AU8528182A - Reflective means for cable - Google Patents

Description

Description

Electrical Cable with Light Reflective Means and Method of Making

Technical Field

The present invention relates to a cable utilized as a power transmission cable carrying a continuous reflective ribbon which renders the cable highly visible. Power transmission cables as described herein have use, among other uses, in supplying power to a shuttle car for face haulage in underground coal mines.

Background Art

Transmission cables for supplying electric power to mobile mining machines are used extensively. Typically, the cable trails out from behind the machine to some point in the rear where it is connected to a permanent electric power line. Thus, as the machine advances cable is payed out from a cable reel to trail the machine, and when the machinery retreats the cable is wound back on the reel.

It is well-known that cable used in service of this type is subjected to severe mechanical abuse. The cable that trails out behind the machine lies on the floor of the mine or other working environment and is subject to being walked upon, struck by falling rocks and other objects, otherwise mishandled, and oftentimes the cable may be run over by other machines. Mechanical abuse of the severity as last-mentioned, even though the cable is ruggedly con¬ structed, oftentimes will result in the development of a short-circuit to ground causing problems as are well-known.

The problem of the cable being run over by other machines becomes particularly acute when the cable is used with machinery in an environment, such as an underground mine, wherein the cable that trails out behind the machine is particularly difficult to see. In an attempt to overcome this problem, prior art cables have been colored, that is, a coloring ingredient has been compounded with the jacketing material thereby in the final product to provide a colored jacket. For example, the cable may be fabricated to include a jacket which is yellow, or orange in color. However, the use of a colored cable has not solved the problems of the prior art and in use in environments wherein the mine is wet and muddy the color of the cable has been found to provide no significant enhancement in visibility of the cable. All in all, these power cables have been found to have a service life of approximately three to four months.

Accordingly, an important aspect of -the invention is to overcome the aforementioned problems and disadvantages, and to provide a cable which is readily visible as desirable from a safety and identification standpoint. In fact, the cable of the present invention, more particularly described below, has been found to have significantly extended service life in environments of underground mines wherein mechanical abuse because of a lack of visibility and run over by mining machines is an acute problem._.

Summary of the Invention

The invention is in a power transmission cable for low, medium and high voltage applications. The ^'cable may be of a flat design, or of a round design generally including a core having at least one power conductor and a jacket pro¬ viding an outer encasement for the core. Cable construction of these basic designs are sold by the assignee of the present invention under the registered trademark "SECURITYFL Particulars of representative cables and their construction may be gleaned from cable data, identified as Data Section 7 21, dated September, 1976; 7 133, dated September, 1976; a 7 571, dated November, 1976. These data are incorporated herein by^* reference as to a construction of a cable contempl by the present invention. The cable includes at least one continuous ribbon which extends from one end to the other end. In the embodiment wherein the cable is of flat design, a pair of ribbons are disposed along the flat cable faces. In the embodiment wherein the cable is of round design, a single ribbon is disposed in a helical outline.

The ribbon preferably provides a quality of luminosity to render the cable readily visible. The ribbon may include a multiplicity of reflective elements through each increment of length. The ribbon is applied to an unvulcanized jacketing material, preferably immediately after the jacketing material is extruded on or otherwise formed about the core, and it has been found that the ribbon has little or no effect on the overall toughness, flexibility, durability and abrasion resistance of the cable, The ribbon is vulcanized directly on the jacket of the cable by a tenacious bond and, by this means, permits the realiza¬ tion of many desirable ends in cable construction, among others, -of longer service life, reduced accidents, and, as a consequence of longer service life, reduced down-time of equipment.

Brief Description of the Drawing

Figure 1 is a schematic presentation of a series of process steps in the fabrication of a power transmission cable of the present invention;

Figure 2 is a partial perspective view of a cable of flat design illustrating a pair of ribbons disposed on opposed surfaces ' and

Figure 3 is a view like Fig. 2 illustrating a cable of round design and a ribbon disposed helically therealong. Best Mode for Carrying Out the Invention

A power transmission cable of the invention, generally described above and more particularly described below, may be seen in Figs. 2 and 3 of the drawing. The cable 10a_ of 5 Fig. 2 is of the type characterized as being of flat design, whereas the cable 10b of Fig. 3 is of the type characterized as being of round design. Either design of cable is contem¬ plated by the present invention and typically the cable will be suitable for low, medium and high voltage applications. _Q Full particulars of the cable construction may be determined from the aforementioned cable data. Generally, however, the cable includes a core defined by a plurality of conductors which may include power conductors, ground check and grounding conductors within an outer jacket formed of a 5 tough, durable, heavy duty abrasion resistant material. In the flat design, the conductors of the core are arranged along a major dimension of the flattened oval configuration. As indicated in the cable data, the power conductors are spaced apart at least by their own 0 insulation, or by a grounding conductor (in a two power conductor form) , or by both a grounding conductor and a ground check conductor (in a three power conductor form of cable) . In the round design, the power conductors are arranged in a rope-lay-stranded form, insulated from one 5 another, and the other conductors are located in the interstices between power conductors. The power conductor may be insulated by neoprene, ethylene propylene (EP) insulation, among others; the ground check conductor may be insulated by polypropylene; and the jacket may be of _Q neoprene or a chlorosulfonated polyethylene (CSP) elastomeric polymer, such as that vended under the tradename HYPALON by the duPont Company. These materials will not militate against a needed characteristic of flexibility of cable. 5 The present invention insofar as a discussion of Fig. 1 is concerned will be directed to fabrication of the flat design of power transmission cable. - -

The jacket 12 which surrounds the core of the power transmission cable (with Fig. 2 and Fig. 3 suffix) is extruded or otherwise applied to the core of the cable. As illustrated in Fig. 1, the jacketed cable is shown emerging from the nozzle (not shown) of extruder 14 which is of a construction and operation conventional in the industry. The nozzle generally determines the final dimension of the cable, that is the major and minor dimensions of the flat design and the diameter of the round design, although there may be some slight reduction in dimension during curing. The cable exiting the extruder may be considered to be of flat design (Fig. 2) .

A first tape or ribbon 16 and a second tape or ribbon 18 are supported on individual payoff rolls (not shown) , guided toward the jacketed cable by means of an applicator stand instrumentality (also not shown} to be positioned to the nip between opposed flat surfaces along the major dimension of the cable and rollers 20, 22. The rollers are disposed above and below the cable respectively, in a position closely adjacent the nozzle of extruder 14. A close proximity of each of the rollers to the nozzle of the extruder will assure that each tape is applied to the cable when the temperature of the jacketing material is at or close to the temperature at the nozzle, namely at about 93.3° to about 98.9°C.

Each roller 20, 22 is mounted on an axle for revolu¬ tion substantially in synchronism with the speed of move¬ ment of the jacketed cable exiting extruder 14.

The tape 16 in the nip between the surface of roller 20 and the upper surface of the cable (the direction as in Fig. 1) is embedded in the jacketing material to the depth of its thickness. The tape 18 which passes between the roller 22 and the lower surface of the cable is similarly embedded in the jacketing material to the depth of the thickness.

In all likelihood the tapes 16, 18 will be disposed in positions of symmetry along the flat surface of the major dimension of the cable, but this is not necessary. What is necessary is that the tapes are disposed along the flat surface so that one tape is in a position to reflect light during use of the cable.

The tape 16, 18 may be any form of material capable of being vulcanized with the jacketing material, and one that will bond tenaciously to the jacket thereby to be nonremovable. Further, and importantly, the tape must provide a characteristic of luminosity thereby to reflect light from a source back to the region of the source. This characteristic permits the identification of cable trailing from a machine in the darkness of an underground mine, even under conditions when the mine is wet and muddy; and, as such, is an important factor in both safety to personnel and the prevention of damage to cable. Thus_> light reflected from the tape will enable the miner to steer clear of cable which may whip about upon sudden movement of the machine, and by- the same token the tape will enable the operator of the machine to see trailing cable under substan¬ tially all conditions. According to a preferred form of the invention, tape or ribbon 16, 18 is a material sold by the 3M Company under the tradename identification "SCOTCH-LITE" Brand Reflective Sheeting No. 8190 Silver.

The cable thereafter moves continuously toward a cooler 24 which functions to lover the temperature of the jacketing material to approximately room temperature prior to further operations. The cooler, through which the cable moves, may comprise a bath or it may provide nozzles for a spray of cooling liquid, such as water, through which the cable moves.

A plurality of nozzles 26 are located along the path of movement of the cable downstream of the cooler 24 and upstream of an extruder 28. The nozzles are preferably disposed at several attitudes about the cable and each nozz is in fluid connection with a source (neither the source no fluid connection is shown) of a lubricant which may be a silicone material. Suitable pumping apparatus within the fluid connection will provide for a spray of lubricant completely over the surface of the cable as it moves toward the extruder 28.

Typically, in the fabrication of cable of the type under consideration herein lead in a semisolid state is extruded

_ about the cable thereby to completely encase the jacket, b

Extruder 28 which may be a screw-type extruder, likewise, is conventional in structure and operation, and the lead- covered cable thereafter is reeled on a take-up reel 30. The silicone lubricant will prevent the lead from adhering to the jacketing material of the cable so that the lead following a curing operation may be stripped from the jacket of the cable.

While not shown in Fig. 1, although it should be apparent, the cable is suitably supported in movement in a continuous fashion from the nozzle of extruder 14 to and through the several operative stages of the process after which the cable is reeled onto the take-up reel 30.

In completing the fabrication procedure, the take-up reel 30 and the length of cable which it supports is physically located to an autoclave 32 within which the cable is cured. A cable of flat design including a neoprene jacket generally will be cured for a period of about sixty minutes at a temperature of about 137.8°C. Total residence time of the cable in the autoclave, however, will be approxi¬ mately ninety minutes thereby to provide a period during which the temperature within the autoclave is elevated so that the cure may be carried out at the aforementioned temperature. A cable of round design including a jacket of a CSP polymeric material generally will have the same residence time within the autoclave and undergo curing at a temperature of about 126.7° to about 132.2°C throughout a period of about sixty minutes. The lead in the lead-cure process applies a degree of pressure to the cable through gravity forces and, accordingly, the lead to some degree may affect the final dimension of the cable. However, the final dimension is fairly well set by the dimension of the nozzle of extruder 14. Once the cable has been cured, reel 30 becomes a payoff reel, and the cable is continuously moved from the reel toward a skive 34. The skive functions in a well- known manner to strip the lead encasement from the jacket. The lead which may have a slight effect in determining the final cross section of the cable is believed to assist in creating the tenacious bond of the tapes 16, 18 to the jacket.

Referring to Fig. 2, the tapes 16, 18 are illustrated as extending along the flat surfaces throughout the total length of the cable of flat design. Referring to Fig. 3, a tape 36 is illustrated as extending in helical pattern along the total length of the cable of round design. The tape 36 is of the type heretofore described and the fabri- cation process, and the bonding of tape to the jacket, is as previously described.

Cable having a pair of tapes along opposed flat surfaces of the flat design and in helical wrap about the surface of the round design has been found to have increased service life, well beyond the normal 3-4 month service life of present cable. Actually, in one instance cable after 7 months of service under ordinary circumstances of operation was taken out of service, tested, and found to be as structurally and operationally sound as the day the cable went into service. The tape is considered to render the cable several hundred times more visible than could be expected if the cable were provided with color, such as an orange or yellow, or even white coloration. This is because of the characteristic of luminosity of the tape and the millions of reflective elements per each, meter or portion thereof.

Claims (5)

Claims .

1. A power transmission cable having a core including at least one power conductor and a jacket surrounding said core, the improvement comprising means disposed on said jacket and extending as a continuous ribbon $ from one end of said cable to the other end, said continuous ribbon having a quality of luminosity so that said cable may be readily visible.

2. The power' transmission cable of Claim 1 having an overall flattened, oval configuration to provide a • pair of opposed, relatively flat surfaces along a major dimension, and said means disposed on said ^■ jacket comprising two continuous ribbons, with one ribbon extending along one surface and the other ribbon extending along the opposed surface.

The power transmission cable of Claim 2 wherein said continuous ribbons are disposed symmetrically along said cable.

The power transmission cable of Claim 1 having- an overall round configuration, and wherein said means disposed on said jacket comprises a single ribbon extending in a helical pattern.

5. The power transmission cable of any one of Claims 1, 2, 3 or 4 wherein said means comprises a tape having a multiplicity of reflective elements within each increment of length which act to reflect light from a source as shall strike said cable. A process for fabrication of a power transmission cable having a quality of luminosity thereby to render said cable readily visible comprising forming the material of a jacket continuously about a core having at least one power conductor and prior to curing of said jacketing material moving at least one continuous ribbon including a multiplicity of reflective elements within each increment of length for reflecting light which shall strike the cable into intimate contact with said cable, and curing said jacketing material under conditions that each said continuous ribbon is embedded to its thickness within said jacket and tenaciously bonded to said jacket.