JPS5951684B2 - Manufacturing method of plastic insulated cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing crosslinked plastic insulated cables, and in particular crosslinked polyethylene cables.

When manufacturing a cross-linked polyethylene cable, as shown in FIG. crosslinkable polyethylene coating layer b
' is crosslinked in the section of the long land die 2, and the crosslinked polyethylene coated conductor b coming out of the long land die 2 may be cooled with high pressure cooling water in the cooling cylinder 3.

A long cooling cylinder with a length of several tens of meters is used for this cooling cylinder, and the coated conductor is moved while being in contact with the bottom of the inner surface of the cooling cylinder. In the above, since the plastic in the tip of the long land die 2 is crosslinked, the pressure of the uncrosslinked plastic in the die 2 is received by this bridged portion, and the bridged portion and the conductor are substantially bonded. There is.

Therefore, if the outer diameter of the conductor is d and the inner diameter of the long land die 2 is Do, a driving force Fo due to the plastic extrusion pressure Po is acting on the conductor. F0=π/4(Do2-d2)
Furthermore, the crosslinked plastic coating layer immediately after exiting the long round die has not yet been cooled and solidified, and is in a state where the pressure of pressurized cooling water can be propagated.

Therefore, the pressure of the cooling water is propagated to the apparent end surface of the completely cooled and solidified coating layer portion in the cooling cylinder via the incompletely or uncooled solidified portion. This surface pressure F is given by F, ■π/4(D, "-d")P, where the cooling water pressure is Ph and the outer diameter of the plastic insulating layer is D.

Further, if the contact length between the coated conductor and the cooling tube is L, the coefficient of dynamic friction of this contact is μo, and the weight of the cooling water per unit length of the coated conductor is Wo, then the friction force acting on the coated conductor is F.

is F2■LμoWo ・It is.

In Fig. 3, the back tension acting on conductor a supplied to the extruder is To, and the tensile force of coated conductor b is T.
1, Ti+F1+F0=F2+T0, and the plastic-coated conductor is pulled by the tensile force of Ti*F2+To-(F1+Fo)1.

By the way, in the early stage of the above manufacturing, the cooling tube is in a non-pressurized state, and the plastic-coated conductor is emerged from the long land die by the driving force FO due to the extrusion pressure of the plastic tube, and at the emerging end, it is placed in the cooling tube in advance. The lead wires are connected, and the tip of the plastic-coated conductor is moved to the exit of the cooling cylinder by the pull of the lead wire and the above-mentioned propulsive force, and the tip of the plastic-coated conductor is cooled. It is inserted into the seal packing at the outlet of the cylinder.

However, in the past, it was unavoidable that the coating layer of the coated conductor that was manufactured in the early stage and extending inside the cooling cylinder became thicker as it reached the die side.

The reason for this thickening is that when the tip of the plastic-coated conductor that appears at the tip of the die touches the bottom of the cooling cylinder, the linear velocity of the conductor passing through the die decreases due to the frictional force of this contact. By being lowered. Therefore, as the contact length between the coated conductor and the cooling tube increases, that is, as the coated conductor advances inside the cooling tube, the above frictional force increases. The outer diameter of the coating layer of the coated conductor is increasing more and more. The above-mentioned coated conductor portion at the initial stage of manufacture has not been subjected to pressure cooling, and the insulation properties of the coating layer are poor.

Therefore, this coated conductor portion is eventually removed and is not used as a cable. From that point of view, there is no need to consider the above-mentioned thickening of the coating layer of the coated conductor at the initial stage of production as a problem. However, when pressurized cooling water is injected into the cooling cylinder for steady operation, If there is the above-mentioned thickening, the outer diameter of the sheathing layer of the sheathed conductor passing through the seal packing at the outlet of the cooling cylinder will constantly increase at the beginning of steady operation, so the seal at the outlet of the cooling cylinder cannot be reliably guaranteed. The inconveniences mentioned above are unavoidable.

In such a state, it is difficult to maintain the cooling water pressure in the cooling cylinder at a predetermined pressure, and there is concern that the quality of the coated conductor manufactured at the beginning of steady operation may be adversely affected. As mentioned above, in the production of plastic coated conductors using long land dies and pressurized cooling tubes, due to the special manufacturing method,
It is necessary to strictly control the outer diameter of the coating layer of the coated conductor at the time of initial manufacturing.

The method of manufacturing a plastic insulated cable according to the present invention was invented in view of the above points.

That is, in the method for manufacturing a plastic insulated cable according to the present invention, a long land die is connected to an extruder, a cooling cylinder is connected to the long land die, and a crosslinkable plastic ivy coating layer coated on a conductor is lengthened in the extruder. When manufacturing a cable by cross-linking in a land die and cooling the cross-linked plastic covering layer with pressurized cooling water in the cooling cylinder while the cross-linked plastic-coated conductor coming out of the long land die passes through the cooling cylinder. At the beginning of the process, while the tip of the plastic-covered conductor coming out of the long round die is moved to the outlet of the cooling tube with no pressure inside the cooling tube, the plastic-covered conductor coming out of the long round die and This method is characterized in that the tensile force of the conductor is increased in accordance with the increase in the frictional force due to the increase in the length of contact with the bottom surface of the cooling cylinder. The present invention will be explained below with reference to the drawings.

1 to 3, 1 is the crosshead of the extruder, 2 is a long round die connected to the crosshead 1,
3 is a cooling cylinder connected to the long round die 2.

41 is a sending machine, and 42 is a taking machine.

51 is a weight for adjusting the bouncing tension of the conductor a, and 52 is a weight for adjusting the pulling tension of the covered conductor b.

FIG. 1 shows a state in which the conductor a is being moved within the long land die 2 by the driving force FO due to the extrusion pressure of the plastic, and during this movement, the plastic coating layer b'' is crosslinked by the die 2.

As mentioned above, the driving force FO is FO=π/4(DO-D2)PO, where DO is the inner diameter of the long land die 2, d is the outer diameter of the conductor, and PO is the extrusion pressure of the plastic.

This driving force and the back tension TO acting on the conductor are balanced. That is, the amount of slack in the conductor a caused by the weight 51 is set so that the conductor tension TO is equal to the propulsive force FO. In FIG. 1, the cooling tube 3 and the long land die 2 are separated.

Further, the lead wire R has already been inserted into the cooling cylinder 3. When the plastic-coated conductor described above emerges from the die 2, a lead wire R is connected to its tip, and the cooling tube 3 and the die 2 are connected.

Thereafter, as shown in FIG. 2, the coated conductor b is
It is moved by being pulled by the lead wire R while being in contact with the inner bottom surface.

The present invention controls the pulling tension of the lead wire R to prevent the coating layer of the covered conductor b from becoming thicker as described above.

In FIG. 2, as the coated conductor b advances inside the cooling cylinder 3, the contact length X with the bottom surface of the cooling cylinder increases.

This frictional force is expressed as the weight per unit length of the coated conductor, WO',
Letting the coefficient of friction be μo', it is μo'WO'x. Ideally, the pulling tension of the lead wire R is adjusted based on control of the slack amount of the lead wire R by the weight 52 so that the tension is equal to the above-mentioned frictional force.

Therefore, the above-mentioned frictional force is canceled by the pulling tension of the lead wire R, and no movement restraining force is applied to the conductor a passing through the die 2. Therefore, the conductor a inside the die 2 is moved only by the driving force based on the extrusion pressure of the plastic, and the outer diameter of the coating layer of the coated conductor emerging from the die 2 is the same as in the case of Fig. 1. has a constant outer diameter. Of course, even if a movement resistance force acts on the conductor a passing through the inside of the die 2, there is no problem as long as the resistance force can keep the variation in the inner diameter of the coating layer within the permissible value. stomach.

Therefore, the amount of deflection of the lead wire R can be adjusted with a certain degree of margin. There is a relationship between the slack of the lead wire R and the tension T of the lead wire R, where the maximum dip of the slack is λ, the span of the slack is l, and the weight of the weight 52 is Q. Until the conductor b passes through the packing 31 at the outlet of the cooling cylinder,
In order to cancel the above-described frictional force, the tension of the lead wire R is increased by adjusting the dip based on the second equation.

By adjusting the tension of the lead wire R as described above, the outer diameter of the coating layer of the initially extruded coated conductor b extending into the cooling cylinder 3 can be made constant.

When the tip of the coated conductor b passes through the outlet of the cooling cylinder 3, cooling water is forced into the cooling cylinder 3, and from then on, steady operation is performed as shown in FIG.

In this case, since the outer diameter of the coating layer of the coated conductor b in the cooling cylinder 3 in FIG. There is no concern about fluctuations in cooling water leakage. That is, the cooling water pressure is extremely stable, and a stable traction force F can be obtained. Regarding the traction of the coated conductor during steady operation, the dip^1 is set so as to satisfy the first equation. According to the method for manufacturing a plastic insulated cable according to the present invention, as described above, in the method for manufacturing a coated conductor using a long land die and a pressurized cooling cylinder, pressurized cooling using pressurized cooling water is possible even at the initial stage of steady operation. This can be done without worrying about fluctuations in water leakage.

Therefore, it is extremely useful for improving the workability of the above manufacturing method.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are explanatory diagrams for showing the present invention. FIGS. 1 and 2 are during initial manufacturing, and FIG. 3 is during manufacturing when the device is in steady operation. It shows the status of each. In the figure, 1 is a head of the extruder, 2 is a die, 3 is a cooling cylinder, R is a lead wire, and 52 is a dip for adjusting the pulling tension.

Claims (1)

[Claims] 1. A long land die is connected to the extruder, and a cooling tube is connected to the long land die, and the crosslinkable plastic coating layer coated on the conductor is crosslinked in the long land die in the extruder, and the material comes out from the long land die. While the cross-linked plastic coated conductor passes through the cooling tube, the cross-linked plastic coating layer is cooled with pressurized cooling water inside the cooling tube.In the initial stage of manufacturing a cable, the inside of the cooling tube is left unpressurized. While the tip of the plastic-coated conductor coming out of the long land die is moved to the outlet of the cooling cylinder, the frictional force increases due to the increased contact length between the plastic-coated conductor coming out of the long land die and the bottom of the cooling cylinder. A method of manufacturing a plastic insulated cable, characterized by correspondingly increasing the conductor tensile force.