Abstract:
A window arrangement on a pressure pipe, with a casing in the train or at the end of the pressure pipe, said casing featuring flanges on diametrically opposing sides having radially directed passages, whose axes are standing perpendicular to the longitudinal axis of the pressure pipe and are located in a measurement plane for an x-ray measurement device, an x-ray source being associated to the one passage on the outer side and a receiver sensitive to X-rays to the other passage, and with window plates that are transmissive for X-rays which are sealingly arranged in the associated passage and are fixed in the passage with the aid of a fastening member and which consist of a material which is resistant against high temperatures and process-due etchings by chemically aggressive substances.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention is related to a window arrangement on a pressure pipe, preferably for the vulcanisation or crosslinking of sheathings of electric cables. 
         [0004]    In the manufacture of cables, the cable sheathing is extruded on the cable core with the aid of an extruder. By crosslinking the cable coating consisting of plastic material, the plastic mass is made elastic. The crosslinking or vulcanisation, respectively, of the plastic material takes place in a pressure pipe, in which there are relatively high temperatures and a significant overpressure, for instance temperatures up to 550° C. and pressures up to 30 bars. 
         [0005]    It is known to determine the diameter of cable sheathing and/or the thickness of individual layers of the cable sheathing with the aid of an x-ray measurement device. The x-ray measurement device features an x-ray radiation source and an x-ray sensitive receiver. The latter is for instance made up of individual x-ray sensitive elements, which are sensed in series. 
         [0006]    When a determination of wall thickness and/or diameter of a cable is to be performed during its passage through the pressure pipe, the x-ray measurement device must be arranged in the train of the pressure pipe. It is known to use separate casings for this, which are aligned to diametrically opposing passages in the pressure pipe, through which the measurement plane of the x-ray measurement device extends perpendicularly to the longitudinal axis of the pressure pipe. The passages are sealingly closed by a window plate, which is easily transmissive for x-rays. 
         [0007]    It is known to provide thin window plates made of beryllium. Of the metals, beryllium has the lowest absorption of x-rays, at equal values of strength. The beryllium plates are fixed against a shoulder in the passage together with a flat seal, namely by a projection of a so-called T-flange, which is fastened on the casing on the outside by screwing. The beryllium plate is pressed against a passage shoulder via the seal under high pressure with the aid of the T-flange. 
         [0008]    Beryllium is considered to be highly toxic, and beryllium dust is carcinogenic. 
         [0009]    For this reason and in order to improve the corrosion resistance of the beryllium plates, the same are overlaid with a ceramic layer for instance. During the operation in the pressure pipe, condensate accumulates in the lower region of the beryllium window, and together with sulphur- and chlorine containing components it causes corrosion of the beryllium. Carcinogenic beryllium particles can reach the operation control region when beryllium plates become permeable by corrosion pressure and are ejected into the atmosphere through this. Ceramic and also metal coatings of the beryllium plate in order to avoid corrosion have proven to be effective only in a limited extent, because of too small layer thicknesses. 
         [0010]    It is also known to arrange a protective foil before the beryllium plate for protection purposes. Like a coating, the same can be damaged when solid residues which had been precipitated on the beryllium foil are being removed. 
         [0011]    Finally, in the conventional arrangement of beryllium plates a sumptuous examination of the placement of the seals is necessary after the installation, in particular in order to avoid a leakage, because in such cases beryllium particles could arrive in the air of the surroundings. 
         [0012]    The present invention is based on the objective to provide a window arrangement on a pressure pipe, preferably for the vulcanisation or crosslinking of sheathings of electric cables, which is less prone to corrosion and permits a drain-off of the condensate. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    The present invention provides for condensation of the gas atmosphere on the window plate. The latter is arranged such that the condensate can drain off without hindrance and drags dirt particles along in doing so. The condensate loaded with dirt flows into the pressure pipe. This self-cleaning effect reduces the corrosion of the window plate and increases its operation life. 
         [0014]    In the window arrangement of the present invention, the window plate is preferably formed of a ceramic material. Ceramic material is corrosion resistant, as is commonly known. Moreover, ceramic material is physiologically unobjectionable. An additional coating as a corrosion protection is not necessary. Solid deposits can be easily removed from a window plate made of ceramics without impairing the window plate in its function. 
         [0015]    In fact, ceramics has lower transmission ability for x-rays than beryllium; 
         [0016]    however, the higher attenuation can be compensated by increasing the x-ray current or the x-ray energy. 
         [0017]    Alternatively, titanium, carbon fibre reinforced plastics, or a combination of these materials can also be used. Particularly preferred is PEEK (polyetheretherketone). Plastics tolerate relatively high temperatures, for instance 250° C., but are then no longer pressure resistant. One embodiment according to the present invention therefore provides to coat the plastics on the inner side with a metal foil, preferably titanium foil. 
         [0018]    By the coating, an improved heat dissipation, a reflection of the heat radiation from the hot protective gas (up to 400° C.), and due to the bright surface, a self-cleaning ability are achieved. Because of its smooth surface, the window allows easier cleaning. The window of the present invention is non-toxic, mechanically stable and chemically resistant. The cited properties lead to a longer operating lifetime. 
         [0019]    According to one embodiment of the present invention, the window plate bears against a ring seal on the pressureless side, against an O-ring for instance. The mounting of the window plate can be such that the same bears against the seal with a certain bias. With increasing pressure in the pressure pipe, the window plate is pressed more strongly against the sealing ring. This measure permits a more uniform distribution of the forces which act on the window plate and the seal. A window plate made of a brittle material, like ceramics e.g., is therefore not inadmissibly loaded. 
         [0020]    According to another embodiment of the present invention, the window plate is held by lateral holder elements, which can be formed by longitudinal clamps according to a further embodiment of the invention, which on their part are fixed by the side walls of the passage or of the pressure pipe, respectively. The clamps are preferably U-shaped and bear against the pressure pipe side of the window plate with one leg, and with the other leg they engage into a recess that is stationary with respect to the pressure pipe, in order to effect the fixation of the window plate. In this, the legs extend approximately over the length of the window plate and cover a part of its area. However, the portion of the area located between the legs is sufficiently large to permit the passage of x-rays. 
         [0021]    Moreover, the mounting of the window plate is such that condensate draining off on the window plate can flow back into the pressure pipe, bypassing the holder element in the region thereof without accumulating on a certain spot and impairing the window plate. 
         [0022]    In order to reduce the impairment of the window by heat, in the region of the lower window in particular, and to facilitate the condensation in particular, one embodiment of the present invention provides that at least one cooling channel for the flow of a cooling agent is associated to the window arrangement, for instance of water. When a so-called T-flange is used against which the window plate bears, it is advantageous to surround the flange by an annular body in which a cooling channel is formed. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0023]    An example of the realisation of the present invention is explained in more detail in the following by means of drawings. 
           [0024]      FIG. 1  shows a portion of a pressure pipe for the production of electric cables with a window arrangement according to the present invention; 
           [0025]      FIG. 2  shows a section through the arrangement after  FIG. 1  along the line  2 - 2 ; 
           [0026]      FIG. 3  shows a section through the arrangement after  FIG. 2  along the line  3 - 3 ; 
           [0027]      FIG. 4  shows a view according to the arrow  4  of the depiction after  FIG. 2 ; 
           [0028]      FIG. 5  shows the view  5  of the depiction after  FIG. 2 ; 
           [0029]      FIG. 6  shows a part of the detail  6  after  FIG. 3  in a magnified view; 
           [0030]      FIG. 7  shows the detail  6  after  FIG. 3  in a magnified view; 
           [0031]      FIG. 8  shows a section similar to  FIG. 6  or  7 , but according to the state of the art; 
           [0032]      FIG. 9  shows the detail  9  after  FIG. 3  in a magnified view; 
           [0033]      FIG. 10  shows a section through a window plate for the shown window arrangements; and 
           [0034]      FIG. 11  shows a section through a modified embodiment of a lower window arrangement. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated. 
         [0036]    In the figures, a portion  10  of a pressure pipe is shown, for instance for crosslinking sheathings of electric cables  13 . However, the pressure pipe portion  10  can also be provided as an independent portion, which is welded into the train of the relatively long pressure pipe. 
         [0037]    The pressure pipe portion  10  has diametrically opposing flanges  11  and  12 , radially directed towards the outside, which form a passage  14  or  15 , respectively, approximately slit-shaped in cross section. The shaping of the flanges  11 ,  12  and the further parts, respectively, that are associated to the passages  14  and  15 , respectively, emerge more clearly from the  FIGS. 6 and 7 . In  FIG. 7 , a flange body  34  can be recognised with an outer flange  32 , which is screwed against the wall of the pressure pipe portion  10  at the outside, with the aid of screws  33 . As can be recognised in  FIG. 3  in particular, the pressure pipe portion  10  is reinforced towards the inside in this region by a thickening  37 . When “inside” and “outside” are mentioned above and below, this refers to the pressure pipe, i.e. to its interior or exterior, respectively. The flange body  34  features a sleeve portion  30   a,  which is introduced into the passage  15 . The perimeter of the sleeve portion  30 , which is longitudinal perpendicularly to the drawing plane, is shaped corresponding to the cross section of the passage  15  and longitudinal, wherein a gap is left free between the outer side of the sleeve portion  30   a  and the wall of the passage  15 . A seal  31  is inserted between the flange  32  and the outer side of the pressure pipe  10 . 
         [0038]    The flange  32  with sleeve portion  30   a  forms a continuous passage  39  with a slit-shaped cross section. 
         [0039]    A window plate  20  made of ceramics or plastics is laid against the free end of the sleeve portion  30   a.  In an annular recess on the front side of the sleeve portion  30   a  is embedded an O-ring  24 , which projects somewhat over the front side of the sleeve portion  30   a  in its released condition. The window plate  20  is pressed against the free end of the sleeve portion  30   a  with the aid of two longitudinal clamps  26 ,  28  having a U-shaped cross section, and is held in place on it by doing so, the O-ring  24  being set under a small bias. The one inner leg  29  of the clamps  26 ,  28  is sunk in a corresponding recess of the window plate  20  in  FIG. 6 . Therefore, the leg  29  is flush with the outer side of the window plate  20 , which faces the interior of the pressure pipe  10 . The other leg  27  engages into a recess  33  at the outer side of the sleeve portion  30   a,  in order to fix the window plate  20 . The leg  27  is somewhat bent in the direction of the other leg  29 , in order to generate a torque in the direction towards the window plate  20 . The bridge of the U-clamps  26 ,  28  extends in the gap between the wall of the passage  15  and the outer side of the sleeve portion  30   a.    
         [0040]    Condensate being formed in the pressure pipe  10  can drain off, as indicated in  FIG. 1  by the arrow  17 . The pressure pipe has a down-grade α ( FIG. 1 ). Besides to that, it flows according to the arrow  25  in  FIG. 2 . This is caused by the skew arrangement of the window plate  20  ( FIG. 2  or  6 ). Therefore, it can be recognised in  FIGS. 6 and 7  that condensate depositing on the window plate  20  can drain off from left to right, without being prevented from doing so by measures for fastening the window plate  20 . The condensate flows back directly into the interior of the pressure pipe  10 . 
         [0041]    The arrangement of the window plate  20  can be such that the temperatures always remain below the dew point of the gas atmosphere in the pressure pipe  10 . However, it is also conceivable to provide suitable cooling measures, so that the temperature of a window plate  20  is always below the dew point. 
         [0042]    In  FIG. 4 , the shape of the window plate  20  and the extension of the legs  29  of the springs  26 ,  28  can be clearly recognised. The springs are formed from a suitable flat material. The legs  29  extend over a great part of the length of the window plate  20 , but have a sufficient distance between them to permit the passage of x-rays. With respect to this, it has to be mentioned that suitable measures for the through irradiation of the interior of the pressure pipe  10  with an x-ray beam, and for receiving the x-ray beam by a suitable x-ray receiver (not shown) are associated to the flanges  11 ,  12 . This x-ray arrangement serves for measuring the sheathing of electric cables which are crosslinked in the pressure pipe, as is per se known. However, this is not depicted in detail. 
         [0043]    The detail  9  after  FIG. 3  is depicted in  FIG. 9 . One recognises a window plate  18  according to the state of the art, which is set into a recess of the flange  11 , a seal or a sealing ring  37  being interconnected there between. The window plate  18  is pressed against the flange  11  with the aid of a flange  22 . The flange  22  is screwed onto the flange  11  with the aid of screws  39 . However, the window plate can also consist of plastic material, of PEEK for instance, which is coated with a titanium foil in order to achieve the advantages mentioned above. 
         [0044]    In  FIG. 6 , the thickening  37  on that side of the passage  15  that is at the front side in the production direction features a portion  50 , which projects farther into the pressure pipe  10  than the window plate  20 . In case that a cable slacks downward, it is prevented from coming into contact with the window plate  20  by this. The window plate  20  is in addition protected by the clamps  26 ,  28  in  FIG. 7 . 
         [0045]      FIG. 8  shows a lower window arrangement in the position of  FIG. 2  according to the state of the art, with a flange body  34   a,  which receives a window plate from beryllium in a recess located in the interior, which is pressed against the shoulder and the passage  15   a  by way of a seal  24   a.    
         [0046]    The window plate  20  is shown in a section in  FIG. 10 . It consists of a longitudinal plate  60  from plastics, PEEK in particular, which is coated with a titanium foil  62  on the inner side. The titanium foil  62  faces the interior of the window plate; therefore it effects a dissipation of heat as well as a reflexion of the heat radiation which is caused by the protective gas in the pressure pipe. The bright surface of the titanium foil  62  permits a self-cleaning effect, and moreover it can be cleaned easily. A window plate as depicted in  FIG. 10  can also be used for the upper window arrangement, like that depicted in  FIGS. 2 and 3  or  9 , respectively. 
         [0047]    In  FIG. 11 , the sleeve-shaped portion of the flange body  34  is surrounded by one of the ring bodies  64 , which is connected to the pressure pipe in a suitable way (not shown). The ring body  64  projects somewhat over the window plate  20  towards the inside, as can be clearly recognised in  FIG. 11 . By this, it provides a protection against a collision of a cable with the window  20 . 
         [0048]    The ring body  64  is provided with a cooling channel  66 , through which water can flow as a cooling agent. 
         [0049]    This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.