Abstract:
A composite gland sealing for the interlocking coupling of a housing end piece ( 8 ) including an anchoring groove ( 82 ), a plastic ring ( 14 ) and several locking inserts ( 20 ). Each locking insert ( 20 ) includes a radially external head ( 30 ) provided with a first front projection ( 50, 52 ) applicable against the annular front surface ( 90 ) of the anchoring groove ( 82 ). The head ( 30 ) comprises includes a second frontal projection ( 52, 50 ) radially shifted from the first front projection ( 50, 52 ).

Description:
The present invention relates to a gland seal and a corresponding assembly. 
     BACKGROUND OF THE INVENTION 
     The present invention applies in particular to tight and locked assemblies of two cast iron pipes. 
     Document EP-A-526 373 describes a composite seal comprising a sealing body and an anchoring heel made of resilient material and a plurality of locking inserts made of rigid material embedded in the anchoring heel. These inserts are distributed uniformly over the whole circumference of the body. Each insert is produced from metal and has an anchoring head designed to rest on the bottom of an anchoring groove arranged in a socket end, and also catching teeth adapted to engage in the outer surface of a spigot so as to prevent axial movements that might separate the spigot from the socket end under the action of axial forces caused by the pressure of the fluid circulating through the spigot and the socket end. 
     The inclination of each locking insert depends on the play between the external diameter of the spigot and the internal diameter of the socket end. Catching of the insert on the spigot induces a reaction force, the angle of inclination of which over the median direction varies depending on the play present between the assembled ends. 
     The greater this angle of reaction, measured in relation to the radial direction, the more the locking resists the internal pressure of the fluid circulating through the assembly. On the other hand, catching of the inserts in the outer surface of the spigot improves as the angle of reaction gets smaller. Indeed, if the angle is too great, there is a risk that the teeth of the inserts may not catch on the spigot when it is put under pressure, and may slide thereon causing faulty locking. 
     The risk of poor performance under pressure is critical with regard to the maximum amounts of play where the angle of reaction is naturally small, while the risk of poor catching of the inserts is critical with regard to the minimum amounts of play where the angle of reaction is naturally high. 
     SUMMARY OF THE INVENTION 
     The object of the invention, starting from the known assembly of the aforementioned document, is to optimize the compromise between the reliability of catching of the insert on the spigot and the performance under pressure of the locking. 
     Accordingly, the invention relates to an assembly comprising novel features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood on reading the description that follows, given purely as an example and with reference to the accompanying drawings, in which: 
         FIGS. 1 to 3  are half-views in a meridian section of an assembly of two pipes and a composite seal interposed between them, respectively before, during and after producing the locked assembly according to the invention; 
         FIGS. 4 and 5  are enlarged views in a meridian section of a portion of the assembly according to the invention at different stages of assembly, the socket end and the spigot defining minimum play therebetween; 
         FIGS. 6 and 7  are enlarged views in a meridian section of a portion of the assembly according to the invention at different stages of assembly, the socket end and the spigot defining maximum play therebetween; and 
         FIG. 8  is a meridian view of a locking insert according to a variant of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrated in  FIGS. 1 to 3  is a tight and locked assembly according to the invention, designated by the general reference numeral  2 . 
     The tight assembly  2  comprises a spigot  4  or male end integral with a first pipe  6 , a socket end  8  or female end integral with a second pipe  10 , and a seal  12 . 
     The assembly  2  extends along a centre line X-X. Hereinafter, the expressions “radially”, “axially”, “circumferentially” and “meridian” will be used in relation to this axis. 
     The seal  12  comprises, in a meridian section, a resilient ring  14  produced from flexible or resilient material, for example from an elastomer, which extends around the centre line X-X, in which are embedded a plurality of locking inserts  20 . 
     The resilient ring  14  comprises a solid annular body  16  towards the bottom of the socket and, on the entry side of the socket, an anchoring heel  18  projecting radially outwards and a circular sealing lip  26  projecting radially inwards. 
     The body  16  and the heel  18  are separated by a peripheral groove  22 . In a variant which is not illustrated, this groove  22  may be replaced by recesses which are aligned circumferentially with the inserts. 
     The lip  26  extends substantially radially towards the axis X-X until it approaches the minimum internal diameter of the body  16 . The inserts  20  are distributed uniformly over the whole of the circumference of the ring  14 . Each locking insert  20  is of very hard, extruded or sintered material, a hard metal alloy or ceramic, for example. 
     Each insert  20  comprises, in a meridian view, a radially external head  30  and a radially internal foot  32 . The head  30  extends substantially radially in relation to the axis X-X, while the foot  32  is inclined to this axis, in such a way that it converges towards the axis X-X in an introduction direction I of the spigot  4  into the socket end  8 . The insert  20  therefore has a bent profile. 
     Each insert  20  is partly embedded in the anchoring heel  18  of the seal  12  and partly covered by the resilient material of the heel  18 . However, the heel  18  comprises recesses  36  in line with the inserts  20 . The recesses  36  are radially open towards the exterior, in such a way that the radially external end of the head  30  is free of resilient material. The recesses  36  are also axially open in the introduction direction I. 
     Similarly, the seal  12  comprises recesses  38 , open radially towards the interior, and located at the site of the inserts  20 , in such a way that the radially internal end of the feet  32  is free of resilient material. 
     As can be seen more precisely in  FIG. 6 , the head  30  comprises at its radially external end a profile forming two radial projections  40 ,  42  which are axially offset from each other. The head  30  also comprises a retention tip  48  with a sharp edge directed axially in the direction I. The tip  48  is free of resilient material because of the recess  36 . 
     The head  30  also comprises two frontal projections  50 ,  52  radially offset from each other and extending substantially parallel to the centre line X-X. 
     A substantially planar surface S 1  extends between the two radial projections  40 ,  42  and a substantially planar surface S 2  extends between the two frontal projections  50 ,  52 . These surfaces S 1 , S 2  form between them an angle α which is less than 90°. 
     In addition, the foot  32  comprises at its radially internal end three axially offset catching teeth  56 ,  58 ,  60  which are adapted to catch on the outer surface  70  of the spigot (see below) and which, when the seal is in the rest state, extend beyond the resilient ring  14 . In a meridian view, the teeth  56 ,  58 ,  60  extend over a convex curve C. In addition, the foot  32  comprises, on the axial side opposite the head  30 , a catching end stop  62  embedded in the body  16 . The catching end stop  62  has, in a meridian view, a profile which is rounded compared to the profile of the catching teeth  56 ,  58 ,  60 . 
     The end stop  62 , the function of which is to limit the penetration of the insert  20  into the spigot  4  so as not to damage said spigot, has a rounded or domed shape to promote the “flow” of the elastomer when fitting the spigot  4 , so as to avoid stress concentrations that could cause tears in the elastomer. Advantageously, the lateral faces  63  of the end stop  62  of the insert in axial view are chamfered or rounded so as to avoid sharp edges that might also tear the elastomer during fitting. 
     Referring once again to  FIG. 1 , it can be seen that the spigot  4  comprises a cylindrical outer surface  70  of diameter d provided with an entry chamfer  72 . The spigot  4  is manufactured with diametral tolerances such that the actual diameter d may be situated between a maximum external diameter d max  and a minimum external diameter d min . The diameters d max  and d min  are indicated in dot-dash lines in  FIG. 1 . 
     The socket end  8  comprises in succession, axially from the entry of the socket towards the bottom, an entry collar  80 , an annular anchoring groove  82  serving to accommodate the anchoring heel  18  of the seal, a tiered portion  84 , an internal rib  86  and a reception cavity  88 , freely receiving the end of the spigot  4 . 
     The annular anchoring groove  82  is delimited by an annular frontal surface  90  of the entry collar  80 , by a cylindrical bottom surface  92  of circular cross-section with the axis X-X, and by a frontal surface  94  of the tiered portion  84 . Generally, the frontal surface  90  extends at an angle of at least 80° to the centre line X-X and has an axial component directed in the direction I. Preferably, the frontal surface  90  produces an angle of at least 85° with the axis X-X. In addition, the annular frontal surface  90  is directly connected to the bottom surface  92 , in such a way that, for any play between the surfaces  70  and  92  within the range of accepted tolerances, the insert  20  is applied to the frontal surface and to the bottom surface  92  when the pipes are subjected to the internal pressure of the fluid they transport. 
     Moreover, the annular frontal surface  90  and the bottom surface  92  define between them an angle which is greater than the angle α between the planar surfaces S 1  and S 2 . 
     The frontal surface  94  is directed towards the entry collar  80 , opposite to the direction I. 
     As indicated in  FIG. 3 , the bottom surface  92  is also subject to manufacturing tolerances, so that its actual diameter D may vary between a maximum diameter D max  and a minimum diameter D min . 
     The assembly according to the invention is assembled in the following way. 
     The seal  12  is first introduced into the socket end  8 , the body  16  being placed against the tiered portion  84  and the anchoring heel  18  being seated in the annular anchoring groove  82 , in such a way that the axis of the seal  12  merges with that of the socket end. 
     The spigot  4  is then aligned with the socket and introduced through the seal  12  in the direction I by first folding back the lip  26  which is applied with some pressure to the outer surface  70 . When the spigot  4  crosses the threshold of the inserts  20 , these inserts are tilted by angular deflection against the body  16 . The introduction of the spigot  4  continues until its chamfer  72  approaches the bottom of the cavity  88 . The spigot  4  is then taken backwards axially so as to cause the inserts  20  to be pushed back. The inserts  20  alter their tilt in relation to the axis X-X by a small angular deflection counter to the previous one. During this brushing up, at least one of the teeth  56 ,  58 ,  60  catches on the outer surface  70  of the spigot  4  and thus offers substantial resistance to the continuation of the axial withdrawal movement of the spigot  4 . The assembly is therefore locked. 
     Next, referring to  FIGS. 4 to 7 , the operation of the seal according to the invention will be described in terms of the diametral tolerances on the diameters d and D under the action of the fluid under pressure. In these Figs., the ring  14  has been omitted for greater clarity of illustration. 
     After the aforementioned angular deflection of the inserts  20  during assembly of the pipes  6  and  10 , each insert  20  assumes a tilted position which varies according to the play present between the diameters d and D. 
     In  FIG. 4 , the position of an insert  20  is illustrated during catching on the spigot  4  when put under pressure in the case where the play between the pipes is the minimum play J 1 . Accordingly, the socket end  8  comprises an anchoring groove  82  the diameter D of which corresponds to the minimum diameter D min , while the spigot  4  has a surface  70  the external diameter d of which corresponds to the maximum diameter d max . The two diameters D min  and d max  thus define a minimum play J 1  between the two surfaces  92  and  70 . 
     It can be seen that, when catching on the spigot  4 , the insert  20  is placed at two points against the groove  82 , firstly with its second radial projection  42  against the bottom surface  92  and secondly with its first frontal projection  50  against the frontal surface  90 . Moreover, only the catching tooth  56  nearest the socket entry is placed against the outer surface  70 . 
     The insert  20  is tilted at an angle of reaction defined in the following way. In a meridian view, the two lines L 1 , L 2  which extend perpendicular to the surfaces  92 ,  90  in the region of the respective projections  42 ,  50  for applying the insert  20  against the groove  82 , intersect at a point P. The point of application of the tooth  56  on the surface  70  defines with the point P a third line L 3  serving to support the reaction force of the insert  20 . The angle β  1  measured between this line L 3  and a plane perpendicular to the axis X-X is called the “angle of reaction”. 
     The smaller the angle of reaction, the better the catching of the insert  20 . The presence of the second radial projection  42 , nearer axially to the tooth  56  than the first radial projection  40 , ensures that point P is in a position that is axially relatively close to the tooth  56 , in such a way that the angle β  1  is small for the given play J 1 , which promotes catching of the locking insert  20  on the surface  70 . 
     In  FIG. 5  the portion of the assembly of  FIG. 4  is illustrated when the pressure is established. 
     It can be seen that, after the insert  20  has been caught, it has rocked in a clockwise direction compared to  FIG. 4 , and that the three catching teeth  56 ,  58 ,  60  now penetrate into the material of the spigot  4 . 
     The locking insert  20  is no longer placed with its second radial projection  42  against the bottom surface  92 , but is now placed exclusively with its first radial projection  40  against the surface  92 , and exclusively with its first frontal projection  50  against the frontal surface  90 . 
     The point P is the intersection of the lines L 1 , L 2 , normal to the surfaces  92 ,  90  in the region of the projections  40 ,  50 . 
     The assembly defines a line L 3 , which extends between the point P and a point M situated midway axially between the catching teeth  56  and  60 . 
     The line L 3  defines with the radial direction an angle of reaction β  2  which is therefore relatively large for the given play J 1 , and this leads to good performance under pressure of the locked assembly. 
     It should be noted that, when the insert  20  rocks when put under pressure, the loss of contact in the region of the second radial projection  42  allows the angle of reaction to be increased and among other things thus compensates for the reduction in the angle of reaction resulting from the rocking of the insert in a clockwise direction; a sufficiently large angle β  2  is thus achieved to guarantee good performance under pressure. 
       FIG. 6  shows a similar assembly to that of  FIG. 4  with the following differences. 
     The surface  92  has a diameter D max , while the surface  70  has a diameter d min , such that these two surfaces define between them a play J 2  greater than the play J 1 . This play J 2  is the maximum play accepted for the manufacturing tolerances of the spigot  4  and the socket end  8 . 
     It can be seen that, when catching on the spigot  4  once put under pressure, the insert  20  is placed at two points against the groove  82 , firstly with its first radial projection  40  against the bottom surface  92  and secondly with its first frontal projection  50  against the frontal surface  90 . Moreover, only the catching tooth  60  farthest from the socket entry is placed against the outer surface  70 . 
     The angle of reaction β  3  obtained is measured between the radial direction and a line passing through the point P, substantially identical to that of the assembly of  FIG. 5 , and by the point of contact between the surface  70  and the tooth  60 . This angle β  3  is small and therefore compatible with correct catching of the insert  20 . 
       FIG. 7  shows the assembly of  FIG. 6  once the pressure has been established, and therefore after catching of the insert  20  and after rocking thereof in the clockwise direction. 
     At the end of this rocking, the insert  20  is placed exclusively with its first radial projection  40  against the bottom surface  92  and exclusively with its second frontal projection  52  against the frontal surface  90 , while the other projections  42  and  50  are out of contact with the surfaces  90  and  92 . Furthermore, only the intermediate tooth  58  and the tooth  60  farthest from the socket entry are caught in the surface  70  of the spigot  4 . 
     At maximum play J 2 , contact in the region of the second frontal projection  52  allows an increase in the angle of reaction and among other things compensation for the reduction in the angle of reaction resulting from the rocking of the insert in the clockwise direction when put under pressure; this projection  52  which generates a point P situated close to the axis X-X therefore allows a final angle of reaction β 4  to be obtained that is large enough to guarantee good performance under pressure of the locked assembly. 
     In  FIG. 8  a variant of the insert  20  according to the invention is illustrated. 
     Hereinafter, only the differences in relation to the previously described insert  20  will be mentioned. Like elements have like reference numerals. 
     This locking insert  20  comprises three radial projections  40 ,  42 ,  44  which are axially offset, and which extend, in a meridian view, over a convex curve C 2 . 
     Furthermore, the locking insert  20  comprises three frontal projections  50 ,  52 ,  54  radially offset from the axis X-X, and situated, in a meridian view, on a convex curve C 3 . 
     The geometric characteristics of the inserts  20  allow the aforementioned seal to produce a good compromise between the catching of the inserts on the spigot and performance under pressure, regardless of the actual play between the surfaces  70  and  92 . 
     Moreover, the recesses  36  give more reliable support to the inserts  20  with regard to the minimal play, by reducing the fitting stress of the spigot  4  and avoiding compression stresses in the elastomer that could lead to poor positioning of the inserts  20  by rocking in a direction that tends to increase the angle of reaction (and therefore to impair correct catching of the inserts  20  at minimum play). Furthermore, in combination with the groove  22 , the recesses  36  facilitate the overall deformation of the ring  14  when the seal is put in place in the socket end.