AU684166B2

AU684166B2 - A coupling assembly

Info

Publication number: AU684166B2
Application number: AU24838/95A
Authority: AU
Inventors: Colin George Leaves
Original assignee: AYMROO Pty Ltd
Current assignee: AYMROO PTY Ltd
Priority date: 1994-07-04
Filing date: 1995-07-04
Publication date: 1997-12-04
Anticipated expiration: 2015-07-04
Also published as: AU2483895A

Description

p00011 Regulation 3.2

AUSTRALIA

Patents Act, 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: ACTUAL INVENTOR(S): AYMROO PTY LIMITED (ACN 003 426 435) COLIN GEORGE LEAVES S.ADDRESS FOR SERVICE: INVENTION TITLE: DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO(S): Peter Maxwell Associates Blaxland House, Suite 10, 5 Ross Street, NORTH PARRAMATTA NSW 2151 A COUPLING ASSEMBLY AU PM 6617 dated 4/7/94 The following statement is a full description of this invention, including the best method of performing it know to me:cl -2- The present invention relates to the coupling of plastic coated metal pipes to either like plastic coated metal pipes or to pipes constructed of a like plastic material. The invention has particular application in the field of gas or water meter pipes, where an above ground plastic coated copper pipe needs to be connected to a plastic fitting for a below ground plastic pipe. In the context of the present specification, the term plastic coated metal pipe is intended to also include plastic coated metal tubes of a metal fitting.

There is a statutory requirement in Australia that above ground pipes or fittings to gas and water meters be made of copper. As below ground pipes or tubes to the main gas or water supply pipe are made of polyethylene, there is a 15 need to be able to connect together the copper and polyethylene tubes so as to ensure gas or water flow continuity without leak or impediment.

In the past, copper tubes leading to gas or water meters have been connected to polyethylene tubes with either ':20 a compression fitting or a threaded fitting.

Both these types of fittings require substantial time for installation and may suffer degradation and ultimately leakage over time. For instance, suh compression fittings involve the compression of the plastic material from which the tube or pipe is formed, against and relative to the metal of a pipe or fitting, such that after the initial connection involving the compression of the plastic material, the plastic material may expand and move away from the metal AC I -3material, thus resulting in leakage and general inefficiencies.

Another approach has been to bond or adhere plastic pipes or tubes to metal fittings, such as by using appropriate adhesives and glues, but while this has worked for a period of time, such connections have not been sufficiently lasting, in that the glue between the plastic material and the metal has been found to deteriorate with time. This results in the deterioration and loosening of the connection between the plastic tubo or pipe and the metal fitting, such as to cause leaking, inefficiencies and the like.

More recently, it has been sought to improve the coupling of metal pipes or fittings to plastic pipes by 15 firstly providing the metal pipe or fitting with a permanent coating of a plastic material adjacent the end to be coupled to the plastic pipe and then using an adhesive material, such as a glue, to join the coated end of the metal pipe or fitting to a selected end of the plastic pipe. The end of the plastic tube may be located and adhered to the metal pipe or fitting either within a plastic coated inner end or over a plastic coated outer end thereof.

While this approach has met with some success, the general limitations associated with using an adhesive, which, by its very nature, is not of the same composition as the plastic used in the coating of the metal pipe or fitting or in the contruction of the plastic pipe, still apply. For instance, adverse weather conditions, or impact shock on the coupling may compromise the long term bonding strength provided by the adhesive and lead inevitably to leakage.

It is an object of the present invention to overcome or substantially ameliorate the shortcomings of the prior art.

According to the invention, there is provided a coupling assembly between first and second pipes, each having end surfaces formed of plastic, with at least one of said first and second pipes being fabricated of a metal with a plastic coated end surface, said coupling assembly comprising said first and second pipes coupled together along a common longitudinal axis by a heat welded joint formed across the plastic end surfaces, wherein the heat welded joint comprises a region of fused plastic between respective plastic end surfaces in overlapping relationship, whereby the region of fused plastic is formed by a process of polyfusion jointing using a metal socket polyfusion tool.

15 It is preferred that one of said first and second pipes includes 'circumferential grooves formed on the metal which are covered by a surface coating of plastic to produce plastic coated grooves.

It is further preferred that the other one of said first and second pipes is a moulded plastic fitting.

According to a further aspect of the invention, there is provided a process for coupling together in overlapping relationship first and second pipes across plastic end surfaces thereof, with at least one of said first and second pipes being fabricated of metal with a plastic coated end surface, said process comprising the steps of:heating a r ietal socket polyfusion tool to a sufficient temperature for melting the said plastic, the said tool including a first female member for receiving therewithin a plastic outer end surface of a first pipe and a second male member for receiving therearound a plastic inner end surface of a second pipe, (ii) locating said plastic end surfaces of said first and second Spipes snugly and releasably onto said heated metal socket polyfusion tool T 0

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for a sufficient time to enable localised melting of the plastic surfaces received on the said tool, (iii) withdrawing said first and second pipes from the said tool, and (iv) bringing together in overlapping relationship the plastic outer end surface of said first pipe and the plastic inner end surface of said second pipe whilst said plastic surfaces are in a melted state so that a heat welded joint is formed across the plastic surfaces after cooling and solidification of the melted plastic surfaces together.

In order that the invention may be readily understood and put into practical effect, reference will be made to the accompanying drawings, in which:- Fig 1 is a longitudinal cross-sectional view of an electrofusion socket about to be used to form a heat welded joint across 15 plastic coated outer end surfaces of two metal pipes, ee o:' i o ee e 6 j -6- Fig 2 is a longitudinal cross-sectional view of a coupling assembly formed from the joining of the electrofusion socket with the plastic coated outer end surfaces of the metal pipes shown in Fig. 1, Fig 3 is a longitudinal cross-sectional view of a metal socket polyfusion tool about to be used to form a heat welded joint across respective plastic end surfaces of a plastic coated metal pipe and a plastic pipe fitting, and Fig 4 is a longitudinal cross-sectional view of the metal socket polyfusion tool, plastic coated metal pipe and pipe fitting of Fig. 3 assembled together for the step of melting desired plastic 15 end surfaces of the pipe and pipe fitting so that they may be welded or fused together in overlapping relationship.

The electrofusion socket or fitting 11 shown in Fig. 1 is of a conventional type and, as will be readily appreciated by skilled persons, works on the principal of heating coil welding or fusion. There is a single heating coil 12 permanently incorporated or embedded in the polyethylene moulded body 13 of the socket 11 and the ends of the coil 12 are connected to respective terminals 14 and 15 partly enclosed in protective shrouds 16 and 17 for safe connection to a welding machine (not shown).

A plastic coated metal pipe 18 is to be heat welded to another plastic coated metal pipe 19 with the use of the i electrofusion socket 11. The pipes 18 and 19 are fabricated from copper, and have plastic coated outer end surfaces and 21 respectively. In this instance, the plastic coating material is polyethylene for compatibility with the socket 11.

The pil)e 18 has three circumferential grooves 22 which are formed on the copper pipe prior to application of the plastic coating so that, when heat welding occcurs, the strength of the bond formed between the socket 11 and pipe 18 is enhanced as e result of migration and penetration of polyethylene from the socket body 13 into the polyethylene coated grooves 22.

The following is a description of a preferred process for producing a stable surface coating of a polymeric material on a copper tube or pipe.

A standard sized copper tube or pipe adapted for use as an above ground connection to a gas meter has an end region swaged by three circumferential grooves located 10 mm apart.

Each groove is 2.5 mm wide and 0.5 mm deep. As will be apparent later in the specification, the swaging of the copper tube will assist in the bonding of a polymeric fitting to the coated copper tube as the grooves provide an increased surface area or key for fusion welding the polymeric fitting thereto.

The swaged end is dipped in an acid solution which removes the film or coating of oxidation products which are on both the inside and outside surfaces of the copper tube.

The acid solution includes about 10% v/v sulphuric acid and about 10% v/v hydrofluoric acid.

The copper tube is then rinsed with water to remove any surface fragments.

Following rinsing, the copper tube is abraded in a circular motion around its circumference with emery paper so as to provide score lines around the tube in the region to be coated. The score lines increase the mechanical key or surface area for bonding of the polymer coating. The abrading of the copper tube should be undertaken before re-oxidation of the copper surface occurs.

The copper tube is then introduced into a chamber heated at about 3500C and is left for about two to three minutes so as to heat the inside and outside tube surfaces evenly.

After heating, the copper tube is dipped into a fluidized bed of a scintered polymeric material, such as that referred to as PPA 571, available from Peter Snell Plastics Pty. Limited. Both the inside and outside surfaces of the region to be coated are submerged in the polymeric material which binds onto the heated copper tube. The fluidized bed is ventilated with warm air fed through the bottom of the bed so as to keep the scintered polymeric material dry.

The length of time the heated copper tube is dipped into the fluidized polymeric bed determines the thickness of the polymer coating. The resulting thickness of the outer diameter of the coated copper tube should ideally be identical to the thickness of the appropriate polymeric tube of pipe to which it is to be connected.

-9- The coated copper tube is allowed to cool after removal from the fluidized bed.

Where the dipping and cooling is done manually by a person, that person may blow against the coated copper tube to put out any flame or glowing material.

Subsequent cooling to ambient temperature may be achieved by allowing the coated tube to stand at ambient temperature or dipping the tube in a quenching solution of water and softening agent.

The plastic coated metal pipe 19 is prepared in a similar manner except that circumferential grooves are not formed prior to application of the coating.

The pipes 18 and 19 are brought together in end to end relationship in the electrofusion socket 11 as shown in Fig.

"15 2, and an electric current is applied through the coil 12.

Heat generated in the coil 12 passes through the polyethylene o body 13 of the socket 11 and is transmitted through contact simultaneously to the adjacent plastic coated surfaces 20 and 21 of pipes 18 and 19 respectively. The adjacent polyethylene srrfaces are thereby reliably and permanently welded together in a region of melted and fused polyethylene, with the socket 11 acting as a sealed "bridge" between the pipes 18 and 19.

The metal socket polyfusion tool 25 shown in Fig. 3 is also of a conventional type and enables plastic end surfaces of a plastic coated metal pipe 26 and a moulded plastic fitting 27 to be heat welded together. The plastic which coats the pipe 26 and from which the fitting 27 is moulded is polyethylene.

The pipe 26 has three circumferential grooves 28 which are formed in the same manner as the grooves on pipe 18, and the polyethylene coated outer end surface 29 of pipe 26 is preferably produced in the manner as earlier described.

The tool 25 has a pipe outer end surface receiving member 30 and a fitting inner end surface receiving member 31, each member 30 and 31 adapted to receive snugly and releasably its respective end surface of the pipe 26 and fitting 27 to be welded together, as shown In Fig. 4.

The tool 25 is heated in the conventional manner to a desired temperature and the pipe 26 and fitting 27 are brought together on the tool 25 for localized surface melting of the polyethylene coated outer end surface 29 of the pipe 26 and the inner end surface 32 of the polyethylene fitting 27.

After a suitable melting and softening of the surfaces 29 and 32 has occurred, the pipe 26 and fitting 27 are withdrawn from the tool 25 and, without undue delay, are pushed together symmetrically and with even force so that the still soft and hot outer end surface 29 of pipe 26 will fit 4 snugly within the still soft and hot inner end surface 32 of the polyethylene fitting 27. The adjacent polyethylene surfaces are thereby reliably and permanently welded together in overlapping relationship through a region of ktsed polyethylene which bonds directly the pipe 26 to fitting 27.

As will be readily appreciated by persons skilled in the art, other processes for forming heat welded joints I, -11between plastic end surfaces of pipes and fittings may be employed without departing from the scope of the present invention. For instance, in some circumstances, butt fusion using a suitably heated tool may be employed, providing that the plastic coating on the end surface of the metal pipe used in the coupling is suitably located for the purpose.

Varous modifications may be made in details of design, condtruction and process steps without departing from the scope of the invention.- 2

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Claims

1. A coupling assembly between first and second pipes, each having end surfaces formed of plastic, with at least one of said first and second pipes being fabricated of a metal with a plastic coated end surface, said coupling assembly comprising said first and second pipes coupled together along a common longitudinal axis by a heat welded joint formed across the plastic end surfaces, wherein the heat welded joint comprises a region of fused plastic between respective plastic end surfaces in overlapping relationship, whereby the region of fused plastic is formed by a process of polyfusion jointing using a metal socket polyfusion tool. S

2. The coupling assembly of claim 1 wherein one of said first and second pipes includes circumferential grooves formed on the metal which are covered by a surface coating of plastic to produce plastic coated grooves. S

3. The coupling assembly of claim 2 wherein the other one of said first and second pipes is a moulded plastic fitting.

4. The coupling assembly of any one of claims 1 to 3 wherein the said plastic is polyethylene.

The coupling assembly of any one of claims 1 to 4 wherein the said metal is copper.

6. A process for coupling together in overlapping relationship first and secGnd pipes across plastic end surfaces thereof, with at least one of said i 7-r' Y r ^u) 13 first and second pipes being fabricated of metal with a plastic coated end surface, said process comprising the steps of:- heating a metal socket polyfusion tool to a sufficient temperature for melting the said plastic, the said tool including a first female member for receiving therewithin a plastic outer end surface of a first pipe and a second male member for receiving therearound a plastic inner end surface of a second pipe, (ii) locating said plastic end surfaces of said first and second pipes snugly and releasably onto said heated metal socket polyfusion tool o* for a sufficient time to enable localised melting of the plastic surfaces received on the said tool, (iii) withdrawing said first and second pipes from the said tool, and (iv) bringing together in overlapping relationship the plastic outer a.. end surface of said first pipe and the plastic inner end surface of said C O second pipe whilst said plastic surfaces are in a melted state so that a heat welded joint is formed across the plastic surfaces after cooling and solidification of the melted plastic surfaces together. Dated this 2 day of September, 1997 AYMROO PTY LIMITED Patent Attorney for the Applicant PETER MAXWELL ASSOCIATES ABSTRACT A coupling assembly between two pipes (18,19) that have end surfaces (20,21) formed of plastic. One of the pipes (18) is fabricated of a metal with a plastic coated end surface while the other pipe may be similarly fabricated or fabricated as an exclusively plastic pipe or fitting. The two pipes (18,19) are coupled together along a common longitudinal axis by a heat welded joint formed across the plastic end surfaces (20,21). The heat welded joint may be produced by means of an electrofusion socket (11) or a metal socket polyfusion tool 0 to 9o* 4o I