for and use it to optimize service life.
Handle Your Crucible With Care When your crucible arrives on your
receiving dock, perform an inspec- tion to verify it did not suffer ship- ping damage. First, make sure it was well protected with packing materials during shipment and the materials are intact. Next, clear away enough of the packing to gain a clear view of the entire crucible. Examine the crucible as you would a new car delivered to you off the showroom floor. Look for chips, visible cracks, abrasions or other surface damage. If you see or suspect damage, contact your crucible supplier. Never place a damaged crucible in ser- vice. It is likely to fail and is a serious safety hazard. If the new crucible passes your
inspection, move it carefully to stor- age or the furnace. Ideally, crucibles should be moved on the pallet or in the shipping carton. Certain actions must never be performed when moving a crucible: • Never roll the crucible. Rolling it on its side, base or top will crush the protective glaze and possibly damage the underlying material. Damage to the glaze will lead to oxidation of the crucible.
• Never stack one crucible inside another. The weight of the top crucible can fracture the lower one, while abrasion where the inner and outer surfaces make contact will damage the pro- tective glaze. When stacking crucibles, separate them with hardboard or similar material.
• Never set crucibles directly on the floor. The hard surface may dam- age the bottom. More importantly, the crucible may absorb humidity coming from the floor and create thermal shock when heated. Set the crucibles on pallets.
Fig. 1. A properly positioned base for crucible mounting should be level, properly centered in the furnace, and larger than the crucible bottom.
• Never use banding directly on the crucible to secure it during move- ment. Add padding under the band to protect the surface. Crucibles should be stored at
temperatures above 32F (0C) in a dry area. Cold or wet crucibles should not be placed into service because they could cause dangerous water or molten metal explosions.
Installing Your Crucible Furnace crucible installation
processes differ based on furnace type, size and design, but several standard practices should be followed: • Inspect the crucible immediately before installation to be certain it is not damaged from handling and storage and its temperature is above the freezing point of water. If the crucible was subjected to high humidity, it could be damaged by thermal expansion in the walls if the temperature drops below the freez- ing point. A damaged crucible must not be installed.
• Make sure the base block is level, properly centered in the furnace, at
Once the crucible is purchased and
delivered, it’s up to you to properly care for and use it to optimize service life.
Fig. 2. Gripping blocks located too close to the top of this crucible produced a vertical crack.
September 2011 MODERN CASTING | 43
the correct height and larger than the crucible bottom (Fig. 1).
• For larger crucibles, use secure straps or a lifting mechanism designed for the specific crucible to lift it into the furnace. Center it on the base block and ensure it is level.
• Provide at least a 0.33-in. (8-mm) gap between the crucible and the top and sides of the furnace to allow for crucible expansion. An insufficient expansion gap will result in cracking.
• If the crucible has a spout, be sure at least a 1.5-in. (38-mm) gap exists between the spout and the furnace
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