8m borosilicate honeyqomb spin casting: Material developments

Creep and strength of candidate glass contact refractories for honeycomb casting molds were measured at 1200 C. Based on performance and cost, one material, Rex Roto Corp.'s R1162-17 speciality fiber mix, was chosen for the Steward's first 3.5m casting mold. More extensive measurements of firing shrinkage, thermal expansion, room temperature Young's Modulus, bulk density, and creep were carried out on R1162-17 samples cut from hexagonal box preforms. Test results indicate that R1162-17 hex boxes have acceptable creep resistance and the potential strength to withstand hydrostatic loading up to 66cm of borosilicate melt. In November of 1987, blocks of a low-expansion borosilicate glass, Corning Code 7761, was spin cast into a 1.2m honeycomb for the Smithsonian Astrophysical Observatory. The casting contained a relatively high density of small-scale striae and small bubbles along the remelted block surfaces. Origin of the small bubbles was traced to graphite particles imbedded in the glass surface during the forming operation. In spite of small-scale striae, the measured expansion coefficient variation over spacial scales greater than 1mm was less than t7x10~9/c.