CA1298823C - Apparatus for comminuting soil-contaminated tree stumps and the like - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Apparatus is disclosed for comminuting heavy fibrous materials, such as tree stumps. The apparatus includes a cylindrical drum rotor having a fixed impact cutting bar projecting from the drum surface. The rotor is enclosed in a housing which includes an anvil directing feed into contact with the cutting bar in a primary comminution zone. The cutting bar strikes the feed material as it is delivered and/or guided by the anvil, producing a partially comminuted product. The rotor is also partially enclosed by a grate, forming a secondary comminution zone in which the partially comminuted product is confined between the rotor drum surface and the grate. The grate includes apertures that momentarily restrain partially comminuted particles such that a following cutting bar shears the particle to finished product dimen-sions. The length of the finished product is determined by cutting bar height, while the cross section of the finished product is determined by grate aperture dimensions.

Description

l~g8823 The invention relates to comminuting-pulverizing apparatus capable of handling fibrous waste materials. More particularly, the invention relates to heavy duty comminut-ing-pulverizers and rotors that are capable of comminuting tre~e stumps contaminated with debris.
Prior devices are shown and described by Stanton in U.S.
Patent No. 3,627,212; Wahl et al. in U.S. Patent No.
3,430,873; and Strom et al. in U.S. Patent No. 4,009,836.
Deister, in U.S. Patent No. 4,151,959, describes a pulverizer that directs the feed through the machine in a relatively concurrent, axially spiral manner with respect to the impact rotor.
Relatively light weight material has been handled between the rotor blades and the stationary blades as shown by Steffenson in U.S. Patent No. 4,545,539, as well as by DeLuca, U.S. Patent No. 2,830,770, and Covey, U.S. Patent No.
3,680,797.
None of the known apparatus is completely satisfactory where the matsrial to be comminuted is a heavy, tough material that includes a substantial quantity of fiber. Such material, for which no suitable machine is presently available with respect to control of product and energy consumption, is represented by wood stumps contaminated with soil and rocks.
It is an object of the present invention to provide a comminuting apparatus that is particularly useful for comminuting tough, heavy fibrous material. It is an object of the invention to provide a shearing action to better comminute the fibrous material components and to provide a high kinetic energv rotor action to drive through the feed material. The invention is particularly useful for comminut-ing contaminated tree stumps to produce a wood chip product suitable for ground mulch or, preferably after cleaning, for pulping or fuel.
It is an object of the invention to provide a comminut-ing apparatus that permits close clearances between housing B

and cutting elements such that unnecessary tumbling of the feed in the machine is reduced and energy efficiency is enhanced. Clearances are adjustable, permitting choice in the size of finished pulverized or comminuted products.
According to the present invention there is provided a rotary type apparatus for carrying out a plurality of size reduction actions, including impact fragmentation, crushing, cutting and shearing of heavy feedstock. The apparatus has a housing means defining a feedstock inlet, an outlet for finished product and a working chamber. A unidirectional rotation rotor means is mounted for solely unidirectional rotation within the working chamber for providing the plurality of size reduction actions on feedstock during each such unidirectional rotation of the rotor means. The rotor means includes a drum presenting an external surface sym-metrically disposed with relation to the centrally-located axis of rotation of the rotor means, and an impact-cutter bar means is provided in a fixed positional relationship project-ing from the drum external surface so as to maintain a fixed uniform diameter cylindrical-configuration peripheral path for the impact-cutter bar means during such rotation of the rotor means. A plurality of work surfaces are provided within the working chamber and include an extended-area substantially-planar work surface presented by anvil means which can be selectively positioned in angled relationship with the peripheral path of rotation of the impact-cutter bar means to define a confined space between the anvil means work surface, the drum exterior surface and the peripheral path of the fixed impact-cutter bar means during rotation of the rotor means. The anvil means work surface and the rotor means coact to provide size reduction by impact fragmentation of frangible feedstock impelled by the rotor means against the anvil means work surface. Size reduction is provided by cutting and/or crushing action of other feedstock to form intermediate work product by coaction in the confined space between the anvil means work surface and the drum external `` 1298823 surface and/or the impact-cutter bar means of the rotor means as the peripheral circumferential path of rotation defined by rotation of the drum and impact-cutter bar means approaches and passes in contiguous relationship to the anvil means work surface. The plurality of work surfaces within the working chamber further include an apertured grate surface presented by grate means for providing additional size-reduction by coaction between the rotor means and the grate means. The grate means circumscribes a major portion of the peripheral circumferential path of rotation of the impact-cutter bar means. The portion circumscribed by the grate means is located subsequent to the anvil means in the direction of rotation of the impact-cutter bar means in passing contiguous to the anvil means work surface so as to define a work zone which is between at least a portion of the drum surface and the grate means for carrying out the additional size reduc-tion of intermediate product. The grate means working surface confronting the interior of the working chamber with spacing means being provided between the circumscribing portion of the grate means working surface and the peripheral path of the impact-cutter bar means being controllably and releasably fixed during size reduction operation of the rotary-type apparatus. The grate means presents apertures which extend through the grate means from the working chamber to the outlet for finished product and which are positioned such that rotation of the rotor means drives intermediate product into the grate apertures. The apertures have a cross-sectional configuration facilitating a shearing action along the peripheral circumferential path of rotation of the impact-cutter bar means. The shearing action takes place on intermediate product being held by the grate apertures and protruding into the working chamber by passage of the impact-cutter bar means contiguous to the grate means working surface with the shearing action causing release of sheared product enabling passage through the apertures toward the outlet for discharge of finished product.

1','~'~3 Thus, it can be seen that apparatus of the invention includes a primary comminution zone in which the material to be reduced in size is initially fed into contact with a housing-enclosed rotating drum rotor having Eixed thereto at least one rigid impact cutting bar. The material is fed into a -top inlet of the mill toward an anvil surface that slopes downwardly toward the rotating rotor. The impact cutting bar on the rotor strikes the feed material, producing a partially comminuted product of a size that discharges from the primary zone, confined between the rotor drum and the bottom or discharge edge of the anvil surface.
The partially comminuted product is received in a secondary comminution zone that includes a grate adjacent the rotor that confines the partially comminuted product between the rotor and the grate. The grate includes apertures sized to allow comminuted product of a desired finished dimension to pass through. The grate apertures are oriented and shaped such that a partially comminuted product particle, under influence of high centrifugal forces, is momentarily restrained in an aperture, and a portion sheared therefrom, by the rapidly moving impact cutting bar. When the partially comminuted product has been reduced sufficiently, it falls through the grate and is discharged as finished product.
Additional contributions and advantages of the invention are considered in more detail in relation to the accompanying drawings, in which:
Figure 1 is a perspective view of an apparatus of the present invention.
Figure 2 is a cross-sectional view of the pulverizer taken along the line 2-2 of Figure 1 showing the rotor positioned in the housing of the apparatus.
Figure 3 is a cross-sectional view of a preferred rotor of the invention design taken along line 3-3 of Figure 1.
Figure 4 is a cross-sectional end view of a preferred impact cutting bar taken along line 4-4 of Figure 1.
Figure 5 is a plan view of a portion of a grate of the i,1 S' ~J

invention viewed along line 5-S of Figure 2 showing an aperture arrangement that is satisfactory for achieving shearing in the secondary comminution zone.
Referring to Figures 1, 2 and 3, a preferred embodiment 10 of the invention is shown. A rotor 11 including impact cutting bars 12, is enclosed in a strong housing 13. The housing 13 includes frame supports 14, including end panels 15 that are provided with additional supporting frame members (not shown), on which are mounted conventional bearing blocks for supporting the rotor 11, for rotation about a rotor axial shaft 16.
The housing 13 includes a top opening 17 for receiving material to be comminuted. The feedstock enters between the rotor 11 and the surface of anvil 18, that slopes downwardly adjacent to the rotor 11. Initial comminution is carried out by impact, splitting and cutting actions.
The comminuting apparatus includes a grate 19 supported in circumscribing relationship adjacent the peripheral path of rotor bars 12, as shown in Figure 2. The grate 19 defines a plurality of apertures 20 that help to finish reducing the initially comminuted material into a product of acceptable size that passes through the grate 19. The housing 13 includes an open-bottom discharge 21 from which finished comminuted material falls for further transport or processing (not shown).
The rotor 11 is preferably initially formed as a substantially hollow cylindrical drum 22, including internal strengthening ribs 23. The drum is fitted with an axial shaft 16, keyed to the drum by means of fittings 24 fixed by bolts 25 to the drum heads 26. The shaft 16 may be made of a continuous cylindrical member extending through the drum, as shown, or comprised of two stub shafts. Either arrangement is keyed to fittings 24.
The drum is fitted with one or more of the impact cutting bars 12 fixed to the external surface of the drum 22 by a series of countersunk bolts 27. Preferably, the impact 12g8823 -bars 12 are arcuate in cross section (see Figure 4).
Preferably, the hollow interior of the drum 22 is filled with a ballast material. For example, the interior cavity is preferably filled with lead ballast after the impact-cutting bars 12 are mounted on the drum. The ballast may be a permanently flowable material, such as lead shot. Alterna-tively, the ballast material may be melted, poured into the drum cavity, and solidified in place. The ballast insures that the rotational energy of the cutting bars is sufficient to drive them through hard, tough fibrous material, such as wood stumps. An additional benefit of the ballast is that it greatly reduces the sound level of operation and helps smooth out power requirements.
The impact-cutting bars 12, the surface of the anvil 18, and adjacent portions of the housing 13 define a primary comminution zone 30 that provides initial, at least partial comminution of the feed material. The top of the anvil 18 is pivotally mounted to an upper portion of frame support 31 by means of a hinge pin 32, as shown in Figure 2. The lower portion of the anvil 18 is pinned to a frame support 31a by means of a shear pin 33 fitted into one of a number of pin apertures 34a, 34b, 34c that establish the desired clearance between the rotor bar 12 and its closest approach to the surface of the anvil 18. Preferably, the clearance may be adjusted to approximately 1/4, 1/2 or 3/4 inch, for example, for the wood stump material of particular interest. The anvil clearance is adjustable in order to achieve efficiency in the primary comminution zone. The chosen clearance depends upon the character of the material being comminuted.
An advantage of the swing-away anvil 18 is that if an uncrushable material such as tramp iron is pinched between a bar 12 and the surface of the anvil 18 the pin 33 will shear.
The anvil 18 then pivots about pin 32 to clear the uncrush-able item without damage to the rotor or other elements.
An additional feature of the anvil 18 is the inclusion -`- lZ98BZ3 of wedge-shaped cleats 44 that present angled edges to the feed surface that restrain the feed stock from moving upwards while in contact with the advancing cutting bar. The cleats help establish an unimpeded gravity feed.
The machine is designed for ease of access for main-tenance or adjustment. Advantageously, the swing-away anvil 18 may be opened to allow access to the internal wearing parts, such as the cutting bars. Special removable chute work is unnecessary with this machine, as all maintenance can be preformed through the swinging anvil door. Many of the internal wear surfaces are protected with replaceable abrasion-resistant plate.
The grate 19 is a perforated plate that is formed into a half-cylinder for enclosing an area adjacent to a lower portion of the impact rotor 11. As shown in Figure 2, the grate may preferably extend for about a 180 arc with respect to the rotor. An operable range of arc of the grate is from about 90 to about 225. The grate includes supporting and stiffening members 35. The grate 19 is supported adjacent the rotor by a housing frame support hinge pin (not shown) fitted into an upper grate aperture 36.
The lower portion of the grate 19 is supported adjacent the rotor 11 by means of a bolt 37 threaded into a frame support member 38 such that the end of the bolt 37 bears upon a lower great surface 39. The threaded bolt arrangement permits adjustment of the clearance from cutting bar 12 to grate 19, typically up to 1/8 inch.
The area bounded by the grate 19, the rotor cylinder 11, and the projecting impact bars 12 constitutes a secondary comminution zone 40 that receives the partially comminuted product from the primary zone 30, i.e., that material passing through the pinch line between anvil 18 and cutting bar 12.
The function of the grate 19 is to reduce the size of the partially comminuted product to a finished comminuted product.
In operation, the rotor 11 causes the partially com-lZg8823 minuted product particles from the primary zone to beprojected by centrifugal force into contact with the grate 19 and its apertures 20, such that particles are momentarily restrained by the apertures 20 and then struck by a following cutting bar 12 which shears off portions of the particle.
The sheared-off portions in the apertures are sufficiently reduced in size to pass through the grate apertures 20 as the finished product of the apparatus.
The finished dimensions of the product are determined by the dimensions of the grate apertures 20 and the height 12a of the cutting bar 12 (see Figures 4 and 5). A key advantage of the grate, rotor and cutting bar arrangement is that no particle of the product will be significantly greater in length than the cutting bar height 12a. Limiting the length of the product allows easier subsequent handling through conventional feeders and air transport systems, which is often difficult with the product from prior apparatus.
Another feature of the invention relates to the shape and arrangement of the grate apertures 20. The dimensions and orientations of the apertures are selected so that the leading and rearward edges 20a of each aperture, with respect to rotor rotation (direction indicated by arrow), define an acute angle with respect to the direction of rota-tion of impact-cutting bar 12. In a preferred embodiment the grate defines hexagonal apertures having a pair of sides which are substantially parallel to the rotational direction of the rotating cutting bars, particularly where these sides have been lengthened to create elongated hexagonal apertures. the arrangement provides an efficient scissoring or shearing effect upon particles which are momentarily restrained by an aperture 20. The shearing action is particularly effective in cutting fibrous materials.
As shown in Figure 5, the apertures 20 may be hexagonal in shape where the cutting bars are mounted upon the rotor .~

lZ988Z3 lateral surfaces in axial alignment with the drum. Where the cutting bar alignment is not axially parallel, a pattern of staggered rectangular grate apertures is suitable. In such an arrangement, the grate is formed from 3/4 inch steel plate and defines 4 square inch perforations on approximately one inch centers aligned along staggered rows. Because the openings 20 are symmetrical, the grate can be reversed to allow use of the edge opposite edge 20a before replacement is necessary. The dimensions of the apertures are selected to achieve a desired finished product size.
The comminuting apparatus of the invention operates at a higher efficiency than prior art machines because the cutting bars are rigidly attached to a heavy, rotating rotor and the material is cut with efficient utilization of the kinetic energy of the rotor. On impact within the primary comminu-tion zone, a partially comminuted product is formed that is then pushed in a tight arc into contact with the discharge grate. While in the secondary comminution zone, the high centrifugal force exerted upon product particles assists in producing the finished comminuted product by driving the particles into momentary restraining contact with the grate, where the particles are sheared by the cutting bars. There are no unnecessary clearances available for the pieces to tumble about in the housing, consuming and wasting energy, such as is typical of conventional hammermills. The ap-paratus of the invention is particulary suitable for com-minuting tough, hard wood stumps that are contaminated with rock and other debris. The arrangement of the primary comminuting zone presents the cutting bar initially contact-ing an incoming feed stock at a decreasing angle with theanvil 18, which greatly tends to break up pieces by splitting or cutting along the grain.
The rotor turns at a speed to give the cutting bar a preferred velocity of between 100 and 150 feet per second.
The rotor is designed to operate with one or more cutting bars, and typically, operates with four high strength steel .

- 129~BZ3 cutting bars fixed to the drum, either in axial alignment, or at an angle of less than 45 with respect to the axis 16 of the rotor. The cutting bars are arranged about the periphery of the drum uniformly in order to balance rotation.
In a preferred embodiment having four cutting bars, three of them may be removed from the machine in order to decrease the rate of flow through the grinder for materials that require up to 400% of normal comminuting energy. The drum is provided with a chamber 42 from which ballast may be removed in order to balance the rotor for a single cutting bar operation.
As shown in Figure 4, a preferred cutting bar 12 is substantially arcuate, trapezoidal, or rectangular in cross section. It is generally provided with hardened cutting elements 43 to resist wear. The leading and trailing edges of the outer surface 12b of the cutting bar are each provided with hardened elements, permitting reversal of the bar to utilize each edge before replacement or refinishing is required. The bar's cutting edges are normally hard-sur-faced, with tungsten carbide or an embedded tungsten carbide edge. The preferred cutting bar is milled, as shown in Figure 4, to conform to the curvature of the drum. The dimensions of the cross section of the bar are selected to provide the desired angles of the leading and trailing edges.
From the foregoing, it will be appreciated that, although embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

- lZ9~3823 SUPPLEMENTARY DISCLOSURE

The present invention may include additional features, such as those illustrated in additional figures 6 to 8, wherein FIG. 6 is a cross-sectional partial view of another embodiment of the invention, FIG. 7 is a detailed view of an impact-cutting bar and rotor arrangement of the embodiment of FIG. 6, with portions cut away, and FIG. 8 is a cross-sectional partial view of another embodiment of the invention.

In the embodiment of FIG. 6 anvil 60 is pivotally mounted about axis 61 and is vertically oriented in tangen-tial relationship to the circumferential path of impact-cutter bars 62 unless broken away by shearing of shear pin 63. A relief zone 64 is provided at the entrance portion to apertured grate 65; the latter is pivotally mounted about axis 66 but is held in the position shown unless broken away by shearing of grate shear pin 67.
Impact-cutter bars 62 are mounted on the drum surface using holder-support structures 68 which are aerodynamically shaped to reduce wind resistance. Another feature of the embodiment of FIG. 6 is fiber stripper 69 which cuts fibrous streamers (such as hosiery made from man-made fibers found in urban solid waste) which can attach to impact-cutter elements 62 if not completely cut by the shearing action at the leading edges of the grate apertures. Stripper 69 cuts such streamers and is controllably located by adjustment means 70,71 on the frame member.
As better seen in FIG. 7, the impact-cutter is divided into individual impact-cutter elements 62 in the embodiment of FIG. 6. With this feature, impact-cutter elements 62 can be replaced individually long the full length of holder support structure 68.
B

lZ9~823 In the embodiment of FIG. 8, anvil 80 is mounted for pivotal movement about axis 81 upon release by shearing of shear pin 82. Anvil 80 presents separate working surfaces 84,85. In the illustrated embodiment, work surface 85 is offset from 84 in the direction of rotation of impact-cutter bars 86. These dual impact surfaces provide dual confinement zones 88,89 and dual cutting actions which are advantageous for certain types of solid waste. Anvil surface 84 is directed vertically into close proximity to the peripheral circumference of impact cutter bars 86; and, anvil surface 85 is substantially tangential to the radius of rotation.
Relief area 90 is provided to allow for some loosening of the work product, after the compacting action in confinement zones 88,89, before entry along the cylindrical surface of grate 92. The latter is mounted for pivotal movement about axis 94 in the event that some material which cannot be cut or crushed causes shearing of shear pin 96.
As described above, such embodiments provide: a range of size-reduction systems with weighted rotors for maximizing torque and increasing efficiency, a cutting system capable of cutting fibrous materials, wire belting or other man-made fibers and, having replaceable wear surface(s) and a release system on the anvil and/or grate to prevent damage due to oversized items, which cannot be crushed or cut, occurring the solid waste work product.
Typical rotor sizes range from sixty (60) to twenty-four (24) inches in diameter (at the peripheral circumference of the impact-cutter bars) and from one hundred twenty (120) to thirty-six (36) inches in length; rotor and ballast weights range from fifty-five (55) tons to six (6) tons providing capacities for tree stumps, railroad ties or vehicular tires form three hundred (300) tons per hour to twenty (20) tons per hour at 600 to 1200 RPM; maximum particle dimension can be selectable between about six (6) to about four (4) inches.

-.f~

Claims (16)

1. Rotary-type apparatus for carrying out a plurality of size reduction actions, including impact fragmentation, crushing, cutting and shearing of heavy feedstock, comprising (A) housing means defining a feedstock inlet, an outlet for finished product, and a working chamber, (B) unidirectional rotation rotor means, such rotor means being mounted for solely unidirec-tional rotation within such working chamber for providing such plurality of size reduction actions on feedstock during each such unidirectional rotation of such rotor means, such rotor means including a drum presenting an external surface symmetrically disposed with relation to a centrally-located axis of rotation for such rotor means, and impact-cutter bar means in a fixed positional relationship projecting from such drum external surface so as to maintain a fixed uniform diameter cylindrical-configura-tion peripheral path for such impact-cutter bar means during such rotation of such rotor means, and (C) a plurality of work surfaces within such working chamber, including:
(i) an extended-area substantially-planar work surface presented by anvil means which can be selectively positioned in angled relationship with the peripheral path of rotation of such impact-cutter bar means to define a confined space between such anvil means work surface, such drum exterior surface and such peripheral path of such fixed impact-cutter bar means during rotation of such rotor means, such anvil means work surface and rotor means coacting to provide size reduction by impact fragmentation of frangible feedstock impelled by such rotor means against such anvil means work surface, and size reduction by a cutting and/or crushing action of other feedstock to form intermediate work product by coaction in such confined space between such anvil means work surface and such drum external surface and/or the impact-cutter bar means of the rotor means as the peripheral circum-ferential path of rotation defined by rotation of such drum and impact-cutter bar means approaches and passes in con-tiguous relationship to such anvil means work surface; and (ii) an apertured grate surface presented by grate means for providing additional size-reduction by coaction between such rotor means and grate means, such grate means circumscribing a major portion of such peripheral circumferential path of rotation of such impact-cutter bar means, such portion circumscribed by such grate means being located subsequent to such anvil means in such direc-tion of rotation of such impact-cutter bar means in passing contiguous to such anvil means work surface so as to define a zone which is between at least a portion of the drum surface and such grate means for carrying out such additional size reduction of intermediate product, such grate means working surface confronting the interior of such working chamber with spacing between such circumscribing portion of the grate means working surface and such peripheral path of the impact-cutter bar means being controllably fixed during size reduction operation of the rotary-type apparatus, such grate means presenting apertures which extend through such grate means from such working chamber to such outlet for finished product and which are positioned such that rotation of such rotor means drives intermediate product into such grate apertures, such apertures having a cross-sectional configura-tion facilitating a shearing action along such peripheral circumferential path of rotation of such impact-cutter bar means, such shearing action taking place on intermediate product being held by such grate apertures and protruding into such working chamber by passage of such impact-cutter bar means contiguous to such grate means working surface with such shearing action causing release of sheared product enabling passage through such apertures toward such outlet for discharge of finished product.

2. The apparatus of claim 1 in which such rotor drum has a substantially cylindrical configuration external surface, and in which incoming feedstock impacting with such rotor means initiates size reduction upon frangible portions of such feedstock.

3. The apparatus of claim 1 in which such impact-cutter bar means in fixed positional relationship projecting from such drum external surface comprise a plurality of fixed position impact-cutter bars disposed about such drum external surface in symmetrical relationship to such axis of rotation.

4. The apparatus of claim 3 in which such impact-cutter bars project from such drum surface to provide a uniform diameter cylindrical-configura-tion circumferential path of rotation.

5. The apparatus of claim 4 in which such circumferential path of rotation passes in contiguous relationship with such anvil means work surface, and, further including means for adjusting the angled relationship of such anvil means work surface and controlling spacing between such anvil means work surface and such circumferential path of rotation where such path passes in contiguous relationship with such anvil means work surface.

6. The apparatus of claim 3, further including means for preliminarily controlling spacing between such peripheral path of rotation of such impact-cutter bars and the working surface of such grate means confronting the interior of such working chamber, and release means for opening such spacing between the grate means and such peripheral path of rotation of such impact-cutter bars for oversized non-crushable or non-cuttable work product while otherwise maintaining such fixed controlled spacing during normal size-reduction usage of the rotary-type apparatus.

7. The apparatus of claim 3 in which location of such work surface portion of the anvil means contiguous to such rotor means peripheral path is adjustable by selective positioning of shear pin means coacting with such housing means to anchor such anvil means during normal size reduction usage, such shear pin means permitting movement of one end of the anvil means away from such peripheral path of such rotor means so as to dislodge oversized contaminant which cannot be cut or crushed between such rotor means and such anvil working surface.

8. The apparatus of claim 1 in which such rotor drum defines an internal space symmetri-cally disposed in relation to such axis of rotation, and such internal space is filled with ballast to increase inertia of such rotor means during its rotation.

9. The apparatus of claim 8 in which molten metal of high specific gravity is added to and solidified in stages within such internal space so as to maximize the weight of, and uniformly distribute, such ballast.

10. The apparatus of claim 1 in which an aperture as defined by such grate means presents shearing edges in acute angled relationship which converge in the direction of rotation of such impact-cutter bar means so as to facilitate shearing of fibrous materials by such rotation.

11. The apparatus of claim 10 in which apertures as defined by such grate means have an elongated hexagonal configuration confronting such working chamber with such acute angled edges being located at the longitudinal end of such configuration which is oriented in the direction of rotation of such rotor means.

12. The apparatus of claim 3 in which such grate means extends over an arc in the range of about 90° to about 225° of the size-reducing rotation of such rotor means.

13. The apparatus of claim 12 in which such rotor means rotates at a rate to provide a peripheral speed for such impact-cutter bar means in the range of about 100 to about 150 fps.

CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE

14. The apparatus of claim 3 in which such impact-cutter bars include a replaceable cutting tool located contiguous to the periphery of such impact-cutter bars, at the leading edge thereof in such direction of rotation of such bars, such cutting tool presentation a cutting edge defining the peripheral dimension for such path of rotation of such bar means.

15. The apparatus of claim 14 in which holders for such impact-cutter bars are aerodynamically shaped in radial cross section in approaching trailing edges thereof so as to reduce drag and improve efficiency during size reduction rotation of such rotor means.

16. The apparatus of claim 1, wherein said grate means provides a relief area in said portion circumscribed by said grate means, said relief area being immediately subsequent to said anvil means in said direction of rotation to allow for loosening of said intermediate work product entering said zone for additional size reduction.