Abstract:
The invention concerns a device for homogenizing, mixing and/or granulating chemicals which consist of at least one component, particularly additives, by means of an extruder consisting of several housing segments, at least one worm, a nozzle arrangement and at least one cutting device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device for homogenizing, mixing and/or pelletizing chemical substances comprising of at least one component by means of an extruder which exhibits several casing sections, at least one endless screw, a die arrangement and at least one cutting mechanism. 
     2. State of the Art 
     Certain pellets of chemical substances, in particular additives, require a high production rate. Since these chemical substances frequently consist of components with the most varied of physical properties (melting point, water content, melting viscosity, miscibility, adhesiveness, etc.), difficulties are encountered during pelletization, in particular at a high throughput. For example, the extruder develops undesired deposits, the dies become clogged, thereby making pelletization more difficult or no longer possible. In addition, the individual components can exhibit varying behavior while being fed in. 
     Known in the art from DE 38 32 006 A1 is an extruder for pelletizing a molding material and the use of such an extruder. The extruder makes it possible to achieve a uniform distribution of the molding material to be processed over the entire cross section of the forming plate. 
     DE 39 34 592 describes a perforated plate for pelletizing plastic strands. The perforated plate is designed in such a way as to prevent deposits and associated product contamination. 
     DE 42 93 549 A1 discloses the fabrication of compacted, superficially sticky pellets as well as the device suitable for executing the process. This process is intended to prevent the pellets from baking on and adhering to the inner wall of the pelletizing shaft, even at very high throughputs and without limiting the range of formulations. 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the invention is to propose a device of the aforementioned type which enables an optimal homogenization and mixing of the extrusion mass on the one hand, and a uniform pelletization with the desired pellet properties on the other, both at the highest possible throughput. 
     According to the invention, the object is achieved by virtue of the fact that the extruder exhibits at least one opening for metering purposes, and that the extruder casing and/or individual die sections are thermally decoupled and separately heatable and/or coolable. 
     Since the different starting materials have varying temperature properties, it is necessary to set a specific temperature profile throughout the entire extrusion process. In this case, high temperature jumps may become necessary, which are then achieved via the thermal decouplings and ability to heat and/or cool the individual extruder casing sections. The extrusion process often starts out at a high temperature, with a low temperature at the extruder output. A specific endless screw configuration can also help bring about a good result. 
     To achieve a uniform distribution of the extrusion mass, the extrusion strand is shaped into a ring before entering the die arrangement, with the diameter of the ring-shaped stand increasing toward the die arrangement. In this case, a uniform pressure distribution is in place in front of the dies. 
     In addition, the invention provides for the use of eccentric dies, in particular during stand pelletization. 
     The extrusion strand divided into individual die strands can be broken down in an advantageous manner by means of a cutting mechanism located directly in back of the die arrangement or to the side of the extruder. 
     Additional preferred features and combinations thereof are outlined in the subclaims and following descriptions to the figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments are illustrated based on the drawings below. Shown on: 
     FIG. 1 is a schematic representation of the extrusion process; 
     FIG. 2 is a schematic representation of the extruder setup; 
     FIG. 3 is a die arrangement; 
     FIG. 4 is sectional view A—A of FIG. 3; 
     FIG. 5 is a die insert; 
     FIG. 6 is a sectional view depicting the transition from the extruder output to the die arrangement; 
     FIG. 7 is an additional die arrangement; 
     FIG. 8 is a knife configuration of the cutting mechanism; 
     FIG. 9 is a sectional view of the cutting mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an example for a schematic representation of the extrusion process according to the invention. The starting materials are transferred from storage tanks  1  and  2  into feed devices  3  and  4 . Depending on the starting materials, the latter are premixed in a mixer  5  or introduced directly into metering devices  6  and  7 . Should more components be needed for better process execution, they can be introduced into the process, for example, by means of an additional metering device  8 . 
     Extruder  9  with drive  10  and gearing  11  comprises of several extruder casing sections  12 . Individual extruder casing sections  12  exhibit openings  13  and  14  for purposes of metering in. The extruder output has a die arrangement  15 , behind which is a cutting mechanism  16 . The freshly pelletized final product subsequently makes its way to a conveyor belt  17  for cooling and drying by means of a ventilator  18 . For additional drying, the extrudate can be relayed by a conveyor  19 , dust removal system or cyclone  20  to a dryer  21 , and then to an extractor  22 . 
     FIG. 2 shows a possible extrusion path. Extruder  9  here comprises of twelve extruder casing sections  12 , which are separated from each other by disk-shaped insulators  24 . This thermal decoupling makes it possible to set a precisely defined temperature profile. It is particularly advantageous to start the extrusion process at a high temperature, and to proceed at a low temperature at the extruder output. The initial temperatures of the casing typically range from 15° C. to 250° C., preferably from 100° C. to 200° C., while the temperature at the last casing section typically ranges from −30° C. to 220° C., preferably from 20° C. to 150° C. However, any product-dependent temperature profile is conceivable. Openings  13  and  14  are used to meter in various components in a staggered manner, if desired. In addition, at least one extruder casing section provides a connection  23  for a vacuum pump in order to remove excess moisture. 
     FIGS. 3 and 4 present a possible die arrangement  15 , with FIG. 4 showing a section along line A—A in FIG.  3 . Die arrangement  15  exhibits a die plate  25  with a cover plate  36 , which is secured by screws  26  to the last casing section  43 , if necessary via adapters  44  and  47 ; and via centering devices  27  (see FIG.  6 ). Die plate  25  accommodates bore holes  35  for the dies  29  arranged on circles  28 ,  28 ′ and  28 ″ concentric relative to the middle  87  of die plate  25 , wherein the middle area  95  of die plate  25  is closed, so that the die circles  28 ,  28 ′ and  28 ″ are located as far out on the outside peripheral area  94  of die plate  25  as possible. The diameter  96  of outside die circle  28  is here greater than the diameter  97  of the free cross section at the extruder output (see FIG.  6 ). In addition, dies  29  can be cooled and/or heated. To this end, cooling and heating channels  30  are incorporated on both sides of bore holes  35  for dies  29 . Along with feed and discharge lines  31 ,  32 ,  33  and  34 , channels  30  form two circulation systems  88  and  89 . This arrangement ensures an optimal temperature distribution on the die plate. 
     FIG. 5 shows a section of the actual die  29 . The design of the die allows only the surface of die holes  38  and  41  to be cooled or heated, and not the entire die body. Die  29  is cylindrically shaped on the outside surface  37 , with an incremental narrowing  40 . A beveling  39  is incorporated at the transition to narrowing  40 . The die input  42  is funnel-shaped on the inside surface, while the die output  41  is cylindrical. The die temperature setting is of considerable importance in the process. It measures 120° C. to 210° C., preferably 180° C. to 200° C. 
     FIG. 6 shows the transition from extruder  9  to die arrangement  15 . A compensator  44  and adapter  47  are located between die arrangement  15  and the last extruder casing section  43 . The two extruder screws  45  and  46  are indicated. Adapter  47  exhibits two funnel-shaped areas  51  and  52 , wherein the larger cross section of area  51  faces the extruder, while the larger cross section of area  52  faces the die arrangement. The maximal diameter of opening  49  in area  51  is identical to diameter  97  of free extruder cross section  48 . A baffle  53  is accommodated in middle area  95  of nozzle arrangement  15 , and in area  52 . Baffle  53  in conjunction with adapter  47  produces a ring-shaped opening  54 . This ring-shaped, resistance-generating passage  55  ensures a uniform distribution of the extrusion mass on the periphery of nozzle arrangement  15 . The contours of the funnel-shaped areas are streamlined according to the extrusion mass in order to avoid dead zones in corners. In addition, the selected geometry of the adapter, in particular of area  51 , is such that a uniform pressure is established on all dies  29 . All components  43 ,  44 ,  46 ,  53  and  15  can be thermally decoupled from each other. FIG. 6 shows disk-shaped insulators  56  and  56 ′ between die arrangement  15  and adapter  47 , and between die arrangement  15  and baffle  53 . In addition, adapter  47  can be cooled or heated by means of circulation provided by feed line  57 , discharge line  58  and channel  59 . 
     FIG. 7 shows another die arrangement  86 . It comprises of two die plates  61  and  62 , which in turn can be thermally decoupled by a disk-shaped insulator  60 . In addition, both die plates have channels  71 ,  72 ,  73  and  74  and lines  63 ,  64 ,  65 ,  66 ,  67 ,  68 ,  69  and  70  to provide a circulation system  90 ,  91 ,  92  and  93  for heating or cooling. The die inserts  76  are visible in die holes  75 . The die plate  61  facing the extruder exhibits cylindrical bore holes  77 . This die arrangement  86  is used in particular to make a nearly fluid product at the extruder output behind the die arrangement capable of pelletization. 
     FIGS. 8 and 9 show the cutting mechanism  16 . It exhibits a knife head  79 , knife holders  80  and knife blades  81 . The knife holders  80  are secured to the knife head, for example by screws  83 , and the knife head in turn accommodates the knife blades  81  with screws  84 . The knives can radiate outward or, as depicted by the imaginary radii  82  in the figure, form a specific angle  99 , wherein the selected angle  99  ensures an optimal number of knives. The knife head  79  can have heating and cooling means. This can take place via blowing, circulation of cooling or heating agents, or heating cartridges  85 . 
     In addition, the extruder output can exhibit a sprayer that sprays the exiting hot product with water, during which the evaporation heat is used to cool the product. The sprayer is not depicted on the drawing. 
     In particular, the advantages associated with the invention have to do with the ability to homogenize, mix and make pelletizable extrusion masses comprised of sticky, clot-forming starting products, with the pellets being formed as uniformly as possible. The process is suited in particular for multiple-component materials with the most varied of physical properties. 
     It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.