DE1815911A1 - Abrasives for grinding stainless steel and high carbon steel - Google Patents

Description

The Carborundum Company
1625 Buffalo Avenue

Niagara Falls, New York, USA December 18, I968

22 454 R / Like.

Abrasives for grinding stainless steel and high carbon steel.

The invention relates to a sintered, alumina-containing abrasive grain with finely comminuted bauxite and a method for the production of this abrasive grain as well as a grinding wheel for grinding stainless steel and high carbon Stole.

As an abrasive material, it is known to have various compositions, such as silicon carbide, electro corundum, sintered bauxite, and both electro corundum and sintered ones To use alumina, which are modified by the addition of metal oxides. The different abrasive materials are each highly satisfactory for grinding a certain material, however, it is well known that the abrasives perform less when they are used for grinding other types of material. For example, silicon carbide is commonly used for grinding Used by softer metals and low carbon steels, however, it is due to its brittleness Not very suitable for machining harder metals such as stainless steel or high-carbon steel. Sintered bauxite, on the other hand, is known to be well suited for machining stainless steel billets, however again, it is inconvenient for application to high carbon stems. Corundum improved with zirconium oxide In contrast, 8.1s sintered bauxite has proven to be a more suitable abrasive for sanding high carbon Steels exposed. In the same way, the various other abrasive materials can be related to their appropriate application form, and it is fixed

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provide that each abrasive material for application / εη a particular workpiece material is suitable and generally tends to have poorer performance on materials for which it is not intended.

It has for these reasons been pursued the goal of becoming a universal to find usable abrasive grain, i.e. an abrasive grain that is evenly applied to every type of material performs well. This "objective becomes all the more understandable when it is considered that the user of abrasive articles is forced to use different types of abrasive articles to keep in stock, each having different abrasive compositions for grinding and finishing Be prepared for the various types of material required as part of normal operations. While it is unlikely that a truly universal abrasive grain will ever be made, at least is There is a need for an abrasive material that is equally useful for machining stainless steel as well of high carbon steel is usable.

The invention aims to provide an abrasive grain and abrasive product that can be used both on high carbon steels as can also be used on stainless steels and behaves consistently well in these areas of application.

According to the invention, the sintered alumina-containing abrasive grain with finely comminuted bauxite has contents of chromium oxide of up to 20 $. The chromium oxide content of the abrasive grain according to the invention is preferably 2 % to 20 %.

In the novel process for the preparation of alumina-containing abrasive grain, an image same mass with 2% - 20 fo finely divided chromic oxide, 98% - 80% of finely crushed bauxite, auxiliary binder and a Pließzusatz produced, the mass geometrical to grain of a certain size and uniform

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Shear shape, the grain of a variety of Bauxite and chromium oxide particles, and then the grain is dried to remove the flow additive, whereupon the Particles are sintered.

The grinding wheel of the invention, for the grinding of stainless steel and high carbon steel with an alumina-containing abrasive grain and the abrasive grain into a unitary body unifying bond is according to the invention characterized by a sintered abrasive grain with bauxite and a 2 fo - 20 fo-lgen content of chromium oxide.

In the following the invention is based on several exemplary embodiments described. The drawing shows the grinding performance:

1 shows a representation of the metal removal versus the grinding loss as a characteristic value related to the grinding pressure of grinding wheels containing an abrasive grain according to the invention and of grinding wheels, which have previously used abrasive grains; the grinding wheels were in use on stainless Steel tested.

FIG. 2 shows the same representation as FIG. 1, again with grinding wheels that have the abrasive grain of the invention and with grinding wheels that have hitherto The types of abrasive used show their application on high-carbon steel.

The grinding properties of bauxite are significantly improved if, according to the invention, the bauxite is modified by the addition of chromium oxide up to about 20%. However, best results are obtained with the addition of around 10 % chromium oxide. Only very small additional improvements in the properties of abrasive grain according to the invention are achieved in comparison with sintered bauxite if the abrasive grain according to the invention has more

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IAD OBlGINAL

modified as 20 % chromium oxide. Not only does such abrasive grain perform inferiorly to the abrasive grain containing 20 % and less chromium oxide, it should also be taken into account that the addition of chromium oxide significantly affects the cost of making the grain and an additive in excess of $ 20 makes use as an abrasive material in abrasive products economically unfavorable.

In the production of the abrasive grain according to the invention, finely comminuted, burnt bauxite is preferably used, because this material is inexpensive and readily available. However, unfired bauxite or raw bauxite ore can also be used be used.

In its natural state, bauxite contains hydrous clay and less Amounts of silicon dioxide, titanium dioxide, iron oxide and other impurities. During the roasting process becomes the largest Part of the water is removed from your bauxite. For the invention is the use of finely ground bauxite with an average Particle size from about 4 to about 2 microns is preferred. The composition of the calcined bauxite can be in Depending on its deposit vary. This is shown in Table I, where a bauxite analysis of two different Deposits with the information in percent by weight is given.

SiO ₂

Table I. Bauxite deposit Surinam Demerara 85.67 87.57 1> M 6.51 5.85 2.00 2.85 BpiH? En 0.10 • 0.10 traces 1.21 0.97

CaO

MgO
'Losses ,

^ ** '00', 100.00

21 § "- 5 -

INSPECTED

-D-

In addition to the Demerara and Surinam bauxites as the place of origin of the bauxites suitable for carrying out the invention it goes without saying that other types of bauxite, such as Arkansas bauxite, can also be used. To the However, Demerara or Surinam bauxite was used to carry out the tests according to the exemplary embodiments.

The chromium oxide used had a high purity with a Cr ₂ O content of over 95.0 %. The use of the dye-containing grade was preferred because it is commercially available in a finely divided state and has an average particle size of about 2 microns.

When carrying out the method according to the invention, as it is is explained in more detail below, the addition of an auxiliary binder to the bauxite and the chromium oxide is proposed, in order to obtain sufficient green strength, which makes it easier to carry out the further process steps. Under such auxiliary binders for use within suitable within the scope of the invention include bentonite, starch, dextrin, methyl cellulose and mixtures thereof. It Synthetic resins such as the condensation products of aldehydes and phenols can also be used. the Selection of a particular auxiliary binder depends largely on the flow additive that is added to the dry mix, to make this graphic and also of the type of shaping device available. In the below detailed For example, bentonite is preferred as an auxiliary binder because it does not burn out of the individual particles before sintering must become.

Basically, the following process steps are used in production of the abrasive grain according to the invention one after the other:

1. Production of a mixture of 2 - 20 % chromium oxide and 98 % 80 % bauxite and an auxiliary binder, which is

additive, such as water, is mixed.

2. Production of abrasive grain of a certain shape and size from the mixture.

3 · Drying the pressed grains to remove excess moisture to remove and to free the auxiliary binder.

4. Heating the grain at a temperature sufficiently high to thereby sinter the particles.

An additional process step for heating the material between drying and sintering may be necessary, when an organic binder is used.

The bauxite is brought to its fineness in the particle size with the usual, known comminution processes, such as e.g. Wet or dry grinding in a ball mill with alumina balls as grinding means, the grinding operation is continued until the desired homogeneity, particle size and size distribution is achieved. In addition, however satisfactory results have been obtained with a vibratory mill employing steel or alumina grinding agents or with a jet mill which uses compressed air or steam to crush the particles by impact. With the wet working one A ball mill procedure removes the slurry of ground bauxite particles from the mill and removes the slurry then dried. The dried bauxite has the shape of a soft cake, which is then easily broken down can be, for example by being passed through a roll crusher.

The finely divided ingredients are then mixed, and one Flow additives such as water are mixed with the dry ingredients to make them pressable or otherwise malleable

"Make mixture.

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The grain formation is preferably achieved by pressing a certain Amount of the wet mixture carried out through a die. To To shape rods of uniform geometric cross-section, which are then divided into grain, which is in the individual composed of many of the aforementioned particles of bauxi, chromium oxide and binding agent. The grain is preferably a full one Body and cylindrical in cross section. The ratio of the length to the diameter of the grain can vary if desired however a length to diameter ratio of 2: 1 is preferred. The grain will last a sufficiently long time usually about 24 hours, dried at a temperature high enough to remove excess moisture remove and release the binder.

The grain can have any desired cross-section, which is adapted to the use in the respective abrasive product. When used in Grinding wheels, for example, have a diameter in the range from about 0.76 mm for 24 grit to about 2.54 mm for 8 grit (English 8-grit) lie. When pressing the grain, it is permitted to make the grain about one size larger than the grain the desired finished size as the grain will decrease in volume during the various stages in the process can.

When an organic binder has been used, the particles after drying must be subjected to baking in order to burn off the organic binder. The purpose of this process step is to avoid porosity and brittleness in the finished abrasive grain. Such properties would make the abrasive grain unsuitable for grinding, especially for heavy-duty plastering work. The Verfahrenssehritt is performed by aas grain is held in an oxidizing atmosphere at a temperature in the range of about 700 ⁰ C to about 1100 ⁰ C, is burned out until the auxiliary binder. This temperature is below the sintering temperature. the

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The length of time for which the grain must be kept at the combustion temperature depends on the temperature used and must be varied in inverse proportion. It has been found that a period of two hours at 100O ⁰ C is sufficient for complete combustion of the binder. As has already been said above, an organic binder can be replaced by an inorganic binder. In this case, the additional process step of combustion can be dispensed with.

The sintering is carried out in a furnace at a temperature between approximately 1550 ^° C. and approximately 1700 ^° C. The exact sintering temperature and time can be determined without experimentation by sintering test pieces of the bauxite-chromium oxide composition at different temperatures and times within the specified range and by a subsequent compression test to determine the compressive strength of the composition. For Demerara bauxite chromium oxide, a sintering temperature of about 1600 ^° C. is preferred, since the maximum compressive strength of the composition is present at this temperature. For Surinam bauxite, the best temperature was determined to be around 1500 ^° C.

The sintering time can depend on the temperature and the Vary the type of sintering furnace used. For example, in a conventional gas-fired kiln, the particles become gradual heated to 16OO ° C within 16 hours and then held at this temperature for 60 minutes. If a rotary kiln is used, the particles are held in the hot zone at 1615 ° C for approximately 4 minutes while in use a vibrating furnace of the vibrating furnace described in American patent application No. 625,661, the particles in the hot zone for about 2 minutes at 1675 ° C being held. Consequently, the use of rotary kilns and vibratory furnaces in the manufacture of the invention Abrasive grit is preferred, as it results in extremely short sintering times.

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The sintering atmosphere can be set from an oxidizing atmosphere to a reducing atmosphere, whether or not. arguably a nutral atmosphere or an oxidizing atmosphere is more favorable for maximum hardness and graininess of the finished grain. A typical atmosphere consists of: Ng - 89 * 8 fo ', Op - 1.9 % i COg - 9 * 5 % · The abrasive grain according to the invention then obtained has a dense, fine grain structure, and the individual particles have a density of more than 85 fo the theoretical on.

That. Abrasive grain produced according to the invention can be in various Abrasive products are used and especially in resin-bonded grinding wheels, such as Grinding wheels for billets, foundry grinding wheels and cutting wheels. The abrasive grain of the invention has good wetting characteristics with organic resins and therefore can be used in abrasive articles made of the various known synthetic and natural resins, such as phenol-formaldehyde resin, resorcinol-formaldehyde resins, polyester resins, Contains polyether resin, shellac, lacquer and the like.

The grinding wheels of the present invention are highly effective for grinding both high carbon steel and stainless steel. A significant advantage of the invention can be seen in the fact that the "consumer can grind different types of steel without having to change the grinding wheel and without having to keep grinding wheels of different abrasive grain compositions in stock, each of which is only suitable for grinding certain materials are.
to

The following embodiment illustrates the production co »·

c *> and the properties of the abrasive grain of the invention. ο

J ^ example 1.

12-grit size abrasive grit, the one Diameter of about 1.8 mm and a mean length of about

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3.55mm was made from the following blends.

AWAY

Calcined Demerara Calcined

Bauxite '90 parts Demerara Bauxite 80 parts

Chromium oxide 10 parts chromium oxide 20 parts

Bentonite 3 parts Bentonite 3 parts

Water 20-25 parts Water 20-25 parts

The bauxite, chromium oxide and bentonite were finely divided and had an average particle size of 4 microns and less. The chromium oxide had a purity of 99 % , and the bauxite and bentonite had the following composition.

Bauxite bentonite

Al ₂ O ₃

SiO ₂

TiO ₂

89.15 3.49 5.67 64.32 3.17 20.74 1.87 3.49 - 0.48 - 2.28 - " 2.90 - 0.55 0.14 5.15

CaO MgO Na ₂ OK ₂ O

loss

Each of Mixtures A and B were treated as follows:

The ingredients were first dry in for 5 minutes mixed in a 914 mm diameter mixer, then the water was mixed and mixed with the dry ingredients for 15 minutes until the mixture is suitable for pressing Had consistency.

The mixture was then fed into a 101 mm Auger extruder Durohmesser inserted and through a 6.3 mm thick die

pressed. Rods with a diameter of 2.16 mm and a length of 50.8 to 609.6 mm were produced. The pressed bars were then broken in a steam-heated rotary dryer at a temperature van about 105 ⁰ C dried and during the drying process to grain mm an average length of 2.5 to 5 mm was obtained.

The grain was then cased and staged over a period of 16 hours to a temperature of 160 ° C heated in a gas-heated kiln in a neutral atmosphere. When the temperature reached 160 ° C, the particles became Maintained at this temperature for 60 minutes and then cooled. The sintered abrasive grain had a medium diameter of about 1.8 mm and a mean length of about 3 * 6 mm.

The finished abrasive grain of mixture A and mixture B was examined for physical petrographic properties, and the results are in the following Table II listed.

Table II

mixture

AWAY

250 9 208 9 4, 7, 1680 64 1541 74 3, 7th 3, 4th 88 88

Pressure in kg fracture index Knoop 100 hardness Grain density (g / cmr ^)

Percent of theoretical density

The index of rupture used herein is an inverse measurement of toughness. This means that as the index increases, the toughness decreases. The breaking index shows more precisely the reduction in cross section in the shape of the grain

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that has been subjected to carefully controlled, uniform milling conditions. When measuring this amount, the grain of the particular grain size is first classified between two adjacent sieves, so that 100 % passes through the sieve with the larger mesh size, which is one size larger than the nominal grain size and 100 % remains on the finer sieve, that corresponds to the nominal grain size. A specified amount of the abrasive material is then ground under uniform conditions and again classified on a sieve that is one sieve number finer than the nominal grain size. The percentage of abrasive material that passes through this screen is the index of breakage. This is a relative index because it is based on a standard test for electric alumina grain of the average toughness, in which the grain, a 50 $ strength break (ie, 50 fo the starting material passes through the screen which is finer than the nominal grain size of a number ) for each examined grain size.

Relate the Kileg3? Afflffl breaking loads in kilograms for shredding focus on grain particles with a length / diameter ratio of 3 ί 1 and are determined by placing the grain in Is placed lengthways between a pair of jaws and subjected to sufficient pressure to break the grain. The pressure at which the grain breaks is given in kg in the table.

Upon petrographic analysis, the abrasive grain of Mixture A was found to have a crystal structure with 95 % of the crystals below 20 microns. It was found that many acicular crystals were present. Mixture B abrasive grain had a crystal structure with 90 ^c / o of crystals under 20 microns. There were also many needle-shaped crystals.

Both grain of Mixture A and Mixture B were in a hot-pressed, synthetic resin-bonded grinding wheel is used, using the usual and known methods

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BATH ORIGINAL

arrived. The grinding wheels had the following composition;

Abrasives phenol-formaldehyde resin FeS ₂

K ₂ SO ₄

NaCl CaO

Two 406.4 mm by 6 ^ mm by 152 mm grinding wheels were each made with grade A and grade B abrasive grit. The grinding wheels, which contained abrasive grain of mixture A, were designated as type A grinding wheels, while those containing abrasive grain from mixture B were designated as type B grinding wheels were marked.

For comparison, two grinding wheels of identical dimensions and compositions were made but using an abrasive material consisting of sintered bauxite abrasive grain of the same size and shape as used in the A and B grinding wheels. The grinding wheels that contain sintered bauxite as an abrasive have been labeled as C grinding wheels. In addition, so-called D-type grinding wheels of the same dimensions and shape were produced, but containing electro corundum with 40% zirconia as the abrasive grain.

The C grinding wheels were selected for comparison as such Grinding wheels are considered to be among the best for grinding stainless steel. The D grinding wheels were selected because this grade is best suited for grinding high carbon steels. Every grinding wheel has been tested on both stainless steel of classification j) 04 and carbon steel of classification C1045, using a three-speed automatic grinder.

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Me grinding wheels were 'a 20-minute contact process exposed, with a peripheral speed of 63.5 m per second and a pressure of I92 - 226 - 261 kg is observed became. The results of these tests are shown in Tables III and IV. Table III lists the results of Grinding tests of the various grinding wheels on stainless steel 305. Table 4 lists the results of the grinding tests with carbon steel C1O45.

Table III

Results of the grinding tests with grinding wheels of type A, B, C and D on stainless steel 305 (American classification)

(M) (W) M / W

Type pressure, kg metal removal, kg / h grinding wheel ratio wear kg / h nis

A 192 91.5 1.95 47.0

^ 9.5 42.0

B 192 86 2.32 57.0

36.0

192 91.5 1.95 226 116.5 2.35 261 117 4.21 192 86 2.32 226 120.5 3.35 261 125 3.67 192 86 1.48 226 130 2.26 261 190 4.39 192 60.5 1.31 226 95 2.61 261 147 4.39 Table IV '

C 192 86 1.48 58

57.5

D 192 6o, 5 1.31 46.0

36.5 33.5

Results of the grinding tests with grinding wheels of type A, B, C and D on carbon steel C1O45 (American classification)

Type pressure, kg metal removal, kg / h grinding wheel ratio wear kg / h nis

A 192 67.3 1.13 59.5

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226 95 261 147 192 130 226 159 261 - 192 34.3 226 43, 261 63.5 192 61 226 56.3 261 103

1815911 1.81 52.5 3.62 40.5 2.82 46, ο 4.97 32.0 1.49 23.0 2.26 19.0 3.03 21.0 1.49 41.0 1.54 36.5 3.42 30.6

As can be seen from Table III, the metal removal is of both type A and type B of the grinding wheels 3 abrasive grain according to the invention essentially the same as for the type C containing sintered bauxite when the grinding wheels tested on stainless steel. It can also be seen that the grinding wheel wear for the types A and B can also be compared well with the wear of type C and that the ratio M / W for type A grinding wheels is almost as good as the ratio M, 'W of the type C grinding wheels. It is evident that the Type A grinding wheels are superior to the Type B grinding wheels in terms of performance. Both type A and type B grinding wheels are type D grinding wheels, which contain alumina-zirconia abrasive grain, think.

Referring to Table IV, it can be seen that when grinding carbon steel C1O45, both Type A and Type B grinding wheels have a greater metal removal rate than Type C and D grinding wheels. Furthermore, the metal removal from the A and B grinding wheels on C1O45 steel can be compared with the metal removal from the A and B grinding wheels on 304 stainless steel.

As a result, it can be seen from the tables that the grinding wheels, containing the abrasive grain of the invention, im

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perform substantially the same on both stainless steel and high carbon steel, while the comparison grinding wheels, which contain conventional abrasives, only perform well on one of the materials, on which they were tested.

The graphs in Figs. 1 and 2 of the grinding ratio M / W based on the grinding pressure for the grinding wheels of type A, C and D illustrate the results when the grinding wheels are used on stainless steel (Pig. 1) and on carbon steel (Fig 2) to be tested. The ratio M / W (ratio of metal removal to grinding wheel wear) is a factor that is often used to evaluate the effectiveness of a grinding wheel. As can be seen from Figure 1, the grinding wheels containing sintered bauxite abrasive grain perform best at 192 kg and 226 kg grinding pressure, but drop rapidly at 261 kg grinding pressure to an M / W ratio substantially equal to that of the type A grinding wheels containing bauxite abrasive grain modified with 10% chromium oxide according to the invention. The M / W ratio obtained with the type A grinding wheels on stainless steel is very acceptable and is only 15 % lower than the values of the type C grinding wheels containing sintered bauxite abrasive grain.

As can be seen from Fig. 2, the grinding wheels containing 10 % chromium oxide and bauxite abrasive grain perform significantly better than the type C or D grinding wheels. Prior to the invention, the type D grinding wheels with alumina-zirconia abrasive grain were used for grinding Preferred high carbon steels.

Although not shown in Figures 1 or 2, the Type B grinding wheels containing 20 % chromium oxide modified sintered bauxite abrasive grain have grinding ratios slightly better than Type D when ground on 304 stainless steel became. The grinding

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ratio was better than in tests on C1045 steel Type C or D grinding wheels

Example 2

In the same way as described above, particles of a mixture were again made which had the same composition as the mixture A of Example 1, pressed into grain and dried. The grain was sintered in a 89O mm rotary kiln. The temperature in the hot zone of the furnace was maintained at 1615 ° C and the oven rotated at a speed of 2.2 revolutions per minute. The atmosphere in the oven was neutral. The green particles were introduced into the furnace at a rate of 182 kg / hour and stayed in the hot Zone approximately 4 minutes. The finished particles, the abrasive grain, had a specific gravity of 5 * 55 and a fracture index from 4.1 to. The mean Knoop 100 hardness was I363. The petrographic analysis found that the grain had the following crystal structure:

80 fo less than 5 microns

15 % 5/10 microns

5 % 10/20 microns

Traces 20/50 microns

Many of the crystals were needle-shaped and the crystal structure was essentially the same as was already determined for the abrasive grain according to Example 1.

The abrasive grain then became a series of twenty 6.5 mm times 203 mm hot-pressed, resin-bonded grinding wheels processed. A series of so-called standard grinding wheels was used for comparison made, the abrasive grain consisted of electric corundum with 10 pounds of zirconia. This material is a Standard material and available as a commercially available abrasive.

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Both the experimental grinding wheels and the standard grinding wheels were application testing under, the same Exposed to grinding conditions. The grinding wheels were tested on both stainless steel and tool steel. The results are listed below and represent average values over all experimental grinding wheels.

Average mean

rather metal removal abrasive

kg cost /

Experimental grinding wheels (bauxite - 10 % Cr ₂ O,

Abrasive grit) 955 0.05

Standard grinding wheels (10 % ZrO ₂ - Al ₃ O,

Abrasive grain) 570 0.0725

In other application tests, standard grinding wheels (without center, 24 times 3) were examined for their suitability, To clean carbon steel billets. The results are shown below.

Average average metal removal, kg abrasive costs, P-rurid-

k £

Experimental grinding wheels

(10 % Cr ₉ O-, - bauxite
SchleifKoAi) 1260 0.089

Standard grinding wheels (10 % ZrO ₂ - Al ₃ O ₅

Abrasive grain) 1030 0.139

The data given above show that grinding wheels with the abrasive grain according to the invention have more kg of metal per grinding wheel than the standard grinding wheels do. Furthermore, the grinding wheels work with the one according to the invention Abrasive grit on high-carbon steels with

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significantly lower grinding costs per unit weight metal removal than the usual grinding wheels.

Example 3.

An abrasive grain containing 10 % chromium oxide and 90 % Suriname bauxite was produced in the same manner as in Example 2 using a rotary kiln. The temperature of the hot zone was about 1500 ^° C. The finished grain was used in bonded grinding wheels which had the same composition and size as the grinding wheels according to Example 1. The grinding wheels were tested for their grinding characteristics on 304 stainless steel and C1O45 carbon steel using the three-speed grinder of Example 1.

As comparison disks, as in Example 1, those using standard sintered clay and 10% chrome ore with 90% Demerara bauxite were produced. The grinding wheels were tested under identical conditions as the grinding wheels, which contained Suriname bauxite abrasive grain modified with chromium oxide. The results are listed in Tables V and VI below and represent the mean values of two grinding wheels.

Table V

Results of the comparative tests on stainless steel, type

Sole medium grade Metal removal 1-κΙι
(M) Grinding wheel
ben wear Relationship
nis M / W kg / h, (W) GL ^ intertes Al ₅ O ,,
10 70 C ^ O- - 90 %
Demerara bauxite 122
143 1.98
2.51 61.5
56.9

10, a Cr ₂ O ₃ - 90 %

Surinam bauxite 171 3 * 30 51.7

+ Test conditions: grinding pressure 260.82 kg; Grinding wheels ^ eschwindigkeit 63, ο m / sec.

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BATH ORIGINAL

Table VI

Results of the comparative tests on carbon steel C1O45 ⁺⁺

Abrasive metal removal Grinding wheel ratio grades kg / h (M) wear ■ M / W

kg / h "(W)

sintered 24, 27 1, 102 21, 6th aluminum 10 % Cr _p 0 ^ -90 ^ 59, 19th 0, 965 61 , 3 Demerara bauxite 10 fo Cr ₂ O, -90 ^ 57 , 15 1, 035 55 , 5 Surinam bauxite

Test conditions: grinding pressure 226.8 kg; Grinding wheel speed 63.5 m / sec.

From the above description and the test results it can be seen that the abrasive grain according to the invention has almost the characteristics of a "universal grain". The abrasive grain according to the invention has excellent properties Grinding properties on the different types of steel, the shape and size of the grain can depend on the Uses can be varied, and its application in abrasive articles is not to bonded abrasive articles limited. Multi-layered abrasive products are also suitable for use.

The percentages and information in parts given in the data relate to weight, if not in the text otherwise stated.

Patent claims:

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Claims (16)

Patent claims: / 1.! Sintered alumina-containing abrasive grain with finely ground bauxite, characterized by a chromium oxide content of Ms to 20 Ji. 2. Abrasive grain according to claim 1, characterized in that the chromium oxide content is 2 % - 20 % . 3. Abrasive grain according to claim 1 and 2, characterized in that the chromium oxide content is 2 % - 10 % . 4. Abrasive grain according to one of claims 1 - 2 / characterized in that the chromium oxide content is around 10 % . 5. Abrasive grain according to one of claims 1-4, characterized in that that the bauxite is Demerara and / or Surinam bauxite. 6. Abrasive grain according to one of claims 1 -5, äaä «3? Ek characterized through a uniform geometric design in cross-section and a certain length / diameter ratio . ¹ J. Abrasive grain according to one of Claims 1-6, characterized by a length / diameter ratio of approximately 2: 1. 8. A method for producing alumina-containing abrasive grain according to one of claims 2 - ¹ J _3, characterized in that a malleable mass with 2 % - 20 fo finely comminuted chromium oxide, 98 fo - 80 fo finely comminuted bauxite, auxiliary binder and a flow additive is produced which Mass is formed into a grain of a certain size and uniform geometric shape, which consists of a large number of bauxite and chromium oxide particles, that the grain is dried to remove the flow additive and then the particles are sintered. 909830/1 21 9 - 22 - SAD ORIGINAL 9 · The method according to claim 8, characterized in that 3 parts of bentonite as an auxiliary binder and 20 parts-25 parts of water were added to the malleable mass as an additive will. 10.Verfahren.nach claim 8 or 9 »characterized in that that the malleable mass is pressed into rods of uniform cross-section, and the rods in lengths of about twice that Bar diameter are divided. 11. The method according to any one of claims 8-10, characterized in that that the bauxite has an average particle size of about 2 microns to 4 microns and the chromium oxide an average Particle size of about 2 microns is given. 12.Verfahren according to any one of claims 8-11, characterized in that the particles are sintered ^{at a temperature between 14OO C and 1700 0 C.} 13.Verfahren according to claim 12, characterized in that the particles ^{are sintered at a temperature between 1500 0} C and 165O ° C in a neutral atmosphere. 14. Grinding wheel for grinding stainless steel and high-carbon steel with an abrasive grain containing alumina and a bond that unites the abrasive grain into a single body, characterized by a sintered abrasive grain with bauxite and a 2 % - 20 $ content of chromium oxide according to one of claims 1 -7 ^ • Grinding wheel according to claim 14, characterized in that the abrasive grain contains Demerara bauxite and around 10 % chromium oxide and has an average length / diameter ratio of 2: 1. 16.Schleifscheibe according to claim 14, characterized in that the abrasive grain Surinam contains bauxite and 10 % chromium oxide. 909830/1219