GB1152783A - Process for Producing Shaped Glass-Ceramic Articles - Google Patents

Abstract

1,152,783. Glass-ceramic articles. OWENS-ILLINOIS Inc. 1 July, 1966 [1 July, 1965], No. 29558/66. Heading C1M. A process for the production of shaped glassceramic articles, which have an inner surface, e.g. bottom and side-wall and a top edge, comprises pressing a gob 22 of a crystallizable glass composition in a mould 24 to its desired shape 32, removing the shaped article from the mould, annealing the article after its removal from the mould and effecting controlled nucleation and crystallization of the glass, at least the inner surfaces of the hot, shaped article being heat-glazed by means of externally applied heat while the article is still in the mould, the heat glazing being sufficient to initiate uniform softening of the crystallizable glass but insufficient to cause premature crystallization thereof. Preferably the externally applied heat is that of a directly applied flame swept across the inner surfaces of the hot, shaped article for 0À2 to 3 seconds at a flame temperature of 2500‹ to 3300‹ F. A gob 22 of suitable composition is fed from a feeder into a mould at a station 12 of a rotary turret press-moulding machine. At the first index the gob 22 is pressed out (e.g. at 5500 to 11,000 p.s.i.) to form the article. The plunger retracts and the machine indexes one or two stations at each step depending whether the machine has an even or an odd number. Here a plurality of burners 34, mounted for vertical reciprocation or horizontal rotation only about the vertical axis passing through the centre of the mould, heat-glaze the inside walls and top edge of the article to eliminate haze formation in the glass. The article is then indexed to a cooling station and is finally removed to an annealing lehr where nucleation and crystallization is also effected. The heat-glazing step may be effected over several stations if desired. The machine may also operate on double-gob. If desired during the heat glazing a water-cooled ring may be suspended above the mould. A suitable glass composition would fall within the ranges in weight per cent -SiO 2 66-73, Al 2 O 3 15-19, Li 2 O 2À5-4, MgO 3-7À7, ZrO 2 1-1À7, TiO 2 1- <1À9, SnO 2 0-1À7, P 2 O 5 0-3, BaO 0-5, ZnO 0-3 where the total of ZrO 2 + TiO 2 + SnO 2 + P 2 O 5 is at least 2À8 and the total of Li 2 O + MgO is from 6À3 to 10À5. However, the TiO 2 content may fall within the range 1À9-<2À4 weight per cent.