GB2226257A

GB2226257A - Powdering cables

Info

Publication number: GB2226257A
Application number: GB8827990A
Authority: GB
Inventors: Geoffrey Sharp; Cyril Mallinson; John David George Arnold
Original assignee: CITY ELECTRICAL FACTORS Ltd
Current assignee: CITY ELECTRICAL FACTORS Ltd
Priority date: 1988-11-30
Filing date: 1988-11-30
Publication date: 1990-06-27
Anticipated expiration: 2008-11-30
Also published as: GB2226257B; GB8827990D0

Abstract

An apparatus for coating electrical cables with French chalk before the sheathing is applied thereto includes an enclosed container (10) for holding a bulk stock (14) of chalk and an application zone (18) through which the cable is fed for dusting. Air or other gas supplied by a blower passes through a porous floor (20) of the container to fluidise the bulk stock and also induce a flow of entrained chalk along a feed duct (28) connected to the application zone. From this zone excess chalk is returned to the container. <IMAGE>

Description

CABLE MANUFACTURE This invention relates to the manufacture of sheathed cables of the kind comprising one or more strands or cores, typically insulated electrical conductors, within an outer sheathing which may be unitary or comprise a plurality of protective or other layers. The invention is particularly but not exclusively applicable to multi-core flexible electric cables of the kind having conductor wires individually insulated by an extruded coating of plastics or rubber material, the set of insulated wires themselves being covered by an extruded sheathing also of plastics.

One of the problems associated with cables of the above types, particularly flexible multi-core electric cables (known in the trade as "flexibles") as used for the leads of domestic and other portable electrical appliances is that known as sticking. The elements of the flexible' or other cable (strands or cores and sheathing layers) tend to bind and adhere to each other which makes flexing and handling of the cable difficult and may even contribute to actual damage by resisting attempts to remove excessive kinking or twisting.To avoid this it is well known to coat the surfaces of the elements within the cable during formation with a powder, normally French chalk, to act as a lubricant and prevent sticking and the object of the invention is to provide effective, economical and reliable apparatus for applying the lubricant powder during manufacture.

A known method of applying the powder involves passing the elements of the cable during manufacture through a bulk quantity of the powder in a container or bath. To avoid the powder settling and consolidating and to prevent the formation of a tunnel through the powder along which the elements pass without effective coating some form of agitation of the powder bath is usually provided but the application is still haphazard and inefficient.

According to the invention there is provided a powder applicator for use in the manufacture of sheathed electrical and other cables comprising an operatively enclosed container for receiving a bulk stock of the powder in use, an application nozzle through which an element or elements of the cable is or are operatively passed in the course of formation of the cable, and blower means operable to circulate a flow of the powder entrained in air or other gas from said bulk stock by way of said nozzle to coat said element or elements passing therethrough in use with return of surplus powder to said bulk stock.

Conveniently the powder is applied by means of the nozzle to the core element or elements of the cable immediately prior to their enclosure in at least an inner layer of sheathing. In the case of plastics and/or rubber insulated and sheathed multi-conductor electrical cable the powder may be applied immediately adjacent to a die or the like which extrudes a sheathing thereon.

Preferably the container is provided with heating means for warming the bulk stock to ensure that the powder remains dry and friable.

The blower means may include a porous floor or other wall section of the container through which the compressed air or other gas is forced to fluidise at least part of the bulk stock within the container so as to induce a flow of the entrained powder along a feed duct leading to the application nozzle, the air or other gas and surplus power exiting from the nozzle directly back into the container so that the surplus powder returns to bulk without any substantial wastage or atmospheric pollution externally of the applicator, the container being provided with filter and venting means for the exhaust air or gas.

The applicator may be formed as a portable or semiportable self contained unit for easy positioning and removal from a production line along which the cable elements pass.

One embodiment of the invention is now more particularly described with reference to the accompanying drawing which is a diagrammatic vertical sectional view thereof.

The applicator shown comprises an operatively closed tank-like container 10 having a hopper shaped bottom portion 11 and supported on a frame 12 having trolley wheels 13 for mobility.

In use container 10 holds a bulk stock 14 of dusting powder, typically French chalk filling approximately its lower half at maximum capacity.

The upper part of container 10 includes a laterally projecting portion 16 whose side wall mounts an application nozzle 18 well clear of the bulk stock in this example.

A lowermost horizontal floor 20 of bottom portion 11 is formed from porous material which will allow pressurised air to pass through it into the container and the underside of said floor is enclosed by an air distribution box 22 which is operatively fed with clean dry pressurised air from a compressor or air pump (not shown) by way of a moisture trap 24.

The inclined side walls of bottom portion 11 mount electrical heater panels 26 for warming the powder within the container to keep it dry and friable.

A feed duct 28 extends from an open downwardly directed bell-shaped mouth 30 disposed immediately above a central region of the porous floor 20 to connect with the applicator nozzle 18 within the container.

An exhaust opening 32 at the top of the container remote from nozzle 18 connects with a filter box 34 externally of container 10 for trapping any residue of powder which may be carried out with the air exhausting through opening 32.

In operation the applicator, which is built as a self-contained unit, filled with the powder to the stated level, is positioned as part of the continuous production line for multi-conductor plastics or rubber insulated electric "flexibles" or other cables so that the previously formed and insulated core elements of the cable i.e. the conductors pass through the applicator nozzle 18 as indicated diagrammatically by broken lines and exit from it in the direction of arrow A in immediate proximity to their passage through an extrusion head (not shown) which applies a plastics outer sheathing to the assembly of conductor elements.

At the same time controlled pressurised air is passing continuously through floor 20 both to provide a fluidising effect on the stock of powder 14 within the container so that it is agitated and kept free flowing, and to induce a flow of the powder entrained in air up feed duct 28 to the nozzle 18. The powder is warmed by the heater panels 26 to prevent it becoming damp and again to assist in maintaining it in a friable free flowing condition.

The action of the blower means constituted by the components providing said flow operates nozzle 18 so that the elements of the cable passing therethrough receive a consistent and uniform coating of powder before they pass on to be covered by the outer sheathing. There is no excess or wastage of powder on or carried out with the cable elements and the blowing action ensures that the powder reaches all the surfaces of the elements to provide maximum protection against sticking. Little or none of the air flow exits from nozzle 18 to the exterior of container 10 apart from slight unavoidable leakage where the cable elements exit therefrom, instead the air circulates back from nozzle 18 into the interior of container 10 carrying with it the excess powder not applied to the cable elements. The air flow passes eventually from the exhaust opening 32 but most of the excess powder will be retained in the container 10 to return to the bulk stock 14 and so be recycled. Thus the powder and entraining air are effectively contained in a substantially closed circuit.

As previously mentioned any slight amount of powder passing through opening 32 will be trapped for periodic recovery by the filter box 34, thus the operation of the applicator causes practically no atmospheric pollution or wastage of powder.

The invention may have application to the application of powder to the elements of other types of cable, not necessarily electrical cable and/or to the use of various powder materials other than the French chalk referred to above. For some applications gases other than air might be used and said gases need not be exhausted to atmosphere, it will be appreciated that the apparatus could readily. be adapted to operate with a completely closed gas circuit recirculating the gas to the blower means after it leaves the application nozzle.

Claims

1. A powder applicator for use in the manufacture of sheathed electrical and other cables comprising an operatively enclosed container for receiving a bulk stock of the powder in use, an application nozzle through which an element or elements of the cable is or are operatively passed in the course of formation of the cable, and blower means operable to circulate a flow of the powder entrained in air or other gas from said bulk stock by way of said nozzle to coat said element or elements passing therethrough in use with return of surplus powder to said bulk stock.

2. An applicator as in Claim 1 wherein the blower means includes a porous floor or other wall section of the container through which the compressed air or other gas is operatively forced so as to fluidise at least part of the bulk stock within the container in use and induces a flow of the entrained powder along a feed duct of the blower weans leading to the application nozzle.

3. An applicator as in Claim 1 or 2 wherein air or other as and surplus powder exits fro the nozzle directly back into the container to return said surplus power to the bulk stock in use.

4. An applicator as in Claim 3 wherein the container is provided with filter and venting means for the exhaust of air or gas therefrom.

5. An applicator as in any preceding claim in the form of a portable or semi-portable self-contained unit.

6. An applicator as in any preceding claim including heating means for warming the bulk stock in use.

7. A powder applicator for use in the manufacture of sheath electrical and other calls substantially as hereinbefore dscribeL with reference to and as show, in the accompanying drawing.

8. A continuous production line for multi-conductor plastics or rubber insulated electric "flexibles!' or other cables including an applicator as in any preceding claim, means for feeding previously formed and insulated core elements of the cable through the applicator nozzle of said applicator, and means for applying an outer sheathing to the assembly of conductor elements following their exit from the applicator nozzle.