US2555171A

US2555171A - Material reduction mill

Info

Publication number: US2555171A
Application number: US749131A
Authority: US
Inventors: Weston David
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-05-20
Filing date: 1947-05-20
Publication date: 1951-05-29
Anticipated expiration: 1968-05-29

Description

y 1951 D. WESTON 2,555,171

MATERIAL REDUCTION MILL Filed May 20, 1947 4 Sheets-Sheet l Alva/rap.- Onwo Mfesrom EY/W TOR/YE) y 1951 D. WESTON v 2,555,171

" MATERIAL REDUCTION MILL Filed May 20, 1947 4 Sheets-Sheet 2 INVENTOR:

DAVID WESTON ATTORNEY y 1951 D. WESTON MATERIAL REDUCTION MILL 4 Sheets-Sheet 3 Filed May 20, 1947 INVENTOR:

DAVID WESTON Y E N R o T A y 1951 D. WESTON MATERIAL REDUCTION MILL 4 Sheets-Sheet 4 Filed May 20, 1947 Qmq ' INVENTOR:

DAVID WESTON ATTORNEY Patented May 29, 1951 [TED STATESPATENT OFFICE This invention relates to a new and useful mill for the reduction of material such as ore, rock and the like material, and is particularly directed to providing a mill in which such mate: rial may be reduced in a single stage by the combined effect of impact, crushing and attrition.

Processes and apparatus for the reduction of materials such as ore, rock and the like are well known and widely used. The reduction normally is eifected in a series of stages, the number of stages depending upon the desired size of the end product. For example, the run-ofmine material may be crushed in a primary crusher, one or more secondary crushers, and rolls and then passed to a rod or ball mill for final fine grinding. This sequence of crushing and grinding operations involves a relatively high capital investment for crushers, screens, rolls,

conveyors and rod or ball mills with attendant high operating cost which results in a high cost per ton of material treated.

An important object of this invention is to provide a novel design of rotatable mill or drum in which the feed material is reduced to a predetermined size in a single stage by the combined efiect of shattering by impact, crushing and attrition reduction operations.

A further object of the invention is to provide a design of a rotatable mill in which the contents of the mill are maintained in a state of agitation as a relatively homogeneous mixture and packing or bedding of fine materials and segregation by size or specific gravity are prevented to maintain a high productive capacity.

A further object of the invention is to provide a design of a rotatable mill in which the feed thereto is dispersed and maintained therein as a substantially uniform mixture to maintain a live charge in the mill with consequent high efiiciency in all factors entering into the size reduction of the material.

A further important object of the invention is to pr-ovide a mill in which the interior arrangement of parts substantially reduces slippage of the charge therein to permit rotation of the mill at relatively high speeds from which is obtained a high efiiciency in all factors entering into the reduction of the material.

A further important object of the invention is to provide a novel arrangement for extracting moisture from the feed material prior to charging into the mill.

A further object of the invention is to provide a novel arrangement of elements for withdrawing particles from the mill Within a predetermined range of sizes, separating the oversize particles from the withdrawn material, and returning the oversize particles to the mill for further reduction in size.

A further object of the invention is to provide a material reduction mill into which run-of-mine material may be charged without preliminary crushing and which may be employed to reduce the material to the desired size in a single stage operation with or without the use of a grinding medium. 7

A further important object of this invention is to regulate the rate at which the material to be reduced is fed into the mill, the feed being automatically controlled by the power required to drive the mill, to maintain in the mill the volume of feed material from which the maximum reduction rate and efiiciency are obtained.

The material reduction mill of the present invention, comprises in general: a combination capable of reducing run-of-the-mine size feed material to a comparatively fine state in a single stage and includes a cylindrical drum having a cylindrical wall joining two end walls and a diameter considerably greater than its length, the drum being rotatable in a vertical plane about its cylindrical axis and incorporating transverse crushing bars on the inner surfaces of the cylindrical wall of said drum and disposed in spaced apart relation a distance suificient freely to accommodate the largest particle of feed material between any adjacent pair of such bars, an opening in each end wall of the drum co-axial with the rotary axis thereof to form respectively, material inlet and outlet openings through which material may be introduced and reduced material removed, respectively; an annular distributing member secured to the interior of one end wall of the drum concentric with but spaced radially outward from the inlet opening, said annular member projecting inwardly of the end wall towards the other and having a substantially frustro-conical deflecting surface flaring away from the axis of rotation of said drum as it extends away from said end wall towards the other and forming a deflector in the path of the trajectory of feed material fed to the drum, a corresponding annular distributing member secured to the opposite end wall concentric with but spaced radially outward from the outlet opening, said second annular member registering co-axially with the first one and having a corresponding substantially frustro-conical deflecting surface also disposed in the path of the trajectory of feed material fed to the drum, said annular distributing members co-operating to deflect said feed material towards a mid-region of the drum between said end walls to deliver said material to said crushing bars toward the bottom of the 3 drum as a substantially uniformly distributed mixture.

Figure 1 is a front elevation partly in section of a mill incorporating the improvements of the present invention and associated parts;

Figure 2 is a perspective view of the feed end of the mill;

Figure 3 is a perspective view of a section of the angularly disposed liner elements;

Figure 4 is a perspective View of a portion of the ring liner and radial bars;

Figure 5 is an end view of the transverse crushing bar and plate assembly;

Figures 5A and 5B are respectively perspective views of a transverse plate and a transverse crushing bar;

Figure 6 is a schematic view of the mill and associated parts, illustrating the movement of the charge to and through the apparatus;

Figure 7 is a diagrammatic View of the electrical circuit to the mill and its associated parts.

Like reference numerals refer to like parts throughout the specification and drawing.

Referring to the drawings, the numeral 28 indicates a rotatable drum having vertical end walls 2| joined by the cylindrical or horizontal wall 22. In the preferred embodiment of the invention, the diameter of the drum is substantially greater than the length, the actual dimensions of course, being determined by the productive capacity desired from the drum. The end and cylindrical walls of the drum are preferably formed of relatively heavy steel or alloy steel plates. The parts are secured rigidly together, such as by angle irons, to form, in effect, a unitary structure which may be dismantled, if desired, for shipment and repairs.

The drum is supported on hollow trunnions 23 which are journalled in bearings 24 supported on a foundation such as concrete blocks 25. The trunnions 23 are joined to the end walls 2! such as by rivets or bolts, and are in substantial axial alignment with the horizontal axis of the drum, the passageway through each trunnion being in substantial alignment with an opening in the adjacent wall 2|. For the purpose of identification, one opening is identified as the inlet opening 26 and the other opening is identified as the outlet opening 21.

An annular liner preferably formed in sections 30 and constituting a feed material distributing member, is secured to each end wall 2| of the drum. These distributing members are mounted concentric with but spaced radially outward from, the respective inlet or outlet opening as the case may be, in the end walls 2] and project inwardly of each end wall towards the other. Each of these members has a substantially frustro-conical deflecting surface flaring away from the axis of rotation of the drum as it extends away from its end wall towards the other and which forms a deflector in the path of the trajectory of feed material as it is fed into the drum. As illustrated in Figure 3, each section 38 is preferably in the form of a wedge shaped block, with a flat base drilled or cored as indicated by the number 3|, for securing to the wall of the drum by bolts with the sides converging toward each other at an angle of about 60 to the apex 132. The exposed surfaces and apices of the sections may be faced with an alloy steel of hard, wear resisting properties such as a tungsten compound. The sections 30 when assembled form a circular liner. This liner serves particularly to distribute the feed material and the oversize particles returned to the mill into the centre of the mill, wherefrom it is dispersed as a relatively uniform mixture without any appreciable segregation according to size and specific gravity. Also, this liner serves to prevent slippage of the charge and wear on the shell during rotation of the mill. The liner is designed to extend inwardly into the drum a distance sufficient to serve these two important purposes.

The ring liner 40 is positioned between the assembled sections 30 and the cylindrical wall of the drum. This liner 4!] is in the form of a relatively heavy ring-like base formed, for example, of cast iron or cast steel with upstanding bars ll which extend radially across the base. The ring is drilled or cored, at spaced intervals,

.as indicated by the numeral 42, for securing the rings to the drum. This liner serves to prevent slippage of the charge and wear.

The transverse liner which extends between the ends or vertical walls of the drum is formed of plates 5i? and bars 5! described in detail hereinafter.

The plates 53 are designed to extend transversely from end to end of the drum with the ends terminating adjacent to the exposed face of the ring liner 40. Each plate preferably slopes toward its longitudinal centre line, openings 52 being drilled at spaced intervals along that line for securing the plate to the cylindrical wall of the drum by bolts. The crushing bars 51 are formed on or carried by each plate and extend a short distance above the surface thereof. These liners may be provided with upstanding transverse ribs 53 which also serve to prevent slippage of the charge and wear on the outer shell of the mill.

The transverse crushing bars 5i are preferably in the form of steel rails which preferably are capped with an alloy which is hard and highly resistant to wear such as a tungsten compound, as indicated by the numeral 54. The web of each rail is preferably tapered slightly uniformly from the base of the cap to the flange to eliminate any pocket in which material would tend .to collect. The crushing bars 5| are spaced at relatively wide intervals to prevent fine material from accumulating or bedding between them and to permit engagement between them of relatively large pieces of material without wedging.

The crushing bars may be held in position in the drum by bolting or by overlying the flanges with the longitudinal edges of the plates 50 as illustrated in Figure 2.

The drum may be driven directly by a belt from a motor, but is preferably driven as illustrated in Figure 6, from a motor 64 through a belt 65 to a drive shaft 66 on which is mounted a pinion 61 meshed with the spur gear which is mounted on one end of the drum. The gear 60 may be secured to the drum according to standard practice. This arrangement for drivin the drum has the advantage that on a high starting load the belt may slip a little and there is no undue strain on the gears.

Material is fed into the drum from a, belt conveyor BI which feeds the material to a chute 62 which, in turn, communicates with the inlet opening 26. The motor 83, Figure 7, which drives the conveyor is interconnected with the motor 64 which drives the drum, for purposes explained in detail hereinafter.

The reduced material is withdrawn from the drum through the outlet opening 21 by an exhaust fan 10, Figure 6,'through the conduit H to a receptacle 12. Preferably, a by-pass valve 13 is provided in the conduit 1| between the drum 20 and the receptacle 12 by means of which the fineness of the grind may be increased or decreased by decreasing or increasing the velocity of the air blast. Also, the conduit 1| is preferably designed to return oversize material to the drum. Alternatively, the velocity of the air may be regulated by employing a variable speed motor to drive the exhaust fan 10.

The volume of the charge in the drum is controlled to produce the maximum eiliciency in several operations entering into the reduction of the material. This may be readily determined for the type of material fed to the drum. A preferred arrangement of regulating the rate at which the material is fed to the drum is by connecting the drum driving motor through a make-and-break ammeter 80 to which is also connected the feeder or feeder drive motor 8|, as illustrated in Figure '7. If desired, the motor 63 which drives the conveyor drive motor also may be connected to the ammeter 80. The ammeter 80 is calibrated within a predetermined load range, within which the feeder motor 8|, and the conveyor motor 63 are driven to feed material to the drum and above which the circuits to these motors are opened to stop the feeding of material to the drum. As the material accumulates in the drum, the load on the drum driving motor 64 increases towards its maximum permitted. load. When the load reaches the permitted maximum, the ammeter needle trips the cut-01f switch to open the circuits to the feeder and conveyor motors to stop the feed of material to the drum. As reduction pro ceeds and reduced material is withdrawn, the load in the drum is decreased until the ammeter needle has reached the predetermined minimum at which instant the circuits to the feeder and conveyor motors are closed and the feed to the drum is resumed. This arrangement makes possible a close control over the rate of feed to the mill and permits operation of the mill at its maximum efiiciency.

In the preferred operation of the apparatus, air is drawn, by the cyclone fan, through the feed material stored in the storage bin, and into the mill. This is accomplished by having the storage bin and the unit in the same enclosed building with the only building opening for air being through openings in the storage bin. In its passage through the stored feed material, the air extracts at least a portion of the moisture therefrom. Further moisture is extracted from the feed material undergoing reduction in the mill with the result that the material is in a relatively dry condition during its reduction from its coarse state to its fine state.

In the event that the feed material contains a moisture content such that suflicient moisture cannot be extracted by the employment of air at atmospheric temperature, the air may be preheated.

In the mill, the feed material is reduced in size by three types of operation, (a) by shattering which results from the impact of particles raised by centrifugal force aided by the crushing bars to drop by gravity on the body of the.

mill is designed to obtain the maximum efficiency in the several operations involved in the reduc-' tion of material fed into the mill.

In operation, the mill is brought up to its operative speed and the circuits to the feeder and conveyor motors are closed to start the feed ofmaterial into the mill. The material discharged into the mill is directed, by the liner sections 30, to the centre of the mill wherein it accumulates as a relatively homogeneous mass without segregation. In this respect, certain finer material will pass over the distributing member formed by sections 30 disposed on the end wall adjacent the inlet opening. Other sizes of the material and including the largest material, as well as oversize particles returned to the mill through the discharge opening, have a path of trajectory which is intercepted by the distributing members, as shown in Figure l of the drawings and which members will deflect said material into the centre or mid-region of the drum between said end walls to accumulate as a relatively homogeneous mass or substantially uniform mixture. As the mill rotates, the material is dispersed as a live, agitated mixture, the sections of the mass moving at varyin rates of speed depending on the distance from the walls 2|.

The interior construction of the mill serves several important functions. Firstly, the arrangement of the liners and crushin bars. serves to maintain the load in a state of constant agitation, the load being raised by centrifugal action aided by the bars 4| to drop on the material below to effect reduction by impact. As a result of the novel arrangement of the liners, slippage of the charge is substantially eliminated and it is possible to operate the mill without slippage of the charge at high speed up to about of the critical speed, which permits particles of feed material to be carried by centrifugalforce close to the top of the mill to obtain a maximum shattering effect on the material below.

The transverse'crushing bars 5| effect an important reduction by a crushing action as they descend into the heel of the charge in the bottom of the mill. The flat rectangular surface of the caps or heads and the tapered sides of the bars 5| serve, in effect, as the movable jaw of a crusher, to crush lumps of material adjacent the peripher and/or in contact with the bars extending into the charge against the slower moving charge in the bottom of the mill, which functions as a stationar jaw. The taper of the web from the cap to the flange aids in the crushing operation in that the engaged particles are unsupported above and below the cap. It is also found that the spacing and design of the bars 5| and the arrangement of the plates 50 are important inasmuch as they are designed to provide a maximum crushing effect and to prevent bedding or packing of charge material between the bars.

The efliciency of the reduction by attrition is dependent on several factors, for example, by maintaining the charge in the mill as a substantially uniform, actively agitated mixture. This condition is obtained by the novel arrangement of the liners which, in addition to substantially eliminating any possibility of slippage, permits driving th mill without slippage of the charge at speeds up to about 90% of its critical speed. The rotation of the drum produces layers of material in the drum moving at different velocities and/ or at different angles to each other, the layer most adjacent to the periphery moving at the fastest rate and the other layers moving at progressively slower rates as they are further removed from the periphery. Reduction by attrition is effected by the grindin action on contacting surfaces of opposin particles.

The velocity of the air drawn into the mill is readily regulated to draw from the mill the particles within a predetermined size range. Any oversize particles drop from the air column and return to the mill for further reduction by sliding down the conduit ll, being directed to the centre of the mill by the liner 38 for mixturewith the feed material.

The mill is ideally adapted for the use of a ball charge to expedite the reduction operation. The balls, normally, have a higher specific gravity than the feed material and are raised by centrifugal action and aided by the bars 51 to a point above the bottom of the mill, as illustrated by Figure 8, to drop on the material below to improve greatly the reduction by impact. Also, the material engaged between the hard surfaces of contacting balls is rapidly reduced in size by attrition. When a ball charge is used to increase the impact efficiency, it is preferred to em ploy relatively large balls of high specific gravity such as those described in my co-pending application Serial No. 738,785, filed April 2, 1947.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. A material reduction mill capable of reducing run-of-the-mine size feed material to a comparatively fine state in a single stage, comprising in combination: a cylindrical drum having a cylindrical wall joining two end walls arranged substantially perpendicularly to the end walls and a diameter considerably greater than its length, said drum being rotatable in a vertical plane about its cylindrical axis, transverse crushing bars mounted on the inner surfaces of the cylindrical wall of said drum and disposed in spaced apart relation a distance sufficient freely to accommodate the largest particle of feed material between any adjacent pair of such bars, each end wall of the drum having an opening coaxial with the rotary axis thereof to form respectively, material inlet and outlet openings, r

through which material may be introduced and reduced material removed respectively, an annular distributing member secured to the interior of one end wall of the drum concentric with, the axis of the drum and having a projecting surface spaced radially outward from, the inlet opening intermediate the inlet opening and the cylindrical wall of the drum, said annular member projecting inwardly of the end wall towards the other and having a substantially frustro-conical deflecting surface flaring away from the axis of rotation of said drum as it extends away from said end Wall towards the other and forming a deflector in the path of the trajectory of feed material fed to said drum, a corresponding annular distributing member secured to the opposite end wall concentric with, but spaced radially outward from, the outlet opening, said second annular member registering co-axially with the first one and having a corresponding frustroconical deflecting surface also disposed in the path of the trajectory of feed material fed to said drum, said annular distributing members co-opcrating to deflect said feed material towards a mid-region of the drum between said end walls to deliver said material to said crushing bars toward the bottom of the drum as a substantially uniformly distributed mixture.

2. A material reduction mill capable of reducin run-of-the-mine size feed material in the single stage, as claimed in claim-1, in which the distributing members are formed from a plurality of wedge-shaped sections arranged continuously to form an annulus.

3. A material reduction mill capable of reducing run-of-the-mine size feed material in the single stage, comprisin in combination: a cylindrical drum having a cylindrical wall joining two end walls arranged substantially perpendicularly to the end Walls and a diameter considerably greater than its length, said drum being rotatable in a vertical plane about its cylindrical axis, transverse crushing bars mounted on the inner surfaces of the cylindrical wall of said drum and disposed in spaced apart relation a distance suflicient freely to accommodate the largest particle of feed material between any adjacent pair of such bars, each end wall of the drum having an opening co-axial with the rotary axis thereof to form respectively, material inlet and outlet openings, through which material may be introduced and reduced material removed respectively, an annular distributing member secured to the interior of one end wall of the drum concentric with, the axis of the drum and having a projecting surface spaced radially outward from, the inlet opening intermediate the inlet opening and the cylindrical wall of the drum, said annular member projecting inwardly of the end wall towards the other and having a frustroconical deflecting surface flaring away from the axis of rotation of said drum as it extends away from said end wall towards the other and forming a deflector in the path of the trajectory of said feed material, a correspondin annular distributing member secured to the opposite'end wall concentric with, but spaced radially out Ward from, the outlet opening, said second annular member registering co-axially with the first one and having a corresponding frustro-conical deflecting surface also disposed in the path of the trajectory of the feed material, said annular distributing members co-operating to deflect the feed material towards a mid-region of the drum between said end walls to deliver said material to said crushing bars toward the bottom of the drum as a substantially uniformly distributed mixture, and an annular liner having gripping lugs thereon mounted on each end wall of the drum and located between said distributing members and said transverse crushing bars, said gripping lugs cooperating with said crushing bars to enhance both the crushing action of the bars and the shattering action of the material.

DAVID WESTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 413,388 Coward Oct. 22, 1889 1,307,952 Ball June 24, 1919 1,690,493 Marc Nov. 6, 1928 1,872,036 Hardinge Aug. 16, 1932 2,274,331 Howes Feb. 24:, 1942 FOREIGN PATENTS Number Country Date 7,801 Great Britain Mar. 29, 1911