Abstract:
An apparatus for comminuting large pieces of cuttable material, particularly bales of rubber, is provided. The apparatus includes a first comminuting stage for carrying out a pre-comminuting, and a second comminuting stage for carrying out a fine comminuting, whereby the second comminuting stage includes a comminuting system that rotates around an axis of rotation, to which the material is conveyed via a supply channel. The first comminuting stage is integrated in the supply channel to the second comminuting stage. In this way, a largely even feeding of material to the second comminuting stage can be achieved so that comparatively low machine performances are sufficient and the performance capacity of the second comminuting stage can be better utilized.

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on German Patent Application No. DE 2004051217, which was filed in Germany on Oct. 20, 2004, and which is herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and a cutting unit for comminuting large pieces of cuttable material 
     2. Description of the Background Art 
     The purpose of industrial comminuting of material is oftentimes the fabrication of an intermediate product of defined shape and size, which is subsequently used as source material for the production steps of another production process. The production of granulate is an example, which is further processed in extrusion devices. The uniformity in shape and size are thereby the determining factors for the quality of the intermediate product. 
     The operators of comminuting devices are regularly presented with a challenge, when large pieces of material, for example, bales of rubber, are to be reduced to a relatively small end size, for example, to granules. Generally, multi-step comminuting is used for applications of this kind, whereby several cutting mills of varying size, one behind the other, are provided. The end product of the previous cutting mill thereby serves as the source material for the next cutting mill. In this way, a step-by-step comminuting of the material to the desired end size takes place. 
     The advantage of this method is that it yields high-quality granulate material. The disadvantages, however, are economical because several cutting mills have to be on hand. Due to the need and operation of several comminuting machines, there are, apart from the expenditures for their acquisition, maintenance, and operation, additional costs for the required surge tank capacities, means of transportation, and the additional space requirement. 
     To circumvent these disadvantages, devices have been made for special applications, for example, the comminuting of bales of rubber, which make it possible to comminute inside a housing the original material to the desired fineness of the end product. Devices of this kind have a rotating, cylinder-shaped rotor provided with axially oriented knives, which are evenly distributed around its periphery moving in a mutual blade flight circle. For the purpose of comminuting, the knives interact with stator knives, which are tangent to the blade flight circle. A perforated strainer is arranged over a partial area of the blade flight circle, via which the sufficiently comminuted material is discharged. During comminuting, the material remains in the cutting area of the knife until the particles are small enough to pass through the perforations of the strainer. In other words, in devices of that kind, the pre and post comminuting is done simultaneously with one piece of equipment with the same comminuting tools. 
     One of the advantages thereof is the need for only one comminuting device, which in contrast with the previously described multi-step variation is a cost and space-saving way of comminuting. However, the consequence of the one-step comminuting is that the entire comminuting process, that is, coarse and fine comminuting, is done by the same comminuting tools. However, since the individual comminuting steps have different objectives due to different initial conditions, it would be desirable in view of quality improvement to adjust the respective comminuting tools to the specific requirements of each comminuting step by using particularly suitable comminuting tools. This would not be possible with one-step comminuting, which is the reason why, from a technical viewpoint, one-step comminuting is a compromise. 
     An additional factor in the comminuting of bales of rubber or extruded synthetic hollow sections is that for the initial cutting of the material, very high forces must be applied to make comminuting possible. During that process, high impact forces are applied to the material by the comminuting tools. These cause extremely high mechanical stress, which must be taken into consideration in regard to the dimensional design of the device. Furthermore, this way of comminuting characteristically generates considerable noise, which makes it necessary to encapsulate the device to protect the personnel. 
     Additionally, the resistance encountered at the initial cutting of the material by the comminuting tools causes a reduction of the rotational speed of the comminuting rotor. To offset this loss of rotational speed, a strong short-term power surge to the drive motor occurs. Since energy costs are calculated not by the average energy consumption but by peak demand, this leads to a superproportional increase in energy costs. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to comminute large pieces of material in an economical way, without having to make sacrifices with regard to the quality of the end product. 
     The invention is based on the idea to carry out the comminuting of the material in two steps, whereby a pre-comminuting device is arranged in a material delivery unit of the fine-particle comminuting device. In this way, it is possible to combine the benefits of two-step comminuting with the benefits of a one-step comminuting device. 
     As a result of the step-by-step comminuting of the material, the determining factors for each comminuting step remain constant for the most part during the comminuting process. By introducing material that is defined in shape and size, it is possible to adjust the comminuting tools for each comminuting step to the characteristics of the material and the specific requirements for the intermediate or end product to be fabricated. 
     The result is primarily a high-quality comminuted product, which both in shape and in size remains within narrow tolerances. This is critical for its usability as a source material in other production processes, for example, in extruding. 
     Furthermore, it makes it possible to always operate a comminuting device of the present invention at its optimal capacity. In this way, performance fluctuations are very considerably reduced, which is noticeable in the largely constant energy intake of the device. Peak consumptions, which are the basis for calculating energy costs, are mostly evened out, which makes an economical comminuting operation possible. 
     The average comminuting efficiency of the pre-comminuting is not higher than the average comminuting efficiency of the fineness comminuting. At continuous feeding, the comminuting devices of both comminuting steps thus manage the same material throughput. The fluctuation-deficient comminuting thus achieved results in an evenness of the mechanical stress and makes it possible for the designer of devices of the present invention to avoid overdimensioning on account of load peaks. Thus, devices of the present invention can be constructed smaller and more compact at comparable machine capacities with the benefit of lower production costs and fewer spatial requirements for installation. 
     In a further embodiment of the present invention, the machine performance of the pre-comminuting device is regulated in dependence from the machine performance of the fine comminuting device, for example, in dependence from the power intake of the drive motor. In this instance, the pre-comminuting device not only has a comminuting function but also a feeder function to assure that the device for fine comminuting operates at optimal capacity. 
     In a further embodiment of the invention, the fine-comminuting device is preferably provided with a knife that cuts the material in the supply channel into pieces of defined size by linear form-feeding. In contrast to the rotating knives of a cutting mill, this method allows comminuting at a low cutting speed. The beneficial result is that noise emissions occur only to a marginal degree. Furthermore, the knife cutting into the material does not subject the material to impact energy, which due to heat transfer would otherwise lead to a heating of the material and high wear and tear. 
     Preferred is also the arrangement of the knife inside a slidable frame. The frame stabilizes the knife while cutting through the material, thus assuring a precise cut even at high cutting frequency. 
     In a further embodiment of the invention, the cutting unit is provided with a frame-shaped knife guide for the knife, that is, for the knife frame. The knife guide can be thereby inserted into the supply channel, which it replaces in this segment. In this way, even existing comminuting devices can be retrofitted in a simple way with a pre-comminuting device. 
     It is thereby beneficial if part of the knife guide, against which the knife moves, also forms a back stop for the knife blade. The back stop can be a self-contained, replaceable component that is manufactured with high precision and is mounted to the knife guide without tolerance. This assures a precise interaction between the knife and the back stop and thus a total severance of the material. 
     To operate the knife, a spindle drive or a hydraulic-driven cylinder piston unit is preferred, as this allows a power or path/direction-dependent control of the knife. Beneficially, the power to activate the cutting motion of the knife is derived from two asymmetrically arranged cylinder piston units. The symmetrical loading averts a tilting of the knife, that is, the knife frame during the form-feeding, thus increasing operational safety. 
     In a particularly beneficial embodiment of the invention, a retaining element for the material is provided below the knife. The retaining element thereby assumes two functions. On the one hand, it keeps the material in a cutting position during the comminuting process. On the other hand, by setting the distance to the knife, it determines the size of the parts to be cut off the material. In order to make the size of the parts to be cut adjustable, the distance between retaining element and knife is adjustable, according to an embodiment of the invention. 
     Furthermore, it is preferable to couple the activation of the retaining element to the motion of the knife. With a linearly slidable retaining element, this can be achieved by arrangement within the same frame that also serves for the mounting of the knife. Thus, both the knife and the retaining element can be actuated with only one drive in a most simple way. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
         FIG. 1  is a vertical cross section of a device of the present invention; 
         FIG. 2  is a horizontal cross section of the device illustrated in  FIG. 1  along the line II-II in the area of the cutting unit; 
         FIG. 3  is a cross section of the device illustrated in  FIGS. 1 and 2  along the line III-III; 
         FIG. 4  illustrates various modes of operation during the comminuting process; and 
         FIG. 5  is a vertical cross section of a further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an example of the implementation of the invention in combination utilizing a cutting mill  1  as a second comminuting step, without being limited to a cutting mill. The cutting mill  1  includes a box-shaped housing  2 , which serves as the receptacle for a cutting rotor  3  that is rotatably mounted around a horizontal axis. The cutting rotor  3  has three arms, each supporting a knife  4  that is oriented parallel to the axis of rotation. When the cutting rotor  3  is rotating in the direction of the arrow  5 , the knives  4  form a mutual blade flight circle  6 . 
     The comminuting of the material is carried out via two stator knives  7 , which are mounted to the housing  2  and are positioned diametrically opposed to one another in relation to the axis of rotation, the cutting edges of which are tangent to the blade flight circle  6 . The lower area of the blade flight circle  6  is covered by a perforated strainer  8 , through which the sufficiently comminuted material exits the cutting area of the cutting mill  1 . Downward from the housing  2 , a funnel-shaped material discharge  9  is connected, via which the comminuted material is conveyed from the cutting mill  1  for further processing. 
     The upper circumference of the cutting rotor  3  is enclosed by a funnel-shaped housing part  10 , which is adjacent to the supply system  11  for the material. 
     The upper segment of the supply system  11  is formed by an intake chute  12 , which has a lateral opening  13 . The material can be fed to the supply system  11  via the opening  13 . The preferred material in  FIG. 1  are parallelepiped bales of rubber  14 , which can be between 300 and 400 millimeters wide, between 120 and 180 millimeters high, and between 400 and 600 millimeters long, for example. 
     The intake chute  12  extends downward toward the cutting mill  1  in the shape of a rectangular supply channel  15  and connects with a cap-shaped end piece  16  to the housing part  10  that is open on the top. Via flange connections, a cutting unit  17  is interposed in the supply channel  15  and is thus integrated in the supply system  11 . 
     The detailed construction of the cutting unit  17  is illustrated in  FIG. 1  and particularly in  FIGS. 2 and 3 . The cutting unit  17  comprises a knife guide  18  designed as a closed rectangular frame, which is fixedly attached to the supply channel  15  via circumferential flanges ( FIGS. 1 and 3 ). The opening  20 , which is enclosed by the knife guide  18 , corresponds to the cross section of the supply channel  15  and forms a cutting chamber. The longitudinal sides  19  of the knife guide  18  are formed by U-sections, the open sides of which point toward the opening  20 . The inner sides of the U-section are covered with a slideway lining  21 . In this way, the longitudinal sides  19  having slideway linings  21  form a linear guide transversely to the longitudinal axis of the supply channel  15 . 
     Inside the knife guide  18 , a knife frame  22  is slidably mounted. The knife frame  22  includes lateral longitudinal spars  23 , the ends of which are connected to one another via a crossbeam  24  and a yoke member  25 . The yoke member  25  thereby extends beyond the longitudinal spars  23  thus forming a projecting length on both sides. 
     Commencing at the yoke member  25 , the upper side of the knife frame  22  is covered by a knife  26 , the blade  27  of which ends approximately at half-length of the knife frame  22 . Likewise, commencing at the crossbeam  24 , the lower side of the knife frame  22  is covered by a retaining element  28 , which with its free edge  29  also ends in the middle of the knife frame  22 . Thus, the knife  26  and the retaining element  28  are arranged in plane-parallel planes on top of one another, and the free edge  29  and the blade  27  are aligned with one another in a vertical projection to the frame plane. In this way, the knife frame  22  forms a kind of sled, the one frame half of which is solely taken up by the knife  26 , and the other frame half is occupied in a parallel plane and at a distance by the retaining element  28 . 
     The knife frame  22  is slidably arranged within the linear guides of the knife guide  18  via its longitudinal spars  23 . To drive the motion of the knife frame  22 , two hydraulic cylinder piston units  30  are provided. Their cylinders are fixedly attached to the outer sides of the longitudinal sides  19 , whereas their slidable pistons are attached to the projecting segments of the yoke member  25 . By activating the cylinder piston units  30 , the knife frame  22  can be moved linearly to and from, as indicated by arrow  31 . As an alternative, it is also possible to swivel the knife  26  in the knife plane around an axis of rotation that is vertical for this purpose. 
       FIGS. 4   a  to  4   c  are greatly simplified illustrations of the above-described invention, with the aid of which the method of operation of the cutting unit  17  is therebelow described.  FIG. 4   a  thereby shows the initial position of the cutting unit  17  for the feeding of the device with material, here in the form of bales of rubber  14 . By extending the cylinder piston unit  30 , the knife frame  22  is brought in a first end position, whereby the knife  26  completely deblocks the opening  20 , and the retaining element  28  completely closes the opening  20 . The free edge  29  of the retaining element  28  thereby abuts to the inner side of the knife guide  18 . 
     As indicated by the arrow  32 , a bale of rubber  14  is conveyed lengthwise through the supply channel  17  to the area of the cutting unit  17  until it comes to rest on the retaining element  28 . 
       FIG. 4   b  shows the start of the comminuting process. By running in the cylinder piston units  30 , a movement of the knife frame  22  in the direction of the arrow  33  takes place. The knife  26  thereby penetrates the bale of rubber  14 . Simultaneously, the retaining element  28  begins to clear the opening  20 . 
     By sustained advance of the knife  26 , the cutting unit  17  is put into a second end position. This position, which is achieved by completely running in the cylinder piston units  30 , is illustrated in  FIG. 4   c . The knife  26  thereby moves across the entire cross section of the supply channel  15  until the blade  27  abuts to the inner side of the knife guide  18 , which is designed as a back stop for the knife  26  for this purpose. The retaining element  28  is complete retracted from the opening  20 , thus clearing the entire cross section of the supply channel  15 . This allows the severed part  35  of the bale of rubber  14  to be conveyed by force of gravity to the second comminuting step in the direction of the arrow  34 , where in the cutting mill  1  fine comminuting takes place. 
     Once a cutting cycle is completed, the cutting unit  17  is returned to its first end position by extending the cylinder piston units  30 , and thus to the starting position for the next cutting cycle. Shifting between two end positions, the knife frame  22  thus executes a sled-like linear movement transversely to the supply channel  15  during the comminuting process, whereby for the feeding of the cutting unit  17 , the opening  20  is cleared by the knife  26  and closed by the retaining element  28 , and for cutting and further conveying of the material, the opening  20  is closed by the knife  26  and opened by the retaining element  28 . 
     Further, the relation movement between the knife  26  and the retaining element  28  forms a shield. Thus, during the commuting process by the cutting mill  1 , the material  14  is substantially prevented from entering the supply channel  15  above the cutting unit  17 . Therefore, supplemental filters or retaining systems are not required in order to prevent the material  14  from escaping the supply channel  15  through the opening  13 . 
     Lastly,  FIG. 5  shows an alternative embodiment of a cutting unit in its basic components. Again, the middle section of a supply channel  15  is illustrated having a cutting unit  40  interposed therein. The cutting unit  40  has a tubular knife guide  41  with a cross section corresponding to that of the supply channel  15 . Approximately half-way up and mounted laterally to the knife guide  41 , there is a cantilever  42 , which extends transversely to the longitudinal extension direction of the supply channel  15 . The cantilever  42  serves as the receptacle for a spindle drive  44 . For this purpose, two bearings  46  are arranged on the top side of the cantilever  42 , in which the spindle  45  is positioned. 
     The free end of the cantilever  42  supports a console  43 , on which a stepping motor  54  is arranged, with the aid of which the spindle  45  is relocatable during rotation. A knife holder  47  having a threaded bore is positioned on the spindle  45  and is movable along the spindle  45  during its rotation. The knife holder  47  supports the knife  48  in a parallel orientation to the cross section plane of the supply channel  15 . At the level of the knife  48 , a suitable opening  55  is provided in the knife guide  41  for the passage of the knife  48 . In addition, a rigid lever  49  extends from the bottom side of the knife holder  47 . 
     On the side of the cutting unit  40  that is opposite the cantilever  42 , there is a stationary horizontal pivot bearing  50 , which extends vertically to the plan view. A retaining element  51  is pivotably mounted thereon, with a triangular shank  52  attached to its bottom side. The rigid lever  49  and the triangular shank  52  are flexibly attached to one another via a push rod  53 . 
     The illustration in  FIG. 5  again shows the starting position of the cutting unit  40  prior to the cutting process. The knife  48  is thereby completely retracted from the cross section of the supply channel  15 , whereas the retaining element  51  is swiveled upwards, thus closing the supply channel  15 . A bale of rubber  14  is resting on the retaining element  51  waiting to be comminuted. 
     By activating the stepping motor  54 , the knife holder  47  is moved along the spindle  45  in the direction of the bale of rubber  14 , whereby the knife  48  cuts into the bale of rubber  14 . Simultaneously, a force is applied to the shank  52  via the push rod  53 , which causes a gradual pivoting up of the retaining element  51 . When the bale of rubber  14  is completely severed by the knife  48 , the retaining element  51  opens up the entire cross section of the supply channel  15  so that the severed part of the bale of rubber  14  can pass on to the second comminuting step. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.