US2140544A - Lead-bismuth-lithium cable sheath - Google Patents

Description

Dec. 20, 1938. H. osBORG LEAD-BISMUTH-LITHIUM CABLE SHEATH Filed Nov. 9, 1935 3 Sheets-Sheet l I INVENTOR. HHNS 0 $5 0/? 6 Y B am.

ATTORNEY.

Dec. 20, 1938. H. OSBORG LEAD-BISMUTH-LITHIUM CABLE SHEATH Filed Nov. 9, 1935 3 Sheets-Sheet 2 3 a m :Uz umqaom Nmml WOT-3a ILIMvZUNF-l N IWZUF.

% ELONGATION IN ZmcHES INVENTOR. Hfl/VS OSBORQ BY (1 4 ATTORNEY.

Dec. 20, 1938. OSBORG 2,140,544

LEAD-BISMUTHLITHIUM CABLE SHEATH Filed Nov. 9, 1935 3' Sheets-Sheet s LEAD-ens VIUTH-LITHIUM 65 ELECTROLYTIC) LEAD-LITHIUM ELECTRO LYTBEMD/ TENSILE STRENGTH. POUNDS PER sauna; men N v o 5 IO 5 2o 25 3o 35 %ELONGATION IN ZINCHES 1N VENT OR.

I HANS OSBORC;

Patented D... 20, 1938 LEAD-BISMUTH-IJTHIUM CABLE SHEATH Hans Osborg, Bronxville, N. Y., assignor to Maya wood Chemical Works, Maywood, N. J., a corporation of New Jersey Application November 9, 1935, Serial No. 48,987

2 Claims.

The present invention relates to lead-bismuthlithium cable sheath and to an extrudable and workable lead-bismuth-lithium alloy therefor.

Heretofore, a number of lead alloys have been 5 used commercially and others have been proposed for the manufacture of leaden cable sheaths, "but none of these alloys has been found to'possess the necessary combination of the essential and salient features which a lead alloy should have ii it is to meet the requirements for high strength cable sheathing. The history of and the requirements for cable sheathing, especially high strength cable sheathing have been described in an authentic manner by R. S. Dean and J. E.

Ryjord in their article in Metals and Alloys (vol. 1, No. 9, March 1930). In essence, Dean and Ryjord have concluded thatz-In selecting mechanical properties it is necessary to compromise between pliability and high strength. A study for installation and service conditions leads to a tensile value of around 4000 lbs. per sq. in. as the most desirable value. .This strength should,- of course, be accompanied by the maximum possible fatigue limit. In other words, it has been recognized by the experts and outstanding authorities in the art that the desired combination of essen-- tial properties was only attained in industrial practice by sacrificing pliability or strength or both. The various attempts to improve lead cable sheathing by the addition of alloying metals have been described fully and authoritatively by Schumacher and Boulton in their article in Metals and Alloys (volume 1, No. 9, March 1930).

Among the attempts may be mentioned the addition of calcium, lithium, antimony, tin and/or cadmium to lead as disclosed in U. S. Patents Nos. 1,880,746; 1,890,013; 1,890,014 and 1,926,545. For some years, 1 to 3% tin was added to lead, but after 1907 a 1% antimony-leadralloy was adopted as the standard sheathing {for cables. Due to failures in service of antimony-lead cable sheathing, endeavors were made to replace the antimony-lead with calcium-lead, lithium-lead, cadmium-lead, cadmium-antimony-lead or cadmium-tin-lead, but, as far as I am aware, none of these lead alloys have been adopted and antimony-lead is still used despite its shortcomings and disadvantages.

I have made the surprising discovery that a superior cable sheathing can be produced from lead containing not only bismuth but also lithium within critical and special ranges.

It is an object of the present invention to provide a special lead-bismuth-lithium alloy which possesses the desired combination of the essential properties required for high strength and pliable cable sheaths and which is superior to other known lead alloys.

It is a further object of the invention to pro- 0 vide a process of producing and manufacturing the special lead-bismuth-lithium alloy which permits, the production under industrial conditions of superior, more uniform and more economical results than standard or customary industrial procedure. I

It is also within the contemplation of the present invention to provide a cable sheath constituted of a lead alloy containing about 0.03 to about 0.09% of bismuth, about 0.005 to about 0.025% of lithium, and the balance commercially pure lead.

Another object of the invention is to provide a novel lead alloy which contains simultaneously as its essential constituents lithium and bismuth.

A further object is to provide a new lead-bismuth-lithium alloy possessing physical and mechanical properties which are considerably superior to other known lead alloys.

The invention likewise contemplates the provision of a novel leaden cable sheath or leaden pipe containing bismuth and lithium.

It-is also an object 01' the invention to provide a new process of manufacturing. leaden. cable sheaths and leaden pipes containing bismuth and lithium.

Other objects and advantages of the invention Figs. and 8 depict comparative charts of lead and lead alloys showing the relation of strength to ductility.

Generally speaking, the novelty of the new lead-bismuth-lithium alloys may be clearly seen by comparing Fig. 6 with Figs. 1 to 5. From these figures, the structures 'of the alloys and their diiferences may be appreciated. Thus, the

electrolytic lead illustrated in Fig. 1 has relatively large grains and the crystals have sharp edges. The addition of lithium refines the grain as shown in Fig. 2, but this grain refinement does not resuit in substantial improvement of physical properties, especially strength. The presence of small amounts of copper, say of the order of 0.06%, likewise produces a refined grain which is still further refined by the addition of lithium (see Figs-3 and 4). A closer examination of the various crystal structures shows, however, that the presence or even such small amounts as 0.06

of copper in lead produces a fine, dark precipitate, the quantity and particle size of which is obviously increased by the addition of lithium to copperized lead. The occurrence of these insoluble (foreign) particles in such quantities and large sizes may have some bearing on the rather low physical properties of this lead-copperlithium alloy. Bismuth-lead shown in Fig. 5 is generally considered as an inferior brand of commercial lead and it has been generally regarded as unsuitable for the production of high strength or other lead alloys of high quality. Lead containing bismuth is known to possess lower physical and inferior mechanical properties than other brands of commercial lead, such as lead containing copper, or electrolytic lead, or antimonial lead. In other words, the presence of bismuth in lead has heretofore been considered as impairing and not improving the mechanical properties of commercial lead or lead alloys. In contradistinction to practical experience, I have discovered that a lead which contains not only bismuth but also lithium produces a lead alloy of superior and outstanding properties and qualities which make it especially suitable for high strength and ductile cable sheathing. As may m seen from Fig. 6, the size of the grains is not as fine as in Figs. 2, 3 and 4. The grains are arranged in a honey-comb like structure with distinct grain boundaries and clear faces. The microphotograph shows that no precipitates, particularly of a granular, globular or spheroidal type, occur within the grains or on the grain boundaries.

Tests have demonstrated the pronounced distinctions between prior conventional lead alloys and my new lead-bismuth-lithium alloy. Thus in Tables Nos. I, II and III, the results of some of these tests are presented. These tables are self explanatory and bring out the remarkable fact that an addition of lithium improves electrolytic lead or copperized lead only moderately while the simultaneous presence of lithium and bismuth in lead increases the tensile strength of the lead alloy approximately 2000 lbs. per sq. in. over "copperized lead, 3000 lbs. per sq. in. over lead, and about 1000 lbs. per sq. in. over lithiumcontaining copperized or electrolytic lead.

In Figs. 7 and 8 based on Tables Nos. IV and V, the tensile strengths of various lead alloys have been plotted against elongation. It may be clearly seen from these tables and figures that lead which contains bismuth possesses the lowest strength and the lowest modulus of elasticity while my new lead-bismuth-lithium alloys have a far greater strength and a considerably higher modulus of elasticity than lead or the other lead alloys. The high modulus of elasticity places the novel lead-bismuth-lithium alloys in a distinct class. The high strength and ductility of the new alloys distinguish them as superior to other known high strength lead alloys. The outstanding and typical characteristic of the new lead-bismuthlithium alloys is the combination of properties which usually are not compatible with each other or which affect each other adversely. In prior alloys, an increased tensile strength, hardness and stiffness was accompanied by a decreased ductility and vice versa, whereas in the present novel alloys a considerably increased tensile strength, hardness and stiffness are accompanied not only by good ductility but also by remarkable toughness.

Results obtained on fatigue tests are of special significance and importance. A number of specimens of the new lead-bismuth-lithium alloys were subjected to fatigue tests in comparison to other lead alloys. The specimens were taken from 1 in. pipes and the tests were conducted at the same time and under identical conditions. The results of these comparative fatigue tests are presented in Table VI and clearly demonstrate the great superiority of my novel lead-bismuthlithium alloys with respect to resistance to fatigue.

Lead-bismuth-lithium alloys have been subjected to various corrosion tests, including electrolytic and Philadelphia sewer water corrosion tests, the latter of which were extended over a period of nearly two years. The results of all of the corrosion tests have been very satisfactory. The corrosion resistance of lead-bismuth-lithium alloy compares favorably with the best corrosion resistant lead and lead alloys known to the industry.

After it had been clearly established that the lead-bismuth-lithium alloys were far superior to lead-lithium alloys, to other lithium-containing lead alloys, and also superior to other high strength lead alloys adopted or recommended for cable sheathing, such as the 1% antimony lead alloy or the recently developed ternary cadmiumtin-lead or cadmium-antimony-lead alloys (see Department of Scientific and Industrial Re search, Building Research, Special Repart No. 19: B. N. F. Ternary Alloys of Lead. Their Use in Buildings; London, 1933, His Majestys Stationery Office), the invention was carried into practice on an industrial scale.

The industrial process of making the leadbismuth-lithium alloys and manufacturing cable sheaths from these alloys can be carried out in many ways, but I have found that the following method produces better results than standard practice.

Lead, containing bismuth in amounts of about 0.03 to 0.09%, is heated to at least about 800 F. and then the desired amount of lithium is added. The lithium can be added in any convenient form, such as metallic lithium, as a master alloy containing a few percent of lithium, in lumps, as rod or wire, or the like. The amount of lithium added to the molten lead, or lead alloy, should be approximately 0.005% higher than the lithium percentage which is actually desired as lithium content in the finished alloy.

I have discovered that an amount of approximately 0.005% of lithium is always required for the scavenging of lead, even if the lead is of the high purity available in commercial brands, as for example in electrolytic lead. These 0.005% of lithium perform a scavenging action producing a boiling effect in the molten lead. The casting properties of the molten lead alloy and the quality of the finished product are considerably improved by this scavenging action. In order to obtain a uniform distribution of the alloying constituents, the temperature of the bath should be kept at approximately 800 F. for some time, while the bath is thoroughly stirred. If these simple but important rules are followed, the undesirable wet drossing which occurs in the beginning of the alloying procedure will be reabsorbed by the lead alloy and will disappear leaving only a slight amount of a practically dry dross on the surface of the thus treated alloy.

In the industrial production of leaden pipes, leaden cable sheaths, or the like, a holding furnace, containing a large amount of molten lead or lead alloy, is employed. The production of the desired lead alloy takes place in this furnace 7 from which the extrusion press is charged in certain intervals of time. I have discovered that better and superior results and greater economy are obtainable by not following the standard practice. Instead; only the lead containing the desired amount of bismuth is kept molten in the holding furnace. Just before charging time, slightly more lead than is necessary to fill up the extrusion press, for example some 800 lbs. of the molten metal, are transferred from the furnace into a heated pot, or kettle, or container in which the addition of and the alloying with lithium is carried out in accordance with theabove given instructions, and without difliculty. After the alloying procedure is finished, the extrusion press is charged by pouring the molten lead alloy into the press. in any convenient manner. Another suitable alloying method consists in adding the lithium, e. g. in the form oil a .M; in. wire, to the sufliciently hot metal while it is flowing from the holding furnace into the press. 01' course, the temperature of the press has to he kept high enough to prevent the lead alloy from freezing before the scavenging action is over. If this method is applied, the necessary stirring action is performed by the whirling of the flowing metal itseli.

The industrial production of the present leadbismuth-lithium alloy cable sheathing was also carried out the manufacture of oil iilled high tension cables. It is known that the cable sheathing for this type of cables has to meet higher requirements than for other of cables. Tests conducted on iead-bisinuth-lithium cable sheathing proved that the cable can be easily reeled and unreeled, i. e., that it is pliable. Electrio tests as well as long time pressure tests were also satisfactory. The outcome oi these tests is of special importance because usually a tensile strength as high as 4000 pounds per sq. in., if combined with a pronounced stiffness, should he expected to cause failure in the aforesaid tests. The satisfactory hehavior or the lead-bismuthlithium alloy cable sheaths under these severe practical plant and service tests confirms the results of the physical tests which showed that the lead-bismuth-lithium alloy possesses, at the same time, great strength and good ductility as well as stiffness and toughness. In other words, contrary to practical experience the tensile strength is not increased at the expense of plialoility or ductility.

Under industrial conditions, best results and properties are obtained with an actual lithium content of about 02% in the finished alloy or product. noteworthy, that the very nature of the iead-bismuthrlithiurn alloy permits flexibility in physical properties. By keeping the bismuth content within a range of about 0.03% to about 0.00% and varying the lithium content, the physical properties, especially the strength. can be increased or decreased as desired.

in the present lead-bismuth-lithium alloy, the hardness is a comparatively unimportant subfeature, while its outstanding characteristics are to he found in its great strength and good ductility, stiffness and toughness, in its remarkably high fatigue limit, and in its good corrosion resistance. None of these properties, nor the unusual combination of, e. 52;, high strength and good ductility nor the high modulus of elasticity, nor the application of the essential element bisninth are mentioned in or can be anticipated or predicted from the prior art.

Further improvements oi the novel lead-bismuth-lithium alloy can be obtained by the application of a special heat treatment. Tests have shown that a considerable increase in tensile strength and stillness without an objectionable reduction in ductility have been obtained by heat treating the novel lead-bismuth-lithium I alloy in the plastic state. At temperatures of about 250 C. a period of about one hour is sufficient to produce a considerable increase in tensile strength and stillness. It has been found that temperatures ranging from about 100 C. to nearly 300 C; can be used for the heat treatment. The time necessary to produce the maximum possible increase in tensile strength will be indirectly proportional to the temperature, i. e. the higher the temperature the-shorter the time and vice versa. Thus, about one hour is required at the upper range while a longer time is required at the lower temperatures, say, about 2 to 3 hours. The practical and economical advantage of the special heat treatment becomes readily apparent if it is realized that the tensile strength of a lead-bismuth-lithium alloy con taining 0.012% of lithium is increased, for instance, acout 500 lbs. per sq. in. in other Words, the utilization of a heat treatment permits not only the production of still higher tensile strengths than heretofore but also the manutacture of articles of manufacture from the novel alloy with a smaller amount of lithium. Thus, in the aforesaid illustration a saving of about of lithium has been effected the use of the heat treatment.

0. 5 Sb {0. 125 C(L- 3250 35 0. 5.0 8b.--- {0. 186 Cd" 12 3900 24. 6

0. e63 Sb... {0.31 Cd 12 3900 24.6

0.457 Sb-.- 0.186 Cd" 12 3410 25.4 0. 315 Cd" 12 3230 25. 5

1 TS=tensile strength, lbs/ins.

Touts E Electrolytic lace Percent Other elc Test No. Li ments Bends TS 1 alga/.512.-

26 2810 52 23. 5 2700 60 13 3170 84 12 3470 35 0.463 Sl) 10 3400 {0. 156 Cd 12 3700 48 0. 463 Sbii.

1 TS tensile strength, lbs/in TABLE III Bismuth-lead Percent Test N0. Bi Li 2, 53, Bends Te 1 elongatlon 1 TS=tensile strength, lbs/in 4-0=limit oi TS machine. 1 Broke at limit of TS machine.

TABLE IV responding number of cycles to failure are given in the following table:

1. An extrudable and workable lead alloy having great strength with good ductility, stiiIness and toughness, high fatigue limit and good corrosion resistance with respect to ordinary lead Tensile strengths and elongations of various lead alloys Test No.

A Pb+0.06 Cu B Pb-HLOG Gui-0.005 Ll 2560 Pb+0.06 Cu+0.005 Li+0.l8 Cd Pb+0.06 Gui-0.005 Li+0.l8 Cd+0.50 8b.. Pb+0.05 Bi+0.0l Li Pb+0.00 Cu+0.01 Li. Pb+0.05 Cu+0.01 Li+0.50 Sb H. Pia-+0.05 Bi-HlOl Li+0.l8 Cd I lb-l-Ollfi (Du-+0.01 Li+0.18 Cd+0.50 Sb.

TABLE V Tensile strengths and elongations of lead and various lead alloys and containing about 0.005% to about 0.025% lithium, about 0.03% to about 0.09% bismuth, and the balance consisting of substantially pure lead.

Percent elongation 25a Lead-bisinuth-lithium alloy ("bismuth-lead with muth; plus 0.01% lithium).

about 0.06%? 0.02 bis- 25b Lead-bismuth-lithium alloy (bismuth lead with about 0.06%; 0.02 bismuth;

plus 0.01% lithium).

26a Lead-co per-lithium alloy (copperized lead with about 0.06% copper; plus 26b Leadco per-lithium alloy (copperized" lead with about 0.06% copper; plus 0.01% lithium 27a Lead-lithium alloy (electrolytic" lead; plus 0.01% lithium). 27b Lead-lithium alloy (electrolytlc load; plus 0.01% lithium). 28a Bismuth-lead" (lead containing about 006915 002 bismuth). 28b Bismuth-lead" (lead containing about 0.00%=F0.02 bismuth); 29a Copperized" lead (with about 0.06% Cu). 291': Copperized" lead (with about 0.06% Cu). 30a Electrolytic lead. 300 Electrolytic load. a=water cooled. b=eir cooled.

TABLE VI Fatigue tests The pieces were taken from 1" pipes and were slit and rolled to 0.032 inch gauge. Fatigue specimens were milled from /2 inch strips of this metal and tested in fatigue machines according to regular procedure.

The deflections of the specimens and the cor- 2. A lead cable sheath having great strength with good ductility, stillness and toughness, high fatigue limit and good corrosion resistance with respect to ordinary lead and containing about 0.005% to about 0.025% lithium, about 0.03% to about 0.09% bismuth, and the balance consisting of substantially pure lead.

HANS OSBORG.

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