Title:
METHOD OF MANUFACTURE OF AN INCANDESCENT LAMP
United States Patent 3850489
Abstract:
A method of manufacturing an incandescent lamp which includes the stretching of a filament, previously clamped to lead wires, by straightening a premeasured bend in one of the lead wires. In a variation of the method, an open spiral filament support is closed around the filament following the stretching process.
Inventors:
Jarc, Robert A. (Kent, OH)
Ritzinger, Fredrick (Parma, OH)
Application Number:
05/424875
Publication Date:
11/26/1974
Assignee:
General Electric Company (Schenectady, NY)
International Classes:
H01K3/06; H01K3/00; H01K3/00; (IPC1-7): H01J9/38
Field of Search:
29/25.15 313
Primary Examiner:
Lake, Roy
Assistant Examiner:
Davie, James W.
Attorney, Agent or Firm:
Sos Jr., Emil Kempton Lawrence Neuhauser Frank F. R. L.
Claims:
What we claim as new and desire to secure by
Letters Patent of the United States is
1. The method of manufacturing an incandescent lamp comprising the steps of:
2. The method of manufacture claimed in claim 1 wherein said holding means has two movable jaws which move in a direction away from each other to straighten the wire and tension the coil.
3. The method of manufacture claimed in claim 1 wherein a ceramic bridge is attached to said unitary piece of wire to hold portions of the wire in fixed relation to each other.
4. The method of manufacture claimed in claim 3 wherein said ceramic bridge contains one end of a filament support with the other end being an open spiral located near the center of the filament, closing said open spiral around said filament after the filament has been tensioned to prevent said filament from touching the envelope.
5. The method of manufacturing an incandescent lamp comprising the steps of:
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a method of manufacturing an incandescent lamp. More particularly, the invention relates to a method of stretching a clamped filament to a predetermined length by straightening a bend in one of the lead wires.
2. Description of the Prior Art
In the manufacture of incandescent lamps, particularly tungsten-halogen lamps, filament tensioning between lead wires and filament location are very important to lamp life and performance. Prior art practices included clamping one leg of a filament to a lead wire and then manually stretching the other end of the filament until it could be clamped to a second lead wire. This becomes especially time-consuming if a filament support is used which necessitates the threading of the filament through a loop or spiral before attaching the filament leg to the second lead. The use of a filament support is one method of preventing the filament from contacting the bulb wall.
Efforts to automate the filament mounting process and associated processes of pinch sealing, flushing, filling and tipping have been unsuccessful because of space limitations created by the lamp geometry. In other words, a means for stretching and tensioning the filament would interfere with the means used to clamp the filament legs to the lead-in conductors. This problem would be further complicated if a filament support were used because a mechanism would have to be provided to thread the filament through a support during or prior to the filament stretching process.
As previously mentioned, incandescent lamps, especially tungsten-halogen lamps, with improperly positioned and tensioned filaments are undesirable. Too little tension may cause the filament to sag and possibly fail touching the bulb wall, whereas too much tension may cause premature rupture or fracture of the filament. Filament location is also important because a fraction of an inch for a powerful light source as is used in tungsten-halogen lamps can cause a substantial decrease in projected light when the lamp is placed in an appropriate reflector.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method of lamp manufacture which is adaptable to automated equipment. A further object of the invention is to provide a method of properly stretching the filament in a rapid automatic process. Yet another object of the invention is to accurately position the filament with respect to the remainder of the mount structure. Still another object of the invention is to provide a method for making a mount structure which contains a filament support but does not require threading the filament through the support.
The objects of the invention are accomplished by providing a lead-in conductor with a predetermined bend which eventually is straightened to provide tension to the filament. In one form of the method or process, a unitary piece of ductile molybdenum wire is provided with a bend and two clamping ends. This wire is held in a pair of jaws, at least one of which is movable, with the bend positioned between the jaws.
When the wire lead is in position, the unstretched filament is placed between the clamping ends of the molybdenum wire with a portion of each coil leg extending beyond the clamping end of the lead wires. The clamps are then closed over the coil legs. In the next processing step, one or both of the jaws move in a direction away from the bend thereby straightening it and stretching the filament to an appropriate length. Unitary molybdenum wire is then severed and each end is attached to a thin molybdenum foil portion which in turn is connected to an outer lead wire also generally made of molybdenum. This assembly of leads, foils and coil is usually referred to as a mount. The mount may contain a bridge of quartz material located perpendicular to and near the severed ends of the lead wires.
An envelope of vitreous material is placed over the mount and the foil portions are pinch sealed in the envelope. The lamp is then exhausted, flushed and filled with a fill gas mixture containing a small quantity of a halogen. Following this, the envelope exhaust tube is tipped off in a customary manner to form a finished lamp.
In another embodiment of the invention, an open spiral filament support is attached at one end to the quartz bridge. The other end containing the spiral is open and located near the center of the filament. Following the tensioning of the filament, the spiral is closed to provide support and prevent the filament from touching the bulb wall.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a lamp made according to the invention;
FIG. 2 is a perspective view showing an attached, unstretched coil and an open spiral filament support; and
FIG. 3 shows the tensioning of the filament by movement of the stretching jaws and the closing of the spiral.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The particular lamp, 10, illustrated in FIG. 1 is a 250-watt, 120-volt single-ended tungsten-halogen lamp. It is comprised of an envelope 11, generally of quartz or other vitreous material of a high silica content, pinch seal 12 and mount structure 13. Filament 14 has leg portions 15, 16 clamped to leads 17 and 18 which may be individual leads or leads formed by severing unitary molybdenum wire 19, shown in FIGS. 2 and 3.
Mount structure 13 is comprised of outer lead wires 20 and 21, usually of molybdenum, foliated portions 22 and 23, also of molybdenum, inner leads 17, 18, bridge 24, support wire 25, and filament 14. Portions of this mount structure are shown in FIGS. 2 and 3.
Unitary wire 19, of the illustrated example, is 0.020-inch-diameter molybdenum wire having a tensile strength of between 40-45 kg/mg/200 mm. As illustrated in FIG. 2, filament legs 15 and 16 are clamped by hooks 26, 27 which curl back on the lead wires approximately 0.050 inch over the legs to assure a mechanical and electrical connection. Bridge 24, preferably of quartz, holds wire portions 17 and 18 in fixed relationship to each other. Portion 18 is firmly held in jaws 28 and 29, at least one of which is movable. Premeasured bend 30 is located between the jaws so that it may subsequently be straightened to impart the proper tension to filament 14. After the mount is secured in the jaws with attached but untensioned filament 14, one or both of the jaws may be moved in a direction away from the bend as illustrated by arrow 31 in FIG. 3.
This movement of the jaw straightens the bend 30 to a degree necessary to impart the proper amount of tension to the filament. It is not necessary that the bend be entirely straightened so long as the filament is stretched to a predetermined length and predetermined tension. The radius of the bend in the example is 0.187 inch and it stretches a coiled-coil 8 filament from a relaxed leg-to-leg coil dimension of 15 mm to a tensioned coil dimension of 18 mm. The overall wire length, before severing, of unitary molybdenum wire 19, which consists of portions 17 and 18, is 1.390 inch of which approximately 0.150 inch will be cut from the U-shaped portion before the inner leads are attached to foils 22 and 23. Following the filament stretching operations, unitary wire 19 is severed to form inner leads 17 and 18, as indicated above. The ends of the leads are then attached to molybdenum foils 22 and 23 by welding, for example. Foils 22 and 23 are in turn attached to outer leads 20 and 21 to form mount 13.
The mount is placed in a suitable holding device, and envelope 11 is placed over the mount so that the lower portion of the envelope can be pinch sealed to the molybdenum foils 22 and 23. The next step in the processing is to exhaust the envelope through an exhaust tube, the residue of which is shown at 32. The exhausted lamp is flushed with nitrogen to remove impurities and filled with a gas mixture such as nitrogen, argon and a halogen gas. Both iodine in the form of CH3 I and bromine in the form of CH3 Br have been found to be effective regenerative cycle agents. After filling, the lamp exhaust tube is tipped off as shown at 32 to form a finished lamp.
In an embodiment containing filament support 25, which can be made of molybdenum or tungsten, the spiral portion 31 is initially in an open position, as shown in FIG. 2. By having the spiral portion in an open position, it is not necessary to thread the filament through the spiral during the clamping and stretching processes. This technique facilitates rapid manufacture. After the filament is stretched, the spiral portion is closed around the filament by jaws 32.
Another variation of the invention is the use of separate lead wires 17 and 18 in place of unitary wire 19 which is subsequently severed to form leads 17 and 18. In this embodiment, lead 18 would contain bend 30 which would be straightened to tension the filament.