US2128226A - Grinding machine - Google Patents

Description

F. c. 'ATWOOD 2,128,226

GRINDING MACHINE Filed. Feb. 1, 1932 2 Sheets-Sheer. 1

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, Aug. 30, 1938. F. c. ATWOOD GRINDING MACHINE Filed Feb. 1, 1952 2 Sheets-Sheer. 2

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Patented Aug. 30, 1938' PATENT OFFICE GRINDING MACHINE Francis Clarke Atwood, Newton, Masm, asaignor, by mesne assignments, to Atlantic Research Associates, Inc... a corporation of Delaware Application February 1, 1932, Serial No. 590,017

2 Claims.

This invention relates ,to a grinding machine and more particularly to a wet grinding machine.

The most common grinding machines which have been heretofore used for grinding paint and other liquid or paste products have comprised horizontal stone mills and mills involving a multiplicity of rolls. The operation of such machines is relatively slow and the capacity limited so that a large number of units are required to take care of the output in a paint concern oi any substantial size. Attempts have been made to increase the capacity of the stone type of mill by the use of pressure in forcing the material through the mill, but these attempts have not proven successful for the reason that they detract from the efiiciency of the grinding operation. For grinding lacquers and other paints with volatile thinners, closed mills of the ball and pebble mill type have been employed, and for some purposes so-called colloid or high-speed mills have been used. The latter type of mill requires tremendous power for its operation and is suitable only for thin slurries. Colloid mills do no real grinding but only help to disperse pigment whose ultimate particle size is already suillciently small.

As distinguished from a real process of grinding, it has been recognized that it is possible to break down the globules of two liquids not otherwise miscible (to which there may have been added a minute amount of some emulsifying agent) by forcing the same through a very fine orifice or through some path which is extremely small. The globules of the liquids are broken down by such treatment into such minute particles that they lose their tendency or ability to thereafter coalesce and the process is called homogenization. In practice the most successful process which has heretofore been used for homogenizing liquids involves the application of high pressure to a valve, holding it against a valve seat at this high pressure and then forcing the liquids to be homogenized in between the valve and its seat. The homogeninn'g process continues only so long as the valve is held to its seat, and when any solid particles, or particles which are not readily deformed and broken up, are forced between the valve and its seat, then the extremely small passage becomes clogged very rapidly or the valve is forced from its seat enlarging the passage to such an extent as to terminate the homogenizing process.

The present invention contemplates a process of grinding comprising. a combination of a grinding and a homogenizing action, and in the preierred form of apparatus the slurry to be ground is forced under high pressure through an extremely small passage formed between the .cooperative faces of a pair of grinding elements which are themselves pressed together with relatively high pressure, and provision is made for relatively rotating the elements toperform a cutting or grinding action (so that the faces are fundamentally grinding faces rather than a valve and a valve seat) upon the material being 0 forced through the extremely small passage, and in this manner the homogenizing action, together with the grinding performed by the grinding elements, cooperate to produce a very finely ground product and to permit a large capacity to be obtained with a relatively small machine and at relatively slow speeds. I

Accordingly one object of the invention is to provide anovel and highly eflicient grinding machine which may be used with advantage .in 20 grinding paints, enamels, lacquers and allied materials, in grinding chocolate, and in fact for the 'efllcient grinding and dispersion of any solid ma, terial in a liquid, "and also to provide such a machine which is simple in construction, durable, requiring a' minimum power for its operation, and with which a much greater capacity of ground product may be obtained than with other comparable prior grinding machines 0! which I amaware; 1 T

A further object of the invention is to provide a novel and superior method of wet grinding involving a, combination of a. grinding and homogenizing action and by which a superior ground product may be produced at a maximum rate and with minimum power consumption.

With these general objects in view, the invention consists in the grinding machine particularly defined in the claims at the endof this specification. A

In the drawings illustrating the preferred embodiment of the invention, Fig. 1 is a side elevation of the improved grinding machine with por-' tions in section; Fig. 2 is an end elevation'of the grinding machine shown in Fig. 1; Figs. 3 and 4 45 are plan views of different forms of grinding elements which may be used with advantage in the present grinding machine; and Figs. 5 and 6 are sectional details illustrating the rifts in the grinding elements; Fig. '7 is a side elevation with portions in section illustrating a duplex grinding machine embodying the present invention; Fig. 8

I is an end elevation ohthe same; Fig. 9 is a detail in elevation of the drive for the grinding machineshown in Fig. -'l; Figs. 10 and 11 are details in plan of grinding elements showing different forms of rifts; and Figs. 12 and 13 are details in section illustrating the formation of the rifts in the grinding elements.

Referring now to Figs. 1 and 2-, the grinding machine illustrated therein comprises a pair of grinding elements I0. I2, one of which is provided with a generally concave and conically shaped grinding surface, and the other of which is provided with a generally convex and conically shaped grinding surface. I0, l2, may and preferably will comprise heat treated and hardened tool steel elements, and the cooperative conical faces thereof are preferably surfaced so as to permit them to fit in fluidtight relation when subjected to pressure, in a manner analogous to a valve and valve seat. As herein shown the grinding elements I0, I2 are mounted upon a hollow shaft I5 and upon a solid shaft I6, respectively, supported in bearings II, I8 in uprights 20 bolted to the base 22 of the machine frame. The shafts I5, I6 are stationary and as herein shown the grinding element I0 is keyed, pinned, or otherwise secured to the shaft I5 to form a part thereof. The other grinding element I2 is rotatably supported upon a bearing 23 upon the shaft I6 and an end bearing 26 is provided between the end of the grinding memthreaded and provided with the compression nut 21 arranged toengage the end bearing 26 and to transmit pressure therethrough to cause the movable grinding member to be moved and pressed into intimate contact with the'stationary grinding member. A look nut 30 is also provided in order to hold the parts in a predetermined position.

Oil may be supplied to the bearing 23 between I the movable grinding member I2 and the shaft 24 through an oil duct 32, as illustrated.

In order that the grinding machine may operate in accordance with the present invention to grind and disperse the material by a combination of a homogenizing and grinding action, relatively heavy pressure is set up by means of the I nut 21 between the cooperating and contacting faces of the grinding elements, and provision is made for rotating the movable grinding element in order to effect a grinding action between the faces of the grinding elements herein shown by means of a large driving gear 35 to which the movable grinding element I2 is bolted to rotate therewith and through'a driving pinion 36 cooperating with the gear 35 and mounted upon the end of a drive shaft 38 rotated from a pulley 39 or other convenient source of power;

Provision is made for introducing'the slurry to be ground at the center of the grinding elements, under pressure so that a homogenizing action may be obtained by the forcing of theslur- .ry through the minute opening or passage formed between the cooperating and tightlypressed together faces ofthe grinding elements I0, I2. As herein shown the slurry is withdrawn from a supply tank 46 by the force pump 48 and discharged through a discharge pipe 49 and fitting 50 into the end of the hollow' shaft I5. as shown.

In order to increase the efficiency of the grinding action between the two cooperating grinding elements, one of the members and preferably The grinding elements the stationary member may and preferably will be provided with a series of rifts 5|. The rifts may be formed as illustrated in Figs. 3, 4. 5 and 6, comprising an annular ring from which a series of radial and spirally formed rifts extend for conducting the fluid from the central inlet outwardly toward the periphery of the grinding element. The rifts may be of angular section, as illustrated in Fig. 5, or formed by angular and vertical cuts. The walls of the rifts exert acutting or shearing action upon the particles being ground and serve to assist in increasing the efficiency of the grinding action between the cooperative grinding faces.

, In the embodiment of the invention illustrated in Fig. 7 a duplex form of machine is illustrated wherein provision is made for rotating both of the grinding elements I0, I2 in opposite directions to thereby increase the relative movement between the grinding surfaces at any given speed of operation, and as herein shown the general construction and mode of operation of the grinding elements I0, 12 comprises that illustrated in connection with the movable section of the previously described grinder illustrated in Figs. 1 and 2. The second grinding element I2 instead of being secured to a hollow shaft I4 is arranged to be rotated thereon, on a suitable bearing 10 and an end bearing 18 is provided between a collar interposed between the end bearing 18 and thestati'onary bearing 82 in which the shaft is supported, so that the requisite pressure between the contacting surfaces of the grinding elements may be obtained by screwing up the nuts 84, 21 on the shaft 15.

The driving mechanism for effecting relative rotation of the grinding elements includes a driven pulley 8B driven from any convenient source of power, upon a shaft 81 journalled in suitable bearings 88 in the machine frame. Upon one end of the shaft 81 one of two cooperating ring gears 90, 9| are mounted and the other ring gear is mounted upon a corresponding shaft 92 journalled in suitable bearings, not shown. Pinions IIO, III upon the ends of the shafts cooperate with driving gears 96, 91 bolted to and forming a part of the rotatable grinding members, I0, I2 and with this construction it will be observed that both grinding members are geared together and driven in opposite directions from a single pulley.

In order to. rotate the pump I00 for forcing the slurry to be ground through the hollow shaft I4, a pinion I02 is geared through the gear train I04 to a large gear I06 on the counter shaft I00 connected by a' clutch to the pump shaft, as shown in Fig. 7.

"In order to prevent the slurry from being forced out along the shafts upon.which'the rotatable grinding elements are mounted, in either of the illustrated forms of grinding machines, fluid pressure either by grease, oil, air, or the like, may be utilized to counteract the normal working pressure upon the slurry. As illustrated in Figs. 1 and '7, such fluid pressure may be introduced from any suitable source through a pipe line to a groove 92 in the bearing between the rotatable grinding member and its shaft, and}! illustrated in Fig.7 suitable counteracting fluid pressure may be conveniently supplied to a groove 90 in the bearing between the grinding element I2 and itsshaft by a fluid conduit 95 connected to the supply line through which the slurry is forced under pressure into the fiuid'inlet between the grinding elements. Asa result of this arrangement it is possible to operate the machine, utilizing a substantial pressure for forcing the fluid through the minute passageway between the grinding elements without any material leakage of the slurry between the rotating grinding elements and their bearings or shafts.

In order to protect the machine from operation without the presence of slurry between the contacting faces of the grinding elements, the machine is provided with a pressurestat indicated generally at 98 and which may comprise any of the known forms of pressurestats now on the market, operatively connected into the pipe line through which the slurry is 'being forced under pressure into ,the machine and the pressurestat 98 is wired to the driving motor so as to control the operation of the latter and to render it impossible to start the rotation of the grinding element or elements until a pressure has been built up in the inlet line to a point sufllclent to insure the pasasge of fluid slurry between the tightly pressed together contacting faces of the grinding elements. In practice I prefer to set the pressurestats to a pressure of at least 10 pounds per square inch and preferably to a greater pressure so that the operation of the machine ina dry condition will be prevented.

In the operation of the machine, the contacting faces of the grinding elements fit together in fluid-tight relation, being machined or surfaced to form in effect a valve and a seat. The pressure exerted by the nuts 21, 84, upon these contacting faces will be at least 10 pounds per square inch so that the fluid pressure required to force the slurry through the minute passageway between the contacting faces of the grinding elements will be a pressure of at least 10 pounds per square inch and preferably a substantial differential over the pressure exerted on the grinding elements. In the operation of the machine, the slight elasticity in the parts enables the grinding surfaces to yield slightly under the differential pressure and to provide a minute passageway through which the slurry may be forced. The relative rotatlon between the faces of the grinding elements producespa grinding action, and the forcing of the slurry under pressure through a minute passageway between the contacting faces of the grinding elements imparts a homogenizing action, and the combination of both actions results in the production of an extremely finely ground product. The amount of yield of the contacting faces of the grinding elements under the fluid pressure is estimated to be in the neighborhood of .0001 of an inch.

An important advantage of the present invention resides in the ability to produce a machine which is capable of operating at. relatively slow speed, as for example 50 to 75 revolutions per minute to produce a very finely ground product and which at the same time possesses a relatively large capacity as compared with prior art machines now being used in commercial practice. Of course, the capacity is increased by increasing the speed of rotation and the degree of fineness to which the product may be ground is in certain respects controlled by the amount of pressure established between the contacting faces of the grinding elements so that at higher speeds a less differential pressure is required between the fluid pressure on the slurry and the pressure on the grinding elements. The present machine may be manufactured at a minimum expense and is simple and durable. The grinding elements themselves may be easily replaced when worn and the machine is adaptedto eillciently grind a wide variety of slurrles at minimum operating expense,

'Thegrinding elements may of course be made of performing the grinding operation. It will be observed that)when the material to be ground is forced under pressure through the minute passage between the grinding surfaces, the frictional resistance to the flow of the material between the grinding surfaces is relatively great and operates to exert a shearing action on the material being forced through the minute passage. In addition to this grinding effect there is a shearing action due to the differential speed and movement of the contacting grinding elements which is exerted substantially at right angles to the above mentioned shearing action. The combination of these two forces probably imparts an unusual motion to the material being ground so that all agglomerate particles are readily dispersed and any sizable particles which need real grinding or fracture are either broken due to this action or, if too large or too hard to be so reduced, they are ultimately cut between the shearing edges of the riffs previously described.

It will also be observed that, in accordance with the present invention, the contacting faces of the grinding elements are pressed together so as to form a passage sufficiently minute as to set up relatively great frictional resistance to the flow of material between the faces and sufllcient pressure is utilized upon the slurry to be ground I claimed is:

1. In a grinding machine, in combination, a pair of grinding members having cooperating faces capable of maintaining a fluid-tight joint when pressed together, means for relatively moving the grinding members, means exerting pressure upon the grinding members normally tending to press said faces tightly together,

means for pressurally forcing a slurry between the facesof the grinding members while said faces are pressed together, and means responsive to the pressure upon the slurry controlling the means for moving the grinding members to prevent their operation until a predetermined pressure sufficient to separate said faces and provide a grinding gap has been established between said faces, said pressure responsive means being operative to cause operation of the means for moving the grinding members when said predetermined pressure is attained.

2. In a grinding machine, in combination, a pair of rotary grinding members having cooperative faces fitting in fluid-tight relation and forming in effect a valve, means normally tending to press the faces of said grinding members together, means for pressurally forcing a slurry between the faces of said grinding members while said faces are pressed together, means for relatively rotating the grinding members and means responsive to the pressure upon the slurry controlling the rotation of the grinding members to prevent rotation thereof until a predetermined pressure suflicient to separate said faces and provide a grinding gap has been established between said faces, said pressure responsive means being operative to cause operation of the means for rotating the grinding members when said predetermined pressure is attained.

FRANCIS CLARKE ATWOOD.

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