Insulated electrical connectors
US 3123663 A
Description (OCR text may contain errors)
March 3, 1964 5. M. MULDOON 3,123,553
INSULATED ELECTRICAL CONNECTORS Filed April 17, 1961 IN VEN TOR.
4 EDWARD IVI. lV/ULDOON Z QM-W 4 A fforneys United States Patent 3,123,663 INSULATED ELECTRICAL CONNECTORS Edward M. Muld'oon, University Heights, Ohio, assignor to ETC incorporated, Cleveland, Ohio, a corporation of Ohio Filed Apr. 17, 1961, Ser. No. 103,294 4 Claims. (8. 174-84) This invention relates generally to solderless electrical connectors of the type that are adapted to be crimped on the ends of electrical conductors, and more specifically to improved insulated connectors and methods of manufacturing the same.
The basic construction of an insulated connector of the type described has heretofore commonly included a malleable metal ferrule surrounded by a plastic insulating sleeve. In use, the bare end of a wire conductor (to be terminated or connected to another conductor by the connector) is inserted into the connector ferrule, and a crimping force is applied through the insulating sleeve to cold forge the ferrule into electrical and mechanical union with the conductor. The plastic insulating sleeve, in some instances, has been substantially coextensive with the inner ferrule and, in other instances, has extended beyond the wire receiving end of the inner ferrule for embracing the insulation of the wire conductor and providing what has been termed an insulation support. In the latter case, it has also been common practice to apply a second crimping force to the plastic insulating sleeve beyond the inner ferrule to collapse the plastic insulating sleeve more closely about the insulation of the conductor and thereby enhance the insulation support.
Frequently, the outer, plastic, insulating sleeve has been reinforced with an intermediate metal tube of thin malleable metal disposed between the outer plastic sleeve and inner metal ferrule over substantially the length of the inner ferrule and extending beyond the wire receiving end of the inner ferrule within the outer plastic sleeve. The electrical crimp applied to forge the inner ferrule to the conductor and the insulation crimp applied to support the insulation of the conductor acted through the outer plastic sleeve and through the intermediate, metal, reinforcing tube.
The outer insulating sleeves of solder-less connectors are commonly formed from a number of different plastics which have the required qualities of toughness and resistance to fracture on bending and cold forming, and which possess varying degrees of resistance to the different environmental conditions encountered in use, such as retention of the required physical characteristics over widely varying temperature ranges, resistance to attack by solvents (such as are contained in hydraulic brake fluids), acids, alkalines, etc. For example, nylon has been found to be the most desirable material for many applications because of its excellent resistance to most of the environmental conditions encountered, and because it may be readily molded to a desired shape conforming to the metal connector structure enveloped thereby. For other applications, various vinyl chlorides, vinyl chloridevinyl acetate copolymers, vinylidene chloride polymers, vinylidene chloride-vinyl chloride copolymers (Saran), and the like, have been found to be suitable and, in some instances, preferable to nylon. Although most of the plastics of this latter group are inferior to nylon as reice gards at least some of the environmental conditions encountered in use of the connectors, a number of them have insulating properties superior to nylon; however, they are generally difiicult or impossible to mold into desired shapes and are more comonly extruded as long tubes that are subsequently cut to length.
The advantages offered by all of the various plastic insulating materials have been offset to a considerable extent by certain inherent characteristics of the materials which have adversely affected their protective functions for the connectors to which they are applied. One of the most pronounced and serious of these disadvantages results from the so-called plastic memory of the plastic materials, which causes the insulating sleeve to recede outwardly even though crimped with a pressure exceeding the elastic limit of the plastic insulating material. This results in a pulling away of the plastic insulating material from the underlying metal surface of the inner ferrule or intermediate reinforcing tube after the crimping pressures employed to form the electrical crimp and the insulation support crimp have been removed. This tendency of the plastic insulating sleeve to return at least partially toward its original uncrimped shape produces air gaps between the plastic sleeve and the metal surface covered thereby. These disadvantageous air gaps constitute reservoirs into which moisture, dirt, corrosive atmospheres, and other foreign matter may penetrate and promote corrosion, as well as shorting or arcing from the metal structure of the connector to an adjacent connector or other adjacent conducting surface.
The corrosion and arcing tendencies of conventionally formed, insulated connectors are accentuated where the outer plastic insulating sleeve has been punctured or torn during the crimping operation and the rupture has not been fully and tightly closed by the gradual recovery of the'plastic material. When such air gaps are formed at the conductor-receiving end of the connector ferrule or intermediate metal reinforcing tube, stray wire strands from one conductor may accidentally be thrust into the air gaps under the insulating sleeve of an adjacent connector, thereby causing electrical shorts. These various causes of electrical shorting or arcing are particularly serious when the connectors are employed in relatively high voltage circuits.
Another disadvantage of the various plastic materials, which is particularly pronounced in the case of nylon, is a tendency of the material to extrude from the areas where high crimping forces are applied. The direction of such extrusion may be circumferential, axial, or both, depending upon the shape of the crimping dies. Regardless of the direction of such extrusion, it has the obvious effect of thinning the wall thickness of the plastic insulating sleeve and thereby decreasing its dielectric properties. This promotes the puncturing and tearing of the insulating sleeve and consequent impairment of its protective functions referred to above.
A variety of measures have been resorted to in the past in attempting to overcome the foregoing difficulties. For example, it has been proposed to treat the interior of the insulating sleeve and the adjacent metal surfaces to increase the coeficient of friction therebetween to resist axial extrusion of the sleeve. Another frequently used practice has been to bond the insulation sleeve to the connector ferrule or to the metal reinforcing tube.
Still ot ier attempts have been made to design special insulation crimping dies and to devise insulated connector constructions which would, at least to some extent, compensate for the undesirable characteristics of the plastic insulating materials. While these measures have had different degrees of success in the particular applications for which they were intended, the increased manufacturing costs involved frequently made them economically unfeasible. Moreover, none of the efforts of the prior art have been universally acceptable in meeting the large number of commercial requirements imposed by the many different conditions to which insulated connectors are exposed.
The present invention has for one of its principal objectives the provision of a novel, insulated connector construction which is effective to overcome the problems and difficulties discussed above, and more particularly the problems and disadvantages resulting from the plastic memory characteristics of plastic insulating materials and from the extrusion tendencies of these materials as they have heretofore been applied to. solderless connectors.
Another general object of the present invention is to provide an insulated electrical connector of the broad class described which is protected from corrosion, shorting and arcing even though air gaps may form between the outer insulating sleeve and the adjacent inner surface enveloped thereby.
till another object of the invention is to provide an improved, insulated connector of the solderless type having high voltage-breakdown characteristics as a result of added insulation provided in those areas where the outer insulating sleeve may be thinned, punctured, torn, or otherwise damaged by the crimping operation or operations.
Still another object of the invention is to provide a simplified, insulated electrical connector of the solderless type that is suitable for use in applications not requiring a high insulating value for the insulated portion of the connector, but where an insulation support is required for the conductor insulation.
A further object of the invention is to provide an inexpensive, color coded electrical connector and methods of manufacture.
The foregoing objects and advantages of the invention are attained by directly coating the outer metal surface of the connector with an insulating skin having physical and electrical properties equal or superior to those of the separately formed plastic insulating sleeves heretofore commonly employed. According to one form of the invention, this insulating skin may be directly applied to the conductor-gripping ferrule portion of the connector. In another form of the invention, the insulation skin is applied to a metal reinforcing tube that surrounds the ferrule portion of the connector and extends over an adjacent portion of the conductor insulation to provide a suitable conductor insulating support; in this case, the skin preferably covers all interior and exterior surfaces of the reinforcing tube. According to still another and generally preferred form of theinvention, the insulation skin is applied to an intermediate, metal, reinforcing tube which is, in turn, constrained with a separate, more or less conventional, plastic insulating sleeve to enhance the total insulating effect.
Since the metal surface proposed to be coated is not intended to serve any electrical function, the intended conductivity of a connection made according to the present invention is not adversely effected. I have found, on the other hand, that by completely insulating the outer metal surface of the connector with an insulating coating or skin, the connector is protected in an improved manner against possible corrosion, shorting, and arcing.
The direct bond of the insulating skin to the metal ferrule of the connector or to the optional intermediate metal tube effectively prevents the skin from being extruded from under the crimping dies during the crimping operation and from receding by plastic memory upon release of the crimping pressures, thus preventing puncturing and tearing of the insulation skin and the formation of air gaps between the skin and the coated metal surface. In instances where a separate, outer, plastic insulating sleeve is provided to enhance the total insulating effect, such air gaps as may be formed between this outer insulating sleeve and the coated surface beneath the sleeve are entirely lined with insulating material, thereby protecting the connector against corrosion, shorting and arcing caused by foreign matter which may enter the air gaps. Likewise, any air gaps formed beneath the insulation support crimp in the generally preferred form of the invention are entirely lined with insulation material to resist shorting of the connector by a stray strand of wire from another conductor which may he accidentally thrust into these air gaps.
In addition to effecting a marked improvement in the dielectric properties of insulated connectors and provid-' ing a connector which is suitable for use under widely" varying conditions, the provision of an insulating skin in accordance with the invention makes it possible to color code electrical connectors in an inexpensive manner. As is known to those skilled in the art, color coded connectors are frequently required in order that the wire ranges which can be accommodated by the connectors can be quickly and accurately determined. Color coded connectors also are used to advantage in the construction of electrical apparatus, since they provide a convenient means for tracing out the wiring systems. Heretoi'ore it has been the practice to color code terminals by applying suitably colored, outer insulation sleeves of the type described above. However, in those applications which did not necessitate the use of insulated connectors, this common practice of color coding made the connectors unduly expensive.
These and other objects and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings wherein:
FIGURE 1 is an exploded perspective view showing a particular connector construction formed according to the invention, together with the conductor on which the connector is to be crimped.
FIGURE 2 is a perspective view showing the assembled connector of FIG. 1 crimped on the end of the conductor.
FfGURE 3 is a cross-sectional view taken on the line 3-3 of FIG. 2.
FIGURE 4 is a cross-sectional view taken on the line 4--4 of FIG. 1.
Referring to the drawing, the invention is illustrated in connection with a conventional terminal type of connector. However, it is to be understood at the outset that the particular connector shown is not limiting of the invention, but has been chosen only for the purposes of clearly illustrating the principles and preferred practices herein disclosed and indicating to those skilled in the art how the invention may be employed to advantage in this and other connector constructions.
Reference numeral 10 generally designates the terminal connector which is comprised of a conductive metal ferrule 11 and an integral extending tongue 12. As shown in FIGS. 2 and 3, the ferrule 11 is adapted to be forged into mechanical and electrical union with the bared end. 13 of a stranded or solid wire conductor by an electrical crimp 15, with the insulation 14 of the conductor in abut-- ment with the rear end of the ferrule.
The connector It) is primarily insulated by an outer insulating sleeve 24) which surrounds the ferrule portion 11 and, in the illustrated construction, extends beyond the rear end of the ferrule over the conductor insulation 14. It has been found advantageous to support the sleeve 20 by a substantially coextensive, insulation coated metal tube 21 (FIGS. 3 and 4) having its outer end crimped around the conductor insulation by an insulation support crimp 22. In addition to supporting the outer insulating,
sleeve 20, the coated metal tube 21 serves the desirable mechanical functions of supporting the conductor to prevent fiexing and breaking of the conductor wires and preventing the conductor insulation from slipping away from the ferrule.
As is well known to those skilled in the art, the connector may be stamped from a flat sheet of suitably conductive metal, such as copper or a copper alloy, into a shape having oppositely extending ear portions which are thereafter rolled or bent into edge abutment to form the ferrule 11. If desired, the seam of the ferrule may be brazed to prevent the ferrule from opening during the crimping operation. The metal portion of the coated metal tube 21 usually is formed of tin-plated brass and the tube is forced over the ferrule 11 with a press fit.
Preferably, the outer insulating sleeve 20 is formed of nylon because of the desirable properties of this materal referred to above. Other materials may be used, however, such as an extrusion of a plasticized vinyl chloride-vinyl acetate copolymer, without departing from the invention.
In accordance with the present invention, the metal portion of the tube 21 is coated with a tough insulating skin 25. As shown most clearly in FIG. 4, the skin 25 preferably completely envelopes and insulates the metal of the utbe and is permanently adhered directly thereto. Since the metal portion of the tube 21 is employed only to strengthen the insulation sleeve 20 and to support the conductor, the complete insulation of the metal does not detract from the desired conductive characteristics of the connector. In applications which do not require the mechanical functions of the metal portion of the tube 21, the tube may be dispensed with and the insulating skin 25 may, instead, be applied to the outer surface only of the ferrule 11 without effecting the desired conductivity of the connection. If it is also desired to provide this modified connector construction with the outer insulating sleeve 20, the sleeve may be directly mounted over the coated ferrule.
The preferred composition of the skin 25 of the tube 21 depends in part upon the intended use of the connector; however, a synthetic resin of the epoxy resin systems is preferred because of the numerous beneficial properties exhibited by this class of resins. In general, it has been found that the provision of an epoxy skin of one mil to one and one-half mils in thickness not only assures a reliably insulated connector, but greatly extends the range of permissible applications of the connector over prior art connectors insulated only with nylon or vinyl plastic materials. A compared with nylon, for example, which has a relatively low impact strength and a modulus of elasticity of approximately only 100%, and which is subject to cold embrittlement and moisture absorption, suitable epoxy resins generally have a modulus of elasticity as high as 400% or more and high impact, tensile, and fiexural strengths, and are highly resistant to chemical attack. Other significantly important advantages possessed by the epoxy resins include their dimensional stability and abrasion resistance, and the fact that they will successfully withstand severe temperature conditions. Typically, epoxy resins also have a high coefficient of electrical resistance and a dielectric rating of at least 600 ohms per mil thicknose.
The epoxy resin composition used to form the skin 25 may consist generally of a two-part formulation of an unmodified epoxy resin dissolved in a proper solvent which includes a suitable curing agent. The particular epoxy resin system employed may, for example, be either an epoxy resin-phenolic coating system, an epoxy resinurea coating system or an epoxy resin-polyamine coating system. A resin of the last class, which includes the polyamide resins, is preferred because it presents a favorable balance of the beneficial properties discussed above. A typical formulation for an epoxy-amine resin coating system which has been found particularly successful for the purposes herein disclosed consists of an epoxy resin such as EP'ON 1001 (a trademark of Shell Chemical Corp.), a leveling agent such as an alkylated ureaformaldehyde condensation product sold as Beetle 2l6-8 (a trademark of American Cyanamide C0.), a conventional amine curing agent, and a solvent comprised of methyl isobutyl ketone, xylene, and an ethylene glycol monoethyl ether, such as Cellosolve (a trademark of Union Carbide and Carbon Corp). A pigment also may be added for purposes hereinafter discussed.
The above may be combined in the following exemplary The exemplary formulation given above is an air-drying coating system which may be expeditiously applied as a thin coating to the metal tube 21 by spraying or dipcoating in accordance with known surface coating techniques. The epoxy resin coating is then cured either at room temperature or at an elevated temperature of approximately 200 F. to form the tough skin 25. Thereafter, the outer plastic sleeve 20 may be forced over the coated tube 21, and the coated tube and sleeve may together be pressed over the connector ferrule 11 to complete the insulated connector construction.
A property of the epoxy resins which make them especially well adapted to the foregoing process is the tenacity with which these resins bond to the metal. As a result, the insulating skin 25 resists any appreciable amount of extrusion during the crimping of the connector to the bared connector ends 13 and is retained as an insulation coating of substantially uniform thickness over the deformed tube and/or ferrule. The tough epoxy skin also resists cracking and puncturing while, at the same time, yielding during deformation by the crimping dies to permit the effective crimping of the ferrule onto the conductor. Thus, even though an outer insulating sleeve 20 may be punctured or partially destroyed by the crimping operation, the presence of the skin 25 assures a reliably insulated construction.
The adverse effects of the air gaps, which tend to be primarily produced under the insulation supporting crimp 22 in the illustrated embodiment of the invention as the insulation sleeve 20 recedes somewhat toward its original shape after the crimping pressures are relieved, are effectively overcome by the insulating effect of the skin 25. This results not only from the complete insulation of the tube 21, but from the high ohm resistance and dielectric rating of the epoxy resin, which prevent arcing even though the connector is subjected to high applied voltages. The chemical resistance of the epoxy skin also protects the connector from the corrosive action of moisture, air and dirt which may become trapped in the air pockets or gaps beneath the insulation sleeve.
Suitable pigments may be included in the epoxy resin composition in order to improve the appearance of the formed connectors and, more importantly, to color code the connectors in accordance with the range of wire sizes to which each connector may be applied. This is of particular advantage in those applications where the full insulating effect afforded by the sleeve 20 is not required. In such instances, the suitably colored, epoxy skin 25 is applied directly to the ferrule 11 to provide an inexpensive, color coded connector.
Obviously many modifications, variations, and applications of the invention will be apparent to those skilled in the art in light of the above teachings. It is to be understood therefore that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically disclosed.
What is claimed is:
1. In an insulated electrical connector of the type having a malleable metal ferrule portion adapted to be crimpcd on a conductor and an outer electrical insulating sleeve surrounding said ferrule portion, said outer sleeve being held on said connector with a gripping, mechanical fit, but being otherwise free of connection therewith, the improvement comprising an intermediate insulating coating bonded to the outer metal surface of said connector beneath said outer sleeve, said coating consisting essentially of an epoxy resin.
2. The connector as claimed in claim 1 wherein said coating of epoxy resin is approximately one mil to one and one-half mil in thickness.
3. An electrical connector comprising a malleable metal ferrule adapted to crimpingly receive a wire conductor within a specified WlI6 size range, and an adherent coating of epoxy resin covering the outer surface of said 20 ferrule, said coating being distinctively colored to designate the Wire range which may be accommodated by said ferrule.
4. An insulated electrical connector comprising a malleable metal ferrule portion adapted to be crimped on an electrical conductor, a metal sleeve telescoped over said ferrule portion and being at least coextensive therewith in an axial direction, an adherent coating of electrical (insulating material bonded to and covering the outer surfaces of said metal sleeve, said coating consisting essentially of a synthetic epoxy resin approximately one References Citeziin the file of this patent UNITED STATES PATENTS 2,654,873 Swengel Oct. 6, 1953