US2673647A - Classification of indurated metalliferous agglomerates - Google Patents

Description

March 30, 1954 HALEY ET AL 2,673,647

CLASSIFICATION OF INDURATED METALLIFEROUS AGGLOMERATES Filed April 10, 1952 2 Sheets-Sheet l INVENTORS KWA/ETHM HALE) BY HneaLa Zensk M /M,

flrramy s March 30, 1954 K. M. HALEY ET AL CLASSIFICATION OF INDURATED METALLIFEROUS AGGLOMERATES Filed April 10, 1952 2 Sheets-Sheet 2 j 10 M0 ,4: f2 0 PELLET/Z/NG 7E/WH- "5 Z6 IN Gksew Aaaaomsmrs INVENTORS A elvue r M l-lmey BY flaw/.0 1 Z'msk M m, 67 Q6 Patented Mar. 30, 1954 CLASSIFICATION OF INDURATED METAL- LIFEROUS AGGLOMERATES Kenneth M. Haley and Harold v. Trask, Ashland, Ky., assignors to Oglcbay, Norton and Company, Cleveland, Ohio, a corporation of Delaware Application April 10, 1952, Serial No. 281,628

11 Claims. (01. 209-215) This invention relates to classification of indurated metalliferous agglomerates and, more particularly, to a method by which such agglomerates may be classified or separated in accordance with their relative abilities to withstand impact, abrasion and like stresses occurring during transportation and handling by conventional equipment employed for transporting and handling ore.

A number of metalliferous materials either occur or are produced in a finely divided state which is unsuited for reduction or like operations in conventional metallurgical apparatus such as blast furnaces or the like. Blast furnace flue dust, fines of natural ores or ore concentrates may be mentioned as examples of such materials. It is now known, however, that such finely divided materials maybe agglomerated into bodies of suitable size for use in blast furnaces or the like by rolling or tumbling the material while in moist condition in a drum or cylinder thereby producing ball-like bodies which, in the case of iron oxides, may be subsequently indurated or hardened by heating. Such procedures have been found especially advantageous for agglomerating the finely divided concentrates resulting from the benefication of lowgrade magnetite.

The temperature range of the heating required to produce suitable indurated agglomerates is, however, relatively close to the point where the agglomerates tend to weld or fuse together, and hence care must be exercised to remain below that temperature range to prevent difficulties in the furnace or other indurating apparatus. Consequently, it is difficult, if not impossible, to insure that each agglomerate will have reached at least the minimum desired indurating temperature and have been maintained at that temperature for at least the minimum period of time during its movement through the furnace or other indurating apparatus since in treating large quantities of agglomerates thereis inevitably some variation with respect to the paths taken by the separate agglomerates through a furnace or the like. Therefore, not all the agglomerates discharged from the furnace or other indurating apparatus will be equally hardened so that some may not possess suitable decrescence resistance and would produce an undesirable amount of fines and fragments during normal transportation and handling thereof as Well as within the upper portion of a blast furnace or the like thereby rendering them unsuitable for normal use in such apparatus.

An object oi this invention. is to provide an improved method for rapidly classifying. indurated agglomerates of metalliferous material containing iron oxide in accordance with their abilities to withstand decrescence as the result of impact, abrasion or like stresses resulting from transportation or handling of the agglomerates by conventional ore transporting and handling apparatus.

Another object of the invention is to provide an improved method for rapidly classifying indurated agglomerates of iron oxide particles, in accordance with their relative extents of induration, through the action of a magnetic field of force upon the agglomerates.

A further object of the invention is to rapidly and easily classify indurated agglomerates of finely divided material containing iron oxide in accordance with their abilities to Withstand decrescence due to impact, abrasion or the like by subjecting a moving stream of the agglomerates to a magnetic field of force so that the agglomcrates of different decrescence resistance are separated inaccordance with the efiect thereon of said magnetic field, the strength of which is selected in accordance with its effect on agglomerates of known decrescence resistance.

A more specific object of the invention is to provide an improved method of classifying indurated agglomerates of iron oxide particles in accordance with their abilities to withstand decrescence due to transportation and handling which comprises determining the FeO content of indurated agglomerates having satisfactory decrescence resistance, determining the magnetic force required to separate agglomerates of such FeO content from those of lesser FeO content, subjecting a moving stream of the agglomerates to a magnetic force of the determined value and collecting those agglomerates which are deflected from said stream separately from the undefiected agglomerates.

Further objects and advantages of the invention will be apparent to those skilled in the art to which it pertains from the following descrip tion of the present preferred embodiment thereof, which is described with reference to the accompanying drawings, in which:

Fig. 1 isa schematic representation of an apparatus for producing agglomerates of finely divided metalliferous material and illustrating the manner in which the procedure of this invention is employed therewith;

Fig. 2 is an enlargedv sectional view through the agglomerate classifying portion of the apparatus shown in Fig. 1 illustrating the manner in which the indurated agglomerates are subjected to a magnetic force while moving in a stream for effectingclassification thereof;

, Fig; 3 isa graphical representationof the relationship'of the percentage of iron as FeO in the agglomerates to the decreascence resistance of the agglomerates;

Fig. 4 is a graphical representation of the effect of the percentage of iron in the form of FeO in the agglomerates upon the attraction of a magnet therefor;

Fig. 5 is a graphical representation of the relationship between the indurating temperature of the agglomerates and the percentage of iron thereof in the form of FeO when the agglomerates are made with or without the inclusion of a small percentage of carbon; and, I

Fig. 6 is a graphical representation of the variation of the percentage of iron in the form of FeO in agglomerates as the result of varying the percentage of carbon included therein, the relationship being shown for several different indurating temperatures.

The invention may be advantageously employed with indurated agglomerates formed from a variety of finely divided metalliferous materials containing iron oxide. However, for the sake of brevity, this description will be restricted to the application of the novel procedure to agglomerates formed from finely divided concentrates of magnetite. Also, to facilitate disclosure of the invention a schematic representation of an apparatus for producing ball-like agglomerates from such material has been illustrated in the drawings. It is to be understood, however, that the invention is not limited to use with finely divided magnetite nor to employment with the disclosed apparatus for forming and indurating the agglomerates since the invention may be practiced with agglomerates composed of other iron oxide containing materials and which have been formed and indurated by means other than those here shown.

The apparatus schematically illustrated in Fig. 1 for agglomerating and indurating finely divided materials does not, per se, constitute a part of this invention and hence will not be described in detail. It is sufiicient for the present purpose to note that the finely divided metalliferous material, such as magnetite concentrates or the like, is suppliedfroin a suitable source, here indicated as a bin or container 10, to a belt conveyor H. The conveyor H transports the material either directly, or through means of intermediate conveying apparatus such as indicated by the conveyor [2, to the entrance of a balling drum l3. The metalliferous material is preferably in moist condition and may or may not have had a small percentage of carbon, in the form of finely divided anthracite or coke, added thereto prior to its introduction into the balling drum. This addition of carbon may be effected by supplying a small quantity thereof from a suitable source such as a bin or storage receptacle M to the metalliferous material as it traveled upon one of the conveyors, such as H, on its way to the balling drum I3.

The finely divided metalliferous material, with or without the addition of a small percentage of carbon, is tumbled and rolled within the balling drum due to rotation of the latter thereby forming ball-like agglomerates or bodies of the material which are discharged through the end of the drum opposite that into which the material was introduced. This discharge end of the drum may be provided with a screen or trommel [5 to remove fragments of the ball-like bodies and those of smaller sizes so that only bodies larger than a predetermined minimum are delivered to the subsequent apparatus for further treatment-while the fragments and smaller bu digasv are returned to the balling drum, by means not shown, for reforming therein.

As mentioned heretofore, it is now known that these ball-like bodies issuing from the balling drum I3 are quite friable or fragile and this friability increases with drying thereof so that the bodies are not satisfactory for use in a blast furnace or the like in their green state. However, the bodies may be materially hardened by heating them to an elevated temperature. This heating may be effected in a variety of different ways, one convenient mode being that employing countercurrent flow of the bodies with respect to heated air or other gases as occurs in a shaft furnace such as is schematically indicated at l6. Hence, the bodies, equal to or larger than a predetermined minimum size, delivered from the balling drum are charged into a furnace l6 through a suitable mechanism such as, for example, a reciprocating cover and conveyor mechanism H which is movable over the top of the furnace 16 for distributing the green bodies therein, the bodies being delivered to the conveyor mechanism from the balling drum by a suitable conveying means such as l8.

The ball-like bodies in the furnace l6 gradually move downwardly therethrough as the result of the operation of suitable discharging mechanism, not shown, at the bottom of the furnace. While thus moving downwardly, the bodies in the furnace are heated to an elevated temperature, which may be in the order from 1750 F. to 2 100 F., with the result that the bodies discharged from the bottom of the furnace it are indurated to an extent that they are quite hard and will withstand appreciable shock and abrasion. These bodies, which are hereinafter referred to as indurated agglomerates, may be screened adjacent their discharge from the furnace, by a suitable means designated [9, to remove any fines produced during the induration after which they are customarily stockpiled or transported to a point of utilization.

Although the agglomerates are all indurated during their passage through the shaft furnace or equivalent apparatus, it has been found that some of the bodies better withstand transportation and/or handling by conventional equipment utilized for handling and transporting ore than do others of the bodies. That is, the bodies or agglomerates which have not been sufficiently indurated produce an undesirably large quantity of fines in the form of broken fragments, dust or the like during such transportation and handling. Since only a predetermined percentage of fines can be used when the material is to form part or all of the ore charge in a blast furnace, the fines in excess of this percentage are an economic detriment since they must be dis carded, reagglomerated or otherwise specially handled thereby increasing the actual cost of the agglomerates. Consequently, it has been necessary heretofore either to exercise special care in handling the agglomerates or to employ ore for a blast furnace charge. Asa. resultof these studies it was found that agglomerated metalliferous material coarser than that which would pass through a 28 mesh screen is gen erally satisfactory for blast furnace use and that indurated agglomerates of in. or larger original diameter which did not produce more than 20% fines of minus 28 mesh size (that is, material which will pass through a screen having openings .0232" x .0232) are acceptable. It was also determined that the forces and stresses to which the agglomerates are subjected during transportation and handling are in general of the impact, crushing and abrasion type which can be satisfactorily simulated by tumbling a quantity thereof in a drum. Specifically, it has been found that a tumble drum unit constructed in accordance with the A. S. T. M. specification No. D294-28T, as shown on page 973 of that societys publication for 1948, affords a suitable apparatus for simulating the conditions to which the agglomerates are customarily subjected by employing a 50-pound sample thereof in the drum and tumbling the same for a total of 260 revolutions at a speed of 24 R. P. M. The amount of decrescence or disintegration of the pellets or agglomerates subjected to such action is representative of that which would result from their normal bulk transportation and/or handling from the point of manufacture to the point of consumption.

These tests readily established the extent of induration required of suitable agglomerates but it left unanswered the question of how agglomcrates of the hardness necessary to withstand such a test could be determined from those which were not of such hardness since the aglomerates are mixed both when they issue from the indurating apparatus and when in the stockpiles thereof. Although it was known that the temperatures to which the agglomerates were subjected influenced their degree of hardness, there was no way of insuring that each individual agglomerate would be subjected to the proper temperature for the proper length of time within the indurating apparatus since commercial scale operations require continuous production of the agglomerates in a furnace or the like of a size such that a given agglomerate requires several hours for passage therethrough. Moreover, while the properly indurated agglomerates differ somewhat in appearance from those which are insufficiently indurated, such visual inspection and selection based thereon was impractical for all but experimental purposes.

It was discovered, however, that the degree of induration of the agglomerates and the corresponding ability to withstand the stresses of transportation and handling bore a direct re1aticnship to the response of the agglomerates to a magnetic field. This discovery was unexpected since, although the metalliferous material from which the agglomerates were formed comprised magnetite particles, the conditions in the indurating furnace were-oxidizing so that substantially all of the metalliferous material was converted to the non-magnetic form. Hence, it was originally surmised that residual magnetism would indicate the extent to which this conversion was incomplete and hence would indicate that the agglomerates were not properly indurated. The aforementioned discovery indicated that this assumption was either in. error or that the properly indurated agglomerates had undergonea further conversion.

Chemical analysis of properly indurated agglomerates indicated the presence of a small percentage of the iron in the form of FeO. The fact that the degree of induration was correlated to the percentage of iron-in the agglomerates in the form of FeO was substantiated by analyses of multiple samples of the indurated agglomerates which were also subjected to the aforementioned tumble test. A multiple correlation of such data based upon samples of the agglomcrates produced during several weeks operation of an agglomerating plant is reproduced in the form of the graph comprising Fig. 3. From this graph it will be apparent that although the percentage of iron as Fe() in the agglomerates was relatively small in all cases it evidently had an important effect uponthe decrescence resistance of the agglomerates. Thus, it is readily seen that agglomerates which produced less than 20% of minus 28 mesh fines when tumble tested had 4.2% or more of their iron in the form of FeO, while those agglomerates which produced a greater quantity of fines had a lesser percentage of their iron in the form of FeO.

It was also discovered that although the percentage of iron in the form of FeO was small in all cases the diiierences in this percentage was not only indicative of the degree of induration but also is the reason for the difierence in response of the agglomerates to a magnetic field. This is evidenced by the graph comprising Fig. 4 which represents the relationship between the iron as FeO in indurated agglomerate having diameters in the order of A", and the magnetic pull thereon in grams by a magnet of 8'70 gauss strength.

Thecause for the discovered relationship between the degree of induration of the agglomerates and the percentage of iron as FeO therein is evidently partially the temperature in the indurating apparatus and partially the composition of the green or unhardened agglomerate. Thus, for a given temperature in the indurating furnace, a much higher percentage of FeO is produced in the indurated agglomerate when carbon is added to the green agglomerate than when no carbon i used. This relationship is shown in Fig. 5 of the drawings which is a graphical representation of the percentage of iron as FeO in agglomerates that have been indurated at difierent temperatures and which agglomerates either contained no carbon in the green form or had 1% carbon added thereto prior to the formation thereof. Representative data illustrated in Fig. 4 may be tabulated as follows:

Pelletizing irat Degree F 1.115 0. 91 1, 910 0. 98 2,120 o. as 2, 210 1. 51 2, 240 2.16 2, 325 3. as 2, 350 3.93

The influence of the quantity of carbon in the green agglomerates with respect to the percentage of their iron in the form of FeO after induration to different temperatures is also represented in the graphs reproduced as Fig. 6 of the drawings. Representative data illustrated by these graphs may be tabulated as follows:

gsgzg g Percent Iron Agglomeratcs as Feo The d fferences in the FeO content of indurated agglomerates when subjected to equivalent furnace temperatures but having different carbon content are evidently due to the fact that, since the carbon supplies fuel in the indurating operation, the interiors of the agglomerates containirr such fuel are apparently raised to higher temperatures than the temperature of the furnace as a Whole so that a portion of the oxide converted to F6203 is further converted to the FeO form. The reducing action of the carbon may also play a part in this operation. But whatever may be the reason or reasons for the presence of FeO, it has been definitely established that the presence of iron in this form is a reliable measure of the degree of induration of the agglomerates and of their relative abilities to withstand decrescence in normal transportation and handling.

It is also definitely established that the properly indurated agglomerates, both those to which carbon had been added and those which had not had such addition of carbon, responded more strongly to magnetic attraction than the agglomerates which were not satisfactorily indurated and the degree of response is directly related to the percentage of iron as FeO. Consequently, separation of properly indurated agglomerates from those which will not withstand transportation and handling stresses without the production of excessive fines can be effected by magnetic means. Therefore, in accordance with this invention the agglomerates are subjected, after induration, to a magnetic field of force of sufiicient strength to separate the agglomerates having at least the predetermined minimum FeO content from those whose FeO content is of lesser amount.

In performing the procedure of this invention tests are first conducted of indurated agglomerates to determine the percentage of iron as FeO in those agglomerates which satisfactorily withstand the aforementioned tumbling test, as determined by the fines produced being 20% or less of minus 28 mesh in size. The pull exerted upon such agglomerates by a magnet is then determined in terms of the strength-of the magnetic field necessary to deflect such agglomerates from a moving stream thereof. The agglomerates to be classified or separated are then caused to move in a stream and are subjected to a magnetic field of the determined strength so that the properly indurated agglomerates are deflected from that stream to one location while the agglomerates which are not so indurated, and hence have a lower FeO content, are not thus deflected and continue to a different location.

In applying the invention to the production of indurated agglomerates of iron oxide, which are produced as described above, the indurated agglomerates issuing from the furnace l6 and which pass over the screen l9 are received on a suitable conveyor, such as the belt conveyor 20, and are transported thereby as a stream to and over the head pulley 2|. The pulley 2| may itself be a magnet or a suitable means for producing a magnetic field is disposed adjacent thereto with the result that the properly indurated agglomerates are deflected from the stream issuing from the conveyor 20 while the agglomerates which are not thus properly indurated are substantially undefiected.

In the preferred embodiment of the invention, the means for providing the magnetic field comprises an electromagnet 22 stationarily supported within the hollow interior of a rotating non-magnetic drum comprising the head pulley 2 i, see Fig. 2. Consequently, the properly indurated agglomerates and which have an FeO content equal to or greater than the predetermined minimum tend to cling to the belt 20 as the latter passes over the head pulley 2| and only drop from the belt after they have traveled substantially around to the under side thereof and hence beyond the infiuence of the electromagnet 22. The agglomerates which contain less FeO are not thus strongly attracted to the belt 20 and hence fall therefrom either in a substantially undiverted stream or are only carried around the head pulley a relatively short distance. Consequently, the properly indurated agglomerates, designated 23, may be collected in one stockpile or container such as 24 While the improperly indurated agglomerates 25 may be collected in a separate stockpile or container such as 26. This separation may be facilitated by provision of a suitable division member or wall such as 21 with inclined surfaces to direct the agglomerates 23 and 25 to their respective containers or stockpiles. In place of stockpiling the agglomerates they may, of course, be transported to other locations, if desired, by suitable conveyors located in the position of the containers 24 and 26.

The strength of the magnetic field will, of course, depend in part upon the size and speed of movement of the agglomerates and upon the percentage of FeO determined as minimum for ability to withstand a given type of transportation and handling. By way of example, but Without limitation thereto, it has been found that agglomerates in the order of A in., diameter can be satisfactorily classified by a belt conveyor having a head pulley 3 ft. in diameter, traveling at a peripheral speed of ft./min., and equipped with an electromagnet of 2500 gauss strength. Representative samples of the agglomerates passing over this pulley and which were deflected from the stream thereof as being properly indurated were tumble tested in 50-pound samples for 200 revolutions at 24 R. P. M. and the resulting fines were 20% or less of minus 28 mesh size, thus indicating the agglomerates were of satisfactory induration to withstand normal handling and transportation by conventional equipment.

Although the invention has been disclosed as having the properly indurated agglomerates defiected from a flowing stream thereof through the use of a conveyor belt with a magnetic field at the head pulley, it will be apparent, that other means of effecting the magnetic separation may be employed. For example, the agglomerates may be caused to flow in a stream down a chute or the "h with a means for producing a magnetic field adjacent the discharge end of the chute to deflect the agglomerates of proper induration to one location while allowing the other agglomerates to fall freely to a different location. It will also be evident that although the invention has been described with respect to production of ball-like agglomerates indurated in a shaft furnace, the invention is not limited'to use with any particular agglomerate forming or indurating apparatus. Furthermore, the invention may be applied to agglomerates which have been placed in a stockpile or other storage as well as to those directly issuing from an indurating apparatus. It will be understood, therefore, that in view of these and other possible modification and adaptations, the invention is not to be considered as limited by the specific values and. dimensions set forth above by way of example nor to use with the structures illustrated and described except as may be re-' quired by the spirit and scope of the appended claims.

Having thus described the invention, we claim:

1. The method of classifying, in accordance with their abilities to withstand decrescence due to impact and abrasion, agglomerates of finely divided metalliferous particles containing iron oxide which have been indurated by heating which comprises subjecting the agglomerates to a magnetic field of force having a strength such that agglomerates of proper decrescence resistance are removed from the agglomerates of lesser decrescence resistance.

2. The method of separating agglomerates of iron oxide particles which have been indurated to a predetermined extent by heating from those agglomerates which have been indurated to a lesser extent comprising moving a quantity of mixed agglomerates in a stream past a region of magnetic influence and segregating the substantially undefiected agglomerates from those which are appreciably magnetically deflected from said stream.

3. The method of classifying, in accordance with their abilities to withstand decresence due to impact and abrasion, agglomerates of finely divided metalliferous particles containing iron oxide which have been indurated by heating comprising delivering the agglomerates to a conveyor and subjecting the agglomerates to a magnetic field of force while they are carried by said conveyor with the said field of force having a strength such that agglomerates of proper decrescence resistance are directed by said field of force to one location while agglomerates of lesser decrescence resistance are delivered to a separate location.

4. The method of separating agglomerates of iron oxide particles which have been indurated to a predetermined extent by heating from those agglomerates which have been indurated to a lesser extent comprising supplying the agglomerates to be separated to a moving belt-type conveyor thereby producing a moving stream of said agglomerates over the head pulley of the con- 10 veyor, creating a magnetic field of force through said conveyor at the head pulley thereof, and collecting those agglomerates which cling to said conveyor a predetermined distance of the travel thereof over its head pulley separately i'rom the agglomerates which do not so cling.

5. The method of classifying agglomerates of finely divided metallir'erous particles containing iron oxide which have been indurated by heating comprising determining the magnetic properties of such agglomerates which satisfactorily withstand impact and abrasion tests representative of the stresses encountered in shipping and handling of ore, moving untested agglomerates in a stream, and subjecting the moving agglomerates to a magnetic field of force of a strength sufficient to divert from said stream those agglomerates having magnetic properties equivalent to those which withstood the impact and abrasion tests.

6. The method of classifying agglomerates of finely divided metalliferous particles containing iron oxide which have been indurated by heating comprising subjecting a quantity of such agglomerates to conditions representative of those encountered in shipping and handling ore, determining the magnetic properties of those agglomerates which endure said conditions with less decrescence than the amount permissible in the metallurgical process in which the agglomerates are to be used, moving untested agglomerates in a stream, and subjecting the moving agglomerates to a magnetic field of force of a strength sufficient to divert from said stream those agglomerates having magnetic properties equivalent to those which were determined.

7. The method of classifying indurated agglomerates of finely divided particles including iron oxide comprising determining the percentage of iron in the form of FeO in those agglomerates which W111 withstand a predetermined amount of impact and abrasion with a decrescence less than a preselected amount, and subjecting the agglomerates to be classified to a magnetic force of strength suflicient to cause removal of those agglomerates having an FeO content equal to or greater than the aforedetermined content from those agglomerates whose FeO content is less than the said determined amount.

8. The method of classifying indurated agglomerates of iron oxide particles which comprises determining the percentage of iron in the form of FeO of those agglomerates which will withstand a predetermined amount of impact and abrasion with a descrescence less than a preselected amount, moving the agglomerates to be classified in a stream, and subjecting the moving agglomerates to a magnetic force of strength sufficient to divert from said stream those agglomerates having an FeO content equal to or greater than the said determined content.

9. The method of classifying indurated agglomerates of iron ore concentrates which comprises determining the percentage of iron in the form of FeO of such agglomerates which will withstand a predetermined amount of impact and abrasion with a decrescence less than a preselected amount, determining the magnetic force necessary to separate agglomerates having an FeO content equal to or greater than the determined content from those having a lesser FeO content, moving the agglomerates to be classified in a stream, and subjecting the moving agglomerates to a magnetic force of the determined value thereby deflecting from said ll stream the agglomerates having satisfactory decrescence resistance.

10. The method of classifying agglomerates, formed from finely divided material containing iron oxide and indurated by heating, with respect to their abilities to withstand forces incident to transportation and handling by conventional ore handling apparatus comprising, determining the percentage of iron in the form of FeO of such agglomerates which produce 20% or less of minus 28 mesh fines when subjected to forces of impact and abrasion equivalent to those produced in ordinary transportation and handling of ore, determiningthe magnetic force required to separate agglomerates of the determined or greater FeO content from those of lesser FeO content, and subjecting the untested agglomerates while moving in a stream to a magnetic force of the determined value and acting in a manner which deflects from the normal path of travel of the agglomerates those which have an FeO content at least equal to the determined value.

11. The method of classifying agglomerates,

formed from finely divided material containing 25 iron oxide and indurated by heating, with respect to their abilities to withstand forces incident to transportation and handling by con- 12 ventional ore handling apparatus comprising, determining the percentage of iron in the form of FeO of such agglomerates which produce 20% or less of minus 28 mesh fines when subjected to forces of impact and abrasion equivalent to those produced in ordinary transportation and handling of ore, determining the magnetic force required to separate agglomerates of the desired or greater FeO content from those of lesser FeO content, delivering the agglomerates to be classified to a moving belt-type conveyor provided with a magnetic field adjacent the head pulley having an intensity of the determined value, and collecting those agglomerates which cling to said conveyor a predetermined distance of the travel thereof over its head pulley separately from the agglomerates which do not so cling.

KENNETH M. HALEY.

HAROLD V. TRASK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,071,460 Grave Feb. 23, 1937 2,131,006 Dean Sept. 20, 1 38 2,2 2, 19 Maynard Feb. 10, 1942 2,557,059 Marchi June 19, 1951

Images