JP7734607B2 - discharge lamp - Google Patents

Description

The present invention relates to discharge lamps such as short arc discharge lamps, and in particular to heat dissipation from electrodes.

When a discharge lamp is lit, the electrode tips become very hot, causing electrode materials such as tungsten to melt and evaporate, blackening the discharge tube and reducing the lamp's illuminance. To prevent overheating of the electrodes, including their tips, a known structure is one in which a heat conductor such as a metal is enclosed inside the electrode (see Patent Document 1). In this structure, a heat conductor made of a metal with high thermal conductivity and a relatively low melting point, such as silver, is sealed inside the anode. As the electrode temperature rises when the lamp is lit, the heat conductor melts and liquefies, creating thermal convection within the enclosed space and preventing overheating of the electrode tips.

On the other hand, a known configuration is one in which a plate-shaped member that forms a flow path around the electrode axis is placed within the sealed space to promote thermal convection (see Patent Document 2). Also known is a configuration in which a plate-shaped member that restricts the circumferential flow of the molten heat transfer material is placed within the sealed space to prevent high-temperature creep deformation caused by temperature differences within the sealed space due to thermal convection in the heat transfer material (see Patent Document 3).

Japanese Patent Application Laid-Open No. 2004-006246 Patent No. 6259450 JP 2012-28168 A

When the lamp is lit, convection occurs in the heat transfer material, and the plate-like member placed in the sealed space is subjected to force from the heat transfer material. Furthermore, as the heat transfer material repeatedly solidifies and melts when the lamp is turned off and back on, the rate at which the temperature drops and rises varies depending on the spatial region within the sealed space, resulting in a time lag between solidification and melting. This makes it easy for loads to be placed on specific parts of the plate-like member. This load can cause cracks in the plate-like member, potentially resulting in damage.

Therefore, it is necessary to prevent cracks from occurring in the plate-shaped member placed in the sealed space that encloses the heat transfer material in the electrode.

A discharge lamp according to one aspect of the present invention comprises a discharge tube and a pair of electrodes arranged opposite each other within the discharge tube. At least one of the electrodes forms an enclosed space in which a heat transfer material that melts when the lamp is lit is sealed, and a plate-shaped flow rectifier is arranged within the enclosed space.

The "flow regulator" here can be composed of a structure, component, etc. that performs an action or function related to the flow of the heat transfer material within the enclosed space. For example, the flow regulator can be shaped and arranged to form a flow path around the electrode axis. Furthermore, the flow regulator can be shaped and arranged to regulate the flow along at least one of the circumferential direction of the heat transfer material and the electrode axial direction within the enclosed space.

In the present invention, at least a portion of the flow rectifier is formed in a multi-layered structure in the thickness direction. In other words, it has a structure in which layers are stacked. There are various configurations for such multi-layered flow rectifiers. For example, the flow rectifier can be configured to have a layered structure (texture, etc.) in its cross section, and a multi-layered flow rectifier can be formed by plastic processing. A plate-shaped flow rectifier with a layered structure can be formed by, for example, rolling processing, to form a structure in which layers are formed along boundaries approximately parallel to the plate surface.

On the other hand, it is possible to form a multi-layered flow regulator by stacking multiple thin metal sheets or foils. For example, the flow regulator can be constructed by stacking metals made of different materials.

The present invention makes it possible to prevent cracks from occurring in discharge lamp electrodes, such as in flow regulators placed in an enclosed space that encloses a heat transfer material.

1 is a plan view of a discharge lamp according to an embodiment of the present invention; FIG. 2 is a schematic cross-sectional view of an anode. 1 is a schematic cross-sectional view of an example of an anode in a state where the heat transfer body is solidified. FIG. 2 is a schematic perspective view of a flow regulator. FIG. 2 is a diagram schematically illustrating a partial cross section of a flow regulator. FIG. 2 is a diagram showing an optical microscope photograph of a partial cross section of a flow regulator according to an embodiment.

The short arc discharge lamp 10 is a large discharge lamp capable of outputting high-intensity light. It has a roughly spherical discharge tube (light-emitting tube) 12 made of transparent quartz glass. A pair of tungsten electrodes 20, 30 are arranged facing each other (coaxially) within the discharge tube 12. On either side of the discharge tube 12, quartz glass sealing tubes 13A, 13B are connected to and integrally formed with the discharge tube 12. Mercury and rare gases such as halogen and argon gas are sealed in the discharge space DS within the discharge tube 12.

Electrode 20, which serves as the cathode, is supported by electrode support rod 17A. Sealed within sealed tube 13A are a glass tube (not shown) through which electrode support rod 17A is inserted, lead rod 15A that connects to an external power source, and metal foil 16A that connects electrode support rod 17A to lead rod 15A. Similarly, electrode 30, which serves as the anode, is sealed with mounting parts such as a glass tube (not shown) through which electrode support rod 17B is inserted, metal foil 16B, and lead rod 15B. Furthermore, caps 19A and 19B are attached to the ends of sealed tubes 13A and 13B, respectively.

When a voltage is applied to the pair of electrodes 20, 30, an arc discharge occurs between the electrodes 20, 30, and light is emitted toward the outside of the discharge tube 12. A power of 1 kW or more is applied here. The light emitted from the discharge tube 12 is guided in a predetermined direction by a reflector (not shown).

Figure 2 is a schematic cross-sectional view of the electrode (anode) 30. Figure 3 is an example of a schematic cross-sectional view of an anode in a state where the heat transfer material has solidified. Figure 4 is a schematic perspective view of a flow regulator. Note that the electrode (cathode) 20 can also have a similar structure.

As shown in FIG. 2, the anode 30 is composed of a cylindrical body 34 and a truncated cone-shaped tip 32 having an electrode tip surface 30S. The body 34 is joined to a sealing lid 60 to which an electrode support rod 17B is attached, and a sealed space 50 is formed within the body 34. Here, the body 34 and tip 32 are formed from the same metal material, such as tungsten, but they may also be formed from different materials. The sealing lid 60 may also be formed from a different material.

Here, the sealed space 50 is formed as a cylindrical space, and is coaxial with the electrode axis E. A heat transfer material M is enclosed within the sealed space 50. The heat transfer material M is made of a metal (e.g., silver) with a lower melting point than the body portion 34 and the sealing lid 60, and melts into liquid when the lamp is lit, causing convection within the sealed space 50. Figure 2 shows the molten heat transfer material M convecting.

A flow rectifier 40 is arranged coaxially with the sealed space 50. The flow rectifier 40 is configured as a plate-shaped member that adjusts the flow of the molten heat transfer material M. The flow rectifier 40 can be configured with a shape and arrangement that forms a flow path for the heat transfer material M along the electrode axis E, and can also be configured with a shape and arrangement that regulates the flow of the heat transfer material M in a certain direction (for example, flow along the circumferential direction).

The flow rectifier 40 here is shaped to form a flow path around the electrode axis E. The flow rectifier 40 is positioned a predetermined distance from the sealed space bottom surface 50B and the sealed space top surface 50T along the direction of the electrode axis E, and a predetermined distance radially from the sealed space side surface 50S. The flow rectifier 40 is fixed, for example, by a rod-shaped or plate-shaped fixing member (not shown), or is installed directly within the sealed space 50 without being fixed.

The example of the flow rectifier 40 shown in Figure 4 is composed of curved plates 40A and 40B with a semicircular (C-shaped) cross section, arranged facing each other with a gap ST. The curved plates 40A and 40B are symmetrical with respect to the electrode axis E, and the distance between the flow rectifier 40 and the sealed space side surface 50S is approximately equal throughout the entire circumferential direction. Here, the flow rectifier 40 is made of a high-melting-point metal (e.g., tungsten, molybdenum, tantalum, etc.) or an alloy with potassium additive.

When the lamp is lit, the flow rectifier 40 functions as a plate-like member that forms a flow path for the heat transfer material M around the electrode axis E from the opening 41A on the bottom side of the sealed space to the opening 41B on the top side of the sealed space, and heat from the tip of the electrode is transported to the electrode support rod 17B side.

When the lamp is turned off, the heat transfer material M solidifies, as shown in Figure 3, for example. When the lamp is turned off, the temperature of the heat transfer material M in the internal space of the flow rectifier 40 drops relatively slower than in the external spatial region. Therefore, there is a time difference in the solidification of the heat transfer material M depending on the spatial region, and the heat transfer material M inside the flow rectifier 40 solidifies when its liquid level is lower than that of the heat transfer material M outside the flow rectifier 40, forming a recess of appropriate depth.

Figure 5 is a schematic diagram showing a partial cross section of the flow regulator 40.

As shown in Figure 5, the cross section of the flow straightener 40 forms a multilayered structure along the thickness direction. This structure is created by the formation of an aggregate structure accompanying plastic deformation. The cross-sectional layered structure of the flow straightener 40 shown in Figure 5 is created by plastic processing, with crystal grains elongating in the rolling direction to create the cross-sectional layered structure. Furthermore, each layer here is approximately parallel to the rolling direction, i.e., along the surface of the flow straightener 40, and each layer is formed to have approximately the same width (thickness) t, which can be within the range of several tens of micrometers to several hundred micrometers.

A flow rectifier 40 with such a layered cross-sectional structure can suppress crack propagation even if cracks occur internally. In other words, the boundaries of the texture stop the crack propagation at the boundaries. This prevents damage to the flow rectifier 40, allowing it to perform its function (suppressing electrode temperature) until the end of the lamp's life.

Such a flow regulator 40 can be manufactured using a manufacturing method involving plastic processing, with the processing temperature, reduction rate, etc. being determined depending on the raw material and layer thickness. The processed plate material can then be curved by pressing, such as bending. For example, hot rolling can be applied, or cold rolling can also be used. The surface can also be treated by annealing.

The flow regulator 40 described above is made from a single metal material and has a multilayered texture in its cross section, but it can also be formed into a layered cross section by joining multiple thin plates (foil plates) and then rolling them. By adjusting the joining conditions, it is possible to form gaps on the order of microns between adjacent foil plates (layers). When gaps are formed between adjacent layers, the progression of cracks is effectively stopped.

On the other hand, it is also possible to eliminate gaps between some adjacent layers. Even in this case, cracks progress along the grain boundaries (layers), so even if peeling occurs at the grain boundaries, it does not lead to the destruction of the crystal grains themselves, thereby preventing damage to the flow rectifier 40. The layered cross section may be formed in only a portion of the flow rectifier 40.

The multilayer cross section may be formed by plastic processing other than rolling (for example, extrusion, drawing, etc.). Alternatively, the multilayer cross section may be formed using a metal 3D printer. In either case, the thickness can be constant, or the thicknesses can vary.

The flow rectifier 40 is not limited to the shape of a curved plate with a semicircular cross section shown in Figure 4. It may also be configured with two rectangular metal plates arranged facing each other. Even if the flow rectifier 40 is configured with a pair of metal plates with such flat surfaces, heat transport along the electrode axis E can be effectively achieved. Furthermore, instead of being configured with a pair of metal plates, the flow rectifier 40 can also be configured with three or more metal plates arranged at a predetermined distance from each other.

The flow regulator 40 can be tapered toward the electrode support rod, or triangular. Furthermore, the flow regulator 40 can be configured as a tube that forms an internal space. For example, the cross section can be circular or polygonal (including triangular).

As mentioned above, the flow regulator 40 can be configured as a plate-like member that restricts the flow of the heat transfer body M in the circumferential direction of the enclosed space. For example, the flow regulator can be configured as a single plate, or it can be formed as a plate-like member with a cross- or T-shaped cross section.

In this case, the above-mentioned layered cross section can be formed in at least a portion of the flow straightener. Even in such a flow straightener that regulates the flow of a heat transfer material, having the above-mentioned layered structure can prevent cracks and breakage when subjected to force from the heat transfer material.

The flow straightener 40 described so far has a configuration with a layered structure in its cross section, but the layered structure is not limited to this. Regardless of whether or not it has a layered structure due to plastic processing, it may also have a configuration with a layered cross section made by combining plate-shaped materials such as different thin metal plates or foil-shaped metals. By stacking plate-shaped members made of multiple materials in this way, cracks will progress along the boundaries between adjacent layers, thereby preventing damage to the flow straightener due to cracks.

For example, a layered flow straightener can be constructed by sandwiching a thin (foil) sheet of molybdenum between two thin (foil) sheets of tungsten. Compared to tungsten, molybdenum is more likely to absorb internal stress through its own expansion, providing a buffering function and preventing damage to the flow straightener. Alternatively, a material with a higher melting point than the heat transfer material (such as ceramics) can be laminated with the metal sheet, or a recrystallized thin (foil) sheet can be used.

The following describes an example. The flow straightener in this example is a rectangular, single-plate flow straightener. The raw material powder, tungsten, was pressed into a mold, sintered, and the sintered body was hot-rolled according to the specified processing temperature, reduction, etc. Here, a partial cross section of the flow straightener was observed using an optical microscope.

As shown in Figure 6, in the flow straightener of the example, texture boundaries with a width (thickness) of approximately 30 μm were formed along the rolling direction (sheet surface direction), and a layered structure was confirmed. Furthermore, due to the influence of cross-section preparation for cross-sectional observation, some cracks have occurred along the grain boundaries.

The cross-sectional layered flow straightener shown in Figure 6 is merely one example, and is not limited to the layered structure shown in Figure 6. By determining the processing temperature and rolling reduction rate based on factors such as the thickness of each layer, it is possible to create a variety of cross-sectional layered flow straighteners.

10 Discharge lamp 30 Anode (electrode)
40 Flow regulator 50 Closed space

Claims (7)

A discharge tube;
a pair of electrodes disposed opposite each other within the discharge tube;
At least one of the electrodes has a sealed space formed therein in which a heat transfer material that melts when the lamp is lit is sealed, and a plate-shaped flow rectifier is disposed in the sealed space;
A discharge lamp characterized in that at least a part of the flow rectifier is formed in a multi-layered manner in the thickness direction. A discharge lamp as described in claim 1, characterized in that the flow rectifier has a layered structure in its cross section. A discharge lamp as described in claim 2, characterized in that the flow rectifier has a structure in which layers are formed along boundaries approximately parallel to the plate surface. A discharge lamp as described in any one of claims 1 to 3, characterized in that the rectifier is constructed by laminating multiple thin metal plates or foils. A discharge lamp as described in claim 4, characterized in that the flow rectifier is constructed by laminating metals made of different materials. A discharge lamp as described in any one of claims 1 to 5, characterized in that the flow rectifier is shaped and arranged to form a flow path around the electrode axis. A discharge lamp as described in any one of claims 1 to 5, characterized in that the flow regulator is shaped and arranged to regulate flow in at least one of the circumferential direction of the heat transfer body and the electrode axial direction within the sealed space.