Aluminum wire has great attraction as opposed to copper wire. Aluminum is one of the most plentiful and most easily accessible elements occurring in the world. Copper, on the other hand, is in short supply and has been becoming progressively more expensive. Furthermore, most of the leading copper supplying countries of the world are at the present time cursed with unstable governments, thus making both supply and costs highly erratic.
Furthermore, although aluminum has a slightly higher resistance than copper for a given cross-section of conductor, on a weight basis aluminum is a better conductor. Stated otherwise, on a pound for pound basis, or also on a dollar for dollar basis, aluminum carries more current than does copper. This is well known, and is exemplified in practice by the fact that practically all long distance high tension lines in use today use aluminum wire.
However, aluminum also has certain outstanding disadvantages which have not heretofore been fully solved to permit use of aluminum as a direct replacement for copper in wires in many applications. Outstanding among these is the fact that aluminum exposed to air very rapidly forms a surface oxide or film which is a fairly effective insulator. If a terminal or other connection is made to aluminum wire simply by crimping, the oxide film acts as an insulator between the wire and the terminal, thus inhibiting the flow of electricity. (Incidentally, this oxide film makes soldering aluminum extremely difficult.) It is recognized that the oxide film can be cleaned from aluminum for the application of a crimp terminal or a like connection. Although a solid wire can be cleaned very readily, it may be questioned whether cleaning of solid wires is practical on a production basis. The more common stranded wires present so many surfaces that surface cleaning is not practical.
There is another significant disadvantage to aluminum as a conductor, and this is that aluminum expands a great deal more with heat than does copper, approximately 45 % more. Thus, even if a satisfactory crimp termination is provided to aluminum wire, as by cleaning the wire before crimping, or by some other scheme, when the wire is put into use, the conduction of current will cause a certain amount of heating, thereby causing differential expansion of the aluminum wire and of the brass or the metal terminal. Aluminum is relatively soft and flows readily, and such differential expansion causes the trapped aluminum to flow axially within the crimped terminal. Subsequently, when the current is shut off, cooling of the aluminum wire and of the brass terminal causes the aluminum wire to pull away from the terminal, resulting in a loose connection, and leaving an exposed surface which will quickly form an oxide film. The oxidized surface, as noted before, is a partial insulator, and this subsequently increases the heating of the aluminum, besides making a poor contact, thus creating a regenerative effect which leads to failure of the termination.
Accordingly, it is an object of the present invention to provide a crimp terminal which is satisfactory for use with aluminum wires, and which also may be used with copper wires.
It is particularly an object of the present invention to provide a crimp terminal for use with aluminum wires that does not require any cleaning of the aluminum wire to remove surface oxidation, which does not subsequently loosen up and which furthermore does not permit reoxidation of the aluminum wire after installation.
In accordance with the present invention we have provided a crimp terminal having an outer shell which is substantially identical with existing crimp terminals. In addition, we have provided a partial inner liner of very thin conductive material such as copper alloy, for example, on the order of 0.003 inch thickness, substantially a foil. This foil is secured to the outer terminal shell such as by soldering, welding, or mechanically, as by staking. The foil has a large number of asperities stamped into it projecting inwardly of the terminal. These asperities, somewhat resembling open-top volcanoes, bite into the aluminum wire during application of the crimp terminal to the wire, cutting through the surface oxide on the aluminum wire and forming an excellent electrical engagement therewith. We are aware there have previously been connectors or terminals having lances, asperities or other projections thereon or therein to bite through the oxide film on aluminum wire. The present asperities are developed so that aluminum is actually extruded into the asperities and forms a tight mechanical interlock which does not losen upon heating and cooling as current is carried and subsequently interrupted. Furthermore, the outer shell of the terminal covers the back of the foil, substantially excluding air and moisture therefrom, thus precluding reoxidation of the freshly exposed aluminum in the contact area.
The invention will be better understood with reference to the following specification when taken in connection with the accompanying drawings wherein:
FIG. 1 is a perspective view on a greatly enlarged scale of a crimp-on terminal in accordance with the present invention immediately before crimping onto a wire;
FIG. 2 is a perspective view on the same enlarged scale of the terminal after crimping onto the wire;
FIG. 2A is a cross-sectional view taken substantially along the line 2A--2A in FIG. 2;
FIG. 3 is a fragmentary plan view of the terminal before crimping;
FIG. 4 is a longitudinal, sectional view taken substantially along the line 4--4 in FIG. 3;
FIG. 5 is a cross-sectional view taken substantially along the line 5--5 in FIG. 3;
FIG. 6 is an end view of the terminal
FIG. 7 is a fragmentary plan view of the liner or foil with the asperities stamped therein;
FIG. 8 is a cross-sectional view through one of the asperities and taken along the line 8--8 of FIG. 7; and,
FIg. 9 is a view similar to FIG. 8 after association of an aluminum wire therewith.
Turning now to the drawings in greater particularity, and first with special reference to FIGS. 1 and 2, but also referring to FIGS. 3-6, there will be seen a crimp-on terminal 10 constructed in accordance with the present invention. The crimp-on terminal may have a tip or end of any desired type, illustrated somewhat stylistically as a male pin terminal 12. The male pin 12 has been substantially simplified in the present disclosure, and will be understood as having the usual structure for mounting in a housing. One such satisfactory terminal may be seen, for example, in John H. Krehbiel U.S. Pat. No. 3,178,673. Rearwardly of the pin or body portion 12 there are provided two integral portions, respectively, a conductor-gripping portion 14 and an insulation-gripping portion 16. The conductor-gripping portion 14 is subdivided into a conductor crimp portion 13 of high crimp force for good current conductivity and a portion 15 of lesser crimp force and greater mechanical strength and comprises a pair of wings 18 and an interconnecting bight 20 in a generally U or V-shaped configuration. The rear portion 15 of the conductor-gripping section or portion 14 is provided with serrations or embossed ribs 22 for aid in mechanically gripping the wire.
The insulation-gripping section 16 is separated from the wire-gripping section 14 by notches 24, and comprises a pair of wings 26 of slightly greater dimension than the wings 18, interconnected by a bight 28, again in a generally V-shaped configuration. As can be seen particularly with reference to FIGS. 4 and 6, the bight 28 may be offset from the bight 20 on a diagonal as indicated at 30 to accommodate the insulation, the wings similarly being spaced somewhat outwardly by a transition section 32.
In FIGS. 1, 2 and 2A, there is shown an electric conductor 34 comprising a stranded wire 36 of aluminum and an overlying or encircling insulating cover 38. When the terminal, as hereinafter described, is crimped about the conductor from the shape shown in FIG. 1, for example, to the shape shown in FIGS. 2 and 2A, a modified B configuration, the conductor portion 14 grips the stranded (or solid) conductor 36, mashing and extruding the individual strands out of their normal round configuration so that voids are eliminated while the insulationgripping section 16 grips the insulation in known fashion to form a strain relief.
The foregoing structure as heretofore shown and described is generally well known in the art, and it will be understood that the terminal is of a suitable metal such as copper alloy. The improvement in the present invention resides in the provision of a thin sheet of suitable metal 40, having a hard or spring temper, cartridge brass being one satisfactory example. A suitable thickness of the liner material 40 is 0.003 inch, although greater or lesser thicknesses are contemplated. As will be appreciated, the material thus is scarcely more than a foil. The liner material 40 is within the conductor-gripping portion or section 14 and may be riveted, staked, clinched, soldered or welded to the terminal 10, but preferably is attached to the main terminal as indicated at 42, forward of the ribs 22, for example. Specifically, a protrusion 44 is stamped into the metal of the terminal in the bight area 20 which protrudes through a corresponding hole 46 in the liner 40, the protrusion being flattened or mushroomed if required at 46 to hold the parts together.
As may be seen in FIG. 3, preferably the projection and corresponding aperture for the staking is non-circular, thereby preventing turning of the liner 40 about the staked position prior to formation of the terminal from a flat blank.
The liner 40 is provided with a plurality of asperities 48 which are punched thereinto in regularly spaced relation. As may be seen in FIG. 8, the asperities are somewhat in the nature of open-topped volcanoes, having conical, inner surfaces 50 and a ragged upper edge 52. The edge 52 may be sharp, as well as ragged. By way of example, with a 0.003 inch thickness material 40 the median height of the asperities from the upper surface of the liner 40 is on the order of 0.008 inch. The diameter of the outside of the base of each asperity is on the order of 0.020 inch, while the inside diameter, at the upper end, is on the order of 0.010 inch. The total included angle of taper of the inner surface 50 is approximately 20°. The previous dimensions are known to provide proper function but it is thought considerable variance from these dimensions will still result in good performance.
The asperities bite into the aluminum wire 36 upon crimping, somewhat as illustrated in FIG. 9. Not only do the jagged upper edges 52 cut into the wire, thereby breaking the oxide film and making a good electrical contact therewith, but the outer surfaces 54 impinge tightly against portions of the freshly exposed aluminum while other portions of the aluminum wire extrude within the asperities as indicated at 56, again exposing fresh aluminum for good conductivity. These extruded portions are of prime importance. Not only do the asperities form a good contact with the aluminum at the start of operation, but they maintain good physical engagement and electrical contact after prolonged use. When the aluminum expands with heat, upon conducting of electricity, to a greater extent than the brass liner material 40, the extruded portions 56 wedge tightly within the asperities 50 and being attached to the main body of aluminum wire within the crimp barrel prevents axial extrusion. The crimp barrel having a seam on the top surface breathes with the wire, thus maintaining good physical and electrical contact. Furthermore, when the parts cool, the aluminum extrusions 56 do not move out of engagement with the inner walls 50 of the asperities, but pull upward axially of the asperities, thereby remaining in wedging engagement with the inner surfaces 50, pulling the crimp barrel walls back to their original position, and maintaining both excellent physical and electrical engagement therewith. As will be appreciated with regard to FIG. 9, the wire-gripping portion 14 of the main terminal lies outside of the liner material 40, in tight engagement therewith, thereby substantially excluding air and moisture from the aluminum contact surfaces engaging the inner and outer surfaces of the asperities 48. As will be appreciated, during the crimping operation, there is a considerable degree of extrusion and reforming of the individual strands of the wire 36, as these strands are mashed together substantially to eliminate voids and reduce interstrand resistance by breaking of the oxide films covering the wire strands. Such extrusion and reforming of the aluminum causes a flowing and shearing of the outer wire oxide surfaces, whereby there is excellent electrical engagement with the liner material 40 in addition to that which is effected by biting of the asperities thereinto.
Due to the extra thickness of material as provided by the liner material 40, the crimp is tighter in the conductive contact portion 13 at the possible loss of some physical strength, while maximum physical strength is provided with a somewhat less tight crimp at 15.
A large number of asperities of rather small diameter is necessary in order to insure a first-class electrical engagement with the aluminum wire, bearing in mind that in some conductors the individual strands of aluminum wire, for example of 30-gauge, are quite small, being on the order of 0.010 inch diameter.
If the asperities were of large size, it could be expected that in some cases significant numbers of the individual strands would simply be sheared upon crimping, and this is obviously undesirable. If a heavy gauge material were used with the asperities formed directly therein, the punches used with female dies to produce the asperities would have a very short service life since the diameter to material thickness ratio would be too low. The use of substantially a foil material for the asperities assures long punch life. Obviously, a material as thick as the present liner material could not be used for the entire terminal, as it would have substantially no physical strength.
It will be appreciated that during the crimping operation the foil, along with the outer portions of the terminal is folded in, whereby the open tops of the asperities are somewhat reduced in diameter, thereby being significantly smaller than the strands of wire, and thus avoiding any tendency to sever the individual strands.
It is known that the electrical characteristics of copper or copper alloy and aluminum are such that galvanic action can occur between them. Accordingly, in accordance with the present invention the terminal may be tin-plated or otherwise protected. To avoid any possibility of removal of the protective coating from the base material during fabricating of the terminal, the protection may be applied after the terminal has been completed, i.e., substantially as in FIG. 1.
The cross-sectional shape of the asperities 48 is essentially circular (or approximately so), and this is critical to obtaining good surface engagement with the aluminum extruded thereinto. Good surface engagement maximizes current carrying capacity and minimized mechanical problems.
It would be apparent that we have now disclosed a crimped terminal which is satisfactory for use with aluminum wire, either stranded or solid. The terminal as so disclosed can be handled by conventional, existing terminating machinery, and, if so desired, terminal can be used with copper wire.
The specific example of the invention, as herein shown and described, will be understood as being for illustrative purposes. Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of the present invention insofar as they fall within the spirit and scope of the appended claims.