WO1983000459A1

WO1983000459A1 - Extrusion apparatus and methods of splicing ropes or cables utilizing such apparatus

Info

Publication number: WO1983000459A1
Application number: PCT/GB1982/000230
Authority: WO
Inventors: Belt Limited Cable
Original assignee: Thomson, Ian, Main
Priority date: 1981-08-06
Filing date: 1982-07-27
Publication date: 1983-02-17
Also published as: ES8308258A1; GB2114503A; ZA825708B; ES514764A0; GB8308855D0; EP0085063A1

Abstract

An extruder die for plastics material has a predetermined cross-sectional area and can be deformed to change this cross-sectional area to allow variation of the cross-section of the extrusion. This finds particular application in the re-covering of a spliced plastics covered rope where the diameter of the rope increases between an uncovered spliced section and the covered remainder of the rope. Such a die can be used to extrude a plastics covering over the splice section and, at the end of the uncovered section, expand over the existing cover to provide a continuously covered rope.

Description

EXTRUSION APPARATUS AND METHODS OF SPLICING ROPES OR CABLES UTILIZING SUCH APPARATUS

The invention relates to extrusion apparatus for extrudin plastics material and to methods of splicing cable utilizing such apparatus.

Extrusion apparatus includes an extrusion die formed wit a predetermined cross-sectional area and when a molte plastics material is forced through a die outlet, a elongate extrusion is formed which has a cross-sectio determined by the area of the outlet. In order t alter the cross-sectional area of the extrusion, it i necessary to replace the die.

It is an object of the invention "to mitigate thi disadvantage,

According to a first aspect of the invention there is provided an extrusion apparatus comprising an extrusion die for extruding a plastics material and including at least one die member having an outlet of predetermined cross-sectional area, said cross-sectional area being variable by the application of a force thereto for varying the cross-section of the extrusion.

The die may further comprise an outer die member arranged around the first-mentioned, inner, die member to form therebetween an outlet passage for the extruded plastics mat

extrusion temperatures as to allow controlled deformation of the outlet nozzle by the application of a force thereto.

A further disadvantage of conventional extrusion dies is that they cannot extrude onto an elongate member having a cross-sectional area which varies along the length of the member.

In a preferred embodiment, the die is for extruding a covering of thermoplastics material onto an elongate object of varying cross-sectional area along the length thereof, the inner die having a passage therethrough for the elongate object, and the undeformed cross-sectional area of the inner die is generally equal to the minimum cross-sectional area of the elongate object, the inner die member in use, being expanded by a force applied thereto from contact with portions of the elongate member of greater cross-sectional area than said minimum cross- sectional area during relative movement therebetween to produce an extruded covering of varying cross-sectional area along the length thereof.

According to a second aspect of the invention, there is provided a method of splicing a rope or cable of the kind comprising a plurality of strands each formed from a plurality of wires twisted together, the strands being themselves twisted together and all the strands together being covered by an outer covering of a thermoplastics mater a t thermoplastics material from two rope or cable ends splicing the two rope or cable ends together so that th spliced rope or cable ends have a diameter equal to o substantially equal to the diameter of an unsplice uncovered rope or cable and then re-covering the splice rope or cable ends with a covering of a plastics materia by use of an extrusion apparatus according to the firs aspect of the invention.

The following is a more detailed description of on embodiment of the invention, by way of example, reference being made to the accompanying drawings in which:-

Figure 1 is a plan view, partly in section, of a cross head die assembly of an extrusion machine;

Figure 2 is a perspective view of an inner die for use in the cross head die assembly of Figure 1;

Figure 3 is an elevation of a half-portion of the inner die of Figure 2 ;

Figure 4 is a general view of the cross-head die assembly in position in the extrusion machine and with the die closed;

Figure 5 is a similar view to Figure 4 but showing the die assembly open;

Figure 6 is a schematic cross-sectional view of the machine of Figures 1 to 5 during the extrusion of a covering onto a tapered portion of a covered cable; and

Figure 7 is a similar view to Figure 6 but showing the machine of Figures 1 to 5 covering an uncovered portion of the cable.

Referring first to Figure 1, the extrusion machine includes a cross head die assembly comprising an outer casing 10 of generally rectangular cross-section and divided in a vertical plane,into two halves 11, 12. One half, 11, is fixed to the remainder of the machine while the other half, 12, is pivotally connected to the remainder of the machine to allow it to be moved into and out of register with the fixed half 11. Each half-casing 11, 12, is formed with a semi-cylindrical recess 13, with the recesses 13 in the two casing halves 11, 12 being in register to define, in the closed die, a passage through the casing 10. Each recess 13 comprises first and second portions 14, 15 of greater and lesser constant diameters, respectively, and connected by a tapering portion 16.

An inner half-die holder 17 is held in each first recess portion 14 by screws 18 and has an end part 19 which has a frusto-conical outer surface 20, an inner annular groove 21 and a radially extending end wall 22. The frusto- conical outer surface 20 extends parallel to but spaced from the tapering recess portion 16 to define therewith part of an annular outlet 23 which communicates with an Each half-casing 11, 12 carries an outer half-die 25 an each inner die half holder 17 carries an inner half-di 26. Each outer half-die is made from steel and is in th shape of a hollow half-cylinder, with the division bein in a plane including the die axis, and is secured in th associated half casing 11, 12 by a screw 27. A radiall inner surface of each half-die includes a f usto-conica portion 28, which forms a continuation of the taperin recess portion 16, and also has an outlet portion 2 parallel to the cylinder axis.

An inner half-die 26 and the whole inner die formed b two half-dies 26 are shown in Figures 3 and respectively. Each inner half-die 26 is made from a plastics material such as polytetrafluoroethylene and is generally the shape of a half annulus divided longitudinally. The interior surface of each inner half- die 26 comprises an initial converging portion leading to an outlet portion of generally constant diameter. The outer surface of each inner half-die 26 is formed with an end half-flange 30, and an annular surface 31 connected by a radially extending step to a frusto-conical outlet portion 32.

As seen in Figure 2, the two inner half-dies 26 together form a die having an end flange, a frusto-conical outer surface and a passage extending therethrough.

Each inner half-die 26 is located in the inner half-die holder b e a eme of t - a annular groove- 21 of the associated inner half-die holder 17 as seen in Figure 1. The frusto-conical portion 32 of each inner half-die 26 terminates adjacent the smaller diameter end of the inner surface of the outer half-die 25 and is arranged so that the annular outlet passage formed between the frusto-conical surfaces of the inner and outer dies 25, 26, converges towards the outlet end.

The extruder 24 receives a particulate plastics material from a hopper (not shown) and conveys it to the cross-head die assembly. During this conveying, the plastics material is heated to a molten state.

The cross-head die assembly is mounted on a machine base 34 (Figs. 4 and 5) together with an electrically operated control system 35 for controlling and monitoring the operation of the extruding machine. The base is movable on rails (not shown) and a capstan winch (not shown) mounted on the base and a wire and pulley system 37 allow the extruding machine to be moved along the rails at a controlled rate.

The machine, base, pulley system and wires can be disassembled for transport.

The machine is for extruding a covering onto a rope or cable 36 (Figs. 4 and 5) comprising a plurality of strands twisted together with each strand formed by wires twisted together. The machine can be used for applying a contin cable. Alternatively, where the cable is already provide with a covering of a plastics material, the machine can b used to re-cover a section of the cable from which covering has been removed for, for example, making splice in the cable. The following description is of th splicing and re-covering of a section of the cable fro which a covering has been removed, but it will b understood that the same technique can be readily adapte to provide a continuous covering on an uncovered cable.

The rope or cable comprises strands formed of steel wire twisted together. One strand is covered with a plastics material and serves as a core strand; its overall diameter may, for example, be 12 mm. The remaining strands are not individually covered but are twisted around the core strand. They may have a diameter of 7.66 mm to give diameter of the rope or cable over the strands of 26.5 mm. The outer strands are together covered by an outer covering of a thermoplastics material having an outer diameter of 32 mm.

In forming the splice, two rope or cable ends are brought together. The outer cover is stripped back about 20 feet from each end.

A long splice is then formed by any one of several known methods; for example, as described in British Patent Specification No. 1244693 or as described in our British Patent Publication No. A2011969.

OMFI The method may involve the application of a material around each of the strand tails formed during the splicing step before the strand tails are tucked into the centre of the rope or cable to replace the core strand. The material is chosen so that the diameter of the wrapped tail is substantially the same as the diameter of the core strand so that, after the tails have been inserted into the core, the overall diameter is not reduced. in addition, the material tends to resist the removal of the tails from the centre of the core, thus strengthening the splice.

Suitable materials include a spirally wound wire, as described in British Patent Specification No. 1244693 or a hollow cylindrical braided wire tube or perforated hollow flexible cylinder. These two latter wrappings may be arranged to have the property of decreasing in diameter under tension so that they grip the associated strand tail more firmly when a force is applied to the strand tail which tends to pull the strand tail from the core. Alternatively, a plastics material may be placed around the strand tails, for example, by extrusion or injection moulding, for a purpose to be described below. Alternatively, a spirally wound single solid metal strand may be placed around each strand tail.

During manufacture, the outer strands are generally wound so that each outer strand is spaced from the next adjacent strand by, for example, 1 to 2 mm. This allows the coverin mate ia to e

this spacing, after the splice has been formed, spacer are inserted between and at intervals along adjacen strands. The spacers may be formed by wires of circula cross-section or suitable plastics members may be used. Their diameter may be such that the correct spacing is established when each contacts the inner core, or a wrapped tail. The wire may be pre-for ed as a part of a helix which is the same as the helix described by each strand.

It will be appreciated that other strand diameters and other constructions of the rope or cable could be used and that different materials and cross-sectional shapes may be used for the wrapping material and the spacers. The material used, however, must withstand the covering process now to be described in which the temperature may exceed 220° C.

Next the track is set up and the base mounted on the track with the wires positioned around the pulleys and connected to the winch. The dimensions of the half-casings 11, 12, the half-die holders 17 and the inner and outer half-dies 25, 26 are chosen to match the dimensions of the cable being covered.

The two half-casings 11, 12 are separated and the cable 41 to be covered is fixed in a horizontal position by guides 40 (Figure 4) at such a height that the cable passes through the fixed half-casing 11 with the stretch of the cable to be covered intermediate the ends of the The cable is prepared for covering by tapering the ends of the existing plastics coverings to provide a smooth transitional bevel between the existing coverings and the uncovered portion. In addition, the uncovered section of the splice may be covered with a grease to reduce friction between the cable and the covering, when applied, to assist in the displacement of air or gases containing moisture and to lubricate the strands. The grease may be applied under pressure or may be dissolved in a solvent and applied to the cable by spraying or dipping. The gaps between adjacent strands are kept clear to allow penetration of the covering to the core, when applied. The grease may be of any suitable type but must not melt or emit gases at the temperatures encountered during recovering, which may be up to 250°C.

The extruding machine is then taken through a starting-up procedure which includes starting-up the extruder 24 to pass molten plastics material to the cross-head die. The flow of molten plastics material around the frusto-conical portion 32 of the inner die 26 increases the flexibility of this portion of the die. Next, with the extruder barrel halted, the capstan winch is operated to move the machine along the rails in a forward direction (i.e. in the direction of the arrow A in Figure 1) . As the die reaches the end of the uncovered portion of the cable, the tapered portion at the start of the existing covering passes through the inner die 26. This taper expands the frusto- conical portion 32 of the inner die 26 so that the inner die 26 remains in close contact with the existin covering of the cable 41.

The capstan winch is then reversed and the machine move back along the rails until the opposite tapering portio is contacted. The extruder barrel 24 is re-started to re commence the flow of molten plastics material and th capstan winch is operated to move the inner die 26 slowl up the tapered portion. The inner die 26 is expanded b the taper and the capstan winch is halted when the tapere portion, and a short stretch of the existing covering, emerge from the casing 10, 11. In this position, the end of the inner die 26 is so expanded that it is closely adjacent the outer die 25, thus largely closing the gap between the two dies 25,- 26 thus preventing plastics flow.

The cable 36 is then cleared of all plastics material extruded during start-up.

The capstan winch is then started in a forward direction an the extruder 24 started to feed molten plastics material to the die at a slow rate. Only slow feed is necessary because the gap between the outer and inner dies

25, 26 is very small and so, even with a slow feed, the pressure of the plastics material emerging from the die is high and the quantity very small. As the die reaches the first tapered portion 46 (see Fig. 6), the extruder feed and the capstan winch speed are increased steadily. A typical covering speed is ..0.2 m/min. The converging outlet passage provided by the outer and inner dies 25, 26 increases the pressure of the molten lastics material in the outlet and this ensures that, as the inner die 26 passes over the first tapered portion, the frusto-conical portion 32 contracts inwardly to remain in contact with the surface of the tapered portion 46 so increasing the cross-sectional area of the annular die outlet passage (see Fig. 6). Since the outer die 25 is fixed, there is extruded from the annular die outlet an annular covering 47 of plastics material of constant outer diameter but of decreasing inner diameter and thus of increasing cross- sectional area. Due to the expansion of the inner die, this inner diameter of the extruded covering matches the outer diameter of the existing covering.

When the die reaches the uncovered portion of the cable 36, the inner die is fully contracted and the extruder feted rate and the capstan winch rate are correlated to provide a satisfactory covering on the cable 36 (see Fig.

7) . For example, the pressure should be sufficient to ensure that the molten plastics material is forced past the spacers into the interstices between the strands. If spacers of a plastics material are used their contact with the molten extruded plastics may cause them to melt and then bond to the extruded plastics to form a key for the extruded covering.

The covering is continued with the inner die 20 eventually expanding over the other tapered portion of the existing covering to provide a covering of increasing inner diameter and decreasing cross-sectional area in correspondence with the increase in diameter of the taper. As the die passes on to the existing covering of the cable, the extruder feed rate is decreased and the capstan winch speed decreased also until both are finally halted.

The casing 10, 11 is then separated and the cable 41 removed. The machine and rails can then be dis-asse bled and packed for removal.

It will be appreciated that the section of the extruded covering which is in contact with the tapered portion of the existing covering may not be firmly adhered to the tapered portion. Accordingly, means may be provided for forming a bond between this section and the tapered portion. These means may be of any known type. For example, -a heater 43 (Fig.4) may be used to heat the tapered portions of the existing covering before the covering is extruded so that, as the covering is extruded, it welds to the heated tapered portions. The heater may of an air or gas or infra-red or induction heater or a combination of such heaters. The heater may be mounted immediately in front the casing for movement with the casing or may be separate from the machine and be brought to the covering after completion of the re-covering.

Where the tail ends in the splice are covered with a plastics material, the heater or another heater may be used to heat the plastics material on the tail ends before the cover is extruded so that, as the cover is extruded, the ^* extruded plastics material bonds to the coverings on the tail ends. In this way, the coverin is held more firmly in the spliced section and the tail ends are locked in position. These tail coverings need not, of course, be solely used with the extruder die described above. They may find useful application in other splicing and recovering arrangements.

Thus, the spliced section of the cable is re-covered with a plastics covering which is firmly fixed to the cable and which, when a heater is used, is sealed to the existing covering to provide a continuous homogeneous covering which is impervious to the ingress of gases, liquids or solids thus increasing the tensile strength of the rope and the useful service life of the cable loop.

it will be appreciated that the machine described above with reference to the drawings could be stationarily arranged with the cable being moved through the die.

It will also be appreciated that the inner die 25 has important characteristics which allow such a die and other dies embodying the same or similar characteristics to find wide application. The die 25 has the ability to change its cross-section during extrusion. In the case of the die 25, this change is achieved by external pressure applied to the die either by the tapered portion of the existing covering or by the molten plastics material flowing over the exterior surface of the die. This pressure could, of course, be applied in any convenient way by magnetic .or electrical or mechanical means arranged either in the material of the die or actin on exterior of the die. For example, magnets may be place within the material of the die and be used to generate force to change the cross-sectional area of the die by us of a controlled magnetic field around the die. Alternatively, a system of levers could be used to apply mechanical pressure directly to the outer surface of th die. A fluid could be supplied under pressure to the interior of the die to alter the shape of the die. The change in cross-sectional area could be controlled in conformity with a predetermined pattern. in this way, such a die could be used to extrude solid rods or hollow tubes whose cross-section varies along their length, the cable or other elongate member being omitted.

In the embodiment of the invention described above with reference to the drawings, the characteristics of the die 25 allow the covering of a cable of varying cross- sectional area along its length. The die 25 may also be used to cover any elongate article of varying cross- sectional area along its length, provided, of course, the variation is within the limits of expansion and contraction of which the die is capable. For this reason, the size and flexibility of the die should be matched to the range of cross-sectional areas which are required from the die.

Claims

1. Extrusion apparatus of the kind comprising an extrusion die for extruding a plastics material and including at least one die member having an outlet of predetermined cross-sectional area, characterised in that said cross-sectional area is variable by the application of a force thereto, for varying the cross-section of the extrusion.

2. Apparatus according to claim 1 characterised in that the die further comprises an outer die member (25) arranged around the first-mentioned, inner, die member (26) to form therebetween an outlet passage (23) for the extruded plastics material, the inner die member being so flexible at extrusion temperatures as to allow controlled deformation of the outlet nozzle by the application of a force thereto.

3. Apparatus according to claim 2 and of the kind for extruding a covering of thermoplastics material onto an elongate object of varying cross-sectional area along the length thereof, characterised in that the the inner die has a passage therethrough for the elongate object (36) , and the undeformed cross-sectional area of the inner die is generally equal to the minimum cross-sectional area of the elongate object, the inner die member being expanded by a force applied thereto from contact with portions (41) of the elongate member of greater cross-sectional area than said minimum cross-sectio l a r n a -movement therebetween to produce an extruded covering o varying cross-sectional area along the length thereof.

4. Apparatus according to claim 3 and characterised b further comprising a feed and melt device (24) for meltin the plastics material and for feeding said molten plastic material to the annular gap between said inner and outer dies for extrusion thereby.

5. Apparatus according to claim 3 or claim 4 characterised in that the apparatus is mobile to allow the covering of stationary elongate objects.

6. Apparatus according to any of claims 3 to 5 and characterised by further comprising means (43) for bonding an extruded plastics covering to an existing plastics covering of the elongate article in a section or sections of the article where said coverings overlie one another.^"

7. Apparatus according to claim 6 characterised in that said bonding means comprise a heater for heating the coverings to form a bond between the extruded covering and the existing covering.

8. Apparatus according to any one of claims 3 to 7 characterised in that the inner and outer dies (26, 25) are both divided into two parts, the division being, in each case, in a plane including the central longitudinal axis of the respective die to allow the inner and outer ' dies to be placed around an elon ate ob ect which is to covered.

9. Apparatus according to any one of claims 2 to 8 characterised in that at least the outlet of the inner die member is made of a plastics material, for example, polytetrafluoroethylene.

10. Apparatus according to any one of claims 2 to 10 characterised in that the annular outlet passage (23) between the inner and outer die members (26,25) is of decreasing cross-sectional area along the length thereof.

11. A method of splicing a rope or cable of the kind comprising a plurality of strands each formed from a plurality of wires twisted together, the strands being themselves twisted together and all the strands together being covered by an outer covering of a thermoplastics material, the method being characterised by the steps of removing the covering of thermoplastics material from two rope or cable ends, splicing the two rope or cable ends together so that the spliced rope or cable ends have a diameter equal to or substantially equal to the diameter of an unspliced uncovered rope or cable and then re¬ covering the spliced rope or cable ends with a covering of a plastics material by use of apparatus according to any one of claims 1 to 10.

12. A method according to any one of claims 11 to 13 characterised by further comprising, after the removing s bevel on each end of the existing covering of the rope o cable.

13. A method according to claim 11 or 12 characterised in that the re-covering commences on one end of the existing covering, proceeds along the uncovered splice and terminates on the other end of the existing covering.

14. A method according to any one of claims 11 to 13 characterised by further comprising, after the splicing step and before the re-covering step, the step of inserting spacers between, and at intervals along, adjacent strands which are in the uncovered portion and which form the exterior of the rope or cable, to separate said strands to allow the extruded plastics material of the covering to penetrate to the core of the rope or cable.

15. A method according to any one of claims 11 to 14 and for use with a rope comprising a central core strand covered with a plastics material and a plurality of outer strands which are not individually covered with a plastics material and which are arranged around the covered core strand, characterised in that the splicing step comprises placing a material around at least some of the strand tails of the outer strands formed during the splicing step so that each of said strand tails has a diameter substantially equal to the diameter of the covered core

- -- cable and then inserting the at least some strand tails strand, which has been removed.