US2974400A - Method of making an insulated electrical connector - Google Patents

Description

March 14, 1961 F. J. sowA 2,974,400

METHOD OF MAKING AN INSULATED ELECTRICAL CONNECTOR Filed March 11, 1952 2 Sheets-Sheet 1 INVENTOR March 14, 1961 F. J. sowA 2,974,400

METHOD OF MAKING AN INSULATED ELECTRICAL CONNECTOR Filed March 11, 1952 2 Sheets-Sheet 2 INVENTOR flPJ/VK 77 Son A United States METHOD OF MAKING AN INSULATED ELECTRICAL CONNECTOR This invention relates to a method of making electrical connectors and connections and more particularly those having insulated ferrules. This application is a continuation-in-part of my co-pending application Serial No. 560,785, filed October 28, 1944, and now' abandoned.

It is an object of this invention to provide an effective method of making an inexpensive connector and connection having a ferrule portion thereof insulated against peripheral contacts. A particular object of the invention is to provide a method of making an electrical connector having a metallic ferrule and an insulating sleeve thereon capable of crimping onto a wire by pressure of dies applied to the exterior of the insulating sleeve to form a mechanically secure and electrically good connection with the wire or other conductor onto which the terminal is applied.

Although in this specification and the accompanying drawings I am showing and describing a particular example and various modifications thereof, it should be understood that these are not intended to be exhaustive or limiting of the invention, but on the contrary are chosen and presented for purposes of illustration and in order to explain the principles of the invention and the practical employment of those principles in applying the invention to practical use, and thus to so fully instruct others skilled in this art that they will be enabled readily to modify and to select and substitute alternatives, each as may be best suited to the particular conditions of any given application or use.

In the accompanying drawings,

Figure 1 is a view in axial Section of a terminal connector made by a method embodying the invention;

Figure 2 is a cross-sectional view of the same terminal connector taken on line 2--2 of Figure 1;

Figure 3 is a view in axial section of a similar connector crimped onto an insulated wire;

Figure 4 is a view partly in axial section and partly in side elevation of another terminal connector made by the invention;

Figure 5 is an isometric view of the connector of Figure 1 after its application to a wire and crimping in the same manner as the ferrule shown in Fig. 3; and

Figure 6 is an isometric view showing the connector of Figure 1 in process of being crimped to the form shown in Figure 5.

Referring to these drawings, the reference character 10 identifies an electrical terminal connector of conventional form. This may be made, for example, from fiat strip of annealed high conductivity pure copper stamped out to form the tongue portion as shown with the hole 11 for reception of a binding post, and a substantially rectangular portion 12 which is rolled up as shown to atent C form a ferrule portion of cylindrical form, bringing the p, seamless sleeve 15 is formed, e.g., by extrusion of I plastic insulating material of the type which can be expanded under conditions such that it retains so-called elastic memory or fplastic memory, i.e., tends more or less slowly to return to a form and dimensions approaching that from which it has been expanded or deformed. Such return is generally delayed or inhibited by cold and hastened by heat. Among such plastics known to the trade, I have found especially suitable the vinyl polymers, especially plasticized vinyl chloride, vinyl chlorideacetate copolymer and vinyl chloride-vinylidene chloride copolymer, etc.

I have found particularly suitable for such use an extruded tubing manufactured from a plasticized copolymer of vinyl chloride and vinyl acetate, such as is sold commercially for insulating wiring connections, e.g. under the trademark Irv-o-lite;

Such material for best results is of the commercially available grade which, at ordinary temperature and when .dry and relaxed, is tough and resistant to deformation, although it is capable of molding at higher temperatures; moreover, it can be stretched mechanically or otherwise deformed without heat so as to retain a tendency to return to the form which it had before such expansion or deformation. This latter property I take advantage of, according to my present invention, primarily to facilitate the assembly of the parts and in some cases to give a constricting force on the ferrule which both holds the plastic sleeve in place and later, after performance of the present method is completed, may press the ferrule against the wire, counteracting any tendency for the ferrule 'to spring back from its contact. The property of memory (i.e., the ability to retain substantially a deformation imposed on it by a crimping die at a temperature below that at which the plastic would be molded without tendency to recover) is increased as the proportion of plasticizer is reduced, down to the point where the plastic becomes too brittle or too resistant to accept the deformation without fracture at the low temperature, and this, as will appear below, is important in the practical use of the connectors made according to the invention.

Referring once more to Figure 1, it will be noticed that the interior diameter of the free end of the sleeve 15 is smaller than the exterior diameter of the ferrule 12. This relationship is purposely chosen so that after the sleeve has been expanded and fitted over the ferrule the elastic recovery will grip the ferrule with a relatively high constrictive pressure with the consequences: first, that the seam 13, where the ends of the ferrule portion are abutted together, is sealed and closed against the entry of corrosive influences; secondly, that the ends of the sleeve are drawn in over the end of the ferrule giving more complete insulation and holding the sleeve securely in its desired longitudinal position; and thirdly, that the ferrule is held against springing open under the influence of the crimping tool. The projecting portion 16 may be left as shown or stretched to a larger diameter depending upon the thickness of wire insulation which must be received therein.

Before this small sleeve can be fitted onto the ferrule, it is, of course, necessary that it be in sbme way er!- larged. Broadly, according to my invention this may be done by swelling in solvents, as set forth and claimed in my copendin-g application Serial- No. 254,516 filed October 1, 1951, now abandoned, or by stretching the tube mechanically, or by extruding the tubing to a diameter larger than the ferrule 13 but with enough vaporizable plasticizer so that its evaporation will cause the tubing to shrink down onto the ferrule.

It is ordinarily an advantage to have more plasticizer present during extrusion of the plastic tubing tram which the sleeve is cut than during the crimping of the ferrule on which the sleeve is mounted. Th1s rs done, according to my invention, by baking the sleeves or subjecting them to vacuum or other controlled treatment for evaporating a part of the plasticizer after their application to the ferrules.

As one example of my invention, I have used an extruded tubing sold commercially under the trademark Irv-o-lite. This tubing is applied onto the copper connector ferrules by mechanical stretching and is baked in a closed oven for one-half to one hour at temperatures of 375 F. to 390 F. Air circulation in the oven is desirable to maintain conditions substantially uniform in various parts of the oven so that the connectors in various parts of the oven will receive substantially the same treatment.

In this treatment I remove enough of the plasticizer to avoid excessive extrusion or shearing under the crimping dies, but not so much as to render brittle or to prevent cold molding during crimping. If the sleeve becomes brittle, too much of the plasticizer has been removed.

The sleeve 15, when thus baked, shrinks firmly and strongly onto the ferrule, but retains toughness and suflicient pliability so that subsequently when the terminal is crimped onto a conductor by an ordinary crimping tool, the pressure of the crimping die is transmitted evenly through the plastic to the metal. By applying the sleeves onto the ferrule-forming part before the baking, the metal seals the inside surface of the sleeve against loss of plasticizer. Since the plasticizer escapes .by diffusion to and beyond its outer surfaces, the proportion of plasticizer increases from the outer to the inner surface and this gives better crimping characteristics. To the extent that the plastic is extruded, or even .if it should be punctured, by the crimping die during this operation, there is a tendency to close the puncture .by elastic recovery. One may take immediate advantage of this tendency by heating the crimped connection, e.g., in the range 100-350 F.

As another example, tubing may be extruded from the following formula:

100 parts Exon 402 resin, a vinyl chloride vinylidene chloride copolymer sold commercially by Firestone Tire & Rubber Company;

16.15 parts Atomite, a finely ground calcium carbonate sold by Thompson Weinman- & Company;

8.07 parts Tribase, a stabilizer sold by John T. Lewis Bros. Company, believed to be tribasic lead sulphate, a product of National Lead Company;

.8 part DS 207, a lead stearate used as stabilizer and lubricant;

16.15 parts Paraplex G50, an alkyd type resin plasticizer of low volatility made by Rohm & Haas Com- 19.35 dibutyl phthalate;

.8 high boiling mineral oil lubricant; .25 chrome yellow medium.

This composition after mixing in a plastic mill is extruded to an inside diameter of about .15 inch and wall thickness of .027 inch, cut into suitable lengths, expanded and applied to a ferrule .175 inch outside diameter, and heated in an oven to a temperature about 325 for four and a half hours.

' During the baking, the insulation is hardened and becomes substantially rigid and is shrunk securely onto the ferrule. The resulting insulation on the connector has compressive strength to stand full crimping pressure required to forge a copper ferrule together with a copper wire into a substantially solid cross section. The insulation after this baking is tough so that it is deformed to retain the impress of the crimping die and yet transmit crimping pressure without excessive extrusion from under the die and without brittleness. The

plastic has high softening point so that it can be used at temperatures where ordinary insulation wire can be used.

As another example:

parts Geon 101 EP, a hard polyvinyl chloride resin sold by B. F. Goodrich Company;

16 parts Paraplex G25;

25 parts dibutyl phthalate;

10 parts Calcene T, a fine calcium carbonate pigment manufactured and sold by Pittsburgh Plate Glass Company, Columbia Chemical Division;

3 parts Silene EF, a calcium silicate pigment manufactured and sold by Pittsburgh Plate Glass Company;

3 parts ZMXA, a stabilizer believed to be barium recinoleate sold by Decy Products Company;

3.5 Tr-ibase;

.5 Acrawax C, a synthetic wax lubricant sold by Glyco Products Company;

1.0 part calcium stearate, a lubricant and stabilizer;

.20 part Titanox AMD, a titanium oxide pigment containing a magnesium silicate sold by Titanium Pigment Corporation;

.22 Chrome Yellow Medium coloring agent sold by Calco Chemical Division of American Cyanamid Company;

.001 part Monastral Green 486 D, a coloring agent sold by Du Pont Company.

This formula may be treated in the same manner as given above for the preceding example and shows a loss of weight from 2 to 3% during the milling operation and approximately 11% in the baking operation, which is believed to be almost entirely the dibutyl phthalate plasticizer.

The extent of plasticizing, degree of polymerization and, in general, the nature of the plastic composition chosen for the insulating sleeve, should be such that its resistance to plastic flow is of the same order as that of the soft copper of which the ferrule is made, i.e., the plastic of the sleeve on the ferrule should flow to some extent under the crimping die, when the metal flows by force and runs therethrough, but not so readily as to squeeze out from under the crimping die and expose the metal during a crimping operation which forces the wire and ferrule into solid cross-section but does not excessively weaken the metal by extrusion from under the die. Such metal flow is essential to a high quality insulated electrical connection.

If the plastic did not flow at all, it would so far distribute the pressure of the die as to impair or prevent the localized action on the metal ferrule required for a good connection; and on the other hand if the insulating material flows too readily or fails by puncture before any plastic flow, the squeezing out of the material from under the die will expose the metal or excessively reduce the thickness of insulation and thus impair its insulating function. Even if the plastic is pressed excessively thin, however, advantage may be taken of the preent invention if the plastic is one with sufficient elastic memory so that it will creep back into the crimped areas, with or without heating, as mentioned above, and thus restore a suflicient thickness of insulation. It is important that this return should be a delayed elastic (memory) action rather than a prompt elastic recovery, so that the exterior of the insulated connection will retain until final inspection the impress of the die, whereby the inspector can determine whether the correct tool was used for the crimping and whether a proper degree of crimping pressure was applied.

I have found it advantageous, under ordinary production conditions, to mechanically stretch the sleeves before application. After this stretch, the lower the temperature at which the sleeve is maintained when released, the slower will be its recovery, whereas if the temperature is increased the recovery is accelerated. By such heating, the sleeve may be brought down into gripping relation within a very brief period. By this means sleeves which are normally smaller than the ferrule are nevertheless readily applied over the ferrule and then come down into strongly gripping relation thereon and with their ends drawn down tightly over the ends of the ferrule as shown in Figure 1. The sleeves in this condition should be tough in their resistance to deformation and yet substantially plastic so that they lend themselves well to the crimping operation and advantageously have, as described above, some tendency to elastic recovery after deformation which improves any condition of excessive extrusion or puncturing if such should occur during the crimping operation. Ordinarily these properties will be developed in the plastic by removal of some plasticizer, advantageously by baking as described above.

Although I have referred above specifically to copper as the most advantageous connector metal, I may use the other metal ordinarily used for malleable electrical connectors such as soft brass, aluminum, iron and soft steel. Such metals are of relatively high conductivity i.e. having resistivity of the order of 10- ohm-centimeters at C., pure annealed copper being about l.7 10-- and pure iron about 9 l0- with soft steel a little higher and brass and bronze about 6.5-8 10- and aluminum 2.8 10'- as distinguished from such metals as lead, tin, cadmium and platinum with resistivities of the order of 10'- and bismuth with resistivity and medium high tensile strength i.e., of the order of 340x10 lbs./in. as distinguished from low tensile metals such as lead and tin and the high tensile metals such as alloy steels, nickel tantalum, tungsten, etc.

The plastics to be used are, as indicated above, those which are good insulators, are tough in resistance-to deformation characterized by plastic flow with resistance about the same order as that of copper, and yet are sufficiently pliable and stretchable for use in the manner described, exhibiting delayed elastic response releasable by raising the temperature. The plastic flow with such substantial resistance results in a crimped connection which will bear the impress of the crimping die so that external inspection of the plastic will reveal whether the proper die has been used and whether sufficient pressure has been exerted, to satisfactorily forge the metal of the connector onto the wire in a good electrical connection.

Although it is not essential in all cases that the plastic be heat-cured after it is applied to a metal backing, experience has shown that that gives important advantage in greater resistance to puncture and to voltage breakdown after crimping. This I believe to be due, at least in part, to a gradation in the proportion of residual plasticizer from the outer surface of the surface which is covered with the metal-i.e., since the plasticizer leaves from the exposed surface. It may be due in some part also to a further polymerization in the plastic during the baking operation.

Although, in Figures 1 and 2, I have shown the insulating sleeve applied to the terminal before crimping,

onto the wire, it may in some cases be more convenient, and it is entirely feasible in accordance with my invention, to apply the insulating sleeve at the same time that the terminal is applied to the wire or after the terminal is applied. Forexample, a terminal such as shown, in Figure 3, may be applied to the bared end 20 of an insulated electrical conductor 21 and the ferrule of the terminal crimped to produce a secure electrical connection.

A sleeve a is made of an insulating plastic and formed with bore substantially less than the cross-ectional area of the crimped connection. Thereafter the sleeve is stretched with or without heat, but below the temperature at which elastic memory would be lost and is chilled if necessary to a temperature at which recovery is slow. The sleeve is then slipped over the wire 21 and the connector 12a crimped onto the wire. Then the sleeve is pulled back over the ferrule 12, overlapping slightly on the end toward the terminal portion 11 and overlapping substantially at the opposite end so as to engage and secure the insulated portion of the wire 21. With the sleeve thus in place it is warmed to a temperature at which it tends to recover its original diameter and thus is shrunk into secure gripping relation both to the ferrule 12 and the wire 21. Conveniently, the sleeve 15a is threaded cold onto the wire before the terminal is applied and is slid beyond the ferrule 12a on themsulated wire 21 until the ferrule has been crimped onto the bared end of the conductor 20. The sleeve 15a is then slid back along the wire to the position shown in Figure 3, where it is heated to shrink it onto the wire and terminal; but if the terminal portion 10a is not too large, or is omitted, it is also feasible to stretch the sleeve so that it can be slipped over the terminal from its outer end after application.

Because of the strength with which the shrunk tube of plastic insulation grips the metal parts which lie'within it and the partial deformation which causes it to engage them with a mechanical interlock, my invention makes possible a number of simplifications in the design of terminals and like articles. One example of this is shown in Figure 4 wherein a terminal of utmost simplicity is made by merely bending a copper tongue 10b of suitable shape to a right angle and either forming thereon or applying thereto a spear 25. This spear may be of the same or a similar metal as the tongue 10b, advantageously integral therewith, or it may be of a brazing or soldering alloy as more fully described and claimed in the copending application of Robert C. Swengel, Serial No. 517,779, filed January 11, 1944, now abandoned.

An insulating sleeve 15b expanded and shrunk into place, in accordance with the present invention, grips and molds itself to this terminal so as to form a rigid plastic ferrule securely interlocked therewith for gripping'and suporting theend of the insulated wire 21. As suggested above, the sleeve 15b may be applied to .the terminal portion 11b during the manufacture of the terminal and shrunk thereon. The wire 21 may be subsequently inserted into the end of the shrunk ferrule and the latter then engaged with the wire, if desired, by a crimping or hot molding operation; or the ferrule portion 15b may be stretched to a larger bore after the terminal is thus assembled, and held at a temperature at which the stretch is retained with elastic memory. When the wire has been inserted, the temperature is raised sufliciently to shrink the tube and grip the wire; or the terminal portion can be applied to the end of the insulated wire and the sleeve 15b then slipped over the end of the wire and the adjacent end of the terminal and allowed to shrink into place; engaging securely both the end of the terminal and the end of the wire and binding them securely together in conducting relation and sealing the connection against corrosive influences. When the spear 25 is of solder or braze, the heating by which it is fused onto the wire serves also for heating and final shrinking of the sleeve 15b.

The expansion of the tubes can be done hydraulically by coupling one end to a fluid pres'suresource and-closing the other, or advantageously coupling it to a pressure regulating valve or other means for permitting flow under pressure. The tube is first filled with water at a tempera: ture and pressure at which the plastic has the desired flow properties and is expanded thereby to the required diameter, and then is chilled, e.g. by a flow of cold water therethrough.

I claim:

1. The method of making an insulated electrical connection which comprises forming a tube of a tough, flexible insulating vinyl plastic, inserting a malleable metal contact portion of an electrical connector into said tube and shrinking the plastic so that it engages the inserted portion of the connector with constrictive force, and compressing together in a limited area said contact portion of the connector and an electrical conductor within said .tube, with-extrusion of metal from the area of compression.

2. The method as defined in claim 1 in which the eonnector is applied to a wire in pressure contact therewith and the plastic tube is applied over the contact area, whereby its constrictive force maintains pressure contact between the conductor and said contact area.

3. The method as defined in claim 1 in which the plastic tube is applied to an open ferrule of the connector, an electrical conductor is inserted into the ferrule, and the tube and ferrule are crimped together and onto the conductor by pressure applied externally to the tube and through it to the ferrule, while said ferrule is under said constrictive force, thereby re-forming by plastic fiow both the tube and, theferrule, said pressure being increased until such flow occurs and being relieved before puncture of the tube or serious weakening of the ferrule occurs. 4. Themethod of making an insulating electrical connector having a malleable soft metal ferrule insulated with a plastic insulating material of the type which is tough in its resistance to deformation and yet substantially plastic so. as to evenly transmit therethrough to the metal ferrule localized presusre of crimping dies, with flow of metal from under the crimping dies, but avoid such excessive flow in itself as would expose the metal ferrule during crimping and thus impair the insulating function, which comprises forming from a composition of said plastic with excess plasticizer of said plastic a tubular piece of lesser'internal diameter than the external diameter of said ferrule, expanding the tubular piece, assembling the tubular piece over the ferrule, thereafter removing part of the plasticizer from the outer surface of said piece while its inner surface is pressed against the ferrule, and thereby increasing the tendency of the tubular piece tightly to grip the ferrule.

5. The method of making an insulating electrical connector having a malleable soft metal ferrule insulated with a plastic insulating material of the type which is tough in its resistance to deformation and yet substantially plastic so as to evenly transmit therethrough to the metal ferrule localized pressure of crimping dies, with flow of metal from under the crimping dies, but avoid such excessive flow in itself as would expose the metal ferrule during crimping and thus impair the insulating function, which comprises forming from a composition of said plastic with excess plasticizer of said plastic a tubular piece longer and of lesser internal diameter than the external diameter of said ferrule, mechanically expanding the tubular piece and assemblingover theferrule, thereafter evaporating said excess plasticizer by heating and thus increasing the tendency of the tubular piece tightly to grip the ferrule.

6. The method of claim 5 in which the heating is bakingat temperatures between about 375 F. and 390 F. for about, one-half hour.

7. The method of making an insulated electrical connector having a ferrule that comprises forming a tubular piece of vinyl-chloride vinyl-acetate copolymer containing an excess of a vaporizable plasticizer of said co-polymer, said tubular piece being adapted to be pushed onto the external diameter of the ferrule, assembling the tu- ,bular piece-over the ferrule and thereafter baking to evaporate excess plasticizer from the tubular piece.

8. The method of insulating an electrical connector .which comprises extruding a vinyl insulating plastic to a uniform cross-section characterized by a longitudinal opening adapted to receive a ferrule-forming part of an electrical connector, said plastic having an excess of plasticizer of said plastic to facilitate extrusion but being of the type which except for said excess plasticizer is tough in its resistance to deformation and exhibits plastic flow from under a crimping die of lesser area than the plastic with resistance to plastic flow of about the same order as that of metallic copper, inserting into its said opening a malleable metal ferrule-forming part of an electrical connector, and removing said excess plasticizer to develop said property of flow resistance approximating that of copper.

9. The method as defined in claim 8 in which the plasticizer is removed from the outer surface While the inner surface is covered by metal.

10. The method as defined in claim 8 in which plasticizer is evaporated from the plastic while it is assembled and its inner surface covered by said metal part.

11. The method of insulating an electrical connector which comprises forming an electrical connector from malleable metal, extruding to a cross-sectional shape characterized by a longitudinal opening corresponding to, but smaller than, the exterior form of a wire-receiving part of the connector, a vinyl insulating plastic material of the type which is tough in its resistance to deformation but with an excess of plasticizer of said plastic facilitating said extrusion, cutting a length of said extruded insulation, stretching said insulation over the wire-receiving part of the connector, removing excess plasticizer from the exterior surface of the extruded plastic, inserting a wire into said wire-receiving part and thereafter crimping said part onto the Wire by pressure applied externally to a limited area of said insulation, with extrusion of metal from the area of the connector.

12. The method as defined in claim 11 in which the wire-receiving part is made of a metal of resistivity of the order of 10* ohms-centimeters at 0 C. and tensile strength of the order of 10 pounds per square inch.

References Cited in the file of this patent UNITED STATES PATENTS 2,027,961 Currie Ian. 14, 193 2,027,962 Currie Ian. 14, 1936 2,236,552 Ushakoff Apr. 1, 1941 2,276,571 Grypma Mar. 17, 1942 2,338,787 Ushakoif Ian. 11, 1944 2,410,321 Watts Oct. 29, 1946 2,429,585 Rogoff Oct. 21, 1947 2,565,316 Lucas Aug. 21, 1951 FOREIGN PATENTS 468,762 Great Britain July 12, 1937 OTHER REFERENCES Handbook of Plastics. Simonds, Weith, Bigelow, 2nd edition, 1949, pp. 340-341 (1st edition, 1943) D. Van Nostrand, New York.

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