Abstract:
An apparatus for the agglomeration of feed material with thermoplastic properties has a radially symmetrical hollow chamber with a perforated die defining its periphery and a front wall element and a rear wall element closing off ends of the hollow chamber. A material feeding system is connected to the hollow chamber. An agglomerating vane arranged in the hollow chamber rotates in a direction of rotation about a longitudinal axis of the hollow chamber. The agglomerating vane has a front side in the direction of rotation. The front side, the front and rear wall elements, and the perforated die define a revolving plasticizing chamber. The front and rear wall elements have inner surfaces facing the hollow chamber and at least one of the inner surfaces has profiles running from an inner area of the inner surface to an outer area of the inner surface for transporting the feed material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an apparatus for the agglomeration of feed material with thermoplastic properties, comprising a radially symmetrical chamber delimited peripherally by a perforated die and at its end faces by a front wall element and a rear wall element, and comprising an agglomerating vane supported in the hollow chamber so as to be rotatable about the longitudinal axis of the hollow chamber and forming with its leading side in the rotational direction together with the two wall elements and the perforated die at least one revolving agglomeration chamber. 
     The invention further relates to a disc-shaped or ring-shaped wear element suitable for use with an apparatus of the aforementioned kind for delimiting a hollow chamber of radial symmetry. 
     2. Description of the Related Art 
     In the course of reutilization of waste material, the recycling of thermoplastic materials, e.g., films, fibers, filaments etc. made of plastic materials, gains more and more importance. In this connection, the thermoplastic waste material is transformed into an intermediate product in the form of granules which are then returned into the production process as starting material for use in extruders, injection molding machines and similar equipment. 
     During the expert treatment of thermoplastic waste material in an apparatus of the aforementioned kind, the feed material is always subjected to high agglomeration and shearing forces causing a great heat development within the agglomerator. This effect is desired within a temperature range below the type-specific melting point of the feed material since only by means of this heat development agglomeration is made possible. If during agglomeration the material-specific melting point is exceeded, there will be an irreversible alteration of the mechanical properties of the feed material which makes the valuable starting material unusable for further processing. 
     An apparatus for the agglomeration of thermoplastic wastes of the aforementioned kind is described in German Patent Specifications 26 14 730 C2 and 197 06 371 A1. These references disclose a disc-shaped annular chamber which is enclosed by a perforated die and into which the feed material is fed in the axial direction. A coaxially arranged agglomerating vane rotates in this chamber and forms with its effective flanks two revolving agglomeration chambers. The heat generated during compaction or agglomeration leads to a plasticizing of the feed material which, in turn, effects the passage of the feed material through the perforations of the die. To avoid thermal damage of the feed material, the agglomerator is equipped with a cooling system for dissipating the excess heat developed during the agglomeration and, in this way, the working temperature of the agglomerator is maintained within a range which is not critical to the feed material. 
     From the German Patent Specification 38 42 072 C1 an agglomerator is already known which differs from the already mentioned agglomerators insofar as the radially symmetrical chamber narrows radially towards the perforated die. This effects a three-dimensional processing of the feed material thus intensifying the compacting and plasticizing of the feed material and increasing in this way the specific throughput efficiency. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to improve the known agglomerators so that the efficiency of the apparatus is increased without affecting negatively the heat generated in the agglomerator. 
     In accordance with the present invention, this is achieved in connection with the apparatus in that the surfaces of the front and/or rear wall elements facing the radially symmetrical chamber have profiles running from the inside to the outside for the transport of the feed material. 
     In accordance with the present invention, this is further achieved in connection with the wear element in that the wear element is configured to confine a radially symmetrical chamber wherein the wear element has profiles running from the inside to the outside. 
     The arrangement of the profiles on the inner surface of the wall elements according to the invention leads to a mostly defined flow of the feed material within the radially symmetrical chamber. In this connection, the feed material is moved on the shortest possible path along the profiles to the peripheral area of the hollow chamber where the actual plasticization and agglomeration takes place. In this way it is prevented that parts of the feed material reside too long in the central area of the hollow chamber where, even though they are entrained by the agglomerating vane, reach the plasticization area of the compacting chamber too slowly and are thus exposed to the high temperatures longer than necessary. 
     The configuration of the circular disc-shaped hollow chamber according to the invention achieves a forced material flow resulting in a shorter residence time of the feed material in the radially symmetrical hollow chamber. This provides, on the one hand, the advantage that, due to the shortened exposure time, the thermal stress is reduced and, accordingly, the danger of thermal damage to the feed material is minimized. On the other hand, the shortened residence time of the feed material in the agglomerator leads to a higher material throughput and thus to an increase of the efficiency of the agglomerator over all. 
     According to the invention, the profiles are preferably grooves worked into the inner surface of the wall elements. In this connection, the efficiency and thus the suitability of the grooves for the material transport depend mostly on their configuration details to be explained in the following. 
     The configuration of the grooves according to the invention provides the advantage of interacting with the rotating agglomerating vane which effects the advance of the feed material within the grooves during its rotation. Accordingly, the grooves according to a preferred embodiment have a longitudinal, plane guiding surface which acts counter to the rotating direction of the agglomerating vane such that the feed material being rotated by the agglomerating vane reaches the grooves and comes into contact with the guiding surface thereat. This prevents the feed material from continuously rotating and forces the feed material to change its direction of movement so that movement is parallel to the orientation of the grooves. The advance of the feed material is effected by the outer edges of the agglomerating vane; the outer edges define an intersecting point with the grooves, which point moves outwardly during rotation. 
     Compared to other configurations, the groove with a plane guiding surface has the advantage that its efficiency is not much impaired even after the first signs of wear are detected. In contrast to this, in the case of grooves having, for example, a concave cross-section, wear very quickly leads to small intersection angles α of the groove with the inner surface of the wall elements, and the efficiency of the guiding surface is thus lost in this way. 
     Good results are obtained with grooves having a guiding surface which forms with the inner surface of the wall elements an angle α of 60 to 90°, wherein the optimum angle α always depends on the type of feed material and the specific configuration of the agglomerator. 
     In a further embodiment of the invention, the guiding surface forms with only one further plane surface the groove according to the invention, so that the groove has a triangular cross-section. The surfaces constituting the groove form preferably an angle β of 70 to 110°. The preferred angle β of 90° provides, in addition to a good material flow, further advantages with regard to a simple manufacture of such a groove. 
     Another embodiment of the invention is moreover preferred, in which the outer border of the groove is formed by a concave surface which is a continuous extension of the guiding surface. This measure offers the advantage that the outwardly directed material flow, when leaving the groove, undergoes a directional change counter to the rotational direction of the agglomeration vane and thus enhances the compaction and plasticization process considerably. 
     Apart from the special configuration of the grooves, their arrangement on the inner surface of the wall elements enclosing the radially symmetrical hollow chamber is of utmost importance for a rapid material flow within the agglomerator. An arrangement of the grooves on the inner surface of the wall elements, wherein the grooves form an angle γ of approximately 90° with the front side of the agglomerating vane, in the direction of rotation of the agglomerating vane, has proven to be especially suitable because in this configuration the feed material is advanced by the conveying edges of the agglomerating vane parallel to the direction of extension of the grooves. Due to the specific curvature of the front side of the agglomerating vane, an angle γ of 90° cannot generally be realized over the whole length of the groove. A good transport of the feed material by the agglomerating vane is achieved with an angle γ of 70° to 110°. 
     The invention comprises also a disc-shaped or ring-shaped wear element whose end faces facing the hollow chamber show the above described profiles and which thus can claim all the mentioned advantages. Moreover, the use of a wear element according to the present invention within an agglomerator offers the advantage that, when wear is at an advanced state, the quantity of parts to be replaced is limited to a minimum. It is furthermore possible to have the wear parts made of an especially wear-resistant material in order to increase the service life of the wear parts without increasing the production cost of the agglomerator significantly. 
     According to a further embodiment of the invention, the side walls (cooling disc and cooling ring), onto which the wear parts are fastened, are provided with channels suitable for receiving a coolant, so that excessive heat generation can be counteracted as closely as possible to the location of origin of the heat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing: 
     FIG. 1 is a longitudinal section view of an apparatus according to the invention; 
     FIG. 2 is a section view of the central area of the apparatus shown in FIG. 1, taken along the line II—II of FIG. 1; 
     FIG. 3 is a section view of an apparatus according to the invention, taken along the line III—III of FIG. 2; 
     FIG. 4 shows another section view in the area of a groove according to the invention, taken along the line IV—IV of FIG. 3; 
     FIG. 5 is a section view of the constructive embodiment of a groove according to the invention; 
     FIG. 6 is a top view of a disc-shaped wear element; and 
     FIG. 7 is a top view of a ring-shaped wear element. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an axial longitudinal section view of an agglomerator according to the invention. The machine housing  1  is traversed in the horizontal direction by a driven shaft  2 . The end of the shaft  2  resting in the interior of the agglomerator is formed as a shaft journal  3  serving as a seat for an agglomerating vane  5  designed as a symmetrical double blade vane and serving also as seat for a conveyor screw  6 . The shaft  2  of the agglomerating vane  5  and the conveyor screw  6  form a unit cantilevered in the bearings  7  arranged in the tubular passageway  8  in the rear of the housing. 
     The face of the machine housing  1  has a coaxial circular opening closed by a door  9  that can be opened coaxially to the shaft  2 . The housing door  9  forms simultaneously the front passageway of the housing for the conveyor screw  6  and serves for fastening the conveyor screw housing  10 . 
     The agglomerating vane  5  is arranged in a circular disc-shaped hollow chamber  43  positioned concentrically to the drive shaft  2 . On its periphery the chamber is enclosed by a perforated die  11  and on its ends by a wear disc  12  and a wear ring  13 . The axial depth of the accordingly configured hollow chamber  43  corresponds approximately to the thickness of the agglomerating vane  5 . Radial openings  14  are evenly distributed on the periphery of the perforated die  11 . The wear disc  12  and a cooling disc  50  are screwed together and fastened to the housing flange  15  formed at the tubular passageway  8  of the housing whereas the wear ring  13  is connected to the housing cover  9  via a cooling ring  53 . Cooling disc  50  as well as cooling ring  53  have ring channels  17  and  18 , intended to receive the coolant which is supplied via the line  19  provided in the tubular passageway  8  of the housing and via a line  20  penetrating the housing cover  9 . 
     On the outside of the perforated die  11 , two revolving stripper knives  21  and  22  are positioned diametrically opposite to each other and are adjustably fastened in a holder  23  and  24 , respectively. Both knife holders  23  and  24  are seated on a hub  25  which is rotatably supported on the rear housing passageway  8  by means of a bearing  26 . The hub  25  carries a V-belt pulley  27  driven in rotation by a drive which is not shown in the drawing. 
     FIGS. 2 and 3 show clearly the agglomerating vane  5  as well as the perforated die  11  forming the radially symmetrical chamber  43 , the wear disc  12  and the wear ring  13 . An agglomerating vane  5  is shown, which has two diametrically opposed blades, rotating in the direction indicated by the arrow  28 . In the direction of rotation  28 , the front side of the two blades of the agglomerating vane  5 , whose thickness corresponds to the thickness of the agglomerating vane, has a steadily curved contour  42 . A sickle-shaped plasticizing chamber  29 , steadily narrowing counter to the direction of rotation  28 , is formed by the front side and the perforated die  11  and is closed relative to the perforated die  11  by the thrust piece  30  fastened at the end of the blade. Both blades of the agglomerating vane  5  have zones  31  and  32  of reduced thickness which allow a substantially free rotation of the agglomerating vane  5  in the circular disc-shaped hollow chamber  43 . To form the pockets  33  and  34 , the thickness of the agglomerating vane  5  in the feeding zone defined by the conveyor screw  6  is further reduced, thus achieving a more uniform distribution of the feed material  38  within the hollow chamber  43 . 
     The profiles according to the invention in the form of grooves  35  and  35 ′ and their arrangement are shown in detail in FIGS. 3 to  7 . The grooves  35 ,  35 ′ have an elongate shape whose ends have the shape of a quarter circle. In this special embodiment, the grooves  35 ,  35 ′ are formed by a first plane surface  36  which takes over the function of a guiding surface and a second plane limiting surface  37 , wherein the intersection lines of the surfaces  36  and  37  define an angle β of 90° between them. The limiting surface  37  may also have a concave cross-section. The guiding surface  36  defines with the adjacent surface of the wear disc  12  and the wear ring  13 , respectively, an angle α of 75°, so that an intersection angle of 15° results between the limiting surface  37  and the surface of the wear disc  12  and the wear ring  13 , respectively. 
     In this particular embodiment, the limiting surface  37  provides in good time and gradually enough space for the feed material penetrating into the grooves  35 ,  35 ′, wherein the feed material then impinges frontally on the guiding surface  36  where the flow of material, with the aid of the agglomerating vane  5 , is deflected towards the perforated die  11 . 
     A good material flow can be obtained with grooves  35 ,  35 ′ having a width B of 16 mm and a depth T of 4 mm because this provides a sufficiently large volume for receiving the feed material  38 . 
     The arrangement of the grooves  35  and  35 ′ on the inwardly facing end face of the wear disc  12  and the wear ring  13  is illustrated, in particular, in FIGS. 6 and 7. The grooves  35  and  35 ′ are uniformly distributed over the periphery of the wear elements  12 ,  13  and extend in the direction of rotation  28  tangentially to a reference circle  41  and  41 ′, respectively. The guiding surface  36  forms a kind of leading ramp toward the perforated die  11  for the incoming material flow. 
     The grooves  35  extend from an inner area or central zone  39 , located within the dashed line  40  and opposite to the outlet section of the conveyor screw  6 , to the outer area or peripheral zone of the wear disc  12 . In this connection, a radial minimum distance to the perforated die  11  of {fraction (1/20)} to {fraction (1/60)} of the outer diameter of the wear disc  12  and the wear ring  13 , respectively, is observed depending on the machine size in order not to impair the compacting and plasticizing effect which is greatest in the outer periphery of the hollow chamber. Two grooves  35  adjacently positioned in the peripheral direction define an angle of 45° between them. 
     Between two grooves  35  there is another groove  35 ′, respectively, which is shorter in the longitudinal direction and consequently does not reach as far into the central zone  39 . The grooves  35 ′ are located on a bisecting line of an angle between two grooves  35 . Since in the central zone  39  there is naturally less surface area available for receiving the grooves  35  and  35 ′ than in the outer area of the wear disc  12 , this alternating arrangement of longer and shorter grooves  35  and  35 ′ avoids criss-crossing of the grooves  35  and  35 ′ with one another which would impair a defined material flow at least in the zone where the grooves  35  and  35 ′ would cross. 
     When operating an apparatus according to the invention, the feed material  38  is first conveyed through the conveyor screw housing  10  to the conveyor screw  6  which transports it into the circular disc-shaped hollow chamber  43  where the agglomerating vane  5  rotates in the direction shown by the arrows  28  and forms with its two blades two revolving agglomeration chambers  29 . In the chambers  29  the feed material  38  is first precompacted by the continuous feeding of material via the conveyor screw  6 . 
     The front side  42  of the agglomerating vane  5  in direction of rotation  28  pushes the precompacted feed material  38  ahead in a circular or helical movement within the hollow chamber  43 . As a consequence of the expansion pressure of the feed material  38  it reaches the grooves  35 ,  35 ′ where the circular and helical movement of the feed material  38  is stopped by the guiding surface  36  (FIG. 4) and is deflected in a linear movement direction along the grooves  35 ,  35 ′ toward the perforated die  11  (FIG.  3 ). The advancing force acting on the feed material  38  is realized by the front edges, in direction of rotation of the agglomerating vane  5 , facing the wear elements  12 ,  13 . Due to the continuous curvature of the front edges, the front edges form with the grooves  35 ,  35 ′ an intersecting point moving outwardly to the peripheral zone of the hollow chamber  43  during rotation. At the outer end of the grooves  35 ,  35 ′ the guiding surface  36  becomes a concavely curved surface so that the feed material  38 , when exiting the grooves  35 ,  35 ′, experiences a directional change counter to the movement direction  28  of the agglomerating vane  5 . 
     The main compacting and agglomeration work, however, is done in the peripheral zones of the hollow chamber where, as a consequence of the tapering compacting chamber  29 , the feed material  38  is steadily reduced to a smaller volume until it begins to plasticize as a result of the increasing pressure conditions and the resulting frictional heat and exits from the compacting chambers  29  in the form of plastic filaments via the radial openings  14  of the perforated die  11  to then be cut to granules by the revolving stripper knives  21 . 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.