Patent Application
20140070695
The subject matter of the present disclosure relates generally to voidless ceramic metal halide lamps.
Ceramic metal halide (CMH) lamps (sometimes referred to as ceramic discharge metal halide lamps) generally include a tube or lamp body constructed of a ceramic material such as sintered alumina that forms a chamber into which a dose of e.g., mercury, argon, and halide salts are introduced. Electrodes are positioned at ends of the tube that, when energized, will cause the lamp to emit light. Depending upon the mixture of halide salts, the emitted light can closely resemble natural daylight. Additionally, for a comparable light output, CMH lamps can be operated with significantly less energy than a traditional, incandescent light bulb. Also, unlike lamps constructed with fused quartz, the alumina is less subject to attack from metal ions inside the tube.
A conventional construction for CMH lamps has used e.g., a tube having legs extending from the ends of the tube body. For each leg, an electrode extends within the leg and into the inside of the tube. Although placed into contact with legs, the electrodes typically have a diameter slightly smaller than the inside of the legs. This difference in diameter creates a void or crevice through which one or more of the dosage materials could escape from the discharge tube. To prevent this result, for each leg a sealing frit is typically introduced at one end of the leg into at least a portion of the voids between the electrodes and the leg.
Challenges exist with this construction, however. Even though each leg is sealed, a portion of the leg near the chamber of the lamp may still have a void into which e.g., metal halide salts can migrate. Some of the metal halide salts dosed into the tube are corrosive, particularly at the high temperatures of lamp operation. As these salts move in and out of the leg, they can eventually cause corrosion of the leg and color instability problems. Also, the salts will attack the sealing frit particularly if the temperature of the sealing frit reaches a high temperature such as e.g., about 750° C. Once the sealing frit is penetrated by the salts, the salts and other materials dosed into the tube body will escape and the lamp will become non-functional.
Accordingly, a CMH lamp having a construction that lacks these deficiencies would be useful. Such a CMH lamp that can be constructed in a variety of different shapes would also be useful. A method of creating such a CMH lamp would also be beneficial.
The present invention provides a voidless CMH lamp and a method of making such a lamp. The CMH lamp includes an arc-tube body that receives at least one end plug. The end plug is constructed from a core of cermet material received within an outer layer of a ceramic material, such as e.g., alumina (Al2O3). An electrode is placed into the cermet material. The relative density of the cermet material and the outer layer of ceramic material are carefully controlled. A sintering process is used to eliminate voids between the cermet core and the outer layer of ceramic material. Sintering of the plug to the arc-tube body provides a hermetic seal by promoting grain growth across all interfaces so that the use of a sealing frit can be avoided. Sintering of the ceramic material surrounding the cermet can be also used to improve light output and photometric performance of the lamp. The creation of one or more indentations in the end plug can also provide performance improvements. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.
In one exemplary embodiment, the present invention provides a lamp that includes an arc-tube body defining a chamber and a pair of openings spaced apart from each other at opposing sides of the chamber. A pair of plugs are provided, with each of the plugs positioned in one of the openings at opposing sides of the chamber. Each plug includes an outer layer having aluminum oxide and having a sintered density ρSOD. A core is positioned within the outer layer and includes a ceramic material and an electrically conductive material, the core having a sintered density ρSCD, wherein ρSOD≧ρSCD. A pair of electrodes are provided, with one each positioned within the core of each plug.
In another exemplary embodiment, the present invention provides a lamp that includes an arc-tube body defining a chamber and an opening positioned on one side of the chamber. A plug is positioned in the opening. The plug defines radial and axial directions. The plug includes an outer layer having a ceramic material with a sintered density ρSOD. A core is positioned within the outer layer and includes a ceramic material and an electrically conductive material. The core is co-sintered with the outer layer and has a sinter density of ρSCD, wherein ρSOD≧ρSCD. An electrode is positioned within the core of the plug.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
A pair of plugs 112 and 114 are inserted into openings 122 and 124, respectively, of body 102. For this exemplary embodiment of lamp 100, openings 122 and 124 are provided by legs 104 and 106 that are connected to body 102 and extend away from chamber 120. Plug 112 includes a core 130 positioned within an annular outer layer 126. More particularly, for this exemplary embodiment, annular outer layer 126 is positioned radially outward (radial direction denoted by arrow R) of core 130. By way of example, annular outer layer 126 may be constructed from e.g., aluminum oxide or other ceramic materials. Although shown as circular or annular, outer layer 126 may be constructed from other shapes as well.
Core 130 may be constructed from e.g., a cermet—i.e. mixture of a ceramic material and an electrically-conductive metal. For example, core 130 may be constructed from a mixture of aluminum oxide and molybdenum; other compositions may also be used. Plug 114, including core 132 and annular outer layer 128 is constructed in a similar manner.
A pair of electrodes 108 and 110 are positioned in cores 130 and 132. Electrodes 108 and 110 each include a tip 116 and 118, respectively, that extends into chamber 120. A variety of materials and constructions may be used for the electrodes. For example, each electrode 108 and 110 may be a single wire lead as shown or may be wrapped within coils formed by another wire lead. Electrodes 108 and 110 may be constructed from materials such as e.g., tungsten, tungsten with molybdenum section welded together, molybdenum, or tungsten with a cermet section.
Each electrode 108 and 110 has an electrode diameter along radial direction R. Each core 130 and 132 also has a core diameter along radial direction R. In one exemplary embodiment of the invention, the core diameter is less than about 10 times the electrode diameter. Other ratios may also be used.
During construction, plugs 112 and 114 are inserted into openings 122 and 124 as previously stated. Plugs 112 and 114 can each be provided with features for accurately controlling the amount by which plugs 112 and 114 extend into legs 104 and 106, respectively, to close openings 122 and 124. Referring to
IL=Ah−Sh Eqn. 1
IL≧1.2mm Eqn. 2
0≧SI<½*(Ad) Eqn. 3
0≦Sw≦Ad Eqn. 4
0≦Sa<180 Eqn. 5
Referencing
Two other parameters that can be used to define the stop used with an exemplary plug of the present invention are Sw, the Stop width, and Sa the stop Angle. These parameters are constrained by Eqn. 4 and 5. As used with an exemplary plug of the present invention, the stops define an insertion length that contributes to good hermeticity, and the above equations define the range of effectiveness of this feature. In one exemplary embodiment of the present invention, a stop such as stop 112 has the following values: SI=1.1 mm, Ad=5.2 mm, Sw=2.1 mm, Ah=3.76 mm, Sh=1.3 mm, and Sa=45 degrees. Variations of this are possible, especially if they meet the inequalities described in Equations 1 through 5.
It should be noted that plugs 112 and 114 are not limited to constructions where cores 130 and 132 extend completely through along the axial direction. For example, a plug may be provided where the core extends only partially through the plug and lacks a cylindrical shape. As shown in
During construction, lamp 100 is subjected to high temperature in a controlled atmosphere. More particularly, as used herein, sintering refers to a process in which the parts are heated to a high temperature (e.g., ˜1850° C.) in the presence of a specifically selected gas such as e.g., hydrogen. The sintering will lead to e.g., grain growth between various particles used to make e.g., plugs 112 and 114. It will also cause e.g., cores 130 and 132 to contract along all radial directions R to form a hermetic seal around electrodes 108 and 110 and eliminate or prevent voids or crevices that could cause lamp failure. In addition, under such conditions, co-sintering will occur. For example, cores 130 and 132 may be co-sintered with annular outer layers 126 and 128, which may in turn be co-sintered with the legs 104 and 106 of lamp arc-tube 102. In such co-sintering, diffusion between these parts provides for grain growth that also helps form the hermetic seal that will retain the materials dosed into chamber 120 while minimizing or eliminating voids and other crevices.
Additionally, for certain exemplary embodiments, outer layers 126 and 128 of plugs 112 and 114 are constructed from aluminum oxide. During sintering, these materials will become transparent or translucent to provide lamp 100 with certain advantageous characteristics. For example, unlike a plug constructed from an opaque material, plugs 112 and 114 will allow light to pass through—increasing the light output from lamp 100. Also, by allowing more energy to escape in the form of light, a thermal benefit is provided as less heat must be dissipated from lamp 100. For this exemplary embodiment, providing a cermet diameter that is smaller than the outer layer diameter provides a unique advantage for allowing more energy to escape in the form of light.
While a variety of shapes may be used for arc-tube body 102, the shape and dimensions shown in
Table I provides exemplary dimensions, as defined by in
Table II defines by way of example, relevant dimensions for a cylindrical embodiment of this invention. Radius in this table refers to the radius of the cylindrical body where the port joins the cylindrical body. Other dimensions may be used in other exemplary embodiments of the invention.
The present invention is not limited to a lamp 100 having a plug, constructed with a core and outer layer, in each end of body 102. For example, referring now to
Referencing
Eqn. 6 defines the depth of this blind hole, which should be less than the feed through diameter in order to ensure a press fit. The height of the blind hole Hh should be greater than the diameter of blind hole, Hd, as defined by Eqn. 7. Finally, Hh should be less than the height of the cermet section Ch of the plug, as defined by Eqn. 8. By way of example, in one exemplary embodiment, Hd is about 0.644 mm, Hh is about 0.97 mm, and Ch is about 3.5 mm.
As shown in
For the embodiments previously described, the core of each plug has been shown as a relatively homogenous material. For example, the core can be made from a material having a relatively uniform coefficient of thermal expansion throughout the core. However, the present invention also includes the use of graded cores—e.g., cores constructed from layers having different coefficients of thermal expansion. For example,
The exemplary embodiment of lamp 100 with body 102 described in
More particularly,
Ceramic material in the form of e.g., a powder is placed into mold cavity 408 around mandrel 404. The powder could include e.g., aluminum oxide. The powder is compressed around the mandrel 404 in the mold cavity to create an end plug intermediate 409 (shown with dotted lines) having an opening 431 (
First shaft 402 includes a first guide channel 403 into which mandrel 404 is received. Mandrel 404 slides within first guide channel 403 during compression of the powder. The intermediate end plug might appear, e.g., as intermediate end plug 206 shown in
After compressing the powder to create end plug intermediate 409, second mold portion 410 and mandrel 404 are replaced with a third mold portion 411, which connects with first mold portion 400 as shown in
Another mold portion 411 is then placed on top of barrel 400. The electrode is fed through a through channel 420, which is slightly larger (e.g., one hundredth millimeter) than the electrode diameter. This operation can also be performed for a plug that does not include an electrode in the pressing process called the blind hole method. Instead of using shaft 412 with channel 415, use shaft 412 without a channel. When guiding shaft 412 without a channel through barrel 400, shaft 412 will touch the surface of plug 409. Once the plug 409 and barrel 400 are resting on shaft 412, fill opening 431 with cermet material. Place another mold portion 411 without a through hole on barrel 400.
Second shaft 412 is then moved along an axial direction in
Another exemplary method of manufacturing a lamp of the present invention and, more particularly, an end plug such as e.g., end plug 112 or 114 is shown in
Next, in step 320, a cermet material is placed into the opening 202 of intermediate 200. The cermet material may be prepared from e.g., a ceramic material and an electrically conductive metal. End plug intermediate 200 is compressed to provide a core 208 of the cermet within outer layer 206. Outer surface 204 is then machined to create a flange or rim 212 that can be used e.g., as stop when the resulting plug is placed in the body of lamp such as e.g., body 102. A hole 209 may be created in core 208 for receipt of an electrode.
In step 330, an electrode 210 is inserted into core 208. Electrode 210 may be placed into hole 209 or, if no hole is provided, then inserted partially into—or completely though—core 208.
Table IV provides experimental results used to develop embodiments of the invention where cracks in the cermet or alumina portions of the plug would be avoided. Hermeticity between the plug and lamp body can be obtained by well-established principles of cosintering. Under “Factors,” Table IV lists parameters varied by established statistical principles with the alumina weight in grams and the dimension in mm. Under “Response,” Table IV lists all the measured values for the plugs in millimeters (mm).
With the results of such experiments, the inventors have discovered that specific conditions should be used get certain desirable results such as crack free plugs. These conditions will now be described.
With reference to
The hourglass shape provides a lower stress design for the cermet portion 130 of plug 112. If the above inequalities are met, a plug with no cracks can be provided. By way of example, in one exemplary embodiment, Cm was 0.2 mm, Ce=0.34 mm, and Cermet D=1.55 mm.
The plugs created in Table IV allowed for density of sintered cermet and alumina sections of the plugs to be determined. The inventors have discovered that the sintered density of the outer layer of ceramic material, ρSOD, should be greater than, or equal to, the sintered density of the cermet core, ρSCD. Stated mathematically, ρSOD≧ρsCD. In still another embodiment, the inventors have determined that the following inequality can provide components that are free from cracks:
Providing parts that meet this inequality provides for proper functioning of the plugs. Additionally, it should be noted that the cermet density formed by this process is significantly less than the cermet density of a plug made of only cermet. For such a cermet, i.e., pressed cermet by itself, if the percent of molybdenum in the alumina is 50%, then the density will be about 7 gm/cc. In the cermet of the plugs described as exemplary embodiments of the present invention, the densities of the cermets are typically in the 3-4 gm/cc range. This lower density, or a smaller packing fraction, creates lower stresses in the interface between the cermet and the alumina portions of the plug and is an important and novel feature for success of this design.
For a plug such as plug 112 to have the desired properties, the cermet diameter, Cd, must be less than the plug diameter, Ad. Also, the first two inequalities (Eqn. 12 and 13) define the range of permissible plug and cermet diameters. The fourth inequality describes the relationship between Cd and Ad that should be used to make successful crack free plugs. The inventors have discovered that an indentation defined by Id and I1 and I2 in
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/700,006, filed Sep. 12, 2012, which is incorporated herein by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61700006 | Sep 2012 | US |
