FR2565887A1 - Continuous vulcanisation and/or crosslinking line, especially for producing insulating synthetic layers on cables - Google Patents

Abstract

This installation comprises means 1 for feeding with insulating material, means 2, 3 for extruding this material around the core 7 of a cable and a tube 5, 6 for vulcanising the covering of the cable obtained. The extrusion means comprise a double-screw extrusion stage 2 for plasticising the material at a controlled temperature, a single-screw extrusion stage 3 for compressing the plasticised material and an extrusion head 4 traversed by the core 7 of the cable. Means 10 for preheating the core of the cable are arranged upstream of the extrusion head and there is provision for an automatic device 12 for managing, controlling, monitoring and regulating the supply of the preheating means, the speed of the cable, the output of the extrusion stages and their supply with insulating material.

Description

The present invention relates to vulcanization lines for cables and relates more particularly to improvements made to these lines in order to improve their productivity,
The vulcanization lines of cables, intended for the production by extrusion of the layers of synthetic material (PRC, Elastomers or others) are units for continuous baking or vulcanization of insulating materials on a metallic core of copper or aluminum, of section variable.

 The concept of speed of passage, linked to a length of cooking in a steel tube, generally in the form of a chain and linked to a length of cooling coming after cooking, defines a level of cooking (which results in a rate crosslinking) and a cable receiving temperature, which are a function of the thickness of the insulation to be treated.

The performance of a vulcanization line therefore depends on the following two conditions:
- a sufficiently long residence time
to ensure good product quality,
- an acceptable temperature at reception
to avoid sticking on winding,
About ten years ago, the performance of the extruders, which produced around 200 kg per hour, led to the installation of lines a hundred meters in length.

Lines of this type include conventional single screw extruders on which it is difficult to control the following factors:
- High flow
- Low temperature
- High pressure.

 In these installations, a displayed speed always corresponds to a flow rate and a temperature for a given pressure.

 More recently, the Applicant has developed a very efficient machine comprising a twin screw extruder and another single screw. This technique was the subject of two patents no. 217364 and no. 2,212,229.

 It makes it possible to double the flow rates and to bring them to 400 to 600 kg / h depending on the mixtures while reducing energy consumption.

 The use of an installation of this type ensures a harmonious combination of the three aforementioned factors.

We get:
- in a first phase, mixing and kneading by counter-rotating friction, with a high flow rate and at low temperature;
- in a second phase, degassing, extrusion and filtration at high pressure.

This process is applicable to the production of low voltage cables in chemically crosslinked polyethylene (PRC), ethylene propylene diene monomer (EPDM), elastomers, etc. of medium voltage cables in PRC, EPDM, ethylene propylene rubber (EPR), polyethylene (PE) etc, ... of high and very high voltage cables in PRC, PE, halogen mixtures etc .;
- possibility for very high voltage cables to ensure continuous filtration at low temperature, with or without peroxide injection.

 However, the installation of an extruder of this type requires a significant increase in the length of the vulcanization tubes in order to obtain suitable times of day and temperatures.

 Of course, the increase in the length of 1 installation leads to an increase in its cost price. The invention aims to remedy the drawbacks of the installations of the prior art by creating a continuous vulcanization installation in particular for the realization of the insulation of electric cables, which while having a shorter length than the conventional installations makes it possible to ensure the operations coating with a suitable residence time and reception temperature.

It therefore relates to a vulcanization installation in particular for coating electrical cables comprising means for supplying the installation with material intended to form the insulation, means for extruding said material around the core of a cable to be coated and a tube for vulcanizing the coating of the cable obtained by extrusion, characterized in that said extrusion means comprise a double screw extrusion stage for plasticizing said material at controlled temperature, a single extrusion stage screw for pressurizing said plastic material and an extrusion head through which the core of said cable to be coated and in that it further comprises means for preheating the core of the cable disposed upstream of the head d extrusion on the path of said core and an automaton for controlling, controlling, monitoring and regulating the supply of said preheating means, the speed of movement of the cable, the flow rate of the stages of ext rusion and their food in insulation
The invention will be better understood on reading the following description made with reference to the accompanying drawings, given solely by way of example and in which:
- Fig.1 is a schematic view of a vulcanization installation according to the invention applied to the manufacture of a low voltage cable, an insulating layer;
- Fig.2 is a schematic view of a vulcanization installation according to the invention applied to the manufacture of a high voltage cable with three layers of insulator and semiconductor material.

 The installation shown in Fig. 1 includes a hopper 1 intended to receive a granular or pulverulent material with a view to conveying it to an extruder having a twin-screw extrusion stage 2 intended to ensure the plasticization at controlled temperature of the material cited above.

 The outlet of the twin-screw extrusion stage is connected to the inlet of a single-screw extrusion stage 3 for pressurizing the plasticized product by the twin-screw extrusion stage. In practice, stages 2 and 3 are part of a single machine sold under. the name BDV (double screw extruder) which is the subject of the two aforementioned patents.

 At the exit from stage 3, an extrusion head 4 is placed placed at the entrance to a vulcanization tube comprising a cooking zone 5 followed by a cooling zone 6.

 The head ~ 4, and the vulcanization tube 5, 6 are crossed by a cable 7 unwound from a coil 8 carrying a bare cable and wound on a coil 9 for receiving insulated cable driven by a capstan not shown.

 Upstream of the extrusion head 4, on the path of the cable 7, the installation comprises an inductor 10 for heating the cable, the supply circuit 11 of which is connected to a circuit 12 for driving, controlling, monitoring and regulation of the intensity of the supply current of the inductor 10 of the capstan driving the take-up coil 9 of the cable, of the flow rate of the extrusion stages 2 and 3 and of the flow rate of insulation material supplied to stages 2 and 3, whose measurement is obtained using a flow detector 13.

 In the installation of FIG. 1, the extrusion head 4 is constituted by a so-called "single layer" head supplied by the simple twin-screw extruder.

 The installation shown in Fig. 2 is intended to provide medium and high voltage cable insulation, formed of a layer of semiconductor material surrounding the metallic core of the cable, a layer of insulating material and a layer of external semiconductor material.

 Like the installation in FIG. 1, the installation in FIG. 2 includes a hopper 15 for receiving the material intended to constitute the insulating layer.

 The hopper 15 feeds a high-speed extruder 16 having a double screw stage 17 and a single screw stage 18 arranged in cascade.

 For the inner and outer layers of semiconductor material, the installation also includes two single screw extruders 19 and 20 whose flow characteristics are sufficient to perform this function.

 The extruders 16, 19 and 20 are connected to an extrusion head 21 which is a "three-layer" head capable of depositing, in a single pass, the three coatings of the cable core.

 Like the installation described above, the installation in Fig. 2 includes a preheating inductor 22, the supply circuit 23 of which is connected to a controller 24 for controlling, controlling, monitoring and regulating similar to the circuit 12 of installation of Fig. 1.

 Of course, this automaton also controls the operation of the single-screw extruders 19 and 20.

 The three-layer extrusion head 21 is, as in the embodiment of FIG. 1, traversed by a cable 25 which unwinds from a supply reel 26 and which passes through a vulcanization tube comprising a zone of cooking 27 and a cooling zone 28 to be wound on a take-up reel 29.

 Such an arrangement makes it possible to improve the efficiency of new lines but it can also be used successfully on existing installations.

 For example a cable of 20 KV with a core of aluminum 2 minium having a section of 150 mm2 is manufactured, using a preheating device of 50 KW, at a speed of 20 m / min while without preheating such a cable is delivered at only 12 m / min.

 The preheating power of the core is determined by each application.

 The control machines 12 of Fig. 1 and 24 of Fig. 2 can advantageously be constituted by suitably programmed computers, which are used to ensure optimum control of each production on the line, as a function of parameters such as time of stay in the cooking zone which results in a crosslinking rate and the reception temperature when the finished product is rolled up.

Claims (4)

 1. Vulcanization installation in particular for the coating of electric cables comprising means (1; 15) for supplying the installation with material intended to form the insulation, means  (2,3,4; 17 to 21) extruding said material around the core (7; 25) of a cable to be coated and a tube (5,6; 27,28) for vulcanizing the coating of the cable obtained by extrusion, characterized in that said extrusion means comprise a twin-screw extrusion stage (2; 17) for plasticizing said material at a controlled temperature, a single-screw extrusion stage (3; 18) pressurizing said plastic material and an extrusion head (4; 21) through which the core (7; 25) of said cable to be coated and in that it further comprises means (10; 22) preheating of the core of the cable arranged upstream of the extrusion head on the path of said core and an automaton (12 ;; 24) for driving, controlling, monitoring and regulating the supply of said preheating means , the speed of movement of the cable, the flow rate of the extrusion stages and their supply of insulation material.  2. Installation according to claim 1, intended for the production of a cable coated with an insulation formed by an internal layer of semiconductor material, an intermediate layer of insulating material and an external layer of semiconductor material. , characterized in that said extrusion means comprise an extruder (16) for the insulating material having a double screw stage (17) and a single screw stage (18) arranged in cascade, a single screw extruder (19) for the inner layer of semiconductor material and a single screw extruder (20-) for the outer layer of semiconductor material. said extruders (16,19,20) being connected to a three-layer extrusion head (21) capable of simultaneously extruding said internal and external layers of semiconductor material and said intermediate layer of insulating material.  3. Installation according to any one of claims 1 and 2, characterized in that said means for preheating the core of the cable consist of an inductor (10; 22) whose power supply (11; 23) is connected to said circuit (12; 24) for driving, controlling, monitoring and regulating.  4. Installation according to one of claims 1 to 3, characterized in that said control circuit (12; 24) of control, command, monitoring and regulation is a computer suitably programmed.