Four melt shops compared a precast, segmented crucible lining with rammed, brick and monolithic linings, heat by heat.
Nickel superalloys, vacuum melting, thermal spray powders and aluminum composites.
Four furnaces, one lining principle, counted in heats
In four coreless induction furnaces from 1,500 lb to 12,000 lb, a precast, segmented crucible lining from Blasch ran more heats per campaign than the lining each melt shop used before: about 50% more than a rammed lining and than magnesia brick in nickel alloy furnaces, about twice as many as a rammed lining on aluminum composites, and five times as many as a monolithic crucible at up to 1,780 °C. Blasch documented the four cases in its case histories under the name Modular Lining System.
From about 500 kg of melt upward, thermal stress rather than wear decides how long a crucible lining lasts. A 3 ton alumina or magnesia lining can grow up to 7 mm in height as it heats. A rammed or monolithic lining has to absorb that growth inside one body, and it cracks.
The cracks let metal and slag in, the lining erodes at the melt line, and the furnace is relined before the refractory is worn out. Brick linings bring mortar joints that erode and leak.
A segmented lining is cracked on purpose, at joints that were designed to open and close, so the heat cycles that destroy a rammed crucible have nowhere left to break it.
A crucible lining built from precast, fired tongue and groove segments, set without mortar, with gaps that take up the thermal growth. A finite element comparison in Blasch's 2016 white paper shows clearly lower stresses for a segmented lining with expansion gaps than for rammed or mortared linings. A spring loaded hold down system keeps the stack in place.
| Furnace and alloy | Lining before | Heats before, typical | Heats with the segmented lining, typical | Payback |
|---|---|---|---|---|
| 12,000 lb, nickel alloys 625, 713, 718, pour at 1,590 to 1,700 °C | rammed | 18 to 20 | 25 to 30 | about 15 heats |
| 6,000 lb, nickel and cobalt alloys in vacuum, 1,590 to 1,700 °C | magnesia brick | 18 to 20 | 30 to 35 | 25 to 35 heats |
| 2,000 lb, Ni, Co, Cr, Al and Y alloys for thermal spray powder, 1,670 to 1,780 °C | monolithic crucible | 3 to 5 | 20 to 25 | about 10 heats |
| 1,500 lb, aluminum metal matrix composites with up to 20% SiC or alumina, 770 °C | rammed | 75 | 150 | 75 to 100 heats |
Blasch's tongue and groove crucible lining for coreless induction furnaces in air or vacuum.
Crucibles and linings for nickel and cobalt superalloys melted in vacuum. Vacuum induction melting
Crucibles, linings and flow control for foundries and melt shops.
Alloy, temperature and how many pours run at the top of the range all change lining life. Yttrium in particular is aggressive and builds slag.
The material can cost more, about twice a rammed lining in the aluminum furnace. Each shop calculated its own payback, between about 10 and 100 heats.
In the 6,000 lb vacuum furnace it did: the lining was cycled over weekends, while the magnesia brick before it had to be kept hot.
No. They come from four melt shops with different alloys and furnace sizes.
Send the furnace capacity, the alloys and how many heats a lining lasts today. A Blasch engineer sizes a segmented lining for your coil.
