DE2642360A1 - Plastics-insulated, heavy-duty, power cable - is extrusion-coated with polypropylene polyethylene compsn. applied under closely controlled processing conditions - Google Patents

Abstract

Mfr. of a plastics-insulated, heavy-duty, power cable, comprises extrusion-coating the conductor with an insulation contg. polypropylene, and cooling. An insulating compsn. is used which has a major portion of polypropylene and a minor portion of polyethylene and/or ethylene copolymer. The compsn. is applied under conditions of supply, plasticising, compounding and discharge temp. that prevent the max. MFI of 0.65g/10 min (measured according to DIN 53735) at 190 degrees C and under 2.16kg load, from being exceeded. This processing control is achieved using an extruder screw having a suitably dimensioned zone at 250-300 degrees C and applying a temp. profile that rises in controlled manner. from the feed-in zone to beyond the plasticising zone. Subsequent cooling is effected in at least 2 different temp. stages and/or by cooling media. The insulation is thermally stable whilst still in uncrosslinked state. The resulting coated cable can be readily wound onto reels or corded together. The coating has good low-temp. resistance.

Description

Method and device for the production of a plastic

insulated electrical cable high load capacity The invention relates on a method and a device for producing a plastic insulated electrical cable or line of high load capacity, the polypropylene containing insulation is extruded onto the conductor and then cooled.

Because of the increasing demand for electrical energy, one is on a higher load capacity due to the lowest possible loss of transmission links interested in the use of electrical cables and wires, their insulation thermoplastic material as high a heat resistance as possible have low dielectric losses, with the same conductor cross-section without Increasing the operating voltage to be able to transmit larger amounts of energy. It exists hence the constant tendency, ie previously customary thermoplastics, such as Polyvinyl chloride or polyethylene, increasingly with more heat resistant ones Insulation, for example from a crosslinked polyolefin, in particular Polyethylene, or from other insulating materials with the necessary properties, on the basis of polypropylene, for example, which allow an increased operating temperature, to replace.

However, during the manufacture of electrical cables with insulation made of cross-linked polyethylene or the like. Because of the necessary, only with great effort feasible crosslinking process that is carried out on the finished product must be, much more expensive than those with uncrosslinked plastic insulated cables brought the use of highly heat-resistant insulating materials on the basis of polypropylene or mixtures of the same with polyethylene or of Copolymers or copolymers of propylene, such as those from FR-PS 1 141 019 have long been known to present considerable technological difficulties.

On the one hand, these are due to the fact that the usual casing is electrical Head by extrusion of a thermoplastic insulating material with such highly heat-resistant Only allows insulation materials based on propylene to be carried out under difficult conditions, and on the other hand, in addition to the increased thermal also increased mechanical Strength, stiffness and brittleness of such extrudates, thus making them isolated electrical lines, cables or cable cores are difficult to bend. Therefore let These drum up badly or for laying a cable route again unwind without taking damage. Cable cores insulated in this way can also be made the aforementioned reasons only with great difficulty or not at all to the usual, multi-phase cables, for example three- or four-core power cables, stranded will. Therefore, despite the existing good electrical and thermal properties such insulating materials, such as one known from DT-OS 24 17 093, for example Molding compound, consisting of a mixture with a high proportion of polypropylene, minor Alzeilen of polyethylene and an ethylene-propylene copolymer additive, with such Fabric-insulated electrical cables have only rarely been used for special purposes. Such a cable whose insulation is made from a mixture of sequence polymerizates consists of ethylene and propylene, is described for example in DT-OS 20 65 726, however, little is known about its production.

The invention is based on the object of an economical process and a device for producing a plastic-insulated electrical cable or a cable core or electrical line with high load capacity and heat resistance indicate whose insulation is highly heat-resistant in the extruded, non-crosslinked state as well as bendable, drum-type and strandable and also good low-temperature behavior having. This task is based on a method of the type outlined above solved according to the invention in that an insulating mixture with a predominant proportion of polypropylene as well as with polyethylene and / or ethylene blends or copolymers, this insulating mixture under feed, plasticizing, homogenizing and ejection temperature conditions, exceeding the specified maximum melt index value of the same 0.65 g / 10 minutes, measured according to DIN 53735 at 190 ° C and 2.16 kg load, prevent with an extruder screw with appropriately sized zones at temperatures from 250-300 ° C and one rising from the feed zone to the plasticizing zone controlled temperature profile and then extruded in at least two different Temperature levels and / or cooling media is cooled.

It is essential that the insulation mixture used not only for their suitability as cable or wire insulation or sheathing required properties m has, but also after extrusion maintains.

This is because propylene-containing molding compounds tend to be mechanical Processing, such as extrusion in particular, to a solidification that increases with increasing melt index leads to increased rigidity and brittleness of the extrudate, which - for example as core insulation - is no longer sufficiently flexible and pliable for further processing, E.g. stranding the all insulated cores to form a. multi-core cable. Therefore, such extrusion conditions must be created that the inherently low Melt index of the mass increases as little as possible and also with the extruded product does not exceed the specified limit.

However, this is optimal - apart from the selection of each suitable insulating mixture - the temperature control according to the invention during the Feeding, plasticizing, ejecting and cooling processes in accordance with one another coordinated zones and compliance with certain upper and lower temperature limits, in particular the extrusion temperature is required, as well as gradual cooling of the extrudate, which is precooled gradually before more intensive cooling causes at relatively low heat dissipation.

In a further embodiment of the invention, it is advantageous if the Temperature of the insulating mixture in the extrusion process after a from 100 ° C to at least over half of the passage steadily up to the processing temperature increasing and, moreover, essentially constant temperature profile will.

This is the required extrusion temperature in a way achieved that sufficient plasticization and homogenization of the insulating mixture guaranteed before their extrusion molding, but at the same time burning them prevents that both when the upper limit of the extrusion temperature is exceeded as well as when the temperature rises too steeply. If the extrusion temperature is too low or too shallow temperature rise, however, the insulating compound does not experience the necessary Plasticization and homogenization of all in granulate or powder form supplied Quantities and thus not the required uniformity of its structure. However, this is to achieve and maintain advantageous properties of eminent importance.

In a further embodiment of the invention, it is also advantageous when the extruded insulation in several FUhlstufe with a liquid medium is cooled, the temperature of which in the first cooling stage is at least 80 ° C, to the formation of mechanical, in extreme cases, at the highest production speed prevent stresses leading to cracking in the extruded insulation. the however, step-by-step cooling can be used in another, likewise advantageous variant the invention take place so that the extruded insulation initially by means of a gaseous medium, for example air, and then with a liquid coolant, e.g. water until it is cooled to room temperature.

In this way, by means of the over a certain cooling distance Gaseous cooling medium acting on the extrudate gradually pre-cools it achieve with relatively little heat dissipation, before the more intensive cooling by means of the larger amounts of heat dissipating liquid coolant. This yields because of the thereby enabled the advantage of increased manufacturing speed Economics of the process and causes a particularly good structure of the Cable or wire or line insulation forming extruded and gradually intensified feeling specifically controlled hardening insulating mixture.

The electrical insulation produced by the process according to the invention Cables, cable cores or lines have all the desired properties in excellent form Way on: The thermo-mechanical properties of the same depend as with all Polyolefins depend on the semi-crystalline structure of the material. At room temperature the crystallites cause the material to have high strength. With increasing temperature will you increasingly melted, resulting in a slow Loss of mechanical properties leads. The extruded polypropylene insulation mixture As a crosslinked material, it behaves similarly to crosslinked polyethylene. But only between 155 ° X and 160 ° C do the mechanical values drop, because they are Temperatures the main part of the crystallites is melted. As shown by experiments are the curves of mechanical strength as a function of temperature of the polyethylene or the polypropylene shifted parallel by about 50 0C. Therefore is the polypropylene insulation compound itself to the crosslinked polyethylene at temperatures from 90 Oa to 150 OC clearly superior, since they still have their full potential in this range Has strength. Endurance tests have excellent behavior according to the invention produced insulation after long-term exposure to heat up to 130 On. The insulation became brittle after exposure to 135 ° C after 6 months, and at 10 ° C after 3 months.

The manufactured according to the invention behaves even at low temperatures Insulation so that the cable can be laid even at around -10 oC to -15 OC without Difficulty is possible. In long-term tests there was no effect of the deep Temperatures on the electrical strength can be proven. A cold impact test in accordance with VDE 0471 § 611, which is carried out on a four-conductor cable (4x150 se 0.6 / 1 kV) meets the requirements of those with crosslinked or uncrosslinked polyethylene insulated cables at -15 OC (according to VDE 0273 § 5.5.9.1) have to withstand even still at a temperature of -55.00. After 20 hours of storage of this cable at -12 OC, these tests did not reveal any noticeable damage, even if the The VDE-compliant laying radius was significantly undercut.

In addition to these advantageous properties, there is also the fact that such insulated cable cores, for example 1 kV segment conductor power cable cores insulated according to the invention, Process well due to the good flexibility and flexibility of the insulation, in particular strand into multi-conductor cables and jointly heat-resistant in the manner according to the invention encased or wrapped. It should also be emphasized that the inventive The method can be used excellently with hose tools, which increases the economy the manufacture of segment conductor cores insulated according to the invention for power cables increased very substantially.

It is understood that the use of printing tools for Forming the insulation is possible within the scope of the invention, as well as the Manufacture of a thermally and mechanically particularly resistant outer Cladding of a bundle of wires, for example a control line or a special telecommunication cable.

As already mentioned, the insulation produced according to the invention possesses excellent electrical and dielectric properties, making such insulated Cables, for example power cables @ as the investigations carried out show - Can be used in continuous operation at 90 ° C and in emergency operation up to over 130 ° C, in the event of an emergency, considerable overload reserves, up to 500 in total Hours, are available. Although the conductor temperature in the event of a short circuit is in is usually limited to 160 O, short-circuit tests have shown that that the permissible short-circuit temperature with this insulation is above 200 ° C lies. The cable or wire insulation or sheathing produced according to the invention is thus the other plastic insulation, including those made of cross-linked polyethylene, in the entire operating temperature range and beyond to 150 0C at about the same electrical properties, especially with regard to mechanical strength clearly superior, as they do not only have ladder temperatures of 90 oC in continuous operation allows and thus has the desired high current carrying capacity, special about it In addition, there is ample reserve for localized unfavorable environmental conditions and Has emergencies, whereby the permissible emergency operating temperature of 130 oO for a short time offers a high possibility of overload.

The invention also relates to one for performing the foregoing described method extremely suitable device with one in a heatable Pressure cylinder rotatable and drivable arranged extruder screw with feed, Plasticizing and ejection channels and a cooling device assigned to the extruder outlet. Such devices are used in cable manufacturing and plastics processing Industry well known. It has been found, however, that for optimum performance this method reduces the length dimensions of the screw from the usual screw dimensions must deviate largely, and that a precise control of the course of the temperature is required in the various zones.

This gave rise to the task of finding a solution that would meet these requirements To create device. This device is known for solving this problem compared to the known devices of this type according to the invention in that the extruder screw one twenty to twenty-five times the diameter having a total length, with its feed zone approximately equal to a third to half of its length, the plasticizing zone equal to a fifth to a quarter of its length Length and the ejection zone is approximately the same as the feed zone, and the pressure cylinder has a number of thermally separately controllable sections. For a large output the device is more adapted to the intended speed range of the screw As great a flight depth as possible is desired. on the other hand are, however, to achieve the high mixing quality and homogeneity that are absolutely necessary of the propylene mass extrudate required small thread depths, so that for the specified intended use a thread depth corresponding to these two requirements the different zones must be selected.

The extruder screw according to the invention is designed so that it the material to be processed degrades as little as possible, i.e. the chains of the molecules same in the course of the plasticizing, Homogenizing and ejecting form Vorgatges As is well known, with long molecules, a! '. `` f-- as is well known with long molecules, @@ @: correspondingly high viscosity, which is too pliable remain. Furthermore, it is necessary for the continuous operation of the device at a high production speed an excessively long feed zone is required to prevent the reflux of this as granules or powder supplied propylene material, which in the area of the transition and plasticizing zone gradually with a considerable reduction in its volume is plasticized and compressed. Likewise, in particular, to achieve the desired high degree of mixing quality of the homogenization a correspondingly long discharge zone the extruder screw is required.

To achieve the necessary for processing these polypropylene blends desired extrusion conditions, which must be adjusted so that the melt index does not exceed the limit value mentioned at the beginning, however, this alone is not sufficient the screw geometry described above but it must also be the screw surrounding pressure cylinders - for targeted control of the temperature profile in the course of the processing process - sections that can be heated or cooled accordingly which precisely regulate the temperature in the various zones allow. This design of the device is the result of numerous attempts Surprising knowledge gained based on that for the success of the extrusion a thermoplastic mixture based on polypropylene on the one hand the screw geometry and, on the other hand, this and a suitable temperature control as well as speed determination of the screw imposed temperature profile of essential It is important to maintain the decisive factor for the flexibility of the extrudate Melt index value of the extruded insulation mixture.

In a further embodiment of the invention, it is also advantageous if the extruder screw has a flight depth of 0.1 to 0.2 d, and the outlet zone from 0.02 to 0.05 d, where d is the screw diameter is designated.

This thread depth ratio corresponds optimally to the previous ones requirements outlined, taking into account the volume reduction of the insulation mixture to be processed, at its transition from the powdery or granulated solid to plastic, compressed and homogenized state, in which it is finally extruded. This thread depth ratio enables im With regard to the previously mentioned requirements of the lowest possible Material degradation with the highest possible mixing quality of the extrudate, high production speeds with high output of the device.

Also to increase the mixing quality of the extrudate in the discharge zone it is of advantage according to the further invention if the extruder screw with at least is equipped with a mixing and / or shearing part arranged in the discharge zone, wherein the relevant section of the printing cylinder with a heating-cooling device is equipped with increased cooling capacity. Such, possibly exchangeable The mixing or shearing part ensures optimal processing of the plasticized Mass shortly before it leaves the extruder, and thus an optimal structure the extruded cable or core insulation. Because here - according to the shear effect -much heat is generated in the mass is to prevent it from being exceeded the upper limit of the extrusion temperature, which leads to a combustion of the mass could lead to the increased cooling of the extruder cylinder required in this area.

In a further embodiment of the invention, it is advantageous if the Cooling device as aligned with this at a variable distance from the extruder outlet arranged, trough-shaped or tubular ones equipped with cable routing devices Kühikanal is often formed even if - according to another variant of the invention - the cooling device as directly connected to the extruder outlet, in separate sections or chambers for receiving different, In particular, liquid coolants having different temperatures are subdivided Coolant tank it is designed Further details and advantages of the invention go from the following explanations of an embodiment of the same based on the drawing. The drawing shows: FIG. 1 in a schematic representation one for the production of a plastic-insulated electrical cable according to the invention or a line with a high load-bearing capacity and Fig. 2 partly in view and partly in section as an essential part of the invention Apparatus a screw extruder according to the invention.

The illustrated in Fig. 1 cable production line has a Unwinder 1 for an electrical conductor 7 to be encapsulated, one of these one Extruder 3 feeding pusher device 2, for example in the form of a caterpillar, the extruder 3 with a cooling device 4, a take-off device downstream of this 5, e.g.

in the form of a traction bead and a winder 6 for receiving the isolated electrical conductor 8 on. The said route is designed so that the conductor 7 in a process that takes place continuously at a constant speed in the formed according to the teachings of the invention extruder 3 to form a heat-resistant insulation 8a made of a molding compound based on polypropylene encapsulated and the all so formed insulation 8a of the conductor 7 after its exit from the extruder 3 in a suitable manner until the polypropylene molding compound has solidified in the one set up for their gradually intensified cooling down to skin temperature Kühleinrichtui g 4 cooled and finally solidified as a result of the cooling, in the non-crosslinked state heat-resistant, permanent insulation provided electrical Conductor 8, for example a simple electrical line, one Cable core intended for the production of a power cable, in particular segment conductor core, or as le of a single-conductor energy cable intended for higher voltages and is applied to the winder 6.

As mentioned earlier, the heat-resistant is essential for the successful manufacture electrical conductors or cable insulation with the required properties are decisive, that the processing of the insulating mixture is carried out under conditions which are continuous Plasticization as well as mechanical and thermal homogenization of the material and its shaping output with a correspondingly controlled temperature curve throughout the entire process cause to ensure that the melt index of the extrudate that mentioned does not exceed the maximum limit of 0.65 g / 10 min. Essential for the structure and mechanical properties of the extruded conductor insulation is also the stepped intensity of the cooling by means of the embodiment shown in the embodiment cooling device 4 designed as a cooling trough.

This is with guide devices 9, for example in the form of Rollers or rollers, for the insulated conductor 8 as well as with an extendable end section equipped, and so at a certain distance from the extrusion outlet on a optionally arranged with the extruder 3 common base plate that the with the extruded insulation provided conductor 8 a first the extrudate 8a; st "soft" cooling air gap depending on the respective conditions, such as conductor cross-section, exit speed, -temperature and thickness of the insulation as well as the ambient temperature adjusted length, runs through before it is in the with a "hard", preferably liquid oil charged or provided Kühleinrichtuig 4 enters, which in turn in several Cooling levels different wher temperature can be divided.

The cooling device 4 can with appropriate subdivision into sections or chambers of different temperatures connected directly to the extruder outlet be, the extrudate in the cooling section next to the extruder with a coolant elevated temperature, for example a high-boiling liquid of over 1000 or water of about 900 is pre-cooled, followed by more in a graduated order Sections with a coolant each have a different lower temperature up to about 400 are lined up.

The illustrated in Fig. 2 screw extruder 3, the essential Forms part of the production line, has an extruder screw 10, which in a Printing cylinder 11 is rotatably arranged and driven by a drive motor 13 via a gear 12, the housing of which also serves as a support for the printing cylinder 11, is driven is. The extruder 3 is provided with a hopper 14 for feeding the selected Polypropylene insulation mixture in the form of powder or granules for feed zone 15 the extruder screw 10 and at the free end of the pressure cylinder 11 with a this connected Ouerspritzkopf 18 provided, which an injection tool 19, for example carries a hose nozzle from which the conductor provided with the insulation 8a 8 exits.

The extruder tendon 10 and the pressure cylinder 11 surrounding it have A feed zone 15, a plasticizing zone 16 and an ejection zone 17 each, whose Cross-sectional and length dimensions are coordinated so that the Total length of the screw 10 at least twenty times, preferably four to twenty-five of its diameter is d, a sufficient one is essential Dimensioning the length of the feed zone 15, which is up to half of the total length of the screw 10, but at least nine to ten times the screw diameter should be, with a thread depth of at least 0.1, preferably up to 0.2 des Screw diameter. The discharge zone 17 is in terms of their length approximately the same as the indented 15, but has a wassntlich lower Passage depth than this, namely of at most 0.05 of the snow condenser diameter Length of the previous transition 16, in which the grain diameter of the Schnoeke from the lower front of the catchment zone 15 gradually conical to jonon the Ausstoexone 17 increases, is dimensioned much shorter than the other zones, However, it must be long enough to allow the material to undergo erodichonde plasticization ver its exit into the thormisch and mechanically honed discharge zone to ensure. At the same time, however, it must be taken into account that, due to the pressure build-up, the friction and shear effects, and the external heat supply, the plasticization of the Material boreits in the Binzugazeno, in particular its end area, initiated In order to improve the mixing quality of the extrudate, know in the discharge zone 17 a mixing or Schortoil 23 be voron on the screw 10. To adapt the screw to untorchiodliche Icoliormischungen, the mixing part 23 on the Screw 10 arranged soin interchangeably.

To enable a gozielton disruption of the temperature profile in the course of the extrusion process, because the temporal nature of the mass precedes it the feed zone gradually bie about 150 ° and in the flastifying zone 16 about another 100 ° increases and in the course of the remaining extrusion process essentially remains constant, the pressure cylinder 11 is separated with thermally controllable sections 21 in advance, on donations each separately controllable, combinable hoist and cooling facilities 22 are grounded. These can consist of ontsprochond laid out electrical heating elements and cooling ducts through which the coolant has been passed as required. Sio can also be made up individually with a heating or cooling mode, as required loadable, separate pipe systems exist, which are thermally against the outside are isolated. In this way, each section of the extruder can be separated to determine the desired optimal Control temperature curve, in order to achieve that the melt undex of the extrudate and with it its structure roll Structure does not overshadow the optimal values.

Claims (9)

Claims: 1. A method for producing a plastic-insulated electrical cable or wire with high load capacity, in which the polypropylene containing insulation is extruded onto the conductor and then cooled, d a d u r c h e k e n n n n z e i c h n e t that an insulating mixture with predominant Polypropylene as well as with polyethylene and / or ethylene blends or copolymers used this insulating mixture under feed, plasticizing, homogenizing and Ejection temperature conditions that exceed the predetermined maximum Sohmel index value thereof of 0.65 g / 10 min, measured according to DIN 53735 at 190 ° C and 2, 16 kg load, prevent having an appropriately sized zone Extruder screw at temperatures of 250-300 ° C and sinem from the intake to above the plasticizing zone is extruded with an increasing controlled temperature profile and thereafter cooled in at least two different temperature levels and / or cooling media will. 2. The method according to claim 1, d a d u r c h g e k e n n z e i ohn e t that the temperature of the insulating mixture in the extrusion process after a from 100 ° to at least over half of the passage continuously down to the processing tempera ture increasing and, moreover, essentially constant temperature profile is controlled. 3. The method according to claim 1 or 2, d a d u r c h g e k e n n -z E i c h n e t that the extruded insulation in several cooling stages with a flilsoigen Medium is cooled, the temperature of which in the first cooling stage is at least 80 oC amounts to. 4. The method according to claim 1 or 2, d a d u r c h g e k e n n -z E i c h n e t that the extruded insulation initially by means of a gaseous Medium, for example air, and then with a liquid coolant, e.g. I3. Water, bi3 is cooled to room temperature. 5. Device for performing the method according to one of the claims 1 to 4, with a rotatable and drivable arranged in a heatable pressure cylinder Extruder screw with draw-in, plasticizing and ejection zones and one of the extruder exit associated cooling device, that is, that the Extruder screw (10) one twenty to twenty-five times its diameter (d) has a length, its feed zone (15) being approximately equal to one third up to half of its length, the plasticizing zone (16) equal to a fifth to a quarter their length and the ejection zone (17) approximately equal to the feed zone (ins) is, and the pressure cylinder (11) a number of thermally separately controllable sections (21) has, 6. Apparatus according to claim 5, d a d u r c h g e k e n n -z e i c h n e t that the extruder screw (10) has a flight depth in the area of the feed zone (15) from 0.1 to 0.2 d and the ejection zone (17) from 0.02 to 0.0 d, with d the screw diameter is designated. 7. Apparatus according to claim 5 or 6, d a d u r c h g e k e n nz E i c h e t that the extruder screw (10) with at least one in the discharge zone (17) arranged mixing and / or shearing part (23) is equipped, the relevant Section of the pressure cylinder (11) with a lleiz-Lühleineinrichtung (22) increased Kühlleistui1g is equipped. 8. Device according to one of the claims 5 to 7, d a d u r c h gek It is noted that the cooling device (4) as in a variable distance from the extruder outlet (20) aligned with this, with cable routing devices (9) equipped, trough-shaped or tubular cooling channel is formed. 9. Device according to one of claims 5 to 7, d a d u r c h g e It is not noted that the cooling device (4) is considered to be connected to the extruder outlet (20) directly connected, in separate sections or chambers for inclusion different, in particular having different temperatures, more liquid Coolant subdivided coolant tank is formed.