HOLLOW INGOT Russian patent published in 2013 - IPC B22D7/04 

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy. Ingot features wall expanding upward to taper φ and annular discard all around the ingot top perimetre. At H_in / T_w ≥ 1 wall taper at distance 2T_CT from ingot end makes 5-6%, while annular discard thickness T_an makes 1.1 T_wt ^av( 1+1/a) or, for heat-insulation discards, 0.9T_w ^av(1+1/a), where T_w ^av is ingot wall mean thickness, mm, a is preset value of discard height-to-thickness ratio- H_an to T_an = 1.0-2.0.

EFFECT: ruled out shrinkage defects.

1 dwg