US2327256A - Carbon-steel alternating-current conductor - Google Patents

Description

lAug. 17, 1943. F. G. FowLE ET AL CARBON-STEEL ALTERNATING-VCURRENT CONDUCTOR Original Filed Aug. 2, 1941 www@ NN m. m. .mw m IWW.. \N

' Panarea-Aug. 17,1 1943 UNITED sTATEs-PATENT oFFlcE v 2,327,256'

CARBON-STEEL ALTERNA'rmG-CURRENT ooNDUo'roa Frank F. Fowle, Winnetktnv Ill., and Frederick M.

Crapo,` Muncie, Ind.`

original application August 2, 1941, sei-mno.

Divided and this application May 16, A1942, Serit No. 443,312

1o claims; (015174-134) lOur invention relates to high-strength car.- bon-steel alternating-current conductors, hav.-4

-ing lowered magneticpermeability and lowered skin effect, resulting, in lowered effective alterhating-current resistance and reactance.

'I'he present invention, in certain aspects, is an improvement over certain things thatare disclosed in the following patents, granted to one or both of us.: I

Crapo, No. 1,942,411, granted January 9, 1934, Crapo, No. 2,019,445, granted October 29, 1935,

Fowle and `Crap'o, No. 2,019,447, granted October 29, 1935, Crapo, No, 2,118,008, granted May 17, 1938, Crapo, No, 2,118,758, granted May 24, 1938.

August 2, 1941, and is filed in compliance with a requirement for division in that co-pending application. In addition,^1ike that co-pending application, itis a continuation in part of our other co-pending .applications Seriah Nos. v207,351 and 207,352, both filed May 11, 1938, and

, of our co-pending application Serial No. 256,112,

led February 13, 1939, which last application is 'l now Patent No. 2,283,868, granted May 19, 1942.

` It is the object of our presentdnvention to obtain a carbon-steel conductor having .characteristics--meclrianical, v magnetic, vand electrical -,whi`ch make it exceptionally suitable for alternatingfcurrent transmission lines, especiallyv overhead lines. The term alternating curren is used to include pulsating current.

The carbon-steel conductor "contemplated vby the present application, intended'primarily foi` TheI present application is a division of our*4 co-pending application Serial No. 405,232, filed endurance. By a combination of these mechann vuse in an overhead alternatingwurrent trans- 1 mission line, is of hypoeutect'oid steelwhici contains over 0.20% and desirably at least 0.25% of carbon and for best results not over 0.65% of'carbon, not'in excess -of 0.30% of manganese, desirably not in excess 'of 0.10% of silicon, and desirably not 'in excess of 0.05% 'of phosphorus. This matter of composition or analysis is an es'- y sential-part of our invention; but it is only one part of our invention, for an vequally important part, if not a more .important part, is the treatment to which the wire of this composition or analysis is subjected in-its fabrication.

We have discovered the surprising fact that if in the fabrication of a wire ofvthis composition or analysis we subject the rod to aspecial heatvtreating operation byheating lit to a temper- 'ature' above the Aca temperature and quenching it from above that Aca temperature in a bath of molten lead (or equivalent molten metal) maintained within a certain range of tem-per'- ature, hereinafter discussed more fully, and thereafter subject that specially eat-treated rod to wire drawing, even if. therea ter we sub- 4ject the drawn wire (as we may and preferably do)v to a process tempering Within a, certain range of temperature, we get an ultimatevwire vwhichnot only.has\a high tensile strength and a good elongation but has a lower alternatingcurrent resistivity than has any prior ferrous wire of which we know,'

vIn addition toA this 'electrical effect, which isinterrelated with a lowered magnetic perme.

ability and hence with a lowered skin effect and Aa lowered reactance, we get certain highly advantageous mechanical effects, of great importance in a conductor for an overhead electric transmission linesuch as high tensile strength and good elongation `(above referred to), and toughness, resistance to shock, and high fatigue icalproperties with the above electrical and magnetic properties, we get an optimum set of characteristics that is most surprising.

The molten lead (or equivalent metal) used forthe special heat-treating bath is maintatined between 700 and 935 E. `But forvbest results, the temperature of the molten-.lead bath is not only within that range, but is in a certain part of thatv range dependent upon and increasing with the carbon contentof thewire. A rough formula for the optimum temperature 'of the molten-lead bath is the sum of 675 F. and a therefore increasing the skin-effect resistance ratio and hence the A.C. resistivity), and may have a slight directly reverse eect of lowering the permeability and., the skin-effect resistance ratio and the A.C-. resistivity.

This peculiarcombination'of yeffects adds up to a set of properties in the conductor which make it especially advantageous for use in an overhead alternating-current transmission line-in z 0.85% and for best `results below 0.65%, manga` nese not in excess of 0.30% and desirably as low as possible, silicon desirably not in excess of 0.10% and. as low as possible, phosphorus desira- .bly not in excess of (205%, sulfur low although not necessarilyabsent, and some copper present if it is desired to have a copper-bearing steel. By, the term rod, as here used, we include the Alarger wires which may havebeen produced from the original rod by one or more passes through l wire-drawing d ies but which are still to be drawny to make smaller wires.

`1. We rst heat-treat this rod in our special way, which has never been used in producing wires of this composition or analysis, and which with such wires, is found to have the especially benecial eilects above referred to, on electrical, magnetic, and mechanical properties. This special heat-treating involves,v heating the rod lof the speciiied composition or analysis t'o a temperature above the upper critical temperature (the Aca temperature), and 4then quenching through the critical range in a molten-lead bath having a. temperaturebetween 700 and 935 F.being higher (other things being equal) for increased carbon content. The optimum temperature oi this bath is determined by the formula given above.

2. After the rod has been thus specially heattreated, it is thensubjected to suitable pickling and/or other preparations for wire drawing, and is then drawn .to a wire of the desired'sizebr substantially the desired size. This drawing increases the tensile strength, and usually produces a rather high tensile strength, perhaps of the order of 150,000 to 200,000 pounds per square inch; but this high tensile strength is accompanied by a low elongation, `of the order of about- 1% to 2% (measured in 10-.inch lengths). The ductility of the wire in this condition is undesirably low for a. conductor of an overhead electric transmission line. The wire-drawing not only increases the tensile strength, but, with the special-composition wire that has hadA the aioresaid special heat-treatment, the drawing also lowers the magnetic permeability, and so l'owers the skin eiect and the A.C. resistivity.

3. When the desired sizeshas been obtained,

- the wire is preferably process-tempered. I n that process-tempering, which is agpartial annealing, we heat the wire to a selected temperature, which is well below the lower critical temperature (the Acil temperature). That selected temperature may vary somewhat, as with the composition of the wire, being higher (other things being equal) for increased carbon content. It may also vary according to the tensile strength and elongation desired, being higher for greater elongationand position or analysis, and so on the skin effect and less tensile strength. This process-tempering orfv partial annealing increasesv the ductility and elongation markedly, often yseveral fold; and

825 and 1075 F. It may be obtained in various ways,.as by passing the wire through a muiiie i'umace, or through a molten-material bath (such as molten lead or molten salt) maintained at that temperature. ,After the wire has reached this selected temperature, it is then allowed to cool, as by being passed. through ordinary air.

process-tempering may be In some cases this omitted. i

4. The wire may be used in this condition, or it .may be suitably coated or covered with any desirable metal, such for. instance as zinc, lead, copper, or aluminum, and/or with a non-metal vof any suitable character. If zinc,the most Vcommon coating metal, is used for the coating, it may be applied .by either hot-dipping orelectrodepositi'on., To put on any coating, the wire must be suitably prepared, for instance by passing it through a pickling bath, 'one or more waterwashing baths, and an electrolytic cleaning bath. Ii-the wirel is coated, itmay be further slightly diJawn following the application of the coating.

Whether with or without a coating, our carbon-steel wire, of the specified composition or analysis and produced by the specified treatment,.

is found tbbe particularly effective as aconductor in an overhead electric transmission line, especially for alternating currents. 'Ihe special heat treatment makes thev wire tough and more resistant to shock; and produces a type of sorbitic structure, which is probably the so'urce of the `increased toughness and resistance to shock. 'I'hat increasedv toughness permits more wiredrawing; and the cold-working pro'duced by the wire-drawing raises the tensile strength to high values. 'I'he subsequent process-tempering, under the conditions speciiled, lowers the tensile strength somewhat, but if done carefully it raises the ductility and the elongation in greater proportion than it lowers the tensile strength; for it may double or treble or sometimes even quadruple the elongation, 'while lowering the tensile strength by 'only a relatively small amount. The nnal conductorv thus has persisting in its grain structure electrical, magnetic, and mechanical enects produced (a) by quenching through the critical range in a bath of molten material having a temperature between 700 and 935 F., (b) by cold-working. and (c) by subsequent partial-annealing.

The effect of. our special heat-treatment on the magnetic permeability of a wire of this comon the A.,C. resistivity of such wire, is unexn pectedly markedly greater, and to us unexplain, ably greater,

. a. 'li'iijan` if a wire of the same composition or analysis is subjected to the so-called "air patenting (or Old Process patenting"), in which air is used as the cooling medium,

b. 'I'han iLa wire of' the same composition or analysis is subjected to patenting in aliquid medium (whether metal or not) maintained at a lower or a higher temperature than the one we' here maintain, and

c. Than if a wire of a different composition (in which the carbon content and the manganese content are outside the ranges which we have indicated) is subjected to patentingl of any character.

^ This marked lowering of magnetic permeability of our special-composition wire, and so of its skin effect and its A.C. resistivity, is augmented by the f cold-working or the im which individuati result is'not in itself unexpected, but which when combined with the special heat-treatment of our special-composition wire produces in such wire a sistivity no greater than they were, and often reduces them. This effect which we obtain from our process-tempering is .dependent both ron the composition or analysis of the wire and on the heat-treating of the wire in our special way; for

otherwise the process-tempering raises the magnetic permeability and the skin effect and the A.C. resistivity.

Thus the three steps of special heat-treatment, wire-drawing,/and process-tempering, when applied to wires of our specified composition or. analysis,fcooperate in a new and useful way, and one which is' distinctly unexpected and which we can not at presentexplain. 't

As a result of this co-operation, our wire is lower A.C. resistivity than has ever been known result from lsuch processespecially suitable for the conducting of alter nating currents both of power frequency (usuor 60 cycles per second) and audio fre-v ally 50 quency (between about 100 and several thousand cyclesper second) Also, its mechanical properties make it especially suitable for overhead electric transmission lines, both power lines and communication lines; forv the high tensile strength permits thewire to be supported overhead in longer spans thanis possible in wires of less tensile strength, and its good elongation, its toughness, its resistance to shock, and its high fatigue endurance, co-'operate with that high tensile strength to this end.

The accompanying drawing illustrates an apparatus in which the process for making our high-strength carbon-steel alternating-current conductor is performed. In such drawing: Fig. 1 is a diagrammatic view of an apparatus for performing our special heat-treatment; Fig. 2 is a diagrammatic view of an apparatus for performing the wire-drawing step or steps; and Fig; 3 is a diagrammatic view of an apparatus for performing our special process-tempering step Vand for electro-galvamzing,'with some intervening steps.

The hot-rolledrod of the specified composition or analysis, outlined above, is obtained from a rolling mill. 'I'his requires special heats of steel to get that vdesired composition or analysisselected between 0.20% and 0.85% carbon but desirably above 0.25% carbon and for best results -below 0.65% carbon, and between zero and 0.30%

From the heating furnace, the rod II is passed directly into a molten-lead bath I3 in which the proper temperature is maintained 'as explained above-in any case between '100 and 935 F.

From the molten-lead bath I3, the rod II, afterpassing if desired over reverse rollers I4 to remove scale, passes to a take-up block I5.

The specially heat-treated `rod II is' then removed from the take-up block I5, suitably cleanedv and otherwisev prepared for drawing, and put on a supply reel IB (Fig. 2); from which it is fed l through wire-drawing dies I1, in which the rod II is drawn to a wire I8. The wire is pulled throughthe dies I1 by a take-up block I9, on

which the drawn wire is coiled. If there are a large number of wire-drawingdies I1, as there may be when the wire I8 is drawn to smalldiameter from a large rod, it may be desirable to do the wire-drawing in several steps; and even to repeat the special heat-treating at an intermediate stage in the drawing of the wire,'with the lead-quenching temperature. as set forth above, as in the apparatus shown in Fig. 1. x

When the wire I8 has been drawn to the proper size, it is removed from the takefup block I9 and put on a wire-supply reel 20 (Fig. 3) from which it is fed to obtain the special process-tempering, and then if desired a suitable coating, such for instance as zinc coating. To this end, the

wire I8 passes from the wire-supply reel 20 into al molten-lead or molten-salt bath 2i, in which the leador salt is maintained at a temperature between 825 and 1075 F. For higher carbon conmanganese, and desirably between zero and 0.10% silicon and between Vzero and 0.05%'phosphorus, suitably little sulfur, and if desiredl some copper-forsteel mills seldom'if ever produce such a steel. Indeed, so far as we known, no steel mill has ever produced such steel except in accordance with our instructions.

lA coil of rod, after some preliminary drawing vif desired, is put on a supply reel I0' (Fig. 1), from which the Irod .I I passes through a 'heating furnace I2, suitably heated so that` the lrod is raised-l to a, temperature above the Aca temperature."

tentsthe temperature of the molten lead or molten salt isdesirab-ly in the upper part of this range, while for lower carbon contents it is de 'The molten lead or molten salt in the bath 2l is a temperature-raising liquid, 'as distinguished from the temperature-lowering liquid of lthe molten lead of the bath I3. After passing through the molten-material bath 2|, the wire .I8 is cooled in any suitable manner, as by being passed through the air.

The wire I8 before it is passed into the molten-l material bath 2| has a very high tensile strength, butits elongation and its ductility are too low. In the molten-material bath 2l there is a tempering action that is very .carefully controlled, to increase the ductility and the elongation to desired values without lowering thev tensile strength too greatly. By careful selection of the temperatures within the rangeindicated, it is possible to keep the tensile strength above 120,000 pounds per square inch, andin most cases above `130,000 pounds-per square inch, and yet to increasethe elongation to a final value of the order` of 4% to 8%-, in ten-inch lengths. With such tensile-strength and elongation values, the wire is an eminently suitable 4conductor for overhead electric transmission lines.

In addition, the wire is an eminently suitable alternating-current conductor, because of its low A.-C. resistivity, explained above.y

If desired, andas the drawing shows, after the wi e I8 has left the bath 2| it may then be passed though various baths in preparation for coating-here shown as zinc coating by electro-galvanizing. In that case, such preparatory baths may include a washing bath 22, containing washing water, a pickling bath 2 3, another washing. bath 2l also containing washing water, an electrolytic cleaning bath 25 in which through suitable electrical connections a flow of current from a' generator 26 is produced between the wire I8 'cleaning of thewire in known manner, and a rinsing bath 2110i ai'lnal rinsing just prior to electro-platingwlth zine. From the rinsing bath 21 the wire I8 passes into an electro-galvanizing bath 28, containing a lsuitable electrolyte vfor .electro-depositing zinc on the surface of the wire, and provided with suitable anodes 29 for the electrolyteused.A Current from a generator 30 is y for pulling the wire through all the apparatus shown in Fig. 3.

The unexpected results obtained with our conductors are apparent by contrasting the properties of our conductors with those of conductors of' the earlier patentsrefeired to above, and by the following table comparing certain of our conductors with certain -other conductors of identical composition but differently treated. The five samples'of wire of. the following table were alldrawn to. No, 12 BWG size from No. 5

hot-rolled rod, all were bare (uncoated) wires, and `all had r the following composition:

' Percent C v 0.40 Mn 1 0.22V Si r 0.01 P 0.015 S 0.025

A. No heat-treatment of rod-no process-tempering of Wire. l l

B. No heat-treatment of pered (850 FJ,

C. Our special heat-treatment of rod--no process-tempering of wire.

rod-wire process-tem- D. Our special heat-treatment of rod-wire process-tempered (850 F.) E. Our special heat-treatment of rod-wire process-tempered (1020 F.)

Properties of these sample conductors are shown by the following table:

.iig-C. res tance A l Tensile llonga- `ohms per lsigt fn Sam strength, tion, p er 1,000 it. ratio, abimv le pounds cent, 1n 5 mllli- 5 mm 5 mim.

p per Sqare 110mg! lanogerelg; am peres at amperes at inc eng s cy l Meured 1,000 cycles 1,000 cycles at 80 F f v Per cent A.. 128,000 2.0 8.58- 1. 297 64. 0 B 127, 000 3. '5 8. 93` 1.359 08. 0 C 178, 000 2. 7. B9 l. 189 52. 2 D, 170, 000' 7. 0 7.8i 1.183 52. 3

These ngu'res ,vary somewhat with variations in composition'and in treatment within the ranges which we have specified. For instance, ii the initial rod with whichjwe startv has a carbon of about 99.55%, and a maximum of about 0.15%

The-respective samples of the tablewere subjected to the following treatments:

2,337,256 and* a suitable electrolyte in the bath to cause a for the surnof the manganese, silicon, phos- 1. phorus, and sulfur, a conductor may be produced by our process with a tensile strength of about140,000 pounds per square inch, an elongation-of about 8%, and an effective A.C. resistance, measured, at 80 F. in bare (uncoated) wire of No. 12 BWG size, as low as 7.2-7.3 ohms per thousand feet to currents of 5 milliamperes at 1000-cycles per second. In general, bare wires of No. 12 BWG size produced by our process have an effective A.C. resistance to currents oi 5 milliamperes at 1000 cycles per second of the order of 7.2' to 8.3 ohms per thousand feet, measured at 80 F.

We claim as our invention:

1. A carbon-steel alternating-current conductor which is made of hypoeutectoid steel containing at lea-st 0.20% of carbon, not in excess of 0.30% of manganese, not in excess of 0.10% oi content of about 0.30%-0.35%, an iron content silicon, and not in excess of 0.05% of phosphorus, and which has a tensile strength above 120,000 pounds per square inch, has anelongation of the order of 4% to 8%, and when in bare wire of No. 12 BWG size has an eiiective A.C. resistance to currents of 5 milliamperes at 1000 cycles per second of the order of '7.2 to 8.3 ohms per thousand feet, measured at F.

2. vA carbon-steel alternating-current conductor which is made of hypoeute'ctoid steel containing atleast 0.20% of` carbon,v not in excess of and which when in bare wire of No. 12 BWG size has an effective A.C. resistance to currents of 5 milliamperes at 1000 cycles per second of the order of 7.2 to 8.3 hms per thousand feet, measv ured at 80 F.

4. A carbon-steel alternating-current conducto-r having lowered magnetic permeability and lowered skin effect, resulting in lowered effective alternating-current resistance and reactance, which conductor is made of hypoeutectoid steel containing at least 0.20% of carbon, not in excess of 0.30% of manganese, not in excess of 0.10% of silicon, and not in excess of 0.05% of phosphorus, and which has persisting in its grain structure electrical, magnetic, and mechanical effects produced (a) by quenching through the critical range in a bath of molten material having a temperature between 700 and 935"` F., (b) by cold-working, and (c) by subsequent partialannealing.

5. A carbon-steel alternating-current conductor having lowered magnetic permeability and lowered skin eii'ect, resulting in lowered effective alternating-current resistance and reactance, which conductor ls a wire of hypoeutectoid steel which has a tensile strength above 120,000 pounds persquare inch, hasan elongation of the order of 4% to 81%, and when in bare wire of No. 12 BWG size has an eiective A.C. resistance to currents oi 5 milliamperes at 1000 cycles per second of the -order of 72to 8.3-ohms per thousand feet, measuredat 80 F.

.permeability and which 'when in an eective A.C. resistance bare wire of No. 12 BWG size has to currents of milliamperes at-100 cycles 'per second ofthe order measured o! 7.2to 8.3 ohms per thousandfeet,

'1. A carbon-,steel ualternating-current conductor having lowered magnetic permeability and lowered skin effect, resulting in lowered eiective alternating-current resistance and reactance,

which conductor is made of hypoeutectoidy steel containing at least 0.20%of car n, not in excess I containing at least 0.20% of carbon, not in excess of 0.30% oiy manganese, not in excess of 0.10%*01 silicon, and not in excess of 0.05% of-phosphorus,

and which has a sorbitic structure, and which has been subjected'to cold-working and to subsequent partial'annealingby which the effects oi the coldworking have been partially but only partially eliminated so that eiIects of in part persist, and which has a tensile strength above 120,000 *poundsv per square inch and'an elongation of the order of 4% to 8%.

.8. A carbon-steel alternating-current conductor having lowered magnetic permeability and lowered skin effect, resulting in lowered effective alternating-current'. resistance and reactance, which conductor is made of hypoeutectoid steel containing. at least 0.20% of carbon, not in excess of 0.30% of manganese, not in excess of 0.10% 'oi silicon, and not in excess of 0.05% of phosphorus, 'and which has a sorbitic structure, and which has been subjected to cold-working, and which has a tensile square inch. 9. Acarbon-.steel alternating-current conductor having lowered magnetic permeability and that cold-working I lowered skin effect. resulting in lowered effective alternating-current resistance and reactance. which conductor is made of hypoeutectoid steel of 0.30% oi manganese, not in e cess of 0.10% of silicon., and not in excess of 0.05% of phosphorus, and wlichihas persisting electrical, magnetic, and mechanical effects produced by quenching through the critical range in a bath of molten material having a temperature between. '700 and 935 F., and which has been subjected to cold-working and to subsequent partial annealing by which the effects of the coldworking have been partially but only partially eliminated so that effects of that cold-working in part persists; and which has a tensile strength above 120,000 pounds per .square inch.

10. A carbon-steel alternating-current conductor having lowered magnetic permeability and lowered skin effect, resulting in lowered effective alternating-current resistance 'and reactance,

` which conductor is made of hypoeutectoid steel containing at least 0.20% of carbon, not in excess 010.30% of manganese, not in excess of 0.10% of silicon, and not in excess of 0.05% of phosphorus, and which has la sorbiticfstructure, and which has been subjected to, cold-working and to subsequent partial annealing by which theeffects oi the cold-working have been partially but only partially eliminated' so that effects of that coldworking in persist, and which when in bare wire of No. 12 BWG size has an effective A.C. resistance to currents of 5 milliamperesat 1000 cycles per second of the order of '1.2 to 8.3 ohms strength aboge 120,000 pounds per per 1000 feet, measured at 80 F.

FRANK F. nowrn. FREDERICK M. CRAPO:

CERITFICATE I(IF CORRECTION. Patent No. 2,527,256. August 1T', 19H5.

FRANKF. Eo/JLE, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring wcorrection as follows: Page 5, first column, line 6, claim 6, forl "100 cycles read 1O0 cycles",i andthat the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office, I

Signed and sealed this 18th day of December, A. 1914.5.

Leslie Frazer (Seal) First Assistant Commissioner of Patents.

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