170 Control for Aluminum Production
But, there was something not right. Rob scanned the other control points.
They showed
• increased long anode effects on some pots due to these getting
sludged up badly, as they had experienced before;
• mechanical problems with anode jacking systems due to failure of
jacks when making down orders during metal tapping; heavy bot-
tom deposits and ledging on these pots; and
• looking closer at the voltage chart, the box and whisker chart
showed a tendency for increased variation in voltage across the
potline over the last month or so, even as the average voltage was
still coming down.
Rob had that familiar, queasy feeling in the pit of his stomach. Something’s
not right—the needle in the haystack feeling. But ...