Gas ranges for home and commercial applications typically include gas burners 10 (see FIG. 1) located on the top cooking surface of the range. Gas is delivered to these top burners 10 as indicated by gas flow arrow 22 through the burner base 12 from a distribution manifold (not shown) which is controlled, typically, by twist-type control valves to allow the user to adjust the amount of gas flowing to the surface burner, thus allowing an adjustment of the flame setting resulting therefrom. Many of these gas burners 10 are circular in shape and contain an inner manifold defined between the burner base 12 and the inner surface burner cap 14 which distributes the gas evenly to each of a plurality of openings 24 which are defined by a vertical portion 23 on the burner base 12, and which are accommodated by a ridge 19 defined in the inner surface, and through which the gas flows to establish the cooking flames. Mixing of air and gas may be aided by the inclusion of a concave surface feature 20 included on the inner surface of the burner cap 14 which results in a more efficient burn mixture. Once the air/gas mixture has left the internal manifold through the plurality of openings 24 it is ignited to produce a plurality of cooking flames around the periphery of the gas burner 10 to allow for cooking on the surface of the range. For cosmetic appearance, a burner cover 16 may be included in the burner assembly 10.
As discussed briefly above, each of the individual gas burners 10 includes a gas burner cap 14 which forms the upper wall of the internal manifold and the upper surface of the gas burner itself (or may alternatively be covered by the burner cover 16 as desired). A typical gas burner cap 14 includes spacer/locator legs 18 which allow the cap to be properly positioned in relation to the burner base 12 of the individual burner assemblies 10. Because these gas burner caps 14 are subjected to high heat, at times approaching 900.degree. F. to 1000.degree. F., these caps have typically been manufactured from a cast iron material which is coated with a porcelain coating. The use of cast iron with a porcelain coating allows the burner cap to survive the high cap temperature which results from a low flame burner setting where the flames are allowed to exist just at the edge of the burner cap, and may slightly curl around the edge of the burner cap. While to use of porcelain coated cast iron allows the burner caps to survive these high temperature situations, the use of such a cap is cost prohibitive. Specifically, the use of cast iron is relatively expensive, compared to other materials which are available on the market. Additionally, the porcelain coating process of cast iron often results in bubbles or cracks in the coating on the cast iron burner cap. Since such cracks or bubbles may result in premature failure of the burner cap, not to mention having a poor appearance, such caps cannot be used and must be rejected in the quality review process, making it difficult to maintain acceptable yields from this process. Such problems result in unacceptably high scrap rates, thereby increasing the overall cost of manufacture of the burner caps as well as adding to the cost of the completed gas cooking range itself.
An alternative to the use of porcelain coated cast iron burner caps is to use burner caps which are constructed from forged brass. While the use of brass is advantageous due to its excellent heat transfer properties, the cost of using such material, as well as the cost of the process to form the burner cap itself, is also cost prohibitive. In the consumer appliance industry, where literally hundreds of thousands of units are manufactured, such cost inefficiencies as exist with using conventional porcelain coated cast iron burner caps or forged brass burner caps unacceptably adds to the overall cost of manufacturing these ranges, thereby unacceptably affecting the profitability of the product. Because of the cost impact of this one area of the range, cost reduction of the burner cap and its method of manufacture has been the focus of a concerted effort throughout the industry.
As part of this effort to reduce the cost of material and manufacture of burner caps, the use of aluminum as the material from which to manufacture these burner caps has been investigated. Aluminum was initially chosen to be investigated because it is light weight, inexpensive, and easily molded into various shapes through conventional and relatively inexpensive die casting processes. However, it was found that when gas range burner caps were manufactured from aluminum using a conventional die casting process, the aluminum burner caps failed under the high cap temperature condition of a low flame setting on a conventional gas range. As explained above, this low flame setting of a conventional gas range results in the temperature of the gas burner cap reaching temperatures of between 900.degree.F. to 1,000.degree. F. While initially believed to be only approximately 95% of the eutectic temperature of the aluminum material used to construct the burner caps, such conditions resulted in the melting of the die cast aluminum burner caps.
In view of these initial failures, it became important to characterize the reasons for the failure, and to determine a method to overcome these failures if an actual cost reduction in the overall cost of manufacture of these burner caps would be realized.