Abstract:
A flat ring packing to be placed between two flanges comprises two packing layers of packing material and an intermediate ring of metal, which is disposed between the two packing layers and has a common central longitudinal axis therewith. Each packing layer is fixed on the intermediate ring substantially without play radial and parallel to the axis by means of a connection.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a flat ring packing to be placed between two flanges and comprising two packing layers of packing material and an intermediate ring of metal which is disposed between the two packing layers and has a common central longitudinal axis therewith. 
     2. Background Art 
     Flat ring packings of the generic type are used for instance in pharmaceutical and foodstuff industry. In this case, a prerequisite resides in that the flanged joints do not exhibit any so-called wake spaces, i.e. spaces of poor flow. This is why the flat ring packings on the one hand and the pipes and apparatuses which the flanges are mounted on are to have identical inside diameters. 
     In known flat ring packings provision is made for an intermediate ring which is inserted into a sleeve of packing material. This one-piece sleeve forms packing layers which are joined to each other undivided in the radially inner area. In this case, radial play and also axial play must be available between the intermediate ring and the sleeve which comprises the packing layers in order that any tearing of buckling of this sleeve during assembly be avoided. It is difficult to center the sleeve of packing material and the intermediate ring of metal between the to-be-connected flanges in such a way that no wake spaces will form relative to the pipes. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to embody a flat ring packing of the generic type such that the packing layers and the intermediate ring are accurately centered relative to each other. 
     According to the invention, this object is attained in that each packing layer is fixed on the intermediate ring substantially without play radial and parallel to the axis by means of a connection. This design helps achieve that any displacement of the packing layers relative to the intermediate ring in the radial direction is precluded. In this way no wake spaces can form on the flanged joints. The layers can be mounted in the way of a snap connection on the intermediate ring and can again be released therefrom and replaced by fresh ones. The kind of connection of the packing layers to the intermediate ring ensures that there are no materials such as glue which might be passed on to the media flowing in the pipes. The flat ring packing consists exclusively of the two packing layers and the intermediate ring. 
     Numerous advantageous embodiments will become apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a cross-sectional view of a flanged joint with a flat ring packing according to the invention; and 
     FIG. 2 is an illustration of the portion X in FIG. 1 on an enlarged scale. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a flanged joint of two pipes  1 ,  2 , the ends of which turned toward each other are provided with a flange  3  and  4 . The flanges comprise drilled holes  6 ,  7  which are in alignment concentrically of the central longitudinal axis  5  of the pipes  1 ,  2  and of which only one pair is illustrated. The flanges  3 ,  4  and thus the pipes  1 ,  2  are tightly joined to each other through these drilled holes  6 ,  7  by means of screws  8  and nuts  9 , a washer  11  and  12 , respectively, being placed between the head  10  of the screw  8  and the adjacent flange  3  and between the nut  9  and the adjacent flange  4 . A flat ring packing  13 , which is illustrated on an enlarged scale in FIG. 2, is disposed between the flanges  3 ,  4 . The inside diameters D of the pipes  1 ,  2  and of the packing  13  are identical. 
     The flanges  3 ,  4  have an annular packing surface  14 ,  15 , against which bears the flat ring packing  13 . The flanges  3 ,  4  may additionally have annular ribs  16 ,  17  which encircle between these packing surfaces  14 ,  15  and the drilled holes  6 ,  7  and which serve to center the flat ring packing  13  relative to the axis  5 , i.e. against which the flat ring packing  13  bears radially. 
     As seen in FIG. 2, the flat ring packing  13  comprises two packing layers  18 ,  19  and an approximately cylindrical intermediate ring  20  disposed therebetween, i.e. it has a sandwich design. The packing layers  18 ,  19  consist of PTFE (polytetrafluoroethylene) as an elastically deformable and consequently flexible packing material. The packing layers  18 ,  19  are joined to the intermediate ring  20  by means of connections  21 ,  22  which are mirror-inverted relative to each other. Each connection  21  and  22  comprises a recess  23  in the intermediate ring  20 , the recess  23  encircling concentrically of the axis  5  and comprising a rear recess which is formed by a locking surface  24  in the shape of a truncated cone tapering in a direction away from the respective packing layer  18  and  19  towards the inside of the intermediate ring  20 . In the vicinity of its periphery, the respective packing layer  18  and  19  comprises a locking rib  25  which encircles concentrically of the axis  5  and engages with the corresponding recess  23  and which is also rear-recessed such that its inner surface turned toward the axis  5  constitutes an opposite surface  26  in the shape of a truncated cone which rests on the locking surface  24  tightly and without play over the full surface. 
     As further seen in FIG. 2, the recesses  23  comprise an annularly encircling clearance  27  radially outside the locking rib  25  and underneath the locking rib  25  in the direction of the axis  5 . A suitable tool may be inserted into this clearance  27 ; it reaches under the locking rib  25 , lifting same from the locking surface  24  and forcing it out of the recess  23 . In this way, the packing layers  18 ,  19  are detachable from the intermediate ring  20  and can be replaced. Since the opposite surface  26  of the respective locking rib  25  rests tightly on the locking surface  24  of the respective recess  23 , the respective packing layer  18  and  19  is centered accurately relative to the intermediate ring  20 . Since furtheron the packing  13  as a whole, i.e. the layers  18 ,  19  and the intermediate ring  20 , have identical inside diameters D, no wake spaces can arise. Since the material of the packing layers  18  and  19  is elastically deformable, the locking ribs  25  can be snapped into place by elastic deformation. Fixing the packing layers  18 ,  19  on the intermediate ring  20  takes place in the way of a snap connection. 
     The frontal surfaces of the intermediate ring  20 , which the packing layers  18 ,  19  rest on, are provided with a profile in the shape of grooves  28  of a cross-section in the form of a segment of a circle and which run concentrically of the axis  5  and into which the packing layers  18 ,  19  are pressed partially upon clamping of the flanges  3 ,  4 .