perature (2,000F). Similarly, the center thermocouple measured 1,982F, which was 18F below the target temperature. Table 1 displays a summary of all the
OP-AID trials. The time savings results displayed in this table assumed that the filtering time necessary to interpret the derivative of the infrared signal is absorbed in the control soak portion of the heat treatment cycle. Addition- ally, it was assumed that the window of time used to verify that the signal was within its upper and lower limits was also absorbed in the control soak period. The OP-AID method provided significant time savings under these previously mentioned assumptions.
So What? Based on the results of the recent
trials, the use of the OP-AID method is independent of load characteristics
Table 1. OP-AID Summary of Rusults Trial
On-Heat Time
Rectangle Cylinder
Rod Bundle
and is applicable to most furnace types. The method also can be easily implemented since it requires mini- mal operator input. Furthermore, the method fulfills the basic requirement of effectively eliminating the use of contact temperature measurement. The OP-AID method, however, is not
without disadvantages. First, the method requires the operator to be mindful of load placement in the heat treatment furnace relative to the infrared sensor. The infrared sensor must be positioned in a direct line of sight to the load. In the small scale gas fired batch furnace where testing of this method was conducted, the sensor was installed in the middle of the furnace and 3 in. above the furnace hearth. This placed the infrared sensor in a natural position that maintained a line of sight for virtually all typical load placements. The infrared sensor also has a manual
Time Savings
(minutes) Rule (minutes) 66 82 53
24
158 37
Surface
Over Hour/Inch Temperature (F)
1,587 1,993 1,595
Temperature Difference Between Load Surface and Furnace Set-Point (F)
13 7 5
sighting port so the operator can verify that the sensor is targeting the load. In large furnaces, it might be necessary to design a positioning device that permits the sensor to be repositioned to maintain load line-of-sight for all load placements. The sensor placement would need to be determined based on further testing and observation of the loading characteristics inherent to large scale furnaces in a pro- duction setting.
MC About the Author
Thomas Karnezos is a research assistant in the field of industrial engineering, Pennsylvania State Univ., University Park, Pa. Robert Voigt is a professor in the university’s Harold & Inge Marcus Department of Industrial & Manufacturing Engineering and co-director of the Master of Manufacturing Management Degree Program. The authors would like to acknowledge the generous support of this work by Jim Heilmann and Gary Dispensa at Carpenter Technology Corp., Reading, Pa.
For More Information
“Ignite Your Business,” MODERN CASTING, March 2007, p. 34-37.
Center
1,580 1,982 1,565
Temperature Between Load Center (F)
20 18 35
Temperature Difference and Furnace Set-Point (F)
50
MODERN CASTING / March 2010
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