Patent Publication Number: US-3880361-A

Title: Apparatus for comminuting trash

Description:
I Apr. 29, 1975 United States Patent [1 1 Schwarz 3.63L9U7 l/l972 241/2921 3.664.592 5/1972 Sehweigcrt et al Z4l/l9l X FOREIGN PATENTS OR APPLICATIONS I APPARATUS FOR COMMINLTING TRASH [75] Inventor: Werner Schwarz. Sindelfingen.  
 Germany 06 I973 Asxixmn! h&#39;.\umim&#39;rCraig R. Feinberg [22] Filed:  
 [2|] Appl. No.: 402.585  
  Related U.S. Application Data [63] Continuation of Scr. No. M01187. Sept. 15. l97l.  
 abandoned.  
 [30] Foreign Application Priority Data shafts through which the motor drives the shafts. a re- Oct. 22. i970 versing device for driving the motor in different direc- H7519 tions and a plurality of groups of disc-shaped blades disposed at regular intervals on each shaft and ar- [52] US. Cl. 241/36: 24l/l9l; 24l/236:  
 ranged such that the groups on one shaft engage in the interstices between the groups on the other shaft are provided. The inner distance between two adjacent 2 2 2 5 C 2W 0 Bl :9 0l u 6 m3 l 24 7. b 6 ur a .8 S m m as IF un 55 groups on the shaft having substantially no axial play is equal to the degree of play plus the width of the group on the shaft having a degree of play. Each blade has at least one step region including a tongue with [56] References Cited UNITED STATES PATENTS the surfaces which define the tongue forming an opening angle of the order of magnitude of 30. The step regions ofthe blades on each shaft are angularly offset with respect to one another.  
 Lil/33h I6 Claims. l4 Drawing Figures I.477.5()2 lZ/I923 l.939.246 l2/l933 AntonsenW...  
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 PAYENTEEAPMQIQIS SHEET EEG-F 1O PATENTEEAPRZQiHTS 3,880,361  
 SHEET Ck 0F 10 Fig 3a PATENTELAPRZQ ems SHEET OSDF 10 PATENTEEAPRZQBYS SHEEI CEUF 1O PATENTEMmsms SHEEI O7BF 1O llllll PATENTEDAPRZQ 1925 SHEET CBBF 1O PATENTEDmzsms 3.880.361  
 sum 10 0F 10 POLARlTY REVERSING SWITCH 1/ MOTOR WINDING Fig. 13  
  APPARATUS FOR COMMINUTING TRASH This is a continuation of application Ser. No. l8().687 filed Sept. 15. 197i. now abandoned.  
 BACKGROUND OF THE INVENTION The present invention relates to an apparatus for eomminuting trash such as bottles. borings. crates or the like. More particularly. the present invention relates to an apparatus for eomminuting trash including a motor. reduction gearing connected with the motor. at least one shaft driven by the reduction gearing. blades fastened to the shaft. an inlet opening disposed above the blades and an outlet opening disposed below the blades for ingress of the trash and egress of the comminutant respectively.  
  A larger number of devices for eomminuting trash are known. These. however. are specialized and to not possess the desired versatility since they do not process everything that accumulates in industrial operations such as the boring and grinding industry. in warehouses and retail businesses. etc. There are also a variety of automobile batteries. plastic containers. oil barrels. wooden crates. catalogs. television tubes. bottles. steel shavings resulting from boring and grinding. etc. which they cannot process and comminute. Moreover. known devices of this type require more operating experience from the operating personnel and more care than might be expected. Fruit crates. for example. must first be broken up before being inserted for comminution.  
  Such a device must be able to handle the problems of glass dust resulting from smashing bottles and the comminution of metal objects which wrap themselves around the shaft and jam the device instead of being comminuted by the blades.  
 SUMMARY Of THE INVENTION It is. therefore. a general object of the present invention to provide an apparatus for eomminuting trash such as bottles. borings. crates or the like.  
  It is a more particular object of the present invention to provide a eomminuting apparatus which can be operated with practically no operational knowledge.  
  It is another particular object of the present invention to provide a eomminuting apparatus which is compact in size and yet is sufficiently versatile to accomplish the comminution of a variety of items such as automobile batteries, plastic containers. oil barrels. trash accumulations in industrial operations such as the boring and grinding industry. etc.  
 It is yet another particular object of the present invention to provide a eomminuting apparatus including a plurality of groups of disc-shaped blades mounted on a pair of driven shafts disposed parallel to each other with one shaft having a degree of axial play and the other shaft having substantially no axial play and with the inner distance between two adjacent groups on the shaft having substantially no axial play being equal to the degree of play plus the width of the group on the shaft having a degree of play.  
  It is still another particular object of the present invention to provide a eomminuting apparatus including a reversing device which can be either time or torque dependent.  
  It is yet another particular object of the present invention to provide a eomminuting apparatus including an improved blade design.  
  These and other objects are accomplished according to the present invention by the provision of an apparatus for eomminuting trash including two parallel shafts with one ofthe shafts having a degree ofaxial play associated therewith and the other shaft having substan tially no axial play associated therewith; a plurality of groups of disc-shaped blades disposed at regular intervals on each shaft. so that the blade groups of the one shaft mesh in the interstices between the blade groups of the other shaft. and so that the inner space between two adjacent groups on the shaft having substantially no axial play associated therewith is equal to the degree of play plus the width of the intermeshing blade group on the shaft having a degree of play associated therc with. and further so that the shafts move during operation in opposite rotational directions and at a slightly different speed: a motor; reduction gearing disposed between the motor and shafts through which the motor drives the shafts. a reversing device for driving the motor in different directions; an inlet opening disposed above the blade groups through which trash is supplied to the blade groups; and an outlet opening disposed below the blade groups through which the comminutant is removed.  
  The forward direction of rotation ofthe shafts is such that when viewing the blade groups through the inlet opening. the blades move toward one another. That is. if one were to view a point on a blade on each of the shafts. these points would appear to approach each other as the two shafts are caused to rotate in the opposite directions.  
  The blades have one or a plurality of step regions where they deviate from a larger diameter to a smaller diameter. The step regions include surfaces which deline a tongue and generally sickle-shaped recesses. The tongues extend in one direction of rotation of the blade. The surfaces defining the tongue form an opening angle of the order of magnitude of 30. A retreating area of the step region disposed below the tongue and toward the smaller diameter can accommodate items of the dimensions of ordinary wine. beer. liquor bottles or bottle necks thereof. The blades are mounted on each shaft so that the step regions thereof are angularly offset against one another.  
  Because of the axial play. room is provided between the sides of the blades for the glass dust mentioned above. However. the axial play is still small enough so that no metal pieces can get stuck in the resulting gap which then. instead of being comminuted. would only be pulled through the apparatus whole. Because of the different number of revolutions (speeds) of the two shafts. the items to be comminuted are caused to rotate if required and as a result are chewed by the blades from different sides. The different speeds prevent sudden stresses and jamming of the apparatus. The reversing device also serves to prevent the apparatus from becoming jammed.  
  In one embodiment of the present invention the blades are provided with a hexagonal bore. These blades are then mounted on a shaft which has a hexagonal circumferential configuration. In this embodiment. a substantially improved torsion connection between the blades and shaft results. However. this blade configuration is expensive to fabricate because the bore can only be produced by means of removal of material and must be carefully and slowly machined. Hexagonal shafts are more easily fabricated and commercially available in a relatively large number of different dimensions. However. they are substantially more expensive than circular shafts which can be turned much more easily. for example.  
  In order to obtain a substantially improved torsion connection between shaft and blade which is much less expensive. which requires no removal operations, which permits precision work where necessary to be done at relatively low cost. and which finally permits the arrangement of the blades in such a manner that their cutting tongues are offset by any desirable angular relationship, such as. for example. angles of I80&#34;, Ill)&#34;, 90&#34; etc.. other embodiments of the blades and shafts are possible. For example. the blades are provided with a cylindrical bore. with recesses provided parallel to the bore at regular angular spacings. The inner surfaces ofthe recesses follow a circular arc. The shaft has a cylindrical circumference and fits into the blade bore. The shaft has at least one longitudinal groove parallel to its longitudinal axis whose inner surface complements the inner surface of one of the recesses in the blade. so that together they define a cylindrical bore. A cylindrical rod is fitted into the cylindrical bore de fined by the shaft groove and blade recess.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of the apparatus of the present invention to scale.  
  FIG. 2 is a sectional view taken along line 22 of FIG. I, to scale, but without motor, reversing device. fill funnel and feet.  
  FIG. 3 is a sectional view taken along line 33 of FIG. 2, showing the blade groups on one of the shafts as well as part of the gearing.  
  FIG. 3a is a vertical sectional view of the gear box showing the two shafts and the meshing gearing to drive each shaft.  
  FIG. 4 is a sectional view, to scale taken along the line 44 of FIG. 2, showing the other shaft as well as part of the gearing associated therewith.  
  FIG. 5 is a full scale side view of a blade according to one embodiment of the invention showing the stepped region thereof.  
  FIG. 6 is a view of FIG. 5 as seen in the direction indicated by arrow A.  
  FIG. 7 is a side view of a mounted blade according to another embodiment of the invention showing the stepped region thereof.  
  FIG. 8 is a view of FIG. 7 as seen in the direction indicated by the arrow C.  
  FIG. 9 is a side view of a blade according to a further embodiment of the invention showing three stepped regions.  
  FIG. I is a view of FIG. 9 as seen in the direction indicated by arrow D.  
  FIG. II is a schematic representation of the angular offset of the stepped regions of two successively mounted blade groups.  
  FIG. I2 is a schematic partial view as seen in the direction indicated by the arrow B of FIG. 3.  
  FIG. 13 is a schematic circuit diagram of one embodiment showing the reversing capability for the drive motor.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus according to the present invention is supported on four legs II, as shown in FIG. I. The legs I I support a hopper or basket 12 or the like, into which the trash to be comminuted is placed through an inlet opening 12&#39;; a 7.5 HP electric motor I3, whose shaft is perpendicularly disposed with respect to inlet opening 12&#39;&#39;, a box 14, in which fuses. on and off switches as well as the known reversing device are provided, a gear box I6; a blade box [7; and an outlet duct 18 including an outlet opening 18&#39;.  
  The gear box 16(FIG. 2) has an upper wall 19 and a lower wall 2] which serve as the bearing supports for a perpendicularly disposed worm gear shaft 22. The worm gear shaft 22 has at its upper end an internal multi edge opening or socket 23 into which the shaft of electric motor I3 fits. In the center region of the gear shaft 22 a worm 24 is provided which is seated secured against rotation in any conventional manner. A bearing 26 in the upper wall I9 and a bearing 27 in the lower wall 21 mount the worm shaft 22 to the bearing supports. Bearing 27 includes a double tapered roller bearing and can support an axial thrust load whose direction depends on the rotational direction of motor 13.  
  A worm tooth gear 28 meshes with worm 24. The worm gear 28 is mounted on a shaft 31 and secured against rotation thereon in any conventional manner. As can be seen from FIGS. 3 and 3a shaft 31 also supports a smaller toothed wheel 32 to the right of gear 28. The right-hand end of shaft 31 is mounted to be freely suspended and rotatable in a bearing 33. The bearing 33 is screwed to the left-hand end of the cylindrical portion 34 of a hexagonal shaft 36. Bearing 33 and shaft 31 can thus rotate independently of one another, but are coaxial.  
  A larger toothed wheel 37 meshes with gear 32. The toothed wheel 37, (FIG. 4), is securely fastened as, for example by welding, to a hub 46. The hub 46 is wedged on the left-hand cylindrical portion 38 of a second hexagonal shaft 39. The cylindrical portion 38 includes a plurality of spline-type keys 38&#34; each of which engages a key way 46&#39; formed in the hub 46. The keys 38&#34; are preferably press-fitted into the key ways 46&#39; resulting in the wedging action. For purposes of clarity, FIG. 4 does not shown the worm 24 or the worm shaft 22. The cylindrical portion 38 is stepped toward the left and terminates in a reduced diameter extension 38&#39; which is supported in a bearing 41 of sidewall 42 of the gear box 16. At its other end, the cylindrical portion 38 passes through the right sidewall 44 of the gear box 16 and is there supported in a bearing 43. The hub 46 includes a smaller gear 47 which is integrally formed thereon. The gear 47 thus rotates at the same speed as gear 37. The gear 47 meshes with a larger gear 48 which, however. has a somewhat smaller diameter than gear 37. The gear 48 is wedged on the cylindrical por tion 34, (FIG. 3), in a manner similar to that of hub 46 on cylindrical portion 38. It is thus possible to substantially reduce the number of revolutions of motor 13 and to drive the two hexagonal shafts 36 and 39 in opposite directions and at a different speed. Also, it is possible to have a ratio of shaft revolutions of approximately 40:70, for example. Of course, it should be understood that other ratios may be achieved as desired.  
  The gear box 16 can, for example, have a width of 19 cm, an inner height of 22.5 cm and an inner length of 59.5 cm. The gear box 16 is designed to be oil tight so that the gearing can be splash lubricated from the sump level 49. This gear box construction has been found to successfully withstand the high axial and radial forces which develop during the comminuting operation.  
  The blade box 17 has a stable frame structure which is open at the top to receive the trash from the hopper 12, and opened at the bottom to discharge the comminutcd trash to the outlet duct 18. The frame structure includes the sidewall 44 which forms a party wall with the gear box 16. The three remaining walls 51a. 51b and a third. not shown. are generally U-shapcd or channel beams which are preferably welded together. FIG. 3 shows in crosssection the channel 51!) which is exemplary. The channel 511) includes. typically. a web portion 52 and flanges 52a and 52h. The upper flanges of all three walls are joined in a conventional manner such as through the use of bolt joints with a corresponding three-sided flange portion (not shown) of the hopper 12. The U-shaped beam 51h is provided in its web portion 52 with two bearing supports 52c and a second support. not shown. for the end pins 53 of the two hexagonal shafts 36 and 39 and their associated bearings 53a and a second bearing. not shown. Each hexagonal shaft 36 and 39 bears fourteen blades 54 which are preferably similarly configured and which are each combined into groups of two 56. S7. 58. 59. 61. 62. 63. For reasons of simplicity. FIG. 3 shows only the blade groups of the hexagonal shaft 36. These blade groups are spaced apart by spacer sleeves 64, which are all of the same dimension. but which are 0.02 mm wider than the width of a blade group which in turn are preferably mm in width. This difference of 0.02 mm corresponds to the degree of axial play of one of the shafts 36. It should be noted at this time that the degree of axial play is not shown in FIG. 12 because it is of such a small magnitude in comparison to the size of the elements shown. Pressure rings 66 and 67 axially pretension the entire arrangement of the blade groups and the spacer sleeves 64 when assembled as shown in FIG. 3, so that any axial displacement on the hexagonal shaft 36 is substantially eliminated.  
  Referring to FIG. 12 it can be seen that an equal number of blade groups 68 on the hexagonal shaft 39 are provided. These blade groups fit into each interstice between adjacent blade groups on shaft 36 so that a gap opening 69 remains through which the comminuted material can fall downwardly and through outlet opening 18&#39;. The blades according to the present invention have a generally polygonal shape.  
  In one embodiment of the present invention. the blades 54 have the shape illustrated in FIGS. 5 and 6. In this embodiment the blades 54 have a hexagonal opening or bore 54&#39; which is adapted to fit in a conforming manner on the hexagonal shafts 36 and 39. The hexagonal shafts are intentionally hardened so that their toughness index will be enhanced. The shafts 36 and 39 are made from an unhardened chromium steel. preferably 12% chromium steel. In contradistinction. however. the blades 54 are hardened to a Rockwell hardness of 60-62. The blades 54 are made from a material identified by the number 2090 according to DIN [Deutsche Industrie Normen. German Industrial Standards]. which is a 12% chromium steel.  
  From point 72 to point 73. i.c.. over an angle of 200, the peripheral surface 74 defines a circular region 74&#39; of the blade with a radius of I40 mm. The peripheral surface 76 which follows point 73 in a clockwise direction also follows a circular path whose center 77 is offset downwardly by 29 mm and to the right by 34.5 mm  
 with respect to center 78. A region 76&#39; defined by the peripheral surface 76. when viewed from the center 78. has a continuously increasing radius. A step region 79&#39; follows the region 76&#39; and includes a tongue 79. The tongue 79 has a planar upper surface 81 which is perpendicular to the plane of the drawing and a lower surface 82 which is also planar but is inclined downwardly at an angle of 10 perpendicularly to the plane of the drawing. The surface 82 is preferably ground. From the tip 83 of the tongue 79 to the beginning of region 74&#39; at point 72. a recess 84 is formed in the approximate shape of a sickle. This recess 84 forms the receding portion of the step region 79&#39;. More precisely. the ground surface 82 transitions into a curved surface having a radius of IS mm and extending through an arc of approximately 120. and this curved surface blends into the surface 86, which is perpendicular to the plane of the drawing and which in turn extends to point 72 of region 74&#39;.  
  The vertically measured distance between surface 86 and the tip 83 of tongue 79 is 40 mm. while the surface 81 forms an angle of with respect to the vertical (FIG. 5 Except for the surface 82 and a portion of the adjacent curved surface having the radius of [5 mm. nothing is ground along the circumference of blade 54.  
  Edges 88 and 89 are rounded so that they are not very sharp. The side surfaces 91 and 92. however. are ground to be plane and parallel. the thickness of the blades being preferably 15 0.0I mm. The opening angle of the tongue 79 defined by the surface 81 and 82 is preferably 30 as shown in FIG. 5. It has been found that variations of this angle up to i 20/( are acceptable.  
  The approximately 30 angle is important particularly when comminuting metal. On the one hand. it prevents the forces produced by the entrance of the metal from increasing too rapidly. which would be the case with larger angles. such as eg. 50; while on the other hand. the angle is sufficiently large to effectively produce a large hole in the metal sheet and also large enough so that it can be pulled out of the metal sheet during each reversing process. A tongue with too small an angle would more easily penetrate into the metal. but would have difficulty in being withdrawn from the hole during reversal.  
  In the other embodiment of the present invention which is illustrated in FIGS. 7 and 8, blade has the shape of blade 54 shown in FIGS. 5 and 6. but blade 110 has a cylindrical bore 112 which is concentric with center 111. Blade 110 also has parallel surfaces 127 and 123&#39;. which like blade 54 and 40 mm apart. Recesses 113. 114, and 116 are provided at an angular offset with respect to each other according to the relationship 360/n. where n 2. 3. 4 etc., and is preferably 3. The inner surfaces 117 of the recesses follow a circular arc of approximately 200. The distance of the center 118 of all recesses 113. 114, 116 from center 111 is the same. In the embodiment illustrated. the center 118 is disposed on the extension of the inner surface of the bore 112.  
  A cylindrical shaft 119 is provided which corresponds to the hexagonal shafts 36 and 39 and which has a diameter such that it can be inserted through the bore 112, so that all blades 110 can be disposed thereon. The shaft 119 has a longitudinal groove 121 which extends over the entire length of the shaft over which the blades 110 are to be mounted. As is shown in FIG. 7,  
 the groove I2l supplements with its inner surface the inner surface I17 of recess I13 to form a circular bore I21 Thus. when recesses I13 and longitudinal groove I21 are congruent to form the bore 121. a cylindrical rod I22 can be placed therethrough so that shaft 119 will carry the blade in both directions of rotation ofthe shaft. For the next blade 110. the recess I16 supplements longitudinal groove 121; for the blade [10 after that. recess 4 supplements longitudinal groove l2l. etc so that tongues 123 of blades III], which are designed in the same manner as tongues 79 of blades 54 and which here have an opening angle of 30 i the variation stated above. are offset with respect to one another by a preferred angle of 120. Preferably. the bore l2l&#39; is formed such that more than one-half of the bore is within the blade body.  
  Alternatively. additional longitudinal grooves 121a and 121)) could also be provided at the periphery of shaft 119 parallel to the longitudinal groove 12] and offset by l2ll so that additional bores may be formed with recess [14 and recess I16. It must be noted here, however. that any practical number of additional grooves and resulting bores are possible, but that too many longitudinal grooves would not be desirable since they would tend to weaken the shaft 119. This would also have the drawback that the longitudinal grooves would have to be manufactured on a machine with graduated circle devices since the angular offset of l2tl or the like must be precise. If, however. only a single longitudinal groove I21 is provided these angular relationships need not be of concern.  
  During the manufacturing process, holes are first drilled to correspond to the recesses [13, I14 and 116. Then bore 112 is drilled and worked with a reamer. if required. The only tool required is thus a drill.  
  With respect to the rod 122, the shaft 119 and the blades H0 or 125, it has been found that a rod diameter of mm i 4.5 mm, a shaft diameter of 40 mm i l2 mm and a blade width of28l) mm :42 mm is preferable.  
  The blade 125 which was fabricated according to a further embodiment of the present invention as illustrated in FIGS. 9 and I0 is carried along in a form&#39; fitting manner by shaft 119. However, it has three tongues 123. each offset by 120. The blade 125 has, therefore, the general outline of a triangle with regions each having a surface 124 which lies on a circular arc and having the same length partly defining the sides of the triangle.  
  The surfaces I27 and [28 define a recess 127&#39; which is generally sickle shaped and which is large enough so that it can hold bottle necks and the like. The back of the tongue 123 is a smooth continuation of the surface 124. Tongue 123 of blade 125 like blades 54 and 110 opens at an angle of 30 i the variation stated above. Tongue 123 may be undercut in the same manner as tongue 79 of biade 54 to an angle of [0 to form the surface 128.  
  Each one of the blade groups has the individual blades 54, 110 or 125, respectively, arranged next to one another without spacings therebetween so that the tips 83 or 126 of the step regions 84 or 127 of the tongues 79 or 123 are offset by [80&#34;. This explains why in FIG. 3 the right-hand blades extend higher than the left-hand blades, while the left-hand blades protrude lower than the right-hand blades. Each blade group is offset by 60 with respect to the next blade group.  
  Let us now consider the tips 83 or 126 ofthe tongues of the righvhand blades 54 or III] of each blade group 56 w 63. For example. the tip of the tongue of one blade for the blade group 56 is on a radius 93, (FIG. 1]), and the tip of the tongue of a corresponding blade for the biade group 57 is on a radius 94 etc. The angular deviation is preferably 60. The preferably 60 deviation continues with succeeding blade groups until the tip of the tongue of a corresponding blade for the blade group 63 lies on radius 93. This then results in the sche matic arrangement shown in FIG. 11.  
  The spacing between the hexagonal shafts 36 and 39 or ofthe cylindrical shafts H9 is such that with a given blade configuration, the blades always overlap and define an overlap portion 95, as shown in FIG. 12. This has the result that the blades on one shaft can be guided laterally. i.e., parallel to the shaft axis. by the blades on the other shaft and that no common gap opening along the hexagonal shafts 36 and 39 or along the cylindrical shafts H9 appears, except the limited gap openings 69, as shown in FIG. 12.  
  The shafts 36, 39 or 119 preferably have a center spacing of approximately l30 mm. The distance between the parallel sides of the hexagonally configured shafts 36 and 39 is preferably 41 mm.  
  The peripheral surface 76 makes it possible for a blade to remain in engagement as long as possible with an adjacent or: &#34;h ft. Metal cans or the like are then not only crushed but also cut apart. It is insignificant which shaft receives the axial play. However, both shafts must not have the axial play.  
  Blades are also arranged in blade groups and are arranged to be offset with respect to one another by 60 within the blade groups in a corresponding manner to blades 54 and 110.  
  A motor of 7.5 HP was selected for the embodiments. The motor permits the use of sufficiently long hexagonal shafts 36 and 39 or cylindrical shafts 119 for the gears employed so that fruit crates can be thrown whole into the hopper l2 and need not be broken up first. The motor 13 is also able to produce a torque which produces, with respect to the moment arms between the recesses 84 or 127&#39; and the geometrical longitudinal axis of the shaft, moments sufficient to effect the desired comminution. Standard motors with 4 or l0 HP cannot be used because the 4 HP motor would not be powerful enough and the l0 HP motor would be too powerful. An apparatus which would be provided with a 10 HP motor would be too cumbersome for the intended purposes. A 7.5 HP motor is fed with 15 amperes. This is a value which can be handled by normal electrical lines.  
  The point at which motor reversal takes place can be made time or torque dependent. With respect to time dependent reversals, one would only require a clock, which would switch the motor, for example, every 5 minutes into a reversal of rotation. Also, a revolution counter could also be used so that the motor could be reversed, for example, every 10 revolutions.  
  With respect to torque dependent reversals, one could measure by how many angular degrees the ends of shaft 3], for example, are twisted with respect to one another and the reversal could be effected when a certain torsion has been reached. Also, it has been found that with a strong load, the 7.5 HP motor requires l2 amperes of current and that from this point on the motor rotation should be reversed. Since the current through the motor is proportional to the torque. the current can also be used as a criterion under the torque dependent category. In this regard consider. for example. the circuit diagram of FIG. 13. A current coil whose armature is attracted whenever the current through the motor winding has reached a certain level. for example 12 amperes. is connected in the lead to the motor winding. The armature controls a bistable mcm her which produces the pulses shown at its output. With these pulses the polarity reversing switch is controlled from the solid line position to the dashed line position.  
  it will be understood that the above description of the present invention is susceptible to various modifications. changes and adaptations. and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.  
 I claim:  
 . Apparatus for comminuting trash comprising:  
 a motor:  
 at least two parallel shafts;  
 means for rotatably supporting said shafts.  
 . gearing connected between said motor and said shafts for rotating said shafts in opposite directions and at different speeds with respect to one another;  
 e. means for reversing the rotation of both of said shafts;  
 f. a plurality of solid disc-shaped blades disposed on each of said shafts and secured thereto for rotation therewith. at least some of the blades one each of said shafts being spaced from adjacent blades on the same shaft with the blades on one shaft extending into the spaces between blades on the other shaft;  
 . the peripheral contour of each of said blades comprising a cutting tongue portion extending in the direction of rotation and proceeding in the opposite direction in a continuous. smooth. inward. spiral curvature to a step region.  
 said step region comprising a sickle-shaped recess portion receding from a cutting tongue portion to said spiral curvature.  
  2. Apparatus as defined in claim 1. wherein said shafts have a hexagonal circumferential configuration. and have a width between parallel sides of 41 mm and consist of non-hardened chromium steel. preferably l2/r chromiun steel.  
 3. Apparatus as defined in claim 1 wherein each blade group comprises two blades which are arranged next to one another without spacings the re between and whose step regions are offset with respect to one another. preferably by I&#34;.  
  4. Apparatus as defined in claim 1 wherein seven groups of blades which are each substantially l5 mm wide are provided on each shaft.  
  5. Apparatus as defined in claim I wherein the peripheral contour forms a triangle. and wherein there are three regions including recesses forming the sides of said triangle.  
  6. Apparatus as defined in claim 5. wherein the triangle has side surfaces which substantially form circular arcs.  
  7. Apparatus as defined in claim 1. wherein the tongue of said step region has an opening angle of sub stantially 30.  
  8. Apparatus as defined in claim 1. wherein the tongue of said step region has an opening angle of 30 3.  
  9. Apparatus as defined in claim 1. wherein the tongue of said step region has an opening angle of 30 1 6.  
  10. Apparatus as defined in claim l wherein a portion of the sickle-shaped step region has a cutting edge. while the remaining portion of the peripheral contour does not.  
  11. Apparatus as defined in claim 1, wherein the blades consist of an oil-hardened approximately l2&#39;/z chromium steel with the material number 2090 and with a Rockwell hardness of approximately 6O.  
  12. Apparatus as defined in claim 1 wherein the actuation ofsaid means for reversing rotation is time dependent.  
  13. An apparatus according to claim 1 wherein each of said plurality of blades has at least one further cutting tonguc portion and step region.  
  14. An apparatus according to claim I wherein said step region recedes substantially below said smooth spiral curvature.  
  15. An apparatus according to claim 1 wherein said sickle-shaped recess is shaped to accommodate the necks of bottles. with a radius in the order of magnitude of 15 mm.  
  16. An apparatus according to claim I wherein said plurality of blades has a Rockwell hardness of between 60-62 and consists of 127: chromium steel.