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US3674218A - Process and mill for grinding pulverulent materials, and the materials thus ground - Google Patents

Process and mill for grinding pulverulent materials, and the materials thus ground Download PDF

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Publication number
US3674218A
US3674218A US849324A US3674218DA US3674218A US 3674218 A US3674218 A US 3674218A US 849324 A US849324 A US 849324A US 3674218D A US3674218D A US 3674218DA US 3674218 A US3674218 A US 3674218A
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United States
Prior art keywords
shoes
disc
grinding
liquid
openings
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Expired - Lifetime
Application number
US849324A
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English (en)
Inventor
Anatol Globus
Paul Duplex
Roger Vautier
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Bpifrance Financement SA
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Agence National de Valorisation de la Recherche ANVAR
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
    • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
    • B02C19/00—Other disintegrating devices or methods
    • B02C19/10—Mills in which a friction block is towed along the surface of a cylindrical or annular member

Definitions

  • ABSTRACT Foreign Application Priority Dam The material or materials to be ground are put in suspension in Aug 13 1968 France 68162875 a liquid, and this liquid is made to pass in a continuous and repeated manner between two rubbing surfaces.
  • the pressure of 52 U.S.Cl ..24l/46.06 241/254 241/290 applicati)" Surface against the other is P 51 Int.
  • This invention relates to processes and mills for finely grinding materials which are already in the form of grains of small dimensions, as well as to the fine powders obtained according to these processes and with the aid of these mills, and also to the products made with these powders, in particular by diepressing and sintering.
  • the ball mills used in industry are generally made of steel, as are the balls that they contain.
  • the steel is hardened by incorporating into it elements such as carbon, tungsten, chromium, molybdenum, vanadium, etc. It is true that due to these products of addition, the hardness of the steel is increased, and the wear of the mill and of the balls is decreased, but this wear, inevitable in spite of everything, causes the addition, to the materials undergoing treatment, not only of the principal constituent of the steel, that is to say iron, but also of the elements such as carbon, tungsten, chromium, etc., some of which can be very troublesome according to the properties that one has in view.
  • Another disadvantage of the prior art resides in the relatively large grain size of the powders obtained and of the constituent grains of the sintered products obtained from these powders.
  • the chief object of this invention is to mitigate these various disadvantages.
  • the pulverulent material to be ground is put in suspension in a liquid which is not a solvent for this material, and this liquid, loaded with this material, is made to pass continuously and in a repeated manner between two hard parallel rubbing surfaces urged one against the other by elastic means or by gravity and driven with a relative movement parallel to these surfaces.
  • At least one of the rubbing surfaces is constituted of the same material as the material to be ground.
  • FIG. 1 is a longitudinal section of a mill for carrying out the process of the invention
  • FIG. 2 is a section along II--II of FIG. 1, with parts cut away;
  • FIG. 3 is a section along Ill-Ill of a part of FIG. 2.
  • the liquid phase loaded with the grains is made to circulate in a continuous and repeated manner between at least two hard parallel surfaces facing each other, which are urged elastically one against the other and which are movable one with respect to the other.
  • the grains are subjected to an action which is more akin to laminating than to abrading, and these grains are thus progressively reduced to smaller and smaller sizes, while the wear of the surfaces facing each other remains always a minimum.
  • the surfaces are of the same nature as the grains, the disintegration of these surfaces-whose wear remains relatively slight-will not introduce impurities into the treated product.
  • mills of various types can be used, in particular the embodiment which is going to be described hereafter.
  • the liquid carrying the grains is led to pass between a rotary disc and flat shoes resting on this disc.
  • the mill comprises a tank 1, closed at the top by a cover 2 bolted by bolts 3, the disc 4 mentioned above being provided horizontally in the lower portion.
  • This disc 4 is supported and driven in rotation by a vertical drive shaft 6, on which it is fixed, for example by a screw 7; this shaft passes through the cover 2, is guided in a support 8 by at least one bearing 9 and is driven by a motor (not shown).
  • the shoes 5 are for example four in number and support freely rods 10 which, they too, pass freely through the cover 2 and the support 8 and can receive, at: their emerging upper ends, weights 11 for regulating the pressure of contact of the shoes 5 on the disc 4.
  • a guide or perforated plate 12 is provided having four openings 13 passing therethrough from one side to the other so as to provide a passage for these shoes.
  • the profile of the openings 13 is visible in FIG. 2: it is constituted by a rear part 13b following with play the rectangular shape of the shoes 5 and by a trapezoidal forward part 13a, in which the liquid is engulfed, as will be seen later on.
  • the guide 12 is fixed to the base of a fixed sleeve 14 surrounding the shaft 6. This sleeve flares out at its upper portion 14a, where the rods 10 pass through thanks to openings 15 and where the cover 2 is fixed by the bolts 3.
  • a cross piece 16 fastened at two opposite points on the guide and whose role is to avoid rotation of the liquid as a whole.
  • the forward face 5a of the shoes 5 is bevelled towards the bottom in order to facilitate the penetration of the liquid between these shoes 5 and the disc 4.
  • the surfaces of contact of the shoes 5 and of the disc 4, or of a lining 40 carried by this disc and facing the shoes 5, are preferably constituted of a material such that in case of wear the products worn away from these surfaces do not constitute impurities for the mixture.
  • At least one of the pieces 4 and 5 can be constituted or coated with a material of the same nature as that of the materials to be ground.
  • One of the rubbing surfaces can alternatively be coated with a layer of harder material. Nevertheless, neither of the two rubbing surfaces should be abrasive under the pressure used in the process.
  • the disc 4 can be a conventional diamond-set grinding wheel whose surface has been rendered smooth by preliminary wear.
  • the tank 1 is cylindrical and the shoes 5 are disposed in a circle about the shaft 6.
  • the tank can have any desired shape permitting easy cleaning.
  • the liquid in which the materials are in suspension is introduced into the tank.
  • the disc 4 is set in rotation by means of the shaft 6 in the direction for which it leads the thus-stirred liquid to penetrate, through the openings 13a, between the shoes 5 and the disc 4 (arrow F).
  • the materials that the liquid contains are rubbed, crushed and finely pulverized.
  • the liquid serves as a lubricant for the rubbing of the rubbing surfaces.
  • the agitation of the liquid can be increased, for better stirring, by disposing an agitator or any other accessory, for example a helix, in the tank, which has the further advantage of ensuring a more intimate mixture of the constituents in the case in which there are more than one, and even of ensuring continuous circulation. This is the role of the flanges 17 of the disc 4.
  • the rubbing surfaces can be arranged in a different manner so long as they remain freely applied one against the other (by gravity or by other elastic means) along insignificant areas.
  • the disc 4 could be replaced by a cone or a cylinder rotating about its axis and the shoes 5 by shoes having complementary conical or cylindrical rubbing surfaces.
  • shoes 5 could also be made to move, either in rotation about themselves, or in rotation about the shaft 6.
  • the regulable application pressure of the surfaces one against the other can be relatively low and is preferably comprised between a few tens of grams per cm and a few kilograms per cm
  • the degree of dilution of the starting powder should be such that the loaded liquid remains fluid and not pasty, the weight of powder per unit volume being preferably comprised between 20 and 200 grams per liter.
  • EXAMPLE 1 In order to obtain yttrium-iron garnet of formula 3 y O 5 F6 0,, the powders of iron oxide Fe O and of yttrium oxide Y O are put in suspension in water in the molecular proportion corresponding to the above garnet formula and in the amount of 100 g of the mixture per liter.
  • the disc is constituted by a worn diamond-set grinding wheel.
  • the shoes 5 are constituted by blocks of yttrium-iron garnet.
  • the mean linear speed of the disc is 9 meters/second (m/s) and the application pressure of the shoes 5 on the disc is 100 g/cm.
  • the suspension After 72 hours of operation, the suspension is collected in a heated receptible in order to make the water evaporate.
  • the dry powder obtained is exceptionally fine (grain size very much smaller than 0.1 micron), pure and homogenous.
  • Another advantage is that the die-pressing pressure can be chosen in order to regulate the density of the raw die-pressed product.
  • the raw die-pressed product is then heated to l,250 C for 4 hours in oxygen, and a garnet is obtained whose grains measure about 2 microns and whose specific mass is 5.15 g/cm": as the theoretical specific mass of this garnet is 5.17 g/cm the porosity is only 0.4 percent.
  • the operation is much longer and it is necessary to use high temperatures for the sintering in order to obtain low porosity: for example, for the porosity to be lower than 2 percent, the sintering temperature must exceed l,400 C.
  • the specific mass of the product obtained is 5.30 g/cm, which corresponds to a porosity of 0.4 percent, whereas with a conventional grinding mill, a porosity of 3 percent is obtained after 14 days of grinding and 10 days of thermal treatment at 1,200 C in oxygen.
  • the present invention permits the grinding and the mixing of the pulverulent materials to be carried out with numerous advantages with respect to the prior art processes, and in particular the following advantages if the mechanical part is constructed with a little care (but following the rules of mechanics which are completely conventional, nothing more), the process described is very quiet, incomparably quieter than ball mills (or mills using shocks in general);
  • this process can replace not only the other grinding processes, but also chemical co-precipitation, and this is very advantageous for the present process is applicable to any composition;
  • the powder obtained can have a very high fineness (thus it is possible to obtain powders of common metal oxides: iron, manganese, nickel with a fineness such that their time of sedimentation in water exceeds several weeks);
  • the powder obtained is formed of grains having a much more homogenous grain size that can be obtained with conventional grinding processes;
  • the die-pressing is much easier and does not require any binder; furthermore, even sintering at low temperature provides a sintered material of high density, this density exceeding any that can be obtained with a ball mill and sintering in the same conditions; it is thus possible to obtain a material of high density which has a sufficiently fine grain size, whereas these two qualities are normally contradictory; it is also possible to use the die-pressing pressure as a parameter for regulating the final density (or the porosity);
  • the relative density (with respect to the theoretical density calculated from the atomic masses and from the spacing of the crystaline network) of the raw product, after die-pressing, can already be very high; consequently, the shrinkage in the course of sintering is much smaller, which constitutes an important advantage for the mechanical precision and for the mechanical resistance of the finished pieces;
  • this process can be used for increasing the reactivity of a product.
  • these ferrites have considerably improved qualities due to their density as well as due to the fineness and the regularity of their grains, in particular with respect to the widening of their band of linear operation for certain hyperfrequency applications, the precision of their sides (an appreciable advantage for example for heads for reading magnetic tapes), and the quality of the permanent magnets which can be made from them.
  • Apparatus for preparing a pure fine powder from a pure, hard, homogeneous, pulverulent material in suspension in a liquid comprising: a receptacle for containing said suspension, at least one pair of first and second hard and smooth twodimensionally parallel rubbing surfaces disposed facing one another within said receptacle and means urging said rubbing surfaces resiliently against one another; means for providing movement of first and second surfaces with respect to one another parallel to each other, a shoe providing said first rubbing surface, said shoe being held substantially stationary with respect to said movement and having an upstream edge (with respect to the relative direction of flow of the liquid in which the shoe is immersed) so shaped as to facilitate the introduction of the suspension between the two rubbing surfaces, wherein said second surface is the upper face of a horizontal disc rotatable about a vertical axis.
  • Apparatus according to claim 1 including a fixed perforated horizontal plate having openings in which the shoes are located and guided.
  • Apparatus according to claim 2 comprising vertical rods resting on the shoes and loaded by weights, whereby said first and second rubbing surfaces are urged against one another.
  • a grinding mill comprising in combination,
  • a grinding mill constructed in accordance with claim 4, wherein said disc has projecting flanges for circulating the liquid in the tank to cause it to pass upwardly into said openings in the plate.

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  • Engineering & Computer Science (AREA)
  • Food Science & Technology (AREA)
  • Crushing And Grinding (AREA)
  • Compounds Of Iron (AREA)
  • Soft Magnetic Materials (AREA)
US849324A 1968-08-13 1969-08-12 Process and mill for grinding pulverulent materials, and the materials thus ground Expired - Lifetime US3674218A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR162875 1968-08-13

Publications (1)

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US3674218A true US3674218A (en) 1972-07-04

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US (1) US3674218A (de)
DE (1) DE1940930A1 (de)
FR (1) FR1597435A (de)
GB (1) GB1284773A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6070815A (en) * 1997-11-13 2000-06-06 Shizuoka Seiki Co., Ltd. Grain milling machine
US20110168820A1 (en) * 2010-01-12 2011-07-14 Wildcat Discovery Technologies Stirred ball mill assembly with magnetic drive system

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US326483A (en) * 1885-09-15 Amalgamator
US522807A (en) * 1894-07-10 Amalgamator and settler
US701346A (en) * 1900-06-07 1902-06-03 Nelson T Shields Amalgamating apparatus.
US789983A (en) * 1903-09-19 1905-05-16 William R Macklind Slip-mill.
US1308008A (en) * 1919-06-24 forsyth
US1958035A (en) * 1927-04-11 1934-05-08 Coursey William De Method and apparatus for treating materials
US2246846A (en) * 1940-01-31 1941-06-24 Daniel E Hennessy Mulling mill
US3521825A (en) * 1967-02-13 1970-07-28 Westinghouse Electric Corp Milling process

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US326483A (en) * 1885-09-15 Amalgamator
US522807A (en) * 1894-07-10 Amalgamator and settler
US1308008A (en) * 1919-06-24 forsyth
US701346A (en) * 1900-06-07 1902-06-03 Nelson T Shields Amalgamating apparatus.
US789983A (en) * 1903-09-19 1905-05-16 William R Macklind Slip-mill.
US1958035A (en) * 1927-04-11 1934-05-08 Coursey William De Method and apparatus for treating materials
US2246846A (en) * 1940-01-31 1941-06-24 Daniel E Hennessy Mulling mill
US3521825A (en) * 1967-02-13 1970-07-28 Westinghouse Electric Corp Milling process

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6070815A (en) * 1997-11-13 2000-06-06 Shizuoka Seiki Co., Ltd. Grain milling machine
US20110168820A1 (en) * 2010-01-12 2011-07-14 Wildcat Discovery Technologies Stirred ball mill assembly with magnetic drive system
US8056846B2 (en) * 2010-01-12 2011-11-15 Wildcat Discovery Technologies Stirred ball mill assembly with magnetic drive system

Also Published As

Publication number Publication date
DE1940930A1 (de) 1970-04-09
FR1597435A (de) 1970-06-29
GB1284773A (en) 1972-08-09

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