Pipes and tubular conduits – Flexible – Braided – interlaced – knitted or woven
Patent
1998-06-04
2000-06-13
Kashnikow, Andres
Pipes and tubular conduits
Flexible
Braided, interlaced, knitted or woven
138141, F16L 1100, F16L 914
Patent
active
060736577
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for producing homogenous material with an extruder at least two annular conical feed gaps situated between a rotatable rotor and a stator so that the material to be extruded is supplied between the rotor and the stator.
The invention further relates to an extruder comprising at least two annular conical feed gaps situated between a rotatable rotor and a stator, and which comprises means for supplying the material to be extruded between the rotor and the stator.
The invention also relates to a multilayer plastic pipe comprising an inner and outer pipe and an intermediate layer formed of softer material and situated between the inner and outer pipe.
U.S. publication 3,314,108 discloses an extruder comprising two conical stators and a conical rotor that is placed rotatably between the stators. The plastic material to be extruded is supplied via two separate conduits to different sides of the rotor. The rotor is provided with screw-shaped grooves by means of which the material is transferred towards an orifice at the narrower end of the extruder. The intermixing of the materials to be fed via different conduits is prevented with seals at the end where the material is supplied, wherefore the materials situated on different sides of the rotor only come together after the rotor near the end of the extruder, wherefore the intermixing of the materials remains insignificant. Further, unequal pressures may easily occur on different sides of the rotor due to the feed rates of the separate material flows fed from different conduits, and the pressure difference stresses the rotor and may damage it.
European patent application 89 906 779.7 discloses an extruder comprising several conical stators, and conical rotors that are rotatably placed between the stators. The material to be extruded is supplied along one conduit to the beginning of each rotor, whereupon the inlet of the rotor comprises openings via which the material can also flow to the other side of the rotor. By means of grooves provided on each side of the rotor, the material is transferred towards the end of the extruder. Also in this apparatus, the material flows passing on different sides of the rotor come together only near the orifice, wherefore the materials situated on different sides do not intermix efficiently. Further, there may be a great difference in pressure on different sides of the rotor and it stresses the rotor and may damage it.
When multilayer pipes are prepared, the intermediate layer or layers are typically made less strong than the outer and inner layers, or less strong materials are commonly used in the intermediate layer compared to the outer and inner layers. The material of the intermediate layer is preferably for example waste plastic, since this arrangement decreases the pollution of the environment and is also very advantageous economically. Another alternative is the foaming of the plastic material of the intermediate layer, but the foaming can naturally also be performed on waste plastic. However, especially the use of waste plastic requires that the equipment to be used has better mixing and processing properties than usually. Also, it may be necessary to mix reinforcing fibres in the intermediate layer, and the even distribution of the fibres in this layer requires very efficient mixing.
The extrusion apparatuses for multilayer pipes that have been developed so far have not provided sufficient mixing of the intermediate layers in the aforementioned cases.
U.S. Pat. No. 4,364,882 discloses a conventional foamed pipe made of PVC. The PVC is foamed to the density of 500 kg/m.sup.3, which in fact represents the minimum that can be achieved with the conventional technology. A typical foaming degree for PVC foam is 57%, in which case the density is 800 kg/m.sup.3, since with lower values the strength properties of the PVC foam deteriorate rapidly. The patent discloses a pipe having an outer diameter of 315 mm and the following structure:
the inner pipe has a thickness of 1.25 mm, the intermediate lay
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Hippelainen Esko
Jarvenkyla Jyri
Kirjavainen Kari
Hwu Davis
Kashnikow Andres
Uponor Innovation AB
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