Electrical cable and method and equipment for the obtention thereof

Abstract: The method includes a step in which a conductor wire (4) is coated with a fused plastic material (7) and a step in which said plastic material is cooled, and it is characterized in that it includes a step in which a lubricating material (9) is sprayed onto the surface of the cable (2). Said cable (2) which includes at least one conductor core (4) and at least one coating of plastic material (7) incorporates a lubricating material (9) on the exterior coating. The equipment (1) for the manufacturing of electrical cables (2) which includes a reel (3) for supplying a conductor wire (4) to an extruding head (5), which has a tank (6) containing plastic material (7) for coating the aforesaid conducting wire (2), and a reel (11) for taking up the cable (2), includes a device (8) for the application of a lubricating material (9) onto the surface of the cable (2).

Description: The present invention relates to an electrical cable and a method and equipment for reducing its coefficient of friction. BACKGROUND OF THE INVENTION Electrical cables which include at least one conductor core and at least one coating are well known. Said cables present the disadvantage that their exterior surface has a high coefficient of friction, so that they are awkward to fit in internal sections of walls and ceilings, since when they come into contact with the adjacent surfaces (pipes, cables, etc.) they become stuck. In order to overcome said difficulty, alternative materials such as vaselines are currently used to coat the exterior surface of the cable, thereby reducing the coefficient of friction. In a complementary manner, guides of small diameter are also used, one end of which is inserted through the cavity through which the cable has to pass and the other is attached to the end of the cable which must be inserted into the cavity. Thus, once the guide has emerged at the desired place it is pulled until the end of the cable appears again after having passed through the entire section. Whatever the method used, the installation of said cables involves a considerable loss of time and an economic cost, since alternative materials are required. EP-A-0 905 717, prior art falling within the terms of Article 54(3) EPC, discloses a device for coating a solid lubricant on a cable, in which a film of lubricant film is deposited onto a extruded cable sheath by spraying in the plasma phase (sputtering). EP-A-0 949 635, prior art falling within the terms of Article 54(3) EPC, describes a pre-lubricated cable and its method of manufacture. The cable is provided with an outer covering and having a dry, non-tacky lubricating coating layer adhering to the outermost surface of the outer covering. DE-A-3 429 745 describes a process for increasing the output of cable-sheathing installations for the production of plastics-insulated electrical conductors. Electrostatic charging of the plastic-insulted cores produces an adhesive effect between the pulverulent lubricant and the plastics insulation of the cores. FR-A-2 674 364 discloses a cable having a low coefficient of friction, and the process and device for manufacturing this cable. The cable is characterised in that it includes, around its outer jacket, a peripheral sliding jacket made of composite material formed from plastic and silicone resin. DE-A-2 528 307 discloses an electrical cable which includes at least one conductor core and at least one coating of plastic material. The cable incorporates a lubricant material coated on the surface of the plastic material by spraying. DESCRIPTION OF THE INVENTION With the method, the cable and the equipment of the invention said disadvantages can be solved, while providing other advantages which will be described below. The method for the manufacture of electrical cables according to claim 1 is characterized in that it includes a step in which a lubricating material is sprayed onto the surface of the plastic material, said spraying step being carried out between the step of coating the conductor wire with plastic material and the step of cooling said material. A cable with low coefficient of friction is achieved thereby, so that subsequent installation of the same is considerably simplified, since it slides over the surfaces with which it comes into contact. It also means a clear economic and time improvement, as no type of alternative materials are required for installing it. This position of the spraying step in time is important since, when the conductor wire is coated with the plastic material, said material is in a state of fusion (approximately 150°C), the high temperature of which causes volatilization of the solvents present in the lubricating material, which means that there is greater adherence of said lubricating material on the surface of the plastic material. The subsequent cooling (down to approximately 20°C) of the plastic material together with the lubricating material leads to drying of the surface, leaving the two materials bonded to form a coating of low coefficient of friction. Suitable lubricating material can involve the use of a fluorated organic resin, such as a polymer of one or more fluorated monomers selected from amongst, for example, tetrafluoroethylene, vinylidene fluoride, chlorotrifluoroethylene and the like. The use of polytetrafluoroethylene (PTFE) is particularly preferable. The fluorated resin is preferably used in the form of an emulsion or aqueous dispersion The electrical cable according to claim 3 is characterized in that it incorporates a lubricating material impregnated on the surface of the plastic material by spraying. The exterior coating of the cable is thus well impregnated with said material, forming a fine layer on the plastic material, since it emerges at high pressure and the plastic material is at high temperatures. The equipment for the manufacturing of electrical cables according to claim 4 is characterized in that it includes a device for the spraying of a lubricating material in a semi-fused state on the surface of the plastic material. Said device includes a box section through which the cable passes, a plurality of nozzles for spraying the lubricating material mounted inside the box section, a tank for said lubricating material, and a pressure pump to carry the lubricating material from the tank to the spraying nozzles. Moreover, the device also includes a pressure adjusting valve, a level indicator of the lubricating material tank, and a pressure gauge. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of all that has been outlined, drawings have been attached in which, schematically and solely by way of non-restrictive example, a practical case of embodiment is shown. In said drawing, Figure 1 is a schematic elevation view of the equipment for the manufacturing of the electrical cables, according to the method of the invention; and Figure 2 is a schematic plan view of the device for the application of the lubricating material onto the surface of the cable. DESCRIPTION OF A PREFERRED EMBODIMENT As can be appreciated in the figures, the equipment 1 for manufacturing electrical cables 2 object of the invention includes a reel 3 which supplies conductor wire 4 to an extruding head 5, which in turn includes a tank 6 of plastic material 7; a device 8 for the application of the lubricating material 9 by spraying onto the exterior surface of the cable 9; a cooling box 10 for cooling the exterior surface of plastic material 7 which is in a state of semi-fusion on the conducting wire 4; and a reel 11 for taking up the resulting cable 2. As can also be seen in the figures, the device 8 for the application of the lubricating material 9 onto the surface of the cable 2 includes a box section 12 through which the cable 2 passes; two nozzles 13, 14 mounted inside the box section 12 for spraying the lubricating material 9 ; a tank 15 for storing said lubricating material 9; a pressure pump 16 for making the lubricating material 9 travel from the tank 15 to the spraying nozzles 13, 14; a valve (not shown) for adjusting the pressure at which the lubricating material 9 must emerge through the spraying nozzles 13, 14; an indicator (not shown) of the level of the tank 15 for the lubricating material 9; and a pressure gauge (not shown) to measure the pressure of the circulating gases. The spraying nozzles are of the gas oil burner type, with a flow rate of 25 litres/hour and projection cone angle of 45°. The pressure pump is an electrical geared pump, having a flow rate of 500 litres/hour, maximum pressure of 10 6 N/m 2 (10 bar), motor output of 0,373 kW (0.5 hp), speed of 1450 rpm, voltage of 220/380 V, 1,9 cm (3/4") gas aspiration thread and 0,95 cm (3/8") gas impulsion thread. The method of the invention for the obtention of electrical cables 2 includes a first step in which the conductor wire 4 is coated with the fused plastic material which is at an approximate temperature of 150°C; a second step in which spraying of the lubricating material 9 is carried out, forming a fine layer on the plastic material 7 of the coating, taking advantage of said plastic material being still in state of semi-fusion in order to enhance adherence of the lubricating material 9 on said plastic material, since there occurs volatilization of the solvents which form part of the lubricating material; and a third step in which cooling of the plastic material 7 is carried out (down to approximately 20°C) together with cooling of the lubricating material 9, to provide an exterior coating of the cable 2 with a low coefficient of friction. A cable 2 is thus obtained with at least one conducting core and an exterior coating, the main characteristic of which is that its coefficient of friction is low, which makes it easier to install since it slips on the surfaces with which it comes into contact. It is important to stress that the temperature of the plastic material 7 at the time of the application of the lubricating material 9 must not be less than 85°C. The cables 2 on which the lubricating material 9 is applied can be of any desired configuration. It has been found experimentally that the use of an aqueous emulsion of a fluorated, liquid and translucent organic resin, of the polytetrafluoroethylene (PTFE) type is suitable for providing a considerable reduction of the coefficient of friction of the cable, which means that it is easier to install without adding any external element to it, which is one of the objectives sought in the present invention. It is advisable for the aforesaid aqueous emulsion to have a density of 1.0+0.02 g/ml and a boiling point of 100°C.

Claims: Method for the manufacture of electrical cables (2) which includes a step in which a conductor wire (4) is coated with a fused plastic material (7) and a step in which said plastic material is cooled, characterized in that it includes a step in which a lubricating material (9) is sprayed onto the surface of the plastic material, said spraying step being carried out between the step of coating the conductor wire (4) with said plastic material (7) and the step of cooling said plastic material (7). Method according to claim 1, characterized in that the lubricating material is an aqueous emulsion of a fluorated organic resin, of the polytetrafluoroethylene (PTFE) type. Electrical cable (2) which includes at least one conductor core (4) and at least one coating of plastic material (7) characterized in that the electrical cable (2) incorporates a lubricating material (9) impregnated on the surface of the plastic material (7) by spraying. Equipment (1) for the manufacturing of electrical cables (2) which includes a first reel (3) suitable for supplying a conductor wire (4) to an extruding head (5) which has a tank (6) containing plastic material (7) suitable for coating the aforesaid conducting wire (2), and a second reel (11) for taking up the cable (2), characterized in that it also includes a device (8) for the spraying of a lubricating material (9) in a semi-fused state onto the surface of the plastic material (7). Equipment according to claim 4, characterized in that the device (8) suitable for the spraying of the lubricating material (9) on the surface of the plastic material (7) includes a box section (12) through which the cable (2) passes, a plurality of nozzles (13, 14) suitable for spraying the lubricating material (9) mounted inside the box section (12), a lubricating material tank (15), and a pressure pump (16) to carry the lubricating material (9) from the tank (15) to the spraying nozzles (13, 14). Equipment according to claim 5, characterized in that the device (8) suitable for the spraying of the lubricating material (9) onto the surface of the plastic material (7) includes a pressure adjusting valve, a level indicator of the lubricating material tank (15), and a pressure gauge.

Inventors: VALLS PRATS AGUSTI, VALLS PRATS, AGUSTI
Applicants: PIRELLI CABLES Y SIST S S A, PIRELLI CABLES Y SISTEMAS, S.A.
Application year: 1999
Main classification: H01B13
IPC codes: H01B13