US2374515A - Heat treatment of the insulating coverings of electric wires and cables - Google Patents

Description

April 24, 1945. G. H. WALTON x-:T Al.

HEAT TREATMENT OF THE INSULATING COVER INGS OF ELECTRIC WIRES AND CABLES Filed March 30, 1943 Patented Apr. 24, 1945 i A2,374,515v` l asians marmr or misnm'rmc COVEBINGS F ELECTRIC WIRES AND CABLES rie Hall Walton, Helsby, near Warrington, VJoshua Creer Quayle, Manley, vHelsby, and Peter Jones, Kelsall, neat Chester, England, asslgnors to British Insulated Cables Limited, Prescot, England, a British company Application March 3o, 194s, serial No. 481,082

1Claim.

For the heat treatment of the insulating coverings of electric wires and cables, a method has been proposed in which heat is generated within the material by treating it as the dielectric between two electrodes across which a suitable potential difference alternating at a high frequency is maintained. In such an arrangement the dielectric loss in the'material causes it to absorb energy from the electric el'd, resulting in the liberation of heat throughout the part of the material which lies within the'electric ileld.

The present invention provides an alternative method of heating certain kinds of rubber mixes and other material by the use of high frequency electric currents. It is applicable to conductively loaded insulating material, i. e. to material which contains a large quantity of conductive material, in the form of small grains or vpowder distributed throughout it for the purpose of conferring on it certain properties. An example is provided by the use of powdered carbon black as a reinforcing agent in rubber. The method operates by the production of high frequency electric currents within the mix by 'the aid ofthe conductive material distributed therein. The apparatus for carrying out this method may also operate and will generally operate for the generation of heat,

to some extent, by the method of the production of dielectric losses.

It has been found that the latter method alone cannot be applied, to practical advantage, to the vulcanising of conductively loaded materials in certain conditions, namely where such materiall lies in the dielectric field inthe form of a layer in series with another layer of comparable thickness and substantially higher dielectric qualities. The conditions arise where the covering of an electric wire or cable comprises an inner layer of good insulating quality (serving as the dielectric layer) and an outer layer (provided for mechanical protection) consisting of rubber loaded with a large quantity of conductive material, for instance, powdered carbon black, to provide a tough Great Britain April 18, 1942 (Cl. 21S-47) cordingly, in this case the method of heating by dielectric losses cannot be used to practical advantage because the application of the electric field, while producing vulcanisation or other heat treatment ofv the inner layers, doesA not vulcanise the sheathing. t,

The case just mentioned is dealt with satisfacy. torily by the method in accordance with the present invention.

`In this method the rubber to be vulcanised or otherwise heat treated is carried through a short cylindrical coil to,the^terminals of which a high frequency alternating voltage is applied, so that the coil produces within it a high frequency magnetic field. Within this eld the .conductively loaded rubber provides 'a' closed turn of a transformer, within which heat is generatedby the passage of the high frequency currents. In this way heat is generated rapidly in the rubber and vulcanisation is carried out. In speaking of high frequency in' connection with theinvention it is to b e understood that reference is made to the range of frequencies from 20 to 200 million cycles per second. This is the range which is of practical importance for the invention and in most cases it will be preferable to use the upper part cf this range, that is frequencies of the order of. 100 to 200 million cycles per second, It seems probable that with such frequencies the currents in the conductively loaded material are in part I conduction'currents through the conductive par- I or preferably each provided stressed rubber cannot be produced there. Ac-

ticles and in part displacement currents through the intervening insulating material.

It will be understood that for the high frequencies in question the effective operation is dependent on the design of thevcoil. The coil will be- Y practically desirable high speed through the coil,

it will generally be necessary to -arrange several of these coils, one behind the other on the same axis, so that the rubber can pass through them in succession. These several coils can be connected in parallel across high frequency mains, with a separate oscillator for supplying the high frequency energy.

For the frequencies in question it is practicable to design coils of convenient size which will be approximatelyat resonance. Due to the large potential drop in the coil there will be a large potential difference between the two ends of the coil so that there will be associated with it a strong electric field, which will. extend into any dielectric material which may be associated with the conductively loaded material, and will generate in such ydielectric material heat b y the dielectric loss method.

Theinvention willbe further described by the aid of the accompanying drawing, in which Fig- K ure 1 shows in longitudinal section part of Van apparatus embodying the invention and Figure 2 lshows one of the coils and the material within 1it during. its operation, also in longitudinal secprimarily intended tion. The apparatus shown is for the continuous vulcanisationofathe covering of electric wire e, consisting ofanV inner layer a (Figure 2), adielectric material outer layer b of insulating materiali loaded v.with conA ductiveparticles. The layer a may be rubber y compound of the quality used for providing the insulation of the wire, andjthe layer b maybe rubber compound heavily loaded with:- carbon- I blaclgso-'as to producea tough sheathing.; Each coil c is formedv of a few Awitirthe icou arrangeaasindi'ad-in Figure '2,"across'the terminals oan oscillator o, working .-at aire qu'ency between 100-and 200million cycles per second, the'coilzisin approximate resonance with Vfreciuenc'zy Tof ythe 'supply and, accordingly,

. 1hasealargepotentiaidiieijence acrossitanda. largecurrent oscillating'within it.` This current` produces a strong magneticiield, which` extends` into the layer b, and there 'generates circulating L currents, resulting in the production of heat withinfthat layer. Owingv to the peculiar 'forni and.:

structure of the layerl la'Y it does not prevent `the establishment of 2in-electric'` eld between the" different parts of the :colc byA way of` the layer a so that heat maybe-generatedlin this layer by the dielectric loss method'. As shown in Figure 1, the apparatus comprises a casing d, in which are enclosed three similar coils c, arranged co-axially andfspaced av'short ydistance apart.

- This casing d` is ,preferably 'made' ofI metal and i's of such dimensions and formin relation to the coils that it doesv not provide in its wallsa sufviiciently complete conductive path to absorb en`A turns, well spaced apart, I

' ing" chosen to givethegrequiredduration of treat- 40 In a method of processingythe covering of'a f lies in'aliianged aperture a to the outer part of which is connected a metal tube h forming with the coil conductor a concentric cable suitable for forming a connection betweenthe coil and its osci1lator. l

At the left-hand end o f the Vcasing d is an aperture i, on the outside of which is arranged a gland i of rubber, which, as' shown, has a cylindrical bore and ay tapering wall lsurrounding it and a i'lange adjacent to' theaperture i by which ange it is clamped in position against the aperture'. This 'gland is enclosed in a 'short auxiliary casing I c, withfa mouth through which the cov. lered Wire'ca'n enter. The' gland v'is' .of-, such ini5v` ternal diameter. thatgit has fa small "clearanceonly over the'fouter surface ofthe covering ofi-the wire. There..is"another aperture iat the right hand end of4 the casing d and .a simi1ararrange4 ment o f'gland i and casing lc'imay b'eprovided here. Alternatively, however, fa furtherfcasing such as d may be attached lso as to. give extended' treatment to the covered wire 'as it passes through; 'l

ifjthis is necessary, the'number of casings d be;

ment; vIn any case at theright-hand en d'ofthe seriesoi casings d a-gland is' pifovidedi l A pipe- 1.' provides gas or vapour. under 'pressurftc the interior of the casing, orc'asings, also as to min- Q tain pressure `o n l`i e" surface ofthe' 'covering of. ;jthelwire .when'thi's isnecessary orvadvantageous i,

, Gas canvbe supplied 'adequatelyV tokeplupithe l, pre'ssurewithinlthe chamber' Place at the glandsj; f 11i-will' required. y What we claim as ourinvention is:

` Vconductor havinginner and 'outer layersjofvI elecrgy by electro-magnetic'induction from the coils the casing. The ends'lof the coils are -each led lout of theeasing d fnrugiran insulating `bush to any large -eXtent, nor to'fabsorb4 any substantial quantity of energy'from theelectric fields produced 'by the coils. As shown, the-casing issplit on' the horizontal centre plane and an insulating gasket p inserted:` gasket breaks the elecv trie-continuity ofthe wall and lassists in making va pressure-tightdoint between thei-.wo halves of j which forms a tight joint with the conductor and with the wall ofthe casingd. bush "sufficient to heat 'theA vinruil' laye'riby dielectric *GEORGE-Hm "WALTON.L

' JQSHUA-CREERKQUAYLE-`- .i

meal insuiating 'material of which'on1y-'the-ouer-- f layer vis conductively loadedgthesteps including 4 f passing the conductor axially;4 through an induetor lieatingcoil consisting of ia'few [spaced turns,

the coil having a length'of. substantially thes'ameVV order asgitsdiameter, 'and operating`appoxi'- mately in resonance withi'asoregof'alternating current of'afrequency'in therange of .f2( ).num'y cycles per second" and upwards,fth'ereby heating.

theouter layer by induced.l cu`rrent:ad `simul 'taneously maintaining` a'voltage. acrossthe coi-1 i Q Purina Jo las leemte-talig be'see that this apparatuslpermits'jof 1 f theI continuous passage .through it ,ofxacovered wire;at,an"appropriatejratejand for the`heat treatment of it duringthat vpassagetothe extent j

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