Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Production of continuous or running length
Patent
1994-04-28
1995-09-12
Thurlow, Jeffery R.
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Production of continuous or running length
264 85, 264557, 264235, 264236, 264237, 425113, 425445, B29C 4788
Patent
active
054494885
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method in which plastic material is extruded into at least one layer on the surface of a conductor or the like, and the conductor or the like coated with the plastic material is cooled in a predetermined manner in connection with an insulating or sheathing process.
In the production of cables, there occurs problems due to the large change of the specific volume of plastic materials, such as polyethylene, on transition from the melting point to the room temperature. This is because the large change of the specific volume causes a disadvantageous shrinking phenomenon to occur in the cable, which tends to shorten the plastic layer around the conductors, thus causing problems in cable extensions and terminals. The shrinking effect has previously been reduced by applying a heat treatment to the finished cable or conductor wound on a reel. A problem therewith is, however, that as the stresses are released, when the cable is bent around the reel, further stress states are created in the plastic material when the cable is straightened. The heat treatment of the cable wound on a reel also requires plenty of time, at least 2 to 3 days, as well as plenty of energy.
The object of the invention is to provide a method by means of which the disadvantages of the prior art can be eliminated. This is achieved by means of a method according to the invention, which is characterized in that after the cooling of the conductor and the plastic material in vicinity to it to a predetermined level in the insulating or sheathing process, the surface layer of the plastic material and the plastic material portions in vicinity to it are reheated to a predetermined temperature in a pressurized space filled with a medium.
An advantage of the invention is mainly that the above-mentioned shrinking problems can be eliminated in a very short time and by a considerably lower consumption of energy as compared with the previously used technique. An example of the savings obtained in terms of energy consumption is that the heat treatment of a specific cable required an amount of energy of about 32 kWh/km when applying the method according to the invention. When using the prior art heat treatment with a corresponding cable wound on a reel, the energy consumption is about 46 kWh/km if the temperature of the cable is raised from 20.degree. C. to 100.degree. C. In addition, a considerable amount of energy is consumed in heating the reel and in the losses of the heat treatment space. A further advantage of the invention is that, contrary to the prior art technique, no new stress states are created in the cable as the heat treatment according to the invention is performed on straight cable in place of cable wound on a reel.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be described more closely by means of an example shown in the attached drawings, wherein
FIG. 1 shows a typical cross-section of an insulated conductor of a high-voltage cable;
FIG. 2 is a graphical presentation illustrating variation in different parameters when the cable conductor enters the cooling step of the process;
FIG. 3 illustrates variation in the parameters of FIG. 2 when applying the method according to the invention; and
FIG. 4 illustrates the diameters of the plastic material layers calculated from FIGS. 2 and 3 as compared with the actual diameters when the temperature drops to 20.degree. C.
FIG. 1 shows a typical cross-section of an insulated conductor of a high-voltage cable. A thin semi-conductive plastic layer, a conductor shielding 2, is provided around the conductor 1. The conductor shielding 2 is covered by an insulation 3, and the outermost layer also consists of a rather thin, semi-conductive corona shielding 4. The finished cable further comprises a varying number of different layers, which, however, are well-known to one skilled in the art, and are not as such directly related to the invention. These layers will not be described in greater detail herein. The thickness of the plastic layer on the conductor in
REFERENCES:
patent: 3553042 (1971-01-01), Cocco
patent: 3635621 (1972-01-01), Miyauchi et al.
patent: 3849192 (1974-11-01), Schmidt
patent: 3997288 (1976-12-01), Takaoka et al.
patent: 4035129 (1977-07-01), Karppo et al.
patent: 4078111 (1978-03-01), Yamaguchi et al.
patent: 4110062 (1978-08-01), Summers
patent: 4150082 (1979-04-01), Brick et al.
patent: 4259281 (1981-03-01), Lanfranconi
patent: 4457975 (1984-07-01), Bahder
patent: 4980001 (1990-12-01), Cornibert et al.
Nokia-Maillefer Oy
Thurlow Jeffery R.
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