Method for the forming of glass or glass ceramics
A process for forming glass or glass ceramics is disclosed, wherein a glass ceramics form ( 12 ) is made from a starting glass by molding, which is transformed by a heat treatment into a keatite glass ceramic comprising predominantly keatite mixed crystals. With such a keatite glass ceramics form ( 12 ) formed bodies can be prepared from blank parts by sagging under gravity force at a temperature above the glass transition temperature of the blank part ( 14 ) (FIG. 1 ).
1. A method for the hot forming of X-ray mirror substrates from a borosilicate glass comprising the following steps:
preparing a mold from a lithium-aluminosilicate base glass by casting and subsequent heat treatment for transforming into a keatite glass ceramic comprising at least 80 vol.-% of keatite mixed crystals;
mechanically finishing the mold to a desired shape and surface quality;
preparing a blank plate of a borosilicate glass for hot forming;
polishing said blank plate on both surfaces;
sagging said blank plate under gravity force onto said mold at a temperature above the glass transition temperature of the blank plate; and
cooling the blank plate, after sagging, to room temperature at a controlled cooling rate of about 0.1 K/min, thereby producing a formed body.
2. The method of claim 1 , wherein sagging of the blank onto the glass ceramic mold is assisted by applying a vacuum.
3. The method of claim 1 , wherein sagging of the blank onto the glass ceramic mold is assisted by applying an excess pressure.
4. The method of claim 1 , wherein producing of the formed body is performed under clean room conditions.
5. The method of claim 1 , wherein the glass ceramic mold is designed concavely when the coefficient of thermal expansion of the mold is smaller than that of the blank.
6. The method of claim 1 , wherein the glass ceramic mold is prepared with a Wolter's profile.
7. The method according of claim 1 , wherein the formed body after having been formed is mechanically finished.
8. The method according of claim 1 , wherein a reflective coating is applied to the formed body.
9. The method of claim 1 , wherein said blank plate of borosilicate glass is one of the group consisting of BOROFLOAT® (borosilicate glass) glass plate, a DURAN® (borosilicate glass) glass plate and a PYREX® (borosilicate glass) glass plate, and wherein said sagging step is performed at a temperature between 550° C. and 850° C.
10. A method for the hot forming of glass or glass ceramics comprising the following steps:
preparing a mold from a lithium-aluminosilicate base glass by casting and subsequent heat treatment for transforming into a keatite glass ceramic mainly comprising keatite mixed crystals;
providing a blank plate of glass or glass ceramics for hot forming;
polishing said blank plate on both surfaces;
sagging said blank plate under gravity force onto said mold at a temperature above the transition temperature of the blank plate;
cooling the blank plate, after sagging, to room temperature at a controlled cooling rate of about 0.1 K/min.