Patent ID: 8317926

Claim:
A fluidized bed furnace for heat treatment of metal substrates, said fluidized bed furnace including: a retort having an access opening for introduction into and removal of metal substrates from said retort and containing inert particulate refractory material adapted to be fluidized in use; heat supply means to maintain a predetermined temperature or temperature range within said retort; a first gas supply means arranged to provide a first inert gas flow entering said retort at a lower region thereof through first distributor means to fluidize the particulate refractory material in said retort; a second gas supply means arranged to provide a second gas flow entering said retort at or adjacent said lower region thereof separately to said first inert gas flow through second distributor means, said second gas supply means including heating means to heat said second gas flow before said second gas flow enters the retort; means to combine a halide gas in a predetermined proportion with an inert carrier gas to form said second gas flow externally of the retort; cover means to open or close said access opening, said cover means closing said access opening during a treatment process; and a first seal means operable between said cover means and said retort when said cover means is positioned to close said access opening; wherein said first seal means includes a first inner peripheral seal and a second outer peripheral seal each surrounding said retort access opening and defining a first seal zone therebetween, means being provided to introduce an inert gas under pressure into said first seal zone substantially continuously when said cover means is closed during a said treatment process whereby, in use, any inert gas in said first seal zone tends to leak in a direction towards the access opening providing access to said retort; wherein said first seal means includes a third peripheral seal located inwardly of said first inner peripheral seal, said third peripheral seal including a peripheral flange portion positionable in a third seal region containing inert particulate refractory material when the cover means is positioned to close said access opening, a gas flow supply means being provided to said third seal region to fluidize the inert particulate refractory material therein at least when the cover means is being moved to a position closing said access opening.