US1987944A - Colloid mill and method of operating the same - Google Patents

Description

Jan. 15, 1935. H, R RAFTQN coLLoID MILLV AND METHOD 0F OPERATING THE SAME n .Il

Filed June 7, 195o #moLoQQArra/y Patented 15, 1935 UNITED STATES PATENT OFFICE Harold Robert Rafton, Andover, Mass., assigner to Raffold Process Corporation, a corporation of Massachusetts Application June 7, 1930, Serial No. 459,816

9 claims.

This invention relates vto an improved colloid mill and method of operating the same.

Colloid mills, which are machines for reducing materials to a very fine state of subdivision, are of several types, but the present invention concerns the type of mill wherein a material in liquid suspension is passed through a gap of definite and controllable size, formed by the cooperating surfaces of two substantially rigid or non-exible elements, at least one of which is rotatable at high speeds. The present invention also is applicable to colloid mills wherein bothof the elements are movable, such movement usually being imparted by rotat-ing the elements in opposite directions.

The gap existing between the cooperating surfaces of the elements usually is controllable as to size by a micrometer screw adjustment. The two cooperating surfaces which define the gap through whichnthe material in liquid suspension passes. may be of the smoot-h type. vor either or both surfaces may have depressions or projections Aof various designs thereon, provided such depressions or projections are not of such a nature as to interlock and prevent rotation if the surfaces be brought together..

The cooperating .surfaces may be of any desired shape. For example. these .surfaces may be of a fiat disc or annular shape. or they may be more or less conical or frustro-conical. orsections of a sphere one fitting within the other so that by movement such as coaxial movement) of one within the other the surfaces may be brought more closely together.

Mills of the type referred to with substantially smooth cooperating surfaces are supposed to subdivide materials by a shearing action which takes place within the liquid lm between the two cooperating surfaces. and not by any grinding action. In cases where the cooperating surfaces are not smooth. the mills are supposed to have. in addition to the lm shearing action, a cutting or impacting action.

When substantially immiscible liquids have been run through colloid mills of the adjustable gap substantially rigid element type above described. fine dispersions of the liquids one in the other have been obtained in some cases. but where solids in liquid suspension have been run through such mills. the results as to particle subdivision, in many cases have been disappointing. Colloid mills of this type are not suitable for reducing the particle size of extremely finely divided solids,

and even with relatively coarse particle size solids the results have been poor. This is particularly true where the material .originally contained only a relatively small proportion of oversize material, which may be considered as particles larger than .001".

An important object of the present invention is to provide a novel method of operating a colloid I mill to provide more satisfactory results as to the reduction of oversize particles.

A further object is to provide a method of operating a colloid mill by subjecting the material to the action of the cooperating surfaces while subjecting the latter to a yieldable pressure tending to move them toward each other.

A further object is to provide a. colloid mill f which is adapted to produce a more satisfactorily subdivided material when materials of relatively coarse particle size are to be treated.

A further object is to provide a colloid mill wherein the improved results referred to are obtained by subjecting the cooperating `surfaces to yieldable pressure tending to move them toward each other while the material being acted upon passes between such surfaces.

Other objects and advantages of the invention will become apparent during the course of the following description.

As stated above, the usual adiustable gap substantially rigid element type colloid mills rely for their operation on the transmission of a shearing action to the lm between the cooperating surfaces and/ or an impacting action inherent in the operation of the mills when the cooperating surfaces thereof are arranged with a xed gap therebetween. I have found that instead of relying upon the actions referred to, a grinding action may be inducedby bringing the cooperating sur- 35 faces of the rigid elements sufficiently close together, and maintaining this relationship by pressure. The degree of reduction of particle size obtainable under such conditions with material of relatively coarse particle size is greatly lmproved. and the reduction of oversize particles in materials containing a relatively small proportion thereof can be successfully carried out. However, stoppage of the mill with frequent consequent damage theretoresults if the gap between the cooperating surfaces is reduced to nearly zero by non-yielding pressure during the operation of a high speed mill.

I have found that this difficulty can be overcome if the cooperating surfaces be brought substantially together by a yieldable pressure during the operation of the mill. 'I'he gap between the surfaces by this expedient can be reduced to an almost negligible size, if desired, without interfer- 55 ing with the operation of the mill or causing damage thereto.

In the practice of my invention, I apply pressure yieldably through the agency of one or both of the substantially rigid element or elements to the cooperating surfaces thereof. Such yieldable pressure may be applied in several ways. For example, a spring may be mounted in such a manner that pressure applied thereto will bring the two substantially rigid elements yieldably together. The desired results similarly may be accomplished by the application of hydraulic pressure, by the application of a Weighted lever system, or by the application of the yieldable pressure electrically. As an example of the latter method, one or both of the cooperating elements may be magnetized in such a Way as to tend to bring the cooperating surfaces thereof together, or this result may be accomplished by using a solenoid acting on the shaft of one of the elements. Other methods will occur to one skilled in the art. In order to illustrate my invention, its application has been shown to a colloid mill in which the element bearing one of the cooperating surfaces is stationary, and may be called a stator and in which the element bearing the other cooperating surface is rotatable at high speed, and may be called a rotor. Such a mill is of the type illustrated in the patent to F. J. E. China, No. 1,523,632, which is commercially available and in more or less common use. It is to be understood, however, that the invention is equally applicable to other colloid mills of the adjustable gap substantially rigid element type described above.

As stated above, the present method contemplates the application of yieldable pressure to one or both of the cooperating surfaces to tend to move them toward each other. More specifically, the method contemplates the initial operation of the mill Without the application of such yieldable pressure, the feeding of the material to the mill, and the subsequent application of the desired yieldable pressure tending to move the cooperating surfaces toward each other to effect a combination milling action, which includes the subjection of the material to a grinding action whereby greatly improved results are obtained.

In the drawing I have shown one organization 'of apparatus elements adapted for practicing the invention. In this showing,

Figure 1 is a central vertical sectional view showing the parts in the initial operating position, and,

Figure 2 is a similar view showing the parts substantially in the fully operative position.

The illustrated embodiment of the invention includes a preferably cast main body 10 having inlet and outlet ducts 11 and 12 respectively. 'Ihe duct 11 is adapted for connection at its outer end to a suitable source of raw material supply and communicates at its inner end with a vertical duct 13 closed at its lower end by a plug 14.

The upper end of the duct or passage 13 communicates with a basin 15 from which the material is fed upwardly past the frustro-conical treating face 16. As previously stated, the embodiment of the invention illustrated is of the type which includes stationary and rotating cooperating faces, and accordingly the face 16 may be considered as forming a part of a stator 17. After passing the stator, the treated material flows over into a receiving chamber 18, the lower face of which is inclined downwardly as at 19 toward the Outlet duct 12.

The body 10 is provided at the lower end thereof with an outstanding annular ange 20 having openings 21 therethrough. These openings are for the reception of bolts for securing the device to a suitable supporting surface. The upper end of the body 10 also is provided with an outstanding annular flange 22 for a purpose to be described.

The receiving chamber 18 is closed by a preferably cast cover 23 having a peripheral flange 24 seating upon the flange 22. Bolts 25 pass through suitable openings in the anges 22 and 24 for securing the body 10 and cover 23 to each other. Access to the chamber 18 may be had through an opening 26 normally closed by a suitable plug 27.

A support indicated as a whole bythe numeral 28 is arranged over the cover 23. This support includes a bottom plate 29 seating against the top of an upstanding flange 30 formed integral with the cover 23. The support may be secured in the position illustrated by any suitable means (not shown). The plate 29 is provided with a central depending sleeve 31 fora purpose to be described.

A rotor shaft 32 extends upwardly through the plate 29 and sleeve 3l. 'Ihis shaft carries a rotor 33 at its lower end, provided with a frustro-conical face corresponding to and arranged concentric with the face 16, in close proximity thereto.

The rotor shaft is mounted to rotate in a bearing 34 which may be of a standard type including a plurality of anti-friction balls running in inner and outer races as shown. The inner race of the bearing rests upon an annular shoulder 35 formed on the shaft 32. Packing 36 is arranged within the bottom of the sleeve 3l to minimize the leakage of lubricant downwardly along the shaft, and the packing is held in position by a. retainer 37. Any lubricant leaking downwardly beyond the packing 36 is intercepted by a throw-ofi flange 38. When the shaft is rotating at a high speed, the centrifugal force developed by the flange 38 is adapted to throw any lubricant intercepted thereby outwardly to the adjacent top face of the cover 23.

'I'he support 28 includes a tapering body 39 which is open at one side as at 40. The body of the support carries a split internally threaded sleeve 41 at its upper end, and the split ends 42 of the sleeve are adapted to be drawn toward each other by a suitable clamping bolt 43. A micrometer head 44 is threaded in the sleeve 41 and is adapted to be retained in adjusted positions therein by operating the clamping bolt 43. A peripheral flange 45 is carried by the head 44 above thesleeve 41 and is adapted to be engaged by a spanner wrench or other suitable tool to permit rotation of the head 44.

The upper end of the shaft 32 extends through a bearing 46 mounted in the head 44. This bearing also may be of a standard type including a plurality of anti-friction balls running in inner and outer races. 'Ihe bearing 46 preferably is of a type adapted to operate as a thrust bearing, but if the rotor is intended to be subjected to very heavy end thrust, it is advisable that a bearing of the usual type for thrust alone be suitably employed adjacent the top of the shaft 32, preferably in addition to bearing 46.

The inner race of the bearing 46 contacts at its upper end with the lower of a pair of lock nuts 47 when the parts are in the positions illustrated in Figure 1. The outer race of the bearing 46 is supported at its lower` end by the head 44 and contacts at its upper end with a, portion of a cover i surrounding the shaft 32.

, shaft 32, as indicated atV thence to the pulley 53 48 secured to the top of the micrometer head 44. Accordingly it will be apparent that the outer race of the upper bearing is positively fixed with respect to the head 44.

It will be apparent that the inner race of the upper bearing does not seat upon the head 44, the latter being provided with a small recess 49. The lower end of t-he inner race of the bearing 46 contacts with a. vertically movable sleeve 50 The lower end of this sleeve contacts with the upper end of a compression spring 51 mounted in an annular recess 52 formed in a pulley 53 through which power is delivered to the device. The pulley is keyed to the 54. The belt for the pulley is adapted to extend through the open side 40 of the body of the support 28.

The lower end of the pulley 53 contacts with the upper end of the sleeve 55, and the lower end of this sleeve contacts with the upper end of the inner race of the bearing 34. The sleeven55 extends through a cover plate 56 arranged on the upper end of the sleeve 31 and is held in position thereon by screws 57 or similar fastening elements.

The operation of the device is as follows:

When the micrometer head 44 is raised so that there is a relatively large gap between the cooperating faces of the stator 17 and rotor 33, as shown in Figure 1, the spring 51 is uncompressed so that the bottom of the compression sleeve 50 is level with the top of the pulley 53. and the locl; nuts 47 are in contact with the upper end of the inner race of the bearing 46. The parts are arranged in t-he positions described when it is desired to start the operation of the device. Under such conditions, the material to be treated is supplied from the source under suitable pressure, to the duct 11 from whence it flows into the duct 13 and basin 15. and thence upwardly between the cooperating faces of the stator 17 and rotor 33. The operation of the rotor, of course, will have been started at such time. and the speed of rotation will be determined in accordance with the desired results sought to be obtained.

rThe gap between the cooperating faces. as illustrated in Figure 1. is somewhat exaggerated. but it will be apparent that this gap is somewhat greater when the operation of the machine is initiated'than after the parts have been placed in the fully operative positions to be described. This being the case, the material flowing from the treating surfaces will be incompletely treated. This material flows over into the chamber 18 and thence drains downwardly to the outlet duct 12. and the initially incompletely treated material preferably is returned to the source for retreatment.

After the device has been placed in operation in the manner described. the bolt 43 is loosened and the micrometer head is turned downwardly. This movement is transmitted through the upper bearing 46 to the compression sleeve 50. and through the spring 51. Owing to the relatively large gap initially provided between the coacting faces of the mill. the spring 51 will not be compressed. and accordingly the pulley will' move downwardly' to transmit movement to the shaft 32 and to the rotor 33. thus bringing the conical face thereof into close proximity to the face 16. Under such conditions. the rotor 33 will occupy substantially the position shown in Figure 2. while the sleeve 50 and pulley 53 will still occupy substantially the relative positions shown in Figure 1. In this connection it will be noted that the cooperating faces have been illustrated in Figure 2 as being in contact with each other. Actual contact however never takes place under the correct conditions of operation, the film of material between the two faces preventing such contact. However, the surfaces are brought very close together, to an almost negligible gap if desired, and in this manner the grinding is accomplished.

Actual operation takes place with the rotor exerting substantial pressure downwardly against the film of material passing between the cooperating faces. Accordingly the micrometer head is turned downwardly beyond the point described without causing substantially any further actual axial movement of the rotor, and accordingly the small gap referred to between the cooperating faces is retained. Under such conditions, however, the spring will be compressed as shown in Figure 2, the lower end of the sleeve 50 moving .downwardly fora short distance into the lannular recess 52. Accordingly actual operation is carried out with a substantial pressure exerted on the film of material, and when the'device is properly operated under the condition referred to, that is, with proper spring tension exerted downwardly on the rotor, the latter will not seize with respect to the stator, and thus damage to the device is prevented. At the same time, the application of such resilient pressure provides far more eicient results than can be obtained with the usual relative movement between cooperating faces formed on inherently rigid members which are arranged to provide a fixed gap between the operating faces.

Should the film between the rotor and stator be broken down, as by shutting off the supply of material, or by screwing down the micrometer head beyond the compressive limit of the spring, it is apparent that seizing will take place with the consequent chance of injury to the mill. Thus care must be taken to prevent the occurrence of either of these conditions.

Instead of the screw micrometer device. the bearing 46 may be held in a similar suitable holder sliding in the sleeve 4l (which in this case would not be threaded) and the pressure applied to such device by a lever or toggle joint (not shown) instead of by a screw. In such case the mill may be fitted' with a suitable mechanical or electrical device to release the pressure automatically in case of a failure of supply.

The illustrative example of my invention shows a belt driven mill. Of course, a direct motor or turbine drive may be employed instead of a belt, in which case however there should preferably be a flexible coupling connecting the shaft of the motor orl turbine with the shaft of the rotor which coupling should provide for suicient longitudinal motion to permit the operation of the pressure applying device.

It will be apparent that a spring of any desired compressive strength may be employed. Although it is understood that I do not limit myself in any way to springs of any particular strength. I have found it feasible to employ springs of a wide range, e. g. of 40 to 1.000 lbs. compressive strength in a mill employing a 5 inch rotor. In general. I have found that springs with higher compressibility give better results. In this connection it will be noted that the spring can be mounted in any desired manner so long as it acts to allow pressure to be yieldably applied. It also will be apparent that the rotor may be mounted rigidly against longitudinal movement `and that the spring pressure may be applied to are employed, in which is further applicable to types of mills other than those illustrated and referred to, for example to so-called paste mills which are cclloid mills adapted for treating relatively concentrated suspensions or semi-solid pastes.

The feed may be supplied to the mill under any pressure desired according to the design of the mill and the spring pressure employed, but in actual operation of the mill illustrated. I have found that a pressure corresponding to that of a head of liquid of a few feet from a feed tank is sufficient. With paste mills pressure feed is preferable.

As previously stated, it is desirable that the portion of the materialpassing through the mill at the initiation of the operation thereof should be by-passed to the original feed tank until the mill has been adjusted to the position shown in Figure 2. This likewise applies to the material passing through the mill just at the end of the run. In this connection, it is noted that when it is desired to shut down the operation of the mill, the spring pressure is released before cutting off the supply of material to prevent seizure between the cooperating surfaces.

The invention upon solids in apparatus.

The invention obviously is not limited to any definite relative rotative speeds between the cooperating surfaces. For example, the mill illustrated has been operated from 3,200 to 14,000 R. P. M., but I have found in general that bet-ter results are obtainable at higher rotative speeds.

win be obvious that forthe same peripheral speed rotors of large diameter operate at lower shaft speeds.

In certain cases, the desired results may not be obtained by one passage of the material through the mill. In such cases the material may be given more than one passage through the mill, or in some cases, part of the eiliuent may be bypassed to the inlet side of the apparatus so as to obtain continuous operation.

The rotor and stator have been illustrated as mill. that the cooperating surfaces be made detachable and thus renewable when worn.

The advantages of the apparatus will be apparent from the foregoing description. The in- With a substantial gap therebetween, initiating a continuous feed of material between the cooperating faces, and then moving the cooperating faces toward each other and maintaining them in close proximity under the influence of yieldable force. The practice of the method obviously provides the desirable efficient results referred to above.

While I have described in detail one embodiment of my invention, it is to be understool that I do not intend to be limited thereby, as it is apparent that various changes may be made in the device and in the procedure of the method without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

of a liquid suspension of such solids through a 1 passage of material therebetween.

4. In a colloid mill comprising a pair of relatively rotatable respectively rigid elements having yieldable pressure means and then movable further in the same direction in engagement with said rst named element for positively moving the second named element.

ward said second named element to tend to hold said4 surfaces in cooperative relationship, and means contacting with said yieldable pressure means and movable in one direction to increase the force thereof tending to move said first named element toward said second named element, said last named means being movable initially in the other direction for releasing said yieldable pressure means and then movableY further in the same direction in engagement with said first named element for positively moving the latter away from the second named element.

6. In a colloid mill comprising a pair of respectively rigid elements having cooperating material treating surfaces, that improvement which consists in mounting one of said elements for unrestricted movement toward the other element, a spring compressible in contact with said first named element to tend to move it axially toward said second named element to hold said surfaces in cooperative relationship, and means contacting with said spring and movable in one direction to increase the degree of compression thereof, said last named means being movable initially in the other direction for releasing the compression of said spring and then movable further in the same direction in engagement with said first named element for positively moving the latter away from the second named element.

'7. In a colloid mill comprising a pair of respectively rigid elements having cooperating material treating surfaces, that improvement which consists in mounting one of said elements for unrestricted movement toward the other element, at least one of said elements being rotatable at high speeds, means for rotating said last mentioned element, a spring compressible in contact with said rst named element to tend to move it axially toward said second named element to hold said surfaces in cooperative relationship, and means contacting with said spring and movable in one direction to increase the degree of compression thereof, said last named means being movable initially in the other direction for releasing the compression of said spring and then movable further in the same direction in engagement with said first named element for positively moving the latter away from the second named element.

8. A colloid mill comprising a rotor and a stator having cooperating surfaces, said rotor being slidably mounted for movement toward said stator to bring said cooperating surfaces into yclose proximity, yieldable pressure means acting on said rotor for maintaining said cooperating surfaces in close proximity, and means contacting with said yieldable pressure means and movable in one direction for increasing the active pressure thereof against said rotor, said last named means being movable initially in the other direction for releasing said yieldable pressure means and then movable further in the same direction in Contact with said rotor for positively moving the latter away from the stator.

9. A colloid mill comprising a rotor and a stator having cooperating surfaces, said rotor being slidable axially to bring said cooperating surfaces into close proximity, a compression spring acting on said rotor axially thereof for maintaining said cooperating surfaces in close proximity, and

means contacting .with said compression springv and movable in one direction for compressing the latter. said last named means being movable initially in the other direction for releasing the tension of said spring and then movable further in the same direction in contact with said rotor for positively moving the latter axially away from the stator.

HAROLD ROBERT RAFTON.

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