JPS6329942B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-pressure discharge lamp consisting of a discharge vessel made of ceramic material with a filler containing an alkali metal producing vapor. More specifically, the present invention provides a high pressure sodium discharge lamp containing sodium and mercury having a pressure of 30 to 1000 torr of sodium and 0.1 to 5 atm of mercury at a cold fill pressure of 5 to 1000 torr. Regarding those that may contain torr xenon. Other lamps that may be used with the present invention include lamps containing a gas fill of xenon, argon,
There are lamps with a gas filling of a small amount, preferably 2 to 10% of the total, mixed with xenon, selected from neon or a combination of both, filled to a total pressure of 5 to 1000 torr at 300 m . The object of the invention is an improved structure of a sealed end and electrode assembly for a high pressure discharge lamp. According to the invention, a high pressure discharge lamp is presented,
The lamp includes a ceramic arc tube having an end wall extending inwardly from the arc tube wall to define a central hole, and an electrical introduction member sealed within the hole along the length of the hole. the introduction member is coupled to an electrode shank member supporting an electrode element, the end wall including an inner surface exposed to radiation from the electrode element during lamp operation, the inner surface being adjacent to the central hole; a shoulder member, the height of the shoulder member above the inner surface is not so high as to substantially occlude the inner surface from the electrode element, and the width of the shoulder member is between the top surface of the shoulder member and the inner surface. is designed such that the temperature difference between the amalgam and the amalgam is sufficient to prevent contact with the electrically conductive member. In high pressure discharge lamps, there is a problem experienced with edge blackening caused by material sputtered from the electrodes and deposited on the discharge vessel walls, which affects lamp life. For 250 watt, 150 watt, and 50 watt high pressure sodium lamps (although this does not mean that the problem is limited to these wattages), we have found that the edges caused by spatter of material on the discharge tube wall are It has been discovered that blackening problems are mixed with rectification problems which further reduce the achievable lifetime.
If there is a difference in the time at which establishing thermionic emission at the electrode end (i.e., establishing normal operation for the electrode) occurs, the rectifying action
This occurs when the lamp starts lighting. The rectification effect appears as a higher lamp voltage in one half cycle or part of a half cycle rather than in consecutive half cycles. For a choke-operated lamp circuit, the DC component of the resulting current flowing tends to saturate the magnetic core of the inductance, lowering its impedance and causing a fairly high current to flow. In the worst case, the peak DC component exceeds ten times the peak value of the steady AC lamp current. During the initiation phase, there is a tendency for the arc to terminate on the amalgam filling, which is found only at one end of the lamp and not on the electrodes. This results from the electrode being in contact with the amalgam. Particularly severe rectification occurs at this point. The resulting large DC current component causes excessive spatter or evaporation of radioactive material, which accumulates on the arc tube wall and causes blackening. As a result, there is an increase in the temperature of the metal amalgam at the end of the arc tube, which causes
It increases the vapor pressure of sodium and metals, which also results in an increase in lamp voltage. The voltage increases until the AC mains voltage can no longer sustain the lamp discharge and the lamp goes out. Arc tube end darkening also causes a reduction in light output, thereby affecting lamp efficiency. At the same time, the arc terminating on the amalgam causes significant damage to the alumina tube. Although various proposals have previously been made involving some form of shielding, we unexpectedly found that it is not necessary to actually cover the electrode elements, and yet provide a barrier to the metal amalgam in electrical contact with the electrode support. It has been discovered that a simple, small shoulder member forming a . For example, British Patent No. 523923 discloses a method of surrounding the main electrode along its entire length with a quartz sleeve. GB 1414442 discloses a high pressure discharge lamp provided with a reservoir for mercury or amalgam which is said to prevent arc growth near the electrodes. The structure of the embodiments of this patent are designed to form a reservoir screen from the discharge space and, incidentally, also form a screen covering at least a portion of the electrode elements. As mentioned earlier, we have discovered that it is not necessary to actually shield the electrode elements to prevent rectification effects. In another embodiment of this patent, the reservoir is formed in a ceramic plug sealed to the wall of the discharge space, and the passage to the amalgam reservoir is formed in a sealed ceramic plug between the current introducing member and the plug part. Pass through the missing part. This, of course, does not preclude the amalgam from making electrical contact with the electrode assembly as it passes through the space into the reservoir. GB 1465212 discloses a high pressure sodium discharge lamp in which a closure member consisting of a relatively long piece of polycrystalline alumina is sealed to the end of a polycrystalline discharge vessel. A tubular current conducting member is coupled to an electrode supporting shank member or rod, and the tubular member is sealed within a hole formed in the alumina end closure member. The problem with this patent is
Hot sodium vapor has a tendency to react with the sealing material, and in order to protect and prevent this, the connection between the current conducting member and the shank is made with an annular shield of polycrystalline alumina at the point of connection. This is achieved within the bore of the end closure member so as to be protected. The problem with this, however, is that since the bond points are below the surface of the annular shield, pockets are formed where condensation collects. In contrast, the present invention is concerned with correcting the rectifying effect rather than protecting the sealing material, and in order to prevent the formation of such pockets, the connection point between the current introduction member and the shank member must be , the current introducing member is preferably located outside the sealed hole. As mentioned above, we have found that covering the electrodes is not necessary and in fact a simple shoulder member is sufficient. This is advantageous in that it is easier to manufacture than known lamps which include a shield that partially or completely covers the electrode elements.
However, for such small shoulders, there is a tendency to reduce the temperature difference between the top and bottom of the shoulder. There is therefore a risk that amalgam will condense on the top of the shoulder member rather than on its bottom. However, we have discovered that this can be compensated for by suitably adjusting the width of the shoulder members. If we assume that the heat radiated from the shoulder member follows the Stefan-Boltzmann equation for radiation from a hot body, and that heat is transferred according to Fourier's law, then the temperature difference between the top and bottom surfaces is This can be maximized by making the width of the shoulder member as small as possible within manufacturing constraints. The formula regarding the temperature of the top surface of the shoulder member to the temperature of the bottom surface of the shoulder member is given by the following formula. 12r ₁ σεl/K(r ₁ ² −r ₂ ² )=1/T ₁ ² −1/T ₂
^2Where , r ₁ : Inner diameter of shoulder member (m) r ₂ : Outer diameter of shoulder member (m) T ₁ : Temperature at the lowest end of the shoulder member (〓) T ₂ : Temperature at the uppermost end of the shoulder member (〓 ) K: Thermal conductivity of alumina (assumed to be 8.87 Wm ^-1 K ^-1 ) σ: Stephan's constant (5.67×10 ^-8 Wm ^-2 K ^-4 ) ε: 0.4116 (radiation activity of alumina) l: Length of the step (m) The table below shows the temperature difference for shoulder widths of 0.2 to 0.5 mm and lengths of 1.5 mm, 2 mm, 3 mm and 4 mm. This table was calculated using a cool spot temperature of 973㎜ for a low power lamp using a plug with a hole with radius r ₁ of 0.92 mm.

[Table] From this table, for any height (l) of the shoulder member,
It is clear that the temperature difference is greater when the thickness is thinner, that is, when w is smaller. A temperature difference of at least 10° C. is believed to be sufficient to ensure that the amalgam does not make electrode contact with the electrode assembly. Of course, a temperature difference larger than this can also be used. From a theoretical point of view, of course, there is no limit to the minimum width that produces this effect. However, considering actual manufacturing, it is believed that 0.2 mm to 0.5 mm is the minimum width that can be manufactured with the industry's current manufacturing technology and knowledge. 0.2mm is a limit based on machining technology,
On the other hand, 0.5 mm is a limitation of using press processing.
Additionally, it should be appreciated that the electrode assembly was placed approximately 5 mm from the end of the arc tube to maintain the amalgam temperature between 700°C and 750°C. In imposing this restriction, it is desirable to have a clearance of 1 mm between the electrode element and the shoulder so that the discharge area is not covered by the shoulder to any extent. Preferably, the shoulder member is formed integrally with the end wall structure of the unitary arc tube. One way to do this is to first make a suitably shaped plug of ceramic in its unsintered state, insert it into the preform of an arc tube also made of ceramic in its unsintered state, and then are sintered together to form a unitary structure. Other methods can also be used to manufacture a single arc tube. An advantage of the unitary construction is that there are no sealing problems other than those related to the electrical introduction member within the arc tube. Instead of a unitary structure, another option is to utilize "top-hut" shaped members that are made and machined as separate preforms. The advantage of this is that it can be used in combination with wire or rod-shaped current introduction members rather than the tube-like introduction members common in the prior art. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a 70 watt high pressure sodium vapor discharge lamp to which the present invention is applied. The lamp includes a discharge tube 1, a glass envelope 2 and a lamp base 3 with terminals 4. A discharge tube 1 containing sodium amalgam is enclosed within a metal framework 5 within an outer envelope 2.
is supported in a well-known manner by An electrode assembly 10 is located at each end of the discharge tube 1. Operating conditions are set such that the temperature of the sodium amalgam at the coldest point of the tube is in the range of 650-800°C. FIG. 2 shows one end of the discharge tube 1 of the lamp.
The use of a single tube 12 with an integral shoulder member 11 is shown. The current introducing member 14, in this case a niobium tube 15, is sealed within the hole 8 in the end wall 7a of the arc tube 12 with a suitable sealing glass 16. The electrode element 17, which is in the form of a conventional spiral coil and which is provided with electron-emissive material in a known manner to prevent interruption of the discharge, is provided with a support shank member 18.
Supported by. On the other hand, the shank member 18
is held within the compression wall 19 of the niobium tube 15, and the bond is completed by depositing a fill of titanium braze metal (not shown) inside the niobium tube. By arranging the tube 15 so that it is at least flat against the shoulder 11 or extends beyond the shoulder, ie projects into the discharge space, a pocket is created in the bore 8 in which condensation can collect. Not done.
It is clear from FIG. 2 that the current conducting member is sealed along the length of the hole 8 in the end wall 7a, including the part of the shoulder member 11 which forms part of the hole 8. Cap member 21 can optionally be added as an additional seal member sealed to outer surface 22 by a sealing glass. In accordance with the present invention, arranged to minimize the width "w", the temperature difference between the top surface 11a and the bottom surface 11b of the shoulder member over the length "l" is such that the amalgam is in contact with the electrical introduction member. is sufficient to prevent It is believed that a minimum temperature difference of about 10°C can achieve this. It is clear from FIG. 2 that the width "w" is a function of the inner diameter r ₁ and the outer diameter r ₂ and also depends on the size of the niobium tube or other introduction member used. The operating temperature of this lamp is between 700℃ and 750℃.
In order to maintain this range, it is desirable to set the electrode height to about 5 mm. In this way, by setting the maximum height "l" of the shoulder member to 4 mm, a clearance of 1 mm is obtained between the bottom of the electrode element 17 and the top surface 11a of the shoulder member 11. That is, the end wall 7a
The bottom surface 11b forming the inner surface of the electrode element 17 is not substantially shielded from radiation from the electrode element 17. The above theoretical considerations are equally applicable to other embodiments. The arrangement shown in FIG. 3 is similar to that of FIG. 2 insofar as it includes a single tube 12 with an integral shoulder member 11. The current introducing member in this case includes an electrically conductive porcelain alloy 26 in which the shank 27 of the electrode element 17 is embedded. Electrical connections 28 are also embedded in the porcelain alloy 26 sealed to the unitary tube 12 by the sealing glass 16. The use of this conductive porcelain alloy 26 is particularly useful in that it obviates the provision of a separate seal for the current conducting member. FIG. 4 shows an electrode assembly in greater detail in accordance with another feature of the invention. Although electrode assembly 10 is shown at one end of discharge vessel 1, a similar assembly will generally be provided at the other end. The discharge vessel 1 includes an envelope wall 6 made of translucent polycrystalline alumina. An annular body 7, also made of translucent polycrystalline alumina and forming a sealing element, is arranged at the end of the envelope wall 6. Formation of the assembly begins by obtaining a polycrystalline alumina discharge tube in a green state and a ring of similar material, and the assembly is tightly sintered with a sealing element placed within the envelope wall. The assembly is sintered into a bonded unitary seal. That is, a unitary structure forming a gas-tight seal is formed by sintering over the length of the sealing element. The gas-impermeable seal is illustrated by cross-hatching in FIG. However, the thickness is exaggerated for clarity. Of course, it will be appreciated that such a joint will not actually appear due to the sintered assembly forming a monolithic structure. The construction of the arc tube is therefore substantially the same as that shown in FIG. 2, the difference being that the arc tube shown in FIG. The point is that it does not include what is shown in the figure. Electrode assembly 10 includes an electrical introduction member 38 in the form of a niobium tube. The niobium tube clamps the shank member 9 and is fixed by titanium brazing (not shown). On the other hand, the shank member 9 supports an electrode element 10a in the form of a normal overwound coil, which includes an electron-emitting material in a well-known manner so as not to interrupt the discharge.
The closure assembly comprises a member 32 having a sealing element annulus 7 and a cover portion 33 extending radially outwardly to cover the end of the envelope wall 6 or arc tube shown in FIG. This closure member 32 also includes a body 34 extending axially through the inner surface 35 of the sealing element annulus 7. The body 34 extends beyond the inner surface 36 of the sealing element annulus 7 and forms a shoulder 37 . It will be clear that the inner surface of the ring body 7 serving as the sealing element is equivalent to the inner surface (bottom surface) 11b of the end wall described in the previous embodiment. FIG. 5 shows another embodiment of the invention, in which, like in FIG. 4, the discharge tube 1 has an envelope wall 6 made of translucent polycrystalline alumina and an annular sealing element 7 made of polycrystalline alumina. 4, both of which are sintered together to form a unitary structure, as described in connection with FIG. This example also includes a closing member 32 having a cover part 33 and a body part 34 inside the ring body 7 serving as the sealing element. The body 34 projects beyond the inner surface 36 to form a shoulder member 37, all as previously described. However, in this example, the electrode assembly 10 including the electrode element 10a is supported by a wire-like current introduction member 38 that includes a tungsten shank portion 39 and a niobium introduction portion 40 sealed within a hole in the body 34. Ru.
The shank portion 39 is connected to the electrical introduction member at a portion indicated by the reference numeral 41, for example by welding. This design is advantageous in that dissimilar metals can be selected because of their respective favorable properties.
For example, niobium has expansion properties that are well matched to alumina member 32, while tungsten can better withstand the high temperatures encountered near electrode element 10a. In order to avoid the problem of cracking of the alumina member due to the difference in expansion coefficients of dissimilar metals, it is preferable to form a joint 41 on the outside of the body 34 in the discharge space, as shown in FIG. This closure member 32 can be remade as a polycrystalline alumina "preform" by pressing in preference to matching, which
It is the assembly of the inner body 34 of the annular sealing element 7 forming a shoulder member 37 which acts as a barrier to the metal amalgam coming into contact with the supporting shank member. As previously mentioned, this assembly is sealed with a suitable sealing glass, as shown by the unidirectional hatching in the figures, which are somewhat exaggerated for clarity. In this example,
The use of the wire-like current introducing member 38 results in a very small annular area of the sealing material being exposed to the corrosive atmosphere within the discharge tube during lighting. Figure 6 shows
Another embodiment of the invention is shown. This example includes an envelope wall 6 made of polycrystalline alumina and an annular shaped sealing element 7 made of polycrystalline alumina, which sealing element has a fourth
As explained in connection with the figures, the whole is sintered to the envelope wall 6 for a unitary construction. However, in this case the closure member consists of an integrated electrically conductive porcelain alloy and a non-conductive material, either alumina or a porcelain alloy, as disclosed in GB 1571084. Briefly, this is shown in Figures 4 and 5.
It consists of a member 42 having a similar shape to the closing member 32 shown, and includes a cover portion 43 and a body portion 46 . The cover part 43 includes the sealing element 7 and the enveloping wall 6.
, while the body 46 extends axially within the inner surface of the annular sealing element 7 . As taught in the aforementioned GB 1571084, the body 46 includes an outer ring portion 49 of non-conductive material bonded to a core 45 of conductive porcelain alloy. This bonding is typically accomplished by sintering a ring portion 49 around the core 45. Assembled integrated porcelain alloy closure member 42
is then inserted into the annular sealing element 7, with the body 4 extending beyond the inner surface 48 of the sealing element 7.
The extension of 6 forms a shoulder member 50. Electrode assembly 10 includes electrode element 10a, and as can be seen, shoulder member 50 does not extend far enough to cover electrode element 10a. A support shank 51 for the electrode element 10a is attached to the conductive core 45, as is a conductive lead-in member 52. In all the embodiments described here, the discharge tube is 3
It has holes in the range of 12 mm to 12 mm, and the minimum width w shown in FIG. 2 is about 0.2 mm. As explained above, the height of the shoulder member ranges from 1.5 mm to 4 mm.
Typical discharge tube lengths are 30 to 250 mm.
The diameter of the niobium tube is 1.5 to 4 mm, and the wire material used is 0.5 to 1.0 mm in diameter. The test life of lamps incorporating the invention exceeded, in some cases, over four times that of conventional lamps. For example, according to the invention a height of 2 mm and a thickness of 0.5 mm
A 70 watt lamp with a shoulder member of 17650
Still alive and working after hours. The lifespan of this type of lamp without shoulders is 4000 hours.

[Brief explanation of the drawing]

FIG. 1 is a front view of a discharge tube of the type according to the invention. FIG. 2 is a front cross-sectional view of one end of a discharge lamp arc tube with a shoulder formed as an integral part of the arc tube end wall. FIG. 3 is a cross-sectional front view of an arc tube in accordance with another feature of the invention in which a shoulder member is formed as an integral part of the arc tube end wall. FIG. 4 is a front cross-sectional view of one end of the discharge lamp arc tube in which the shoulder member is formed by a "top-hat" shaped member. FIG. 5 is a front cross-sectional view of a discharge lamp arc tube according to another feature of the invention in which the shoulder member is used in a lamp arc tube with a wire-like current conducting member. It is formed by a "top-hat" shaped member. FIG. 6 is a front cross-sectional view of an arc tube according to yet another feature of the invention, in which the shoulder member includes a lamp with a conductive porcelain alloy as the current conducting member;
Formed by a "top hat" shaped member used in arc tubes. 1...Discharge tube, 2...Glass outer envelope, 3...
Lamp base, 4...terminal, 6...covering wall, 7
... Ring body (seal element), 8 ... Hole, 9 ... Shank member, 10 ... Electrode assembly, 10a ...
Electrode element, 11... Shoulder member, 12... Single tube (arc tube), 14... Current introduction member, 16... Sealing glass, 17... Electrode element, 18... Support shank element, 21... Cap Member, 26... Ceramic alloy, 32... Closing member, 33... Cover portion,
34...Body part, 35...Inner surface, 36...Inner surface,
37...shoulder member, 38...electricity introduction member, 39...
...Shank part, 40...Introduction part, 41...Joining part, 42...Closing member, 43...Cover part, 4
4... End face, 45... Core, 46... Body, 48
... Inner surface, 49 ... Outer ring portion, 50 ... Shoulder member, 51 ... Support shank, 52 ... Conductive introduction member.

Claims (1)

Claims: 1. A light-emitting ceramic arc tube having an end wall extending radially inwardly from the arc tube wall to define a central hole, and a light-emitting ceramic arc tube having an end wall extending radially inwardly from the arc tube wall to define a central hole; A high pressure discharge lamp comprising an electricity introduction member, the introduction member being coupled to an electrode shank member supporting an electrode element, the end wall comprising:
an inner surface exposed to radiation from the electrode element when the lamp is energized, the inner surface having a shoulder member adjacent to the central hole, and a height of the shoulder member above the inner surface extending from the electrode element; the width of the shoulder member is not sufficient to substantially shield the inner surface from the element;
A high-pressure discharge lamp characterized in that the temperature difference between the top surface and the inner surface of the shoulder member is such that it is sufficient to prevent contact between the amalgam and the electrical introduction member. 2. A high pressure discharge lamp according to claim 1, wherein the shoulder member is an integral part of the end wall. 3. A high-pressure discharge lamp according to claim 1, characterized in that the shoulder member is formed by a portion of a top-hat-shaped member sealed in a hole in the end wall. 4. The high pressure discharge lamp according to any one of claims 1 to 3, wherein the shoulder member has a width of 0.2 to 0.5 mm. 5. The high pressure discharge lamp according to claim 1, wherein the shoulder member has a length of 1.5 to 4 mm. 6. Claims 1 to 5, characterized in that the width of the shoulder member is determined according to the following formula:
The high-pressure discharge lamp according to any one of paragraphs. 12r ₁ σεl/K(r ₁ ² −r ₂ ² )=1/T ₁ ² −1/T ₂
^2Where , r ₁ : Inner diameter of the shoulder member (m) r ₂ : Outer diameter of the shoulder member (m) T ₁ : Temperature at the lower end of the shoulder member (〓) T ₂ : Temperature at the upper end of the shoulder member (〓) K : Thermal conductivity of alumina (assumed to be 8.87 Wm ^-1 K ^-1 ) σ: Stephan's constant (5.67×10 ^-8 Nm ^-2 K ^-4 ) ε: 0.4116 (emissivity of alumina, dimensionless) l : Length of step part (m) 7 The height of the shoulder member is 2 mm, and the width w is
The high pressure discharge lamp according to claim 1, characterized in that the diameter is 0.5 mm. 8. A high-pressure discharge lamp according to claim 1, characterized in that the shoulder member does not shield any part of the electrode element. 9. The electricity introduction member projects beyond the shoulder member onto the side surface of the end wall that is exposed to radiation from the electrode element when the lamp is lit, and the coupling between the electricity introduction member and the electrode shank member takes place in this discharge space. A high-pressure discharge lamp according to claim 1, characterized in that: 10. The high-pressure discharge lamp according to claim 9, wherein the electricity introducing member is made of a niobium tube. 11. Claim 9, wherein the electricity introduction member is made of niobium wire.
High-pressure discharge lamps as described in . 12. The high-pressure discharge lamp according to claim 9, wherein the electricity introducing member includes an electrically conductive porcelain alloy. 13. The high-pressure discharge lamp according to claim 1, wherein the arc tube is made of polycrystalline alumina.