Patent Publication Number: US-2007107480-A1

Title: Device for forming a peripherally closed hollow profiled element by means of fluidic internal high pressure

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
      This invention relates to a device for forming a peripherally closed hollow profiled element by means of fluidic internal high pressure.  
      A device of this general type is known from German document DE 199 05 849 C1. The device described there comprises an internal high pressure forming die, in the forming space of which a hollow profiled element can be laid, while the peripherally closed hollow profiled element is to be expanded into a final form by means of fluidic internal high pressure during the closing of the internal high pressure forming die. The device comprises, furthermore, an axial plug, by means of which the hollow profiled element is to be sealed off on the end face and which possesses an axial passage duct, via which a pressure fluid can be introduced into the hollow profiled element interior for expansion. The plug head of the axial plug penetrates into the hollow profiled element according to  FIG. 5  and  FIG. 7  of the German document, is designed as an elastic sealing body, and consists of polyurethane. The elastic sealing body has, on its end face, a trough-like depression, of which the peripheral wall projecting into the hollow profiled element can be spread radially elastically, during the expansion process, by means of a pressure fluid, until it comes to bear sealingly against the inner wall of the hollow profiled element. If, then, an axial plug designed in this way is pushed into the hollow profiled element, the sealing body of the axial plug comes unavoidably into contact with the sharp inner edge, often having metal chips, of the hollow profiled element end, so that the sealing body is damaged simply even when being pushed into the hollow profiled element. Further damage to the sealing body occurs when the axial plug is drawn out after the expansion of the hollow profiled element has taken place. Admittedly, this problem is to some extent remedied, on the one hand, in that the sealing body has integrated into it beforehand a wearing strip which comes into contact essentially with the inner edge of the hollow profiled element end or, on the other hand, by the arrangement of a steel attachment which carries the sealing body, only its outside coming in contact with the inner edge of the hollow profiled element end. However, these measures, on the one hand, are relatively complicated in terms of production and, on the other hand, do not afford sufficient sealing off of the hollow profiled element with respect to the pressure fluid flowing into the hollow profiled element for expansion. Furthermore, the wearing strip and that part of the steel attachment which comes in contact with the hollow profiled element are likewise subjected to wear, thus leading to a failure of sealability after multiple uses of the axial plug.  
      The object on which the invention is based is to develop a device having a sealability which is maintained permanently.  
      This object is achieved, according to the invention, by means of the features claimed.  
      By designing the plug and the sealing body according to the invention, the latter is sufficiently protected from contact with the inner edge of the hollow profiled element end by that projection of the plug head which is formed by the annular collar of the latter, when the plug head is being pushed into the hollow profiled element. In the pushed-in position of the axial plug, the annular collar lies with only slight play within the hollow profiled element, so that it is possible that the annular collar comes briefly into contact with the hollow profiled element end when the axial plug is pushed in. Since the annular collar does not necessarily have to implement the provisional sealability of the axial plug, but, instead, this provisional sealability is fulfilled by a radially projecting stop, adjoining the annular collar, of the axial plug, the wear on the annular collar which may occur due to contact with the hollow profiled element end is only marginal. Thus, in the position of use of the axial plug, the annular collar lies within the hollow profiled element, without a press fit, which is known from the prior art, being formed between said annular collar and the hollow profiled element end. By designing the sealing body as a sealing ring, the latter can be mounted in a simple way on the plug head. Moreover, the sealing body can easily be exchanged when this is considered necessary in the case of different hollow profiled elements. It is therefore not necessary to employ a different axial plug in each case for each intended use, that is to say for different hollow profiled elements having a different diameter or cross section. The outlay in terms of apparatus for the device according to the invention is therefore simplified considerably. Owing to the protection afforded to the sealing ring by the annular collar, the sealability of the axial plug and consequently of the device is maintained permanently.  
      In a preferred configuration of the invention, the margin of the annular collar narrows conically toward the end face of the plug head. This gives rise within the hollow profiled element, behind the sealing ring, to an annular chamber into which the pressure fluid entering the hollow profiled element via the axial passage duct of the axial plug can partially flow past the sealing ring. This gives rise to a suction action on the sealing ring, with the result that the peripheral wall of the latter is spread open more quickly.  
      In a particularly preferred embodiment of the invention, the sealing ring is supported on the end face of the annular collar. As a result, the sealing ring acquires particularly reliable large-area bearing contact and is fixed on the plug head on one side in the axial direction against slipping out of place. The end face at the same time forms a stop for the sealing ring, so that the sealing ring acted upon by the flow can spread open.  
      In a further preferred configuration of the invention, the sealing ring is supported on its depression bottom, in the direction of the end face of the plug head, by means of a positioning ring which is embedded in a groove of the extension. As a result of the arrangement of the positioning ring, the sealing ring is fixed axially with respect to the end face of the plug head.  
      In a further preferred configuration, a spacer ring is arranged between the positioning ring and the depression bottom of the sealing ring. By virtue of the arrangement of a spacer ring, not only can the positioning ring and consequently the sealing ring be mounted more simply in its fixing, but it is then also possible, during mounting, to press the sealing ring against the annular collar via the spacer ring and, after the positioning ring has been embedded in the groove of the extension, to leave the sealing ring in its prestressed position. What is achieved by the sealing ring being pressed against the annular collar is that the pressure fluid, which, when it flows into the hollow profiled element, flows for a short time around the sealing ring, cannot penetrate into the gap between the sealing ring and the annular collar of the plug head and consequently undermine the sealability of the sealing ring.  
      In a further advantageous embodiment of the invention, an annular bead, which projects radially beyond the entire annular collar of the plug, is formed on the outside of the sealing ring. By means of the annular bead, which has a slight oversize with respect to the inside diameter of the hollow profiled element, provisional sealing off is achieved even when the axial plug is being pushed into the hollow profiled element, since the annular bead can bear elastically against the inner wall of the hollow profiled element. Although the annular bead undergoes specific wear when it penetrates into the hollow profiled element since it comes into contact with the inner edge of the hollow profiled element, the sealabilty of the sealing ring as a whole is not adversely affected, since the wear does not encroach upon the actual sealing ring. Owing to this provisional sealing off, when the pressure fluid flows into the hollow profiled element interior there is no leakage which could escape from the gap occurring during bearing contact between the stop of the plug body and the hollow profiled element.  
      In a further preferred embodiment of the invention, on the outside of the sealing ring has incorporated in it, near its end face facing away from the annular collar, a peripheral groove, which receives a retaining ring possessing an elasticity identical to or deviating from that of the sealing ring. The retaining ring, which may consist of a hard material, such as, for example, polytetrafluoroethylene or the like, and is so thin that it does not come into contact with the inner edge of the hollow profiled element when the plug head penetrates into the latter and therefore does not undergo any wear, has the effect that the sealing ring is best protected against being folded round and extruded into the gap occurring during bearing contact between the stop of the plug body and the end of the hollow profiled element. Within the scope of the invention, however, it is also conceivable that the retaining ring, which to some extent holds the sealing ring together when the latter is spread open, is actually configured such that it can assume the function of the abovementioned annular bead.  
      In a further preferred configuration of the invention, a circular centering plate provided with eccentric passage bores and projecting peripherally beyond the sealing ring radially is arranged, with a central leadthrough, on the extension, so as to precede the sealing ring toward the end face of the plug head. The arrangement of the centering plate has an advantageous effect, in the case of nonround tubes, in that it is introduced into the hollow profiled element virtually as a protective shield in front of the sealing ring and at the same time centers the axial plug within the nonround tube. The sealing ring consequently cannot come into wearing contact with the hollow profiled element. The eccentric passage bores are intended to allow the introduced pressure fluid to flow onto the sealing ring, so that the latter can exercise its spreading-open movement and therefore its sealability.  
      The invention is explained in more detail below by means of several exemplary embodiments illustrated in the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a lateral longitudinal section through a detail of an axial plug of a device according to the invention, in the position of use within the hollow profiled element,  
       FIG. 2  shows a lateral longitudinal section through the axial plug of  FIG. 1 , with an annular bead formed on a sealing ring of the axial plug,  
       FIG. 3  shows a lateral longitudinal section through the axial plug of  FIG. 1 , with a retaining ring embedded on the outside on a sealing ring of the axial plug,  
       FIG. 4  shows a lateral longitudinal section through the axial plug of  FIG. 1 , with a centering plate preceding a sealing ring of the axial plug on the end face. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  illustrates a device for forming a peripherally closed hollow profiled element  1  by means of fluidic internal high pressure, said device containing an internal high pressure forming die  2 , in the forming space  3  of which the hollow profiled element  1  is laid. The device contains, furthermore, at least one axial plug  4  for sealing off the hollow profiled element  1  on the end face. The axial plug  4  possesses a centrally running axial passage duct  5  which supplies pressure fluid to the hollow profiled element  1  and which is connected at an end  6  facing away from a hollow profiled element to a fluid high pressure generation system conveying the pressure fluid and which issues on the end face  7  of its plug head  8  penetrating into the hollow profiled element  1  in the position of use. The plug head  8  capable of being pushed into the hollow profiled element  1  is rigidly connected to the remaining plug body  9  of the axial plug  4  and is formed by an annular collar  10  shaped out on the axial plug  4  and by a narrowed extension  11  adjoining said annular collar toward the end face  7  of the head  8 . The extension  11  is arranged centrally and has the passage duct  5  passing through it. The axial plug  4  has, furthermore, on its plug body  9 , a radially peripheral stop which, in the position of use of the axial plug  4 , bears against the closing edge  12  of the hollow profiled element end  13 . The stop is formed here by the end face  14  of a sleeve  15  screwed onto the plug body  9  or fastened to the plug body  9  in another way. For positioning the sleeve  15  during mounting on the plug body  9 , the end face  14  of said sleeve butts against the rear side  16  of the annular collar  10 .  
      The axial plug  4  carries a sealing body which is designed as a sealing ring  17  pushed or slipped onto the extension  11  of the plug head  8 . In this case, the sealing ring  17  is supported on the end face  18  of the annular collar  10 , said end face facing the hollow profiled element  1 . The sealing ring  17 , spreadable in a radially elastic manner, consists, for example, of an elastomer or polyurethane. It has, on its end face  19  facing the hollow profiled element  1 , a trough-like depression  20 , the peripheral wall  21  of which, by means of the inflowing pressure fluid, undergoes the spread within the hollow profiled element  1  until it comes to bear sealingly against the inner wall  22  of the hollow profiled element  1 . The sealing ring  17 , furthermore, is supported on its depression bottom  23 , in the direction of the end face  7  of the plug head  8 , by means of a positioning ring  24  which is embedded in a groove  25  of the extension  11 . Moreover, a spacer ring  26  is arranged between the positioning ring  24  and the depression bottom  23  of the sealing ring  17 . By support by means of the positioning ring  24  and the spacer ring  26 , on the one hand, and by support on the end face  18  of the annular collar  10 , the sealing ring  17  is fixed axially to the plug head  8 . The outside diameter of the sealing ring  17  is selected such that it lies with some play within the hollow profiled element  1  in the position of use of the axial plug  4 . Furthermore, the outside diameters of the outside  27  of the sealing ring  17  and of the margin  28  of the annular collar  10  are coordinated with one another such that the latter projects peripherally beyond the sealing ring  17  at least one point in the radial direction. That is to say, on the annular collar  10 , there is at least one point which is peripherally larger radially than the entire outside  27  of the sealing ring  17 . The margin  28  of the annular collar  10 , moreover, narrows conically toward the end face  7  of the plug head  8 , thus forming, between the margin  28  of the inner wall  22  of the hollow profiled element  1  and the rear side  29 , supported on the annular collar  10 , of the sealing ring  17 , a small annular chamber  30  into which a part quantity of the pressure fluid can briefly flow during filling.  
      If, then, the hollow profiled element  1  is filled via the passage duct  5  of the axial plug  7  with the pressure fluid conveyed by the fluid high pressure generation system, said pressure fluid flows in back stroke into the depression  20  of the sealing ring  17 , with the result that, on account of the flow pressure on the peripheral wall  21  of the elastic sealing ring  17 , the latter spreads open until said wall is pressed against the inner wall  22  of the hollow profiled element  1 . At the same time, as already mentioned, a part quantity of pressure fluid flows past the sealing ring  17  into the chamber  30 , with the result that a suction action occurs which assists the spreading of the sealing ring  17  and consequently accelerates sealing off during filling. The trough shape of the depression  20  serves in this case for a better conversion of the flow force of the inflowing pressure fluid into a radial spreading movement of the peripheral wall  21  of the sealing ring  17 . If, then, the hollow profiled element  1  is formed, the pressure fluid is put under high pressure, with the result that the peripheral wall  21  of the sealing ring  17  is pressed to an extreme extent against the inner wall  22  of the hollow profiled element  1 , so that a sealing off of the hollow profiled element  1  which is tight to fluid high pressure is ensured outwardly.  
      A variant of the invention is shown in  FIG. 2 . In this case, on the outside  27  of the sealing ring  17 , an annular bead  31  is formed, which projects radially beyond the entire annular collar  10  of the plug  4  and which is located near the end face  19  of the sealing ring  17 . The annular bead  31  may be injection-molded onto the sealing ring  17  at a later stage or else be shaped at the same time as the production of the latter. On account of the annular bead  31 , sealing off is afforded even during the penetration of the axial plug  4  into the hollow profiled element  1  before the filling operation.  
      In a further variant of the invention according to  FIG. 3 , contrary to the variants of  FIGS. 1 and 2 , the outside  27  of the sealing ring  17  has incorporated in it, near its end face  19  facing away from the annular collar, a peripheral groove  32  which receives a retaining ring  33  possessing a lower elasticity than the sealing ring  17 . If there is an oversize of the retaining ring  33  with respect to the diameter of the inner wall  22  of the hollow profiled element  1 , the retaining ring  33 , preferably designed as a quad ring or O-ring, assumes the provisional sealing function at the commencement of the filling process. By virtue of its contracting action on the sealing ring  17 , the retaining ring  33  gives the sealing ring  17  better protection against being folded round and extruded into the interspace between the plug head  8  and the inner wall  22  of the hollow profiled element  1 .  
      In contrast to the preceding exemplary embodiments, in a variant of the invention according to  FIG. 4 , the extension  11  has arranged on it a centering plate  34  which peripherally projects radially beyond the sealing ring  17  and the annular collar  10 . The centering plate  34  precedes the sealing ring  17  toward the end face  7  of the plug head  8  and is fastened to the extension  11  by means of a central leadthrough  35 , and, for mounting, it is advantageous if, as here, the centering plate  34  can be screwed onto the extension  11 . So that the introduced pressure fluid can flow onto the sealing ring  17  in spite of the preceding centering plate  34 , with the result that the spreading movement can take place, eccentric passage bores  36  are formed in the circular centering plate  34 .  
      In all the abovementioned variants, it is additionally conceivable that one or more radial ducts, which issue into the depression  20  of the sealing ring  17 , branch off from the passage duct  5  of the axial plug  4  at the location of the depression  20 . The peripheral wall  21  of the sealing ring  17  can thereby be acted upon, even in an early phase of the filling operation, by pressure fluid via the radial ducts as a result of a branch-off and at the same time be spread open. Very early sealing off is provided in this case.  
      By means of the device according to the invention, which makes it possible for the hollow profiled element  1  to be sealed off outwardly without any axial force, it is possible, as compared with seals not free of axial force, to expand hollow profiled elements  1  by means of internal high pressure and to calibrate them, without shortening the component length, since the axial force, which, when the hollow profiled element  1  is being sealed off, leads to a component-shortening thickening of the hollow profiled element end, is dispensed with. At the same time, creases are also avoided, which normally arise due to the sealing force fraction of the axial plugs in the case of seals not free of axial force. Moreover, via the sleeve  15 , an axial secondary push during forming may take place at any time, as required, during the forming process.