US3413511A - Electric lamp having in situ molded base of foamed plastic - Google Patents

Description

Nov. 26, 1968 PLA E 3,413,511 v ELECTRIC LAMP HAVING IN SITU MOLDED BASE OF FOAMED PLASTIC Filed June 1, 1966 1 l2 n a s r e 6 l Q f:;.5 1: :1, '-1;-. .1\1-24 QC: 0 I Q |6 s: Q02 3b l8 o o I 23 I420 20 14 23 F I62 26 FIGS.

WITNESSES INVENTOR Vernon L. Plagge AGEN United States Patent 3,413,511 ELECTRIC LAMP HAVING IN SITU MOLDED BASE OF FOAMED PLASTIC Vernon L. Plagge, East Orange, N.J., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Continuation-impart of application Ser. No. 473,028, July 19, 1965. This application June 1, 1966, Ser. No. 554,493

6 Claims. (Cl. 313-318) ABSTRACT OF THE DISCLOSURE An electric incandescent or fluorescent lamp is provided with a base composed of foamed plastic that is molded in situ on and bonded directly to the end of the lamp envelope. The lead-in conductors are partly embedded in the foamed plastic base and constitute, or are connected to, contact members anchored in the plastic. In the case of an incandescent lamp and a screw type base, one of the lead-in conductors is located at the bottom of the base threads and constitutes an engagable side contact. A mold is placed in surrounding and abutting relationship with the end of the envelope, a foamable plastic resin is introduced into the mold cavity and is activated by heat, and the mold is removed after the resulting foamed plastic base has cured and rigidifled.

This application is a continuation-in-part of application Ser. No. 473,028, filed July 19, 1965, entitled Electric Lamp Base and Method of Manufacture, and now abandoned.

The present invention relates to electric lamps and, more particularly, to an electric lamp having an improved base and terminal structure.

Heretofore in the art it has been the customary practice to form plastic bases for fluorescent lamps by compression molding a suitable resin in a die. These separately-fabricated bases, which usually are made from a thermosetting plastic such as a phenolic condensation product or the like, are then provided with one or more hollow metallic contact pins that are staked or riveted to the bottom of the base shell. After the lamp has been scaled and tipped off, the lead-in wires are threaded through the pins and the preformed plastic bases are then cemented to the ends of the tubular glass envelope. The protruding ends of the lead wires are then severed and the pins are joined to the leads by welding or soldering. The separate production operations of base forming, cementing, etc., together with the additional transportation costs in transferring the bases from the molding machines to the lamp-basing machines, increase substantially the overall manufacturing cost of fluorescent lamps.

It is accordingly the general object of the present invention to reduce the manufacturing cost of electric lamps by utilizing a base structure that is formed as an integral part of the lamp itself rather than as a separate lamp component.

Another object of the present invention is to provide a lamp having a base that is composed of a suitable thermosetting plastic material and can be formed as an integral part of the lamp to provide an improved low-cost base and terminal structure.

The foregoing objects of the present invention, together with other objects which will become apparent to those skilled in the art from the following description, are achieved by molding a plastic base directly onto the end of the lamp envelope. In the case of a fluorescent lamp, this is achieved by providing a mold having a cavity shaped and dimensioned to conform to the outside configuration and dimensions of the desired base. The mold has suitable openings into which the hollow base pins are placed and, thereafter, a predetermined amount of plastic resin and a foaming agent are introduced into the mold. The mold is then fitted around the sealed-in end of the tubular fluorescent lamp envelope and the lead-in wires simultaneously threaded through the contact pins. The mold assembly is then heated to a suitable temperature so that the contained resin foams and fills the mold cavity, thereby conforming to the contour thereof. At the same time, the resin contacts and adheres to the surface of the vitreous envelope and the contact pins :and finally cures to a rigid cellular structure. The assembly is subsequently allowed to cool and the mold is removed from about the lamp end, leaving a finished base firmly aflixed to the envelope and contact pins.

A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIGURE 1 illustrates a completed fluorescent lamp provided with a base structure at each end formed and applied thereto in accordance with the present invention;

FIG. 2 is an enlarged fragmentary crosssectional view of the mold and a sealed end of the fluorescent lamp seated therein just after the plastic has expanded into place around the lamp envelope and the base pins;

FIG. 3 is an elevational view of an incandescent lamp having an integrally-formed base according to the invention; and

FIG. 4 is an enlarged cross-sectional view of the basal end portion of the incandescent lamp shown in FIG. 3.

Referring now more specifically to the drawing, in FIG. 1 there is shown a fluorescent lamp 5 which comprises the customary tubular vitreous envelope 6 having a suitable ultraviolet-responsive phosphor coating 7 on its interior surface and a pair of oppositely disposed electrodes 8 that are supported within the envelope adjacent the ends thereof by a pair of lead-in wires 9 and 10 and a vitreous stem 11. Attached to each sealed end of the envelope 6 in accordance with this invention is a plastic base member 12 of generally cylindrical configuration. Each base 12 is provided with a pair of rigid terminals such contact pins 14 to which the lead-in wires 9, 10 are connected for transmitting electrical energy to the interiorly disposed electrodes 8. The base 12 at each end of the lamp is secured to the glass surface of the tubular envelope 6 by direct union therewith entirely independent of any cement or other such material whatsoever, since the base 12 itself is formed in situ on the end of the envelope.

By reference now more particularly to FIG. 2, it will be noted that a mold 16 of resilient material such as silicone rubber or the like is therein shown which has a cavity 17 conforming to the shape and dimensions desired for the finished base 12 This mold may, if desired, be reinforced by a thin outer metallic casing 18. The mold 16 is provided with a pair of elongated recesses 20 into which the hollow metallic contact pins 14 are inserted with their upper flared ends spaced slightly above the inner surface of the mold, as shown in the drawing. A predetermined amount 22 of a suitable thermosetting plastic resin and a foaming agent are then introduced into the mold cavity 17, after which the end of the sealed and exhausted lamp envelope 6 is inserted into the mold 16 by threading the outer exposed ends of lead-wires 9 and 10 through the respective contact pins 14 until the shoulder of the envelope seats against the peripheral edge of the resilient mold and forms a seal therewith.

The lamp and mold assembly is then vertically supported upon blocks 23, or other suitable members, in a surrounding furnace 24 and heated to a temperature rang ing from approximately 50 C. to 0, depending on the type of plastic resin used. Such heating is continued until the resin 22 foams and fills the mold cavity 17 and thereby contacts and covers the ends of the envelope 6 and pins 14 disposed within the mold 16. The gas and excess foamed material are discharged through a vent tube 26 extending from the bottom of the cavity 17 to the outside of the furnace 24. The foamed resin then cures to a rigid cellular structure within a short period of time, the length of which depends upon the temperature and particular type of plastic resin employed, leaving the lamp base 12 of the desired configuration firmly bonded to and locked in place on the sealed end of the glass envelope 6 and with the contact pins 14 firmly anchored therein. Since the foamed resin surrounds the outer ends of the lead-in wires 9 and 10 and partly fills the end of the reentrant stem 11, as shown in FIG. 2, it aso serves as an insulator that locks the wires in spaced apart relationship and thus prevents short circuits from developing within the base.

The resin 22 may be of any suitable thermosetting electrically-nonconductive type plastic, such as a phenolic condensation product, a polyvinyl chloride, an epoxy, or the like, while (when admixed with a suitable foaming agent such as benzene sulfonyl hydrazide or other nitrogen blowing agent) will foam when heated to an elevated temperature. The foaming agent in this case can be introduced separately into the mold cavity 17 through the vent tube 26.

However, the base 12 can just as readily be formed by using a material that consists of a mixture of resin and a foaming agent which will likewise foam when heated to an elevated temperature. Such foaming plastics are well known in the chemical art and comprise polyurethane foams, polystyrene foams, epoxy foams, silicone foams, cellulose acetate foams, etc. Foaming plastics of various kinds are described in detail in an article entitled Plastic Foams, May 1966 issue of Materials Engineering magazine (vol. 63, No. 5, pp. 87-102). Any of the materials referred to in the aforesaid article can be used. The only limitations are that the plastic be of the type which cures to a hardened rigid cellular structure that is not too porous as to weaken the base 12 to the extent that it will crack when the contact pins 14 are subjected to the strain normally encountered in inserting and removing the lamp from its fixture sockets, and that the plastic be electrically non-conductive to avoid short-circuiting the lead wires. Of course, the plastic should also be of a type that will remain sufliciently rigid at the operating temperature of the lamp that it will support the lamp in its socket.

Preferably the plastic resin, whether self-foaming or one which requires a separate foaming agent, is selected so that it is completely cured in a relatively short period preferably within ten to fifteen minutes) to a hardened strong base member having a minimum of voids which, if they do occur, are of minute size. Also, the cooling time should likewise be of short duration to enable removal of the base lamp from the mold 16 as soon as possible preparatory to the formation of a base on another lamp envelope. If the times for curing and cooling the plastic are not excessive, the actual molding of the base 12 directly on the end of the lamp 5 can very readily be done on an automatic lamp-making machine by performing the molding, curing and cooling operations at various work stations to which the lamp-making machinery is periodically indexed.

After the base lamp 5 is removed from the mold 16, the protruding ends of the lead-in wires 9 and are trimmed and the wires are attached to the pins 14 by welding or the like in the usual manner.

The invention can also be utilized in the manufacture of incandescent lamp types with the same functional, cost and manufacturing advantages. As shown in FIG. 3, a lamp of this type having the usual pear-shaped envelope 26, and filament mount 28 is provided with a screw-type plastic base 30 that is molded in situ directly onto the sealed end of the envelope. As shown more particularly in FIG. 4, one of the lead wires 31 connects with a rivet-like member 32 anchored in the end face of the base to provide an end contact, whereas the other lead 33 is positioned at and is partly exposed by the base threads to provide the necessary side contact.

It will thus be apparent from the foregoing that a base structure for an electric lamp, such as fluourescent or incandescent lamp, has been provided which is actually molded in place directly onto the end of the envelope and hence is securely fastened to and forms an integral part of such envelope. Moreover, a method and apparatus for molding the base directly on the lamp end has been described which enables the base and terminal structure to be formed on and as part of the operation of an automatic lamp-making machine, thereby materially reducing the manufacturing cost of both the base and lamp.

Although several embodiments have been herein shown and described, it is to be understood that still further modifications thereof can be made without departing from the spirit and scope of the invention. For example, a single-ended incandescent lamp could be based by using a foamable resin as a mean for cementing a metal base shell to the bulb, which resin would also seWe as the insulator member at the bottom of the shell and hold the eyelet or end contact in operative relationship with he shell. In addition, a translucent or color-coded base can very readily be provided for fiuorcescent lamps simply by selecting the proper type of plastic resin.

The mold can also be made from any suitable material, providing it does not stick to the cured plastic or otherwise interfere with the removal of the formed base. In addition, incandescent lamps can be provided with various types and shapes of all-plastic bases simply by altering the configuration of the mold cavity. Thus, plastic bases of complex shapes, such as those for miniature lamps of the type designed for use in conjunction with panels having printed electrical circuits and disclosed in US. Patents No. 2,892,992 issued June 30, 1959, can also be readily fabricated in situ in accordance with the present invention.

I claim:

1. In an electric lamp, the combination comprising:

a vitreous envelope having an end portion that is susceptible to breakage when stressed and has a deformable conductor depending therefrom,

a base member of foamed insulating plastic bonded directly to said envelope end portion and holding the conductor in fixed position relative to the envelope, and

a terminal anchored in said base member and electrically connected to said conductor.

2. The combination of claim 1 wherein said base member is composed of foamed thermosetting plastic.

3. The combination of claim 1 wherein:

said envelope contains an incandescible filament,

said conductor comprises one of a pair of lead wires that are connected to said filament and are sealed through said envelope end portion, and

said foamed plastic base member is composed of cured thermosetting resin and is molded in situ onto said envelope end portion.

4. The combination of claim 3 wherein:

said base member is of the screw-in type,

the outer ends of said lead wires are embedded in the base member,

one of said lead wires is connected to a terminal anchored in the free end of the base member, and

the other of said lead wires is located in the threaded portion of said base member and constitutes an engageable second contact for the lamp.

5. The combination of claim 1 wherein:

said envelope is of tubular configuration and the said end portion comprises a sealed end thereof,

said base member encircles the sealed end of the envelope and is molded in situ thereon, and

said conductor comprises a lead wire that extends from the sealed end of the envelope and is connected to a rigid terminal that is anchored in and protrudes beyond the end face of said base member.

6. The combination of claim 5, wherein:

said lamp comprises a fluorescent lamp,

said base member is composed of cured thermosetting resin,

a second lead wire extends from the sealed end of the envelope,

parts of the lead wires are embedded in said base member which thus serves as an insulator, and

said lead wires are connected to a pair of rigid terminals anchored in the end face of said base member.

References Cited 2,771,589 11/1956 Thomas 313-318X 6 2,884,555 4/1959 Peterson 313-318 X 3,010,045 11/1961 Plagge et al 313-318 X 3,218,500 11/1965 Wright et al. 313-318 X 3,322,992 5/1967 Parker et a1 313-315 X 2,983,838 5/1961 Pechy 313-318 3,077,022 2/1963 Cullis 313-317 FOREIGN PATENTS 413,127 7/1931 Great Britain.

OTHER REFERENCES IBM Technical Disclosure Bulletin, Packaging of Miniature Lens-End Lamps, by R. J. Keller et a1., vol. 7, No. 5, October 1964, p. 399 (copy in group 250, class 313, subclass 318). 15

JOHN W. HUCKERT, Primary Examiner. A. J. JAMES, Assistant Examiner.

Images