Gas igniter

This application is a continuation-in-part of my pending application Ser. No. 223,451, filed Feb. 4, 1972, now abandoned.

It is, more particularly, concerned with an improved solid-state silicon carbide gas igniter of the type shown in such co-pending application in which it is there shown in association with a particular type of gas stove burner assembly. However, it should be understood, and will become readily evident from the following, that the new igniter is not limited to use in such an appliance, but has wider applicability in gas-ignition systems in either cyclical or continuous operating modes.

The previously available silicon carbide igniters presented problems in the attachment of the leads or electrical connectors for energizing the same where such connections were exposed to fairly high temperatures, for example, on the order of 1,400° F, since the joints were effected by ordinary flame spraying of aluminum and failed under the noted high temperature exposure. Securing of the leads to the igniter by means of silver soldering over a thin nickel or stainless steel coating was found likewise unsatisfactory, in this case, because of the substantial difference in thermal expansion which occured between the silicon carbide and the solder. For these reasons, as explained in the aforesaid co-pending application, high temperature plasma and flame spraying were tested and found successful, that is, as providing for the first time reliable connections of the leads to the igniter under the relatively severe operating temperatures required.

The technique of plasma spray coating is, of course, well-known and, briefly, comprises the injection of powders into an arc, together with a flow of gas through the arc region to carry the material to the surface on which deposition and bonding takes place. The powders are melted, vaporized and deposited on the substrate where they freeze and form a tightly bonded coat, the surface being effectively pre-roughened and the melt freezing into the surface imperfections, with some metallurgical bonding also occurring. For further details and illustration of typical plasma spray apparatus, reference may be had to the herein incorporated disclosure thereof found in "The Plasma State," by E. J. Hellund, published in 1961 by Reinhold Publishing Corp., N.Y., and particularly pages 167-170 of such work. High temperature flame spraying, for example, as carried out with apparatus available from METCO INC., Westbury, N.Y., which also supplies plasma spray equipment and coating materials for both methods, will provide like results, at a lower temperature than the latter but still well above the noted 1,400° F desired for the end coating.

The present improvement has as a further primary objective an improved configuration of the bond produced by such spray coating of the electrical leads to the igniter body.

An additional object is to provide such an igniter by using a preferred method for producing such a bonded electrical lead attachment thereto.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

FIG. 1 is a schematic diagram of gas burner apparatus using the improved igniter as shown in the above-referenced co-pending application;

FIG. 2 is a perspective view of the igniter body with its connecting leads in place but not yet bonded;

FIG. 3 is a fragmented comparable perspective of the igniter after bonding of the leads in accordance with the invention;

FIG. 4 is a fragmentary elevation of the completed igniter, with the attached lead end shown in cross section; and

FIG. 5 is an end view of the connector end of the new igniter.

Referring now to the drawing in detail, the illustrative range gas burner shown in FIG. 1 and designated generally by reference numeral 10 is fully described in the above-noted co-pending application and reference may be had thereto, if desired, for details of the internal construction of the burner and its operation. For present purposes, it will be pointed out that this burner receives the gaseous fuel to be combusted from an available source through a thermal fuel valve 11 having an electrical resistance element 12 as its actuator and a pipe 13 extending from the output side of the valve to the interior of the burner. Combustion air is supplied through a peripheral opening 14 about the top of the burner housing and beneath, in this assembly, a glass ceramic top 15 on which pots and pans and other utensils are supported for heating by the burner.

There is, moreover, an exhaust line 16 leading from the burner to a discharge blower 17, so that this particular burner is of powered type operating under negative pressure.

The burner is ignited by a glow coil element 18 of solid state silicon carbide the terminal end of which extends as illustrated outside of the burner housing 19. One lead or wire 20, for example, of nichrome extends to a terminal 21 of an electrical energy source, while the other igniter connecting lead 22 is in electrical series with a ballast coil 23, the resistance actuator element 12 of the thermal valve 11, a variable duty cycle motor driven mechanical switch 24, a fuse 25, and an air switch 26 to the other energy source terminal 27. The air switch in this system is intended and operative to preclude operation of the burner unless the exhaust blower is operating, as a safety interlock feature.

The igniter element 18 comprises in effect a helically wound body 28 of the silicon carbide, as a double helix, and has as terminal portions two semicircular and spaced apart extensions 30, 31 .Iadd.having oppositely facing outer exterior and interior surfaces joined together at the side edges thereof. .Iaddend.This configuration of the element is known and available, for example, from the Carborundum Company.

However, in accordance with the present improvements, the ends of the terminal parts 30, 31 of the igniter are provided with diametrically opposite and centered slots 32, 33 into which the connecting leads 20 and 22 for energization are inserted .Iadd.to provide appreciable direct overlapping interengagement between the terminal portions of the leads and the igniter terminal parts. .Iaddend.As indicated previously, this area of connection is in a fairly high temperature environment and the leads are bonded to the igniter body in such placement by high temperature flame or plasma spraying. More particularly, the pre-assembly illustrated in FIG. 2 is subjected to such metallizing spray, with the centerline of the spray, which is typically cone shaped, directed at the terminal end of the body preferably at an angle of approximately 45° while the body with its inserted leads is rotated fully. This operation produces the bonding shown in the remaining figures, with a slight .[.built-up.]. .Iadd.build-up .Iaddend.of sprayed material 34 in the area of the igniter end about the leads and tapering longitudinally in both directions, as shown most clearly in FIG. 4. Moreover, the described application of the bonding material results in the same being adhered fully peripherally about the igniter terminals 30, 31, with the extent of the application to the interior surfaces as well as the exterior and the edges of such parts being achieved by the noted direction of the spray and of somewhat lesser longitudinal extent at the interior surfaces due to the partial shielding of the latter which occurs.

As shown most clearly in FIG. 5, the sprayed material 34 not only secures the inserted leads in place .Iadd.with respect to the appreciably larger size terminal parts of the igniter, .Iaddend.but thus fully and continuously encases the terminal parts of the igniter for an extremely secure and reliable attachment of the leads.

Various powders for producing the sprayed coating are commercially available, with one found successful having a composition of nickel, chrome, and aluminum. This material is available from METCO INC. as METCO 443, METCO 450, and METCO 451, the last being somewhat more exothermic and the first (75 percent Ni; 19 percent Cr; 6 percent Al) most closely approximating expansivity of the particular silicon carbide tested.

Another source of apparatus and powders is Plasmaydne Division of Geotel, Inc., Santa Ana, Cal., and METCO INC. also supplies other powders specifically for the flame spraying technique in which, as is known, only oxygen and acteylene are used and the cost thus somewhat reduced as compared to plasma spraying. The aforenoted illustrative METCO powders can be used as well for flame spraying, although very high temperature materials must be plasma sprayed.

The disclosed high temperature spraying or metallizing fully meets the desideratum of withstanding temperatures on the order of 1,400° F or even higher, which cannot be realized with the conventional aluminum spray, and the total encasement of the leads eliminates any problem of failure, such as by spalling, due to differential thermal expansion of the materials.

Also unlike the conventional igniter, there is no need for clips between the leads and the igniter terminals.

The inserted leads instead of being round and straight as shown, can be of ribbon form and include a crimp or a rebent inner end adding a spring engagement in the slots to assist in holding them more firmly in place if needed during the metallizing operation.

It will also be clear to those skilled in the art that this improved igniter assembly can be used for long service life in all types of gas-fired domestic appliances, water heaters, laundry dryers, furnaces and the like and, additionally, as a source of infrared heat where spot or localized heating is desired. The igniters, as is known, can operate over a temperture range of about 2,100° to 2,400° F. The plasma arc spraying as described can be conducted with the igniter either pre-heated or at room temperature, with the leads ordinarily made of nichrome, as previously indicated in the different forms thereof. The igniter itself can be made of other materials than the described silicon carbide, e.g., molybdenum di-silicide or combinations of these and comparable available materials.