Patent Publication Number: US-2006017192-A1

Title: Process for the continuous production of a component comprising a bent tubular body

Description:
BACKGROUND OF THE INVENTION  
      The invention proposes a process for the continuous production of a component comprising a bent tubular body and end-fittings at each of its ends.  
      More particularly, the invention proposes a process for producing a component comprising a tubular body made of a thermoplastic, consisting of at least two generally straight sections joined together by an elbow section, of the type comprising: 
          a step of producing a tubular extrudate by extrusion or by injection;     a step of forming the said elbow section by the hot bending of an intermediate section of the extrudate between two straight sections.        

      In current manufacturing processes, such a component, or pipe, is produced by bending a straight tube that has been produced beforehand by extrusion, cut to the necessary length and then temporarily stored.  
      Next, the straight tube is removed from the storage area and then bent so as to have the required shape.  
      Finally, the end-fittings are fitted onto the ends of the bent tube.  
      By temporarily storing the straight tube it is possible for the line for bending the straight tube to be placed independently of the line for extruding the straight tube, and therefore the two lines may be located at two different locations.  
      However, this requires the provision of facilities for temporarily storing the straight tubes, and also means for transferring the tubes from the extrusion line to the place for temporary storage, as well as means for transferring the tubes from the temporary storage place to the bending line.  
      In addition, in order to bend the tubes, which are made of a thermoplastic material, it is necessary to raise the temperature of the zone of the tube which is to be bent, or of the entire tube, up to a temperature called the “bending temperature”, which lies between the melting point of the material and the glass transition temperature of the material.  
      When the material is heated up to this bending temperature, the material is “softened”, which simplifies the bending operation.  
      After the straight tubes have been produced by extrusion, they are cooled down to a temperature below the glass transition temperature, in order to allow them to be temporarily stored and handled. In addition, the straight tubes cool down naturally by contact with the ambient air.  
      Consequently, before the bending operation, it is necessary to reheat the straight tube to the bending temperature.  
      Depending on the material used, the operation of reheating the straight tube up to the bending temperature also modifies the crystalline structure of the material by what is called an “annealing” effect, which modifies the mechanical properties of the material and also reduces the length of the tube.  
      Furthermore, this operation of reheating the straight tube consumes a large amount of energy, due to the amount of heat to be supplied to the tube.  
      After the cylindrical tube has been bent, coupling end-fittings are fitted onto each end of the bent body.  
      Thus, the production of a single component requires a large number of handling operations due to the fact that the straight tube is temporarily stored after it has been produced by extrusion.  
      These additional handling operations increase the time needed to produce the component and therefore the cost of this component.  
     SUMMARY OF THE INVENTION  
      The object of the invention is to propose a process for the production of such a component, which comprises a tubular body made of a thermoplastic, consisting of at least two generally straight sections joined together by an elbow section, and including at least one end-fitting that is fitted at a first free end of the tubular body, which comprises a reduced number of steps, allowing the manufacturing time for a component to be reduced.  
      For this purpose, the invention proposes a process of the type described above, characterized in that the end-fitting is fitted onto the downstream free end of the extrudate before the bending step.  
      According to other features of the process according to the invention: 
          before the bending step, the process includes a step consisting in lowering the temperature of the extrudate down to a bending temperature;     the process includes a step of sectioning the tubular body, this being carried out after the bending step;     an end-fitting is fitted onto the upstream free end of the body after the sectioning step;     the process includes a step consisting in introducing a flexible core coaxially with the extrudate into the extrudate during its production and before the said step of bending the extrudate;     the process includes a step of extracting the flexible core from the extrudate immediately before the sectioning step;     the process includes a step of forcibly cooling the tubular body after its production by bending and before the sectioning step;     the cooling step consists in making a heat-transfer fluid circulate within the flexible core; and     the bending step consists in carrying out, in succession, several bending operations on the hot extrudate in different orientations.        

      For this purpose, the invention proposes an installation for producing components comprising a tubular body, by applying the production process according to the invention, of the type which includes a device for producing the tubular extrudate by extrusion or by injection, and a bending head for bending the tubular extrudate, characterized in that the bending head is placed immediately downstream of the production device.  
      According to other features of the installation according to the invention: 
          the installation includes a device for regulating the temperature of the extrudate to a temperature called the bending temperature, which device is placed between the production device and the bending head;     the installation includes a device for sectioning the extrudate, placed downstream of the temperature regulation device or downstream of the bending head;     the installation includes a device for introducing a flexible core coaxially into the extrudate, so that these two elements leave the head of the production device continuously;     the device for introducing the flexible core comprises a feed device for feeding the core into the head of the production device;     the feed device comprises a mechanism for driving the flexible core so that the speed of advance of the flexible core and the speed of the extrudate output by the production device are substantially equal;     the drive mechanism is capable of retracting the flexible core, in order to extract it from the bent extrudate, immediately before the sectioning step;     the flexible core is tubular and a heat-transfer fluid can be made to pass through it; and     the flexible core is made of polytetrafluoroethylene or a silicone.        

      The object of the invention is also to propose an installation for producing a component by applying the process according to the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other features and advantages of the invention will become apparent on reading the following detailed description, for the understanding of which the reader may refer to the appended figures in which:  
       FIGS. 1   a  and  1   b  are schematic representations of two parts of an installation according to the invention for producing an element comprising a bent tubular body;  
       FIGS. 2   a  to  2   c  are detailed views on a larger scale of the installation shown in  FIG. 1   a , representing the operation of the installation at various steps of the process; and  
       FIG. 3  is a schematic perspective representation of an element produced by the installation shown in  FIGS. 1   a  and  1   b , by applying the process according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      In the following description, identical, similar or equivalent elements will be denoted by the same reference numbers.  
       FIG. 3  shows a pipe  10  intended for example to be mounted on the engine of a motor vehicle.  
      This pipe  10  comprises a body  12  and end-fittings  14 ,  16 .  
      The body  12  is a bent tubular element, made of a thermoplastic; it thus comprises straight sections  18  joined together by elbow sections  20 . The elbow sections  20  are produced here so that the body  12  is an element that does not lie in one plane.  
      The end fittings  14 ,  16  are fitted onto the respective free ends  12   a ,  12   b  of the tubular body  12 .  
       FIGS. 1   a  and  1   b  show an installation  22  for producing the pipe  10 .  
      As may be seen in  FIG. 1   a , the installation  22  comprises a device for producing an extrudate  38 , which device consists here of an extruder  24  of known type, which includes a thermoplastic feed device  26 , a screw  28 , which rotates inside a barrel  30 , means  32  for rotating the screw  28 , an extrusion head  34  and a die  36 , which gives the stream of plasticized material its shape.  
      Since the body  12  of the pipe  10  is tubular, the die  36  includes a mandrel (not shown) allowing the body to have a hollow profile.  
      On leaving the die  36 , the stream of plasticized material forms a continuous tubular element  38 , hereafter called the extrudate, which is intended to form the body  12  of the pipe  10 .  
      The extruder  24  here is an extruder of the single-screw type, that is to say it has only a single screw  28 , the pitch of which may or may not vary. However, it will be understood that the extruder may also comprise several parallel screws, in which case the extruder  24  is of the multi-screw type.  
      In the following description of the installation  22 , the main axis A of the extruder  24 , which is the main axis of the screw  28 , will be considered to be parallel to the longitudinal main direction L. However, it will be understood that the invention also applies to an installation  22  for which the orientation of the main axis A of the extruder  24  is different, especially an orientation parallel to the vertical direction V.  
      The installation also includes a bending head  42  for producing the elbow sections  20  of the body  12 .  
      According to the preferred embodiment, the bending head  42  is of the numerical-control and multi-axis type, thus allowing the elbow sections  20  of the extrudate  38  to be bent in several orientations, thus making it possible to have a tubular body  12  that extends in three dimensions.  
      The bending head  42  is of known design—it comprises here a bending finger  44  and a bending pulley  46 , these being mounted so as to pivot about an axis B perpendicular to the longitudinal axis A of the extruder  24  and cooperating together to form the elbow sections  20  of the tubular body  12 .  
      The tubular body  12  comprises several elbow sections  20  which, depending on the specifications of the pipe  10 , may have different radii of curvature.  
      Now, the pulley  46  of the bending head  42  makes it possible for a single radius of curvature of the elbow section  20  to be obtained.  
      Thus, according to an alternative embodiment of the invention, the bending head  42  comprises several pulleys  46  of different dimensions, each of which is associated with a radius of curvature of the elbow sections  20 .  
      These pulleys  46  are furthermore mounted so as to slide along the axis B, in order to bring the pulley  46  associated with the elbow section to be obtained in line with the extrudate  38 , and their movement along the axis B is numerically controlled.  
      The bending pulley  46  is then said to be a staged or “multi-radius” pulley.  
      The finger  44  and the pulley  46  are mounted on a body  48 , which is mounted so as to pivot with respect to a fixed frame  50  about the longitudinal axis A, thereby making it possible to modify the orientation of the axis B. This thus allows the extrudate  38  to be bent in order to form elbow sections  20  having different orientations.  
      The body  48  is placed here between the extruder  24  and the assembly formed by the finger  44  and the pulley  46 , that is to say a tubular element which extends coaxially to the extruder  24  and through which the extrudate  38  passes.  
      The bending head  42  also includes a device  52  for moving the finger  34  and the pulley  46  translationally with respect to the body  48 , parallel to the axis B, in order to disengage them when the entire tubular body  12  has been bent, thus allowing the tubular body  12  to be subsequently handled, for example by means of a handling arm  54 .  
      The finger  34 , the pulley  46  and the body  48  are driven in their respective movements by means of various motors  56  which are electronically controlled individually.  
      According to the invention, the bending head  42  is placed directly downstream of the extruder  24 , thereby preventing the temperature of the extrudate  38  from dropping too rapidly below the glass transition temperature, and thus allowing the extrudate  38  to be bent directly after it has been produced.  
      The temperature of the extrudate  38  after it has left the extruder  24  is close to the melting point of the material, which is above the glass transition temperature of the material. At such a temperature, the consistency of the extrudate  38  does not allow it to be bent. It is therefore necessary to lower the temperature of the extrudate  38  down to a temperature Tb called the bending temperature, allowing it to be bent under optimum conditions.  
      To do this, the installation  22  includes a device  58  for regulating the temperature of the extrudate  38 , which device is placed between the die  36  of the extruder  24  and the bending head  42  and which is designed so that the temperature of the extrudate  38 , on leaving the regulating device, is substantially equal to the bending temperature Tb.  
      By way of example, the tubular body  12  here is made of a nylon-12, known by the name RILSAN, the melting point of the material of which is 172° C., and the bending temperature Tb is about 160° C.  
      Here, the installation  22  also includes a duct  60  which connects the exit of the die  36  to the inlet of the regulation device  58 . This duct  60  allows the extrudate  38  to be guided through the body  48 , protecting the extrudate  38  from coining into contact with the body  48 , and it also partly contributes to regulating the temperature of the extrudate  38 .  
      The regulation device  58  opens directly onto the finger  44  and the pulley  46  of the bending head  42 , so that when the extrudate  38  leaves the regulation device  58 , it is at the bending temperature Tb, to be immediately bent in order to form elbow sections  20  of the tubular body  12 .  
      The installation  22  also includes a device  40  for sectioning the extrudate  38 , which allows that portion of the extrudate  38  which has been bent to be separated from the rest of the extrudate  38 , thus forming the tubular body  12 .  
      The device  40  for sectioning the extrudate  38  is placed so as to section the extrudate  38  at the exit of the regulation device  58 . Here, it is fixed to the regulation device  58 .  
      As mentioned above, the pipe  10  includes an end-fitting  14 ,  16  at each of the ends  12   a ,  12   b  of the tubular body  12 .  
      According to another aspect of the invention, the installation  22  includes a mounting device  62  for fitting a first end-fitting  14  into the downstream free end  38   a  of the extrudate  38 .  
      As may be seen in greater detail in  FIG. 2A , this mounting device  62  is capable of fitting the end-fitting  14  when the free end  38   a  of the extrudate  38  projects from the regulation device  58 .  
      The mounting device  62  comprises a manipulator arm  64 , which can slide longitudinally so that the end-fitting  14  moves coaxially to the extrudate  38  during the operation of fitting it into the free end  38   a  of the extrudate  38 .  
      The manipulator arm  64  is furthermore mounted so as to move on a drive device  66  translationally with respect to the fixed frame  50  along an axis C orthogonal to the longitudinal axis A of the extruder  24 , which here is vertical.  
      The mounting device  62  also includes a magazine  68  in which several end-fittings  14  are stored, and the manipulator arm  64  moves with respect to this magazine  68  so as to take an end-fitting  14  from the magazine  68  and then fit it into the free end  38   a  of the extrudate  38 .  
      Here, for taking the end-fitting  14  from the magazine  68  and then for fitting it into the free end  38   a  of the extrudate  38 , the manipulator arm  64  can move so as to pivot about a longitudinal axis D, and the manipulator arm  64  is also mounted so as to move translationally along this same longitudinal axis D in order to fit the end-fitting  14  into the free end  38   a  of the extrudate  38 .  
      Depending on the cross-sectional dimension of the tubular body  12  and on the radius of curvature of the elbow sections  20  to be produced, it is necessary to introduce a flexible core inside the elbow section  20 , which is in the process of being bent, in order to prevent this elbow section  20  from forming a pleat, instead of a bend.  
      According to yet another aspect of the invention, the installation  22  includes a device  70  for introducing a flexible core  72  coaxially into the extrudate  38 , during production of the extrudate  38 .  
      This device  70  for introducing the flexible core  72  is shaped so that the extrudate  38  and the flexible core  72  leave the head  34  of the extruder  24  continuously.  
      The introduction device  70  comprises, for this purpose, a device  74  for feeding the flexible core  72  into the head  34  of the extruder  24  so that the flexible core  72  is coaxial with the mandrel of the die  36 .  
      The feed device  74  comprises a drive mechanism (not shown) for driving the flexible core  72  so that the speed of advance of the flexible core  72  and the speed of the extrudate  38  leaving the die  36  are substantially equal.  
      The mechanism for driving the flexible core  72  is also capable of retracting the flexible core  72  with respect to the extrudate  38 , when all of the elbow sections  20  of the tubular body  12  have been formed.  
      Thus, when the bent part of the extrudate  38 , which forms the tubular body  12 , is being sectioned, the flexible core  72  is no longer inside the section of the extrudate  38  that will be sectioned.  
      This avoids having to section the flexible core  72 , and consequently it allows it to be used again.  
      Here, as shown in  FIG. 1   a , the feed device  74  is mounted on the outer wall of the barrel  30  so that the flexible core  72  is introduced radially into the head  34  of the extruder  24 .  
      However, it will be understood that the invention is not limited to this embodiment and that the feed device  74  may be mounted on the extruder  24  so as to introduce the flexible core  72  in another direction.  
      Thus, according to an alternative embodiment of the invention, the flexible core  72  is generally introduced coaxially with the extruder  24 , for example through the screw  28 .  
      According to a preferred embodiment, the flexible core is made of a material having a low coefficient of friction with the material used to form the tubular body  12 , for example made of a silicone or of polytetrafluoroethylene.  
      The use of such a material makes it easier for the flexible core  72  to be retracted, while hardly damaging the internal surface of the extrudate  38 . In addition, the material used does not deform when it is heated to the melting point of the material forming the tubular body  12 .  
      According to an alternative embodiment of the invention, the flexible core  72  is also a tubular element through which a heat-transfer fluid can circulate.  
      This heat-transfer fluid, which is for example air or nitrogen, is chilled and then injected into the flexible core  72  so as to rapidly cool that section of the extrudate  38  that has will be sectioned, thus allowing the tubular body  12  to undergo its final solidification.  
      As may be seen in  FIG. 2   b , the installation  22  also includes means for introducing the second end-fitting  16  into the associated end  12   b  of the tubular body  12 , using a known method of introduction.  
      These means thus comprise a splaying cone  76 , which allows the end  12   b  of the tubular body  12  to be elastically deformed, increasing the inside diameter of this end  12   b , and a magazine  78  in which several end-fittings  16  are stored.  
      The end-fitting  16  that will be fitted into the end  12   b  of the tubular body  12  is positioned in the magazine so that its end, which will be introduced into the end  12   b  of the tubular body  12 , projects from this magazine  78 . Thus, the end  12   b  of the tubular body  12 , which has just been deformed, is directly positioned around this end of the end-fitting  16 , immediately after its deformation.  
      Next, when the end  12   b  of the tubular body  12  elastically resumes its initial shape, said end retracts around the end of the end-fitting  16 , the end-fitting  16  thus being fitted into the end  12   b  of the tubular body  12 .  
      Finally, the installation  22  includes a test set-up  80  for testing the finished pipe  10 , especially for checking its impermeability and its pressure resistance.  
       FIGS. 2   a  to  2   c  show the various steps of the process for producing the pipe  10 , which process is carried out by the installation  22  according to the invention.  
      As may be seen in  FIG. 2   a , a first step of the process consists in fitting the first end-fitting  14  into the downstream free end  38   a  of the extrudate.  
      Here, the first end-fitting  14  is carried by the manipulator arm  64 , which is capable of moving longitudinally with respect to the extrudate  38 .  
      During this step, only the downstream end  38   a  of the extrudate  38  projects from the regulation device  58 , and the bending head  42  is moved away, here vertically under the arm  64 , in order to allow the manipulator arm  64  to pass.  
      After the first end-fitting  14  has been fitted into the downstream end  38   a  of the extrudate  38 , the arm  64  is withdrawn to a disengaged position, shown in particular in  FIGS. 1 and 2   b , in which it is capable of taking a new end-fitting  14  from the magazine  68 .  
      Next, the bending head  42  is positioned at the outlet of the regulation device  58 .  
      Next, as shown in  FIG. 2   b , the process includes a step of producing the extrudate  38  by extrusion.  
      Next, in another step of the process, the temperature of the extrudate  38  is lowered down to the bending temperature Tb.  
      To do this, during this temperature-lowering step, the extrudate  38  passes through the duct  60  and then the regulation device  58 , which are produced so that the temperature of the extrudate  38  leaving the regulation device  58  is equal or relatively close to the bending temperature Tb.  
      After this step of lowering the temperature of the extrudate  38 , and in accordance with the invention, the process includes a step of bending the extrudate  38  leaving the regulation device  58  at the bending temperature Tb.  
      This bending step is carried out by means of the bending head  42 , and more particularly by the mutual action of the finger  44  and of the pulley  46  of the bending head  42 .  
      The extrudate  38  is produced by continuous extrusion. Thus, the step of lowering the temperature of the extrudate  38  while it passes through the duct  60  and through the regulation device  58  is also carried out continuously, progressively as the extrudate  38  is being produced and output by the die  36 .  
      Consequently, the step of bending the extrudate is also carried out continuously on the extrudate  38 , progressively as it is output by the temperature regulation device  58 .  
      The step of bending the extrude  38  consists in forming, in succession, the elbow sections  20  and the straight sections  18  of the tubular body, by carrying out several consecutive bending operations on the extrudate  38  in different orientations.  
      To do this, the bending head  42  is capable of pivoting about the main longitudinal axis A of the installation, as described above, in order to position the finger  44  and the pulley  46  along the curvature and orientation to be obtained for each elbow section  20  to be obtained.  
      Thus, it is possible to have elbow sections  20  having different orientations and different curvatures. Here,  FIG. 2   c  shows a bent part of the extrudate  38 , which lies in one plane. However, it will be understood that the curvatures and the orientations of the bent sections  20  may be different, so that the tubular body  12  is an element not lying in one plane.  
      After the bending step, the bent part of the extrudate  38  has the shape of the tubular body  12 .  
      The bending head  42  is then disengaged from the outlet of the regulation device  58 , here by moving vertically downwards.  
      The process according to the invention also includes a step consisting in introducing the flexible core  72  into the extrudate  38  during the step of producing the extrudate  38 .  
      This step is carried out by the extruder  24  and by the feed device  74 , so that the flexible core  72 , on leaving the die  36 , is housed inside the extrudate  38 .  
      The flexible core  72  is thus introduced into the extrudate  38  before the bending step—this thus dispenses with the provision of additional means for introducing the flexible core  72  into the extrudate leaving the extruder  24  and before the bending step.  
      In addition, since the flexible core  72  is introduced into the extrudate  38  during the extrudate production step, the temperature of the flexible core  72  is then close to that of the extrudate, and this reduces the risk of excessive local cooling of the extrudate  38  down to a temperature below the bending temperature Tb.  
      Next, after the step of bending the extrudate  38 , the process includes a step of forcibly cooling the bent part of the extrudate  38 .  
      This cooling step causes the bent part of the extrudate  38  to solidify, preventing any subsequent deformation and then allowing the tubular body  12  to be sectioned and then handled.  
      According to the invention, this cooling step consists in making a heat-transfer fluid circulate inside the flexible core  72 .  
      For this purpose, as mentioned above, the flexible core  72  is tubular and the heat-transfer fluid is chilled air or any other similar gas.  
      Next, as may be seen in  FIG. 2   c , the cooling step is followed by a step of extracting the flexible core  72  from the extrudate  38  followed by a step of sectioning the tubular body  12 .  
      This step of extracting the flexible core  72 , which is carried out by the feed device  74 , prevents the flexible core  72  from being sectioned during the sectioning step, thus making it possible for the same flexible core  72  to be reused very many times and without having to systematically scrap part of the flexible core  72 .  
      The sectioning step allows that portion of the extrudate  38  that has been bent to be separated from the rest of the extrudate  38 , in order thus to obtain the tubular body  12  of the pipe.  
      The tubular body  12  is then moved to the installation  76 ,  78  for mounting the second end-fitting  16  by the manipulator arm  54 , then to the test set-up  80  for testing the finished pipe  10  and finally, depending on the result obtained by the test set-up  80 , the pipe  10  is stored in a container  82 , or scrapped.  
      After the step of sectioning the cylindrical body  12 , the outlet of the regulation device  58  is cleared and it is then possible for the process according to the invention as described above to continue for the production of a new pipe  10 .  
      The process according to the invention has been described in relation to a pipe  10  comprising a tubular body  12  comprising a single layer of a single material.  
      It will be understood that the invention is not limited to this embodiment and that the tubular body  12  may comprise several layers of the same material or of different materials.  
      The structure of the extruder  24  will therefore be modified accordingly, using known extrusion techniques.  
      The installation and the process according to the invention have been described with reference to the production of the extrudate  38  by extrusion. However, it will be understood that the invention is not limited to such a method of production and that the extrudate  38  may also be produced by injection.  
      In this case, the device  24  for producing the extrudate  38  consists of an injection device of known type, which for example includes a piston that injects the stream of plasticized material through the die  36 .  
      A pipe  10  is produced according to the invention in a continuous manner, that is to say without temporarily storing the tubular body  12  being produced.  
      This allows the space needed for the installation  22  to be reduced.  
      In fact, since most of the operations on the tubular body  12 , or the extrudate  38 , are carried out near the outlet of the regulation device  58 , several components of the installation  22 , especially the bending head  42  and the device  40  for sectioning the extrudate  38 , are placed within a small volume located at the outlet of the regulation device  58 .  
      The production process dispenses with the temporary storage areas, and also the areas for access to these temporary storage areas, thus simplifying the stock management procedures.  
      As mentioned above, the step of bending the extrudate  38  takes place directly after the step of producing the extrudate  38  and the step of cooling the extrudate  38  down to the bending temperature.  
      Thus, the extrudate undergoes no phase of cooling down to a temperature below the bending temperature Tb followed by a phase of heating it back up to the bending temperature Tb.  
      The material therefore undergoes no annealing operation, which would modify its crystalline structure.  
      It is thus easy to distinguish a pipe  10  obtained by the process according to the invention from a pipe obtained by known processes, since the crystalline structures of the various pipes  10  are different.  
      In addition, when the pipe  10  obtained by the process according to the invention is subjected to an “annealing” operation, that is to say one in which it is reheated up to the bending temperature Tb, the crystalline structure of the tubular body is modified, which in particular has the consequence of modifying the dimensions of the tubular body.  
      When the pipes obtained by known processes are subjected to this same “annealing” operation, their crystalline structure is not modified, and consequently the dimensions of the tubular body remain unchanged.  
      Finally, the process according to the invention makes it possible to reduce the time needed to produce each pipe  10 , thereby increasing the productivity and reducing the production costs.