Method of manufacturing an electrical cable having a surface with reduced coefficient of friction

187574/2

TECHNICAL FIELD

[0001] The present invention relates to an electrical cable and to a method fo and equipment for reducing its coefficient of friction.

BACKGROUND ART

[0002] Electrical cables which include at least one conductor core and at least one coating are well known.

[0003] Such 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 or conduits, since when they come into contact with the surfaces they become stuck or difficult to pull, etc.

[0004] In order to overcome said difficulty, alternative materials such as vaselines and the like have been used to coat the exterior surface of the cable, thereby reducing the coefficient of friction.

[0005] In a complementary manner, guides of small diameter are sometimes 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.

[0006] In numerous fields of application, and in particular telecommunications, electric or fiber optic cables are inserted into ducts. There is therefore a need to minimize the coefficient of friction between cables and the inside walls of ducts.

[0007] In one solution, the core of the cable passes via a first extruder which applies a conventional sheath thereto, i.e. a jacket and/or insulation, often made of polyethylene. The sheathed core then passes through a second extruder which applies a lubricant layer thereto, such as an alloy of silicone resin and polyethylene. The cable lubricated in that way then passes in conventional manner through a cooling vessel. 1 187574/3 [0008] A second solution provides for an extruder to cover the core of a cable with a sheath. At the outlet from that extruder there is disposed a coating chamber for applying granules of material to the still-hot sheath, which granules are designed to become detached when the cable is inserted in a duct. Finally, the coated cable passes through a cooling vessel.

[0009] In both of these two prior solutions, it is necessary to interpose additional equipment between the extruder and the cooling vessel. That gives rise to a major alteration of the manufacturing line.

[0010] In addition, the equipment for depositing the lubricant must be very close to the sheath extrusion head since otherwise it is not possible to control the thickness of the sheath properly. In any event, the additional equipment occupies on-negligible space and such an arrangement is not favorable for control over the dimension of the sheath. [0011] Whatever the prior art method used, the manufacture and/or installation of said cables involves a considerable loss of time and an economic cost, since alternative materials are required. US Patent No. 4,356,139 discloses a method for continuously lubricating cable during continuous dry curing of cable insulation and insulation shield to reduce friction between the cable surface and the dry curing apparatus, thereby eliminating cable oscillation and vibration and increasing product quality and the speed of production. The method comprises coating insulation compound pellets and insulation shield compound pellets with incompatible lubricant immediately prior to extrusion of insulation and insulation shield on to the cable. US Patent No. 4,299,256 discloses a flexible coextruded tubing having an outer portion of polyvinyl chloride plastic containing a minor amount of intimately mixed silicone oil and having an inner portion of plastic free of silicone oil. FR Patent No. 2674364 discloses a cable characterized in that it includes, around its outer jacket (sleeve), a peripheral sliding jacket made of composite material formed from plastic and from silicone resin, forming an overjacketing of the said outer jacket. US Patent No. 5,460,885 discloses a high service temperature electrical wiring product comprising a jacketed polyvinyl chloride insulation incorporating a relatively volatile plasticizing system and manufacturing process therefore. The wiring product comprises an electrical conductor and an insulation covering on the conductor having a UL-83 01918077\206-01 2 187574/3 service temperature classification of at least 90 DEG C. The insulation is formed of a primary coating of a polyvinyl chloride resin which contains a relatively volatile plasticizing system for the resin, specifically, one having a vapor pressure at 200 DEG C. of at least 0.3 torr. A jacket surrounding the primary insulation coating is formed of a poly (alkylene terephthalate) having a melt temperature in excess of that of the primary insulation coating. A specific plasticizer system is an organic acid ester plasticizing system in which the predominant ester component is a di (R, R') phthalate ester in which R and R' are each independently an alkyl group and which together contain a total of no more than 20 carbon atoms. Such a system comprises a mixture of a predominant dialkyl phthalate, in which each alkyl group contains from 8-10 carbon atoms, and a minor amount of a dibasic aliphatic acid ester. US Patent No. 6,160,940 discloses a fiber optic cable having a cellularized cable component, the cellularized cable component including at least one optical fiber and a cable jacket. The cable jacket can include surface irregularities having crests and hollows for reducing surface-to-surface contact with a surface in the cable passage way. The cable jacket can include a friction reducing additive for lubricating the interface between the cable jacket and the cable passageway or objects in the cable passageway. Japanese Patent No. H01110013 discloses that, at the time of laying a telecommunication cable, optical cable, power cable or the like, several dividing conduit lines are arranged in a conduit line and a cable is laid in each dividing conduit line. As plastics constituting said dividing conduit lines, there is used polyethylene, in which four kinds of lubricants, that is: a; erucylamide, b; stearic acid, c; polyethylene wax, d; microwax are mixed while changing the amount of addition. For example, said lubricants a-d are mixed while changing the amount of addition as shown in the table to make a dividing conduit line 2 of 36mm diameter, in which there is laid a polyethylene-sheathed optical fiber cable of 22mm diameter.

OBJECTS AND SUMMARY OF THE INVENTION

[0012] The present invention thus seeks to provide a method for making a cable having a surface with reduced coefficient of friction that does not significantly alter the geometrical characteristics of the cable so produced. 2a 187574/3 [0013] The invention thus provides a method of manufacturing a electrical cable having a conductor core and a sheath of material surrounding at least said conductor core and defining the outermost exterior surface of the finished cable, the method comprising: (a) introducing lubricant into said material prior to the formation of said sheath in order to provide a reduced coefficient of friction of said outermost exterior 2b 187574/2 sheath in order to provide a reduced coefficient of friction of said outermost exterior surface and reduce the amount of force required to pull the cable during its installation through building passageways, in which said lubricant is of the type which either migrates through, or permeates, said material to be available at said outermost exterior surface; and (b) thereafter extruding said so-lubricated material to surround at least said conductor core.

[0014] The invention also provides a method of manufacturing a electrical cable of the type having a conductor core, and at least two sheaths surrounding at least the conductor core, an inner sheath of a first material, and an outermost sheath of a second material different than said first material, the outermost sheath defining the exterior surface of the finished cable. The method comprises: (a) forming said inner sheath of said first material; (b) introducing a lubricant into the said second material to provide a reduced coefficient of friction of the exterior surface of said outermost sheath at the time of installation of the cable through wall or ceiling cavities conduits or ducts, thereby to reduce the amount of force required to pull the cable and increase the resistance to cable bum-through during its installation, said lubricant being of type which either migrates through or permeates, said second material, to be available at said exterior surface of the cable at the time of its installation; and (c) extruding said so-lubricated material to surround at least said conductor core, therein providing said finished cable with a lubricated outer surface at the time of installation without the external application of a lubricant to said outer surface.

[0015] The invention also provides a use of an electrical cable having a cable core and an external jacket with an exterior surface defining the outermost exterior surface of the cable wherein the external jacket of the cable is formed of extruded plastic material characterized in that: the electrical cable is utilised in installation through wall or ceiling cavities conduits or ducts; the cable core is comprised of an electrical conductor; the jacket incorporates lubricating material that blooms, migrates toward the exterior surface of or permeates the jacket, the lubricating material being incorporated into the sheath during or prior to the extruding; and the jacket contains sufficient lubricating material to provide a reduced coefficient of friction of the exterior 3 187574/1 surface of said external jacket sufficient to reduce an amount of force required to pull the cable through said wall or ceiling cavities conduits or ducts during its installation.

[0016]-[0018] As used herein the term sheath means a jacket and/or insulation applied to the core of a cable.

DISCLOSURE OF THE INVENTION

[0019] With the method and cable of the invention said disadvantages can be solved, while providing other advantages which will be described below.

[0020] The method for the manufacture of electrical cables is characterized in that it includes a step in which a lubricating material is mixed with the sheath material and this mixture is applied to the core of the cable.

[0021] 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 surface with which it comes into contact.

[0022] The step of mixing the lubricating material and the sheath material may be carried out with the lubricating material heated or not and the sheath material heated or not.

[0023] The sheath material normally is introduced in pellet form to an extruder which heats and directs the sheath material onto the cable or doctor core. The present invention includes the embodiment of incorporating the lubricating material into the sheath pellets 3a WO 2007/081372 PCT/US2006/011069 during the formation of the sheath pellets and introducing this mixture of sheath pellets and lubricant material into an extruder, the embodiment of mixing the lubricant material with the sheath pellets and the embodiment of introducing this mixture into the extruder, and introducing the sheath pellets into the extruder and subsequently introducing the lubricating material into the extruder prior to contacting the cable core.

[0024] Advantageously, the lubricant material is selected from the group consisting essentially of fatty amides, hydrocarbon oils, fluorinated organic resins, and mixtures thereof. The lubricant material may be incorporated at any point in the manufacturing process before the formation of the sheath, and depending upon the material, may be heated prior to mixing with the sheath material.

[0025] In instances where the sheath material has a high melting or softening temperature, or for other reasons such as processibility, efficiency of the process, etc. the lubricant material may be added to the sheath material as the sheath material is being formed. If the final cable construction is such that there are two or more different sheath materials applied to the cable core, the lubricant material need only be incorporated into the outermost sheath material.

[0026] Advantageously, the lubricating materials include fatty amides, fatty acids, fatty esters and metallic fatty acids and more advantageously include fatty amides, fatty acids, fatty esters, and metallic fatty acids having from about 10 to about 28 carbon atoms preferably from about 10 to about 2 carbon atoms and include, but are not limited to erucamide, oleamide, oleyl palmitamide, stearyl stearamide, stearamide, behenamide, ethylene bisstearamide, ethylene bisoleamide, stearyl erucamide, erucyl stearamide, capric acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, eleostearic acid, arachidic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, cerotic acid, montanic acid, caprate, laurate, myristate, palmitate, palmitoleate, stearate, oleate, vaccinate, linoleate, linolenate, eleostearate, arachidate, arachidonate, behenate, lignocerate, nervonate, cerotate, montanate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol dipalmitate, pentaerythritol palmitate stearate, pentaeiythritol distearate, and the like. Advantageous hydrocarbon oils include, but are not limited to, mineral oil, silicone oil, and the like. Lubricating materials suitable for the present invention further include plasticizers, dibasic esters, silicones, anti-static amines, organic amines, ethanolamides, mono-and di-glyceride 4 WO 2007/081372 PCT/US2006/011069 fatty amines, ethoxylated fatty amines, fatty acids, zinc stearate, stearic acids, palmitic acids, calcium stearate, lead stearate, sulfates such as zinc sulfate, etc., and the like. The above lubricating materials may be used individually or in combination.

[0027] The electrical cable is characterized in that it incorporates a lubricating material in the sheath coating, which lubricating material blooms, migrates toward the exterior, or permeates the cable sheath. If desired the sheath material may be somewhat porous, thereby resulting in the lubricating material more readily migrating toward the exterior surface of the sheath.

[0028] The sheath of the cable thus contains sufficient lubricating material to provide an exterior surface with reduced coefficient of friction.

[0029] The equipment for the manufacturing of electrical cables is characterized in that it may include a device for the incorporation of a lubricating material into the sheath material prior to application to the cable core.

[0030] Said equipment may also include a tank to maintain the lubricating material, a section for mixing the lubricating material and sheath material and a section for applying the mixture to the cable core.

[0031] Moreover, the equipment may also include a pressure adjusting valve(s), a level indicators) of the lubricating material tank and sheath material tanks, and a pressure gauge(s).

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] For a better understanding of the present invention, a drawing is attached in which, schematically and by way of example, an embodiment is shown.

[0033] FIG. 1 is a schematic elevation view of equipment for manufacturing electrical cable, according to the method of the present invention. 5 WO 2007/081372 PCT/US2006/011069

BEST MODE FOR CARRYING OUT THE INVENTION

[0034] As can be appreciated in the figure, the equipment 11 for manufacturing electrical cable 12 of the present invention includes a reel 13 which supplies conductor wire 14 to an extruding head 15, which in turn includes a tank 16 of plastic material 17; a tank 18 of lubricating material 19 for mixture with plastic material 17 and for application onto the exterior surface of the conductor wire 14; a cooling box 20 for cooling the exterior surface of the plastic material 17 - lubricating material 19 mixture which is in a state of fusion or semifusion on the conductor wire or cable core 14; and a reel 21 for taking up the resulting cable 12.

[0035] As can also be seen in the figures, the tank 18 may include a section 22 through which the lubricating material can pass into tank 16 and be mixed with plastic material 17 and a section 23 through which lubricating material 19 can be introduced directly into extruding head 15 at a point after plastic material 17 has been introduced into extruding head 15.

[0036] Plastic material 17 includes known materials used in electrical wire and cable products such as polyethylene, polypropylene, polyvinylchloride, organic polymeric thermosetting and thermoplastic resins and elastomers, polyolefins, copolymers, vinyls, olefin-vinyl copolymers, polyamides, acrylics, polyesters, fluorocarbons, and the like.

[0037] The present inventive method and the novel cable produced thereby includes the step of coating conductor wire or cable core 14 with the mixture of plastic material 17 and lubricating material 19 and optionally cooling the coated cable formed thereby.

[0038] Cable 12 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.

[0039] Another beneficial property gained by the present invention is an increased resistance to “bum-through.” “Burn-through,” or “pull-by,” results from friction generated by pulling one cable over another during installation, causing deterioration and eventual destruction to its own jacket as well as the jacket of the other cable. When using a lubricated cable of this 6 WO 2007/081372 PCT/US2006/011069 invention the number of six-inch-stroke cycles required to produce burn-through was increased from 100 to 300, [0040] The present inventive cable may also enhance ease in stripping the jacket from the cable end - termed stripability.

[0041] A further benefit of the present invention is the reduction of jacket rippling. Jacket rippling results from the friction of the jacket against building materials, causing the jacket material to stretch and bunch. Jacket damage may result. Installation situations, which repeatedly caused jacket rippling in unlubricated cable caused no rippling in lubricated cable jackets.

[0042] Despite the fact that reference has been made to specific embodiments of the invention, it will be clear to experts in the subject that the cable, the method and the equipment described can be varied and modified in many ways, and that all the details mentioned can be replaced by others which are technically equivalent without departing from the sphere of protection defined by the attached claims.

[0043] For example, cable 12 on which plastic material 17 and lubricating material 19 are applied can be of any desired configuration and can be an optical fiber cable or the like.

[0044] It has been found experimentally that the use of a lubricating material disclosed herein 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.

EXAMPLE

[0045] To understand the affects of the jacket lubricant system on the ease of pull variations of the UL (Underwriters Laboratories, Inc.) joist pull test was utilized.

[0046] The joist pull test outlined in UL 719 Section 23 establishes the integrity of the outer PVC jacket of Type NM-B constructions when subjected to pulling through angled holes drilled through wood blocks. 7 WO 2007/081372 PCT/US2006/011069 [0047] The test apparatus consists of an arrangement of 2”x4” wood blocks having holes drilled at 15° drilled through the broad face. Four of these blocks are then secured into an frame so that the centerlines of the holes are offset 10” to create tension in the specimen through the blocks. A coil of NM-B is placed into a cold-box and is conditioned at -20°C for 24 hours. A section of the cable is fed through corresponding holes in the blocks where the end protruding out of the last block is pulled through at 45° to the horizontal. The cable is then cut off and two other specimens are pulled through from the coil in the cold-box. Specimens that do not exhibit tom or broken jackets and maintain conductor spacing as set fort in the Standard are said to comply.

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UL Joist-Pull Test [0048] Pulling wire through the wood blocks provides a more direct correlation of the amount of force required to pull NM-B in during installation. Because of this relationship, the joist-pull test is initially the basis for which ease of pulling is measured, but a test for quantifying this “ease” into quantifiable data had to be established.

[0049] A variable-speed device was introduced to pull the cable specimen through the blocks. An electro-mechanical scale was installed between the specimen and the pulling device to provide a readout of the amount of force in the specimen. To create back tension a mass of known weight (5-lbs) was tied to the end of the specimen. 8 WO 2007/081372 PCT/US2006/011069 [0050] Data recorded proved that NM-B constructions having surface lubricates reduced pulling forces.

[0051] A 12-V constant speed winch having a steel cable and turning sheave was employed; the turning sheave maintains a 45 degree pulling angle and provides a half-speed to slow the rate of the pulling so that more data points could be obtained. Holes were drilled in rafters whereby specimens could be pulled by the winch.

[0052] It was found using this method that lubricated specimens yielded approximately a 50% reduction in pulling force when compared to standard, non-lubricated NM-B specimens. The results are shown in Tables 1 and 2 wherein the data was recorded at five second intervals.

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Modified Joist-Pull Test 9 WO 2007/081372 PCT/US2006/011069 TABLE 1

Test Pt. Descr. Specimen Description Manufacturer A1 Manufacturer A2 Manufacturer A3 Manufacturer B1 Manufacturer B2 Manufacturer B3 Control 1 Control 2 Present Invention 1st Point 26.8 48.3 37.8 37.4 16.5 41.9 24 2nd Point 34.6 51.1 35.2 38.1 41.6 42 20.5 3rd Point 33.7 46.8 32 33 40.2 38.7 20 4th Point 38.6 49.8 34.7 34.6 41.3 29.5 17.4 5th Point 33.1 44.8 34.2 32.5 41.3 34.3 20.2 6th Point 28.6 44.7 32.2 33.2 42.5 35.9 15.8 7th Point 5.5 51 32.2 33.9 41.1 37 17.2 8th Point 26.8 49.2 33.9 33 40.9 38.4 17.3 9th Point 21.9 52.5 32.6 30.6 42.7 37.3 21.9 Average 30.51 48.69 33.87 34.03 41.45 37.22 19.37 AAA - Denotes Outlyers

Test in Table 1 performed at a constant speed with winch using 1/2 speed pulley Test in Table 2 performed on cable with a 5# weight suspended at building entry

Std. Prod.

Average Present Invention 37.6289 19.37 10 WO 2007/081372 PCT/US2006/011069 TABLE2

Test Pt. Descr. Specimen Description Manufacturer A 14-2 Manufacturer B 14-2 Control 1 14-2/12-2 Control 2 14-2/12-2 Control 3 14-2/12-2 Invention A 14-2/12-2 Invention B 14-2/12-2 1st Point 34 32.6 50 47.5 40.2 21.5 12.3 2nd Point 35 35.7 50.6 38.3 37.5 22.9 12.8 3rd Point 35.5 31.2 46.7 43.2 27.5 29 12.1 4th Point 37.7 35 44.5 46 36.8 22.4 14.9 5th Point 40.5 30.6 46.2 39.5 36 23.3 11.9 6th Point 32.9 28.8 40.9 35.7 41.2 21.1 12.5 7th Point 44.2 32.4 52.8 37.5 37 21.6 11.7 8th Point 43 32.4 40.7 27.7 31.7 22.5 11.7 9th Point 43.4 30.5 40 31.1 19.2 11 10th Point 40 11.6 Average 38.62 32.13 45.82 38.50 35.99 22.61 12.25 14-2/12-2 14-2/12-2 14-2/12-2 Control Avg. Invention A Invention B 40.103241 22.61 12.25 11