GB2232330A

GB2232330A - A method of producing electrically fusible pipe connectors and of connecting pipes

Info

Publication number: GB2232330A
Application number: GB9009645A
Authority: GB
Inventors: James A Inhofe
Original assignee: Central Plastics Co
Current assignee: Central Plastics Co
Priority date: 1989-05-01
Filing date: 1990-04-30
Publication date: 1990-12-05
Anticipated expiration: 2010-04-30
Also published as: JPH0361525A; GB9009645D0; JP2870662B2; GB2232330B

Abstract

Electrically fusible sleeve connectors for connecting large diameter thermoplastic pipe sections are produced by winding a tape (10) of molten thermoplastic material onto a large diameter drum (14) whereby adjacent windings are fused and upon being cooled a solid sleeve (22) is formed, embedding an electric resistance heating wire (16) in a surface of sleeve 22 while the thermoplastic material is still in the molten state and removing sleeve (22) after cooling with wire 16 embedded therein from demountable drum 14 by deflating a bladder 28. The wire 16 may be embedded in the internal or external surface of sleeve 22 by winding wire 16 on drum 14 before or after winding tape 10 on drum 14. Two end sections of pipes can be thermofused to sleeve 22 by placing sleeve 22 to overlap the end sections either internally or externally and by passing electric current through wire 16. Alternatively adjacent end sections of pipes can have windings of the wire while a thermoplastic split sleeve is placed over the windings through which current is passed. <IMAGE>

Description

A METHOD OF PRODUCING ELECTRICALLY FUSIBLE PIPE CONNECTORS AND OF CONNECTING PIPES The present invention relates to a method of producing electrically fusible thermoplastic pipe connectors, and of sealingly connecting adjacent ends of large diameter thermoplastic pipe sections by electric fusion.

Various extrusion and molding methods have been developed and used heretofore for producing large diameter pipe from thermoplastic materials. A number of such methods include the steps of wrapping extruded plastic in the molten state about a mandrel so that adjoining edges and surfaces of the tape are fused. Upon removing the wrapped thermoplastic material when cooled from the mandrel a solid tubular pipe is formed.

Large diameter pipe formed of thermoplastic material is finding increased acceptance in applications such as large water and sewer lines due to the excellent deterioration resistance, light weight and substantially unlimited service of such pipe. However, because of the large diameter of the pipe, sealingly connecting the ends of adjacent pipe sections has heretofore been burdensome and expensive.

According to the present invention, there is provided a method of producing an electrically fusible thermoplastic sleeve connector for connecting thermoplastic pipe sections comprising the steps of: (a) winding a tape of molten thermoplastic material onto a core drum whereby adjacent windings are fused and upon being cooled a solid sleeve is formed; (b) embedding at least one electric resistance heating wire in a surface of said sleeve; and (c) removing said sleeve with said electric resistance heating wire embedded therein from said core drum.

The electric resistance heating wire can be placed on the core drum prior to winding the tape of thermoplastic material thereon whereby the wire is embedded in the internal surface of the resulting sleeve. Alternatively, the electric resistance heating wire can be wound onto the external surface of the sleeve while the thermoplastic material thereof is in the molten state so that the wire is embedded in the external surface of the sleeve.

In another aspect of the present invention, there is provided a method of sealingly connecting adjacent ends of a pair of large diameter thermoplastic pipe sections by electric fusion comprising: (a) moving a large diameter thermoplastic sleeve connector over the end and a distance down the length of a first of said thermoplastic pipe sections; (b) placing the second of said pipe sections in alignment with said first pipe section whereby an end of said second pipe section is positioned adjacent an end of said first pipe section; (c) wrapping an electric resistance heating wire around the external surfaces of said pipe sections next to the adjacent ends thereof; (d) moving said sleeve to a position over the adjacent ends of said pipe sections and over said electric resistance wire wrapped on said pipe sections; and (e) applying an electric current to said electric resistance heating wire for a period of time such that the thermoplastic materials making up adjacent portions of said sleeve and pipe sections are sealingly fused together.

In a preferred embodiment, the large diameter sleeve connector includes a longitudinal split formed therein whereby the internal diameter of the sleeve can be enlarged by spreading the faces of the split apart. Also, the faces of the split can be cut back to reduce the internal diameter of the sleeve connector if required by variations in the external diameter of the pipe sections to be connected. The faces of the split can be fused together prior to electrically fusing the sleeve to the pipe sections utilizing either heating iron butt fusion techniques or electrofusion techniques. When the faces of the split are fused together electrically, such fusion can be carried out before or simultaneously with the fusion o= the sleeve to the pipe sections.

In order that the present invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which: Figure 1 is schematic illustration of one embodiment of apparatus for carrying out the method of producing electrically fusible thermoplastic sleeve connectors of the present invention.

Figure 2 is a schematic illustration of the apparatus of Figure 1 in a different mode of operation.

Figure 3 is an enlarged cross-sectional view taken along line 3-3 of Figure 2.

Figure 4 is a side elevational view, partially in cross-section, illustrating a pair of pipe sections with a sleeve connector of the present invention positioned thereon.

Figure 5 is a side elevational view, partially in cross-section, of a pair of pipe sections having an alternative form of sleeve connector of the present invention positioned thereon.

Figure 6 is a perspective view Or a large diameter thermoplastic pipe section having a split sleeve connector disposed thereon.

Figure 7 is a perspective view illustrating the pipe section of Figure 6 after a second pipe section has been aligned therewith and an electric resistance heating wire has been wound on the end portions of the pipe sections.

Figure 8 illustrates the pipe sections of Figure 7 during the movement of the split sleeve connector towards a position over the adjacent ends of the pipe sections.

Figure 9 illustrates the pipe sections of Figure 8 after the sleeve connector has been positioned over the adjacent ends of the pipe sections and the faces of the split in the connector have been fused.

As shown in Figure 1, a tape of molten thermoplastic material 10 extruded from a conventional extruder 12 is wound onto a large diameter core drum 14.

The thermoplastic material can be any suitable thermoplastic composition which melts and is moldable at relatively low temperatures, and when cooled, form high strength, corrosion resistant durable objects. Such compositions include organic polymer resins and various additives such as plasticizers, mold release agents, corrosion inhibitors, etc. Particularly suitable materials are those containing polyolefin resins such as polyethylene and polybutylene.

As illustrated in Figure 1, a continuous length of the tape 10 is wound onto the large diameter core drum 14 whereby adjacent edges of each winding are fused. In the embodiment illustrated, a continuous length of an electric resistance heating wire 16 is placed on the drum 14 prior to winding the tape 10 thereon. An example of a suitable electric resistance heating wire 16 is copper wire having a diameter in the range of from about 0.4 mm to about 3 mm.

The opposite ends 18 and 20 of the wire 16 extend outwardly and are passed between adjacent thermoplastic material windings so that they extend to the exterior of the sleeve 22 formed on the drum 14 as illustrated in Figure 2.

One layer or multiple layers of the molten thermoplastic material can be wound onto the core drum 14 whereby adjacent edges and other contacting surfaces of the windings are fused. Upon completion of the winding process as illustrated in Figure 2, the tape is severed and the formed sleeve connector 22 is allowed to cool on the core drum 14.

The winding of the molten thermoplastic material onto the electric resistance heating wire 16 causes the heating wire to be embedded in the thermoplastic material adjacent the interior surface of the sleeve 22. When it is desirable to produce a sleeve connector having electric resistance heating wire embedded therein adjacent the external surface thereof, the tape 10 of molten thermoplastic material is first wound onto the core drum 14 followed by the winding of heating wire on the external surface of the formed sleeve 22 whereby the heating wire is embedded therein. As will be understood, the core drum 14 can be heated if required to maintain the thermoplastic material in the molten state while the electric resistance heating wire is wound thereon and/or to facilitate the fusing of multiple tape layers.The terms "embedded" or "embedding" are used herein to mean the placement of an electric resistance heating wire within and adjacent a surface of a sleeve connector.

While the drum 14 can take any convenient form it must be capable of disassembly to the extent required for the formed sleeve connector 22 to be removed therefrom In the form illustrated in Figure 3, the drum 14 comprises two opposing cylindrical parts 24 and 26 which can be assembled to form the cylindrical core drum 14 as shown. Disposed around the exterior surface of the core drum 14 is an inflated bladder 28 formed of flexible material. The exterior surface of the bladder 28 forms the winding surface on which the sleeve 22 with electric resistance heating wire embedded therein is formed. An inflating or deflating nozzle portion 30 of the bladder 28 extends through an opening 32 in the part 24 of the core drum .14. A valve 34 is connected to the nozzle 30 within the interior of the core drum 14.

In removing the formed sleeve connector 22 from the core drum 14, the bladder 28 is deflated by opening the valve 34 and then the part 26 of the core drum 14 is withdrawn from within the bladder 28 and removed. The formed and cooled sleeve connector 22 is then also removed from the bladder 28.

In Figure 4, the sleeve connector 22 is illustrated positioned over the adjacent aligned ends of a pair of thermoplastic pipe sections 36 and 38, with the heating wire 16 lying adjacent the external surfaces of the end portions of the pipe sections 36 and 38. In order sealingly to connect the pipe sections 36 and 38 to the sleeve connector 22, an electric current is applied to the heating wire 16 by way of the ends 18 and 20 for a period of time such that the thermoplastic materials making up adjacent portions of the sleeve connector 22 and pipe sections 36 and 38 are sealingly fused together.

Referring now to Figure 5, a pair of large diameter thermoplastic pipe sections 40 and 42 are illustrated positioned end-to-end, and a sleeve connector 44 which includes electric resistance heating wire 46 embedded within the exterior surface thereof, is positioned within the ends of the pipe sections and the opposite ends 48. and 50 of the wire 46 extended out between the ends of the pipe sections 40 and 42. The sleeve connector 44 is fused to the pipe sections 40 and 42 by applying an electric current to the electric resistance heating wire by way of the ends 48 and 50.

In another aspect of the present invention, methods of sealingly connecting adjacent ends of a pair of large diameter thermoplastic pipe sections by electric fusion are provided. The methods utilize a thermoplastic sleeve connector which does not include electric resistance heating wire embedded therein. Instead, the heating wire is wound on the external surfaces of the end portions of the pipe sections to be connected.

Referring to Figure 6, a thermoplastic sleeve connector 52, which includes a longitudinal split 66, is placed over the end of a pipe section 54 and moved a distance in the direction of the arrow 56 down the length of the pipe section 54. As shown in Figure 7, a second pipe section 58 is then positioned with an end thereof adjacent the end of the pipe section 54, and an electric resistance heating wire 60 is wound onto the end portions of the pipe sections 54 and 58 next to the adjacent ends thereof.

Opposite end portions 62 and 64 of the heating wire 60 extend outwardly from the external surfaces of the pipe sections 54 and 58, respectively.

Because of the longitudinal split 66, the internal diameter of the connector 52 can be made larger by spreading the faces of the split 66 apart, to facilitate movement of the connector on the pipe sections 54 and 58.

Referring now to Figure 8, the sleeve connector 52 is next moved in the direction of the arrow 68 to the position illustrated in Figure 9, in which the sleeve connector 52 is over the adjacent ends of the pipe sections 54 and 58 and over the electrical resistance heating wire 60 wound on the pipe sections. Once properly positioned, the end portions 62 and 64 of the heating wire 60 are passed through the split 66 and the faces of the split 66 are moved together and fused using known butt fusing or electrofusion apparatus and techniques.In order to sealingly connect the adjacent ends of the pipe sections 54 and 58 to the sleeve connector 52, an electric current is applied to the heating wire 60 by way of the end portions 62 and 64 thereof for a period of time sufficient for the thermoplastic materials making up adjacent portions of the sleeve connector 52 and pipe sections 54 and 58 to be fused together.

In order to further illustrate the methods and sleeve connectors of the present invention, the following examples are given: Example 1 A continuous molten tape of polyethylene thermoplastic material is extruded having cross-sectional dimensions of about 125 mm x 3 mm. The molten tape is wound on a core drum having an external inflatable bladder winding surface of about 61 cms in diameter and having about 30.5 metres of about 2 mm diameter electric resistance heating wire wound thereon. The tape of thermoplastic material in the molten state is wound on the core drum in multiple layers whereby adjacent edges of the tape are fused, and a sleeve connector having an internal diameter of about 61 cms, an external diameter of about 66 cms, and about 14 windings of electric heating resistance wire embedded therein adjacent the internal surface thereof is formed.

After cooling whereby the sleeve connector is solidified, the connector is removed from the core drum.

Example 2 A connector produced as described above is used to sealingly connect adjacent ends of a pair of 61 cms outside diameter thermoplastic pipe sections formed of polyethylene thermoplastic material. Once positioned over the adjacent end portions of the pipe sections, an electric current is applied to the heating wire in a known manner whereby the thermoplastic materials making up adjacent portions of the sleeve connector and pipe sections are sealingly fused together.

Example 3 Thermoplastic pipe sections having external diameters of about 61 cms are sealingly connected by electric fusion as follows. A thermoplastic sleeve connector of about 61 cms inside diameter, about 66 cms outside diameter and a length of about 61 cms is placed over the end of one of the pipe sections and moved a distance down the length thereof. The sleeve connector includes a longitudinal split formed therein. The second pipe section is placed in alignment with the first pipe section whereby an end of the first pipe section is positioned adjacent an end of the second pipe section. A 30.5 metre length of about 2 mm diameter copper electric resistance heating wire is wrapped around the external surfaces of the pipe sections next to the adjacent ends thereof. The sleeve connector is moved over the adjacent ends of the pipe sections and over the heating wire wrapped thereon. The opposite end portions of the heating wire are passed through the split in the connector. The faces of the split in the connector are fused together using heating irons and an electric current is applied to the resistance heating wire by way of the ends thereof whereby the thermoplastic materials making up adjacent portions of the sleeve connector and pipe sections are sealingly fused together.

Claims

1. A method of producing an electrically fusible thermoplastic sleeve connector for connecting thermoplastic pipe sections comprising the steps of: (a) winding a tape of molten thermoplastic material onto a core drum whereby adjacent windings are fused and upon being cooled a solid sleeve is formed; (b) embedding at least one electric resistance heating wire in a surface of said sleeve; and (c) removing said sleeve with said electric resistance heating wire embedded therein from said core drum.

2. A method according to claim 1, wherein said electric resistance heating wire is embedded in the internal surface of said sleeve by placing said wire on said core drum prior to winding said tape of thermoplastic material thereon.

3. A method according to claim 1, wherein said electric resistance heating wire is embedded in the external surface of said sleeve by winding said wire onto the external surface of said sleeve while said thermoplastic material is in the molten state.

4. A method according to claim 1, 2 or 3, wherein said core drum includes an inflated bladder attached thereto which forms the winding surface thereof and upon which said tape of molten thermoplastic material is wound in accordance with step (a).

5. A method according to claim 4, wherein said bladder is deflated prior to removing said sleeve from said core drum in accordance with step (c).

6. A method any preceding claim, wherein said thermoplastic material comprises a polyolefin resin.

7. A method any preceding claim, wherein the tape of molten thermoplastic material is extruded immediately prior to winding of said tape of molten thermoplastic material onto the core drum.

8. A method of sealingly connecting adjacent ends of a pair of large diameter thermoplastic pipe sections by electric fusion comprising: (a) moving a large diameter thermoplastic sleeve connector over the end and a distance down the length of a first of said thermoplastic pipe sections; (b) placing the second of said pipe sections in alignment with said first pipe section whereby an end of said second pipe section is positioned adjacent an end of said first pipe section; (c) wrapping an electric resistance heating wire around the external surfaces of said pipe sections next to the adjacent ends thereof; (d) moving said sleeve to a position over the adjacent ends of said pipe sections and over said electric resistance wire wrapped on said pipe sections; and (e) applying an electric current to said electric resistance heating wire for a period of time such that the thermoplastic materials making up adjacent portions of said sleeve and pipe sections are sealingly fused together.

9. A method according to claim 8, wherein said thermoplastic pipe sections and said thermoplastic sleeve connector are comprised of polyolefin resins.

10. A method according to claim 9, wherein said sleeve includes a longitudinal split formed therein.

11. A method according to claim 10, and further including the step of fusing the faces of said split in said sleeve together prior to or simultaneously with carrying out step (e).

12. A method according to claim 11, wherein the ends of said electric are passed resistance heating wire wrapped on said pipe sections in accordance with step (c) are passed through said split in said sleeve prior to fusing the faces of said split together and carrying out step (e).

13. A method of producing an electrically fusible thermoplastic sleeve connector, said method being substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 4 of the accompanying drawings.

14. A method of sealingly connecting adjacent ends of a pair of large diameter thermoplastic pipe sections, said method being substantially as hereinbefore described with reference to and as illustrated in Figures 5 to 9 of the accompanying drawings.