US2924735A - Incandescent lamp - Google Patents

Description

Filed Jan. 31, 1957 FIG.2.V

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INVENTOR. J A CK MARTIN United States Patent() INCANDESCENT LAMP Jack Martin, Paramus, N.J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 31, 1957, Serial No. 637,447 "3 Claims. (Cl. 313-271) As presently manufactured virtually all the incandescible elements employed in electric lamps are of the coiled variety wherein a long strand of refractory metal wire, such as tungsten, is wound in the form of a helix to provide a coiled filament having a plurality of accurately formed and spaced turns. In order to facilitate connecting the filament with the lamp lead wires a seg- 1 ment of uncoiled wire is usually left at each end of the filament to provide generally straight end sections or so-called coil legs.

It has been the standard practice in the industry when mounting lamp filaments of the foregoing character to permit the end sections or legs of the coil to retain their substantially straight-line transverse relationship with the mount axis and lead wires which relationship is introduced during the mounting operation in order to facilitate the attachment of the filament to the leads. art mounting is illustrated in Fig. 3 and it will be observed that with the coil legs in this transverse position the adjoining unsupported coiled body portions of the filament Another object of theinvention is to provide a method for mounting a filamentary light source whereby the end portions of the light source adjacent their points of anchorage are automatically rendered more rigid and less susceptible to the deteriorating effects of mechanical forces. i a a The foregoing objects and others which will become obvious to those skilled in the art as the description proceeds are achieved byadjusting the filament after it has been mounted on the lamp lead wires so that its end sections inward of the leads are bowed outwardly in a manner such that the adjoining body portions of the filament are permanently strained and rigidified.

A better understanding of the invention may be obtained by referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views, wherein:

1 Fig. 1 is a perspective view of an incandescent lamp including as a part thereof the improved filament mount structure of this invention;-

Fig. 2 is a front elevational view on an enlarged scale of the filament mount employed in the lamp shown in Fig. 1 and illustrates more clearly the configuration of the filament according to the invention;

Fig. 3 is a view of a filament mount similar to that illustrated in Fig. 2 but shows the prior art mode of mounting the filament on the lead wires;

Figs. 4 and 5 are enlarged fragmentary views of one of the filament-lead wire junctions employed in the mount shown in Fig. 2 and illustrate in greater detail the spatial relation between the leads and various parts The prior proper are relaxed, so to speak, and hence easily influenced by and responsive to gravitational or other mechanical forces. Consequently, when the filament is heated to its operation temperature and the wire expands and becomes more pliable, these unsupported portions tend to sag and, should the lamp be subjected to vibration or sudden impacts, develop a pronounced whip-like motion or sympathetically vibrate at their resonant frequencies or at harmonics thereof resulting in the permanent deformation and progressive deterioration of the coil. The rate of deterioration increases as the unsupported sections of the filament are stretched and lengthened until the wire breaks or the coil becomes so badly entangled that segments are shorted out thus reducing the lighted length of the filament and increasing its temperature and vaporization rate. In either case, the filament is quickly rendered inoperative causing premature failure of the lamp.

It is accordingly the general object of this invention to provide an incandescent lamp which will have a longer useful life under adverse operating conditions.

Another object of the invention is to provide a filament mount construction for incandescent lamps wherein unsupported portions of the filament are rigidified and better able to withstand the deteriorating effects of mechanical forces normally encountered during the usage of the lamp.

A further and more specific object of the invention is to improve the hot shock and vibration strength of a coiled filament by minimizing the elfect of the sag and vibratory movement induced therein by mechanical forces encountered during operation of the lamp.

of the filament before and after the adjustment of the filament, respectively, and the manner of effecting such adjustment according to the invention;

Fig. 6 is a graphic representation of comparative test results obtained on lamps manufactured according to the prior art construction versus those incorporating the present invention illustrating the mortality rate of each lamp type when subjected to physical shock during operation;

Figs. 7, 8 and 9 are alternative embodiments illustrating the manner in which the invention may be incorporated in various types of mount assemblies and structures.

Although the principles of this invention are broadly applicable to other types of electrical devices wherein the gradual deterioration of a filamentary element is efiected by gravitational or other forces or where additional strengthening of such an element is desired, the invention is especially suited for use in miniature type lamps incorporating coiled filaments having unsupported sections of considerable length and hence has been so illustrated and will .be so described.

Referring now to the drawing, in Fig. 1 there is illustrated a miniature incandescent lamp 10 comprising gen erally a light-transmitting envelope 12 having sealed therein a mount assembly 16 upon which an elongated incandescible element 24, suchas a coiled filament of tungsten or other suitable refractory metal wire, is mounted and arranged in accordance with the principles of this invention. In order to facilitate electrical connection of the lamp 10 with a source of electrical energy a base member 14, such as the bayonet type illustrated, is provided and dependingly secured to the sealed end portion of the envelope 12 in the customary manner.

As particularly shown in Fig. 2, the mount assembly 16 comprises a pair of lead wires 20 and 22 held in spaced relation by a body of insulating material 18, such as a glass bead, which is fused to andspans intermediate portions of the said lead wires. The filament 24 is mounted on the end portions of the lead wires 20 and 22 and may be conveniently maintained in the desired configuration, such as the inverted V or so-called 02V shape shown in Fig. 2, by an elongated supportits looped end portion supportingly engages an inter.

mediate part of the filament. The coiledfila'ment 24 is desirably provided with generally straight end sections or legs 28 of uncoiled wire which serve tofacilitaltethe attachment of the filament 24 to the lead Wires 20 and '22.

In mounting the filament 24 according to the invention, each of its end sections 28 are first secured as by clamping or other suitable means to the ends of the lead wires 20 and 22 in transverse relation therewithand the filament proper draped over the looped end of the supporting member 26' in accordance with the present mounting practice so that the filament 24 is arranged in a generally straight-sided inverted V as in the prior art mount 30 shown in Fig. 3. The portions of the end sections 28 inward of and remote from the leads Z and 22 are then fiaredor b'ent upwardly from their as-mounted straight-line transverse relation with the mount and lead wire axes by means of a suitably actuated forming member 52 in the' manner illustrated in Figs. 4 and 5, respectively; The movement and orientation of the forming member 52 are such that it contacts the end sections 28 at a point inward of and remote from the leads 20 and 22, preferably at a point adjacent the coiled portion of the filament 24 (see Fig.

4). The upward thrust of the member 52 is of suificient magnitude that the sections 28 are permanently deformed with a wiping action so that the aforementioned parts of the filament end sections 28 are inclined or flared outwardly from each other and the mount axis toward parallelism with the connecting ends of the lead wires 20 and 22, as illustrated in Figs. 2 and 5. With the end sections 28 deformed inthis manner the adjoining unsupported segments of the coiled body portion of the filament 24 are strained and bowed outwardly so that in its finally adjusted condition the filament 24 has the arch-like configuration depicted in Fig. 2. It should be noted that with the foregoing arrangement the parts of the end sections 28 adjacent the main body portion of the filament 24 are wiped by the forming member 52 so that instead of the sections 28 being sharply bent at the inward edges of the lead wires 20 and 22 they are gradually bent at a point remote from the leads thereby minimizing the stress imparted to the filamentary material and the danger of fracturing the filament wire during the forming operation. In practice the wiping action effected by the forming member 52 may be accomplished by a pair of tweezers, which are manipulated to suitably deform and adjust the filarnent end sections 28.

By virtue of its permanently strained condition and arch-like configuration the main body portion of the filament 24 is rigidified and its mechanical strength materially improved in much the same manner as the rib members and the covering material of an umbrella are stifiened and form a rigid structure when locked in their expanded or opened position. Hence, should the lamp be subsequentlysubjected'to vibrational or other destructive forces, particularly during operation when the filament 24 is in a hot pliable condition, the gradual collapse and deterioration of the unsupported end spans of the coiled portion normally produced by such forces will be retarded inasmuch as the upward thrust and rigidifying effect derived from the strain pattern and shape imparted to the filament must first be overcome and neutralized, so to speak. Continued use of the lamp .110 under such adverse operating conditions will, of course, eventually cause the filament 24 to gradually assume its normal shape and strain-free condition where- 7 upon it will deteriorate in substantially the same manner andatthe same rate as heretofore.

It is also a significant feature of the invention that the rigidifying and strengthening effect obtained from the foregoing adjustment of the mounted filament 24 will be especially long-lived by virtue of the fact that the deformation which produces the effect is confined to the end sections 28 which, because of the cooling effect of the adjoining lead wires 20 and 22, operate at the lowest temperature and are the least pliable or yieldable parts of the filament structure considered as a whole.

In the prior art type mount assembly 30 illustrated in Fig. 3, while the lead wires 32 and 34, support member 38, insulator 36, and filament 40 are substantially the same with respect to structure and spatial relationship as those employed in the improved mount 16 embodying the above-described principles of the invention, the end portions 42 of the filament 40 were permitted to retain their as-mounted transverse relation with the mount and lead wire axes so that the adjoining coiled portions of the filament 40 were substantially straight and in a relaxed condition. With this arrangement the expansion and pliability of the filament 40 incident with the operationof the lamp'soon caused the unsupported sections of the coil to sag inwardly toward each other and the support 38 and by virtue of the proximity of the parts would, in a very short period of time, result in entanglements and short circuits which rendered the lamp virtually useless ifnot totally inoperative.

. Inorder to evaluate the effectiveness of the strengthening action obtained from the wiping-up procedure and the resultant spatial adjustment of the mounted filamerit, comparative tests on regular product lamps and lamps employing the improved mount construction were conducted. The tests consisted of operating the lamps at of their design voltage'in a horizontal position from sockets mounted on a horizontally-disposed five pound steel plate which was dropped vertically through a distance of two inches thus simulating the hotshock conditions which prevail when the lamp receives a sudden impact while the filament is energized. -The foregoing schedule was repeated at one-second intervals with the lamps burning continuously until a total of fifty impacts were successively applied to the lamps at which point the test was terminated. At the end of each drop the number of lamps which failed were recorded so that the percent failures versus the number of impacts applied could easily be determined.

In the graph shown in Fig. 6, the percent failures after each drop are plotted along the ordinate While the number of impacts is plotted along the abscissa so that a so-called mortality curve for each lamp \type is shown. Two groups of twenty lamps each of identical structure and manufacture, except for the configuration of the filaments, were comparatively tested on three different occasions and the data averaged so that the figures in the graph represent the mean values derived from sixty lamps of each type. As indicated by the curve A, the first regular product lamp failed after the seventh drop of the plate whereas the first lamp embodying the new construction, represented by curve B, did not fail until after the twenty-third drop or more than three times the number of drops required to make the first regular product lamp fail. After the first failure occurred the rate of deteriorationof the filaments in the remaining lamps, as evidenced by the rate at which the lamps subsequently failed and the generally parallel relationship of curves A and B, was approximately the same for each of the lamp types so that at the conclusion of the test 60% of the lamps with regular or standard construction had failed Whereas only 30% of the lamps with the improved filament shape were inoperative. Hence, the introduction of a predetermined contour and strain pattern in the mounted filament in accordance with the principles of the invention contrary to all expectations efiected over a 300% improvement in the life span of the initia' failure or-weakest-lamp mediate supporting members.

'5 in any given lot and a 100% improvement in the overall strength quality of the lamps under sustained shock conditions.

As shown in Fig. 7, the invention may also be utilized in a so-called C2F miniature lamp mount assembly 16a which comprises the usual pair of spaced lead wires 20a and 22a, an insulator 18a, and two supporting members 44 and 46 disposed to support intermediate portions of a relatively longer filament 24a, as compared to that employed in the 02V type mount illustrated in Figs. 2 and 3, so that a generally rectangular filament configuration is obtained. The filament end sections 28a inward of the leads 20a and 22a are bent upwardly from their normally transverse relation with the leads as heretofore explained in connection with the above-described embodiment of the invention to efiect substantially the same contour, strain pattern, and rigidification of the unsupported end spans of the filament proper set forth above.

The invention is equally applicable to stem-type mount assemblies 16b of the character illustrated in Fig. 8 and customarily employed in larger lamps and to other butttype mount assemblies, such as the so-called 02R. mount 16c shown in Fig. 9, wherein a shorter filament 24c is employed and suspended in toto on a pair of leads 20c and 22c by its end portions 28c without the use of inter- In the former type mount construction the usual stem tube 50 having a fused end portion or press through which the leads 20b and 22b are sealed and a higher-wattage coiled filament 24b of considerable length are employed which filament is anchored by its end sections 28b and intermediately coupled to a plurality of support members 48 of appropriate length to provide a generally M-shaped light source, commonly referred to in the art as a C13 mount.

It will thus be obvious from the foregoing that the objects of the invention have been achieved insofar as an improved filament mount construction and method of filament mounting for incandescent lamps are provided whereby the rigidification resulting from the permanent deformation and resultant straining of the mounted filament is advantageously utilized to greatly improve the mechanical strength of the filament and the life quality of the lamp as a whole which improvement was not only entirely unexpected but is exceedingly convenient and inexpensive to attain.

Although one preferred and several alternative embodiments of the invention have been described in accord- 6 ance with the patent statutes, it will be understood that further modifications and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. An electric lamp comprising, an envelope, a pair of lead wires sealed through and extending into said envelope, and a filament mounted on said lead wires, said filament having a bend in each of its ends inward from the connecting portions of said lead wires that displaces the adjoining unsupported section of said filament from its as-mounted configuration and permanently imparts thereto a configuration and a strain that rigidifies and mechanically strengthens said unsupported filament section.

2. An electric lamp comprising, an envelope, a pair of lead wires sealed through and extending into said envelope, and a filament mounted on said lead wires, said filament having generally straight end sections fastened to the ends of said lead wires and initially disposed in transverse relationship therewith, each of the straight end sections of said filament inward from the connecting ends of said lead having a bend therein that displaces the adjoining unsupported sections of said filament from their as-mounted configuration into a configuration that rigidifies and mechanically strengthens unsupported filament sections and renders them less susceptible to sag.

3. A filament mounting comprising, a lead wire, and a coiled filament having an uncoiled generally straight end section that is fastened to said lead wire in transverse relationship therewith, said filament end section at a point inward from said lead wire having a bend therein of such character that the innermost portion of said filament end section is displaced from its as-mounted transverse position toward parallelism with the connecting part of said lead wire, thereby stressing the adjoining coiled body portion of said filament and imparting a rigidifying con figuration thereto that renders it less susceptible to sag.

' References Cited in the file of this patent UNITED STATES PATENTS 1,023,357 Beckwith Apr. 16, 1912 1,869,559 Gustin Aug. 2, 1932 2,214,974 Scott Sept. 17, 1940 2,542,326 Greiner Feb. 20, 1951 2,716,714 Adams et a1. Aug. 30, 1955

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