RU2768789C1 - Method of making an insulated wire or cable - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electrical engineering, in particular to the use of wires or cables with insulation of silanol cross-linked polyethylene, and can be used in cable industry in production of insulated wires. Method of making an insulated wire or cable consists in the fact that for cross-linking, a conventional container with hot water and vertical loading of drums with a wire or cable is used, but container and cover are made with possibility of their tightness, capable to withstand internal overpressure of up to 1.0 bar, cross-linking is carried out in said sealed container with hot water at an excess pressure created by feeding air inside the container at pressure of 0.2–0.7 bar, cross-linking is carried out in water at temperature of 90–95 °C at excess pressure created by supplying air inside the sealed container for 0.5–1.5 hours.

EFFECT: method combines the advantages of a hot water bath and a steam autoclave and at the same time eliminates the need to discharge the heat carrier during reloading.

1 cl, 1 tbl

Description

The invention relates to the field of electrical engineering, in particular to the use of wires or cables with silanol-crosslinked polyethylene insulation, and can be used in the cable industry in the manufacture of insulated wires.

A known method of manufacturing a wire, which consists in the fact that a conductive core is extruded with thermoplastic polyethylene insulation, after which the wire is cooled in a water bath, in the first section of which the water has a temperature of 80-95 ° C, in the second - 60 ° C and in the third - 15-20 ° C (see Cables and wires, vol. 3, M.-L., ed. "Energy", 1964, p. 90-95).

This method has a number of disadvantages, which are as follows.

When cooled, thermoplastic polyethylene changes from a viscous to an amorphous-crystalline state. In the area of this transition, there is a significant decrease in its volume (compression) and a sharp increase in the elastic modulus. During cooling, the outer layer of polymer insulation first passes into the amorphous-crystalline state with the formation of a solid tube. With further cooling, the material inside the formed solid tube contracts, which leads to the appearance of pores in it, and a gap appears between the insulation and the core, which ultimately adversely affects the performance of the resulting wire due to its poor-quality insulation.

A known method of manufacturing a wire, including the imposition of a conductive core by extrusion insulation of thermoplastic polyethylene, followed by cooling in a water bath, the cooling is carried out in water under pressure of 0.3-1.2 MPa and having a temperature of 5-15°C less than the lower the boundaries of the phase transition of polyethylene from a viscous to an amorphous-crystalline state until the temperature of the core is reached, corresponding to the lower limit of the specified phase transition, and then in water at room temperature.

As a wire insulation material in the proposed method, industrial grades of polyethylene are used: low-density polyethylene (LDPE), obtained by polymerization of ethylene at high pressure, and high-density polyethylene (HDPE), obtained by polymerization of ethylene at low pressure.

The region of the phase transition of polyethylene from a viscous to an amorphous-crystalline state is in the temperature range for LDPE - 100-115°C, and for HDPE - 125-145°C. In the area of this transition, there is a significant decrease in the volume of polyethylene (compression) and a sharp increase in the elastic modulus, the maximum compression value is observed at temperatures of 103–105°C for LDPE and 130–135°C for HDPE.

With increased pressure, the outer layer in the form of a hardened tube is compressed, which prevents the appearance of pores inside the insulation, shells near the core and peeling of the insulation from the core. After that, the wire is cooled in water at room temperature.

In parallel, a similar wire is made according to a known technology in two technological cycles with an insulation thickness of 1.5 mm each, for which the wire leaving the extruder enters a water bath with a water temperature in the first section of 85 ° C, in the second - 60 ° C, in the third - 20°C (see patent RU No. 2161833 C1 IPC NO1V 13/06, 2001).

The disadvantage of the known method is that when using silanol crosslinkable polyethylene as insulation, an additional period of the wire or cable being in an aqueous medium at an elevated temperature (85-90°C) is required, during which the main crosslinking process takes place. To do this, the cooled wire or cable is wound on a drum and then this drum with wire (cable) is placed in a special container with water heated to the required temperature and kept in water at this temperature until the end of the crosslinking process. At the same time, the wire (cable), the insulation of which has not yet acquired the necessary strength properties due to the incompleteness of the crosslinking process, is subjected to static and periodic mechanical loads on the drum under the action of gravity during the rotation of the drum, which leads to additional mechanical stresses. The total time of manufacturing the wire (cable) is also significant, since the latter is initially cooled to a temperature at which it can be taken onto the drum, and then reheated in an aqueous medium to the required temperature. This also leads to a significant consumption of thermal energy.

The closest technical solution to the proposed method is a method for manufacturing an insulated wire or cable, which consists in the fact that insulation from silanol-crosslinked polyethylene is laid on the conductive core of the wire or cable, then the wire or cable thus obtained is cooled and placed in horizontal turns in a basket of water , after which either a current is passed through the wire or cable and thereby the specified wire or cable is heated to a temperature not exceeding the maximum possible temperature at which the resistance of the insulation to thermal deformation is ensured, and maintained at this temperature for a period of time necessary to ensure the silanol crosslinking polyethylene, or the basket is placed in a heated container filled with water, water vapor or a steam-water mixture, and kept in this container at a specified temperature for a period of time necessary to ensure the silanol crosslinking of polyethylene, or water is drained from the basket and then the basket is placed in a heated container filled with water, water vapor or a steam-water mixture, and kept in this container at the specified temperature for a period of time necessary to ensure the silanol crosslinking of polyethylene (see. patent RU No. 2295792 C1 IPC NO1V 13/06, 2007).

However, the known method of manufacturing an insulated wire or cable is quite laborious, energy-consuming, and also leads to a significant consumption of thermal energy.

The task was to develop a technology for the manufacture of insulated wire or cable with the aim of improving the quality and speed of crosslinking 3-5 times faster than traditional methods in a hot bath and a steam autoclave.

The task is achieved by the fact that for crosslinking, a container with hot water, traditional for the method of crosslinking, and vertical loading of drums with wire or cable is used, but the container and cover are made with the possibility of their tightness, capable of withstanding internal overpressure up to 1.0 bar, crosslinking is carried out in of the specified sealed container with hot water at an overpressure created by supplying air inside the container at a pressure of 0.2-0.7 bar, cross-linking is carried out in water at a temperature of 90 ° -95 ° C at an overpressure created by supplying air inside the sealed container for 0.5-1.5 hours.

The advantage of this method is that it combines the advantages of a hot water bath and a steam autoclave and at the same time eliminates the disadvantage of the latter, which consists in the need to dump the coolant when restarting.

The quality and speed of crosslinking in a pressurized hot water tank is several times higher than traditional methods in a hot bath and a steam autoclave.

Silane crosslinking belongs to the category of chemical crosslinking, so the percentage of crosslinked material is directly determined by the amount of added agent. Depending on the polymer formulation, the amount of the agent is added in the amount of 2-5%. The reaction for some types of materials can occur in the presence of a catalyst - dicumyl peroxide (earlier, in connection with this, there was a 3-stage loading). Today, this catalyst can be omitted, because modern chemical materials do not require it. Silane crosslinking is possible only in the presence of water molecules (crosslinking begins when leaving the forming head).

In order for crosslinking to occur, it is necessary to tear off the radical (OCH ₃ ). The detachment of the radical (OCH ₃ ) occurs due to the addition of a hydrogen molecule (H ₂ ) to this radical (OCH ₃ ). During the reaction, water (H ₂ O) is released. On the surface of the insulation there is a layer of water (in a bath or sauna) due to which the upper layers are crosslinked. Those water molecules that are released during the crosslinking of the upper layers, crosslink the lower layers, and so on. Thus, due to the fact that water cannot 100% penetrate the entire thickness of the insulation, a fairly strong heterogeneity of properties across the thickness of the insulation is obtained. That is, a very high degree of crosslinking is achieved on the surface, while on the lower layers the degree of crosslinking catches up after a very long time (several months).

Hot set test.Due to water molecules in the air, crosslinking will occur sooner or later. Therefore, not full cross-linking is considered here, but 85% (i.e., 85% of the cross-linked material should be accumulated over the insulation thickness). The quality of the silane crosslink can be assessed by: - dissolution test (gel fraction);

hot set test.

Сиоплас;

Моносил. Сиоплас - прививка самого силана происходит непосредственно в технологическом процессе (т.е. отдельно добавляют силановый компонент и отдельно полимер). В связи с возможностью непромеса в экструдере, сегодня широкое распространение получил вид процесса сшивки моносил. Отличай от сиопласа в том, что молекула силана одной или двумя связями привита к молекуле полимера (получается более упорядоченная структура).Conducting a dissolution test (gel fraction), this test is quite lengthy. The crosslinked material is taken, placed in tricresol (and other solvents) and boiled for 18 hours and then the initial and final are weighed and the gel fraction is determined (how much is left). Hotsettest - allows you to indirectly determine the quality of the stitching. The essence of hotsettest: take a sample (crosslinked material), place it in a heating oven and fix one end, and hang a weight from the other. Accordingly, heating is performed if the elongation exceeds the required limit; in this case, the material is not finished (it takes 5-7 minutes). To date, there are two main types of material that are used for silane crosslinking, these are:

Sioplas;

Monosil. Sioplas - the grafting of the silane itself occurs directly in the technological process (i.e., the silane component and the polymer are added separately). Due to the possibility of non-mixing in the extruder, a type of monosil crosslinking process has become widespread today. It differs from sioplas in that the silane molecule is grafted to the polymer molecule by one or two bonds (a more ordered structure is obtained).

In the case of the Sioplast cross-linking process, several cross-linking agent molecules can be attached to one polymer molecule, and in the case of Monosil, an active cross-linking agent is already attached to each polymer molecule and a more ordered structure is obtained. In this case, a higher quality is obtained, but, accordingly, leads to a slight increase in the cost of the material itself (initial blank).

To date, two main types of silanes are used, these are silanes of the type:

Visico - предназначен для сшивки в паровой среде (в среде газа),

Visico - designed for cross-linking in a vapor environment (in a gas environment),

Drysil - предназначен для сшивки в жидких средах, в частности в ванне.

Drysil - designed for crosslinking in liquid media, in particular in a bath.

But both can be used in the same way, in both cases, the efficiency will just be slightly different (relative to crosslinking in their environment).

Silane technology. The imposition of silane materials is carried out in the classical way on standard equipment with standard presses. The only condition is the sealing of the loading devices (this is due to the fact that moisture is present in the air). Therefore, multi-component loading occurs. The silane is not photostabilised, i.e. The chemical bond is broken by ultraviolet radiation. To photostabilize the insulation material, a photostabilizer (soot) must be added. Therefore, when designing the unit, it is necessary to provide for a 3-component loading, i.e. these are: - loading of the main polymer; - catalyst loading; - Loading photostabilizer (soot). Laying takes place on standard presses (for PE), with a combined barrier screw and a screw length of 24D. The simplest and cheapest, but longest (from 2 weeks) cross-linking process is cross-linking in air under normal conditions (temperature - 18-22 ° C, relative humidity - 60-70%). Therefore, standard methods of crosslinking are used: - in water - bath; - in steam - a steam boiler (sauna). A bathtub is a large metal tank that contains hot water and, accordingly, has heating elements to maintain the temperature.

The temperature of water heating in the baths is 65-95°C. The approximate time of crosslinking in the bath, unlike crosslinking in air, is (depending on the thickness of the insulation) 2-4 hours. As a rule, bathtubs are designed for 2 drums.

Sauna (steam boiler). There are saunas with vertical or front loading. Sauna with vertical loading. Either electric heaters or a steam jacket (coolant-steam) are used. The main difference from a bath is that the steam must be dumped. Inside the steam is under pressure, the temperature of the steam is 125-130°C, but not higher than 140°C (so that the non-crosslinked polymer does not melt and does not stack from the product). Crosslinking time in a vapor environment is reduced by about 2 times and in most cases is up to 2 hours. When using a boiler, time is saved twice, but there is a need for energy resources, so it is advisable to use a steam boiler (sauna) if the plant has its own boiler room (then steam will cost almost free of charge). If the external energy carrier is steam, then it is advisable to use a bath. The boiler is more versatile (the boiler can be filled with water, but the steam bath is problematic).

Determination of the stitching time. To determine the insulation crosslinking time, there is an empirical formula:

where T - vulcanization time, min; X - insulation thickness, mm; Rh - relative air humidity:

- in water 100%;

- in saturated steam 96%.

K - temperature coefficient (comes directly with each batch of material).

For Visico:

95°С - K=1.2*10 ^-4

80°С - K=1.0*10 ^-4

75°С - K=0.8*10 ^-4

20°С - K=0.1*10 ^-4

It can be seen that with increasing temperature, K increases significantly; the crosslinking time (T) is reduced. Since the dependence is quadratic, the crosslinking time is significantly reduced already at a temperature of 80°C. However, after the end of the crosslinking process in a bath or sauna, the crosslinking process does not end, because according to the requirements, the cable (insulated core) must be aged for at least 2 days in the open air (under normal conditions) before further technological operation. At this time, additional cross-linking occurs, especially for the inner layers.

In the proposed method for the manufacture of an insulated wire or cable, the optimal values of the internal overpressure of the sealed container up to 1.0 bar were calculated and experimentally determined, and the crosslinking temperature was 90 ° -95 ° C at an overpressure created by supplying air inside the sealed container at a pressure of 0.2 -0.7 bar, within 0.5-1.5 hours. It should be noted that, going beyond the indicated values of the technological process, polyethylene crosslinking does not satisfy the quality of cable or wire crosslinking.

Experimental studies were carried out: SIP samples with sections of 35 mm ² and 95 mm ² made of the material "Polysil-01K" were used.

The insulation crosslinking test was carried out in a muffle furnace for 15 minutes at a temperature of 200°C.

The statistics of tests for cable stitching are given in the table, which shows a positive result from using the proposed method for manufacturing an insulated cable.

The advantage of this method is that it combines the advantages of a hot water bath and a steam autoclave and at the same time eliminates the disadvantage of the latter, which consists in the need to dump the coolant when restarting.

The quality and speed of crosslinking in a sealed container with hot water at excess pressure is several (3-5) times higher than traditional methods in a hot bath and a steam autoclave.

Claims (1)

A method for manufacturing an insulated wire or cable, which consists in laying silanol-crosslinked polyethylene insulation on the conductive core of the wire or cable, then placing the wire or cable thus obtained in a container filled with hot water and keeping it in this container at a temperature for a period the time required to ensure the silanol crosslinking of polyethylene, characterized in that the container is made airtight with the ability to withstand an internal overpressure of up to 1.0 bar, the crosslinking is carried out in water at a temperature of 90°-95°C at an overpressure created by supplying air inside the sealed container under a pressure of 0.2-0.7 bar, for 0.5-1.5 hours.