When discussing furnace compliance, we might ask ourselves the following question:
“If my thermocouples and control instruments are calibrated, and my SATs are performed successfully, does that mean the temperatures inside my furnaces are correct?”
Your immediate response might be “Yes”, however the correct answer is “Not necessarily”. A successful calibration and SAT only tells us that our furnace’s temperature system is accurate at one location: the tip of our sensor. Unfortunately, we don’t yet know the temperatures of any other locations inside our furnace.
This is why we must evaluate temperature uniformity, meaning the temperature variation of several locations within the furnace work zone (expressed in ±degrees) with respect to the temperature set point. To do this we must perform Temperature Uniformity Surveys (TUS)
A TUS is a test or series of tests where calibrated instrumentation and sensors measure temperature variations inside the furnace. By identifying where in the work zone these temperature variations exist, heat treaters can answer important questions such as:
- Where are the cold and/or hot spots in my furnace?
- Why are there cold and/or hot spots, and how do I fix them?
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Repeatability, repeatability, repeatability!!!!!!!
The TUS test helps ensure the entire work zone produces a repeatable metallurgical result. It also encourages proper maintenance of thermal processing equipment by identifying where non-homogeneous temperatures exist within your work zone. Above all else, performing TUSs tests reduces the likelihood of scrap and/or quality issues that could potentially lead to product RECALLS.
Since TUSs are a proactive measure (not reactive), the true costs related to performing TUSs can only be measured by NOT performing the TUSs and waiting for the bad news. Unfortunately, far too many companies have “paid the price” for NOT performing TUSs. This decision has oftentimes resulted in recalls measured in the many millions of dollars!
In conclusion, if TUSs are not performed, the heat treater needs to quantify what potential liabilities might he/she inherit if metallurgical related recalls were to take place as a result of poor temperature uniformity.