US2925226A - Roller mills - Google Patents

Description

Feb. 16, 1960 Filed Dec. 5, 1956 J. PRATIQUE ROLLER MILLS 4 Sheets-Sheet l INVENTOR.

Jean Prafique BY J. PRATIQUE ROLLER MILLS Feb. 16, 1960 4 Sheets-Sheet 2 Filed Dec. 5, 1956 INVENTOR. Jean Pracique J. PRATIQUE 2,925,226

ROLLER MILLS Feb. 16, 1960 4 Sheets-Sheet 3 Filed. Dec 5, 1956 Fie.3

Feb. 16, 1960 J. PRATIQUE 2,925,226

ROLLER MILLS Filed Dec. 5, 1956 4 Sheets-Sheet 4 uvmvrm Jean Praci ue BY KM ROLLER MILLS Jean Pratique, Paris, France Application December 5, 1956, Serial No. 626,423

Claims priority, application France December 21, 1955 .6 Claims. (Cl. 241-225) The present invention is directed to improvements in milling machines of the roller type. It is a particular object of this invention to improve the grinding operation and to increase the output of such machines. While the invention will be described with reference to its application to flour mills, it will expressly be understood that the improved machine of the present invention can be advantageously applied to the grinding of other products of whatever origin, mineral or vegetable as sugar, coal, salt, etc.

In order that the nature of the improvements over the prior art machines, brought about by the present invention, may be better understood, there is set out below a brief description of a conventional roller mill.

A conventional roller mill consists essentially of two rolls forming a single passage, or of three rolls forming two passages. Special machines may include a larger number of rolls and passages. The rolls or cylinders revolve at difierent speeds in order to exert upon the stock a cutting action simultaneously with application of pressure.

The stock is fed to the rolls either by one or two feed rolls, or by a surface having a more or less rapid reciprocating movement in the longitudinal or transverse di- .accelerator, for feeding stock to the working, i.e. grinding, zone of a roller mill, so that the particles of stock have their full velocity and are packed closely together to eliminate voids or blank spaces between the particles in the grinding zone. In the case of the prior feeding schemes, the stock falls in a thin layer on one of the grinding rolls which carries the layer into the grinding rzone. Applicant has carefully observed the said layer during its fall and has established that the proportion of voids orblank spaces between the particles of the stock is very high relative to the spaces occupied by the particles themselves and, further, that when the stock is introduced between the rolls, the speed of the particles .yincreases suddenly, but simultaneously, there is again created and maintained a high ratio of'blank spaces to .spaces occupied by particles and, as a. consequence thereof, the Working space is utilized inefiiciently.

The present invention involves the addition to a machine of the type described above, of special feed or guide devices, for the purpose of enhancing the efficiency of the grinding operation and increasing the output of the machines; these additional devices may beemployed in combination with each other or singly.

ates Patent Patented Feb. 16, 1960 In the accompanyng drawings, there are illustrated non-restrictive examples of devices of the present invention, it being clearly understood that the details of the constructional embodiments of the devices can be varied without departing from the essential principles of the invention. In the drawings,

Figure 1 shows a vertical cross-section of a two-roller mill provided with a compacto-accelerator device A, essentially characterized by a concave surface of a special shape;

Figure 2 shows a vertical cross-section of a three-roll mill provided with the above mentioned. device A;

Figure 3 is a detail showing of device A;

Figure 4 illustrates further the construction of the device A.

Referring to the drawings: The compacto-accelerator device A is essentially constituted of a surface element or plate having a concave (incurved) lower section a the curvature of which is related to that of the grinding roll R located adjacent thereto, in a manner which will be described further on; in the limiting adjusted position, this concave section will approximately fit on the surface of the roll. The contour (outline) of the upper section of this element sweeps away from the surface of the "roll so as to form an inlet opening (angle) a for the stock, which is submitted to a preliminary grinding in the zone formed between the lower concave portion of the plate a and the adjacent portion of the roll R by the action of the roll and the reaction of the plate; simultaneously, the stock is subjected to an increase in speed as well as to a compacting action over the entire lower surface a of the plate.

While for the purposes of description, the plate A has been shown as facing with its working surface the roll R which rotates at the greater speed, it may be desirablein the case of certain products-to position the plate so that its working surface faces the grinding roll R which turns at the lower speed. Further, a plurality of such compacto-accelerator plates A of the type described above can be used in the case of mills having several pairs of rolls; .this is exemplified in Fig. 2 of the drawings, which and (1 two at each end of the feed plate and operable from the outside of the machine, the two upper eccentrics making possible an inlet opening which is different from the lower opening regulated by the two lower eccentrics a The operation of the device A is as follows: 7 A sheet of the stock to be milledfed from the supply hopper-arrives at the inlet a and contacts with the high speed roll R which drives the product sheet by friction. This sheet, which is thick in the inlet region designated al on the drawing, comprises sever layers, that is, several superposed streams of particles. The layer in contact with the roll R is subjected to progressive acceleration up to the instant when its speed attains the speed of the cylinder. At the same time, the layer in contact with the roll R entrains the adjacent layer by rapid interchange of particles from one layer to another and by projection of the concave surface, (which interchange facilitates the subsequent reduction or grinding action by the rolls. The motion of the Its optimum mass as a whole increases, as well as its mean speed. As

a result, the thickness of the layer diminishes, the various layers interpenetrate to form a single compact layer at the inletof the working zone, a layer which is characterized by an absence of voidspaces and which can" be milled by the rolls R R in'a highly etlicient manner. If the feeding operation is carried out'by using a projector and feed plate, i.e. by the arrangement proposed in applicants French Patent No. 1,058,697, granted 'November 4, 1953, then, the inlet of the deflector feed plate D (Fig. 1) must terminate at the inlet a between the plate A and the roll R the feed roll r used as projector, feeds the stock underneath the deflector D,'which guides their trajectory (path) up to the inlet a Theoretical considerations as well as applicants investigations have established that for optimum results the shape, dimensions and position of the plate A should preferably be selected in the manner outlined below:

of the base circle varies according to the stock to be milled. For the purpose of the present invention, the involute of the circle can be traced by the extremity of -its radius vector when the polar (vectorial) angle increases either in a clockwise or counter-clockwise direction.

The diameter of the base circle d; (Fig. 4) varies in accordance with the products to be milled, with the diameter D of the milling roll cooperating with the surface a; and with the direction of movement (increase) of the polar angle. Thus, where a faces R and the polar angle increases in a clockwise direction,

d varies from to 3 On the other hand, when the polar angle increases in a counter-clockwise direction,

d varies frontO to In the case where the surface a, of the plate A faces the roll R a D 7 d varies from 0 to when the-polar angle increases counterclockwise-D, here being the diameter of the roll R while d ranges from 0 to when the polar angle increases clockwise.

Further, the radius of curvature of the directrix a varies from 0.2 to 0.8 D The length of directrix curve of the surface a ranges betwen the limits 0.1 D and 0.7 D,. The distance of the surface a from the milling roll facing it is everywhere less than about 1 inch (25.4 mm.) and, greater than the particles of the stock to be milled. v

Assuming that the surface a; faces the roll R -as shown in Figs. 3 and 4-then, the distance of the lower end of the surface a to the surface of the roll R should be less than about 1 inch, the distance varying with the products-being milled, in order to obtain a favorable effect from the air entrained by the roll R While the data given above indicates the preferred theoretical shape to be given to the surface a nevertheless, the present invention is not limited to the use of such precise shapes based on involutes- From the standpoint of manufacturing, it may be desirable to use shapes which approximate those derived from involutes. For

. example, there can be used a cylindrical surface of revo= sse s s 4 lution which can be readily produced by simple means. Such a cylindrical surface can have a radiuswhich is approximately the mean of the radii of curvature of the theoretical involute shape. Actual tests have demonstrated that such a cylindrical surface of revolution is satisfactory for practical applications The automatic supply arrangement V, schematically illustrated in Fig. l, is analogous to other known feeding systems, but its dimensions and the location of the flap v upon which the stock exerts pressure, are novel.

The pressure of the stock exerted on the flap v causes the latter to pivot about its axis v and displaces arm v the latter pushing the arm v of the valve v which, in turn, pivots about the axis v The large surface of the flap v renders the latter highly sensitive to the action of the stock, and because the normal distance of its extremity to the interior surface of the valve v is selected to be substantially equal to the distance of that extremity from the distributing roll r;, the height of the mass of the stock near v will remain constant; as a result thereof, the gravity effect of the column of stock of variable height in the hopper will be counteracted. More particularly, the products streaming outbetween roll r and the extremity of the flap v form a natural slope (talus) between v and v whereby the angle made by the slope with the horizontal remains constant. As a result, the height of the column of stock in the hopper near v does not affect the flow between roll r and valve v The automatic feeding device S, T, illustrated in Fig. 2, consists of:

(1) A hopper T the wall of which pivots about an eccentric shaft 1 and which is balanced by a counterweight t or by springs. This hopper, the inlet of which at its upper part is substantially square in shape, becomes narrower transversely from top to bottom, while it widens out in the longitudinal direction of the rolls, so

as to distribute the stock all along the feeding area. The

sides of the hopper which extend in that direction are' inclined at an angle substantially equal to the natural angle of repose (slope) of the stock;

(2) A vibratory plate (surface) S driven, for example,

' by an eccentric and connecting rod. The upper part s of this plate is concave, but its curvature is not concentric with the trajectory of the lower section t of the feed hopper. The contour (curve) of the vibrating platefrom the top thereof to its lower end-deviates away gradually from the trajectory of the lower part t, of the feed hopper and the vibrating plate terminates in an inclined plane s This arrangement, by leaving more and more space between the plate and hopper when the latter pivots as a result of the increased weight of the stock, makes it possible to increase very gradually the thickness of the feed layer'and, hence, the flow of the stock, ac-

cording to the supply.

7 This plate S can terminate first in 'a landing (platform).

.9 on which the feed stream is homogenized and, thereafter, again in an inclined plane s which either feeds a projector roll, or feeds directly into the inlet a formed by the plate A and the roll.

The two feeding arrangements V and S, T'by insuring great uniformity of feed, or a very gradual variation thereof, contribute in a certain measure towards assuring maximum reduction efiiciency of a machine employing the above-described device A.

It should be noted that the eccentric a can be proly of the roll. R adjusting thereby the relative spacing of the lower edge of surface a from R and from'the grinding zone.

I claim:

1. In a roller mill for granular material having at least first and second cooperating grinding rolls providing betweep ;them a-grinding zone through which particles of a When so provided,

desired granular material are to be passed, a supply hopper for said material and movable feeding means for supplying a moving sheet of particles of the granular material to the rolls, the improvement which comprises, in combination with saidmill, of a guide member cooperating with one of said rolls, said guide member having a surface extending axially substantially the full length of the rolls with a first edge of the surface close to the grinding zone; the said surface having a first portion adjacent said first edge which has a curvature closely following the curvature of the roll with which the surface cooperates, and a second portion extending beyond said first portion to the opposite or second edge of the surface, said second edge being curved away from the surface of the roll with which it cooperates to provide an inlet into which the particles are supplied by said feeding means, said surface forming with the roll with which it cooperates a substantially wedge-shaped space gradually decreasing in width in the direction of said first edge and the grinding zone, whereby said first portion of the surface provides a compacting-accelerating zone from which a continuous compact layer of particles is fed to the grinding zone at substantially the peripheral velocity of the roll with which the surface cooperates.

2. In a roller mill having at least first and second cooperating grinding rolls providing between them a grinding zone through which particles of a desired material are to be passed, and feeding means for supplying the material to the rolls, the improvement which comprises a guide member cooperating with one of said rolls, said guide member having a surface extending axially substantially the full length of the rolls with a first edge of the surface close to the grinding zone, the said surface having a first portion adjacent said edge which has a curvature closely following the curvature of the roll with which the surface cooperates, and a second portion extending beyond said first portion to the opposite or second edge of the surface, said second portion of the surface being curved away from the surface of the roll with which it cooperates, to provide an inlet into which the particles are supplied by said feeding means, and said first portion of the surface providing a compactingaccelerating zone from which a continuous compact layer of particles is fed to the grinding zone at substantially the peripheral velocity of the roll with which the surface cooperates, and a plurality of independently operated adjusting means for adjusting the relative spac ing of said first edge of the guide member from the roll with which it cooperates.

3. A roller mill according to claim 1, including means for adjusting the position of the guide member surface circumferentially of the roll with which it cooperates, and thereby adjusting the relative spacing of said first edge from the other of said rolls and from the grinding zone.

4. A roller mill according to claim 1, in which the first portion of said guide member surface is a portion of a cylindrical surface, the generatrix of which is parallel to the axis of the roll with which it cooperates, and the directrix of which is an involute of a circle.

5. A roller mill according to claim 4, in which the diameter of the base circle of said involute surface is in the range of 0% to 25% of the diameter of the roll with which it cooperates.

6. A roller mill according to claim 1, in which said first portion of the guide member surface extends from said first edge and along the circumference of the roll with which it cooperates, for a length equal to at least 10% of the diameter of said last mentioned roll.

References Cited in the file of this patent UNITED STATES PATENTS

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