US3564682A

US3564682A - Method of making a spark gap

Info

Publication number: US3564682A
Application number: US688795A
Authority: US
Inventors: Joseph J Carroll Jr; Ferdinand A Rocchi
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1967-12-07
Filing date: 1967-12-07
Publication date: 1971-02-23
Anticipated expiration: 1988-02-23

Abstract

AN ELECTRICAL SPARK GAP COMPONENT COMPRISING A CYLINDRICAL BODY OF AN ELECTRICAL INSULATING PLASTIC HAS A TRANSVERSELY EXTENDING RECESS IN THE CYLINDRICAL SURFACE THEREOF. A PAIR OF WIRES OF AN ELECTRICALLY CONDUCTIVE METAL ARE EMBEDDED IN THE BODY AND EXTEND SUBSTANTIALLY LONGITUDINALLY ALONG THE BODY. ONE END OF EACH OF THE WIRES PROJECTS FROM A SIDE OF THE RECESS IN SPACED RELATION FROM THE PARTIALLY ACROSS THE RECESS IN SPACED RELATION FROM THE SURFACE OF THE RECESS. SUCH ENDS OF THE WIRES PROJECT FROM OPPOSITE SIDES OF THE RECESS AND ARE ARRANGED IN CLOSELY SPACED RELATION TO PROVIDE A GAP THEREBETWEEN. THE OTHER ENDS OF THE WIRES PROJECT FROM THE ENDS OF THE BODY. THE SPARK GAP IS MADE BY MOLDING A CYLINDRICAL PLASTIC BODY AROUND THE MID-PORTION OF A WIRE WITH THE ENDS THE WIRE PROJECTING FROM THE ENDS OF THE PLASTIC BODY. A SLIT IS CUT TRANSVERSELY ACROSS THE PLASTIC BODY WITH THE SLIT BEING DEEP ENOUGH TO ALSO CUT THROUGH THE WIRE. THE PLASTIC AT EACH SIDE OF THE SLIT IS REMOVED FROM AROUND THE CUT ENDS OF THE WIRE TO FORM A RECESS AND EXPOSE THE END PORTIONS OF THE CUT WIRE.

Description

Feb. 23, 1971 J L, JR; ET AL 3,564,682

METHOD OF MAKING A SPARK GAP Filed Dec. '7, 1967 INVENTORS. JOSEPH J. CARROLL,JR. FfRD/IVA/VD A. ROC'CH/ ATTORNEY United States Patent O US. Cl. 2925.17 1 Claim ABSTRACT OF THE DISCLOSURE An electrical spark gap component comprising a cylindrical body of an electrical insulating plastic has a transversely extending recess in the cylindrical surface thereof. A pair of wires of an electrically conductive metal are embedded in the body and extend substantially longitudinally along the body. One end of each of the wires projects from a side of the recess in the body and extends partially across the recess in spaced relation from the surface of the recess. Such ends of the wires project from opposite sides of the recess and are arranged in closely spaced relation to provide a gap therebetween. The other ends of the wires project from the ends of the body.

The spark gap is made by molding a cylindrical plastic body around the mid-portion of a wire with the ends of the wire projecting from the ends of the plastic body. A slit is cut transversely across the plastic body with the slit being deep enough to also cut through the wire. The plastic at each side of the slit is removed from around the cut ends of the wire to form a recess and expose the end portions of the cut wire.

BACKGROUND In the application for Letters Patent of Michael I. Kavcak et al., Ser. No. 642,550, filed May 31, 1967, entitled Spark Gap and Method of Making the Same, there is described an electrical spark gap which comprises a cylindrical body of an electrical insulating plastic having a slit extending transversely thereacross. A pair of wires of an electrically conductive metal are embedded in the body with each of the wires extending from a separate side of the slit longitudinally through the body and projecting beyond an end of the body. The end of the wires at the sides of the slit are flush with the sides of the slit and are exposed so as to provide the electrodes of the spark gap with the slit being the gap. Although spark gaps of this construction generally operate satisfactorily, and can be made easily and inexpensively, these spark gaps have been found to have an operational problem. It has been found that, when the spark gaps are operated at high energy dissipation levels, there is a tendency for the spark gap to short out relatively quickly. Thus, under such operating conditions, the spark gap has a relatively short operating life.

SUMMARY It is an object of the present invention to prOVide an electrical spark gap which is of relatively simple construction and which has a good operating life even when operated at high energy levels.

It is another object of the present invention to provide a spark gap which can be operated satisfactorily at high energy levels and which is simple and inexpensive to manufacture.

It is a further object of the present invention to provide a spark gap in which a cylindrical body of insulating material is molded around a portion of a wire with the wire extending beyond the ends of the body, a slit is provided transversely across the body and through the wire to provide a gap between the cut ends of the wire, and the material of the body is removed at each side of the slit to expose the end portions of the wire and space such end portions from the body.

Other objects will appear hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIG. 1 is a perspective View of the spark gap of the present invention.

FIG. 2 is a longitudinal sectional view of a spark gap of the present invention in its first stage of manufacture.

FIG. 3 is a longitudinal sectional view of the spark gap of the present invention in its second stage of manufacture.

FIG. 4 is a sectional view of the completed spark gap of the present invention taken along line 44 of FIG. 1.

FIG. 5 is a sectional view taken along line 55 of FIG. 4.

DESCRIPTION OF INVENTION Referring initially to FIGS. 1 and 4, the spark gap of the present invention is generally designated as 10. Spark gap 10 comprises a solid, cylindrical body 12 of an electrically insulating plastic material. The body 12 has a transverse recess 14 therein substantially midway between the ends of the body. Preferably, the recess 14 extends less than one-half way through and one-half way around the body 12. The body 12 may be of any desired length and diameter and preferably is of a length and diameter corresponding to that of the other electrical components with which the spark gap 10 is to be used as a circuit.

Embedded within the body 12 are a pair of identical, longitudinally extending

electrodes

16 and 18 of an electrically conductive metal wire. The

electrodes

16 and 18 are in direct alignment at opposite sides of the recess 14 just below the cylindrical surface of the body 12. The end portions of the

electrodes

16 and 18 project beyond the sides of the recess 14 and extend toward each other partially across the recess with the adjacent ends thereof being in closely spaced relation. Thus, the end portions of the

electrodes

16 and 18 are spaced from the surface of the recess 14 and are exposed to the ambiance. As shown in FIG. 5, the

electrodes

16 and 18 are rectangular in transverse cross-section. However, they may also be circular or of any other desired shape. A pair of

terminal wires

20 and 22 of an electrically conductive metal extend longitudinally from the center of the ends of the body 12. As shown in FIG. 4, the

terminal wires

20 and 22 extend into the body 12 and are connected to the

electrodes

16 and 18 respectively by connecting

portions

24 and 26 respectively.

To make the spark gap 10 of the present invention, the electrodes 16- and 18 and their

related terminal wires

20 and 22 are formed from a single length of wire 28 (see FIG. 2). A mid-portion 30 of the wire 28 is flattened to a rectangular cross-section and offset from the longitudinal axes of the wire 28 so that the longitudinal axis of the mid-portion is parallel to but spaced from the longitudinal axis of the wire. The cylindrical body 12 of the electrical insulating plastic material is molded around the mid-portion 30 of the wire 28 and portions of the wire on each side of the mid-portion (see FIG. 2). The diameter of the body 12 is such that the end portions of the wire 28 extend from the center of the ends of the body and the mid-portion 30 of the wire extends just below the cylindrical surface of the body.

As shown in FIG. 3, a slit 32 is then cut transversely across the. body 12 at the place on the body where the mid-portion 30 of the wire 28 is located. The slit 32 is cut deep enough so as to extend through the mid-portion of the wire. This divides the mid-portion of the wire into the two

electrodes

16 and 18 with the slit providing the gap between the ends of the electrodes. Thus, the width of the slit 32 will determine the voltage at which the spark gap will break down. The wider the slit 32, the higher the breakdown voltage of the spark gap. The slit 32 can be cut with any well-known cutting means, such as a circular saw, which will provide a slit of controlled width.

The final step in making the spark gap 10 is removing portions of the body 12 at each side of the slit 32 so as to form the recess 14 and expose the end portions of the

electrodes

16 and 18. One method of so removing the material of the body 12 is by means of a sand blast directed at the body. The sand blast can be controlled to remove the softer plastic material without damaging the metal of the electrodes. The material of the body 12 can also be removed to form the recess 14 by chemical means. For example, the surface of the body 12 can be coated with a suitable resist material except for the area to be removed and then the exposed area of the body is subjected to a suitable solvent or etching material. Also, prior to applying the body 12 to the wire 28, the center of the mid-portion 30 of the wire may be coated with a thick layer of a material which can be dissolved by a solvent which does not attack the material of the body 12. After the body 12 is formed around the wire 28, the coating on the wire is removed by the solvent leaving the recess in the body. For example, the thick layer may be polyvinyl alcohol, which is water soluble, or an acrylic resin, which is soluble in methylene chloride, whereas the body 12 may be any solvent resistant plastic, such as a phenolic, epoxy, etc.

In making the spark gap 10 of the present invention, it is preferable to make a plurality of the spark gaps at one time in the manner described in the patent application of Michael J. Kavcak et al., Ser. No. 642,550. This may be achieved with a two-part mold having a plurality of mold cavities for forming the bodies 12. A separate wire 28 is placed across each mold cavity with the midportions 30 of the wire 28 all extending in the same direction. The mold cavities are filled with a plastic mold material which is heated and compressed when the two sections of the mold are brought together so as to fuse and cure the plastic mold material around the wires. During the fusion of the plastic mold material, the excess material flashes from the mating mold cavities and flows between the mating surfaces of the mold sections. This flash provides a thin web of the plastic material which extends between and connects the bodies 12 of the spark gap 10. The connected spark gaps are removed from the mold as a single unit and the slit 32 is then cut in all of the spark gaps by a single cutting operation. The material of the bodies 12 on each side of the slits 32 is then removed from all of the spark gaps in one operation and the spark gaps 10 are separated by breaking the interconnecting webs and removing any excess flash.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claim, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. A method of making an electrical spark gap device comprising the steps of:

(a) molding a solid cylindrical body of an electrical insulating plastic around a portion of a length of a wire of an electrically conductive metal so that the wire projects from both ends of the body;

(b) forming a recess transversely across and partially through the body with the recess being formed deep enough to cut the wire into two pieces and to space the exposed end portions of the wire from the bottom of the recess;

(c) removing the material surrounding the wires on both sides of the recess to form a wider recess and to expose the cut end portions of the two pieces of wire in opposed spaced apart axially coaligned relationship to each other;

(d) the step of molding including the initial step of coating the wire with an initial material which can be dissolved by a solvent that does not dissolve the insulating plastic, and the step of removing the material including removing the coating of initial material on the wire by dissolving said coating in said solvent.

References Cited.

UNITED STATES PATENTS 2,180,779 11/1939 Stribeck 29-25.11X 2,876,601 3/1959 McFadden 51-321 2,966,608 12/1960 Magnussen et al.

3,202,873 8/ 1965 Feldman.

3,205,104 9/1965 Sibley 51-319X 3,276,106 10/ 1966 Bester et al 29-625 3,322,995 5/1967 Hansen et al 313-325 3,484,842 12/ 1969 Cole 229-2542 JOHN F. CAMPBELL, Primary Examiner C. E. HALL, Assistant Examiner US. Cl. X.R.