Abstract:
An extrusion method and an extrusion device, whereby at least two different flows of material are supplied from the extrusion device to a nozzle. The nozzle comprises at least two nozzle chambers such that the material flowing through the first nozzle chamber forms an outer part of a product, and the material flowing through the second nozzle part forms an inner part of the product. The capacity of the nozzle chambers is changed, whereby the relative proportion of the different parts of the product can be varied. When the capacity of the nozzle chamber is decreased, the amount of material flowing therethrough increases at the outlet of the nozzle, and when the capacity of the nozzle chamber is increased, the amount of material flowing out there-through decreases at the outlet of the nozzle.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to an extrusion method which uses an extrusion device comprising a nozzle such that the extrusion device comprises means for supplying at least two different materials through the nozzle, and a product is produced by the nozzle, the product comprising at least two different materials whose relative proportion varies in an end product, the nozzle comprising at least two nozzle chambers such that the material flowing through a first nozzle chamber forms an outer part of the product and the material flowing through a second nozzle chamber forms an inner part of the product. 
   The invention further relates to an extrusion device comprising a nozzle and means for extruding at least two different materials through the nozzle, the nozzle comprising at least two nozzle chambers such that the material flowing through the first nozzle chamber forms an outer part of a product to be produced and the material flowing through the second nozzle chamber forms an inner part of the product. 
   EP 0 891 769 discloses a solution wherein two different extruders are used for supplying material to a two-layer nozzle. In the two-layer nozzle, the material flow in the inner layer is disrupted by a valve mechanism. So-called encapsulated extrusion products are thus produced wherein the inner material is arranged discontinuously inside the outer material. Disrupting the material flow by the valve mechanism, however, disturbs the operation of the extruder because the extruder is subjected to pressure pulsation. The operation of the extruder is thus disturbed, which means that the product will not be equal in quality. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to provide an improved extrusion method and extrusion device. 
   The extrusion method of the invention is characterized in that the capacities of the nozzle chambers are adjusted such that when the nozzle chamber decreases, the amount of material flowing therethrough increases at the outlet of the nozzle, and when the capacity of the nozzle chamber is increased, the amount of material flowing therethrough decreases at the outlet of the nozzle. 
   The extrusion device of the invention is characterized in that it comprises means for changing the capacities of the nozzle chambers such that when the capacity of the nozzle chamber is decreased, the amount of material flowing therethrough increases at the outlet of the nozzle, and when the capacity of the nozzle chamber is increased, the amount of material flowing therethrough decreases at the outlet of the nozzle. 
   The idea underlying the invention is that at least two different flows of material are supplied from the extrusion device to the nozzle. The nozzle comprises at least two nozzle chambers and at least one movable nozzle part such that the nozzle part can be used for changing the capacity of the nozzle chambers. The material supplied from a first nozzle chamber forms the outer part of the product and the material supplied from a second nozzle chamber forms the inner part of the product. By changing the capacity of the nozzle chambers, the relative proportion of different parts of the product can be varied in the end product. When the capacity of the first nozzle chamber is increased, the material flow discharged therefrom decreases, and if the capacity of the second nozzle chamber is simultaneously decreased, a larger amount of the inner material is then supplied, i.e. there is a larger amount of the inner material at that point in the end product than at some other point of the product. Correspondingly, when the capacities of the nozzle chambers are adjusted such that the capacity of the first nozzle chamber is decreased while the capacity of the second nozzle chamber is increased, the nozzle supplies a larger amount of the material from the first nozzle chamber and a smaller amount of the material from the second nozzle chamber. The underlying idea of a preferred embodiment is that the nozzle chambers are conical. The underlying idea of a second preferred embodiment is that the extruder which supplies the material to the nozzle chambers is conical such that it comprises at least two convergent, conical supplying slots within each other. The underlying idea of a third preferred embodiment is that the capacities of the nozzle chambers are controlled such that the inner part of the product is discontinuous, i.e. at some stage, the capacity of the second nozzle is increased so much that no material at all flows out therefrom. The underlying idea of a fourth preferred embodiment is that a part which forms the part between the nozzle chambers is integrated in the rotor of the extruder. 
   An advantage of the invention is that the proportions of the parts of the product to be produced can be adjusted in a versatile manner without causing pressure pulsation in the extruder which supplies the material to the nozzle. The total flow of the material to be extruded can be stabilized, i.e. if desired, the product can be arranged even throughout. When necessary, the thickness and shape of the product can be adjusted as desired. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in closer detail in connection with the accompanying drawings, in which 
       FIG. 1  is a schematic, cross-sectional side view of an extrusion device, 
       FIG. 2  is a schematic, cross-sectional side view of another extrusion device, 
       FIGS. 3   a  and  3   b  schematically show an embodiment of a solution according to the invention, and 
       FIG. 4  schematically shows a detail of a nozzle of a third extrusion device. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows an extrusion device  1 . The extrusion device  1  comprises an outer stator  2  and an inner stator  3 . A conical rotor  4  is arranged between the stators  2  and  3  such that an outer conical and circular supplying slot  5  is provided between the outer stator  2  and the rotor  4 , and an inner conical and circular supplying slot  6  is provided between the inner stator  3  and the rotor  4 . The rotor  4  comprises grooves  4 a such that when the rotor  4  rotates, a material flows along the supplying slots  5  and  6  towards the outlet of the extrusion device  1 . In addition to or in place of the rotor  4 , grooves can also be arranged in the stators  2  and/or  3 . For the sake of clarity,  FIG. 1  lacks supplying devices to supply the material to the supplying slots  5  and  6 . Further, for the sake of clarity,  FIG. 1  lacks rotating devices of the rotor  4 . The aforementioned devices are obvious to one skilled in the art; therefore, they will not be discussed in closer detail in this connection. 
   The extrusion device  1  further comprises a nozzle  7 . The nozzle  7  comprises an outer nozzle part  8 , an inner nozzle part  9  and a middle nozzle part  10 , i.e. an intermediate part. The middle nozzle part  10  is arranged to be integrated in the rotor  4 , in which case the middle nozzle part  10  rotates with the rotor  4 . The outer nozzle part  8  and the inner nozzle part  9  are nonrotating. Instead, the outer nozzle part  8  is moved in the axial direction by an operating device  11 , and the inner nozzle part  9  is similarly moved in the axial direction by an operating device  12 . The operating devices  11  and  12  may be, for example, hydraulic or electromechanical ones. An outer circular and conical nozzle chamber  13  is provided between the outer nozzle part  8  and the middle nozzle part  10 . An inner circular and conical nozzle chamber  14  is provided between the inner nozzle part  9  and the middle nozzle part  10 . 
   The to-and-from motion of the outer nozzle part  8  is illustrated by designation v 1 , which variable v 1  also describes the movement rate of the outer nozzle part  8 . Similarly, the to-and-from motion of the inner nozzle part  9  in the axial direction is illustrated by designation v 3 , which similarly describes the movement rate of the inner nozzle part  9 . The rightward direction as seen in  FIG. 1  is determined to be the positive direction of rates v 1  and v 3 . 
   When the outer nozzle part  8  is moved rightwards as seen in  FIG. 1  at a rate v 1 , the capacity of the outer nozzle chamber  13  increases. Hence, the material flow supplied along the outer supplying slot  5  out of the nozzle  7  decreases. If the inner nozzle part  9  is simultaneously also moved rightwards as seen in  FIG. 1  at a rate v 3 , the inner nozzle chamber  14  decreases, and a larger amount of the material supplied along the inner supplying slot  6  flows out of the nozzle  7 . If, on the other hand, the outer nozzle part  8  is moved leftwards as seen in  FIG. 1 , the outer nozzle chamber  13  decreases, and a larger amount of the material supplied along the outer supplying slot  5  flows from the nozzle  7 . If, again, the inner nozzle part is simultaneously moved leftwards as seen in  FIG. 1 , the capacity of the inner nozzle chamber  14  increases, and a smaller amount of the material supplied along the inner supplying slot  6  flows from the nozzle  7 . In the case shown by  FIG. 1 , the inner nozzle part  9  is moved leftwards at such a high rate that, at intervals, no material supplied along the inner supplying slot  6  flows from the nozzle  7  at all. A product  15  is thus achieved comprising an outer part  15   a  and, as discontinuous parts inside the outer part  15   a , an inner part  15   b . The product  15  may be, for example, a plastic product wherein the outer part  15   a  and the inner part  15   b  are made of different plastic materials. The product  15  may also be, for example, a product of food industry wherein the outer part  15   a  and the inner part  15   b  are made of different food materials. The product  15  can also be used as a blow moulding blank such that the softer part  15   b  is arranged inside the outer part  15   a , and, when blow moulding, air is blown inside the inner part  15   b , which results in the outer part  15   a  becoming a plastic bottle, for example. 
   The material flow flowing along the outer supplying slot  5  is indicated by designation Q 1 . Correspondingly, the material flow flowing along the inner supplying slot  6  is indicated by designation Q 2 . A material flow Q discharged from the nozzle  7 , i.e. the output of the extrusion device, is obtained from the formula
 
 Q=Q   2   +πR   2   v   3   +Q   1   −πR   2   v   1 ,
 
where R is the radius of the nozzle chambers  13  and  14 . The radius of the nozzle chambers  13  and  14  may also differ in size, the radius of the outer nozzle chamber  13  being used in connection with rate v 1  in the aforementioned formula, and the radius of the inner nozzle chamber  14  being used in connection with rate v 3 . In the case of  FIG. 1 , the output Q is always constant, i.e. Q A  equals Q B . Q A  describes the material flow at a point where the product  15  is provided with the inner part  15   b  and the outer part  15   a , and, correspondingly, Q B  describes the material flow at a point where the product  15  is only provided with the material which forms the outer part  15   a . The material flow Q A  is thus formed according to the following formula:
 
 Q   A   =Q   2   +πR   2   v   3   +Q   1   −πR   2   v   1 .
 
   If the outer nozzle part  8  and the inner nozzle part  9  are immovable in the axial direction, i.e. v 1  and v 3  equalled 0, then Q A =Q 2 +Q 1 . At point Q B  is
 
 Q   2   +πR   2   v   3 =0.
 
   The rate of the inner nozzle part  9  has thus been negative and so high that the increase of capacity of the inner nozzle chamber  14  has compensated for the material flow Q 2  supplied along the inner supplying slot. Hence,
 
 Q   B   =Q   1   −πR   2   v   1 
 
     FIG. 1  also illustrates the changes of rates v 1  and v 3  when the product is being produced. 
   Rates v 1  and v 3  are synchronized according to the output of the extrusion device  1  by using the operating devices  11  and  12 . The operating devices  11  and  12  can be controlled by microprocessors, for example, in which case rates can be adjusted quickly and accurately, and complex functions can also be utilized in the adjustment. 
     FIG. 2  shows an extrusion device  1  comprising no separate nozzle  7 , but stators  2  and  3  and a rotor  4  form the nozzle, and the outer supplying slot  5  corresponds to the outer nozzle chamber  13  and the inner supplying slot corresponds to the inner nozzle chamber  14 .  FIG. 2  also shows an outer supplying device  16  to supply the material into the outer supplying slot  5 , and inner supplying devices  17  to supply the material into the inner supplying slot  6  in a manner known per se. 
   The rotor  4  comprises grooves  4   a  such that when the rotor  4  rotates, the material flows out of the extrusion device along the supplying slots  5  and  6 . In addition to or in place of the rotor  4 , grooves may also be arranged in the stators  2  and/or  3 . The rotor  4  is arranged to be movable by operating devices  18  corresponding to the operating devices  11  and  12 . Arrow v 2  illustrates the to-and-from motion in the axial direction and the rate of movement of the rotor  4 . Compared with the case of  FIG. 1 , only one part movable in the axial direction is thus needed. In the case of  FIG. 2 , however, the capacity of the outer supplying slot  5  and the inner supplying slot  6  proportionally varies in a substantially similar manner. Consequently, in the embodiment of  FIG. 1 , it is possible to adjust the characteristics of the end product in a more versatile and variable manner. In the embodiment of  FIG. 2 , the rotor  4  is equipped with circular gear system which can be moved backwards and forwards in the axial direction. Said structure is known to one skilled in the art; therefore, it will not be disclosed in closer detail in this connection. The circle of the extruder  1  can be provided with several operating devices  18  at three different points, for example, such that by adjusting the operating devices in a different manner, the rotor  4  can be inclined. Then, by inclining the rotor  4 , the product can be centralized or the material flow can be directed eccentrically, if desired. By changing the inclination, for example, a product is achieved which varies spirally in its thickness at different points. In the supplying slots  5  and  6  located inside and outside the rotor  4 , seals  19  are arranged capable of varying their thickness so as to prevent the material from flowing out from the wider end of the rotor  4 . 
     FIGS. 3   a  and  3   b  show a situation wherein a point of discontinuity is formed in the inner part  15   b  of the product  15 . In order to ensure that the material flow forming the inner part  15   b  is disrupted, the inner nozzle part  9  is overcontrolled, i.e. rate v 3  is temporarily arranged higher than rate v 1 . The change in rate v 3  is illustrated by a curve in  FIG. 3   b . A suction effect towards the left as seen in  FIGS. 3   a  and  3   b  is then formed in the inner material flow at the end part of the middle nozzle part, which interrupts the inner material flow. 
     FIG. 4  shows a solution wherein the nozzle  7  comprises three intermediate parts  20   a ,  20   b  and  20   c  between the outer nozzle part  8  and the inner nozzle part  9 . Every other intermediate part, i.e. the intermediate part  20   a  and the intermediate part  20   c , is arranged to be moved backwards and forwards, which is illustrated by arrows v in the figure. A product can thus be achieved which comprises several layers whose relative proportions can be varied.  FIG. 4  further shows a solution wherein a continuous material or a material flow  21 , which can, for example, be a cable, particularly an optical cable, or another coating product, is supplied from the middle of the nozzle  7 . 
   The drawings and the related description are only intended to illustrate the idea of the invention. The extent of the invention may vary within the scope of the claims. Hence, the inner part  15   b  in the product  15  may be continuous and the outer part  15   a  discontinuous. Furthermore, if desired, the product  15  may have varying external dimensions, i.e. total thickness. The nozzle chambers of the nozzle may also have another shape than that of a cone. They can, for example, be sheet-like. The most preferably, however, the nozzle chambers are conical, thus enabling the easiest way to adjust the extrusion device; thus, an even discharge flow can also be more easily achieved. The rotor and the stator may also have another shape than that of a cone, but a conical rotor, stator and nozzle part provide the simplest and easiest solution to adjust. Furthermore, the extrusion device  1  can also be implemented such that a stator is provided between the outer supplying slot  5  and the inner supplying slot  6 , and a rotor outside the outer supplying slot  5  and another rotor inside the inner supplying slot  6 . Naturally, there can be several rotors and stators, in which case a nozzle according to  FIG. 4  is used. The shape of the outlet opening of the nozzle  7  may also vary. The outlet opening can thus be, for example, circular or angular, a profile shape or having a shape to produce a sheet-like product.