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VERSION:2.0
METHOD:PUBLISH
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ORGANIZER;CN=ESTAD 2023:mailto:info@metec-estad.com
LOCATION:Room 19b
SUMMARY:Vacuum induction melting (VIM):  Elimination of crucible spout skull build-up
DESCRIPTION:Liberty Speciality Steels operates a Vacuum Induction Melting (VIM) facility to produce high-performance iron and nickel-based alloys for applications in the aerospace and auto-sport industries. The paper describes process development work designed to minimise the incidence of spout skull build-up, the accumulation of solidified metal within the crucible pouring spout during ingot casting. Skull build-up must be manually removed after pouring of the heat, which requires unnecessary breaking of the vacuum between melts and leads to operational delays.

A bespoke thermal model has been developed to help identify potential root causes of spout skull formation. Model simulations with the initial VIM power profile (kW as a function of crucible tilt angle), indicated that the pour stream temperature can fall below the solidus towards the end of pouring resulting in skull build-up. A revised power profile was devised, with the aim of maintaining a constant pour stream temperature. It was recognised that this could impact the solidification dynamics in the ingot head and the formation of the shrinkage cavity.
 
A series of casting-simulations was carried out using the Magmasoft 3D package to determine the sensitivity of shrinkage-cavity size and depth to final pour stream temperature. Simulations for a constant pour stream temperature indicated a small decrease in the extent of pipe-cavity compared with the cooling pour stream situation. Predicted changes to cavity depth for different power profiles were judged to be insignificant. Measurements of cavity depths from sectioned ingots showed close agreement with model predictions. Production trials were undertaken across a range of alloy grades, using various power profiles designed to maintain a more constant pour stream temperature. Significant reductions in the extent and frequency of skull accumulation in the pouring spout were achieved, with associated reductions in operational downtime.

CLASS:PUBLIC
DTSTART:20230615T145000
DTEND:20230615T151000
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