Abstract:
An apparatus for comminuting material is provided. The apparatus includes two disks, which are arranged coaxially to one another inside a housing that encloses a comminuting room. The rim areas of the disks are positioned opposite one another, thus forming a milling gap, and are provided with interacting comminuting tools. To generate a mutual relative movement of the disks, at least one of the disks carries out a rotational motion around the mutual axis. To comminute the material, it is first fed into the comminuting room and subsequently radially channeled to the milling gap. For additional cooling, the disk on the intake side is arranged at an axial distance to the intake side of the housing front wall, thus forming a ringwheel-shaped cool air conduit. This can be charged with cool air, which flows through the conduit in a radial direction. In this way, the machine capacity can be increased without causing thermal damage to the material to be processed.

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on German Patent Application No. DE 102004050003.7, which was filed in Germany on Oct. 14, 2004, and which is herein incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for comminuting material having a cool air channel. 
   2. Description of the Background Art 
   During the comminuting of materials in conventional devices, a considerable part of the energy required for the comminuting is converted into heat. This is caused by friction and impact forces the materials are subjected to during the comminuting process, and which primarily affect the comminuting tools. 
   A characteristic of conventional devices during operation is air flow, which, apart from the centrifugal force, is the force that moves the materials. This so-called self-ventilation can be generated by the device itself and/or initiated from the outside. If the material is not heat-sensitive, the innate self-generated flow of air in conventional devices is sufficient to cool down the comminuting tools such that any adverse effects on the material are eliminated. 
   Problems occur on a regular basis, when heat-sensitive materials are to be comminuted. Especially when plastics with a low melting point are to be comminuted, operators of conventional devices face a difficult task. On the one hand, the milling of the material is to be done at barely below the melting point in order to attain as high a machine output as possible. If the material-dependent temperature limit is thereby exceeded, the material softens and begins to melt with the result that individual particles bake together such that the size of the particles and the particle distribution of the milled material are no longer within the desired range. On the other hand, the overheated particles bake onto the machine parts, particularly the milling tools, so that the machine efficiency as well as the quality of the finished product leave much to be desired. 
   This problem is compounded when fine-milling heat-sensitive materials because it was found that the finer the finished product is to be, the more comminuting work has to be done, and the greater the heat generation in the area of the comminuting tools will be. 
   To avoid thermal overstress of the material during the comminuting process, it is common to lower the machine output of comminuting devices. In this way, less comminuting work is done per unit of time, thus generating less excess heat. However, as a consequence, the comminuting apparatus does not operate at full capacity, which goes against the fundamental requirements for an economical operation of such devices. One conventional solution is to increase the air volume beyond the self-ventilation of a conventional comminuting device by adding blowers in order to be able to vent additional heat. 
   Moreover, a device is known from DE 360 295 A1 having two axially spaced milling disks for forming a milling gap. The disk on the material-intake side is rigidly attached to the housing and is provided with openings for feeding the material into the device. The rear disk is positioned on a drive shaft to execute a rotational movement. For additional cooling, the rear disk is thick-walled and provided with a hollow space. The drive shaft, which is formed as a hollow shaft, has two channels, one of which feeds cooling fluids into the hollow space, whereas the other serves as the return line for the cooling fluids from the hollow space. 
   From U.S. Pat. No. 3,302,893, a device is known, wherein two axially opposed and rotating milling disks form a radial milling gap. The disk at the material-intake side has two openings to feed the material to the milling gap. The drive shaft for the rear milling disk is a hollow shaft for forming a cooling channel, from which cooling lines that are arranged in a star-shaped pattern in the area of the rear disk, lead to the comminuting tools. Cooling fluids from the cooling lines are directed to the area of the comminuting tools. 
   An additional device of this class is disclosed in U.S. Pat. No. 3,584,799. A milling disc rotates opposite a stationary milling ring, which is arranged at the intake side of the housing. The stationary milling ring is cooled with cool water, which is introduced via an annular groove in the housing, and distributed. 
   The disadvantage of this device is the need to provide a further cooling medium in addition to air. The additional technical expenditure necessary for storing, cooling, and conveying the cooling medium makes this device costly, in regard to both acquisition and operation. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to increase the machine efficiency of conventional devices without thereby exposing the material to additional thermal stress. 
   A first benefit of the invention is that in addition to cooling the milling gap with self-generated air, additional cool air is introduced into the device in accordance with the present invention. The thus increased air volume makes it possible to discharge additional heat so that the comminuting tools and the materials to be milled are exposed to considerably less heat. This allows the improvement of the operational performance, and thus also the cost effectiveness of devices of the present invention. 
   An additional benefit is derived from using air as a cooling medium. Air is available free of charge and in unlimited quantities everywhere, and can be introduced in a simple way via the openings in the intake side of the front housing wall, for example. After the heat transfer from the comminuting tools into the cool air, it can be released into the ambient air without much effort, after first filtering out the milled material, if necessary. This does not require much in technical equipment so that cool air can be utilized very economically as a cooling medium. Furthermore, air is neutral to the material, that is, it does not alter its chemical or physical characteristics. 
   In a beneficial embodiment of the invention, the openings on the intake side for feeding the cool air conduit with cool air are connected to one another via an annular channel. This simplifies the construction, particularly in connection with the use of cool or compressed air, which otherwise would have to be channeled individually to each opening. 
   To improve the heat transfer from the disks into the cool air, it is suggested in a preferred embodiment of the invention to provide radial ribs in the cool air conduit, which are mounted to the disk that is located at the intake side. The cooling effect thus achieved occurs in stationary, as well as in rotating milling disks. An additional feature of the rotating milling disks is that the radial ribs cause an outward radial movement of the cool air stream. Thus, the radial ribs support the cool air flow. 
   It is thereby beneficial for the radial ribs to extend nearly across the entire width of the cool air conduit in order to make available as large an area as possible to the cool air for heat exchange. In combination with rotating disks, larger radial ribs have the additional benefit of higher tractive power of the cool air flow. 
   By arranging the radial ribs near the comminuting tools, the location of the heat generation and the location of the heat removal are in close proximity to one another, which results in an optimized heat removal. In this way, excess heat is very quickly and efficiently removed. 
   In a further embodiment of the invention, air-conducting elements are arranged in the cool air conduit, which ensure a flow path that is effective for the cooling down of the comminuting tools. It is thereby achieved that the cool air brushes over the areas of the disk that are affected the most by the excess heat. Since the cooling potential of the cool air is thus fully utilized, the best possible cooling effect is thereby achieved. 
   The geometric shape of the air-conducting elements can be such that the air stream follows the geometry of the surface of the disk. When the surface of the disk is not even, the flow path and thus the contact time between cool air and disk is extended, resulting in a high heat transfer. This measure is of particular importance with devices of the present invention that have a milling gap that is tilted towards a radial plane, and/or an existing intake cone. 
   Preferably, the air-conducting elements are provided in the area of the radial ribs in order to obtain an interaction of radial ribs and air-conducting elements, particularly with rotating disk. In this way, the supportive effect of the radial ribs on the cool air flow is increased. 
   An air-conducting element that is suitable for this purpose has a trapezoidal cross section and is annularly arranged around the axis of rotation. This takes into account aerodynamic considerations on the one hand, and on the other hand, allows the ring surface, which is located opposite the trapezoidal base, to interact with the radial ribs. 
   According to a particularly beneficial embodiment of the present invention, a further cool air conduit is provided in a corresponding fashion between the rear wall of the housing and the rear disk. Thereby, the comminuting tools that are arranged on the rear disk are also cooled. In this way, a symmetrical and thus even cooling of all comminuting tools is achieved. The comminuting tools are thereby cooled down on their active side by the self-generated air flowing through the milling gap, and on the opposite outer side by the cool air flowing through the cool air channel. Thus, the greatest-possible heat removal of a device of the present invention is achieved. 
   In a preferred embodiment of the present invention, the comminuting room is divided into two chambers. One chamber is thereby entirely dedicated to the material and the second chamber exclusively to the cool air. This allows an independent supply of the device with material or with cool air, which further optimizes the comminuting process. 
   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. For example, the illustrated embodiment relates to a disk mill having an inclined milling gap, however, the invention is also applicable to disk mills with a radial milling gap, pin mills, refiners, etc. 

   
     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 front view of a device of the present invention, with the housing door open; 
       FIG. 2  is a front view of the device illustrated in  FIG. 1 , with the housing door closed; 
       FIG. 3  is a vertical cross section along the line III-III of the device illustrated in  FIG. 2 ; 
       FIG. 4  is a partial cross section of the upper part of the device illustrated in  FIG. 3 ; and 
       FIGS. 5 and 6  each illustrate a partial cross section of the upper part according to a further embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIGS. 1 and 4  illustrate the detailed construction of an apparatus of the present invention. To begin with,  FIGS. 1 and 2 , which show a front view of the device with the housing door  7  open and closed, respectively, illustrate a machine substructure  1 , the feet  2  of which rest on the ground/floor. The upper part of the machine substructure  1  forms a platform, on which the comminuting apparatus of the present invention is mounted. 
   The comminuting apparatus includes a drum-shaped housing  3  about an axis  14 , and which encloses a comminuting room  4 . On its front side  5 , the housing  3  has a central circular opening  6 , which can be closed with a housing door  7  that is pivotable around a vertical axis  8  and can be bolted shut with bolts  9 . 
   The housing door  7  also has a central circular feeder opening  10 , into which a chute  11 , connected by a flange  12 , terminates, the chute extending from the outside in a vertical direction, and in the bottom area in a transverse direction. From the interior of the housing door  7  is a short, conically expanding connecting piece  13 , which encloses the rim of the feeding opening  10 . 
   Furthermore, the housing door  7  has a plurality of equally spaced openings  15 , which are located on a circumference that is concentric to the axis  14 , and which connect the comminuting room  4  with the exterior of the mill. A ring channel  16 , which also extends concentrically to the axis  14 , covers the openings  15  on the exterior of the housing door  7 , thus connecting them with one another. The ring channel  16  is fixedly attached to the housing door  7  and has a connector  17  in the lower apex, through which air can be introduced from an air conditioning system (not illustrated). The flow of the cool air is indicated by the arrows  18  ( FIG. 3 ). 
   On the inner side of the housing door  7 , in the area between the openings  15  and the edge of the housing door  7 , an annular air-conducting element  38 , which is also arranged concentrically to the axis  14 , is shown. The air-conducting element  38  is formed by a sheet of metal with a trapezoidal cross section, which is attached to the inner side of the housing door  7  with its larger base. When the housing door  7  is closed, the side opposite the base of the air-conducting element  38  forms a ring surface  39 , which extends in a radial plane into the comminuting room  4 . 
   The finely-milled material  21  is discharged via a material discharge  20 , which in the illustration plane of  FIGS. 1 and 2  extends tangentially upwards from the housing  3 , and to which a suction device can be attached, for example. Alternatively, the material discharge  20  can extend in other directions as well. 
   The rear wall  22  of the housing  3  is reinforced in order to form an annular ring channel  23 , which is located in a radial plane to the axis  14 , on the one hand, and, in the area of the axis  14 , to form a horizontal bearing area  27  with bearing groups  28  on the other hand. The ring channel  23  is connected to a cool air system  25  via a connector  24 . The cool air channel  23  is connected to the comminuting room  4  via a plurality of openings  26  in the rear wall  22 , which are located on a peripheral line around the axis  14 . 
   Through the rear wall  22  extends a shaft  29 , which can be hollow, and which is rotatably positioned in the bearing groups  28 , and with its front end reaches into the comminuting room  4 , with, for example, a multiple-groove pulley  30  attached to its exterior end. The multiple-groove pulley  30  can be connected by straps to the drive motor  31 , which is only illustrated in  FIGS. 1 and 2 . The straps extend thereby inside protective sheathing  32 . 
   At the opposite end of the hollow shaft  29  that is located in the comminuting room  4 , a first disk  33  is mounted. The disk  33  has a central area  34 , which is level in a radial plane. In contrast, the rim area  35  adjacent thereto in a radially outward direction is angled towards the front housing side  5  in the shape of a dinner plate. On the inside of the bent rim area  35 , comminuting tools  36  are arranged in the shape of a milling ring. On the side opposite from the rim area  35 , air blades  37 , which extend radially in the area between the disk  33  and the circumference of the housing  3 , are mounted. 
   In addition, a plurality of radially extending ribs  55  are provided in an outer peripheral area of the central area  34  of the disk  33 , which are fixedly connected to the disk  33 . The ribs extend nearly across the entire width of the gap between the disk  33  and the rear wall  22  of the housing. For example, the ribs  55  can be 5-25 mm high and can be arranged at mutual circumferential intervals of 20-100 mm. 
   Inside the hollow shaft  29 , an additional drive shaft  40  is rotatably positioned in the bearing groups  41 . The rearward end of the drive shaft  40 , which runs horizontally through the rear wall  22  of the housing, also has a multi-groove pulley  42  for connecting to an additional electric motor. At the end of the drive shaft  40  extending into the comminuting room  4 , a second disk  44  is seated by its hub  43  ( FIG. 4 ). The first disk  33  and the second disk  44  are arranged coaxially to one another and rotate around a mutual axis  14 . 
   As can be particularly seen in  FIG. 4 , adjacent to the hub  43  of the second disk  44  and extending in a radial direction is an essentially plane disk element  45 , which is separated into several sector-shaped partitions  46  that are bound by radial tie bars  56 . On the front side of the disk element  45  in close proximity to the axis, the partitions  46  form trenches, which radially outwards form channels  47 , which allow the passing of material from the front to the rear side of the second disk  44 . 
   To assure that the entire material reaches the channels  47 , a concentric, truncated hollow cone  48  is arranged on the front side of the disk element  45 , the base of which connects to the trenches in the area of the sector-shaped partitions  46 . With its narrow opening, the truncated hollow cone  48  forms a gliding connection to the hollow cylinder-shaped connecting piece  13 . The rim area of the second disk  44  supports the comminuting tools  49 , which are positioned at a parallel distance opposite the comminuting tools  36  of the first disk  33 . In this way, a milling gap  53  is formed that is tilted toward a radial plane. 
   Between the truncated hollow cone  48  and the comminuting tools  49 , on the side that is assigned to the housing door  7 , the second disk  44  has a plane ring surface  50 , which extends at the same radial distance to the axis  14  as the ring surface  39  of the air-conducting element  38 . Starting at the openings  15  in the housing cover  7  between air-conducting element  38  and the truncated hollow cone  48 , the ring surface  50  as well as the comminuting tools  49  of the second disk  44 , a cool air conduit  51 , through which cool air can flow radially, is thus formed. 
   On the ring surface  50  of the second disk  44 , a plurality of ribs  52 , which are radially oriented and extend nearly across the entire width of the cool air conduit  51 , that is, almost all the way to the ring surface  39 , are evenly distributed around the circumference. For example, the ribs  52  can be 5-25 mm high and can be arranged at mutual peripheral intervals of 20-100 mm. 
   In practical application, a device of the present invention works as follows: With the disks  33  and  44  counter-rotating, or rotating unidirectional with rotational speed difference, the material indicated by arrows  54  is introduced into the chute  11 . In this way, it is conveyed, via the feeder opening  10 , to the comminuting room  4 , where it first encounters, in an axial direction, the second disk  44 . There it is received by the recessed partitions  46 . As a result of the rotating of the disk  44 , it is rerouted by centrifugal forces into a radial direction and then flows through the channels  47 , which subsequently transport it to the milling gap  53 . In the milling gap  53 , the material  54  is comminuted by impact and friction forces generated by the comminuting tools  36  and  49 . Part of the energy supplied to the device is thereby converted into heat. After exiting the milling gap  53 , the milled material, together with the air generated by the radial air blades  37  while rotating around the axis  14 , arrives at the peripheral area of the housing  3 , which it exits tangentially through the material discharge  20 . 
   The heat generated during the comminuting process causes the comminuting tools  36  and  49  to heat up, whereby a part of this heat is transferred to the first disk  33  and/or the second disk  44  due to heat conduction. A first cooling of the comminuting tools  36  and  49  occurs through self-generated air, which, together with the material  54 , flows through the device, including the area of the milling gap  53 . 
   An additional cooling of the first disk  33  is accomplished by introducing cool air from the air conditioning system  25  via the connector  24  into the ring channel  23 . From there, the cool air flows through the openings  26  into the ring-wheel shaped gap between the real wall  22  of the housing and the first disk  33 , from where it flows along the ribs  55  radially outward, whereby a heat transfer from the ribs  55  into the cool air takes place. The ribs  55  rotating with the disk  33  thereby generate an additional propulsion impulse onto the cool air. 
   On the front side  5  of the device, cool air  18  flows into the annular channel  16  via the connector  17 . In the annular channel  16 , a distribution of the cool air  18 , and thus an even supply of the openings  15  with cool air  18 , takes place so that cool air  18  is evenly distributed through the openings  15  into the cool air conduit  51 , through which it flows radially. The cool air  18  brushing by the radial ribs  52  thereby absorbs heat, at the same time receiving a motion impulse from the radial ribs  52  that are brushing past the ring surface  39  at close proximity. The heat-loaded cool air  18  exits the housing  3  via the material discharge  20 , together with the self-generated air and the milled material. 
     FIG. 5  shows the application of the invention to a mill construction, whereby one milling ring is stationary and the other milling ring is rotating. Otherwise, the mill is rather identical with the mill described in  FIGS. 1 to 4  so that the description thereof applies here also. 
   Illustrated in detail is a drum-shaped housing  61  encircling an axis  60  and enclosing a comminuting room  62 . On its front side, the housing  61  is accessible via a housing cover  63 , which can be swung open for this purpose. In its center, the housing cover  63  has a feeder opening  64 , adjacent to which is a chute  65  (only partially shown) for feeding material into the mill. 
   In addition, there are a plurality of openings  66 , which are arranged at equal intervals on a periphery that is concentric to the feeder opening  64 . In the area of the axis  60 , the rear wall  67  of the housing has an aperture  68  for a horizontal drive shaft  69 . The mounting and powering of the drive shaft  69  are essentially the same as described in  FIGS. 1 and 4 . 
   Mounted to the end of the drive shaft  69 , which is located in the comminuting room  62 , is a disk  70  arranged in a radial plane. The outer rim of the disk facing the rear wall  67  of the housing is provided with a first milling ring  71 . In order to form a milling gap  72 , a second milling ring  73  is arranged opposite the first milling ring  71  in an axial distance on the inner side of the rear wall  67  of the housing. 
   The opposite rim section of the disk  70  facing the housing cover  63  has a plurality of radial ribs  74  that are evenly distributed around the periphery. The radial ribs  74  thereby extend almost across the entire width of the annular chamber, which is located between the disk  70  and the housing cover  63 , forming a cool air conduit  79 . 
   In the area between the outer rim segment and the drive shaft  69 , there are material passages  75 , which connect the front and rear sides of the disk  70 . In order to direct the material flow to the material passages  75 , a truncated hollow cone  76  is attached to the disk  70  on the intake side and concentric to the axis  60 , which forms a gliding connector to the feeder opening  66  of the housing cover  63 . 
   As is illustrated in  FIG. 5 , with the disk  70  rotating, the material indicated by arrows  77  is channeled through the feeder opening  66  into the comminuting room  62  during operation. From there, guided by the truncated hollow cone  76 , it travels through the material passages  75  to the area between the disk  70  and the rear wall  67  of the housing, where it is fed by centrifugal forces into the milling gap  72 , and thereby milled. The milled material is removed from the comminuting room via a material discharge (not shown). 
   To cool down the milling ring  71 , a stream of cool air indicated by arrow  78  is channeled through the mill of the present invention. Cool air  78  is thereby drawn through the openings  66  in the housing cover  63  and channeled into the cool air conduit  79  formed by the disk  70  and the housing cover  63 . Due to the prevailing centrifugal forces and pressure conditions, the cool air stream  78  is rerouted radially outwards, thereby brushing along the radial ribs  74 . Thereby, a heat transfer from the radial ribs  74  to the cool air stream  78  takes place so that excess heat is removed from the mill in this way. 
   It is noted that the present invention is also applicable to embodiments of mills, whereby the milling gap extends between the rotating milling disk and the housing door. In these instances, the milling ring on the material-intake side is arranged in an axial distance to the housing door for forming a cool air conduit so that, in turn, radially extending cooling ribs can be mounted in the area of the milling ring to offset an overheating of the comminuting tools, and thus the material. 
     FIG. 6  is, for the most part, identical to the embodiment illustrated in  FIG. 5  so that the same reference numerals indicate the same components, and reference is made to the corresponding part of the description. 
   Otherwise, the embodiment of the invention illustrated in  FIG. 6  differs such that the comminuting room  62  is formed like a chamber. For this purpose, the peripheral side of the disk  70  is surrounded by a coaxial ring wheel  80 . With its outer periphery, the ring wheel  80  is fixedly connected to the housing  61 , whereas its inner periphery forms a gliding connection to the disk  70 . In this way, a partition arranged in a radial plane is formed in the comminuting room  62 , comprised of the disk  70  and the ring wheel  80 , the partition dividing the comminuting room  62  into a first disk-shaped chamber  81  and a second disk-shaped chamber  82 . Consequently, this partition also continues into the material discharge  20  ( FIG. 1 ). In the area of the material discharge, a first pipe line  83  is connected to the chamber  81 , and a second pipe line  84  is connected to the chamber  82 . The pipe line  83 , for example, can lead to a filter device (not shown), where a separation of the gaseous phase of the material  77  from the solid phase takes place. The pipe line  84  can lead directly into the ambient air. 
   The advantage of such a device in practical application is that the material  77 , a combination of gaseous and solid material, which is fed into the comminuting room  62  does not mix with the additional cool air  78  that is channeled into the comminuting room  62 . Rather, the material  77  and the cool air  78  pass through the comminuting room  62  in two spatially separate systems so that for the extraction of the milled material as the end product, it is merely necessary to channel the gaseous and solid material mixture of the material  77  passing through the chamber  81  through subsequent filter devices. The cool air  78  flowing through the chamber  82  can directly and without additional measures be discharged into the ambient air. The thus reduced volume to be filtered allows the employment of smaller filters. 
   It goes without saying that the chamber-like construction of the comminuting room  62  is also possible in comminuting devices of this class that have two rotating disks, whereby cool air is channeled into the comminuting room from the front as well as from the rear, similar to the embodiments illustrated in  FIGS. 1 to 4 . In such an instance, the comminuting room  62  is divided into three corresponding chambers, whereby the one in the middle is designated for the self-generated air and solid material part, whereas the remaining chambers, which are adjacent to each side in an axial direction, are exclusively dedicated to cool air for the comminuting tools, with the resulting benefits as previously described. 
   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.