US3514043A - Fluid energy mill for milling friable materials - Google Patents

Description

i May 26, 1970 R. A. SLEP'ETYS 3,514,043

FLUID ENERGY MILL FOR MILLING FRIABLE MATERIALS Filed Aug. 4, 1967 v 2 Sheets-Sheet 1 F INVENTOR.

Richard A. Slepetys AGENT 2 Sheets-Sheet 2 INVENTOR. Richard A. Slepetys AGENT May 26, 1970 R. A. SLEPETYS FLUID ENERGY MILL FOR MILLI ENG FRIABLE MATERIALS Filed Aug. 4, 196'? Fig.

United States Patent O 3,514,043 FLUID ENERGY MILL FOR MILLING FRIABLE MATERIALS Richard A. Slepetys, Bricktown, N.J., assignor to National Lead Company, New York, N.Y., a corporation of New Jersey Filed Aug. 4, 1967, Ser. No. 658,526 Int. Cl. B02c 19/06 US. Cl. 2415 17 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a fluid energy mill for milling friable materials by utilizing a plurality of individual streams of high velocity milling fluid directed into a substantially straight tubular milling chamber from rings of jet apertures surrounding said milling chamber and spaced along the length thereof wherein the streams of milling fluid from some of said jet apertures enter the tubular milling chamber substantially perpendicular to its longitudinal axis and others make an acute angle to the longitudinal axis of said milling chamber.

The term friable material, as used herein, will be understood to include graphite, mica, clay, gypsum, organic and inorganic pigments and similar pulverizable particulate materials and for purposes of illustration has special reference to a Ti0 pigmentary material.

BACKGROUND OF THE INVENTION There are of course many types of mills for milling friable materials typical of which are roller mills, chaser mills, hammer mills and fluid energy mills, the latter being sometimes referred to as jet mills, micronizers, impact pulverizers and the like. The apparatus of the present invention relates in general to the fluid energy type of mill which utilizes highly turbulent streams of fluid. such as air or steam, to impart violent agitation to a friable material within a milling chamber, whereby the coarse particles are continually thrown into contact with the mill surfaces and in particular with each other with sufficient force to fracture the particles and hence produce a finer material.

All fluid energy mills are subject to severe wear and deterioration both because of the high temperature and pressures at which they operate and also the abrasive action of the friable material being ground. There is a need therefore for a fluid energy mill which is not only highly efficient and of relatively simple, inexpensive construction but also so designed that its worn parts may be readily replaced at relatively low cost and the shortest possible down-time.

SUMMARY OF THE INVENTION The improved fluid energy mill of this invention is characterized by a milling chamber comprising a substantially straight tube having a plurality of jet apertures in the wall thereof through which streams of a milling fluid i.e., air or steam are delivered into the milling chamber at subsonic, sonic or supersonic velocities, the jet apertures being spaced both circumferentially around the tubular milling chamber and longitudinally thereof, said jet apertures being arranged preferably, in the form of two or more rings of apertures around the tubular milling chamber and spaced longitudinally therealong.

The jet apertures are of two distinct types, the one type having its longitudinal axis substantially perpendicular to the longitudinal axis of the milling chamber; and the other type having its longitudinal axis at an acute angle with respect to the longitudinal axis of the milling chamber and oriented in either of two directions i.e. in a direction such that its jet streams will augment the flow of material through the mill or in a direction such that its jet streams will oppose the flow of material through the mill.

The effect of the high velocity streams from the perpendicular jet apertures passing through the tubular milling chamber is to catch up the friable material and subject the material to such violent agitation that the individual particles are fractured or broken up to form a finely divided material; and the effect of the angular sets of high velocity fluid streams is two-fold, namely, in the one case, to augment the flow of material through the milling chamher and in the other case to hold back the flow of material and in particular any unfractured or coarse particles and return them to the turbulent fluid streams of the preceding jets for additional milling, only the finely divided particles moving into the center vortex of the mill from which they are discharged at the exit end thereof.

The jet apertures having their longitudinal axes substantially perpendicular to the longitudinal axis of the milling chamber are sometimes referred to hereinafter as the perpendicular jet apertures; and those having their longitudinal axis at an acute angle to the longitudinal axis of the milling chamber either in a direction opposed to or in the direction of flow of the material through the milling chamber are sometimes referred to as angular jet apertures. Moreover the longitudinal axes of both types of apertures are arranged substantially tangential to a cylindrical surface coaxial with said milling chamber the diameter of which is no greater than and preferably slightly less than the ID. of said chamber.

These rings of perpendicular and angular jet apertures, respectively, may be arranged along the length of the milling chamber in any one of several ways, as for example alternately along the length thereof or as sets of two or more rings each set of rings defining, in effect a segregated grinding zone. v

In as much as the milling chamber is simply a straight tubular member it embodies no moving parts nor any of the complex passages, shields, vanes and the like that characterize the mills of the prior art. Moreover the milling chamber is adapted to be assembled within a mill casing by a simple screwthread connection such that the milling chamber may be readily replaced either because of excessive wear or for the substitution of milling chambers formed of diiferent materials of construction. Thus for some purposes the tubular mill may comprise a plastic material such as nylon which has been used successfully to grind pigmentary TiO using high velocity air jets. For other applications however particularly where high temperatures are incurred, the tubular milling chamber may be formed of a suitable ceramic material, a refractory, stainless steel or other suitable metal alloy.

The mill casing comprises a cylindrical sleeve surrounding the milling chamber and spaced radially therefrom to provide a plenum chamber into which the milling fluid is introduced and from which the milling fluid is injected into the milling chamber via the jet apertures. The mill casing may be designed to form a single plenum chamber extending the length of the milling chamber or it may be divided by one or more transverse partitions so as to form two or more separate plenum chambers along the length of the milling chamber whereby the milling fluid in the separate plenum chamber may be introduced into the milling chambers at diiferent intensities along the length thereof.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematic elevation, partly in section, of the improved fluid energy mill of this invention shown in conjunction with material feed means;

FIG. 2 is an enlarged horizontal sectional view of the improved mill of this invention showing a preferred embodiment of the milling chamber;

FIG. 3 is an enlarged horizontal sectional view of a modification of the milling chamber for use in the mill of FIG. 2;

FIG. 4 is a horizontal sectional View of a further modification of the milling chamber;

FIG. 5 is a transverse section of the tubular milling chamber on line 5-5 of FIG. 2;

FIG. 6 is an enlarged elevational view of the feed deflector and deflector support used at the entrance end of the milling chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the invention is shown in FIGS. 1 and 2 of the drawings in which the fluid energy mill of this invention is indicated generally at 10 with its entrance end 12 connected by a feed pipe 13 to a source of friable material 14 which is adapted to be fed into the entrance end of the mill at relatively high velocity by means of a venturi air jet 15 or its equivalent. The friable material passes through the mill in which it is ground and the finely ground material is discharged from the exit end 16 of the mill into a suitable receiver (not shown) which may be a cyclone separator, electrosatic precipitator, a bag collector or the like.

Turning now to FIG. 2 the fluid energy mill per se is shown as comprising two principal elements namely an inner tubular member 18 which serves as and is sometimes referred to hereinafter as the milling chamber; and an outer tubular member 19 which comprises the mill casing, the latter surrounds the inner tubular member in concentric relationship and is spaced circumferentially therefrom sufiiciently to provide a plenum chamber 20 therearound for a high pressure milling fluid. Other elements of the mill include the two end- plates 21 and 22 between which the concentric inner and outer tubular members are secured in the manner shown by means of a plurality of drawbolts 23. In order to insure fluid tight seals between the ends of the respective tubular members 18 and 19 and the corresponding inner faces of the endplates 21 and 22 suitable gaskets 24 and 24 are used.

A novel feature of the mill is the arrangement by which the milling chamber is removably mounted in the assembled end plates 21 and 22 and outer tubular member 19. As shown especially well in FIG. 2 the exit end 16 of the milling chamber 18 is threaded externally so as to engage the screw threads of a centrally located aperture 25 in the end plate 22. The opposite end or entrance end of the milling chamber merely abuts the adjacent gasket 24 and is securely held in sealing engagement therewith by screwing the inner tubular member 18 tightly thereagainst. Usingthis construction, the milling chamber 18 may be readily removed from the assembled outer tubular member and end-plates by simply unscrewing the milling chamber 18 therefromthus affording a simple, convenient and quick way of replacing a worn milling chamber; or substituting a milling chamber of different materials of construction and/or different arrangements of jet apertures. The jet apertures connect the plenum chamber 20 with the milling chamber and are arranged in circumferentially spaced relationship therearound, for example at intervals of 45 or 60; and are designed to inject high velocity streams of milling fluid into the milling chamber. To this end the apertures may have straight Walls for producing gas streams of subsonic and sonic velocities; or the walls of the jet apertures may be of the converging-diverging type, as characterizes turbine jets, for producing supersonic gas velocities.

In the embodiment of the invention shown in FIG. 2 the jet apertures are shown with straight walls and comprise both perpendicular jets 26 and angular jets 27 the longitudinal axes of the latter extending in a direction opposed to the flow of material therethrough.

Further, as shown in FIG. 5 the longitudinal axes of both types of jet apertures i.e. perpendicular and angular, are arranged tangential to a cylindrical surface coaxial with the milling chamber. The diameter of the said cylindrical surface may be substantially equal to or smaller than the ID. of the milling chamber depending upon the particular angle of tangency desired. Moreover for effective grinding it is expedient to have a plurality of each of these two types of jet apertures; and to arrange a plurality of jet apertures of the same type in the form of a ring of apertures around said milling chamber with successive rings of jet apertures spaced longitudinally along the milling chamber. Also in the embodiment of the invention shown in FIG. 2 two rings of jet apertures of the same type are grouped together to form a milling zone. Thus each of the groups of two rings of perpendicular jet apertures 26 is identified as milling zone A while the group of two rings of angular jet apertures 27 is identified as milling zone B the latter being located between milling zones AA.

While there are thus thre successive milling zones shown in this embodiment of the invention it will be understood that the number of milling zones may be more or less than three and that the sequence of zones may be modified depending upon such factors as the intensity of milling required, the nature of the friable materials, variable fluid pressure for supplying the high velocity jets and the like.

In this connection the invention also contemplates a modification of the mill casing such as indicated by the dotted lines in FIG. 2 wherein one or more transverse partitions 20 are arranged in the mill casing to from two or more separate plenum chambers along the length of the milling chamber such that milling fluids at different intensities may be injected into the successive milling zones along the length of the milling chamber.

Turning now to the function of the perpendicular jet apertures 26 of the milling zones AA these straight bore jet apertures serve to introduce a milling fluid i.e. air or steam as the case may be, at subsonic or sonic velocity from the plenum chamber 20 into the milling chamber where the turbulent streams of fluid subject the friable material to violent agitation such that the large individual particles are broken up into smaller sizes. To these ends the fluid may be introduced into the plenum chamber 20 at a pressure of from 50 to 250 p.s.i.g., the fluid, if air is used, entering the milling chamber at a velocity ranging from 400 to 1130 ft./sec. at 20 C.; and if steam, entering at a velocity ranging from 400 to 1600 ft./sec. at 260 C. Influenced by these jet streams the material moves down the length of the milling chamber, the path of the material being substantially helical, and is brought into milling zone B. The function of the angular jet apertures 27 of the milling zone B is to augment the milling action of zones AA but more importantly the jets of fluid from the apertures 27 pick-up any large unmilled particles and return them against the flow of friable material through the mill to the preceding milling zone A for further milling. The high velocity jets 27 thus serve to increase the retention time of the friable material and particularly the coarse material in the mill until such time as all of the material is reduced to a uniformly fine particle size which drifts towards the center vortex of the mill and is discharged from the exit end thereof.

In the sense that one or more milling zones perform conventional milling and one or more milling zones return the coarse particles by centrifugal classifying action for further milling the successive milling zones may be said to mill and classify the friable material during its passage through the mill.

Concerning the size of the jet apertures and their arrangement in the milling chamber excellent results have been achieved using a milling chamber having an ID. of one inch with jet apertures spaced circumferentially therearound 60 apart to form a ring of jet apertures, each aperture having a diameter ranging from 0.025 inch to 0.035 inch and each ring of apertures being spaced approximately 0.5 inch apart, or equal multiples thereof, along the length of the milling chamber. For those jet apertures arranged at an acute angle to the longitudinal axis of the milling chamber acute angles ranging from 30 C. to 60 C. have been used successfully. The particular selection of jet apertures both as to their diameter and orientation of their longitudinal axes are not critical but are dependent on such factors as the size of the milling chamber, the available fluid pressure, and other considerations within the skill of the operator.

While the present embodiment discloses jet apertures having straight walls for effecting subsonic and sonic velocities the invention also contemplates the use of jet apertures of the converging-diverging type for effecting supersonic velocities. Using air as a milling fluid with jet apertures of the latter type jet velocities of as high as 1640 ft./sec. could be expected at a plenum chamber pressure of 200 p.s.i.g. and temperature of 20 C.; while jet velocities of as high as 2610 ft./sec. could be expected using steam at a plenum chamber pressure of 200 p.s.i.g. and temperature of 260 C.

As mentioned at the outset the friable material is fed by air steam, or the equivalent, into the entrance end of the mill via feed pipe 12. It has been found that milling results are optimum when the incoming friable material is brought into contact with the high velocity jets immediately adjacent the Wall of the chamber and hence the invention embodies deflector-means, indicated at 28, at the entrance end of the milling chamber, for deflecting the friable material against v the inner walls thereof. Details of the deflector-means are shown especially well in FIG. 6 wherein the deflector-means 28 is shown as comprising a top-shaped member supported opposite the entrance and of the milling chamber by pins 29, or the equivalent, which in turn are secured in a centrally apertured ring 30 adapted to be seated in a counter-bore 31 (see FIG. 2) formed at the entrance end of the inner tubular member 18. The leading surface of the deflector 28 is conical and hence as the friable material enters the grinding chamber it strikes the conical surface and is deflected against the inner walls of the chamber.

The preceding description relates in particular to the preferred embodiment of the invention as shown in FIG. 2. It will be understood however that the invention is comprehensive of milling chambers having other ring arrangements of jet apertures. Thus FIG. 3 shows a milling chamber in which single rings of jet apertures 26 of the perpendicular type alternate with single rings of apertures 27 of the angular type the several rings of jet I apertures being spaced substantially equi-distant along said chamber.

A still further modification of the grinding chamber is shown in FIG. 4-. In this modification angular jet apertures 27 are used in conjunction with the perpendicular jet apertures 26 and angular jet apertures 27 hereinabove described. The angular jet apertures 27 have their longitudinal axes disposed at an acute angle to the longitudinal axis of the milling chamber but in the direction of flow of the material therethrough and serve thus to augment the flow of material through the chamber. Moreover as arranged in the milling chamber shown in FIG. 4 the angular jet apertures 27' serve also, in conjunction with the jet apertures 26 and 27, to create a milling zone of maximum turbulence within the chamber. To this end the three types of jet apertures are arranged in sets, the first set comprising two rings of angular jet apertures 27' having their longitudinal axes in the direction of the flow, a second set comprising two rings of jet apertures 26 having their longitudinal axes perpendicular to the direction of flow, and a third set comprising four rings of angular jet apertures 27 the longitudinal axes of which are in a direction to oppose the flow material through the mill. It has been found that with this arrangement the streams of fluid from the angular jets 27 and 27' converge from both sides on the streams of fluid issuing'from the perpendicular jets 26 and create a zone of maximum turbulence within the milling chamber.

The following examples will serve to further illustrate the invention.

EXAMPLE I A tubular fluid energy mill was used having a straight tubular milling chamber such as shown in FIG. 3 substantially 11.0 inches long, an inside diameter of about 1.0 inch and a wall thickness of about 0.25 inch. Starting about 1.75 inches from its entrance end a plurality of jet apertures were drilled through the wall of the tubular milling chamber the apertures being arranged in the form of four separate rings of six jet apertures per ring each aperture spaced circumferentially 60 apart around the tubular chamber with the individual rings of jet apertures spaced 1.5 inches apart along the length thereof. The jet apertures were of two types, the jet apertures in successive rings of apertures alternating in type. Thus the jet aperture 2 6 in the ring of apertures adjacent the entrance end of the milling chamber had their longitudinal axes perpendicular to the longitudinal axis of the chamber and also tangential to a cylinder of substantially 0.75 inch diameter. The diameter of these jet apertures was 0.035 inch. The jet apertures 27 of the next ring of apertures had their longitudinal axes at an acute angle of 45 to the longitudinal axes of the milling chamber and in a direction opposed to the flow of material therethrough, and were tangential to the aforesaid inner circle the diameter of these jet apertures also being 0.035 inch. The third and fourth sets of rings of jet apertures 26 and 27 respectively were similar to the first and second.

The fluid used in this case was air which was introduced into the plenum chamber at a pressure of 83.0 p.s.i.g., and issued from the several jet apertures at a linear velocity of 750 ft./sec.

A friable material in this instance, calcined TiO was air borne into the entrance end of the milling chamber at the rate of 15 gms./min. where it was milled by the turbulent action of the air jets. The retention time of the friable material in the mill was about 0.025 sec.

The milled product was a finely ground Ti0 of extremely uniform particle size.

The effectiveness and unexpected superiority of the tubular fluid energy mill of this invention became apparent when the pigmentary roperties i.e. tinting strength and spectral characteristics of the milled Ti0 were compared, as shown in the table below, with those of a TiO milled by conventional milling devices.

TINTING STRENGTH TEST Tinting strength was determined based on the tinctorial strength test method wherein the pigment is dispersed in an alkyd vehicle i.e. Araplaz 1248-ML-70 (Archer- Daniels, Midland, 700 Investors Bldg. Minneapolis 2, Minn.) on a 2:1 weight ratio using a three roller mill. The resulting paste is then thoroughly mixed with a predispersed black colorant (Dutch Boy 990, National Lead Co., Perth Amboy, NJ.) and an opaque film of the tinted paint is drawn down on a cardboard chart and air dried overnight. A standard pigment is similarly treated. The green, red and X-blue reflectance values of the tinted paint test chart and the standard test chart are determined by a Colormaster Differential Colorimeter manufactured by Manufacturers Engineering and Equipment Corp., Hatboro, Pa. The percent green reflectance of the standard test chart is then subtracted from that of the tinted paint chart and the tinting strength determined from a chart equating Ad (green reflectance) with tinting strength.

SPECTRAL CHARACTERISTIC The spectral characteristics of the pigment in a paint vehicle was determined by mixing the pigment with a soya alkyd vehicle, containing carbon black and forming the mixture into a paste the ratio of pigment to carbon black in the paste being 5.0:0.06. This paste was then spread onto a lacquered sheet and the wet film was immediately tested in a Colormaster Differential Colorimeter manufactured by Manufacturers Engineering and Equipment Corp. Hatboro, Pa. The blue and red reflectance values were obtained and the spectral characteristics of the pigment determined by subtracting the blue reflectance value from the red reflectance value and comparing the difference with the spectral characteristics of a standard pigment.

EXAMPLE II In this case a milling chamber of modified construction was substitutued for the chamber used in Example I "by simply unscrewing the latter from the mill. The modified milling chamber had the same dimensions as the previous chamber but the successive rings of the jet apertures were arranged in segregated sets of two as illustrated in FIG. 2 of the drawing the longitudinal axes of the jet apertures 26 in the first and third groups of rings being substantially perpendicular to the longitudinal axis of the grinding chamber, and the longitudinal axes of the jet apertures 27 of the intermediate sets of rings making an acute angle of 45 with the longitudinal aXis of the chamberand in a direction opposed to the flow of material :therethroughthe axes of all of the jet apertures being tangential to a cylinder of substantially 0.75 inch diameter inside the chamber. The diameter of the jet apertures of each type were the same and equal to about 0.035 inch.

The calcined TiO was fed into the chamber in the manner described in Example I and air was supplied to the plenum chamber at a pressure of 80.0 p.s.i.g. and issued from the jet apertures at a velocity of 670 ft./sec. The retention time of the TiO in the mill was about 0.025 sec.

A comparison of the pigmentary properties of a TiO milled by the milling chamber of FIG. 2 and that milled by conventional mills is also included in the table.

EXAMPLE III For this example a milling chamber was used corresponding to that shown in FIG. 4 wherein the jet apertures were arranged in sets of two rings of angular apertures 27', followed by two rings of perpendicular apertures 26 and four rings of angular apertures 27. The angular apertures 27' and the perpendicular apertures 26 all had diameters of 0.035 inch. The four rings of angular apertures 27 were divided into two rings having jet apertures 0.025 inch in diameter and two rings having jet apertures 0.03 inch in diameter. Compressed air at 80 p.s.i.g. was supplied to the plenum chamber and issued from the jet apertures at a mean velocity of 633.0 ft./sec. The spacing of the rings of apertures longitudinally along the milling chamber was approximately 0.5 inch and the angle of each of the angular jets 27 and 27 was 45 In this instance a Ti calciner discharge was used which had already been milled by conventional milling techniques and then coated with a metal oxide, filtered, washed and dried. This milled and coated Ti0 was fed into the tubular milling chamber in the manner described in Example I. A comparison of the pigmentary properties of the TiO milled by this mill as against a conventional mill is shown in the table below:

EXAMPLES IV-VI To provide a comparison between the effectiveness of the mill of this invention and conventional mills a series of runs were made using both fluid energy mills commonly referred to as micronizers, and chaser or edgeroller mills. In Example IV a two inch air micronizer was used at milling fluid velocities similar to those used in Examples I-IV. In Example V a four inch steam micronizer was used under comparable operating conditions and in Example VI, a chaser or edge-roller mill was used, wherein gms. TiO calcine was milled for 15 minutes and then pulverized. The pigments produced by these conventional mills were then tested for pigmentary properties using the tests hereinabove described and the results are shown in the table below.

TABLE-PIGMENTARY PROPERTIES OF MILLED TiOz TiOz pigmentary properties From the accumulated data shown in the table above it is clear that in each instance wherein the novel tube mill of this invention was used the tinting strength and spectral characteristics of the milled Ti0 pigment were superior to those of a Ti0 pigment milled by conventional milling techniques.

What is claimed is.

1. Fluid energy mill for milling friable materials comprising: a substantially straight tubular milling chamber, and a purality of jet apertures in the wall of said tubular milling chamber for injecting a milling fluid therein, said jet apertures having their longitudinal axes tangential to a cylindrical surface within said chamber coaxial therewith, said jet apertures being constructed and arranged to form a plurality of rings of jet apertures around said tubular milling chamber, said rings of jet apertures being arranged successively along the length of said milling chamber, the jet apertures of at least one ring of apertures being arranged perpendicular to the longitudinal axis of said milling chamber and the jet apertures of at least one other ring of apertures being arranged to make an acute angle to the longitudinal axis of said milling chamber.

2. Fluid energy mill for milling friable materials according to claim 1 wherein rings of perpendicular jet apertures alternate with rings of angular jet apertures.

3. Fluid energy mill for milling friable materials according to claim 2 wherein the jet apertures of at least one ring of angular jet apertures are arranged to inject said milling fluid against the flow of friable material through said milling chamber, and the jet apertures of a second ring of angular jet apertures are arranged to inject said milling fluid in the direction of flow of a friable material through said milling chamber.

4. Fluid energy mill for milling friable materials according to claim 1 wherein a plurality of rings of perpendicular jet apertures are grouped together to form a first milling zone and a plurality of rings of angular jet apertures are grouped together to form a second milling zone, said first and second milling zo-nes being arganged alternately along the length of said milling cham- 5. Fluid energy mill for milling friable materials according to claim 4 wherein the groups of jet apertures are arranged so as to provide a milling zone of perpendicular jet apertures between two milling zones of angular jet apertures the jet apertures of one of said two milling zones of angular jet apertures being arranged to inject said milling fluid against the flow of friable material through said milling chamber and the jet apertures of the second of said two milling zones of angular jet apertures being arranged to inject said milling fluid in the direction of flow of a friable material through said milling chamber.

6. Fluid energy mill for milling friable materials comprising: a substantially straight tubular milling chamber, a purality of jet apertures in the wall of said tubular milling chamber for injecting a milling fluid therein, said jet apertures having their longitudinal axes tangential to a cylindrical surface within said chamber coaxial therewith, said jet apertures being constructed and arranged to form a plurality of rings of jet apertures around said tubular milling chamber, said rings of jet apertures being arranged successively along the length of said milling chamber, the jet apertures of at least one ring of apertures being arranged perpendicular to the longitudinal axis of said milling chamber and the jet apertures of at least one other ring of apertures being arranged to make an acute angle to the longitudinal axis of said milling chamber, and deflector-means constructed and arranged at the entrance end of said milling chamber for deflecting incoming friable materials against the inner wall of said chamber.

7. Fluid energy mill for milling friable materials comprising: a straight tubular milling chamber, a second tubular member comprising a mill casing constructed and arranged to form a plenum chamber surrounding said straight tubular milling chamber, means arranged to introduce high pressure milling fluid into said plenum chamber, a plurality of jet apertures in the wall of said tubular milling chamber constructed and arranged to inject milling fluid from said plenum chamber into said milling chamber as high velocity jet streams, the longitudinal axes of said jet apertures being arranged tangential to a cylinder within said chamber coaxial therewith, said jet apertures being constructed and arranged in circumferentially spaced relationship around said tubular milling chamber and spaced along the length thereof, and deflector means constructed and arranged at the entrance end of said tubular milling chamber to deflect the incoming friaable material against the inner wall thereof.

8. Fluid energy mill for milling friable materials comprising: a straight tubular milling chamber, a second tubular member comprising a mill casing constructed and arranged to form a plenum chamber surrounding said straight tubular milling chamber, means arranged to introduce high pressure milling fluid into said plenum chamber, a plurality of jet apertures in the wall of said tubular milling chamber constructed and arranged to inject milling fluid from said plenum chamber into said milling chamber as high velocity jet streams, the longitudinal axes of said jet apertures being arranged tangential to a cylinder within said chamber coaxial therewith, said jet apertures being arranged to form a plurality of rings of jet apertures around said tubular chamber, said rings of jet apertures being arranged successively along the length of said milling chamber, and deflector-means constructed and arranged at the entranceend of said tubular milling chamber to deflect the incoming friable material against the inner wall thereof.

9. Fluid energy mill for milling friable materials according to claim 8 wherein the jet apertures of at least one ring of apertures are perpendicular to the longitudinal axis of said tubular milling chamber and the jet apertures of at least One other ring of apertures make an acute angle to the longitudinal axis of said milling chamber.

10. Fluid energy mill according to claim 9 wherein rings of perpendicular jet apertures alternate with rings of angular jet apertures.

11. Fluid energy mill according to claim 9 wherein said rings of jet apertures are arranged in groups of two or more, said groups of rings defining segregated milling zones spaced longitudinally along said milling chamber.

12. Fluid energy mill according to claim 11 wherein said mill casing is constructed and arranged to provide a first plenum chamber surrounding the group of jet aperture rings of one milling zone and a second plenum chamber surrounding the group of jet apertures of a second milling zone.

13. Fluid energy mill according to claim 9 wherein a plurality of rings of perpendicular jet apertures are grouped together to form a first milling zone and a plurality of rings of angular jet apertures are grouped together to form a second milling zone said first and second milling zones being arranged alternately along the length of said milling chamber and the jet apertures of one of the milling zones of angular jet apertures being arranged to inject said milling fluid against the flow of friable material through said milling chamber and the jet apertures of another of said milling zones of angular jet apertures being arranged to inject said milling fluid in the direction of flow of a friable material through said milling chamber.

14. Fluid energy mill according to claim 7 wherein said milling chamber is a substantially straight tubular member constructed and arranged to be removably mounted in said mill casing.

15. A process for milling friable materials comprising feeding said friable materials through a substantially straight tubular milling chamber of substantially uniform cross section and injecting a milling fluid into said tubular milling chamber at spaced intervals along the length thereof, said milling fluid being injected into said tubular milling chamber in the form of circumferentially spaced jet streams injected both perpendicularly and at an acute angle, respectively, to the longitudinal axis thereof.

16. vA process for milling friable materials according to claim 15 wherein said jet streams of milling fluids are injected into said tubular milling chamber tangentially to a cylindrical surface within said tubular milling chamber coaxial therewith.

17. A process for milling friable materials according to claim 16 wherein said angular jet streams are injected into said milling chamber both in the direction of flow of said friable material therethrough and against the flow of friable material therethrough, respectively.

References Cited UNITED STATES PATENTS 2,261,560 11/1941 Pellas et al.

2,474,314 6/1949 Koehne 241-39 X 3,184,168 5/1965 Feld et al. 241-39 3,315,900 4/1967 Twist et al. 24139 JAMES M. MEISTER, Primary Examiner U.S. Cl. X.R. 24118, 39, 42

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