Heat treating glass sheets on a roller hearth conveyor

An apparatus for heat treating glass sheets comprising:

• a tunnel-type furnace having entrance and exit openings in the ends thereof and provided with means for heating glass sheets to a temperature suitable for tempering, at which temperature the glass sheets are in a softened condition which renders them susceptible to roll ripple distortion, a quenching station having means for directing tempering medium against opposite surfaces of glass sheets, and a roller conveyor adapted for transporting glass sheets sequentially through said furnace and then said quenching station along a generally horizontal path, said roller conveyor comprised of a plurality of rolls each having a cylindrical sheet-supporting portion extending transversely to the direction of glass sheet movement and presenting a substantially horizontal line of contact with the glass sheets, said conveyor having a predetermined zone extending from a location within the furnace close to the exit end of the furnace to a location within the quenching station, a portion of the conveyor upstream from said predetermined zone presenting roll ripple inducing conditions to glass sheets passing thereover, the rolls in said predetermined zone having small diameters and being sufficiently closely spaced and being aligned with one another to a sufficient degree of accuracy such that the lines of glass contact lie essentially within a common horizontal plane to significantly reduce the severity of roll ripple distortion caused by said roll ripple inducing conditions upstream from said predetermined zone.