US2404775A

US2404775A - Hammer for impact crushers

Info

Publication number: US2404775A
Application number: US422205A
Authority: US
Inventors: Leslie G Ehmann
Original assignee: Electric Steel Foundry Co
Current assignee: Electric Steel Foundry Co
Priority date: 1941-12-09
Filing date: 1941-12-09
Publication date: 1946-07-30
Anticipated expiration: 1963-07-30

Description

uly 39, W460 a... s. EHMANN- 2,404,775

HAMMER FOR IMPACT GRUSHERS Filed Dec. 9, 1941 3 Sheets-Sheet 1 INV'E ATTORNEY.

" LESLIE a. EHMAILVN July 3G,, 1% 1.. G. EHMANN HAMMER FOR IMPACT CRUSHERS Filed Dec. 9, 1941 3 Sheets-Sheet 2 ATTORNEY i L. G, ETH-MANN 4 9 7 5mm FOR IMPACT ciwsnmns Filed 1 9, 1941. s Sheds-Sheet s ATTORNEY Patented July 30, 1946 Leslie G. Elimann,

Portland, 0reg., assignor to Electric Steel Foundry Company, Portland,

0reg., a corporation of Oregon Application December 9, 1941, Serial No. 422,205

12 Claims.

The present invention relate to rotary impact crushers or reducers, and more particularly to a new and improved hammer for use therein.

Rotary impact crushers usually comprise a driven shaft having a plurality of discs arranged thereon with one or more hammers pivotally attached to the periphery of each disc. The rotor element is mounted within a casing including a plurality of cylindrically arranged breaker bars, and is driven at high speed so that material fed thereto is crushed or pulverized between the hammers and the casing. The hammers usually are of a one piece construction and, depending upon the size and capacity of the crusher, are of relatively massive proportions. Wear occurs at the outer edges of the hammer heads, and after a certain period of use the amount of wear becomes such that the hammer must be replaced. Since only about fifteen to twenty percent of the total mass of one piece hammers away by use at the time the hammer is replaced, a relatively high proportion of the metal comprising the hammer is scrapped. Crusher hammers, particularly of the type used for reducing ore, cement and the like, are made of a very T tough and hardened steel which in itself is very expensive, and the loss of so great a proportion of the metal occasioned by the replacement of the entire hammer becomes an item of major expense in the maintenance of a hammer mill.

It has been proposed to use hammers having renewable heads or wearing portions which alone would need replacement after having become worn to an ineflicient condition. Such hammers as have been devised heretofore have had renewable heads attached to the shank portion by means of bolts, rivets, or similar means. These require the expenditure of a considerable time to loosen and replace, necessitating a costly cessation of operation of the mill because of time involved in reversing or renewing the hammer heads. Moreover, because of the extreme conditions of vibration and other forces attendant upon the operation of crushers, such fastening means have become loosened failed, permitting the release of the hammer and causing considerable damage to the crusher before it can be brought to a standstill. A renewable head hammer for crushers which will withstand severe service and be incapable of flying apart when in operation has been greatly needed in the art.

It is, therefore, an object of the present invention to provide a new and improved hammer for rotary impact crushers and the like having has been worn or otherwise have 2 a renewable head so attached to the shank that it cannot separate therefrom during operation of the crusher.

A further object of the invention resides in the provision of a new and improved impact hammer havinga renewable head wearing portion which is secured to the hammer shank without the use of separate attaching means.

It is a still further object of the invention to provide a novel impact hammer of the character described which is simple and sturdy in construction, which is long lived and economical i use, and in which the head is so attached to the shank that it may be renewed or reversed with a relatively small expenditure of time.

In accordance with an illustrated embodiment of the invention, a crusher impact hammer is provided comprising a hammer head having a socketformed in one surfacethereofincluding integral portions forming overhanging shoulders. The head is attached to a shank comprising a pair of arms having a first pair of ends cooperatively arranged in the socket, the arm ends having opposed lateral projections extending cooperatively beneath corresponding shoulders. The arm are so shaped that they may readily be assembled into the head without the need of special tools or fastening means, and so that when the outer ends of the arms are mounted on the crusher rotor discs, separation of the head from the arms is positively precluded.

Further objects and advantages of the invention will become apparent as the description proceeds, while the features of novelty characterizing the invention will be pointed out with greater particularity in the appended claims.

In the drawings, Figure l is a fragmentary longitudinal sectional view of a portion of a crusher illustrating the arrangement of a plurality of hammers therein constructed in accordance with one form of the present invention; Figure 2 is a cross sectional view through the structure illustrated in Figure 1, taken along the line 22; Figure 3 is an exploded view in perspective of an impact crusher hammer of the type shown in Figures 1 and 2; Figure 4 i an end view of the hammer shown in Figure 3; Figure 5 is a longitudinal view, partly in cross section, of the hammer assembly shown in Figures 3 and 4; Figure 6 is an exploded view in perspective of a hammer constructed in accordance with a modification of the invention; Figure '7 is an end View of the assembled hammer of the modification shown in Figure 6; Figure 8 is a vertical cross sectional view. of the hammer, taken along the line 8-8 of Figure 7; Figure 9 is a cross sectional View taken along the line 9+9 of Figure 7; Figure 10 is an end view of a hammer constructed in accordance with a further modification of the invention; Figure 11 is an exploded view in perspective of the hammer head and a fragmentary portion of the shank arms of the modification shown in.'Figure 10; and Figures 12 and 13 are end views of structures similar to those illustrated in Figures 4 and 7, respectively, showing the invention as embodied in knives for shredding ensilage, sugar cane, pineapple and'o-ther similar fibrous materials.

Impact hammers embodying the present invention are adapted for use in various types and kind of crushers or reducers, and for purposes of illustration one form of hammer of the present invention is shown in connection with a crusher of conventional design in the fragmentary views of Figures 1 and 2. The crusher comprises a casing including a plurality of axially extending and cylindrically'arranged bars ll. Extending axially through the casing is a shaft !2 having a plurality of discs 13 mounted thereon and keyed thereto in a spaced apart relation. Pivotally attached to the periphery of the discs it are a plurality of hammers H comprising, shanks l4 having. ey s for cooperativelyreceiving. a through rod idpivotally securing the hammers to the discs l3; and having heads 18 which, in the extended position of the hammerarevolve closely adjacent the bars H of the casing. It will be understood that in operationthe"rotohfinoluding the discs 13 and hammers H, i revolved. at very high speeds and hence is subjectedto heavy centrifugal forces, and that the leading edges of the hammers are subject to considerable wear under impact with .the material beingcrushed. I

The primary feature of the present invention resides in the provision of an impact hammer H orsimilar implement in which'the head portion 18 is renewable, and which is removably attached to the shankportion It in such manner that misalignment ofthe. arms comprising the shank is all that is required to remove it therefrom. During the operation of the crusher misalignment of the shank arms, and consequent removal of the head therefrom, is precluded, An important advantag o-fthe invention resides in the fact that the head l3 may be reversed or renewed within aminimum of time. T v

Referring to Figures 3 to 5, inclusive, each hammer H comprises a reversible and renewable tip or head portion {Shaving a socket formed by a longitudinal recess W in the inner surface thereof and extending longitudinally of the hammer hea/d.

Portions

22 and 23 integral with the hammer head t8 extend over the opposite ends of the recess 2} forming relatively rugged overhanging shoulders. The hammer shank comprises two pieces, namely, a pair of

arms

26 and 25 which have afirst or outer pair of ends having opposed

lateral projections

26 and 27 of a cross section corresponding generally to that of the" recess ii in head 13. I The arms 2d and 25 are separately insertable into the recess 2!, arm 24 being adapted for insertion-first, after which it is moved furthermost to the right, as viewed in Figure 5, with theprojectioh 25 extending cooperatively under the shoulder 23. The surface 2 9 of the arm 2 opposite the projection 25 is concavely curved, and the adjacent surface 39 of the arm 25 i convex l y curved, the two curvatures being similar so thatin the assembled po- 'sition of the arms they abut against each other.

4 The center of the curve it is at some point 32 in the shoulder portion 22, so that the projection 27 of arm 25 may beinserted into the left of the recess ill by rotating the end of arm 25 about the shoulder 22 as indicated by dotted lines 33 in Figure 5.

The innermost ends of the

arm

24 and 25 are provided with

eye openings

34 and 35, respectively, for cooperatively receiving a through rod such as I5 for securing a plurality of similar hammers to the rotor discs iii of the crusher. With the arms thus retained in a predetermined aligned relation of the

eyes

34 and 35, withdrawal of the hook ends of the arms from the hammer head is positively precluded.

It is preferred to tie the inner end of the arms together to facilitate the assembly of the hammers in the crusher. Thi tying means comprises a keeper 3? inserted through the eyes 34 and 3.5 and dropped downwardly into cooperating slots 38 and in the arms 2 and Z5, respectively. The opposite. ends of the keeper 3? are provided with heads i2 and 53 which fit cooperatively into recesses provided therefor in the outer surfaces of the arms about the ends of the slots 38 and 352. The upper surface of the keeper 3? is concavely curved so as to conform generally with the curvature of the

eyes

34 and 35. It will be understood, however, that little or no wear will occur'on the. surface of the keeper by virtue of the fact that due to centrifugal force the weight of the hammer will be borne entirely by the surface of the eyes opposite the keeper 3?. In order to facilitate removal of the keeper 3'! from the slot 33 and 353, additional recesses 4d are provided in the outer surfaces of the

arms

24 and 25 for the insertion of a punch into an engaging relation with the lowermost edge of the keeper heads.

In the assembled condition of the hammer the shank arms extend generallyparallel with respect to each other and in which relation they are secured when mounted upon the rotor discs by means of the through rod l5 extending through the eyes in the inner ends of the shank arms. In the operation of the crusher, the hammers will e maintained in a radially extended position with respect to the periphery of the discs, due to the centrifugal force acting outwardly on the hammers. Depending upon such factors as the length and weight of the hammer, the diameter of the rotor discs, and the speed of rotation of the rotor, the centrifugal force acting on the hammers will be relatively great, aside from the tangential forces resulting from the impact of the hammers with the material being crushed. The anchorage between the shank and the head is made rugged and sufIicient-ly strong so as to be able to withstand anysuch forces as may be imposed upon the unit. Thus the

bridging shoulders

22 and 23 over the opposite end of the head recess 2i and the lateral projections 28 and 21 hooking underneath such shoulder portions aremade as heavy as may be required.

The centrifugal force acting upon the hammer head 18 will normally be such as to prevent a rocking movement thereof on the ends of the shank arms even under the force of impact upon material being crushed. But in order further to preclude the occurrence of any such rocking movement, the cross section of the recess 2! in the hammer head, and of the ends of'the shank arrns'jfitting cooperatively therein, is generally elliptical injshane the long axis extending in the longitudirial'direction of the hammer, as

viewed, for example, in Figure 4. It will furthermore be observed that this cross section is somewhat wider at the top than at the bottom, and with particular respect to the shank arms the corner between the projections and the adjoining right angular portion of the shank arms is rounded so as to provide greater strength in the region of the corner against the tension forces concentrated at this point. The opposite sides of the

shank arm

24 and 25 are further provided with shoulders 45 and 41 which, in the assembled relation of the hammer, engage against the upper edges of the side walls of recess 2| further to preclude relative sidewise movement of the head on the ends of the shank arms.

Referring again to Figure 1, it will be observed that the distance between the opposite sides of the pair of shank arms of each hammer is just somewhat less than the axial spacing between a pair of adjacent rotor discs l3 in order to provide for free pivotal movement of the hammers therebetween. It will also be observed that the width of the hammer heads [8 is somewhat less than the center plane distance between adjacent discs l3, but greater than the distance between adjacent surfaces of a pair of adjacent rotor discs so as to prevent the hammersfrom being pivotally movable into the space between the discs.

The hammer of the modification illustrated in Figures 1 to 5, inclusive, is designed for mounting in a crusher in such manner that the wide, fiat side of the hammer is presented for impacting against the material being crushed. In a further modification of the invention, illustrated in Figures 6 to 9, inclusive, a hammer is shown which is adapted for mounting in a crusher in such manner that the relatively narrow end of the hammer head is presented to the work.

Referring now to Figures 6 to 9, inclusive, the hammer of this modification comprises a head 5| and a two piece shank formed by

arms

52 and 53. The inner surface of the hammer head 5| is provided with a socket in the form of an elongated recess 54 having

shoulders

55 and 55 integral with the head and overhanging the opposite ends of recess 54. A web 51 extending lengthwise of the recess 54 and perpendicularly from the base thereof divides the recess 54 substantially centrally. The web 5! is integral with the head at the base of the recess 54, and with the

opposite shoulders

55 and 56.

The

shank arms

52 and 53 have a first pair of ends adapted for fitting cooperatively into the recess 54 in the head 5|, having lateral projections 59 and El, respectively, for fitting snugly under the overhanging

shoulders

55 and 56. The endsof the shank arms are slotted as indicated at 62 and 63, respectively, over the web 51.

The shank arm ends fitting into the socket in head 5| may be of substantially the same width as that of the head. The inner, widened end portions of the shank arms are of a reduced thickness and are so shaped that in the assembled relation they fit cooperatively together in an overlapping relation as illustrated more clearly in Figures 7 and 8. The opposed edges of the for fitting cooperatively

shank arms

52 and 53 are provided with tapered laterally extending flange portions as indicated at and 65, respectively, which strengthen the tip portions of the shank arms.

In assembling the hammer, the shank arm 53 is inserted first into the recess '54 in the head 5| and moved furthermost to the right, as viewed in Figure 7, so that the lateral projection GI engages under the cooperating overhanging shoulder 56. The surface of the shank arm end opposite the lateral projection 6| is concavely curved as indicated at 68, while the adjacent surface 69 of the end shank arm 52 is convexly curved to permit assembly of the last mentioned arm in a manner similar to that described in connection with the hammer H of the first modification. Holding the shank arm 52 in the angular relation indicated by dotted lines II, the tip 59, is inserted into the space between the shoulder 55 and the arm 53 and, by rotating the shank arm 52 in the clockwise direction, as viewed in Figure '7, into a parallel overlapping relation with respect to the first arm 53, the projection 59. will move under the overhanging shoulder 55, while the adjacent

curved surfaces

68 and 59 of the shank arm ends fit snugly against each other.

The widened inner ends of the

shank arms

52 and 53 are provided with eyes 12 and i3, respectively, which in the assembled relation of the shank arms align with each other forcooperatively receiving a through rod or bolt corresponding with the rod l5, described in connection with the hammer of the first modification, for mounting the hammer on the periphery of the crusher rotor discs. The inner ends of the shank arms being thus secured in a predetermined aligned parallel relation, the head 5| is fixedly secured on the opposite ends of the shank arms. By virtue of the web 5'! provided in the head recess 54 which is straddled by the corresponding ends of the shank arms, lateral movement of the head with respect to the shank arm ends is positively precluded. o Many other modifications of the invention will readily occur to those skilled in the art. For example, it will be obvious that it is not essential to the practice of the present invention that the ends of the shank arms fitted into the socket in the hammer head be cooperatively convexly and concavely curved, asshown in the first two modifications. If desired, the hammer may be constructed as illustrated in Figure 10 which is a slight alteration of the design of the second described modification. The hammer of this modification comprises a head 8| and a pair of

similar shank arms

82 and 83. The hammer head 8| is similar to the hammer head 5| except that extending centrally upwardly from the base of the recess 84 and at right angles with respect to the web 8! is a transverse ridge 88 having oppositely curved sides merging smoothly with the base of the recess. The

shank arms

82 and 83 have a first pair of ends for cooperatively fitting into the recess 84 in the head 3| for securing the hammer head thereto. The ends of the

shank arms

82 and 83 are provided with lateral projections 89 and 9|, respectively, the ends of the shank arms being furthermore provided with

slots

92 and 93 for cooperatively straddling the web 81. It will be observed that the two

shank arms

82 and 83 are substantially similar to the one shank arm 52 of the previously described modifications. That is, instead of the adjacent surfaces of the shank arm ends arranged within the head recess being oppositely curved for cooperatively abutting together, in this instance these surfaces are both convexly curved as indicated at 94 and 95, respectively, for fitting smoothly against the opposite surfaces of the ridge portion 88 extending transversely in the head recess 84. Thus formed, the shank arms are insertable separately into the correspond-ing head sockets by inserting the tips holding'the shankarms at an angle with "respect thereto, and then pivoting the shank arms upwardly toward each other to the final vertical position, causing the projections 89 and 9I3 to engage underneath the

overhanging'shoulders

96 and 91,.respectively, of the head.

In'other respects the

arms

82 and 83 of this modification are similar to the .

arms

52 and 53 previously described. It will be obvious that the 1 hammer shown in Figures 1 to "5,, inclusive; may also be modified in a manner as last described.

It will be obvious that the recess in the hammer head forming a socket or sockets for the ends 'of thesha'nk pieces and defining overhanging shoulders for retaining the enlarged ends of the shank pieces in place may be of still other configurations than those shown. Considerable variation also is possible in the design of the shank pieces as well as of the enlarged ends fitting :into the head recess. The present invention resides in the provision of a hammer construction having a two piece shank, at least one of which shank pieces is insertable into a socket provided in the head at an angle with respect'to the final assembled position and pivotall'y movable therein to the final position to secure :the head firmly to the :shank. As the shank pieces are .fastenecl'relative to each other in the final "assembled relation by means for mounting the hammer on the crusher :rotor, .separation ofithe hammer head from the shank is positively precluded. Thus the means fastening the head to the shank does not :require the use of any belts or similar devices :likely to work loose during the operation of the crusher. The head is readily reversible on the shank and, as required, may be replaced when worn with .a minimum expenditure of eifort and time.

In Figures '12 and :13 are illustrated shredder hammers of the type used in swing hammer shredders for'reducing chips, bark, cane, paper, and the like, and in which the hammer head is'provided with knife-like edges for cutting such material. mer IOI having cutting edges I02 providedon its narrow end faces. The shank arms I03 and IM may in all respects be similar to the

shank arms

52 and 53 illustrated in Figures 6 to 9, inclusive, and are cooperatively received in a recess I05 in the hammer head IllI :in the manner 'hereinbefore described. Figure 13 illustrates a shredder hammer having'a head I06 which-is an adaptation of the head l8 shown in Figures 1 to 5, inclusive. The head I06 is mountedon shank arms corresponding to, those shown in Figures 3 and 5, and is provided with cutting edges IIJI presented to the work in the same manner'as the impact surfaces :of the head I8.

.Having described the principleof operation of my invention in What is considered to be operative embodiments thereof, I desire to have it understood that the specific :details describedin connection with the various modifications are merely "illustrative and that the invention may be carried :out-in other ways.

I claim:

1. 5A1). impact hammer for rotary crushers comprising a hammer head, 'an elongated recess in the upper surface of said head, a pair of ,shoulders overhanging the opposite ends of said 1recess,.a pair of arms each having an end extending into corresponding ends of said recess, said arm ends having lateral projections extending cooperatively under corresponding of Figure 12 illustrates *a shredder ham- 7 said overhanging shoulders, said arms being ins sertable separately into said recess, a first of said pair of arms having -a concave curved surface opposite the lateral projection thereof, the second of said arms having a convex curved surface.

opposite the lateral projection thereof for abutting cooperatively against the curved surface of said first arm when said two arms are assembled in said recess for preventing disengagement of said projections from said shoulders, the curvatures of said convex and concave curved surfaces being such that-said second of the arms is moved into assembled relation with the first arm and head from a position angularly away from said first arm. I g

2. A reducing implement for use in reducing mills comprising, in combination, a suspending shank and a Work performing head replaceably mounted .on said shank, said work performing head having a practically elliptical opening extending laterally therethrough and an adjoining transverse shank receiving recess, said head also having integral shoulders of substantially arcuate contour in opposed relation at oppositegends of the recess and adjacent said elliptical Op ning, said suspending shank including apair of members having complementary shapes comprising oppositely projecting ends adapted to ,fit into said opening and extend practically to the opposite ends thereof when the shank is assembled with the head, one of said members havingon one side a concavely curved and substantially arcuate surface adapted to fit the surface ofone of said shoulders and having .on its opposite side a second concavely curved surface, the otherof said members having on one side a concavely curved surface adapted to fit against the other of said shoulders and a substantially concentric convexly curved surface on its opposite side adapted to fit closely adjacent said secondconcavely curved surface, said other of the members being insertable into assembled relation with the head by angular movement about the ,adjacent arcuate shoulder surface, and the .end of said shank practically filling said opening and recess.

3. A reducing implement for use in reducing mills comprising, in combination, ,a suspending shank and a workperforming head replaceably mounted on said shank, said work performing head having an opening extending laterally therethrough and an adjoining transverse shank receiving recess, said head also having integral shoulders of substantially arcuate contour in opposed relation at opposite ends of .the

recess and adjacent said opening, said suspending shank including a pair of members having complementary shapes comprising oppositely projecting ends adapted to fit into said opening and extend practically to the opposite ends thereof when the shank is assembled with the head, one of said members having on one side .a .concavely curved surface adapted to fit adjacent the surface of one of said shoulders and having on its opposite side ,a second concavely curved surface, the other of said members having on one side a concavely curved surface adapted to fit against the other of saidshoulders and a convexly curved surface on its opposite jacent arcuate shoulder surface.

,4. :Ameducing .implementjfor use in reducing mills comprising, in combination, a suspending shank and a work performing head replaceably mounted on said shank, said work performing head having an opening extending laterally and an adjoining transverse shank receiving recess, said head also having shoulders in opposed relation at opposite endsof the recess and adjacent said opening, said suspending shank includinga pair of members having complementary shapes comprising oppositely projecting ends adapted to fit into said opening and extend practically to the opposite ends thereof when the shank is assembled with the head, one of said members having on one side a surface adapted to fit adjacent the surface of one of said shoulders and having on its opposite side a concavely curved surface, the other of said members having on one side a surface adapted to fit against the other of said shoulders and a convexly curved surface on its opposite side adapted to fit closely adjacent said concavely curved surface, said other of the members being insertable into assembled relation with the head by angular movement about the adjacent arcuate shoulder surface, and the end of said shank practically filling said opening and recess.

5. In a reducing implement for use in reducing mills, the combination of a suspending shank comprising a pair ofmembers having complementary shapes and substantially aligned oppositely projecting end portions of non-circular section, one of said members having on one side a substantially arcuate curved surface adjacent the projecting end portion thereof and on its opposite side a concavely curved surface, the other of said members having a substantially arcuate curved surface adjacent the projecting end portion thereof and a substantially concentric curved surface on the opposite side thereof adapted to fit said concavely curved surface of the first defined member so that said oppositely projecting end portions together form a practically continuous end portion of non-circular section.

6. In a reducing implement for use in reducing mils, the combination of a suspending shank comprising a pair of members having complementary shapes and angularly projecting end portions of somewhat elliptical section, one of said members having on one side a curved surface adjacent the projecting end portion thereof and on its opposite side a concavely curved surface, the other of said members having a substantially arcuate curved surface adjacent the projecting end portion thereof and a substantially concentric curved surface on the opposite side thereof adapted to fit said concavely curved surface of the first defined member.

'7. A reducing element for use in a reducing mill or the like and comprising, in combination, a suspending shank and a work performing head replaceably mounted on said shank, said shank including a pair of members having complementary shapes, each of said members including a shank arm having at one end an integral foot portion comprising an outwardly projecting'toe part and an oppositely disposed heel surface, and each of said members having a substantially arcuate surface adjoining said shank arm and said outward projecting toe part, one of said members having a concave heel surface, the second of said members having a convex heel surface substantially concentric with respect to said arcuate surface thereof and adapted to fit snugly adjacent said concave surface, and said work 1.0 perform-ing head. comprising abody-having in one side thereof a recess adaptedto conform to said foot portionswhen the heel surfaces thereof are. incontact; said-body, also having; integral shoulders with opposed arcuate, surfacesadapted to overlie said toe portions, said, workperforming head being, placed in, interlocked relation 'on'said shank by angular swinging movement: of said second of the membersabout thejadjacentflarcuate surface of oneof said shoulders to a position .such that said foot portions practically-fill said I recess andnthe toe portions underlie saidgshoulde'rs. I 111" 8. A re'ducingelement for use in a reducing-mill or the like and comprising, incombinationha suspendingyshank and .a "workperforming head replaceably mounted on said shank, said shank including a pair of members having complementary shapes, each of said members: including a shank arm having at one end an integral foot portion comprising an outwardly projecting toe part and an oppositely disposed heel surface, and each of said members having a curved surface adjoining said shank arm and said outward projecting toe part, one of said members having a concave heel surface, the second of said members having a convex heel surface adapted to fit snugly adjacent said concave surface, and said work performing head comprising a body having in one side thereof a recess adapted to conform to said foot portions when the heel surfaces thereof are in contact, said body also having integral shoulders with opposed surfaces adapted to overlie said toe portions, said work performing head being laced in interlocked relation on said shank by angular swinging movement of said second of the members about the adjacent surface of one of said shoulders to a position such that said foot portions practically fill said recess and the toe portions underlie said shoulders.

9. A reducing element in accordance with claim 8 wherein said suspending shank is characterized by having side surfaces of said shank arms adapted to overlap in assembled relation and in a plane substantially longitudinal of said foot portion.

10. A reducing element in accordance with claim 9 wherein the recess in said work performing head is divided by a partitioning wall extending between said shoulders, and the foot portions of said shank are longitudinally slotted to fit over said partitioning wall.

11. A reducing element for use in a reducing mill or the like and comprising, in combination, a suspending shank and a work performing head replaceably mounted on said shank, said shank including a pair of members having complementary shapes including oppositely offset leg portions adapted to overlap in assembled relation, each of said members having a foot portion at one end including a heel surface and a toe part projecting outwardly in a sidewise direction with respect to sa d offset leg portions, each of said members having a curved surface adjoining said projecting toe part, and said foot portions being slotted intermed ate the sides and longitudinally thereof, said work performing head comprising a body having in opposite sides thereof similar recesses separated by an integral partition, said recesses being of a shape closely conforming to said foot portions when the heel surfaces are in contact and said partition extends through the slots in the feet, said body also having integral shoulders with opposed curved surfaces adapted to overlie said toe portions, said work erforming '11 head being placed in interlocked relation on said shank by angular swinging movement of at least one of said members about the adjacent curved shoulder surface and in a direction such that said oifset leg portions move across overlapping relation.

12; In a reducing implement for use in a re- V ducing mill or the like, the combination'of a replaceable work performing head adapted to be carried in interlocked relation by a suspending shank composed of a pair of" members having longitudinally slotted and oppositely projecting curved feet swingable into said interlocked relation with the work performing head about axes substantially perpendicular to said longitudinal slot, said work performing head comprising a one another into body having top,

I2 end and side walls, said side walls having oppositely facing recesses therein open at the topand separated by. an integral partition adapted to fitsaid longitudinal slots, said recesses being shaped to provide shoulders at 0p-' posite ends adjacent the top wall and adapted to overlie said oppositely projecting feet on opposite sides of said partition, the opposed surfaces of said shoulders being substantially arcuate, and said recesses also being curved to conform to said feet. in' the assembled relation therewith and to permit swinging movement of at least one of said feet about the adjacent arcuate shoulder surface to efiect the interlocked assembled relation of said head and shank.

LESLIE G. EHMANN.

Certificate of Correction Patent No. 2,404,775. July so, 1946. LESLIE G. EHMANN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 10, line 48, for the claim reference numeral 9 read 8; and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 29th day of October, A. D. 1946.

LESLIE FRAZER,

First Assistant Commissioner of Patents.