US 3755773 A
A lamp-retaining socket for a screw type lamp which prevents the lamp from accidentally becoming loose in the socket due to vibration or the like.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 Johnson Aug. 28, 1973  Assignee: Levltron Manufacturing Co., Inc.,
 Filed: Dec. 7, 1971  Appl. No.: 205,487
Primary Examiner-Marvin A. Champion Assistant Examiner-Lawrence J. Staab Attorney-l-lanse I-I. Hamilton 5 7] ABSTRACT A lamp-retaining socket for a screw type lamp which prevents the lamp from accidentally becoming loose in the socket due to vibration or the like.
The lamp retainer comprises a thin strip of flexible and deformable material which is interposed between rolled threads of a screw shell and rolled threads on a lamp base. The strip extends over at least two of the threads and increases frictional engagement between the threads of the shell and lamp base without interfering with introduction of the lamp into the screw shell or its removal therefrom. The retainer strip may be assembled with the screw shell prior to installation in a housing or it may be a clip which can be attached to the screw shell prior to the lamp being installed.
2 Claims, 7 Drawing Figures PATENTEDMIBZB 191s 3.755773 IIIIII INVEN OR wggf. wovso/v ATTORNEY LAMP-RETAINING SOCKET The present invention relates to a lamp-retaining socket of the screw shell type;
An object of the invention is to provide a screw shell type of socket with a retainer which will prevent the threaded base of a lamp from accidentally becoming loose in the socket. A screw type lamp can readily become loose in a screw shell of a socket due to vibration of the lamp or other causes. Such loosening presents a particular problem with respect to a large or mogul type of lamp socket, especially when the socket is mounted so that the lamp hangs downwardly from the socket. Under such conditions, the inclination of the threads tends to promote loosening of the lamp. This not only interrupts the electrical circuit to the lamp, but the loosening readily progresses to a point where the lamp can drop from the socket and present a hazard. The present invention prevents or minimizes such loosening.
While various attemps have been made to prevent such loosening, including the use of spring biased center contacts and deformation of the screw shells, such attempts have not been entirely successful.
Other objects and advantages of the invention will be better understood from the accompanying drawing and the following description. In the drawing:
FIG. 1 is a side elevation in partial section illustrating a lamp-retaining socket embodying the invention with a lamp screwed therein and which is drawn to a reduced scale;
FIG. 2 is a vertical section view of the lamp-retaining socket shown in FIG. 1, with a portion of the screw shell broken away and which is drawn to an enlarged scale;
FIG. 3 is a horizontal section view taken along line 3-3 of FIG. 2 of the screw shell and retainer shown in FIG. 2;
FIG. 4 is a fragmentary view in section of a portion of the screw shell and retainer shown in FIG. 3 after insertion of a lamp therein;
FIG. 5 is a perspective view of the screw shell shown in FIG. 3 with the retainer being installed therein;
FIG. 6 is a fragmentary view in vertical section illustrating a modified form of lamp-retaining socket embodying the invention; and
FIG. 7 is a perspective view illustrating the screw shell and retainer shown in FIG. 6 being assembled.
Referring to the drawings in detail, there is a socket 10 which has an outer shell or housing 1 1 of a ceramic or other suitable insulating material.
The socket 10 is of conventional construction and employs a metal screw shell 12 of brass or other conductive material. The screw shell 12 has rolled internal threads 12a and is open at one end to receive a lamp 13.
The base 14 of the lamp 13 includes a metal collar which surrounds the lower end of the lamp and has external threads 14a rolled therein to threadably engage with the threads 12a of the screw shell 12. A center contact 15 is located at the end of the base and is insulated from the collar 14 to engage with a center contact (not shown) in the socket 10 when the lamp is screwed in place.
While a mogul lamp and socket have been illustrated, it will be understood that the present invention is not limited to a particular size of the socket or lamp. As illustrated, the lamp 13 may hang down from the socket l0 and when the lamp is suspended in this manner, the downward inclination or slope of the mating threads 12a and 14a relative to the vertical axis of the screw shell 12 and the lamp 13 aids or promotes loosening of the lamp base in the screw shell.
The threads 12a and 14a of the screw shell 12 and lamp base 14 are formed by rolling and consequently, large tolerances or differences are permitted in the dimensions of the male threads 14a of the lamp base 14 and the female threads 12a of the screw shell 12. Under approved standards, the difference in these dimensions for a mogul socket will vary from about 0.010 inches to about 0.032 inches and thus, a loose fit is made between the threaded base of the lamp and the screw shell.
In a mogul socket, for example, the diameter of the female threads 12a of the socket shell 12 may vary from 1.576 inches to 1.565 inches (root diameter) while the diameter of the male threads 14a of the lamp base 14 may vary from 1.555 inches to 1.542 inches (root diameter). Thus, the differnce in these dimensions can be as great as 0.034 inches and due to such built-in tolerances, the lamp 13 can readily become loose in the screw shell 12 from many causes. Once such loosening starts, it is aided by the downward inclination of the threads relative to the axis of the socket when the lamp hangs down. In such a case, the lamp will tend to unscrew itself and presents a hazard by eventually dropping onto the floor. In open installations, wind or air currents may cause movement of the lamp in the socket and loosening of the lamp, particularly where a large open area such as a warehouse is involved.
In accordance with the present invention, loosening of the lamp in the socket is prevented or substantially eliminated by interposing a retainer strip 16 of thin flexible and deformable material between the male threads on the lamp base 14 and the female threads 12a of the screw shell 12. As shown, the retainer strip 16 may be installed in the screw shell prior to assembly of the shell in the housing 11. In this case, the ends of the strip 16 extend through spaced slots or openings 17 cut in the sides of the screw shell 12. The slots 17 are spaced by about 30 or less and preferably, are wide enough to receive the strip 16 without bending for ease of installation.
The retainer strip 16 may be made of a thin flexible strip of metal such as stainless steel or other deformable material including plastics. In a mogul type socket, the strip should not exceed 0.010 inches in thickness and preferably should be of about 0.005 inches in thickness to avoid interference with introduction of the threaded end of the lamp base into the socket.
Preferably, the strip 16 is wide enough to bridge or extend over the crests of at least two of the female threads 12a and bends transversely to conform to the undulating contour of the threads as the lamp base 14 is screwed into place. The strip 16 also bends in a lengthwise direction to conform to the curvature of the lamp base 14. The bending of the strip 16 takes place in two directions and the resiliency of the strip insures firm engagement of the strip 16 with the threads 14a on the lamp base 14 without interfering with introduction of the lamp base 14 into the screw shell 12.
The strip 16 may or may not be permanently deformed depending on the material employed and the temper and hardness of such material.
The slots 17 in the shell 12 are spaced to receive the strip 16 in a position where the strip will not interfere with introduction of the threads 14a on the lamp base into the screw shell 12. As noted above, the strip 16 will conform to the configuration of the threads 14a on the lamp base 14 as the base is threaded into the screw shell 12. The strip 16 presses on the lamp base 14 and increases frictional engagement between the threads 14a on the lamp base 14 and the threads 12a on the screw shell 12 which reduces the possibility of the lamp accidentally becoming loose in the socket without requiring that undue force be exerted on fragile parts of the lamp as the lamp is inserted or removed. The strip 16 also tends to position the lamp 13 vertically in the socket 10.
In the modification shown in FIGS. 6 and 7, a clip 18 is employed as a retainer. The clip 18 may be installed prior to insertion of the lamp and is made of a thin strip of flexible and deformable material. The clip 18 illustrated is U-shaped and is installed with legs of the clip extending on opposite sides of the screw shell 12. The inner leg of the clip 18 extends over a number of the threads 12a of the screw shell 12 and conforms to the threads 14a on the lamp base 14 when the lamp base is threaded into the screw shell. For a mogul socket, the clip 18 may be about 0.005 inches in thickness and about 0.75 inches wide. To facilitate proper bending of the U-shaped clip 18, an aperture 19 may be pierced where the legs are joined. When the lamp 13 is screwed in place, the clip 18 also prevents accidental loosening of the lamp in the socket. The outer leg of the clip 18 is placed between the screw shell 12 and the housing 11 to held the clip 18 in place.
Various changes may be made in the embodiments of the invention illustrated and described herein by those skilled in the art without departing from the spirit or scope of the invention.
What is claimed is:
1. In a lamp-retaining socket for an electric lamp having a screw type base, the combination comprising:
a. a metal screw shell forming an opening for a threaded lamp base;
b. said opening in the screw shell containing internal rolled threads mating with external rolled threads on the lamp base;
c. said mating rolled threads on the screw shell and the lamp base entering into loose engagement with each other and defining a space between opposing surfaces thereof;
d. a pair of angularly spaced vertical slots formed in the screw shell; and
e. a strip of deformable material extending through said vertical slots in the screw shell and being supported therein at one side of the opening in the screw shell;
f. said deformable strip having a width extending over a plurality of the threads of the screw shell and having a thickness less than a difference between root diameters of the rolled threads on the screw shell and the rolled threads on the lamp base;
g. said spaced vertical slots in the screw shell positioning the strip at one side of the opening in the screw shell and permitting introduction of the threaded lamp base therein without interference.
2. In a lamp-retaining socket for an electric lamp having a screw type base, the combination as defined in claim 1 wherein:
a. the vertical slots in the screw shell are spaced apart by an angle of about 30.
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