US2544430A

US2544430A - Method of making shielded electrical conductors

Info

Publication number: US2544430A
Application number: US2378A
Authority: US
Inventors: George L Mccutchan
Original assignee: Rome Cable Corp
Current assignee: Rome Cable Corp
Priority date: 1945-02-24
Filing date: 1948-01-15
Publication date: 1951-03-06
Anticipated expiration: 1968-03-06

Description

March 6, 1951 G. MCcuTcHAN 2,544,430

METHOD oF MAKING SHIELDED ELECTRICAL coNnucToRs Original Filed Feb. 24, 1945 2 Sheets-Sheet 1 Geo/zei L. Afke L17-MN /W/ Mw'- muut.

G. MCCUTCHAN METHOD 0F MAKING SHIELDED ELECTRICAL CONDUCTORS March 6, 1951 2 Sheets-Sheet 2 Original Filed Feb. 24, 1945 MEZ G50/zag L. /VlcCL/raf/M/ Patented Mar. 6, 1951 METHOD OF MAKING SHIELDED ELECTRI- CAL CONDUCTORS George L. McCutchan, Rome, N. Y., assignor to Rome Cable Corporation, Rome, N. Y., a corporation of New York Original application February 24, 1945, Serial No. 579,625. Divided and this application January 15, 1948, Serial No. 2,378

One of the objects of this invention is to pro-v vide a method for making a structure of the above-mentioned character in which terminal insulating members, at one or both ends of the radio-shiclding Conduit in which the conductor with `suitable insulating material is contained, may be dependably and reliably molded onto the project- 4fing end or ends of the conductor without caus- `ling detrimental shift inwardly of the conduit itself.

Another object is to provide a method for making a structure of the above mentioned kind while dependably preventing such bending or distortion of the conductor within the conduit, more particularly kinking of the wire at the end or Another object is to provide a practical and dependable method and apparatus for mounting a metal terminal onto the end of the conductor and for molding about the conductor, intermediate of its end and the shielding conduit, an insulating sleeve under conditions of pressure in a manner to reliably avoid detrimental shifting of the terminal or its mounting or of the conductor ends of the conduit, as will cause disturbance of` the desired dielectric relationships, and more particularly as will cause a condition where corona or breakdown effects are encouraged or can be brought into being.

Another object is to provide a practical and reliable method for molding, externally of the conduit and about the projecting portion of the conductor, an insulating element under suitable conditions of pressure and the like that will avoid detrimental shift or knking of the conductor relative to the parts or elements enveloping it.

Another object is to provide a method by which a metal terminal and an insulating sleeve or bushing may be dependably interrelated, both mechanically and dlelectrically, to each other and to the shielding conduit and to the portion of the conductor projecting from the latter'. and more particularly to achieve such interrelation where the conductor is per se insulated.

Another object is to provide a method by which a durable and dependable mounting is provided for a metal terminal or connector element at the extreme end of the conductor projecting from the shielding conduit and for an insulating sleeve or bushing thereabout, and in a manner whereby undesirable or detrimental shift of the conductor inwardly of the conduit during processing of the insulating sleeve may be dependably avoided.

relative to the shielding conduit, the insulating sleeve itself, and related parts.

Another object is, in general, to provide a'n improved spark plug lead construction and an improved method of achieving thesame, and other objects will be in part obvious or in part pointed out hereinafter.

The invention, accordingly, consists in the features of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of the same to one or more of the others, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which are shown certain illustrative embodiments of the mechanical features of my invention- Figure 1 is an elevation, partly broken away and partly in central horizontal section. of a spark plug lead as it appears in one step of its fabrication and as it appears in relation to certain molds; y

Figure 2 is a transverse sectional view along the line 2 2 of Figure 1;

Figure 3 is an enlarged central longitudinal sectional view of a terminal mounting;

Figure 4 is a transverse sectional view along the line 4 4 of Figure 3;

Figure 5 is a fragmentary view showing a modined form of apparatus employable in relation to the molds of Figure 1;

Figure 6 is an elevation showing the completed spark plug lead;

Figure 7 is a sectional view on a larger scale as seen along the line l-l of Figure 6; and

Figure 8 is a fragmentary view illustrating a modification of method and structure employable in the process step illustrated in Figure 1.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Referring, first. to Figure 1, I preferably employ a conduit, generally indicated by the reference character I0, which, for purposes of effecting radio-shielding, is metallic and preferably comprises a flexible tube IllIIL made of helically wound. corrugated strip sheet-metal-such as is shown in United States Patent No. 1.198.392- employing, if desired, suitable means, such as solder, for achieving improved tightness and strength-in the manner shown and described in United States Patent No. 2,127,943-and preferably a covering Il of braided metal strands-as shown and described in United States Patent No. 1,340,818`snugly envelops the flexible tubing Il, being, of course, iiexible therewith. The ends of the conduit Ill are received in suitable counter-bores I Il of a suitably shouldered ferrule II, to which they are secured in any suitable way to eiect a sealed connection, for example, as by soldering. 'I'he fel-rules II have shoulders or flanges II", with which engage .the end shoulders I2* of nuts I2, internallylthreaded as at I2", whereby the respective ends of the conduit I and related parts, later described. may be secured. for example, to the externallythreaded shielding barrel or well i3 of a spark plug and to a similarly externally-threaded cylinder, or well. or socket I4 associated with the manifold (not shown) in which the various spark plug conductors are contained. By means of the nuts I2, a mechanically secure connection to the parts I3 and I4 may be made, and, moreover, in coaction with other parts later described, dependable sealed junctions can be effected-#all while achieving, also, a desirable quick detachability of the lead and terminal structural unit.

Extending within the conduit I0, and suitably insulated therefrom, is a conductor I B, which is preferably flexible and, hence, may be a stranded conductor. The high potential energy required to energize the spark plug is conveyed by way of conductor I6. To insulate conductor I 6 from the radio-shielding metal parts of the conduit I Il I prefer to employ an insulating covering I1 about the wire I6, and this insulation Il may be of any desired or suitable construction or composition, or of combinations of insu' ating compositions or elements, preferably adequate to dependably insulate the wire IE for the voltage of the energy it is to carry, with usual or appropriate margins of safety. The wire I6 extends preferably coaxially of the conduit I0, which contains a suitable insulating compound I8 which can, if desired, be of a dielectric strength such as to provide for the adequate insulation of the wire I6 from the conduit Ill independently of the insulating covering or sheath I l which, in such case. need not be employed, if desired, in so far as certain features of my invention are concerned. The compound I8 may be of any desired composition of material, preferably reatively flexible, and where the insulation I1 about the wire I5 is omitted, the consistency of compound I8 is preferably such as to coact in maintaining the conductor substantially coaxially within the conduit IB, or any other known means may be employed to maintain substantial coaxial relation.

With the insulating sleeve I1 about the wire Il, however, many advantages are achieved; for example, precise coaxial relation need not be provided for; the compound I8 can, desirably, be of more advantageous consistencles, preferably relatively soft or ilowable, and thus better achieve, particularly when under compression, a more eiiicient and more reliable filling of all of the space within the conduit Il and about the insulated conductor IB-I'I, and thus better guard against corona eilects and against possible dielectric breakdown.

Any suitable means may be employed to inject the insulating compound Il into the space beany suitable apparatus for injecting the material I8.

Having injected a suitable quantity of the compound I8 into the space between the conductor and the conduit walls, the compound Il being in suitable plastic condition and being, lllustratively, made up of any suitable uncured rubber-like material-such as natural rubber, any of the synthetic rubbers. or the like-each suitably compounded, such of the compound Il as projects beyond the outer ends of the ferrules Il is removed or cleaned oil, so as to leave the end boundary of the material I8 substantially along a plane indicated at I9. Thereupon a suitable insulating material-such as a material analogous to that employed in making up the compound or iiller IB-is made ready to be applied to the substantial length of conductor projecting beyond the plane I9. Illustratively, the material may be in the form of tape-like elements which are wrapped about the projecting portion of the conductor, the wrapping being carried on preferably in a. manner to simulate generally the ultimate shape or configuration which It is desired to provide. In Figure 1 the insulating material or compound so applied is indicated by the reference character 2I, and in its initial application it is made to extend up against the end plane I9 of the compound or l.er I8 and also to ll in the angularities at the outer ends o! the ferrules II, and to provide a shoulder 2|* which abuts flat-wise against the annular end face IIc of the ferrule II.

However, before applying the insulating compound 2I to the projecting portions of the conductor, I rst apply to the end of the conductor I6-which, where it has an insulating sheath Il, is suitably bared by stripping the insulating sheath I1 thereof throughout a short length at its outer end-a metal sleeve or tube-like element 22 (see Figure 3) which supports a contact or connector element later described and which has a hole 23 in it to snugly receive the wire I6, onto which it is sleeved, to bring its one end into abutting relation to the end annular face of the insulating sheath I1. The tube-like element 22 is preferably closed at its outer end, as at 22. The external diameter of the element 22 may substantially match the external diameter of the insulating sheath Il, but it may be of lesser diameter, as shown in Figure 8. Suitable means are then employed to insure a dependable mechanical and electrical connection between the wire IB and the metal element 22. In the illustrative form, element 22 is preferably threaded externally, as at 2|.

Where it is desirable to avoid the use of solder or the likeas may be the case Where soldering fluxes may detrimentally ailect the materials employed, or may subsequently encourage corrosion- I effect such mechanical and electrical interconnection -by compressing the metal element 22 radially inwardly so as to cause the resultant restriction of the hole or bore 23 to securely clamp or grip the wire I6. In Figure 3 such clamping restriction is indicated at 25, and may be effected by any suitable means-preferably by a suitable tool or implement-that compresses the heavy-walled tubular element 22 radially inwardly from diametrically opposed sides, as ls better indicated in Figure 4, and such operation of such an implement may be repeated throughout as many angularly-displaced, dla` metrlcally-opposed portions as may be desired, illustratively, and as indicated in Figure 4, by repeating such radially inward compression at points, indicated at 26, displaced 90 degrees from the points 25. A dependable mechanical anchorage of the part 22 to the wire I6 results, and the resultant cold-flow of metal effects also good electrical interconnection between the two parts throughout substantial or large areas of contact.

Such clamping action is preferably confined to the upper portion, as viewed in Figure 3, of the part 22, for some mutilation of the external threads results, and the free half-portion or so of the part 22 with its threads remains unmutilated. As indicated in Figure 1, the uncured insulating compound 2| is applied also about the Just-mentioned upper portion of the member 22, thus also covering over and interlocking with the mutilated threads.

The mass of insulating compound 2|, at each end of the structure, is now ready to be conformed to its nal, finished shape or configuration, and for this purpose I preferably employ a sectional mold M, conveniently made up of two blocks M1 and M2 of metal, each provided with a mold cavity 28, the two mold cavities 28 being complemental to each other, and, when assembled and brought in face-to-face contact, as shown in Figure 2. the complemental mold cavities 28, 28, preferably circular in cross-section, provide a configuration of the shape and dimensions which it is desired to give the insulating material 2|. The mold sections M1, M2 may be provided with suitable dowels and dowel cavities, indicated at 28, to guide and align them for assembly one to the other, and are preferably also provided with arcuate recesses 30, each of 180 degrees extent, shaped to snugly envelop and encase portions of the outwardly-projecting radial flange or shoulder II" of the ferrules |I, so that the mold sections Ml and M2 can envelop the flange or shoulder Il and thereby become dependably secured to the conduit and ferrule assembly, the nuts I2 being at each end sleeved away from the ferrules so as not to interfere with the application of the mold sections.

The sectional mold M has an end closing wall 3|, half of which is in one mold section and the other half being in the other mold section, the end wall 3| being provided with a cylindricaly walled hole 32, of which half is in each halfportlon of the end wall 3| of the mold sections, and the end hole 32 envelops and receives therein the correspondingly-diametered shank 33 of a member 34 that is internally threaded so that it may be screwed onto the threaded end portion of the part 22 which is anchored to the Wire I6, as above described, thus serving to rigidly and dependably center and align the extreme end portion of the conductor I6 and to hold it coaxially of the companion mold cavities 28-28. The member 34 preferably also is dimensioned or shaped to provide at its inner end an end face 35 that is of substantial or suitable area in relation to certain forces and actions that take place-all as is later explained-and, in the embodiment shown in Figure 1, this end face 35 may be formed by the end face of an annular flange 3B projecting from the threaded hub 33, having an external diameter to snugly fit it into the complementa] mold cavities 28, 28 when the two mold sections are tightly pressed together.

The member 34, as is preferred where lt is to serve as an end terminal, is preferably of metal, and also preferably it is applied to the member 22, which thus serves as a mounting member, just prior to the application, as-by wrapping, of the compound 2|, so that it may function as an end support or barrier for the latter and also as a general guide to the diameter to which the compound 2| is to be applied.

The material 2I-which may be applied by hand, particularly when wrapped-is applied in an amount somewhat in excess of the volume of the mold cavity 28, 28 when the two sections are brought tightly together, and, hence, when the sections of the mold are applied externally thereto, it requires the application of adequate force I or pressure to bring the sections of the mold together and to bring their mating faces 38 and 39 into substantial contact, with the result that the moldable or plastic compound 2| is subjected to increasing compression as the escape orifice between the approaching mold faces 38-39 is diminished and finally closed.

The substantial pressure thus exerted upon the compound 2| not only compacts it tightly against and about the conductor structure which it envelops, including the exposed part of the threaded tube member 22, but it also is made to partake of flow or movement in directions parallel to the axis of the mold cavity 28-28. The resultant hydraulic force or pressure is exerted against the end face 35 of the member 34, the area of which is great enough so that the total force exerted against it holds the member 34 tightly and securely against the inside face of the end wall 3| of the mold, thus anchoring the extreme end of the wire I6 against movement inwardly away from that end wall so that flow or movement of the compound 2| takes place axially toward and into the interior of the ferrule II and conduit I8, without taking with it the wire which, in the preferred embodiment, comprises the conductor I8 and the insulating jacket or sheath II; this axial flow or displacement of the compound 2| acts somewhat like a piston upon the compound or filler I8 within the conduit I0, engaging it initially at the plane I9 and subjecting the compound I8 to substantial compression within the conduit I0, thus contributing toward compacting of the filler material I8 against both the conductor and the walls of the conduit. During this action at one end of the spark plug lead, any suitable means may be employed at the other end to prevent the exerted axial pressure upon the filler I8 from causing it to emerge from the other end, and a convenient means for this purpose is illustrated, in Figure 1, in the form of a sectional mold and wire anchored thereto similar to those just described, so that the processing steps may be carried on substantially simultaneously at both ends of the spark plug lead, the closed mold at one end, with its already anchored conductor and compressed insulating compound 2|, serving to block escape of filler material I8 while the compression at the remaining end is being concluded.

Were the wire I6 not to be held against axial inward movement during the compression of the external sleeve compound 2|, at either end, the flow or movement of the compound 2|, in a direction inwardly of the ferrule II or conduit I0, exerts such a grip upon the conductor structure which it envelops as to move that portion of the conductor that projects from the conduit III bodily toward and inwardly of the conduit itself, causing a kinking of the conductor, usually within the conduit Ill and in a region closely adjacent its end; and this action is greatly enhanced where the conductor has an insulating jacket, such as the jacket I1, of substantial diameter for thereby the jacket exposes a relatively large surface of contact throughout which the moving compound 2I engages and grips it to carry it along. Even though the jacket II of the wire I6 may be of suflicient dielectric strength to function at the operating voltages of the system, the kinking just described provides in the wire one or more bends of usually small radius, not concentric with the metal conduit I0, and it ls at such a. bend or bends that dielectric stresses can become concentrated, with the possibility of resulting in dielectric breakdown or puncture, usually preceded by corona effects. Such kinking is less liable to occur where bare conductor is used-though the forces acting upon it, to kink or bend it, can be of substantial magnitude, according to circumstances-and kinking is greatly facilitated where the bare conductor is stranded, as is desirable for greater flexibility. However, the method and construction according to my invention have been found dependably to prevent such detrimental bending or kinking.

Any suitable means (not shown) may be employed to force the mold sections together to exert the above-described hydraulic forces and to hold them securely assembled upon having brought their mating faces 38-38 into engagement with each other; such a means may be a screw clamp or the like, which, in holding the mold sections together, thus also holds the assembled mold securely to the ferrule I I. With both ends of the spark plug lead thus provided with assembled and clamped molds, as indicated in Figure l, the entire entity may now be subjected to suitable heat treatment to effect curing of the compound I8 within the conduit I and of the compound 2I at each of the terminal ends, it being noted that the compounds are so selected as to materials and compounding thereof that the filler compound I8 in the conduit II) becomes integrally joined or united with the compound 2| at each end thereof, thus forming a continuous and uninterrupted insulating envelope about the conductor from one end thereof to the other. Where rubber. or synthetic rubber, or like materials are employed, the curing or heat treatment effects vulcanization thereof, and, though, in Figure l, there appears a line of demarkation, at 43, between the compound I8 and the compound 2I, it will be understood that this line or plane, in the completed article, is but the region of interflow or intermingling between the compounds where they are integrally united as though no dividing line or plane had been employed in processing them. Dielectric strength is thus in these regions not impaired, nor does there result a possible leakage path or paths at the line or plane 40. Preferably the materials employed for the filler I8 and also for the sleeve insulating material 2| are compounded, in known manner, to include ingredients so that, upon the application of heat for curing or vulcanization, swelling of the compounds takes place, thus increasing the already-applied compression, and thus also I may guard against the creation of crevices or voids such as would be caused if substantial shrinkage took place during or after curing.

The curing having been completed, the mold sections are removed and the resultant radioshielded spark plug lead is ready for installation,

and the member 34 may serve as an end contact or conductive terminal with which electrical connection may be made to the electrode or contact elements in the spark plug well I3 or the manlfold sleeve I4, it being noted that the now-cured compound 2I, at each end, provides a shoulder 2| which, at either end of the spark plug lead, abuts against the externally-threaded part I3 or I4, as the case may be, so that, when nuts I2 are tightened up, the annular shoulder 2IIIL is under compression and serves as a gasket to seal the mechanical junction eiected by the threaded connections.

The part 34 above described may take other forms or configurations. For example, it may take the form shown in Figure 5, and indicated at 34s, where, in addition to the hub 33 and the flange 36 that provides the pressure-responsive face 35, it is also provided with an end annular flange 4I, thus to provide an annular recess between the flanges 36 and 4I adaptable for the attachment therein or thereto of certain types or kinds of electrical connecting devices. Where it takes such a form, the sectional end wall 3l of the mold sections is given a thickness to be accommodated in this annular recess so that the end flange 4I overlies the outer face of the end wall 3| and thus serves as a rigid mechanical anchorage of the part 34, and, hence, of the mounting tubular member 22 and the conductor I6, and thus the above-described detrimental kinking may also be prevented.

0r, the device 34 of Figure 1 or the device 34 of Figure 5 may be made to serve only temporarily as a means coacting to hold the conductor against inward axial movement, so that after curing, as above described, the part 34 or the part 34, as the case may be, is removed from the metal mounting element 22 by simply unscrewing it therefrom, and onto the exposed threaded portion of the mounting member 22 any suitable form of contact or terminal element may be threaded, such as the dome-like contactor or terminal 42 of Figure 7. The terminal cap 42, in such case, is preferably provided with an end face 43 dimensioned to match the end face 2llb of the now-cured insulating compound 2I, which, as above indicated, may be and preferably is compounded and cured so that it has a suitable degree of resiliency, particularly where its shouldered portion 2In is to function as a. gasket; the conductive terminal member 42 of Figure '1 may then be simply threaded onto the projecting threaded shank of the mounting member 22 to an extent to exert some compression against the end of the member 2|, thus locking it in place, and, where the insulating sleeve member 2I is resilient, a highly dependable locking is effected due to the compression of the resilient material and its resultant resiliency or follow-up action in maintaining dependable holding engagement with the end face of the member 42.

The above-described arrangement for effecting and utilizing hydraulic pressure or force in the compounds to act upon an end face, such as the faces 35 of Figures 1 and 5, to tension the wire or conductor against hydraulic pressures or forces acting elsewhere along its length in a direction to tend to weaken it, has been found in practice to be dependable and eflicient, and rejects because of the above-mentioned kinking and its detrimental effects, virtually eliminated. Moreover, these advantages can be achieved without having to exercise extremes of precision, or, stated differently, they can be achieved under example, it is not vital that the outside end face of the flange 38 in the arrangement of Figure 1 engage the inside face of the end mold wall 3|, even though the threaded connection of the part 3l to the mounting member 22 permits quick adjustment to bring-that relationship about if it is desired, for the'parts 34, at both ends of the construction, can occupy positions such that thev flange 36 is out of contact with and spaced inwardly somewhat from the end wall 3|. In such case it is preferred to avoid substantial taper at the end of the mold cavity 23-23, so that the flange 36 in effect functions as a piston that isv slideable, with a snug sliding fit along the end portion of the mold cavity. The compound 2| having been initially applied in a quantity in excess of the desired final volume, is then made, when the mold sections are forced together, to function as a motivating fluid under pressure to act against'the inside face 35 of the piston-flange 36, effecting some movement of the part 34 so as thus to subject the conductor I6 to tension-an action which may be continued or maintained during curing when the heating of the compounds causes them to swell or expand. Where s uch piston-like movements at either or both ends take place, they are limited by the engagement of the part 34 with the end mold wall 3|, the mold and these actions thus insuring that all of the parts successively produced thereby are uniformly dimensioned or standardized throughout, even though there may be some variation in over-all length of the conductor and part 3l assembled thereto, when initially assembled to the molds.

The element that may be employed at either or both ends may, as above already indicated, assume various shapes or configurations, particularly where it is desired to have it function ultimately also as a contact or conductive terminal. Thus the part 34 oflilgure 1 may be given a shape like that indicated at 3| in Figure 8, in which, again, there is presentthe flange 36 of a size and shape to tension or hold the conductor I6 in response to hydraulic pressures exerted by the compound 2|; but the hub portion is given a dome shape, as indicated at 33, with external curved surfaces suitably merging into the flange 36, which may also be provided with curved external surfaces, if desired, and as indicated in Figure 8. The hole 32 in the end wall 3| of the mold may, if desired. be also given suitable curvatures to match those of the part Mb when the latter has its movement toward the left in Figure 8 limited by engagement of the flange 36 with the end wall 3| Thus the member may serve not only as a hydraulically-responsive element to prevent kinking of the conductor, but also as a terminal contact member of any desired or suitable conflgur-ation.

As earlier above pointed outJ Yit is preferred that the outer end tube-like element 22 be closed off, as at 22H. Thereby certain additional advantages and coactions are achieved, in that gases under pressure, such as might be developed to a substantial extent in a spark plug well, are precluded from entering the completed terminal construction by way of the hollow interior of the mounting element` 22 or by Way of any spaces between the conductor therein and the Walls of the hole in the element 22. If gases under pressure were to find ingress into the internal structure, it 1s possible, particularly when the terminal structure or lead is removed from the spark plug or other well, that the resultant internal gas under pressure bloats or somewhat inflates the insulating jacket Il about the conductor I6, effecting separation between the two.v Where the insulating jacket I1 includes, as is preferred, some suitable means such as internal or'external braiding or Wound tension elements, such bloating or lnflation can be resisted, but the possibility still exists that such gas under pressure would seep or nd its way along or through the region or regions where the reinforcing elements exist and thus effect an internal cleavage within the jacket I1 itself. Such effects are undesirable, in that they also affect detrimentally the dielectric strength of the terminal insulator, effecting undesired redistribution of dielectric stresses and tending, therefore, to give rise to electrical breakdown. However, by closing off the end of the element 22-and that relation is preferably achieved by not drilling the hole 23 all the way through the element 22, leaving an end closing wall 22 that is integral with the part 22--such ingress of gas under pressure may be avoided.

Moreover, good adhesion between the insulating compound 2| and the external portion of the mounting element 22 is effected in the manner earlier above described, and in providing the threads 24 also through that portion of element 22 with which the compound 2| directly engages, any possible path for leakage therealong of gas' under pressure is made materially longer than the shortest distance from the end annular face of the lterminal insulator 2| to the inner end face of thev mounting element 22, and thus tendency for gas leakage along such a path is substantially counteracted.

pounded out of any suitable insulating materials and ingredients, all for the purposes above described. Illustratively, and preferably, neoprene is employed for both, the compounding thereof being suitably or appropriately varied according to the respective characteristics desired for the filler I8 and terminal insulators 2|. Whatever materials are employed, such, as those earlier above mentioned, the respective compounding thereof for the filler I8 and for the terminal insulators 2| may be effected, in any known manner, to give the filler I8, when cured, a Shore durometer reading on the order of 15 and a Shore durometer reading for the material of the insulators 2|, when cured, on the order of 65.

Where substantial swelling of the filler |8 during cure is desired, suitable ingredients are added greater swelling thereof during heat treatment than it might normally have, and also some control of the factor of swell may be effected by correspondingly controlling the extent and character of mechanical working of the compound, as on mill rolls. Additions, during mechanical working-of oilssuch as anoil of petroleum base, or of other suitable oleaginous'y substances which become well and highly dispersed throughout the materialmay also be employed to materially increase the swelling characteristics, and, when employed, they have the additional -advantage of plasticizlng the compound and acting as a lubricant, to facilitate injection of the filler I8 into the space between the conductor and the internal walls of the conduit; in such case the rubber-like base material employed is preferably selected from the types that are oil-resistant, of which neoprene is a good illustration. And it will be understood that other fillers and ingredients usually employed in otherwise plasticizing and processing rubber or rubber-like materials-and including plasticizng agents, vulcanizing agents, accelerators, retardants, or the likemay and preferably are also employed in respective amounts or proportions to give the desired processing and curing characteristics.

It will thus be seen that there has been provided a method and apparatus by which the various objects hereinbefore set forth, together with many thoroughly practical advantages, are successfully achieved, It will be seen that there has been provided a method for making radioshielded electrical conductor and terminal constructions in which detrimental kinking of the wire or conductor is dependably avoided, and that the same can be readily and efficiently carried on in practice with the attainment of dependably uniform results.

As many possible embodiments may be made of' the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. The improvement in the method of manufacturing radio-shielded leads having a flexible fluid-tight conduit that has a fitting at an end thereof for mechanical attachment of the lead and that has therein a relatively flexible conductor with relatively flexible insulating compound filling the annular space between the conductor and the conduit, said conductor projecting beyond said end of the conduit and beyond the end faces of said relatively flexible insulating compound, the said improvement comprising securing to the end of the conductor a pistonlike member, and conforming under pressure an insulating material about the projecting portion of the conductor by means of a mold secured in fluid-tight relation to said fitting and having a mold cavity with an end portion in which said piston-like member is receivable thereby to cause the material under pressure to exert force against said piston-like member to cause it to slide along a conforming cylinder portion of said mold cavity in a direction away from said conduit to hold the conductor against axial movement and against kinking under the drag of insulating material that otherwise would move axially in a direction inwardly of the conduit.

2. The improvement in the method of manufacturing radio-shielded leads having a flexible fluid-tight conduit that has a fitting at an end thereof for mechanical attachment of the lead and that has therein a relatively flexible conductor with relatively flexible insulating compound filling the annular space between the conductor and the conduit, said conductor projecting beyond said end of the conduit and beyond the end face of said relatively flexible insulating compound, the said improvement comprising securing on to the end of the conductor a mounting element and piston-like member conforming and curing under pressure a curable moldable insulating compound about the projecting portion of the conductor and against the inner face of said piston-like member and about the adjacent portion of said mounting member by detachably securing to said fitting a mold having a mold cavity to shape the insulating compound and cause the compound under pressure to exert force upon said piston-like member, applying said force to said member to resist axial movement of the conductor inwardly of the conduit under the drag imposed thereon by compound forced in a direction inwardly of the conduit itself, and to slide said piston-like member along a conforming cylinder portion of said mold cavity in a direction away from said conduit whereby said relatively flexible conductor is tensioned during cure and held against material radial displacement relative to both of said compounds.

3. The improvement in the method of manufacturing radio-shielded leads having a flexible fluid-tight conduit that has a fitting at an end thereof for mechanical attachment of the lead and that has therein a relatively flexible conductor with relatively flexible insulating compound filling the annular space between the conductor and the conduit, said conductor projecting beyond said end of the conduit and beyond the end face of said relatively flexible insulating compound, the said improvement comprising securing to the end of the conductor a conductive mounting element and piston-like member conforming and curing under pressure a curable moldable insulating material about the projecting portion of the conductor by a mold that is in fluid-tight connection with said fitting and has a mold cavity with an end portion to accommodate said element and piston-like member whereby expansion of the insulating material under pressure in the mold exerts force on said piston-like member to slide said member in a direction away from said conduit and resists the exertion by said material of such forces of compression upon the conductor within said firstmentioned and flexible insulating compound as would cause detrimental kinking or radial displacement thereof.

4. The method of claim 2 in which after completion of the conforming and curing of said insulating compound said piston-like member is removed and there is secured in its place a conductive terminal contact having an end face substantially mating the end face of said cured insulating material.

GEORGE L. MCCUTCHAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Date