US2276218A - Wire seal, particularly for use in incandescent lamps and discharge tubes - Google Patents

Description

March 10, 1942.

l -L-liLEMMENS A 2,276,218

WIRE SEAL PARTICULARLY FOR USE IN INCANDESCENT LAMPS AND DISCHARGE TUBES Fig.1.

Filed June 15, 1940 5 mmD His A1: torneg.

-wire thickness is about 0.03 millimetre.

Patented Mar. 10,- 19 42 UNITED STATES PATENT- OFFICE WIRE SEAL, PARTICULARLY FOR USE'IN IN CANDE SCENT TUBES Hendricus Johannes Lemmens, Eindhoven, Neth- LAMPS AND DISCHARGE erlands, assignor to General Electric Com- Application June 15, 1940, Serial No. 340,829 In the Netherlands May 27, 1039 8 Claims. (c1. 49-92) also been suggested to seal band-shaped metal in layer may be used than in the case of a metal such as molybdenum. A tungsten wire will be chosen for example when the seal is. to be given a high thermal load; in this casexuse'is made of the fact that tungsten has a very high melting point and does not volatilise rapidly.

If molybdenum is used as the wire material the layer of quartz or quartz-glass fused to the wire It has quartz but again the thickness of this band is but,

The known seals are therefor only suitable for use at comparatively low current strengths and if a seal is desired for higher current strengths somewhat complicated solutions must be resorted to, use being made, for example, of a plurality of j seals connected in parallel or the like. This renders the use of such seals rather expensive whilst the manufacture oftenentais difficulty and requires operators of high skill.

The invention provides means permitting of obtaining a very reliable seal which, owing to the fact that wires of very considerable thickness, for example of a few millimeters, can be sealed, may also be used for comparatively high current strengths.

In the seal according to the invention the wire is made of a material having a melting point exceeding 2000 C., has a diameter D of at least 0.05 mm. and has a layer of quartz or quartz-glass fused to it, the thickness of the layer being not more than 0.24 mm. with wire thicknesses of less than 0.6 mm. and not more than 024+ ('D- 0.6) 0.16 mm. for wire-thicknesses exceeding 0.6 mm.

r The invention is based on recognition of the fact that seals which remain gas-tight at high temperatures even after a long time of operation, and in which comparatively thick wires are sealed into quartz can be obtained if care is taken that the film of quartz or quartz-glass isvery thin compared with the wire.

The value indicated above for the thickness of the quartz or quartz-glass layer on the wire is a maximum value. If the layerathickness is chosen in accordance with the maximum admissible value a seal is obtained which, although a certain wastage occurs in manufacture, satisfies all requirements when in use and continues to satisfy them and notably does not manifest the defect of known seais of eventually losing gas-tightness.

In the case of a metal such as tungsten a thicker preferably has a thickness d of not more than 0.24 mm. with wire thicknesses D less than 0.6 mm; and a thickness of not more than 024+ (D-0.6)0.l6 0.8 min. for wire thicknesses exceeding 0.6 mm.

Molybdenum is preferably chosen as the ma: terial for the wire if a small evolution of. heat, resulting from the heat evolved in the .wire, is desired or because of further treatment.

Apart from molybdenum and tungsten other metals, alloys and compounds having a melting point higher than 2000 C. may naturally be used for the wire in the seal. Thus, for example, tantalum may be'mentioned.

The seal described above is of value if it is desired for any reason to have a wire of a metal having a melting point higher than 2000 C. to which an insulating film is fused, for example if the occurrence of'flashing-over between two electrodes is to be avoided in a discharge tube; in this case one of the electrodes or both may be provided with the layer according to the invention.

The seal according to the invention is con- 'veniently made with the'aid of a quartz tube.

invention is of great importance in connecting with the attachment of metal wires of the abovementioned kind and dimensions to a bulb of an electric incandescent lamp or discharge tube. For this purpose the quartz layer of the seal may have a glass or quartz bead fused to it. The choice of the material of thebead depends inter alia on the material of the bulb.

It is preferable with such a lamp or discharge tube that the part of the bulb which is immediately adjacent a seal should be substantially normal to the Wire.

The seal according to the invention when equipped with a bead can be used by itselfjor various purposes. Thus, for example, such a bead can be used as a support for metal members. For example the ears which support the'filament of an electric incandescent lamp could be inserted in such a bead secured to a tungsten wire.

In order that the invention may be clearly understood and readily carried into effect it will now be described more fully with reference to the accompanying drawing.

Fig. l is a graph showing the relation that exists between a wire thickness D and an associated quartz layer having a thickness d, that is to say the graph indicates at each value of the wire thickness the maximum admissible thickness of the quartz or quartz-glass layer. The wire thicknesses are plotted as abscissae, the layer thicknesses as ordinates. The relation ,registered in the graph was ascertained by experiment. The line ABC shows the relation which applies if tungsten or another metal or alloy having a melting point exceeding 2000 C. is chosen as the material for the wire. Dots indicate those seals which proved durable with tungsten sealed in quartz, whereas those seals, formed of the samematerials, which failed are denoted by circles. It is found that the line ABC satisfies the following relation: d =0.24+(D-0.6) 0.16 mm.

From this graph it follows, for example, that with a tungsten wire of 2 mm. thickness the maximum permissible thickness of the quartz layer fused to such a wire is 0.47 mm. For a wire thickness D= mm. the thickness of the quartz layer has a maximum value of 0.94 mm. It is obvious that the great advantage is obtained whenfollowing the rule given that even thick tungsten wires can be sealed into quartz.

It is found that it is generally undesirable to choose the maximum permissible thickness for the thickness of a quartz layer to be fused to a metal wire since in this case wastage is liable to occur in manufacture. Thus, it has been found -by us that when the wire to be fused in the quartz is made of molybdenum, it is desirable that the thickness of the quartz layer should not be higher than d=0.24+(D-0.6) 0.16X0.8 mm. This line is designated in the graph shown in Fig. 1 by ABD.

Fig. 2 shows, on a larger scale, a seal according to the invention in which the tungsten wire I has a thickness D of 2 mm. In this case the thickness d of the layer 2 is 0.4 and this is slightly lower than the maximum permissible value of 0.47 as follows from the line ABC of Fig. 1. It is found that the quartz layer 2 is so firmly sealed on the tungsten wire that if attempts are made to break this seal it is more likely that quartz fragments break from the quartz layer 2 than that the adhesion between the wire I and the layer 2 is disturbed.

the adhesion which occurs between the tube 4 and the wire 3 due to the heating operation. When the heating has been finished the lefthand part of the tube 4 is removed along the plane TI and the seal has thus assumed its final shape.

Fig. 4 shows a tungsten wire 5 having mounted on it a quartz layer 6 and on top thereof a glass Fig. 3 shows another method of providing-a which is contained in the space R and in the annular space between the wire 3 and the tube 4 is driven off so that it escapes at S. The oxide which is formed is also driven off and this prior to bead l. The figure shows that the quartz layer 6 extends on either side of the glass bead. This projecting portion may be removed, for example, by grinding but due to the fact that the bead is made of material different from that of the layer it is possible to ascertainthat the glass bead is applied tothe metal wire by way of an intermediate layer of quartz. In addition, the fact that the portion of the layer which extends from the bead is ground away can be discerned due to the subjacent wire surface not being burned at the area where the layer'is ground off, this burning being always present to a greater or less extent with the metal surface that has not been coated with quartz. This latter fact is due to the action of the flame used during sealing.

Fig. 5 again shows the tungsten wire of Fig. 4, the glass bead I mounted on the quartz layer 0 being, however, sealed to a glass wall I, for example, the bulb of an electric incandescent lamp. The figure shows that the portion of the lamp bulb which is immediately adjacent the seal is normal to the tungsten wire 5 existing in th seal.

What I claim is:

1. A gas-tight, electrically conducting seal comprising a metal wire and a layer of quartz fused to said wire, said wire having a melting point higher than 2000 C. and a diameter of at least 0.05 mm., the thickness of the quartz layer and the diameter of the wire being in such relation that the layer is not more than 024mm. thick when the diameter of the wire is less than 0.6 mm. and not more than 0.24+(D-0.6) 0.16 mm. thick when the diameter of the wire is greater than 0.6 mm. where D is the diameter of the wire.

2. A gas-tight, electrically conducting seal comprising a tungsten wire and a layer of quartz fused to said wire, said wire having a diameter of at least 0.05 mm., the thickness of the quartz layer and the diameter of the wire being in such relation that the layer is not more than 0.24 mm. thick when the diameter of the wire is less than 0.6 mm. and not more than 0.24+(D-0.6)0.16 mm. thick when the diameter of the wire is greater than 0.6 mm. where D is the diameter of the wire.

3. A gas-tight, electrically conducting seal comprising a molybdenum wire and a layer of quartz fused to said wire, said wire having a diameter of at least 0.05 mm., the thickness of.

0.24+ (D 0.6) 0.16X0.8 mm. thick when the diameter of the wire is greater than 0.6 him. where D is the diameter of the wire. 4. A gas-tight, electrically conducting se comprising a metal wire, a layer of quartz fused to said wire anda head of vitreous material fused to said quartz layer, said wire having a melting point higher than 2000 C. and a diameter of at least 0.05 mm., the thickness of the quartz layer and the diameter of the wire being-in such relation that the layer is not more than 0.24 mm. thick when the diameter of the wire is less than 0.6 mm. and not more than 0.24+(D-0.6)0.16

mm. thick when the diameter of the wire is greater-than 0.6 mm. where D is the diameter of the wire.

5. A gas-tight, electrically conducting seal for a vitreous envelope having a planar portion, said seal comprising a metal wire normal to the planarportion of said envelope, a layer of quartz fused to said wire and a bead of vitreous material fused to said quartz layer for fusion with said envelope, said wire having a melting point higher than 2000 C. and a diameter of at least 0.05 mm., the thickness of the quartz layer and the diameter of the wire being in such relation that the layer is not more than 024mm. thick when the diameter of the wire is less than 0.6 mm. and not more than 0.24+(D-0.6)0.l6 mm. thick when the diameter .of the wire is greater than. 0.6 mm. where D is the diameterof the wire. 7

6. A gas-tight, electrically conducting seal comprising a metal wire, a layer of quartz fused to said wire and a glass bead fused to said quartz layer. said wire having a melting point higher than 2000 C. and a diameter-of at least 0.05 mm., the thickness of the quartz layer and the diameter of the wire being in such relation that the layer is not more than 024mm. thick when the diameter of the wire is less than 0.6 mm. and

the diameter of the wire is greater than 0.6 mm. where D is the diameter of the wire.

7. A gas-tight, electrically conducting seal than 0.6 mm. where D is the diameter of the wire.

8. A gas-tight, electrically conducting seal comprising a tantalum wire and a layer of quartz fused to said wire, said wire having a diameter of at least 0.05 mm., the thickness of the quartz layer and the diameter of the wire being in such relation that the layer is not more than 0.24 mm. thick when the diameter of the wire is less than 0.6 mm. and not more than 0.24+(D-0.6) 0.16

'mm. thick when the diameter of the wire is greater than 0.6 mm. where D is the diameter of the wire.

HENDRICUS JOHANNES LEMMENS.

, 3 not more than o.'24+ n-o.s) 0.16 mm. thick when.

Images