Abstract:
Plastics articles with continuous reinforcement strands are normally produced by pultrusion. Pultrusion methods are known for producing straight or curved plastics profiles. It has not hitherto been possible for reinforced plastics articles of more complex form to be produced by pultrusion methods. The invention provides a pultrusion method in which a part of a curved plastics article serves, together with a mold ( 15 ), for the pultrusion of a reinforced plastics article. In this way, it is possible for complex plastics articles, for example a plastics pipe ( 10 ), to be produced by pultrusion.

Description:
STATEMENT OF RELATED APPLICATIONS 
     This patent application is the US National Phase of International Application No. PCT/EP2012/004389 having an International Filing Date of 19 Oct. 2012, which claims priority on German Patent Application No. 10 2011 117 297.7 having a filing date of 1 Nov. 2011. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to a method for producing a reinforced plastics article, wherein a continuous reinforcement composed of strands, fabric and/or the like is guided through a mold and, in the mold, is embedded in plastic, and the mold is periodically moved relative to the preferably static plastics article, and a method for producing a reinforced plastics article, wherein a continuous reinforcement composed of strands, fabric and/or the like is guided from a material supply through a mold and, in the mold, is embedded in plastic, the mold is periodically moved relative to the plastics article and a gripper is periodically moved on the plastics article relative to the mold. 
     2. Prior Art 
     Plastics articles, in particular plastics profiles, with a continuous reinforcement composed of strands, fibers, fabrics and/or knits embedded in preferably thermosetting plastic are predominantly produced in continuous form as a plastics strand or are formed from at least one plastics strand. This is preferably performed using the pultrusion method. For this purpose, the reinforcement is guided through a mold, and in the mold, the reinforcement is embedded in the liquid plastic. The mold yields an at least partially hardened plastics strand with the profile predefined by the mold. 
     The pultrusion method is normally used to produce straight strand-like plastics profiles. Pultrusion methods are however also known which make it possible to produce curved plastics profiles as plastics strand profiles. With regard to the complexity of curved plastics profiles in particular, known pultrusion methods reach their technical limits. As a result, it has hitherto only been possible to a limited extent for technically complex plastics articles to be produced by pultrusion methods. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is now based on the object of providing a method with which complex reinforced plastics articles can be produced in particular by pultrusion methods. 
     A method for achieving said object is a method for producing a reinforced plastics article, wherein a continuous reinforcement composed of strands, fabric and/or the like is guided through a mold and, in the mold, is embedded in plastic, and the mold is periodically moved relative to the preferably static plastics article, characterized in that a part of the curved plastics article contributes, together with the mold, to the formation of the plastics article. By virtue of the fact that, according to said method, provision is made for the mold and a part of the already manufactured plastics article to be used in the molding process for the formation of the plastics article, it is possible to form plastics articles whose overall form differs from the pultruded plastics strand profile. These may be plastics profiles of a form more complex than that of the respectively pultruded plastics strand. 
     The method is preferably configured such that a pipe-shaped plastics article is formed from multiple windings lined up in coiled or spiral fashion. The windings are pultruded as a continuous reinforced plastics strand, wherein the cross section of the windings is predefined both by the mold and by a part of the already produced plastics article. It is preferable for an already formed (preceding) winding to be used, together with the mold, for forming, in particular pultruding, the subsequent winding. As a result, the mold does not need to completely surround the winding pultruded in strand-like fashion, which makes it possible for the plastics article to be formed from contiguous and preferably interconnected windings. The windings are connected to one another at a location or wall of the subsequent winding part to be produced which is influenced in terms of shaping not by the mold but by the preceding winding. In this way, the windings can be fixedly and permanently connected, specifically fused, during the pultrusion process. 
     As a result of the formation of the plastics article from contiguous spiral-shaped windings, there is formed by means of the mold during the pultrusion process a reinforced plastics strand which runs in spiral fashion owing to a corresponding curvature of the mold in the production direction of the plastics strand. It is preferably provided here that the axis about which the winding of the plastics article runs in spiral fashion coincides with a longitudinal central axis of the overall plastics article to be produced, in particular of a pipe-shaped plastics article. A rigid plastics pipe or a plastics pipe that is flexible within certain limits or a plastics hose is thus generated. 
     It is preferably provided that the mold is open on one side and performs a relative movement on a part of the preceding winding and of the subsequent winding of the plastics article. The preceding, already previously produced winding accordingly serves not only for forming a delimitation of the subsequent winding on one side at the side left open by the mold but also for guiding, in particular, the subsequent winding to be produced. It is achieved in this way that the subsequent winding corresponds in terms of its curvature to the preceding winding. 
     It is also preferably provided that the periodic relative movement of the mold with respect to the plastics article takes place in such a manner that the mold is moved periodically on and along the profile of the winding, which is to be produced, of the plastics article, specifically in particular relative to the plastics article or winding that is static in this case. During said periodic movement of the mold, the plastics part, in particular a part of the preceding, finished winding, is held static. This may be realized in a variety of ways, for example by means of a gripper, clamps or the like. Provision is preferably made for the mold to be moved back and forth in discontinuous or stepped fashion, wherein, during the backward movement of the mold counter to the pultrusion direction, the mold performs a relative movement on a part of a winding of the plastics article. In this way, gradually in the manner of a pilgering process, a piece of a winding is pushed out of the mold in the pultrusion direction, specifically preferably after the respective part of the winding has solidified or hardened in the mold at least to such an extent as to be adequately stable. 
     It is also provided that, during the periodic backward movement, counter to the pultrusion direction, of the mold on the winding of the plastics article, the plastics article is held static, for example by a gripper, preferably in the region of an already produced preceding winding. In this way, with the preceding winding held fixed, a part of the subsequent winding can be pulled out of the mold. Thereafter, the gripper is opened again, that is to say released from the winding. The gripper is then moved in front of the mold again counter to the pultrusion direction, and then the mold with the gripper together with the winding is moved forward by a short distance in the pultrusion direction, wherein the already produced part of the plastics article is rotated about its longitudinal central axis. 
     A further method for achieving the object mentioned in the introduction is a method for producing a reinforced plastics article, wherein a continuous reinforcement composed of strands, fabric and/or the like is guided from a material supply through a mold and, in the mold, is embedded in plastic, the mold is periodically moved relative to the plastics article and a gripper is periodically moved on the plastics article relative to the mold, characterized in that the mold, the gripper and the material supply are moved periodically around a shell surface of a cylindrical core, wherein the gripper and the material supply are moved jointly, in a fixed relationship, periodically around the shell surface. According to said measures, the mold, the at least one gripper and the material supply can be moved around the core in order to produce the plastics article. As a result, for the production of the plastics article, the core does not need to be moved, in particular does not need to be rotated. This makes it possible in particular for the plastics article to be produced around large cores. The core may be removed after the production of the plastics article. Provision is however preferably made for the plastics article to be left on the core, that is to say for an article to be provided which has a plastics article arranged around it, wherein the plastics article remains fixedly and permanently connected to the core. Provision is preferably made for the at least one gripper and the material supply to always be moved jointly and simultaneously around the core. By contrast, the mold is moved separately from and independently of the at least one gripper and the material supply. By virtue of the fact that the at least one gripper and the material supply are moved simultaneously, the strands, fabrics or the like that serve for the reinforcement of the plastics article are not, when pulled through the mold, stretched to such an excessive extent that they concentrate at particular locations in the mold; in fact, the strands instead maintain the intended relative position within the mold. 
     Provision may also be made for a spiral-shaped plastics article with windings preferably spaced apart from one another to be produced around the preferably static core. The plastics article accordingly forms a spiral of reinforced plastic surrounding the core at the outside. Said spiral may serve for the reinforcement and/or protection of the core, wherein said spiral is flexible when the windings are spaced apart from one another. The core may be a pipe composed of various materials, for example metal or plastic, or else may be a hose, a line, a cable or the like which is reinforced by the external spiral-shaped plastics article. 
     In a preferred refinement of the invention, provision is made for the windings of the preferably spiral-shaped plastics article to have their form or shape imparted to them both by the mold and also by the shell surface of the cylindrical core. The mold therefore surrounds the profile of the respective winding only partially, specifically from three or only two sides. A side of the winding that bears against the core is formed or shaped by the cylindrical shell surface of said core. Here, the core may bear the windings of the plastics article and be connected by fusion or adhesive bonding to the cylindrical shell surface. 
     Provision is preferably made for the mold, the gripper and the material supply to move on a spiral path around the shell surface of the cylindrical core. The spiral-shaped winding of the plastics article around the core is generated by means of an advancing movement of the mold, of the at least one gripper and of the material supply in the longitudinal direction of the core. By means of a corresponding advancing movement of the mold, of the at least one gripper and of the material supply in the longitudinal direction of the core, it is possible for the individual windings of the plastics article to have any desired spacing from one another without these making contact with one another. 
     A further advantageous refinement of the method provides for the gripper and the material supply to be moved jointly in stepped, that is to say discontinuous fashion relative to the mold and the cylindrical core on the spiral path around the core. Here, in at least one production phase of the plastics article, the mold is static relative to the gripper and the material supply. The mold then also does not move relative to the cylindrical core. In this way, the relative spacing to the gripper and to the material supply remains constant as a result of joint movement and joint standstill phases. By contrast, the mold can be periodically moved relative to the core and relative to the windings of the plastics article to be produced. In one production phase of the plastics article, said relative movement of the mold with respect to the windings of the plastics article may take place in standstill phases of the gripper and of the material supply. In particular, for demolding of a part of a winding, the mold is moved backward relative to the winding and relative to the core counter to the pultrusion direction while the gripper and the material supply remain static. 
     In another preferred refinement of the method, provision is made for the at least one gripper to be arranged directly in front of the mold as viewed in the pultrusion direction of the plastics article or along the windings. Here, the spacing between the gripper and the mold can be varied by alternating movement of the mold or of the gripper with the material supply, in particular for the ejection of a newly produced hardened section of the winding from the mold. 
     In another refinement of the method, it is conceivable for a spacer material, in particular a spacer or spacer strip, to be provided between the individual successive windings of the plastics article. In particular, during the production of the plastics article with continuous formation of the windings, a continuous spacer strip can be inserted continuously between two successive windings. As a result, the windings do not make contact even though they are situated in close succession. The windings are separated from one another only by the preferably thin spacer strip. The spacer strip has the effect that a preceding winding, during the shaping of the side or wall, abutting against said preceding winding, of the winding to be produced subsequently, can be demolded by virtue of the fact that said side or wall is molded onto the exposed side of the spacer strip. Owing to the spacer strip, the hose-like or pipe-shaped plastics article encasing the core can be flexibly deformed despite the adjacent successive windings making contact with both sides of the spacer strip. This is the case in particular if the spacer strip is composed only of a, for example, siliconized material or is provided with siliconized surfaces which prevent adhesion of the walls of successive windings to the spacer strip. 
     Further advantageous refinements of the method for producing the spiral-shaped plastics article, or plastics article composed of windings, will emerge from the subclaims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred methods according to the invention will be explained in more detail below on the basis of the drawing, in which: 
         FIG. 1  is a schematic illustration of a part of a device for producing a plastics article, 
         FIG. 2  shows a longitudinal section through a part of the plastics article with a mold, 
         FIG. 3  is a perspective illustration of a device for producing a plastics article in accordance with a method according to a second exemplary embodiment of the invention, 
         FIG. 4  shows a perspective longitudinal section through the device of  FIG. 3 , 
         FIG. 5  shows a central longitudinal section through the device of  FIGS. 3 and 4 , 
         FIG. 6  is a schematic illustration of a first method step, 
         FIG. 7  is a schematic illustration of a subsequent method step, 
         FIG. 8  is a schematic illustration of a further subsequent method step, 
         FIG. 9  is a perspective illustration of a device for producing a plastics article according to a further exemplary embodiment of the invention, 
         FIG. 10  shows a perspective longitudinal section through the device of  FIG. 9 , and 
         FIG. 11  shows a central longitudinal section through the device of  FIGS. 9 and 10  with a plastics article in a partially produced state. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  illustrate the production of a plastics article that is reinforced with fibers, strands or the like. Said plastics article is a plastics pipe  10  composed of contiguous, interconnected sections of the helically or spirally continuous winding  11 . The winding  11  is pultruded as a continuous strand. The winding  11  loops in helical fashion around a longitudinal central axis  12  of the plastics pipe  10 . Adjacent annular sections of the winding  11  are connected to one another at their abutting face surfaces  13 ,  14  by virtue of that section of the winding  11  which is presently being pultruded being placed, in the still-unhardened state, by way of its face surface  13  against the face surface  14  of the previously produced section of the winding  11  and, in the process, the face surfaces  13  and  14  being permanently fixedly connected to one another, by adhesive bonding or fusion, to form the plastics pipe  10 . 
     The face surfaces  13  and  14  by which the individual ring sections of the winding  11  are connected to one another have, in the exemplary embodiment shown, an angled, roof-shaped form. The face surfaces  13  and  14  may however have any other desired forms. They are preferably profiled, though may also be planar. 
     A device that is used for the continuous pultrusion of the plastics pipe  10  is illustrated partially and schematically in  FIGS. 1 and 2 . The device has substantially a mold  15 , a gripper  16  and a material supply (not illustrated in the figure) for the fabric, strands or fibers that serve for the reinforcement of the plastics pipe  10 . The material supply normally has one supply roll for each of the strands, of which there are normally several. The strands are drawn off the supply rolls during the pultrusion of the winding  11  for the production of the plastics pipe  10 . 
     The mold  15  only partially surrounds the winding  11  to be produced, specifically on only three sides in the exemplary embodiment shown, that is to say the face surface  14 , the cylindrical outer shell surface  17  and the cylindrical inner shell surface  18 . As a result, a groove-like mold cavity  19  which is open on one side is situated in the mold  15 . The groove-like mold cavity  19  of the mold  15  is closed by the face surface  14  of the already produced preceding section of the winding  11 . In this way, the winding  11  itself contributes, in part, to the formation and shaping of the face surface  13  of that section of the winding  11  which is presently being pultruded. The mold cavity  19  in the mold  15  has a profile which both corresponds to the diameter of the plastics pipe  10  and corresponds to the gradient of the winding  11  for forming the plastics pipe  10 . Said gradient corresponds, in one rotation of the winding  11 , to the distance between the tips of the face surfaces  13  and  14  as viewed in the cross section of the winding  11 . 
     The groove-like mold cavity  19  has a depth in the direction of the longitudinal central axis  12  of the plastics pipe  10  to be produced, said depth being greater than the length of the profile of the winding  11 , specifically of the spacing of the face surfaces  13 ,  14 . As a result, the mold  15  also extends over a part of the previously produced ring of the winding  11 , whereby adjacent rings of the winding  11  are guided and centered by the mold  15  during the fusion of their face surfaces  13  and  14  that abut against one another. 
     The mold  15  extends over a part of the circumference of the plastics pipe  10 . In the exemplary embodiment shown, the mold  15  extends over approximately half of the circumference of the plastics pipe  10 . Said region may however be larger or smaller depending on the diameter of the plastics pipe  10 , on the plastic that is used and on the pultrusion parameters. The strands (not shown), passing from the material supply, for the reinforcement of the plastics pipe  10  enter into the mold  15  at an open entry surface  20 . The mold  15  is thus supplied, through the entry surface  20 , with the strands for the reinforcement, or else other reinforcement materials such as fibers or the like. 
     A gripper  16  is arranged in front of an exit surface  22 , situated opposite the entry surface  20  in the pultrusion direction  21 , of the mold  15 . At the exit surface  22 , a section of the pultruded winding  11  exits the mold  15  in gradual fashion. Here, the direction in which the winding  11  emerges from the exit surface  22  of the mold  15  is referred to as the pultrusion direction  21 . Oriented oppositely to the pultrusion direction  21  is the production direction of the winding  11 , specifically the so-called “growth direction” of said winding. The following description will refer to the “pultrusion direction  21 ”. “Front” refers to that side of the mold  32  which is situated in front of the exit surface  22  as viewed in the pultrusion direction  21 . Consequently, “rear” refers to that which, as viewed in the pultrusion direction  21 , is situated behind the entry surface  20  of the mold  15  at which the strands that serve for the reinforcement of the plastics pipe  10  enter into the mold  15  in the pultrusion direction  21 . This point of view or terminology usage also applies to subsequent exemplary embodiments. 
     The gripper  16  has two opposite gripper parts  23 ,  24  which are assigned to the outer shell surface  17  and to the inner shell surface  18  of the winding  11 . The gripper  16  is designed to be shorter than the mold  15  such that said gripper extends only over a small part of the circumference of a ring or of a turn of the winding  11 . The gripper parts  23 ,  24  can be moved together in order to firmly hold the winding  11  at the outer shell surface  17  and at the inner shell surface  18 . For release from the winding  11 , the gripper parts  23 ,  24  can be moved apart. The gripper  16  is dimensioned in the longitudinal direction of the plastics pipe  10  such that it can grip the outer shell surface  17  and the inner shell surface  18  of multiple rotations of the winding  11  when it holds or fixedly clamps the winding  11 . Those surfaces of the gripper parts  23  and  24  which come into contact with the outer shell surface  17  and the inner shell surface  18  of the winding  11  are formed correspondingly to the radius of the outer shell surface  17  and inner shell surface  18 . 
     The method for producing the plastics pipe  10  ( FIGS. 1 and 2 ) proceeds as follows: 
     During the production process, the plastics pipe  10  is rotated about the longitudinal central axis  12  in phases. Here, the strand-like winding  11  of the plastics pipe  10  to be produced is produced in a gradual, specifically preferably stepped, fashion. Here, the plastics pipe  10  is, in sections, rotated out of the mold  15  in the pultrusion direction  21 , specifically similarly to a screw being unscrewed from a nut. The mold  15  and the gripper  16  are moved back and forth only periodically in the pultrusion direction  21  and counter to the pultrusion direction  21  about the longitudinal central axis  12  of the plastics pipe  10 , wherein, in certain pultrusion phases, a periodic movement of the mold  15  relative to the winding  11  also occurs, specifically counter to the pultrusion direction  21 . In another pultrusion phase, the mold  15  and the gripper  16  are advanced, in particular by one step, together with the winding  11  in the pultrusion direction  21 . Here, the winding  11  is produced in stepped fashion in the pultrusion direction  21 , specifically in the manner of a pilgering process. 
     When, in the mold  15 , that part of the winding  11  which is situated therein has fully or at least partially hardened, said part of the winding  11  is, so to speak, “demolded” by means of a backward movement of the mold  15  counter to the pultrusion direction  21 . Here, at least one previously produced part of the winding  11  that has already moved out of the mold  15  is held static by the closed gripper  16 . As a result, during the backward movement of the mold  15  counter to the pultrusion direction  21 , the mold  15  performs a relative movement with respect to the winding  11 , whereby a hardened part of the winding  11  exits the mold  15  at the entry surface  20 . During said backward movement of the mold  15  counter to the pultrusion direction  21 , strands are drawn off the material supply into the still-empty mold cavity  19  of the mold  15 , which strands are then subsequently encased, in the mold  15 , with solidified plastic. Furthermore, the mold  15  travels further in the growth direction of the winding  11 . 
     After the backward movement of the mold  15  counter to the pultrusion direction  21 , the gripper  16  is opened and subsequently moved backward counter to the pultrusion direction  21  to a point a short distance in front of the exit surface  22  of the mold  15 . Subsequently, by virtue of the gripper  16  being closed, the winding  11  is gripped by the gripper  16  again and subsequently the mold  15  and the gripper  16  are moved forward together in the pultrusion direction  21 , specifically are rotated about the longitudinal central axis  12  of the plastics pipe  10 . Said rotation takes place over a sub-region of the circumference of the plastics pipe  10  which is smaller than the sub-region surrounded by the mold  15  of the plastics pipe  10 . 
     After that section of the winding  11  which is situated in the mold  15  has at least mostly hardened, the above-described process begins again in that, with the winding  11  held static by the gripper  16 , the mold  15  is moved backward again counter to the pultrusion direction  21  and, during the resulting relative movement of the mold  15  with respect to the winding  11 , which in this phase is not rotated about the longitudinal central axis  12 , of the plastics pipe  10 , a newly pultruded section of the winding  11  is demolded and the mold  15  is again moved further in the production direction, specifically the growth direction of the winding  11 . 
     The above-described pultrusion method is described in more detail in WO 2008/116560 A1, wherein reference is made to the entire content of said document. 
     In the above-described method for producing the plastics pipe  10 , the cross section of the winding  11  is partially, specifically at the outer shell surface  17 , at the inner shell surface  18  and at the face surface  14 , formed in the groove-like mold cavity  19  of the mold  15 , whereas the face surface  13  is formed by the previously pultruded section of the winding  11 , which for this purpose enters partially into the open side of the groove-like mold cavity  19  and closes off the latter. It is thus the case that the mold  15  and another, already previously pultruded part of the winding  11  of the plastics pipe  10  participate in the shaping of the winding  11 . 
     At the start of the production of the plastics pipe  10 , when an annular section of the winding  11  that can close off the open side of the groove-like mold cavity  19  of the mold  15  still does not exist, the open side of the mold cavity  19  is closed off by means of an auxiliary profile whose face surface projecting into the mold cavity  19  corresponds to the shape of the face surface  14 . Said auxiliary profile is removed when an encircling section of the winding  11  has been pultruded which then—like the subsequent encircling sections of the winding  11  also—contributes together with the mold  15  to the shaping or cross-sectional formation of the winding  11 . 
       FIGS. 3 to 8  show the production of a core in the form of a pipe  25  surrounded by a reinforced plastics article. The pipe may be composed of any desired material. It is also conceivable, instead of the pipe  25 , for some other cylindrical article to be provided with the plastics article on the outside. The plastics article is a plastics spiral  26  reinforced with multiple continuous strands  40 . The plastics spiral  26  is preferably connected in non-positively locking fashion by means of adhesive bonding or shrinkage, or connected in a frictionally engaging fashion, to the outer cylindrical shell surface  27  of the pipe  25 . The plastics spiral  26  surrounds the pipe  25  as an endless winding  28 , wherein face surfaces  29  and  30 , which are oriented toward one another, of successive turns of the winding are spaced apart from one another. In the exemplary embodiment shown, the face surfaces  29 ,  30  of successive turns of the winding  28  are spaced apart from one another by a spacer strip  31  arranged in between. Here, the spacer strip  31 , which is preferably also endless and wound in spiral fashion, fills the intermediate space between the face surfaces  29 ,  30  of successive turns of the windings  28  in that opposite sides of the spacer strip  31  bear against the face surface  29  of one turn of the winding  28  and against the face surface  30  of the subsequent turn of the winding  28 . 
     In the exemplary embodiment shown, the cross section of the winding  28  is selected such that the face surfaces  29 ,  30  are profiled, and specifically in the exemplary embodiment shown have a Z-like profile with two bends. Here, the two face surfaces  29 ,  30  run parallel to one another. The invention is however also suitable for windings  28  with any other desired cross sections, in particular for face surfaces  29 ,  30  that are profiled in any other desired way. The face surfaces  29 ,  30  may optionally also be straight. 
     To produce the plastics spiral  26  in continuous fashion around the pipe  25  or around some other cylindrical article that serves as a core, use is also made here of a mold  32  and of a gripper  33 . The mold  32  surrounds the pipe  25  over a part of the circumference, specifically over approximately half of the circumference in the exemplary embodiment shown. Depending on the production conditions and dimensions of the pipe  25 , it is however also possible for the mold  32  to surround a smaller or greater part of the circumference of the pipe  25 . The mold  32  has a cavity  34  with which two profile sides of the winding  28 , specifically the face surfaces  30  and an outer shell surface  35 , can be formed. An opposite, inner shell surface  36  of the profile of the winding  28  is formed by the shell surface  27  of the pipe  25 . The opposite face surface  29  of the cross section of the winding  28  is formed by the face surface  30  of the previously produced turn of the winding  28  or by a surface of the spacer strip  31  between the face surfaces  29  and  30  of two successive turns of the winding  28 . Thus, not only the mold  32  but also the pipe  25  and a previously produced part of the winding  28  contribute to the formation of the cross-sectional shapes of the winding  28 . By virtue of the fact that the face surface  29  of one part of the winding  28  is formed, during the pultrusion, by the face surface  30  of the preceding section of the winding  28  or by the spacer strip  31  bearing against said face surface, the mold  32  is open in the direction of the plastics spiral  26 . On the opposite side, for forming the face surface  30  of the winding  28 , the mold  32  is sealed off with respect to the shell surface  27  of the pipe. 
     The gripper  33 , which is arranged in front of the mold  32  in the pultrusion direction  37 , is designed to abut against a point on the outer shell surface  35  of the already produced plastics spiral  26 . The gripper  33  can be pressed against the winding  28  from the outside by a drive (not shown). In the process, that part of the winding  28  which is covered by the gripping surface of the gripper  33  is pressed against the shell surface  27  of the pipe  25 . By means of a movement away from the outer shell surface  35  of the winding  28 , the gripper  33  releases the winding  28  of the plastics spiral  26  again. 
     The production of the plastics spiral  26  on the pipe  25  ( FIGS. 3 to 8 ) may basically take place as explained in the above-described exemplary embodiment of  FIGS. 1 and 2 . It is merely the case here that the pipe  25  also participates in the shaping of the winding  28 . Furthermore, at the entry surface  38  for the entry of the strands or fibers into the mold, the spacer strip  31  is fed between adjacent turns of the winding  28  in continuous fashion. If said spacer strip  31  is composed of a material to which the plastic of the winding  28  does not adhere or the outer surfaces of the spacer strip  31  are not of adhesive form or provided with an adhesive coating, the plastics spiral  26  is flexible even though it, together with the spacer strip  31  between the face surfaces  29  and  30  of the winding  28 , forms, in effect, a closed ring around the pipe  25 . 
     In an alternative refinement of the invention, it is conceivable for the gripper  33  illustrated in  FIGS. 3 to 5  to be coupled to a material supply  41  (not illustrated in the figures), in particular multiple supply rolls for the individual strands  40  that serve for the reinforcement of the plastics spiral  26 . Said coupling is realized in such a way that the gripper  33  and the material supply (not shown) are jointly moved periodically around the pipe  25 , specifically in stepped fashion. The individual coupled movement steps of the gripper  33  and of the material supply extend in each case only over a part of the circumference of the pipe  25 . The mold  32  is also moved periodically around the pipe  25 , specifically preferably always to the same extent as the gripper  33  with the material supply  41 . However, the mold  32  on the one hand and the gripper with the material supply  41  on the other hand are moved around the static pipe  25  at different times. Owing to the stepped movement of the mold  32  on the one hand and of the gripper  33  with the material supply  41  on the other hand around the pipe  25 , the plastics spiral  26  surrounding the pipe  25  is formed without the pipe  25  being moved about its longitudinal central axis  39 . Accordingly, in this exemplary embodiment, by contrast to the exemplary embodiments described above, the plastics spiral  26  is not rotated in the manner of a screw out of a nut corresponding to the mold  32 , but conversely, the mold  32 , as a nut, is rotated onto the screw, the pipe  25 . Here, the plastics spiral  26  is produced around the altogether static pipe without the pipe  25  having to be rotated about its longitudinal central axis  39  and having to be moved, correspondingly to the gradient of the winding  28 , in the axial direction along the longitudinal central axis  39 . 
     The method for producing the plastics spiral  26  pultruded around the static pipe  25  by means of the mold  32  and gripper  33  with the material supply  41 , which are moved around the pipe  25 , will be explained below with reference to  FIGS. 6 to 8 , which schematically show the individual production steps: 
     The strands  40  or the like that serve for the reinforcement of the plastics spiral  26  are drawn off the material supply  41 , which is merely indicated in the illustration. Here, the strands  40  enter the mold  32  via the entry surface  42 . The pultruded plastics spiral  26  exits the mold  32  at the exit surface  43 . Here, the direction in which the plastics spiral  26  emerges from the exit surface  43  of the mold  32  is again referred to as pultrusion direction  44 . Oriented oppositely to the pultrusion direction  44  is the production direction of the plastics spiral  26 , the so-called “growth direction”. 
     In the illustration of  FIG. 6 , the mold  32  and the gripper  33  have been moved together as far as possible. Here, the entry surface  42  for the entry of the material supply  41  into the mold  32  is at a maximum distance from the material supply  41 . The strands  40  are encased with plastic in the mold  32 . After the plastic has adequately hardened at least in the front part, pointing toward the gripper  33 , of the mold  32 , the mold  32  is moved backward around the static pipe  25  counter to the pultrusion direction  44 , as per  FIG. 7 . Here, the plastics spiral  26  is held static by the gripper  33 , such that the mold performs a relative movement on the plastics spiral  26  counter to the pultrusion direction  44 , specifically in the production direction of the plastics spiral  26 , specifically in the so-called “growth direction” of the plastics spiral  26 . Here, a part of the plastics spiral  26  produced most recently in the mold  32  emerges from the mold at the exit surface  43 . This means that said most recently produced part of the plastics spiral  26  exits the mold  32  at the exit surface  43  in the pultrusion direction  44 . During the backward movement of the mold  32 , new sections of the strands  40  enter the mold  32  through the entry surface  42 , wherein the entry surface  42  of the mold  32  moves toward the material supply  41 . 
     In the next step ( FIG. 8 ), the gripper  33 , which has been released from the plastics spiral  26 , is moved, counter to the pultrusion direction, into a position in front of the exit surface  43  of the mold  32  again. Owing to the connection  45 , merely schematically illustrated in  FIGS. 6 to 8 , of the gripper  33  to the material supply  41 , the material supply  41  is driven along by the gripper  33  as the gripper  33  moves toward the mold  32 , whereby the material supply  41  moves away from the entry surface  42  of the mold  32  again. The mold  32 , the gripper  33  and the material supply  41  have now assumed a position corresponding to that in  FIG. 6  again. By contrast to  FIG. 6 , it is the case in the illustration of  FIG. 8  that the mold  32 , the gripper  33  and the material supply  41  have moved around a part of the circumference of the static pipe  25 . The circular arc path covered by the mold  32 , the gripper  33  and the material supply  41  in the production direction or “growth direction” of the plastics spiral  26  corresponds to the newly produced part or region of the plastics spiral  26  produced during one method cycle during the pultrusion of the plastics spiral  26  by the pultrusion steps illustrated in  FIGS. 6 to 8 . 
     During the pultrusion of the plastics spiral  26 , the spacer strip  31  is fed continuously, specifically, in principle, in the same way as the strands  40 . The spacer strip  31  is preferably fed between the face surfaces  29  and  30  of two successive turns of the winding  28  of the mold  32  via the entry surface  38 . 
       FIGS. 9 to 11  show an exemplary embodiment of the invention which corresponds in principle to that of  FIGS. 3 to 8 . In this exemplary embodiment, too, a plastics spiral  26  is produced around a pipe  46 . In this case, too, the pipe  46  remains static during the production of the plastics spiral  47 . 
     The plastics spiral  47  has spaced-apart turns or rings of a winding  53 . The opposite face surfaces  48 ,  49  of the plastics spiral  47  are profiled. In the exemplary embodiment shown, the face surfaces  48  and  49  are of identical profile, specifically are each provided with a central groove  50 . Any other desired designs of the face surfaces  48  and  49  can be produced by means of the exemplary embodiment shown. 
     A planar inner shell surface  51  of the plastics spiral  47  bears against the pipe  46 , which has a smooth cylindrical outer shell. The inner shell surface  51  is connected to the shell surface of the pipe  46 . This may be realized by shrink-fitting, sealing and/or adhesive bonding during the production of the plastics spiral  47  around the pipe  46 . In the exemplary embodiment shown, an inner shell surface  52  of the plastics spiral  47  is of smooth form. The outer shell surface  52  may however also have any other desired profiles, in particular may be profiled in the same way as the face surfaces  48  and  49 . 
     The plastics spiral  47  that is shown is flexible, in particular owing to its spaced-apart windings  53 , such that it does not significantly impair the bending characteristics of the encased pipe  46 , or some other cylindrical article, that serves as a core. For the pultrusion of the plastics spiral  47  that is reinforced with strands (not shown in  FIGS. 9 to 11 ), use is made of a mold  54  which completely surrounds the pipe  46  and which extends over the pipe  46  along a longitudinal central axis to such an extent that the mold  54  engages over multiple turns of the winding  53  of the plastics spiral  47 . In the pultrusion direction  56 , that is to say the direction in which a newly pultruded section of the plastics spiral  47  is pushed out or ejected from the mold  54  in stepped fashion, the mold  54  is followed by a gripper  57  which, like the mold  54 , completely surrounds the pipe  46 , specifically also covering multiple turns of the winding  53  of the plastics spiral  47 . When the gripper  57  has been moved into contact with the mold  54 , it is the case in the exemplary embodiment shown that an exit surface  58  of the mold  54  bears against a starting surface  59  of the gripper  57  ( FIG. 9 ). 
     The mold  54  has a cutout  62  in a cylindrical surface  61  which is situated at the front in a gradient direction  60  of the plastics spiral  47 . A surface of the cutout  62  running in an approximately radial orientation with respect to the pipe  46  surrounds an entry surface  63  for the entry of the strands, which serve for reinforcement, into the mold  54  ( FIG. 9 ). The strands, fibers or the like that serve for reinforcement can enter the mold  54 , from a material supply which is not shown in  FIGS. 9 to 11 , through the entry surface  63 . In this exemplary embodiment, too, the at least one material supply (not shown) for, in particular, multiple strands is connected to the gripper  57  such that the two form a unit and are jointly movable. 
     The method for the pultrusion of the plastics spiral  47  on the pipe  46  proceeds, in principle, in the same way as in the preceding exemplary embodiment ( FIGS. 6 to 8 ). Accordingly, the mold  54  and the gripper  57  with the material supply are moved around the, in this case, static pipe  46  during the pultrusion of the plastics spiral  47 , wherein, as the production of the plastics spiral  47  progresses, the mold  54  and the gripper  57  with the material supply rotate in spiral fashion around the pipe  46  counter to the pultrusion direction  56 , that is to say in the “growth direction” of the plastics spiral  47 , and, in the process, perform an upward (ascending in the views in  FIGS. 10 and 11 ) screw-type movement in the longitudinal direction of the pipe  46  and gradient direction of the plastics spiral  47 . 
     Here, too, the mold  54  is rotated clockwise about the pipe  46  in stepped fashion through a certain angle range, wherein a newly pultruded section of the plastics spiral  47  emerges from the exit surface  58  of the mold  54  rearward, so to speak, in the pultrusion direction  56 . Here, the mold  54  travels onward on the pipe  46  in helical fashion in the production direction, specifically the “growth direction” of the plastics spiral  47 . After a new piece of pultruded plastics spiral  47  has been demolded from the mold  54  with the plastics spiral  47  being held by the gripper  57 , it is provided that, analogously to the illustration in  FIG. 7 , the gripper  57 , which has been released again from the plastics spiral  47 , is moved, together with the material supply, behind the mold  54  again, specifically by being rotated about the longitudinal central axis  55  of the pipe  56 . Subsequently, the mold  54  on its own is again moved onward in the production direction or “growth direction” of the plastics spiral  47  with the gripper  57  closed, and then the opened gripper  57  together with the material supply then performs, so to speak, a follow-up movement. 
     Because it is the case in the exemplary embodiment shown that both the mold  54  and also the gripper  57  completely surround the pipe  46  and furthermore extend over multiple windings  53  of the plastics spiral  47 , it is possible for every production step, specifically rotation firstly of the mold  54  relative to the plastics spiral  47 , which in this case is held static by the gripper  57 , and secondly of the gripper  57  together with the material supply, to be larger than in the above-described exemplary embodiment of  FIGS. 6 to 8 . One full rotation of the mold  54  and subsequently of the gripper  57  with the material supply about the longitudinal axis  55  of the pipe  46 , and possibly even more than one rotation, would be conceivable. 
     In a further exemplary embodiment of the invention (not shown), the exemplary embodiment of  FIGS. 9 to 11  is modified such that the mold  54  and the gripper  57  do not extend as far as the pipe  46  between successive rings or turns of the winding  53 , but rather end with a spacing to the outer shell surface of the pipe  46 . In this way, the pipe  46  is surrounded by a continuous plastics outer wall, wherein the plastics spiral  47  is formed integrally on the outside of the plastics outer wall. By means of a corresponding thickness of the outer wall that completely surrounds the pipe  46 , the flexibility of the plastics spiral  47  with the plastics wall completely surrounding the pipe  46  can be varied as desired. By means of the albeit only thin outer plastics wall, the pipe  46  is completely coated with plastic, specifically even between the turns of the winding  53 . This results in a pipe  46  that is completely protected against external influences, or some other article that is surrounded by the plastics spiral  47  with continuous inner plastics pipe or hose. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  Plastics pipe 
           11  Winding 
           12  Longitudinal central axis 
           13  Face surface 
           14  Face surface 
           15  Mold 
           16  Gripper 
           17  Outer shell surface 
           18  Inner shell surface 
           19  Mold cavity 
           20  Entry surface 
           21  Pultrusion direction 
           22  Exit surface 
           23  Gripper part 
           24  Gripper part 
           25  Pipe 
           26  Plastics spiral 
           27  Shell surface 
           28  Winding 
           29  Face surface 
           30  Face surface 
           31  Spacer strip 
           32  Mold 
           33  Gripper 
           34  Cavity 
           35  Outer shell surface 
           36  Inner shell surface 
           37  Pultrusion direction 
           38  Entry surface 
           39  Longitudinal central axis 
           40  Strand 
           41  Material supply 
           42  Entry surface 
           43  Exit surface 
           44  Pultrusion direction 
           45  Connection 
           46  Pipe 
           47  Plastics spiral 
           48  Face surface 
           49  Face surface 
           50  Groove 
           51  Inner shell surface 
           52  Outer shell surface 
           53  Winding 
           54  Mold 
           55  Longitudinal central axis 
           56  Pultrusion direction 
           57  Gripper 
           58  Exit surface 
           59  Starting surface 
           60  Gradient direction 
           61  Front surface 
           62  Cutout 
           63  Entry surface