US2172704A

US2172704A - Mechanical mixer

Info

Publication number: US2172704A
Authority: US
Publication date: 1939-09-12
Anticipated expiration: 1956-09-12

Description

Sept. 12, 1939. 'P GENT|LL| 2,112,704

MECHANICAL MIXER Filed Dec. 1a, 1937 a i a a 6 k? I V Patented Sept. 12, 1939 PATENT OFFICE MECHANICAL MIXER Paolo Gentilli, Trieste, Italy Application 2 Claims.

This invention relates to the intimate commixing of coarsely pre-mixed pulverulent substances of different kinds; whether in a dry or in a moist condition, and consists essentially in employing,

5 for effecting such fine mixing, a device of the type of the known grinding machines or mills having two discs adapted to rotate in the same direction about axes out of alignment with each other, but using discs having no teeth, grooves, or grinding roug'hnesses, i. e. with'substantially smooth bearing faces, whereby all the particles of the thin layer of material entrained between these faces are caused to travel in paths consisting of a large number of closely consecutive loops intersecting each other at a multiplicity of points.

It is known to employ, for the purpose of mixing pulverulent materials, devices of the type of stirrers or of the grinding machines used for comminuting solids. Mechanical mixing with the aid of stirring devices or agitators can never yield more than a merely coarsely mixed product, since these devices never eiiect more than coarse displacement of material and are incapable of effecting minute displacements such as are necessary for separating the extremely small particles of pulverized material which tend to adhere to each other and to form diminutive agglomerations. Such separation, and with it an improvement in the mixing efficiency, may it is true he achieved to a certain degree, when working with agitators, by adding liquid to the pulverulent mixture handled; since this expedient diminishes the adhesion between the particles of the material, but this method of working is attended by the drawback that the finished mixture has to be separated from the liquid after undergoing the mixing operation.

When grinding and pulverizing machines, such as ball mills, pug mills, and the like, are used as mixers it may indeed be possible to obtain perfect intermixture, but to achieve this result the material to be mixed has to be left for a very long time in the machine, since the nipping surfaces on the stationary and moving parts of these machines (primarily intended for the comminuting of coarsely disintegrated materials, between which the pulverulent mixture is worked, are only relatively small, so that only a small fraction of the total quantity of mixture in the machine is actually being worked under pressure between surfaces at any one time.

In contrast to these prior proposals, I use for the purpose of mixing dry or moist pulverulent materials a machine similar to the known pulverizers having two discs pressedagainst each December 18, 1937, Serial No. 180,628 In Germany June 3, 1936 other and adapted to revolve in the same direction about axes of rotation out of alignment with each other, between which discs the coarsely premixed pulverulent material is introduced. But whereas in the known grinding machines or pul- 5 verizers of this type the discs are provided with grooves, teeth, or at least, as in the case of millstones, a very rough surface, in order that a grinding and comminuting action may be exerted, since it is only in this case that the individual particles of the material are held fast by the one disc'and subjected, by the other disc moved relatively to the first, at small portions of their surface, to the very high pressure requisite for disintegration in my mixer the use of discs having bearing surfaces like those in the known grinding and pulverizing machines (1. e., with teeth, furrows, and the like, would be unsuitable, and I therefore provide the discs with substantially smooth working faces.

With the use of a machine of this description a particularly efiicient mixing action is achieved by virtue of the fact that the pulverulent material is subjected to the mixing action not in bulk as in the case-of the known types of mixers but in a 25 very thin superficial layer entrained between the relatively moving discs. Owing to the friction set up between the thin layer of material and the discs on both sides thereof all the particles of the material are constantly worked during the whole of their passage through the machine, and it is impossible for portions of the material to partake but slightly in the mixing operation as in the case of the known mixers.

In the mechanical mixer according to the pres- 35 ent invention all portions of the thin layer of material entrained between the two discs move simultaneously in paths consisting of a multiplicity of closely consecutive and repeatedly in-. tersecting loops (loop-shaped epicycloids). The loops of this path are very closely crowded up together when the'difference in speed of rotation as between the two discs is slight, and this condition may be brought about for example by mounting one of the two discs so that it will rotate idly and causing it to be driven by the other disc (which is directly driven), through the intermediary of the layer of pulverulent material entrained between the two discs. In this case the number of intersections between the loops per unit of area is very great, and consequently highly thorough intermixing of the different constituents of the pulverulent material is achieved.

These kinetic operations are of no significance in connection with devices for grinding and com- 55 minuting, that is to say devices for working a single substance as distinct from a mixture of different substanca, since the efficiency of such devices depends solely upon the duration of the treatment, that is to say upon the length of the distance travelled between the working surfaces, and not upon the arrangement and displacement of the particles of the one material relatively to each other. On the other hand, in a machine for eiiecting the fine intermixing of diiferent materials such rearrangement and displacement of the individual particles is of paramount importance, and the more thoroughly and constantly such displacement is eii'ected the better and more efllcient the intermixing action will be.

Owing to the described action of the mixer according to the present invention the further result is achieved that perfect intermixture of the diiferent constituents of the material handled is obtained in a comparatively short time, the more so since, in view of the light weight of the pulverulent particles and of the adhesion and friction between these particles and the working faces of the discs, these discs must be revolved at high speeds of rotation such as could not be employed in connection with the grinding or pulverizing operation in the known types of mills, so as to impart to the particles entrained between the discs the necessary amount of centrifugal force to convey them to the outer edge of the discs.

In order to prevent the particles of the mixture fiung out with great velocity from between the discs at the periphery from becoming lodged and accumulating against the walls of the housing this latter is made, in accordance with the invention, in the form of a funnel with steeply pitched sides.

A form of construction of fine mixer embodying the invention is shown, by way of example, in the accompanying drawing, in which:

Fig. l is a vertical section of the mixer.

Fig. 2 shows diagrammatically the path described by a particle of the mixture under treatment entrained between the working faces of the disaligned discs according to the'invention.

Referring to Fig. 1 of the drawing, the disc I, which is driven by the shaft 3, drives the annular disc 2, which is mounted so that its axis of rotation is out of alignment with the axis of the shaft 3 by the amount 1', in the same direction as itself by reason of the friction set up between these two discs through the intermediary of the matter entrained therebetween. The pressure of the disc i against the disc 2 may be regulated in any convenient and known manner, for example by displacement of the weight 4 on the lever arm 5 adapted, by means of .the pinion 6, to shift the sleeve 9 which is provided with a rack I adapted to mesh with the pinion 6, and relatively to which the disc boss 8 is free to rotate. The disc 2 is supported, e. g. by means of a ball bearing it with spherical running surface, at the lower end of the hopper ill so that its axis of rotation can swivel to a slight extent about the center of curvature of the ball hearing it (thereby permitting the disc 2 to oscillate so that under all conditions the pressure is uniformly distributed over the entire area of the disc) axis and the disc 2 can bear with its entire surface against the corresponding surface of the disc 2. For the purpose of bringing the axes of rotation of the two discs i and 2 out of alignment with each other to a desired extent the hopper l0 may for instance be so mounted on the upper edge of the discharge funnel I2 that it can be displaced relatively to the latter by means of the adjusting screws I I.

In order to prevent the finely pulverized dry or moist mixed material flung out with great velocity from between the discs from adhering to and accumulating on the walls of the housing within which the discs are confined there is provided immediately adjoining these walls a discharge funnel with steeply pitched sides.

Fig. 2 shows diagrammatically the path described, on rotation of the discs, by each individual particle of the mixture entrained between the working faces. This path consists of a number of closely crowded loops overlapping each other and forming a spiral of which the individual turns may also be made to overlap by suitably determining the amount of eccentricity or disalignment between the axes of rotation of the two discs (in Fig. 2 the turns of the, spiral are indicated as being further apart than they would be in practice, in order to simplify the drawing and to avoid confusion) I claim: a

1. A mechanical mixer for the fine intermixing of coarsely pre-mixed pulverant material comprising two superposed discs, means to mount one of said discs to rotate on a fixedly located axis, means to mount the other of said discs to rotate on another axis parallel to the first axis but eccentric thereto, means for adjusting the position of said other axis to a greater or lesser distance from the fixedly located axis, variable means to press one disc toward the other, the upper disc having an aperture, means to deliver material through said aperture onto the lower disc, and means to collect and discharge material thrown off from between said discs.

2. A mechanical mixer for the fine intermixing of coarsely pre-mixed pulverant material comprising two superposed discs, means to mount one of said discs to rotate on a fixedly located axis, means to mount the other of said discs to rotate on another axis parallel to the first axis but eccentric thereto, means for adjusting the position of said other axis to a greater or lesser distance from the fixedly located axis, variable means to press one disc toward the other, the upper disc having an aperture, means to deliver material through said aperture onto the lower disc, and means to collect and discharge material thrown oil from between said discs, the mounting means of one of said discs having means to permit oscillation of the same.

PAOLO GENTILLI.