FR2512828A1 - METHOD OF MAKING ABRASIVE AND ABRASIVE COMPOSITION - Google Patents

Abstract

THE INVENTION RELATES TO THE MANUFACTURE OF ABRASIVE GRAINS. IT RELATES TO A PROCESS WHICH INCLUDES THE FORMATION OF A GEL CONTAINING ALUMINUM OXIDE MONOHYDRATE, A DISSOLVED SINTERING ADDITIVE, AND A MAXIMUM 1.8 BY WEIGHT OF SODIUM AND CALCIUM TOTAL IN RELATION TO THE WEIGHT OF THE SOLID MATERIALS CONTAINING METAL. THE PERCENTAGE OF CALCIUM IS BETWEEN 0 AND 1.8 AND THAT OF SODIUM BETWEEN 0 AND 0.4. THE DISPERSION IS FROZEN THEN DRYED AND CRUSHED IN THE FORM OF GRAINS WHICH ARE QUICKLY HEATED TO OVER 1200C IN LESS THAN 10 MINS, BEFORE SINTING BETWEEN 1200 AND 1650C. THESE ABRASIVE GRAINS HAVE CUTTING PROPERTIES WELL SUPERIOR THAN CONVENTIONAL GRAINS OF MELTED ALUMINA. APPLICATION TO THE MANUFACTURE OF ABRASIVES USED FOR METAL MACHINING.

Description

2 1282 B

  The present invention relates to abrasive grains

  sifs and more precisely sintered abrasive grains.

  The grains were conventionally manufactured

  abrasives, especially those containing metal oxides

  such as alumina, by melting the oxide and then grinding the molten oxide after cooling so that the abrasive grains are formed More recently, we have

  manufactured abrasive grains by sintering the metal oxide

  such as alumina These grains, although they wear out

  in a reasonable manner, however, do not have a resistance

  as much as desirable and moreover

  they do not cause cutting as fast as desired

table.

  It is known that ceramic materials which may be in the form of abrasive products may be prepared by bonding ceramic oxide particles with a colloidal mineral gel as described in US Pat. It is also known that colloidal dispersions can be gelled, dried and calcined to form ceramic materials.

  porous as described in the United States patent of

No 4 181 532.

  It is also known that spheres of pure or mixed oxide, forming a very fluid material, can be produced by dispersion of a hydrate of an oxide and then by formation of a gel in the form of spheres and by sintering, as described. in the article "Application of Sol-Gel Processes to

  Industrial Oxides, 13 January 1968, Chemistry and Industry.

  It has also been known since 1971 at least that such

  particles in spherical form or even in form

  can be used as abrasives This phenomenon

  leads was described in a report by The United Kingdom's Atomic Energy Authority, Harwell, England, at Carborundum

  Company, Ltd, and it was later transmitted to several

  members of The Carborundum Company in the United States of America. U.S. Patent No. 4,314,827

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  concerning an oxide-based abrasive mineral

  of non-melted alumina was issued and

  more precisely its manufacture and products

abrasives containing it.

  THE aforesaid iaevt of the United States of America

  No. 4,314,827 generally indicates that a mineral abrasive

  The randomly oriented crystallites having diameters in the order of 3000 Å or less may be prepared by gelation of a colloidal dispersion or a hydrosol of alumina and a modifying ingredient.

  then by baking the gel The description clearly shows

  that the mineral must be free of calcium and

  of an alkali metal (less than 0.05% by weight in total).

  Given this criterion, complex processes for purifying

  cation should be used when calcium and

  Many alumina or modifying ingredients, for example, are present in commercially available water and in magnesium-containing modifying ingredients unless there are

  and purification complexes are used for extrac-

  In a similar way, sodium is usually

  many alumina unless removed from it during additional operations

  In this patent, there is nothing to suggest the use of

  a process which could be used in the presence of calcium or an alkali metal, and in fact no process is used with a high content of calcium or alkali metal, and does not allow the results to be obtained.

  in the presence of such high concentrations of calcium

cium or an alkali metal.

  The invention relates to a method for forming ceramic particles from a gelled dispersion (sol gel) by drying and sintering the gel. The particles according to the invention can be used for many

  suitable applications They can be used

  especially in all applications where a

  good resistance to heat, good mechanical resistance

  However, for example, they can be used as fillers, in aggregates, in distillation columns, or, because of the superabundance of porosity, they can be used as fillers.

  some of the particles, as

  The most common use of these particles is in the field of abrasives. These particles are therefore referred to as "abrasive" in the remainder of this specification, but it should be noted that the terms "abrasive particle" or "abrasive grain" refer to particles independently. of

the intended final application.

  Although the product in the form of abrasive grains

  formed by carrying out the invention usually contains

  Over 0.05% by weight of sodium and calcium in total, it is significantly higher than the conventional abrasive of fused alumina. The sodium and calcium content can be high in the grains, thanks to rapid heating.

  dried gel sol in a well-defined temperature range.

  completed between less than 800 ° C and more than

  1200 ° C. The grains are then sintered at a temperature of

higher than 1200 ° C.

  The most advantageous method comprises the pre-

  dispersing a dispersion containing about 2 to 60% by weight of aluminum oxide monohydrate, a metal-containing sintering aid, dissolved or dispersed, with an atomic ratio of metal to alumimium between 1/2 and 1/35 and preferably between 1/7 and 1/25, and about 0.05 to 1.8% of sodium and calcium by weight, by

  in relation to metal-containing solids,

  dissolved and dissolved in the dispersion.

  The weight percentage of calcium added to that of sodium is preferably less than 0.6 and very advantageously less than 0.15. The weight percentage of calcium may be between 0 and 1.8% and that of sodium between 0 and 0 The percentage by weight of calcium is preferably between 0 and

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  About 0.6% and advantageously between 0 and about 0.15%, and the weight percentage of the sodium is preferably between about 0 and 0.25% and preferably between

0 and 0.1%.

  After preparation of the dispersion, it is generally

  lifted and dried at a temperature below

  frothing of the gel so that the free water is expelled.

  Any suitable method of drying known to the men of the

  The term "drying" as used herein refers to dehydration by any method, including solvent extraction. The dried solid is then milled to form grains.

  are usually heated to between about 500 and 800 ° C.

  The grains are then rapidly heated to above about 1200 ° C, in less than 10 and preferably in less than 5 min.

  The grains then continue to be heated to a temperature of

  sintering temperature between about 1200 and 16500 C,

  with sufficient sintering time for the grains to be sintered to a density of about 85% of the theoretical density, at least a portion of the sintering temperature heating having

  place of preference above 1300 'C.

  The resulting grains are in the form of a sintered sol gel based abrasive, having a combination of wear resistance and sustained cutting speed which is significantly better than that of known melted alumina grains and which is comparable to that of known sintered sol gel abrasive grains which require a very small amount of sodium and calcium (less than about 0.05% by weight) described in the aforementioned U.S. Patent No. 4,314,827. "significantly better" indicates that the relative cutting performance is at least 1.5 times better and usually at

less two times better.

  The invention also relates to bonded, coated and non-woven abraded articles containing the grains according to the invention. For example, not only coated abrasives

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  manufactured from the abrasive grains according to the invention retain a high cutting speed until the wear of the grains carried by the support but also the amount

  total material cut by the abrasive object is greater than

  than most known grains. According to the invention, the grains are prepared from a liquid dispersion (preferably in

  water) containing about 2 to 60% and usually

  10 to 40% by weight of alumina oxide monohydrate (AIOOH), a metal-containing sintering aid,

  dissolved form, with an atomic ratio of the metal of the ad-

  aluminum sintering fraction of between 1: 2 and 1: 35, and not more than 1.8% and usually 0.05 to 1.8% combined alkali metals (especially sodium) and

  calcium, relative to the weight of the dispersible solids

  dissolved and dissolved in the dispersion.

  The sum of the weight percentages of calcium and sodium is preferably less than 0.6% and very

  advantageously at 0.15% by weight.

  It can be between 0 and 1.8% and that of sodium between 0 and 0.4%. The weight percentage of calcium is preferably between about 0 and 0.6% and very preferably

  advantageously between 0 and about 0.15%, and the percentage

  weight of the sodium is preferably between 0 and

  and 0.25% and most preferably between 0 and 0.1%.

  The amount of aluminum oxide monohydrate

  in the dispersion is usually between

  10 and 40% and preferably between about 15 and 35% of the weight of the dispersion. The term "aluminum oxide monohydrate" as used herein refers to the

  aluminum oxide hydrates having the stoichiometric formula

  1/2 (A 1203 x H 2 O) in which x is between 0.5 and 3 Aluminum oxide monohydrate is also known

  under the name of "boehmite" Alumina oxide monohydrate

  nium also includes, in the context of the invention, the pseudo-

  boehmite. In general, all solids of the

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  dispersion are preferably dissolved or

  The dispersion is formed by a suitable device

  nable that can be simply the mixture of aluminum oxide monohydrate with water The liquid is almost always water but it can be any liquid such as

  including a low molecular weight alcohol.

  such suitable may be used, especially

  high or low speed gradient

  Dispersants such as an acid are often used.

  For example, 0.02 to 0.25 moles and preferably 0.05 to

  About 0.15 moles of HNO 3 or other volatile mineral acid

  til per mole of aluminum oxide monohydrate greatly promotes dispersion The term "volatile mineral acid"

  means an acid that evaporates on separation from the dispersion

  dried gel or gel at a temperature below the sintering temperature or in all residues or evaporates or forms part of an oxide in the finished grain Examples of such acids are

  nitric, hydrochloric, acetic and formic.

  The solids contained in the dispersion

  completed can contain up to 50% by weight of

  additional ingredients other than aluminum oxide monohydrate, preferably compounds such as silica, magnesia, chromium oxide and titanium dioxide in colloidal or dissolved form, or precursors thereof

  compounds in colloidal or dissolved form.

  The metal-containing sintering aid, in dissolved or dispersed form, is added to the dispersion with an atomic ratio of metal to aluminum included

  between 1/2 and 1/35 and preferably between 1/7 and 1/25.

  Sintering excipient is a metal oxide or precursor

  of a metal oxide, that is to say a compound which

  forms a metal oxide by drying, calcining or frying

  in a soluble or dispersible form.

  In general, the sintering aid is usually a precursor of magnesium oxide, zinc oxide, cobalt oxide or nickel oxide and, when in liquid form in water, is a water-soluble compound or can be dispersed in magnesium, zinc, nickel or cobalt water. Specific examples of such precursors are the nitrates and the chlorides of these metals. The nitrates of these metals, especially magnesium,

  sium are particularly advantageous. Frying adjuvant

  can be prepared in situ, for example by addition of magnesium oxide or hydroxide to an aqueous solution of a mineral acid such as hydrochloric or nitric acids, so that a water soluble magnesium salt is formed. The adjuvant sintering is usually a salt

  water soluble but may be a water-soluble base.

  Sodium and calcium present in the dispersion

  usually form naturally from the calcium-based impurities of the other ingredients of

  dispersion The usual source of sodium is alumina.

  The usual source of calcium is the impurities of the sintering aid containing magnesium or water. The terms "calcium" and "sodium" refer to

  the present memory calcium and sodium related chemical-

  which, given the electropositive nature of the

  and calcium, are almost always in the form of calcium or sodium ions, ie free calcium or sodium ions or sodium or calcium bound by

Ionic.

  According to the process of the invention, relatively high amounts of calcium and sodium can be tolerated in the dispersion so that

  complex and expensive purification are superfluous.

  According to the invention, about 1.8% of sodium and calcium

  in combination may be present at most in the

  persion, and the finished abrasive grains obtained have

  better properties than traditional aluminum grains

  molten mine Preferably, the combined amount of sodium

  calcium present does not exceed 0.6%.

  The above sodium and calcium levels are percentages by weight relative to solids

25128 Z 8

  containing the metals, in dispersed form or dissolved in the dispersion The percentages are practically the same

than those of finished abrasives.

  After preparation of the dispersion, it undergoes gelation. The addition of the sintering aid con-

  holding a metal, dissolved or dispersed, preferably of

  magnesium, in the dispersion usually causes

  the gelation of the dispersion If the

  solids dispersion is very low, the li-

  which may either evaporate in order for the dispersion to gel or another gelling process

  to be used, i.e. the addition of a gelling agent.

  When the dispersion has gelled, it undergoes drying at a temperature below the foaming temperature of the gel so that the free water evaporates.

  terms "dried" and "drying" used in this

  moire indicate that at least 90% of the free (unbound) water is removed and allows the formation of a solid material. The "foaming temperature" is the temperature at

  which the gel forms a foam or foam at the pressure of

  applied to the gel Drying can be carried out by

  any device known to those skilled in the art.

  When heating, the drying temperature is usually between 80 and 1200 C. The duration of the drying depends on the quantity of water or other liquid

  present, the pressure of drying as well as the temperature

  Drying time The drying time is usually

  between 1 and 72 hours at atmospheric pressure

  The resulting dried gel is usually a material

  solid translucent material, that is to say a solid material

  to which the light passes in diffuse form, but this

  the characteristic is not essential.

  When the solid material is dry, it is milled or crushed in any suitable manner using a ball mill or hammer mill so that grains or particles form. Any suitable method of reducing the size of the solid material can be

  used, and the term "shredder" covers all these

  assigned. After grinding, the grains are usually heated to a temperature of about 500 to 800 ° C until substantially all the water is removed and until all the constituents of the grains are in the form. a ceramic (usually metal oxides) or vapor form When the grains reach a temperature between about 250 and 3000 C, the acid residues are driven between 250 and 800 'C

  approximately and usually between 300 and 600 ° C approximately,

  All of the water is usually expelled. The term "practically" indicates in this submission that any

  free water and more than 90% of bound water are expelled.

  The calcination time required for almost all the water to be flushed is usually between about 5 and 20 minutes. After drying and after calcination, the grains are rapidly heated to more than about 12000 C. The term

  "quickly" indicates that the heating is sufficiently

  pide to allow the formation of an abrasive having a good cutting speed and a good resistance to wear Fast heating is usually done in less

  10 min and preferably in less than 5 min and very

  tagbly in less than a minute This rapid heating allows

  makes the formation of abrasive grains excellent from a gelled dispersion (sol gel) containing quantities

  relatively high levels of calcium and sodium.

  Suitable method or method for rapid drying of the grains may be used, for example the injection of the grains into a form other than bulk, that is to say separately, in an oven preheated to more than 12000 C and preferably at over 13000 C. The calcination step can be eliminated, the grains being at the heated range rapidly to more than 12000 C after drying This particular method is particularly advantageous for the manufacture of certain

types of abrasives.

  When the grains have been rapidly heated to above 1200 ° C, they continue to be heated to a sintering temperature of from about 1200 to 16500 ° C and preferably from about 1250 to 15000 ° C for a sufficient sintering time for the grains are sintered to a density exceeding about 85% of the theoretical density When the abrasive is essentially formed of aluminum oxide with about

  6% magnesium oxide relative to the weight of aluminum oxide

  The desired density is greater than about 3.3 g / cm 3. At least a portion of the heating is usually at more than 13000 ° C. The time required for sintering the grains depends on the sintering temperature and is usually between about 5 and 30 minutes but it may be less than about 5 minutes, for example between about 1 and 5 minutes. When we observe thin and polished sections

  sintered grains manufactured according to the invention at the micros-

  transmission optical fiber with magnitudes of

  500 or 700 between cross polarizers, it is found that the microstructure of the material having a nominal composition of alumina with 6% of magnesium oxide, has areas having a nominal diameter of between about 5,000 and 200,000 A which cause extinction as a whole during a rotation of the sample It is thought that the extinction is due in this case to the predominant alpha-alumina birefringent phase. It is believed that, for these zones, they cause extinction as a whole. they must either be in the form of continuous grains of alpha alumina or in the form of zones of smaller grains of alumina oriented in a non-random manner If the grains of alpha alumina have a diameter of between 000 and 200 000 A or have much smaller diameters but have an orientation that is not random, the weight percentage of calcium and sodium in combination

  in grains may be less than 0.05%.

  The microstructure of the alumina grains according to the invention is very different from that of normal grains of sintered or fused alumina of similar composition by the degree of homogeneity of the distribution of the sintering aid in the form of a metal oxide. When firing a previously calcined material, it is believed that an atomically homogeneous distribution of

  magnesia in gamma-alumina is transformed into a

  microscopically homogeneous and intimate alumina and

spinel.

  Normal sintering of the abrasive grains comprises consolidation either by a mechanism for diffusing pre-existing alpha alumina crystals or by a liquid phase densification mechanism. Sintering of the sol gel abrasives may comprise a polymorphic transformation by alumina displacement ranging from alpha alumina and in

  spinel, implying a minimum diffusion This trans-

  original training normally causes a very

  net of the sintering temperature.

  The invention also relates to bonded and non-woven bonded abrasive articles containing the abrasive grains according to the invention. In general, abrasive grains according to

  the invention may be considered abradable grains.

  sintered sintered liquids containing alumina, a metal oxide which promotes sintering and at most about 1.8% and usually about 0.05 to 1.8% and preferably about 0.6%, most preferably at most 0 , 15%

  in weight of calcium and sodium in total.

  As previously described, the sintered grains prepared by the process of the invention have excellent

  characteristics of wear resistance and furthermore

  serve a high cutting speed and remove

  larger carbon steel plants than most

  known grains Known grains with concentra-

  high concentrations of sodium and calcium do not show a combination of cutting speed and wear resistance as favorable as the best abrasive grains

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made according to the invention.

  As previously described, the sintered ground gel abrasive according to the invention has relative cutting characteristics in the form of coated discs machining carbon steel, which are better than those of melted alumina abrasives. Ground gel abrasives according to the invention have such a cutting speed which is at least equal to twice and usually at least three to four times that of conventional alumina abrasives

  The relative cutting characteristics are deter-

  as described in the examples that follow.

  The following examples are given as examples

  purely illustrative and not limiting.

  EXAMPLE 1 Prior Art High-calcium sol gel abrasive grains are prepared substantially by the use of a method of known type in which a sol gel having a content of

  high calcium and dried is slowly heated to a

  In particular, 199,199 grams of Condea Chemie boehmite "Dispural" was dispersed in 77.6 liters of water, and 473 cc of concentrated nitric acid was added to form a solution. sol (colloidal solution) 73.9 g of titanium isopropoxide IV dispersed in 450 cm 3 of isopropanol and 36.5 g of "Nalcoage" 1034 from Nalco-Chemical are then mixed with the soil.

  which is a colloidal silica dispersion.

  3162 g of magnesium nitrate is dissolved in 7.57 liters of water and the solution formed is added to the soil,

  with stirring Gelation takes place almost immediately

  Stirring is continued for about 5 minutes.

  The gel is then placed in plastic trays at a height of about 10 cm. The trays are placed in a steam-heated drier.

  of water so that the gel dries, the operation taking 60 hours

  ron. The dry gel is passed through a roller crusher to reduce it to pellets of size

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  less than 0.595 mm A fraction is separated by sieving

  of dimension between 297 and 595 microns.

  Dry granules are placed in casettes

  coated with aluminum oxide and placed in an oven.

  This is brought to 13700 C over a period of 6 hours and kept for 30 minutes at this temperature.

  the oven and allow it to cool. The cooked beans resulting

  tants are porous and, on analysis, they are found to have

  a calcium content of 0.14% by weight

  is less than 85% of this theoretical value.

  The sintered granules are classified according to their size, on a conventional sieving apparatus so that the granulometry corresponds to the ANSI standard.

  74.18-1977 corresponding to grains of 0.508 mm.

  A single-coated abrasive material is prepared by electrostatically depositing these grains on

a vulcanized fiber support.

* The selected fibers are 0.76 mm vulcanized fibers of abrasive quality, having a nominal mass of 0.99 kg / m

  An adhesive mixture of

  taking a commercial liquid phenol resin of the single component type having a formaldehyde / phenol ratio of about 1/1 and ground limestone having a mean particle size of between 15 and 25 microns, with

  a net weight proportion of the mixture of 1/1.

  This mixture of binders is then heated to 320 ° C. and rolled onto the fiber support On

  thus applies about 0.21 kg / m of adhesive.

  The abrasive of 0.508 mm is electrostatically sprayed onto the fibers carrying the adhesive mixture at the rate of 0.56 kg / m 2 of grains, using an apparatus

  classic emery paper manufacturing.

  The adhesive coated abrasive carrier is then heated at 800 ° C. for one hour and 930 ° C. for two hours in the manufacturing rack. After drying, a coat of primer is applied by conventional application.

  roll at a rate of about 0.31 kg / m.

  prepared at the same 1/1 ratio of phenolic resin and filler However, unbuffered synthetic cryolite having a particular average particle size of 25 microns is used as the filler. Drying and curing are carried out by heating the coated material for 1 hour. at 660 ° C., 4 hours at 80 ° C. and 16 hours at 1070 ° C. After curing, the material is conventionally moistened to a lower moisture content

  at 8% by weight It is then subjected to a uniform flexion

  form and punch it out as discs

  178 mm in diameter is determined on a pneumatic grinder.

  1018 type cold rolled steel forming the properties of these discs and compared to a control disc formed and handled in exactly the same way but having abrasive grains of alumina During the test, the abrasive disc is placed on the grinder in a conventional manner and a piece of 2.54 x 5.08 x 27.94 mm is placed in contact with the disc on the flat side. 2.54 mm, with an inclination of 10 to 15

  pass the disc alternately along the piece.

  The abrasive disk rotates at a nominal speed of 5,400 rpm in this test, on a hard rubber support of 17.8 cm diameter. The workpiece is exerted on the part with a pass force of 36 N passively. 30 S and then measure and record the amount of material removed from the bar (comparison

  weight before and after grinding).

  until the measured material removed is less than

  less than or equal to 5 g per grinding interval.

  The total amount removed in this way corresponding to the discs tested is compared to the total material removed.

  by the control disc (cutting characteristics).

  Abrasive soil gel slowly heated to

  high in calcium (0.14% by weight) corresponding practically

  abrasive, has cutting characteristics

  which are only 97% of those of abgra-

  classical and inexpensive fused alumina.

EXAMPLE 2

  Example 1 is practically repeated, but instead of slowly heating the dry granules of this example, they are calcined at 550 ° C. for about 30 minutes and then introduced into a 13900 ° C. tube rotary kiln.

  so that they are heated to more than 12000 C according to the

  The granules (grains) are heated to 13900 C in about 10 minutes and remain at 13900 C for about 30 minutes so that the grains are sintered The other differences with Example 1 are minor The resulting grains

  Sintered grains are analyzed. The analysis of sintered grains results

  tants shows that their calcium content is 0.11% by weight and their density exceeds 3.3 (more than% of the theoretical value). After the tests indicated in Example 1, it is found that the discs have relative cutting characteristics equal to 395% of those of abrasive grains of molten alumina In other

  In other words, the grains according to the invention have characteristics

  Cutting ticks 3.95 times higher than grain

of melted alumina.

EXAMPLE 3

  Example 2 is practically repeated, but the dried grains are calcined at 6000 ° C. instead of 5500 ° C. Grains having a calcium content of 0.12% by weight and a density greater than 85% of the theoretical value. cutting related are

  4.39 times higher than melted alumina grains.

EXAMPLE 4

  Example 2 is practically repeated, but

  the magnesium nitrate used by dissolving

  720 g of magnesium hydroxide in 6.28 liters of water

  holding 1660 cm 3 of concentrated nitric acid The solution

  The resultant is then added to the soil with stirring.

  As in Example 2, gelation is immediate and stirring is continued for 5 minutes. The resulting grains have a calcium content of almost 0.08% by weight, a density exceeding% of the theoretical value and the characteristics of

  cutting of the order of 4.5 times that of the fused alumina.

  In addition, the resulting grains have about 2.4 times higher cutting characteristics than commercially available fast-cooling fused zirconia and alumina grains, and the cutting characteristics are comparable to those of a grain containing alumina formed from a low-calcium sintered sol gel, previously coated on a commercial disc, the grains being similar to those having a low calcium and sodium content and which are described in the patent

  aforesaid United States of America No. 4,314,827.

EXAMPLE 5

  High calcium and sodium sol gel abrasive grains were prepared substantially as in Example 2. In particular, 559 g of Conden Chemie boehmite "Dispural" was dispersed in 126.8 liters of water and then to dispersion 1250 cm of acid

  concentrated nitric acid, diluted by 7.65

  very water to form a soil (colloidal solution).

  6341 g of magnesium nitrate are dissolved in 1 liter of water and the resulting solution is added to the sol with stirring. The gelation is almost immediate.

  Stirring is continued for about 5 minutes.

  The gel is then placed in trays of

  plastic sheet on a height between 2.5 and 3.75 cm The trays are placed in an electric dryer

  in order to dry the gel, the operation taking 48 hours

viron.

  The dry gel is passed through a rotary mill.

  in the form of granules smaller than 0, 841 mm.

  of dimension between 297 and 841 microns.

  The granules are then calcined at 550 ° C. for approximately one minute and then cooked rapidly in a rotating tube rotary kiln at a rate of 1.2 rpm to approximately 139 ° C. so that they are rapidly heated to above 1200.degree. Granules (grains)

  are then heated to 1390 ° C for an additional 10 min.

  The resulting grains have a calcium content of about 0.07% by weight and a sodium content of 0.015% by weight. The density exceeds 85% of the

theoretical value.

  The sintered granules are then classified into

  their size with a conventional tamper

  wise so that they correspond to ANSI 74 18-1977

for grains of 0.706 mm.

  A single layer abrasive material is prepared by electrostatic coating of

  0.706 mm on a vulcanized fiber support.

  The selected fibers are 0.76 mm vulcanized fibers of abrasive quality, having a nominal mass of 0.99 kg / m. An adhesive mixture is then prepared using commercial liquid phenol resin having a single component having a ratio of formaldehyde / phenol of about 1/1 and crushed limestone of average particle size between 17 and 25 microns, with a weight ratio resulting

1/1.

  The mixture is then heated to 329 ° C. and rolled onto the fiber support.

, 4 kg / m 2 of adhesive.

  The electrostatic

  0.706 mm thick with a conventional manufacturing device

  of emery paper, on fibers bearing the adhesive mixture

  sif at a rate of 0.92 kg / m 2 of grain.

  The support coated with the adhesive and the abrasive is then heated at 80 ° C. for 1 hour and at 930 ° C. for 2 hours in the manufacturing rack. After drying, a coat of primer is applied by conventional roller coating. approximately 0.34 kg / m The mixture is made of the same phenolic resin material and

  load ratio 1/1 Drying and hardening

  are obtained by heating the coated material for 1 hour at 660 C, 4 hours at 80 ° C and 16 hours at

107 C.

  After curing, the material is moistened

  conventionally so that it has a moisture content

  less than 8% by weight is then subjected to uniform bending and cutting in the form of discs 17.9 cm in diameter The properties are then evaluated

  five of these discs on a conventional pneumatic grinder.

  With a hardened and annealed 4140 piece of steel (having a Brinnel hardness of 285 to 320), the properties are compared to those of a control disc used and handled in the same manner but with abrasive grains formed. of molten alumina During the test, the abrasive disk is placed on the grinder in a conventional manner

  and there is a piece of 2.54 x 5.08 x 27.94 mm of

  that it is in contact with the disk on the flat side of 2.54 mm with an inclination of 10 to 150

  pass alternately along the room.

  During the test, the disc rotates at 5400 rpm

  <nominal value) and is supported by a rubber

  hard rubber 17, -8 cm in diameter The passively exerted force is 36 N The test lasts 30 seconds and the material removed from the bar is measured (comparison of the weight before and after grinding) and recorded The sequence

  is continued until the quantity of material re-

  taken and measured to be less than or equal to 5 g

  grinding scale The total quantity removed from this

  the disc is compared to the total quantity

  pulled by the control disc (cutting characteristics

  lative). The rapidly heated high-sol gel soil grit with a high calcium and sodium content (0.07 wt.% Total) gives an average cut of 612 g (almost 7 times that of normal fused alumina).

following table.

EXAMPLES 6 TO 19

  The procedure of Example 5 is followed, but various known amounts of calcium and sodium are added

  to the dispersion before addition of magnesium nitrate.

  These metals are added in the form of sodium nitrate and calcium solutions. The sodium nitrate solution contains 0.54 g / cm 3 of Na NO 3 equivalent to 0.2 g / cm 3 of Na 2 O, and the solution of calcium nitrate contains 0.58 g / cm 3 of Ca (NO 3) 2 equivalent to 0.2 g / cm Ca O The results appear in the table The sodium and calcium of the grains are analyzed by emission spectroscopy The small variations between the amount added and the actual amount in the grains are probably due to the additional calcium present in the magnesium nitrate and in the water, and the small variation between the added sodium and the sodium actually present in the grains is due

  doubtless to the impurities of the grain ingredients,

  with water, and some evaporation of sodium

  during calcination and sintering.

  The table also gives a comparative

  average amount removed by conventional aluminum grains

molten mine.

Exneple

9

15

  alumina Ca ++ cm O 24.9 o 24.9 373.5 o O o O 373.5

BOARD

Na +% Ca in cm 3 grains

0 0.06

0 0.08

83 0.06

0 0.13

l 66 0.06

83 0.08

0 0.18

166 0.13

0 0.33

166 0.18

270 0.19

270 0.06

270 0.13

481.5 0.06

481.5 0.36

  % Na in grains 0.01 0.02 0.06 0.01 0.12 0.07 0.04 0.13 0.02 0.12 0, 21 0.18 0.20 0.27 0.36 Average cut g 612.0 644.8 504.8 494.6 437.6 424, 0 424.0 383.2 369.8 326.4 275.4 270.0 242.4 197.2, 4 88.2

EXAMPLE 20

  Examples 7, 11 and 15 are repeated, but the grains are slowly cooked in a manner analogous to that of

  In particular, the grains are cooked slowly

  in a fixed oven from room temperature to 15000 C for a period of 16 hours and are then maintained for 30 min at 15000 C The resulting abrasives have such poor properties that we can not even get

their cutting characteristics.

  The above examples clearly show

  the excellent cutting characteristics of abra-

  of calcium and sodium high sol gel produced according to the invention and show that when the

  rapid heating of the dried soil gel with a high cal-

  and sodium at the sintering temperature is removed.

  as in the known processes, the resulting grains

have bad characteristics.

Claims (8)

  1 Process for producing abrasive grains,   characterized in that it comprises: a) preparing a dispersion containing about 2 to 60% by weight of aluminum oxide monohydrate, a metal-containing sintering dissolved builder in an atomic ratio of the metal of the aluminum sintering aid of aluminum oxide monohydrate between 1/2 and 1/35, and about 0.05 to 1.8% by weight of sodium and calcium in total relative to the weight dispersed solid and dissolved solids containing a metal present in the dispersion, the weight percentage of calcium being between 0 and about 1.8% and that of sodium being between 0 and about 0.4%, b) the gelling of the dispersion, c) drying the gelled dispersion at a temperature below the foaming temperature of the gel so that the free water evaporates, d) grinding the dried solid material so that grains are formed, e) the calcination of grains, f) rapid heating of grains to more than 1200 About 0 C in less than 10 min, and   (g) the continued heating of grain at a time   sintering temperature between about 1200 and 16500 C for a sufficient sintering time for the grains to be sintered at a density greater than 85%   about the theoretical density.   2 Process for the manufacture of abrasive grains, characterized in that it comprises:   a) the preparation of a dispersion containing   2 to 60% by weight of aluminum oxide monohydrate, a metal-containing dissolved sintering aid with a   atomic ratio of the metal of the sintering aid to aluminum   aluminum oxide monohydrate between 1/2 and 1/35, and 0.05 to 1.8% by weight of sodium and calcium relative to the weight of the solids   dispersed and dissolved containing a metal in the dispersion   the percentage weight of calcium being included in   O and about 1.8% and that of sodium between 0 and about 0.4%, b) gelation of the dispersion, c) drying of the gelled dispersion at a temperature below the foaming temperature of the gel so that the free water evaporates, d) the grinding of the dried solid matter so that grains are formed, e) the rapid heating of the grains to more than about 1200 ° C in less than 10 min, and f) the continuation of the heating the grains at a sintering temperature of between about 1200 and 16500 C for a time sufficient for sintering grains at a density greater than about 85% of the theoretical density.   A method of manufacturing abrasives having alpha alumina grains having a diameter of about 5,000 to 200,000 A, characterized by comprising a) preparing a dispersion containing   about 2 to 60% by weight of aluminum oxide monohydrate   nium, a dissolved metal-containing sintering admixture with an atomic ratio of the metal of the builder to aluminum of aluminum oxide monohydrate between 1/2 and 1/35, and at most 1.8% by weight about total weight of sodium and calcium relative to the weight of solids   dispersed and dissolved containing a metal in the dispersion   the weight percentage of calcium being between 0 and about 1.8% and that of sodium between 0 and about 0.4%, b) gelation of the dispersion, c) drying of the gelled dispersion at a lower temperature. at the frothing temperature of the gel so that the free water evaporates, d) the grinding of the dried solid so that grains are formed, e) the rapid heating of the grains to more than 1200 ° C in less than 10 min and f) the further heating of the grains to a sintering temperature of between about 1200 and 16500 C for a time sufficient for the grains to be sintered at a density greater than 85%   about the theoretical density.   4 Process according to claim 3, characterized   in that it includes, before the rapid heating, calcina- grain.   A process for the production of abrasives having nonrandomally oriented alpha-alumina grains, characterized in that it comprises: a) the preparation of a dispersion containing   about 2 to 60% by weight of aluminum oxide monohydrate   nium, a dissolved sintering admixture containing a metal   with an atomic ratio of the metal of the adjuvant to aluminum   aluminum oxide monohydrate between 1/2 and 1/35, and not more than about 1.8% by weight of sodium and calcium in total, based on the weight of the solids dispersed and dissolved and containing a metal in the dispersion, the weight percentage of calcium being between 0 and about 1.8% and that of sodium between 0 and 0.4%, b) the gelation of the dispersion, c) the drying of the gel dispersion at a temperature below the frothing temperature of the gel so that the free water evaporates, d) the grinding of the dried solid matter so that grains are formed, e) the rapid heating of the grains to more than 12000 C approximately less than 10 min, and f) the further heating of the grains to a sintering temperature of between about 1200 and 1650 ° C for a time sufficient for the grains to be sintered to a density greater than about 85%. the theoretical density. 12828   Process according to claim 5, characterized   in that it comprises, before the rapid heating, calcification nation of grains.   Process according to any one of the claims   1 to 6, characterized in that the sintering aid is a water-soluble compound of magnesium, zinc, nickel or cobalt.   8 Composition of sintered abrasive grains, characterized   in that it is manufactured by carrying out a process which comprises   a) the preparation of a dispersion containing   2 to 60% by weight of aluminum oxide monohydrate, a metal-containing dissolved-sintering aid with an atomic ratio of the aluminum adjuvant metal to aluminum oxide monohydrate monohydrate between 1 / 2 and 1/35, and about 0.05 to 1.8% by weight of sodium and calcium   in total in relation to the weight of solids dis-   Persistent and dissolved metals containing a metal in the dispersion, the weight percentage of calcium being between 0   about 1.8% and sodium between 0 and 0.4%   viron, b) gelling the dispersion, c) drying the gelled dispersion at a temperature below the foaming temperature of the gel so that the free water evaporates, d) grinding the dried solid material so that grains are formed, e) the calcination of the grains, f) the rapid heating of the grains to more than about 1200 ° C in less than 10 min, and g) the further heating of the grains to a sintering temperature between about 1200 and 16500 C, for a time sufficient for the grains   sintered at a density greater than 85% in   viron of the theoretical density.   9 Composition of sintered abrasive grains, characterized   in that it is manufactured by implementing a 12828   process which comprises a) preparing a dispersion containing   about 2 to 60% by weight of aluminum oxide monohydrate   nium, a dissolved metal-containing sintering admixture with an atomic ratio of aluminum adjuvant metal to aluminum oxide monohydrate between 1/2 and 1/35, and about 0.05 to 1.8% by weight of sodium and calcium in total, based on the weight of dispersed and dissolved solids and containing a metal in the dispersion, the weight percentage of calcium being between 0 and about 1.8% and that of sodium between 0 and about 0.4%, b) gelling the dispersion, c) drying the gelled dispersion at a temperature below the foaming temperature of the gel so that the free water evaporates, d) the grinding the dried solid material so that grains are formed, e) rapidly heating the grains to above about 1200 C in less than 10 min, and f) further heating the grains to a sintering temperature of between about 1200 and 16500 C for a time sufficient for the grains to be f at a density greater than about 85% of the the theoretical density.   Abrasive grains, characterized in that they   contain alumina, a metal oxide and not more than approximately 1.8% by weight of sodium and calcium in total, the weight percentage of calcium being between   O and about 1.8% and that of sodium between 0 and 0.4% viron. CABMET SMONNOT Representative