Glass sheets are tempered to provide increased mechanical strength and the characteristics of breaking into small pieces without forming sharp slivers as is the case with annealed glass. Conventionally, tempering of glass is performed by heating and subsequent sudden chilling performed at a quench station between opposed blastheads. Quenching gas, which is conventionally air, is supplied to the opposed blastheads to perform the sudden chilling that tempers the glass. Best results are obtained when the quenching gas is supplied in a perpendicular relationship to the glass sheet since a more uniform distribution of the gas and the consequent cooling is achieved.
U.S. Pat. No. 4,300,937 discloses a glass tempering blasthead which includes, in a first embodiment, jet assemblies which are made by welding complementary stampings together and filling in the open ends with matching plates. In a second embodiment, each jet assembly is fabricated by welding a series of spacer elements between opposite side members to thereby produce a series of tubes.
U.S. Pat. No. 3,936,291 discloses a glass tempering blasthead that is fabricated from stamped metal components of a generally U-shaped cross section. Each of the stamped metal components includes legs that are formed to define nozzle passages when placed adjacent another like component. With such a blasthead, a single stamping die set can be utilized to stamp the required components. This blasthead has particular utility when utilized to temper flat glass as each of the nozzle passages discharges the cooling gas in an orientation perpendicular to the plane of the heated glass sheet to be tempered.
U.S. Pat. No. 3,393,062 discloses glass sheet tempering apparatus which, in one embodiment, includes individual tubes that are disposed along curved manifolds extending therefrom so as to be oriented generally perpendicular to a curved or bent glass sheet to be tempered. Such orientation provides better quenching gas distribution during cooling of a bent glass sheet and thereby provides a better product than would be the case with parallel tubes or passages. However, fabrication of this type of apparatus would be relatively expensive since the manifolds and tubes would have to be individually designed and fabricated for each particular bent shape to be tempered.
It is important with these types of apparatus to maintain uniform air flow and pressures. Conversely, it is highly undesirable to subject the heated glass sheet to any significant variation in pressure over its surface, especially for thin glass.
It is also desirable that the passages through which the cooling gas flows be constructed so as to reduce the amount of energy required to provide the cooling air while at the same time minimize back pressure effects particularly for thin glass.