Title of Invention

A MODULAR IGNITER SYSTEM

Abstract

This invention relates to a modular igniter system comprising: a) a ceramic igniter comprising: (i) a ceramic hot surface element comprising first and second ends, and (ii) a metallized coating which covers at least a portion of each end of the ceramic hot surface element; b) a socket comprising fIrst and second contacts which are in electrical connection with the metallized coatings of the igniter, wherein the contacts have a melting point of at least 48SoC.

Full Text

Ceramic materials have enjoyed c|real i Uccess as igniters in gas fired furnaces, stoves and clothe:-, dryers. A ceramic igniter typically contains conductive end portions and a highly resistive middle portion. When the Icjnitor ends are connected to electrical leads and a current is run through the igniter, the highly resistive portion rises in temperature. In conventional igniter systems, tho nlectrical circuit is typically formed by connecting the metallized coatings B which cover the ends of a ceramic hot surface element C to the silver solder-coated ends AG of nickel clad copper (NCC) wires L which lead to a socket S or other electrical connection. See Figure 1. Although this system is suitable for many igniter applications, its design does engender some problems. For example, when it is determined the ceramic hot surface element C must be replaced, the repair technician must disconnect the igniter at the interface between the NCC lead wire L and the socket S, and then introduce a new iqniter at the same , interface. Because the NCC lead wire is often at least 12 inches (and sometimes over 36 inches) in length, the situs of the lead wire/socket interface is often far removed from the service position of the hot surface element C, and is typically in a less accessible place. Since this interface is remote/the technician often expends considerable time arid effort merely removing and replacing the failed igniter. In addition, use of conventional igniter designs has become problematic at higher service tentperatures. In particular, it has been observed that the NCC wire begins to degrade at about 450°C (the maximum service temperature of appliance grade wire) and the silver solder becomes liquid at about 600°C. Moreover, the thermal expansion coefficient of NCC wire is so much greater than that of the typical ceramic that it promotes cracking in the ceramic at temperatures starting at about 450°C. Since these phenomena become common when the igniter system is used in an application exceeding! about 450°C, use of this conventional igniter system is generally limited to applications having a "service temperature lower than 450°C. Accordingly, use of tl}e above design is precluded in many potential applications (such as self-cleaning ranges) which operate above 485°C Therefore, there is a need for a high temperature-resistant igniter system which also provides for easy access by a repair technician. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a modular igniter system comprising* a) a ceramic igniter comprisingi i) a ceramic hot surface n J.m€- \\t comprising first and second ends, and ii) a metallized coating which '.'.overs at least a portion of each end of the cervuile hot surface element; and . b) a socket comprising first ahc} secolul contacts which are in electrical connection with the iflolullized coatings of the igniter, wherein the contacts have a melting point; of at least 485 °C. Also in accordance with the pr€>seiyt invention, there is provided a metallized coating for uoe in bonding ceramic igniters to electrical contacts or leads, the metallized coating comprising: ' a) a first layer selected from the group consisting of titanium, zirconium and mixtures thereof, and having a thickness of between about 1000 and 10,000 angstroms, b) a second layer selected from the group consisting of molybdenum, tungsten, tantalum, columbium and mixtures thereof, and having a thickness of between about 2000 and 20,000 angstroms, and c) a third layer selected from the group consisting of nickel, chromium, silver, gold, platinum, palladium, ; manganese and mixtures thereof, and having a thickness of between about 10,000 and 100,000 angstroms, ! DESCRIPTION OF THE FIGURES Figure 1 is a drawing of a prior art igniter system foV smaller hot surface elements which contain silver solder and nickel clad copper wire. Figure 2 is a drawing of the first preferred embodiment of the igniter system of the present invention* Figure 3 is a drawing of the second preferred embodiment of the igniter system of the present invention. Figure 4 is a drawing of the third preferred embodiment of the igniter system of the present invention. ! Figure 5 is a drawing of the fourth preferred embodiment of the igniter system of the present invention. DETAILED DESCRIPTION OF THE INVENTION Simply substituting a conventional high temperature lead wire (such as 18 gauge Ni-Cr wire) for the silver solder-tipped NCC lead wire was considered by the present inventor. Although this high temperature lead wire bonds well to conventional metallized coatings and would likely withstand the high temperatures surrounding the igniter, it is also very expensive. Moreover, the extreme rigidity of the Ni-Cr wire imparts significant stress on the hot surface element, leading to igniter failure. Lastly, since the distance between the hot surface element and the socket in conventional systems is often quite long, simple substitution would result in an expensive igniter system prone to disconnection. Accordingly, further modification of the conventional system *wi pursued. The present invention has overcome t\m drawbacks of the conventional NCC wire-based system by eitlitu t a) plugging ends of the hot surf-^P* t1 lament directly into a socket having high temperature inetal contacts (and which is located next to the service position of] the hot surface element) so that the met it "(..li ;;ec| coatings covering the ends of the hot surface element m^ke direct electrical connection with the high temperature Hiatal contacts of the socket, or b) electrically connecting the hot surf nee element to the high temperature contacts of a socket (which is again located next to the service position of the hot surface element) through a pair of short, high temperature wires. In each of these systems, there is no longer an easily ; degradable material (e.g., NCC wire or low temperature contact) near the hot surface element. The high temperature contacts of the socket can then be connected to NCC wire (not shown) on the opposite side of the socket, where the more moderate temperatures (i.e., about 450°C) do not threaten the integrity of the NCC wire. Moreover, since the socket is now close to the igniter, both the plug and the uhprt, high temperature wire embodiments provide a "modular" igniter which can be disconnected from its socket at the situs of the hot surface element, thereby allowing its easy original installation or replacement. The socket of the present invention can be any conventional socket used in the igniter field which can provide an electrical circuit through the ceramic hot surface element (either directly or through an intermediate wire) and maintain its integrity when exposed to temperatures of: at least 485°C, preferably at least 650°C. Typically, the socket contains two parallel grooves which extend into the socket for reception of either the igniter ends or the high temperature wire. In some preferred embodiments wherein the emits c: f the hot surface element are plugged into the socket, the grooves are large enough to securely receive the entire ent'tu of the hot surface element and further contain pad-like high t eifiperature contacts which are positioned on the sidewalk of the groove for direct electrical connection with the metallize;:} costings pf the igniter. In other preferred embodiments utilizing high temperature lead wires, the grooves i\r:e appropriately shaped for reception of the short high temperatme wires and contain high temperature contacts shaped as tubes J;or direct reception of and connection to the high temperature wires. Materials suitable for use as a socket substrate include cordierite. On the face of the socket opposite its grooves, the socket! usually possesses electrical ports which are in electrical connection with the high temperature contacts. These ports provide a : means of electrically connecting the high temperature contacts to an NCC lead wire in a less extreme environment. r The contacts of the present invention can be any high . temperature material which can conduct a current and resist; degradation up to a temperature of no less than 485 C, ? preferably no less than 650°C. Typically, the contacts are! made of metal or a metal alloy. Some materials suitable for use as the contact include nickel alloys, nickel, gold, silver and platinum. The size and shape of the obniacts depend upon the type of electrical connection des tred. For example, the contacts can be shaped as flat pads and positioned along the sidewalls of a groove in the socket (If vjlrect connection to the metallized coating of the hot surface element is desired), or as tubes which essentially line the groove (if indirect ; connection to the metallized coatincjf* through a high temperature lead wire is desired) . in s ])i)^ embodiments, the contacts can comprise a spring metal base having a noble metal-type coating. The ceramic hot surface element: of the. present invention can be made of any ceramic typically user) In the igniter field, including silicon carbide, silicon nitride, aluminum nitride,-or tungsten carbide-based,compositions. preferred compositions include a bimodal silicon carbide blend an4 those compositions disclosed in U.S. Patent No. 5,045,237, the specification of which is incorporated by reference. Hot surface elements comprising a refractory metal element encased in a ceramic (as in U.S. Patent No. 4,357,526) are also suitable for use with the present invention. The size and composition of the hot surface element should be selected to be suitable for use in at least part of the voltage range between about 3 and about 300 volts, and in at least part of the temperature range of between about 980°C and about 1700°C. The one basic shape requirement is that the hot surface element have two ends for conducting an j electric circuit. However, the shape can be any shape typically adopted in igniter geometries, including hairpins, coils, rods, serpentines and fibers. In some embodiments of the present invention having AIN-baseci compositions, the hot surface element has a hairpin design (as in Figure 2), a height of between 1 cm and 8 cm, and a thickness of between 0.5 mm and 2.0 mm. In some embodiments having bimodal silicon carbide compositions, the hot surface element has a serpentine configuration (as in Figure 4), a height oj: 5 to 10 cm, and a thickness of 2 to 13 mm. In embodiments employing a high temperature lead wire to provide electrical connection between the metallized coatings i of the igniter and the contacts of the socket, the high temperature lead wire has a melting point of at least 485°Cr preferably at least 650°c. Generally, the I'fttfh temperature lead wire is a metal or metal alloy. Materia I!' miitable for use as the high temperature lead wire include nn:|;i.H alloys, nickel, silver, gold, and platinum. Typical Vjy, 1;'"Mr fl i9h temperature lead wire has a length of 1 cm to 15 cm, Jcrnsfierably 1 cm to 2 cm. Likewise, its diameter is typically )ust.ween 0.5 and 1.5 mm. The metallized coating covering the igniter ends can be any coating commonly used to electrically connect ceramic hot -surface elements and lead-wires. In aoitio preferred embodiments, the metallized coating is a fc>raze, preferably an active metal braze. When AIN-based hot surface elements are selected, the metallized coating is preferably a braze.1 In other preferred embodiments, the metallized coating is a flame spray coating, preferably comprising a nickel alloy. When bimodal silicon carbide-based hot surface elements are selected, the metallized coating is preferably a flame spray coating (although a braze can also be suitably used). With either of these coatings, the metallised coating is applied to the ends of the ceramic hot surface element ih an amount sufficient to provide good electrical and physical connection j between the ceramic hot surface element and the high temperature contacts or lead wires. ( i When a braze is used as the metallized coating, it is typically (but not exclusively) applied on one face of each, end of the ceramic hot surface element, in regions of about 0.5 to 4 sguare millimeters (mm ), by either brushing or silk-screening. To obtain the required high degree of adhesion to the ceramic, the braze typically contains an active metal which can wet and react with the ceramic materials and so provide adherence thereto by filler metals contained in the braze. Examples of specific active metals include titanium, zirconium and niobium. Preferably, the active metal is titanium or zirconium. In addition to the active metal, the braze typically contains one or more filler metals such as silver, copper, indium, tin, zinc, lead, cadniiujn, and phosphorous. Preferably, a mixture of filler metals is used. Most preferably, the braze will comprise titanium as the active I metal and a mixture of copper and silver mn the filler metal. Generally, the braze will contain between about 0.1 weight percent ("w/o") and about 5 w/o active inut al, with the balance being filler metal. Suitable commercial brazes include Lucianex 721, available from Lucas' Milhaupt, the. o|: CUdahy, WI and Cusil & Cusin Braze, available from Wesgo, Itic of Belmont,! CA, each of which contains about 70.5 w/o silver, 27.5 w/ojcopper, and about 2 w/o titanium. If a flame-sprayed coating is used, any conventional flame spray method can be employed for its delivery. The coating is typically resistant to degradation at temperatures of at least 485°C, preferably at least 650°C. Preferably, the flame-spray coating is a nickel alloy. It is typically applied in a thickness of between 0.1 and 0.3 mm. In conventional systems, the region of the system around the NCC lead wire/metallized coating connection becomes unwieldy if the lead wire is too long (i.e., more than three inches). This problem is conventionally solved by encasing \ this region in a ceramic block. Since the present invention typically requires either a short lead wire or no lead wiret at all, the reduced mass of the assembly could he adequate for, maintaining stability without requiring the stabilizing ceramic block. Accordingly, another advantage of the present invention is the possible elimination of the ceramic block. Referring now to Figure 2, there is provided in a first preferred embodiment of the present invention, a modular igniter system comprising: a) a ceramic igniter 1 comprising: i) a ceramic hot surface element 2 comprising first and second ends 3, and » ii) a metallized coating 4 covering at least a portion of each end of the ceramic hot surface element; b) a socket 5 comprising first and suioond contacts 6 having a melting point of at leu^t 4HB'd/ and c) a pair of lead wires 7 having £ length of less than 15 cm and a melting point of at leftst 41:16'0, wherein the lead wires electrically connect tfre metallized ? coatings 4 of the first and second ends 1; ci: the igniter 1 with i the first and second contacts 6 of the socket 5, respectively. In more preferred embodiments of thoHfi^st preferred embodiment, the hot surface element comprises A1N, preferably a blend of A1N, SiC and MoSi2- It typically has a height of 1^8 cm and a thickness of 0,5 - 2 cm. The metallized coating is preferably a braze which comprises H liver, copper and titanium. The lead wires are preferably nickel find preferably have a length of less than 3 cm and a diaifl&ber :>|:: about 0.8 mm. The contacts are also preferably made o:|: liicvjM and are shaped to receive the lead wire. More preferably, 1:1 IU; contacts are shaped in the form of a tube having a depth of ;ij:>i:iut: 13 mm and a diameter of 1 mm. Referring now to Figure 3, there is provided in a second preferred embodiment of the present invention, a modular igniter system comprising: a) a ceramic igniter 41 comprising: i) a ceramic hot surface element 42 having two ends 43, and ii) a metallized coating 45 covering at least a portion of the ends of the hot surface element 42, and b) a socket 46 having grooves 48 adapted to receive the ends 43 of the ceramic hot surface element 42, the socket comprising two contacts 47 positioned within the grooves for direct electrical connection to the metallized coatings 45, wherein the contacts 4 7 have a melting point i of at least 485°C. In more preferred embodiments of the second preferred j embodiment, the hot surface element comprises A1N, preferably a blend of A1N, Sic and MoSi2- It typically has a height of 1-8 cm and a thickness of 0.5 - 2 cm, and the cross-section of its ends are typically between 0.75 and 5 mm . The metallized coating is preferably a braze which comprise© silver, copper and titanium. The contacts are preferably a Ni-Cr alloy shaped as pads having a surface area of between 0.3 and 3 mm and positioned on the inner surface of the groove. Referring now to Figure 4, there is provided in a third preferred embodiment of the present invention, a modular igniter system comprising: a) a ceramic igniter 51 comprising: L) a ceramic hot surface element 52 comprising first and second ends 53, each end having a notch 54, and ii) a metallized coating 55 covering each end; b) a socket 56 comprising first and second contacts 57, wherein the contacts have a melting point of at least 485°C; c) a pair of lead wires 58 having Hirst and second ends, a length of less than 15 cm, and a malting point of at least 650°C; and wherein the first ends of the lead wires are in electrical connection with the notched portion of l:t>e igniter ends, and the second ends of the lead wires aye ir c||rect electrical connection with the first and second cor tacts of thfe socket. In more preferred embodiments <:: f th third preferred embodiment the lead wires are held in tin notches by capping first end of wire with a ni- cap bending below form hook inserting into notch so thcjt it is place spring tension and flattie spraying assembly metallized coating to provide additional mechanical electrical connection.> In especially preferred embodiments of the third preferred embodiment, the hot surface element comprises a bimodal blend of SiC. It preferably has a height of 5 to 8 cm, a thickness of 2-5 mm, and has ends whose cross-section is between 40 and 80 mm . The metallized coating is preferably a flame-sprayed Ni-Cr alloy. The lead wires are preferably a Ni-Cr alloy, and have a length of less than 3 cm inch and a diameter of about 0.8 mm. The contacts are preferably Ni-Cr receptors shaped in a tube form to receive the lead wire, the tube having a diameter o:f about 1 mm and a depth of between 10 mm and 2 0 mm. Referring now to Figure 5, there is provided in a fourth preferred embodiment of the present invention, a modular * igniter system comprising: a) a ceramic igniter 61 comprising* i) a ceramic hot surface element 62 comprising fiirst and second ends 63, and ii) a metallized coating 64 covering at least a portion of the ends; b) a socket 66 having grooves 68 adA^tdd to receive the ends 63 of the ceramic hot surface element 62, the socket comprising two contacts 61 positioned tor direct electrical connection to the metallised coating 64, wherein the contacts 67 have a melting point of at least 485°C. In especially preferred embodiments of tlie fourth preferred embodiment, the hot surface element coitip.K: ;l seta a bimodal blend of SiC. It preferably has a height of 5 to 8 cm, a thickness of 2-5 mm, and has ends whose cross-sect: ion 1 *a tifetween 40 and 80 2 mm . The metallized coating is prefer^bl^ \% J:lame sprayed Ni-Cr alloy. The contacts are preferably Ni-C:r Jpucjs having a surface 2 2 area of between 10 mm and 2 0 mm . Solid-state circuitry may be dewignect into the socket to allow for an output voltage of between 5-1 unci 95% of the nominal input voltage. In particular, a thyfistor circuit (a device which switches on and off rapidly and in a controlled manner during each cycle of the applled alternating voltage so as to substantially provide to the igniter the effect oi a lower voltage) can be incorporated into the socket, thereby eliminating the need for a step down transformer. Also in accordance with the present invention, it has been found that the metallized coatings of the present invention can, be provided through conventional Rf sputtering techniques to produce thin, multi-layered metallized coatings. A multi-layered metallized coating provides two advantages over conventional painted-on or silk-screened metallized coatings. First, whereas metallized coatings applied by conventional means have a thickness of at least 0,05 jnm, Rf sputtered \ metallized coatings can have a thickness of only between 0.0:03 I and 0.020 mm. The thinner metallized coating provides a lower stress resulting from the inevitable thermal expansion • mismatch. Second, whereas the compon&hts of the conventional metallized coatings are applied en mn^se, the components of the Rf sputtered metallized coating may be applied in discrete layers. For example, a titanium layex may foe applied to thel ceramic hot surface element, a molybdenum layer may then b€ applied thereon, followed by a silver or nickel layer for connection to the high temperature metal contact. Since I Claim: 1- A modular igniter system comprising! a) a ceramic igniter comprising i) a ceramic hot surface element. comprising first and second ends, anc| ii) a metallized coating which covers at least a portion of each end of the ceramic hot surface element; b) a socket comprising first and second contacts which are in electrical connection with the metallized coatings of the igniter, wherein the contacts have a melting point of at least 485°C. 2. The system of claim 1 wherein the socket contains two parallel grooves which extend into the socket, the grooves having sidewalls. 3. The system of claim 2 wherein the ends of the hot surface element are plugged into the grooves. 4. The system of claim 3 wherein the grooves contain pad-like high temperature contacts which are positioned on the i sidewalls of the groove for direct electrical connection with the metallized coatings of the igniter. 5. The system of claim 2, wherein the grooves contain the | tube-shaped contacts. 6. The system of claim 1 wherein the contacts have a melting point of at least 650°C. 7. The system of claim 1 wherein the contacts are selected from the group consisting of a metal and a metal alloy. 8. The system of claim 1 wherein the contacts are selected from the group consisting of nckel alloys, nickel, gold, silver and platinum. 9. The system of claim 1 wherein the contacts are shaped as flat pads. 10. The system of claim 1 wherein the contacts are shaped as tubes. 11. The system of claim 1 wherein the ceramic hot surface i element comprises one of silicon carbide, silicon nitride, i aluminum nitride, or tungsten carbide, 12. The system of claim 11 wherein the ceramic hot surface element has a height of between 1 cm and 8 cm, and a thickness of between 0.5 mm and 2.0 mm. 13. The system of claim 1 wherein the ceramic hot surface element comprises a bimodal silicon carbide blend. 14. The system of claim 13 wherein the ceramic hot surface element has a height of 5 to 8 cm and a thickness of 2 to 5 mm. 15. The system of claim 1 further comprising a high temperature lead wire electrically connected between the metallized coatings of the igniter and the contacts of the| socket, wherein the high temperature lead wire has a melting point of at least 485°C. 16. The system of claim 15 wherein the high temperature lead wire has a melting point of at. least 650°C. 17. The system of claim 16 wherein the high temperature lead wire is selected from the group consisting of a metal or metal alloy. 18. The system of claim 16 wherein the high temperature lead wire is selected from the group consisting of nickel alloys, nickel, silver, gold, and platinum. 19. The system of claim 15 wherein the high temperature lead wire has a length of 1 cm to 15 cm.. 20. The system of claim 15 wherein the high temperature lead wire has a length of 1 cm to 2 am. 21. The system of claim 20 wherein the high temperature lead wire has a diameter of between 0.5 and 1.5 mm. 22. The system of claim 1 wherein the the metallized coating is an active metal braze. 23. The system of claim 1 wherein the metallized coating is a flame spray coating. 33. A modular igniter system comprising! a) a ceramic igniter comprising: i) a ceramic hot surface element having two ends, and ii) a metallized coating covering at least a portion of each end of the hoi. surface element, and b) a socket having grooves adapted to receive the ends of the ceramic hot surface element, the socket comprising two contacts positioned within the grooves for direct electrical connecting to the metallized coatings, wherein the contacts helve a melting point of at least 485°C 40. The system of claim 33 wherein the contacts are pads 2 2 having a surface area of between 10 mm and 2 0 mm . 41. A modular igniter system comprising: a) a ceramic igniter comprising: i) a ceramic hot surface element comprising first and second ends, each end having a notch, and ii) a metallized coating covering each end; b) a socket comprising first and second contacts, wherein the contacts have a melting point of at least 485°C; c) a pair of lead wires having and second ends, a length of less than 15 cm, and 4 melting point of at least 650°C; and 46. A metallized coating for use in bonding ceramic igniters r to electrical contacts or leads, the metallized coating comprising: a) a first layer selected from thta group consisting oof * titanium, zirconium and mlKtures thereof, and having a thickness of between about 1000 and 10,000 angstroms, b) a second layer selected from the group consisting!of molybdenum, tungsten, tantalum, columbium and mixtures thereof, and having a thickness of between about 2000 and 20,000 angstroms, and c) a third layer selected from the group consisting of nickel, chromium, silver, gold, platinum, palladium, manganese and mixtures thereof, and having a thickness of between about 10,000 and 100,000 angstroms. 47. A modular igniter system substantially as herein described with reference to the accompanying drawings♦

Documents:

1341-mas-1996-abstract.pdf

1341-mas-1996-claims duplicate.pdf

1341-mas-1996-claims original.pdf

1341-mas-1996-correspondance others.pdf

1341-mas-1996-correspondance po.pdf

1341-mas-1996-description complete duplicate.pdf

1341-mas-1996-description complete others.pdf

1341-mas-1996-drawings.pdf

1341-mas-1996-form 1.pdf

1341-mas-1996-form 26.pdf

1341-mas-1996-form 3.pdf

1341-mas-1996-form 4.pdf