Graphite Crucible: Storage, Maintenance, and Precautions

Storage and Handling

• Keep Dry: Store crucibles in a dry, well-ventilated area. Moisture is the biggest enemy of graphite and can cause cracking or spalling during initial heating.

• Avoid Direct Ground Contact: Place crucibles on wooden pallets or shelves, never directly on the damp floor.

• Stacking Rules: Avoid stacking smaller crucibles inside larger ones unless they are properly padded to prevent scratching or cracking.

• Handle with Care: Move crucibles using rolling pads or soft carts. Never roll them on their edges or drop them.

Installation and Preheating

• Correct Grip: Use tongs that fit the curvature of the crucible perfectly. Ill-fitting tongs will create localized stress concentration and crack the crucible.

  Base Support: The pedestal (base block) should have the same diameter as the crucible bottom and be made of the same material to ensure even expansion.

• The Crucial Preheating Process: Never heat a cold crucible rapidly. Follow this preheating cycle before first use or after a long shutdown:

  1. Heat slowly from room temperature to 200°C over 2 hours (to drive off moisture).

  2. Heat from 200°C to 600°C over another 2 hours at a steady pace.

  3. Rapidly increase to the working temperature.

Maintenance and Operation Precautions

• Feeding Material: Add charge material gently. Do not drop heavy ingots into the crucible, as the impact can cause mechanical fracturing.

• Thermal Expansion Space: Place ingots vertically, not horizontally. Metals expand when heated and can wedge against the walls, splitting the crucible.

• Flux/Additives Management: Add refining fluxes or additives only after the metal is fully molten. Do not let fluxes touch the empty crucible walls, as they are

  highly corrosive to the graphite matrix.

• Dross Cleaning: Scrape out remaining dross and slag while the crucible is still red-hot at the end of each shift. Hardened dross will contract differently than

  graphite during cooling, causing cracks.

• Avoid Over-Tightening: If using a furnace with burners, ensure the flame tangential circle does not hit the crucible directly, which causes localized overheating.