US3010661A - Wet material reduction mill - Google Patents

Description

Nov. 28, 1961 D. WESTON WET MATERIAL REDUCTION MILL 5 Sheets-Sheet 1 Filed Feb. 9 1959 Nov. 28, 1961 D. WESTON WET MATERIAL REDUCTION MILL 5 Sheets-Sheet 2 Filed Feb. 9, 1959 Nov. 28, 1961 D. WESTON 3,010,651

WET MATERIAL REDUCTION MILL Filed Feb. 9, 1959 5 Sheets-Sheet 3 Nov. 28, 1961 D. WESTON WET MATERIAL REDUCTION MILL 5 Sheets-Sheet 4 Filed Feb. 9, 1959 Nov. 28, 1961 D. WESTON WET MATERIAL REDUCTION MILL 5 Sheets-Sheet 5 Filed Feb. 9. 1959 in mm W 2 m 1 MM] m m f/ m n m I Q. M M /N D M MN I NN M m 3 mm piH H QB |I|| N\ m QMN @N N saw QR QNN vN United States Patent 3,010,661 WET MATERIAL REDUCTION MILL David Weston, Toronto, Ontario, Canada, assignor to Aerofall Mills Inc., Columbus, Ohio Filed Feb. 9, 1959, Ser. No. 792,025 Claims priority, application Canada Jan. 28, 1959 13 Claims. (Cl. 241-30) The reduction of materials in the wet state has for many years been a conventional practice in a great many metallurgical and industrial milling operations. One of the generally accepted limitations of wet has been the necessity to maintain separate milling stages for the reduction of different particle size ranges of materials. Thus a conventional plant for the wet reduction of material has generally consisted of a number of stages of crushing designed to reduce the material to a suitable rod or ball mill feed, i.e. to a maximum particle size of around /8 to inch, followed by a rod mill or primary ball which in turn is followed by a secondary ball or pebble mill close circnited with a classifier which is in turn followed by one or more additional stages of grinding.

Several proposals have been made from time to time in the art in respect to reducing or eliminating the necessity for multiple stages in the wet reduction operation. One such proposal is described in Hadsell United States Patent No. 2,094,842 of October 5, 1937, where the material in the form of a wet slurry as a run-of-mine or primary crusher product was elevated and dropped within a large diameter mill by means of buckets. Other proposals sought to overcome the difficulty through the use of special mill cross-sectional shapes designed to accommodate both large and small particles of feed in the pulp within the mill on the theory that the larger lumps of material could be made, in the course of their own reduction, to act "as reduction media upon the smaller particles.

Although certain of these prior proposals have had limited success, especially as regards smaller milling units designed to produce relatively low tonnages, there has not as yet been a proposal for wet reduction which has effectively solved the existing problems on a commercial scale of operation.

I have now found that the above enumerated dithculties may be largely overcome and an effective Wet milling of run-of-mine or coarse crushed materials can be carried out by employing as a milling unit a novel design of mill adapted to perform a wet milling operation on the basis of principles previously applied by me to the reduction of materials in the dry state.

A wet reduction mill according to the present inven tion broadly comprises a cylindrical drum having a diameter which is at least twice the length thereof and which is mounted for rotation about a substantially horizontal axis. Said drum is provided about its interior periphery with a plurality of highly upstanding transverse crusher bars spaced apart a suflicient distance fully to. accommodate and engage the largest particles of the material which is to be used as feed to the mill. Additionally, there are mounted on the end walls of the said drum annular liners which extend inwardly into the interior of the drum a substantial distance, as will hereinafter be defined in greater detail, so as to present a frusto-conical surface facing the peripheral regions of the mill and concentric the axis thereof, which frusto-conical surface is so positioned as to maintain during operation of said mill 2 keying action zone in the space between said annular liners and the periphery.

In my prior United States Patent No. 2,704,636, I disclosed the significance of the maintenance of a keying action zone in connection with combined dry crushing and grinding mills. In connection with such dry mills,

2 the principal eifect of the keying action resides in the maintenance of the charge the keying zone as a more compact mass which more readily absorbs useful grinding Work input so that for a milling unit of given size working on a given ore the capacity of the unit is increased substantially.

I have found surprisingly that in connection with wet milling the maintenance of a keying action zone produces the further advantage that it permits the element of pulp density to be to a substantial extent disregarded insofar as its elfect upon circulation of the charge is concerned. Thus, the keying of the charge enables the use of high pulp densities enabling a greater amount of solid material to be usefully worked upon in the charge, and hence making possible such increases in capacity as render practical the application of large diameter short length mills to the wet reduction of materials which hitherto have required plurality of stages of wet reduction in conventional equipment with the attendant advantages of saving of plant space, capital cost and other advantages which flow from the ability to conduct a reduction operation as a unit process rather than as a series of separate stages which require detailed integration and expansive plant layout.

A number of different embodiments are contemplated by'the present invention having regard to the nature of the operation intended and the characteristics of the material which is to be treated.

In connection with operations requiring a product of fine particle size, e.g. of the order of size which might normally be produced in conventional plant operations where one or more secondary ball mills are employed, the mill of the present invention is so designed as to provide for discharge through grates in the downstream mill trunnion.

Where the mill product is intended to be of a coarser particle size in general it is preferred so to construct the as to provide for peripheral discharge through grates situated at the periphery. With peripheral grate discharge, the mill may be provided with a false wall and lifters so as to conduct the peripherahy discharged material radially inwardly for flow out through the downstream trunnion. According to a further embodiment of the invention and in particular where it is desired to operate at high pulp densities and especially where the material being reduced is of a very fine grain structure and is readily broken down, the peripheral grate may be exposed, and means provided for scraping or sluicing the mill discharge product for conduction by suitable means to a classifier or screen. Where, as in the case just discussed, the viscosity cf the product is so high that effective flowability of the mill discharge cannot be obtained without the use of scrapers, sluicers and the like, there are various means which may be applied to deliver the dis charge from the In some instances, use may be made of an airstream, high velocity air jets, steam jets and the like. Similarly, in connection with trunnion overflow discharge, in addition to steam, air and water jets, various mechanical arrangements are known in the art which may be used to assist transfer, such as screws, lifters, buckets, scrapers and the like. In this specification and in the appended claims, when I use the expression assisted discharge, I contemplate, unless otherwise specified, that any of such means may be employed whether in reference to peripheral or to trunnion overflow discharge.

The invention and its operation will be more completely understood from the following detailedspecification in conjunction with the accompanying drawings wherein:

FIGURE 1 is a vertical cross section through the axis of a mill according to one embodiment of the invention 3 provided with trunnion overflow grate discharge means;

FIGURE 2 is an end view of the mill illustrated in FIGURE 1 taken from the discharge side thereof and illustrating details of the grate discharge; v

FIGURE 3 is a perspective of the general layout of a mill according to the present invention illustrated in closed circuit with a spiral classifier;

FIGURE 4 is a top elevation of the layout illustrated in FIGURE 3;

FIGURE 5 is a fragmentary perspective view illustrating peripheral discharge with lifters for returning mill product for discharge through the downstream trunnion thereof; V

FIGURE 6 is a fragmentary perspective view of a preferred form of trunnion grate discharge;

FIGURE 7 is a fragmentary perspective view of a mill according to the invention illustrating peripheral grate discharge directly from the periphery of the mill;

FIGURE 8 is a fragmentary detail section illustrating the flow path of the mill product illustrated in the embodiment of FIGURE 7;

FIGURES 9, 10 and D1 are fragmentary cross-sectional details illustrating various alternative forms of structure for the annular liners which establish a keying action zone within the mill.

Referring now more particularly 'to the drawings wherein like numerals refer to like parts throughout, the mill illustrated in FIGURES 1 and 2 has the end walls 11 and 12 separated by the peripheral cylindrical wall 13. As is apparent from the drawing, the length of the peripher'al cylindrical wall 13 is short compared to the diameter of the end walls 11 and 12, the peripheral internal diameter length ratio being at least 2:1. The radial ribs 14 are provided to strengthen the end walls 11 and 12 structurally and trunnion flanges 16 and 17 extend outwardly from the end walls 11 and 12 concentrio with the axis thereof to provide the journal bearing surfaces 18 and 19 on which the mill is supported for rotation.

Spaced about the interior of the peripheral cylindrical wall 13 are the highly upstanding crusher bars 20 which are held in place by appropriate base and retaining plates in a manner such for instance as that which is illustrated in my prior United States Patent No. 2,555,171 where a similar type of crusher bar construction is illustrated.

' On the interior of each end wall 11 and 12, there are mounted the ring shaped liner elements 21 and 22 and the annular keying liner elements 23 and 24. As illustrated, the latter keying liner elements each have two circular radially spaced apart apices 25 and 26 presenting keying surfaces 27 and 28 respectively in the direction of the periphery of the mill. Other forms of keying liner elements may replace keying liner elements 23 and 24 depending upon the nature of the operation and type of ore to be treated. Three such alternative forms are illustrated in FIGURES 9, 10 and 11 which are generally preferred for particular purposes which will be hereinafter described.

The trunnion flange 17 is formed to provide a conical interior surface 29 having an interior flanged lip 30 over which projects the lip 31 of the feed chute 32 whereby to provide a flow path into the mill for feed material and make-up water and oversize return which are delivered by delivery chute 33.

Mounted in the trunnion flange 16 is a grate discharge 34 which is formed with the generally conical inner surface 35 and the grate indicated generally at 36. The grate is formed with a solid interior portion 37 surrounded by the radially open grate structure 38, the whole being supported rigidly the portion 35 by the bracer elements 39 which also function as lifters in assistingthe discharge of material through the grates.

Mounted at the periphery of the end wall 12 in the drive girth gear 40, which is driven throughpinion 41 (see'FIGURE 3), which in turn is driven by the electric motor '42 through speed reducer 43. I

The mill discharge is deposited in a classifier feed box 44 and is fed into the spiral classifier 45, the product being discharged at the classifier overflow at 46, the oversize being returned together with the make-up water provided by supply 47 tothe delivery chute 33, which delivers it to the feed chute 32 where it returns to the mill to gether with the mill feed which is delivered to the feed chute by conveyor 47a.

Alternatively, the discharge from the mill may pass directly to a screen, the undersize going directly tometallurgy and the oversize being recirculated to the mill, e.g. by conveyor. I

' The flow paths of discharge fi'om the mill are indicated generally with relation to theembodiment illustrated in FIGURES 1 and 2 in the fragmentary perspective shown in FIGURE 6.

A form of peripheral grate discharge is shown in FIG- URE 5. In this embodiment, the mill is provided with the false inner wall 50 having the radially disposed peripheral grate openings 51 adjacent the cylindrical peripheral wall of the mill. The end wall -11 of the mill is separated from the false inner wall 50 by a plurality of radially disposed lifters 52 which carry mill discharge radially inwards where it is deflected by the conical surface 53 of the central portion of the false wall 50 which overlies the trunnion opening and is permitted to flow over the trunnion liner member 54 for discharge, the flow paths being substantially as illustrated.

In this embodiment, it is to be understood that the peripheral cylindrical wall 13 forms a water-tight closure with the end wall 11 so that the grate 51 and lifters 52 are completely closed at the periphery.

An alternative form of peripheral grate discharge is illustrated in FIGURE 7. In this instance, the false inner wall 50 of the mill, the radially disposed peripheral grates 51 and lifters 52 are disposed in the same manner as in FIGURE 5, but in this case, the inner extremity of the space between the false wall 50 and the wall 11 is sealed oil by the flange 53A whereas the peripheral cylindrical wall 13 is provided with a plurality of discharge grates 54 permitting the mill discharge to pass directly radially outwardly for collection in the trough 55, the flow paths being illustrated in FIGURE 7 and in substantially greater detail in the section shown in detail in FIGURE 8.

The alternative forms of keying liners 23a, 24a, 23b, 24b, 23c and 240 illustrated respectively in FIGURES 9, l0 and 11 may, as previously mentioned, be substituted .for the forms of keying'liner 23 and 24 illustrated in FIGURE 1. The particular function of these liner elements will be described in connection with the operation of the invention which follows.

In relation to operation of the invention, it is necessary first of all to take into account the type of feed which is to be fed to the mill. In this connection, it is important to note that the spacing of the crusher bars must be such as to prevent wedging of individual pieces of large feed so that the space between the crusher bars is such as to provide for effective engagement by the crusher bars 13 of the largest particles of feed.

Secondly, account must be taken of the reduction characteristics of the material. If the material is tough, the breakdown of the largest pieces will be more gradual than the breakdown of such large pieces will be if the material breaks down readily, and consequently where the material is tough, the most effective keying action will be achieved if a relatively large keying zone is provided. If the large pieces of material break down quite readily, it will be necessary to reduce the size of the keying zone in order to maintain efiective keying action. Some materials break down readily at the largest particle size, but tend to form somewhat tougher pebbles at an intermediate size range, and with such materials it'may be desired to establish zones within 1 the keying zone especially adapted to develop the maximum keying effect from the mixture in the charge consisting of relatively few of the largest pieces and a relatively large'number of such pebbles. Y Y

Thirdly, the ultimate particle size er the product to be produced must be taken into account, and once again, having regard to the factors alreadydiscussed, aselec tion must be made between trunnion discharge and overflow discharge. Generally speaking trunnion overflow grate discharge is, preferred for fine grinding applications especially wherethe flowability of the pump is reasonable, within the range er pulp Ldensities which must be used having regard tothe follow-up plant. For coarse grinding applications, peripheral grate discharge with flow directed back to- ,the ;trunnior 'i as illustrated in FIGURE 5.is preferred. However, where the ilowability of the pulp discharged from the -ini1l is poor withinthe permissible range of pulp densities, peripheral grate discharge of the type illustrated in FIGURE 7 will be used. It will be' appreciated that in any of, the foregoing cases use may be made of assisted discharge of any suitable form in-order. to extend, the range of pulp densities in which the particular embodiment of the invention may be effectively used. 4

V The keying zone may be defined as. the space within 6 of the'surfa'cesf90 or 100 toprovide the optimum rela-' tive size of the keying zone". The dotted lines 9011 and 90b illustrate how the design of liners 23a and 24a may be modified to produce a larger relative keying zone.

What I claim as my invention is: 'j

. 1. A wet combined crushing and grinding mill comprising; a'horizontally rotatable drum having a cylindrical wall and two end walls, the ratio of the interior diameter of the drum to the interior peripheral length thereof being at least 2: 1; a plurality of highly upstanding transverse crusher bars mounted in spaced apart relation around the cylindrical wall to eifectively engage the largest particles of feed; meansfor feeding feed material,

- including liquid to said mill;'means for withdrawing the'mill lying between the most radially inward'apic'es forming about 45 of the mill volume is preferred. The

effective zone sizes fortougher materials will be somewhat larger, while'those form'ore fiiable materials Will be somewhat smaller. v

The distance of lateral penetration of the api'ces of the keying liners into the interior of the mill is also most important. This may be measured conveniently as the percentage of the length of the miles measured along a line through the apices of the keying liners which is subtended by the keying liners. The length of the mill thus measured is termed herein the efiective mill length. A relative penetrationof from about 20% to about 80% of the cifective mill volume represents the efiective range. Generally speaking, the more friablethe material the greater penetration is desirable. For materials of medium grindablity a penetration of about 40% of the effective mill length is preferred when operating with a mill charge having good flow characteristics.

Where the material develops pebbles in the medium size ranges to a larger extent than normal, it may be desirable to have a number of apices on each keying liner at varying distances from the periphery and with varying penetrations, taking into consideration the relative volumes of the various sized particles which are present in the mill during operation along the lines illustrated in FIGURE 11.

For fine grinding with trunnion overflow discharge an arrangement such as is illustrated in FIGURE 1 is preferred. The surfaces 27 are designed to effectively key the larger pieces of material in the charge, while the surfaces 28 key the much larger mass of finer particles present, and in doing so permit the water and fine products to pass more rapidly towards the mill axis. This results in a concentration of fines and water at the trunnion overflow giving good flowability and a relatively low viscosity despite the high pulp density of the charge taken as a whole. This is an outstanding advantage of the present invention.

The arrangements illustrated in FIGURE 9 or 10 are more suitable, in the case of peripheral discharge. Here there is no desire to concentrate the fines and water at the mill axis and the governing factor is the location product comprising solids and liquids from said mill; and a pair of opposed annular keying liners mounted one on each of the end walls of the drum, said keying liners collectively penetrating. into the mill interior from about 20% to about of the elfective length, and defining a keying zone which is from about 30% to about 75% of the efiective mill volume.

2. A Wet combined crashing and grinding mill comprising; a horizontally rotatable drum having a cylindrical wall and two end walls, the ratio of the interior diameter of the drum to the interior peripheral length thereof being at least 2:1; a plurality of highly upstanding transverse crusher bars mounted in spaced apart relation around the cylindrical wall to effectively engage the largest particles of feed; means for feeding feed material, including liquid to said mill; grate means for withdrawing product comprising solids and liquids from said mill; and a pair of opposed annular keying liners mounted one on each of the end walls of the. drum, said keying liners collectively penetrating into the mill interior from about 20% to about 80% of the efiective mill length, and defining a keying zone which is from about 30% to about 75% of the effective mill volume.

'3. A wet combined crushing and grinding mill comprising; a horizontally rotatable drum having acylindrical wall and two end walls, the ratio of the interior diameter of the drum to the interior peripheral length thereof being at least 2:1 a plurality of highly upstandingtransverse crusher bars mounted in spaced apart relation around the cylindrical wall to effectively engag'ethe larg est particles of feed; means for feeding feed material, including liquid to said mill; peripheral. grate means for withdrawing product comprising solids and liquids from said mill; and a pair of opposed annular keying liners mounted one on each of the end walls of the drum, said keying liners collectively penetrating into the mill interior from about 20% to about 80% of the efiective mill length, and defining a keying zone which is from about 30% to about 75% of the effective mill volume.

4. A wet combined crushing and grinding mill comprising; a horizontally rotatable drum having a cylindrical wall and two end walls, the ratio of the interior diameter of the drum to the interior peripheral length thereof being at least 2:1; a plurality of highly upstanding transverse crusher bars mounted in spaced apart relation around the cylindrical wall to effectively engage the largest particles of feed; means for feeding feed material, including liquid to said mill; trunnion overflow grate means for withdrawing product comprising solids and liquids from said mill; and a pair of opposed annular keying liners mounted one on each of the end walls of the drum, said keying liners collectively penetrating into the mill interior from about 20% to about 80% of the effective mill length, and defining a keying zone which is from about 30% to about 75 of the efiective mill volume.

5. A mill as defined in claim 2, in which said keying liners collectively penetrate into the mill interior about 40% of the effective mill length, and define a keying zone which is about 45% of the effective mill volume.

6. A mill as defined in claim 4 which comprises a false end wall in said drum mounted so as to leave a space between the same and the end wall of the mill, a plurality 7 of radial grate openingstabout the periphery of said false wall; a pluralityof radial. lifters between said false wall,

and end wall, and fiow'directingmeans for directing mill product from sa'id lifters outwardly through the mill trunnion. e 7. A-mill as defined in claim 4 comprising a false wall s'paced' apart'from' the end wall of the mill; a plurality of radial grate openings about the periphery of said false wall; a plurality of openings in the cylindrical wall of the mill arranged to permit peripheral'discharge of mill product which is passed through said grate openings, and means forcollecting the discharge from said openings. 8. A mill as defined in claim .6,;wherein means are provided for accomplishing assisted discharge of mill product. 7 V p p i 9. A mill as defined in claim7, wherein means are provided for accomplishing assisted discharge of mill product. 7

10. A method for the wet comminution of rock, ores and the like which comprises feeding solid and liquid feed material to a material reducti'onmill having a cylindrical wall and two end walls, the ratio of the interior diameter of the drums to the interior peripheral length thereof being at least 2:1, a plurality of highly upstanding transverse crusher bars mounted in spaced apart re- 8 2 0% to about 80% of the efiiective mill length, said keying zone being from about 30% to about 75% ofthe effective mill volume, withdrawing the product from said mill bygrate means, and collecting said product.

12. A method for thewet comminution or rock, ores and the like which-comprises feeding solid and "liquid feed material toa material reduction mill having a cylindrical wall and two end walls, the ratio or the interior diameter of the drum to the interior peripheral length thereof being at least 2:1, a plurality of highly 'upstand ing transverse crusher bars mounted in spaced apart relation around the cylindrical wall efiectively engage the largest particles of feed, maintaining during operation akeynig action zone defined by the pariphery 0f themill and a pair of opposed annular keying liners mounted one on each of the'end walls of the drum,' said keying-liners collectively'penetrating into the mill interior from about 7 mill by peripheral. grate means, and collecting said lation around the cylindrical wall to etfectively engage t the largest particles of feed, maintaining during operation a keying action Zone defined by the periphery of the mill and a pair of opposed annular keying liners mounted on each of the end walls of the drum, said keying liners collectively penetrating into the mill interior from about 20% to about 80% of the effective mill length, said keying zone being from about 30% to 75% of the effective mill volume; withdrawing and collecting the product of said mill.

11'. A method for the wet comminution of rock, ores and the like which comprises feeding solid and liquid feed material to a material reduction mill having a cylindrical wall and two end walls, the ratio of the interior diameter of the. drums to the interior peripheral length thereof being at' least 2:1, the plurality of highly upstanding transverse crusher bars mounted in spaced relation around the cylindrical wall to eifectively engage the largest particles of feed, maintaining during operation a keying action zone defined by the peripheryiof the mill and Ya pair of opposed annular keying liners mounted oneon each of the end walls of the drum, said keying liners collectively penetrating into the. mill interior from about product. I

, 13. A method for thewet comminution of rock, ores and the like which comprises feeding solid and liquid feed material to a material reduction mill'having a cylindrical wall and two end walls, the ratio of the interior diameter of the drum to the interior peripheral length thereof being at least 2:1, a plurality of highly upstanding transyerse crusher bars mounted in spaced apart relation around the cylindrical wall to ,eflectively'engage the largest particles of feed; maintaining during operation a keying action zone defined by the periphery of the mill and a pair of opposed annular keying liners mounted one on each of the-end walls of the, drum, said keying liners collectively penetrating into the mill interior from about 20% to about 80% of the effective mill length, said keying zone I Williamson' Apr. 25-, 1922 1,670,005 7 Pratt May 15, 1928 2,704,636 Weston Mar. 22, 1955 Klugh. July 10, 1956

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