Patent Application
20070242457
Other features and advantages of the present discharge lamp will be apparent from the ensuing description, taken in conjunction with the accompanying drawings, in which:
Description of an embodiment will be given below, referring to drawings.
In such a discharge lamp, by supplying electric power from the external power supply, arc discharge is generated between the anode 14 and the cathode 16 thereby emitting light. In addition, the discharge lamp is a so-called vertical setting lighting type discharge lamp in which the anode 14 is arranged above the cathode 16, i.e. the arc tube portion of the arc tube 11 is supported so that the tube axis thereof is vertical to the ground.
The base portion 20 of the anode 14 is a cylinder having an opening 21 on the end surface of a base end portion (end portion opposite to the tip of the anode 14), an interior space 22, and a bottom portion, and further a base portion side flange portion 24 which projects in a diameter outside direction is formed in the base end portion. The base portion side flange portion 24 has a base portion side flat portion 23 which extends in a diameter direction, and a base portion side slope portion 26 which is continuously formed from the perimeter edge of the base portion side flat portion 23 in a diameter inside direction so as to extend toward the tip portion of the base portion (in a lower side of the figure. The base portion side flange portion 24 has an annular groove 25 which is formed in a circumference of the base portion 20 in a position close to the basis end portion thereof, in which the base portion side slope portion 26 is formed as part of the annular groove 25. The outer diameter of the base portion side flange portion 24 is smaller than the outer diameter of the base portion 20. Accordingly, there is an advantage that even after the base portion and the lid portion are welded together, no part becomes larger in diameter than the outer diameter of the base portion, and glass tube material for a conventional arc tube structure can be used at time of the assembly of the discharge lamp.
The lid portion 40 of the anode 14 has a lid portion main body 41 whose shape is a circular truncated cone as a whole, and a cylindrical insertion portion 42 which is integrally formed so as to project from the center of the bottom of the lid portion main body 41. The diameter of the insertion portion 42 is determined so as to fit in with the inner diameter of the interior space which is continuously formed from the opening 21 of the base portion 20. The lid portion main body 41 has a lid portion side flange portion 44 which has the same outer diameter as that of the base portion side flange portion 24. This lid portion side flange portion 44 whose shape is a circular truncated cone has a lid portion side flat portion 43 which extends in a diameter outside direction, and a toric lid portion side slope portion 46 which is continuously formed from the perimeter edge of the lid portion side flat portion 43 so as to extends in a diameter inside direction toward the base end which is opposite to a direction toward the tip). And the insert portion 42 is formed so as to project in the tip direction from the lid portion side flat portion 43. A hole 48 for welding rod connection, with which a welding rod is pressed so as to be fit in, is formed in the center of that base side end surface 47 of the lid portion 40.
As shown in
The insertion portion 42 of the lid portion 40 is inserted in the interior space through the opening 21 of the base portion 20. The lid portion side flat portion 43 of the lid portion side flange portion 44 is brought into close contact with the base portion side flat portion 23 of the base portion side flange portion 24. In that state, the perimeter edge (the tip portion and portion extending therefrom in a cross sectional view taken along in an axial direction) of the base portion side flange portion 24 and the perimeter edge (the tip portion and portion extending therefrom in a cross sectional view taken along in an axial direction) of the lid portion side flange portion 44 which overlap each other are welded, so that an annular welding portion W can formed. The width d in the diameter direction of this annular welding portion W is set to 0.8 to 3.0 mm.
The anode 14 and the cathode 16 are made of metal with a high melting point, for example, metal whose melting point is about 3000 degrees Celsius or more, such as a tungsten, a rhenium, and a tantalum. Among the above metals, the tungsten is preferred. On the other hand, metal for the heat conductive member M which is higher in thermal conductivity at time of lighting, than that of metal for the electrodes, is used. For example, when the electrodes which are made of tungsten, is used, the heat conductive member M is made of a silver, copper, gold, indium, tin, zinc, a lead, etc. Among them, silver, copper, and gold are excellent and, specifically, silver is especially preferred.
The anode is manufactured a method as set forth below. That is, the base portion 20 and the lid portion 40 are produced by performing cutting of a cylindrical member made of tungsten. The heat conductive member M is filled in the interior space of the base portion 20, and the insertion portion 42 of the lid portion 40 is inserted through the opening 21 of the base portion 20 into the interior space of the base portion 20, thereby bringing the lid portion side flat portion 43 into contact on the base portion side flat portion 23, so that the perimeter edge of the base portion side flange portion 24 and the perimeter edge of the lid portion side flange portion 44 which adjoins the base portion side flange portion 24, are welded over all the circumferences thereof. And rare gas is introduced in the sealed enclosed space C through a gas introduction hole (not shown) formed in the lid portion 40. After that, an opening end portion of the gas introduction hole is melted by heat so as to carry out sealing, and the one end of an electrode rod (not shown) is press-fit in a hole 48 for electrode rod connection formed in the lid portion 40, by a pressing unit.
In a discharge lamp having such a structure, overheating of the tip portion 14A (specifically the other end portion of the base portion 20) of the anode 14 can be prevented by enclosing the heat conductive member M which is a heat transferring member, in the sealed enclosed space C of the anode 14.
Moreover, the heat transfer function of the heat conductive member M is explained, below. The thermal conductivity of tungsten is about 100 W/mK in the high temperature region of about 2000 K. On the other hand, each of silver and copper has the thermal conductivity higher than the tungsten. For example, the thermal conductivity of the silver in 2000 K is about 200 W/mK and the thermal conductivity of copper is about 180 W/mK. Therefore, the heat accumulated near the anode tip portion 14A is effectively transferred to the anode back portion 14B which is lower in temperature than the anode tip portion 14A, so that it is possible to prevent the anode tip portion 14A from being overheated. And since any of silver, copper, and gold do not alloy with the tungsten so that they have a function of stably transferring heat as a heat transferring member.
Moreover, when rhenium (the thermal conductivity at 2000 K is about 52 W/mK) is used as a high melting point metal which forms the anode 14, tungsten can be used as the heat conductive member M. If such a structure is applied to a discharge lamp such as a mercury lamp or a metal halide lamp which contains halogen, the anode 14 is not corroded, so that the life span of the discharge lamp can be extended.
Thus, it is possible to prevent the anode tip portion 14A from being overheated, by using the heat conductive member M which has a thermal conductivity higher than that of the anode 14 so that a current flow rate of the discharge lamp can be increased.
Metal having a melting point lower than that of the metal which forms the anode 14 as a heat conductive member M can also be used, instead of the metal which has a high heat conduction property.
For example, when tungsten of which the anode 14 is made, is used, silver, copper, gold, indium, tin, zinc, lead, etc. can be used as the heat conductive member M. In such an anode 14, since the heat conductive member M melts and a convection occurs in the interior of the sealed enclosed space C of the anode 14 at time of lighting of the discharge lamp, so that the heat of the anode tip portion 14A is transferred to the anode back portion 14B, the problem that the electrode melts can be avoided by efficiently transferring the heat accumulated near the anode tip portion 14A. Furthermore, it becomes possible to pass large current through the discharge lamp, so that a large output can be attained.
In the sealed enclosed space C, rare gas is enclosed so as to form a predetermined pressure. In detail, when the heat conductive member M is enclosed as much as 50% or more of the internal volume of the sealed enclosed space C, rare gas of one or more atmospheric pressure is enclosed, thereby preventing generation of air bubbles in the boundary face between the heat conductive member M and the inner surface of the sealed enclosed space C. On the other hand, when a small amount of the heat conductive member M is enclosed compared with the internal volume of the sealed enclosed space C, the heat transfer effect according to boiling can be improved by changing the inner pressure of the sealed enclosed space C into a pressure lower than the atmospheric pressure, thereby accelerating boiling of the heat conductive member.
In the base portion side flange portion 24 of the anode 14 having the above-mentioned structure, the base portion side flange apex angle α which is formed by the base portion side slope portion 26 and the base portion side flat side 23, is an acute angle of 30 degrees or more but less than 90 degrees in a cross sectional view taken along in the axial direction.
In the lid portion side flange portion 44, the lid portion side flange apex angle β which is formed by the lid portion side slope portion 46 and the base portion side flat portion 43, is an acute angle of 30 degrees or more but less than 90 degrees in a cross sectional view taken along in the axial direction. The sum total (α+β) of the base portion side flange apex angle α and the lid portion side flange apex angle β is set to 160 or less degrees. In the case where the above condition of the angle α and β is met, since the base portion side flange portion 24 of the base portion 20 and the lid portion side flange portion 44 of the lid portion 40 which are welded together, have small heat capacity, it is possible to certainly set the width d in the diameter direction of the toric welding portion W to 0.8 mm or more but 3.0 mm or less (0.8 mm≦W≦3.0 mm).
As mentioned above, the diameter direction width d of the toric welding portion W formed by welding the base portion side flange portion 24 and the lid portion side flange portion 44 entirely in a circumferential direction, in a state where the lid portion side flat portion 43 is brought into contact with the base portion side flat portion 23, is set to 0.8 mm or more but 3.0 mm or less. Further, the angles α and β are acute angles of 30 degrees or more. In such a case, the following effects are acquired when the sum total of the angles α and 8 is 160 degrees or less.
(1) In case of the diameter direction width d of welding portion w is 0.8-3.0 mm, since light emitting material has not evaporated in an arc tube portion 11 at time of starting of a discharge lamp, the internal pressure of an arc tube portion 11 has not reached a predetermined pressure. However, the temperature of the anode 14 rises promptly and the pressure of the interior space rises, so that the internal pressure of the anode 14 becomes about 4 MPa since the heat conductive member M is enclosed in the sealed enclosed space C of the anode 14. Thus, since the difference between the internal pressure of the arc tube portion 11 and the internal pressure of the anode 14 is large, a force acts in a direction of making the lid portion 40 and the base portion 20 separated from each other. Therefore, when the diameter direction width d of the welding portion W is 0.8 or more, it is possible to obtain sufficient durability against the force. However, when the diameter direction width d of the welding portion W is too short, there is a possibility that the welding portion W may be damaged at time of start of lighting.
On the other hand, when the diameter direction width d of the welding portion W exceeds 3.0 mm, as the required welding energy increases, the welding time becomes longer, so that the base portion 20, the lid portion 40 and the heat conductive member M become very high in temperature, and thereby, the amount of the heat conductive member M may decrease due to evaporation and boiling. Therefore, there is a possibility that it may become impossible to acquire the intended heat transfer effect, and there is a possibility that part of the boiled and dispersed heat conductive member M may enter into the welding portion W, so as to deteriorate the welding portion W, whereby the strength thereof may become low.
For the above reasons, in the embodiment, when the diameter direction width d of the welding portion W is set to 0.8 to 3.0 mm, the strength required for the welding portion W is sufficiently obtained. In addition, there is no possibility that at time of start of the discharge lamp, the anode 14 may be damaged. Furthermore, it is possible to avoid excessive welding energy or welding time at time of welding.
(2) In the case where the base portion side flat portion 23 of the base portion side flange portion 24 and the lid portion side flat portion 43 of the lid portion side flange portion 44 are welded entirely in a circumferential direction in a state where they are brought into close contact with each other, the following effect can be acquired.
As shown in an
Moreover, in the conventional electrode shown in
(3) In case where the angle α+angle β is 160 degrees or less, when the wall thickness of the base portion side flange portion 24 and that of the lid portion side flange portion 44 becomes large when the sum total of the angle α and the angle β exceeds 160 degrees, it is hard to promptly increase the temperature thereof at time of welding, so that it is necessary to increase welding energy or the weld time. However, as discussed above, in such a case, due to evaporation and boiling of the heat conductive member M, it is difficult to acquire the intended heat transfer effect, and part of the boiled and dispersed heat conductive member M may enter into the welding portion W, so as to deteriorate the welding portion W, whereby the strength thereof may become low. Therefore, since the temperature can promptly rise at time of welding when the angle α+the angle β is 160 degrees or less, it is possible to set the diameter direction width d of the welding portion W to 0.8-3.0 mm, so that it is possible to fully obtain the strength required for the welding portion W, and in addition, it is possible to avoid damage to the welding portion W at time of starting of the discharge lamp, and to avoid the excessive welding energy at time of welding.
(4) In case that angles α and β are 30 degrees or more, since when both or one of the angles α and β are less than 30 degrees, the temperature of the base portion side flange portion 24 and/or the lid portion side flange portion 44 rapidly and locally rise at time of beginning of welding, there is a possibility that cracks (crack) may occur in the base portion side flange portion 24 and/or the lid portion side flange portion 44. Especially, when the base portion 20 and the lid portion 40 are made of tungsten which is a brittle metal, it is easy to produce such a phenomenon. When cracks do not extend in depth, it may be able to get rid of them. However, in case of both or one of the angles α and β are less than 30 degrees, it is difficult to carry out such a repair, so that the cracks remain after the welding. As a result, there is a possibility that the enclosed heat conductive member M leaks out. Accordingly, in the present embodiment, since the angles α and/or β is 30 degrees or more, it is possible to prevent generation of cracks in the base portion side flange portion 24 and the lid portion side flange portion 44 which are caused by welding, and to prevent the cracks from remaining therein after the welding.
Thus, although the embodiments are explained above, it is possible to make various changes thereto.
In
In
Moreover, in
In
The following experiments were conducted in order to check the effect of the embodiments.
The anode having the base portion and lid portion as described below are prepared by cutting.
The outer diameter of the cylinder of the base portion was 29 mm, the height thereof was 60 mm, the outer diameter of the base portion side flange portion was 27 mm, the width of the base portion side flat portion was 4 mm, and the angle α of the base portion side flange apex angle was 60 degrees. The outer diameter of the lid portion side flange portion was 27 mm, the width of the lid portion side flat portion was 3.8 mm, and the lid portion side flange apex angle β was 60 degrees. The base portion and the lid portion were welded, and silver was enclosed as a heat conductive member M in the sealed enclosed space, so that electrodes are prepared, but in each of which the diameter direction width d of the annular welding portion varies so that welding condition varies.
Next, arc tubes, in each of which the internal volume of an arc tube portion was 850 cm3, are produced. Each electrode was installed in an arc tube which was produced by the above method, and the discharge lamps in which mercury of 50 mg/cm3 was enclosed as a light-emitting material in the arc tube were produced.
Each discharge lamp produced in the above manner was turned on under the lighting conditions of electric power 12000 W, and existence of peeling of the welding portion in the base portion and the lid portion, and existence of evaporation of the heat conductive member M due to heat generated by welding when the electrode was formed were examined.
The result of the experiments is shown in Table 1.
Moreover, base portions and lid portions were made under cutting conditions shown in the Table 2 in which the base portion side flange apex angle α and the lid portion side flange apex angle β varied. The diameter direction width d of the welding portion formed by welding one of the base portions and one of the lid portions, existence or nonexistence of cracks generated in the base portion and the lid portion due to heat at time of welding, and the existence or nonexistence of evaporation of the heat conductive member M due to heat at time of welding, were examined. The result is shown in Table 2.
The diameter direction width d of the annular welding portion was measured as set forth below. Namely, a cross section obtained by cutting the electrode along a plane including the axis thereof was ground and a portion to be welding portion was etched. In a state where the crystal state of the electrode structure material in a cross section of the welding section could be easily seen, the crystal of the electrode structure material in the cross section of the welding section was observed by a microscope, and based on the difference between the crystal state of the welding section and the crystal structure of other portions, the diameter direction width d of the welding section was obtained by measuring, with a slide caliper, the width of a portion whose crystal state is different from that of the other portions.
From the experimental result shown in Table 1, when the diameter direction width d of the welding portion exceeds 3.0 mm, it is considerable that the heat conductive member M enclosed in the sealed enclosed space evaporates. Moreover, from the experimental result of Table 2, when the angle of α+β exceeds 160 degrees, when trying to obtain the diameter direction width of 0.8 mm or more, the heat conductive member M evaporated.
The preceding description has been presented only to illustrate and describe exemplary embodiments of the discharge lamp according to the present invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-110588 | Apr 2006 | JP | national |
