US2712416A - Centrifugal grinding mills - Google Patents

Description

July 5, 1955 w. BEUSHAUSEN ETAL 2,712,416

CENTRIFUGAL GRINDING MILLS 2 Sheets-Sheet 1 Filed April 19, 1951 4 m z 5 M M; M m 3 E NwM m W50 0 m Wm M mfliw W 8.

Filed April 19, 1951 July 5, 1955 w. BEUSHAUSEN ETAL 2,712,416

CENTRIFUGAL GRINDING MILLS I 2 Sheets-Sheet 2 INVENTORS ATTORNEYS CENTRIFUGAL GRINDING MILLS Walter Beushausen and Hans Rnmpf, Augsburg, Germany, assignors to Alpine Aktiengesellschaft, Eisengiesserei und Maschinenfabrik, Augsburg, Germany, a company of Germany Application April 19, 1951, Serial No. 221,818 Claims priority, application Germany April 22, 1950 2 Claims. (Cl. 241-55) This invention relates to sieveless centrifugal grinding mills in which the material to be ground is comminuted by impact with pegs; projections or notches on two coaxially mounted grinding disks adapted to rotate at high speeds with respect to a housing, and more particularly to a construction of the housing and disks which minimizes clogging of the mill by the ground product.

A difficulty with which peg mills have been long beset is the tendency for the ground product to collect in compact masses on the housing in such quantity as finally to stop the mill. To prevent such clogging it has been proposed to fit stripping blades to one or more of the rotating disks in order continuously to remove the material which comes to adhere to the walls of the housing. However with high speeds for the grinding disks such stripping blades cannot be fitted in view of the mechanical stresses involved and in View of the heat generated thereby.

I have found that a free space within the housing, in the plane of the grinding disks, properly proportioned to their diameter and peripheral speeds in accordance with the invention, substantially prevents or greatly retards the accumulation of the ground product on the inside walls of the housing. According to another feature of the invention the disks are rotated at high but unequal speeds with respect to the housing, and the more slowly rotating disk is preferably mounted on a large door which gives access to the housing interior. According to still another feature of the invention one of the disks is rotated at high speed and the other is rotated at low speed. The direction of the rotation of the two disks may be equal or unequal. In a preferred embodiment of the invention the housing is given an annular constriction at the periphery of the disks. This constriction forms in conjunction with the disks themselves a throat or nozzle through which a current of air passesradially or tangentially toward the periphery of the housing, preventing the impingement of the ground material on the housing Walls until it has lost a large part of its kinetic energy in flight through the'free space provided between the periphery of the disks and the surrounding housing wall.

It is still another feature of the invention to provide for introducing a gaseous medium into the grinding mill for cooling, drying, chemically influencing or otherwise treating the product after it has been ground, during grinding and/or before grinding takes place;

The invention will now be further described in conjunction with the accompanying drawings with relation to preferred embodiments, but persons skilled in the art will readily perceive other means for accomplishing the same results, and the claims are therefore to be construed as broadly as possible, consistent with the prior art.

In the drawings Fig. 1 is a vertical axial section through a mill according to one embodiment of my invention;

Fig. 2 is a view in side elevation of the mill of Fig. 1, shown at a reduced scale;

Fig. 3 is a partial axial section similar to that of Fig.

l but showing a modified form of mill;

Fig. 4 is a plan view of a mill according to another modification, and I Fig. 5 is a sectional view of the mill of Fig. 4, taken on the line 5-5 of Fig. 4.

In Fig. 1 two disks 1 and 3 are respectively mounted on shafts 5 and 7 for coaxial rotation when the mill is in' operative position as shown in the figure, with the door closed. The shaft 5 is journaled at bearings 9 in a housing generally indicated at 11 and is driven by means of a suitably coupled motor 13 at a high speed. The motor 13 may be supported from the heirsing 11 by means of a bracket 14 as shown. For example with a disk 1 of the order of cm. diameter the shaft 5 will be typically rotated at 12,000 R. P. M. to give the disk 1 a peripheral velocity of approximately 150 meters per second.

In the embodiment shown the disk 3, which is customarily operated at a lower speed than the disk land in the same or the opposite direction, is mountedin a large door 15 which gives ready access to the interior of the housing for cleaning and maintenance purposes. Bearings 17 in the door support the shaft 7, and rotation is imparted thereto by means of a motor 19 which may also be mounted on the door as indicated in Fig. 2. In

the embodiment shown the motor 19 is coupled to the shaft '7 through a pulley 6 and belt 8.

Each of the disks bears an array of comminutinv members such as pegs or similar projections 21, by impact with which the particles of material to be ground are reduced to suitable fineness. When the door 15 is closed as shown in Fig. 1, the pegs 21 of the two disks engage or mesh with each other (but without contact) in order to insure impact of the particles first with pegs of one disk and then with pegs of the other.

The disk 3 includes a generally conical hub 23 and an annular plate 25 fastened to the hub by means of web portions 27. The webs 27 are circumferentially spaced apart about the axis of rotation of the disk to permit the material to be ground to pass into the space between the two disks, together with a controlled stream of air or gas entering at a conduit 28, provided with a valve or throttle 30.

The material to be ground is fed into the mill through a conduit 29 which communicates with the interior of the housing adjacent the axis of rotation of the disks.

In the embodiment shown in Fig. l the conduit 29 is formed in the door 15; generically however it forms a part of the housing. An annular lip 31 in the housing insures that the material to be ground will pass between the hub 23 and plate 25 of the disk 3 into the space between the two disks before moving out to their periph cry and hence into the free space from which they subsequently fall through a discharge conduit 34 where the ground product is collected.

.To prevent collection of the ground product on the walls of the housing 11, the latter is shaped to have in the planes of the disks a substantially greater diameter thanthe disks. In Fig. l, d represents the diameter of the grinding disks, which are of approximately equal diameter, and .12 represents the radial separation of the disks from the housing wall in the planes of the disks. I have found that when the disk rotating more quickly is operated with peripheral velocities of the order of 100 meters per second the radial separation a should be not less than that given by the relation in which dimensions are given in centimeters. When the without substantial axial component of motion by which of the order of 150 meters per second, the radial sepa- I V ration a should at least satisfy the relation.

in which the dimensions are given in centimeters. When. the housing is given minimum dimensions in accordance with these relations, the particles of ground material are sufliciently slowed down in their flight from the disks to the housing walls so that they strike the housing without the energy required for their agglomeration into a cornin which dimensions are given in centimeters. When the peripheral velocity is of the order of 150 meters per second, the radial separation a, in a preferred embodiment, is not less than The velocity of the disk rotating more slowly may be considerably lower than that of the disk rotating more quickly. The disk rotating more slowly may rotate in the same direction as the disk rotating more quickly or in the reverse direction. In any case the velocity of the disk rotating more quickly and the ratio of the velocities of the two disks are being selected in adaption to the quality of the goods to be ground. a

In a further preferred embodiment the housing is given a constriction 33 in the vicinity of the disk peripheries. The disks themselves are beveled at '35 to conform to this constriction. The bevel preferably terminates in a sharp-edged periphery at 36 for reduced turbulence of the stream of air and ground particles emerging from between the disks. The resulting openings between the outer faces of the disks and the housing are in the form of annular throats or nozzles 38 through the air or other gaseous medium within the housing moves rapidly outward to prevent impingement of the high speed ground particles on the adjacent walls of the housing. To assist in the production of such currents vanes 37 may be affixed to the outer faces of the disks, to function in the usual manner of a centrifugal blower.

It has been found advantageous to provide control of the gas pressure within the mill. To this end the material to be ground is fed into the housing through a conduit 29 which communicates with a screw conveyor generally indicated at 39 by means of which, when half full or more, the conduit 29 can be closed off from the outer atmosphere. A hopper 41 permits continued feeding of the conveyor 39.

To supply a gaseous medium under controlled conditions to the grinding zone between the disks, a throttled input conduit 23 is provided, opening separately into the material input conduit 29. Adjustment of the throttle valve 30 permits control of the fineness of grinding achieved with given rates of rotation for the disksl and 3.

Additional throttled air inlet passages 43 and 44 are provided. communicating with the interior of the housing on the remote faces of the grinding disks radially inside their periphery, for regulation of 'the annular streams of air which pass out between the disks and the constriction 33 .in the housing. The passages '43 and 44 further permit control of the temperature and humidity conditions of the material ground. i

To further inhibit the deposit of ground material on the housing walls, the disks of the mill are in a preferred embodiment of my invention given a particular shape which promotes the flight of the ground particles toward the housing walls in the plane of the disks themselves,

they would be led into earlier contact with the housing. The comminuting members 21 are confined within an area of the adjacent disk faces having a diameter considerably smaller than the diameter of the disks themselves. In passing through the annular space between the outside limit of the comminuting members and the peripheral limit of the disks, the turbulent motion of the ground particles is dissipated so that they leave the space between the disks without substantial axial component of velocity. To this end particularly the disks terminate preferably in sharp edges as indicated at 36.

The machine of Fig. l is shown in side elevation in Fig. 2. The door 15 is there shown as hinged in the housing at47 and provided with suitable closing means 49. The motor 19 which drives the shaft 7 via belt 8 and pulley 6-is supported on a hinged bracket 55 which swings with the door 15. Adjustment of the tension of belt 8 is made at a threaded spindle 56.

In an alternative embodiment of my invention illus trated in Fig. 3 a different construction is adopted in order to minimize the adhesion of the ground product with the housing walls. In this embodnnent one of the grinding disks 61, preferably the more rapidly rotating of the two, is so journaled that its inside face 63 lies substantially flush with the inside surface 65 of the housing generally indicated at 67. To this end the housing is provided with an axially extending recess portion 6h accommodating the thickness of the disk 61 together with its blower vanes'71. The other grinding disk 73 may be of essentially the same construction as described for,,the disk 3 of the embodiment'shown in Fig. 1. On leaving the grinding zone between'the adjacent faces of'the disks 61 and 73 the ground material moves radially or tangentially outward along the surface 65 until it meets the surface 68 having a large radius of curvature. By the time the ground material reaches the curved surface 68, it has lost most of its kinetic energy and is there slowly deflected towards the center plane of the mill and the opposite wall 7% of the housing.

In a further embodiment of my inventionillustrated in Figs. 4 and 5, a plurality of input conduits 75 connect with nozzles 77 passing through one end wall 79 of the housing 31 radially 'outsidethc diameter of the grinding disks 83. Air or a similar gaseous medium adapted to act on the product in a desired manner, such as e. g. drying or cooling the product is sent from a blower $5 through the conduits 75 to the nozzles 77. The nozzles '77 are oriented with respect to the housing to direct the streams passing therethrough generally tangentially of the grinding disks but with'a component of velocity parallel to the axis of rotation of the disks. By the action of the streams of gas emerging from the nozzles 77, the particles of ground material emerging from between the grinding disks are deflected in their flight and impingement there of on the walls of the housing in the plane of. the grinding disks is prevented, so that reduced radial clearances be tween the disks and the housing suffice.

While I have illustrated and described what I regard to be the preferred embodiments of my invention, nevertheless it will be understood that such are merely exemplary and that numerous modifications and rearrangements may be made therein without departing from the essence of the invention. We claim: 1 l. A centrifugalgrinding mill comprising two disks supported for independent coaxial rotations at unequal speeds, a plurality of comminuting members aflixed to the adjacent faces of the disks, a housing substantially enclosing the disks with large radial clearance therefrom,

a flat wall in the housing perpendicular to the axis of rotation'of the disks, a recess in said wall, one of said disks being positioned within said recess with its face adjacent the other disk substantially coplanar with said wall, said wall being joined to an opposite wall of the housing by a surface of large radius of curvature, and material evacuating means disposed in said housing radially outside the periphery of said disks.

2. A centrifugal grinding mill comprising two disks supported for independent coaxial rotations at unequal angular speeds, a plurality of comminuting members affixed to the adjacent faces of the disks, means to rotate said disks at unequal angular speeds of which the higher speed gives to one of said disks a peripheral speed of the order of one hundred meters per second, a housing enclosing said disks, the minimum radial clearance in centimeters between the periphery of the disk driven at said higher speed and the housing being 15 plus 3 times the square root of the diameter of the disk so driven, a flat Wall in the housing perpendicular to the axis of rotation of the disks, a recess in said wall, one of said disks being positioned within said recess with its face adjacent the other disk substantially coplanar with said wall, said wall being joined to an opposite wall of the housing by a surface of large radius of curvature, and material evacuat- References Cited in the file of this patent UNITED STATES PATENTS 312,215 Nagel et al. Feb. 10, 1885 1,734,661 Wood Nov. 5, 1929 1,752,902 Farner Apr. 1, 1930 1,855,171 Holbeck Apr. 19, 1932 1,885,251 Gaiser Nov. 1, 1932 2,033,757 Crites Mar. 10, 1936 2,068,071 Quehl Jan. 19, 1937 2,199,015 Toensfeldt Apr. 30, 1940 2,561,043 Ayers July 17, 1951 FOREIGN PATENTS 12,713 Great Britain June 4, 1904 14,003 Great Britain June 15, 1909 292,830 Germany June 30, 1916

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