Method for the precision moulding of glass articles, method of manufacturing a mould, and mould for the precision moulding of glass articles

A method for manufacturing a mould for precision moulding glass articles comprising the steps of

• forming a glass preform capable of ion exchange by at least one of the operations of grinding and drilling,
• etching said preform to form a smooth surface,
• treating said glass preform by at least polishing to form an optically smooth surface and,
• carrying out a chemothermal ion exchange treatment of said glass preform to substantially prestress and reinforce said preform, such that said preform has a positive compressive stress at the surface of said preform, said compressive stress increasing to a maximum value and thereafter decreasing to zero within said glass preform, a core zone subject to a tensile stress, and a stress-free zone between said tensile stress and said compressive stress.

A mould for the precision moulding of glass articles comprising

• a glass mould structure having
• an edge zone with a penetration depth from the surface in the range of 100 to 200 .mu.m,
• said edge zone having a compressive stress profile which is positive at zero penetration depth at said surface, increases to a maximum value, then decreases to zero,
• a core zone subject to a tensile stress, and
• a stress-free zone between said edge zone and said core zone.

A method for precision moulding glass articles comprising the steps of

• preparing a glass mould having a positive compressive stress at the surface, said compressive stress increasing to a maximum value and thereafter decreasing to zero, a core zone subject to a tensile stress, and a stress-free zone between said tensile stress and said compressive stress,
• inserting a glass article into said glass mould,
• heating said glass article to a moulding temperature in the vicinity of the American softening temperature of said glass article,
• pressing said glass article in said glass mould at a pressure between 400 to 700 kPa to form a moulded glass article, and
• removing said moulded glass article from said glass mould.