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Graphite Properties and Application in Molten Metal Pumps

20
Dec

Graphite Properties and Application in Molten Metal Pumps

Graphite Shapes

Graphite components at various process steps.

Graphite is the refractory material of choice for many non-ferrous molten metal pump applications. Below is a list of graphite characteristics that are important in pump applications:

  1. Dimensional Integrity – Graphite maintains mechanical dimensional integrity across a wide range of temperatures. Unlike steel alloys that bend and twist, graphite remains dimensionally stable and displays relatively low thermal expansion.
  2. Thermal Shock Resistance – Graphite can tolerate significant thermal stresses better than many other refractory materials including silicon nitride.
  3. Floats in Molten Metal – Graphite’s relatively low specific gravity of 2.26 causes it to be buoyant in most molten metal applications.
  4. Non-Wetting in Zinc – Graphite does not wet in zinc, so a drip-dry graphite pump sheds 99% of the zinc. This makes servicing the pump faster and easier.
  5. High Thermal Conductivity – Graphites high thermal conductivity reduces preheat times (and reduces the risk of thermal shock.)
  6. Chemical Compatibility – Graphite is impervious to most chemistry, aiding in economic rework of certain pump components. Unlike most refractories, it is compatible with most molten salt solutions as well.
  7. Long Shelf Life – Graphite can be machined, treated, and retains a very long operational shelf life.
  8. Reuse and Rebuilds – Graphite components that are not exposed to oxidizing agents at high temperatures can usually be rebuilt several times before replacement is required.
  9. Oxidation Resistance – Impregnated with a proprietary oxidation inhibitor that substantially increases oxidation resistance, and improves atmospheric moisture resistance for improved shelf life. 
  10. Economical – From an overall ROI perspective, graphite is by far the best choice compared to the other refractory materials with favorable characteristics for building molten metal pumps.