Abstract: A constitution of cover glass, the compositions consist in terms of weight % on the oxide basis, of from 64 to 69 wt. % of SiO2; from 7 to 11.5 wt. % of Al2O3; from 1.5 to 2.5 wt. % of B2O3; from 4.5 to 7.5 wt. % of MgO; 0%<CaO?2.5%; 0%<ZnO?2%; 0%<ZrO2?0.2%; 0%<TiO2?1%; from 14.5 to 16.5 wt. % of Na2O; from 1 to 4 wt. % of K2O; and 0%<SnO2?0.4%. The constitution then can be melted to form cover glass. Thereafter, the cover glass is dipped in KNO3 solution so that sodium ions, which is smaller in volume, contained in certain depth from the surface layer of the cover glass can be substituted by potassium ions, which is larger in volume. In this manner, squeezing effect is generated on the surface layer so as to form cover glass having high strength and resistance in both abrasion and scratch.

Abstract: A composite glass forming system applied in the process of producing sheet glass mainly comprises a slotted nozzle downdraw glass forming device and an overflow downdraw glass forming device. The slotted nozzle downdraw glass forming device possesses a nozzle and the overflow downdraw glass forming device is located below the said nozzle. When glass liquid is injected into the slotted nozzle downdraw glass forming device, the glass liquid will flow down through the nozzle to a flow guiding surface formed on the overflow downdraw glass forming device. Then, the overflow downdraw glass forming device makes glass liquid in shape of thin smooth surface sheet glass by using overflow downdraw method.