Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
1998-04-08
2001-03-06
Pyon, Harold (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S108000, C264S171290, C264S209800, C264S211100, C425S113000, C425S133100, C425S204000, C425S377000, C425S378100, C425S379100, C425S380000, C425S381200, C425S382300, C425S462000
Reexamination Certificate
active
06197239
ABSTRACT:
FIELD OF INVENTION
The invention relates to an extrusion apparatus for preparing a cylindrical plastic product or for coating the product at least with one layer of plastic, the extrusion apparatus comprising at least one conical stator, at least one conical rotor, and at least one conical supply opening between them for pressing the plastic material to be extruded into an extrusion conduit. The invention also relates to a method for defibering and/or orienting a plastic material during the manufacture or coating of a cylindrical plastic product with the aforementioned extrusion apparatus. The cylindrical plastic product may be for example a plastic pipe, a plastic film or some other similar product.
BACKGROUND OF INVENTION
Previously when pipes were coated, an outer pipe was first formed on top of the pipe to be coated. In such a case, it was not possible to provide the outer pipe with the desired orientation, for example. Further, when a long screw is used in the present manner, the pipe to be coated warms up.
Norwegian Published Specification 159,841 discloses a crosshead tool provided with a rotating mandrel in connection with the extruder. With this arrangement, it is possible to form, but not maintain, the desired orientation during the coating of a cable, even though the coating layer can be pressed at least in principle against the cable with pressure, so that the adhesion of the coating to the surface to be coated can be improved.
The purpose of the present invention is to avoid prior art problems and to produce an extrusion apparatus that provides the product with the primarily desired permanent orientation.
SUMMARY OF INVENTION
This aim is achieved with an apparatus according to the invention, which is mainly characterized in that at the end of the rotor there are means for defibering and/or orienting the plastic material.
The aforementioned means most preferably comprise a substantially cylindrical extension that extends to the extrusion conduit at the end of the rotor.
These means may also comprise openings extending through the rotor and/or its extension.
There may be an annular flange at the end of the rotor or its extension, the flange preferably comprising bores extending through it.
The method according to the invention is in turn characterized mainly in that the rotor or rotors are rotated so rapidly that the helical orientation has almost the same direction as the circumference, and that the cylindrical plastic product exiting the extrusion apparatus is drawn with a drawing device in such a way that the orientation of the plastic molecules in the circumferential direction is reduced, so that the orientation angle of the finished product is smaller, preferably about 50 to 60° .
With the rotor formed in the manner according to the invention, the plastic material to be extruded can be provided with helical orientation that can be made permanent by cooling the pipe or the piece to be coated in a suitable manner and possibly by also cooling the extrusion apparatus from the outside. The helical orientation is mainly produced by the motion of the rotating rotor and the helicity can be maintained by means of the cylindrical extension. The orientation is improved by the possible interior cooling of the material to be extruded.
An essential feature of the present invention is that the extrusion product can be cooled into the product form at the same time as it is crystallized, i.e. the apparatus discharges a finished product that thereafter does not necessarily have to be subjected to any operations for increasing its strength. However, the radial orientation is preferably improved by treatment with a mandrel, and the axial orientation is adjusted with a drawing device to the desired level, which is preferably about 50% lower than in the radial direction.
An advantage of the invention is that, when several relatively thin layers are prepared, they can be cooled and the orientation can thus be frozen. This is both very expensive and difficult with the conventional extrusion techniques. In the arrangement according to the invention, it is possible for example to prepare two thin layers and to perform the intercooling with one machine and to manufacture more layers with another machine. Due to the compact structure of the machine, the saving in space and money is significant.
For the purpose of supplying preferably several thin layers of plastic, the extrusion apparatus comprises at least two rotors provided with for example cylindrical extensions and stators surrounding the rotors, the directions of rotation of successive rotors being mutually opposite. In such a case, it may also be preferable that between the rotors there are intercooling apparatuses for ensuring that the orientation of the thin layers is frozen.
Especially when plastic material is being spun, crystallized or cross-linked, it is advantageous that the cylindrical extension of at least one rotor enlarges substantially conically in the direction of flow of the plastic material, and that there are means for conducting the plastic material that flows in the supply opening at the back of the rotor to the outer surface of the extension and thus to be mixed with the plastic material flowing in the supply opening at the front of the rotor, and that there are means for conducting the plastic material on the outer surface of the extension further through the extension and into its interior.
If the extrusion apparatus is intended for coating an existent product, for example a cable, the inlet end of the extrusion conduit preferably comprises a cooling device for the initial cooling of the product conducted into the conduit.
On the other hand, if the extrusion apparatus is intended for the production of a plastic pipe, the extrusion conduit is provided with a cooling mandrel.
In a preferred embodiment of the method according to the invention, a cylindrical preform that exits the extrusion apparatus is drawn with a drawing device over a tempered mandrel following the extrusion apparatus in such a way that the stretching of the plastic molecules in the circumferential direction increases further, but due to the simultaneous axial stretching, the orientation angle has a value that is below the original, preferably the aforementioned 50 to 60° .
The plastic material fibers can be spun and crystallized on a product moving through a cold mandrel or extrusion apparatus.
The mixture of cross-linked and non-cross-linked plastic material can be heated to the cross-linking temperature by means of a hot mandrel.
It is also possible to start the method at a higher temperature and to form a product with a standard diameter that is drawn to the other devices, such as a cooling basin, in the production line, whereafter the manufacturing temperature of the product is lowered near the orientation temperature, so that the orientation can be made permanent.
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Richard, K., et al. “Verfestigte Rohre Aus Ziegler-Polyathylen”,Kunatoffe, VAL 50, NO 7, 1960, pp. 371-375.
Derwent's Abstract of JP50-24109 of Feb. 1993.
Derwent's Abstract of JP1-114418 of May 1989.
Derwent's Abstract of SU 1384394 o
Jarvenkyla Jyri
Kirjavainen Kari
Leyson Joseph
Nextrom Holding S.A.
Pyon Harold
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