US1587521A - Leading-in conductor - Google Patents

Description

June 8 1926q J. A. HEANY LEADING-IN CONDUCTOR Filed Nov. 18, 1918 container.

Patented Julie y 8, '1926.

UNITED STATESv PATENT OFFICE..

Y J DEIN ALLEN HEANY, QF EW HAVEN, CONNECTICUT.

LEADING-IN conmuc'ron.4

Application led November 18, 1918. Serial No. 263,038.

- l My invention relates to thel provision of an improved means of forming, in certain types of electrical appliances, a seal between the vitreous material of the container incident to these types of electrical appl-iances and the conductors through which 'electric cur rent is introduced into the interior -of the The container above referred to may be either of the evacuated type or,v the gas filled type. In either case, it is essential that a perfect sealvbe )formed between the vitreous material composing the container the condition exists is the'incandescent electric lamp. For this reason, I shall disclose my invention with respect more particularly to that type of appliance, although the invention is not limited in its application to the particular form of appliance.

The formation of the seal of an incandescentelectric lamp may be accomplished in different ways, but the best known and usual way is to insert the leading-in wires through the hollow stem of the lamp, then soften the 'inner endof the stem by the application of heat until the glassl becomes plastic after which the glass is pressed into contact with the wires. The degree of heat necessary to bring about a sufficient softening of the glass is considerably greater than that to which the glass of the lamp is subjected under or@ dinary operating conditions. j After the plas- The best d tic glass has been pressed into contact with the wires, the same i'stallowed to cool. Dur-l ing the cooling and, more especially, as nor.- nial-temperature is approached, a contraction of the glass and the ,wires takes place.

Vheninuse, lamps of this character undergo considerable changes of temperature in the vof the leading-in wires and the glass results in a series of minute cracks or fractures around the wire, which is known as checking.

In the past the problem of forming a satisfactory seal'has been attacked` many4 different ways; y It was very early discovered' that wlres of "course of which alternate expansions and lamps without making use of platinum is short length of platinum wire to the ends of platinum could be successfully used in making the seals .for incandescent electric lamps. Thev reasons why platinum could be used to advantage in making such seals are quite 00 numerous.v The several physical characteristics of platinum/all seemed to meet'the conditions requisite for. a good seal. The coefficient of expansion of platinum is .more nearly that of glass than anyv of the .other metals capable of withstanding the degree of heat necessary to soften the glass of the stem, and incident of the formin of the sea as has been previously mentione Furthermore, platinum is non-oxidizable at the tem- 'perature at which the sealing operation is performed, and thus an effective clinging s union is formed between the glass and wire. Another characteristic of -platinum is that itis a fairly good conductor of electricity. Therefore it--pan be made use of in the form of wires halving a small enough di'-l ameter so that the difference in the expansion of the glass and the wire is compensated by the available elasticity of the glass and its. adhesive qualities to assure a permanent union between the glassuand the wire. Since the discovery that platinum could be advantageously used in forming the seals of incandescent lamps, many experiments have been tried to cut down the amount of platinum used, because of its cost and scarcity. The most successful expedient to accomplish the result has been to make use of avery which were attached other wires formed'of a cheaper metal.A This wire was placed in the stem ofthe lamp andthe glasscompressed around the platinum'portion. Thus, that portion of the leading-in wire formed of platinum and perfectly sealed 4with the glass gives the desired result, but still the vscarce metal platinum is necessary to such result.' A recent attempt to solve the problem of forming a seal yfor incandescent electric to seal into the vitreous wall -of the container a leading-in wire having a nickel-iron alloy core whose coefficient of expansion is materially less than that of the glass with which it isto be used, this core carryinga sheath y' of high melting' and high conductive ma' terial, whose coefficient of expansion is considerably above that of such glass, the sheathv and core beingsofrmly unitedthat .the com= ,l 0

si'on 'longitudinally 'and transversely, which is' the resultant of the coefficient of the core and sheath respectively and which is somewhat less than that of the glass in which it is to be used. The result is to produce strain in the glass around the wire. Leading-in wires of this type have somewhat supplemented platinum leading-in Wires, due to the extreme scarcity of platinum, but they are by no means entirely satisfactory. Unless the. resultant coefficient of expansion is exactly right, all the described objections incident to the othei` leading-in wires characterized above are present. If the coefficient of expansion is to'o great, the clinging union between the glass and the wire is broken; il the coeflicient of expansion is too small, then the glass is fractured. lvloreover, unless a sheath of certain character is used, the surface of the sheath will become oxidized and interpose the objectionable oxidized film, to cause leaks. Due to the great difficulty of obtaining the exact coeicient 'to an alloy core, making it impractical to use these wires in high power lamps.

All of the above attempts to avoid the use of platinum were predicated upon a wrong assumption. It was very evidently considered to be impossible to select from the elementary metals, .other than those of the platinum group, iridium, palladium, etc., a. material suitable for leading-in wires, because, in any such cons-ideraton, there was apparently either too wide a difference in the coefficient of expansion between such other metals and glass, or the electrical conductivity was very poor, or the melting point was too low, or a film of oxide resulting in leaks would be formed in making the seal.

I have discovered, however, that gold in its pure state will serve the purpose. Gold, being an element, has all theY advantages which an alloy lacks to make a good seal.

i Its properties and characteristics in its pure state are so fixed and constant that it is lcommonly known as a true metal. It does not have the tendency common in many metals ofl taking on different properties'and characteristics under diHerent conditions. There is no shifting of the molecular structure, as in the alloys. Gold is known too be a good conductor of electricity. For this reason, it can be used in theform of a wire of very small diameter. urthermore, in its p ure state it is highly ductile and malleable, and does not oxidize.y I have found that, with the conditions existing under which my seal is made when gold wire is used, there is no tendency for the glass to check.' Because of the good conductivity of gold, a very fine wirecan be used and therefore the total difference of expansion between gold and the glass in the range of temperature to which they are subjected in this use is quite small. Within this difference of expansion, the adhesive properties between the gold and glass exceed the tensile strength of the materials, so` that they will not separate. The natural elasticity of the materials under the conditions of use allows them to be distorted the slight amount necessary in order to'preserve the union between them. This is apparent-ly true, however, only when the gold is in substantially as pure a state as it can be obtained and has a clean surface and is used in the form of a fine wire. Since gold is such a good 'con- `ductor of electricity, the diameter of the sealing-in wire necessary to use for high power lamps is not suflicient to result in a difference of expansion between the glass and wire to break their sealing union. Preferably, use is made of buta very short piece of gold wire, so that the longitudinal difference of expansion is very slight and is not sulicient to overcome the described relation of adhesiveness and tensile strength. The ends of the gold wire may be joined to the outer and inner sections of the leadingin wires with little metal knobs, which act as anchors and force longitudinal expansion and contraction of the gold wire in conformity with the glass.

A seal constructed in accordance with my discovery is free from the disadvantages attendant when the seal is made as heretofore attempted without the use ofplatinum. It has all the advantages of a platinum seal, as long as the gold is pure and of small crosssection, and also the added advantage that it is not so expensive and is reasonably. easy to obtain. It is not necessary, as heretofore considered in avoiding the use of platinum, to go to all the trouble of compounding alloys or vadding sheaths with their attendant difficulties and unsatisfactory results. It is necessary only to refine the gold to a chemical purity, then draw it into wires of suitable size. The seal itself is free from any film of oxide and there is a strong union .between the gold and glass. There is therefore no opportunity for a leak through the union.

In illustrating my-invention, Ihave shown it as adapted for use in connection with an incandescent-electric lamp. The invention, however, is not limited in its use to an, i..- candescent eectric lamp, but is applicable wherever it is desirous lof obtaining a seal between a vitreous container and the leadingin wires.

Referring now to the single figure of the drawing: l

A bulb of the type common to the 4ordinary incandescent electric lamp is represented by the reference character 1 and is provided with the customary threaded mellO iso

tallic base 2. The wires 3 running from the base to the stem are of the usual typeand are preferably of copper. Attached to these wires and sealed in the lower part of the stem are the gold sealing-in wires 4. To the sealing-in wires are attached the supporting wires 5 which are of some stiff wire, such as steel or nickel or nickel-steel, and carry the luminant 6.

In one method of making the seal, two pieces of pure gold wire, preferably of as small cross-section and short length as the practical or desired electrical conductivity will permit, are used. As these pieces have been cut the proper length, it is important to keep them of the-original length and pr vent their shrinkage in the act of joining them, by heating the metals, to the copper and steel sections. Each seal is made in the same manner.

Under the practical conditions met inthe making of the seal according to this method,-

yI have found it particularly advantageous to form a globule of molten or plastic copper on the end of the copper section and push the gold wire into it just before it sets. Another like globule of copper is formed on the end of the steel section and the other end of the gold wire is pushed into it, just before it sets. In this manner, the proper and desired length is retained in the sealing-in gold wire and the copper and steel wire are effectively joined to it at the ends. The differences in the melting points between the three sectionsof the leading-in wires necessitated by their desired characteristics and the desire to avoid shortening the gold wire due to the joining of the sections by heat, present a problem in this particu ar art which I have solved successfully in the manner described. I

Another way in which the -sections of the composite wire may be joined 1s as follows: The gold4 and steel wires are first joined in a Anovel manner. The ends of these two wires are respectively heated to different derees. The end of the gold wire is heated sufficiently to melt and forni a globule; the end of the steel Wire is heated but notsufiiciently to cause it to become dull red. This is accomplished by holding the wires in different portions of the flame. The steel wire is then thrust into the gold globule and then both Iwires are withdrawn from the flame. The steel has not been subjected to sufficient heat to cause the formation of an oxide coating thereon and the gold will tightly adhere to the steel.. The gold wire is then trimmed to ,the proper length and the copper Wire joined thereto as previously outlined.

In either way, there are formed at each end of the gold wire metal globules 7 ,I which act as anchors and force longitudinal eX- pansion and contraction ofthe gold wire in yconformity with the glass.

and no traces of checking or gas bubbles is discovered. The seal is tight and when placed in a lamp, in the manner from this point well known, will absolutely prevent any leakage.

Thus, it is seen that I have discovered that a seal can be made without the numerous disadvantages encountered in the previous seals by the utilization of the element gold, freed "from all,impurities and preferably joined with the other sections'of the leading-in wires as in the manner described.

I claim as my invention:

l'. The method of joining copper, gold and nickel steel wires, which consists in fusing a copper globule on the ends of the copper and nickel-steel wires, and then inserting the ends of the gold wire in these globule-s.

2. The method of joining copper, gold and nickel steel wires, which consists in fusing the gold wire'to the copper wire, fusing a copper globule on the end of a steel Wire, and fusing the gold wire toy the copper globule. v

3. The method of connecting gold wire "to vother wires which consists in inserting the ends of said gold wire in molten globules of copper in connection with the other wires, and permitting the globules to harden.

4. The method of connecting gold wire to a wire formed of a substance having greater rigidity than gold which consists in applying molten globules of copper to the ends of/said gold wire and inserting in said globules while molten, the ends of the connectlng more rigid w1re.

JOHN ALLEN HEANY.

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