Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1999-02-04
2001-06-26
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S385000, C219S521000, C373S112000, C432S258000, C432S135000, C433S032000
Reexamination Certificate
active
06252202
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a kiln, furnace or the like and more particularly to a furnace for use in firing and/or pressing of dental materials.
BACKGROUND OF THE INVENTION
Dental materials include porcelain facings, veneers, porcelain bridges, porcelain inlays, ceramic jacket crowns, all ceramic crowns, and a multitude of other porcelain dental products. Dental ceramics are typically fired in an inert environment such as in a vacuum atmosphere. Bottom loading furnaces can be used to heat treat the materials whereby the material to be heat treated is set on the lower shelf and is raised to an upper heating chamber for the heating process. Alternatively, a furnace, such as a pressing furnace, may have a stationary bottom shelf for placement of the material to be heat treated which may include the step of pressing the material into a desired form. In this type of furnace, the heating chamber is lowered over the material and the heating process commences. Although bottom-loading furnaces tend to have more uniform heating within the heating chamber than front loading furnaces, which experience cold spots at the front of the unit, nonuniform heating may still occur. The placement of the piece to be treated on the lower unheated insulation block may result in the occurrence of cool spots or insufficient predrying of the piece. As a result, longer soak times are required to heat the pressing mold and/or firing plate. Moreover, if the temperature distribution is uneven, workpieces treated in the same lot will be subject to variation in quality.
There remains a need to reduce cold spots in the furnace and provide uniform heating throughout the heating chamber of the furnace. It is desirable to provide a furnace for heating dental materials having a uniform heating atmosphere without compromising the efficiency and operation of the furnace.
SUMMARY OF THE INVENTION
These and other objects and advantages are accomplished in a furnace generally including an upper heating chamber and a lower work base or firing platform. The upper chamber provides the main source of heat to the materials to be heat-treated. The upper chamber contains a muffle within which is located a heater ring assembly. The heater ring assembly is located in the middle to upper half of the muffle and includes an annular heating element that is located between an outer insulation ring and an inner quartz sleeve. A cavity or channel extends through the muffle into which insulation materials and the heater ring assembly is located. The channel area in the muffle below the heater ring assembly allows for the placement of the firing platform therein. The firing platform includes insulation material and a heating element located in the upper portion thereof. The heating element located in the firing platform provides heat to the firing platform such that when the firing platform is positioned within the muffle channel, heat is more evenly distributed throughout the heating area. Cold spots which typically occur in the lower section of the heating area in conventional furnaces are reduced or eliminated in the furnace of the present invention due to the incorporation of the heating element in the firing platform. In one embodiment, the furnace of the present invention may be designed with the firing platform in the form of a stationary work base and the upper chamber movable from open to closed position. Accordingly, the furnace may be utilized as a pressing or porcelain furnace.
In an alternate embodiment, the furnace may be designed with the firing platform being movable from open to closed position. A movable firing platform in accordance with the present invention may include a linear support assembly that operates to move the firing platform into the muffle channel. A linear conductor assembly is also included to provide power to the heating elements. The linear conductor assembly includes copper conducting rods and a brush holder assembly that includes spring loaded brushes. The brushes maintain contact with the conducting rods to provide power to the heating elements without the inclusion of loose or stray wires. Accordingly, the possibility of the breakage of loose wires is reduced or eliminated by the incorporation of the linear conductor assembly.
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McPhee ER, “Hot Compressed Porcelain Process for Ceramo-Metal Restorations”, pp. 245-250.
Jeffery John A.
Jeneric/Pentron Inc.
Knab Ann M.
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