Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2001-12-03
2004-09-07
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S034700, C428S036300, C138S153000, C138S174000
Reexamination Certificate
active
06787207
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a multi-layer pressure pipe of a plastic material.
BACKGROUND OF THE INVENTION
Pipes are used, for example, for the conveying of liquids and gases and as various structural parts in machines and apparatus, in transport vehicles, in the building industry, etc. By the use of plastic pipes, significant advantages over metal pipes can be gained in many applications. Typical advantages of plastic pipes over metal pipes include their light weight, corrosion resistance, moldability in manufacture, and electrical and thermal insulation capacity.
Plastic pipes are manufactured typically by extrusion. Reinforced-plastic pipes are manufactured most commonly by pultrusion, winding, rolling or compression molding.
Non-reinforced plastic pipes are manufactured from, for example, PVC, poly-ethylene, polypropylene, polybutene, and crosslinked polyethylene. Reinforced plastic pipes are commonly manufactured from glassfiber and thermoset plastic, which may be, for example, polyester, vinyl ester or epoxy.
It is known that lightweight and corrosion-resistant structures can be achieved by using thermoplastic pipes. The problems involved with thermoplastic pipes typically include low mechanical strength properties and susceptibility to creep when loaded.
Furthermore, their impact resistance is poor at low temperatures, and for pressure resistance the pipes must be made thick-walled.
On the other hand, it is known that pressure-resistant and rigid structures can be obtained by the use of reinforced-plastic pipes. However, reinforced-plastic pipes are easily damaged by impact, whereupon they lose some of their mechanical strength properties and become susceptible to environmental effects, such as corrosion. Furthermore, the wear resistance of reinforced-plastic pipes is low in some conditions.
Attempts have been made to improve the weak properties mentioned above by manufacturing composite pipes by forming a reinforced thermoset layer around a thermoplast pipe. With pipes thus manufactured, a good inside wear resistance and chemical resistance, as well as a good resistance to pressure and good rigidity, are achieved. However, brittleness typical of thermoset plastics renders the pipe susceptible to impact break. In such a case the thermoset outer pipe may break, whereupon its structure is exposed to corrosion and its mechanical strength is reduced. Furthermore, sufficient adhesion is not achieved on the interface between the thermoset and thermoplastic pipes, and so delamination, i.e. detaching of the layers from each other, will occur on the interface when the pipe is subjected to sufficient stress. This phenomenon will cause the reduction of both mechanical and chemical strength in the pipe.
In addition, attempts have been made to correct the above-mentioned weaknesses of plastic pipes by combining thermoset and thermoplastic pipes with each other in different orders, or thermoplastic pipes have been combined with other thermoplastic or thermoset pipes so that their interfaces are tightly fitted to each other. However, these structures do not eliminate from the pipes the discontinuity points caused by the interfaces, which discontinuity points cause weakening of the structure owing to the above-mentioned impact damage, to material-specific thermal expansion coefficients of the different pipe types, or to elongation.
In order to eliminate the discontinuity points in the joints between the different layers of a pipe, U.S. Pat. No. 3,900,048 discloses a manufacturing method for reinforced plastic pipes wherein a glassfiber-reinforced, thermoplastic, non-crosslinked polymer is attached around a thermoplastic core pipe by means of a solvent. According to the method disclosed in the publication, the clear interface between the layers can be caused to disappear by means of a solvent.
Success according to U.S. Pat. No. 3,900,048 presupposes that the thermoplastic pipe and the polymer matrix of the glassfiber-reinforced polymer layer are soluble. However, materials which are not soluble or which are very difficult to dissolve are commonly also used in pipes. The dissolving of a polymer is in many cases time-consuming, and therefore such a method is often not suitable for practical applications. Furthermore, non-desirable solvent residues of the solvent used may be left in the pipe.
Patent application WO 9507428 discloses a thermoplastic composite pipe which is made up of a thermoplastic core pipe and, surrounding it, a composite material made up of a thermoplastic and continuous reinforcement fibers. The thermoplastic core pipe and the surrounding composite material made up of a thermoplastic and continuous reinforcement fibers are thermally fused to each other seamlessly.
The thermoplastic matrix polymer of the composite material and, when so desired, the thermoplastic core pipe are heated at their joint to the melting or fusion point of the thermoplastic in order to produce a seamless joint.
The thermoplastic composite pipe is manufactured by winding a windable composite material made up of a thermoplastic and continuous reinforcement fibers around a thermoplastic core pipe by using a winding angle of 0-180° or different angles in selected layers, preferably a winding angle by means of which the composite material being wound can be wound into an even layer
A thermoplastic composite pipe may be manufactured by a so-called prepreg method described in WO 9507428 by applying onto a selected thermoplastic core pipe a composite material made up of a thermoplastic and a continuous reinforcement phase in such a manner that a tape-form composite material of suitable width, selected according to the core pipe diameter and the selected winding angle, is directed from a reel onto the periphery of the rotating core pipe. The seamless fusion of the composite material tape and the thermoplastic core pipe is achieved by heating the composite material to its softening or melting temperature before it is directed onto the core pipe surface. Furthermore, it is also possible to heat the surface of the core pipe at the fusion point so that the outermost surface of the pipe is at a temperature at which softening and/or melting can occur. The fusion of the thermoplastic phases in molten state to each other is ensured by tension of the composite-material tape being wound around the core pipe, the tension causing a pressure advantageous for the fusion, at the point at which the said melt phases meet. Fusion occurs when the melted meeting point of the composite material and the core pipe cools from the melting temperature while the said composite-material tape is still under tension. The fusing of the composite-material layers subsequent to the first composite-material layer onto the periphery of the strong thermoplastic pipe blank is carried out in a corresponding manner. The fission can also be ensured by compression molding the pipe at the point of fusion, by means of a pressure roll or the like.
It is known that plastic sewer pipes, such as PVC pipes, have been manufactured by using an extruder. The strength of such a sewer pipe is determined by the additives used in the material being extruded and by the amounts of such additives. However, when a conventional axial single-screw extruder is used, for example the reinforcement fibers settle only in the longitudinal orientation of the pipe, for which reason the bending strength of the pipe will remain low.
In the so-called winding technique disclosed in WO 9507428, the reinforcement fibers of, for example, glassfiber are short fibers, usually in the order of magnitude of fractions of a millimeter. Furthermore, such a multiple-step manufacturing method is relatively expensive, for which reason it is not the best possible method for manufacturing pressure pipes.
Publication DE 2551525 discloses fiber reinforced pipes, process and arrangement for their production. It is particularly concerned with fiber reinforced pipes containing one fiber reinforced layer which can be provided on the inside and/or on the outside with a thin layer
Ek Carl-Gustaf
Heikkila Pekka
Lindstrom Helge
Nymark Anders
Borealis Technology OY
Chevalier Alicia
Pyon Harold
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