JPS5826762B2 - Coaxial cable manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of manufacturing a coaxial cable.

FIG. 1 shows the structure of a submarine coaxial cable as an example of a coaxial cable, and FIG. 2 schematically shows a conventional method for manufacturing an insulator for submarine coaxial cables.

In the figure, 1 is the inner conductor, 2 is the insulator, 3 is the outer conductor,
4 is a jacket, 5 is an extrusion molding machine, and 6 is a cooling water tank.

When manufacturing an insulator for a coaxial cable, the insulator 2 is continuously solidified from the outer layer by cooling water in a cooling water tank 6.

During the period from when the outermost layer of the insulator begins to solidify to when the entire insulator finishes solidifying, a solidified layer is formed on the outer layer of the insulator, while the inner layer of the insulator is in a molten state. .

When an insulator extruded in a molten state is cooled, voids will occur if the volumetric contraction of the solidified layer due to cooling is smaller than the volumetric contraction of the molten layer. If the amount of volumetric shrinkage is equal, no voids will occur.

In order to equalize the amount of volumetric contraction of both the solidified layer and the molten layer, it is necessary to reduce the temperature difference within the insulator during step 1 when the entire insulator is solidified.

Therefore, firstly, the temperature difference TD between the innermost insulator layer and the outermost layer does not exceed the critical value T8 at the time when the outermost insulator layer starts solidifying, and secondly, the entire insulator is solidified. 1, it is necessary that the difference in temperature between the outermost layer and the innermost layer of the insulator does not become large.

Regarding the critical value T8 of button TD, it is assumed that under cooling conditions such that the amount of volumetric contraction of the solidified layer of the insulator is equal to the amount of volumetric contraction of the molten layer, the temperature at which the outermost layer of the insulator starts solidifying is The temperature difference TD within the insulator (difference between the temperature of the outermost layer and the temperature of the innermost layer of the insulator) is defined as the critical value T8 of TD.

T8 varies depending on the density of the insulator, the volume shrinkage rate of the insulator, the Young's modulus of the insulator, and the outer diameter of the insulator.

Manufacturing conditions that make T8 possible will be described later.

The temperature distribution inside the insulator when manufacturing an insulator for submarine coaxial cables using the conventional manufacturing method shown in Figure 2 is shown in Figure 3.
As shown in the figure.

A is the temperature at the boundary between the insulator and the center conductor, B is the temperature at the outermost layer of the insulator, C is the water temperature distribution in the cooling water tank with respect to the cooling time, T
1. T2゜T3. T4. T5 is No. 1, 2, 3, respectively.
4.5 Water temperature of cooling water tank.

to is the time at 1 when the entire insulator finishes solidifying, and t8 is the time from when the entire insulator finishes solidifying to when the insulator leaves the cooling water tank (cooling time - 16).

To is the temperature at which the insulator begins to solidify.

TD is the temperature difference (A-B) inside the insulator that is turned on at the time when the temperature of the outermost layer of the insulator reaches B-To.

In the conventional manufacturing method of insulators for submarine coaxial cables, a molten insulator 2 is passed from an extrusion molding machine 5 to a center conductor 1.
The conventional method used was to extrude and coat the material on top of the material and then slowly cool it continuously to room temperature using two or more cooling water tanks 6, which had the following drawbacks.

First, when moving from the first cooling water tank to the second cooling water tank, and from the second cooling water tank to the third cooling water tank, there is a
A-B) increases temporarily, making voids more likely to occur.

Second, if the manufacturing speed is increased, the outermost layer of the insulator will start to solidify in the cooling water tanks after the second cooling water tank, so when the temperature of the outermost layer of the insulator reaches BfJ''-Tc, When the temperature difference TD becomes greater than the critical value T8, voids occur.

Thirdly, T8 (the time from the time when the entire insulator has finished solidifying to the time when cooling of the insulator has finished) is 5 of the total cooling time.
0%, and it takes more time than necessary to manufacture the insulator.

The present invention has been proposed to improve the above-mentioned drawbacks.

The present invention is based on a method of manufacturing an insulator for coaxial cables, in which a core covered with an insulator is heated in a cooling water bath such that the temperature difference within the insulator after the time when the outermost layer is solidified is below its critical value. , is characterized by cooling at 1 to solidify the entire insulator, and then rapidly cooling to room temperature in a water bath at 1, the purpose of which is to suppress the generation of voids between the insulator and the central conductor. Another object of the present invention is to shorten the manufacturing time of buttons and insulators.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 4 shows an embodiment of the present invention, in which 1 is the center conductor, 2
5 is an insulator, 5 is an extrusion molding machine, 7 is a slow cooling water tank, and 8 is a quenching water tank.

To operate this, the resin temperature TR of the insulator extruded from the extrusion molding machine 5, the cooling water temperature T7°T8:b, and the time for cooling the insulator 2 in the slow cooling water tank T are set as follows. .

The resin temperature TR of the insulator is 170 to 220°C, and the cooling water temperature T7 is 75 to 100°C.
Conditions must be set so that the temperature difference TD within the insulator at the time when the outermost layer of the insulator begins to solidify does not exceed a critical value T8.

Figure 5 shows a density of 0.92 to 0.94? /crA low density polyethylene with an insulator outer diameter of 46 and a center conductor outer diameter of 1.
TD when manufacturing 27nrIL submarine coaxial cable
critical value T8 (temperature difference inside the insulator at the time when the outermost layer of the insulator starts solidifying, which is necessary to equalize the amount of volumetric contraction of the solidified layer of the insulator and the amount of volumetric contraction of the molten layer) The relationship between the resin temperature TR1 and the cooling water temperature T7 of the slow cooling water tank is shown.

The solid line in the figure indicates the conditions under which the temperature difference TD within the insulator at the time when the outermost layer of the insulator starts solidifying is equal to the critical value T8 (resin temperature TR of the insulator and cooling water temperature T7).
) is shown.

Under the conditions indicated by the diagonal line on the upper left of the solid line, T8>TD,
No voids occur.

Under the condition at the bottom right of the solid line, T8<TD, and a void occurs.

Therefore, the resin temperature TR of the insulator and the cooling water temperature T7 should be set so that the intersection of the two falls within the shaded range in FIG. 5. For example, the resin temperature T of the insulator
In the case where R=194° C., as shown by the mark ◎ in FIG. 5, if the temperature of the cooling water in the slow cooling water tank TR≧94° C., a condition in which no voids occur can be obtained.

Nafu・○ mark 1 in Figure 5. The x marks indicate the experimental results, the ○ marks indicate manufacturing conditions in which voids did not occur, and the X marks indicate manufacturing conditions in which voids occurred.

The cooling water temperature T8 of the quenching water tank is desirably a temperature of 5 to 30'C in order to reduce the temperature of the insulator core by 1 to room temperature at the end of cooling.

The insulator is cooled in a slow cooling water bath for at least 25 minutes.

Using the conditions set above (insulator resin temperature TR1, cooling water temperature T7s TBsy in the cooling water tank, and time for cooling the insulator in the slow cooling water tank), the temperature distribution inside the insulator will be as shown in Figure 6. Become.

FIG. 6 shows an embodiment of the present invention, in which the resin temperature of the insulator is 194°C, the cooling water temperature of the slow cooling water tank is 95°C, the cooling water temperature of the rapid cooling water tank is 15°C, and the insulator is placed in the slow cooling water tank. The figure shows the temperature distribution inside the insulator when the insulator for a 43 mm 1 m bottom coaxial cable is cooled by setting the insulator to cool for 30 minutes.

A is the temperature at the boundary between the insulator and the center conductor, B is the temperature at the outermost layer of the insulator, and C is the water temperature in the cooling water tank.

The cooling water tank consists of two tanks: a slow cooling water tank (cooling water temperature T7) and a rapid cooling water tank (cooling water temperature T8).

In addition, solid lines A, B, and C represent temperature distribution when manufacturing at manufacturing speed V1, and dotted lines A' I B'jC' represent manufacturing speed v2 (
This is the temperature distribution when manufacturing according to v2>■1).

The insulator 2 is cooled in an annealing water tank 7 at 1, where the entire insulator is solidified, and then rapidly cooled to room temperature in a quenching water tank 8 at 1.

As described above, in the present invention, since the temperature B of the outermost layer of the insulator is slowly cooled, the temperature difference (A-B) within the insulator between 1 and 1 when the entire insulator is solidified can be made small. .

Furthermore, after the entire insulator is solidified, the insulator 2 is cooled in the quenching water tank 8.
Since the insulator is quickly cooled to room temperature at 1, the time at which the insulator leaves the cooling water tank is 1 after the entire insulator has finished solidifying.
The time at (cooling time - 19) can be shortened.

Furthermore, even if the manufacturing speed is increased from v1 to v2, the outermost layer of the insulator is always solidified in the slow cooling water tank, so the temperature difference TD inside the insulator at the time the outermost layer of the insulator starts solidifying is the critical value T8. Since this will not happen, no void will occur between the insulator 2 and the center conductor 1.

button, the slow cooling water tank 7 of the embodiment shown in FIG. 4 has a cooling water temperature of T7.
It is also possible to divide the tank into 2-3 tanks with water temperatures approximately 5° C. lower from button and T7.

In this case, it is necessary to set the cooling water temperature of each water tank so that the temperature B of the outermost layer of the insulator always starts solidification in the first slow cooling water tank.

As explained above, the entire insulator is solidified in the first water tank, which has a water temperature T7 that provides a temperature distribution such that the temperature difference TD within the insulator does not exceed the critical value T8 when the outermost layer solidifies. By carrying out a manufacturing method in which the insulator is slowly cooled in step 1 and then rapidly cooled in a second water tank having a water temperature T8 that is 50°C or more lower than T7, the entire insulator solidifies.
, B does not become large, and the cooling time after the entire insulator has solidified can be shortened, and even if the manufacturing speed is increased, the temperature difference inside the insulator will be reduced at the time when the outermost layer of the insulator is solidified. Since the TD can be kept constant, even when manufacturing a cable with a thick insulator 2, it is possible to insulate without creating voids without increasing the length of the cooling water tank and increasing the manufacturing speed. It has the advantage of cooling the body.

The present invention can be applied not only to coaxial cables but also to methods of manufacturing cables in which the core wire is coated with an insulator, such as electric cables.

[Brief explanation of the drawing]

Figure 1 shows the structure of a submarine coaxial cable, Figure 2 shows an outline of the conventional manufacturing method for insulators for submarine coaxial cables, and Figure 3 shows the water temperature distribution in the cooling water tank and insulation during cooling according to the conventional manufacturing method. Temperature distribution inside the body, Fig. 4 is an outline of an embodiment of the present invention, and Fig. 5 shows the critical value T8 of the temperature difference TD within the insulator and the resin temperature of the insulator at the time when the outermost layer of the insulator starts solidifying. T
The relationship between R1 and cooling water temperature T7 is shown in FIG. 6, which shows the temperature distribution inside the insulator according to the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Center conductor, 2... Insulator, 3... Outer conductor, 4... Outer cover, 5... Extrusion molding machine, 6... Cooling water tank, I... Annealing water tank , 8...Quick cooling water tank.

Claims (1)

[Claims] 1. The core covered with an insulator is heated to a water temperature such that the temperature difference between the outermost layer and the innermost layer of the insulator after the outermost layer solidifies is equal to or less than the critical value of the insulator. Cool the entire insulator in a set water tank to solidify it,
A method for producing a coaxial cable, which is then cooled to room temperature in a water tank.