JPS6254217B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a cross-linked insulated cable, and more particularly, to a method for manufacturing a cross-linked insulated cable. , relates to a method for manufacturing a cross-linked insulated cable that is heated from both outer surfaces.

The process of crosslinking or vulcanizing the uncrosslinked insulator that is extruded and coated around the cable conductor is an important process that affects the manufacturing efficiency of cables with extruded insulators. ) Because the vulcanization cylinder part where the process is carried out occupies a very large portion in terms of both equipment space and cost, it is not permissible to simply increase the size of this vulcanization cylinder part, so it is necessary to use the smallest vulcanization cylinder. Techniques that can be used to maximize crosslinking efficiency have been the subject of research and development in cable insulation crosslinking methods.

Since the efficiency of crosslinking of cable insulation is determined almost entirely by heating, improvements in the efficiency of heating in vulcanizing tubes have recently been pursued, and in particular, various methods using induction heating have been developed. To explain the conventional method of utilizing induction heating, as shown in FIG. 5, an induction heating coil 104 is placed on the outer periphery of the heating area of the vulcanizing tube 101, and the cable conductor 102 is heated by this. As a result, the uncrosslinked insulator 103 in contact with the conductor 102 is heated. The reference numeral 105 indicates a high frequency oscillator, and the reference numeral 106 indicates an extruder crosshead.

In such a conventional induction heating method, the moving cable conductor 102 is heated, and the conductive heat is used to heat an uncrosslinked insulator such as rubber or synthetic resin, so the heating efficiency is poor, and Since the moving conductor serves as the heating medium, it is impossible to measure the heating temperature and, therefore, to control the temperature.
Furthermore, since the induction heating coil 104 is located outside the vulcanizing tube 101, the vulcanizing tube itself, which is mainly made of steel, generates heat and the strength of the magnetic field inside it is insufficient.
There are disadvantages such as insufficient heat generation.

The present invention has been made to eliminate the drawbacks of the prior art, and includes induction heating of both the die and the nipple in the crosshead,
The gist of this method is to simultaneously heat the uncrosslinked insulator extruded from the annular passage between the die and the nipple from both the inner and outer surfaces thereof.

First, an example of an extrusion apparatus used for carrying out the method of the present invention will be explained with reference to FIG. Reference numeral 1 indicates the crosshead of the extruder as a whole, and there is a die 2 provided here in the shape of a hollow column, and a nipple 3 in the shape of a hollow truncated cone coaxially provided inside the die 2. As clearly shown in FIGS. 2 and 3, a passage 10 having an annular cross section is defined, and a total of four channels are defined outside the die 2.
An induction heating coil shown in is arranged. An insulator 8, such as uncrosslinked polyethylene, is extruded from the annular passageway 10 and is coated around the conductor 7. The cable is then crosslinked to produce a crosslinked insulated cable.

An important feature of this device is that the die 2 is divided into two parts in the axial direction, and the two parts are made of different materials. That is, for example, the downstream half is a non-magnetic part 21 made of a non-magnetic material such as glass or ceramics, and the upstream half is made of a ferromagnetic material such as stainless steel or iron. The ferromagnetic material portion 22 is formed as a ferromagnetic material portion 22.

The induction heating coil 4 may be a single one, and the part corresponding to the ferromagnetic part 22 of the die 2 is used as the die heating coil 4A, which is also the non-magnetic part 2.
The portion corresponding to 1 may be an induction coil separate from the nipple heating coil 4B, and may be connected to a separate oscillator (not shown). Note that 11 is a cooling jacket for the crosshead 1, and 12 is a temperature measuring wire such as a thermocouple or a thermistor, which are attached to appropriate positions for measuring the temperature of the ferromagnetic portion 22 of the die 2 and the nipple 3.

Next, the operation of this extrusion apparatus, that is, the steps of the method of this invention will be explained. When a high frequency current from an oscillator is passed through the induction heating coil 4, the ferromagnetic portion 2 of the die 2
2 generates heat. Furthermore, since the non-magnetic portion 21 of the die 2 does not weaken the magnetic field produced by the induction heating coil 4, the front portion of the nipple 3, which is made of a magnetic material such as steel and faces the non-magnetic portion 21, similarly generates heat by induction. As a result, the insulator 8 passing through the annular passage 10 defined between the die 2 and the nipple 3 is disposed within the radial direction of the passage, as shown by the arrow in FIG.
It will be heated from both the outside. By the way, the temperature of the ferromagnetic part 22 of the heated die 2 and the nipple 3 can be measured by the temperature measuring line 12, so the magnitude of the current flowing through the induction heating coil 4 can be adjusted using this measured temperature as an index. Temperature control can also be carried out easily. In this case, the induction heating coil 4 is not a single one, but the die heating coil 4A and the nipple heating coil 4 as described above.
It should be noted that if they are kept separate from B, the temperature control of the die 2 and nipple 3 can be carried out individually and more precisely.

FIG. 4 shows another configuration example of the apparatus used in the method of the present invention, and here, the ferromagnetic portion 22 and non-magnetic portion 21 of the die are arranged in the axial order as shown in FIG. 1. It is the opposite. That is, in the figure, the upstream half of the die 2 is a non-magnetic part 21, and the downstream half is a ferromagnetic part 22, and in this case, the nipple 3 is located at its downstream end in the axial direction. Even if the part extends to the inside of the ferromagnetic part 22 of the die 2, that part is not heated. A nipple that is axially short enough to extend to the desired position may also be used. The operation of this device example can be explained in exactly the same way as the previous device example, so a detailed explanation will be omitted. It will be appreciated that conduction heat is received from the radially inner side of the passageway 10 and, on the downstream side of the passageway, from the die 2 side, ie from the radially outer side of the passageway 10. Note that measurement points of the temperature measurement line 12 are provided at the ferromagnetic portion 22 of the die 2 and the nipple 3, and thereby the annular passage 1
Similarly to the case of FIG. 1, heating temperature control of 0 can be performed.

As detailed above, according to the present invention, (i) the method heats the uncrosslinked insulator coated on the cable conductor immediately after extrusion before entering the vulcanizing tube; The efficiency of the cross-linking process can be greatly improved without increasing the length of the insulator. (ii) The insulator is heated simultaneously from both the inner and outer sides of the annular passage between the die and nipple, resulting in excellent heating efficiency. (iii) Since it uses an induction heating method, the heating equipment is simple, and since a fixed die and nipple are heated, temperature control is easy, leading to improved crosslinking quality, and many other effects can be obtained. .

[Brief explanation of the drawing]

FIG. 1 is a side cross-sectional view showing an example of an apparatus used for carrying out the method of the present invention, FIGS. 2 and 3 are cross-sectional views taken along lines - and -, respectively, in FIG. 1, and FIG. FIG. 5 is a side sectional view showing another example of the apparatus used for carrying out the method, and FIG. 5 is a side sectional view showing an example of the prior art. DESCRIPTION OF SYMBOLS 1... Crosshead, 2... Die, 21... Nonmagnetic material part, 22... Ferromagnetic material part, 3... Nipple, 4... Induction heating coil, 7... Cable conductor, 8... Insulator, 10... Circular passageway.

Claims (1)

[Claims] 1 The die and nipple in the crosshead for extruding uncrosslinked insulators such as rubber or synthetic resin are heated by induction, and the extruded uncrosslinked insulator is heated from both inside and outside of the annular passage surrounded by the die and nipple. A method for producing a cross-linked insulated cable characterized by simultaneous heating.