US2293659A - Insulated wire - Google Patents

Description

Aug.

.J w. MURRAY INSULATED WIRE Filed June 27, 1940 FIG72 TENDENGY To TIGHTEN oN 7 @TRANDS AND wlRE DIRECTION OF TWIST SMM TENDENCY To RAvl-:Ll FROM 7 sTRANDs AND WIRE DIRECTION 0F TwlsT` JOHN w. MURRAY INVENTOR.

BY Ulu-LA Nammmg.

Patented Aug. 18, 1942 INSULATED WIRE John W. Murray, Kingston, N. Y., assigner to Hercules Powder Company, Wilmington, Del., a

corporation of Delaware Application June 27, 1940, Serial No. 342,603

2 Claims.

This invention relates to an improved insulated electrical conductor and more particularly to a fabric encased wire suitable for use as lead wires for electric ring devices. The invention relates specifically to lead wires of electric blasting caps which are insulated by lapping on warps without weft.

It hasy been known heretofore that in order to provide a fabric encased electrical conductor, the fabric could be appliedV by braiding, lapping or taping the conductor. Braiding gives the most satisfactory results in the majority of instances but is also the most expensive and diflcult insulation to apply. Braiding is applied by weaving individual threads about the conductor.

Lapping is used on fine wire; i. e., wire of less than 20 gauge, about which it is not very practical to braid insulation, and on wire of any gauge which is not intended for use which requires prolonged handling. Lapping is applied by winding warp Without .weft about the conductor, usually in a spiral or helical manner.

Taping is used on conductors of large diameter such as cables of the compound t'ype. Taping is applied by winding woven fabric in the form of a tape having a desirable width to allow easy wrapping about the cable to be insulated.

Braiding and tapingV types of insulation may be applied in single layers and this single layer material will give results comparable to double or triple layers of lapping. However, all of the Vvarious types of insulating methods may incorporate the placing of a plurality of layers about the wire, and in lapping it is normal to apply at least two layers of strands or warps. A plurality of layers of strand is necessary in lapping operation to obtain a completely insulated wire, and the layers will normally be wrapped in opposite direction to each other.

In the ring device art the lead wires of the various ring devices are' generally insulated by lapping on' two layers of strands, the strands normally being applied in layers each of which comprises four or more individualstrands disposed parallel to each other and each layer wrapped in a direction opposite to the adjacent layer. A serious disadvantage of this method of insulating wires is encountered in blasting caps since the lead wires have a portion of the wire, at the free ends thereof, bare and the insulation strands terminating on the bare surface of the wire ravel and expose additional bare wire and thus pro. duce an unsightly frayed group of strand ends.

Even after impregnating the lapping with materials such as paraffin, paraffin-resin or similar mixtures, the raveling and frayed ends of strands are encountered. The handling, movement, shipment, packing and unpacking operations which are necessary in the firing device art all tend to cause the raveling to become more pronounced and the frayed ends to look more unsightly and become more of a nuisance.

Many different types of impregnating materials have been used in the firing device art to iix lapped insulation so that it will not ravel but no satisfactory method of preventing raveling has been found. Raveling presents a further disadvantage in that electric firing devices are usually shunted and the shunts are normally attached to bare ends of lead wires of various iiring devices as close to the insulated portion thereof as possible. However, with normal usage and handling, the lapping insulation ravels back so that. bare wire is exposed between theinsulated portions and the shunt. Due to this raveling man'y rejects are found in the production of firing devices such as electric blasting caps, delay electric blasting caps. squibs, igniters and the like. Further, there are many complaints due to the lack of properly insulated wires, due to the unsightly appearance of the devices, and due to added difficulties in making connections.

It is the object of this invention to produce a lapped insulated wire which exhibits a lack of raveli`ng.

A further object of this invention is to produce a lapped insulated wire which presents a good appearance.

A further object of this invention is to provide a means of preventing excessive raveling oi' lapped insulation.

A further obj'ect of this invention is to provide a wire with lapped insulation which will not tend to ravel.

A further object of this invention is to provide lead `wires for firing devices which do not have frayed ends. A still further object of thisinvention is to provide improved electric ring devices and the like. Other objects of this invention will appear hereinafter.

In general, the objects of this invention are accomplished by applying a layer of strand of insulating material to a wire in a manner so that thetwist of the strand is opposite to the direction of lapping. By controlling each layer of strands s0 that their twist is opposite to the direction of lapping, an assembly is provided which tends to become more tightly wrapped about the wire at all times and thus prevents raveling.

In the textile art strands of material may be obtained with two different types twist. The type twist of yarn is denoted by the letter S and by the letter Z. Thus, a yarn or cord has S twist if, when held in a vertical position, the spirals conform in slope to the central portion of the letter S; and Z twist if the spirals conform in slope to the central portion of the letter Z. Throughout this specification `and claims these two letters of determination will be used to indicate twists of the insulating strands. Further, these two letters will also be used to indicate the direction of lapping or wrapping of the strands -bottom layer of insulation being lapped in a Z direction is composed of eight strands of S twist material and the top layer is composed of eight strands of Z twist material lapped in an S direction.

Fig. 3 is a fragmentary, sectional View of the lead wire of Fig. 2V on line 3--3 indicating the tendency of movement'of the strands wrapped in accordance with this invention.

Fig. 3A is fragmentary, sectional view similar to Fig. 3 but indicating the tendency of move- 'ment of strands having atwist opposite to the strands of this invention. l

Referring now to the drawing and more especially to Figs. 1 and 2, there is shown a firing device I having' a pair of lead wires 2 extending therefrom. The device l may be an instantaneous electric blasting cap, a delay electric blasting cap, a squib, or an igniter, but for the purposes of illustration a normal electric blasting cap is shown. The lead wires 2 extending from the blasting cap I may comprise'copper or iron wire 4 of any desired gauge, but in the blasting cap art, it is normal to use either 22 gauge copper or iron wire or 20 gauge copper wire as illustrated and as normally used the wire is composed of a single solid strand instead of a plurality of twisted strands as used in other arts. About the metal lead wires `4 there is wrapped, by lapping, insulating material' 5 which may be composed of a plurality of layers of threads l usually cotton comprising, usually 4 to 12 ends. The bottom layer of threads 1 Fig. 2, are sh'own to be lapped about the wire in a S direction and the top layer of threads are lapped in a Z direction.

The free ends 8 of the leg wire 2 are stripped of all insulation so that there is-provided a means of connecting the blasting cap to a source of E. M. F. The lapped insulation stops at point 9,v and at this point the various strands of insulation normally tend to ravel and fray but by lapping in accordance with this invention, they are caused to adhere closely to the electrical conductor. Adherence to the electrical conductor is increased because the underlayer of insulation composed of S twist threads are wrapped in Z direction and the top layer of Z twist threads are wrapped in S direction, and all tendency of the individual threads to ravel results in the layers winding more tightly about the wire.

By referring to Fig. 3 and Fig. 3A, the reason S twist threads when wrapped in a Z direction adhere to the conductor and the reason why Z twist threads wrapped in a Z direction do not adhere tightly to the electrical conductor becomes apparent; Thus, it will be noted that when the S twist threads tend to unwind (Fig. 3) all of the force of the raveling is directed towards effecting a more tightly wrapped electrical conductor as the thread moves more closely to the adjacent strands, while when the Z twist thread tends to unwind (Fig. 3A) all of the force of the raveling is directed toward effecting a looser wrapped electrical conductor.

While the above description points out that each layer of insulation contains strands having a twist opposite to the direction of lapping, it has been found that a considerable decrease in the tendency of insulation to ravel may be effected by applying to the wire only the outside layer of insulation strands in accordance with this invention; that is, by applying a material twisted in one direction by lapping in the opposite direction,

while placing the strands below the outside layer in any convenient manner. Thus, for example, a layer of S twisted material applied in a S direction maybe held against'the wire by applying thereover a layer of S twisted material in a Z direction. The raveling and fraying, while considerably reduced by placing only the outside layer in accordance with this invention, is not equal to the decrease in raveling and fraying obtained when'all layers of insulation are placed in accordance: with this invention.

It has also been found that where it is desirable to use twined thread or strands for lapping the tendency to ravel is reduced when the twined l material is lapped in a direction opposite that of like, of course, materially aids in reducing raveling and fraying no matter what the relation between twist and lapping directions, but with any particular type impregnated Wires, it is found that application of the strands in accordance with this invention improves the appearance, re-

'duces the raveling and eliminates substantially all fraying.

Further advantages of wires insulated by lapping the threads opposite to their direction of Y wires.

twist or opposite to the direction of twining if twined material is used are noted during'the Ymanufacture of firing devices as there is less trouble in the preparation of the free ends of the The burning and brushing operations or the crushing and stripping operations necessary to prepare bare ends suitable for connecting to av flring line and for bridging and the tin'riing of the bared ends are more easily accomplished.

'Ihe positioning of the wires in molds before pouring of the bridge plugs is simplified due to less fraying. Also the positioning of shunts upon the bare ends of the lead wires is facilitated due to reduced fraying and raveling. Many other advantages will become apparent to those skilled in the art upon use of this invention.

:It will be understoodthat the details and examples hereinbefore s et forth are illustrative only, and thatthe invention as broadly described and claimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

1. A lead wire for an electric firing device comprising a single solid metallic wire, not greater than approximately 20 guage, insulated with a self-sustaining covering comprising a, plurality of layers of cotton servings; said layers comprising between 4 and 12 single strands of cotton and said servings covering the wire from the device to a predetermined point on said wire to provide a portion of bare wire suicient to allow electrical connection to a source of E. M. F.; the said covering comprising the insulation having some of the layers wrapped about said wire in a Z direction and other layers wrapped about said wire in an S direction, the strands of cotton in the layer wrapped in the Z direction having an S twist and the strands of cotton wrapped in the S direction having a Z twist, whereby the ends of said servings terminating at said predetermined point act against the wire and raveling of said ends is prevented.

2. A lead wire for an electric iring device comprising a single solid metallic wire, not greater than approximately 20 guage, insulated with a self-sustaining covering comprising a layer of Z twist strands wrapped in an S direction and a layer of S twist strands Wrapped in a Z direction about said metallic wire, said layers each comprising between 4 and 12 single strands of cotton and said layers covering the wire from the device to a predetermined point on said wire to provide a portion of bare wire sunlcient to allow electrical connection to a source of E. M. F., whereby the ends of said layers terminating at said predetermined point act against the wire and raveling of said ends is prevented.

JOHN W. MURRAY.

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