US 2919422 A
Description (OCR text may contain errors)
Dec. 29, 1959 R. B. THOMAS ETAL 2,919,422
ELECTRIC LAMP BASE Filed July 15. 1955 INVENTORS RALPH B. THOMAS OLIVE/P MANN M W -m,
A TTOR/VEY United States Patent ELECTRIC LAMP BASE Ralph B. Thomas, Salem, and ()liver Mann, Danvers,
Application July 15, 1955, Serial No. 522,241 1 Claim. (Cl. 339-446) This invention relates to contact bases for electric lamps and the like and particularly to lamp bases of the externally threaded type.
Such bases are used on incandescent and other types of electric lamps. They generally have a threaded metallic outer shell with a metal eyelet contact fixed to one end of the shell by a plug of insulation such as glass. The other end of the base is attached to a lamp bulb, and the device inserted in a suitable threaded receptacle by turning.
However, for the threads to engage properly, the bulb must be held so that the axis of the base is closely aligned with that of the recepteacle. Such alignment is difiicult to achieve in the dark, or when inserting the bulb in a receptacle hidden from view by a diffusing bowl, reflector or other housing, or when the receptacle is overhead, and in other circumstances. A small deviation in alignment while inserting the bulb in the receptacle will prevent engagement of the threads, with consequent difficulty in inserting the bulb in the receptacle. In present commercially-used bases, this is because the threads extend nearly to the eyelet end of the shell and that end is rounded oil? to a large radius.
It is-found, however, that by leaving the eyelet end of the shell free of threads for a short distance, and making that end of a diameter equal to or smaller than the outside root or minor diameter of the threads, the insertion of the bulb is greatly facilitated, and it is then easy even for example to insert the bulb in a receptacle behind ones back. The unthreaded end of the base can be made to the inside minor diameter of the threads of a standard receptacle and will then slip easily and smoothly into such a receptacle, without diificulty.
The number of threads on the base cannot be greatly reduced, because the base has to fit a variety of existing types of receptacles, and hence the required unthreaded portion cannot be provided merely by reducing the number of threads. On the other hand, the unthreaded portion cannot ordinarily be provided by making the base longer, because in that case also the base would fail to fit existing receptacles. However, the present commercial base has a rounded end portion on its shell, near the eyelet contact, and the rounded end has a fairly large radius of curvature, generally of about one-quarter inch. It is found that by reducing the radius of curvature to a very small value, for example, about inch, the cylindrical wall of the base shell can be extended for a considerable distance beyond the threads, without increasing the overall length of the base, the unthreaded portion occupying the space otherwise taken up by the rounded end of the base. In the embodiment herein described, the end of the shell is turned inwardly at substantially a right angle, that is, turned inwardly over the small radius mentioned above, with the cylindrical side walls of the threaded portion being longitudinally straight, and with the inwardly-turned portion being substantially flat.
The overall length of the base can thus be kept the same as in present commercial bases, and the threaded portion made nearly as long as in such bases, so that the base of my invention will fit existing receptacles and have at least the minimum required thread engagement therewith, yet be more easily insertable therein.
However, a problem arises in bonding the end of the shell to the insulating plug which carries the eyelet. In the present commercial type of base, the threads extend closer to the end of the shell, and provide an anchoring means for the insulating plug, usually of glass, holding it firmly against axial movement. In the base of our invention, however, the end portion of the shell is unthreaded, so that there are no threads which serve to anchor the insulating plug. If there were no other means for holding the plug firmly in place, the axial force exerted by screwing the base into a receptacle would tend to push the insulating plug into the shell, thereby rendering the lamp inoperative and perhaps creating a mechanical and electrical hazard.
We have discovered that this can be prevented, and a firm bond resistant to axial stress provided, without affecting the ease of insertion of the bulb, by forming a groove around the circumferenceof the shell near its unthreaded end. The groove may be a continuous closed groove around the entire circumference of the shell, or a series of shorter grooves, each extending only part way around the circumference. A series of spaced closed grooves can also be used.
The groove, as viewed from the outside of the shell, will appear as a protuberance or bead when viewed from inside the shell, the thinness of the shell making the deformation (bead or groove, depending on the point of view) appear on both inside and outside. But the deformation must be a groove when viewed from the outside, since, if it were an outside bead it would increase the shell diameter and adversely affect the ease of insertion of the base into a receptacle.
The shell of the lamp base is closed at one end by the glass plug and metal eyelet, and is open at the other end, which will eventually receive a lamp bulb. The bulb is generally fixed to the open end of the base by a ring of cement, which is applied before the base is afiixed to the bulb during manufacture of the lamp. The ring of cement is applied to the inside of the shell near the open end, and the application of the cement is generally referred to as filling the base, although only a small part of the interior volume of the base is actually occupied by the ring of cement. In mechanically handling such bases after filling, and in mechanically feeding bases to bulbs on automatic machinery, a number of such cement-containing bases are placed in a hopper, from which they are fed to the bulbs.
A serious problem in such feeding is the nesting of the bases, a condition in which the closed end of one base extends into the open end of the other, often becoming temporarily locked there and/or contaminated on its outside with cement. With the usual type of commercial base, one base cannot extend very far into the other, because the threaded portion starts directly at the closed end, and the nesting problem insofar as it concerns contamination, can be solved by putting the top of the ring of cement a short distance below the inside of the open end of the base. The base of the present invention, however, has a closed end portion of reduced diameter, which can accordingly extend much farther into another base, thereby greatly increasing the nesting problem, particularly the contamination hazard..-
However, we have discovered that the problem can be eliminated by making the inside diameter of the open end of the base somewhat smaller than the outside root (minor) diameter of the threads. The closed end of one shell cannot then fit into the open end of the other, and nesting cannot occur. We find also that even with the reduced diameter of the open end, the base will still seat properly on the lamp bulb to which it is to be aflixed, although the diameter of the end of the lamp bulb should generally be reduced correspondingly.
fOther objects, advantages and features of the invention will be apparent from the following specification, taken with the accompanying drawings, in which:
Figure 1 is a profile view of a lamp having a base according to certain aspects of the invention;
Figure 2 is a cross-sectional view of the base of said lamp;
Figure 3 is a ViCW of the closed or eyelet end of said base;
Figure 4 is a broken view of a base in which the groove is discontinuous;
Figure 5 is a broken View of a base having a series of continuous grooves; and
Figure 6 is a broken View of a base having a reduced diameter at its open end to prevent nesting. By the open end is meant the end attached to the lamp bulb.
Figure 7 is a broken view of a base having a multiplicity of staggered indentations.
In Figure 1, a pear-shaped glass bulb 1 has a lower or sealed end 2 to which a base, denoted generally by reference numeral 3, is attached. Said base, as shown in more detail in the cross-section of Figure 2, has a hollow metal shell 4 with screw threads 5 over a portion of its length, and an unthreaded portion 6 at one end, together with the inwardly-turned portion 7, which is fairly flat. The unthreaded portion 6 carries the groove 8.
A glass insulating plug 9, roughly conical in shape, is afiixed to the shell 4 at its inwardly-turned portion 7 and at the inside of the unthreaded portion 6. The inner edge of the inwardly-turned portion 7 is shown bent back toward the inside of the shell 4 to improve further the bond with the glass, although such bending is not necessary.
The groove indentations 8 engage the glass plug 9 to insure a good bond between said plug and the metal shell 4, which can be for example, of aluminum or brass. A metal eyelet contact 11, having a central opening 12 to receive a lead-in wire from the lamp bulb 1, is carried centrally by glass plug 9, which spaces and insulates the eyelet from the shell 4, the latter being ordinarily connected electrically to another lead-in wire from lamp bulb 1, in a manner well-known in the art.
In Figure 1, a globule 13 of solder is shown for connecting eyelet contact 11 to a lead-in wire from the lamp bulb 1.
In Figure 4, the groove is discontinuous, being made up of a number of short indentations transverse to the axis of the base.
In Figure 5, two grooves 3, 8 are shown in the unthreaded portion 6 of the base. Each of these grooves 8, 8 can be made discontinuous as in Figure 4, if desired, and the indentations 15 of one groove can be staggered with respect to those of the other, as in Figure 7.
In Figure 6, the shell 4 is shown with a portion 14 of a reduced diameter, for example, about equal to that of the root of the threads, to prevent nesting, as pre viously explained.
In Figure 7, the two grooves are discontinuous, being made up of a number of short indentations 15 transverse to the axis of the base.
The base shell 4 is attached to the bulb 1 in the usual manner, for example by a ring of cement inside shell 4.
For the usual size incandescent lamps a typical base according to our invention has an outside crest (major) diameter of 1.034 inch and an outside root (minor) diameter of 0.968 inch. The metal shell is of aluminum about 0.011 inch thick. The outside diameter of the unthreaded portion 6 is 0.968 inch, and the inwardlyturned portion extends for a distance of inch. The eyelet is of brass, and of about inch outside diameter with a hole diameter of about inch, and of a type standard in the art. The insulating plug 9 is of glass, and holds the eyelet about inch from the inwardlyturned portion 7 in an axial direction. The open end 14 of the base shown in Figure 4 is of about 0.965 inch inside diameter.
The unthreaded portion is preferably between and of an inch in length for a base designed to replace the usual commercial type known as a medium-screw base.
In using a lamp having a base according to our invention, the eyelet end of the base is inserted into a standard threaded receptacle not shown, and turned about its axis. The unthreaded, reduced diameter portion 6 of the base will slip easily into the receptacle, past the initial screw threads of the latter, so that the threads 5 of the base engage the threads of the receptacle and can be turned therein until the two are held firmly together.
The axial force on the parts of the base during the above operation is quite high. For example, a turning force of 40 pounds applied along the circumference of the shell will produce a force of 880 pounds along the axis of the base, with the usual base diameter and thread pitch. Lamp bulbs of the common sizes are usually tested with an applied torque of ZO-inch-pounds to determine whether the cement bond between base and bulb is of sufiicient strength for commercial purposes. Such a torque corresponds to a force of 40 pounds applied along the circumference of a base having a radius of about onehalf inch (or a diameter of about one inch). The bond between the glass plug and the metal shell must also be able to stand at least that much pressure, or it will fall before the cement fails.
Frictional losses have been neglected in the computations of the preceding paragraph.
Although the invention has been described with reference to a particular embodiment, various modifications will be apparent to one skilled in the art without departing from the spirit and scope of the invention.
What we claim is:
An electric lamp base comprising a cylindrical metal shell having an inwardly-turned portion at one end, said shell having a threaded-portion and having also a portion of reduced diameter on its cylindrical wall near said inwardly-turned portion and extending from said inwardlyturned portion to said threaded portion for a distance of between about %4 and or" an inch, said portion of reduced diameter having a closed circumferential internal bead, and an insulating plug having a circumferential groove in register with and in engagement with the circumferential internal bead in said portion of reduced diameter in the shell, said plug extending beyond said internal head but not extending into the threaded portion of the shell.
References Cited in the file of this patent UNITED STATES PATENTS 726,929 Howell May 5, 1903 801,260 Packard Oct. 10, 1905 805,131 Gerow Nov. 21, 1905 2,064,364 Thomas Dec. 15, 1936 2,336,529 Cartun Dec. 14, 1943 2,732,878 Bechard et al. Jan. 31, 1956