Abstract:
An electric heating device ( 100 ), especially for an injection molding die, has a material tube ( 101 ), through which passes a duct ( 109 ) for a flowable material, a heater ( 102, 122, 132 ) for heating the flowable material when this is present in the duct ( 109 ) and a thermocouple ( 103 ). The heater ( 102, 122, 132 ) is pushed over the material tube ( 101 ) or is placed round the material tube ( 101 ), so that the material tube ( 101 ) is received in an opening passing through the heater ( 102, 122, 132 ) along the direction in which the material tube ( 101 ) extends. The heater ( 102, 122, 132 ) is arranged detachably at the material tube. The thermocouple ( 103 ) is arranged at least in some sections between a surface of the material tube ( 101 ), which said surface faces away from the duct ( 109 ), and the surface of the heater ( 102, 122, 132 ), which latter surface faces the duct ( 109 ), so that when the heater ( 102, 122, 132 ) is detached from the material tube ( 101 ), the thermocouple ( 103 ) and heater ( 102, 122, 132 ) form separate assembly units. A process is provided for manufacturing such an electric heating device, including the steps of manufacturing a heater, inserting a thermocouple into a groove of the heater or of a jacket tube and pushing the heater over the material tube with the thermocouple inserted into the groove, wherein the thermocouple inserted into the groove is clamped during or after the pushing over of the heater.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Utility Model 20 2010 011 404.7 filed Aug. 13, 2010, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention pertains to an electric heating device, especially for an injection molding tool, with a material tube, through which passes a duct for a flowable material, with a heater for heating the flowable material when this is present in the duct, wherein the heater is pushed over the material tube or is placed around the material tube, so that the material tube is mounted in an opening passing through the heater along the direction in which the material tube extends, and wherein the heater is arranged detachably at the material tube, and with a thermocouple and to a process for manufacturing same. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such electric heating devices are used, for example, in injection molding dies. They have a material tube with a duct for the flowable material and a heater, which surrounds the outer wall of the material tube and can be removed from the material tube. 
         [0004]    Furthermore, accurate temperature monitoring is important, which is achieved in practice by providing a thermocouple, whose sensor tip is brought into contact with the material tube and is fixed there. This means that the thermocouple must pass through the heater, i.e., in a hole, which is prepared in the heater for this purpose and into which the thermocouple must be inserted. An example of such an electric heating device is known, for example, from DE 10 2008 055 640 A1. 
         [0005]    It was found in practice that the service lives of thermocouples and heaters, which are used in electric heating devices, are different from each other in practice. However, it is complicated, if at all possible, in the prior-art embodiments to replace a defective thermocouple of a still functioning heater or to use a functioning thermocouple of a defective heater in conjunction with a new heater that is able to function. 
       SUMMARY OF THE INVENTION 
       [0006]    An object is therefore to provide an electric heater that makes it possible to replace the thermocouple in a simple manner and rapidly and a process for manufacturing same. 
         [0007]    The electric heating device according to the present invention comprises a material tube, through which passes a duct for a flowable material and a heater for heating the flowable material when this is present in the duct. The suitable heaters are especially heaters in which the heating element is formed by a heating layer applied to the outer or inner jacket surface according to a plasma process, by printing or in another manner, thick-layer heaters, heaters with a heating element that is inserted into a groove prepared in the inner or outer jacket surface of the heater, and also heaters in which the heating element is embedded in a powder or granular material between the jacket surfaces. 
         [0008]    The heater is arranged detachably at the material tube and is especially pushed detachably over the material tube or is placed detachably around the material tube, so that the material tube is received in an opening passing through along the direction in which the material tube extends. This does not expressly require that the material tube must be surrounded by the heater in all directions. Embodiments in which the heater has a recess passing through it in parallel to the longitudinal axis thereof are included as well. 
         [0009]    Furthermore, the electric heating device comprises at least one thermocouple. 
         [0010]    The thermocouple is arranged according to the present invention at least in some sections between a surface of the material tube facing away from the duct and the surface of the heater facing the duct, so that the thermocouple and heater form separate assembly units when the heater is detached from the material tube. 
         [0011]    The present invention is based on the discovery that the defined positioning and fixing of the thermocouple, which is absolutely necessary for obtaining reliable and reproducible measured temperature values, can be achieved when arranging the thermocouple between the heater and the material tube by an interaction with these components. This entails that when one of these components is removed, the fixing of the thermocouple is automatically no longer guaranteed, either, so that it can be detached easily or by itself from the other assembly units of the electric heating device. 
         [0012]    It is especially advantageous if, when separating the heater from the material tube, the thermocouple and heater form separate assembly units, which can fall apart and thus they are not, as in a less preferred embodiment of the connection compared to this, connected to one another in an easily detachable manner by holding means, which do not bring about a positioning and fixing of the thermocouple. In the preferred embodiment with separate assembly units, which can fall apart, it is, on the contrary, sufficient for this to pull off the heater from the material tube to replace the thermocouple and, if necessary, to tilt it, unless the thermocouple had already fallen off in the process. 
         [0013]    In an especially compact embodiment of the electric heating device, the thermocouple is guided, at least in some sections, in a groove in the material tube or in a groove of the heater. It is especially advantageous if the groove passes completely through the material tube or heater in the direction in which the material tube extends, i.e., in the direction of flow of the material to be injected. 
         [0014]    In an advantageous variant of the present invention, the groove is prepared in the heater by deforming the heater. It was found that, for example, compaction of the heater on a calibrating mandrel, which has a burr in the form of the groove to be prepared, leads to suitable grooves, which permits, moreover, cost-effective manufacture, because, contrary to the situation seen especially in case of the use of grooves prepared by machining, no additional process step has to be performed any more. 
         [0015]    A preferred process for manufacturing an electric heating device according to the present invention correspondingly has the steps of manufacturing a heater, inserting the thermocouple into a groove of the heater or of the material tube and pushing the heater with the thermocouple inserted into the groove over the material tube, wherein the thermocouple inserted into the groove is jammed during or after the pushing over of the heater. Provisions are made in an especially advantageous embodiment for the groove to be arranged in the heater and to be impressed into the heater during the compaction performed in connection with the manufacture of the heater. This can be achieved especially by the compaction being performed on a calibrating mandrel, which has a burr in the form of the desired groove. 
         [0016]    An especially simple manner of positioning and fixing the thermocouple is obtained if the thermocouple is fixed by being clamped a least in some sections, especially in the area of its sensor tip, between the heater and material tube. Clamping in the area of the sensor tip also ensures, moreover, intimate thermal contact between the temperature-sensitive area of the thermocouple and the material tube, which makes possible especially reliable measurements. 
         [0017]    There are a number of possibilities of bringing about this clamping action, each of which has different advantages. 
         [0018]    Provisions are made in a first embodiment, which is advantageous because of the simple and cost-effective possibility of manufacture associated with it, for a reduction of the cross section of the opening passing through the heater to be present in the area in which the sensor tip is located, so that the clamping action is produced. 
         [0019]    Provisions are made in an alternative advantageous embodiment for an end section of the thermocouple to be guided in a groove in the material tube or in a groove in the heater, whose depth decreases in the direction of the sensor tip of the thermocouple to a value that is lower than the diameter of the sensor tip, so that the clamping action is produced. This embodiment makes possible an especially compact and space-saving design. 
         [0020]    Provisions are made in yet another embodiment for the heater to have a recess, into which a wedge can be inserted, wherein in the state in which it is inserted into the recess, said wedge clamps the sensor tip of the thermocouple between heater and material tube. The special advantage of this embodiment is that even removal of the wedge is sufficient to make it possible to replace the thermocouple. The advantage of a compact design can be additionally embodied in a variant of this embodiment if the wedge has a guide for receiving a section, especially of the sensor tip, of the thermocouple. In addition, the wedge may be shaped in this variant such that it surrounds the sensor tip of the thermocouple on all surfaces that are not in contact with the material tube, so that there is no direct contact any more between the heater and sensor tip of the thermocouple. If the material from which the wedge is made is selected properly, thermal uncoupling from the heater can be achieved as a result, which contributes to coming close to the ideal situation, in which the temperature values determined depend exclusively on the temperature of the material to be injected. 
         [0021]    Provisions are made in another embodiment for the heater to comprise a spring element, which presses the thermocouple onto the material tube, so that the clamping action is produced. This approach has the advantage that the risk of pinching of the thermocouple, which would lead to damage thereto, is minimized because an effective limitation of the forces acting on the thermocouple can be achieved by selecting the stress of the spring element. 
         [0022]    Moreover, especially reliable measured values can be determined with the thermocouple if the sensor tip of the thermocouple is clamped indirectly between the heater and material tube via a heat-conductive piece of material, which is thermally uncoupled from the heater and has a groove or hole, in which the sensor tip of the thermocouple is mounted. 
         [0023]    In another advantageous variant of the present invention, the thermocouple has a positioning section, in which the cross section of the thermocouple is larger in at least one direction of the cross-sectional area than in sections of the thermocouple located adjacent to this section, and the heater has means for locking this section against being displaced in and/or opposite the direction in which the thermocouple extends. It is ensured in this embodiment that no displacement of the thermocouple takes place when the heater is pushed over the material tube, so that the correct positioning of the sensor tip at the desired site continues to be guaranteed. 
         [0024]    An especially simple possibility of embodying the positioning section is to attach a sleeve to the thermocouple, e.g., by pressing, soldering or welding. However, it is also possible to deform the thermocouple in a defined area, e.g., to press the thermocouple flat in the direction of the jacket tube, as a result of which the thermocouple would expand, i.e., widen in the direction at right angles thereto, which is located in the cross-sectional surface. 
         [0025]    The positioning sections are then advantageously fixed by a recess in the projection or in a projection on the surface of the heater, which faces the jacket tube. 
         [0026]    The present invention will be explained in more detail below on the basis of drawings. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    In the drawings: 
           [0028]      FIG. 1   a  is a three-dimensional view of the general design of an electric heating device according to the present invention; 
           [0029]      FIG. 1   b  is the heater pulled off from the electric heating device in  FIG. 1   a;    
           [0030]      FIG. 1   c  is a top view of the electric heating device from  FIG. 1   a  as viewed from the direction of the terminals of the thermocouple and heating element; 
           [0031]      FIG. 1   d  is a section along line A-A in  FIG. 1   c;    
           [0032]      FIG. 1   e  is an enlarged section along line B-B in  FIG. 1   d;    
           [0033]      FIG. 1   f  is an enlarged section along line B-B in  FIG. 1   d  in a second embodiment; 
           [0034]      FIG. 1   g  is an enlarged section along line B-B in  FIG. 1   d  in a third embodiment; 
           [0035]      FIG. 2   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of a first embodiment of a clamping mechanism; 
           [0036]      FIG. 2   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism from  FIG. 2   a;    
           [0037]      FIG. 3   a  is an enlarged section along line C-C in  FIG. 1   d  in case of the use of a second embodiment of a clamping mechanism; 
           [0038]      FIG. 3   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 3   a;    
           [0039]      FIG. 4   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of a third embodiment of a clamping mechanism; 
           [0040]      FIG. 4   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 4   a;    
           [0041]      FIG. 5   a  is an enlarged section along line C-C in  FIG. 1   d  in case of the use of a fourth embodiment of a clamping mechanism; 
           [0042]      FIG. 5   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 5   a;    
           [0043]      FIG. 6   a  is an enlarged section along line C-C in  FIG. 1   d  in case of use of a fifth embodiment of a clamping mechanism; 
           [0044]      FIG. 6   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 6   a;    
           [0045]      FIG. 7   a  is an enlarged section along line C-C in  FIG. 1   d  in case of the use of a sixth embodiment of a clamping mechanism; 
           [0046]      FIG. 7   b  is an enlarged sectional view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism from  FIG. 6   a;    
           [0047]      FIG. 8   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of a seventh embodiment of the clamping mechanism; 
           [0048]      FIG. 8   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 8   a;    
           [0049]      FIG. 9   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of an eighth embodiment of a clamping mechanism; 
           [0050]      FIG. 9   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 9   a;    
           [0051]      FIG. 10   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of a ninth embodiment of a clamping mechanism; 
           [0052]      FIG. 10   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 10   a;    
           [0053]      FIG. 11   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of a tenth embodiment of a clamping mechanism; 
           [0054]      FIG. 11   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 11   a;    
           [0055]      FIG. 12   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of an eleventh embodiment of a clamping mechanism; 
           [0056]      FIG. 12   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 12   a;    
           [0057]      FIG. 13   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of a twelfth embodiment of a clamping mechanism; 
           [0058]      FIG. 13   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 13   a;    
           [0059]      FIG. 14   a  is an enlarged section along line C-C from  FIG. 1   d  in case of the use of a thirteenth embodiment of a clamping mechanism; 
           [0060]      FIG. 14   b  is an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 14   a;    
           [0061]      FIG. 15   a  is an enlarged view of detail Y from the view in  FIG. 1   d  in a first variant of the use of as thermocouple with positioning section; and 
           [0062]      FIG. 15   b  is an enlarged view of detail Y from the view in  FIG. 1   d  in a second variant of the use of a thermocouple with positioning section. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0063]    Referring to the drawings in particular, identical reference numbers are used for identical components of the same exemplary embodiments in all figures. 
         [0064]      FIG. 1   a  shows a three-dimensional view of the general design of an electric heating device  100  according to the present invention with material tube  101 , heater  102  and thermocouple  103 . The material tube has an injection nozzle  104  at the end at which the flowable material is discharged during the operation. The heating element  105  of heater  102 , which can be supplied with supply voltage via the connector plug  106 , protrudes from the heater  102  on the side facing the machine, not shown, at which the electric heating device  100  is arranged. The thermocouple  103  is connected via a connector plug  107 . 
         [0065]      FIG. 1   b  shows the heater  102  pulled off from the electric heating device from  FIG. 1   a  with the heating element  105  and the connector plug  106 . The course of the heating element  105  in the interior of heater  102  is indicated in this form as an example with dash-dotted lines; it is meandering in this example, but it may also be coiled or have any other desired course. In particular, the view of heating element  105  is not shown in any of the enlarged details in  FIGS. 2   a  through  14   b  in order to make it possible to show clearer views of essential aspects. 
         [0066]    It shall be pointed out, in particular, in connection with  FIG. 1   b  that heater  102  has no hole, which would connect its outer and inner jacket surfaces to one another. Such holes are necessary in heaters  102  of electric heating devices known from the state of the art to bring the thermocouple  103  into contact with the material tube  101 . This is disadvantageous because, besides the increasing manufacturing technological effort, it entails the necessity to guide the heating element  105  such that it remains intact during the drilling of the hole. The inner jacket surface of heater  102  has, instead, a groove  108  here, in which the thermocouple is guided between the heater  102  and material tube  101 , as it will be illustrated below on the basis of  FIG. 1   d.    
         [0067]    Another essential point, which is linked with this, is that the heater  102  is a separate assembly unit not connected to the thermocouple  103 . Even though the thermocouple  103  may possibly remain in groove  108 , depending on the orientation of the heater  102  when the heater  102  is pulled off from the material tube  101 , thermocouple  103  and heater  102  fall apart as two separate assembly units at least after a suitable motion of heater  102 . 
         [0068]    A section line A-A is defined in  FIG. 1   c , which shows a top view of the electric heating device  100  from  FIG. 1   a , viewed from the direction of the terminals  106 ,  107  of the thermocouple  103  and heating element  102 .  FIG. 1   d  shows the section along this line A-A. It can be recognized especially clearly in this view of the heater  100  that a duct  109  for the flowable material, which is to be injected from the electric heating device  100 , passes through the material tube  101 . Furthermore, the embedding of the heating element  105  in heater  102 , which is omitted in  FIGS. 1   e  through  14   b  discussed below in the interest of a clear view, is shown here once again as well. 
         [0069]    Another essential feature, which can be recognized in  FIG. 1   d  especially clearly, is the arrangement of the thermocouple  103  between the material tube  101  and heater  102 , more specifically between the surface of the heater  102  facing the material tube  101  (which is defined in the area of a groove by the corresponding surface of the groove) and the surface facing the heater  102 . This is brought about concretely over the entire length of the heater  102  by mounting in a groove in the view according to  FIG. 1   d.    
         [0070]    Furthermore, two section lines B-B are shown in  FIG. 1   d  in the middle section of the electric heating device  100  and C-C as well as an area D marked by a circle drawn by broken line in the end section of the electric heating device  100 , in which especially the sensitive area of the thermocouple  103  is located, and an area Y marked by a circle drawn in broken line in the initial section of the electric heating device  100  in the area around the feed line of the thermocouple  103 . 
         [0071]      FIGS. 1   e  through  15   b  discussed below show enlarged views of various possibilities of designing the general structure of the electric heating device  100 , as it is described in  FIGS. 1   a  through  1   d . The individual embodiments can be freely combined with one another, unless they directly contradict each other, especially the embodiments in area B-B, on the one hand, and C-C and D, on the other hand. 
         [0072]      FIG. 1   e  shows a first possibility of arranging the thermocouple  103  of a heater  102  with a ring-shaped cross section  102 , which completely surrounds a material tube  101  with ring-shaped cross-section, through which a concentric duct  109  passes. Thermocouple  103 , whose diameter is designated by d, is arranged in a groove  108 , whose extension is greater than the diameter, so that thermocouple  103  and heater  102  fall apart when the heater  102  is pulled off from the material tube  101 . 
         [0073]      FIG. 1   f  shows an enlarged section along line B-B in  FIG. 1   d  in a second embodiment of the heater. The arrangement according to  FIG. 1   f  corresponds to the arrangement according to  FIG. 1   e  with the difference that a recess  123  passes through the heater  122  shown in  FIG. 1   f  over the extension thereof. This makes it possible to design the heater  102  as a clamping heater and thus to achieve fixing of the heater  122  on the material tube  101  in a simple manner. 
         [0074]      FIG. 1   g  shows an enlarged detail along line B-B in  FIG. 1   d  in a third embodiment of the heater. The heater used here is a heater  132  that is not in contact with the material tube  101  over its entire surface facing the material tube  101 , but is designed such that an intermediate space  130 , which is dimensioned such that the thermocouple  102  with the diameter d can be received therein, remains between heater  132  and material tube  101 . The processing step of preparing a groove  108  in the heater or material tube  101 , which is often associated with a great effort, is avoided in this embodiment, which reduces the manufacturing costs and manufacturing time. 
         [0075]      FIGS. 2   a  through  14   b  show different manners in which the general design of an electric heating device according to  FIGS. 1   a  through  1   d  can be varied in order to obtain a (detachable) fixing of the thermocouple  103  especially in the area of the sensor tip  103 ′ thereof. 
         [0076]      FIG. 2   a  shows an enlarged sectional view along line C-C in  FIG. 1   d  in case of the use of a first embodiment of a clamping mechanism and  FIG. 2   b  shows an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 2   a . As can be best recognized from  FIG. 2   b , the clamping action is obtained here by the depth of the groove  108  being reduced in the area  108 ′ of the groove, in which area the sensor tip  103 ′ of the thermocouple  103  is received, to a value H, which is equal to or smaller than the cross section of the sensor tip  103 ′ in the clamping direction. 
         [0077]      FIG. 3   a  shows an enlarged section along line C-C in  FIG. 1   d  in case of the use of a second embodiment of a clamping mechanism, and  FIG. 3   b  shows an enlarged view of detail D from the view in  FIG. 1   d  in case of the use of the clamping mechanism according to  FIG. 3   a . A recess  142 , which makes it possible for a spring element  141  attached on one side to the heater  102  to press the sensor tip  103 ′ onto the material tube  101 , is provided in the heater  102  in this embodiment in the area of the sensor tip  103 ′ of thermocouple  103 . 
         [0078]      FIG. 5   a  and  FIG. 5   b  differ from  FIG. 3   a  and  FIG. 3   b  only in respect to the concrete embodiment of the clamping, which is embodied here by a circular ring  147  with an indentation at the site of the sensor tip  103 ′ of thermocouple  103 . 
         [0079]      FIG. 4   a  and  FIG. 4   b  likewise differ from  FIG. 3   a  and  FIG. 3   b  only in respect to the concrete embodiment of the spring clamping. Recess  144  passes through here in the area of the sensor tip  103 ′ of thermocouple  103  of the heater  102  and the clamping action is obtained by the use of a clip-like spring element  143 , which is anchored in recesses  145 ,  146  of the heater. 
         [0080]      FIG. 6   a  and  FIG. 6   b  show an embodiment based on another principle of producing the clamping action, namely, the clamping of the sensor tip  103 ′ of the thermocouple  103  between a wedge  150 , which is inserted into a fittingly shaped recess in the heater  102 , and the material tube  101 . Wedge  150  can act as a closing element, after the removal of which the electric heating device  100  can fall apart into its individual components, material tube  101 , heater  102  and thermocouple  103  practically by itself, without application of a significant force. At the same time, it ensures the intimate thermal contact between the sensor tip  103 ′ and material tube  101 , so that reliable measurements are guaranteed. 
         [0081]      FIG. 7   a  and  FIG. 7   b  show a variant of the principle shown in  FIGS. 6   a  and  6   b , in which only a wedge  151  of a different shape is provided, whose geometric design permits simpler manufacture of the mount of the wedge  151  in heater  102 . 
         [0082]      FIGS. 8   a  and  b  show a variant of the embodiment according to  FIGS. 7   a  and  7   b , in which a wedge  152  with a groove  153  is used. The depth H of this groove  153  is equal to or smaller than the diameter d of the sensor tip  103 ′ of the thermocouple  103 , which said tip is inserted into groove  153 . Furthermore, groove  153  surrounds the sensor tip  103 ′ on all sides, which do not adjoin the material tube  101  and thus contributes to a thermal uncoupling from the heater  102 , which contributes to coming closer to the ideal measuring conditions. 
         [0083]      FIG. 9   a  shows an enlarged section along line C-C in  FIG. 1   d  in case of the use of an eighth embodiment of a clamping mechanism, and  FIG. 9   b  shows a corresponding enlarged view of detail D from the view in  FIG. 1   d . The clamping mechanism shown here is formed by the direct extrapolation of the clamping mechanism that is shown in  FIGS. 2   a  and  2   b  to an embodiment with a heater  122 , as it is shown in  FIG. 1   f.    
         [0084]      FIGS. 10   a  and  10   b  show a clamping mechanism that differs from that shown in  FIGS. 9   a  and  9   b  only in that the reduction of the depth of the end area  108 ′ of groove  108 , which area receives the sensor tip  103 ′ of the thermocouple  103 , takes place abruptly and that a recess  154 , which leads to an at least partial thermal uncoupling of the sensor tip  103 ′ from the heater  122 , is provided in heater  122 . 
         [0085]      FIGS. 11   a  and  11   b  show a variant of the embodiment according to  FIGS. 4   a  and  4   b , in which the clamping of the sensor tip  103 ′ of thermocouple  103  against the material tube  101  takes place indirectly. Sensor tip  103 ′ is guided in the groove of a block  160  made of a material possessing good heat conductivity, which said block is arranged flatly at the material tube  101  in a recess  164  passing through the heater  102  in the direction of the material tube  101 , and is clamped with the material tube  101  together with the block  160  by means of the spring element  163  mounted in recesses  161 ,  162  in the form of a clip, as a result of which an especially good thermal coupling of the sensor tip  103 ′ with the material tube  101  and thermal uncoupling from the heater  102  are achieved. 
         [0086]    The embodiment according to  FIGS. 12   a  and  12   b  differs from that in  FIGS. 11   a  and  11   b  in that block  165  is not designed as a separate assembly unit completely separate from the heater  102 , but thermal uncoupling is achieved due to slots  166 ,  167  and a groove  168 . Furthermore, the sensor tip  103 ′ of the thermocouple  103  is received in a hole. 
         [0087]    The embodiment according to  FIGS. 13   a  and  13   b  differs from that in  FIGS. 12   a  and  12   b  in that block  169  presses the sensor tip  103 ′ of the thermocouple  103  directly against the material tube  101 . 
         [0088]      FIG. 14   a  shows an enlarged section along line C-C in  FIG. 1   d  with the use of a thirteenth embodiment of a clamping mechanism, and  FIG. 14   b  shows the corresponding enlarged view of detail D from the view in  FIG. 1   d . The clamping mechanism shown here is intended especially for an embodiment with a heater  132  as it is shown in  FIG. 1   g . The clamping action is brought about here by a reduction of the cross section of the hole passing through the heater  132  in the area in which the sensor tip  103 ′ of the thermocouple  103  is located. Thus, it becomes unnecessary to provide any groove whatsoever. 
         [0089]      FIGS. 15   a  and  15   b  show as examples two different embodiments of the present invention, in which the position of the sensor tip of the thermocouple  103  arranged between the material tube  101  and heater  102  is better defined by providing a positioning section, so that it is ensured that when the heater  102  with thermocouple  103  is pushed over the material tube  101 , no displacement of the thermocouple  103  will take place. A sleeve  180 , which is pushed over the thermocouple  103  and is fixed there, e.g., by welding, soldering or pressing, is used as a positioning section in the embodiments shown. By providing the sleeve  180  at the thermocouple  103 , the cross section of the thermocouple is enlarged in the positioning section. 
         [0090]    A projection  181 , which meshes with the positioning section and which thus blocks a displacement of the thermocouple  103  in the direction in which the heater  102  is attached, is arranged in  FIG. 15   a  at the surface of the heater  102  facing the material tube  101 . 
         [0091]    In addition to the projection  181  shown in  FIG. 15   a , a projection  182  is also provided in  FIG. 15   b , which meshes with the positioning section, so that the displacement of the thermocouple in and opposite the direction in which the heater is attached is blocked. Instead of using projections  181 ,  182 , the same effect could, of course, also be achieved if recesses, which mesh with the positioning section, are provided in the heater  102 . 
         [0092]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. 
       APPENDIX 
     List of Reference Numbers 
       [0000]    
       
         A-A, B-B, C-C Section line 
         D, Y Detail view 
         H Depth 
         d Diameter 
           100  Electric heating device 
           101  Material tube 
           102 ,  122 ,  132  Heater 
           103  Thermocouple 
           103 ′ Sensor tip 
           104  Injection nozzle 
           105  Heating element 
           106 ,  107  Connector plug 
           108 ,  153 ,  168  Groove 
           108 ′ Area of groove 
           109  Duct 
           141 ,  143 ,  163  Spring element 
           142 ,  144 ,  145 ,  146 ,  154 ,  164  Recess 
           147  Ring 
           150 ,  151 ,  152  Wedge 
           160 ,  165 ,  169  Block 
           161 ,  162  Recess 
           166 ,  167  Slots 
           180  Sleeve 
           181 ,  182  Projection