US2809365A - Electrical connector - Google Patents

Description

OC- 8, 1957 w. F. BRosKr-z 2,809,365

ELECTRICAL CONNECTOR Filed Sept. '7, 1954 T1514- /4a /0 1 5' V424 f T 4d iii INVENTOR: MMM E Pas/ff.

BY 24%, Mflf ATTORNE 2 United States Patent O ELECTRICAL CNNECTOR F. Broske, Camp Hill, Pa., assigner to Ali/[P Incorporated, Harrisburg, Fa.

Application September 7, 1954, Serial No. 454,257

4 Claims. (cl. 339-276) This invention relates to insulated electrical elements that are adapted to be crimped to metallic conductors. More particularly, this invention relates to an improved method of securing plastic insulation to a metal part, for example the ferrule of a connector or terminal, to provide a novel insulated element having superior characteristics.

For many years now there has been a considerable use of metallic connectors and terminals that are adapted to be crimped, i. e. pressure formed onto one or more electrical conductors, as by means of hand or power-operated crimping tools. These so-called solderless connectors typically include a fer-rule portion into which the conductor is inserted, and which is deformable inwardly by the application of crimping pressure so as to firmly engage the conductor and tol be cold-forged thereto. Such connectors, furthermore, provide an excellent and durable electrical connection of stable, low contact resistance, generally superior in most respects to a comparable soldered connection.

Connectors of this type may be formed in various ways, for example from extruded tube, or by drawing a seamless ferrule from an initially at strip of copper or other malleablermetal, or by stamping out a fiat blank and rolling at least a part thereof intov tubular shape with or without brazing or other reinforcement of its seam. Advantageously, the connector is insulated with a rigid plastic so tough that the insulated ferrule portion can be cold-forged underY heavyv pressure onto one or more electrical conductors without destroying or otherwise deteriorating the eectiveness of the insulation.

During a typical crimping operation, severe stresses are necessarily applied to both the ferrule portion and the conductor therein, inorder to flow the connector and conductor together to produce the desired intimate engagement therebetween. It has become accepted as the best practice to cover theferrule portion with a layer of rigid plastic insulating material. See the Watts Patent No. 2,410,321 and myv Patent No. 2,478,082. Additionally, asY settforth in the patent of R. C. Swengal, No. 2,654,873, improved results are obtained by securing this layer of insulation by an adhesive bond firmly to the metal ferrule.

Bonding of the plastic to the metal ferrule is particulariy diicult when using nylon as the insulating plastic. Nylon displays extraordinary resistance to solvents and to relatively high temperatures but has proven diliicult to bond to the metal without impairing its properties for crimping or use under extreme conditions. It has been shown, as disclosed in U. S. patent application Serial Number 418,919, ied by T. C. Freedom on March 26, 1954, that nylon can satisfactorily be bonded to metal by fusing a very thin layer of the nylon, t'ne thinner the better.

It is an object of the present invention to provide an improved arrangement for firmly securing nylon insulation to such a metal part. in a preferred embodiment of the invention disclosed herein, a series of annular serrations are formed on the outer wire barrel surfaces of a tubular metal connector, a tight-tting nylon jacket is next positionjedoverY the connector, and the assembly is then exme j ICC posed for a short time to the field of an alternating current induction coil. In the resulting insulated connector, it is found that the plastic jacket tightly embraces and rmly grips the metal ferrule portion, so that this jacket can transmit crimping pressure to deform the ferrule against a conductive wire without cracking or otherwise interfering with the electrical or mechanical effectiveness of the insulation. Other aspects, objects and advantages of the invention will be partly apparent from, or pointed out in, the following specification considered together with the accompanying drawings, in which:

Figure 1 is a perspective View of a connector constructed in accordance with the present invention, and which is insulated by a clear nylon plastic;

Figure 2 is a cross-section taken along line 2 2 of the connector of Figure 1;

Figure 3 is a longitudinal section taken along line 3-3 of the connector of Figure 1;

Figure 4 is a fragmentary detail section showing an alternative form of serration;

Figure 5 is a flow diagram in block form outlining process steps in the manufacture of a connector in accordance with the present invention;

Figure 6 shows a magnetic induction heating coil arrangement, iu schematic form; and

Figures 7 and 8 show modiiied connector constructions.

One form of an insulated connector adapted for crimping onto and connecting together two or more wires or other electrical conductors is shown in Figure 1. This connector includes two integral ferrule portions 1t) and 12 which together form an extended hollow tube. Such a connector is often referred to as a butt connector, since` in its intended use bared wire conductors (not shown) are inserted into the opposite openings of the barrel portions and are secured in end-to-end (i. e. butt) relation in the connector. Both of the ferrule portions are crimped to form a solid connection between the wires.

The tubes 1i) and 12 are typically formed of copper, brass, aluminum, iron, etc.; if formed of copper, the tube is frequently coated with a thin film of corrosion-resistant material (i. e. tinned), to which it is especially diicult to bond such insulating material as nylon. The exterior of the connector comprises a plastic jacket 14 rmly secured to and surrounding the entire metal tube. This jacket is advantageously formed of nylon but in a broader aspect of the invention may be other substantially rigid plastic advantageously shghtly plasticized, e. g. Vinyl chloride internally plasticized with 2-5% vinyl acetate copolymerized therewith and/or a small percentage of ex,- ternal plasticizer. In general, this plastic is a rigid, tough, very high tensile strength and high melting point plastic, chemically stable and resistant to solvents.

In the approximate longitudinal center of the hollow metal tube formed by the barrel portions 10 and 12, a segment of the tube has been cut away to provide an opening 16. This opening permits a visual inspection of the interior of the tube, through the clear plastic jacket 14, so that it can be determined when the bared conductive wires inserted within the barrel portions 1i) and 12 extend suiiiciently deep within the tube to produce a solidly crimped connection.

Serrations generally indicated at 13 and 25) are formed in the outer surfaces of the barrel portions 10 and 12 througnout substantially the entire area which is to be subjected to c ning pressure. As shown, these serrations are distributed over the entire length. The serrations used in this embodiment are V-shaped, for example with an included angle of 60 between the opposite side surfaces thereof. As shown in the fragmentary section of Figure 4, the barrel portion 16a may alternatively be provided with flat-bottomed serrations 18a, preferably comprising keystone-shaped or truncated bottom and the metal.

barrel andthe conductor to which it is Vtorbe crimped.

Other alternativeconiigurations Vfor the serrations-uhave also been found highly satisfactory e. g. Vround bottom indents; a series of small holes bored through the metal connector `yall (as shown in Figure 7); and knurled serrations (as shown in Figure 8). Y

Such serrations formed in the outer surface of lthe wire barrels have been found to provide remarkable strength in securing a nylon jacket in place when the connector is constructed in a manner to be explained inmore detail hereinbelow;rand the resulting connector is adapted to be used and to give superior results even under a Wide variety VofV adverse environmental conditions. The serrations may be formed in any one of a variety of ways, for example by machining, and especially by stamping the barrel portions with a coining die before they have been rolled into tubular shape.

Figures 2 and 3 show the connector in section along lines 2 2 and 3 3, respectively, of Figure l. The connector may with advantage have a brazed seam 22 (see Figure 2), which runs the length of the interior Wire barrels Vlil and 12. Y

For the purposes of further illustrating the invention yand to point out the nature and principles thereof, certain specific examples of preferred structures and manufacturing processes are described herein and various alternatives suggested. These examples, of course, are not to be taken as exhaustive and limiting the scope of the invention, but rather are to be considered as an aid to others skilled in the art so that they may be able to adapt the invention to such forms as may be best suited for a particular application. Y

Referring now to Figure 5, which is a block diagram of a manufacturing process for producing a nylon-insulated hollow tubular connector of the type described above, a blank of pure electrical copper (oxygen-free) or brass, etc., is stamped with a coining die to form parallel groove serrations running transversely of the ferrule portions, such grooves being V-shaped in section (step 1). The stamped blank is then rolled into tubular shape (step 2), and, if desired, the butt seam of the resulting ferrule may be brazed. Y

The metal connector so formed is then cleaned and .the lands between the serration grooves on the outer thoroughly dried (step 3); alternatively, this step may Y be carried out while the connector is in at shape, i. e. prior to step 2, but in either event the connector should be suitably free of foreign matter prior to the application of the insulating jacket. The cleaning operation ma1 for example, consist of etching the metal surfaces with nitric or sulphuric acid, or electropolishing the surfaces by reverse plating in a phosphoric acid bath, and rinsing with clear water. A nitric acid bath has been found to give superior results in many cases, since it not only leaves the surface substantially free. from harmful impurities, but also tends somewhat to roughen the metal surface a manner advantageous to the further processing of the connector. After the cleaning operation, the metal connector is thoroughly dried, for example by exposing it to a stream of dry air.

A rigid nylon tube, for example formed of FM 3003 Du Pont nylon preformed as extruded tubing, was then forced over the copper connector, and cut to leave a portionextending somewhat beyond the ferrule at each end thereof (step 4). The inner diameter of the nylon tube should be slightly smaller than the outer diameter of the ferrule, to give a tight lit between the nylon jacket This assures that the jacket and the metal ferrule do not slide apart during the subsequent operations, and also insures an ultimately firm locking engagement between the two.

Although it is not essential to establishing the desired iirm gripping lock between the nylon and the metal tube, it may be desirable, prior to fitting the nylon tube over the ferrule, to coat the outer surfaces of the ferrule with a relatively thin hlm of cement chosen to have the best possible adhesion to the metal and the nylon. A preferred cement for this purpose is a partially polymerized resorcinol-formaldehyde condensation resin dissolved in aqueous alcohol. If used, this lacquer is preferably applied in such a manner that, after drying, there remains a coating of approximately l milligram per square centimeter.

After application of the adhesive, excess lacquer may be removed by centrifuging, and the coated surface may be air-dried and/0r baked, e. g. by placing the ferrule in an oven at 320 F. for a period of about 20 minutes, in order to completely dry and partly cure the resin. When such a coating is used, care must be taken in selecting theV nylon jacket inner diameter, and in applying the jacket, to assure that it gives a tight t but does not remove the resin layer when it is forced over the coated ferrule.

. When the nylon jacket is securely in place on the ferrule, heat is applied ("step 5) directly to the copper wall of the tube. This heat is advantageously applied suddenly, and for only a short period of time (e. g. for less than a minute), and should be sufficiently intense to momentarily raise the temperature of the copper above the melting point of the nylon (e. g. to about 500 F.) The duration and intensity of the applied heat is adjustedrso that the heat energy transferred to the nylon jacket raises the temperature of only a very thin band of the nylon adjacent the copper wall (i. e. the first thousandth of an inch or so radially) just barely to, or slightly above, its melting point. It has been found that the serrations advantageously tend to reduce the rate of heat transfer from the metal to the nylon, due to the discontinuous contact between the two materials; and that this elect minimizes any tendency of the nylon to crack when crimped, particularly at low temperatures.

During the period of heat transfer, it is found that copper wall will press slightly into the inner wall of the nylon, and the softened nylon immediately above the heated metal will be forced into the grooves and tight against their sloping walls, so as to achieve a firm locking engagement. By properly adjusting the amount the nylon is stretched over the ferrule and the intensity and duration of the heat, a precise portion of the nylon can be caused to flow into the grooves and, advantageously, to fuse directly tothe copper wall, both in the grooves vand on the land surfaces.

Immediately after suicient heat has been transferred to properly soften the thin inner layer of nylon, without so alfecting the remainder of the insulation jacket, the heating is stopped and, preferably, the assembly is chilled (step 6), for example, by immersion in cold water. The softened inner lm of nylon is promptly resolidied, resulting in a positive gripping engagement between the insulation jacket and the wire barrel Vportions of the connector. It has been found desirable to use nylon jackets slightly thicker (e. g. several thousandths of anV inch) than would normally be required for the voltage breakdown strength speciiied.

Although there are various ways of applying intense heat suddenly to the copper walls, it has been found that this operation is advantageously performed by passing the connector assemblies one or more at a time through the magnetic eld of a high frequency alternating current induction coil, such as shown schematically in Figure 6. For this purpose, the connector assembly 28 may Vbe placed on an endless conveyor belt 30 which is supported by and frictionally engaged with two Wheels 32 and 34, one of which is power driven by a motor 36 so as to produce continuous and even motion of the conveyor belt 30 in the direction of the arrow. Surrounding a part of the upper portion of the belt 38 are a number of turns of wire forming an induction coil 3S, which is connected by two leads 4i) and 42 to a source of A. C. power 44.

The connector assembly 28 is drawn by the conveyor belt 30 into the interior of the induction coil 38, and part of the magnetic field energy therein is converted to heat in the copper Wire barrels of the connector by the resistivity of the copper. The speed of the conveyor belt 30, which determines the duration of exposure to the magnetic field, and the intensity of the magnetic field should be adjusted such that the heat induced in the copper is sniiicient to cause softening of a small layer of the nylon surface immediately adjacent the copper, and preferably just suicient to cause a small amount of fusion between a thin lm of this nylon layer and the copper.

An exposure duration of several seconds (e. g. about 3 seconds) has been found to give satisfactory results with commercially available induction heating apparatus having the following7 characteristics: a power rating of 12.5 kilowatts, a frequency of 1.4 megacycles, and a 13 turn induction coil approximately three inches long with an inside diameter of about 1.25 inches. To insure that the heat transfer into the nylon goes no farther than required, means advantageously are provided for chilling the connector assemblies immediately after they have passed through the induction heating coil, for example, as shown in Figure 6, by providing a tank of cold water 48 in the drop path of the connectors.

It has been found that the gripping engagement formed between the nylon and the copper of an insulated connector, such as described hereinabove, is especially strong and well suited to hold the insulation in place even when subjected to severe crimping pressures under eX- tremes of adverse environmental conditions. The spaced serrations of the outer surfaces of the ferrules cooperate with the softened inner layer of nylon which is forced into the serrations to form strong mechanical keys. The holding power of the keys mating with the serrations combines with the holding power resulting from the fusion between the nylon and copper to maintain the insulation in place during handling and crimping. During the crimping these keys serve to control extrusion of the insulating plastic due to pressure of the crimping dies; and also to assure that the insulation is maintained electrically effective even in the area of maximum pressure. The jacket is sufliciently strong to resist crushing, circumferential and axial displacement even when forces are applied to compressively forge the connector onto one or more conductors.

It should be understood that the specic examples given hereinabove are illustrative of preferred embodiments of the invention, and that other arrangements within the scope of the invention are feasible.

I claim:

1. An insulated electrical connector of the type which is adapted to be crimped under heavy pressure onto a conductive wire, comprising, in combination, a metal ferrule adapted to receive said wire for crimping thereto, serrations on the outer surface of said ferrule and a malleable nylon insulating jacket tightly fitting over said metal ferrule and bonded to the outer surface of said ferrule by a fusion bond comprising a very thin integral layer of said nylon at the interface of the ferrule and the nylon, whereby the nylon jacket is maintained in place on the ferrule by the fusion bond as well as the mating of the inner surface of the nylon jacket with the serrations on the ferrule.

2. An insulated electrical connector of the type which is adapted to be crimped under heavy pressure onto a conductive wire, comprising, in combination, a metal ferrule adapted to receive said wire for crimping thereto, a plurality of V-shaped annular serrations on the outer surface of said ferrule, and a malleable nylon-like insulating jacket tightly fitting over said metal ferrule and bonded to the outer surface of said ferrule by a fusion bond comprising a very thin integral layer of said nylon-like jacket.

3. The method of bonding a deformable plastic sleeve to an inner conductive metal ferrule to form an assembly capable of being `crimped to an electrical conductor including the steps of (1) forming a plurality of notch-like configurations on the outer surface of the ferrule, (2) positioning the insulating sleeve over the metal ferrule in snug engagement therewith, (3) raising the temperature of the metal ferrule until the surface of the plastic sleeve in contact with the metal ferrule adheres to the metal ferrule, and (4) cooling the assembly, whereby the plastic sleeve becomes bonded to the metal ferrule.

4. An electrical connector capable of being cold forged onto a conductor including a metallic ferrule capable of receiving a conductor and having a plurality of indentations on the outer surface and a deformable plastic insulating sleeve surrounding the ferrule with the inside surface of the insulating sleeve permanently bonded to the outside surface of thev ferrule by adhesion or the plastic sleeve directly to the entire outer surface of the metal ferrule, whereby the plastic projects into the indentations and `adheres to the metal forming the indentations.

References Cited in the le of this patent UNITED STATES PATENTS 1,043,179 Weeks Nov. 5, 1912 1,650,737 Quinn Nov. 29, 1927 2,173,668 Smith Sept. 19, 1939 2,278,424 Campbell Apr. 7, 1942 2,288,918 Parker July 7, 1942 2,379,567 Buchanan July 3, 1945 2,385,792 Carlson Oct. 2, 1945 2,410,321 Watts Oct. 29, 1946 2,581,718 Schaffert Ian. 8, 1952 2,598,629 Whyte May 27, 1952 2,617,752 Van Hauteville Nov. 11, 1952 2,654,873 Swengel Oct. 6, 1953 2,721,986 Badeau Oct. 25, 1955 FOREIGN PATENTS 652,163 Germany Oct. 26, 1937 OTHER REFERENCES Plas-

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