Roller hearth furnace for glass sheets

Abstract

A roller hearth furnace having a plurality of horizontally elongated furnace modules aligned with each other in an end-to-end relationship so a roller conveyor may carry glass sheets horizontally through the furnace and thereby heat the glass prior to tempering. Each furnace module has a hollow construction with a circular cross-section defined by a semicircular lower housing portion and a semicircular upper housing portion. A separate counterbalance mechanism associated with each upper housing portion supports it independently of the others for movement between a lower closed position immediately over its associated lower housing portion and an upper open position where the interior of its associated lower housing portion is accessible. The counterbalance mechanisms each include four chains attached to counterweights in a manner that permits counter-balancing of the associated upper housing portion even if one chain should break. One chain of each counterbalance mechanism is driven by an associated reversible electric motor to raise and lower its upper housing portion, and a separate elongated operator handle extending along the length of each upper housing portion is coupled to the motor thereof so an operator can control the motor operation from any position along the length of the particular furnace module. Each upper housing portion includes end walls that mitigate heat loss when one of them is open while adjacent ones are closed. Upper and lower end walls at each end of the furnace are reinforced to maintain horizontal openings of uniform size where glass enters and leaves the furnace.