Rotary Shear-Type Shredder Cutter With Rectangular Feed Tooth

This invention relates generally to rotary shear-type shredders, and more particularly to the configuration and arrangement of cutter discs therefor.

Rotary shear-type shredding devices of the type disclosed incorporate first and second parallel horizontal side-by-side counterrotating shafts mounted in a housing. Circular disc-type cutters are stacked on each shaft with circular spacers interposed between each such cutter disc; each cutter disc typically having one hook attached thereto. Usually the hooks curve or slant toward the direction of rotation of the disc and have a backside tangential to the circumference of the cutter. One typical example of the above is U.S. Pat. No. 4,034,918 disclosing a shredding apparatus driven by a hydraulic motor. Each cutter disc employs one slanted, curved hook to grab and pull gravity fed material into and through the cutters.

One problem with this arrangement, however, is that flat or sheet materials are difficult for the hooks to grab. These difficult-to-grab materials include pallets, plywood, press board, cardboard, etc., as well as rubber tires, sheet metal, and scrap. Accordingly, this type of shredder requires additional means to force such materials through the cutters. As such, some manufacturers include a ram-type assist mechanism that pushes difficult-to-grab materials downward into the cutting chamber. Moreover, manufacturers frequently recommend larger feed openings as an additional measure to further alleviate this problem.

Another problem arises with this arrangement because these machines are designed to reverse briefly in case a jamming condition occurs. Ideally, reversal will rearrange the material being shredded so that it can be shredded more easily when the shredder returns to normal operation. Slanted hooks, however, are only marginally effective in rearranging materials upon reversal. The slanted or tangential rear sides of the hooks slide under the material without grabbing it. Other rotary shear-type shredders are discussed in U.S. Pat. Nos. 4,833,866; 4,793,561; 4,702,422; 4,609,155; 4,560,110; 4,034,918; 3,868,062; 3,845,907; 3,664,592; 3,630,460; 3,146,960.

Another apparatus used to break down the solids found in sewage and sludge is a grinder manufactured by Disposable Waste Systems, Inc. Like a rotary shear-type shredder, this apparatus employs parallel grinder shafts with stacked cutter discs on each shaft. A plurality of block-shaped cutter elements are attached to each cutter disc. Each cutter element has a parallelogram shaped cross-section with two opposite leading edges that can cut in each direction. With this arrangement, however, the primary function of the blocks is to cut and grind, not to grab and pull. Thus, although this arrangement is effective for grinding solids found in sewage, and certain dry solids, it is limited to those applications where difficult-to-grab materials are not processed. Lacking any hook-type teeth and having many cutter elements on each disc, this machine is likely to be ineffective in shredding sheet metal or other flat materials.

Accordingly, there is a need for a configuration and arrangement of cutter discs that improve the efficiency of rotary-type shredders to process difficult-to-grab materials.

One object of the invention is to improve material feed characteristics of rotary shear-type shredders.

Another object of the invention is to efficiently shred difficult-to-grab flat materials.

Yet another object is to decrease the down time of the equipment caused by materials that do not feed properly.

Still another object is to require less labor to operate rotary shear-type shredders.

One advantage of the invention is a more balanced weight distribution on the cutter disc wherein stresses created by rotation are reduced.

Another advantage is that less equipment is required to process difficult-to-grab materials, i.e., no ram mechanism is required to assist in feeding such material through the cutters, and oversize feed openings are unnecessary.

To solve the problems of processing difficult-to-grab materials while retaining the capability of shredding sheet metal, the invention employs a combination of a curved, slanted hook and a rectangular block mounted on the outer peripheral surface of each cutter disc. Each cutter disc is mounted on its respective shaft and aligned so that each hook on a cutter disc coacts with a block mounted on an opposing cutter disc on the parallel shaft. In other words, each cutter disc has an equal number of hooks and blocks: each block coacting with a hook of the opposing cutter disc, and each hook coacting with a block of the opposing cutter disc.

The present invention comprises a rotary shear-type shredder including two parallel horizontal shafts with a plurality of coacting cutter discs mounted thereon. The shafts are located in a housing and are driven in opposite directions, i.e., the shafts are counterrotated by a motor. Each of the cutter discs are separated by spacer discs of smaller diameter; this allows the cutters on opposing shafts to overlap or mesh. Preferably, each cutter disc has only one hook and only one rectangular block, mounted on opposite sides of the cutter disc. The cutter discs preferably are arranged on the shafts so that angular position of the blocks and the hooks on successive cutter discs incrementally change thereby spiraling about each shaft. This arrangement enables flat or sheet materials to be grabbed by the rectangular blocks during either forward or reverse rotation.

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

FIG. 1 is a plan view of a rotary shear-type shredder including shredder housing, cutter shafts, drive unit and cutter discs in accordance with the invention.

FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1.

FIG. 3 is an enlarged elevational view of a single cutter disc in accordance with the invention.

With reference first to FIGS. 1 and 2 of the drawings, a shredder 10 constructed in accordance with the present invention is generally depicted. Generally speaking, shredder 10 comprises an automatically reversible drive 11, which is conventional, and a housing 11 adapted to accommodate the various components of a shear-type rotary shredder.

The shredder housing 12 has an inlet at the top and a discharge at the bottom thereof. Essentially, the shredding components in the housing 12 comprise a first horizontal cutter shaft 14 journaled at opposite ends for rotation within said housing 12, and a second, parallel horizontal cutter shaft 16 journaled at opposite ends for rotation within said housing 12. Each shaft mounts a series of substantially identical annular cutter discs 18 at equally spaced-apart positions along the shafts. The equal spacing is maintained by a circular spacer disc 20 interposed between each cutter disc 18. For reasons more fully explained below, the spacer discs 20, ideally, are approximately 0.014 of an inch larger in width than the cutter discs, and have an outside diameter approximately one half that of the cutter discs.

The cutter discs on the first shaft 14 are positioned to line up with the spacers 20 on the second shaft 16. Likewise, the cutter discs on the second shaft 16 are positioned to line up with the spacers 20 on the first shaft. The above arrangement allows the cutter discs 18 of either shaft to mesh with opposing cutter discs on the opposite shaft. Because the spacer discs 20 are slightly wider than the cutter discs, the cutter discs on both shafts mesh with enough clearance to properly shred and cut materials. Also, the meshing of opposing cutter discs requires that the spacers 20 have a smaller outside diameter than the cutter discs 18: approximately one half the cutter disc diameter as previously stated. Similarly, the smaller outside diameter of the spacers 20 provides space to accommodate the extension of cleaning fingers 40 from the elongated sides of the housing to a position between the cutter discs, just short of the spacers 20. These fingers 40 are inclined inward and downward to help prevent materials from passing around the cutter discs on the wrong side, i.e., the fingers direct material to the proper location between opposing cutter discs 18.

Attention is directed to FIG. 3 for a more detailed description of the structure of the cutter disc 18. Cutter discs 18 preferably comprise one hook 22 and one block 30 that extend outward from the circumferential surface of the disc, although a cutter disc can operate with several hooks and blocks. The hook shaped projection 22 is substantially the same width as the cutter disc 18, and has three sides: a radial front side 24, a tangential back side 26, and a top side 28. The radial side 24 extends in an approximately radial direction away from the circumference of cutter disc 18 approximately a distance of 1/8 to 1/4 of the diameter of the cutter disc. To improve the grabbing characteristics of the hook, the radial side 24 may slant slightly from the cutter disc 18 toward the direction of rotation. A flat top side 28 is optionally used but is not necessary for the operation of the hook. When included, the top side 28 connects the tangential back side 26 to the radial front side 24. Generally, the top side lies in a plane approximately normal to the plane of the radial side, and is nearly the same length as the radial side 24. Finally, the tangential side 26 is defined by a line beginning at the circumference of cutter disc 18, extending therefrom tangentially to a point defined by the end of top side furthest from the radial side.

The block 30 is located angularly 180 degrees from the curved or slanted hook. The hook and block thus lie wholly below a tangent line 42 at a point on the circumferential surface of the cutter disc so that sheet material can contact the cutter disc therebetween. In contrast to the curved hook depicted above, block 30 is rectangular in shape with two parallel front and rear sides 32, 34, perpendicular to the axial end faces of the disc, and one top side 36 extending normal to and connecting the two parallel sides. The block thus has two opposite right-angle edges on both front and rear sides 32, 34. The block is symmetrical about a line extending radially from the center of the disc, i.e., the two parallel sides of the block 32, 34 are parallel to such a line extending radially from the center of the disc through the center of the block. Similar to the curved hook, the block is substantially the same width as the cutter disc, and extends outward from the disc in a radial direction substantially as far as the curved hook, i.e., 1/8 to 1/4 of a cutter disc diameter.

Each cutter disc and each spacer is fixedly mounted to one of the parallel shafts by a key 38 disposed between the cutter disc or spacer, and the shaft. To accommodate the key, a groove 39 or keyway is formed on the radial inner surface of an axial bore 37 that extends through each cutter disc and through each spacer. Similarly, a keyway is formed on the radially outer surface of each shaft 14, 16 to receive the key 38 when the spacers and cutter discs are placed on the shafts. Relative to the shaft, the angular position of the hook, and likewise of the block, is determined by the keyway location on the radial inner surface of the coaxial bore extending through the cutter disc as described above.

For optimal efficiency in processing difficult-to-grab materials, the preferred arrangement of the cutter discs 18 on the two parallel cutter shafts 14, 16 positions the blocks and the hooks so that a block on one cutter disc will coact with a hook on the opposing cutter disc of the parallel shaft. Moreover, to further increase efficiency, the hooks and opposing blocks are positioned so that they do not all coact at the same time, i.e., the hooks and the blocks spiral around each shaft. By doing this, the power required to drive the shafts is distributed more evenly and continuously as the shafts rotate thus reducing high instantaneous power demands that would result if all hooks and blocks coacted simultaneously. To achieve this, the preferred embodiment calls for each cutter disc on each shaft to be successively rotated 22 1/2 degrees in relation to a directly adjacent cutter disc on the same shaft. Thus, the angular position of the hook and the block changes incrementally in relation to the same on successive cutter discs located on the same shaft. As previously stated, this is accomplished by selectively positioning the keyway on the radially inner surface of each cutter disc.

To operate the above-described apparatus, the shafts are driven with a drive means 11 that rotates each shaft in opposite directions. The shafts are driven in opposite directions so that the upper portions of the cutters on the two shafts rotate toward each other. Materials are fed into the shredder from above and forced downward, between the two shafts, through the apparatus.

As each hook 22 moves inward, an opposing block 30 does likewise, to grab and feed material toward one another and shear the material between them. The hook and block on each disc 18 are spaced angularly apart a sufficient distance for flat or sheet material to fall between them, into contact with the circumferential surface, so that the material is reliably grabbed. During reversal, the back sides of the blocks 30 can grab material to rearrange it and to shear it against the cleaning fingers 40.