Abstract:
The geometry of a flow channel ( 1 ) can be varied within wide limits if at least one wall of the flow channel ( 1 ) takes the form of a sheet stack ( 2 ) which is pushed from the rear into the channel to a greater or lesser extent by means of adjusters ( 7 ). The adjustment may be effected either uniformly over the entire width of the flow channel ( 1 ) or only locally at certain points thereof. It is thus possible, while a medium is passing through the flow channel ( 1 ), to alter form outside the flow resistance either of the entire channel or only at certain points and thus alter the entire mass flow or the mass flow distribution as desired. New processing possibilities are given by the greater flexibility of the sheet stack ( 2 ) in relation to solid channel walls.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a division of co-pending parent application Ser. No. 09/043,605, filed Mar. 24, 1998 as international application PCT/EP96/04183, on Sep. 25, 1996, and nationalized in the U.S. on Mar. 24, 1998, which issued as U.S. Pat. No. 6,099,290 on Aug. 8, 2000. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to an apparatus in the form of a tool comprising a flow channel. 
     REVIEW OF THE RELATED ART 
     No method has been known so far in which to change the width of the melt strand during extraction by modification of the geometry of the flow channel in the tool. 
     Various types of apparatuses as described above have been known. They are used especially in the field of plastics processing in flow channels for thermoplastic melts for the possibility of modification of flow channel resistance. EP 0 367 022, DE 35 30 383 A1, DE 44 00 069 C1 and DE-AS 12 1 412 teach extrusion dies in which to change the flow channel height. These known solutions comprise a more or less thick, solid, one-piece metal wall which can be deformed by adjusters pressing on the wall from the rear. They work only as long as the solid wall, during deformation, does not exceed the range of linear elasticity because they depend on the fact that upon return motion of the adjusters, the wall will take precisely its original initial position. Because of the comparatively thick wall required in these apparatuses for reasons of solidity, the possibilities of uniform adjustment of the wall over the entire width of the flow channel (overall adjustment) are restricted as well as the locally defined adjustment of a small portion of the wall (relative adjustment). 
     DE-OS 23 05 877 describes a limitation of a flow channel which consists of several thin individual sheets lying one upon the other over their full surfaces and consequently possesses higher flexibility. But this flexibility is purchased by this solution abandoning the important criterion of absolute leak-tightness towards the fluid flowing in the flow channel, because mobility of all the individual sheets in the marginal areas is required for adjustment. To this end, the marginal areas of the sheets reach into grooves which are located between the two halves of the flow channel body. The surface pressure necessary for leak-tightness in these marginal areas cannot be applied, because it would not allow any motion of the sheets relative to the flow channel halves. 
     Consequently, solutions offering a wide adjusting range accompanied with absolute leak-tightness of the flow channel have not been disclosed in the known apparatuses of the generic type. The known apparatuses neither offer the possibility to put a method into practice in which a melt strand is forced through an absolutely leak-tight tool channel, two independent adjusting systems, which are integrated in the tool and act on a wall of the flow channel, serving to modify the thickness of the melt strand during melt discharge either in its entirety or only locally at certain places or to change both simultaneously, nor to change the width of the melt strand during extraction by changing the geometry of the flow channel in the tool. 
     SUMMARY OF THE INVENTION 
     The invention relates to a flow channel with a width or circumference-to-height ratio greater than 10, and a mechanism for the absolutely leak-tight limitation of a flat flow channel. The mechanism insures that, by means of externally accessible adjusters, at least one flow channel wall can be adjusted in its overall position to the largest extent possible, i.e., uniformly over the entire width, as well as locally, i.e., in strictly defined portions over the width, in relation to the opposite demarcation of the flow channel. 
     The invention further relates to a method, using another embodiment of the invention, for continuously discharging a melt strand by means of a tool having at least one adjustable wall, in which, during the discharge of the melt, the height of the entire flow channel is adjusted by a first adjusting system and portions of the flow channel are adjusted by a second adjusting system independent of the first adjusting system and using a second control system. With this method, during the discharge the thickness of the melt strand changes entirely, or only locally at certain places, or both changes take place simultaneously. 
     It is the object of the invention to embody an apparatus of the generic type in such a way that increased ranges of overall and relative adjustment are possible, accompanied with simultaneous absolute leak-tightness of the apparatus, and based on this to develop methods by which, during extraction, a melt strand can be modified in thickness entirely or locally as well as in width. 
     According to the invention, this object is attained in that adjusters act from behind on a flexible flow channel wall which is produced by individual sheets being placed one upon the other over their full surfaces, the individual sheet that the fluid flows along being a flow channel sheet which cooperates with the flow channel to form a wall and is firmly welded into the flow channel body all around. 
     The method of discharging a melt strand is put into practice in that during the production of the melt strand by means of a tool, the height of the outlet gap of the tool is modified over the entire width or only locally during the melt extraction by means of two independent adjusters which act on at least one of the two outlet lips so that during the time of extraction, the melt strand can be modified in thickness entirely or locally as well as in width. 
     The term sheet stack means a stack of sheets, the undersides of each of which resting tightly on the top sides of the sheet underneath. In one embodiment, a sheet, one surface of which forms a flow channel wall, can also be integrated in a frame which is integrated in the flow channel by screwing, welding or in a similarly leak-tight way. In another embodiment, the desired flexibility of the sheet stack is obtained by the individual sheets having a thickness of less than 2 mm, preferably less than 1 mm. In one embodiment, it can be functional for the apparatus that at least one of the edges of the individual sheets is welded together with a frame or the body into which the flow channel is integrated. As regards the flexibility of the sheet stack, the present invention provides by special advantage that the stack to has a curvature instead of being plane. The invention also provides another extension of the adjusting range is attained by the adjusters being bonded to the sheet stack non-positively so that the latter can be deformed by traction and pressure. 
     The invention provides a special provides a special advantage by using two independent adjusters acting on a flexible wall of the apparatus, it being possible, by the aid of the first adjusters, to effect uniform adjustment of the wall over the entire width and additionally, by the aid of the second adjusters, to deform the wall locally over the width. Maximum adjustment is attained if, two independent adjusters act on two walls of the flow channel, it being possible to effect a uniform adjustment of the respective wall over the entire width by means of the first adjusters and additionally to deform the respective wall locally defined over the width by means of the second adjusters. The non-positive integration once again enlarges the adjusting range, because thus the wall cannot only be pressed into the flow channel, but can also be retracted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     Further details of the invention will become apparent from the ensuing description of some exemplary embodiments, taken in conjunction with the drawing, in which: 
     FIG. 1 is a partially sectional illustration of an apparatus according to the invention inside a flow channel, 
     FIG. 2 is a view of the section A—A of FIG. 1, 
     FIG. 3 is an illustration of another constructional solution of the apparatus according to the invention, in which the sheet stack in welded in a separate frame, 
     FIG. 4 is an illustration of another constructional solution of the apparatus according to the invention with the adjusting screws being integrated for traction and pressure, 
     FIG. 5 is a sectional view through an overture of the apparatus according to the invention which is located at the end of a flow channel, 
     FIG. 6 is a sectional view of another example of an adjuster ensuring adjustment of the wall by traction and pressure, 
     FIG. 7 is a detail of a tool, in which both tool walls are provided with an adjuster, these adjusters each having independent adjusting screws for overall adjustment or relative adjustment, 
     FIG. 8 is an illustration, roughly outlined, of a method for the controlled extraction of a melt strand of variable geometry. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As seen in FIG. 1, the apparatus for the variable limitation of a flat flow channel is located within a tool that consists of an upper  28  and a lower tool half  29 . The flow channel  1  possesses at least one wall constituted by a stack  2  of thin individual sheets  3 ,  4  and  5 . The stack  2  is again composed of a flow channel sheet  3 , which has a wall together with the flow channel and which, for reasons of leak-tightness toward the fluid flowing in the flow channel, is firmly welded all around into the tool half  28 , as well as of at least one supporting sheet  4 . On principle, other methods of joining the flow channel sheet  3  to the tool half  28  that constitutes the flow channel  1  can be used as well, as long as these methods ensure absolute leak-tightness toward the fluid flowing in the flow channel  1 . Depending on the application, any number of further supporting sheets  4  and  5  can be utilized. The supporting sheets  4  and  5  are welded together with, or joined to, the tool half  28  only on one side, however, they can also simply be placed on the flow channel sheet. Non-positive or positive engagement should however ensure that at least at a point or on a line, motions of the individual sheets  3 - 5  relative to each other do not occur for the general position of the individual sheets relative to each other to be secured. For the balancing in length, required during deformation, of the individual sheets  3 - 5  relative to each other to be possible, the surfaces of the individual sheets  3 - 5  should allow displacement relative to each other at least in portions. The individual sheets  3 - 5  may consist of metallic materials, in this case in particular of elastic spring steels, however, they may also consist of other materials for instance of plastics. Also, they need not consist all of the same material. 
     The sheet thickness d of the individual sheets  3 - 5  depends on the respective application and the selected material. In the case of metals, for a high degree of possible deformation, it should regularly be less than or equal to 2 mm, preferably less than or equal to 1 mm. The thickness d of the individual sheets  3 - 5  need not necessarily be the same, as the case may be, the use of sheets of gradually varying thicknesses d can be advantageous. The sheet stack  2  can be plane, but by advantage it is curved as seen in FIG. 1, the curvature reducing the formation of tensile stresses specifically in the flow channel sheet  3  that is fixed by welding. Adjusters  7  act on the sheet stack  2  from behind, by means of which the position of the sheet stack can be altered. It is advisable that the length  1  from the beginning of the sheet stack  2  as far as to the point of application of force of the adjusters  7  be as long as possible so as to obtain a wide adjusting ranges. It should be at least 20 mm, preferably it should be greater than 30 mm. 
     There is a variety of adjusters that can be employed. In the simplest of cases, they can be screws as seen in picture  1 , but use can also be made of expansion bolts, motors, piezo translators or the like. On principle, the adjusting ranges can also be generated by a fluid. One adjuster is sufficient for the apparatus to be able to work, however, it is advantageous to use several adjusters positioned at a defined distance from each other over the width b of the channel as seen in FIG.  2 . This figure shows the cross-section of the flow channel  1  corresponding to the section A—A of FIG.  1 . Noticeably, several adjusting screws  7  integrated in the upper half of the tool  28  by way of a thread act from above on the sheet stack  2 . FIG. 2 also illustrates that the supporting sheets  4  and  5  of the sheet stack  2  are not connected with the tool half  28  laterally. The term flat flow channel means a flow channel of a width b to height h ratio of at least 10. The flow channel may also be round. In this case, the mean flow channel circumference is employed instead of the flow channel width to determine the ratio. 
     FIG. 3 shows another type of integration of the sheet stack  2  in the tool half  28 . In this case, the sheet stack  2 , on which the adjusting screws  7  act from above for adjustment of the geometry of the flow channel  1 , is  5  welded in a separate frame  8  which is then screwed into the tool half  28 . This solution has the advantage that the sheet stack  2  can easily be replaced. 
     FIG. 4 illustrates the apparatus of FIG. 1 with a still enlarged adjusting area. In this case, the sheet stack  2  is positively connected with the threaded sleeves  9  by means of a partially slit pipe  10  which is welded on. Positive engagement is produced by a round rod  26  being inserted in the pipe  10 , the lower portion  27  of which and the sheet stack are welded together and which is partially slit as far as to the depth of the sheet stack; the round rod  26  is passed through the eyelets  25  which are located at the end of the threaded sleeves  9  and reach into these slits. The height h of the flow channel  1  can be increased as well as reduced by the adjusting screws  7 , which support themselves by a thread in the upper tool half  28  and reach into the threaded sleeves  9  by their lower portion. Outside of the welded portion  27 , the surfaces of the individual sheets  3 - 5  can move relative to each other, as a result of which the high flexibility within the sheet stack  2  is maintained. In the case of this solution, the supporting sheets  3 ,  4 ,  5  and the tool half are not welded together. An advantage of the positive integration resides in that the flow channel height h cannot only be reduced, but also increased. Furthermore, one does not depend on the elastic restoring of the sheet stack so that the possible adjusting ranges can still be greater. In the case of sheet stacks of surfaces of great dimensions, this construction serves to achieve adjusting ranges of more than 20 mm. 
     For clear identification, items of identical function have the same reference numeral added by a different letter for each drawing as from FIG.  5 . FIG. 5 shows a section through an overture of an adjusting mechanism according to the invention which is located at the end of a flow channel. The end of the sheet stack  2   a  simultaneously forms the end of the flow channel  1   a . The adjusting screws  7   a , which lodge in a thread in the upper tool half  28   a , again act from above on the sheet stack  2   a  with the individual sheets  3   a ,  4   a  and  5   a . The height h of the flow channel  1   a  can be reduced by manual rotation or by rotation by means of a servomotor  11   a.    
     FIG. 6 is a sectional view of another mechanism for adjusting the position of the sheet stack  2   b . By reason of the positive engagement of the adjusting screws  7   b  with the profiled strip  31   b , which is fixed to the flow channel sheet  3   b  by welding, the position of the sheet stack  2   b  can be altered by means of traction or pressure. To this end, balls  30 b are welded on the extremities of the adjusting screws  7   b , lodging in a hole of a profiled strip  31   b  which is fixed to the sheet stack  2   b  by welding. The adjusting screws  7   b  are connected by way of a thread in a cylinder piece  32   b . The cylinder piece  32   b  again lodges in a hole of the upper tool member  28   b . By rotation of the adjusting screws manually or by means of a servomotor  11   b , the sheet stack  2   b  can be pulled upwards or pressed down. The covering sheet  4   b  is not welded together with the profiled strip  31   b . It rests in a groove between the profiled strip  31   b  and the flow channel sheet  3   b . At the end of this groove, a gap  12  remains between the covering sheet  4   b  and the profiled strip  31   b  for the flexibility of the sheet stack  2   b  to be maintained. 
     FIG. 7 is a sectional view of an example of a tool having two opposed adjustable walls. In this solution, two independent adjusters  13   c ,  13   d  and  14   c ,  14   d  act on the sheet stacks  2   c ,  2   d , the adjusters  13   c ,  13   d  only consisting of two adjusting screws which are positioned on both edges of the tool. By the aid of these screws, the adjusting beams  15   c ,  15   d  can be displaced in their entirety, i.e. the sheet stacks  2   c ,  2   d  too are bent over their full widths. A plurality of adjusters  14   c ,  14   d  is disposed between the adjusting beams  15   c ,  15   d  and the sheet stacks  2   c ,  2   d  over the width of the apparatus, by means of which the sheet stacks  2   c ,  2   d  can be displaced additionally at defined places and locally limited. Seen from the neutral position of the sheet stack  2   c , the solution c only permits a reduction of the flow channel height h by the adjusting range sc. Again it works only as long as complete elastic restoring of the sheet stack  2   c  is ensured. However, it offers a maximum of adjusting and operating convenience, since the overall and the relative adjustment are decoupled, it being possible to adjust the flow channel height h as a whole while relative adjustment is maintained, which is frequently required in practice. On principle, this solution can also be put into practice where a solid flow channel wall is available instead of a sheet stack. The sheet stack only provides for a still enlarged adjusting range. Again, the construction can be integrated only into one flow channel wall or also into two flow channel walls. The same is valid for the embodiment d, in which the adjusters  13   d  and  14   d  are positively joined to the adjusting beam  15   d  and the sheet stack  2   d , respectively. This solution offers a maximum of possible adjustment when it is integrated in two flow channel walls, since, as explained in connection with FIG. 6, it also offers the possibility to enlarge the flow channel height h by means of the adjusting screws  13   d  and  14   d . The adjusting range sd to be achieved amounts to more than twice the adjusting range sc, since in this construction, the sheet stack  2   d  can also be deformed plastically to some minor degree. Adjusting ranges greater than 10 mm are achievable. 
     FIG. 8 sketches a method of extracting a melt strand of variable geometry. New processing possibilities are offered by the considerably increased adjusting range achievable by the apparatuses specified and the integration of two independent and positively engaged adjusters  13   e  and  14   e , which act on at least one flexible wall  2   e  of a flow channel  1   e . By way of example, the sketch illustrates a method according to the invention for the discharge of a melt strand  16 , it being possible to change the thickness y and the width z of the melt strand  16  during extraction. In this case, an extruder  17  serves to convey the melt by pressure through a tool  18 . The flow channel  1   e  is located in the tool  18  and has the flexible wall  2   e , the position of which can be varied by independent adjusters  13   e  and  14   e . Of course, the flow channel  1   e  may also have a different geometric shape. It can for instance be round. By means of the adjusters  13   e , which act on the adjusting beam  15   e , the height h of the outlet gap can be uniformly increased or reduced over the entire width during the discharge of the melt. The adjusting range should be greater than 8 mm, preferably greater than 12 mm. By means of the adjusters  14   e , which are integrated in the adjusting beam  15   e , the wall  2   e  can be adjusted additionally locally at certain places over the width around the position adjusted by means of the adjusters  13   e . In this case, an adjusting range greater than 2 mm, preferably greater than 4 mm, should be available. 
     On principle, both adjustments can be made manually. As a rule, it is however sensible to make this adjustment by way of a control unit  19  and  20 , respectively. To this end, every adjuster is connected with a triggerable actuator  21  and  22 , respectively. For the controlled operation, the thickness y and the width z of the melt strand  16  must be detected continuously. During the extraction of the melt, the thickness y is detected by a thickness measuring unit  23  and the width z by a width measuring unit  24  and passed to the control unit, which then performs a variance comparison, determines the new correcting variables and passes them to the actuators  21  and  22 , respectively. In cases where extremely wide adjusting ranges are required, it is advantageous to design both walls  2   e  of the flow channel  1   e  to be flexible and to provide them with adjusters  13  as well as control units  19  and  20 , respectively. This is of special advantage when during melt extraction also the width z of the melt strand  16  is to be altered simultaneously. The method can for instance be used to fill compression molds of complex geometry with melt, the compression mold and the discharger moving relative to each other. In the field of extrusion blow molding, the method can be used so as to effect, during the tube discharging job, time dependent profiling of the preform in the circumferential direction in addition to the known time dependent profiling of the preform in the direction of extrusion. Thus, the thickness ratio originating in the blow mold can be influenced positively to a considerably improved degree.