Multipurpose composite tubing

Details Multipurpose composite tubing Multipurpose composite tubing

1997-06-24

2001-01-09

Dye, Rena L. (Department: 1772)

Plastic and nonmetallic article shaping or treating: processes

Pore forming in situ

Composite article making

C264S045500, C264S045800, C264S046500, C428S036500, C428S036910

Reexamination Certificate

active

06171533

ABSTRACT:

INTRODUCTION
This invention relates to multi-purpose composite tubing that has a broad range of applications including but not limited to duct work for air conditioning, protective lining for buried pipes, piping for dredging operations and form work for casting concrete.
DESCRIPTION OF THE PRIOR ART
Tubing products presently used for dredging, piping, form work and other applications have a number of drawbacks.
For example cardboard tubing that is used in casting concrete pillars leaves a low grade finish that in some applications requires further rendering to be performed on the pillar. The cardboard tubing is also generally circular in cross section making it unsuitable for casting square pillars.
Air conditioning duct is commonly comprised of spiral wound sheet metal surrounded by insulation material. However in some air conditioning applications where the insulation is insufficient condensation forms on the metal tubing, which can lead to corrosion and other problems.
Piping that is used to pump sand from a dredger to a filter or other collection point frequently requires assistance in the form of attached floats to increase the buoyancy of the pipe These floats increase the labour cost of setting up such a dredging operation along with increasing the capital cost and equipment required.
Buried piping commonly has protective coatings such as paint and galvanising applied to prevent corrosion and other problems occurring. However during backfilling it is necessary to cover the pipe with fine sand so that the coating is protected from moving debris during the back filling operation.
It Is desirable for many of these applications to provide a lightweight, strong tube which is not susceptible to water damage.
Some tubing is known which is formed from composite layers, including a foam material, for example hosing as disclosed in Australian patent application No. 5802086, which discloses a flexible hose material. Composite materials using foam for conduits are disclosed in British patent application No. 2046661, and for tubing as disclosed in U.S. Pat. No. 3,665,968. In the latter two arrangements, the structural strength of the material is provided by a rigid outer layer.
SUMMARY OF THE INVENTION
According to one aspect the present Invention provides a method of manufacturing a composite tube comprising the steps of
a) supporting and locating an inner liner on an inner mould core;
b) locating and supporting a flexible outer liner in axial alignment with the inner liner, so as to create a sealed annular space between the liners;
c) introducing a foaming material between the liners so as to fill the annular space;
d) allowing the foaming material to cure sufficiently to allow removal from the mould; and
e) reducing the cross-sectional area of said inner mould core after forming said tube to facilitate extraction of said tube from said mould.
Reducing the cross sectional area of the Inner mould core once the tube has been formed breaks any surface tension sealing effect that may occur between the inner core and the inner liner before the tube is extracted from the mould. This has been found to aid in the de-moulding of the tube during the manufacturing process.
Preferably the amount of foaming material introduced is chosen so that it will fill the entire void, without leaving any interior spaces. This is desirable to ensure the structural characteristics of the tube are consistent. The use of an expanding foam material according to the inventive method has the capacity to minimise the risk of interior spaces occurring.
Preferably said inner mould core is formed of at least two parts which are relatively displaceable so that the cross sectional area of the inner mould core can be reduced alter forming. Preferably the inner mould parts are relatively displaceable along at least one plane longitudinal with the mould.
Alternatively, the inner mould core may be inflatable or otherwise constructed to allow for reduction of the diameter of the inner core.
Another alternative aspect of the invention provides that the outer liner may also be supported by an outer mould core. Such an outer mould core may be formed of at least two parts that are displaceable to facilitate extraction of a formed tube.
Preferably spacing elements located between said Inner core and said outer core facilitate the correct alignment, and form a closed space for region for the insertion of an expanding foam material.
According to another aspect the present invention provides a tubing material, comprising a flexible outer liner, an inner liner, and a rigid foam material integrally formed between the inner and outer liner, said foam material providing structural rigidity to the tubing material.
Preferably, the inner liner is formed from a flexible material, and the outer liner is formed from a sleeve of non-rigid material, for example a foil or a woven polymer mesh, depending upon the required application.
The inner liner may be of a different cross sectional shape to the outer liner.
In applications encountering great hoop stress a number of outer liners may be located at differing radii throughout the filler material. This is preferably achieved by locating at least two woven liners of different diameters concentric with the mould and then inserting the filler material.
Preferably a polyethylene liner is located between the expanding foam material and the final outer woven structure. The outer liners may be permeable to the uncured foam material.
Preferably the foam is an expandable foam such as polyurethane. The tube may be is constructed of any combination of liners and/or filler material so as to be impact resistant.
The present Invention provides a tube which is lightweight yet strong, and is relatively inexpensive. The use of a flexible inner and outer liner, and a foaming material, means that space requirements for storage of raw materials are minimised, as the liners may be easily dispensed from a roll or the like, and the foam material is only expanded during manufacture. The in-situ foaming also provides a very good bond between the foam and the liners. The tubing may be altered in its constituent components depending upon the application, and the method of manufacture disclosed facilitates easy manufacture of short runs of customised tubing, if required.


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