US1598933A

US1598933A - Pulverizing mill

Info

Publication number: US1598933A
Application number: US415808A
Authority: US
Inventors: Read Alexander Mahaffey
Original assignee: Individual
Current assignee: Individual
Priority date: 1919-12-31
Filing date: 1920-10-09
Publication date: 1926-09-07
Anticipated expiration: 1943-09-07

Description

Sept. 7 1926.

A. M. READ PULVERIZING MILL original Filed DGO 51' .1919

JNVENTOR fxmh/M Sw N ATTORNEY Patented Sept. 7, 1926.

UNITED STATES l Y 1,598,933 -PATENT OFFICE.

ALEXANDER MAHAIFEY BEAD, F ooLirMBUs, OHIO.

PULvEnIzING MILL. A

Original application led December 3l, 1919, Serial No. 348,506. Divided and this application nled. October 9, 1920, Serial Fo. 415,808. Renewed November l, 1924.

The present invention relates to certain new and useful improvements in pulverizing mills of the class in which each consists of a rotatable barrel wherein the material to be pulverized may be tumbled about with freely movable crushing bodies and be pulverized by contact therewith.

In my co-pending application, Serial No. 348,506, filed December 31st, 1919, of which this application is a division, I have disclosed a pulverizing mill comprising a barrel adapted to revolve about its longitudinal axis which is so disposed to the horizontal that the included material will tend to travel on the lower side of said barrel from the receiving to the discharging end of the mill, and in which the barrel is divided into a series of grinding compartments whereby the material is so classified that the coarser fragments are retained in the forward compartment while the iiner particles are passed progressively through thesucceeding compartments towards the delivery end of the vmachine.

The especial object of this invention is to provide a machine of the class described wherein the barrel is divided into a series of pulverizing chambers by partition screens of improved construction which effectively retain the oversize material in the respective pulverizing chambers without undue 0bstruction to the longitudinal flow of the line material through the mill.

The means by which I attain this object is fully set forth in the following specification and illustrated in the accompanying Idrawing which is a longitudinal vertical section of the preferred embodiment of my inventiOn.

As shown in the drawing the numeral l indicates a barrel adapted to revolve about its longitudinal axis which is so disposed to the `horizontal that material within the barrel will tend to travel on the sides of the barrel-from the receiving to the delivery end of the mill as the barrel revolves. To the barrel 1 is attached the bearing rings 2 and 3 which bear upon the rollers 4 and 5 to support the barrel for rotation. The rollers 4: and 5 are mounted in suitable journal bea-rings G and 7 which are supported upon the foundation of the mill. To the barrel 1 is attached a ring gear 8 which is engaged by a pinion 9. The pinion 9 is mounted upon apower shaft from which power is derived to revolve the barrel. The upper end of .the barrel 1 is closed by a plate 10 to which is secured a cylindrical extension 11. The extension 11 is journaled in a pillow block 12 supported upon the foundation casting 13. The pillow block'12 is provided with the customary removable cap 14. in which is formed a lubricant receptacle 15. 16 is a ball bearing interposed between the outer end of the pillow block 12 and the ange 17 of the cylindrical extension 11 to prevent longitudinal movement of the bar? rel. This cylindrical extension 11 and the plate 10 are pierced by al central bore through which extends a cylindrical trough 18 formed at the lower end of the feed hopper 19. Positioned within the cylindrical trough 18 is a screw conveyor 2O to the eX- tended shaft of which is attached a suitable pulley 21 adapted to be connected with any convenient source of power vto rotate the screw conveyor 20 and thereby transfer material from the feed hopper 19 to the interior of thebarrel 1.

The lower end of the barrel 1 is closed by a transverse wall 22 having spherical curva ture with its center of curvature located in the axis of rotation of the barrel at the forward side of said wall. The wall 22 is pierced by a plurality of screening apertures 23 adapted to permit the escape of the fully pulverized material from the interior of the mill while retaining the over size material for further grinding. The size, form and arrangement of the screening apertures 23 are subject to wide variation to suit the requirements of materials of dierent character and the desired ineness of the product. These apertures 23 preferably expand outwardly to prevent the lodgment therein of fragments of material and the consequent choking of the screen.

As the fineness of grinding is directly related to the duration of time the fragments of material are retained within the mill, the aXis of the barrel l is inclined to such an angle with the horizontal that the rate of flow of the material longitudinally of the barrel will carry said material to the discharge end atthe precise moment it is pulverized to the desired degree of iineness. Although I prefer to use a cylindrical barrel with its axis suitably inclined to the horizontal, the form of the barrel may be subject to wide variation without departure from the spirit of my invention. Should the form of the barrel 1 be conical instead of cylindrical 'as shown, the inclination of the axis of `rotation must'be so adjusted as to produce the desired rate of longitudinal flow of material within the barrel. Any increase or decrease of the taper of the barrel would require an adjustment of the inclination of the axis of rotation moreor less closely approaching the horizontal, and if the diameter of the discharge end of the barrel be sutliciently increased it might be necessary to incline the axis of rotation upwardly to prevent too rapid movement( of material through the mill.

The friction of material against the sides of the barrel cause the lower part of the mass to'move upwardly with the ascending side of the barrel while the upper portion of the mass slides downward, maintaining a continuous orbital movement of the fragments of'which the mass is composed, and the friction due to this movement is an important element in producing the grinding action of the mill. The grinding balls, being of greater specific gravity than the fragments of the material which is being pulvel-ized, gravitate toward the lower part of the mass and become buried beneath the lighter material. These balls are carried upward with the side of the barrel to an elevation depending upon the angle of repose which is characteristic of the material under treatment, and to the centrifugal force due to the velocity of rotation. A t the point of maximum elevation the material falls away from the side of the barrel and the grinding balls roll upon the surface of the mass. striking fragments of material lving upon the lower side of the barrel to break them by their percussive action, thereby materially assisting in pulverizing the material.

Vhen a mass composed of freely movable fragments of various size but of the same specific gravity is agitated. the finer particles tend to slip through the interstices between the larger fragments, and the larger fragments tend to tioat to the surface. resulting in a more or less complete stratification of the mass relative to the size of its component fragments. Due to this tendencv to stratification. andthe inclination of the lower side of the barrel. the finer particles of material sift to the bottom of the mass and travel longitndinalh7 of the mill tending to accumulate against the surface of the screen. Owing to the slippage of the material against the surfaces of the mill this accumulation of tine, material slides across the screening apertures as the mass is carried upwardly and the smaller fragments are forced through these apertures bv the weight of material ahove them. From the point of maximum elevation the material rolls downwardly. striking the surface of the screen along lines approximately normal thereto, and small fragments are carried through the screening apertures without change of direction. At the same time the larger and heavier fragments, together with the grindingballs, strike upon the surface of the lower part of the screen producing vibration therein which prevents the lodgment of material in the screening apertures.

As the larger fragments of material can only be broken by Contact with relatively large and heavy grinding bodies, and the most efficient reduction of the liner particles is accomplished by a large number of relatively small grinding bodies, and as the size of the component fragments of the material within the mill is progressively reduced as it travels from the receiving towards the discharge end, it is apparent that a corresponding classification of the grinding bodies is desirable. To accomplish such classification I have divided the barrel 1 into a series of grinding compartments A, B, C and D by the

transverse screens

24, 25 and 26 which are similar to the screen 22 but are' respectively provided with apertures of progressively decreasing dimensions, the screens nearest the receiving end of the mill having the largest apertures. By this arrangement of screens the material in the successive compartments is classified relative to the size of the component fragment, and each grinding compartment may be provided with grinding bodies of a size appropriate to the most ethcient grinding of the material in said compartment.

I am aware that grinding mills have been proposed in which the interior of the barrel is divided into a series of pulverizing chambers by transverse lat screening partitions. Screens of this character have proven to be extremely inefficient because the orbital path ofthe fragments of materia-l is so nearly parallel .with the surface of the screen that the line material on the forward side of the screen is carried past the screening apertures and the pressure of material against the rearward side of such a screen obstructs the passage of material therethrough. By the use of screening partitions of spherical curvature, such as are here illustrated, there is produced a more etlicient screening action clue to the inclination of the active portion of the screeningsurface to the orbital path of the fragments of material and to the peculiar action of the material at the back of such a screen. As the barrel revolves the material adiacentthe rearward side of the

screens

24, 25 and 26 is detiected rearwardly i tudinal iow of the fine material, and by adding to the agitation of the material increasing the effectiveness of the grindingtum bodies thereby still further improving the efficiency of the mill. Y

At the delivery end of the barrel 1 I have provided a receivingchamber 27 having flanges 28 which form dust tight joints with the sides of the barrel 1, and which is provided With a spout 29 through which the material vmay lescape from the receiving chamber to be disposed of in any preferred manner. Y

It will be understood that the broad features of this tube milland a species thereof different from the one hereinafter claimed, are covered in the parent application above referred to. This application is directed simply to one species of such av tube mill, which includes a screen of the .character having a curvature, preferably spherical, transversely of the barrel.

1. In a pulverizing mill, the combination with an approximately horizontal barrel adapted to revolve about its longitudinal axis, of a transverse Vscreen partition d ivid-' ing the interior of the barrel into separate grindingv chambers said screen having a sphericad curvature concentric with the axis of rotation'of the barrel.

- 2. A pulverizing mill comprising an approximately horizontal barrel, a transverse screen Vin said barrel having a- 4spherical curvature, said screenforming a inding, compartment within the "barrel anhaving la screening surface s o inclined to the barrel wall that together therewith it supports the material within the com artment, anda multiplicity of'freely tumb ing crushing elements in said compartment. 3. A pulverizing mill comprisin a barrel having its-wall inclined to the horizontal so that material within the barrel will gravitate on the wall from one end of the barrel toward the other, said barrel being `revoluble about its longitudinal axis, a transverse screen formingla grinding compartment curvature and serving together with a barrell wall :to support material 'in the grinding compartment, and a multiplicity of freely ling crushing elements in said compart ment. y v

.4.- A ulverizing mill comprising avbarrel having its wall inclined tothe horizontal so that material within the barrel will gravitatefrom one end toward the other on the barrel wall, said barrel being adapted to rements.

volve about its longitudinal axis, a transverse screen forming a 'grin'ding compartment in said barrel, said screen having a spherical curvature and serving together with a barrel wall to support material in the grinding compartment, and a multiplicity' of reely tumbling crushing elements in said compartment, tlie interior of said .compartment being free from obstructions .to the assortment of'material.

5. A pulverizing mill comprising a barrel revoluble about its longitudinal axis and having its wall inclined to the horizontal whereby material will tend to gravitate thereon toward one end of the barrelas it revolves, a plurality of transverse screens in vsaid barrel forming grinding compartments, said screens each having a spherical curvature and serving together with the barrel wall to support material VAin a grinding compartment, and a multiplicity of freely tuinling crushing elementsv in said compartments.

6. A pulverizing mill comprising an approximately horizontal barrel, a transverse screen in said barrel curved transversely of the barrel, said screenl forming a grinding compartment within the barrel and havin va screening surface so inclined to the barre Wall .that together therewith it supports .the material within the compartment, and amultiplicity. of freely tumbling crushing elements in said compartment. v 7. A pulverizing mill .comprising a barrel having its wall incline-d to the horizontal so that material within the barrel will gravitate on the wall from one end of the barrel to ward the other, said barrel being revoluble about its longitudinal axis, a transverse screen forming a grinding compartment 1n vsaid barrel, said screen being curved transversely of the barrel and serving together with a barrel wall to support material inthe inding compartment, and a multiplicity of' l reely .tumbling crushing elements in said compartment. Y

8. A ulverizing mill comprising -a barrel revo uble about its` longitudinal axis and in\ivavingits wall inclined to the horizontal said barrel, said screen having a'spherical hereby material will vof the barrel and serving together with the barrelwall to support material in a grinding com artment, and a multiplicity of freely tum ling crushing elements in said compartof the 'barrel as it In testimony whereof, I aliix mysignature.

ALEXANDER n MAHAFFEY READ.