Trough hearth construction and method for plasma arc furnace

Claim 3

The method as claimed in claim 1 wherein each said torch is angled downwardly towards the hearth during initial operation whereby each respective coluMn thereof contacts said depression in a minimum distance, rapidly melts a path in said material and upon sufficient melt collecting in said depression each said column contacts and includes said melt in electrical circuit therewith, and then angling each said torch while its respective column maintains contact with said melt in the depression in a manner to cause stirring of the melt in said depression during the early stages of melting said material.

Claim 4

The method of claim 1 including the step of positioning said torches through means remote to the furnace.

Claim 5

The method of claim 2 including the step of positioning said torches through means remote to the furnace.

Claim 6

The method of claim 1 wherein at least three said torches are employed.

Claim 7

The method of claim 1 wherein said depression takes the form of an annular depression in the hearth floor spaced inwardly from the furnace sidewall and said torches and columns are respectively directed towards and contact the melt in said annular depression.

Claim 8

The method of claim 1 wherein said positioning is effected axially, laterally and vertically by means remote from said furnace.

Claim 9

The method of claim 1 wherein said elongated pool collected in said depression is of sufficient length and positioned on the hearth floor so as to be contactable by the said main arc columns of at least two of said torches during initial melting of said material.

Claim 10

An electric furnace adapted for melting raw metallic materials and having side and bottom walls and a plural number of apertures extending through portions of said sidewalls comprising, in combination: a. a plurality of long arc column forming plasma torches individually mounted in said apertures and adapted for adjustable positioning therein; b. positioning means adapted to adjustably position each said torch with respect to the said hearth; c. a hearth forming the said furnace bottom wall and including a depression therein for collecting an elongated pool of molten metal disposed such that upon appropriate torch positioning a distance between each respective torch nozzle and the said pool may be maintained such that the ratio of depth to diameter of melted path being formed approximate 1 for the material being melted; and d. electrical circuit means connected to said torches and adapted to initiate a pilot arc in each said torch enabling the creation from each pilot arc of a main arc column for each torch, with each respective column including said material in electrical circuit therewith, subsequently enabling the transfer of each main arc column to the melt in said pool to form respective long arc columns passing through respective open melted paths free of said material and of substantially less resistance than provided by paths through the said material.

Claim 11

An electric furnace adapted for melting raw metallic materials and having side and bottom walls and a plural number of apertures extending through portions of said sidewalls comprising, in combination: a. a plurality of long arc column forming plasma torches individually mounted in said apertures and adapted for adjustable positioning therein; b. positioning means adapted to adjustably position each said torch with respect to the said hearth; c. a hearth forming the said furnace bottom wall and including a depression therein for collecting an elongated pool of molten metal disposed such that upon appropriate torch positioning a distance between each respective torch nozzle and the said pool may be maintained such that the ratio of depth to diameter of melted path being formed approximate 1 for the material being melted; and d. electrical circuit means connected to said torches and adapted to initiate a pilot arc in each said torch enabling the creation from each pilot arc of a main arc column for each torch, with each respective column including said material in electrical circuit therewith, subsequently enabling the transfer of each main arc column to the melt in said pool to form respective long arc columns passing through respective open melted paths free of said material and of substantially less resistance than provided by paths through the said material.

Claim 12

A furnace as claimed in claim 9 including control means adapted to remotely effect said positioning.

Claim 13

A furnace as claimed in claim 10 wherein said control means are adapted to effect said positioning axially, laterally and vertically.

Claim 14

A furnace as claimed in claim 9 wherein said depression is annular in form and whose collected melt is adapted to electrically connect at least two said long arc transferred columns.

Claim 15

A furnace as claimed in claim 9 wherein said electrical circuit means provides a multi-phase A.C. source and includes electrical connection of an internal electrode of each said torch being utilized with a separate phase of said source and electrical connection of a nozzle portion of each said torch with an adjacent phase of the source via an electrical choke whereby a potential may be established between said internal electrode and said nozzle of each said torch to initiate said pilot arc, and whereby said pilot arc may be transferred to a proximate raw metallic material to establish a direct phase-to-phase potential between at least two torches having main arc plasma columns in electrical contact with the said raw metallic material.