GB2187118A - Coating telecommunication cable cores - Google Patents

Abstract

Apparatus for use in applying an overall layer of petroleum jelly of constant radial thickness to a telecommunication cable core comprises an elongate chamber 2 having a plastics inlet die 3 at its upstream end, an inlet port 6 for petroleum jelly and, at its downstream end, a plastics support die 4 and, downstream of the support die, a plastics wiper die 5. The inner surface of the support die 4 has a plurality of circumferentially spaced longitudinally extending grooves 8 of such depths as to permit passage of the quantity of petroleum jelly necessary to enable the wiper die 5 to form on the core an overall layer of petroleum jelly of uniform radial thickness. <IMAGE>

Description

SPECIFICATION Coating an elongate flexible body This invention relates to apparatus for use in applying to an elongate flexible body a coating of a waterimpermeable material of a jelly-like consistency (hereinafter referred to as a coating material) that is fluid at raised temperatures but that wiil not readily drain from the body under normal conditions of temperature and pressure. The invention is especially, but not exclusively, concerned with apparatusfor use in applying such a coating material to a flexible core comprising a plurality of plastics insulated conductors stranded or bunched together, such as a core of a multi-conductortelecommunication cable.

In a known method of applying such a coating material to an elongate flexible body, the elongate body is caused to pass in the direction of its length into and out of a closed chamber, containing coating material of a jelly-like consistency, through inlet and outlet dies, the diameter of the outlet die being such that an overall layer of coating material of a desired radial thickness is applied tothe emerging elongatebody.

Initially, coating material is pumped into the closed chamberuntil the coating material in the chamberis at a desired predetermined value when pumping of the coating material into the closed chamber ceases.

Continuous application ofthe coating material to the advancing elongate bodytogetherwith leakage of coating material from the chamberthrough the inlet and outlet dies results in a gradual reduction in volume of coating material in the chamber and ion a consequential reduction in the pressure of the coating material. When the pressure of the coating material in the chamberfallsto a predetermined value, the pump is automatically restarted and coating material is pumped into the chamber until the pressure of coating material in the chamber has again reached the upper predetermined value when pumping of material into the chamber ceases.

We have found that with such an on-offprocedure offilling the chamberwith coating material, an overall layer of coating material of substantially constant radial thickness cannot be obtained because, if the means automatically starting the pumpto pump coating material into the chamber is set to operate at a high pressure, excessive leakage through the dies occurs and if the pressure at which the pump issetto operate to pump coating material into the chamber is set too low, application of coating material to the advancing elongate body is not uniform.

It is an object ofthe present invention to provide an improved apparatus for use in applying an overall layer of coating material to an elongate flexible body by means of which an overall layer can be obtained having a radial thickness substantially more constantthan can be obtained by means of apparatus hitherto employed.

According to the invention, the improved apparatus comprises a chamber of elongate form; an inlet die offlexible plastics material which is at the upstream end of and is positioned coaxially with the chamber and whose orifice has an inner diameter substantially equal to the outer diameter of an elongate flexible body that is to pass through the inlet dieand intothechamber; a portinthechamber through which coating material of a jelly-like consistency can be pumped into the chamber; and, at the downstream end of and coaxial with the chamber, a support die of flexible plastics material whose orifice has an innerdiameter substantially equal to that of the orifice ofthe inlet die and which has in the inner surfaceofthewall bounding itsorificea plurality of circumferentially spaced, longitudinally extending grooves and, adjacentto and downstream ofthe support die, a wiper die offlexible plastics material whose orifice has a diameter substantially equal to the outer diameter of the elongate flexible body with an overall layer of coating material formedtherearound, the grooves in the internal surface of the wall bounding the orifice of the support die being of such depths asto permit passagetherethrough ofthe quantity of coating material necessary to enable the wiper die to form on the advancing elongate flexible body an overall layer of coating material ofsubstan- tially uniform radial thickness.

Preferably, over at least a major part of the length of each ofthe dies, the diameter of the bore ofthe die decreases smoothly in a downstream direction towardsthe orifice ofthe die.

The circumferential wall of the inlet die bounding and immediately adjacent the orifice of the die preferably protrudes into the chamber and is so shaped that the pressure of coating material in the chamber will force this part of the circumferential wall tightly around an elongate flexible body passing through the inlet die to prevent or reduce substantially leakage of coating material through the inlet die.

Preferably, the grooves in the internal surface of the wall bounding the orifice ofthe support die are of substantially the same depth as one another and, ion a preferred embodiment, are of V-shaped transverse cross-section, the lands between the grooves serving to maintain the support die coaxial with an elongateflexiblebodypassingtherethrough.

Conveniently, the inlet, support and wiper dies appropriate to an elongate flexible body of a particular outer diameter can be formed in the same mould, each subsequently being machined where necessary to meetthe requirements of the purpose it is to serve.

By making each of the dies of a flexible plastics material, each die will flex where necessary to ac commodateany irregularity in shape andíorsizeof an elongate flexible body. Preferably,the dies are moulded from polyurethane as we have found that dies made of this plastics material have a long working life. Other flexible plastics materials of which the dies may be made include The invention is further illustrated by a description, byway of example, of the preferred apparatus for applying a coating of petroleum jelly of substantially uniform radial thickness to a cable core comprising a multiplicity of plastics insulated conductors with reference to the accompanying drawing, in which Figure lisa sectional side view of the apparatus; Figure2 is a front end view the inlet die ofthe apparatus shown in Figure 1; Figure3is a front end view of the support die of the apparatus shown in Figure 1, and Figure 4 is a front end view of the wiper die ofthe apparatusshown in Figure 1.

Referring to the drawing, the preferred apparatus comprises a chamber 1 of elongateform having,be- tween its ends, a port 6 through which petroleum jelly can be pumped into the chamber via a flexible delivery hose 18. Secured in the upstream end ofthe chamber1 is an externallyscrewthreaded metal ring 13 having a stepped bore, the step inthe bore constituting an annular shoulder 23.An in let die 3 of polyurethane is positioned coaxially with the chamber at the upstream end of the chamber, a radially extending annularface 53 on the outersurface oftheinletdieabuttingtheshoulder23.Theinletdie 3 is secured in the upstream end ofthe chamber 1 by a internally screw threaded gland nut 33 which is in screwthreaded engagement with the externally screw threaded metal ring 13. Over a major part of the length ofthe inner die 3, the diameter ofthe bore 43 decreases smoothly in a direction towards the die orifice which has an inner diameter substantially equal to the outer diameter ofthe cable core Cthatis to pass through the inlet die and into the chamber 1.

The circumferential wall ofthe inlet die 3 bounding and immediately adjacent the orifice of the die protrudes into the chamber 1 and is so shaped that the pressure of petroleum jelly in the chamber will force this part of the circumferential wall tightly around a cable core C passing through the inlet die to reduce substantially leakage of petroleum jelly th rough the inlet die.

Secured in the downstream end ofthe chamber 1 is an externally screwthreaded metal ring 14 having a stepped bore, the step in the bore constituting an annularshoulder24. Abutting the annularshoulder 24 is the radially extending annular rearface of a support die 4 of polyurethane whose orifice has an inner diameter substantially equal to that of the orifice of the inlet die 3 and which has in the inner surface of the wall bounding its orifice a plurality of circumferentially spaced, longitudinally extending grooves 8 of V-shaped cross-section. The lands between the grooves 8 serve to maintain the support die 4 coaxial with a cable core C passing therethrough.As will be seen, over z major part of the ieny-th of the support die 4, the diameter of the bore 44 of the die decreases smoothly in a downstream direction towardstheori- fice ofthe die. Abutting a radially extending annular face 54 on the outer surface of the support die 4 is the radially extending annular end face of a wiper die 5 of polyurethanewhose orifice has a diametersubstantially equal to the desired outer diameter ofthe cable core C with an overall layer of petroleum jelly formed therearound. The diameter of the bore 45 of the wiper die 5 decreases smoothly in a downstream direction towards the orifice of the die over the whole length ofthe die. The support die 4 and wiper die 5 are fixedly held in the downstream end ofthe chamber 1 byan internallyscrewthreadedglandnut 34 which is in screwthreaded engagement with the externally screw threaded metal ring 14. The shaped grooves 8 in the internal surface ofthewall bounding the orifice of the support die 4 are of such depths asto permit passage therethrough ofthe quantityofpetroleumjellynecessaryto enablethe wiper die 5 to form on the advancing cable core an overall layer of petroleum jelly ofthe desired sub stantiallyuniform radial thickness.

Claims (8)

1. Apparatusfor use in applying an overall layer of coating material to an elongate flexible body, which apparatus comprises a chamber of elongate form; an inlet die of flexible plastics material which is atthe upstream end of and is positioned coaxially with the chamber and whose orifice has an innerdiameter substantially equal to the outer diameter of an elongateflexible body th at is to pass through the inlet die and into the chamber; a port in the chamber through which coating material of a jelly-like consistency can be pumped into the chamber; and, atthe downstream end of and coaxial with the chamber, a support die of flexible plastics material whose orifice has an innerdiametersubstantially equal to that of the orifice ofthe inlet die and which has in the inner surface ofthewall bounding its orifice a plurality of circumferentially spaced, longitudinally extending grooves and, adjacent to and downstream of the support die, a wiper die offlexible plastics material whose orifice has a diametersubstantially equal to the outer diameter ofthe elongate flexible body with an overall layer of coating material formedtherear- ound,the grooves in the internal surface of the wall bounding the orifice ofthe support die being of such depths asto permit passage therethrough of the quantity of coating material necessaryto enable the wiper die to form on the advancing elongate flexible body an overall layerofcoating material ofsubstan- tially uniform radial thickness.

2. Apparatusasciaimed in Claim 1 wherein,over at least a major part of the length of each ofthe dies, the diameter of the bore ofthe die decreases smoothly in a downstream direction towards the orifice ofthe die.

3. Apparatus as claimed in Claim 1 or2,wherein the circumferential wall ofthe inlet die bounding and immediately adjacent the orifice ofthe die protrudes into the chamber and is so shaped that the pressure of coating material in the chamberwill force this part ofthe circumferential wall tightly around an elongate flexible body passing through the inlet die to prevent or reduce substantially leakage of coating material through the inlet die.

4. Apparatus as claimed in any one of the preced- ing Claims, wherein the grooves in the internal surface ofthe wall bounding the orifice ofthe support die are of substantially the same depths as one another.

5. Apparatus as claimed in Claim 4, wherein the grooves in the internal surface of the wall bounding the orifice ofthe support die are of V-shaped transverse cross-section, the lands between the grooves serving to maintain the support die coaxial with an elongate flexible body passing therethrough.

6. Apparatus as claimed in any one of the preced- ing Claims, wherein the inlet, support and wiper dies appropriate to an elongate flexible body of a part icularouterdiameterareformed in the same mould, each subsequently being machined where necessary to meet the requirements of the purpose it is to serve.

7. Apparatus as claimed in anyone ofthe preced ing Claims, wherein the dies are moulded from poly urethane.

8. Apparatusfor applying a coating of petroleum jelly of substantially uniform radial thickness to a cable core comprising a multiplicity of plastics in sulated conductors substantially as hereinbefore de scribed with reference to and as shown in the ac companying drawing.