Electric resistance heating devices – Heating devices – Continuous flow type fluid heater
Reexamination Certificate
2000-06-13
2001-12-04
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Continuous flow type fluid heater
C392S467000
Reexamination Certificate
active
06327429
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to heaters used in automatic coffee makers. More specifically, this invention relates generally to the configuration of the base plate, heater element and water tube found in automatic coffee makers.
2. Description of the Related Art
Drip coffee makers typically include a base plate, a water tube and an electric heater element. The purpose of the heater is two-fold. The heater is used to boil water which flows into the water tube. The heated water expands and flows to the top of the coffee maker where it descends through the coffee grounds and into the coffee pot. The heater also warms the base plate which keeps the brewed coffee hot after it is brewed.
It is known in the art to die cast coffee maker base plates out of aluminum. A known configuration includes a cast channel projecting from the bottom surface of the base plate. An appropriately shaped water tube is press fit into the channel to a position adjacent to the bottom surface of the base plate. A heater element is then press fit into the channel below the water tube so that the water tube is between the heater and the base plate. In this configuration, the heater has direct contact with the water tube at a point along the length of their respective tubular circumferences. The heater has direct contact with the base plate along either side of its tubular circumference where the heater is adjacent to the base plate channel. A heater in this configuration heats water in the water tube by direct contact and indirectly via heating of the base plate.
Another existing design uses an aluminum extrusion where the water tube and heater channel are manufactured as a single part. The heater channel and water tube are extruded so that they share one longitudinal surface. The water tube is placed between the heater and the base plate. In this configuration, the heater heats the water tube directly and the base plate indirectly via the water tube.
These prior art designs share several problems. First, the aluminum castings or extrusions are relatively expensive to manufacture. Second, the aluminum materials have properties (such as a relatively low melting point) which limit the power of the heating element which can be used. Third, these designs produce a narrow contact interface between the heater and water tube. The small contact surface between the water tube and the heater does not permit the efficient transfer of heat from the heater to the water tube. Finally, many consumers claim that the aluminum materials adversely affect the taste of the coffee. Aluminum is reactive with acids found in coffee and may actually be dissolved into the heated water and ultimately the brewed coffee.
SUMMARY OF THE INVENTION
A coffee maker heater in accordance with the present invention comprises a heater, water tube and base plate made of steel materials. In a preferred embodiment, at least the water tube and heater are joined directly to each other by brazing. In an alternative embodiment, the water tube and heater element are separately brazed to a thickened base plate. Another alternative embodiment includes punching tabs from the base plate which extend on either side and between the heater and water tube. The tabs further increase the surface area contact between the heater, water tube and base plate. A still further alternative embodiment may utilize a pre-formed stainless steel channel having a location for the heater element and a portion to house the water tube. The heater and water tube are brazed within the stainless steel channel. This configuration allows for heat transfer via the copper brazing and the stainless channel. The brazing material is preferably copper-based.
The steel materials are preferably stainless steel alloys used in the food service industry. These materials may be standard plate and tubular items, manufactured and sold for food service use. Stainless steel is far less reactive with hot liquids than aluminum and has much improved heat tolerance. According to one aspect of the invention, standard stainless steel products can be formed to the desired configuration and brazed together to form the coffee maker heater assembly. Use of standardized materials eliminates the expensive casting and extruding steps required by prior art designs.
A copper brazed junction between the water tube and heater (or alternatively the heater and base plate) greatly improves both the surface area and the thermal conductivity of the junction between heat producing and heat receiving parts of the coffee maker.
The increased heat tolerance of steel materials permits use of high power heater elements. A high power heater element combined with the improved heat transfer characteristics of the junction between components greatly shortens the brewing time over the prior art designs.
An object of the present invention is to produce a new and improved coffee maker heater which may be cost effectively manufactured from readily available steel materials.
Another object of the present invention is to produce a new and improved coffee maker heater which significantly shortens the brewing time of a coffee maker.
A further object of the present invention is to produce a new and improved coffee maker heater which permits the use of a high power heater element.
A still further object of the present invention is to produce a new and improved coffee maker heater which does not introduce aluminum in materials into the brewing water.
These and other objects, features and advantages of the invention will become readily apparent to those skilled in the art upon reading the description of the preferred embodiments, in conjunction with the accompanying drawings.
REFERENCES:
patent: 3878360 (1975-04-01), Augustine et al.
patent: 3953923 (1976-05-01), Rygmyr
patent: 5367607 (1994-11-01), Hufnagl et al.
Alix Yale & Ristas, LLP
Campbell Thor
Electrical & Electronics Limited
Walberg Teresa
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