Electrical resistors – Incased – embedded – or housed – Element in insulation with outer metallic sheath
Patent
1976-12-01
1978-09-26
Envall, Jr., R. N.
Electrical resistors
Incased, embedded, or housed
Element in insulation with outer metallic sheath
338289, 219552, H05B 306
Patent
active
041172523
ABSTRACT:
A high temperature furnace particularly adapted for fusing crystalline silica includes a housing defining a heating chamber that receives electrically conductive elements with insulators positioned therebetween to establish an electrical flow path for heating the chamber. Resilient gas cylinders located externally of the housing bias graphite connecting rods that extend into the heating chamber to compress and position the conductive elements and the insulators therebetween while allowing expansion thereof during heating of the chamber. Graphite wall panels preferably define the housing heating chamber and have interlocking edges that position the panels relative to each other. Cooperable pairs of resilient gas cylinders at longitudinal ends of the furnace housing compress the wall panels to maintain the edges thereof in their interlocking relationship while permitting expansion during heating of the chamber. Preferably, the furnace is of the counterflow type with upper and lower conveying passages through the heating chamber and upper and lower heating portions that receive the conductive elements and the insulators. Graphite spacer blocks and heater bars provide the conductive elements while boron nitride discs provide the insulators that cooperate with the heating elements to provide a serpentine electrical flow path for heating the chamber. A conveyor automatically conveys graphite trays through the conveying passages in opposite directions. Pushers of the conveyor move the trays along the direction of conveyance while transfer mechanisms at the ends of the furnace automatically move the trays from one conveying passage to the other. Each transfer mechanism includes an indexer for moving the trays into and out of the housing and a table that moves the trays vertically. During indexing back into the housing from the table, scraper bars of the transfer mechanism engage leading and trailing edges of the trays to remove a parting agent that is applied to the trays to prevent the crystalline silica from reacting with the graphite tray material. Electrical terminals extend between an outer skin of the furnace and the heating chamber through carbon black powder insulation and have a construction that accommodates for longitudinal expansion of the heating chamber while maintaining a sealed relationship and limiting outward heat flow.
REFERENCES:
patent: 1533255 (1925-04-01), Little
patent: 1827508 (1931-10-01), Cope
patent: 4011395 (1977-03-01), Beck
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