US2906987A - Stabilized crimped connections - Google Patents

Description

Sept. 29, 1959 H. A. FOX, JR

STABILIZED CRIMPED CONNECTIONS Filed Dec. 28, 1955 JNVENTO dam; Af-Pox, &5". BY

United States Patent STABILIZED CRIMPED CONNECTIONS Harry A. Fox, Jr., Harrisburg, Pa., assignor to AMP Incorporated, a corporation of New Jersey Application December 28, 1955, Serial No. 556,027

3 Claims. (Cl. 339-115) This invention relates to crimped electrical connections and particularly to connections in which one of the members involved is of aluminum.

It is common in the electrical arts to form connections by crimping a ferrule onto a conductor. The ferrule may form part of a terminal as in the US. patent to Freedom, No. 2,535,013, or may form part of a butt connecting device for connecting the ends of two wires. In most cases such crimped connections possess good electrical conductivity, good strength and are resistant to loosening upon vibration. These connections are easy to make in that it is merely necessary to insert the end of the wire into the ferrule and crimp the ferrule with a suitable crimping tool or machine. For these reasons crimped connections have been adopted on a very wide scale in the electrical arts and have replaced other types of connections in many instances.

Where both the ferrule and the conductor or wire are of copper, as is frequently the case, it has been found commonly that nothing beyond crimping the ferrule onto the conductor is necessary to obtain a permanently strong and electrically conductive connection. However, it has also been found that Where either the ferrule or the conductor is of aluminum, the electrical resistance of the crimped connection immediately after crimping will be somewhat higher than the electrical resistance of a crimped copper-to-copper connection involving conductors and wires of comparable size. Also, it has been found that the electrical resistance of a crimped connection involving at least one aluminum member will increase the time; and temperature cycling, such as takes place when a connection is alternately heated and cooled by the intermittent passage of current, greatly accelerates this phenomenon. Crimped connections in which one of the members is of aluminum and the other is of copper exhibit this tendency to a particularly serious degree and crimped aluminum-to-aluminum connections are also subject to the phenomenon although aluminum-to-aluminum connections are not subject to deterioration in this respect to as great an extent as are aluminum-to-copper connections.

The primary cause of the relatively inferior properties of crimped connections involving aluminum members is probably the formation of A1 0 It appears likely that temperature cycling, which causes expansion and contraction of the crimped parts, might tend to cause a loosening of the crimped connection which would permit access of air and moisture to the interface between the conductor and ferrule surfaces with resulting formation of A1 0 to the detriment of the electrical conducting qualities of the crimp. This theory is supported by the observed fact that aluminum-to-copper crimped connections especially those composed of a copper ferrule and an aluminum conductor, are particularly susceptible to deterioration and the materials involved have unequal coefficients of thermal expansion. In accordance with the foregoing theory, it would be expected that where the ferrule and the conductor have unequal expansion co-efiicients the 2,906,987 Patented Sept. 29, 1959 efiects of thermal cycling, in promoting oxidation, wouldbe more pronounced than in the case of a crimped connection in which the ferrule and the conductor have equalexpansion coefficients. It is also probable that in the particular case of aluminum-to-copper crimped connections the close proximity of these two dissimilar metals re-- sults in the establishment of a galvanic couple with re-' sulting galvanic corrosion.

It is known to the art that if an unctious material con-- taining solid particles is packed in the ferrule or spreadover the end of the conductor prior to crimping, the elec-' trical resistance of the crimp will remain more nearly stable for a longer time period than is the case if the crimp is made in the ordinary manner. Petrolatum -is widely used as an unctious material and various solid materials have been suggested, such as zinc and graphite, as suitable for stabilizing compounds. These stabilizing compounds have a beneficial effect in that they improve the initial electrical conductivity of the crimped connection and suppress the tendency of the connection to increase in resistance. It is probable that the metal particles enhance the initial conductivity of the crimped connection by abrading and scratching the surface of the aluminum thus removing the A1 0 coating in part and exposing clean aluminum metal. However, crimped connections in which these prior art compounds are incorporated still have a tendency to increase in resistance under the influence of temperature cycling. Therefore, there is a need for a more effective stabilizer for crimped electrical connections involving at least one aluminum member which Will stabilize the resistance of such connections to the extent that they will be comparable with copper-to-copper crimped connections.

It is an object of the present invention to provide a crimped electrical connection of superior stability insofar as electrical resistance is concerned.

It is a further object of the invention to provide an electrical connecting device containing a stabilizing compound which will effectively prevent deterioration of the electrical properties of the crimped connection under the influence of extreme temperature cycling.

An additional objective resides in the provision of a commercially feasible organization which will be substantially foolproof in use and which overcomes certain well-known disadvantages inherent in the prior art,

In this specification there is shown and described a preferred embodiment of my invention and there are suggested various modifications thereof; but it is to be understood that these are not intended to be exhaustive nor limiting of the invention but, on the contrary, are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify and adapt it in various forms, each as may be best suited to the conditions of a particular use.

In the drawings:

Figure 1 is an exploded view of an uncrimped terminal and the bared end of a section of conductor; and

Figure 2 is a view of the parts shown in Figure 1 after the terminal has been crimped onto the conductor.

I have found that crimped electrical connections, involving an aluminum ferrule or conductor, of low. initial resistance and superior resistance stability can be obtained if a stabilizing material containing an unsaturated fatty acid and metal particles is used. In a preferred embodiment of my invention I mix oleic acid and nickel particles in a ratio of about Ni, 10% oleic acid, spread this mixture over the end of the conductor, and in the case of multistranded conductors within and among the strands, insert the end of the conductor or wire into the ferrule and crimp the ferrule onto the conductor. The

a "200 mesh screen and are preferably of such size as to pass a 300 mesh screen although particles somewhat larger than 200 mesh might be employed if desired or if necessary. I have found upon microscopic examination of cross-sections of crimps made by this method that some of the nickel particles become partially embedded in the surfaces of both the ferrule and the conductor and thus function as electrically conductive bridges crossing the interface between the ferrule and the conductor. I have also observed in the case of a stranded conductor that the nickel particles will work their way among the strands of the conductor and form conducting bridges between adjacent strands. The nickel particles should not therefore be so large as to pfecludetheirbeing partially embedded in this manner.

While oleic acid is preferred as an unsaturated fatty acid, I have also obtained very good results with linoleic acid and with linolenic acid. While I employ a mixture of about unsaturated fatty acid and 90% metal particles in the preferred embodiment of my invention, these proportions are not critical. Mixtures containing as high 'as 90% acid and 10% metal have been used with good results. Both components of the mixture must be present in sufiicient quantity and if the above extreme limits are exceeded, there will either be insufficient fatty acid or an insufiicient number of metal particles. It should also be mentioned that various inert materials, such as silicone grease, petrolatum or a modified bentonite of the type commercially available under the trademark Bentone from the Baroid Division of the National Lead Company can be added to the mixture to produce a desired consistency if desired, however, the addition of such materials seems to detract from the resistance stabilizing effects of the fatty acid and metal particle mixture.

When a single strand conductor is crimped within a ferrule, it suffices merely to dip the end of the conductor in the acid-metal particle mixture or to spread the mixture over the interior surface of the ferrule prior to crimping.

,On the other hand, where a stranded conductor is being used, it is desirable to take some pains to distribute the mixture within and among the strands of the conductor as well as over the exposed strands. I prefer to prepare a stranded conductor for crimping by filling a cup or thimble, having a diameter only slightly greater than the conductor diameter, with the acid-metal mixture, insert the end of the conductor therein and manipulate the conductor in such manner as to cause flow of the acid among the strands and migration of some of the metal particles within and among the strands. Alternatively where the ferrule is filled with the acid-metal mixture, the stranded conductorshould be manipulated within the ferrule prior to crimping in order to achieve uniform distribution of the mixture throughout the strands.

Referring to the drawing, the reference numeral 1 denotes a commonly-used type of terminal having a tongue portion 2 and a barrel portion 4 which barrel portion is adapted to receive the stripped end of a stranded conductor 6. In the practice of the invention, the stabilizing compound is spread over the end of the conductor as indicated at 8 on the drawing and is preferably worked within and among the conductor strands. Also, the stabilizing compound may be spread over the interior surface of the barrel portion 4 of the terminal if desired. Thereafter the end of the conductor is inserted into the barrel portion which is crimped as shown in Figure 2 by the use of a suitable crimping tool.

An alternative method of incorporating the invention into a crimped connection is shown in the copending application of lean J. Redslob, Serial No. 350,653, filed April 23, 1953, for Connector for Aluminum Wire, now Patent No. 2,815,497, issued December 3, 1957. As

: shown and described in this Redslob application, a cup or thimble containing the stabilizing material is provided which fits within the barrelportion of the terminal. To

form the crimped connection the thimble is fitted into the barrel portion of the terminal, the end of the conductor is inserted into the thimble and the parts are crimped together.

The superiority of connections made in accordance with the invention is demonstrated below by the data in Table I. These data were obtained in the following manner:

A number of stabilizing mixtures were prepared, some of these mixtures being prepared in accordance with the invention and others being prepared of prior art materials. Ten crimped electrical connections incorporating each mixture were made between a tin coated copper terminal of the type shown in the U.S. patent to Freedom, No. 2,535,013, and a No. 4 aluminum conductor. The entire group of terminals was then placed in an oven maintained at C. for a period of 100 days. Once or twice in each twenty-four hour period the test pieces were removed from the oven and permitted to cool at room temperature. At intervals the terminals were tested to determine their electrical resistance by passing a current of 101 amperes therethrough and measuring the millivolt drop.

Table I Millivolt drop Mixture Initial After 100 days if? Min. Ave. Max. Min. Ave. Max.

$551511; hydrogen- 6 8 10 16 22 43 256 ated ester of oleic acid 4. 5 6. 0 7. 0 14 21 27 4. 0 5. 0 7. 5 35 76 117 g gic ggi g ggo meta? 3.0 4. 5 6 11 21 34 19 particles) 7. 5 10 14.5 18. 5 50 87 25355133- if??? 3 4 5 23 85 145 (a *Final millivolt drop reading after 119 days.

As is apparent from the data of Table I, the connections incorporating nickel and oleic acid exhibit markedly superior electrical conduction characteristics, and of these connections, test No. 219, incorporating the 90% Ni, 10% oleic acid mixture is outstanding. The tests on these particular specimens were continued beyond the 100 day period and it was found that at the end of two and onehalf years of continuous temperature cycling the millivolt drop remained at substantially the same level as existed at the end of 100 days. Moreover, at the endof two and one-half years. the maximum millivolt drop observed 7 in the specimens of test No. 219 was not significantly nor do I intend that my invention be limited to the theory expressed.

Unsaturated fatty acids have at least one double bond and by virtue of this fact have an aflinity for oxygen. It

is possible that when an unsaturated fatty acid is present in the crimped connection, the oxygen which normally would combine with aluminum to form A1 0 preferentially combines with the acid. Furthermore, unsaturated fatty acids have good film-forming characteristics and tend to cover the surface of the ferrule and the conductor with a continuous monomolecular layer. When the crimp is made, as the ferrule and conductor are pressed tightly together, these films are probably broken at the points of close contact between the ferrule and the conductor. However, these films remain in th area surrounding the areas of metal-to-metal contact and it is probable that these films act as an anti-oxidant grease coating which prevents access of oxygen to the crimped parts. In accordance with the foregoing theory then, the unsaturated fatty acid fulfills a dual function in that it 1) covers the aluminum surface and surrounds the actual crimp in sealing relationship thereto and (2) preferentially unites with oxygen which would otherwise cause formation of A1 0 A comparison of tests 254 and 256 lends support to the theory that the unsaturated fatty acid preferentially unites with oxygen to prevent the formation of A1 0 In test No. 256 a mixture of nickel particles and the commercially available cooking fat Crisco was used. This material consists essentially of a partially hydrogenated ester of oleic acid and could therefore be expected to behave chemically somewhat like oleic acid. However, this material has far fewer double bonds than oleic acid and cannot, therefore, function as efhciently as oleic acid in preferentially combining with oxygen. It is apparent from the data that the crirnps prepared with the 90% Ni, Crisco compound (test 256) are inferior to the crimps prepared with the 90% Ni, 10% oleic acid compound (test Nos. 219 and 254).

The unsaturated fatty acid of itself, however, will not function to stabilize the electrical resistance of the crimp as shown by the test results of test No. 214 in Table I. The metal particles are essential and of the metals tested, nickel gives outstanding results. As previously mentioned, the nickel particles become embedded in the ferrule and the conductor and, in the case of stranded conductors, within and among the conductor strands. this observation it can be theorized that these particles act as conducting bridges,

From

The term aluminum as employed herein is intended to include the commonly known alloys consisting predominately of aluminum which are used as electrical conductors and terminals. Also, the term copper is intended to include commonly known and used materials which consist predominately of copper. The terms nickel and nickel bearing particles as used in this specification and in the claims are intended as being inclusive of metal particles composed predominately of nickel as well as particles composed entirely of nickel.

Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments may be made without departing from the scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only.

I claim:

1. A joint stabilizing compound for electrical connections consisting essentially of from 10% to by weight of oleic acid and from 90% to 10% by weight of nickel particles.

2. An electrical connecting device comprising a conductor receiving ferrule, said ferrule containing a joint stabilizing compound consisting essentially of from 10% to 90% by weight of oleic acid and from 90% to 10% by weight of nickel particles.

3. An electrical connection comprising a ferrule member crimped onto a conductor member, at least one of said members being of aluminum, said connection including a stabilizing compound consisting essentially of from 10% to 90% by weight of oleic acid and from 90% to 10% by weight of nickel particles, said oleic acid being distributed over the interface separating said ferrule and said conductor, at least some of said nickel particles being partially embedded in said ferrule and partially embedded in said conductor.

References Cited in the file of this patent UNITED STATES PATENTS 1,863,429 Willmore June 14, 1932 2,423,290 Bonwitt July 1, 1947 FOREIGN PATENTS 363,075 Great Britain Dec. 17, 1931

Claims (1)

1. A JOINT STABILIZING COMPOUND FOR ELECTRICAL CONNECTIONS CONSISTING ESSENTIALLY OF FROM 10% TO 90% BY WEIGHT OF OLEIC ACID AND FROM 9/% TO 10% BY WEIGHT OF NICKEL PARTICLES.

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