GB2193450A - Filling cables with viscous materials - Google Patents

Abstract

Cable filling equipment for open channel optical fibre cables (1), in which thixotropic filling compound is extracted from the supply drum (8) at high pressure e.g. 300 psi, by pump (9) and fed to a modulating device (11, 11A) in the form of a sliding vane pump driven by an electric motor. A pressure sensor (3) senses the pressure in the injection head (2) and controls the speed of the pump (11) via controller (R, I, A, 13). Thus the core of the cable is filled independently of line speed or core diameter, relying solely on the pressure sensed in the injection head to maintain the pressure in that head within close limits e.g. 1 psi to 3 psi. <IMAGE>

Description

SPECIFICATION Filling cables with viscous materials This invention relates to filling cables with viscous materials.

Traditionaliy cables, particularly telecommunications cables have been filled either completely or discretely with a water blocking compound such as petroleum jelly, but there are disadvantages as discussed in our co-pending patent application No.8429077 (W.E. Simpson 19-3-1). That patent specification discloses an improved water blocking material which is thixotropic and an apparatus for applying the material which mechanically shears the material to enable cable filling to take place.

In the past for e.g. copper cables the filling compound has been pumped directly by a pump to an injection head and the nature of the cable and its conductors has not been adversely susceptible to high pressures produced by such pumps in the applicator head and the resulting overfill. In contrast an open channel optical cable normally has an excess length of fibres within the cable so that the cable strength member takes the strain and not the fibres and it has been found that if the pressure in the head is too high then the fibres are moved around by the filling compound as it is applied, which can cause microbending in the fibres and even move the fibres longitudinally, thus negating the longitudinal excess being introduced into the cable particularly where the impregnation is on-line with the core assembly.

It is an object of the present invention to provide an apparatus for and method of filling a cable which is simple and cheap to implement and significantly easier to operate than hitherto, and which can operate with the types of thixotropic filling compounds disclosed in our abovementioned patent application and such as that currently marketed by the Syntec company their "Rheogel" 210 compound, as well as low density petroleum jelly.

According to the present invention there is provided apparatus for filling a 'cable core cable or element with a viscous filling compound comprising an injection head for injecting the compound into the core or element, a supply port to which filling compound will, in use of the apparatus, be pumped at high pressure, a pressure modulating device located between the port and the injection head, and a pressure sensor arranged to sense the pressure in the injection head, said sensor being arranged to control the pressure modulating device in the sense to increase the flow of compound to the injection head in response to a fall in pressure sensed by the pressure sensor, and reduce the flow in response to an increase in pressure sensed.

According to another aspect of the present invention there is provided a method of filling a cable core with a viscous filling compound, comprising passing said core through an injection head, pumping the filling compound into said injection head via a modulating device, sensing the pressure within said injection head and driving a control signal representative of said pressure, and applying said control signal to the modulating device in the sense to reduce the flow of compound to the head in response to an increase in pressure sensed and to increase the flow of compound to the head in response to a fall in pressure sensed.

In order that the invention can be clearly understood reference will now be made to the accompanying drawings in which: Fig. 1 shows diagrammatically a cable filling equipment and method according to an embodiment of the present invention, Fig. IA showing a detail of Fig. 1; Fig. 2 shows another detail of Fig. 1, and Fig. 3 shows an alternative injection head for the apparatus of Fig. 1, for loose-tubed fibre filling.

Referring to Fig. 1 a cable to be filled with water blocking compound such as that sold by the Syntec company under the type number Rheogel 210 is indicated by reference numeral 1. One form of cable particularly suitable for use in the present invention is a so-called open channel cable which, at the point where it is filled by the equipment of Fig. 1 consists of a core member C (Fig. 1A) with a number of radially extending ribs R defining open channels CH in each of which are located a plurality of loose primary coated optical fibres F retained within the channels CH by a whipping W.The cable is passed through an applicator head 2 where the channels CH are completely filled with water blocking compound, the whipping W having long enough gaps to enable the compound to easily impregnate the channels CH. The applicator head has a pressure sensor 3 and is described in greater detail in Fig. 2.

The cable 1 is drawn through the applicator head 2 by a capstan 4 and excess filling compound is wiped clean by diaphragm wiper 5 prior to a paper tape applicator 6.

The filling compound 7 is extracted from the supplier's barrel 8 by a GRACO-type pump 9 with pneumatic side rams 10 and follower piate 9A to pump the compound 7 out of the barrel 8 and force-feed an electrically driven pump 11.

The GRACO-type pump needs to be a high frequency type (approx. 70 cycles/min. or higher) to give a small delivery off each stroke, and at a ratio of three to one. The rams 10 force the pump and follower plate into the drum 8 to prevent cavitation or misfeed and are secured to the outside of the drum by a clamp frame 12.

An eccentric sliding vane pump 11 which in this embodiment is a cornishe pump having a capacity of 0.5 1/min at 50 revs driven through a reduction chain drive by a D.C. electric motor 11A, receivers the filling compound from pump 9 via an isolating valve V and via a flexible hose H. The electric motor 11 A is interfaced through an electronic drive system 13 controlled by the pressure transducer 3 in the applicator head 2. In an alternative arrangement the isolating valve could instead be located between the pump 11 and the head 2.

The pressure transducer 3 mounted in the applicator head 2 gives a digital readout (pressure) at 14 and also controls the amount of compound being delivered to the head by pressure control.

This system is independant of the main drive of the cable machine capstan 4 but, due to the nature of the control, will automatically adjust to any varying line speeds and stop-start conditions.

The pressure sensor 3 provides an electrical signal to the digital readout display 14 whereby the equipment operator can set the equipment up. The output from the display 14 is fed to a preparation controller R and thence to an invertor I. The controller R is a proportional controller and accepts an input range of 0-250mV and provides a proportional output in the range 420mA. It has a remote set-point potentiometer RP for manual setting up. The invertor I accepts inputs in the range 4-20mA and provides an inversely proportional output in the range 10-0 V.

Thus the input to the controller 13 from the invertor I controls the motor 1 1A and thus the speed of pump 11 and causes the supply of compound to the head 2 to increase in response to a falling pressure sensed by pressure sensor 3 and to decrease in response to an increased pressure sensed. The pump 11 is really acting as a modulating device or control valve since it is fed with a pressure of about 100 to 300 psi by pump 9 and the pressure range provided in head 2 is in the range 0--25 psi at which ever pressure is required and set on potentiometer RP.

An amplifier A provides on lines L1 and L2 a trip signal on a falling input signal from the invertor I and representative of a maximum allowable pressure in the applicator head 2. Above this pressure the isolator valve V will be closed automatically by the trip signal on line L1 applied to a solenoid operated pneumatic valve V1 and this prevents excessive pressure being applied to pump 11 when it is switched off. The trip signal also switches off the drive motor via line L2 and the controller 13.

The applicator head is shown in Fig. 2 and comprises a Maillefer 12/14 extrusion head which has been modified to provide an extended pressure chamber to accommodate the pressure sensor. The head comprises a Maillefer compression point 20 through which the incoming open chennel type optical fibre cable core incorporating the loose fibres will pass from the left hand side as viewed in the drawing. A cartridge housing 21 contains the compression point 20 and has injection ports such as 22 directed inwardly towards the annular gap 23 to provide a substantially equi-pressure annular region in the annular chamber 23. The ports 22 are connected by passageways 24 forming a quasi-manifold with an entrance port 2A corresponding with the port 2A in Fig. 1.

An annular chamber block 27 is screwed on to the threaded end 21A of the cartridge 21 and has an aperture 27A into which is screwed the pressure sensor 3. A compression die 28 is located in the end of the chamber block 27 and a front locking nut 29 secures the die in place in the chamber block via threaded end 27B of the chamber block 27.

In the embodiment described the electronic control parts we used are commercially available items as Pressure transducer 3 - Druck type PDCR 10/F.

Indicator 14 - Druck type DP1.201.

Controller R - Lee Dickens "R" block preparatory controller powered by 220 Volts supply.

Inverter I - Lee Dickens "I" block isolator powered by 220 Volts supply.

Amplifier A - Lee Dickens "A" block trip amplifier, input 10-OV, trip on falling signal powered by 220 Volts supply low fail safe.

Motor 11 K.T.K. "ANYSPEED" geared motor 75-80075 maximum output speed 75 r.p.m.

Valve V - "Kinetrol" valve with 020/100 actuator.

Controller 13 - K.T.K. drive 1.5KW "ANYSPEED" A range, Drive type A3N/B.

Control valve V1 - Martonair 5-port solenoid operated air return, type M1761A/152.

Conveniently the items indicated with the broken line B in Fig. 1 are contained on a mobile framework, requiring only a mains voltage power supply, the flexible hydraulic hose H coupling the supply of filling compound 7 from the pump 9 to the inlet port V2 of the shut-off valve V.

In setting up the equipment the auto set point potentiometer RP is adjusted so that a mid range output from R is achieved at the desired operating pressure in the head 2. The manual adjustment potentiometer 1 3A is adjusted by the operator if it is desired to run the line under manual control e.g. dunng start-up, by watching the display 14 and the surplus filling compound emerging from the injection head.

The pump 9 pumps at a relatively high pressure at least one to two orders of- magnitude higher than the pressure required in the injection head and in the embodiment described the pressure in the hose H is in the range 100 to 300 psi whereas the pressure in the injection head lies in the range 0 to 25 psi as required.

The equipment and method can also be used to fill a loose tubed fibre element for a loose tube optical fibre cable. In this case the injection head would be coupled to a plastics extrusion head as shown diagrammatically in Fig. 3. In Fig. 3 an optical fibre or several optical fibres F are pressure in the direction of the arrow through a plastics tube extrusion head 40 in which plastics 41 is extruded to form a tube 42 around the fibres F. A spring 43 projects in towards the extrusion point 44 and injects the filling compound 7 into the tube 42 as it is being formed. The compound 7 is fed to the port 2A in the injection head 2 and has the pressure sensor 3, and the apparatus works in the same way as previously described where the head 2 of Fig. 2 would be replaced by the head 2 of Fig. 3 and associated extruder head 40.

Claims (13)

1. Apparatus for filling a cable core cable or element with a viscous filling compound comprising an injection head for injecting the compound into the core or element, a supply port to which filling compound will, in use of the apparatus, be pumped at high pressure, a pressure modulating device located between the port and the injection head, and a pressure sensor arranged to sense the pressure in the injection head, said sensor being arranged to control the pressure modulating device in the sense to increase the flow of compound to the injection head in response to a fall in pressure sensed by the pressure sensor, and reduce the flow in response to an increase in pressure sensed.

2. Apparatus as claimed in claim 1, comprising a shut off valve responsive to an increase in pressure sensed by the pressure sensor above a predetermined limit, to isolate the port from the injection head.

3. Apparatus as claimed in claim 1 or claim 2, wherein the pressure modulating device is a sliding vane pump driven by an electric motor.

4. Apparatus as claimed in claim 3, and comprising a wiping device for wiping surplus filling compound from the surface of the filled cable core or element after it leaves the injection head.

5. Apparatus as claimed in any preceding claim, wherein the injection head comprises a compression point, a plurality of ports circumferentially spaced around the compression point and fed from an injection manifold chamber, a compression die spaced longituginally from the compression point, and a chamber block comprising an aperture in which said pressure sensor is located between the compression die and the compression point.

6. Apparatus as claimed in any of claims 1 to 4, wherein the injection head comprises a syringe which projects into a plastics extrusion head for filling a loose tube around an optical fibre.

7. Apparatus as claimed in any preceding claim, wherein the output from the pressure sensor is coupled to drive a visual display device.

8. Apparatus as claimed in any preceding claim including a proportional controller connected to receive the signal from the pressure sensor and an invertor for electrically inverting the signal.

9. Apparatus substantially as hereinbefore described with reference to and as illustrated within the broken line of Fig. 1 of the drawings, with or without Fig. 2 or Fig. 3 of the drawings.

10. A method of filling a cable core with a viscous filling compound, comprising passing said core through an injection head, pumping the filling compound into said injection head via a modulating device, sensing the pressure within said injection head and driving a control signal representative of said pressure, and applying said control signal to the modulating device in the sense to reduce the flow of compound to the head in response to an increase in pressure sensed and to increase the flow of compound to the head in response to a fall in pressure sensed.

11. A method as claimed in claim 10, wherein the compound is pumped at a relatively high pressure and the modulating device reduces the pressure to a relatively low one, at least an order of magnitude lower than said relatively high pressure.

12. A method as claimed in claim 10 or claim 11 wherein the relatively low pressure lies in the range 0--25 psi.

13. A method of filling an optical fibre cable core substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.