US2105766A - Fine grinding mill - Google Patents

Description

' Jan. 18, E. v. FRANCIS 2,105,766

FINE GRINDING MILL Filed Aug. 6, 1934 4 Sheets-Sheet 1 Jan. 18, 1938. E. v. FRANCIS FINE GRINDING MILL Filed Aug. 6, 1934 4 Sheets-Sheet 2 Jan. 18, 1938. E. v. FRANCIS FINE GRINDING MILL Filed Au 6, 19:54

4 Sheets-Sheet 4 Patented Jan. 18, 1938 UNITED STATES FINE GRINDING MILL Earle V. Francis, Columbus, Ohio, assignor to The Jeffrey Manufacturing Company, a corporation of Ohio Application August 9, 1934, Serial No. 739,118

8 Claims.

- This invention relates to a fine grinding or pulverizing mill assembly, particularly of the impact type which is designed to produce comminuted particles of coal as used in powdered or pulverized fuel combustion furnaces.

An object of the invention is to produce a compact and unitary structure including the elements necessary to produce powdered fuel.

Another object of the invention is to provide a fine grinding mill of restricted over-all dimensions but which provides adequate grinding of the material to reduce it to a finely divided or comminuted state.

Still another object of the invention is to provide a fine grinding mill of simple, rugged and compact design, which has separately removable wearing pieces which may be individually or collectively renewed in an easy manner.

I Other objects of the invention will appear here- 30 inafter, the novel features and combinations being set forth in the appended claims.

In the accompanying drawings,

Fig. 1 is an elevational view of my invention showing a typical application thereof as applied 2,; to a boiler using powdered or pulverized fuel, parts being shown in, section for clearness; 1

Fig. 2 is a plan view of my invention;

Fig. 3 is an end view of my invention looking in the direction of the arrows GG of Fig. 2;

Fig. 4 is an end view of my invention looking in the direction of the arrows H--H of Fig.2;

Fig. 5 is a sectional view of my invention taken on the line F'F of Fig. 2, certain parts being shown in elevation for clearness;

Fig. 6 is a sectional view taken along the line CC of Fig. 5;

Fig. 7 is a sectional view taken along the line A-A of Fig. 5, looking in the direction indicated by the arrows, certain parts being removed;

Fig. 8 is a sectional view taken along the line 3-3 of Fig. 5, looking in the direction indicated by the arrows, certain parts being removed;

Fig. 9 is an end view of the mill rotor of my invention at the coal entrance end thereof;

Fig. 10 is a section of the mill rotor on the line D-D of Fig. 9, the shaft being shown in elevation for clearness;

Fig. 11 is a plan view of a wearing shoe or seg-- ment of the mill rotor;

Fig. 12 is a plan view of a modified form of wearing shoe or segment of the mill rotor; and

Fig. 13 is an elevation of a wearing shoe or segment of the mill rotor and may illustrate either the type of Fig. 11 or the type of Fig. 12.

.Referring to Fig. 1 of the drawings, there is illustrated a powdered or pulverized fuel boiler unit and-the auxiliary equipment for supplying powdered fuel thereto, including my invention. The fuel to be powdered is fed by any desired 60 means to a hopper A which directs it to a m c grinding mill or pulverizer indicated generally at B. After the fuel is properly pulverized by the mill B and reduced to a finely divided or comminuted state it is carried by the primary air introduced into the mill- B by blower C over the conduit D to a mixing chamber E. Secondary air is supplied by the blower F to the mixing chamber E over conduit G whereby the proper mixture of air and fuel may be provided for combustion in the boiler combustion chamber I-I.

Any well known type of ignition system, as gen- At the left hand end, as viewed in Figs. 1, 2

and 5, shaft is provided with a coupling device 25, illustrated in Fig. .1, to which a driving motor 21, as an electric motor, may be connected. As illustrated in Fig. 1, the driving motor 21 and the mill assembly are mounted on a common foundation 28, the axis of the motor be ing insubstantial alignment with the axis of the mill assembly. That portion of the shaft 25 projecting beyond the bearing 24, to the right as seen in Figs. 1, 2 and 5, provides a stub shaft for the secondary air fan indicated generally by F. Said secondary air fan may be of the centrifugal type and, as illustrated, is provided with the rotor blades 29 carried by hub 30 keyed on said shaft 25. A casing 3| for said secondary air fan F is provided with an air outlet port 32 and a variable air inlet 33, of well known construction. Said casing 3i is preferably detachably connected to the housing of mill B by brackets 34 and 35 whereby fans of different sizes may be employed.

This removable construction of said fanF also provides for separate construction of the fan unit and allows easy assembly of the parts, also providing for easy disassembly of the mill B for repairs or renewal of any of the parts thereof. Fan rotor 29 is detachably secured to the shaft 25 to provide for its removal for replacement of a different size rotor or for making any necessary. repairs.

At the left hand end of the mill assembly, as viewed in Figs. 1, 2 and 5, is the primary air and fuel blower, preferably of the centrifugal type, designated generally by C. This blower C is positioned adjacent the bearing 23 and between the two bearings 23 and 2!. It comprises a circumferential casing 36 mounted by feet 31, best seen in F g. l, on lateral projections 33 of standard 2|, by bolts and nuts. Said casing 36 is provided with an outlet port 39 for discharging the fuel and primary air received from the mill B. The outer face of housing 36 comprises a separate plate 40 attached to the housing 36 by cap screws. The inner face of said housing providesan inlet opening 4| in direct communication with the outlet opening of mill B. A fan blade 42 is carried by shaft 25 and keyed thereto in the proper relationto housing 36. The function of blower C is to provide a flow of air through the mill B which'tends to draw the particles of fuel through said mill whereby they will be subjected to the disintegrating action thereof and to force the resulting comminuted particles, which are suspended in the air, through the outlet port 39 and through any conduits leading therefrom to a position where it may be ignited.

The mill, designated generally at B, is provided with a two-part outer housing 426 including a lower part 43 formed integral with the standards 2| and 22 and an upper part '44. Said outer housing 420 is split on a plane passing through the axis of the shaft 25, preferably horizontal with the base 26. The upper housing 44 is provided with a lifting ring 45 whereby it may belifted from the rest of the mill and provide ready access to the inner parts thereof. Removably attached to the mill housing at the entrance side thereof is a hopper chute 46 having entrance 41 adapted to guide fuel from the hopper A to the mill B. Said chutev 46 is removably attached to both the upper housing 44 and the lower housing 43 by bolts and nuts and the bottom wall thereof is preferably in the plane which determines the bottom of the upper housing. 44. The lower part 48 of chute 46 and a cooperating part 49 of the lower housing 43 provide a guiding entrance for the fuel from hopper A to the entrance opening 56 of mill B.

The lower housing 43 provides at 51 a tramp bin for the reception of foreign matter, as scrap iron, which may enter the mill. Said tramp bin 5| is provided with a removable door 52 whereby the accumulated tramp material may be removed.

Within the housing 426 of the mill B there is provided a series of pulverizing or impact elements defining a pulverizing zone, which are effective to reduce the coal to a powdered or comminuted state. These elements include a series of semi-cylindrical stationary removable liner plates rigidly molmted in the housing 420, some of which are provided with projecting disintegrating fingers or lugs, and a series of sectional rotating plates, carried on a rotor cage mounted on the shaft 25, which plates carry fingers or lugs moving in overlapping relation with the lugs on said stationary plates and cooperating therewith to produce the above mentioned result. The series of semi-cylindrical stationary plates are preferably severed along the plane which defines the limits of the upper housing 44 and the lower housing 43. By this construction easy removal of any one or more of said sections may be accomplished upon the removal of upper housing 44. As best seen in Fig. 5, said sections, as viewed from right to left in this figure, are provided with a ring-shaped liner section 55 and have a circumferential deflecting flange 56, the purpose of which will be explained hereinafter.

Adjacent said section 55, is a ring-shaped section 51, provided with a series of radial lugs or breaking fingers 58, best seen in Fig. 6. The section 51 is of unequal thickness at its opposite edges. The purpose of this specific construction will be explained hereinafter.

Adjacent said section 51, is another ringshaped section 59, provided with a series of radial lugs 66. The section 59 is of uniform thickness. The lugs 58 and 60 may be either in angular alignment, as illustrated in Fig. 5, or they may be angularly displaced. The number of lugs 58 and 60 may be any number which produce the desired fineness of material and, if desired, sections 51 and 59 may carry a different number of lugs. As illustrated in the drawings, eight lugs are provided for each of said sections 51 and 59.

Adjacent the section 59 is another ring-shaped section 6| which comprises a ring devoid of any lugs and which presents a substantially cylindrical inner surface as best seen in Fig. '7. This ring has a radial thickness greater than that of ring 59 for a purpose hereinafter set forth.

Adjacent the section 6| is the final section 62 of the pulverizing zone. This section has a circumierential ring 63 and an integral disc section 64 forming an end plate for the pulverizing zone. The end plate 64 is provided with a series of projectirg lugs 65, the axis of which is parallel with the axis of the mill. The lugs may be. of any desired number and are eight in number in the illustration given. The inner peripheral edge of the end plate 64 provides an axial circular outlet 64 of somewhat restricted area and has a tapered edge 66 for a purpose hereinafter set forth. The inner surface provided by section 62 is devoid of any sharp edges except for such as may be presented by the lugs 65.

Mounted for rotation on the shaft 25 are a series of elements which cooperate with the above mentioned stationary elements to provide a pulverizing zone and to reduce the coal entering'the inlet'50 to a powdered or comminuted state, which coal when so reduced is removed through the outlet opening 64' by the blower C. Said elements comprise a series of removable parts indicated generally by the character R, Figs. 9 and 10. V

Mounted upon the shaft 25 and keyed thereto is a cylindrical cage 69. Said cage carries at its right hand end, as viewed in Figs. 5 and 10, a series of initial coal breaking lugs H6 which are adjacent the coal inlet opening 56. These lugs H9 are of heavy construction suitable for producing the initial breaking of the coal as fed to the mill B. Any desired number may be employed, and four have been illustrated in the drawings, as best seen in Fig. 9.

Removably mounted on the outer periphery of cage 69 are a plurality of arcuate wearing shoes 16. Said shoes are preferably formed with a base constituting a quarter of a cylinder, as illustrated by Figs. 6 and 13. The base of each shoe is provided with axially inwardly extending legs 'H with projecting locking feet 12. Two of said legs H with feet 12 are adapted to be held in end to end relation by a cooperating recess in the cage 69. The external periphery of each of said shoes 19 is provided with a plurality of axially staggered lugs 13 and 14. The lugs 13 are angularly spaced and form a group around a circumference of the rotor adapted to rotate in substantially the same space. Likewise, the lugs 14 are angularly spaced and form a group around a circumference of the rotor adapted to rotate in substantially the same space which is longitudinally spaced with respect to the first mentioned space. As illustrated in the drawings, each shoe 10 carries two of each of the groups of lugs 13 and 14,, making a total of eight around a. circumference of the rotor. It is obvious that any other desired number of either group may be employed, and each group need not have the same number. As illustrated in Fig. 11 of the drawings, the opposite faces of each of the lugs 13 and 14 are parallel to a plane perpendicular to their axis of rotation. In addition, the longitudinal faces of lugs 14 are preferably contiguous with the longitudinal faces of lugs 13 though, of course, longitudinally displaced therefrom. If desired, either one or bothof said groups of lugs I3 and I4 may have a face or faces set at an angle to a plane perpendicular to the axis of rotation thereof. In Fig. 12 I have illustrated the lugs 13' and 14 with both of their facesat an angle to a plane perpendicular to the axis of rotation. The setting of said lugs with one or both faces at an angle to a plane perpendicular to the axis of rotation provides a fan action and the setting thereof is so related to the direction of rotation that the fan action preferably tends to oppose the action of the blower C. By this expedient the coal particles undergoing disintegration are retarded in their movement through the pulverizing zone, whereby more complete comminution is accomplished. If it is desired to encourage the travel of the coal particles through the pulverizing zone the pitch of the lugs 13' and 14 may be reversed.

Carried on the cage 69 at the left hand end thereof as seen in Figs. 5 and 10, are a series of four plates 88. The plates 80 are removably attached to cage 69, as by cap screws. Said plates also have a peripheral flange with a tapered edge 8i which cooperates with tapered edges on the base of shoes 10 to wedge them to the periphery of said cage 69, which is also provided with a. cooperating tapered edged flange at its right hand periphery. The outer peripheral edge of the plates 80 is substantially cylindrical. Each plate 60 carries adjacent its outer periphery and on' the face thereof, one or more longitudinally projecting lugs or fingers 82. As illustrated in the drawings, two of such lugs are carried by each of the plates 80, though any desired'number may be employed.

Also carried on the shaft 25, and adjacent the outlet opening 64' of the mill is a rejector, the purpose of which is to scoop from the coal particles coming from the pulverizing zone any large particles, and throw them back into the pulverizing zone. This rejector may comprise a pair of radially grooved arms 83 carried by an appropriate hub on shaft 25. The outer extremity of the arms 83 is bent to conform to the tapered edge 66 and is in close proximity therewith, thereby directing the returned coal particles to the tips of the lugs and also preventing the escaping of any large particles through the area between the outlet edges 66 and said arms. The open sides of the'grooved arms 83 are on the leading edges or faces thereof. 7

The pulverizing elements" comprising the rotary elements R are rigidly but removably carlied on the shaft 25 in the following manner. Cage 69 is keyed to the shaft 25 and carried thereby. on suitable hubs. The removable shoes 18 are placed on the rotor cage 69 by placing one end of thelegs II and feet 12 in the cooperating recess of said cage 69 and sliding it axially with respect thereto. I Each of said shoes Ill may be thus placed on the cage 69 until they are all in place. After all of said shoes 10 are in place on cage 69, the ring sections 88 are placed on said cage 69 and rigidly attached thereto by appropriate cap screws. Upon the tightening home of said cap screws, a supplemental clamping action for retaining the sectional shoes 10 is accomplished by the cooperating tapered surfaces of said cage 69, shoes 10 and plates 88, of which surface 8l of a plate 80 is illustrative. This retaining action for the shoes 10 is, of course, only supplemental to the main retaining action aiforded by the legs II and feet 12 which look in the cooperating recesses in the cage 69 to prevent dis placement of said shoes Ill due to centrifugal forces.

I The mill may be assembled by first inserting the lower ring sections 55, 51, 59, 6! and 63 in place in lower housing 43' and clamping home the studs 92, which are positioned adjacent one end of the casing 420 with their heads external to the casing. These studs may be restricted to the upper housing 44, but preferably extend to both the upper and lower housings. With the rotor R assembled on shaft 25 and fan rotor 42 and rejector 83 rigidly attached thereto, fan casing 36, plate '40 and bearings 23 and 24 are placed loosely on shaft 25 and rotor R is lowered into position in said lower housing 43 while fan casing 36 and bearings 23 and 24 are moved to position. Bearings 23 and 24 are then attached to the brackets 2| and 22 respectively, the casing of fan C is attached to the projections 38, and plate 40 is attached to casing 36 of said fan C. The upper ring sections 55, 51, 59, 6| and 63 may then be stacked in position and upper housing 44 lowered in place over said ring sections and rigidly bolted to lower housing 43. The studs 92 of the upper housing 44 are then screwed down to rigidly clamp the upper ring sections therein.

The remaining parts, comprising chute 46 and'fan F may then be attached in an obvious manner.

The use of studs 92 is particularly advantageous in connection with the upper housing 44 because by maintaining said studs in a clamping position it is possible to remove all of the upper ring sections at once by the simple expedient of lifting the upper housing 44 by ring 45. If desired, said upper housing 44 may m removed while retaining said upper ring sections in position, by loosening the studs 92. Thereafter, any upper ring section may be individually removed, as desired.

When all of the parts of the mill are in assembled relation, there is provided a fine grinding or pulverizing mill of the impact type with a pulverizing zone from substantially the inlet to the outlet thereof which presents both a horizontal and a vertical pulverizing zone.

Upon entering the inlet opening 50 of the mill through guide chute 46, the coal is first met by the revolving lugs H0 which impact the coal particles and by centrifugal action throw them tangentially against the cylindrical liner section 55, thereby producing the initial crushing of the coal due both to the impact of said lugs I I0 therewith and the consequent, impacting of said particles with the liner section 55. The particles striking the liner section 55 tend to rebound and be again struck by the lugs H8, which action will be repeated as the coal particles move around the axle 25 in a zig-zag path being first struck by lugs H0 and then rebounding from liner 55 to be again struck by said lugs until the coal particles are removed from this preliminary breaking section of the mill. yncrushable heavy particles, particularly of foreign matter, as scrap iron, will fall tothe bottom of the casing 43 and ultimately accumulate in bin The coal particles are removed from this section of the mill and tend to move through the mill due to the suction created by fan C. In addition, the lugs H0 have a centrifugal fan action which will tend to move the coal particles into the central pulverizing zone. This flow of air will only be effective to draw the fine particles of coal into the pulverizing zone, leaving the larger particles to the above described action of lugs III! to be broken into particles of sufliciently small sizes to be carried therein by the air. It is to be noted that the flange 56 of section in cooperation with the fast moving series of lugs 13, which in rotation assimilate, to some extent, a continuous annular ring, provide a restricted annular orifice through which most of the coal particles must pass to enter the central pulverizing zone. In addition, said flange 56, by virtue of the beveled wall 56, directs any larger particles of material which are drawn by the air toward the pulverizing zone into the path of lugs' I3 to be struck thereby and receive a disintegrating action. The annular enlarged chamber within which rotate the lugs 13 formed by the flange 56 and the beveled surface 51' constitute an annular expansion chamber in which the coal particle laden air will form eddy currents, thus retaining the coal particles within this chamber for an appreciable length of time and preventing stream line passing of the air and coal particles through the central pulverizing zone, with a consequent lack of proper pulverizing. Within this chamber, the revolving lugs will strike any relatively large particles of coal and throw them against the opposite breaking surface. In addition, said lugs, due more to fan action, will cause relative movement of the fine particles which,.

by attrition, will be further reduced in size. As the fine particles of material tend to move toward the outlet ll of the mill under the influence of the air currents, they are carried into another chamber of reduced size within which rotate the lugs 14. vides for the aforementioned enlarged chamber within which said lugs 13 rotate but also operates to direct the larger particles of coal in this chamber into the path of the revolving lugs 14 where they are reduced by impact and driven against the liner for further disintegration. Soine of the particles struck by lugs I3 and 14, particularly the smaller ones, will not only have a tangential movement but, due to the influence of the air in said mill will move toward stationary lugs 58 and 60 striking said lugs. The ring 6|, in cooperation with the sections 80, provides another annular orifice through which the particles of material must pass before they can reach the outlet opening 64'. This orifice is more restrictive than the orifice formed by flange 56 and lugs 13 and very effectively prevents the passage of any large coal particles and restricts the passage therethrough to very finely divided or comminuted particles. Within the central pulverizing zone between the orifice formed by flange 56 and the lugs 13 and the orifice formed by ring BI and the plates 80, there is a continual action, first of the larger particles being struck by a rotating lug 18 or' 14, which performs a disintegrating action, and a resulting impacting of the particles against a lug 58 or 80 or the liner wall of said zone, all the while air in moving therethrough tends to carry the particles with it through the latter orifice. current movement of the air in said zone provides further reduction of the finer particles, by attri- The beveled surfacei'l' not only pro- In addition, the eddy tion. when the rotary lugs 13' and ll, of Fig.

12, are employed, the movement of the coal particles through this zone is still further retarded because the faces thereof perpendicular to the axis of rotation of the rotor R have a fan action which, as above set forth, is opposed to the fan action of fan C. That is, the lugs 13, 14' acting alone tend to move the air from the outlet of said mill toward the inlet, thus reducing the effect of fan C in this zone. By reversing the pitch angle of said lugs 13' and H, they may be made to aid the fan C and to encourage the movement of air and coal particles through this pulverizing zone. The inward projection of ring 6| isalso effective to break up any stream line action of the air through the mill and tends to create eddy currents on both sides thereof with the consequent attrition of small particles and retarded movement of coal particles through the central pulverizing zone.

The coal particles upon being drawn through the mentioned flnal orifice from the central pulverizing zone are subjected to a final pulverizing action by the revolving lugs 82, in cooperation with the stationary lugs and wall surfaces of the final pulverizing zone. The comminuted particles upon reaching the outlet 84' are for the most part reduced to a fine powder, suspending in air, and freely pass to the blower C from which they are ejected, in suspension, at the outlet thereof. Any large particles which issue from the final pulverizing zone will be intercepted by the rejector arms 83 and returned to the final pulverizing zone for additional treatment. It is to be noted that in this final pulverizing zone the centrifugal fan action of the lugs 82 and the centrifugal fan action of the ejector 83 directly opposes the action of fan C with respect to the movement of air and coal particles. At the inlet 50, the lugs H0 aid the action of fan C while at the outlet ll the moving parts oppose its action. Due to the angle at which the tips of ejector 83 are bent, there will be an actual movement of air radially outward along the tips of lugs 65 and a pronounced eddy of air current will be produced in the area within which lugs 82 rotate. Adjacent the base of lugs 65, the air will move radially inward carrying with it the very finely divided or comminuted particles of coal which pass to the blower C.

It is to be noted that the pulverizing zones, combined horizontal and vertical, provide a pulverizing path of suiiicient length to properly comminute the material, yet restricts the overall diameter of the mill and also restricts the axial length thereof. A compact mill unit is thereby provided.

A simple, rugged and compact mill assembly is also provided by employing a single shaft for the three units comprising the mill B, primary air and fuel blower C and secondary blower 1'', which shaft is mounted upon two spaced bearings 23 and 24. The entire assembly is thus driven from a single prime mover, as a single electric motor 21.

It is preferred that all of the surfaces of the mill which are subject to wear due to the pul- 4 verizing action be properly hardened to prolong their natural life.

Obviously those skilled in the art may make various changes in the details and arrangement of parts without departing from the spirit and scope of the invention as defined by the claims hereto appended, and I therefore wish not to be ing fingers and said end wall being provided with,

aroavcc restricted to the precise construction herein disclosed.

Having thus described and shown an embodiment of my invention, what I desire to secure by Letters Patent of the United States is:

1. In a pulverizing mill, the combination with a cylindrical housing having an inlet at one end and an outlet at the other end and having an inner peripheral wall presenting breaking surfaces including inwardly projecting radial lugs, and an outlet end wall presenting breaking surfaces including longitudinally projecting lugs, of a rotor comprising a cylindrical cage carried within said housing having preliminary breaking lugs adjacent the inlet of said housing and outwardly projecting radial lugs in overlapping relation with the inwardly projecting radial lugs of said inner peripheral wall, and having'longitudinally projecting lugs in overlapping relation with the longitudinally projecting lugs of said end wall.

2. In a coal pulverizing mill, the combination with a cylindrical housing having a pair of endwalls with an inlet in one end wall and an outlet in the other end wall, an inner peripheral wall and the outlet wall of which are. provided with projecting lugs presenting breaking surfaces, of a rotor comprising-a, cylindrical cage carried within said housing having a diameter greater than the diameter of said outlet, whereby said inner casing walls and said rotor present a pulverizing zone extending both longitudinally and radially, and projecting lugs carried by said rotor in overlapping relation with said first mentioned projecting lugs.

3. In a coal pulverizing -mill, the combination with a cylindrical housing having an inner peripheral wall and an end wall adjacent the outlet end of said housing with a substantially circular central outlet therein, said inner peripheral wall being provided with radially projecting breaklongitudinally projecting breaking fingers, of a rotor comprising a cylindrical cage carried within said casing in axial alignment with said circular outlet and of a diameter greater than the diameter of said outlet and provided with radially projecting breaking fingers on its outer peripheral wall and longitudinally projecting breaking fingers on one end wall, said radial breaking fingers of said rotor and housing and said longitudinal breaking fingers thereof being in overlapping relation, said housing peripheral wall and said rotor outer wall cooperating to provide a longitudinal pulverizing zone and said housing and rotor end walls cooperating to provide a radial pulverizing zone.

4. In a coal pulverizing mill, the combination with a cylindrical housing having an inner peripheral wall and an outlet end wall with a substantially circular central outlet therein, said inner peripheral wall being provided with radially projecting breaker fingers and said end wall being provided with longitudinally projecting breaking fingers, of a rotor comprising a cylindrical cage carried within said casing in axial alignment with said circular outlet and of a diameter greater than the diameter of said outlet and provided with radially projecting breaking fingers on its outer peripheral wall and longitudinally projecting breaking fingers on one end wall, said radial breaking fingers of said rotor and housing and said longitudinal breaking fingers thereof being respectively in overlapping rehousing and said rotor to provide an orifice be-' tween said two pulverizing zones.

5. In a rotor assembly for a pulverizing mill, the combination with a cylindrical cage having longitudinally extending locking channels, of a plurality of segmental wearing shoes each form- .ing a segment of a cylinder and having an inwardly extending locking foot adjacent each longitudinal edge, adjacent pairs of feet of adjacent shoes being adapted to fit into one of said locking channels, whereby said shoes are locked to said cage and cover the cylindrical face thereof.

6. In a pulverizing mill, the combination with a cylindrical housing having an inlet at one end and an outlet at the other end and having an inner peripheral wall presenting breaking surfaces, of a rotor carried within said housinghaving outwardly projecting lugs near the inlet end of said mill and a radial flange near the outlet end thereof, a pair of inner peripheral flanges carried by said inner wall one 'of which is in a plane passing through said radial flange and the other of which is adjacent said lugs, said peripheral flanges cooperating with said rotor lugs and radial flange to provide a pulverizing zone.

7. In a pulverizing mill, the combination with a cylindrical housing having an inlet at one end and an outlet at the other end and having an innerperipheral wall presenting breaking surfaces, of a rotor carried within said housing having outwardly projecting lugs near the inlet end of said mill and a radial flange near the outlet end thereof, a pair of inner peripheral flanges carried by said inner wall' one of which is in a plane passing through said radial flange and the other of which is adjacent said lugs, said latter flange being slightly spaced from said lugs toward sail inlet and having a taperingsurface on the side thereof toward said inlet whereby particles of material will be deflected thereby into the path of movement of said lugs, said peripheral flanges cooperating with said rotor lugs and said radial flange to provide a pulverizing zone.

8. In a coal pulverizing mill, the combination with a cylindrical housing having an inner pe-' gitudinally projecting breaker fingers on one end wall, said radial breaker lugs of said rotor and housing and said longitudinal breaker lugs thereof being respectively in overlapping relation, said housing peripheral wall and said rotor outer wall cooperating to provide a longitudinally extending pulverizing zone and the housing and rotor end walls cooperating to provide a radial pulverizing zone, and a communicating restricting orifice formed between said two pulverizing zones by cooperating parts of said housing and said rotor.

EARIE V. FRANCIS.

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