Pipes and tubular conduits – Flexible – Spirally wound material
Patent
1998-07-28
2000-04-25
Kashnikow, Andres
Pipes and tubular conduits
Flexible
Spirally wound material
138141, 138125, F16L 1100, F16L 914
Patent
active
060532149
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to oriented polymeric articles, and more particularly to a novel oriented polymeric article comprising an oriented crystalline or semi-crystalline thermoplastic polymeric material having improved properties and a method and apparatus for its production.
PRIOR ART
It is well known that the physical and mechanical properties of crystalline and semi-crystalline thermoplastic polymers can be improved by orienting their structures. Polymer processing methods, such as drawing, blow moulding, injection moulding and the like have all been used to fabricate articles of thermoplastic polymers having oriented structures.
In recent years, extensive studies have been directed to methods of deforming thermoplastic polymers in a solid state (ie. below the crystalline melt temperature). In these methods, the polymer is mechanically deformed to obtain a desired uniaxial or biaxial molecular orientation. The polymer may be drawn, extruded or otherwise processed at temperatures ranging from the glass transition temperature to temperatures just below the crystalline melt temperature of the polymer. Products such as strip, tubes, rods and other shaped articles, usually, but not always, having predominantly unidirectional orientation, have been fabricated by such processing methods, for example, as described in U.S. Pat. No. 3,929,960 and U.S. Pat. No. 4,053,270.
Biaxially oriented containers, such as bottles used in the soft drinks industry, are made by a melt extrusion-stretching or injection moulding-blowing expanding process. Such a process is described, for example, in U.S. Pat. No. 3,923,943. The containers are produced by stretching the polymer, typically over 250 percent. Such large stretching deformations can result in non-homogeneous deformation of the structure thereby damaging the spherulitic crystalline aggregates, causing the formation of microvoids and the enlargement of any microvoids already present in the polymer. The density of the polymer is typically decreased and the microstructural sensitive properties, such as stress whitening and low temperature brittleness, remain.
Elongate, relatively thick-walled, high strength tubular polymer products, such as high pressure hoses, tubes and pipes have been produced by plasticating extrusion methods. One such method for producing thermoplastic pipe is described in U.S. Pat. No. 3,907,961. The thermoplastic polymer is heated to a molten state and is extruded with a ram extruder through a conical shaped passage onto a flexible mandrel. A cooling system for the die set is provided to cool the surfaces of the pipe to a solidified state. The polymer is extruded in the molten state and the resultant pipe has an unoriented structure. There is no mentioning of the use of cooling for enhancing orientation.
A further method for producing high pressure pipe is described in U.S. Pat. No. 4,056,591, which is directed to a process for controlling the orientation of discontinuous fibre in a fibre reinforced product produced by melt or plasticating extrusion. The fibre-filled plastics matrix is extruded through a diverging die having a generally constant channel. The walls of the die may taper slightly so that the area of the outlet of the die is larger than the area of the inlet of the die. The amount of orientation of the fibres in the hoop direction is directly related to the area expansion of the channel from the inlet to the outlet of the channel. The product is a reinforced pipe containing fibres that are oriented in the circumferential direction to improve the circumferential properties.
While the fibres may be oriented, the polymer is substantially unoriented, since it is processed in a molten state. In other words, because the fibre reinforced polymer is processed in a molten state, the structure is not composed of platelet or wafer-like, radially compressed spherulitic crystalline aggregates highly oriented both circumferentially and axially, although the fibres added to the polymer may be oriented circumferentially an
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Agren Stig Lennart
Hoving Lars Goran
Jarvenkyla Jyri Jaakko
Josefsson Hans Martin Tony
Lundequist Nils Yngve
Hwu Davis
Kashnikow Andres
Uponor BV
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