Abstract:
An extruder apparatus and method for producing an extruded tubing having varying inner dimensions without changing the outer dimensions. The tubing is forced from the die face of an extrusion head having an extruder die and an internal mandrel determining the outer and inner dimensions, respectively, of the extruded tubing. The outer dimensions of the mandrel varied by the user to change the inner dimensions of the extruded tubing. A pressure is maintained in the extruded tubing to prevent its collapse and that pressure is changed based upon the change of the external dimensions of the mandrel and the wall thickness of the tubing. In one embodiment, the mandrel is comprised of a core and a plurality of telescoping sleeves. Each sleeve is movable between a retracted position where the sleeve is displaced away from the die face and an extended position where sleeve is at the die face. There may be multiple mandrels in the case of multi-lumen catheters.

Description:
BACKGROUND 
   The present invention relates to an apparatus and method for the extrusion of tubing, and, more particularly, to an apparatus and method for extruding a tubing having an variable wall thickness by varying its inner dimensions. 
   There are, of course, many well known and established methods and apparatus used in the extrusion of tubing, particularly plastic tubing, many of which are utilized for extruding such tubing that is to be used for medical purposes, such as in the production of catheters and the like. 
   Typical of such extrusions include the production of multi-lumen catheters and special purpose catheters that are custom extruded for a particular medical purpose. One need, however, is for the production by the extrusion process of a catheter having a relatively constant outer dimension but where the inner dimension can be varied so that such inner dimension can be selectively designed and manufactured by the extruder to have a varying, but predetermined dimension. 
   In U.S. Pat. No. 5,511,965 of Batdorf et al, there is disclosed an apparatus for the production of an extruded tubing where the inner diameter is kept relatively constant but where the outer diameter can be varied. In that patent, extrudable material is forced around a mandrel having a constant diameter, thereby establishing a constant inner diameter, but the outer die aperture is varied as desired in order to vary the outer diameter between a minimum outer diameter and a maximum outer diameter as desired by the operator. 
   While useful for the intended purpose, the apparatus of Batdorf et al is not applicable to the production of extruded tubing where the outer dimension is held to be relatively constant while the inner dimension is selectively varied in a predetermined manner as the extruded tubing is formed. 
   Accordingly, it would be advantageous to have an apparatus that could produce an extruded tubing having relatively constant outer dimensions while having the ability to vary the inner dimensions as desired by the operator in order to produce a particular specialized tubing, especially manufactured for medical use, but which is certainly also applicable to non-medical uses. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention relates to an apparatus and method of extruding a tubing of a thermoplastic or thermosetting material. The present apparatus and method is applicable to a wide variety of tubing, including those having an outer peripheral surface in the configuration of a circle, square, rectangle, hexagon or any other of a wide variety of such configurations that can be extruded for a myriad of purposes. Thus by “tubing” as used herein, the term is intended to cover any of the foregoing external peripheral surfaces as well as other surfaces that can be extruded using the present invention. Tubing, can, as used herein, also describe not only the foregoing variety of external surfaces but also is applicable as well to single lumen tubing and multi-lumen tubing where the individual lumens of a multi-lumen catheter may, themselves, have differing configurations. 
   Accordingly, in accordance with the present invention, there is provided an apparatus and a method for extruding a tubing where the exterior dimension or dimensions of the tubing remain constant while the internal dimension or dimensions can be varied, thereby creating a tubing having a selectively varying wall thickness. 
   In carrying out the present invention, there is an extruder that has a specially constructed extrusion head that allows the user to vary the internal dimensions of the tubing as that tubing is extruded and formed. The internal dimensions of the tubing are basically established by a mandrel over which the material to be extruded flows and the distal end of the mandrel is located at or near the die face where the material emerges from the extrusion head during the formation of the tubing, that is, the die face is in plane generally at a right angle to the flow of the material, or to the longitudinal axis of the mandrel, and is at the very end of the extrusion head. As such, the material flowing outwardly through the die face assumes the dimensions of the mandrel for its internal dimensions and the die for its external dimensions. 
   Thus, with the present invention, the exterior dimensions of the mandrel can be varied by the user in accordance with the desired internal dimensions of the extruded tubing such that the user can predetermine those internal dimensions and still change such dimensions during the course of the extrusion process itself. Since, with the present invention, the outer dimensions or dimension are not variable, it can be seen that the wall thickness of the tubing can be varied by the user to produce a varying wall thickness of the tubing. 
   In the preferred embodiment, the mandrel comprises a core which basically establishes the maximum wall thickness, or smallest internal dimensions of the extruded tubing and there is at least one sleeve, and preferably a plurality of sleeves that are mounted coaxial and exterior of the core and those sleeves are telescoped together such that each sleeve can be moved from a retracted position where the sleeve is displaced away from the die face and therefore does not have an effect on the inner dimensions of the extruded tubing and an extended position where the sleeve is located at the die face of the extrusion head and therefore does control the inner dimensions of the extruded tubing. 
   When a plurality of sleeves are employed, the sleeves are progressively movable to the extended position starting with the smaller of the sleeves and working outwardly to the larger of the sleeves. Thus, by moving a sleeve from its retracted position to its extended position at the die face, the inner dimensions of the tubing can be varied and that is true with respect to the other sleeves. 
   The present invention can also readily be employed in the extrusion of multiple lumen tubing and catheters and, with such embodiment, the extruder can have an extrusion head having a plurality of mandrels interfitted therein and where one or more of such mandrels is constructed so as to be capable of varying the external dimension as will be hereinafter explained and described. As such, a multilumen catheter can be extruded where any one or more of the lumens can utilize the present invention so as to have the internal dimensions of any particular lumen or lumens vary as desired by the user by changing the external dimensions of one or more mandrels. 
   In the preferred embodiment, there is also a motive system that can automatically move the sleeves between the retracted and the extended positions so that the user can automatically or manually select and vary the position of one or more of the sleeves by some remote control system to vary the wall thickness as desired, and, more preferably, in accordance with a pre-programmed control scheme. 
   As a further feature of the present invention, there may be a gas pressure that is established and maintained at the die face so that the tubing extruded therefrom does not immediately collapse while the tubing is being cooled and has the time to set. The set gas pressure can, with the use of the present invention, be varied in accordance with particular dimension of the mandrel, that is, as the mandrel is enlarged to greater dimensions, the pressure established within the tubing is increased to maintain that tubing inflated and to prevent it from collapsing since the tubing wall is thinner and additional pressure is required to maintain the tubing in the desired condition and to prevent its collapse. 
   Thus, the control system for the pressure controls the pressure in accordance with the dimensions of the mandrel or, in the preferred embodiment, the position of each of the sleeves. It is noted that an alternative to the presence of a positive pressure provided to the interior of the tubing, there may be a vacuum tank that produces a negative pressure that is applicable to the exterior of the tubing and either method can be used to prevent the collapse of the tubing 
   These and other features and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of a typical extrusion process; 
       FIG. 2  is a cross-section view of a typical prior art extrusion head; 
       FIG. 3  is a cross-sectional view of an extrusion head constructed in accordance with the present invention and having a plurality of sleeves; 
       FIG. 4  is cross-sectional view of an extrusion head of  FIG. 3  with the sleeves in an alternative position; 
       FIG. 5  is a cross-sectional view of an extrusion head of  FIG. 3  having the sleeves in a still further alternative position; 
       FIG. 6  is a perspective view of the sleeves of the present invention; 
       FIG. 7  is a schematic view of the sleeves of  FIG. 6  in their operative, telescoping positions; and 
       FIG. 8  is a schematic view of the sleeves of FIG.  6  and showing motive systems adapted to move the sleeves. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , there is shown a schematic view of a typical extruder apparatus  10  that can be used in carrying out the present invention. As is conventional in the extrusion process, there is a hopper  12  that contains a reservoir of the material  14  to be extruded. The material from the hopper  12  descends downwardly via a gravity feed into the extruder barrel  16  where the material is progressed forwardly by a spiral screw  18  through a breaker plate  20 . A gear pump  22  may be used to force the material  12  through the extrusion head  26  where the extruded form, such as a tubing, emerges from the die face  28 , that is, the end of the extrusion head  26  and which is in a plane that is generally at a right angle to the flow of the extruded material. 
   Depending upon the particular material being extruded, the material may be heated to flowing temperatures if the material is a thermoplastic material or, alternatively, if a thermosetting material, the material can be cooled as extruded. 
   In any event, after the tubing has been extruded from the extrusion head  26 , there is a water bath  30  through which the extruded tubing is drawn by means of a puller  32  so that the extruded tubing is cooled to achieve a permanent set. Finally, the extruded tubing passes by a cutter  33  that cuts the length of tubing desired by the user. 
   As will be later explained, there is also present a pressure system to establish and maintain a pressure in the interior of the extruded tubing so that the tubing does not collapse during the progress of the tubing as it passes through the water bath  30  until the tubing is sufficiently rigid to maintain itself. There also may be a laser  34  or other measuring device to measure the outside dimensions of the tubing. 
   Turning now to  FIG. 2 , there is shown a cross-sectional view of a typical prior art extrusion head  36 . As can be seen, the extrusion head  36  includes a crosshead body  38  having a helicoid  40  which helps to direct the flow of the material. A mandrel  42  fits into the helicoid  40  and a die  44  and the mandrel  42  extend outwardly from the crosshead body  38  to terminate at a die face  46  which is a face that is formed in a plane that is generally at a right angle to the flow of an extrudable material from the die face  46 . The material to be extruded enters into the crosshead body  38  by means of a flow inlet  48  and passes in the space  50  between the mandrel  42  and the die  44 , such that the outer surface of the extruded material is established by the inner surface of the die  44  and the inner surface of the extruded material is established by the exterior surface of the mandrel  42 . 
   Accordingly, the relative location of the die  44  and the mandrel  42 , governs the inner and outer surfaces of the extruded material. If the material is being extruded into, for example, a hollow, cylindrical tube, the outer diameter of the tubing is established by the inner surface of the die  44  and the inner diameter of the tubing is determined by the outer diameter of the mandrel  42 . Obviously, by having the mandrel  42  or the die  44  of differing configurations, the outer peripheral configuration of the tubing can be square, rectangular, oval, hexagonal or other desired peripheral configuration. In addition, the wall thickness of the extruded tubing is determined by the space between the die  44  and mandrel  42  at the die face  46 . 
   Turning now to  FIGS. 3-5 , there are shown cross-sectional views of an extrusion head  52  constructed in accordance with the present invention. Taking first  FIG. 3 , it can be seen that the mandrel  54  is a specially designed mandrel and comprises a core  56  that can be mounted so as to be in a fixed position relative to the crosshead body  38 . Other of the components shown in  FIGS. 3-5  are the same as described with respect to FIG.  2  and have been given the same identification numbers as they carry out the same functions in the same manner. Therefore, the components and features include the crosshead body  38 , helicord  40 , die  44 , die face  46 , flow inlet  48  and a space  50 . As will be seen, the space  50  does have a changing function in accordance with the present invention as does the specially constructed mandrel  54 . 
   As such, in  FIG. 3 , the mandrel  54  comprises a core  56  that can be non-movably mounted within the crosshead body  38  and has a distal end  57  that extends to the die face  46  of the extrusion head  52  and therefore establishes the internal diameter of a tubing extruded from the die face  46 . Since the core  56  is fixed with respect to the crosshead body  54 , it will be seen that the core  56  establishes the smallest internal dimensions for the hollow tubing extruded therefrom, and, of course, if the tubing is circular, the smallest dimension will be the smallest inner diameter. 
   As will also be seen, however, in  FIG. 3 , there are a pair of sleeves, namely, an inner sleeve  58  and an outer sleeve  60  that telescope over the core  56  and can slide thereover. The inner sleeve  58  has a smaller outer dimension than the outer sleeve  60  in order to provide the telescoping relationship and, again, the sleeves  58 ,  60  may have any of a wide variety of outer configurations and shapes and sizes depending upon the particular tubing being extruded. In addition, as will now be appreciated, while only two sleeves  58 ,  60  are shown in  FIGS. 3-5 , there can be a lesser number or greater number of such sleeves in the spirit of the present invention. 
   In any event, the inner sleeve  58  slides along the outer surface of the core  56  and, correspondingly, the outer sleeve  60  slides along the outer surface of the inner sleeve  58  in a telescoping arrangement. As shown in  FIG. 3 , both of the sleeves  58 ,  60  have their distal ends  62 ,  64  respectively, displaced away from the die face  46  so that, in the positions shown in  FIG. 3 , the sleeves  58 ,  60  do not have any influence upon the inner dimensions of the extruded tubing. 
   In  FIG. 4 , however, it can be seen that the inner sleeve  58  has been moved from the retracted or displaced position of  FIG. 3  to an extended position where the distal end  62  of the inner sleeve  58  is located at the die face  46  and therefore does determine the inner dimensions of the extruded tubing. 
   As can be understood, by moving the inner sleeve  58  from its retracted position of  FIG. 3  to the extended position of  FIG. 4 , the inner dimension of the extruded tubing, that is, the inner diameter if a circular tubing is being produced, is increased. Accordingly, since the outer dimensions of the extruded tubing has not changed, the wall thickness of the extruded tubing has consequently been reduced. The reduction of the wall thickness can be abrupt such as when the inner sleeve  58  is moved rapidly from its retracted position to the extended position, or the change in the wall thickness can be gradual where the inner sleeve  58  is moved at a slower speed from the retracted to the extended positions. 
   Thus, the slope of the changes in the wall thickness can be controlled by the user in accordance with the desired end product tubing profile by controlling the speed of movement of the inner sleeve  58  between its retracted and extended positions and the reverse is equally true, when the inner sleeve  58  is moved back from its extended position to its retracted position of  FIG. 3  so that the wall thickness can again be increased at whatever slope is desired by the user in creating the end product. 
   Taking now  FIG. 5 , there is shown a cross-sectional view of the extrusion head  52  shown with the outer sleeve  60  in its extended position such that the distal end  64  of the outer sleeve  60  is in the die face  46  and therefore the inner dimensions of the extruded tubing are established by the outer dimensions of the outer sleeve  60 , the outer dimensions of the extruded tubing still being the same as the inner dimensions of the die  44 . Therefore, the wall thickness of the extruded tubing has again been thinned over the  FIG. 2  positions of the sleeves  58 ,  60  at the control of the user and, again, the control over the rate of the advancement or retraction of the outer sleeve  60  can be used to shape the inner profile of the extruded tubing. 
   In the movement of the inner and outer sleeves  58 ,  60 , it should be noted that the movement of the sleeves  58 ,  60  should be carried out in a sequential manner, that is, the inner sleeve  58  is advanced to the extended position first and then as it is desired to further narrow the wall thickness of the extruded tubing, the outer sleeve  60  can then be advanced and the same is true of the withdrawal of the sleeves  58 ,  60  back to their retracted positions, i,e, the outer sleeve  60  is retracted first and then the inner sleeve  58  is retracted so that the sleeves  58 ,  60  are moved in a sequential order determined by the outer dimensions of the particular sleeve with the smaller of the sleeves being first moved from the retracted to the extended position and the larger sleeve being moved first from the extended position to the retracted position. 
   The sequence of motion is carried out even if there are more than two sleeves and would be applicable to any number of multiple sleeves used with the present invention. 
   Turning now to  FIGS. 6A ,  6 B and  6 C, there are shown, schematic views illustrating the use of multiple or a plurality of sleeves in accordance with the present invention. In  FIG. 6A  the core  56  is shown and is the innermost component of the mandrel  54  of  FIGS. 3-5 . As also can be seen there is a opening  66  that passes through the core  56  and which will be later explained for its use to produce a pressure within an extruded tubing to prevent the tubing from collapsing. In  FIG. 6B , the inner sleeve  58  is shown positioned in telescoping arrangement over the core  56  and the distal end  62  of the inner sleeve  58  is located at the die face  46  where the outer dimensions of the inner sleeve  58  determine the inner dimensions of the extruded tubing (FIG.  5 ). 
   Next, in  FIG. 6C , there is shown the core  56 , the inner sleeve  58  and the outer sleeve  60  of the extrusion head  52 , all telescoped together with the inner and outer sleeves  58 ,  60  in the extended positions with the distal ends  62  and  64 , respectively, located at the die face  46  ( FIG. 5 ) so that the inner dimensions of the extruded tubing is determined by the outer dimensions of the outer sleeve  60 . 
   Turning next to  FIG. 7 , there is shown a schematic view of a set up for the present invention and basically illustrates the components of the mandrel  54 . The core  56  is held in a fixed position within the extrusion head and that mounting is schematically shown by the clamp  68 . There is also a gas fitting  70  at the proximal end  72  of the core  56  and, as explained, the gas fitting  70  is adapted to be affixed to a regulated and controlled source of gas to establish and maintain a controlled gas pressure at the distal end  74  of the core  56 . Thus, there is also a gas pressure controller  76  that is used to control the pressure of the gas at the distal end  74  of the core  56 . That gas pressure controller  76  can operate off various inputs, one of which being the location of the inner and outer cylinders  58 ,  60  as will be explained. 
   Turning finally to  FIG. 8 , there is shown a schematic view of the inner and outer sleeves  58 ,  60  and also showing the motive means or mechanism that can be used to move each of the sleeves  58 ,  60  between their extended and retracted positions. Thus, taking the outer sleeve  60  first, there can be a clamp  78  that affixes the outer sleeve  60  to a bracket  80  and that bracket  80  moved by a first motive means  82 . As such, the first motive means  82  can be a linear motor  84  that is connected to the bracket  80  and moved by a lead screw  86 . The first motive means  82  can be any means of providing motion to the bracket  80  and, of course, the outer sleeve  60 , and can include a pneumatic system, a hydraulic system or some other type of motive means or system that is effective to slide the outer sleeve  60  between the retracted and extended positions. 
   In a similar manner, there is a second motive means  88  that moves the inner sleeve  58  in the same manner as the first motive means  82  and, again, may comprise a linear motor  90  that acts through a lead screw  92  to move the inner sleeve  58  by moving bracket  94  affixed to the inner sleeve  58  by a clamp  96 . Therefore, as can be seen, the first motive means  82  and the second motive means  88  serve to move, individually, the inner and outer sleeves  58 ,  60  and each can be operated independently of the other and can move at different speeds depending upon the desired internal profile of an extruded tubing. 
   As noted, there is also a control system to establish and maintain a predetermined pressure within the tubing being extruded and that pressure is controlled by the gas pressure controller  78 . The purpose of the gas pressure is to prevent the newly extruded tubing from collapsing while it is being cooled and eventually set and thereby strengthened. In the preferred embodiment, the gas pressure is established and then changed in accordance with the wall thickness of the extruded tubing, thus, as the mandrel dimensions get larger, the wall thickness becomes smaller and additional pressure is needed to maintain the wall tubing and prevent its collapse. The reverse is, of course, also true for the wall thickness as it gets larger, that is, less gas pressure is required within the larger wall thickness extruded tubing. 
   Therefore, there may be a feedback system that changes the set gas pressure established by the gas pressure controller  78  based upon the outer dimensions of the mandrel  54  (FIGS.  3 - 5 ). Accordingly, one such means of providing the necessary feedback can be by means of position sensors  98 ,  100  that sense the position of the inner and outer sleeves  58 ,  60  respectively so that the gas pressure controller  76  can receive the information via communication lines  104  and adjust the gas pressure accordingly. 
   As an example, when the inner sleeve  58  is moved to its extended position, the position sensor  98  can sense that the inner sleeve  58  has reached its extended position and therefore recognizes that the wall thickness of the extruded tubing has been narrowed. That information is provided to the gas pressure controller via the communication line  104  so that the pressure is then raised. 
   Obviously, the pressure can be lowered if the wall thickness is again thickened or increased by the reverse process. In the event some mechanism other than sleeves is used to change the dimensions of the mandrel  54  (FIGS.  3 - 5 ), other means can be used to change the gas pressure within the extruded tubing based upon the outer dimensions of the mandrel and/or the wall thickness of the extruded tubing. 
   Those skilled in the art will readily recognize numerous adaptations and modifications which can be made to the extruder and method of extruding tubing of the present invention which will result in an improvement, yet all of which will fall within the scope and spirit of the present as defined in the following claims. Accordingly, the invention is to be limited only by the following claims and their equivalents.