US2285875A - Electric lamp assembly - Google Patents

Description

June-9, 1942- L. L. STQFFEL 1,

' ELECTRIC LAMP ASSEMBLY Filed May 24, 19.40

0, a f s i s a H /0 i; Z M i z sz m Patented June 9, 1942 ELECTRIC LAMP ASSEMBLY Lester L. Stofiel, Lakewood, Ohio, assignor to The Ohio Carbon Company,-Cleveland, Ohio, a

corporation of Ohio Application May 24, 1940, Serial N 0. 337,005

6 Claims.

This invention relates to improvements in electric lamps and more particularly to an improved electric lamp assembly including a resistor enclosed within the assembly and connected with the electric circuit of the filament or electrode of the lamp, as well as to an improved resistor unit therefor and method of making the same. These, therefore, are the general objects of the present invention.

Certain types of electric lamps ar provided with filaments or electrodes, the current requirements of which are such that it is preferable to use a resistor in the filament or electrode circuit to permit the use of the lamp in standard power supply systems. In some instances, external resistors have been used, or a plurality of lamps have been connected in a series. Either of these methods are disadvantageous. Neither assures protection of the lamp. If the external resistor is omitted or removed and/or a lamp having no resistor is connected with the power line, such lamp may be seriously damaged.

The general object of the present invention is to provide an improved low voltage electric lamp, which may be used on high voltage power lines and in standard lamp receptacles with safety. This is accomplished by incorporating a resistor in the lamp assembly in such manner that the resistor will be inaccessible to the user of the lamp, and, therefore, must remain in the electrical circuit at all times.

Another object of the present invention is to provide an electric lamp with a resistor which may be readily incorporated within the lamp assembly in an economical manner. Further objects of the invention are to provide an improved resistor for assembly in the lamp unit and to provide an improved means of attaching the resistor in circuit with the illuminating element of the lamp.

Other objects and advantages of the present invention will become more apparent from the following description, reference being had to the accompanying drawing in which I illustrate a preferred embodiment of the invention. The essential and novel features of the invention will be set forth in the claims.

In the drawing, Fig. 1 is an axial section through an electric lamp having my invention incorporated therein; Fig. 2 is a perspective View on an enlarged scale of one form of my improved resistor unit; Fig. 3 is a cross section of another form of such unit.

For the most part, the lamp illustrated in the drawing is typical of the standard lamp construction now in general use. This lamp comprises a tubular glass envelope I0 into the base of which a glass header insert II or electrode supporting element extends. A pair of electrodes I2 are shown as being secured to the top of lead Wires I4 and Ida which extend through and are carried by the header insert. The header is tubular as shown in Fig. 1 and is provided with a downwardly extending glass exhaust tube I5. This tube is axially aligned with the envelope II) and extends some distance below the bottom of the header and envelope. The upper end of the exhaust tube I5 is in communication, as by a passageway I6, with the interior of the envelope. This enables the exhausting of the air from the envelope and the formation of a partial vacuum therein. After the vacuum has been formed in the envelope, the lower end of th exhaust tube I5 is closed, as indicated at I1. Secured to the envelope II], as by cement I8, and enclosing the exhaust tube is a metallic base I9. The lower end of the base is closed by insulating compound 20 in which is set an axially positioned metal contactor 2|. The lead wire Ma extends from the header through the contactor 2| and is secured thereto as by soldering. In standard lamp constructions the other lead wire I4 is secured directly to the base shell I9 as by soldering. Thus, the shell itself acts as a second contactor. The size of the lamps vary from miniature lamps, the base and envelope of which may be about one quarter of an inch in diameter and the length of which may be about one inch, to lamps many times this size.

The present invention comprises inclusion in the lamp assembly of a resistor 30. This resistor is placed within the base shell and in series with one of the lead wires and its contactor, preferably between the lead Wire I4 and the base shell.

As the invention is contemplated for use with miniature lamps, it is highly desirable that the resistor be so shaped as to occupy as little space as possible, and thus enable a compact assembly. Likewise, it is desirable that the resistor be so constructed as to facilitate its attachment to the envelope and header structure in such a manner as to enable the positioning and cementing in place of the lamp base with little or no danger of displacement of the resistor and thereby eliminating the need for insulation to protect the resistor against short circuiting.

To the above ends, the resistor preferably is formed as a ring or annulus having an outer diameter which is less than the inner diameter of the base shell and an inner diameter greater than to the resistor.

the outer diameter of thte exhaust tube. When so constructed, the resistor may be positioned in contact with the glass header insert II and encircling the exhaust tube l5, as shown in Fig. 1. The lead wire is is then extended between the tube and the resistor and is secured to the resistor, as will hereinafter be more fully described. The other lead wire [4a may be passed between the resistor and the exhaust tube and extended directly to the contactor 2| in the base. The base may then be cemented to the shell in the usual manner with a resistor terminal wire 3i extending through the cement between the shell and the envelope. Ihe terminal wire 3| is then secured to the shell as indicated at 32.

It is desirable that the resistor have a relatively long life span. I have found that a carbon or carbon composition resistor is most suitable for this purpose as such type of resistors have a life span of some thirty thousand hours as compared with a one thousand hour life span of other types of resistors, such for example, as coated paper and the like.

The use of a carbon resistor presents a serious problem, in that it is extremely difficult to attach terminals or lead wires thereto in an economical manner and yet so as to insure an efficient electrical bond. The ordinary methods of attaching lead wires to resistors include perforation of the resistor, the securing of a metallic eyelet thereto and subsequently soldering the lead Wire to the eyelet. Because of the frangibility of the carbon material, however, this method cannot be used. The carbon, of course, cannot be perforated by a punching operation, but even were it drilled, an eyelet could not be secured in the perforation, either economically or in a manner providing a suitable electrical bond between the eyelet and the resistor. Likewise, such methods entail considerable danger of breaking or cracking the resistor and thus rendering it useless. Other methods of attaching the leads or terminals to the resistor have been tried, but have been found to be equally as damaging to the resistor.

The present invention includes an economical method of fastening the terminals or lead wires To this end the terminals comprise wires SI and 33 which are wrapped around the resistor as shown in Fig. 2 and are attached thereto by a cement 35, which not only securely fastens the wires to the resistor, but which also acts as an electrical conductor and thereby insures an electrical bond between the resistor and the terminal wires.

A cement which has been found to be suitable for this purpose, comprises a mixture of water soluble thermo-setting resin, and flake graphite. These materials are thoroughly mixed by a pebble-tumbling operation. The operation is preferably continuous to retain the material in suspension for a period of about sixteen hours. I have found that a mixture in the proportion of from one hundred and. fifty (150) to four hundred (400) parts of flake graphite, to six hundred (600) parts of resin provides a satisfactory cement. The preferred proportion, however, is two hundred and twenty-four (224) parts of graphite to six hundred (600) parts of resin.

In using the above cement, a paste is made thereof using a suitable liquid such as water, alcohol or acetone for a carrier. The paste is brushed on the wires as indicated at 35 in the drawing, and is then air dried and subsequently baked at a temperature of about three hundred and twenty-five degrees Fahrenheit (325 F.) for about twenty (20) minutes. The baking operation insures an eflicient bond between the ocment and the carbon as it drives all moisture out of both the resistor and the cement. The resistor may then be secured in place in the lamp assembly as heretofore described, thus providing an economical lamp assembly.

In Fig. 3, I have shown a modification wherein the terminal wires, here designated 3m and 33a, instead of being wrapped around the annular resistor, as in the case of the wires 3! and 33 in Fig. 3, are now embedded in the resistor 30a. This resistor 33a is of the same material and has substantially the same dimensions as the resistor 30, but the conductors are embedded in it so as to provide an effective electrical contact therewith.- The embedding may be made at the time of manufacture of the annular resistor, or radial holes from the outside may be made into the carbonaceous resistor and the conductors thereafter inserted and secured by conductive cement.

Reference is made to my divisional application, No. 422,553, filed December 11, 1941, for claims on the resistor per se.

I claim:

1. In an electric lamp assembly, the combination of an envelope, an electrode supporting element within the envelope rising from said base, a carbon resistor in the form of an annulus entirely below the envelope, a metallic base, extending about the lower portion of the envelope and projecting beyond it in the form of a housing enclosing said resistor, there being an annular insulating space between the resistor and the base conductors oneof which is connected to a terminal of the completed lamp, the otherconductor being connected to the carbon resistor, and a conductor extending from the opposite side of the carbon resistor to the other terminal of the lamp.

2. In an electric lamp assembly, the combination of an envelope, an electrode-supporting element within the envelope rising from the bottom thereof a sealing tube carriedby the electrodesupporting element and depending within such supporting element to a regionbelow the bottom of the envelope, a carbon resistor in theform of a comparatively thin annulus surrounding the tube extending below the envelope lying entirely beneath the envelope outside of the extension, a metallic base extending about the lower portion of the envelope and projecting beyond it in the form of a housing enclosing said resistor, the resistor terminating at its edge some distance within the base, terminal conductors extending along the space between the tube and electrode-supporting element, one of said conductors being connected to a terminal of the completed lamp, the other conductor being connected to the carbon resistor and a conductor extending from. the carbon resistor to the other terminal of the lamp.

3. In an electric lamp assembly, the combination of a translucent envelope, an electrodesupporting element within the envelope rising from bottom thereof, a sealing tube carried by the'electrode-supporting element and depending within such supporting element to a region below the bottom of the envelope, a carbon resistor in the form of an annulus. surrounding the sealing tube entirely below the envelope, a metallic base extending about the lower portion of the envelope and projecting. below it in the form of a housing enclosing said resistor, and terminal conductors extending throughthe central opening of the resistor and along the space between the tube and electrode-supporting element, one of said conductors being connected to a terminal of the completed lamp, the other conductor being connected to the carbon resistor, and a conductor extending from the carbon resistor to the other terminal of the lamp,

4. A lamp assembly comprising an envelope having an electrode therein, a sealing tube carried thereby and extending beneath said envelope, a base secured to the envelope and having a pair of electrical contactors, an annular resistor comprising a comparatively thin flat ring of carbonaceous material spaced inwardly from the base and entirely below the envelope and surrounding the sealing tube, and leads to and from the resistor physically attached thereto and in electrical contact therewith, one of said leads being connected to the electrode and the other to one of said contactors.

5. A lamp assembly comprising an envelope carrying at its base a header extending into the envelope, an exhaust tube extending internally of the header downwardly to a region below the bottom of the envelope, a metallic shell secured to the envelope near its lower end and extending beneath the same and constituting one of the terminal contacts, a central contact insulatingly carried by the shell, a resistor made of annular form of carbonaceous material located within the shell entirely beneath the bottom of the envelope itself and surrounding the exhaust tube while leaving air space between the inner periphery of the resistor and the exhaust tube and between the outer periphery of the resistor and the metallic shell, a pair of lead-in wires extending through the annular space between the resister and exhaust tube and through the header between its body and exhaust tube, one of said lead-in wires being connected to one of the contacts of the base, the other lead-in wire being connected to one side of the resistor, and a conductor connecting the opposite side of the resistor to the other contact of the base.

6. The lamp assembly comprising a glass envelope, a header carried by the bottom of the envelope and extending into the envelope, the bottom of the envelope outside of the header being substantially flat and at right angles to the header, an exhaust tube carried by the header and projecting downwardly within it to a region below the bottom of the envelope, there being an annular space within the header and about the exhaust tube, a carbonaceous resistor in the form of a comparatively thin flat annulus having an internal diameter materially greater than that of the exhaust tube, said annulus being located entirely beneath and close to the flat bottom of the envelope and surrounding the exhaust tube but leaving an annular space about the exhaust tube registering with the annular space within the header, lead-in wires occupying such annular spaces, a metallic shell secured to the envelope near its lower end out of direct contact with the resistor itself constituting one of the terminal contacts and insulatingly carrying the other terminal contact, the resistor being in series with one of the lead-in wires and with one of the contacts of the base, and the other lead-in wire being connected to the other contact of the base.

LESTER L. STOFFEL.

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