US2704635A

US2704635A - Pulverizing mill having opposed jets and circulatory classification

Info

Publication number: US2704635A
Application number: US229593A
Authority: US
Inventors: Conrad M Trost
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-06-02
Filing date: 1951-06-02
Publication date: 1955-03-22
Anticipated expiration: 1972-03-22

Description

March 22, 1955 c TRQST 2,704,635

PULVERIZING MILL HAVING OPPOSED JETS AND CIRCULATORY CLASSIFICATION Filed June 2, 1951 4 Shets-Sheet l INVENTOR. Cam/e60 M 720.57

March 22, 1955 TROST PULVERIZING MILL HAVING OPPOSED JETS AND CIRCULATORY CLASSIFICATION 4 Sheets-Sheet 2 Filed June 2, 1951 INVENTOR. do/veno 7. 72067 My A; /'arno March 22, 1955 c, TROST 2,704,635

PULVERIZING MILL HAVING OPPOSED JETS AND CIRCULATORY CLASSIFICATION Filed June 2. 1951 4 Sheets-Sheet 3 Q g Q l INVEN TOR. Co/veaa/vzzasr I #wney March 22, 1955 c, TRQST 2,704,635

, PULVERIZING MILL HAVING OPPOSED JETS AND CIRCULATORY CLASSIFICATION Filed June 2, 1951 4 Sheets-Sheet 4 BEL/477 1 0m. N/aea/vs 7 g ISmaentor Came/w M Z'eaar United States Patent PULVERIZING MILL HAVING OPPGSED JETS AND CIRCULATORY CLASSIFICATION Conrad M. Trost, Moorestown, N. J.

Application June 2, 1951, Serial No. 229,593

12 Claims. (Cl. 241-) This invention refers to a pulverizihg mill of the type wherein the material being coniminuted 1S suspended and carried in a huid medium, and particularly of the type wherein the greater part or the comminuting process is enected by opposed material carrying streams and the classification is carried out by circulatory means.

in presently Known puiverizing apparatus, whether of the impact type as iuustrated by ratent No. 213,566 or of the circulatory type as illustrated by Patent inc. 2,191,093 or no. 2,251,091, there are present, among others, three problems which have tor a long time imposed certain undesirable limits upon the use or' this class or equipment. Une problem relates to classification and is nianirested by the tendency or oversized particles to be carried into the discharge or apparatus of the type illustrated by r'atent N0. Liylamh even when it is operating at a normal load. ln many classes or work, such as pharmaceutical, such inaccurate classification cannot be permitted. in other classes or WOIK it reduces the desirability and value oi the product, Irequentiy requiring an additional step to eirect satisractory separation. '10 remedy this, it has been the practice in the past to operate such a mill at a relatively li ht load where highly accurate classification is required. this secures a satistactory degree or classification, but only at the price of reducing the output or the mill quite seriously. Thus, emciency of operation is greatly reduced and the cost or puiverizing and separating the product consequently raised.

The second problem is to attain a still higher proportion or the nnished product at sizes under one micron. with various agricultural and industrial processes requiring comminution or materials to very fine condition, that is, to particle sizes or less than one micron diameter, it has long been desirable to design apparatus wherein the proportion or material or such particle sizes would be in higher proportion than is now produced by Known equipment.

the third problem has not been as critical in the past as those discussed above. The solution or this problem, however, has been very valuable in that it provides a pulverizing mill which will produce a pulverized material wherein the particles become suhiciently associated according to size during the pulverizing process that a product of a substantially predetermined size, intermediate the extremes of that normally produced by said imll, may be removed. This product wnl be or reasonably consistent size range. Such isolation and separation or intermediate size ranges is of considerable economic value and constitutes an important additional advantage or the present invention.

Further, there has existed a need for apparatus suitable tor carrying out the pulverizing operation with a liquid pulverizing liuid medium. 'lhus, in the paint manufacturing industry, it would be extremely desirable to impart to the paint pigment a final and liner comrninution ot' the pigment, and an intermlxture thereof with the carrying vehicles, which would both improve the quality or the paint and inhibit settling of the pigments out of suspension.

Accordingly, it is a principal object of the invention to provide a comminuting device having more accurate classification means than exists in presently known apparatus- A further object of this invention is the provision of a comminuting device, as aforesaid, wherein over- Patented Mar. 22, 1955 sized particles will not be carried into the product of the device when it is operated at a relatively heavy load.

A rurther object or the invention is to provide a comminuting device, as atoresaid, which will produce a higher proportion of particles having a size under one micron in diameter than has been possible in previously linown equipment.

A further ob ect of the invention is to provide a comnnnuting device, as atoresaid, which is extremely simple in both construction and operation.

A turther ob ect or the invention is to provide a comminuting device, as aforesaid, wherein the cost of operation is extremely low per unit or product produced.

A further ob ect or the invention is to provide a comminuting device, as aroresaid, wherein the operation is extremely sunpie and the cost or maintenance is consequentiy low.

A Iurther object of the invention is to produce a comminuting device, as atoresaid, rrom which may be removed product or size ranges intermediate the extremities or the product size range.

Other ob ects and purposes of the invention will become apparent to persons Iamiliar with equipment of this kind upon a reading or the disclosure and study or the accompanying drawings.

in the QI'aWLHgS;

rigure l is a central, vertical, sectional view of a preierred embodiment of my apparatus.

rigure z is a sectional view taiten on the line 11-11 or rlgure l.

rigure 3 is a sectional view taken on the line HI-Ill of Figure l.

ri ure 4 is a sectional view taken on the line IV-IV oi rigure 1.

ri ure D is a sectional view of my device taken on either or the lines VV of figure 1.

rigure b is a fragmentary sectional view of my device IaKeD on the line Vl-Vi of rigure 1.

rigure IS a sectional view or my device taken on the line vii-Vii or figure 1.

figure 8 is an enlarged, fragmentary view of a portion or figure 1 and showing a modification of my device.

rigure 9 is a fragmentary view of a portion of Figure l and showing a runner modification or my device.

lrigure to is a sectional view taken on the line X-X of bigure 9.

Figure 11 is a sectional view taken on the line Xl-XI of rigure 9. I

klgulffi 12 is a fragmentary, view of Figure 9 showing a modification of one or the ends of the housing shown in rigure 9.

rigure 13 is a side elevation view of a modified shape for the classifier for my improved mill.

Figure 14 is a side elevation view of a further modified shape for the classifier tor my improved mill.

figure 15 is a pertormance graph showing the operation of my improved mill.

General description In meeting the objects and purposes above set forth, I have provided a device utilizing opposed jets with a circulatory classification chamber'leading from and returning to the grinding chamber intermediate said jets. The nozzles of the jets are so spaced that the impact zone is maintained closely adjacent the entrance 3]. to the circulatory classification chamber and, further, the jet 7 which is directed toward this entrance is the stronger of the two jets. The greater part of the classification zone has a cross-sectional shape in which the sides converge radially outwardly so that the radially outward portion thereof is of substantially less volume per unit of radius than is the radially inward portion thereof.

The particles are confined in close contact in the grinding chamber and are initially shattered by impact in a zone adjacent the entrance of the classification chamber. The grinding fiuid and entrained material then pass through a somewhat horse-shoe shaped classification chamber. Because of the centrifugal force acting on the particles travelling a curvilinear path, the larger particles migrate to the outer periphery of the classification chamber and are crowded relatively closely together. A major proportion of the grinding fluid is dlsplaced radially inwardly by this crowding of the larger particles into the restricted area of the outer portion of the classification chamber. As a result, there is no tendency for the fluid from the region having large partlcles to pass through the otftake opening 36 when same is reached. Hence, the tendency of the fluid to carry oversized particles throu h the opening 36 with the finished product is minimized. The oversizcd particles, after by-passing the outlet, are returned to the pulverizing chamber for reprocessing.

While in the preferred embodiment, there is shown feeding means in association with only one of said iets, Figure 8 shows that material may be fed through both of the jets. roviding the same above outlined conditions are met. Figure 9 shows that the material ma be introduced into the grinding chamber by a plurality of iets, suitably opposed respectively to each other, rather than by a single pair of jets.

Detailed description In the detailed description of the device, the following terminology will be employed for c nvenience in description, but it should be understo d that such terminology is for c nven ence only and is not intended in any sense as limiting. The terms inwardly and outwardly. and derivatives thereof, when used in connection with the circulatory chamber, will be understood to refer to directions respectively toward and away from the center about which said circulatory chamber is arran ed. The terms upward and downward. and derivatives thereof, refer respectively to directions toward the top of the drawing, as appearing in Figure l. and toward the bottom thereof. It is. however. emphasized that this terminology has no limiting effect res ecting the position of operati n of this mill since it can be operated successfullv in either a h rizontal or a vertical position.

The terms ri htward and leftward. and derivatives thereof, are used in connection with the machine when positioned as appearin in Fi ure 1 and such other fi ures as are under consider tion when such terminolo is used.

The pulverizing mill consists broadly of a rinding compartment 1. a classifier 2. and an off-take 3 f r pulverized material. The rinding compartment includes a tubular housing 4 closed on each of its ends by plugs 6 and 9 and between the plu s defining a grinding chamber 5. The plug 6 at the ri ht hand end of the rinding chamber 5, as seen in Fi ure 1, seats snugly within the end of the housing 4 and has a central opening throu h which extends the nozzle 7. The plug 6. together with the nozzle 7, is adjustable lon itudinally of the housing 4 and is held in a predetermined position by means of the set screw 8. The primary grinding fluid is admitted through the nozzle 7.

The plug 9 at the left hand end of the grinding chamber 5, as seen in Figure 1, seats snugly within the end of the housing 4. concentrically throu h the center of the plug 9. is a venturi opening 10. The venturi opening 10 and the nozzle 7 are co-axial. Externally of the housing 4, adjacent the plug 9. is a material hopper 11 communieating at its lower end with the venturi opening 10. Coaxial with the venturi opening 10 and extending through the material at the bottom of the hopper 11 is a pressurized fluid supply tube 12 terminating at the junction of the hop er 11 and the venturi o ening 10. The diameter of the tube 12 is substantially less than that of the venturi o ening 10 where the venturi opening communicates with the hopper 11 to permit aspiration of material from the hopper into the venturi opening by the fluid discharged from the tube 12. The secondary grinding fluid is admitted to the grinding chamber 5 by the venturi opening 10.

The housing 4 consists of two

end portions

13 and 14. and a central portion 15. Where the

end portions

13 and 14 abut the central porti n 15 each portion is provided with radially extending flanges. The flanges of the various portions are held together by the bolts 16.

The classifier 2 is preferably a somewhat horse-shoe shaped tube 30 extending upwardly from the housing 4 and having each of its ends in open communication with the grinding chamber 5. The centerline of the classifier 2 is offset from the midpoint between the nozzle 7 and the venturi opening 10 a short distance toward the nozzle 7. By reason of this offset, the venturi opening 10 discharges into the grinding chamber 5 a short distance outwardly of the inlet end 31 of the classifier 2 and the nozzle 7 discharges into the grinding chamber below the discharge end 32 of the classifier 2. The importance of this structural arrangement will appear more fully hereinafter. The flow of rinding fluid and entrained particles through the classifier 2 is from the inlet end 31 to the discharge end 32. The direction of this flow is controlled both by the relative positions of the venturi opening 10 and the nozzle 7 and by the relative strengths 0}: the pressures behind the fluid discharging from each t ereof.

The cross-sectional shape and size of the tube 30 vary appreciably throughout its length. In the preferred embodiment illustrated. the interior passage 33 of the inlet end 31 f the tube 30, at the point where it communicates wi h the rinding chamber 5, is substantially rectangular (Figure 2) As the tube 30 extends upwardly, in said preferred embodiment, the cross-section of the passageway 33 within the tube changes in shape, while remaining of the same area. from a rectangle to a trapezoid with the inward wall 34 of the tube 30 (Fi ure 3) bein the base of the tra ezoid and the altitude of the trapezoid extending radially of the classifier 2. This trapezoidal shape is rea hed substantially bel w the h rizontal reference line X (Fi ure ll. The reference line X represents the base of the degree arcuate segment f rming the top of the classifier 2. At this oint. the radial altitude of the trapez idal passageway 33 is substantiall greater than the width of its base, or inward w ll 34. When the inward wall 34 of the tra ezoid is sli htly more than double the len th of the outward wall 35 and the altitude of the trapezo d is about quadruple the len th of the outward wall 35. a passa eway having excellent nerational characteristics is provided. These size relationships are, however, by way of example and are not limiting.

At a point approximately 45 degrees to the ri ht of the vertical reference line Y. as appearing in Figure 1. an off-take openin 36 is provided throu h the inward wall of the tube 30 (Fi ures 4 and 6). The reference line Y represents the vertical centerline of the arcuate portion at the top of the classifier 2. The opening 36 provides the means through which the fine pulverized material from the classifier is withdrawn. As the tube 30 extends be ond the openin 36, the size of the passa eway 33 rapidly decreases. This reduction in size continues until. at a point below the horizontal reference line X. the tube 30 takes on a constant shape and area which continue down to the rinding chamber 5. as shown. Although the size of the passageway 33 is reduced. the trapezoidal shape is retained. and the inward wall 34 and outward wall 35 remain approximately the same size shown in Figure 5. Only the altitude of the trapezoid is reduced. In the reduction of the cross-sectional size of the passageway 33. the outward wall 35 continues to trace a circular path and the inward wall 34 traces a path of increasing radius. Thus. the reducti n in size is efiected bv the inward wall 34 approaching the outward wall 35. The inlet end 31 and the discharge end 32 of the classifier 2 converge toward each other as they approach the grinding chamber 5.

To simplify construction and reduce the overall cost of the mill. the tube 30 is divided into detachable sections. These sections are joined at their ends along the X and Y reference planes by means of conventional flanges 37 and bolts 38. It will be understood that for convenience in fabrication. the tube 30 may be divided into a greater or lesser number of component sections and the joints between these sections need not lie in the reference planes X" and Y.

The off-take opening 36 is an elongated slot (Figure 6) through the inward wall 34 having its longitudinal axis ali ned with the central axis of the passageway 33 and its ends either pointed or rounded. In the embodiment shown, the opening 36 comes to a tapered point at each end and has a central width constituting a major portion of the width of the inward wall 34. The opening 36 communicates with an off-take conduit 40. of any convenient cross-sectional shape, leading to a collector. The collector is neither shown nor described in detail since it is of conventional design and may be any one of the several commercial designs currently available on the market.

The horse-shoe shape of the classifier 2 described above is a preferred embodiment because of its high efliciency in separating entrained particles according to size. However, the classifier may be designed to have a shape other than that of a horseshoe when the same high efiiciency of separation according to size is not necessary. The classification portion 2 may be modified to that of an elongated loop 2a (Figure 13) having a major portion of its vertical sides straight with only the upper and lower ends curved. Another possible shape is that of a circle 2b (Figure 14). Irrespective of the outline shape of the classifier 2, the trapezoidal, cross-sectional shape of the interior passageway is preferably maintained for best results.

Irrespective of the design of the grinding chamber 5, the relative strength of the jets entering the grinding chamber must be retained in a ratio such that the center of the impact zone within the grinding chamber is maintained adjacent to the inlet end 31 of the classifier 2. The center of the impact zone is indicated in Figure 1 by the line A. It is also essential in the design or the grinding chamber that the stronger of the grinding fluid jets be positioned to aspirate the discharge end 32 of the classifier 2. This is essential to maintain a proper flow pattern through the classifier 2.

In the modified grinding chamber 101 of my mill, shown in Figure 9, the primary and secondary grinding fluids are each introduced into the grinding chamber through a plurality of jets. In addition, a tertiary grinding fluid is introduced into the grinding chamber in association with the secondary grinding fluid.

The grinding compartment housing 100 and the grinding chamber 101 are identical to the housing 4 and grinding chamber 5, respectively. In the end of the housing 100 adjacent the discharge end 32 ot' the classifier 2, a plug 103 is inserted. The plug 103 is provided with a central jet opening 104 and a plurality of circumferentially, equally spaced, jet openings 105 (Figure positioned radially outwardly from the central opening 104. The outward end of the plug 103 has a fluid chamber 106 communicating with the jet opening 104 and the jet openings 105 and sealed on its outward end by the plate 107. Fluid is supplied to the fluid chamber 106 by the pipe 108. The plug 103 is normally inserted into the housing 100 until its inward face is aligned with the outer wall of the discharge end 32 of the classifier 2. Where it is desired to insert the inward end of the

jet openings

104 and 105 further into the stream of flow from the discharge end 32 of the classifier 2, the plug 103 may be beveled as shown at 109 in Figure 12. It is also possible to accomplish this same result by providing tubes in the

jet openings

104 and 105 which extend inwardly beyond the inward face of the plug 103 whereby their point of discharge is substantially within the flow stream at the discharge end 32 of the classifier 2.

At the end of the grinding chamber 101 adjacent the inlet end 31 of the classifier 2, another jet equipped plug 110 is provided. Like the plug 103, the plug 110 seals the end of the grinding chamber 101 against the escape of the grinding fluid even when high pressures are employed. The plug 110 has a venturi opening 111 concentric with the plug. The venturi opening 111 is identical to the venturi opening 10 in the plug 9 and is co-axial with the jet opening 104. Spaced radially outwardly from the venturi opening 111, and equally spaced circumferentially, are a plurality of jet openings 112. At the outward end of the plug 110 is an annular fluid chamber 113 communicating with each of the jet openings 112 and sealed at its outward end by the ring shaped plate 114. The fluid chamber 113 is sealed from the venturi opening 111 by the annular wall 115. The tertiary fluid is admitted to the fluid chamber 113 by means of the pipe 116. The outward end of the venturi opening 111 communicates with the material hopper 117. Aligned with the venturi opening 111, through the lower end of the material hopper is the secondary fluid supply conduit 118. The hopper 117 and conduit 118 are identical to the hopper 11 and the fluid supply tube 12, respectively.

In the modified grinding chamber 200, shown in Figure 8, material to be pulverized is introduced into the grinding chamber 200 from each end. At the end of the grinding chamber 200 adjacent the inlet end 31 of the classifier 2, there is provided a plug 201 having a central venturi opening 202 together with a hopchamber.

per 203 and secondary fluid supply conduit 204. The plug 201, venturi opening 202, hopper 203 and conduit 204 are each identical to the plug 9, venturi opening 10, hopper 11, and fluid supply tube 12, respectively. The end of the grinding chamber 200 adjacent the discharge end 32 of the classifier 2, is provided with a plug 205, venturi opening 206, and hopper 207 identical'to the corresponding parts at the opposite end of the grinding chamber. The conduit 208 for supplying the primary grinding fluid is identical in shape and arrangement to the conduit 204 for the secondary grinding fluid. These two conduits are different only to me extent that the nozzle of the conduit 208 is larger than that of the conduit 204 to admit the larger volume of fluid forming the primary fluid supply. Like the other designs of the grinding chamber previously described, the points of fluid discharge at the ends of the grinding chamber are unequally spaced from their respective adjacent ends of the classifier Z. This is to maintain the described direction and velocity of flow through both the grinding chamber and the classifier.

Operation The operation of the preferred embodiment of my improved pulverizing mill will be apparent from the foregoing description and discussion, but will, nevertheless, be here reviewed in detail for the purposes of completeness and certainty. Although I have stated that the following is a description of the operation of the preferred embodiment of my invention, it will be understood that the various modifications of my invention all operate on the same basic principle. It 15 only the degree of efficiency with which they operate with particular materials that varies.

in the embodiment of my invention shown in Figures 1 through 7, the material to be ground is introduced into the hopper 11 from which it works down by gravity to a point adjacent the end of the fluid supply tube 12 where it is aspirated by the secondary grinding fluid through the venturi opening 10 into the grinding chamber 5. At the same time, the primary grinding fluid is introduced into the grinding chamber through the nozzle 7. The volume of the primary jet of grinding fluid entering through the nozzle 7 substantially exceeds the volume of the secondary grinding fluid entering through the venturi opening 10. In one successful operation the weight of fluid entering through jet 7 was about 60% of the total weight of fluid used. Further, the secondary grinding fluid is burdened by the entrained material aspirated from the bottom of the hopper 11. The discharge end of the nozzle 7 of the jet of primary grinding fluid is positioned closer to the mid-point of the grinding chamber than the discharge end of the venturi opening 10, thus creating an even greater disparity between the relative strengths of the two jets at the center of the grinding chamber. By reason of this disparity between the relative strengths of the grinding jets, the zone of impact, that being the zone where the stream of primary grinding fluid and the stream of secondary grinding fluid substantially neutralize each other, is adjacent the inlet end 31 of the classifier 2. As so positioned, it is much closer to the venturi opening 10 than to the nozzle 7. The grinding action is carried out in this impact zone by the effect of the cross currents set up by the two jets meeting in head on collision and by the resulting impact between the particles entrained in the grinding fluids. The quantities of grinding fluid and entrained material entering the impact zone will escape by the path of least resistance. Since the impact zone is closest to the inlet end 31 of the classifier 2 and the resistance of the jet of secondary grinding fluid will be less than that of the jet of primary grinding fluid this grinding fluid and entrained material will discharge from the impact zone through the inlet end 31 of the classifier.

As soon as the grinding fluid with its entrained particles enters the classifier 2, the larger of the particles will tend to migrate toward the radially outer periphery of the passageway 33. This is the result of the centrifugal force acting upon the particles as the grinding fluid transits the horseshoe shaped classification The finer particles of material will not materially change their position within the stream by reason of this centrifugal force because of the absence of sufficient mass. As the shape of the passageway 33 changes to trapezoidal, the large particles will all crowd into the narrow, outer portion of the trapezoidal passageway. As the larger particles crowd into this restricted, narrow portion of the passageway, they will force a similar volume of the grinding fluid radially inwardly to occupy the broader path on the radially inward side of the trapezoidal passageway. Thus, there will be provided a greater volume of the fluid carrying medium for the finer particles. In addition, the crowding of the larger particles into the narrow, restricted, radially outer portion of the passageway 33 will cause the finer particles to be crowded radially inwardly along with the grinding fluid. The result is a very exacting and precise separation of the larger particles from the fine particles. By the time a given segment of the grinding fluid reaches the off-take opening 36. the inward portion of the grinding fluid is substantially purged of the larger particles. Thus, that portion of the grinding fluid which exits from the classi fier 2 through the ofi-take opening 36 will have entrained in it only particles of a relatively closely controlled, preselected fineness. Since the trapezoidal shape provides the greatest volume of grinding fluid at the radially inward portion of the classifier 2, there will be suflicient fluid entraining only the fine particles to satisfy the tendency of a portion of the grinding fluid to discharge through the oft-take opening 36. All of the fluid necessary to satisfy the tendency to flow through the off-take opening 36 will readily come from that portion of fluid carrying the fine particles. Therefore, there will be no tendency to withdraw any grinding fluid from the radially outer portion of the passageway 33. Since the larger particles are crowded together in the undisturbed radially outer portion of the fluid in the passageway 33, these larger particles will all continue past the off-take opening. This result is assured by the fact that the small cross-sectional area of the radially outer portion of the trapezoidal shape permits only the minimum volume of grinding fluid necessary to carry the larger particles to travel in this space. Further the shape of the classifier 2 is such that as the crosssectional area of the passageway 33 decreases in the vicinity of the off-take opening 36, the area allotted to carry the grinding fluid entraining the larger particles is not diminished while the area allotted to carry the grinding fluid entraining the fine particles is reduced.

This construction forces the portion of the grinding fluid entraining the fine particles to discharge without disturbing the passage of that portion of the grinding fluid entraining the larger particles.

The diminished volume of grinding fluid entraining the large particles is accommodated by the discharge end of the classifier 2 and returns to the grinding chamber 5. The jet of primary grinding fluid entering the grinding chamber at the rightward end accelerates, by its aspirating action, this flow of the remaining grinding fluid and entrained large particles from the classifier 2 into the grinding chamber. The aspirating action of the nozzle 7 accelerates the circulatory flow of the grinding fluid through the classifier 2. The dual action of forcing the grinding fluid into the intake end 31 of the classifier 2 plus the aspirating action acting at the discharge end 32 of the classifier 2 maintains an even, high velocity circulatory flow through the classifier.

It can be seen from this description of my machine that it is important to the efiicient classification of the comminuted material that the cross-sectional shape of the passageway through which the material is carried during the process of classification be such that the portion of this passageway tracing the longer, radially outer path be considerably smaller than the portion of this passageway tracing the shorter, radially inner path. Unless this distinct differential between cross-sectional areas is maintained, there will not be an efficient and thorough separation of the larger particles from the fine particles.

The relative amounts of grinding fluid introduced into the grinding chamber by the primary grinding fluid and the secondary grinding fluid may be varied somewhat according to the fluid used and the material being ground, but the balance thereof should be maintained at such a point that the impact zone remains substantially closer to the intake end 31 of the classifier 2 than to the discharge end 32. Otherwise, circulation through the classifier 2 will be impeded and the acccuracy of the classification will diminish substantially. The position of the nozzle 7 may be moved to the left or to the right within small limits, but once a position generating efiicient circulation through the classifier 2 has been determined further such adjustment is not desirable. If the nozzle 7 is moved leftwardly with respect to the discharge end 32 of the classifier 2, the aspirating effect upon the classifier 2 is materially diminished with a resulting reduction in circulation velocity. If it is moved materially rightwardly from the position shown in Figure 1, there is some tendency for the discharge from the nozzle 7 to flow to the discharge outlet 32 of the classifier 2 thereby reducing or entirely stopping the circulation through the classifier 2.

The horseshoe shape of the classifier 2 illustrated in Figure 1, may be modified to a somewhat U-shape having parallel legs (Figure 13) instead of converging ones. A further modification may be that of employing a semicircular path for the classifier 2 (Figure 14). However, both the semi-circular and the U-shaped forms of the classifier 2 are less desirable than the horseshoe shape for two principal reasons. The first of these reasons is that the horseshoe shape permits the jets of the primary grinding fluid and secondary grinding fluid to be sufficiently close together to effect maximum impact without making it necessary for the curved portion of the classifier 2 to trace an arc of such small radius that the friction between the grinding fluid and the walls of the classifier 2 substantially reduces the velocity of the grinding fluid. The second principal reason is that the horseshoe shape provides a greater amount of curved section. The use of the curved section permits the centrifugal forces to aid and accelerate the particle separation process.

Thus, with the horseshoe shape, the material is directed against the outer periphery of the passageway within the classifier immediately after it enters the classifier 2, rather than after it has traveled approximately a quarter of the length of the classifier as is the case in both the semicircular and U-shaped structures. By reason of this immediate directing of the heavy material to the outer periphery of the passageway, the U-shaped structure effects a more rapid and accurate classification.

The ofi-take opening 36 has been described as being of elongated shape. However, the shape of this opening may be modified to that of a circle, a square or a diagonal slot without departing from the scope of this invention. This is not a preferred construction because the elongated shape or slot provides better classification. The improved classification obtained by the use of the elongated shape of the off-take opening 36 occurs because this shape permits the grinding fluid to discharge through the opening with less turbulence than occurs when the direction of flow is sharply changed as is the case with the circular or rectangular opening. The elongated opening is described as having pointed ends. These ends may be shaped into smooth curves without departing from the scope of the invention and without materially disrupting the flow pattern of the grinding fluid discharging through the opening.

The functional advantage of the cross-sectional shape shown for the classifier 2 is evidenced by the performance curves set forth in Figure 15 wherein the line B represents the operation of a mill of identical construction to that of the preferred embodiment illustrated in Figure l excepting only that the cross-sectional shape of the passageway 33 of the classifier 2 was circular. The line C represents the typical results produced by the preferred embodiment of the mill illustrated in Figure 1 having a trapezoidal passageway 33. The tests which were carried out in both cases with crushed oyster shells, were typical of a large number of other similar tests, and, in details, were as follows:

The modification appearing in Figure 8, wherein the material to be pulverized is fed from each end of the grinding chamber, will be found useful where a material is relatively easy to grind so that the mill will be capable of handling relatively large quantities of the material. The modification of the grinding chamber illustrated in Figures 9, l and 11 is designed for use with materials which are relatively difiicult to grind, as quartz, labradorite mica, plastics and other organic materials. When such diflicult to grind materials are involved, a larger number of jets entering the impact zone should be provided whereby a greater area of impact is produced in a grinding chamber of given size.

The above described mill has been described as it would most frequently be used, that is, with a gaseous grinding fluid. For this purpose air or steam will be the most commonly employed gases. T 0 effect the grinding operation and to supply the mechanical energy necessary to drive the mill, this grinding fluid will be supplied to the mill at a pressure of approximately one to two hundred pounds per square inch atmosphere. Where necessary, gases other than air or steam may be used for the purpose of grinding. For certain grinding operations, particularly that of grinding paint pigments, it is desirable to grind the material by means of a liquid grinding fluid. The above described mill will operate efliciently with a liquid grinding fluid both in its preferred embodiment and in the various modifications of this embodiment. When a liquid is used as the grinding fluid, it will be necessary to follow the same operational details described above when the grinding fluid is gaseous. The liquid supply must be steady and without material pulsations. The impact chamber and the classifier must both be so designed that the liquid, with its entrained solid material, will move with a smooth flow pattern and at a high velocity except in the impact zone. To maintain the proper flow at a high velocity when the grinding fluid is a liquid will require some modification of the proportions maintained in the cross-sectional shapes of the classifier 2 and the grinding chamber 5 from those utilized for a given feed rate when a gaseous grinding fluid is employed. The feeding means and specific nozzle design must also be modified in accordance with conventional practice in order to properly accommodate the liquid grinding fluid.

These and other modifications of my invention may be made without departing from the principle of my invention, and each of these modifications is to be considered as included in the hereinafter appended claims unless these claims by their language expressly provide otherwise.

I claim:

1. In a method of pulverizing a comminuted material, the steps comprising: feeding said comminuted material into a moving fluid stream; directing said stream and another fluid stream co-axially towards each other and causing them to meet in an impact zone, one of said streams being materially stronger than the other; utilizing the energy of the said stronger stream for carrying all of said fluid and the particles of material entrained therein in uni-directional, substantially constant, flow into a classification chamber and conducting same through a curvilinear path; withdrawing fluid and material entrained therein from a point on the radially inward side of said path and conducting the remainder of said material and carrying fluid back to said impact zone and discharging same adjacent said stronger stream for entrainment thereby and conduction thereby again to said impact zone.

2. In a method of pulverizing a comminuted material, the steps comprising: feeding said comminuted material into a moving fluid stream; directing said stream and another fluid stream co-axially towards each other and causing them to meet in an impact zone, one of said streams being materially stronger than the other; utilizing the medium of the said stronger stream for carrying all of said fluid and the particles of material entrained therein in uni-directional, substantially constant, flow into a classification chamber and conducting same through a curvilinear path; restricting the volume of the radially outward portion of said path; moving the larger of said particles into the restricted radially outward portion of said path by centrifugal forces established by said curvilinear path; withdrawing fluid and material entrained therein from a point on the radially inward side of said path and; returning the entrained material in said restricted radially outward portion of said path to said impact zone; aspirating said entrained materiai returning to said impact zone into said impact zone by the stronger of said fluid streams.

3. In a method of pulverizing a comminuted material, the steps comprising: directing a pair of streams of fluid of unequal strength under pressure co-axially toward each other; entraining said comminuted material into the weaker of said streams; passing all of the fluid from both of said streams together with the entrained material in uni-directional flow through a curvilinear path; withdrawing from said path a portion of said fluid and entrained particles intermediate the ends of said path; aspirating the remainder of said fluid and entrained particles transiting said path into the stronger of said streams.

4. In pulverizing apparatus of the fluid jet type, the combination comprising: means defining an impact chamber; co-axial means on opposite ends thereof spaced from each other for discharging co-axial streams of fluid toward each other within said impact chamber; one of said means being larger than the other; means for introducing into one of said streams the material to be pulverized; a classification chamber comprising a curvilinear conduit leading from and returning to said impact chamber at points between said discharging means, the entrance thereto being in a portion of said impact chamber closer to the smaller of said fluid discharging means than to the larger thereof; an ofi-take leading from said classification chamber through the radially inward wall thereof in the portion of said curvilinear conduit returning to said impact chamber.

5. Apparatus for pulverizing solid materials, comprising in combination: means defining an impact chamber; co-axial means for directing a pair of oppositely moving streams of fluid toward each other, one of said streams being stronger than the other to provide an impact zone within said impact chamber; means for introducing mate rial to be pulverized into one of said streams; a substantially tubular classification chamber shaped in an open curve having a pair of legs; said legs communicating with said impact chamber at points intermediate said means for supplying said fluid streams; one of the legs of said curve being larger in cross-sectional area than the other thereof and said larger one being closer to the means for supplying the weaker of said fluid streams and the smaller of said legs being closer to the means for supplying the stronger of said fluid streams; an off-take from an inner wall of said conduit on the side thereof adjacent said smaller leg.

6. In pulverizing apparatus of the fluid jet type, the combination comprising: a housing defining an elongated grinding chamber; a classifier having a curvilinear conduit of trapezoidal cross-sectional shape and a pair of ends; the sides of said conduit converging outwardly from the geometric center of said classifier; each of said ends of said conduit communicating with said grinding chamber; a primary jet for directing grinding fluid, said primary jet mounted in one end of said grinding chamber; the discharge end of said primary jet being in the area of communication of one end of said conduit and said grinding chamber; a secondary jet for directing grinding fluid, said secondary jet mounted in the other of the ends of said grinding chamber co-axially of said primary jet; the discharge end of said secondary jet being outwardly with respect to the center of said grinding chamber and outwardly of the area of communication of the other of the ends of said conduit and said grinding chamber; means for introducing comminuted material into the grinding fluid of one of said jets; said primary jet being adapted to admit a stronger stream of grinding fluid than said secondary jet whereby an impact zone between said jets will be established adjacent said other end of said conduit.

7. The combination described in claim 6 wherein a tertiary jet for directing grinding fluid is mounted in the end of said grinding chamber adjacent and parallel to said secondary jet.

8. In pulverizing apparatus of the fluid jet type, the combination comprising: a housing defining an elongated grinding chamber; a primary jet for discharging grinding fluid under pressure mounted in one of the ends of said grinding chamber; a secondary jet for discharging grinding fluid under pressure mounted in the other of the ends of said grinding chamber co-axially of said primary jet; a curvilinear classifier conduit having a pair of ends communicating with said grinding chamber; the midpoint between said ends of said conduit being offset from the midpoint between the discharge ends of said primary and secondary jets in the direction of said primary jet; said primary jet adapted to admit a substantially stronger stream of grinding fluid than said secondary jet whereby the zone of impact between said streams is adjacent said secondary jet.

9. In pulverizing apparatus of the fluid jet type, the combination comprising: a housing defining a straight, elongated, grinding chamber having end walls, one of said walls being of substantial thickness axially of said chamber; means defining a venturied passageway through said one wall coaxial with said chamber; a fluid nozzle coaxial with said passageway and extending into the end thereof remote from said chamber; means introducing material to be pulverized adjacent said end of said passageway; means providing an opening through the other end wall of said chamber coaxial therewith; means associated with said opening for directing a greater volume of fluid into said chamber than through said nozzle; a classification conduit having a pair of open ends and a curvilinear section intermediate said ends, said ends of said conduit communicating with said chamber at points therein spaced from each other and adjacent said end walls; and an off-take pipe communicating with the interior of said curvilinear section through the radially inner wall thereof.

10. In pulverizing apparatus of the fluid jet type, the combination comprising: a housing defining a straight, elongated, cylindrical grinding chamber having end walls, one of said Walls being of substantial thickness axially of said chamber; means defining a venturied passageway through said one wall coaxial with said chamber; a fluid nozzle coaxial with said passageway and extending into the end thereof remote from said chamber; a material hopper having an outlet adjacent said nozzle and the said end of said passageway; a fluid pipe extending through the other end wall of said chamber, coaxially therewith, to a point within said chamber, said pipe having a substantially greater inside diameter than said nozzle and being closer to the center of said chamber; a classification conduit having a trapezoidal cross-sectional shape, a pair of open ends and a curvilinear section intermediate said ends, the radially inner wall of said conduit being wider than the outer wall thereof; and one end of said conduit communicating with said chamber adjacent said one end wall thereof and the other end of said conduit communicating with said chamber at said point; and an off-take pipe communicating with the interior of said curvilinear section through said radially inner wall thereof.

11. The structure of claim 9 in which the portions of said conduit adjacent said chamber are straight and converge from said curvilinear section to said chamber, said portions both being disposed at an angle of less than to the axis of said chamber.

12. In a method of pulverizing a comminuted material, the combination comprising: directing a pair of fluid streams of unequal volume and substantially equal pressure coaxially against each other in a zone of impact; confining said zone to produce maximum impact of said streams; introducing said material into the stream of lesser volume at a point intermediate the source thereof and said zone; constricting said lesser stream intermediate said point and said zone; conducting the fluid from both streams and material entrained therewith through a path communicating at both ends with said zone, said path having a curvilinear portion intermediate said ends; using the differential force of said streams to urge said fluid through said path; withdrawing one part of said fluid and material entrained therewith from a radially inner point in said curvilinear portion; and using the stream of greater volume to aspirate the other part of said fluid and material entrained therewith from said path into said zone again.

References Cited in the file of this patent UNITED STATES PATENTS 238,044 Luckenbach Feb. 22, 1881 259,206 Pond June 6, 1882 275,566 Bailey Apr. 10, 1883 1,883,218 Wohlenberg Oct. 18, 1932 2,044,915 Mosley June 23, 1936 2,325,080 Stenphanoff July 27, 1943 2,494,153 Andrews Jan. 10, 1950 2,521,000 Crowley Sept. 5, 1950 2,590,220 Stephanoff Mar. 25, 1952