US2216247A - Lamp terminal structure and method of manufacture - Google Patents

Description

w. LEDIG El AL 2,216,247 LAMP TERMINAL STRUCTURE AND METHOD OF MANUFACTURE Oct. 1. 1940.

Filed m 28, 940

Fig. 2.

Inventor Willg Ledig}. Georg Trebbin, Heinz Seffer'i IIJ bww;

Patented Oct. 1, 1940 LAMP TERDIINAL STRUCTURE AND METHOD OF MANUFACTURE Willy Ledig, Berlin-Lichtenrade, Georg Trebbin,

Berlin-Spandau,

and Heinz Seflert,

Berlin,

Germany, assignors to General Electric Company, a corporation of New York Application May 28, 1940, Serial No. 337,730 In Germany April 5, 1939 6 Claims.

Our invention relates to a seal and base construction for electric incandescent lamps and discharge devices particularly of the tubular type, such as the commercially known lumiline and fluorescent lamps. More particularly, our invention relates to a method and apparatus for sealing and basing lamps of the above type.

The most usual method for sealing the customary stem tube to the envelope of electric incandescent lamps and discharge devices consists in sliding the envelope, which is provided with along neck portion, over the glass lamp. mount and in subjecting that area of the neck surrounding the edge of the stem tube flange to scaling fires or flames. As a result, the heated portion of the neck softens and contracts until it comes in contact with the stem tube flange and fuses therewith, the superfluous part of the neck separating and dropping ofii. It has also been proposed to press the envelope neck slightly, near the sealing point, by means of special squeezing clamps or jaws in order that the lamp base which is' secured to the envelope neck, or the cement which is used for fastening the base, may secure a good hold behind the recesses produced by such squeezing jaws.- Methods have also been employed in which the lamp envelope is out exactly to its final length before the sealing of the same, the sealed joint being subjected to the pressing action of squeezing jaws so that the part of the envelope neck which in itself is superfluous and constitutes only waste material can be dispensed with.

The method according to the invention likewise employs a lamp envelope out exactly to its final length. However, the envelope and lamp mount are mounted on a metal ring member whose outer edge is bent or curled upwardly or inwardly towards the lamp envelope preferably in.

a curve somewhat in excess of a 90 are so that when the edges of the envelope neck and the stem tube flange become softened through fusion, the glass will flow into and fill the annular recess formed by the said curled edge. Consequently, when the seal cools, the metal ring member shrinks slightly and in this manner presses with considerable force against the glass bead within its rounded edge; The metal ring member is thus securely fastened to the end of the lamp envelope. A base is then mechanically fastened to said metal ring member in definite relation thereto. In this manner the overall length of elongated tubular lamps and discharge devices can be easily and accurately controlled.

One object of our invention is to provide a seal and base construction for electric incandescent lamps and discharge devices.

Another object of our invention is to provide a method of sealing and basing elongated tubular lamps and discharge devices of the double-ended I type whereby the overall length thereof may be easily controlled and maintained within accurate limits.

Still another object of our invention is to provide apparatus for sealing the envelopes of electric incandescent lamps and discharge devices.

Further objects and advantages ofuur invention will appear from the following description of a species thereof and from the accompanying drawing in which:

Fig. 1 is a longitudinal cross-section of the apparatus employed to form a seal according to the invention, the lamp parts being shown mounted together in position preparatory to the sealing process; Fig. 2 is a top view of the heating element employed in the apparatus according to the invention; Fig. 3 is a longitudinal sectional view of the finished seal comprising our invention; Fig.

4 is a longitudinal sectional view of the end portion of a lamp provided with the seal and base construction comprising our invention; and Fig. 5

is a top view of the metal ring member employed in the formation of the sealaccording to the invention.

, Referring to the drawing, the apparatus there shown comprises a heat-resisting block or base member i of insulating material, having a central hole 2. Mounted on the block l is a heating element or band 3 of suitable heat-resisting metal which can be heated directly by means of an electric current flowing therethrough. This heating band is likewise formed with a central opening 2! which is aligned with the hole 2 in the base member. A hollow stop pin 4 of heatresisting insulating material extends up through the aligned openings 2 and 2i and is formed at its upper end with-a conical head 5. A heat accumulator ring 6 of insulating material, having an enlarged opening 6', is concentrically mounted on the heating band 3, this ring having the function of storing up heat during the sealing process.

, The heating and fusion ofthe glass lamp partsto thereby form the seal is effected by the conduction of heat thereto from a metal ring member I which is concentrically placed on top the heating band 3, within the opening 6' in the heat accumulator ring 6. This metal ring member I is itselfheated by conduction of heat from the heating band 3, the latter being heated bythe passage of current therethrough. To produce an 1 even, uniform heating of the metal ring member I, the heating band 3 must carry, on the surface on which the metal ring member I rests, the same current density throughout. To obtain this result, the heating band 3, because of the presence of the central bore 2| therein, is provided with a number of small holes 22 and cuts 23, as shown in Fig. 2, which are so arranged as to produce substantially equal current densities on the surface on which the metal ring member I rests, i. e. they produce an even distribution of the current density around the central bore 2|.

The metal ring member I may consist of any material which can sufliciently withstand the high temperature to which it is heated during the lamp sealing operation. It may consist, in particular, of a metal whose coeflicient of thermal expansion is higher than that of the glass of which the lamp parts to be sealed are made. For instance, it may consist of copper. It is also possible to use a metal, for instance iron, which will not adhere to the softened glass, since the metal ring member I need not form a hermetically tight seal with the glass. The hermetic seal is accomplished solely between the two glass parts to be sealed together. The metal ring member I is provided at its outer periphery with a curved flange 8 formed by bending or curling back the outer edge in a curve of at least 90 to thereby form an annular recess therewithin. The ring member is further provided with a plurality of inwardly extending bendable prongs 9 which may be partly formed by cutting back into the ring member proper.

In forming the seal according to the invention, the metal ring member I is placed over the head of pin 4 and is concentrically mounted on the heating element 3 with its curled or bent edge 8 extending upwardly so that the said member lies flat against the heating element. A lamp mount, comprising a glass stem I I having a conventional conical flange or flare III, is mounted in an upright position on the metal ring member I so that the outer edge of the flange I0 rests on the said member. The glass stem I I is provided with a pair of leading-in wires I2, I2 which are sealed into the pressed portion of the glassstem and support a filamentary cathode I3 at their inner ends. The stem II is also provided with an exhaust tube I l through which the envelope may be evacuated and, if desired, filled with gas. To accommodate the exhaust tube I4 and leadingin wires I2, I2, the stop pin 4 is provided with a longitudinal bore I5 into which the exhaust tube and leading-in wires are inserted when the lamp mount is first placed on the metal ring member 7. The diameter of the outer edge of the flare Ill corresponds approximately to, but is made slightly smaller than, the bent or curled flange 3 on the ring member I so that the flare I 0 can pass within the curled flange I0 and rest on the flat portion of the ring member. With the metal ring member I and the glass stem I I in place, the open end of a lamp envelope is then placed over the glass stem II. In the example shown, the lamp envelope I6 is of tubular shape and is provided with a neck portion I! of reduced diameter. The outer diameter of the neck I! is made approximately the same as the diameter of the outer edge of the flare I0 so that the neck I! can just rest on the edge of the flare.

To bring about the fusion of the glass envelope I6 and the glass stem I I, a high current is passed through the heating element 3 so that the latter, and the metal ring member I which lies thereon,

attain a temperature exceeding the softening temperature of the glass. The heat is then transmitted, by conduction and radiation, from the ring member I to the glass parts I0 and I! so that the interengaging edges of the latter will soften and fuse together, the soft glass at the same time flowing into the annular recess formed by the bent or curled flange 8. During this sealing operation, a slight downward pressure may be exerted on the lamp envelope I6, In certain types of electrical incandescent lamps and discharge devices, such as the double-ended tubular type, it is necessary to maintain certain longitudinal dimensions. This can be very easily accomplished in our improved sealing method since the downward pressure exerted on the envelope I6 can be so limited by a suitable stop that the envelope, after the fusion, will have just the desired length. The conical surface 5 on the head of pin I is designed to provide a suitable seating surface or stop against which the flare II] can rest to thereby limit the downward movement of the glass stem I I during the fusion process. below the required limit.

When the glass envelope I6 and stem II are fused together completely so as to form a hermetic seal having an annular bead 25 fitting into the curled flange B of the metal ring member I, the current flowing through the heating band or element 3 is discontinued, preferably by slowly reducing the current in order that the stresses in the glass may gradually disappear by virtue of a sufficiently slow cooling process. At this juncture, the lamp envelope I6, with 'its finished seal, may be removed from the sealing apparatus. The metal ring member I is securely held to the end of the lamp envelope by reason of the gripping engagement of the curled edge or flange 8 of said member with the annular bead of glass 25 formed at the end of the lamp envelope. The secure fastening of the metal ring member I to the glass bead 25 results from the shrinking of such member upon cooling; the member being of metal, it shrinks more than the glass. reason, it is not necessary to use. as the material for the ring member, a metal that has substantially the same coefficient of thermal expansion as the glass of the lamp envelope and stem, or a metal which will wet easily to the softened glass. As a result, ordinary iron may be used for the ring member I providing the fusion point of such iron is higher than the softening temperature of the glass.

The metal ring member I not only facilitates the fusion between the lamp envelope I6 and stem I I and the maintaining of accurate lamp lengths, but because of its accurate and solid aflixation to the lamp envelope, it advantageously lends itself to the mechanical fastening of the lamp base to the lamp envelope, 1. e., without the use of cement. To this end, the prongs 9 on the metal ring member I are bent outward at right angles to the plane of said member, as shown in Fig. 3, so as to extend parallel to the longitudinal axis of the lamp envelope. A base I8, provided with openings I9 corresponding to the outwardly bent prongs 9 and through which the latter may pass, is then placed over the end of the lamp envelope with the prongs extending into the openings I9. The base may be located in definite longitudinal relation with respect to the ring member I by means of stop lugs or shoulders 26 formed on the inner side of the base, the lugs being adapted to engage the flat surface of the metal ring mem- Consequently, the glass stem will not drop For this I provided with bases at both ends.

ber l. With the base in this position, the outer ends of the prongs 9 are then bent over the outer side of the base to thereby secure the base to the lamp envelope. The openings I 9 are preferably enlarged at their outer ends, as shown at 21 in Fig. 4, so as to accommodate therein the outer bent portions of the prongs 9 and so conceal them I within the body of the base. Inasmuch as the ring member '1 serves to limit the longitudinal dimension of the lamp envelope l6 during the sealing operation, the accurate positioning of the base it is consequently assured. This feature is particularly important in the case of tubular lamps having bases on both ends. The base l8, which may consist, for instance, of suitable insulating material, is provided with two or more metal pins 2!], extending longitudinally of the lamp, to which the leading-in wires l2, l2 are soldered or otherwise connected. These pins serve as the lamp terminals for conducting the electric current to the cathode l3, and also as means for mounting the lamp in its holders or sockets. However, the base could be provided, instead, with a lateral extension 24 likewise made of insulating material and carrying the lamp contacts or terminals. Such an arrangement permits a particularly short base design, thus minimizing the overall length of the lamp.

If desired, the metal ring member I may be connected to one of the leading-in wires l2 so that it may serve as one of the contacts of the base, for-instance, as an external shell for the base. Furthermore, a metal disc may be used instead of the metal ring member I. In either case, however, a method of mounting the base is provided which permits an accurate and very solid fastening of the same to the lamp envelope with* out the use of the conventional basing cement.

It is evident that the improved method of seal ing and basing lamps according to the invention makes it easily possible to maintain the longitudinal dimensions of lamp envelopes within accurate limits, an advantage which is of especial importance in the case of tubular lamps which are An accurate manufacture is possible because of the fact that a certain definite longitudinal pressure is exerted on the lamp envelope during the fusion process, so that the softened glass mass is formed or gathered up on the metal ring member in such quantities that the entire length of the lamp envelope is reduced to a certain value. As a result of the secure fastening of the metal ring member to the end of the lamp envelope, which takes place during the sealing process, the lamp base can be applied very accurately since it may be fastened to the metal ring member without the use of cement, the accuracy being higher in such case than in the case of the conventional methodof fastening where cement is used.

What we claimas new and desire to secure by Letters Patent of the United States is:

1. An electrical device comprising a glass envelope havinga glass stern hermetically sealed to an end thereof, said envelope being provided with an outwardly extending annular bead immediately adjacent the said end of said envelope, a metal ring member fitting over the end of said envelope and having its outer edge upturned'over said annular bead and secured directly thereto, said ring member being provided with a plurality of prongs, and a base fitting over the said end of said envelope and secured thereto by said prongs.

2. An electrical device comprising a glass envelope having a glass stem hermetically sealed to an end thereof, said envelope being provided with an outwardly extending annular bead immediately adjacent the said end of said envelope, a metal ring member fitting over the end of said envelope and having a curled flange upturned over said annular bead and secured directly thereto, said ring member being provided with a plurality of prongs, and a base fitting over the, said end of said envelope and secured thereto by said prongs, said base having a plurality of openings through which said prongs extend, the outer portions of said prongs being bent over said base to thereby secure said base to said ring member.

3. An electrical device comprising a glass envelope having a glass stem hermetically sealed to an end thereof, said envelope being provided with an outwardly extending annular bead immediately adjacent the said end of said envelope, a metal ring member fitting over the end of said envelope and having its outer edge upturned over said annular bead and secured directly thereto, said ring member being provided with a plurality of prongs, and a base fitting over the saidend of said envelope and secured thereto by said prongs, said base having an abutment shoulder for engagement with said ring member to thereby position said base in definite relation with respect to said ring member in a direction longitudinally of said envelope, said base having a plurality of openings through which said prongs extend, the outer portions of said prongs being bent over said base to thereby hold said abutment shoulder against said ring member and secure said base to said ring member.

4. A method of sealing a lamp mount, comprising a glass stem tube having a flare portion,

.to a glass envelope, which consists in placing said lamp mount in an upright position on a metal ring member the outer edge of which is curled upwardly to form an annular recess adjacent the outer edge of said flare, said ring member be-,

ing made of a metal having a higher fusion point than the softening temperature of the glass of which said envelope and lamp mount are made, placing the open end of said envelope over said lamp mount into contiguous relation to the outer edge of said flare, and heating said metal ring member until the glass of said envelope and lamp mount softens and fuses together and flowsinto the annular recess formed by the said curled edge of said ring member.

5. A method of sealing a lamp mount, comprising a glass stem tube having a flare portion, to a glass envelope, which consists in placing said lamp mount in an upright position on a metal ring member the outer edge of which is curled upwardly to form an annular recess adjacent the outer edge of said flare, said ring member being made of a metal having a higher fusion point than the softening temperature of the glass of which said envelope and lamp mount are made, placing the open end of said envelope over said lamp mount into contiguous relation to the outer edge of said flare, and simultaneously heating said metal ring member and applying downward pressure to said envelope until the glass of said envelope and lamp mount softens and fuses together and flows into the annular recess formed and lamp mount are made, a ring member having its outer edge curled through an arc in excess of ninety degrees and of slightly greater diameter than the outer edge of said flare to thereby 'ireceive said flare therewithin, placing said lamp mount in an upright concentric position on said ring member with the said flare disposed within the said curled edge of said ring member, placing an open end of said envelope concentrically over said lamp mount into contiguous relation to the outer edge of said flare, and heating said ring member until the glass at the end of said envelope and the outer edge of said flare softens and fuses together and flows into the annular recess formed 6 by the said curled edge of said ring member.

WILLY LEDIG. GEORG TREBBIN. HEINZ SEFFERT.

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