Carbon Potential Variation

[gblanchard]

How much variation in actual carbon might one expect from control set point when evaluating by way of carbon shim sample?
IQ atmosphere furnaces are supplied endo-gas at 35 degree dew point and enriching gas is natural gas (no peak shaving is is expected currently). Carbon control is via oxygen probe and automatic,two-channel instruments. Shims (.004" thickness) are soaked for 40 minutes, atmosphere cooled, and evaluated in a LECO carbon analyzer with regular referencing. With typical C/P running between .85% and 1.05%, I was expecting +/- .05, and would like to know if this exopectation is reasonable.

 

[unclesyd]

Have you checked you NG supply?
It's been many a year but I recall on several ocassions that moisture and composition problems with NG caused our heat treating group problems.

 

[gblanchard]

I am not suspicious of any natural gas issues presently. As I am comparing multiple furnaces, there does not appear to be any correlation that would indicate a general source problem. That is, variations are divergent on different units.

 

[unclesyd]

What is the variation on your standard sample?

 

[gblanchard]

Variations I am finding run from -.07 to +.13 from set point in one furnace. Another falls in the narrow range of .05. Three other furnaces are between these extremes. As we work to improve variations, I seek to understand a reasonable expectation of range. Targeting is adjustable through CO2 or process factor settings.