Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3792409 A
Publication typeGrant
Publication dateFeb 12, 1974
Filing dateApr 2, 1973
Priority dateApr 2, 1973
Also published asCA991286A1, DE2353809A1
Publication numberUS 3792409 A, US 3792409A, US-A-3792409, US3792409 A, US3792409A
InventorsGregg P, Smart W
Original AssigneeRansburg Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electrostatic hand gun cable
US 3792409 A
Abstract
An improved high voltage cable for usein electrostatic hand guns and includes a semiconductive stranded fiber glass core within a semiconductive shield surrounded by body of insulative material, a flexible conductive sheath in an outer protective covering; the semiconductive core and semiconductive shield provide resistance of not less than 20,000 and not more than 300,000 ohms per foot of cable length.
Images(1)
Previous page
Next page
Description  (OCR text may contain errors)

United States, Patent 119 Smart et a1.

1451 Feb.- 12, 1974 ELECTROSTATIC HAND GUN CABLE [75] Inventors: William L. Sma t; Paul S. Gregg,

- both of lndianapolis, 1nd.

[73] Assignee: Ransburg Corporation, Indianapolis,

Ind.

221' Filed! Apr. 2, 1973 21 AppL No.2 347,240

I [52] US. Cl 338/214, 174/36, 174/105 SC,

. 174/107 [51] Int. Cl...... 1101c 13/00, H0lb 1/06, l-l0lb 9/02 [58] Field of Search 338/214, 208, 299; 174/36,

174/102 R,102 SC, 105 SC, 110 PM, 120

SC, 120 SR, 107, 126 R, 127

[56] References Cited UNITED STATES PATENTS 3,683,309 8/1972 Hirose .i 338/214 3,680,027 7/1972 Vitale 338/214 3,644,866 2/1972 D8a1'dllrff.... 338/214 3,518,606 6 1970 Barker 338/214 x 3,348,186 10/1967 R6861.. 338/214 3,284,751 11/1966 Barker et a1. 338/214 X 3,167,255 l/l965 Point et a1. 338/214 X 3,105,219 9/1963 Kozinski 338/214 3,105,218 9/1963 Kozinski 338/214 2,790,053 4/1957 Peterson 338/214 X 2,703,356 3/1955 Buchanan et a1. 338/214 X FOREIGN PATENTS OR APPLICATIONS 547,481 8/1942 Great Britain 338/214 1,490,618 2/1970 Germany 338/214 Primary Examiner-Bernard A. Gilheany Assistant Examiner-A. T. Grimley Attorney, Agent, or Firm-Merrill N. Johnson; Harry E. Downer; David H. Badger ABSTRACT An improved high voltage cable for usein electrostatic hand guns and includes a semiconductive stranded fiber glass core within a semiconductive shield surrounded by body of insulative material, a flexible conductive sheath in an outer protective covering;-the semiconductive core and semiconductive shield provide resistance of not less than 20,000 and not more than 300,000 ohms per foot of cable length.

i 1 Claim, 2 Drawing Figures 1 ELECTROSTATIC HAND GUN CABLE The present invention related to a high voltage cable for use in connecting electrostatic spray coating devices with a separate source of high voltage.

Electrostatic coating systems frequently use voltages on the order of 20,000-100,000 volts of direct current. Voltage of this magnitude places great stress upon electrical insulation that is used to isolate it. Being exposed to such stress, high voltage insulation can fail permitting electrical discharge of the high voltage through the body of the insulation or across its surface. In addition, such high voltages can break down surrounding air and initiate a spark that can travel through air to adjacent bodies at lower potential. Electrical isolation of such high voltages is therefore a problem.

Electrostatic coating systems are frequently used with coating materials that have a flammable residue or that produce flammable vapors. Spraying operations are most frequently conducted in a spray booth to confine such flammable materials and to remove them safely from the interior of an'industrial facility. The Sprayers of electrostatic coating systems are thus most frequently used. inside a spray booth. The high voltage source, however, is generally located outside of and at least feet from. the spraying area. The electrostatic charge to. be applied to the spray particles must be carried from the high voltage source to the electrostatic spray device over a distance on the order of 20 feet.

Since the invention of U.S. Pat. No. 3,048,498, hand manipulated electrostatic spray guns have been commercially possible. Commercial embodiments of this invention have included electrostatic hand guns'having insulating barrels containing resistors with resistances on the order of 40-1000 megohms to prevent objectionable. electrical discharges from the spray gun. Such electrostatic hand guns were connected by a high voltage cable to the high voltage source outside the spraying area. To permit the electrostatic hand gun to be easily manipulated by the operator so that he could direct the spray at all surfaces of complexly-shaped articles, the high voltage cablev had to be flexible. The achievement of flexibility, however, was not always consistent with the requirement that the electrical insulation of the high voltage cable withstand the tendency of high voltage to cause insulation failure. I

In such commercial electrostatic hand gun systems, coaxial high voltage cables were used. The high voltage conductor was a metallic wire at the center of the high voltage cable. Surrounding the wire was a body of insulating material, generally a polyethylene. Surrounding the polyethylene insulation was the grounded metallic braid to act as a barrier to any electric discharge which might occur in the event of an insulation failure of the dielectric material, and to prevent such an electric discharge from occurring to personnel who may be using the electrostatic hand gun. For convenience, a protective covering of rubber or plastic was provided as the outermost covering of the cable.

Many attempts were made to improve upon such high voltage cables. Several attempts were made to incorporate into the high voltage conductor at the center of a coaxial high voltage cable, the entire resistance that was otherwise used within the barrel of the electrostatic hand gun. In essence, this approach was an attempt to stretch the high resistance from within the barrel throughout the length of the cable extending to high voltage source. In addition to eliminating a high voltage connection between the resistor and the high voltage cable within the electrostatic spray gun itself, this approach had the advantage of limiting the energy available in any electric discharge occurring in the high voltage cable because of the breakdown of the surrounding dielectric material. British Patent Specification 1,051,184 and U.S. Pat. No. 3,167,255 both disclose such an approach. Because of the technical difficulties in manufacturing such a cable, however, it never became a commercial reality. In addition, high voltage cables for electrostatic systems were manufactured having a central conductor made of a plurality of shortb'ut rigid high resistance segments that extended throughout the length of the cable (see U.S. Pat. No. 3,348,186). Cables of this latter type thus included many high voltage electrical connections at the junctions of the short high resistance segments. Furthermore, such cables included necessarily, a plurality of high voltage conductor surface discontinuities at these connections at which nonuniformly high potential gradients could occur. This plurality of connections of surface discontinuities was undesirable and accentuated the tendency of high voltage to break down the electricalinsulation of the cable.

Our invention is an electrical cable used to connect an electrostatic hand spray gun to a separate high voltage source. Such a cable is generally on the order of at least 20 feet, although somewhat longer and shorter lengths of cable may be used. It includes a high voltage conductor which is smooth throughout its length and has a uniform distributed resistance of at least 0.5 to about 7.5 megohms equally distributed along its length. Preferably, the cable is thirty feet in length and has a total resistance of five megohms, or about 167,000 ohms per foot of cable length. The cable is small, having an overall diameter of 7/16 of an inch. This cable solves the difficulties of providing a cable that can be reliably manufactured for commercial use and provides the flexibility needed for manipulatable hand guns, with the ability to withstand the tendency of high voltage to break down its electrical insulation.

FIG. 1 is a diagrammatic sketch of an electrostatic hand gun system including such a cable.

FIG. 2 is a cross-sectional view of the cable.

FIG. 1 shows an electrostatic hand gun in use in a spraying area. Electrostatic hand gun 10 is connected to the high voltage source 11 by 25 feet of high voltage cable 12. One such electrostatic hand gun includes within its barrel portion a high voltage resistor 13 having a resistance on the order of megohms. The high voltage for such a hand gun produces 60 kilovolts of direct current.

The high voltage cable 12 which carries electrostatic charge from the high voltage source to the hand gun as shown in FIG. 2, includes as the high voltage conductor 14 stranded conductive fiber glass. The central conductor is comprised of many fibers each having a very small diameter. When stranded, they produce a central high voltage conductor having a diameter of 0.015 inches. This stranded fiber glass conductor is treated to provide a resistance on the order of 20,000 to 300,000 ohms per foot. Immediately surrounding the stranded fiber glass conductor is a corona shield 15 of conductive polyethylene, consisting of a homogeneous mixture of polyethylene with a small percentage of carbon black. The conductive polyethylene minimizes variations of potential gradient which might occur at the surface of the high voltage conductor because of gas trapped during the manufacturing process or surface discontinuities. At the boundary between the corona shield and the surrounding insulation, the corona shield is typically 0.050 inches in diameter. The combined resistance of the semiconductive stranded fiber glass conductor and the semiconductive corona shield should preferably measure not less than 20,000 nor more than 300,000 ohms per foot of cable length.

surrounding the corona shield is the high voltage cable insulation 16. The insulation is a high grade polyethylene that isolates the high voltage charge at its center. Such a polyethylene is typically DFD 60005 NT (Natural), manufactured by Union Carbide. Surrounding the insulation is a conductive braid 17. Such a braid is comprised of 160 strands of 30-gauge copper alloy wire braided together around the insulation. Surrounding the braid itself is a sheath 18 typically 0.030 of an inch thick polyurethane. Total diameter of such a cable structure can be 7/16 inch.

Because of the improved conductive fiber glass high voltage conductor, this cable can be easily manufactured. The fiber glass center conductor provides strength and flexibility needed to manufacture the cable. Furthermore, its smooth outer surface is relatively free of surface imperfections, which can accentuate the tendency of the high voltage to break down electrical insulation. The fiber glass provides a chemically and dimensionally stable medium and permits a conductivity which can be controlled within the limits needed for a comercially satisfactory product. Sufficient resistance can be incorporated into the central conductor so that in the event of an insulation failure, the energy stored throughout the cable by the high voltage electric charge present on the high voltage conductor is dissipated by the resistance of the high voltage conductor as the electric charge travels down the cable to the point of the insulation failure. Thus, the energy available in an electrical discharge between the high voltage conductor and the conductive braid may be limited by the action of the resistance of the high voltage conductor. Because of the reliability in achieving stable high resistance values to the high voltage conductor, it is possible to obtain a cable where the energy available in the event of an insulation failure is below the level necessary to ignite most combustible vapors and residues encountered in spray finishing operations. Incorporation of such a cable into an electrostatic hand gun system thus improves the safety of the system.

The specific cable described above is typical of those used in electrostatic coating systems. However, this invention is capable of incorporation into cables other than that specifically described above.

We claim:

1. An electrical cable used to connect an electrostatic spray gun to a separate high voltage source, said cable having a stranded fiber glass core within a semiconductive shield surrounded by a body of insulative material, a flexible conductive sheath in an outer protective covering; the improvement which consists of the core and the shield together having a resistance of not less than 20,000 and not more than 300,000 ohms perfoot of cable length the improvement which consists of the core being semiconductive and with semiconductive shield providing a resistance of not less than 20,000 and not more than 300,000 ohms per foot of cable length.

. j UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,792,409 Dated February 1.2, 1.974

Inventor(s) WILLIAM L. SMART, ET. AL.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 1, "usein" should read use in Column 3, line 11, "surrounding" should read Surrounding Column 4, claim 1 should read as follows: I i Q 1. I'n an'e'lectrical cable'used to connect an electrostatic spray gun to a separate high voltage source, said cable having a stranded fiber glass core within a semiconductive 7 hield surrounded by a body of insulative material, a flexible conductive sheath in an outer protective covering; the improvement which consists of the core and-,gij the shield together having a resistance of not less than 20,000 and not more than 300,000 ohms per foot of cable length.

Signed and sealed this 13th day of August l974.

(SEAL) Attest: I

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents R P0405, (W69) uscoM -oc wan-Poo 1 "-5. GOVERNMENT PRINTING OFFICE: IQ, "'l .:.'l"'

. PUNTTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 792,409 Dated February 12, 1974 Invent-or(s) WILLIAM L. SMART, ET. AL.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 1, "usein" should read use in Column 3, line ll, "surrounding" should read Surrounding Column 4, claim 1 should read as follows: I

-- l. In an electrical cable used to connect an electrostatic spray gun to a separate high voltage source, said cable having a stranded fiber glass core within a semiconductive shield surrounded bya body of insulative material, a flexible conductive sheath in w an outer protective covering; the improvement which consists of the core andgjg the shield together having a resistance of not less than 20,000 and not more than 300,000 ohms per foot of cable length.

Signed and sealed this 13th day of August 1974.

(SEAL) Attest: I

McCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FQRM P0405) USCOMM-DC wan-Pen ".5, GOVERNMENT PRINTING OFFICE l", Q""gl",

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2703356 *Feb 1, 1951Mar 1, 1955Gen Motors CorpHigh ohmic resistance conductor
US2790053 *Dec 27, 1951Apr 23, 1957Peterson Thomas FShielded ignition cable and resistors
US3105218 *Jun 30, 1961Sep 24, 1963Fischer & Co H GElectric resistor
US3105219 *Feb 19, 1962Sep 24, 1963H G Fischer & Co IncElectric resistor
US3167255 *May 7, 1962Jan 26, 1965Sames Mach ElectrostatElectrostatic sprayer system having a separate high resistivity conductor
US3284751 *Oct 11, 1963Nov 8, 1966Eltra CorpResistor ignition lead
US3348186 *Nov 16, 1964Oct 17, 1967Nordson CorpHigh resistance cable
US3518606 *Jun 27, 1968Jun 30, 1970Eltra CorpIgnition cable with terminal construction
US3644866 *Jan 11, 1971Feb 22, 1972Owens Corning Fiberglass CorpTightly bound bundle of filaments and method of producing same
US3680027 *Apr 19, 1971Jul 25, 1972Avnet IncIgnition cable
US3683309 *Jan 14, 1971Aug 8, 1972Yazaki CorpHigh frequency noise prevention cable
DE1490618A1 *Jul 24, 1964Feb 5, 1970Sueddeutsche KabelwerkeTempe?aturunabhaengige Widerstandszuendleitung mit thermoplastischem Masseleiter,in dessen Laengsachse ein zugfester Kern angeordnet ist
GB547481A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3885085 *Jun 11, 1974May 20, 1975Gen Cable CorpHigh voltage solid extruded insulated power cables
US4103276 *Jul 14, 1976Jul 25, 1978Nordson CorporationResistor core cable
US4487057 *Jul 30, 1982Dec 11, 1984Raychem CorporationContinuous sense and locate device
US4576827 *Apr 23, 1984Mar 18, 1986Nordson CorporationHigh voltage cable, silicon carbide fibers, dielectrics
US4584431 *Oct 11, 1984Apr 22, 1986Us Of America Secr Air ForceHigh voltage RF coaxial cable
US4642417 *Jul 25, 1985Feb 10, 1987Kraftwerk Union AktiengesellschaftMultilayer braided silver plated copper wires, polytetrafluoroethylene and polyurethane
US4739935 *Mar 12, 1986Apr 26, 1988Nordson CorporationFlexible voltage cable for electrostatic spray gun
US4924037 *Dec 20, 1988May 8, 1990W. L. Gore & Associates, Inc.Electrical cable
US4978813 *Aug 29, 1989Dec 18, 1990W. L. Gore & Associates, Inc.A conductive wire having layers of expanded microporous polytrafluoroethylene, a polyesterurethane copolymer and a thermoplastic polyester elastomer; wear resistance
US5166477 *May 28, 1991Nov 24, 1992General Electric CompanyCable and termination for high voltage and high frequency applications
US5803372 *Apr 3, 1997Sep 8, 1998Asahi Sunac CorporationHand held rotary atomizer spray gun
EP0416452A2 *Aug 29, 1990Mar 13, 1991ABB Kabel und Draht GmbHElectro-filter cable
EP0829883A2 *Aug 27, 1997Mar 18, 1998Schnier Elektrostatik GmbHDamped high-voltage cable without oscillations
EP1267361A2 *Jun 4, 2002Dec 18, 2002Illinois Tool Works Inc.High voltage cable
Classifications
U.S. Classification338/214, 174/36, 174/105.0SC, 174/107
International ClassificationB05B5/08, H01B7/00
Cooperative ClassificationH01B7/0054
European ClassificationH01B7/00G