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This application is a divisional application of U.S. Ser. No. 08/789,033, filed Jan. 27, 1997. |
BACKGROUND OF THE INVENTION Ceramic materials have enjoyed great success as igniters in gas fired furnaces, stoves and clothes dryers. A ceramic igniter typically has a hair-pin shape which contains conductive end portions and a highly resistive middle portion. When the igniter ends are connected to electrified leads, ... |
U.S. Pat. No. 5,085,804 ("the '804 patent") along with companion U.S. Pat. No. 5,405,237 disclose compositions suitable for a hot zone of a ceramic igniter, the hot zone comprising: |
(b) between 50 and 95 v/o of a material selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, boron nitride, aluminum oxide, magnesium aluminate, silicon aluminum oxynitride, and mixtures thereof. According to the '804 patent, these compositions provide the proper speed, room tempera... |
One conventional igniter, the Mini-Igniter�, available from the Norton Company of Milford, N.H., uses a hot zone composition from the '804 patent which comprises aluminum nitride ("AlN"), molybdenum disilicide ("MoSi2 "), and silicon carbide ("SiC") and a total hot zone length of between about 1.5 cm (for 12V applicati... |
Attempts have been made to increase the speed of these igniters. For example, Washburn and Voeller, "Low Power Gas Ignition Device, presented in the Proceedings of the 1988 International Appliance Technical Conference--Europe" (1988), pp.134-149, discloses achieving speeds as low as 1.5 seconds by reducing the mass of ... |
In addition, these igniters generally experience a very high in-rush current (i.e, a current of about 10 amperes in the first millisecond) before settling down to a conventional 2 to 3 ampere current. Since any transformer designed for use with these igniters must be designed to accept this initial high current, these ... |
Simply lowering the resistivity of the hot zone composition (by increasing its conductive MoSi2 content) has been considered as a method of increasing the speed of the igniter. However, it was found that doing so increases the inrush current to even higher levels (due to a lower room temperature resistivity) and makes ... |
Similarly, raising the resistivity of the hot zone composition (by decreasing its MoSi2 content) has been considered as a method of decreasing the inrush current of the igniter. However, it was found that doing so not only decreased the speed of the igniter(due to a higher room temperature resistivity), it also provide... |
Therefore, there is a need for a ceramic igniter which has high speed but also resists cooling effects, and which has a low inrush current. |
b) a resistive hot zone disposed between and in electrical connection with each of the first ends of the electrically conductive portions, the hot zone having an electrical path length of less than 0.5 cm, and |
For the purposes of the present invention, the "electrical path length" is the shortest path taken by an electrical current through the hot zone when an electrical potential is applied to the conductive ends of the igniter. |
Also in accordance with the present invention, there is provided a method of heating, comprising the steps of: |
a) providing a ceramic igniter comprising: |
i) a pair of electrically conductive portions, each portion having a first end, |
ii) a resistive hot zone disposed between and in electrical connection with each of the first ends of the electrically conductive portions, the hot zone having an electrical path length of no more than 0.5 cm, and |
iii) an electrically non-conductive heat sink material contacting the hot zone, |
b) applying a voltage of between 3 V and 60 V between the conductive ends of the igniter to produce an inrush current and a steady state current such that the ratio of the steady state current to the inrush current is at least 35% (preferably at least 50%), and raising the temperature of the hot zone to about 1350� C. ... |
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a preferred embodiment of the present invention, wherein the electrically insulating heat sink is disposed as an insert between the conductive legs of the igniter. |
FIG. 2 is a cross-sectional view of a preferred embodiment of the present invention, wherein the electrically insulating heat sink contacts the opposing side of the hot zone. |
FIG. 3 is a perspective view of a preferred igniter of the present invention. |
FIG. 4 is a cross-sectional view of an igniter of the present invention wherein the hot zone comprises two resistive sections. |
FIG. 5 displays an exploded view of a preferred green body of the present invention. |
FIG. 6 is a cross section view of an igniter of the present invention made with tape cast conductive legs. |
FIGS. 8a and 8b display the inrush amperage over time for the igniter of the present invention (8a) and the prior art igniter (8b) |
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT It has been found that decreasing the hot zone electrical path length to less than 0.5 cm and contacting the hot zone with an electrically insulating heat sink material produces a commercially acceptable igniter which has high speed, high resistance to convective cooling, ... |
Without wishing to be tied to a theory, it is believed the added thermal mass of the heat sink significantly slows convective cooling of the hot zone, thereby allowing the hot zone to remain hot under convective cooling conditions despite its small length. |
In preferred embodiments, the igniter has a hairpin configuration comprising two parallel conductive legs and a connecting hot zone bridge positioned therebetween, with the remaining space between the legs being at least partially filled by an electrically insulating heat sink material such as aluminum nitride which co... |
The electrical path length of the hot zone, shown as EPL in FIG. 1, is less than 0.5 cm. Insulating heat sink material 19 is provided as an insert to contact the hot zone and substantially fill the remaining space between the conductive legs extending from the hot zone 11. When paired leads 50 and 51 are attached to ea... |
In other embodiments, the electrically insulating heat sink material can contact other surfaces of the hot zone. As in FIG. 2, the electrically insulating heat sink material 18 contacts hot zone 11 on the opposing side of the space 20 created between the parallel conductive legs 9 and 13. This design still provides the... |
Typically, the hot zone has a high temperature (i.e., 1350� C.) resistivity of between about 0.001 ohm-cm and about 3.0 ohm-cm, a room temperature resistivity of between about 0.01 ohm-cm and about 3 ohm-cm, and is usually characterized by a positive temperature coefficient of resistance ("PTCR"). In preferred embodime... |
(a) between about 50 and about 75 vol % of an electrically insulating material selected from the group consisting of aluminum nitride, boron nitride, silicon nitride, and mixtures thereof, |
(c) between about 8.5 and about 14 vol % of a metallic conductor selected from the group consisting of molybdenum disilicide, tungsten disilicide, tungsten carbide, titanium nitride, and mixtures thereof. |
In more preferred embodiments, the hot zone comprises a first resistive material comprising between 50 vol % and 75 vol % AlN, between 13 vol % and 41.5 vol % SiC, and between 8.5 vol % and 12 vol % MoSi2. In other embodiments, the hot zone further comprises between 1 v/o and 10 v/o alumina, preferably in accordance wi... |
Referring now to FIG. 3, the hot zone typically has a thickness Thz of between about 0.05 cm and 0.2 cm, preferably between about 0.06 cm and 0.125 cm. Its length Lhz (which, in FIG. 3, is the same as the electrical path length) is generally between 0.05 cm and 0.45 cm, preferably between 0.15 cm and 0.25 cm. Its depth... |
Preferably, the particle sizes of both the starting powders and the grains in the densified hot zone are similar to those described in the '804 patent. In some embodiments, the average grain size (d50) of the hot zone components in the densified body is as follows: a) electrically insulative material (i.e., AlN): betwe... |
In some embodiments, the hot zone comprises a pair of resistive sections disposed in parallel between the conductive ends. For example, as shown in FIG. 4, the hot zone can comprise first resistive section 15 and second resistive section 17, each of which is in parallel electrical connection with each of the conductive... |
Preferably, second resistive section 17 of the hot zone has the same thickness and length as the first resistive section. Its depth is generally between about 0.25 cm and about 0.125 cm, preferably between 0.05 cm and 0.1 cm. Its room temperature resistivity and its 1350� C. resistivity are typically higher than those ... |
In one embodiment of the invention, the second resistive section is formed in-situ by a reaction between the powders selected to form the first resistive section 15 and powders selected to form electrically insulating heat sink 19 disposed between the legs of a conventional hairpin igniter. Without wishing to be tied t... |
The function of the electrically insulating heat sink material 19 is to provide sufficient thermal mass to mitigate convective cooling of the hot zone. When disposed as an insert between the two conductive legs, it also provides mechanical support for the conductive legs 9 and 13 and so makes the igniter more rugged. T... |
Conductive ends 9 and 13 provide means for electrical connection to wire leads. Preferably, they also are comprised of AlN, SiC and MoSi2, but have a significantly higher percentage of the conductive and semiconductive materials (i.e., SiC and MoSi2) than do the preferred hot zone compositions. Accordingly, they typica... |
Also in accordance with the present invention, there is provided a preferred method of making the present invention, wherein tiles made of warm pressed powder mixtures having predetermined compositions are arranged so that the tile cross-section depicts an electrical circuit. In one preferred process for making the inv... |
In making the present invention, each green tile shown in FIG. 5 comprises an entire layer of the ceramic laminate (e.g., second tile 24 has an insulative portion 26 and resistive section 28). Alternatively, the tiles may consist of only one portion of a layer. In the latter case, it has been found that tiles comprisin... |
Although FIG. 5 presents each layer as rigid green tiles, these portions alternatively can be made by either tape casting, roll compaction, warm pressing followed by slicing, dry pressing or screen printing. In another preferred embodiment, as shown in FIG. 6, green tape 60 having a conductive composition is wrapped ar... |
When the igniter uses the electrically insulating heat sink material as an insert, the igniter may be made by the general method disclosed in U.S. Pat. No. 5,191,508, the specification of which is incorporated by reference. |
The processing of the ceramic component (i.e., green body processing and sintering conditions) and the preparation of the igniter from the densified ceramic can be done by any conventional method. Typically, such methods are carried out in substantial accordance with the '804 patent, the specification of which is incor... |
The igniters of the present invention may be used in many applications, including gas phase fuel ignition applications such as furnaces and cooking appliances, baseboard heaters, gas or oil boilers and stove tops. In one preferred embodiment, four 30 V igniters of the present invention are provided in series and used a... |
Although the igniter of the present invention is typically used in the voltage range of 3V to 60 V, it is more typically used in the range of 12V to 40V. In the 3-9V range, it is believed that using a smaller hot zone length and/or increasing the MoSi2 content would provide the lower resistance needed to produce suitab... |
In addition, the exposed resistive hot zones of the present invention display a higher surface loading of power, measured in watts/cm2 of the hot zone surface area, than the conventional '804 style igniter. The exposed resistive hot zone surface loading of the igniters of the present invention, which is typically betwe... |
In some embodiments, the hot zone and/or the legs can be coated with a layer of a protective ceramic such as CVD AlN or Si3 N4. In these embodiments, the coated igniter is protected from carbon and soot depositing on the small hot zone and causing a short. |
EXAMPLE I A green laminate was constructed in substantial accordance with the design shown in FIG. 5. A composite powder comprising a hot zone powder mixture of 64 v/o AlN, 25 v/o SiC, and 11 v/o MoSi2 next to an electrically insulating heat sink powder consisting essentially of 100 v/o aluminum nitride powder was warm... |
Suitable leads were attached to the conductive portions of the hot surface element and a voltage of about 30 V was applied. |
The electrical performance of the resulting nominal 24V igniter is shown in FIG. 7 in terms of voltage and temperature. Since the low temperature resistance is lower than the high temperature resistance, the hot zone has an effective PTCR. The igniter displayed stable heating performance and reached the design temperat... |
EXAMPLE II This example is intended to show the superior resistance to convective cooling provided by the igniter of the present invention as compared to those in Comparative Example I below. |
An igniter was made in substantial accordance with Example I. The electrical path length of this igniter was 0.25 cm. When this igniter was energized with 24V, it produced a current of 1.8 amps and a stable temperature of 1408� C. |
A gas canister which provides 400 cc/min (ccm) of air was placed about 1 foot from the igniter. A stream from the air jet only reduced the hot zone temperature to about 1182� C. The air jet did not blow out the igniter. |
COMPARATIVE EXAMPLE I A conventional 24V igniter marketed by the Norton Company under the '804 patent was selected for comparison. It had an hot zone electrical path length of about 2.05 cm. When energized with 24V, it reached about 1100� C.-1350� C. in about 2-3 seconds, and produced at stable temperature of 1410� C. ... |
A conventional 12V igniter marketed by the Norton Company under the '804 patent was energized with 12V and produced a stable current of about 2.0 amps and a stable temperature of 1400� C. A stream from the air jet described above reduced the hot zone temperature to less than 600� C. |
EXAMPLE III This example shows the superior life testing results of the igniter of the present invention. |
A 24 V igniter similar to that used in Example II was subjected to life cycle testing, wherein the igniter is turned on for 20 seconds and then turned off for 20 seconds. After 543,000 cycles, the decrease in amperage was only 5.43%. This small change represents an improvement over the standard '804 patent igniter, whi... |
EXAMPLE IV This example examines the behavior of an igniter wherein the hot zone composition is contacted by an electrically insulating heat sink material whose composition inhibits formation of an in-situ formed resistive section. In particular, it shows the benefit provided by the in-situ formed second resistive port... |
An igniter was made in a substantially similar manner to the igniter described in Example II above, except that 4 v/o alumina was added to the insert composition to inhibit in-situ formation of a second resistive composition. |
Examination of the microstructure of the resulting ceramic revealed a lesser degree of insitu formation of a second resistive section. It is believed the alumina addition effectively inhibited the formation of a second resistive section. |
When a 24V voltage was applied to this igniter, it reached about 1350� C. in about 1 second and was stable. As shown in FIG. 8c, its in-rush amperage was only 4 amps, and so was lower than the inrush amperage of the conventional '804-style igniter but higher than that of Example I. It later settled to about 2 amps. |
COMPARATIVE EXAMPLE II This comparative example demonstrates the superior surface loading of the igniter of the present invention. |
A standard 24V igniter was energized with 24V and produced a stable temperature and a 1.57 amperage. When the voltage was increased to 35 volts (thereby producing an amperage of 2.3 amps), the igniter failed. The surface loading of the igniter at failure was only about 60 watts/cm2. By comparison, the igniter of Exampl... |
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS5786565 *Jan 27, 1997Jul 28, 1998Saint-Gobain/Norton Industrial Ceramics CorporationMatch head ceramic igniter and method of using same* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS6002107 *Feb 19, 1999Dec 1... |
After proposing to Elizabeth Bennet despite his reservations, Fitzwilliam Darcy is shocked that she has refused him. He thinks about writing her a letter to explain his position, but instead decides to propose to his cousin Anne de Bourgh instead. A few years have passed, now Anne is dead, and their daughter Kathy, is ... |
I loved this novel and read it quickly. Author Monica Fairview has a vivid understanding of Austen's characters and is able to write them so believably it is like having another Jane Austen novel. I really like the look into the "what if" scenarios and how one small change can ripple through a family and make a differe... |
I really loved a tough conversation that Jane has with Elizabeth. "Think, Lizzy, for once in your life, instead of being guided by emotions." Jane gives her some hard truths about how her emotions have put the family in their current predicament. I loved it! It was a new way to think about Elizabeth. |
I loved Elizabeth's time at Pemberley and the predicament of being a governess which is a difficult situation. She is above the servants, but below the family. It makes for a lonely life. I love how Mr. Darcy thinks of this and helps her to find a new friend in the village. |
Mr. Darcy has had a lonely life without love and I enjoyed how he learns to open up to the possibility of love. It was a romantic story. |
Overall, Fortune and Felicity is a not to be missed Pride and Prejudice variation which perfectly captures Austen's beloved characters while telling a compelling new story. |
Labels: Austen Jane, Fairview - Monica, Historical Romance, Regency |
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Welcome to the 118th China Import and Export Fair |
Time: third October 31, 2015 -11 4 |
Address: China Import and Export Fair Exhibition Hall (No. 380, Zhuhai, Guangzhou, China) |
Welcome to participate in the exhibition by October 6th ~9, the United States Anaheim International Industry<eot>101 volunteers contributed to successful programs in Hohenfels - Bavarian News, U.S. Army Garrison Bavaria |
Christina Wilson April 29th, 2019 |
Lt. Col. Gregory C. Scrivens, U.S. Army Garrison Bavaria Chief of Staff, thanks the volunteers for their dedication and support to the Hohenfels Community at the Volunteer Recognition Ceremony April 24, 2019. |
HOHENFELS, Germany — One hundred one individuals representing the roughly 13,230 hours registered volunteer hours at U.S. Army Garrison Bavaria – Hohenfels were recognized in the annual volunteer recognition ceremony April 25, here, at the Hilltop Club. |
Volunteers provide many services such as making coffee, welcoming you as you walk in buildings, teaching or taking care of children of all ages, as well as coordinating events by setting up tables and chairs, preparing the meals and much more. They spent time coaching on a baseball field or basketball court, working in... |
"Without volunteers, Hohenfels could not provide all the services for the community," said Patrick Rothbauer, deputy garrison manager. "We thank you for all your support and time you gave and continue to give to our soldiers, families and civilians. Job well done!" |
Volunteer of the Year Award Winners, by category: |
Local National – Dominique Schnell |
DA Civilian/Retiree – Angela Hamilton |
Youth – Logan McDougall |
Active Duty – SFC Kurt Legnon |
Family Member – Lauren Gillett |
Ashley McLaughlin was recognized for having the most amount of volunteer hours, with 920 hours in 2018. Lauren Gillett followed her with 766 hours, Jared Overman with 637 hours and Amanda Lauritzen with 655 hours. |
USAG Bavaria – Hohenfels volunteers are not only Soldiers, but also family members, civilians and retirees of all age groups. |
When asking volunteers down here in Hohenfels why they spend their time and energy for the community, many said that it enriches them on every level and this would give them more back than they give to the community they live in. |
"Although having the best job in Hohenfels by hosting new and fun events, many programs could not run without the help of volunteers," said Angela Hamilton, special events, BOSS advisor and Warrior Zone manager. "Knowing how crucial it is to have people step in just motivates me to want to make a difference too." |
The Volunteer Management Information System, managed by Army Community Service, is a program that people can use to find, sign up and log their service hours. If you would like to volunteer, visit www.myarmyonesource.com and register. Select 'Hohenfels' as your community under USAG Bavaria when registering, and search ... |
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