US3157735A - Metallic particle compositions for mechanically joined electrical conductors - Google Patents

Description

. Nov. 17, 1964 STROUP ETAL 3 157,735

P- T. 9 METALLIC PARTICLE COMPOSITIONS FOR MECHANICALLY JOINED ELECTRICAL CONDUCTORS Filed June 27. 1961 lvaiural aluminum oxide film S MW 70 -Aluminum INVENTORS P/zi/fp ZSfraup 9 y Jay MAI/nan ATTORNEY 3,157 735 METALLlQ PARTHJLE COMPOSITEONS FUR MECHANHGALLY JOIYED ELECTRICAL CGNDU -JTGRS Philip T. Stroup, New Kensington, and Jay W. Atrnan Canonsburg, Pa, assignors to Aluminum ompany or America, Pittsburgh, 1 21., a corporation of Pennsylvania Filed lune 27, 1961, Ser. No. 119,811 9 Claims. ((13. Flt-3 3) This invention relates in general to forming mechanical joints between electrical conductors as distinguished from soldered and welded joining of the same. The invention is more particularly concerned with mechanical joints between electrical conductors and conventional fittings employed therewith, in which juxtaposed superim posed surfaces of at least two electrically conductive members are secured under pressure in interfacial surface contacting relationship to form and constitute a mechanical joint therebetween. The mechanical practices thus contemplated include conventional bolt or damp secured lap joints between juxtaposed superimposed contacting surfaces of bus bar elements in electrical distribution systems, as well as joints in electrical transmission systems incorporating conventional compression sleeve and parallel groove connectors in pressure-exerting surface-contacting attachment on electrical conductors or cables.

The current carrying efiiciency of any electrical sys tem is inversely proportional to its resistance, and the joints in such a system can invariably increase the resistance to a level where electrical losses become quite appreciable. It is therefore a primary desideratum to provide joining practices in electrical systems which insure low initial and extended electrical contact resistance characteristics to avoid unnecessary voltage drop in the systems.

It is an accepted fact that metallic conductors, and conventional fittings regularly employed therewith in mechanically joining the same, exhibit natural oxide surface films in their as-fabricated condition. Aluminum and its alloys, widely used in electrical transmission and distribution systems are no exception, although the readily formed natural oxide surface films formed thereon are microscopically thin and are beneficial in the sense that they protect the underlying base metal against the self-consuming oxidation associated with many other metals and alloys. Regardless of these facts, many metallic oxides are practically electricallynon-conductive and joints incorporating contacting surfaces, at least one of which is aluminum bearing its natural oxide surface film, the latter film in the dry state being an accepted electrical insulator, by nature exhibit higher electrical contact resistance than obtains if the effect-of the natural oxidefilm can be eliminated or reduced.

By the term aluminum, as used herein and in the appended claims to define a metallic conductor or electrically conductive surface thereof, is meant commercially pure electrical conductor (EC) grade aluminum and commercially available aluminum base alloys in whichv the elemental metal aluminum is present in amounts of at least 50 percent by weight.

Attempts to'improve the electrical contact resistance of mechanical joints in electrical transmission and dis- 'United States Patent 3,157,735 Patented Nov. 17, 1954 tribution systems have included the use of various types of particles between the interfaces of the juxtaposed contacting surfaces in restraining pressure assembly constituting such mechanical joints. In all such instances, the particles thus employed have been selected from commercially pure elemental metals, alloys thereof, and nonmetallic abrasive materials, the latter being recognized as non-conductive from an electrical standpoint, and the former metals and alloys exhibiting such inherent malleability that they deform and flatten under the pressures employed in making mechanical joints to actually provide metallic interlayer surface areas in superimposed relationship on the underlying non-conducting natural oxide surface films borne by the as-fabricated conductors and fittings employed therewith, Without displacing the complained of non-conductive films.

The present invention is predicated upon the determination and discovery that all particulates between the juxtaposed contacting surfaces of electrical conductors, and conventional fittings employed therewith, neither respend in the same manner nor to the same degree in providing low initial and extended low electrical contact resistance of mechanical joints in electrical transmission and distribution systems. it is to this end that the present invention is addressed in its provision of a particular class of electrically conductive metallic particles for use between juxtaposed pressure-restrained as-fabricated contacting surfaces of electrical conductors and conventional fittings employed therewith, such that the effects of the natural oxide surface films, giving rise to initial and extended high electrical contact resistance, are greatly reduced to the point of substantial elimination.

The general class of particles determined to be productive of the superior results and advantages attributable to the present invention are irregular in shape and are herein and hereinafter in the appended claims defined by the expression intermetallic phases containing aluminum by which expression is meant particles having a composition consisting in major proportion of intermetallic phases containing aluminum and a minor proportion, if any, of element or elements in excess of that entering into the formation of the composition of said intermetallic phases. In this connection, it is an accepted understanding that a true intermetallic compound is an intermediate phase in an alloy system, having a narrow range of homogeneity and relatively simple stoichiometric proportions, in which the nature of the atomic binding can vary from metallic to ionic. The particles responding to the present invention, and defined in their composition by the aforesaid expression intermetallic phases containing aluminum, include not only those particles having a composition consisting in major proportion of true intermetallic compounds containing aluminum, satisfying the above-accepted definition, but the variants thereof, which may or may not be isomorphous therewith.

The particulate or particles of the invention composed of the intermetallic phases containing aluminum have been determined to exhibit a minimum hardness which permits alloys productive thereof to be readily fragmentized or fractured in conventional grinding and hammer mill equipment to produce a frangible or friable aggregate, without the difiiculty associated with the malleable metals and alloys heretofore employed in electrical conductor mechanical joining practices. In addition, the

chanical joint employing the same.

in the mechanical joints.

has revealed that the particles are in themselves better than average electrical conductors and that they are characterized by exhibiting a minimum Viclters Microbardness Number of 24-0. This minimum hardness is j rction of the articles from individual particles in situ in the formation of a me- 5 1T10$t f21V01flb l$ to the P2 a J I? b am The irrpoularity in aluminum alloys productive or he p-aitic es ghconvt d a u: .tioiial impact crushing and grinding practices. c sta e nainreferi shapes i i ndlvldgal P31110128 p und to minimum hardness factor 18 also beneiicial in the re- Tmg to mmlmum apdness as 2 i0 action of particles under conventional pressures employed m and Insure exlstimce of unumera pressure 1 in making mechanical joints of the type herein contem- P the Plana the i Contacting Surface plated to cause fracture of the natural oxide film on areas icgnsmunng the mechanical Joints herein i aluminum su faces and establish metal-to-metal conducplated, with the end result that the interposed particles five bridging ,bctwafin undgrjymg aluminum and l i- 0f the invention compensate fer any Inherent lrregu' num alloy conductors and fittings, in which condition larities and non-uniformities in the asfabricated exposed the embedded particles thgmsejwas am ejcomwpy surface areas in juxtaposed cont acting surface assembly dmtiva Particle size is a desirable, but not necessarily a limit- T11e irregular Shape and hardness 0ft 5 Particles have ing factor to insure optimum interfacial low electrical 8 80 n Observed to react 0n the natural Oxide film contact resistance across a joint between superimposed carri d on t SIIrfaCfiS 0f BIS-fabricated aluminum C911- pressure restrained electrical conductors in accordance dlliibf's, and com/6115011211 fittings p y thaw/1th, to with the present invention. In this regard particles fallfracture the natural oxide films in the areas of the presm Within {k Tyler Standard Scream Sieve rangg 23 to sure points developed in the mechanical joints, with in- 235 d more specifically the Sieve range 80 to 170, dividllal Particles entering the fissures in so-fl'ivctllfed have performed to give excellent low initial and extended natural OXide film and Pfinetmlling into the y g 5 electrical contact resistance values in mechanical joints aluminum 0f conductors and fittings displace between as-faibricated aluminum conductors and cables tallic aluminum al ng the IX f t individual p rhaving conventional mechanically-applied aluminum conticles and thus form innumerable oxide-free aluminum 1160mm tt h d thereto conductors between the superimposed contacting surfaces T bl No, 1 i e re entative of article comprising constituting a rnechanical joint therebetween. 3O intermetallic phases containing aluminum, together with From the .foregoing s ription it will be apparent determined Vicliers Microhardness Numbers therefor, I that a prime desideratum to provide a material in fragwhich have been found to fulfill and satisfy the requireinented particle form for disposition between the conme t of the, invention,

Table No. 1

. Vickers M icro- I Total Composition of Particles Composed hardness Identity of Intermetal- Composition of Particles Composed of of 74% by Weight Intermetallic Phases Numbers for lie Phases Containing 100% by Weight Intermetallic Phases Containing Aluminum and 26% Un- Interinetallic Aluminum Containing Aluminum combined Aluminum Phases Containing Aluminum 54% Gil-46% Al .Q 43s 0 r78% A1 335 41% l e-59% A1 727 lug-65% A1 246 42% Ni58% A1 400 32 Cir-17% Fe-51%Al 625 14% Oil-22% Mir-64% A 397 28% Fe-15% si-57% Al 747 10 7, CL115% Fel5% NIH-60% A 569 tactin-g mechanically-restrained surfaces of joints in electrical transmission and distribution systems, which is capable of insuring direct metal-tounetal contact across such joints, is achieved by the provision of the par-ticles composed of intermetallic phases containing aluminum above described.

It will be further observed that the particles of the invention, through their inclusion in a mechanical joint of the type herein contemplated, have overcome the disadvantages arising out of the presence and non-conductive property of the natural oxide film carried on the exposed surfaces of as-fabricated aluminum conductors p,

and conventional fittings employed therewith.

' Additional advantages will be more fully understood and appreciated by those skilled in the art to which the invention appertains on consideration of the following more detailed description.

FIG. 1 is a plan View of a joint employing the joint composition of the invention.

FIG. '2 is a sectional view taken along lines .22 of FIG. 1. a a

Extensive development and testing in establishing the particular class of particles of the invention as being composed of intcrmetallic phases containing aluminum expressedin terms of low initial and extended electrical.

contact resistance in mechanical joints including the irregular shaped particles. 7

Table No. 2 is included to illustrate Viclcers Microhardness Numbers for typical'wrought aluminum conductors and cast and wrought aluminum accessories, such as compression type and bolt-secured conductor and cable connecting accessories, regularly employed in electrical transmission and distribution systems, between the interfacial contacting surfaces of which the particles of the invention have been successfully employed to provide low initial and extended electrical contact resistance joints. V I

Table No.

the same conductor incorporated in each joint assembly up to and including 1050 hours of repeated heat cycling. Aluminum Viokgrs Conventional sleeve type service entrance connectors Base A oy Product TypeNominaloompositioni Microhaving their as-fabricated tubular bores filled with four Designation and Temper hardness L Numbers diiierent oint compounds comprising unctuous material or grease in admixture with particles of intermetallic Permanent mold casting 7 g% Silicon, phases containing aluminum identifiable as CuAl NiAlg, magnesium balance Substantially fiAl-Cu-Fe and ,BAl-Fe-Si, the intermetallic phase in each 356T4i. j g fil fiiisoiuuon heat treatment roi- 69 instance being present in an amount at least equal to 74 lo y naturalagins at momiemper' percent by Weight of the particles, are presently underature. Permanent mold casting7.0% suieon, going repeated heat cycling test in compressive assembly 356 T6 g g g l balance Substantially 93 on stranded bare aluminum cables. The resistance ratio Temper T6S 0lu tion heat treatment felvalues initially and at the end of 165 hours heat cycling lg gg gg gi gggmf gg pure 990% are quite comparable to the resistance ratio values reotyn aluminum. a0 ported in Table No. 3 for the terminal sleeve cable oint $3 25; z gi iig i g gg l gfg incorporating 50 percent copper-50 percent aluminum 1100-0 99.0% aluminum. H 34 particles, thereby establishing full equivalency for the ge gg g g ggggfjggggggg class of particles defined in terms of intermetallic phases i100-Hi2 99.0%alum m1m- 35 containing aluminum.

23 ,332gfiggfifgfiggggk %515 It will be manifest that the lower initial and extended con, 1% magtnestiufii; 0 .06% ergomium, 91 resistance ratio values exhibited in Table No. 3, which ggfggft fig fiij g i t tg g {0L are comparable to the results being obtained in the tests lgwed gay ar iggfil g s s pure in progress the end or l 65 hours repeated heatcychng, almmnum electrical conductor 41 clearly establish the superior ty of mechanical oints em- ECH19 grade. ploying particles comprising inter-metallic phases contain- Temper H19Oo1dworked extra harding aluminum. Table No. 3, under the heading Repeated Eending of Cable at Joint, lists calculated resist- It Will be Observed that the j Mlcmharqlwss ance ratio values following bending of the cable of each Numbers determined for the materials and products listed joint SEA/6m} firms through an approximate angle of in Table 2 am Censiderabll lfwer and are actually to simulate vibration and whipping action experienced in mere fractions of the VlClifiIS Microhardness Numbers actual practice of 1 invantion' established for theintermetahic phases containing alurnt- The uncmous material or grgase herd-whom mfermd 1111111, constituting 1% and 74 Percent by Walght of me to is a conventional carrier and medium for facile ap- COHIPOSifiOD 0f Parades falling Within the scope Of the plication of the particles between the contacting surfaces inv nt listed in Table of joints in electrical transmission and distribution sys- Extensivc tests were conducted which include electr cal Items, I ill be apparent that other well-known and energization and resistance determinations of mechanical suitable camsrs may b6 gmpjoyed for this PHI-pow Such joints incorporating as-fabricated aluminum sleeve type as adhesivss, lacqugrs, and the like, and tha pa ticlgs terminals compressibly attached to the bare ends of identimay, if desired be sprayed in a Suitable liquid adhasive Cal @IECi l Conductor aluminum Stranded cable" directly on one or more of the sis-fabricated interfaces The tubular bores in one set of the sleeve terminals had to be incorpcmtsd in a mechanical joint f the t her? bcen filled With an UHCWOHS material of gfease column in contemplated. Regardless of the particular nnctuous 5; Particltis colnpssed y Weight of a 59 percent PE material selected, it should be non-toxic, water-repellant, Percent aluminum 3 havillg a Tyler Standard pliable and usable within the temperature range lG Screen Sifive palliclfi Size range between 100 to to 300 F, and exhibit non-corrosive characteristics in fore compressive assembly of the sleeves on the cables. its intended emimnmgnt All number Of terminal SlBVS had tllfiil tubuinvention has been describgd vith pa ficlai' bores filled with a C ml 5 p ular reference to mechanical joints incorporating alumi- P 581.11g an 11116910115 maielial glfiase Containing metal num conductors and aluminum alloy fittings, it is intended C Zinc (1115i, before fl'lsif comliressivfi assembly on the 50 and it should be understood that the particles of the in cablfis, the Samfi t091 and 6 @Ylsd plessums 53mg vention comprising intermetallic phases containing alumi- P Y to assemble bath Sets Of terminal joints. num will function with equal success with other conduc- Each set of 'compressively assembled cables and sleeve fi metals d alloys I th pfgfgfpgd practice of terminals thus pr nfll W insifllifid in El 330 mp the invention, however, it is recommended for optimum hwt Cycling Circuit and the current 1.11 each was Permliled 55 results that at least one of the members or elements of to flow for ne-110111 int vals With a Omit-110111 iniefthe mechanical ioints present an interfacial contacting surruption in the current flow at the end of each hour i'low f c f l i p Rfisismn've Tam) Values Weft: Calculalcd from The Vickers lvlicroliardness Numbers included herein- Kelvin bridge measured electrical resistance and dimeiiabgve were l l t d fro th formula sional measurements for each individual test assembly, 18m} rX D I the resistance ratio values reported in Table No. 3 being "453%; average values of the apparent resistance of a joint assembly exclusive of its conductor beyond its sleeve ter- Where P load in grams, cl the length of the diagonals minal, divided by the resistance of an equal length of of the diamond indentation in microns, and H Vickers V T able N0. 3

Resistance Ratio Values lr iizl d i ng Jomt hours 500 hours 1,000.Hours Repeated 1.050 Hours Initial Heat Heat Heat Bending of Heat Cycling Cycling Cycling Cable Cycling at Joint .94 it as i. as 1. 42 i. 62 2. 0o Unctuous Greaseand Zinc Dust. 1.06 2. 92 3. l4 3. 24 8. 72 11. 63

r i a been employed in measuring and establishing the Vickers Microhardness Numbers appearing in the preceding Tables Nos. 1 and 2.

FIGS. 1 and 2 are representative of a low electrical contact resistance joint falling within the scope of this invention. Therein FIG. 1 is a top plan View of a pressure-restrained joint between the overlapped ends of two substantially rectangular electrically conductive metallic bus bar members it and i2, and FIG. 2 is a transverse section through the joint taken on the plane 22 of Fit. 1, to enlarged scale, restraining means, such as the bolts 14, being provided to secure the joint. At least one of the bus bar members aluminum member bearing a natural oxide film l8, dimensionally exaggerated on the faying joint surface of bus bar element iii, and the layer to between the overlapped faying surfaces of the metallic bus bar r e: ibers ad and His com-posed of electrically conductive intermetallic phase particles, described above asserted in some of the claims, preferably, but not necessarily, in ad nixture with an unctuous or equivalent carrier.

Having thus described the invention and certain em bodiments in support thereof, what is claimed is:

1. Metallic particles for disposition between contacting interfaces of electrical conductors in a prcssure retrained joint therebetween, which particles serve to reduce initial and extern ed electrical Contact resistance of the joint, said particles being frangible and irregular in shape and consisting of at least '74 percent by weight of at least one intermetallic phase, said intermctallic phase consisting essentially of aluminum and at least one metal combined therewith by an atomic bond ranging from metallic to ionic in nature and the balance of said composition of said particles being composed of up to 26 percent by weight of at least one element present in the intermetallic phase in excess of that required to form the phase, and said particles exhibiting at Tyler Standard Screen Sieve or 12 is an particle size range between 28 to 235 and a minimum intermetallic phase consisting essentially of aluminum metal combined therewith by an atomic and at least one bond ranging from metallic to ionic in nature and the balance of said composition of said particles being composed of up to 26 percent by weight of at least one element present the intermetallic phase in excess of. that required to form the phase, and said particles exhibiting inga Tyler Standard Screen Sieve particle size range between 80 to 170 and a minimum Vickers Microhardness Number of 240. i i

4. Metallic particles for disposition between the contacting interfaces of electrical conductors adapted to be assembled in pressure-restrained interfacial contacting relationship, at least one of said conductors presenting an interface of aluminum bearing a natural oxide surface film, which particles serve to reduce the initial and extended electrical contact resistance of the joint, said particles being frangible under pressure and irregular in shape andcomposed of an aluminum-copper alloy in which the aluminum and copper are each present in the amount of 50 percent by weight, the particles fallin within the particle size Tyler Standard Screen Sieve range of 80 to 1.70, and the particles being further characterized by having a Viclcers Microhardness Number of 438.

5. 'A low electrical contact resistance joint composition for use between contacting interfaces in mechanical pressureaestrained joints between electrical conductors, at least one contacting interface in a joint presenting an aluminum surface bearing a natural oxide surface him, said joint composition comprising an unctuous carrier in admixture with irregular shaped frangible metallic particles composed of a composition consisting; of at least 74- percent by Weight of at least one intermetallic phase, said intermetallic phase consisting essentially of aluminum and at least one metal combined therewith by an atomic bond ranging from metallic to'ionic in nature and the balance of said composition of said particles being composed of up to 26 percent by weight of at least one comprising an unctuous carrier material in admixture with irregular shaped frangible particles composed of an aluminum-copper alloy in which the aluminum and copper are each present in the amount of 50 percent by Weight, the particles having a particle size Tyler Standard Screen Sieve range between 80 to 170 and exhibiting a minimum Vickers Microhardness Number of 240.

a Tyler Standard Screen Sieve size range between 80 to 170 and a minimum Vickers Microhardness Number of 240,

position between contacting interfaces of electrical conductors in a mechanical pressure-restrained joint therebetween, one of which conductors presents as fabricated aluminum interfacial surface bearing a natural oxide surface film, said particles consisting of at least 74 percent by weight of at least one intermetallic phase, said intermetallic phase consisting essentially of aluminum and at least one metal combined therewith by an atomic bond ranging in nature from metallic to ionic and the balance 1 of said composition of said particles being composed of up to 26 percent by weight of at least one element pre ent in the intermetallic phase in excess of that required to form the phase, said particles serving to reduce the initial and extended electrical contact resistanceof the joint between the conductoraand said particles exhibit- 3. Electrically conductive metallic particles for dis- 7. A low initial and extended electrical contact resistance joint composition for disposition between interfacial contacting surfaces in a pressure-restrained joint between electri al conductors at least-one of which conductors presents an interfacial as fabricated contacting surface of aluminum bearing its natural oxide film, saidjoint composition comprising an unctuous material in admixture with irregular tive particles consisting of at least 74 percent by weight of at least one intermetallic compound, said intermetallic compound being binary and consisting essentially of aluminum and one of the elements selected from the group consisting of Cu, Cr, Fe, Mg and Ni combined therewith by an atomic bond ranging from metallic to ionic in nature and the balance of said composition of said particle's being composed of up to 26 percent by weight'of at least one of said stipulated elements present in the intermetallic compound in excess of that required to form the compound, and said particles exhibiting a Tyler Standard Screen Sieve particle size range between 28 to 235 and a minimum Viclcers Microhardness Number of 240.

j S. A low electrical contact resistance joint between pressure-restrained contacting surfaces of two or more electrically conductive metallic members, at least one of which members presents a contacting surface composed of aluminum bearing a natural oxide film, metallic parshaped frangible electrically conduc-- ticles disposed between the contacting surfaces, said metallic particles being selected from and composed of at least 74 percent by weight of at least one intermetallic phase, said internietallic phase consisting essentially of aluminum and at least one metal combined therewith by an atomic bond ranging from metallic to ionic in nature and the balance of said composition of said particles being composed of up to 26 percent by Weight of at least one element present in the intermetallic phase in exoess of that required to form the phase, and said particles exhibiting a Tyler Standard Screen Sieve particle size range between 80 to 170 and a minimum Vickers Microhardness Number of 240.

9. A low electrical contact resistance joint between pressure-restrained contacting surfaces of two or more electrically conductive metallic members, at least one of which members presents a contacting surface composed of aluminum bearing a natural oxide film, an electrical joint compound disposed between the contacting surfaces of the joint, said compound comprising an unctuous carrier in admixture with metallic electrically conductive particles, the particles being selected from a composition composed of at least 74 percent by Weight of at least one intermetallic phase, said intermetallic phase consisting essentially of aluminum and at least one metal combined therewith by an atomic bond ranging from metallic to ionic in nature and the balance of said composition of said particles being composed of up to 26 percent by weight of at least one element present in the intermetallic phase in excess of that required to form the phase, and said particles exhibiting a Tyler Standard Screen Sieve particle size range between 28 to 235 and a minimum Vickers Microhardness Number of 240.

References Cited in the file of this patent UNITED STATES PATENTS 2,076,281 Steudel et al. Apr. 6, 1937 2,077,366 Milligan Apr. 13, 1937 2,604,455 Reynolds et a1 July 22, 1952 2,815,497 Redslob Dec. 13, 1957 OTHER REFERENCES Aluminum Casting Alloys, publication by Federated Metals Division of American Smelting and Refining Co., pages 9-11 relied on.

Claims (1)

1. METALLIC PARTICLES FOR DISPOSITION BETWEEN CONTACTING INTERFACES OF ELECTRICAL CONDUCTORS IN A PRESSURE-RETRAINED JOINT THEREBETWEEN, WHICH PARTICLES SERVE TO REDUCE INITIAL AND EXTENDED ELECTRICAL CONTACT RESISTANCE OF THE JOINT, SAID PARTICLES BEING FRANGIBLE AND IRREGULAR IN SHAPE AND CONSISTING OF AT LEAST 74 PERCENT BY WEIGHT OF AT LEAST ONE INTERMETALLIC PHASE, SAID INTERMETALLIC PHASE CONSISTING ESSENTIALLY OF ALUMINUM AND AT LEAST ONE METAL COMBINED THEREWITH BY AN ATOMIC BOND RANGING FROM METALLIC TO IONIC IN NATURE AND THE BALANCE OF SAID COMPOSITION OF SAID PARTICLES BEING COMPOSED OF UP TO 26 PERCENT BY WEIGHT OF AT LEAST ONE ELEMENT PRESENT IN THE INTERMETALLIC PHASE IN EXCESS OF THAT REQUIRED TO FORM THE PHASE, AND SAID PARTICLES EXHIBITING A TYLER STANDARD SCREEN SIEVE PARTICLE SIZE RANGE BETWEEN 28 TO 235 AND A MINIMUM VICKERS MICROHARDNESS NUMBER OF 240.

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