FR2522536A1 - Impact crusher e.g. for car bodies - has rotor built up from discs with free-swinging hammer elements in gaps between discs and wear resistant cover on disc edges - Google Patents

Abstract

The impact crusher, e.g. for car bodies, includes a housing (24) inside which a rotor assembly (22) operates. The car bodies (14) are fed into the crusher down a ramp (12) past flattening rollers (16,18) and are disintegrated by hammer elements (32) of the rotor. The hammer elements are freely rotatable on bolts extending axially through holes near the periphery of the rotor discs, which are mounted on a shaft (30) with spacing discs between them. The hammer elements work together with an anvil surface (34) and the smaller crushed particles drop through a grille (36) below the rotor to a discharge belt conveyor (48). A similar grille (38) is mounted above the rotor for smaller particles ejected upwards by the hammer elements. These particles fall through a channel (44) onto the discharge conveyor, which takes the crushed particles to further work stations.

Description

 The present invention relates to hammer mills and more particularly to a hammer mill equipped with a disc rotor on which are fixed protective caps. your hammers rotate on axes passing through these discs.

 A large number of machines of different types have already been built, designed to cut metal objects out of use. One of the largest sources of scrap metal objects is represented by used automobile bodies. To transform the metal object into scrap metal in order to reuse the metal, it is necessary to pulverize it, grind it or reduce it in another way into small pieces. This has so far been achieved in a number of ways, a typical example of which is US Pat. No. 3,482,788. A rotor is mounted in a hammer mill and a powerful motor spins it at high speed. This rotor consists of a shaft carrying discs spaced apart from one another along its length. Axes pass through these discs near their periphery and carry spacers which separate the discs. Hammers are mounted on these axes at locations which are not occupied by spacers and they can rotate freely on said axes. When the rotor rotates at high speed, these hammers strike the metal object that is to be crushed or reduced to crumbs. If the hammers strike an object that is too hard, which is not shredded, crushed or pulverized all at once, they can rotate freely on the axes, so as to allow the rotor to continue to rotate. However, this system has the disadvantage that the wear on the discs is excessive.

 In order to remedy the wear of the discs mounted on the rotor, protective caps have been studied, as described in US Pat. Nos. 4,056,232. However, these caps have by nature disadvantages which manifest themselves with use. Furthermore, these monkfish are large, bulky and difficult to assemble.

To put the caps in place, remove the pins, insert these caps in place of the spacers and fix them. These caps also add considerable weight and require additional raw material for their manufacture. It has been observed that in service the front edge of the caps tends to lift. Once this front edge has started to lift, the caps can be torn off, damaging the pins, discs or rotor. Whenever it is necessary to replace the caps, this implies an important work of restoration, because it is necessary to remove each axis (which often requires the use of special pin punch), remove the caps from the discs by cutting them if they are there welded, and replace them with new caps. This is a very long job and the caps themselves are quite crusty.

 In another type of hammer mill with rotor, a cross type rotor is used. As the arms of the braces have the same wear disadvantages as the discs of a disc rotor, these braces must be fitted with a cap or end protective insert of one kind or another. A cross-type rotor of this kind, comprising protective caps or inserts, has been described in United States Patent No. 3,727,848. Here too, the hammers oscillate freely on axes which pass through the arms of the braces, but these arms are protected by replaceable caps arranged on their front edge. However, a rotor with braces is less advantageous than a disc rotor, because it normally does not carry as many hammers and as pieces of metal can be lodged between the arms of these crosspieces. your spider rotors are subjected, more than the disc rotors, to direct blows, which increase vibrations, shocks and the risks of deterioration. For example, a spider arm can break and be driven from its tree. These drawbacks are mitigated in the case of disc rotors.

 Another typical example of a spider rotor comprising replaceable caps fixed to the axes which pass through it is given by United States Patent No. 3,844,494. However, this rotor has all the drawbacks inherent in spider rotors, which are to have a lower capacity and to raise problems of vibrations or shocks.

 -The prior art relating to grinders is very old, and grinders were initially used to grind grain products, such as wheat or corn. A typical example of a mill at the beginning of the century is shown in the patent of the United States of America republished under No. 12,659, which was issued in 1907. This mill has a large rotor to which discs or plates are attached , hammers pivoting on axes which pass through these discs.

However, if this model of shredder is modified to shred metal objects, many disadvantages which had not previously appeared begin to appear, for example excessive wear, not only of the hammers and of the grinding surface, but also of the support discs,
Another typical old mill was described in U.S. Patent No. 589,236, issued in 1897, which relates to a cross mill. A whole series of patents of this kind were taken at the end of the last century and at the beginning of this century and deposited, and the corresponding inventions are due to Mr. Milton F. Williams (St-Louis), or were sold to the Williams Patent Crusher Society and
Pulverizer Company, of St. Louis, Missouri (United States of America).

A patent which schematically represents a hammer mill used to crush automobile bodies and equipped with a cross-over rotor is the patent of the States
United States of America No. 3,545,690. In recent years, other improvements have been made to hammers with the use of manganese or manganese alloys, this element tending to cause work hardening, so that reduce wear. But these alloys tend to be ductile during the period during which they undergo this hardening. This particular problem has been investigated in U.S. Patent No. 7,778,586.

 In the past, special heat treatment or welding of hard surface material has been used to cover the external surface of the discs, a very long and expensive treatment.

 In the mill according to the invention, a very simple cap is fixed to the disc and can be easily removed and replaced without having to drive out the axes of the rotor. Tearing up these axes is very important work and requires a lot of pain and material. the invention overcomes all these drawbacks.

In its various aspects, the present invention relates
- a hammer mill comprising a disc rotor fitted with caps
- a rotor with removable outer surface, which is made of a material which can undergo work hardening, such as a manganese alloy and which can be easily removed and replaced;
- a cap which can be fixed to the rotor discs of a metal object crusher, in particular a crusher of the type which can be used for cutting car bodies, and
- a disc rotor fitted with caps for a hammer mill comprising two feed rollers and upper and lower outlet passages, which gives it maximum capacity for minimum energy consumption.

 your present invention relates to t'ii shredder of metal objects, which are typically devices or car bodies more or less well used. In order to increase its capacity, this crusher has two wise exit steps, upper and lower, intended to evacuate the pieces of metal after grinding. The mill is equipped with a disc rotor which is kept apart from each other by spacer rings.

 Shafts are arranged all around the periphery of the rotor, pass through the discs and carry the spacer rings. Hammers are mounted in places on these axes, at locations where there is no spacer ring. These hammers can rotate freely on these axes and between the adjacent discs. While the rotor is rotating at high speed, the centrifugal force drives out the hammers, which strike the metal objects introduced into the crusher.

the impact of these hammers shreds, crushes or crushes these objects. While the objects are introduced and the hammers break them into pieces, these objects strike the discs which carry the axes on which these hammers are articulated. This impact of objects against the discs tends to wear down the outer surface of the latter.

 To prevent the outer surface of the discs from wearing out, manganese or manganese steel (or other alloy steel with similar characteristics) caps are screwed onto this surface. your records, which.

have a generally circular shape, having protrusions whose axis passes through the axis of each cap. Each end of these caps is overlapped by overlapping with the adjacent caps. Bolts passing through the caps and screwed into the discs hold these caps in place. When a crusher fitted with cap discs has been operating for a short time, the manganese, manganese alloy, or manganese austenitic steel has hardened and placed on the discs and hardened. Due to this work hardening and this application of the caps against the discs, it is normally necessary to tighten the bolts twice at the start of the operation of the hammer mill.

 The ends of the caps are nested so that these caps do not have a sharp front edge in the direction of rotation, which therefore prevents them from being lifted and removed by a piece of metal trapped under them. The protrusions (or shoulders) of the discs can have any configuration desired to retain the caps in place. It is also possible to form a mortise and tenon device between the discs and their caps to prevent them from moving laterally. When the caps have hardened by work hardening and are well positioned, there is almost no need to tighten them further.

 the fact of mounting caps on the discs significantly reduces the need to repair or replace them periodically due to wear. your current downtime to repair the discs or replace the caps attached to the axes is appreciable. The use of the system according to the invention makes it possible to reduce the number of downtimes and to increase the production of the hammer mill.

 According to another characteristic, it is possible to more regularly penetrate the body of an automobile into the crusher by using a pair of feed rollers which is articulated on a pivot disposed near the entry opening in this crusher and which can pivot and lift to pass on this bodywork.

The first roller crushes the bodywork and the second completes this crushing. When a body is introduced into the crusher and the hammers strike it, protrusions of the rollers prevent this body from suddenly penetrating too long in this crusher, which ensures a more uniform advance in the latter, including it makes the maximum efficiency. Since the feed speed is more uniform, it is not necessary to have as much power, which increases the efficiency of the mill.

The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting examples, in which
Figure 1 is a schematic perspective view of a hammer mill according to the invention, with partial cutaway of its envelope for illustrative purposes
Figure 2 is a schematic side elevation of a hammer mill according to the invention, part of the casing is torn off, the cover of this casing being raised to give access to the rotor
Figure 3 is a schematic side elevation of part of a mill equipped with a pair of feed rollers
Figure 4 is a perspective view of a disc rotor equipped with caps, before its installation
Figure 5 is a longitudinal elevation of the rotor of Figure 4, partially shown in section by line 5-5 of Figure 6
Figure 6 is a cross section of the rotor of Figure 5, taken on line 6-6 of Figure 5
Figure 7 is a detail section of a disc and caps of a rotor in operation, showing another method of fixing these caps
Figure 8 is a side elevation of an alternative embodiment of the caps
Figure 9 is a schematic perspective view of another embodiment of a disc and caps; and
Figure 10 is an exploded perspective view of a disc mounted in place and one of its caps.

 FIGS. 1 and 2 represent a hammer mill designated as a whole by the reference index 10.

This crusher 10 comprises a feed ramp 12, by which the objects which it is proposed to grind, such as a car body 14, are introduced into this crusher 10. At least two feed rollers 16 and 18, arranged above and generally in a transverse direction perpendicular to the ramp 12, cause the body 14 to penetrate into the crusher 10 through an opening 20. The ramp 12 is inclined up and down towards the opening 20.

 The hammer mill 10, which contains a rotor 22 driven at high speed by coupling to a motor (not shown), is surrounded by an envelope 24. This envelope 24 comprises a cover 26, which covers the upper part of the rotor 22. This rotor 22 comprises several discs 28, mounted on a shaft 30 which is rotated by a power source (not shown). Between the discs 28, hammers 32 are mounted from place to place, which can rotate freely with the rotor 22.

 When the rotor 22 rotates and a used metal object such as an automobile body 14 is introduced into the crusher 10, the hammers 32 strike this body 14. Between these hammers 32 and an anvil surface 34, the body 14 is crushed, shredded and reduced to small pieces. These pieces leave the rotor area by a curved lower grid 36 or by an upper grid 38. your voids between the bars of the lower grid 36 are smaller than those of the upper grid 38. But the impact of the hammers 32 against the object to be ground bounces and passes through this upper grid 38 part of the pieces formed, which are returned by the walls 40 and 42 of the cover 26 and fall behind a partition 44. your pieces which fall through the lower grid 36, or which are projected through the upper grid 38 and fall behind the wall 44, land on a conveyor 46. This conveyor 46 collects the grapeshot to the right in FIG. 1 and pours it onto another conveyor 48. A extractor hood 50, which is connected to a vacuum source (not shown), sucks light particles (of plastics, plastic foams, dust, etc.) through a conduit 52, while the grapeshot is poured out by the he conveyor 46 on the conveyor 48. This conveyor 48 removes heavy particles and transports them to a subsequent treatment station.

 In the case where some of the treated objects break into large pieces which it is difficult or impossible to pass through the lower grid 36 or the upper grid 38, it is possible to open a flap 54 (FIG. 1), mounted on a pivot 56, to bring out these pieces. The operating mechanism of the flap 54 can be of any conventional type and be for example a hydraulic jack 58, as shown in FIG. 2.

 In this FIG. 2, the reference indices used to describe FIG. 1 have been used again, but in this figure, the objects which are to be shredded and ground are not introduced directly into the crusher 10 with hammers. although arrows indicate the direction of advance of these objects as well as the direction in which the organs of this crusher are moved.

The two feed rollers 16 and 18 are both mounted on a U-shaped support 60 (part of which has been torn off), which a pivot 62 articulates on a fixing support 64. A shaft 66, carrying the roller feed 16 and a shaft 68, which carries the roller 18, pass through this support in
U 60, the arms of which are arranged on either side of the feed ramp 12. This support 60 also carries a drive mechanism 70 (such as a motor), which is used to rotate driving sprockets 72 Via chains 74 and 76, these sprockets 72 rotate sprockets 78 and 80, respectively. As these sprockets 78 and 80 are fixed to the shafts 66 and 68 respectively, they also rotate the respective feed rollers 16 and 18. While rotating with the shafts 66 and 68, these rollers 16 and 18 can pivot together on the pivot 62, in a manner which will be described later with reference to FIG. 3. The rollers 16 and 18 carry longitudinal ribs 84 and in places points 82 intended to sink into the object intended to be shredded and crushed .

 When the rotor 22 rotates during the operation of the hammer mill 10, these hammers 32 are projected outward as shown in FIG. 2. Caps 86 are mounted on the periphery of the various disks 28 of this rotor 22. These caps will described in more detail with reference to Figures 4-10. The actuator 58 keeps the shutter 54 closed until it has to be opened to allow one or more large pieces to come out of the grinder. If it is necessary to access the rotor 22, it is possible to raise the cover 26 to the position shown in phantom by actuating a hydraulic cylinder 88. It is naturally necessary to first remove the bolts or other fixing members ( not shown) which hold this cover 26 in its normal service position. the cover 26 is raised by pivoting on a pivot 90 when the jack 88 is actuated. When this cover 26 is lifted, it gives access to the interior of the crusher for carrying out repairs or any other work that may be necessary to execute.

 The feed rollers 16 and 18 will be described in more detail with reference, in particular, to FIGS. 1 to 3. When the automobile body 14 has been placed on the ramp 12, the tips 82 and the ribs 84 of the roller 16 grip it. Under the effect of the traction exerted from top to bottom by a hydraulic cylinder 92 (or under the effect of the dead weight of the rollers 16 and 18), this roller 16 tends to crush this bodywork 14 that the roller 18 tends to crush even more. your ribs 84 and the points 82 prevent the bodywork 14 from suddenly penetrating for too long a length into the hammer mill 10. If, while the feed rollers 16 and 18 rotate on their respective axes 66 and 68 , one of them is unable to properly crush the body 14 (or any other object introduced into the crusher 10), they can pivot on the pivot 62, the whole U-shaped support 60 pivoting upwards as shown dashed (Figure 3), so as to clear a larger passage. When this occurs, the hydraulic cylinder 92, which is connected to the support 60 by a pivot 94 and is connected to an anchoring support 96, tends to pull down this support 60 and its rollers 16 and 18.

This allows a certain adaptability to the nature of the object introduced into the crusher and at the same time compresses or crushes this object. It is much easier to crush objects, such as car bodies, in stages using two rollers, such as the feed rollers 16 and 18, than to introduce them into the crusher 10 using a single fixed position roller.

 Figure 4 shows the rotor 22 in more detail. In this Figure 4, the rotor is not in place, the hammers 32 mounted on axes 110 (described below) being shown partially deployed for illustrative purposes. Each of the discs 28 bears on its periphery caps 86, which are typically four or six in number depending on the type of rotor. These caps 86 are pierced radially with stepped holes 98, which are formed in the axis of radial holes 100 (not shown in FIG. 4) of the discs 28.

Rectangular openings 102, which cut these radial holes 100 of the discs 28, make it possible to fix nuts to bolts (described below) which pass through the stepped holes 98 and into the holes 100, so as to fix the caps 86.

 The entire rotor 22 is rotated by means of the shaft 30, which is supported at its two ends by bearings 104. your discs 28 and any end plates (shown in Figure 5) are held by studs 106 and nuts 108. Bes studs 106 pass through all the discs 28 which are mounted on the shaft 30 of the rotor 22.

 Figure 5 is a side elevation with partial section of the rotor 22 shown in Figure 4. It can be seen that the studs 106 pass through all the discs and that nuts 108 are fixed to one of their ends. As shown in FIGS. 5 and 6, axes 110 of the hammerheads pass through holes 112 drilled near the periphery of the discs 28. These axes can be retained in place in any suitable manner, for example by end plates 114, which abut against the respective ends of said axes and are held by studs 106 and nuts 108.

But it is obvious that it is possible to use any of a variety of methods to hold in place the hammer pins 110. If end plates 114 are used, the caps 86 'mounted on the end discs should in principle be more thick, so as to also cover these plates 114. However, these caps 86 ′ can, like the caps 86 of the other discs 28, have the same width as these.

 Spacers 116, mounted on the hammer pins 110 and disposed between the various discs 28, protect these pins 110 while giving the desired spacing between these discs. At predetermined locations along the length of the axes 110, the spacer 116 is removed and a hammer 32 is inserted. This hammer 32 can rotate freely on the axis 110. Caps 86 cover the entire periphery of the discs, as can best be seen in FIG. 6.

 This FIG. 6, which is a cross section through the line 6-6 of the rotor represented in FIG. 5, makes it possible to better understand the manner in which the caps 86 are fixed to the discs 28. with the exploded detail view of FIG. 10. your caps 86 are fixed, by bolts 118 passing through the stepped holes 98 and through the radial holes 100, to nuts 120 arranged in the rectangular openings 102. There is a cap 86 for each part of the discs 28 in which an axis 110 passes and these caps are screwed (at least near their anterior external level 138 and pos 140) between the locations of these axes. Each of the caps is drilled at each end at least one stepped hole 98 intended to fix it to the respective disc 28. The caps 86 are separated by inclined interstices 122, so that each adjusts to the neighbors by nesting. Each cap 86 covers a radial arc of the discs 28 corresponding to the location of a respective axis 110. The outer face of the caps 86 is curvilinear, so that these caps form a complete circle covering all of the discs 28 when they are fixed end to end on the discs 28. These caps 86 are made of a material capable of undergoing a hardening by work hardening, such as manganese or a manganese alloy. A typical material of which the caps 86 could be made is an austenitic manganese steel or another alloy steel having similar characteristics. A material which hardens by hardening becomes all the harder or the longer it is used. But, during the hardening process, this material (caps 86) tends to be ductile and it must be fixed by means of bolts 118. As the head of bolts 118 is hollow and that the nuts 120 are accessible through the openings 102, or held by the sides of these openings 102, it is possible to tighten these bolts 118 after a short period of use.

 As also shown in FIG. 6, the holes 112 in which the axes 110 are housed are larger than this would be sufficient for these axes 110 to be able to pass through them. In use, said axes 110 and the hammers 32 are driven radially outward, but the enlarged holes 112 allow these axes 110 to recede somewhat in the case where the hammers 32 strike an object exceptionally difficult to break.

 So that the bolts 118 do not have to withstand all the force of the shocks applied to the caps 86 by the objects treated during their grinding, the discs 28 have a protrusion 124 directed outwards in the radial extension of the area of the axes 110 In this way, it is the front edge or shoulder 126 of these protrusions 124 of the discs 28 which absorbs the shocks received by the shoulders 128 formed on the caps 86 by a recess 130. The shoulders 126 and 128 are, in general , parallel to the shaft 30. Of course, this recess 130 of the caps 86 must be complementary to the protrusions 124 of the discs 28. It goes without saying (as explained in more detail below) that the shapes of the recess 130 of the caps 86 and protrusions 124 of the discs 28 can vary, but what is essential is to form on these discs 28 an anterior edge 126 capable of withstanding the shocks applied to the caps 86 by means of their shoulder 1 28.

 To prevent the discs 28 from rotating on the shaft 30, keys 132 are arranged between these members.

Internal spacers 134 (FIG. 5) are also arranged between the respective disks 28, except between those in the middle, the location where the shaft 30 is widened so as to form the shoulder 136 shown in this FIG. 5.

 Because the caps 86 are mounted on the discs 28 in the manner shown in FIG. 6, their anterior outer edge 138 always forms an obtuse angle with the direction of rotation of the rotor 22. Similarly, the posterior outer edge 140 of these caps 86 always make an acute angle. This conformation prevents particles of material from being trapped under the front edge of said caps 86, which would tend to tear them from the discs 28. This particular problem appeared in the case of known rotors, with discs fitted with caps.

 Figure 7 shows in section a detail of a cap disc during its operation, the hammers 32 being fully deployed under the effect of the rotation of the rotor 22. De-caps 86 are fixed to this disc 28. The axes 110 carries - hammers are driven radially outward in holes 112, due to the inertia of rotation. In addition to the bolts 118 described above, which pass through the stepped holes 98 and into the radial holes 100 and open into the transverse openings 102 so as to be connected to the nuts 120, FIG. 7 shows the use of a median bolt 142, intended to close the inclined gap 122 separating the adjacent caps 86. This median bolt 142 is embedded in a stepped hole 144 which is arranged in the axis of a radial hole 146 of the cap 86 from below and a radial hole 148 of the disc 28. This hole 148 also opens out in a rectangular opening 150, which makes it possible to fix a nut 152 to the median bolt 142. The use of this median bolt 142 in addition to the bolts 118 described above gives greater cohesion to the caps 86 by better preventing them from separating during the operation of the shredders.

 FIG. 8 shows a variant 154 of making the caps. This cap 154 is further drilled at each end of a stepped hole 98, intended to accommodate a bolt 118 as described above. But the recess 130 is replaced by a recess 156 having a rounded front shoulder 158. This rounded shoulder 158 offers the impact a larger surface between the cap 154 and the disc (not shown in Figure 8), helping to prevent shocks created during the grinding of objects to be applied to the bolts 118. Of course , the discs used with this modified cap 154 must have a corresponding contour, so as to form a rounded front shoulder intended to be applied against the rounded shoulder 158 of this cap 154.

 FIG. 9 shows a second variant 160 of making the caps. This cap 160 is fixed to the discs 28 in the normal way, by bolts 118 passing through stepped holes 98, as described above. your discs 28 also have protuberances 124 and the cap 160 has a complementary recess 130 intended to house the corresponding protrusion 124. But there is between the cap 160 and the discs 28 a tongue 162 and a groove 164, intended to make an assembly by tenon and mortise. Although the tongue 162 shown is part of the disc 28 and that the groove 164 is shaped in the cap 160, it is obvious that their positions can be reversed. The goal is to achieve an internal radial overlap between the disc 28 and the cap 160, so as to prevent the latter from moving to the right or the left of this disc 28. While the cap 160 is hardened in place , it tends to be ductile and can bend to the right or the left of the disc 28. The assembly by tenon and mortise shown in FIG. 9 or any other arrangement with radial overlap avoids the curvature or the deformation of the cap 160 Although it has not been observed that this deformation constitutes a particularly significant drawback, this overlap can prevent it from occurring.

 Although it is expected to normally mount the caps 86, as described above, on new rotors for hammer mills, it is possible to easily modify the rotors of existing mills to equip their discs with these caps. the rotor 22 will be removed from the hammer mill 10 and the discs 28 will be removed from the shaft 30. These discs will either be replaced by discs 28 such as those described above, or reshaped to the general shape described. your modified discs 28 must have elements intended to fix the caps 86 there, such as the radial holes 100 and the openings 102. Then caps 86 as described above will be fixed on these discs 28 and these will be reassembled on 11 shaft 30. The new disc-cap assembly will have substantially the same diameter as the initial discs. The rotor assembly 22 will then be replaced in the hammer mill 10. If the caps 86 are fixed to the discs 28 by means of bolts 118, these will have to be tightened two or three times during the start of operation of the mill 10 The reason for this need to tighten the bolts 118 is that the caps 86 become nuts and apply more tightly to the discs 28 and, during this time, they tend to be malleable or ductile.

 It goes without saying that it is possible, without departing from the scope of the invention, to make various modifications to the hammer mill, the rotor, the discs and the protective caps shown and described.

Claims (30)

 1. Hammer mill intended to reduce to pieces objects such as car bodies, characterized in that it comprises  a pedestal  an envelope (24) fixed to this base;  a rotor (22), which is arranged in this envelope and which comprises a certain number of disks (28), mounted on a shaft (30) one end of which exits from said envelope, these disks being spaced from each other by spacer rings (116) which are mounted on axes (110) distributed circumferentially, which pass through said discs near the periphery of the latter and which are parallel to this shaft (30);  caps (86), which cover the periphery of the discs (28), which are attached to it removablewent, which are curved and whose outer face forms an arc of a circle  a feed device which comprises rollers (16, 18) and which is intended to penetrate the object (14), which is to be reduced to pieces, in the envelope (24) by an opening d entry (20), this device further comprising a ramp (12) inclined up and down towards this opening (20)  an anvil (34) which, disposed at said inlet opening (20), is intended to cooperate with hammers (32) mounted so as to be able to rotate on axes (110) of the rotor (22) and passing very close to this anvil (34), for shredding and crushing the objects which pass through the opening (20)  an energy generator arranged outside the casing (24) and intended to rotate the rotor (22) via the end of the shaft (30) which comes out of this casing  an outlet passage for said envelope, making it possible to evacuate therefrom the pieces of the crushed object and comprising grids (36, 38), so as to ensure that the object (14) has indeed been reduced to pieces of a predetermined size before being evacuated; and  a group of conveyors (46, 48), intended to move the pieces away from the object and, after the pieces have been removed from the envelope (24), to direct them towards the end of their treatment.  2. Crusher according to claim 1, characterized in that the caps (86) are nested at their two ends, their outer edge (138) which is in front during the rotation of the rotor (22) forming an angle cbtus and their edge posterior exterior (140) forming an acute angle with the direction of rotation of the rotor (22).  3. Crusher according to claim 2, characterized in that the caps (86) and the discs (28) have shoulders (126, 128) applied one against the other, which absorb most of the shocks applied to these caps during grinding of the object (14)  4. Crusher according to claim 3, characterized in that the set of caps consists of a curved cap (86-) for each part of each disc (28) in which an axis (110) passes, these caps being screwed at these discs at least near their anterior (138) and posterior (140) outer edges between the locations of these axes (110).  5. Crusher according to claim 3, characterized in that the caps (86) are fixed to the discs (28) by bolts (142) passing through the superimposed ends (138, 140) of these caps (86)  6. Crusher according to claim 1, characterized in that the rollers are at least two in number (16, 18), are generally perpendicular to an inclined ramp (12), are arranged above it and can, during that they rotate on their shafts (66, 68) so as to push the object (14) to be ground in the envelope (24), also pivot on a fixed axis (62) which is parallel to them, this pivoting movement on this fixed axis lifting and lowering them relative to this ramp (12).  7. crusher according to claim 6, characterized in that the feed rollers (16, 18) have protuberances (82, 84) to prevent them from pushing the object too long in the envelope (14) intended to be crushed, and in that this crusher comprises a device (92) intended to push these rollers downwards so that they crush this object.  8. Crusher according to claim 6, characterized in that the discharge grids consist of an upper grid (38) and a curved lower grid (36), the outlet passage comprising a flap (54) which can be open to allow large pieces to come out which may damage the shredder.  9. Rotor intended to be used in a hammer mill intended to reduce to pieces objects such as car bodies, rotor (22) characterized in that it comprises  a shaft (30) which is supported near each of its ends by a bearing (104) and one of whose ends can be rotated by an energy source  a number of discs (28) of generally circular shape, which are mounted on this shaft (30) perpendicular thereto  keys (132) which prevent these discs (28) from rotating relative to said shaft (30)  pins (110) which pass through holes (112) drilled in said discs (28) near their periphery, and which are removably attached to these discs  spacers (116) which are mounted on these axes (110) and which are intended to separate the discs (28) from each other and to protect said axes  hammers (32) which are articulated on these axes (110) at predetermined locations along the length of the latter and which are intended to strike the objects (14) which are to be crushed; and  caps (86) composed of a material which can harden by work hardening, which are fixed to the periphery of the discs (28) and whose outer face is curvilinear so that these caps form a circle when they are fixed end to end on these discs  these caps (86) and these discs (28) having complementary internal shoulders (126, 128) which are parallel to the shaft (30), and are intended to contribute to the impact resistance applied to said caps.  10. Rotor according to claim 9, characterized in that the ends of the caps (86) are nested, their front outer edge (138) forming an obtuse angle and their rear outer edge (140) forming an acute angle with the direction of rotation of the rotor (22).  11. Rotor according to claim 10, characterized in that the caps (86) are pierced at at least each of their ends with stepped holes (98) intended to allow them to be fixed to the discs (28), and in that the latter are pierced with holes (100) and openings (102) for fixing nuts (120) to bolts (118) embedded in the recesses of the holes (98) of these caps.  12. Rotor according to claim 10, characterized in that recessed bolts (142) pass through the superimposed ends (138, 140) of the respectively adjacent caps, so as to better fix these to the discs (28).  13. Rotor according to claim 9, characterized in that the caps (86) and the discs (28) have grooves (164) and ribs (162) complementary, intended to prevent any lateral movement of these caps relative to these discs .  14. Rotor according to claim 9, characterized in that the complementary internal shoulders (158) have a rounded front edge.  15. Rotor according to claim 11, characterized in that the set of caps comprises a cap (86) separate for each of the axes (110) which pass through the discs (28) and in that these caps are screwed to these discs between the holes (112) for the passage of these axes (110).  16. Cap for hammer mill rotor used to cut into pieces objects such as car bodies, cap intended to be mounted on discs having complementary surfaces and characterized in that it comprises  a curvilinear outer surface comprising an anterior outer edge (128) forming an obtuse angle and a posterior outer edge (140) forming an acute angle with the direction of rotation of the rotor;  a generally curvilinear underside having a recess (130) intended to accommodate a shoulder (124) of the respective disc (28)  stepped holes (98) formed at each end of this cap and intended to allow the latter to be fixed to the respective disc (28)  said caps being shaped and arranged so as to overlap end to end and to protect the periphery of the discs (28); and  being composed for example of an alloy steel and having substantially the same width as the discs.  17. Cap according to rever.dication 16, characterized in that the recess (130) forms a shoulder (128) intended to be applied in service against a shoulder (126) of the respective disc.  18. Cap according to claim 17, characterized in that one of the stepped holes is a hole (144, 146) which passes through the superimposed ends (158, 140) of adjacent caps.  19. Cap according to claim 17, characterized in that it has internally either a tongue (162) or a groove (164) intended to cooperate respectively, either with a groove or with a tongue of the disc (28) corresponding, so as to prevent any lateral movement between this cap and this disc.  20. Cap according to claim 16, characterized in that it is composed of a material hardening by hardening, such as manganese or an alloy containing manganese.  21. Disc intended to be mounted on the rotor shaft of a hammer mill used to cut into pieces objects such as car bodies and intended to cooperate with protective caps having complementary surfaces, disc characterized in what he understands  an outer surface of generally rounded shape, periodically having protuberances (124) which are intended to cooperate with recesses (130) of the caps (86);  a central hole allowing the shaft (30) of the rotor (22) to pass and holes (112) drilled near its periphery and intended to allow axes (110) to pass;  radial holes (100), intended to accommodate bolts (118) passing through the caps (86), and which open into transverse openings (102), intended to allow nuts (120) to be screwed onto these bolts (118)  these radial holes (100) and these transverse openings (102) being formed between the holes (112) for the passage of the axes (110).  22. Disc according to claim 21, characterized in that it comprises two holes (100) for passing bolts and two transverse openings (102) for each cap (86), the number of these corresponding to that of the holes ( 112) for passing the axes (110).  23. Disc according to claim 22, characterized in that it is pierced in addition to holes (148) for passing bolts and transverse openings (150), intended to accommodate bolts (142) which pass through the superposed ends ( 138, 140) of adjacent caps (86).  24. Disc according to claim 21, characterized in that its protuberances (124) have a shoulder with rounded front face.  25. Disc according to claim 21, characterized in that it comprises either a tongue (162) or a groove (164), intended to cooperate either with grooves, or with complementary tongues formed in the caps (86) .  26. Method for equipping existing disc rotors for hammer mills used for reducing objects such as car bodies, by means of protective caps for these discs, process characterized by the following steps  first removing the rotor (22) from the hammer mill (10); then  the discs (28) are removed from the shaft (30) of this rotor, and  either these discs are replaced, or they are redone to give them a generally circular shape, but having protuberances (124)  these openings (28) are shaped in these discs (28) making it possible to fix caps (86) hardening by hardening;  these caps are fixed to these discs via these openings (100, 102), said caps covering the protrusions (124) so as to form a circular disc-cap assembly having substantially the same diameter as the initial discs before the or withdrawal operations, and  these assemblies are reassembled on the shaft (30), then the rotor (22) is reassembled in the grinder (10).  27. The method of claim 26, characterized in that the caps (26) are mounted by overlapping their ends so as to obtain an anterior outer edge (138) obtuse and a posterior outer edge (140) acute.  28. The method of claim 27, characterized in that, to shape the discs, either new or modified, there are drilled radial holes (100) and there are cut transverse openings (102) which cut these radial holes.  29. Method according to claim 28, characterized in that, to fix the caps (86), there are drilled stepped holes (98) corresponding to the radial holes (100) of the discs (28), so as to be able to screw these caps on these discs.  30. Method according to claim 29, characterized in that, after having reassembled the rotor (22) in the grinder (1O),  we operate this shredder for a while  then tighten the bolts (118); and  the operation of the mill is repeated for a determined period and the tightening of the bolts (118).