US2276048A - Lamp making method - Google Patents

Description

March 10,1942. c. A. LAlSE 2,216,048

LAMP MAKING METHOD Original Filed March 23, 1955 l l l' I l I i'g12w. /0 ,Z v/ &2. a 2 v 5 a Q: I

. INVENTOR CLEMENS ALNSE DECEASED av FIDELITY umou TRUST dompmv Ado "7M6 TIME RUDOLPH SIEVERT, ExEcuTo RS ATTORN.

. the lamp construction.

Patented Mar. 10, 1942 LAMP MAKING METHOD Clemens A. Laise, deceased, late of 'lenafly, N. 1., by Fidelity Union Trust Company, Newark, N. J., and Rudolph Sievert, Weehawken Township Hudson County, N. J., executors, assignor to Callite Tungsten Corporation, Union City, N. J., a corporation of Delaware Original application March 23, 1935, Serial No.

1939, Serial No. 277,944

1 Claim.

This invention relates generally to improvement in high efiiciency incandescent lamps, and especially to lamps of the character that utilize metallic filaments as light emitting elements. An important feature of the invention concerns a novel electrical circuit, preferably embodied in the lamp structure itself, which is adapted to produce a higher efliciency combined with longer life than is possible to attain with the lamps of the art' as heretofore known. The invention-is particularly concerned with the construction of such a. lamp and circuit and method of making the same, which is especially well adapted for use in lamps produced in conformity with the principles herein set forth. f

This application is a division of United States Patent No. 2,214,742, issued September 17, 1940.

The expression "high efficiency lamp as used in the present application needs a certain definition. It is probably true that this term has been in use since the early days of the lamp 'art.

of metallic filaments, the lamps utilizing these filaments became known as high eiliciency lamps. The term, however, had meaning only in comparison with carbon lamps and other lamps of lesser efficiency. With the appearance of the tungsten filament lamp, the term acquired a new meaning and when this was followed by the gas-filled lamp with a coiled tungsten filament, it was'thought that a lamp of this type was the high efli'ciency lamp."

Developments of recent years, however, have shown still higher emciencies are possible. For, whereas in 'formertimes each increase in emciency was attained by 'use of an improved filament material or by use of a more suitable gaseous atmosphere, it has lately been the aim to use the same gaseous atmosphere and the same filament material but to attain greater efliciency by applying more exact engineering principles to Divided and this application June 7,

creases. There is, therefore, at the instant of switching on, a sudden surge of current through thefilament which produces a shock sufilcient in many cases to rupture the filament.

It is an object of the present invention to provide a lamp capable of attaining the highest possible emciency and which at the same time will be capable of preventing the surge and consequent shock due to the switching on of the current.

It is a further object of the invention to provide a lamp of the highefliciency described that will have a long commercial life. The elimination of the initial surge, of course, is the pri- It is certainly true that with the introduction In the lamp art, efliciency consists in obtain-'- ing the greatest amount of lumens per watt consistent with a sufficiently long life to satisfy commercial and practical needs. As efiiciency is increased, the life ofthe lamp is shortened, other things being equal. In the-lampart of thepast, however, the highest possible efliciency was rarely attained for the reason that such a lamp was not well adapted to sustain the shock of turning the current on or off. A metal filament is most conductive when coldybut as the mary reason for this longer life, not only because -with the elimination of the surge the shock is leads and the concomitant destruction of the filament at the point -of junction with the leads.

It is a still-further object to provide a lamp of .high efliciencyhaving lead wires of small diameter and hence with only slight cooling effect upon the filament. In lamps of the present art, the cooling effect of the leads is sufficient to cause relatively largedifierences in temperature with the highest temperatures midway between the leads. When suchdifl'erences of temperature exist, the filament frequently ruptures or fuses at the exceedingly hot midway point.

To accomplish these objects of the invention, aspecially designed circuit is provided in the lamp.

The preferred elements of the circuit above suggested comprise a filament of the physical and mechanical structure hereinafter described; a resistance element having resistance characteristics opposed to those of the filament and sumcient to balance the initial current surge;

and leads of small diameter and high conductivity. Such a circuit is represented diagrammatically in Fig. 1 of the annexed drawing. In Figs. 2 and 2 are illustrated cross-sectional and longitudinal sectional views of the filament;

temperature increases, the resistance also in- 56 the circuit and filament may be incorporated in a standard type of lamp; Fig; 5 shows a current-time curve of the initial operation of'an ordinary lamp; and Fig. 6 shows the currenttime curve of a lamp constructed in accordance with the invention; Fig. 7 is an .enlarged section taken along the line 1 1 of Fig. 3 showing the construction of the lead wires.

The above described elements will be described seriatim. First, the filament. The filament of the lamp of this invention may be of the general type described and claimed in Patent No. 1,631,- 493, consisting of tungsten as a base with additions of boron nitride or boron-suboxide and potassium borate which have a scavenging efiect.

The metallic bar from which the filament is drawn is so treated that at the sintering or metallizing temperature a portion of the scavengers distils out and takes along with it detrimental impurities that may be present in the tungsten base. The amount of such scavenger additions is such that in the final filament the amounts remaining are very minute, being one-quarter of minimum, the filament has little tendency to twist or distort after it has been shaped and set into suitable concentrated form.

One prime cause of brittleness in tungsten filaments of the granular type of the prior art,

is the presence of foreign non-metallic sub stances in the grain boundaries. For instance, in the old pressed or squirted tungsten filaments, an organic binder was used which became carbonized during the process of manufacture and formed carbides in the crystal boundaries. In the drawn tungsten filament as first produced, additions of various substances, such as the xides of calcium, aluminum or thorium, were added for the purpose of retarding the growth of crystals. This practice resulted also in compounds in the grain boundaries that tended to produce a brittle filament, particularly after a short period of use. In the later so-called nonsag tungsten filament additions are made to the metal that produce silicon compounds and probably also hydrides in the' grain boundaries with a resulting brittleness after relatively short use.

All such intergranular substances act solely as cements holding the grains together and preventing the grains from coalescing and forming larger grains. In the filament of the present invention, however, the cementing material is composed of scavenging substances which are added to the tungsten powder from which the slugs are made and from which they are drawn down to filament diameters. After the addition of the scavenging material to the powder, the same is worked into slugs in the usual way and the conditions of manufacture and heat treatment so regulated that they have a grain count of approximately 15,000 to 20,000 grains per square millimeter.

The slugs are mechanically worked by swaging and drawing into wire and then concentrated into coils or coiled-coils or rolled into ribbon and corrugated or twisted into concentrated form. In making coiled coils of filament wire, the wire should be so wound that the magnetic effect due to the line of force generated about it will not cause shortcircuiting.

When making coils or coiled-coils, mandrels of nickel or nichrome or other refractory metals soluble in acids may be used and the coil or coiled-coil is heated on the mandrel preferably in an atmosphere of wet hydrogen at temperatures ranging from 1000 C. to 1500 C. until a permanent set is imparted to the filament and the wire has been relieved of all of its strain. Thus, there will be no readjustment of the coil after the mandrel is dissolved out.

Wet hydrogen is used, a practice contrary to that of the present art in which dry hydrogen is used in such operations, for the reason that wet hydrogen tends to decompose carbides on the surface or in the grain boundaries of the filaments. If dry hydrogen is used, carbides are likely to form with the filament metal in the presence of carbon or carbon compounds. As a result of the process employing wet-hydrogen, the pliability and ductility of the filament is not impaired as it would be if dry hydrogen were used.

The heat treated coil and mandrel are then cut to proper lengths togive the proper voltage of lamp and the mandrel is then dissolved in suitable acids such as nitric acid and sulphuric acid if nickel or nickel alloys are used as mandrel wire.

After the coil or other shape of filament treated in the above manner is mounted into the lamp, the lamp is sealed and exhausted or filled with gas and then flashed by connecting the lamp in series with a rheostat or nichrome resistance at about 125% over voltage,--that is, 125% of the rated voltage of the filament for a period of about five minutes, so that the filament quickly attains the germinating temperatures and the grains coalesce or fiow into each other, producing a light emitting medium with long interlocking sections which have little tendency to sag or distort. Such sections may consist of at least one turn'and preferably several turns of coil, especially after the lamp has burned about one hour at its rated voltage.

During the flashing operation it is desirable to use twice the voltage of the greatest voltage of the lamp and so regulate the proper voltage in this temporary circuit so that about 125% drop takes place across the lamp and in the balance of the circuit consisting of a suitable rheostat.

During the heat treatment above described,

the scavenging materials tend to distil out, carrying with them substantially allimpurities, including occluded hydrogen, that may be present in the grain boundaries. With these impurities eliminated, there is little obstruction to rapid grain growth and the formation in the filament of long sections and but few interlocking section boundaries. Instead of the particular scavenging materials mentioned, other refractory nitrides may be used with excellent effect, such as tions of a straight filament composed of interlocking sections 9 and 10, which are representative of the filament structure above described.

It is apparent that this filament of few interlocking sections can be operated at a much higher efficiency or lumen output and longer life than a highly crystallized filament of many grain boundaries. Furthermore, it retains its shape after it is once permanently set or flashed by the special process in the lamp circuit of this invention, so that it does not droop, shrink, twist or short-circuit between the individual sections.

The shape of the light emitting filament may be a round cylindrical wire section, a square or oblong ribbon section, or may be in the form of ribbon corrugated or twisted or in the form of a coilora double coil or helical coil.- For gasfilled lamps, especially of the higher voltage type, a concentrated form such as'a coiled-coil is de-' sirable. In every case, however, the principle of treating the specially prepared filament body remains the same, namely, that the filament body ment ispreferably mounted upon lead wires of the general type described and claimed in the patent to Clemens A. Laise andJacob Kurtz No.

2,120,561, dated June 14, 193 but the diameter.

of these lead wires, by virtue of the exceptional heat and current conductivity characteristics of the material thereof, may be made much smaller than that generally used in lamps of the present art of equivalent wattage andmay be as small as 50% of the cross-sectional area of the lead wire of such generally used lamps.

The wire described and claimed in said Patent No. 2,120,561 may be described generally as being composed of a nickel sheath and a copper core, the nickel constituting a relatively large propor tion of the total wire and at least 10% thereof. In cross section such a wire appears as indicated in the enlarged view of Fig. 1.

A third and very important feature of the invention is that the resistance or ballast disposed in the circuit is incorporated in one of the leads either within the stem as indicated at l5-in Fig: 4, or without it as shown at l5.in Fig. 3; or it may even be arranged outside of the lamp.

The purpose of this ballast or resistance is to eliminate the sudden surge of current through the lainp. It may consist. of a small choke coil or similar device which momentarily has a high resistance'when connected across a difierence of potential and-then, as the current begins to flow, the resistance is practically eliminated so that the loss of power due to the presence of the same is practically negligible.

This coil or equivalent resistance may be imbedded, in metallic oxide and may or may not be enclosed in a ceramic, or resinous, or Bakelite composition which holds it in place and insulates it both electrically and thermally. The conducting oxide may be iron oxide or other equivalent oxide or conducting material which has a high current in the same lamp when operating at its.

rated voltage. This is illustrated by the curves Fig. 5 which indicate the initial surge of the lamps of the present art, and Fig. 6 which indicate the initial performance of a lamp of the present invention.

The resistance or ballast is such that it does' not cause substantial loss of power in the circuit during the normal operation but merely dampens, reduces and tends to preventthe initial surge of current when the circuit. is first connected across a difierence in potential. This elimination of sudden surge of current prevents or retards the sudden rupture of filament at the grain boundaries and also reduces possibility of arcing across the lead wires.

Figs. 5 and 6 above referred to are comparative curves with current plotted against time showing the effect of the circuit of the present invention. In Fig. 5 the initial surge of current. introduced into an ordinary'lamp is considerable but is quickly reduced to a constant value after a few seconds. In Fig. 6 the initial current introduced into a lamp constructed in accordance with the principles of the present invention is shown to rise gradually to a constant value after a few seconds said filament in said lamp at an over-voltage,

resistance when cold and becomes very conductive when heated up slightly.

The surge preventive inthe invention is placed directly into the circuit of theincandescent lamp either inside of the bulb, which is preferred, or

thereby bringing said filament instantaneously up to the germinating temperature of the grains and producing long sections of filament and interlocking boundaries between said sections.

FIDELITY UNION TRUST COMPANY,

By L. G. McDOUALL,

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