DE2739777A1 - Continuous cable insulation crosslinking - using inert gas for heating and silicone oil for cooling - Google Patents

Abstract

Continuous crosslinking bomprises passing through a pressurised tube, in which it is first heated by direct contact with preheated inert gas and by external heating of the tube, until the outer insulation is completely crosslinked. and then cooled with a countercurrent flow of silicone oil coolant through the tube. Used in mfr. of high voltage of high current cables. Use of steam for heating and water for cooling, which cause pores in the insulation, is avoided. The silicon oil is not exposed to the high crosslinking temp. (200-300 degrees C) which causes an increase in viscosity due to polymerisation, and blockage of the circulation. The level of the gas heating/oil cooling interface can be varied to suit the type of cable being treated.

Description

Method and device for continuous

Networking a cable insulation The invention relates to a method for the continuous crosslinking of a cable insulation made of polymers, in which the cable is passed through a pressurized pipe after leaving the extruder, in which the insulation first, to a complete crosslinking of the polymeric material to achieve, heated and then cooled, and d # cable finally through a Seal at the end of the tube is pulled out, using silicone oil as a coolant that is in contact with the cable and in the opposite direction to the cable pull-off direction Direction flows.

In the manufacture of power cables, a process becomes continuous Networking needed, which is the electrical conductor after being in one or more Extruders with one or more Isolatlonshüllet and qgf.

an inner and an outer semiconducting Ha le have been provided is passed through a pressurized pipe in which the insulated conductor First, a heated area that is long enough to cover the polymeric material fully network, and then passes through a cooling area.

The apparatus for performing this procedure is often called Chain line built up, or - if the cables are thicker - than vertical arranged system. It is essential that the cable insulation is still hot is not damaged by mechanical influences.

The most widely used known method uses saturated Superheated steam and high pressure to achieve the necessary crosslinking of the polymer Material, followed by cooling in water, also at high pressure, which continues until the cable insulation has cooled to a temperature at which it can be handled under atmospheric pressure without the risk of damage.

When a polymer material, such as polyethylene, by means of hot steam is crosslinked or vulcanized, for example, then the steam generates a known significant number of micropores in the insulation.

It is believed that these are the electrical properties of the insulation worsen.

About the formation of micropores caused by vulcanization with steam To prevent it is known (US-PS 3,645,656), as a vulcanizing agent under Use pressurized non-condensing gas such as nitrogen. It is has also been suggested to use saturated steam as a vulcanizing agent Use gases such as helium, hydrogen, carbon dioxide and sulfur hexafluoride, which has led to better end products.

Various proposals have become known which relate to measures how the required temperature can be achieved in the vulcanization zone can.

In the aforementioned publication, a method is described, with hot air or hot gas in a jacket surrounding the vulcanizing tube circulates. It is also known (SW patent application No. 74 11 010-7), the vulcanizing tube by heating an organic liquid through the surrounding jacket is directed.

It is also known (US Pat. No. 3,588,954) to pass the inert gas through in the vulcanizing tube to heat arranged radiant heaters. These radiant heaters can be turned on individually however, they are so high in temperature that they cause severe damage of the cable insulation occur when contact occurs.

It has also already been proposed that the networking be effected Gas in addition to the external heating of the vulcanizing tube before letting it in preheat the pipe. There have been proposed arrangements in which the vulcanizing gas stands still as well as those with which it circulates and with those the direction of flow can be changed. However, the usual direction of flow is in Direction of movement of the cable.

As a variant of the process in which vulcanization takes place with gas, it is known (US Pat. No. 3,773,872, the region operated with saturated steam to be shortened by exposing the cable insulation to ultrasound. To this In this way, vulcanization from the inside and outside is achieved.

In another embodiment it is known (SW patent application 72 01 640-9) to replace the vulcanizing tube with a very long extruder head, in which the polymeric active ingredient is fully crosslinked.

After vulcanizing, the cross-linked polymeric cable insulation becomes usually cooled by pressurized water. With the above The known vulcanization processes mentioned are also other coolants, such as gas (Especially mentioned in the pre-cooling area>, glycerine and organic liquids. The coolant circulates in the cooling tube area, usually at the bottom End enters the cooling tube and it via an outlet at the end of the Vulkanisierbereiches leaves again. In some cases, the cooling tube area is a number of individual cooling areas subdivided (U.S. Patent 3,582,416) to provide graded cooling down to acceptable to achieve low cable temperature.

However, it has been found that the use of water has different effects on the networked cable insulation during cooling, even if the vulcanization took place without steam and water. It is therefore known VS-PS 3 909 177), silicone oil as a heating medium in the vulcanization area and as a coolant in the cooling area to use. Silicone oil has benefits as a coolant and possibly a heating medium at temperatures below 2000 C, but it loses at higher temperatures rapidly its low viscosity.

The vulcanization temperature required to produce thick cable cross-sections to network is between 200 and 3000C. At such temperatures, silicone oil tends to to polemerize yourself, clogging the valves in the vulcanizing circuit can. When using silicone oil in the entire vulcanizing and cooling device it is impossible to separate the two circuits, so that blockages also occur in the Cooling cycle can occur. Mechanical barriers between the two areas the device should be avoided to mechanically damage the insulation to prevent. A cold intermediate zone that poses a risk of surface damage of the cable running through, subjects the cable insulation continuously an undesirable temperature shock and can thus have harmful effects.

The object on which the invention is based is to provide a method and a device for the continuous cross-linking of a cable insulation Polymers indicate which the disadvantages of the known methods and devices eliminate and therefore to high current resp.

High voltage cables run completely free of pores in the extruded Insulation or the semiconducting layers are.

This object is achieved in that the isolated Cable in direct contact with an inert gas heated to the required Temperature preheated and so long at this temperature by external heating of the pipe is held until the outer part the insulation completely networked is whereupon the cable has a graduated cooling part of the crosslinking device runs through before it gets into the cooling area.

The device for carrying out the method according to the invention consists of a linear or vertically arranged tube, which is connected in a network and cooling area is divided. The two areas overlap each other so that the intermediate area can be used for either heating or cooling, depending on which type of cable is manufactured. Various conductor dimensions and insulation thicknesses require a variable ratio of vulcanization and cooling area, so the highest possible production speed for all types of cables to be produced is achieved. A high-voltage, low-voltage cable that has a large conductor cross-section and has a low insulation strength, needs a device with a short Networking area but a long cooling area. A low-voltage, high-voltage cable on the other hand, which has a small conductor cross-section and a large insulation thickness, requires a long crosslinking area and a short cooling area.

In the vulcanization area, an inert gas is used as a crosslinking agent, such as nitrogen, and in the cooling section, silicone oil is used as the coolant. The nitrogen gas is preheated before it reaches the top of the vulcanizing tube shortly after the cable leaves the extruder is introduced. However, it has to be on it care should be taken that the extruder does not overheat and prematurely crosslinking is effected in the extruder. The gas outlet is at the end of the required Vulcanizing area arranged immediately above the upper end of the cooling area. The vulcanizing area has outside arranged soldering elements that form the vulcanizing area divided into individual, separately heated vulcanizing sections, so that the cable temperature is kept at a required temperature level until the outer shell of the Isolation is fully networked. After that, the temperature of the high crosslinking temperature from gradually reduced to a slightly lower temperature so that the mechanical The load that occurs in the material when it is cooled from the outside is reduced. It is important that the insulation temperature is not too high when in the Cooling area enters. The gas after it can pass through a filter and a heater has to be fed back into the vulcanization area. But you can after allow one-time use to escape in a controlled manner.

In the cooling area, the silicone oil circulates from an inlet at the bottom End of the area, close to the cable outlet, up through the pipe to an outlet at the respective end of the vulcanizing and cooling area. The 51 is before initiating cooled and filtered in the tube. There is no partition between the gas-filled one Vulcanization area and the oil-filled cooling area are necessary.

The required bl level is set by means of conventional level control devices maintained. It can too several cooling circuits provided be.

The most important advantage of the solution according to the invention over the from US-PS 3,909,177 known solution is that by using an inert gas as a crosslinking agent, higher temperatures in the vulcanization area possible are. This opens up the possibility of the production speed at a to increase the specified length of the vulcanizing tube. Another benefit is there in that the boundary between the vulcanization area and the cooling area changes and can be adapted within narrow limits.

The advantage of the solution according to the invention over that from the SW patent application 74 11 010-7 known solution is that there is no more water in the cooling area is used. In the application, glycerine is also mentioned as a coolant, However, like water, glycerine is a polar substance and also hygroscopic, so it should not be used as a coolant. Another advantage over this known solution is the stepped heating.

After the networking and cooling have been completed, the cable is connected to the now solidified insulation by a packing at the end of the tubular device deducted, whereupon it is drummed in between or immediately afterwards with the reinforcement and the outer jacket is provided.

Further details of the invention are given below with reference to the figures 1 to 3 explained in more detail. They show: FIGS. 1 and 2 schematically, one perpendicular and one inclined networking device according to the invention; and Fig. 3 more Details of a device according to FIGS. 1 and 2.

In Fig.1 is a vertically arranged extrusion and crosslinking system shown. A cable core 1 runs through the extruder 2, in which it is treated with a polymer Insulation and semiconducting layers is overmolded, whereupon they are inserted into the cross-linking and cooling device 3 arrives, runs through it continuously and finally is withdrawn through the packing 4. The upper part of the device 3 consists from a tube 5 which is heated by external heating elements 6. The heating elements 6 are divided into a number of sections so that the temperature of the pipe 5 can be graded according to a certain pattern. The top of the tube 5 inert gas is supplied from a gas tank and preheater 7, which the vulcanizing tube 5 leaves through an outlet just above the cooling area. The consumed Gas can be blown into the open atmosphere; but it can also have a Filter 9 can be returned to the tank 7.

The cooling area is shown as a vertical tube 10 on which a pulley 11 and a horizontally arranged pipe 12 follows. After a cool down the cable with re-solidified insulation is reduced to a permissible low temperature withdrawn through the packing 4. The cooling area is filled with silicone oil, which circulates through the cooling and filtering device 13.

The inlet for the cooling liquid is near the packing 4 arranged so that it flows against the cable withdrawal direction. At the desired The outlet 14 is installed at the level.

It is necessary that the warm cable insulation in the pipe 10 is sufficient is cooled before it reaches the pulley 11. If the height of the vertical Tube is sufficient for complete networking and cooling of the cable Deflection roller 11 and horizontal cooling pipe 12 can be omitted.

In addition to the outer heating elements 6, which heat the tube 5 and thereby generate the required gas temperature, the insulation can also through an additional (not shown) inductive heater of the cable conductor is heated, which is arranged in front of or immediately behind the extruder.

However, care must be taken that the extruder is at the top The end of the tube 5 is not overheated by the hot gas, because - if this occurs - The polymer material begins to crosslink already in the extruder, whereby the outer The surface of the cable insulation becomes uneven.

In order to initiate the crosslinking, it is necessary to use the polymeric material As quickly as possible from the extrusion temperature to the correct crosslinking temperature bring to. Temperatures between 200 and 3000C are considered appropriate, but temperatures above 3000C can damage the material. Preferably that should Gas therefore to a temperature of the heated upper tube part 5 corresponding Temperature to be preheated.

While the temperature should be as high as possible at the beginning of the crosslinking should, it should gradually increase to one in the areas below lower temperature, for example between 150 and 2000C, are reduced, before the cable dips into the cooling area 10 filled with silicone oil. The cooling off can already begin while networking is still in the innermost layers of the Isolation continues because the heat from the outer layers even then continues penetrates further inwards when the temperature of the outer layers is already decreasing.

As can be seen from FIG. 3, the can be the boundary between networking areas and cooling area forming levels depending on the cable being treated to be changed. As mentioned earlier, some cables require a long network area and a short cooling area, while other cables have a short one Require cross-linking area and a long cooling area. But there is also high-voltage power cables, which have a long network area as well as also require a long cooling area. As the length of these areas of the achievable Production speed is directly proportional, each plant must be so dimensioned be that it meets the related requirements.

Fig. 2 illustrates a networking / cooling system arranged in a chain line, which contains the same items as the system according to Fig.1. The properties a system arranged in a chain line compared to a vertical system well known; longer systems are easier to implement than chain line systems.

In addition to a certain lubricating effect, the silicone oil gives the Cable also has a certain buoyancy, so that its central guidance in the pipe is simplified and the emergence of eccentricities on the insulation due to the deliquescence of soft Isolation material is avoided.

The same reference numerals are used in FIGS. 1 and 2 for the same parts been.

In Figure 3, details of a vertical or catenary system for networking and cooling according to the invention. The boundary between the crosslinking area filled with gas and that with silicone oil Filled cooling area is shown indefinitely, while the Ulpegel by level control devices certainly becomes, the boundary between the areas is determined by the slope of the plant at this Place determined.

The cable core 21 is pulled through the extrusion die head 23, which with the extruder 23 a layer of semiconducting polymer material the cable core is sprayed on. The cable core then runs through the double spray head 25, with which from the extruder 24 a polymeric insulation material and an outer layer a semiconducting polymer material is applied with the extruder 26. The coated cable core is then fed into the crosslinking and cooling pipe 27, which leaves it at the packing 28 as a fully networked cable 29.

The tube 27 has a cool zone 30 at its beginning, which is there is provided in order to prevent premature crosslinking in the spray head 25.

Since the cool zone 30 is filled with gas, the cooling effect can - like shown - by forcing a coolant through a cooling jacket at the top Part of the pipe 27 can be achieved from a storage container 30B by means of pump 30A. The direction of flow is indicated by arrows.

The cable is then passed through a number of sections 31A through 31G of the Networking area. Each section is controlled by a thermostat 32A up 32G monitors, which is set to a certain temperature and controlled by a sensor 33A to 33G is controlled. The sections are preferably intended to be electrical Heating elements are heated, for example by means of electric braided cables, which the pipe are wrapped around and insulated from the outside to avoid heat loss to avoid. The heating elements are supplied from the supply line 34 via a manifold 35 fed.

As can be seen from FIG. 3 illustrating an embodiment, One or more of the lower sections 31E to 31G can also be used for cooling as will be explained in detail later. In the illustrated embodiment the sections 31A and 31B are at the high crosslinking temperature, the Sections 31C to 31E have a gradually decreasing temperature and the sections 31F and 31G function as the cooling area, i.e. the heating elements for sections 31F and 31G are not in operation.

The crosslinking tube has a gas inlet 36. Inert gas, such as nitrogen, is from a storage container 37 via a preheating device 38 and a valve 39 supplied. A bypass 40 can also be used instead of a control valve.

The gas outlets are indicated at 41A to 41C, each of which only one is used. The outlets are controlled by switchable valves 42A to C and 43A to C put into operation. Consumed gas is at 45 through a valve 44 directed to the outside.

Instead of letting the gas escape into the open atmosphere, you can it can also be returned to the reservoir 37 through the filter 46. To the Control of the gas flow should be the valve 39 together with a bypass 47 and the Valve 44 can be used together with the bypass 40. It is important, however, that the Gas constantly the required pressure and the desired temperature retains. The bypass 47 is provided for emergencies.

After leaving the cross-linking area of the pipe 27, the with cross-linked insulation conductors in the cooling area 50 and the cooled Cable 29 exits the pipe through packing 28.

The cooling area 50 is filled with pressurized silicone oil, which enters the tube through inlet 48 at the end of the tube, optionally also through the inlet 49.

The silicone oil is supplied from a storage container 51 in which it is cooled to a temperature which is preferably not below -30 ° C because the viscosity at lower temperatures drops to such a value that could impair adequate circulation. If the additional inlet 49 is used, the silicone oil is added to the cooling area 50 Supply container 52 supplied.

As illustrated by the figure, the cooling can be achieved by several cooling circuits be graded. The coolant flows in all cooling circuits against the withdrawal direction of the cable and is therefore gradually heated up by contact with the cable. The additional cooling circuits are arranged parallel to the main cooling circuit.

The flow of the silicone oil is briefly described. From the refrigerated storage container 51 is the oil by means of a hole pressure pump 53 through a level control valve 54 and the inlet 48 pumped into the cooling area 54. The bypass 55 is intended for emergencies. The silicone oil flows in the opposite direction of the cable and is opened by opening a valve 57 and controlling the flow rate by a control valve 58 diverted. The bypass 55 is provided for emergencies.

The silicone oil of the primary cooling circuit is put into the storage tank 51 pumped back, which is provided with cooling surfaces 60, to the required temperature to ensure.

Before the Ul enters the storage container 51, it is through a not shown filter passed to remove impurities.

The silicone oil is extracted from the in the additional coolant circuit cooled storage container 52 by means of a pressure pump 6t through a level control valve 62 and the inlet 49 into the cooling area 50. The reservoir 52 is cooled to a slightly higher temperature than that of the storage container 51. The bypass 63 is again provided for emergencies.

After the silicone oil has passed through the additional cooling circuit in the opposite direction of the cable this is discharged through one of the outlets 41B or 41C. The outlet is selected by operating valves 42D, 42C, 42B and 43C, 43B, 43A. The oil level is controlled by valve 65; The bypass 66 can be used in an emergency will. The oil is then passed through a filter (not shown) into the storage container 52 is pumped back with the cooling surfaces 67, provided that the valve 68 is in the bypass closed.

By closing valves 56, 62, 63, 65 and 66 and opening the valve 68 the additional coolant circuit is bypassed.

The cooling region 50 ends at the sealing packing constructed in a known manner 28. Coolant escaping through possible leaks in the packing 28 is collected in the collecting trough 69 and by the pump 70 into the main storage container pumped back.

It should also be mentioned that the crosslinking and cooling tube 27 with a or several breaks shown) level sensors is provided that the pressure and the To regulate the flow rate of gas and / or oil, so that the boundary between the remains in the desired location in both areas. It can also be known in the pipe Be arranged sensors, which check whether a deflection of the cable takes place. However, these should not touch the surface of the cable. Emigration of the cable from the intended line of movement should be done immediately by adjusting the cable tension be balanced.

One embodiment of the process sequence is that the pressurized gas, from container 37, through tube 27, and through the outlet 41A flows out while at the same time the coolant under one of the Gas pressure identical pressure from the storage container 51 through the pipe 27 and pumped out of outlet 41B. In this case, the level is somewhere between the outlets 41A and 41B. The valves 42A, 42B, 43B and 43C are open in this case and the valves 42C, 42D and 43A are closed. the Elements 31E, 31F and 31G are not turned on. The number of outlets 41A, 41B, 41C and 64 and the heating element is changeable as needed.

Claims (4)

Claims {1. Process for the continuous crosslinking of a Cable insulation made of polymers, in which the cable passes through after leaving the extruder a pressurized pipe is passed, in which the insulation first to a To achieve complete crosslinking of the polymeric material, heated and then is cooled, and the cable finally through a seal at the end of the pipe is pulled out, using silicone oil as a coolant, which is in contact stands with the cable and flows in the opposite direction to the cable pull-off direction, characterized in that the insulated cable is in direct contact with an inert Gas is heated, which is preheated to the required temperature and by external Heating the pipe at this temperature will apply until the outer part the insulation is fully networked, whereupon the cable is one, a graded The part of the crosslinking device that has to cool down before it passes into the Cooling area. 2. Apparatus for performing the method according to claim 1, characterized characterized in that the boundary between the crosslinking area and the cooling areas is designed to be adjustable. 3. Apparatus for performing the method according to claim 1, characterized characterized in that as a stepped external heating of the tubular crosslinking device electrical cables or cables in individually controllable sections the outside of the pipe, isolated from the environment, are arranged. 4. Apparatus according to claim 2, characterized in that the limit is formed by the level of the coolant by controlling the pressure and / or the flow rates of the gas and / or the oil using level sensors on one is held at a predetermined value.