US3672974A - Method of impregnating and coating stranded bodies - Google Patents

Abstract

IN ORDER TO COAT AND FILL THE INTERSTICES BETWEEN THE ELEMENTS OF AN ELONGATED FLEXIBLE BODY, FOR INSTANCE A MULTICONDUCTOR CABLE CORE, FORMED BY STRANDING OR BUNCHING A PLURALITY OF THE ELEMENTS TOGETHER, THE BODY IS IMPREGNATED AND COATED WITH A FILLING MATERIAL BY PASSING IT INTO A BATH OF FILLING MATERIAL, IN A LIQUID STATE, THROUGH AN INLET DIE, THROUGH THE LIQUID IN THE BATH, AND THEN OUT OF THE BATH THROUGH AN OUTLET DIE. THE DIES ARE WHOLLY SITUATED BELOW THE LEVEL OF THE LIQUID AND ARE MAINTAINED AT A TEMPERATURE SUCH THAT THERE IS NO SUBSTANTIAL LEAKAGE OF THE LIQUID FROM THE BATH THERETHROUGH WHILE THE BODY IS PASSING CONTINUOUSLY THROUGH THE BATH. PREFERABLY THE DIES ARE EACH MOUNTED AT THE FREE END OF A METAL TUBE PROJECTING FROM THE WALL OF THE BATH AND ARE MAINTAINED AT THE SAID TEMPERATURE BY MEANS OF EXTERNAL COOLING FINS ON THE TUBES.

Description

June 27, 1972 R. TOMLINSON METHOD OF IMPREGNATING AND COATING STRANDED BODIES 2 Sheets-Sheet 1 Filed Feb. 5, 1970 June 27, 1972 R. TOMLINSON 3,672,974

METHOD OF IMPREGNATING AND COATING STRANDED BODIES 2 Sheets-Sheet 2 Filed Feb. 5, 1970 United States Patent "cc 3,672,974 METHOD OF IMPREGNATING AND COATING STRANDED BODIES Roy Tomlinson, Middleton, England, assignor to Connollys (Blackley) Limited, Manchester, England Filed Feb. 3, 1970, Ser. No. 8,298 Claims priority, application Great Britain, Feb. 6, 1969, 6,450/ 69 Int. Cl. B05c 3/12; 344d 1/02 US. Cl. 117-115 9 Claims ABSTRACT OF THE DISCLOSURE In order to coat and fill the interstices between the elements of an elongated flexible body, for instance a multiconductor cable core, formed by stranding or bunching a plurality of the elements together, the body is impreg nated and coated with a filling material by passing it into a bath of filling material, in a liquid state, through an inlet die, through the liquid in the bath, and then out of the bath through an outlet die. The dies are wholly situated below the level of the liquid and are maintained at a temperature such that there is no substantial leakage of the liquid from the bath therethrough while the body is passing continuously through the bath. Preferably the dies are each mounted at the free end of a metal tube projecting from the wall of the bath and are maintained at the said temperature by means of external cooling fins on the tubes.

This invention relates to a method of and apparatus for coating and filling the interstices between the elements of an elongated flexible body, formed by stranding or bunching a plurality of the elements together, with a waterproof material (hereinafter referred to as the filling material) that will not readily drain from the body under normal conditions of temperature and pressure and that will permit relative sliding movement of the elements over one another during bending of the flexible body. Each element may comprise a single elongated flexible member or two or more such members stranded together.

The filling material is a material that is a liquid at a temperature above normal ambient temperature and sets to a viscous or solid state at ambient temperature. Examples of the material are:

(a) Mixtures of whiting and castor oil (b) Microcrystalline petroleum waxes (c) Mixtures of microcrystalline petroleum waxes and oils, for instance petroleum jelly (d) Low molecular weight, high Melt Flow Index polyethylene of a semi-solid or grease-like nature (e) Mixtures of petroleum jelly, microcrystalline petroleum waxes, polyethylene, polyisobutylene and aluminium stearate (f) Mixtures containing cumerone indene resins (g) A blend of two or more of filling materials (a) to The invention is concerned especially but not exclusively with the manufacture of the so-called fullyfilled telecommunication cable comprising a multiplicity of plastics insulated conductors enclosed within a waterproof sheath, with the interstices between the conductors and between the conductors and the sheath substantially fully-filled from end to end of a cable length with the filling material.

The method in accordance with the invention comprises impregnating and coating the body with the filling material by passing it into a bath of filling material, in a liquid state, through an inlet die wholly situated below 3,672,974 Patented June 27, 1972 the level of the liquid, through the liquid in the bath, and then out of the bath through an outlet die wholly situated below the level of the liquid, the dies being maintained at a temperature such that there is no substantial leakage of the liquid from the bath therethrough while the body is passing continuously through the bath. It will be appreciated that when the body is stationary in the bath for a period of time long enough for its temperature to increase to a value approximating to that of the bath, the relationship between the temperature of the Part of the body in the die and the die temperature may be such that the filling material in the die is at a temperature above its setting point and some leakage may take place.

The inlet die is preferably a closing die by which the bunch or strand of elements or an outer layer thereof is formed and the aperture of the outlet die is preferably slightly greater in cross-section than, although of the same shape as, that of the inlet die. This allows the bunch or strand of elements to expand or bird-cage in the bath after it has passed through the inlet die to cause the liquid to be drawn into its interstices and ensures that the liquid drawn in in this way is not wholly forced out from the strand or bunch when it passes through the outlet die of greater cross-sectional area. When as is normal the dies are of circular cross-section, a suitable difference in diameter between the inlet and outlet dies is ten thousandths of an inch. It will be appreciated, however, that this value will vary in a accordance with the overall size of the strand or bunch and with the size of the individual elements, e.g. single insulated conductors or twinned pairs, from which the strand or bunch is built up.

It has been found that the simplest Way of maintaining the inlet and outlet dies at an appropriate temperature is to mount each of them at the free end of a metal tube projecting from the wall of the bath and to increase the heat loss from these tubes by means of external cooling fins. In the manufacture of plastics insulated telecommunication cable, solid metal dies can be used and these can conveniently be split dies fitting into the ends of such tubes.

When manufacturing such a cable on a conventional stranding or bunching machine, a bath provided with inlet and outlet dies can be mounted on the outlet side of each stranding or bunching head, the inlet die acting as the closing die for the preceding stranding or bunching head. Where the first stranded or bunched layer or single or twin conductors is laid up round a preformed core (e.g. a twin) this core can be passed through a first bath before it enters the first stranding or bunching head, so that it is itself impregnated and coated with the filling material.

When the cable is coated and impregnated, layer by layer, in this way, the liquid in each bath can be at atmospheric pressure but when more than one layer or the whole of a stranded or bunched core consisting of a multiplicity of insulated conductors is to be impregnated and coated simultaneously by passing through a single bath, it may be desirable to maintain the liquid in the bath under a pressure above atmospheric. In this latter circumstance and in other circumstances it may be found necessary to lower the temperature of the dies by forced cooling, eg by means of a water bath, instead of relying on natural cooling.

Each bath is preferably associated with and supplied with liquid filling material from a separate reservoir which is conveniently part of a single container which is divided by a partition to formboth the reservoir and the coating and impregnating baths. When such a divided container is used, it is preferably lagged overall and, if necessary, heated to maintain the filling material at the desired temperature. To enable the liquid to pass from the reservoir into the bath, the partition is preferably provided with one or more valve controlled aperture below the level of the body passing through the bath and each valve or valves is preferably linked with the driving means for passing the cable or other flexible body through the bath in such a Way that the driving means cannot be energised unless the valve is open.

In order that the invention may be more fully understood and readily put into practice a description will now be given, by way of example, of our preferred plant for making multi-core plastics insulated telephone cables, with reference to the accompanying drawings in which:

FIG. 1 is a sectional end elevation of a bath having inlet and outlet dies and forming part of a divided container,

FIG. 2 is a sectional side elevation of the divided container, and

FIG. 3 is a diagram of the lay-out of the plant.

The container 1 shown in FIGS. 1 and 2 has an outer thermal insulating wall 2 and an inner wall 3 which form the boundary walls of a chamber 4 filled with oil that can be heated by means of an immersion heater 5. The container 1 is divided transversely by a partition 6 to form a bath 7 and a reservoir 8, each of which, when the container is in use, will contain filling material such as petroleum jelly which is maintained in a liquid state by the heated oil jacket.

Projecting from opposite sides of the bath 7 are a pair of metal tubes 9 and 10. A split solid metal inlet die 11, which can also serve as the closing die for a preceding stranding head, fits into the free end of the tube 9 and a split solid metal outlet die 12, having an aperture of slightly greater diameter than that of the inlet die 11, fits into the free end of the tube 10'. The tubes 9 and 10 are provided with external radially extending cooling fins 14 which serve to maintain the dies 11 and 12 at a temperature such that there is no substantial leakage of the liquid filling material through the dies during continuous passage of a cable core C through the bath 7.

In the lower part of the partition 6 at a position such that it will lie below the level of a core passing through the bath 7 is a valve-controled aperture 15 which provides free flow of liquid filling material from the reservoir 8 into the bath. The valve of the valve-controlled aperture 15 is linked with a cam 16 which engages a roller 17 of a microswitch controlling the power supply to the machine (not shown) drawing the core through the bath 7 in such a way that the machine cannot be energised unless this valve is open. A pump 18 is provided for pumping liquid filling material from the bath 7 back into the reservoir 8 when required. Thermocouples 19 are connected to a control device which automatically disconnects the power supply to the machine drawing the core through the bath 7 when the liquid filling material reaches a predetermined maximum or minimum temperature.

Filling material in liquid form is fed into the reservoir 8 through a thermally insulated pipe 21 via a supply control valve 22 controlled through a pneumatic actuator 23 by three floats 24, and 26 located at different depths in the reservoir. Float 24 causes the control valve 22 to close when the level of the liquid filling material in the reservoir 8 is at the maximum required and float 25 causes the control valve to open when the level of the liquid is at the minimum required. The third float 26 is provided for controlling a relay which automatically disconnects the power supply to the machine drawing the core through the bath 7 when the level of liquid filling material in the reservoir 8 falls to a dangerous level, i.e. to a level just above the upper surface of the core passing through the bath. To avoid the possibility that, in the event of the valve-controlled aperture 15 becoming inadvertently blocked, the core might continue to be drawn through the bath 7 when the level of the liquid filling medium in the bath has fallen below the upper surface of the core, alternatively the float 26 may be located in the bath 7 or an additional float may be provided in this bath for this purpose.

In the plant shown in FIG. 3 multi-coreplastics insulated telephone cables are made by the conventional stranding process employing two stranding machines 27, each having a plurality of stranding heads, and a bunching machine 28 having a plurality of bunching heads. Each machine is provided with apparatus for coating and filling with a filling material the interstices between the plastics insulated conductors of the cable core under manufacture. Two thermostatically heated, lagged storage tanks 31 containing liquid filling material are connected in parallel in a ring main 32 whose piping 33 is heated and lagged and liquid filling material is pumped around the ring main by pumps 34. Valves 35 are provided for disconnecting a storage tank 31 or pump 34 from the ring main if desired. At spaced locations around the ring main are spur pipes 36 controlled by valves 37 and each connected to a heated and lagged manifold 38, one manifold for each cable making machine.

Each stranding machine '27 is of conventional form and includes a plurality of stranding heads 41, a hauloff capstan 42 and a take-up drum 43. The bunching machine 28 includes an input bobbin stand 44, a plurality of bunching heads 45, a whipping head 46, a haul-01f capstan 47 and a take-up drum 48. Located on the outlet side of each stranding head 41 in the stranding machines and on the outlet side of each bunching head 45 in the bunching machine is a divided container 1 as described in FIGS. 1 and 2, the reservoir 8 of each container being fed with liquid filling material from its associated manifold 38 through the lagged pipe 21.

In place of the ring main 32 if desired each manifold 38 may be connected by a heated supply pipe directly to a storage tank and the liquid filling material may be supplied from the storage tank to the reservoir by a gravity feed or by an appropriate pump.

During the loading of a stranding or bunching machine, the impregnating baths 7 are emptied by pumping the liquid from these baths into their respective reservoirs 8, with the valves of the valve controlled apertures 15 connecting the reservoirs to the bath closed; on completion of the loading operation these valves are opened to refill the impregnating baths before the machine is started. To facilitate loading, the metal tubes 9 and 10 projecting from the baths 7 on which the inlet and outlet dies 11 and 12 are carried are preferably of considerably larger internal diameter than that of the die aperture so that they accept a pulling hawser and a connector between such a hawser and the cores being fed through the machine during threading up, the dies being finally placed in a position after threading up is completed.

A principal advantage of the method and apparatus in accordance with the invention is that recirculation or reuse of excess filling material can be avoided, with the consequence that when (as is usual) the filling material is petroleum jelly there is less risk of degradation of the material.

Another advantage is that the apparatus can readily be reset for the use of filling materials of different set points. Once the thermostats controlling the heating of the supply tank, supply pipes, reservoirs and impregnating baths have been set, the apparatus is self-metering, provided that the dies are appropriately cooled. For example it has been found that for a petroleum jelly with a drop point of about 53 C., an appropriate liquid temperature is 65 C. and adequate cooling of the dies is obtained by mounting them on finned metal tubes about 75 mm. (3 ins.) long.

It is to be understood that in the following claims the expression stranding is intended to include the operation referred to hereinbefore as bunching and the term a strand includes a bunch.

What I claim as my invention is:

1. A method of coating and filling the interstices between the elements of an elongated flexible body, formed by stranding a plurality of the elements together, with a filling material that is liquid at a temperature above normal ambient temperature and that sets to a viscous or solid state at ambient temperature, which method comprises impregnating and coating the body With the filling material by passing it into a bath of filling material, maintained at such a temperature that the filling material is in a liquid state, through an inlet die Wholly situated below the level of the liquid, through the liquid in the bath, and then out of the bath through an outlet die wholly situated below the level of the liquid, the dies being maintained at a temperature such that filling material in each die is in a viscous or solid state and there is no substantial leakage of filling material in a liquid state from the bath therethrough while the body is passing continuously through the bath.

2. A method of coating and filling the interstices between the elements of an elongated flexible body, formed by stranding a plurality of the elements together, with a filling material that is liquid at a temperature above normal ambient temperature and that sets to a viscous or solid state at ambient temperature, which method comprises impregnating and coating the body with the filling material by passing it into a bath of filling material, maintained at such a temperature that the filling material is in a liquid state, through an inlet die wholly situated below the level of the liquid, through the liquid in the bath, and then out of the bath through an outlet die wholly situated below the level of the liquid, the dies each being mounted at the free end of a metal tube projecting from the wall of the bath and being maintained at a temperature such that filling material in each tube is in a viscous or solid state and there is no substantial leakage of filling material in a liquid state from the bath therethrough, while the body is passing continuously through the bath, by means of external cooling fins on the tubes.

3. A method as claimed in claim 1, wherein the inlet die is a closing die by which at least an outer layer of the strand of elements is formed.

4. In the manufacture of a plastics insulated telecommunication cable core by a stranding process employing a stranding machine having at least one stranding head, a method of coating and filling the interstices between the plastics insulated conductors of the cable core, with a filling material that is liquid at a temperature above normal ambient temperature and that sets to a viscous or solid state at ambient temperature which method comprises impregnating and coating each layer of conductors of the core being formed with the filling material successively as the core emerges from each stranding head by passing it into a bath of filling material, maintained at such a temperature that the filling material is in a liquid state, through an inlet die acting as the closing die for the preceding stranding head and wholly situated below the level of the liquid, through the liquid in the bath, and then out of the bath through an outlet die wholly situated below the level of the liquid, the dies being maintained at a temperature such that filling material in each die is in a viscous or solid state and there is no substantial leakage of filling material in a liquid state from the bath therethrough while the cborle1 being formed is passing continuously through the 5. A method as claimed in claim 4, wherein the innermost layer of conductors is laid up round a preformed core which, before it enters the first stranding head, is passed through a bath of filling material provided with the said inlet and outlet dies whereby the preformed core is itself impregnated and coated with the filling material.

6. A method as claimed in claim 4, wherein the bath of filling material is maintained under a pressure above atmospheric and at least two layers of conductors are impregnated and coated simultaneously.

7. A method as claimed in claim 4, wherein the dies are maintained at the said temperature by forced cooling.

8. A method as claimed in claim 4, wherein the dies are each mounted at the free end of a metal tube projecting from the wall of the bath and are maintained at the said temperature by means of external cooling fins on the tubes.

9. A method as claimed in claim 4, wherein each bath is associated with and supplied with liquid filling material from a separate reservoir.

References Cited UNITED STATES PATENTS 3,471,322 10/1969 Medney 117 3,425,861 2/1969 Jones "117-115 3,340,112 9/1967 Davis et a1 156-48 3,233,579 2/1966 Aridsson 1171 19 ALFRED L. LEAVITI, Primary Examiner M. F. ESPOSITO, Assistant Examiner U.S. Cl. X.R.

117ll9; 118-405; 156-48, 441; l74- l26 0C; 117 121 A, 121 SR, 121 R

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