97Diagnosing Variation in Materials Processing
The properties of the anodes and, in particular, their variability should
be studied in parallel from baked anode core data:
• Differential reactivity of pitch due to baking temperature or
composition (sodium content, for example, although this would
also cause dust)
• Carbon resistivity variation
• Permeability and other properties
In fact, there are likely to be a number of factors involved in any case of
airburn. This makes it especially difcult to use classical univariate SPC
(statistical process control) to deduce the cause from an out-of-control
signal and track down a single process change that corresponds to it. In
fact, there may be multiple variables “signaling” in the proximity of the ...