GRAIN STABILITY OF CALCINED PETROLEUM COKE: ASTM D6791
EXPLANATION
The grain stability of calcined petroleum coke determines the resistance to breakdown of +4 mm particles used in the manufacture of carbon anodes for use in the reduction process of aluminum. Cokes have to be relatively easy to grind for fines production but strong enough to withstand forming pressures and thermal stresses occurring when the anodes are used in the reduction process. This test method covers a laboratory vibration mill for the determination of grain stability of calcined coke for the manufacture of carbon products used in aluminum smelting. Calcined coke with poor mechanical strength may become degraded during mixing. Poor grain stability will affect the grain size and may result in poor quality of baked blocks.
TEST SUMMARY
A representative sample of calcined petroleum coke is dried and screened to a 4 mm to 8 mm fraction. The resultant sample is weighed so that two separate portions of 100.0 +/- 0.5 g mass are obtained. The samples are placed into the laboratory mill and ground for a specific period of time. After grinding, the sample is screened and the mass of the +4 mm material is determined. The grain stability is the percent of the original materials remaining on the +4 mm sieve.
No material normally applied to the calcined petroleum coke is found to cause analytical interference with this procedure.
TEST PRECISION
Repeatability: 2%
Reproducibility: 3%
Since there is no accepted reference material suitable for determining the bias for the procedure in this test method, no statement on bias can be made.
