Abstract: A rock crusher comprises a pair of rotors spaced apart to define a throat therebetween and driven in opposite directions. Impactor bars on the rotors crush rock that is delivered to the rotors and passes the broken rock fragments through the throat. The rock crusher may be conveniently provided in a harvesting vehicle such as a potato harvester to crush rock that has been picked up with and separated from the crop. The rocks can be crushed to a sufficiently small size that they may be conveniently returned to the field surface, and thus the arrangement avoids the trouble and expense that would otherwise be entailed in collecting and disposing of the separated rock.

Abstract: A hammermill including a main shaft rotatable about a main axis passing longitudinally through the main shaft. Connected to the main shaft and spaced longitudinally along the main axis are a plurality of substantially parallel plates. Pivotally mounted between the plates along pivot axes parallel to and spaced from the main axis are a plurality of free swinging hammers for crushing material. A plurality of sealing members are positioned along the pivot axes and compressed between the hammers and the plates.

Abstract: The hammers provide multiple impact points for debris, by providing impact points via tips at different radii from the axis of rotation of the hammer mill. The tips preferably are at substantially the same radius from the axis of rotation of the hammer about the hammer support shaft, so that efficiency is maintained even as the hammers lay back. The multiple impact points produce a more effective result, by partially sizing the debris on initial impact, before more precise final sizing in the grinding chamber. Angled surfaces on the hammer tips provide more effective shearing and tearing action than with conventional bar hammers. Wear patterns are such that grinding efficiency as the hammers wear down is maintained throughout the life of the replaceable tips. Preferably, the hammers weigh substantially more than conventional hammers, to provide a higher energy impact, and to reduce the tendency of the hammers to lay back.

Abstract: An improved pulverizing and grinding hammer and methods of making and using such a hammer in a hammer mill are disclosed. The improved hammer has a substantially trapezoidal insert made of a hard metal such as STELLITE 12 that is brazed onto a groove in a conventional hammer to form a contact face having an approximately ten degree layback angle with the vertical. The improved hammer provides a clear visible boundary between the insert material and base metal of the hammer, which acts as a wear indicator when the layback angle wears to approximately 40 to 50 degrees, the critical angle at which the size reduction efficiency of the mill decreases.

Abstract: The flail includes a cutting member which contains a cutting head. The cutting head defines a cutting edge which acts upon material to be comminuted during operation of the rotary impact mechanism. The cutting edge is made wear-resistant by having affixed thereto a plural number of wear-resistant parts made of hard metal and having a basically prismatic configuration.

Abstract: A method and apparatus for reclaiming foundry sand wherein the speed of the rotor and/or the drum and, thus, the resulting striking, shearing and friction forces are adapted or matched to the changing surface hardness of the quartz grains to be processed during the process duration. The drum comprises two drum halves separated transversely to the rotational axis, a sand inlet and a suction removal device.

Abstract: A comminuting machine for waste wood and other waste comminutable material has a vehicle frame and a conveyor in the form of a tub or bed for receiving material to be comminuted. A comminuting assembly has a shaft with a series of rotors with flat radially extending side walls fixed in an angularly offset continuous helical array from one end to the other on the shaft. Comminuting members presenting blunt material shattering beads are releasably secured on the arm mounting surfaces.

Abstract: A hammer for use in shredders and comprising a hammer holder with a dovetail key and a hammer tip having a dovetail groove shaped to receive the dovetail key. The hammer tip is slidably engageable with the hammer holder by sliding the dovetail groove over the dovetail key. Centrifugal force from the hammer rotation keeps the tip secured to the holder. The hammer tip is also wider than the hammer holder in order to protect the holder from wear and tear.

Abstract: A hammermill is presented which includes a plurality of hammers each presenting an arcuate striking profile. The hammermill includes a rotor having rods for swingable carrying the hammers thereon and a motor for rotating the rotor. The hammers are longitudinally spaced along the rotor and preferably helically arrayed thereabout. The hammers present a head and a body, the head having an arcuate striking face which may include a point. As the rotor turns, the hammers are free to swing on the rods and comminute material fed into the hammermill. The hammers preferably present symmetrical striking profiles whereby after one profile becomes worn, the position of the hammer on the rod may be reversed to increase the useful life thereof.

Abstract: A two-piece hammer for use in a shredder comprises a work engaging piece made from a hard, wear resistant material and a supporting piece made from a softer, relatively ductile material having a relatively high tensile strength. The two pieces are secured together by a removable fastener, with a resilient member being interposed between the work engaging piece and a supporting flange of the supporting piece to dampen the transmission of impact forces from the work engaging piece to the supporting piece. The supporting piece comprises an aperture which is adapted to receive a support pin of the shredder when the hammer is mounted in the shredder.

Abstract: A protective shield for a hammer-crusher rotor protects at least the circumferential surfaces of disks attached to and rotating with a rotor shaft. In the spacing between neighboring disks, at least one hammer is tiltably or pivotally supported on an axle rod extending at a radial spacing from the shaft through the disks. Each protective shield is formed by at least one filler body made of an especially wear resistant material. The filler bodies are arranged and secured in the free space between neighboring disks where the hammers are not located. In its installed position, each filler body has a radially outwardly facing wear resistant surface having an axial width substantially the same as or slightly wider than the axial gap width of the respective spacing. The radially outer surface of the filler bodies is approximately flush with or concentric to a circumferential outer surface of the neighboring disks.

Abstract: An impact rotor arranged concentrically to the axis of a drum has preferably four beating blades which are wave-shaped on the outer peripheral side.

Abstract: A spider assembly for a rotary hammer assembly for a hammermill, the spider assembly including a spider having a number of arms, a replaceable end member mounted on the end of each arm and a protective cap mounted on the end of the replaceable member. The replaceable member including a contoured web that matingly engages a corrresponding socket in the spider arm. The web and socket including corresponding abutments for resisting the centrifigal force of the rotary motion of the hammer assembly. The protective cap is provided with a shroud having a contoured surface that matingly engages and protects the face of the end member.

Abstract: An improvement to a hammermill extends the life of the hammers by providing regular and periodic reversal of the rotor of the hammermill without the necessity of disassembly of the hammermill or the necessity of moving or operating levers, screws or other devices in order to reposition the internal apparatus so that the mill can be reversed.The improvement consists of an internal apparatus attached to the hammermill at the inlet to the hammermill. The internal apparatus is formed of a vertical plate extending adjacent the inlet and attached to a mounting plate. The mounting plate is bolted to the hammermill. The vertical plate extends across the width of the hammermill. A plurality of triangular reenforcement plates are welded between the vertical plate and the mounting plate. The mounting plate can have its free edge bent toward the inner wall of the hammermill to insure a tight seal with the inner wall.

Abstract: A hammer assembly for a hammermill of the type having a housing forming a fragmentizing chamber, a hammermill assembly being mounted for rotary motion in the chamber and including a drive shaft, a number of spider assemblies axially aligned on the shaft, each spider assembly including a number of arms having a pin opening at the outer end thereof, a number of discs alternately arranged on the shaft between the spider assemblies, each disc including a number of hammer pin openings corresponding to the number of openings in the spider arms to form axially aligned rows of openings, a hammer pin aligned at each row of openings and a number of hammers randomly mounted on the hammer pins in the spaces provided in the spider arms and between the adjacent discs.

Abstract: The present invention relates to a hammer for use in a hammer mill and particularly provides an improved hammer of separate type in which a hammer head is detachably coupled with a hammer body. A material of the highest level in abrasion resistance such as high chromium cast iron is employed to form the hammer head. In spite of brittleness of the material, there is no such problem as breakdown due to impulse forces applied and transferred immediately because there is no looseness at all in the engagement of the coupled hammer body and hammer head. Energy applied is sufficiently utilized thereby improving energy efficiency.

Abstract: A protective end cap for a hammermill assembly including a drive shaft having a number of spider assemblies mounted thereon, each spider assembly including a hub having a number of spider arms with the spider arms being aligned with the spider arms on the adjacent spider arm assemblies, a hammer shaft extending through each row of spider arms, a number of hammers mounted on the hammer shaft in the spaces between the spider arms and a protective cap mounted on the exposed portions of the hammer shafts between the spider arms, the caps including flanges on one or both sides for protecting the outer ends of the spider arms.

Abstract: A heavy duty hammermill having a fragmentizing chamber and a hammer assembly mounted for rotary motion in the chamber and cooperating with a cutting comb and grate bars for fragmentizing auto parts fed into the chamber, the hammermill assembly being formed from a number of spiders mounted on a drive shaft and an end disc mounted on the shaft at each end of the spider assemblies, the spiders being spaced apart equal distances by spacer members provided between each pair of spiders and the end discs, each spider assembly including a spider having six arms with freely rotating hammers mounted on hammer pins in the spaces between the arms, the spider arms having a hub portion spaced outwardly from the spacer members and protective caps mounted on the impact areas of the spider arms and end discs.

Abstract: A rotary disintegration apparatus comprises a housing with a central material input and a material outlet that is open underneath, an inner rotor fixed to a first shaft and an outer rotor fixed to a second shaft on the same axis that rotates in the opposite direction, and blade rings that follow each other in alternation having blades which are inclined in the direction of rotation, which can be coated with a protective layer, which have front and rear edges of hard wear-resistant material, and which sit on one side on retaining rings and on the other side on assembly rings forming replaceable components of annular assembly ring carriers that are connected to the shafts.

Abstract: Tooth assemblies upon the breaker rings of the rotor of the apparatus each include tooth and seat components having abutting surfaces that prevent forward, rearward, inward and lateral movement of the tooth relative to the seat and rotor. Outward tooth movement during operation of the apparatus is prevented by a pin that extends generally parallel to the rotor axis through aligned bores within the tooth and its seat. The pin is shielded from damaging impacts with the material being ground and from detrimental bending stresses, and is releasably retained within the bores by a detent that permits convenient removal of the pin when replacement or repair of the tooth is required.

Abstract: A replaceable, protective end cap assembly for the end of a spider arm for a rotary hammer assembly, the end cap assembly including a side plate assembly and a protective cap. The side plate assembly including a pair of side plates connected by upper and lower cross members that matingly engage the leading edge of the spider arm with the side plates covering the side wall surfaces in the impact area of the spider arm. The protective cap includes a shroud that overlies the front surface of the spider arm as well as the peripheral edges of the side plates and the side plate assembly and end caps being retained on the spider arms by the hammer shaft.

Abstract: The invention relates to a rotor for a rebound crusher in which the beater blades (5), retained in marginal recesses (4) in rotor discs (3) are positively retained by an axial locking system (7, 8) disposed on the rear side of the beater blades (5). On the front side of the beater blades (5) protective caps (10) are disposed on the discs (3) to maintain the axial positive locking system (7, 8) and protect the discs (3). To secure the beater blades (5) against axial displacement, the beater blades (5) are secured by a positive locking system comprising a recess (22) and a nose (21) engaging therein with clearance. To keep the protective cap (10) free from loading by the beader blade (5), in the side of the protective cap (10) adjacent the beater blade (5) a window (24) is provided into which a projection (15) of the disc (3) extends which forms an abutment (16 ) for a bearing surface (17) of the beater blade (5).

Abstract: An arrangement for securing a cap to the end of a supporting body of a hammer mill rotor. The forward end of the supporting body end is provided with a front projection that is an integral part of the supporting body end and extends parallel to the axis of rotation of the rotor. The rearward end of the supporting body end is provided with a recessed portion for receiving a filler member that forms a rear projection. The front and rear walls of the cap are provided with respective flanges that are directed toward one another, extend parallel to the axis of rotation of the rotor, and extend in a hook-like manner about the front and rear projections. The cap covers all sides of the supporting body end but leaves free spaces between a hammer shaft and the side walls of the cap.

Abstract: A wood chipper is disclosed comprising a large rotational disc with a pattern of blade mounting pockets, usually in a spiral, on the front face, such that mounted chipping knives project diagonally from the face of the disc at an acute angle to the disc, with chip passage slots extending through the disc at these pockets; and hardened elongated ridges protruding from and integral with the disc face, offset from the pockets and slots toward the direction of rotation, these ridges being diagonally oriented relative to a radius of the disc.

Abstract: An impact crushing machine provided with easily repairable strikers fixedly arranged along the circumference of a rotor at regular angular intervals so as to extend radially of the rotor. A plurality of seats fixedly mounted respectively with striking chips formed of a durable hard material such as a hard metal are arranged in lines and rows on and detachably fixed to the radially outer end of the striker for individual replacement. When the striking chip is abraded to an unusable extent, the seat mounted with the worn striking chip and a seat fixedly mounted with an unworn striking chip can be interchanged for the further use of the striker, so that the frequency of replacing the heavy striker with a new one is reduced and the operating cost of the impact crushing machine is reduced.

Abstract: A cage mill includes a housing, a disc rotatably supported within the housing, a plurality of support shafts each fixed at one end to the disc so as to form a cage, a band fixed to the other end of each of the support shafts, a plurality of ceramic pins each having a through-hole in which one of the support shafts is placed so as to support one of the ceramic pins, and a plurality of nuts each engaging with a male screw portion of each end of the support shafts for releasably fixing the support shafts and the ceramic pins to the disc and the band. The support shafts and loosely placed in the ceramic pins, respectively, so that the latter can be turned around the former when the nuts are released.

Abstract: A mineral breaker including at least one breaker drum having breaker teeth projecting radially therefrom, the teeth being arranged so as to define a series of discrete circumferentially spaced helical formations extending along the drum.

Abstract: A disintegrating rotor comprising disks (1) carrying beaters (2) having a hard-faced working surface (4) that is formed by inserts (5 and 6) made from different wear-resistance materials and fitted so that harder inserts are found near the center of the beater (2) and softer inserts, to the periphery.

Abstract: A hammer assembly for attachment to a rotor of a rotary material crusher is disclosed. The hammer assembly includes a hammer member rigidly connected to the rotor and an extension of the hammer member having a longitudinal axis disposed parallel and spaced relative the axis of rotation of the rotor. The extension has a uniform transverse cross-sectional configuration along the length of the extension. A cap means is removably connected to the extension for crushing the material on rotation of the rotor, the cap defining an undercut portion which cooperates with the extension for locking the cap adjacent the hammer member.

Abstract: A hammer mill for treating scrap metal including a rotary hammer means for delivering impact blows to scrap metal is shown. Discharge grates are provided for disposing of the scrap metal through discharge outlets for the hammer mill. The rotor is a disc type with rotating hammers located on pins extending through the discs. A plurality of caps are circumferentially located around each disc and attached thereto for protecting the disc against excessive wear. A dual feed roller feeds the scrap metal to the hammer mill to be shredded.

Abstract: An arrangement for reinforcing and spacing annular hammer rotor disks which are securely mounted on a rotor shaft. Disposed between these disks, there are provided pivotable, replaceably mounted hammers which are offset over the periphery of the rotor and are disposed at a distance from one another. The hammers located close to one another in a row are mounted on a common supporting rod which is parallel to the axis of rotation. A plurality of U-shaped replaceable strips, each of which is provided with a crosspiece, can be placed and secured on one of the annular disks in the circumferential direction thereof. The crosspiece of one strip rests against the crosspiece of the adjacent strip, and the intersection of the abutting ends of two strips is disposed in a radial plane of one of the supporting rods. Each crosspiece, at least on a long side and near an end, is provided with a cutout which corresponds approximately to the radius of pivot and thereof approximately to half the width of the hammer.

Abstract: A rotary mineral breaker has wear tip over which the mineral pieces are passed when discharged from the rotor. A supplementary wear tip is provided as a back up for the main wear tip so that failure of the main wear tip will not result in undue damage occurring to the rotor. Also the main wear tip is provided as two interchangeable pieces to improve the useful life of the wear tip.

Abstract: A cage mill includes a housing having an inlet at a side portion thereof and an exit at a lower portion thereof, a disc rotatably arranged within the housing, a plurality of support shafts fixed at one end thereof to the disc so as to form a cage into which hard materials can enter through the inlet of the housing when the cage rotates as a rotor, a ring fixed to the other end of the support shafts, a plurality of ceramic pins each fixed by way of an adhesive to each of the support shafts, and a stopper mechanism for preventing the ceramic pins from directly contacting the disc and the ring.

Abstract: The tip of a spider arm of a rotor of a reversible hammer mill is protected from wear and damage by a pair of replaceable caps. Each of the caps has a protective shroud for protecting a portion of the extremity of the tip and an adjacent edge of the spider arm. The caps also each have a relatively narrow web which is sized to fit within and cooperate with the web of another cap in substantially filling an open-ended slot in the spider arm. The webs of the two caps are introduced into the slot from opposite ends of the slot and held in place by a hammer pin which extends through collinear openings in the webs and the spider arm.

Abstract: The hammer mill for treating scrap metal including a rotary hammer means for delivering impact blows to scrap metal is shown. Discharge grates are provided for disposing of the scrap metal through discharge outlets for the hammer mill. The rotor is a disc type with rotating hammers located on pins extending through the discs. A plurality of caps are circumferentially located around each disc and attached thereto for protecting the disc against excessive wear. A dual feed roller feeds the scrap metal to the hammer mill to be shredded.

Abstract: When inserting a locking wedge (14) having planar wedge surfaces (16, 17) between an anvil (4; 5) and a hammerhead (1) or an anvil block lining (6) the wedge (14), which is provided with a draw head (18; 22) is drawn in between two mutually converging locking surfaces (9, 7) on the anvil and the hammerhead or the anvil block insert.

Abstract: A hammermill in which the hammers are carried by suspension rods for free swinging movement between a plurality of spaced discs. Each disc is provided with a peripheral hole pattern which includes a greater number of holes than there are hammers carried between each adjacent pair of discs thereby providing for relocation of the hammers one or more times to extend the life of the discs. Further protective shoes or caps cover the peripheral edge and a portion of the machined side surfaces of each disc which are subjected to extreme wear.

Abstract: A method and arrangement for support of contact elements of hammermills and the like are disclosed in which a hardenable liquid bonding material is flowed into a chamber defined by registering recesses in facing relatively slidable surfaces of contact and support elements, the material being allowed to harden to define a key preventing relative slidable movement of the elements. A tongue-and-groove type of connection is provided for allowing the relative slidable movement while positively limiting relative movement in any direction in a plane transverse to the direction of the relative slidable movement.

Abstract: Leading edges of rotor-plates which carry the swing hammers of hammermills are protected from wear by removable caps, each secured by paired pin assemblies, each of which may be shifted axially to permit removal of the cap it normally secures. Each pin assembly includes a pair of tubular pins or pin portions which may be axially abutting one another, each assembly including at least one portion which is short enough to be removed (or moved axially to a position which permits removal of the cap). In the original form of the parent application, each assembly was totally countersunk within the cap, having heads at each end that were countersunk and having in each head the countersunk head or nut of a tie-bolt. In the form preferred at the time of filing this continuation-in-part application, the pair of tubular pivots forming each assembly is held in place by reliable friction resulting from the expanding force of split-spring-tubes forcefully squeezed substantially closed during insertion.

Abstract: A striker bar for a rotary cage grinder in which the impact-receiving portions of the bar are of an abrasion resistant ceramic, such as aluminum oxide, silicon carbide, or tungsten carbide. The bar includes a block of the ceramic, preferably formed in sections abutting end-to end, adhesively affixed to an angle iron mounting, which is removably attached to supporting structural members in the cage.

Abstract: Replaceable protective means for protecting an end disc of a rotor shredder from excessive wear includes a protective cap of hardened, wear resistant metal, and at least two pins and washers of readily weldable metal. The protective cap has a U-shaped channel for receiving a curved portion of the periphery of the end disc. The opposed walls of the U-shaped channel each have at least one pair of pin-receiving openings and the openings in each wall are aligned with those in the opposed wall. When the cap is positioned in place on the end disc with the pin receiving openings in the opposed walls of the cap aligned with openings which extend through the end disc, the pins which have enlarged heads at one end which are larger than the openings in the disc can be inserted into the aligned openings and secured in place by welding a washer which also is larger in diameter than the openings in the disc to the other end of each of the pins.

Abstract: A two-piece hammer for a rotary hammer mill having a separate hammer shank and a separate replaceable hammer tip. The shank and the tip have interlocking portions so that when the two parts are assembled and secured by a transverse pin they form a unitary hammer body that may be mounted on a rotor assembly in a hammer mill used for crushing or shredding materials.

Abstract: A comminution device having replaceable blade assemblies which are used, preferably, as stators. The blade assemblies can be replaceably affixed to the housing of the machine when used as stators or may be replaceably affixed to a rotating arm when used as rotors. The blade assemblies are comprised of a plug member that may have threads on part of its outer periphery in order to be threadedly connected to a stationary housing or rotatable member of a machine. A slotted portion is formed in the plug member and one end of a cemented hard metal carbide blade is disposed in said slotted portion. A collar is shrunk fit over the periphery of the slotted portion and provides the clamping force necessary to hold the blade in assembled relation to the plug member. Tapering cooperating elements of abutment are provided between the walls of the slot and the sides of the blade in order to urge one end of the blade into firm contact with the bottom of the slotted portion.

Abstract: A breaker tooth member for apparatus for the reduction of solid material such as wood, plastics, metal and the like comprises a metal head having an integral projecting mounting shank having an enlarged portion adjacent the head adapted to fit snugly in an enlarged mounting bore portion of a support ring, the head being formed opposite the shank with a recess having a flat back face intersecting a ledge defining a locking formation, and an integral harder wear resistant metal sharp edged element is mounted in the recess flush against the back face, that element being correspondingly formed along one edge to interlock with said ledge, and the element is fixed on the head by a plurality of pins having tight friction fit in aligned bores in the head and the element.

Abstract: In a hammermill or the like and employing hammerheads with sockets which receive the rotor hammer arms, slots are provided in the hammer arms to receive cross pins which extend through apertures in the hammerheads and the slots to hold the hammerheads to the arms. Spacers having a convex outer surface which is complementary to the curved slot ends and a concave inner surface complementary to the curvature of the pins are employed to positively position the pins in the desired position in the slots and thus, by use of different size spacers, enable adjustment of the radial extension of the hammerheads with respect to the arms to compensate for wear and maintain a desired clearance with the working chamber wall and thus maintain a desired particle size.

Abstract: An improved hammer design for a swing-hammer type crushing machine. The hammer is in at least two pieces, a shank and a detachable tip section. The shank is pivotably mounted at one end on a rod extending between a pair of radial discs spaced along the machine rotor. The tip section is joined to the shank by a simple connecting pin which passes through co-aligned holes in a bifurcation on the tip and a lug extending outwardly from the shank. Spaced apart tabs at the free end of the shank co-operate with a stop on the rotor to limit the pivotal movement of the hammer between predetermined limits such that the connecting pin is always confined between the pair of rotor discs during operation of the machine. However, a worn or damaged tip section can be readily replaced in situ by removing the rotor stop, pivoting the hammer so the connection between the shank and tip are outside the rotor, and removing the connecting pin.

Abstract: A hammer is provided for pulverizing and comminutating apparatus of the hammer mill-type with this hammer including both tearing and shearing edges for enhanced effectiveness in obtaining size reduction of both friable and non-friable materials. This pulverizer hammer includes a relatively narrow tearing edge which is disposed in spaced parallel relationship to the pivot bearing of the hammer. A side edge surface of the hammer associated with that tearing edge is formed in arcuately curved, receding relationship thereto for directing and urging particles of waste material radially outward toward the tearing edge where they will be subjected to further pulverizing action. A shearing edge is also formed along one corner of the side edge surface of the hammer and extends radially in receding relationship to the tearing edge. The arculately curved and contoured surface is also configured to extend in receding relationship with respect to the shearing edge.

Abstract: A hammer is provided which is useful in solid waste, e.g. metal, shredding operations. The hammer includes a shank member adapted to be connected to a supporting shaft, and a replaceable tip member which is subject to wear substantially along its leading and lower portions. The shank end and the tip are slidably interconnected along a common face, e.g., by a tongue and groove interrelationship. Cooperating keyway pocket and hooked key interconnecting means are provided on the shank and on the tip, with a significant portion of the keyway pocket/hooked key interengagement being in the shank. A slot passes through the shank and the tip adjacent the trailing edge thereof. A wedge is inserted into the slot. Finally, means are provided for retaining the wedge in the slot. In this way a tip member is provided which is very easily replaced when worn.

Abstract: Rotary processing apparatus is shown having a horizontal rotor made up of a number of flat annular plates secured together to which material processing members such as centrifugal impactors are releasably secured. Stator processing members or impactors are shown which are adjustable from outside the rotor housing. In another form, a rotor operating in a vertical plane and having processing members or impactors on both sides has material to be processed fed to it separately on each side. In both forms, reinforcement of the rotor housing may additionally be achieved by providing a plurality of generally flat annular members secured together and to inside surfaces of the rotor housing. Rotor impactors for the second embodiment have two processing ends and are provided with simple slip-in means for insertion into place through apertures in the laminated rotor.

Abstract: The teeth of the stator and rotor of the refiner are each formed with a surface layer on the leading flanks which is harder than the end faces so as to maintain a sharp cutting edge. The hardness of the surface layer is at least 600 HB while the end face is of a hardness of from 280 to 320 HB.