially on a large scale was Uel.
tz, US Pat. No. 3,079,243. According to the teachings of this patent, by pulverizing calcined bauxite to create a fine particle size raw material, reducing it to abrasive size particles, and firing at approximately 1500C.
Creates polycrystalline alumina pellets that are hard, strong, and tough.

Recently, an abrasive grain composed of alumina and magnesia spinel has been proposed, possibly in accordance with the teachings of U.S. Pat. Abrasive polishing materials have appeared on the market. These materials are prepared by sintering dry alumina gel particles at (approximately 140 DC) 1! #Created.

Bugosh, U.S. Pat. No. 3,108,888, also discloses high density alumina gels made from alpha alumina hydrate (boehmite) or by hot pressing dry powders made from such gels. It teaches the production of alumina (or alumina-containing) products.

Commercial alumina/magnesia-spinel abrasives made from gels contain alumina in the form of cells 5 to 1.5 micrometers in diameter. The cell or "sun/<-st" consists of many elongated alumina arms 0.2 to 0.4 micrometers in diameter (although some of these are roughly spherical arms of 1 micrometer size). ), the arms of each cell appear to extend generally radially from the center of the cell; the arms of a given cell are all apparently crystallographically oriented in the same direction. Such orientation is indicated by the fact that when viewed between perpendicular polarizers in a transmitted light microscope, all areas of a given cell disappear simultaneously when the sample is rotated.

Although commercially available abrasives made from sintered gels containing alumina and magnesia are high quality abrasives, it has heretofore been impossible to produce high purity alumina abrasive grains through gels. This is because Comparative Example 13 of U.S. Pat. No. 4,514,827 is made of alumina gel without the addition of metal oxides or metal salts, but is relatively soft and lacks utility as an abrasive. This is shown by the fact that

The present invention provides improvements in the field of high elongation abrasive manufacturing technology that allow useful abrasive products to be made from alumina gel with or without the addition of spinel formers such as zirconia or magnesia. It is something.

DISCLOSURE OF THE INVENTION The present invention resides in the discovery that by controlling the smoke, product microstructure and eliminating the cellular structure of alumina in prior art abrasives, product performance is improved. The resulting product contains alpha alumina particles (crystallites) of submicron dimensions (0.2-0.4 micrometers) instead of cell areas of 5-10 micrometers in diameter.

When a bacterial concentration (eg, 5% in some cases) of MgO is added, these alumina particles become surrounded by a matrix of spinel.

The formation of gel conditions to achieve the above results is achieved by vibratory milling of the sol-like or dilute gel-like mixture using alumina bodies as grinding media in the mill. It is believed that the main effect of this milling is the introduction of material from the alumina grinding media into the alumina gel.

Similarly, impurities such as zinc and iron are introduced from pipes and related equipment. For example, milling with zirconia bodies is not effective in forming the desired woody non-cellular structure.

The first effective and renewable method we found was to generate the above-mentioned substances in the gel by vibration milling of the gel with an alumina body.

One commercially available vibratory mill is shown in US Pat. No. 3,10088. Typically, the grinding media can be 8 inches in diameter and 4 to 4 inches long. An unbalanced heavy phase connected to the shaft of a motor mounted concentrically with the tab mounted on a spring causes the tab containing the grinding media and mixture to %pl+ in the horizontal plane. Unbalanced use is near the bottom of the tab]
'1'V, attach the second weight below it. The motor typically rotates at 1200 decoys. The combined vibrations cause the grinding media to perform a grinding action on the contents. The inner surface of the mill is preferably lined with rubber or the like to prevent the gold fill Q from being eroded and contaminated.

Various additives can be added to the alumina before or after gelling, such as those taught in US Pat. No. 4,314,827 and British Application Publication No. 2.0'99,012. The most useful additive known today is the associative M! Preferably any of the 10 precursors so that the final product contains as much as 5% MgO. MgO exists in the product as spinel (aluminium magnesium My At20 a), but analysis shows that MgO
! Calculated as IO. Since the additive-free alumina produced according to the invention is itself an excellent abrasive, it is clear that lower amounts of MqO may be added. The milled gel of the present invention can serve as a matrix for various additive materials or abrasive particles.

The milled mixture can be simply poured or placed into a container to dry and then crushed to the appropriate size and any material that is too small can be recycled to the beginning of the process. Optionally, the material can be shaped or molded into shaped particles, such as by extrusion. In the case of extrusion molding, the formed rod is later broken into suitable dimensions. The lowest useful calcination temperature is 1200°C, which is usually considered the temperature at which alpha alumina is converted.
t: substantially lower than '. The upper limit of firing temperature is not critical as long as the melting temperature is not reached. If the firing time is too long or the firing humidity is too high, excessive crystal growth may occur.

Also, since higher temperatures increase the cost of the process, the preferred φ formation temperature range is 1200 to 1500 t:'.

0ondeaSB in a large polymer plastic mixing container
rural Alumina (0ondea)
30 bonds (13,6 kp) and 16 gallons of water (166 kp)
Mixed with littrun. Next, add 14% by weight of HNO3 to 4
．． 12 was added to gel the material. Nitrate Magnesium Hydrate 75 Bond (3.4 kp) dissolved in 3 gallons (13.7 liters) of water was then added to the alumina gel to provide 5% by weight MyO in the final product. That's 15
The mixture was mixed for a minute, transferred to a Model M451 Sweco Mill (TM), and milled for 1 hour with 1700 bond aluminum media.The mixture was recycled through the mill at a rate of about 4 gallons per minute for a 1 hour milling time.

After grinding, it is pumped into aluminum trays to a thickness of approximately 3 inches (76 m) and dried in an electric 9-strip dryer.

The composition of the alumina medium was about 90% alpha alumina and silica as the major impurity.

A series of patches are made from the above preparation, mixed and subjected to crushing and firing.

The dried gel is crushed with a roller and classified before melting.
4 mesh to achieve the desired final particle size. Then pre-fired at 400C for 16 hours and produced 1400t:'
(rotary kiln) for 30 minutes.

After cultivation, all products have a hardness of 19 GPa (Vickers indenter, load 500P) and a very fine microstructure, with no cellular microstructure at all, and almost all of the alpha alumina is approximately axially oriented. It is in the form of small particles (microcrystals) with a diameter of 0.2 to 0.4 μm, and rarely about 5 μm in diameter.
Only angular and rugged shapes of μm size were observed. Rugged shapes were shown to be contaminants. When examined under a scanning electron microscope, the product consisted of a matrix of spinel and a discrete phase of alpha alumina.

When applied to abrasive applications in certain coated abrasive papers, this material outperformed fused alumina-zirconia and also stopped the abrasive grains of commercially available alumina-spinel composition fused gel types.

Example 2 22.7 kp of Pural microcrystalline boehmite alumina was mixed with 225 liters of water and 1.5 liters of 14% HNO3 for 10-15 minutes.

Half of the gel mixture was filled with Ooors grade ceramic bonded alumina, available from Porslain.
88 Al2O5 (main impurities are MgO1, 74%, 5
to2B, 9%, Fe2030.18%, Tto20.
Swe c containing 2%, aao o, 8%, Ma2O0, 34%).

The mixture was ground with m1ll (trade name) for 2 hours and dried. This was the same medium used in Example 1. The remaining half was simply dried and ground without being crushed. These dried gels were crushed, prelit at 450C for 16 hours, and heated at 1400C for 1 hour.
It was fired at C.

The material that has been milled has a hardness of 191 GPa, and the material that has not been milled has a hardness of 11. The hardness was OGPa.

The material from each batch was graded to produce 50 grit abrasive grains, which were used to make vulcanized ta-string based abrasive cloth discs. The pulverized material showed 10% more burr performance in 1020m grinding compared to commercially available alumina-zirconia abrasive grains (14% more metal was removed in the test).

The unmilled material was inferior to the fused abrasive in all grinding tests, which was thought to be due to its lower hardness.

Example 3 A gel was milled for 0.2 hours in a similar example to the milled product of Example 1. The product fired at 140 Dt:' for 1 hour mainly has fine and irregular particles of 0.2 to 0.3
Although it has an am crystal structure, some cell-like appearance was observed.

Examples 4-9 Further experiments were conducted to study the effect of firing time at 1400 tll''. All samples were made according to the general procedure in Example 1. Condea microcrystalline boehmite alumina was used and milling was carried out for 2 hours. After drying, the gel was pre-calcined at 750C for 30 minutes.As the baking time increased, the product became lath-like with alumina irregularly dispersed in fine alumina particles of 0.2-0.4 μm. Crystals began to form.

The results are tabulated as shown below.

Firing time Particle size (micrometer) Ratio 1 None
0.2~03 0 3 1.0~2.0 0.2~0.355 2~5 0
2-0.3 20 10 4-8 0.2-06 50 60 Up to 8 0.2-0.3 80 60 Up to 8 0.2-0.3 95 The presence of rough parts is considered undesirable. If the material is prefired at 75 DC for 30 minutes, the firing time at 140 DC should not exceed 5 minutes to obtain a preferred product.

No cellular structure was seen in all cases.

The microstructure consists of submicron particles without small planes and lath-like crystals with small planes, and no lath-like crystals were observed only when the firing time was 1 minute.

"Non-faceted" means that no regular faceting of microcrystals is observed on the fracture surface when observed and observed with a scanning electron BJR mirror at 5000x magnification. The particles of alpha alumina are rather amorphous, but coaxially oriented.
iaxed), had a roughly curved contour, and very rarely a straight contour was seen. When the magnification was increased to 20,000 times, the facet structure became clearly visible.

The abrasive grains according to the invention have a hardness measured with a Vickers indenter at a load of 500 grams of at least 16 GPa (90% density, 2 mol%
Abrasive grains modified with the presence of spinel precursors or with other additives had at least 14 GI'a.

Purely dense alpha alumina is about 20-21 GPa
hardness, but in certain applications it is lower.
Certain porosity may be desirable, such as having 1 degree. Alumina has a hardness of less than 130 Pa or is too porous for the purposes of this invention. The hardness is preferably 18 GPa or more when measured with a Vickers indenter with a load of 500).

Example 10 A series of abrasives with varying magnesia contents were made.

The procedure of General Example 1 was adopted, including milling with alumina media (but for 2 hours). In all cases, the gel was heated to 200C.
After drying for about 60 hours, crushing, classifying, and
I temporarily turned it off at 500 for 16 hours.

The resulting abrasive grain size is 140D in a rotary kiln.
It was fired at C. The heating time to 1400C was about 15 minutes, and the holding time at '1400C was about 15 minutes.

Before gelation, various types of magnesium nitrate were added. In one experiment no magnesium nitrate was added. My O content and hardness of abrasive 9498 0.1
4 19.9 9499 2.50 19 9500 7, 95 19 9502 12.71 19 In a series of tests on vitrified (glass bonded) wheels using abrasive grains of 54 grit size (mixture of 46 and 60 grit sizes) A grindstone made from grains was compared with the highest quality known fused alumina abrasive (sulfide method abrasive).

Tests were conducted by grinding tool steel (D3) bars at various feed rates. Additive-free abrasive (Mlo)
o, 14%) had a grinding ratio 16 to 18 times that of the fused abrasive (G ratio is the volume ratio of the amount of grinding of the object to be ground to the amount of wear of the grindstone).

In dry grinding tests, all Mg O additives showed better performance than the fused abrasives. M7 in wet grinding test
. At 2 mil, the abrasive without added magnesia was superior to the fused abrasive.

For coated abrasive tests using 50 grit size abrasive grains (OM Engineering Standards), a coated abrasive paper made according to Example 10 and containing 0.6% MgO
A flexible abrasive disc with abrasive grains containing
It outperformed the co-fused alumina-zirconia abrasive for 020 steel (136%) and was nearly equivalent to the fused alumina-zirconia for stainless steel. 2.5% My O and 7,59% M! , 0 was also superior to 1020#. Addition of even larger amounts of My 2 O reduced the effectiveness against stainless steel.

In addition to alumina, 5i02 0.25%, lPe2050
．． M!,OO,14% abrasive grains containing 18%, TiO2o, 28%, OaO0,05% and N(L200,04%) were probably mainly introduced in the milling operation. Exists in abrasive grains.

Although we do not wish to associate the present invention with any particular theory,
We believe that the introduction of particulate matter from the alumina medium may act as a balance for alpha alumina crystallization during furnace formation. Therefore, other impurities introduced during the milling process will inhibit crystal growth in the final product due to their presence at grain boundaries between alpha alumina particles.

As evidence that it is the debris powder from the grinding media that is effective in conditioning the gel to produce the desired dense, microcrystalline, non-cellular alpha alumina when calcined at approximately 1400C. The milled water was added to the alumina hydrate and acid without milling.

Water, nitric acid, and microcrystalline boehmite were mixed as in Example 2. However, with the addition of various types of water (including debris powder abraded from the alumina grinding media during several hours of milling in water without any additives other than water),
I created two batches.

Addition of "milled water" to alumina-hydrate (Oon+iean: 1, 0.0074 1.07 20+2, 0.00
37 0.53 20 3, 0.0019 0.27 19+4, 0.00
075 0.11 175, 0.0003B 0.0
5 156, 0 0 12.5 1 Note: Assume average weight loss due to calcination of 30%.

The hardness of the baked product baked at 14001:'±20 tl for about 10 minutes was measured. The furnace was electrically heated and the atmosphere was air.

Examination of the milled debris powder showed that it was mostly alpha alumina with a surface area of about 39 square meters per gram.

Similarly, high-purity alumina obtained by mixing very fine alumina powder with water and then allowing it to settle and recovering the fine cloudy alumina particles that remain in suspension for a long time can also be used to obtain at least about 0% of a calcined gel. It is effective when used in an amount of .1%.

Tests with commercially available fine alpha alumina powders and with fine alumina obtained by grinding very high purity molten alumina using such alumina itself as the grinding media showed that the dense fine particles of the present invention It has been shown to be very effective in producing crystalline products.

Differential thermal analysis shows that the transformation of gelled alumina from the probable gamma form to the A/7a form occurs at about 109 CI in the presence of alpha alumina seed particles, but at about 11,900 CI in the absence of such seed material. It was shown to happen.

Thus, the theoretical calcination temperature of products according to the invention can be lower than the commonly reported transformation temperatures.

The present invention provides for the first time a particle size of 5 microns and 95%
It becomes possible to produce high purity alpha alumina bodies with higher densities and giving hardness greater than 18 GPa with low temperature firing. According to the method of the invention, it is also possible to produce products other than abrasives, such as coatings, films, fibers, rods, or small imaging elements.

5i02.0r203. Grain growth inhibitors such as MyO and ZrO2 were added to the conditioned gel. My
In experiments in which O was added, it reacted with alpha alumina,
Spinel was observed to form and surround the remaining unreacted alpha alumina. For other additives, the formation of compounds with alpha alumina was minimal, and it was thought that they remained at the grain boundaries. The experiments conducted clearly show that crystal growth due to diffusion and recrystallization was suppressed by the additive. This is the time for sintered products −
It is valuable in that it gives greater freedom in relation to humidity.

The use of grain growth inhibitors is well known in the ceramics field and is not an essential part of the invention, but can be used to achieve the desired microstructure over a wide range of sintering times and temperatures when high purity alpha alumina is not required. Very useful for holding.

Continued from page 1 Procedural amendment February 76, 1985 Manabu Shiga, Commissioner of the Patent Office 1, Indication of the case 1985 Patent application No. 0 (15095 No. 2, Name of the invention Abrasive material and manufacturing method 3, Amendment) Patent applicant name Two-tone Company 4, agent address Shizuko Toranomon Building, 8-10 Toranomon-chome, Minato-ku, Tokyo 105 Phone (504) 07.21 Name Patent attorney (6579) Akira Aomizu (4 others) 5. Column 6 of "Claims" and "Detailed Description of the Invention" of the specification to be amended. Contents of the amendment ill Amend the claims as shown in the attached sheet.

(Corrected to ``Rari'' meeting [yori] on page 12, line 9 of the 21 Specification.

(3) Correct to "Special Jkr Specification" on page 19, line 3.

7. List of attached documents amended scope of patent claims 1 copy 2. Scope of claims 1. A ceramic body containing coaxially oriented submicron alpha alumina crystallites, the alpha alumina having a hardness of at least 16 GPa and a density of at least 90% of the alpha alumina precursor at a temperature below 11400°C. A ceramic body created by sintering.

2. The ceramic body according to claim 1, wherein the alpha alumina is a matrix of ceramic particles of different compositions. 3. The alpha alumina particles? Surrounding Svinerma)
The ceramic body according to claim 1, which contains IJ sokge.

4. Alpha alumina with hardness greater than 16 GPa and density greater than 90% and particle size less than 1 micrometer? Is there a method for creating a ceramic body containing a dispersion of submicron water-containing alumina particles? and wherein the dispersion contains a quantity of submicron alpha alumina crystals so that upon drying and calcination the hydrated alumina particles convert to alpha alumina at a temperature below 1100°C, and at a temperature below 1500°C. How to bake with 05
, by providing fine alumina particles in a form having a theoretical density that is less than the theoretical density of alpha alumina, mixing the fine alumina particles with the alpha alumina seed material of Abmicron, and calcining to a temperature of at least 1090°C. , the polycrystalline alumina body having fine alumina particles transformed into alpha alumina and having a hardness of at least 18 GPa? The oriental structure of claim 4 is made essentially of coaxially oriented, noniaceted alpha alumina sintered particles having a grain size r of less than 61 micrometers! 90% of the theoretical density
Abrasive grain 07 with greater density r, submicron alpha alumina crystals? Abrasive grain according to claim 6, which is prepared from a dried aqueous dispersion of alumina hydrate in an amount and fineness sufficient to effect the conversion of hydrated alumina to alpha alumina. .

8.'fX from alumina matrix and secondary particle material
9. Does the V alumina matrix have a density of at least 95% of the theoretical density and a hardness of at least 18 GPR? 7. The abrasive grain of claim 6 consisting essentially of coaxially oriented submicron alpha alumina particles.

9. An abrasive grain consisting of a matrix of spinel and a discontinuous phase of submicron alpha alumina crystals, the alpha alumina crystals being coaxially oriented and free of facets, such that the abrasive grains have at least a theoretical density of The abrasive grain of claim 6 having a density of 95% and a hardness of at least 18GPa.

10. providing a dispersion of non-alpha alumina particles of submicron size, the dispersion containing submicron alpha alumina seed particles, drying the dispersion, and calcining the dispersion 2; the non-alpha alumina particles are transformed into alpha alumina particles of submicron size;
A method for producing alumina abrasive grains, which comprises:

Cloth paper having a particle size of less than 111 micrometers.

A coated abrasive paper that is coaxially oriented, has no facets, and has abrasive grains.

A whetstone.

18. The grindstone according to the above, wherein the grindstone has a matrix of spinel.

Claims (1)

Claims: 1. A ceramic body containing coaxially oriented (equiaXea) submicron alpha alumina crystallites, wherein the alpha alumina has a
A ceramic body having a hardness of 90% or more and a density of 90% or more and made by sintering an alpha alumina precursor at a temperature below 1400C. 2. The ceramic body of claim 1, wherein said alpha alumina is a matrix of ceramic particles of different compositions. 3 Spinerma surrounding alpha alumina particles)
A ceramic body according to claim 1 containing IJ wax. A method of manufacturing a ceramic body containing alpha alumina having a hardness greater than 4.16 GPa, a density greater than 90%, and a particle size less than 1 micrometer, the method comprising: providing a dispersion of submicron hydrated alumina particles; A method in which the dispersion contains an effective amount of submicron alpha alumina crystals so that upon drying and diaphragm, the hydrated alumina particles convert to alpha alumina at a temperature below 1100C, and is calcined at a temperature below 1500C. An abrasive grain consisting essentially of coaxially oriented non-faaeted alpha alumina sintered particles having a grain size less than 51 micrometers and having a density greater than 90% of the theoretical density. 6. A claim prepared from a dried aqueous alumina-hydrate dispersion containing submicron alpha-alumina crystals in sufficient quantity and fineness to effect the conversion of the alumina-hydrate to alpha-alumina. Abrasive grains according to range 5. Z: Consists of alumina matrix, dust and secondary particle material,
The alumina matrix has a theoretical density of at least 95
% density and a hardness of at least 18 GPa. 8. Abrasive grains consisting of a matrix of spinel and a discontinuous phase of submicron alpha alumina crystals, the alpha alumina crystals being coaxially oriented and free of facets;
and the abrasive grain has a density of at least 95% of the theoretical density and a hardness of at least 18 GPa. 9. providing a dispersion of non-alpha alumina particles of submicron size, the dispersion containing submicron alpha alumina seed particles, drying the dispersion, and calcining the dispersion. Alpha alumina particles transform into alpha alumina particles with submicron dimensions,
A method for producing alumina abrasive grains, wherein the abrasive grains have a density of at least 90% of the theoretical density. 10. A method for producing a polycrystalline alumina body, the method comprising: providing fine alumina particles having a theoretical density smaller than the theoretical density of alpha alumina; mixing the fine alumina particles with a submicron alpha alumina seed material; , and by firing to a temperature of at least 1090C,
A method for producing a polycrystalline alumina body, wherein the fine alumina particles are converted to alpha alumina, and the polycrystalline alumina body has a hardness of at least 180 Pa.