GB2137710A

GB2137710A - Branch pipe fitting

Info

Publication number: GB2137710A
Application number: GB08308801A
Authority: GB
Inventors: Eric Bridgstock
Original assignee: Fusion Plastics Ltd
Current assignee: Fusion Plastics Ltd
Priority date: 1983-03-30
Filing date: 1983-03-30
Publication date: 1984-10-10
Also published as: GB8308801D0; GB2137710B

Abstract

An electro-fusion saddle fitting 1 for connecting a branch pipe to a main pipe is manufactured by winding uncoated resistance heating wire onto a rubber mat (10) having spaced radial webs (13) with grooves (14) to receive the wire and locate the winding, moulding the body of the fitting over the mat and winding, and removing the mat to leave the winding partially embedded in the body. The pipe fitting is suitable for thermoplastic pipes. <IMAGE>

Description

SPECIFICATION Branch pipe fitting for thermoplastic pipe This invention relates to branch of saddle fittings for connecting a branch pipe to a main pipe of Thermoplastic material, such as polyethylene. A saddle fitting generally consists of a part-cylindrical body having a concave surface corresponding to the external shape of the main pipe to which it is to be attached, and an integral tubular boss projecting outwardly from the body for connection of a branch pipe, the fitting being moulded from a material which is compatible with, and preferably the same as that of the main pipe so that the fitting can be welded directly to the main pipe.The invention is particularly concerned with saddle fittings of the electrofusion type which include an electrical resistance heating element to which an electric current can be supplied to heat and fuse the material of the fitting to that of the main pipe.

In order to ensure a satisfactory weld between the saddle fitting and pipe it is desirable that the heating element be located as close as possible to the surface of the pipe so that the material of the pipe is sufficiently heated and softened. The invention resides in a novel method of manufacturing a saddle fitting and more especially of mounting the heating element at the inner surface of the fitting. The invention also includes a fitting made by the method.

The feature of the invention will become clear from the following detailed description which is given with reference to the accompanying drawings in which:~ Figure 1 is a plan view of a saddle fitting; Figure 2 is an end view of the fitting; and Figure 3 is a top view of a preform used in the manufacture of the fitting.

The saddle fitting illustrated in Figures 1 and 2 has a generally semi-cylindrical body 1, an upwardly projecting tubular boss 2 for connection of a branch pipe, lateral flanges 3 for clamping the fitting to a pipe during welding thereto, and electrical connector sockets 5, 6 having pin contacts 7, 8 connected to the opposite ends of an electrical resistance heating winding located at the inner surface of the body 1. The fitting is formed by injection moulding and the heating element is secured in position during the moulding process, as will become clear from the following description of the manufacturing method.

In Figure 3 there is shown a flexible preform in the form of a thin rubber mat 10. The mat has a central aperture 1 1 and a series of uniformly spaced radial openings 12 of substantially segmental shape which separate webs 13. On the upper side of the mat the webs are provided with grooves 14 which constitute successive portions of a continuous spiral.

As a preliminary step before moulding the saddle fitting, uncoated resistance heating wire is wound into the grooves 14 of the mat 10 to form a spiral winding thereon, and the opposite ends of the windings are connected to respective contact pins 7, 8. The mat 10 with the winding carried thereon is then loaded into the injection mould, the mat being supported against the mould surface which forms the inner surface of the eventual fitting and the contacts 7, 8 being inserted into location holes provided in the mould.

After closing the mould thermoplastic material is injected into the mould cavity over the mat 10 and the winding. Those portions of the spiral winding which extend across the openings 12 become embedded in thermoplastic material but those portions within the grooves 14 of webs 13 do not.

When the moulding process is complete the fitting is removed from the mould and the rubber mat 10 is peeled away from the fitting to leave the spiral winding secured firmly in position at the inner surface of the fitting. In the completed saddle fitting alternate sections of the heating wire are fully embedded in the material of fitting and exposed at the inner surface which ensures that the winding is adequately secured but at the same time an underlying pipe will be adequately heated when an electric current is supplied to the winding to weld the fitting to the pipe.

While a single spiral winding has been described it will be understood that other configurations are possible and that the shape of the moulded rubber preform may be varied without departing from the invention. For example, it is not essential to have the openings 12 and the grooves 14 could instead be provided in mat portions 13 separated by mat portions 12 of reduced thickness. The winding portions between the grooves 14 will still become substantially entirely embedded in the fitting material.

1. A method of manufacturing an electro-fusion fitting comprising a body of thermoplastic material and an electrical resistance heating winding, wherein uncoated resistance wire is wound onto a flexible support member having means to retain the winding in a predetermined configuration, the body of the fitting is moulded over the support member and winding, and the support member is removed to leave the winding partially embedded in the body of the fitting.

2. A method according to claim 1, wherein the support member is a flat mat.

3. A method according to claim 2, wherein the mat is made of rubber.

4. A method according to claim 2, wherein the mat includes a plurality of spaced web portions having grooves to receive and locate the wire.

5. A method according to claim 3, wherein the webs extend substantially radially and are separated by either openings or reduced thickness mat portions whereby sections of the winding

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Branch pipe fitting for thermoplastic pipe This invention relates to branch of saddle fittings for connecting a branch pipe to a main pipe of Thermoplastic material, such as polyethylene. A saddle fitting generally consists of a part-cylindrical body having a concave surface corresponding to the external shape of the main pipe to which it is to be attached, and an integral tubular boss projecting outwardly from the body for connection of a branch pipe, the fitting being moulded from a material which is compatible with, and preferably the same as that of the main pipe so that the fitting can be welded directly to the main pipe.The invention is particularly concerned with saddle fittings of the electrofusion type which include an electrical resistance heating element to which an electric current can be supplied to heat and fuse the material of the fitting to that of the main pipe. In order to ensure a satisfactory weld between the saddle fitting and pipe it is desirable that the heating element be located as close as possible to the surface of the pipe so that the material of the pipe is sufficiently heated and softened. The invention resides in a novel method of manufacturing a saddle fitting and more especially of mounting the heating element at the inner surface of the fitting. The invention also includes a fitting made by the method. The feature of the invention will become clear from the following detailed description which is given with reference to the accompanying drawings in which:~ Figure 1 is a plan view of a saddle fitting; Figure 2 is an end view of the fitting; and Figure 3 is a top view of a preform used in the manufacture of the fitting. The saddle fitting illustrated in Figures 1 and 2 has a generally semi-cylindrical body 1, an upwardly projecting tubular boss 2 for connection of a branch pipe, lateral flanges 3 for clamping the fitting to a pipe during welding thereto, and electrical connector sockets 5, 6 having pin contacts 7, 8 connected to the opposite ends of an electrical resistance heating winding located at the inner surface of the body 1. The fitting is formed by injection moulding and the heating element is secured in position during the moulding process, as will become clear from the following description of the manufacturing method. In Figure 3 there is shown a flexible preform in the form of a thin rubber mat 10. The mat has a central aperture 1 1 and a series of uniformly spaced radial openings 12 of substantially segmental shape which separate webs 13. On the upper side of the mat the webs are provided with grooves 14 which constitute successive portions of a continuous spiral. As a preliminary step before moulding the saddle fitting, uncoated resistance heating wire is wound into the grooves 14 of the mat 10 to form a spiral winding thereon, and the opposite ends of the windings are connected to respective contact pins 7, 8. The mat 10 with the winding carried thereon is then loaded into the injection mould, the mat being supported against the mould surface which forms the inner surface of the eventual fitting and the contacts 7, 8 being inserted into location holes provided in the mould. After closing the mould thermoplastic material is injected into the mould cavity over the mat 10 and the winding. Those portions of the spiral winding which extend across the openings 12 become embedded in thermoplastic material but those portions within the grooves 14 of webs 13 do not. When the moulding process is complete the fitting is removed from the mould and the rubber mat 10 is peeled away from the fitting to leave the spiral winding secured firmly in position at the inner surface of the fitting. In the completed saddle fitting alternate sections of the heating wire are fully embedded in the material of fitting and exposed at the inner surface which ensures that the winding is adequately secured but at the same time an underlying pipe will be adequately heated when an electric current is supplied to the winding to weld the fitting to the pipe. While a single spiral winding has been described it will be understood that other configurations are possible and that the shape of the moulded rubber preform may be varied without departing from the invention. For example, it is not essential to have the openings 12 and the grooves 14 could instead be provided in mat portions 13 separated by mat portions 12 of reduced thickness. The winding portions between the grooves 14 will still become substantially entirely embedded in the fitting material. CLAIMS

2. A method according to claim 1, wherein the support member is a flat mat.

3. A method according to claim 2, wherein the mat is made of rubber.

5. A method according to claim 3, wherein the webs extend substantially radially and are separated by either openings or reduced thickness mat portions whereby sections of the winding between the webs become substantially entirely embedded in the material of the body.

6. A method of manufacturing an electro-fusion fitting substantially as herein described.

7. An electro-fusion fitting made by the method of any one of the preceding claims.