Patent 3828112 - COMPOSITE HOSE FOR CONDUCTIVE FLUID
|United States Patent||Patent Number 3,828,112|
|Johansen , et al.||Issued August 6, 1974|
COMPOSITE HOSE FOR CONDUCTIVE FLUID
A composite hose particularly advantageous for use in conveying an electrical conductive paint in an electrostatic paint spray system has a synthetic resinous core tube such as nylon which is resistant to chemical attack by the paint, a contiguous substantially non-porous layer of synthetic resin which insulates the core tube against leakage of static charge therefrom, an extrusion or tape of semi-conductive synthetic resin containing particles of an electrical conductor dispersed uniformly therein lying in intimate contact about the insulating layer, a braided electrical conductor wound in electrical contact about the semi-conductive layer and an abrasion resistant sheath about the braid.
|Inventors:||Hans A Johansen (Mantua OH)|
Dewey E Whittaker (Ravenna OH)
Larry R Phillippi (Mantua OH)
|Assignee:||Samuel Moore (Mantua, OH)|
|Filed:||March 14, 1973|
|Current U.S. Class:||174/47 - 138/125 - 138/126 - 138/127 - 138/137 - 138/177 - 174/106SC - 361/215|
|Current International Class:||F16L011/127 (20060101)|
|Current CPC Class:||F16L 11/127 (20130101)|
|Field of Search:||138/127,103,146,149 174/47,12SC,16SC 317/2R,2J 161/247,190|
|3042737||July 1962||Brumbach et al.|
|3277231||October 1966||Downey et al.|
Assistant Examiner:Daniel M Yasich
Attorney, Agent or Firm:
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A composite hose for conveying electro-conductive fluids comprising a substantially non-porous, synthetic resinous core tube and including an electrical insulating layer, said core tube and said layer preventing leakage of a static charge on said fluids therethrough, a semi-conductive synthetic resinous layer having an electrical resistance of not more than about 500 ohm-centimeters disposed in intimate contact over the said layer, an electrical conductive braid over and contiguous with the semi-conductive layer, and an abrasion resistant sheath over the braid.
2. The hose of claim 1 wherein the core tube is nylon, the insulating layer is polyethylene, the semi-conducting layer is an ethylene-vinyl acetate copolymer, the braid is stainless steel and the sheath is polyurethane.
3. The hose of claim 1 wherein the core tube is nylon.
4. The hose of claim 1 wherein the sheath is polyurethane.
5. The hose of claim 1 wherein the semi-conductive resinous layer has carbon black dispersed therein.
6. The hose of claim 5 wherein the semi-conductive layer has a resistance of from about 10 to about 100 ohm-centimeters.
7. The hose of claim 1 wherein the core tube and the insulating layer are different resins.
8. The hose of claim 1 wherein the core tube is also the insulating layer.
9. The hose of claim 1 wherein the said substantially non-porous insulating layer has a dielectric strength of at least about 300 volts per mil thickness.
This invention relates generally to composite tubing or hose and more particularly to a hose adapted for use as an electrically insulated paint supply hose with air atomizing spray guns.
Electrostatic paint spray systems are widely used in paint spraying. Such systems may have a spray gun to be held by hand or they may have a fixed gun and a conveyor which moves the work in front of the gun. The paint may be charged to a potential of 25 to 150 but more commonly 75 to 100 kilovolts at the spray gun or at the paint supply tank to create an electrical field. The electrical forces on the particles of paint selectively drive the particles to the grounded workpiece to reduce waste from over spray. An electrically insulated hose must be used in such spray systems for conveying conductive paint from the supply to the spray gun.
It is therefore an objecc of this invention to provide a paint hose adapted for use in electrostatic spray systems. Another object of the invention is to provide a composite hose which is adapted to withstand the abuse ordinarily encountered in paint spraying and still effectively isolate an electrically charged paint within the hose. A further object of the invention is to provide a composite hose adapted to convey paint from a source thereof to a fixed spray gun. Still another object of the invention is to provide a flexible composite hose which will effectively isolate an electrically charged paint therein and is adapted for conveying paint from a source to a hand spray gun.
Other objects will become apparent from the following description with reference to the accompanying drawing in which
FIG. 1 is a cut-away side elevation of one embodiment of the invention;
FIG. 2 is a section taken along the line 2--2 of FIG. 1;
FIG. 3 is a cut-away side elevation of another embodiment of the invention; and
FIG. 4 is a section taken along the line 4--4 of FIG. 3.
The foregoing objects and others are accomplished in accordance with this invention, generally speaking, by providing a composite tubing or hose having a core tube which is resistant to chemical attack by a water-based paint or the like, a substantially non-porous layer of electrically insulating synthetic resin which is capable of substantially preventing leakage of a static charge on paint used in an electrostatic spray system, a contiguous semi-conductive layer about the insulating layer, an electrical conductor wound in electrical contact about the semi-conductive layer and an abrasion resistant sheath about the conductor. The core tube and the insulating layer may be combined in a single tube if a synthetic resin which is chemically resistant to the fluid to be conveyed through the hose and a suitable electrical insulator at a practical tube wall thickness is used. Such hose may be used to advantage in any equipment for conveying a paint or other fluid having an electrostatic charge. It is particularly advantageous for conveying water-base or other electro-conductive paints from the supply to the spray gun of an electrostatic spray system such as, for example, the one illustrated and described in U.S. Pat. No. 3,645,447.
Referring now to FIGS. 1 and 2, one embodiment of the invention is illustrated as a composite hose 10. In this embodiment, hose 10 has an extruded polyethylene core tube 11 of sufficient thickness to prevent static charge leakage therethrough, an extruded substantially non-porous ethylene-vinyl acetate copolymer layer 13 containing carbon black disposed in contiguous electrical contact with the surface of layer 11, a stainless steel wire braid 14 wound in intimate contact about layer 13 and an abrasion resistant polyurethane sheath 15. This embodiment is adapted for use with paints which will not chemically attack polyethylene.
Another embodiment of the invention insulated to convey an electrically conductive fluid such as a water base paint without grounding is illustrated in FIGS. 3 and 4 as hose 10'. Hose 10' has a relatively thin walled nylon core tube 11', a substantially non-porous polyethylene layer 12 about core tube 11' which is of sufficient thickness to prevent static charge leakage therethrough, an extruded substantially non-porous ethylene-vinyl acetate copolymer layer 13 containing carbon black disposed in contiguous electrical contact with the surface of layer 12, a stainless steel wire braid 14 wound in intimate contact about layer 13 and an abrasion resistant polyurethane sheath 15.
Core tube 11' is preferably a nylon extrusion if the hose is to be used for conveying a water-base paint because it is resistant to chemical attack by such paint. However, core tube 11' may be any other suitable synthetic resin which is resistant to chemical attack by the fluid to be conveyed by the hose such as, for example, Teflon, a tetrafluorethylene polymer, an elastomeric polyurethane, a polytetramethylene ether glycol and 1,4-butane diol ester of terephthalic acid and isophthalic acid such as Hytrel sold by E. I. duPont de Nemours & Co. or other elastomeric polyester or copolyester, a polyolefin such as polyethylene, polypropylene or an ethylene-propylene copolymer, a thermoplastic rubber such as thermoplastic styrene-butadiene rubber (SBR) and styrene-isoprene thermoplastic rubber (SIR), or blends thereof, or the like.
The insulating layer 12 and core tube 11' when the core tube is to serve as a combined core tube and insulating layer may be any synthetic resin which is extrudable and which has an electrical resistance sufficient to prevent leakage of the static charge on the fluid being conveyed therethrough. For example, any synthetic resin having a dielectric strength of at least about 300 volts per mil thickness may be used. Suitable resins include polyolefins such as polyethylene, polypropylene, ethylene-propylene copolymers, a polyvinyl chloride polymer or copolymer, a polytetramethylene ether glycol and 1,4-butane diol ester of terephthalic acid and isophthalic acid such as Hytrel or other elastomeric polyester of copolyester, a thermoplastic rubber such as thermoplastic styrene-butadiene rubber (SBR) and styrene-isoprene thermoplastic rubber (SIR), or the like, or blends thereof which will prevent leakage of the static charge when used in a practical thickness.
The semi-conductive layer 13 may be of any suitable synthetic resin containing carbon black or other conductive particles such as metallic particles or the like which will form a substantially contiguous coating over the surface of core tube 11' or insulating layer 12 and which has an electrical resistance of not more than about 500 ohm-centimeters and preferably from about 10 to about 100 ohm-centimeters. The metallic particles may be, for example, aluminum. Suitable resins include rubber, an elastomeric polyurethane, a polyvinyl chloride polymer, or copolymer, polyolefins such as polyethylene, polypropylene and an ethylene-propylene copolymer, a thermoplastic rubber such as styrene-butadiene thermoplastic rubber (SBR) and styrene-isoprene thermoplastic rubber, blends thereof, or the like. The semi-conductive layer 13 may be a semi-conductive tape such as a carbon impregnated fabric tape or the like but an extruded coating is preferred because it is of greater uniformity and is in more intimate contact with the underlying layer 11 or 12. However, the coating 13 may be applied by dipping, electrodeposition, spraying or other suitable means.
Wire braid 14 may be any suitable electrical conductor such as, for example, stainless steel wire, copper wire, aluminum wire or the like. The wire should be sufficiently strong to be wound by a conventional wire braider without breaking.
Any suitable abrasion resistant sheath 15 may be used such as, for example, rubber, elastomeric polyurethane, nylon, polyvinyl chloride polymer or copolymer, a polyolefin such as, polyethylene, polypropylene, a thermoplastic rubber such as styrene-butadiene rubber (SBR) or styrene-isoprene rubber (SIR) or the like.
The hose may be manufactured in indeterminate lengths and cut to the required length when it is installed in the spraying assembly. Each layer of the hose extends throughout the length thereof. Consequently, when the hose is severed into shorter lengths for installation, the ends of the wires forming the braid are exposed. In order to avoid grounding by the fitting used to attach the hose to the paint supply tank or by the spray gun, layers 15, 14 and 13 are removed from the end portions which will be disposed therein. Pin point arcing between the exposed end of the wires and paint in the end portions of the hose is avoided by folding the end of layer 13 back over the end of sheath 15 with the ends of the wires covered by layer 13 as illustrated at the left hand end of the hose in FIGS. 1 and 3. After installation, a ground wire is electrically connected to wire braid 14 somewhere along the length of the hose, usually near the paint supply tank, by removing a portion of sheath 15 and connecting the wire to braid. A conductive band on one end of the ground may be secured around the braid to insure electrical contact.
The semi-conductive layer 13 presents a continuous relatively low resistance path to ground thereby eliminating the possibility of points of high electrical stress which would cause rupture of the core tube when discharged to ground. The wire braid 14 serves to make the resistance of all points on any length of hose essentially the same. If braid 14 were eliminated the resistance on long lengths of hose could become great enough to promote discharge at points other than low resistance ground which might again cause rupture of the hose.
Conventional equipment and processes may be used to extrude the various resinous layers of the hose and a conventional wire braider may be used to place the wire braid about layer 13.
Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.
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