US1875296A

US1875296A - friend

Info

Publication number: US1875296A
Authority: US
Publication date: 1932-08-30
Anticipated expiration: 1949-08-30

Description

Aug. 30, 1932.

J. F. c. FRIEND CONCENTRATION OF MINERALS INCLUDING COAL Filed Dec. 15. 1931 2 Sheets-Sheet l Aug. 30, 1932. J, c. FRlEND 1,875396 CONCENTRATION OF MINERALS INCLUDING COAL Filed Dec. 15, 1931 2 Sheets-Sheet 2 Patented Aug. 30,1932 k I i i UNITED TA-res] PATENT OFFICE JOHN FREDERICK COOP FRIEND, 0F NEWCASTLE-ON-TYNE, ENGLAND CONCENTRATION OF MINERALS INCLUDING COAL Application filed December 15, 1931, Serial No. 581,250, and in Great Britain August 2, 1929.

This invention comprises improvements in ponent of the movement of the layer is in a or relating to the concentration of minerals horizontal direction but not that such moveincluding coal. l I ment may not have also a vertical compo- It is an object of the invention to provide nent. The term gas is intended to include a process for the dry concentrationof'min-v atmospheric air and it will be understood 5U erals and particularly coal in-cases where a that the movement of gas referred to is relawet process of concentration is not desirable tive to the 'coal-i.v e. if desired the bed of or possible. .The process according to the coal may be moved so that the gas moves present invention permitsof the treatment relatively to it.)

10 of a wide range of sizes at one operation; It Not only does thedownward movement of is especially advantageous in the treatment gas- (relatively to the coal) assist in the of small coal containing finesor dust. stratification of thematerial but it tendsto Processes are known in which alayer of carry back into the material any fine mineral coal lying upon avperforated screenvis sub- Which might otherwise be carried away as the coal is slightly lifted, or loosened by the of gas acting on the mineral is less than that upward passage of the air and stratification necessary to support the mineral in distendof the material into layers of different spe-- ed. condition. 7 cific gravity is facilitated. It has also been The mineral treated maybe coal of a s1ze ar suggested that the upward passage of air less than one half-inch nlmear dimensions shouldbe efi'ected under a pulsating-pres- (forqexample has maxlmum linear dlIIlGIlr sure. Such processes, however, sufier from s-ionsof one-eighth of an inch), a serious disadvantage as the air carries away: Theinvention furt er c pr app a with it fine material or dust which is difiifor concentrating minerals (for example "1 cult to recover and if left unrecovered makes coal) havingin combination a horizontally the plant a nuisance to theneighbourhood. extending screen, means for causing a layer Moreover, Stratification of fine material or of mineral-to move over the screen horizonof'material of widely difi'ering sizes isnot tally so asto cause material thereon to adsatisfactory. i t vance intermittently relatively thereto, an According to the present invention a proc-- air chamber below the screen anda reciproess of concentration'of minerals (for example eating piston in communication with the air coal) comprises the steps of causing a layer chamber for causing alternations of pos t ve of mineral in subdivided form to travel and negative pressure therein, the positive horizontally in a series of intermittent adpressure being timed to occur between the ad- Vance movements,alternately distending the vance movements of material over the screen. so layer by upward movement of gas intoflit Preferably the air chamber or a part comfrom below and contracting it by downward municating therewith is provided with valves movement of gas out'of-it, so as to cause for the admission of additional air, and stratificationof the mineral into layers of means for operating them at predetermined different components, said distension of the points of the cycle. 85

layer being timed to occur between said ad- In either {form of apparatus the preferred vancemovements, and separating said-laymethodof ensuringfeed ofa layerv of min-" ers from one another. (The term :horizoneral such as coal across the screen cons1st s tally as applied tothe travel of the mineral of means for reciprocating the screen long1- is intended to mean that the-principal coma tudinally, which means are operatively conjected to air pressure from below such, that dust. Preferably the mean upward pressure parts being broken away to show the. in-

ternal construction. r

Figure 3 is a detail of valve mechanism, and v Figure 4 is a further detail. The apparatus comprises a horizontal screen or deck like a concentrator deck havingupstandingside walls 12 and a perfo'-.-

rated bottom or screen portion 11, the openings in which are small enough to maintain:

the layer of material upon the screen asit .passes over the same. Suitable driving means is provided for oscillating the screen longitudinally in such a manner asto cause the material to be concentrated to bepropelled over the screen surface. The driving means comprises a cam 13 upon a shaft 14 which engagesa cam roller 15 on a bracket 16 mounted upon the end' of the apparatus.

The bracket 16 servesa'lso' to form a point of attachment for a swinging link 17 pivoted to a fixed frame element at 18. At the other end of theapparatusis a similar bracket 19 mounted on a swinglng link 20 which 1s'- supported on a frame member 21. Between the frame member 21 and the end' of the apparatus is a spring or springs 22 which serve toreturn the concentrator against the move ment of the cam 13. Reciprocation of the concentrator by the cam 13 is therefore effected upon rotating thelatter, and the shape of the cam must be made such as to impart a suitable well known jerking'movement to the screen whereby'the mineral is propelled forwardly in jerks over its surface.

Below the screen 11 is an inner chamber 3 23 which is closely fitted tothe underside of the screen 11 and arranged to oscillate withv the screen. The bottom of the chamber is a piston 24 of approximately the shape and size of the screen above and connected to the walls ofchamber 23 by canvas'25.

Suitable cam driving mechanism 26 with shaft 27 for the piston is provided and this is so interconnected with the driving shaft 14 for the propulsive action for the screen 11 that the latter will operate to-propel the material at a time when the piston 24 is movingdownwards and the materialis reaching a collapsed condition. 7

The piston 24 is mounted for vertical slid-- ing movement upon a vertical slide 28 which moves in a guide 29. The guide 29 is mounted on a pedestal 31 which houses the cam 26. The longitudinal movement of the screen 11 is allowed for by making the canvas sufliciently loose to permit relative lateral movement between the bottom of piston 24 and the wall of the chamber 23.

The piston 24 as best seen in Figure 4 which shows it in cross-section, is of channelshaped form with a central longitudinal trough to receive a screw conveyor 32. The screw conveyor is. rotated while partaking of the vertical movement of theipiston 24 by a .ratchet 34 operated by a fixed pawl 35. The function of the conveyor is to discharge from the air-chamber 23 any fine material which passesthroughthe screen 11 and to this end it delivers the fine material to a pocket 39-, whence it falls through a bellows 4Q into a fixed trap 41 provided with automatically operated. air locks 42, 43 in series, whichare opened alternately by drive chains from the shaft 27. Thus, the fine material is discharged throughthe valves 42, 43 without permittingpas'sage of air throughthe dis charge pocket 39. a

As will be seen, the conveyor 32 is in two sections having threads of opposite hand so that'one portion of the conveyor worm delivers towards one end of the piston 24, while the other portion ofthe conveyor delivers to wards the other end. The latter portion. de-* livers through bellows-140v and air locks 142, 143'similar tothe bellows and airilocks 42; 43. The air chamber 23 is subdivided by a partition 36 at the-junction'bet-ween the twoi portions of the worm conveyor. 32 and a section 37 of thepartition is fixed to the piston: 24 and joined to'thepartition'36 by'a piece of canvas 38sewn to the bellows 25;

- The

air locks

42, 43 and 142,: 143: are-suit. ably operated by means. not shown 'in the drawings, for example by drive chains from the I shaft; 27. The "operation of .such devices is well understood' and forms no part: of the presentinvention. a

A. hopper 's provided for feeding sub-' dividedmaterial, such as fine coal to becleaned or concentrated, on to the screen 11' at the'entry end thereof in a'laye'r'ofuniform thickness. The hopper 50 is provided with measuring valve 51' at the bottom thereofoperatedby' a variable speed drive 52 of the Humphrey-Sandberg or other type. Below the measuring valve is'asubsidiaryhopper 57- which delivers the material on to the screen At the exit end of thescreen 11 is a weir 5'8 adjustable in height and lower than the thickness of material which it is con't'em plated the screen shall handle. Moreover,"-

the screen stops shortbefore the end of the air-chamber is reached by a sufficient distance" to provide an exit" slot 59 for refuse or 'heavymateria1, Below the exit slot 59 is a rotatprovide means to discharge such material at a predetermined rate. The roller is provided with driving means, not shown in the draws ings, suitable for rotating it at this speed. second weir 61 is provided with a discharge slot 62 in front of it at an intermediate position on the screen 11 between the inlet end and the final discharge and this also has a rotatable vaned discharged member 63. Below the rotatable members 60 and 63 are disposed screw conveyors 64, 65. The screw conveyor from the intermediate slots 62 delivers into a reject chute 66 while the screw conveyor 64 and the final slot 59 delivers into a middlings-returnelevator 67 which returns material to the hopper 50. e

Alongside one of the walls of the airchamber 23. but somewhat spaced therefrom is an air-supply duct 68 having an air-inlet pipe 69 to which air may be supplied if de sired under pressure. WVithin the duct are a plurality of valve boxes 70 which overlie air passages 71 through the walls of the duct 68. The air passages 71 are connected through flexible leather or rubber connectors 72 to air inlets 73 in the walls of the chamber 23. Admission of air to the chamber 23 through the valve boxes 70 is controlled by valves v74: mounted upon a valveoperating spindle 75 which extends in series through all valve boxes. The valve operating spindle is provided with a return spring" 76 and is actuated by a cam 7 7 which bears upon the end of the spindle75. The cam 77 is mounted upon a cam shaft 7 8 and the cam shaft 7 8 is connected by suitable operating means to the other actuating mechanisms of the apparatus in such a way as to maintain its proper time relation therewith. As best seen in Figure 4;, the air duct 68 is mounted on a fixed channel iron 79 which forms part of the framework supporting the apparatus.

At the discharge end of the apparatus is a discharge chute 80. Below the chute 80 isa transversely running belt conveyor 81 for carrying away concentrated material.

In operation of the above apparatus mate rial to be concentrated, say coal, is continuously fed in a condition finer than say to in linear dimensions into the hop-v per 50.

From the hopper 50 the fine coal is delivered through the valve 51 on to the screen 11 of the first portion of the apparatus. Here it forms a layer the thickness of which is determined by the rate of feed and the rate of feed is regulated to keep the thickness constant. Upward movement of the piston 24 compresses air in the chamber 23 below the screen 11 and forces air into the layer of coal above the screen so that the layer-is caused to be swollen and the particles of coal become separated from one another byfilms of air. During the upward movement of piston 24 the material of greater specific gravity becomes free to-move in relation to that of lesser specific gravity and sinks downwardly, readily displacing particles of lesser specific gravity in its-passage. At the top of the piston stroke the-piston 24: is. caused to pause for a time, by suitably shap ing the cam 26, and this pause allows a further very beneficial differential movement ofthe coalparticles to take place in accordance with their specific gravity,-particularlyin the finer sizes of particle- Thereafter the piston 24 moves downwardly causing a suc-;

tionstroke which collapses the mass of c"oal together and at the same time carries the ma- I terial of greater specific gravity in the mass of coal downwardly.

It will be seen that while the layer is distended the air moves upwardly through itand delays the falling movement of the particles and thereafter, 'while still distended, the air moves downwardly through it, accelerating the falling movement under gravity. This action of the air emphasizes the natural tendencyof the particles of less specific gravity to sort themselves out from those of greater specific gravity without (as could an air current of constant direction) imparting a net upward or downward movement beyond that due to gravity.

Thecontinuation of this action leads At the weir 58 only good coal is allowed to pass over and the middlings are returned to the hopper 50 forretreatment.

Fine material, including coal dust, is stratified along with the coarser particles, and owing to the suction it is not allowed to escape fromthe apparatus. Some of the finer valuable material will become concentrated and pass over the chute 80 with the coarser good material- Of the rest a mixed material will pass through the first part of the screen (to the right of partition 38 in Figure 2) and is best returned to the hopper 50 for retreatment; The fine material passing through the screen to the left of partition 38 is waste or reject material.

Owing to the porosityof the coal there may be a slight leakage of air during the upward stroke of the piston 24.- A small quantity of fresh air is, therefore, admitted under pressure through the valves 74 by opening them at the time when the piston is at or near the top of its stroke and more or less at rest... This small quantity of fresh air, admitted under pressure, has a useful effect in enabling the distension of the mass of coal to be maintained while the piston is brought to rest and assisting the pause, during which distension is maintained before suctionbegins; The effect may be varied-by suitably timing the opening of the air ports and the movement of the piston and details of the timing'are best determined by practical tests in accordance with the nature of the material: under treatment. The rate of feed of the material may also be varied by modifying the phase relationship of the feeding movement to the piston stroke.- By these means and by carefully correlating the pis-- ton speed, piston stroke, stroke of screen, and depth of bed of material various grades of material maybe concentrated with success. Clearly it will be desirable that materials to be separated, the constituents of which difler from one another in their specific gravity but little, should rest upon the screen for a longer time than in cases where the differ ences in specific gravity are sharp and stratification rapid. In the case of coal, a suitable depthof bed has been found to be about four inches and a suitable movement for the piston, 160 double strokes per minute, with a lengthof stroke ofthree inches.

'There is, then, a combination of depth of bed, duration and intensity of suction, acceleration of upward pressure, and timing of fresh air valve, which will give the best results in each case. The apparatus will, however, give a certain valuable result within a.

wide range of settings.

The air passing through the mass is so small in quantity and so low in velocity that only'a small quantitiy of the finest particles can remain suspended in it. These can be removed by passing the air through a filter or by mixing it with water in the form of mist; This operation need only be on a small scale and of low cost.

It will be understood that the accompanying drawings are largely diagrammatic, and

it is possible to vary the design of the various parts and-the mechanical construction of the guides, bellows, and other working elements all of which falls within the province of a skilled engineer. It would be within the scope of the invention to eliminate the bellows andpiston mechanism producing alternating pulsatingair pressure below the bellows 25 which tends to alter the form of the pressure-wave in the chamber 23, the canvas may be surrounded by one or more bands 90 "attached to guides 91.

'I' claim 1. A- process of concentration of minerals which comprises the steps of causing a layer ofmineral in subdivided form to travel horizontally in a series of intermittent advance movements, alternately distending the layer 'by upward movement of gas into it from belowandcontracting it by downward movement of gas out of it, so as to cause stratification of themineral into layers of difierent components, said distension of the'layer being timed to'occur only between said advance movements, and separating said layers from one another.

2. A processiof concentration of minerals as-claimed in claim 1', wherein the mean upward pressure of gas acting on the mineral is less than that necessary to support the mineralin distended condition.

3. Apparatus for concentrating minerals having in combination a horizontally extending screen, means for reciprocating the screen horizontally so as to cause material thereon to advance intermittently relatively thereto, an air-chamber below the screen and means in communication with the air-chamber for causing alternations of positive and negative pressure therein, the positive pressure being timed to occur between the advance movements of material over the screen.

4. Apparatus for concentrating minerals as claimed'in claim'3, wherein the air-chamber or a part communicating therewith is provided with valves for the admission of additional air, and means for operating them at predetermined points of the cycle.

In testimony whereof I afiix my signature.

JOHN FREDERICK COOP FRIEND.