US3548241A

US3548241A - Method of incorporating an amalgam or an amalgam-forming metal in a lowpressure mercury discharge lamp,and lamp produced by such method

Info

Publication number: US3548241A
Application number: US726689A
Authority: US
Inventors: Erhard Rasch; Horst Wantosch
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 1968-05-06
Filing date: 1968-05-06
Publication date: 1970-12-15
Anticipated expiration: 1987-12-15

Description

Dec. 15, 1970 E. RASCH ETAL METHOD OF INCORPORATING AN AMALGAM OR AN AMALGAM-FORMING METAL IN A LOW-PRESSURE MERCURY DISCHARGE LAMP. AND

LAMP PRODUCED BY SUCH METHOD Filed May 6, 1968 FIG.2.

h S w R w 0 7- m W E N w m R D N E l S 6 d m0 H r E WITNESSES U.S. Cl. 313-178 9 Claims ABSTRACT OF THE DISCLOSURE The mercury-vapor pressure within a low-pressure discharge lamp, such as a fluorescent lamp, is regulated by a thin layer of an amalgam-forming metal or amalgam that is sprayed onto one of the lamp stems, preferably on the flared portion thereof, while the metal or amalgam is in a liquid state and before the stem is sealed into the envelope. The thickness of the metal or amalgam layer is maintained below 100 microns, and preferably between 20 and 50 microns, to provide a sufiicient amount of metal to properly regulate the mercury vapor pressure during lamp operation and yet prevent the metal or amalgam from falling ofl the stem when the metal or amalgam is in a liquid state during the sealing-in of the stem and, in the case of a fluorescent lamp of non-linear configuration, when the finished lamp is heated and bent into the desired shape.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to mercury discharge lamps and has particular reference to fluorescent lamps and a method of incorporating an amalgam or an amalgam-forming metal within the lamp envelope at a location such that it regulates the mercury vapor pressure and permits the lamp to be operated at high power loadings and under high ambient temperature conditions with improved eificiency and lumen output.

Description of the prior art As is well known, if a fluorescent lamp is operated at higher than conventional power loadings or in enclosed lighting fixtures where high ambient tmeperatures are encountered, the light output of the lamp decreases due to the excessive mercury vapor pressure generated within the lamp by the higher operating temperatures. This problem can be overcome by utilizing an amalgam which is strategically located within the lamp so as to regulate the mercury vapor pressure and permit the lamp to operate etficiently at such high power loadings and high ambient temperatures. The amalgam must not only be placed at the proper location within the lamp but the amalgam composition and choice of the amalgam-forming metal or metals must be such that the amalgam will function properly and provide the desired degree of vapor pressure regulation. A fluorescent lamp having an amalgam that meets all of these requirements is disclosed in U.S. Pat. No. 3,007,071 issued Oct. 31, 1961 to A. Lompe et al.

The use of two sources of amalgam within a fluorescent lamp is also known-one which heats up rather slowly when the lamp is energized and then controls the mercury vapor pressure during operation, and a secondary source of amalgam which is located closer to the electrodes and thus heats up at a faster rate and provides a suflicient amount of mercury vapor to enable the lamp to reach its rated output more rapidly. A fluorescent lamp of this United States Patent type is disclosed in U.S. Pat. No. 3,227,907 issued Jan. 4, 1966 to C. J. Bernier et al.

Various arrangements for retaining the amalgam at the desired location within the lamp and for incorporating the amalgam or amalgam-forming metal as an integral part of the lamp structure are also known. For example in German Pat. No. 1,104,060 an amalgam containing cadmium, indium, thallium, or tin, or alloys thereof, is applied to the inner wall of the lamp envelope in the form of a strip, a film or a bead. In German Pat. Nos. 1,l40,2861,l96,292 and 1,149,818, the amalgam-forming metal is combined with a measured amount of mercury to provide the desired amalgam composition which is then either pasted or rolled onto the bulb wall, as, after being heated to at least partly soften it, is impacted against the bulb wall and thus secured to a predetermined inner part of the envelope.

However, if desired, only the amalgam-forming metal may be incorporated into the lamp initially and the amalgam subsequently formed when the lamp is dosed with mercury in the usual manner. In Japanese patent applications 40-8518 and 40-2875 there are disclosed, for example, fluorescent lamps. in which a ring of indium is applied to the inner surface of the envelope at the middle of the lamp so that the indium combines with the mercury subsequently dosed into the lamp and forms the desired indium-mercury amalgam composition, by an exterior heating element positioned around the middle of the lamp.

In German GM 1,934,678 there is disclosed a discharge lamp in which a strip of indium metal is attached to one of the stem presses. In German GM 1,937,402 there is disclosed another type of lamp in which indium is placed in a sieve-like container that is pasted to the inner surface of the lamp envelope or attached to one of the lead-in wires by insulator means. In another type of fluorescent lamp a wire mesh holder is impregnated with indium and then placed around one of the lamp stems. A fluorescent lamp having this type of pressure regulating assembly is described in Illuminating Engineering, volume 60/1965, paper No. 9, p. 534.

Experience has shown that optimum results will be achieved in amalgam type lamps if the amalgam-forming metal or amalgam is in a form such that it extends over the greatest possible area. This makes it difiicult, on the one hand, to apply the amalgam to such a large surface within the lamp with sufficient adherence at a location where the amalgam will not block radiation, and, on the other hand, it complicates the manufacture of the lamp since portions of the lamp have to be cooled during the exhaust and baking operations in order to prevent the amalgam from melting and flowing away from the desired location. In addition, while some amalgam-forming metals or amalgams are suitable as regards their ability to provide sufflcient mercury vapor pressure regulation, they have such a low melting point that they become liquid at the operating temperatures within the lamp and thus create a situation where the amalgam may not remain at the desired location within the lamp.

OBJECTS AND SUMMARY OF THE INVENTION It is accordingly the general object of the present invention to provide an improved method of incorporating an amalgam or an amalgam-forming metal within a mercury discharge lamp which will avoid or overcome the aforementioned problems associated with the manufacture and use of lamps having this type of mercury-vapor control means.

Another and more specific object is the provision of a method of manufacturing an amalgam-type fluorescent lamp which will permit the amalgam component to be 3 incorporated as an integral part of the lamp structure without disrupting the normal sequence of operation required to produce the lamp on a mass production basis.

Still another object is the provision of an amalgamcontaining fluorescent lamp that can be heated and reshaped after the lamp has been completed without dislodging the amalgam-forming metal from its proper location within the lamp.

The aforementioned objects and other advantages are achieved in accordance with the present invention by heating a suitable amalgam-forming metal, such as indium, until it becomes a liquid and then spraying the metal, while in its liquid condition, onto one of the electrode stems before it is sealed into the envelope. The amalgamforming metal, or amalgam composition itself, is preferably sprayed onto the laterally protruding flared portion of the stem in such a manner that a thin annular layer of metal or amalgam is deposited that extends around the circumference of the flared portion of the stem.

The spraying time is controlled so that the metal layer a is very thin and has a thickness less than 100 microns, and preferably between 20 and 50 microns. The partly metallized stem is sealed into the lamp envelope and the other operations required to complete the lamp are carried out in the regular manner. While a suflicient amount of amalgam-forming metal is contained in the layer to achieve the proper degree of vapor pressure regulation, the thickness of the layer is such that the metal remains in place even when it is in a liquid state during the sealingin of the stem.

The aforesaid properties and characteristics of the amalgam-forming metal layer also permit the sealed-in lamp to be heated to the softening point of the glass envelope and the latter to be bent into the desired shape Without causing the liquid metal to fall off or run off the stem.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing, where- FIG. -1 is a front elevational view of one end of an amalgam-containing fluorescent lamp which embodies the present invention, a portion of the lamp envelope being removed for illustrative purposes; and,

FIG. 2 is an elevational view on a reduced scale of a U-shaped amalgam type fluorescent lamp that includes an amalgam-bearing stern of the type shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With specific reference now to the drawings, in FIG. 1 there is shown one end of a fluorescent lamp having a tubular vitreous envelope 11 which is hermetically sealed to a vitreous stem 12 that is terminated at its outermost end by a laterally extending flared portion 13 and at its innermost end by a press seal 14. The inner surface of the envelope 11 is coated with a suitable ultravioletresponsive phosphor 15 in the usual manner and a pair of lead-in wires 16 are embedded in and extend through the press seal 14. A vitreous exhaust tube 17 is fused to the stem 12 in the region of the stem press 14 and communicates with the interior of the envelope 11 through an aperture in the press in the usual manner to enable the lamp to be evacuated, mercury dosed and charged with fill gas.

The inner ends of the lead-in wire 16 are attached to and support an electrode coil 18 which is enclosed by an annular metal cap 19 of sheet iron that is supported in such position by a support Wire embedded in the stem press 14. A strip v20 of a suitable amalgam-forming metal, such as tin, indium and lead, is secured to the edge of the metal cap 19 to serve as an auxiliary source of amalgam and facilitate starting of the lamp.

In accordance with the present invention, the main mercury-vapor prQSSLll'Q QQ lLFOI means comprises an an- 4 nular band 22 of suitable amalgam-forming metal that is sprayed onto the flared portion 13 of the stem 12 in a manner such that it extends around the circumference of the flare at a region that is spaced inwardly from the rim of the flare that is sealed to the envelope neck.

While the amalgam-forming metal layer 22 can be sprayed onto the flared portion 13 of the stem 12 in various Ways, the stem 12 is preferably rotated about its longitudinal axis and the liquid metal is sprayed onto the flare by means of a nozzle that is inclined at an angle of about with respect to the axis of rotation. The nozzle aperture and its distance from the stem are such that the annular strip of deposited metal is of the desired width. The thickness of the metal layer is controlled by varying the time of spraying and, in the case of the embodiment here shown, a layer of indium about 30 microns thick was spray-deposited in an annular strip such that the total quantity of indium applied to the stem Was about milligrams. This provided an indium-mercury amalgam in the finished lamp which contained at least indium.

The thickness of the layer 22 of amalgam-forming metal is critical in that if it is too great the amalgamforming metal may drop off the stem due to its own weight when the metal is in a liquid condition. This is avoided according to the invention by utilizing a thin layer, preferably one having a thickness less than microns and preferably from 20 to 50 microns. In the case of indium, a layer of this thickness enables the metal to adhere tightly to the flare by virtue of the high surface tension, even when the indium becomes liquid during the sealing in of the stem 12. This is a great advantage insofar as stems with such spray-deposited thin layers of amalgam-forming metals may be processed and sealed into the envelopes in the usual manner without any detrimental aflects on the metal layer. Lamps utilizing such stems can also be exhausted in the usual manner, and upon the dosing of the required amount of mercury into the lamp, the desired amalgam composition is formed within the finished lamp.

The invention provides the additional advantage of permitting the amalgam to be applied to a large surface within the lamp at places which are not located in the direction of radiation and which thus do not prevent light rays from leaving the envelope. Since the indium is located at a region within the lamp which has a relatively high operating temperature, a flatter light output versus temperature curve is achieved. Thus, compared to standard lamps the amalgam-containing lamp of this invention may be operated at high light output over a considerably broader range of ambient temperatures. At the most, the light output of the amalgam lamp decreases by 10% over an ambient temperature range of 25 C. to 75 C., with the maximum light output occurring at 45 C.

Another advantage of the invention is that a smaller quantity of amalgam-forming metal is required compared to that required heretofore, as, for example, when the metal is placed within a wire mesh holder. It has been found that only one-third to one-fourth as much indium is required if it is sprayed onto the stem in accordance with the present invention. In addition, the method of the present invention eliminates the need for special stems or elongating the length of the stem and the need for cool end chambers so that the shortening of the arc length and darkened lamp ends produced by these structures are completely eliminated.

Since special stems are no longer necessary and only small quantities of amalgam-forming metal are required to achieve proper regulation of the mercury vapor pressure, the present invention permits amalgam type lamps to be bent in any desired shape and thus permits the manufacture of lamp types heretofore unavailable. Due to the fact that only a small quantity of amalgam-forming metal is used and it is sprayed onto the stem in a very thin layer, the metal does not drop off of the stem even when it becomes liquid during the heating of the lamp envelope and the manipulation thereof required to bend it into the desired shape. Hence, high output fluorescent lamps and high ambient temperature lamps containing amalgams can be made in shapes heretofore unavailable, as for example, in the form of well-known circleline type and U-shaped lamps.

A U-shaped amalgam-containing fluorescent lamp a embodying the invention is shown in FIG. 2. As shown, the envelope 11a is bent into the shape of a U after the stems 12a have been sealed into the envelope and the fabrication of the lamp is completed. Suitable terminals 23 are connected to the lead-in wires at each end of the lamp and the legs of the envelope are joined together by a suitable strap 23 to improve the rigidity of the lamp. The use of an auxiliary source a of amalgam on the metal cap 19a in conjunction with the main reservoir of amalgam 22a sprayed onto the stem flare is also advantageous in that it facilitates lamp starting.

A U-shaped lamp of the type shown in FIG. 2 manufactured in accordance with the invention produces a light flux of 3300 lumens when operated on a line Voltage of 220 volts, at an ambient temperature of about 45 C., and a power input of 65 watts. Its operating voltage was 85 volts its operating current was 885 milliamps. The efliciency of the lamp was, accordingly, in excess of 50 lumens per watt compared to an efficiency of 43 lumens per watt and an output of 2800 lumens for conventional U-shaped lamps of the same type.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that a very simple and convenient method of incorporating an amalgam-forming metal or amalgam in a fluorescent lamp has been provided which permits the lamps to be manufactured with a minimum amount of amalgam-forming metal and in the usual manner utilizing techniques and operations now employed in the mass production of such lamps. In addition, a high output fluorescent lamp which contains an amalgam and is of nonlinear configuration has been provided which can be manufactured in the usual manner by heating the finished lamp and bending the envelope into the desired shape.

While several embodiments have been illustrated and described, it will be understood that various changes in both the method of manufacture and construction of the lamp may be made without departing from the spirit and scope of the invention.

We claim as our invention:

1. In the manufacture of a low-pressure mercury discharge lamp having a vitreous stem at one end that is joined to the lamp envelope, the method ofincorporating an amalgam-forming metal as an integral part of the lamp and at a location therein such that the metal will regulate the mercury-vapor pressure when the lamp is operated, which method comprises;

heating the amalgam-forming metal until it is in the liquid state,

spraying the liquid metal onto a selected portion of the vitreous stem and depositing a thin layer of said metal thereon before said stem is joined to the lamp envelope, and then joining said stem to the lamp envelope and completing the fabrication of the lamp.

2. The method of claim 1 wherein the spraying time is regulated so that the thickness of the formed metal layer is less than microns.

3. The method of claim 1 wherein:

said stem is terminated at one end by an outwardly flared portion, and

said amalgam-forming metal is spray-deposited on the flared portion of said stem inwardly from the rim of said flared portion.

4. The method of claim 3 wherein said amalgam-forming metal is sprayed onto the flared portion of said stern while the stem is being rotated about its longitudinal axis so that the metal is deposited in a layer of annular configuration that extends around the circumference of said flared portion.

5. The method of claim 3 wherein the metal is sprayed onto the flared portion of the stem until the thickness of the formed metal layer is between 20 and 50 microns.

6. In a low-pressure mercury vapor discharge lamp having a tubular glass envelope which is hermetically closed by glass stems that are located at the respective ends of said envelope and have outwardly flared portions that are sealed to the envelope, the improvement comprising a layer of amalgam-forming metal that (a) is located on the flared portion of one of said stems, (b) has a thickness less than 100 microns, and (c) contains a sufficient amount of said metal to regulate the mercury-vapor pressure within the lamp during the operation thereof.

7. The lamp of claim 6 wherein the thickness of said layer of amalgam-forming metal is between 20 and 50 microns and said layer extends around the flared portion of said stem and is spaced inwardly from the juncture thereof with said envelope.

8. The lamp of claim 6 wherein;

said envelope is of nonlinear configuration, and

said layer of amalgam-forming metal extends around the flared portion of said stem and constitutes an annular strip that is spaced inwardly from the juncture between said flared portion and envelope.

9. In the manufacture of a low-pressure mercury discharge lamp having a vitreous stem at one end that is joined to the lamp envelope, the method of incorporating an amalgam composed of mercury and a selected metal as an integral part of the lamp and at a location therein such that the amalgam will regulate the mercury-vapor pressure when the lamp is operated, which method comprises;

heating the amalgam until it is in the liquid state,

spraying the liquid amalgam onto a selected portion of the vitreous stem and depositing a thin layer of said amalgam thereon before said stem is joined to the lamp envelope, and then joining said stem to the lamp envelope and completing the fabrication of the lamp.

References Cited UNITED STATES PATENTS 1,958,967 5/1934 Kniepen 313-178X 3,287,587 11/1966 Menelly 313--178X 3,392,298 7/1968 Menelly 313-178X RAYMOND F. HOSSFELD, Primary Examiner US. Cl. X.R. 313174; 31625