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ture required to meet the pouring requirements of a particular met- alcasting facility is 2,600F. (1,427C) In this case more coke must be used (to about 9.5% ). Reaching 2,600F can only be accomplished at the peak in the mid-point of the curve which


corresponds to a blast volume ratio of approximately 2.0. Now suppose the metalcasting facility no longer needs the tonnage of iron produced by blowing at the ratio of 2.0, but only needs the tonnage produced by blowing at a ratio of 1.5. Tis would


produce iron at approximately 2,550F (1,399C), which is not suitable for pouring. Te coke percentage would need to be raised to about 13% to reach the 2,600F required. Te cupola is less efficient, but there’s nothing the operator can do about that. Many of the existing furnaces today are too big for what is needed yet it is a significant investment to change it.


What Do You Do? Keeping records of your cupola


operations aids your decision making when something goes wrong with the melt. Flow charts for situations like cold iron, insufficient melt rate or high back pressure are valuable tools to help new operators make better decisions as conditions change. For example, one of the worst things that can occur in a cupola operation is for the coke bed to get too low, causing both low iron temperature and chemistry issues. Tis will take 30 to 60 minutes to cor- rect by putting more fuel at the top. So what are the indications the


coke bed might be too low? The carbon equivalent, carbon or both are decreasing, the chill tests are trending up, spout temperatures are trending down, and in severe condi- tions unmelted metallics are seen through the tuyere. One method to check the coke bed


is to increase the blast by 10% and wait 10 minutes (Fig. 4). If the spout temperature increases, the coke bed is too high for the current blast volume. If the spout temperature increases and then decreases (typically below the initial temperature), the bed is too low. Successfully and efficiently run- ning a cupola cannot be covered in one article, or one training session, but the general rules of operation boil down to three things: 1. Turn it on, let it run, drain it out; 2. Run the cupola at its sweet spot. 3. If following rule 2 makes you violate rule 1, efficiencies will suffer. Operators must keep track of all inputs and outputs in the melt- ing process, using that information to adjust those inputs that can be changed as necessary.


30 | MODERN CASTING August 2016


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