AU6806698A

AU6806698A - Improvements in pipes

Info

Publication number: AU6806698A
Application number: AU68066/98A
Authority: AU
Inventors: Ronald Robin Colin Witter
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-03-05
Filing date: 1998-05-22
Publication date: 1999-09-16
Also published as: GB9904854D0; GB2335158A; GB9804572D0

Description

P/UU/U 1 28/5/91 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE

SPECIFICATION

STANDARD

PATENT

r r Application Number: Lodged: Invention Title: IMPROVEMENTS IN PIPES The following statement is a full description of this invention, including the best method of performing it known to me IMPROVEMENTS IN PIPES This invention relates to improvements in articles of large crosssections, such as pipes, typically of the kind for use in drainage and sewerage systems and schemes.

Hitherto pipes of the kind set forth are generally cast in concrete.

Such pipes are extremely heavy to handle and manipulate requiring specialised lifting equipment, and are brittle and are liable to crack when subjected to impact blows which, if occurring during installation, render the pipes subject to leakage.

It is also known to construct such pipes from filament wound one• ooomaterial to form a twin wall construction, with an air gap between the walls.

According to our invention an article of large cross-section is **moulded as a seamless and jointless one-piece assembly from a plastics material having a closed cell structure and covered, at least internally, by an inner skin which is impervious to liquids and substantially inert to most chemicals.

The plastics material may be a thermo-plastic such as a high or medium density polyethylene which, when foamed with a foaming agent, is sufficiently rigid to form the shell of the article. Alternatively the plastics material can be a thermo-setting material which when foamed possesses the required rigidity to construct the article.

Preferably, the article is also covered externally by a protective skin so that, in a final construction, the pipe comprises a three-layer sandwich foam moulding.

A pipe of this construction is rigid and will withstand, without cracking, impact blows of a magnitude to which pipes of this type are often subjected during handling. In addition such a pipe is relatively light, which facilitates handling, and is relatively cheap and easy to produce.

The inner and outer skins may themselves be constructed from a plastics material, conveniently of the same plastics material as the :..material of the shell. For example, the skins can be thermo-plastics such as polyethylene of appropriate density. Alternatively each skin can be 15 formed from a polycarbonate or a polyvinyl chloride. Yet again the skin can be formed from a thermo-setting material.

pipe in accordance with our invention can be moulded in one piece by a rotational process whereby material is formed about the interior surface of a mould which during the moulding operation is caused to spin or rotate about its longitudinal axis and tilt along its transverse axis.

With a thermo-plastics material, the material is heated to achieve a fluid or viscous state after entry into the mould. The mould is rotated and tilted to cause the material to cover the inside surface of the mould to a substantially uniform depth and the mould can be cooled to enable the plastics material to solidify against the interior of the mould.

With a thermo-setting material, the material is initially in a fluid state and the addition of a chemical catalyst, rather than heating and subsequent cooling, is required to solidify the material after covering the wall of the mould.

The first layer so formed will be the outer skin. Thereafter the procedure is repeated and this time with the plastics material containing a foaming agent. The second foam layer is deposited against, and adheres to, the already formed skin. The procedure is then repeated again to form the inner skin.

In one construction the mould has a nominal bore chosen to produce a pipe substantially of 900mm internal diameter and a length of coo• 3.5 meters, and with a wall thickness substantially of It will be appreciated that the wall thickness and the relative oO.o thicknesses of the three layers can be changed to vary the stiffness of the *°pipe. For example the wall thickness can be increased up to Pipes of any given size can be produced within the dimensional limitations of a given mould.

A flange can be incorporated into the moulding at one or both ends *of the pipe by means of the mould itself, and the polyethylene material can be hot welded to itself to give a fluid, suitably air and water, tight joint. Alternatively pipes without flanges can be butt welded together, or an ring seal may form a fluid tight seal between adjacent flanged pipes.

The first step in the construction of the large diameter pipe involves formation of an outer skin. This can be formed from a thermoplastics material, such as polyethylene. The thermo-plastics material is introduced into the mould and the mould is heated whilst being spun or rotated about its longitudinal axis and tilted about its transverse axis to cause the thermo-plastics material to cover the walls of the mould to a substantially uniform thickness. The spinning is continued whilst the mould is cooled to allow the material to solidify and form the outer skin.

The second step involves the formation of the foamed layer which provides the required rigidity for the pipe. This is formed in a similar manner in the rotating, tilting and heated mould and the thermo-plastics material can be the same as that employed for the outer skin and have the same or different initial density. Alternatively the foamed layer can be oooo 15 formed from a different thermo-plastics material. The foaming agent is incorporated within the charge of thermo-plastics material introduced into the mould and upon spinning and heating of the mould the charge forms a foamed or closed cell layer having a multitude of air pockets or bubbles which bonds to the previously formed outer skin.

Finally the first step is repeated to provide an inner protective skin to the foam layer.

So The time taken to produce such a pipe is substantially two hours.

A sewerage pipe in accordance with our invention is illustrated in the accompanying drawings in which Figure 1 is a perspective view of the pipe; and Figure 2 is a section through the wall of the pipe.

The cylindrical pipe illustrated in the accompanying drawings comprises an outer plastics layer comprising a skin 1 and a foamed layer 2 bonded thereto and having a multitude of air pockets or bubbles 4 therein. An inner plastics layer comprising a skin 3 is bonded to the foam layer 2. An internal flange 5 is formed at one end of the pipe.

The first step in the construction of the pipe involves formation of the outer skin 1. This can be formed from a thermo-plastics material, such as polyethylene. The thermo-plastics material is introduced into the mould and a mould is heated whilst being spun or rotated about its longitudinal axis and tilted about its transverse axis to cause the thermoplastics material to cover the walls of the mould to a substantially uniform o0 00 15 thickness. The spinning is continued whilst the mould is cooled to allow the material to solidify and form the outer skin 1.

oooo A second step involves the formation of the foamed layer 2 which provides the required rigidity for the pipe. This is formed in a similar manner in the rotating, tilting and heated mould as described above, and the thermo-plastics material can be the same as that employed for the outer skin 1 and have the same or different initial density. Alternatively :the foamed layer 2 can be formed from a different thermo-plastics 0 material. A foaming agent is incorporated within the charge of thermoplastics material introduced into the mould and upon spinning and heating of the mould the charge forms a foamed or closed cell layer having a multitude of air pockets or bubbles which bonds to the previously formed outer skin.

Finally the first step is repeated to provide the inner protective skin 3 to the foam layer.

The time taken to produce such a pipe is substantially two hours.

It will be appreciated that the construction of the pipe is not limited to any one particular plastics material. A high density polyethylene is a preferred material for the foam layer in order to provide rigidity, but other plastics, both thermo-plastics and thermo-setting can be employed.

A suitable polyethylene for the foam layer 2 can have an initial density of 0.94 and an melt index of 5. As mentioned the different layers 1 and 3 forming the shell may be formed from the same or different plastics, and be of different thicknesses, as also may be the foamed layer.

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Claims

1. An article of large cross-section is moulded as a seamless and jointless one-piece assembly from a plastics material having a closed cell structure and covered, at least internally, by an inner skin which is impervious to liquids and substantially inert to most chemicals.

2. An article as claimed in Claim 1, in which the plastics material is a thermo-plastic which, when foamed with a foaming agent, is sufficiently rigid to form the shell of the article.

3. An article as claimed in Claim 2, in which the plastics material is a high or medium density polyethylene

4. An article as claimed in Claim 1, in which the plastics material is a thermo-setting material which when foamed possesses the required rigidity to construct the article.

5. An article as claimed in any preceding claim, in which the article is also covered externally by a protective skin so that, in a final construction, the pipe comprises a three-layer sandwich foam moulding.

6. An article as claimed in Claim 5, in which the inner and outer S. skins are themselves constructed from a plastics material.

7. An article as claimed in Claim 6, in which the skins are of the same plastics material as the material of the shell.

8. An article as claimed in Claim 6 or Claim 7, in which the skins each comprises a thermo-plastics. 1 8

9. An article as claimed in Claim 8, in which the skins each comprise a polyethylene.

10. An article as claimed in Claim 6 or Claim 7, in which the skins each comprise a polycarbonate as a polyvinyl chloride.

11. An article as claimed in Claim 10 in which each skin comprises a thermo-setting material.

12. An article as claimed in any preceding claim moulded in one piece by a rotational process whereby material is formed about the interior surface of a mould which during the moulding operation is caused to spin oO.o or rotate about its longitudinal axis and tilt along its transverse axis. tgoo "t'o

13. An article as claimed in claim 12, in which with a thermo-plastics material, the material is heated to achieve a fluid or viscous state after entry into the mould, the mould is rotated and tilted to cause the material to cover the inside surface of the mould to a substantially uniform depth, and the mould is then cooled to enable the plastics material to solidify against the interior of the mould.

14. An article as claimed in Claim 12, in which with a thermo-setting material, the material is initially in a fluid state and the addition of a chemical catalyst, rather than heating and subsequent cooling, is required to solidify the material after covering the wall of the mould.

An article as claimed in any of claims 12-14, in which the first layer so formed is the outer skin, thereafter the procedure is repeated and this time with the plastics material containing a foaming agent, so that a .I 9 second foam layer is deposited against, and adheres to, the already formed outer skin, the procedure being repeated again to form the inner skin.

16. An article as claimed in any of claims 12-15, in which the mould has a nominal bore chosen to produce a pipe substantially of 900mm internal diameter and a length of 3.5 meters, and with a wall thickness substantially of

17. An article as claimed in claim 16, in which the wall thickness can be increased up to

18. An article as claimed in any of claims 12-17, in which a flange is incorporated into the moulding at one or both ends of the article by means .of the mould itself, and the material is hot welded to itself to give a fluid, S 15 suitably air and water, tight joint.

19. An article as claimed in claim 18, in which an ring seal forms a *fluid tight seal between adjacent flanged pipes.

20. An article as claimed in any of claims 12-17, in which articles are butt welded together. 9

21. A method of constructing an article of large cross-section *9 9 o comprising a first, a second and a third step, in which: the first step involves the formation of an outer skin, from a thermo-plastics material which is introduced into a mould and the mould is heated whilst being spun or rotated about its longitudinal axis and tilted about its transverse axis to cause the thermo-plastics material to cover the walls of the mould to a substantially uniform thickness, the spinning being continued whilst the mould is cooled to allow the material to solidify and form the outer skin; the second step involves the formation of a foamed layer which provides the required rigidity for the pipe, the foamed layer is formed in a similar manner in the rotating, tilting and heated mould, a foaming agent being incorporated within the charge of thermo-plastics material introduced into the mould and upon spinning and heating of the mould forms a foamed or closed cell layer having a multitude of air pockets or bubbles which bonds to the previously formed outer skin; and the third step comprises repeating the first step to provide an inner protective skin to the foam layer. see* S. 15

22. An article produced by the method of Claim 21.

23. An article of large cross-section substantially as described herein W .4 with reference to and as illustrated in the accompanying drawing.

24. A method of constructing an article of large cross-section •''substantially as described herein with reference to and as illustrated in the accompanying drawing. :DATED this 22nd day of May 1998. RONALD ROBIN COLIN WITTER WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN. VIC. 3122.