Abstract:
A method for implementing mechanical, chemical and/or thermal processes in a product which is located in a housing ( 1 ) with mixing and cleaning elements and/or transporting elements ( 6 ) on at least one shaft ( 4, 5 ), and is transported via the elements ( 6 ) from an inlet ( 2 ) to an output ( 10 ), the intention is for a cross section of the housing ( 1 ) to be adjusted in variable fashion at least in the longitudinal direction thereof.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a kneader mixer for implementing mechanical, chemical and/or thermal processes in a product that is located in a housing with mixing and cleaning elements and/or transport elements on at least one shaft, and is transportable via these elements from an inlet to an output. 
         [0002]    Devices of such kind are called kneader mixers. They are used in a very wide range of applications. Firstly, they are used for vaporizing with solvent recovery, which is carried out in batches or in continuous operation, often in a vacuum as well. In this way, distillation residues are treated, for example, particularly toluene diisocyanates, but also production residues with toxic or high boiling solvents from the chemical industry and pharmaceutical production, washing solutions and paint sludges, polymer solutions, elastomer solutions from solvent polymerization, adhesives and sealing compounds. 
         [0003]    The devices are further used to carry out contact drying of products that are wet with water and/or solvents in continuous or batch mode, often also in a vacuum. The application is intended mainly for pigments, dyes, fine chemicals, additives such as salts, oxides, hydroxides, antioxidants, temperature-sensitive pharmaceutical and vitamin products, active agents, polymers, synthetic rubbers, polymer suspensions, latex, hydrogels, waxes, pesticides and residues from chemical or pharmaceutical production, for example salts, catalysts, slags and waste lyes. These processes are also used in food manufacturing, for example in the production and/or treatment of block milk, sugar substitutes, starch derivatives, alginates for treating industrial sludges, oil sludges, biosludges, paper sludges, paint sludges, and generally to deal with sticky, crust-forming, gelatinous products, waste products and cellulose derivatives. 
         [0004]    A polycondensation reaction can take place inside a kneader mixer, usually in continuous mode and usually in the melt, and this is used mainly in the treatment of polyamides, polyesters, polyacetates, polyimides, thermoplastics, elastomers, silicones, urea resins, phenolic resins, detergents and fertilizers. It is applied for example to polymer melts after a bulk polymerization operation on derivatives of methacrylic acid. 
         [0005]    A polymerization reaction may also take place, also most often in continuous mode. This is used on polyacrylates, hydrogels, polyols, thermoplastic polymers, elastomers, syndiotactic polystyrene and polyacrylamides. 
         [0006]    Kneader mixers may also be used for degassing and/or devolatilizing. This process is used on polymer melts after one or more monomers have been (co)polymerized, after polyester or polyamide melts have been condensed, on spinning solutions for synthetic fibers, and on polymer or elastomer granulates or powders in the solid state. 
         [0007]    In general, solid, liquid or multiphase reactions may take place in the kneader mixer. This applies particularly to back reactions when processing hydrofluoric acid, stearates, cyanides, polyphosphates, cyanuric acids, cellulose derivatives, cellulose esters, cellulose ethers, polyacetal resins, sulfanilic acids, Cu phthalocyanins, starch derivatives, ammonium polyphosphates, sulfonates, pesticides and fertilizers. 
         [0008]    Additionally, reactions may take place between solid Zgas phases (e.g., carboxylation) or liquid Zgas phases. This is used when treating acetates, acids, Kolbe-Schmitt reactions, e.g., BON, Na salycilates, parahydroxybenzoates and pharmaceutical products. 
         [0009]    Liquid/liquid reactions take place during neutralization reactions and transesterification reactions. 
         [0010]    A dissolving and/or degassing reaction in kneader mixers of such kind takes place with spinning solutions for synthetic fibers, polyamides, polyesters and celluloses. 
         [0011]    A process called “flushing” takes place during the treatment or manufacture of pigments. 
         [0012]    Solid state post-condensation takes place during the treatment or manufacture of polyesters, polycarbonates and polyamides, continuous mashing takes place during the treatment of fibers, for example, such as cellulose fibers with solvents, crystallization from the melt or from solutions takes place when treating salts, fine chemicals, polyols, alcoholates, compounding, mixing (continuously and/or in batches) takes place for polymer mixtures, silicone compounds, sealing compounds, flue ash, coagulation (particularly in continuous operation) takes place when treating polymer suspensions. 
         [0013]    A kneader mixer may also serve as a container in which multifunctional processes are combined, for example heating, drying, melting, crystallizing, mixing, degassing, reacting—all either continuously or in batch processing mode. Polymers, elastomers, inorganic products, residues, pharmaceutical products, food products and printing inks may be manufactured and processed in this way. 
         [0014]    Vacuum sublimation/desublimation may also take place in kneader mixers, as a way to purify chemical precursor materials such as anthraquinone, metal chlorides, ferrocenes, iodine, organometallic compounds, etc. Intermediate pharmaceutical products may also be prepared this way. 
         [0015]    Continuous carrier gas desublimation takes place for example with intermediate organic products such as anthraquinone and fine chemicals. 
         [0016]    A primary distinction is made between single-shaft and double-shaft kneader mixers. A single-shaft kneader mixer is known for example from AT 334 328, CH 658 798 A5, or CH 686 406 A5. In these cases, a shaft furnished with disk elements is arranged to extend axially inside a housing, and so as to be rotatable in one direction about an axis of rotation. This is what advances the product in the direction of transport. Counter-elements are attached immovably to the housing between the disk elements. The disk elements are arranged in planes perpendicular to the kneading shaft and create free sectors therebetween, which cooperate with the planes of adjacent disk elements to form kneading spaces. 
         [0017]    A multishaft mixing and kneading machine is described in CH-A 506 322. In this device, radial disk elements and axially aligned kneading bars between the disks are arranged on one shaft. Framelike mixing and kneading elements from the second shaft engage between the disks. These mixing and kneading elements clean these disks and kneading bars on the first shaft. The kneading bars on both shafts in turn clean the inner wall of the housing. 
         [0018]    The disadvantage of these known double-shaft kneader mixers is that because of the eight-shaped housing cross section there is a weak point in the region where the two shaft housings join. In this region, significant stresses are generated when viscous materials are processed and/or in processes that are carried out under pressure, and these stresses can only be managed with expensive design features. 
         [0019]    A kneader mixer of the kind described in the preceding text is known for example from EP 0 517 068 B1. In this case, two axially parallel shafts rotate inside a mixer housing in either the same or opposite directions. At the same time, mixing bars mounted on the disk elements interact with each other. Besides their mixing function, a further task of the mixing bars is to clean surfaces of the mixer housing, the shafts and the disk elements with which the product comes into contact as thoroughly as possible, in order to prevent unmixed zones. Particularly with products that become very compacted, hardened or form crusts, the wall effect of the mixing bars gives rise locally to high mechanical loads, on the mixing bars and the shafts. These force peaks occur particularly when the mixing bars engage in those zones where the product cannot readily escape, most of all when the receptacle is very full and especially when the fill level approaches 100% unchecked. Such zones occur where the disk elements are joined to the shaft, for example. 
         [0020]    A further kneader mixer of the aforementioned type, in which the bearing elements form a recess in the area of the kneading bars, so that the kneading bar has the greatest possible axial extension, is known from DE 199 40 521 A1. Such a kneader mixer has excellent self-cleaning properties with regard to all surfaces of the housing and the shafts with which the product comes into contact, but on the other hand the bearing elements for the kneading bars render the recesses essential because of the travel paths of the kneading bars, and the shape of the bearing elements has to be complicated. Consequently, this not only necessitates a complex manufacturing process but also leads to local stress peaks at the shaft and the bearing elements under mechanical load, particularly when the fill level approaches 100%. These stress peaks, which occur mainly in the sharp-edged recesses and thickness variations, particularly where the bearing elements are welded onto the shaft core, are responsible for causing cracks in the shaft and the bearing elements due to material fatigue. 
         [0021]    EP 2 181 822 A2 describes an extruder with which a housing cross section may be altered approximately centrally between a mixing zone and an extrusion zone. 
         [0022]    DE 10 2007 051923 A1 also describes an extruder for processing polymer materials, having a first screw conveyer and a second screw conveyer. Pins are evident, and these may be used to optimize mixing efficiency, particularly depending on the respective material. For this purpose, the position of the pins may changed, or they may be removed. 
         [0023]    DE 10 2006 051871 A1 describes a transport device for bulk materials. In this context, the bulk material and liquid are to be mixed together. The mixer contains a shaft with stirring tools. The mixer further comprises a weir disk that is positioned close to the outlet and is mounted so as to be swivelable. The material to be mixed remains inside the mixer depending on the position of the weir disks. In this way, it is possible to set an optimum residence time of the material for mixing in the mixer. 
         [0024]    EP 0 438 772 A1 describes a mixer with a container in which a mixing mechanism is arranged. A backflow prevention device in the form of a “weir” is provided in front of the outlet for the mixed material. This backflow prevention device is used to adjust a given fill level of the container, i.e., the height of a bed for the mixing material in the container. 
       SUMMARY OF THE INVENTION 
       [0025]    An object of the present invention is to better control the fill level of the product between the inlet and the output. 
         [0026]    In order to achieve the object of the invention, the device is provided with both an immovable weir and a baffle plate. 
         [0027]    The present invention is usable preferably in machines with two shafts. However, the inventive thought is framed in such manner that the invention may also be used in single-shaft or multi-shaft machine applications. The fill quantity itself may be controlled by means of load cells, the present inventions relates primarily to the control of the fill level. 
         [0028]    For this purpose, a baffle plate is provided that constricts or enlarges a free cross section of the housing, that is to say a passage, according to the requirement for the product. In this way, the residence time and particularly the fill level and thus also the throughput rate of the product. May be varied by the housing, and in this context of course the processing of the product is also affected (e.g., granulometry). The kneading intensity is controlled and the granulometry of the product is positively influenced by adjusting the baffle plate. 
         [0029]    For example, during polymerization a monomer is fed into the kneader mixer and processed. The input may be made in an aggregate fluid state. Under treatment, the product is transformed into an aggregate viscous state as a result of vaporization of solvent or the like, and ultimately may even reach a state that allows granulation. In this context, it may happen that the viscous or pasty phase migrates farther and farther toward the weir, and may then finally also block the passage. The spatial arrangement of this pasty phase inside the kneader mixer may be defined and delimited by adjusting the weir or the passage. This also helps to improve the operating reliability of the kneader mixer. Particularly also with sticky formulations, this movable weir has proven to be extraordinarily valuable. A further advantage is that significantly less crosslinking agents are needed. 
         [0030]    This movable baffle plate is preferably located in the area between the housing and the transition to the output, but the inventive concept is intended to encompass other positions in the housing as well. 
         [0031]    An immovable weir is allocated to the baffle plate, wherein the baffle plate may be moved along said weir. Of course, the weir itself already narrows the housing cross section somewhat, but also leaves a passage free for the product. The cross section of this passage may then be altered by the movable baffle plate. 
         [0032]    The shafts not only pass through the housing itself, but also an adjacent output, wherein additional transport elements are also provided on the shaft in the area of the output and may be able to process the product further as required. In a preferred embodiment in this context, transport elements may be provided that press the product downwards into the output, and/or elements that transport the product back. In this way, clogging of the output is prevented with certainty. 
         [0033]    The shaft itself is divided into at least two temperature controlled zones, to which a temperature control medium is fed. The temperature control medium may be at different temperatures, so that one area is intended rather for heating the product up, and another area is intended rather for cooling the product down. 
         [0034]    It is further provided that a dedicated exhaust vapor extractor is assigned to the output. The advantage of this is that the product is still surrounded by exhaust vapors even in the output, which acts somewhat as a lubricant for the product, and it is prevented from sticking to the walls of the output. 
         [0035]    The absence of any dome/connecting element between the inlet and the output makes it possible for the machine to operate with a controlled high fill level. This is particularly important for comminuting possible lumps. This operating method is referred to as a “lump free process”. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    Further advantages, features and details of the invention will be evident from the following description of preferred embodiments and with reference to the drawing; in the drawing 
           [0037]      FIG. 1  shows a diagrammatic side view of a device according to the invention for implementing mechanical, chemical and/or thermal processes; 
           [0038]      FIG. 2  shows a cross section through the device of  FIG. 1  along line II-II; 
           [0039]      FIGS. 3 to 5  are diagrammatic representations of further possible ways according to the invention to constrict the cross section of the housing of a kneader mixer. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    A device P according to the invention for implementing mechanical, chemical and/or thermal processes comprises a housing  1  that has an inlet  2  for a product that is to be treated. Housing  1  may be designed such that it is heatable, and this is provided by specific housing jackets  3  with chambers—not shown in greater detail—through which a heating medium is passed. 
         [0041]    The housing itself accommodates two shafts  4 ,  5 , on which mixing and cleaning elements and transport elements  6  are located. Shaft  4 / 5  extends in direction of transport x. In a preferred embodiment, shaft  4 / 5  is designed so as to be heatable, wherein two temperature controlled zones are formed, separated by a wall  7  in shaft  4 / 5 . In this way, it is possible to introduce a temperature control medium  8  and/or  9  into the shaft from both sides of shaft  4 . 
         [0042]    An output  10  is located adjacent to housing  1 , and may be furnished with a cooling jacket  11  for example. Shaft  4  also extends through said output  10 , where it is furnished with additional transport elements, wherein elements  6 . 1  and  6 . 2  are provided and differ from elements  6 . Element  6 . 1  is equipped with a transport bar  12 . 1  which, unlike a transport bar  12  of elements  6 , is positioned at an angle. This means that said transport bar  12 . 1  and element  6 . 1  is suited to pressing the product down into the output. 
         [0043]    On the other hand, a transport bar  12 . 2  of element  6 . 2  is positioned at an angle opposite to transport bar  12  of elements  6 , so that it achieves a transport direction for the product, in a direction opposite to transport direction x of transport bars  12 . Transport bars  12 . 2  serve as return kneading bars to relieve the load on the end plate. 
         [0044]    In the lower area of output  10 , an exhaust vapor extractor  13  is also provided to extract exhaust vapors and/or nitrogen. 
         [0045]    A heated/coolable inspection glass  14  is located on top of output  10 . Inspection glass  14 , which is constructed in the form of a port, is an option to port  13  for recondensing the exhaust vapors (reflux) or for leading the exhaust vapors and/or the nitrogen away. 
         [0046]    At the transition between housing  1  and output  10 , an immovable weir  15  is provided and also a baffle plate  16 , which is indicated in  FIG. 1  by a dashed line.  FIG. 2  shows that the immovable weir  15  closes off a large part of a housing cross section. A passage  17  for the product remains open only in the upper part. But even the cross section of passage  17  may also be reduced further by baffle plate  16 , which in the embodiment shown is guided along weir  15 . It is guided by lateral guide rollers  18 . 1  and  18 . 2  and a bolt  19 , which engages in an elongated slot  20  in baffle plate  16 . It may be clearly seen that at least a part  21  of the contour of baffle plate  16  matches the contour of housing  1 . 
         [0047]    A twin-screw infeed (EDS)  22  with N 2  flushing is also indicated on the side of the housing. This is used mainly to supply fines/powder. 
         [0048]    The present invention functions as follows: 
         [0049]    Any product on which mechanical, chemical and/or thermal processes are to be conducted in device P, is fed in through inlet  2 . The product then enters the area of elements  6  with transport bars  12 , which seize the product and advance it in transport direction x. As it is being transported, the product is kneaded, subjected to shearing forces and the like, and at the same time optionally admixed with initiators, solvents, catalysts, etc. 
         [0050]    In the area of the first zone of the shaft, before wall  7 , the product may be additionally heated not only by the heating medium in housing jacket  3 , but also by the heating medium in the shaft. Then in the second area of the shaft, the product may be cooled as desired, which is also assisted by a medium at a controlled lower temperature or a refrigerant inside shaft  4  and in the second temperature controlled zone there. 
         [0051]    Weir  15  causes the product to build up, so that in this area a very intensive mixing and kneading operation may be carried out before the product reaches output  10 . Free passage  17  is adapted by adjustment of baffle plate  16  to constrict or enlarge said free passage  17  to a greater or lesser degree according to the requirements for the product. 
         [0052]    Afterwards, the product enters output  10  where it is pressed into the lower area of output  10  by elements  6 ,  6 . 1  and  6 . 2 , in such manner as to prevent any clogging. To this end, the interior of the output is preferably also coated with PTFE, which prevents the product from sticking almost entirely. The exhaust vapor extraction, which does not take place until the output, also ensures improved lubrication. 
         [0053]      FIGS. 3 to 5  illustrate further options for altering the housing cross section. The example of  FIG. 3  indicates that the inventive concept applies not only to double-shaft kneaders, but of course also to single-shaft kneaders. If more shafts than two are present, of course the inventive concept is equally applicable to these kneader mixers as well. 
         [0054]    According to  FIG. 3 , an arrow  23  indicates that a weir  15 . 1  may also be displaceable about shaft  4 / 5 . In this case, for example, a baffle plate  16 . 1  may also be disposed to the left of shaft  4 / 5 . Of course, it may also be disposed above shaft  4 / 5 . The options shown are intended purely for exemplary purposes. 
         [0055]    According to  FIG. 4 , a further embodiment of an immovable position weir  15 . 2  is indicated, which weir also partially surrounds shaft  4  or  5 . Semicircular baffle plates  16 . 2  and  16 . 3  may be provided before or after the weir, preferably so as to be rotatable about shaft  4 / 5 . Said plates are indicated by dashed lines. 
         [0056]    According to  FIG. 5 , again an immovable position weir  15 . 2  is provided; the cross section of the remaining free spaces in the housing may be modified by various sword-like baffle plates  16 . 4  to  16 . 6 . 
         [0057]    The absence of any dome/connecting element between the inlet and the output makes it possible for the machine to operate with a controlled high fill level. This is particularly important for comminuting possible lumps. This operating method is also referred to as a “lump free process”.