Apparatus and method for bend-shaping a glass sheet

A method for bend-shaping a glass sheet in a bend-shaping apparatus including a heating furnace having an outlet positioned downstream of a path of transfer of the glass sheet, a plurality of in-furnace beds disposed within said heating furnace, at least one out-furnace bed disposed externally of said heating furnace proximately to said outlet in end to end relation to that one of said in-furnace beds which is positioned proximately to said outlet, said in-furnace beds and said out-furnace bed having upper surfaces curved transversely, said method comprising the steps of:

• elevating a downstream end of said one in-furnace bed and an upstream end of said out-furnace bed to a predetermined bed inclination height H so that said one in-furnace bed and said out-furnace bed jointly form a hill which allows to impart a desired radius of curvature C to the glass sheet, said bed inclination height H being obtained by first determining a first relation between the bed inclination height H and an apparent bed radius of curvature R on a basis of a length L1 of said one in-furnace bed forming an uphill of said hill, a length L2 of said out-furnace bed forming a downhill of said hill, the bed inclination height H, and a length G of the glass sheet in a direction of transfer thereof, and then determining a second relation between the apparent bed radius of curvature R and the desired radius of curvature C of the glass sheet;
• heating the glass sheet in said heating furnace to a substantially softening temperature of the glass sheet and jetting hot air from said upper surfaces of said in-furnace beds to floatingly support the glass sheet in such a manner as to allow the glass sheet to bend by own weight thereof transversely complementarily to the shape of the transversely curved in-furnace beds;
• transferring the transversely bent glass sheet over said hill so that the glass sheet bends longitudinally complementarily to the shape of the hill sloped in said direction of transfer;
• and
• transferring the bi-directionally bent glass sheet past said outlet onto said out-furnace bed and jetting cold air from said upper surface of said out-furnace bed to cool the bi-directionally bent glass sheet while supporting the latter in a floated state.