High rate cooling furnace for metal strips

Abstract

In an apparatus that rapidly cools heat treated metal strips with a recirculating nitrogen-hydrogen cooling gas mixture having a hydrogen content which ranges between 15%-50%, and a recirculation circuit for the gas mixture having a fan for creating a flow though recirculation ducts connected, through expandable compensator corrugations, upstream to at least one gas/water exchanger, a safety system operates with the exchanger. The safety system includes a housing having a main flow area upstream of the exchanger and into which recirculating cooling gas flows. A first register is interposed across the main flow area for selectively switching between open and closed states thereby passing or blocking flow through a major portion of the main flow area. At least one bypass flow area is defined within the housing and located adjacent the main flow area. A second register is interposed across the bypass flow area for selectively switching between open and closed states thereby passing or blocking flow through the bypass area. Respective sensors react to a break in the strip or the corrugation, or an interruption of power, and actuators rapidly respond to a plurality of dangerous conditions for activating the sensing means and for switching the first and second registers in accordance with the particular dangerous conditions.