Abstract:
A coupling for a corrugated conduit has a housing of a rigid plastics material with two resilient spring catches on opposite sides to engage between corrugations on the conduit. A layer of a softer, elastomeric material is continuously joined on both the interior and exterior of the housing. On the interior, the softer material extends on a tapering surface to diametrically seal with a range of conduits. On the exterior, the layer of softer material forms both a flange on an annular ledge to seal with a cooperating coupling and manual gripping regions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of British Patent Application No. 0114055.7, filed Jun. 9, 2001 and British Patent Application No. 0101927.2, filed Jan. 23, 2001. 
   TECHNICAL FIELD 
   This disclosure relates to pipe couplings and assemblies. 
   BACKGROUND 
   Connection to a corrugated pipe or conduit can be made by means of a coupling in which the end of the pipe is inserted, the coupling having a retaining member in the form of a resilient tooth that engages between corrugations to prevent the pipe and coupling being pulled apart after assembly. The coupling may have a tapering bore forming a close fit with the outside of the pipe so as to seal the pipe with the coupling. Couplings of this kind are described, for example, in U.S. Pat. Nos. 5,094,482, 5,041,256, GB2225550, U.S. Pat. Nos. 5,150,930 and 4,923,227 and are sold by Adaptaflex Limited of Coleshill, Birmingham, UK. Although the seal provided by these couplings is satisfactory in many situations, there are some applications where a more effective seal is needed. 
   SUMMARY 
   Described herein is a coupling for a pipe, the coupling including a housing and retaining means for retaining the pipe within the housing, the housing having a bore therein, the coupling being of a relatively rigid plastics material and having a layer of a relatively deformable material continuously molded onto at least a part of both its inner and outer surfaces. 
   The layer on the inner surface is preferably adapted to form a seal with the outside of the pipe and may provide a tapering surface. The retaining means is preferably formed integrally with the housing and may include at least one resilient catch member adapted to engage a projection on the pipe. The pipe may have a corrugated external surface, the catch member being adapted to engage between the corrugations. The layer on the outer surface may include a part formed on an external ledge of the housing to provide a seal with a cooperating member and, or alternatively, it may include a part that provides a manual gripping region. The layer on the inner and outer surfaces is preferably continuous with one another. The deformable material may be an elastomeric material. 
   Also described herein is an assembly of a corrugated pipe and a coupling according to the above one aspect. 
   A method of forming a coupling is also described, the method including the steps of injecting a first material of a relatively hard plastics material to form a housing of the coupling with integral retaining means and subsequently injecting a second, softer material to form a continuous layer on the harder material both on the inside and outside of the housing. 
   Still further described herein is a coupling made by the above method. 
   A coupling, an assembly of the coupling on a conduit and a method of forming the coupling will now be described, by way of example, with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation view of the assembly of coupling and conduit; 
       FIG. 2  is a sectional side elevation view of the coupling; and 
       FIG. 3  is a perspective, cut-away view showing the inside of the coupling. 
   

   DETAILED DESCRIPTION 
   The assembly comprises a conduit  1  and a coupling  2  fitted on the forward, left-hand end  10  of the conduit. 
   The conduit  1  is entirely conventional and is of a rigid but bendable plastics material with a circular section and has corrugations  11  on its external and internal surfaces. The left-hand end  10  of the conduit  1  is cut square. 
   The coupling  2  comprises two parts joined with one another, namely a body or housing  20  and a layer  21 . The housing  20  is similar to previous housings, being a single-piece of a rigid plastics material of substantially tubular shape. The housing  20  has a bore  22  extending axially along its length and divided by a shoulder  23  into two portions, namely an entrance portion  24  and an exit portion  25 . The rear entrance portion  24  at the right-hand end of the housing  20  receives the end of the conduit  1  and a tapers slightly along its length. The forward, exit portion  25  has a reduced constant diameter. Towards its right-hand end, the housing  20  is formed with retaining means in the form of two retaining or locking arms or catches  27  and  28  each having an inwardly-extending tooth  29  at its free, left-hand end extending across the central region of the arms. The coupling could have any number of one or more locking arms. The right-hand end of each arm  27  and  28  is attached integrally with the housing  20  by a hinge portion  30  of reduced thickness, which enables the arms to be flexed resiliently outwardly. Each arm  27  and  28  has two opposite side regions  31 , which are formed with a shallow ramp  32  of triangular section just rearwardly of the teeth  29 . The purpose of the ramps  32  is to aid removal of the coupling from its tool in the manner described in GB 2225550. The side regions  31  project to the left forwardly beyond the teeth  29  a short distance to form stops  131 . The purpose of these stops  131  is to engage the outside of the conduit  1  when the arms  27  and  28  are deflected inwardly as a result of a high force applied to pull the conduit out of the coupling  2 . The stops  131  limit how far the arms  27  and  28  can be pulled in and, therefore, reduce the risk of damage to the arms. The natural position of the locking arms  27  and  28  is with their teeth  29  projecting slightly into the bore  22 , as shown in  FIGS. 2 and 3 . 
   The forward, left-hand end of the housing  20  has an external screw thread  33  by which the coupling  2  can be screwed into a cooperating female coupling (not shown). Instead of a screw thread, the housing could have other forms of fixing formation, such as barbs or spring catches. Externally, the housing  20  has a forwardly-facing face or ledge  40  at the location of the inner shoulder  23 . 
   The layer  21  is of a deformable, resilient thermoplastics material, preferably an elastomer. The layer  21  covers the entire tapered inner surface of the entrance portion  24 , the right-hand end face  41  of the housing  20  and other parts of the outer surface of the housing. 
   That part of the layer  21  on the inside of the housing  20  provides an elastomeric seal  42  with the outside of the conduit  1 . The dimensions of the housing  20 , angle of taper and thickness of the layer  21  are such that the effective diameter of the bore  22  at the right-hand end is slightly greater than the external diameter of the conduit  1  and, at its left-hand end, is slightly smaller than the external diameter of the conduit. This arrangement is such that the end  10  of the conduit  1  can be pushed into the entrance portion  24  of the bore  22  but is prevented by contact with the tapering surface from contacting the shoulder  23 . In this way, the seal  42  is compressed slightly into a tight sealing contact with the outside of the conduit  1  at its forward end  10 . 
   An outer region  43  on one side of the housing  20  towards its left-hand end is covered by the layer  21  and is of a generally tulip shape. There is a corresponding region on the opposite side of the housing. These parts of the layer  21  provide manual gripping regions  43  to enable the coupling  2  to be held more securely by the hand. The layer  21  also provides an annular flange  44  on the external ledge  40 , which has two concentric sealing ribs  144 . The flange  44  and tulip-shape area  43  are continuous with one another via a stem portion  45 . The flange  44  provides a washer or seal with the end of a cooperating coupling (not shown) screwed onto the threaded portion  33 . Alternatively, the flange  44  may seal against the face of a panel around an opening through which the coupling extends. This flange portion  44  can be omitted or provided by a separate component. 
   Preferably, the layer  21  is formed using a two-shot injection moulding process so that the seal is formed by the same machine that moulds the housing  20 . The housing  20  is on one core pin, which is then removed and a smaller diameter core pin is used to the internal elastomeric layer, between the outside of the second core pin and the inside of the housing. The elastomeric material can be injected into the from the right-hand end of the housing so that it flows over both the inner surface and over the outer regions  43  and  45  into the flange portion  44 , as one continuous layer. It will be appreciated, however, that material to form the inner and outer layers could be injected separately. Because the seal part  42  is moulded into the housing  20 , it is securely bonded with it and forms an effective seal with the inside of the housing. 
   In use, the coupling  2  is provided as a single component. The user simply pushes the forward end  10  of the conduit  1  into the rear end of the housing  20 , so that the teeth  29  on the locking arms  27  and  28  ride over corrugations  11  on the conduit. The forward end  10  of the conduit  1  deforms the seal  42  outwardly slightly as it is pushed into the entrance portion  24 . Rearward movement of the conduit  1  is prevented by the locking arms  27  and  28 , which engage the conduit more tightly as force is applied to separate the conduit and coupling. The conduit  1  holds the material of the seal part  42  compressed between the outside of the conduit and the inside of the housing  20  to provide an effective seal. 
   This arrangement enables both an effective seal and external gripping regions to be provided without the need for separate components or separate assembly operations. 
   It will be appreciated that the structure is not limited to use with conduits but could be used on other forms of pipe. Alternative locking means could be used, such as with uncorrugated pipes. The retaining means could be provided by a separate component.