METHOD OF AND APPARATUS FOR MANUFACTURING SMALL-SIZE GAS-FILLED LAMPS

Abstract: A lamp bulb has a closed lens-shaped head received in a recess in a bulb holder jig and an open end held by a heating carbon jig. A bead supporting a pair of lead wires with a filament connected thereto is disposed in the open end of the bulb, with the lead wires being supported on a lead wire holder. The jigs and holder are housed in a chamber in which a vacuum is developed. A gas to be filled in the bulb is introduced into the chamber under a desired pressure irrespective of atmospheric pressure. Then, an electric current is passed through the heating carbon jig to heat the latter for fusing the open end of the bulb and the bead, and at the same time the closed end of the bulb is cooled by the bulb holder jig which is supplied with a coolant liquid. After the bulb and the bead have been fused together, the electric current flowing through the heating carbon jig is cut off to stop the heating of the heating carbon jig. Then, the chamber is removed, and the completed lamp is taken out. A number of such gas-filled lamps can easily be mass-produced by placing the lamp components in the chamber at a time, without producing defective products.

Description: BACKGROUND OF THE INVENTION 1. Field of the invention: The present invention relates to a method for manufacturing small-size gas-filled lamps, particularly small-size halogen-gas-filled lamps, for use in optical instruments, medical instruments, electronic devices and the like, with the features of the preamble of the only claim as known from US-A 3 698 784. Reference is further made to US-A 3311 433. The presently available methods of manufacturing small-size gas-filled lamps suffer from various problems, and has complicated steps. The lamps manufactured by such methods are unstable in quality. The methods have therefore been unsatisfactory for mass-producing lamps of good quality. SUMMARY OF THE INVENTION With the difficulties of the prior methods and apparatus in view, it is an object of the present invention to provide a method of manufacturing many, 500 to 1,000 or more, small-size gas-filled lamps of improved uniform quality at a time in simple mechanized operation without producing defective products during the manufacturing process. This object is solved by the features of the characterising part of the only claim. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view, partly in cross section, of an apparatus for manufacturing small-size gas-filled lamps; FIG. 2 is a cross-sectional view of a small-size gas-filled lamp manufactured by the apparatus shown in FIG. 1; FIG. 3 is a fragmentary cross-sectional view illustrative of a pair of lead wires as it is assembled by a bead; FIG. 4 is a cross-sectional view of the assembled lead wires and bead; FIG. 5 is a cross-sectional view of the lead wire and bead assembly with a filament attached to the lead wires, the lead wires being shaped for positioning the filament and bead in sealing operation; and FIG. 6 is a cross-sectional view of a lamp bulb having a lens end. DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, an apparatus for manufacturing small-size gas-filled lamps according to the method of the present invention includes a pressurized vacuum chamber 1 made of steel plated with hard chromium. An insulating material may be or may not be attached to an interior surface of the chamber 1 dependent on the product to be heated and sealed therein. In the illustrated embodiment, the chamber 1 is constructed of walls which are about 20 mm thick, and can sufficiently seal therein the gas pressure of the order of 20 atmosphere. Heating electrodes 2 are housed in the chamber 1. Each of the heating electrodes 2 is made of copper plated with nickel by electroless plating. Support columns of copper which can be introduced for supplying currents to the electrodes may be or may not be water-cooled dependent on the product to be heated and sealed. The chamber 1 houses therein a lead wire holder 3 mounted on the heating electrodes 2 for positioning the center of a lamp filament in alignment with the central axis of a lamp assembled. If the flament were displaced out of the central axis of a lamp having a lens mounted on the tip thereof, the focus of the lens would be adversely affected thereby, resulting in a defective product. The lead wire holder 3 also serves to attach a bead on which a filament is mounted accurately at a sealing position in an open end of a bulb. A heating carbon jig 4 is mounted on the heating electrodes 2 for fusing and sealing the bead with the filament attached and the open end of the bulb. The heating carbon jig 4 is in the form of a plate having a central hole of a diameter slightly larger than the outside diameter of the bulb, so that the edge defining the central hole will be kept in substantial contact with the outer circumferential surface of the sealing portion of the bulb. Although not shown, the heating carbon jig 4 has a number of thermal barrier slots or holes positioned between the heating electrodes 2 and the central hole for heating a multiplicity of bulbs attached to uniform temperature. A thermal shield plate 5 is disposed immediately below the heating carbon jig 4 with a small space therebetween. The thermal shield plate 5 serves to prevent the heat emitted by the heating carbon jig 4 from heating a bulb holder jig 6 (described later) and a bulb supported thereon to the extent where the bulb is deformed or the gas in the bulb is expanded due to a temperature rise of the bulb holder jig 6. The thermal shield plate 5 also prevents other portions of the bulb than the sealing portion from being heated, thus eliminating any impure gas which would otherwise be generated by the undue heating of the bulb and hence maintaining the desired purity of the gas filled in the bulb. The bulb holder jig 6 is positioned below the thermal shield plate 5 and centrally in the chamber 1 for supporting a bulb 15 thereon. The bulb holder jig 6 has an array of recesses 22 for receiving the heads, respectively, of bulbs 15. The bulb holder jig 6 is centrally aligned with the lead wire holder 3. The bulb holder jig 6 is mounted by supports 7 on a base 21 so as to be securely positioned in the chamber 1. The supports 7 are made of a thermally insulating material. The bulb holder jig 6 is supported by the supports 7 in upwardly spaced relation to an air outlet tube 11. The air outlet tube 11 is connected to an air discharging vacuum pump through a valve 12 which will be opened when developing a vacuum in the chamber 1 and closed when introducing a gas into the chamber 1. A gas to be filled in the bulb can be introduced under a desired pressure through a gas supply tube 8 mounted on the base 21. A sealing O-ring 9 made of thermally insulating rubber is interposed between peripheral edges of the chamber 1 and the base 21 for providing a seal therebetween. Wire cord attachment nuts 10 serve to attach wire cords from a power supply to the heating electrodes 2. Coolant liquid tubes 13 are mounted on the base 21 and coupled to the bulb holder jig 6 for cooling the bulbs supported on the latter. The peripheral edges of the chamber 1 and the base 21 are sealingly clamped with the O-ring 9 interposed therebetween by clamps 14. The apparatus shown in FIG. 1 will be assembled in the following manner: Bulbs 15 are set in place on the bulb holder jig 6 and lead wires to which beads and filaments are attached and which are bent are supported on the lead wire holder 3. At this time, the beads are received in the bulbs 15 which are placed in the holes in the heating carbon jig 4 and the thermal shield plate 5. Then, the chamber 1 is placed on the base 21 with the O-ring 9 interposed between their peripheral edges, which are firmly clamped together by the clamps 14. The valve 12 disposed in the air dischare tube 11 connected to the vacuum pump is opened to develop a vacuum in the chamber 1. Then, the heating carbon jig 4 is heated to heat the interior of the chamber 1 up to a temperature ranging from about 100°C to about 200°C for discharge any impure gas from the chamber 1 to achieve a higher vacuum. When the vacuum has reached a prescribed level, the valve 12 is closed. FIG. 2 shows a completed small-size gas-filled lamp 23 manufactured according to a method of the present invention. The lamp 23 includes an outer bulb 15 made of glass and having a sealing end 24 and an opposite end or top 16 in the form of a semispherical lens, as shown in FIGS. 2 and 6. The lamp 23 also includes a pair of lead wires 18 supported on a bead 19 disposed and sealed in the sealing end 24 of the bulb 15, the lead wires 18 comprising Dumet or molybdenum wires and having the same coefficient of thermal expansion as that of the bead 19. The bead 19 is of a diameter slightly smaller than the inside diameter of the bulb 15, and is made of the same glass as that of the bulb 15. A coiled filament 17 is attached to the ends of the lead wires 18 which are disposed in the bulb 15. A method of manufacturing the lamp 23 will be described with reference to FIGS. 2 through 6. The outer bulb 15 is formed by cutting off an elongate tube of glass and shaping one end of the cut piece into the semispherical mass of glass. Then, a tube of the same glass is also severed into a bead ring 20 (FIG. 3) which is placed in a recess 25 in a jig 26 of carbon with a pair of straight lead wires 18 extending parallel to each other through the bead ring 20. The jig 26 is then heated to fuse the bead ring 20 into a bead 19 around the lead wires 18 as illustrated in FIG. 4. Then, longer end portions of the lead wires 18 are bent, and a filament 17 is attached to bent ends of the shorter end portions of the lead wires 18 as shown in FIG. 5. The filament 17 is placed in an atmosphere of hydrogen, and an electric current is passed through the filament 17 to remove any impurities deposited on the filament 17. The assembly of FIG. 5 and the bulb 15 are placed in the chamber 1 clamped to the base 21 as shown in FIG. 1, and after evacuation a gas to be filled in the bulb 15 is introduced into the chamber 1 by opening the valve 12. The gas is supplied into the chamber 1 at a pressure slightly higher than a prescribed pressure to compensate for any pressure drop in the bulb 15 below the gas pressure in the chamber 1 due to expansion of the gas at the time the bulb 15 is heated and sealed. Then, the valve 12 is closed. An electric current is passed through the heating carbon jig 4 to heat the latter. Since the pressure of the gas filled in the bulb 15 is to be increased, the coolant liquid is introduced through the coolant liquid tubes 13 for cooling the bulb holder jig 6. Then, the current passing through the heating carbon jig 4 is increased to heat the bulb 15 and the bead 19 to the temperature where they are melted and fused together. Immediately before the bulb 15 and the bead 19 are sealed together, the amount of coolant liquid fed into the bulb holder jig 6 is also increased to cool the bulb 15 more intensively to suppress the expansion of the gas in the bulb 15, and at the same time the heating carbon jig 4 is heated up to a higher temperature to seal the bulb 15 and the bead 19 together. After the bulb 15 and the bead 19 have been sealed, the electric current supplied to the heating carbon jig 4 is immediately cut off to stop the heating thereof. The bulb holder jig 6 is continuously cooled by the coolant liquid until the temperature in the chamber 1 is lowered down to a desired temperature, whereupon the forced cooling of the bulb holder jig 6 is stopped. Then, the bulb holder jig 6 is slowly cooled until the temperature in the chamber 1 becomes low enough to allow the completed product to be picked up. The clamps 14 are then unlocked, the chamber 1 is removed, and the finished lamp 23 is removed. One cycle of the process is now completed. Example: Small-size halogen lamp filled with a mixed gas of krypton and methylene bromide were manufactured which have a rated voltage of 6V, a rate current of 1A, an outside diameter of 4.7 mm, and an overall length of about 11 mm. The lamps had outer bulbs made of soft lead glass and processed at a temperature in the range of from about 650°C to 700°C. The lead wires comprised molybdenum wires, and the bead rings were cut off from the same tube of glass from which the bulbs were severed. The bead rings and lead wires were assembled as shown in FIG. 3 on the jig 26, and heated to a temperature ranging from 1,200°C to 1,250°C in the atmosphere of a nitrogen gas. 200 to 500 bead-and-lead-wire assemblies were manufactured in one process. The lead wires were bent at lower end portions and filaments in the form of a tungsten coil having an increased purity for use in halogen lamps were attached to upper ends of the lead wires as shown in FIG. 5. Then, about 300 such assemblies were placed centrally in the heating carbon plate 4 as shown in FIG. 1 within the chamber 1 having a thermal insulator plate disposed therein, and air was discharged from the chamber 1 to create a vacuum therein. Then, the chamber 1 and the base 21 with the O-ring 9 interposed therebetween were clamped together by the clamps 14. An electric current was passed through the heating carbon jig 4 to heat the latter and hence the interior of the chamber 1 up to a temperature in the range of from about 150°C to 200°C for removing any gas deposited in the chamber 1, thereby achieving a higher degree of vacuum. When the vacuum reached 10⁻⁶ mmHg or higher, the valve 12 was closed, and a mixed gas of krypton and methylene bromide was introduced through the gas supply tube 8 up to the pressure of 5 atmosphere. Instead of such a gas, a mixed gas composed of an inert gas and a halogen gas, such as an argon gas and an iodine gas may be introduced. The current flowing through the heating electrodes was increased to raise the heating temperature, and at the same time cooling water was introduced into the bulb holder jig 6 to prevent the bulbs and the gas therein from being heated to a high temperature. Then, the current passing through the heating electrodes 2 was increased to heat the heating carbon jig 4 up to a temperature of about 1,200°C. Immediately before the beads and the outer bulbs were fused together, the cooling water being supplied to the bulb holder jig 6 was increased to further cool the latter, and the current was increased to fuse the beads and the bulbs together, whereupon the current was cut off to stop the heating of the heating carbon plate 4. The quantity of cooling water flowing through the bulb holder jig 6 is slightly reduced. When the temperature in the chamber 1 dropped to 200°C or below, the clamps 14 were removed to detach the chamber 1 from the base 21, and completed small-size halogen lamps filled with an argon gas with the outer bulbs and beads being fused together were taken out. The overall process was thus completed. The pressure of the gas in the finished lamp under normal temperature was about 3 atmosphere. After going through an aging process, all of the produced lamps were found good as a result of a current test, a flux test, and a life test. With the method of the present invention, as described above, the outer bulb and the bead with the filament attached can easily and simply be fused together, and no defective lamps are produced. The cost of manufacture of small-size gas-filled lamps is reduced, and the quantity of such lamps produced in an unit area during a unit time is much greater than that according to the conventional processes. Therefore, the method of the present invention is of great industrial advantage.

Claims: A method of manufacturing small-size gas-filled lamps comprising the steps of: a) preparing an assembly of a bulb (15) having a closed head and an open end, and a bead (19) disposed in the open end of the bulb (15) and supporting a pair of lead wires (18) with a filament thereto; b) placing said assembly in a chamber (1) with the closed head of the bulb (15) supported on a support stand (6); c) surrounding said open end of the bulb (15) by a resistance heating element (4) and supporting said lead wires (18) on a lead wire holder (3), said support stand, said heating element (4) and said lead wire holder (3) all being disposed in said chamber (1), d) developing a vacuum in said chamber (1) to evacuate the air therefrom; e) heating said resistance heating element (4) to fuse the open end of the bulb (15) and said bead (19) together ; f) stopping the heating of said open end of the bulb (15) and said bead (19) which are fused together; g) taking the assembly out of the chamber, characterised in that h) a plurality of said assemblies are placed in the chamber (1) wherein each of the closed heads of the bulbs (15) is received in a recess (22) in a bulb holder jig; i) a carbon jig is used as resistance heating element (4); j) during evacuation, the chamber (1), the jigs (4, 6) and the wire holder (3) are degassed by passing an electric current through the heating carbon jig (4); k) a gas under a desired pressure in excess of atmospheric pressure is introduced in the chamber (1); l) the open end of the bulb and the bead are fused together by increasing the current through the carbon jig and m) simultaneously, a coolant liquid is passed through the bulb holder jig (6) thereby cooling the closed head of the bulb (15).

Inventors: HAMAI, JITSUO
Applicants: HAMAI ELECTRIC LAMP CO., LTD.
Application year: 1984
Main classification: H01K3
IPC codes: H01K3, H01K1