A review of temperature-measurement tools and how to use them.
By Rick Davis
Since the best time to measure the actual temperature of the ink is while the garment is still in the dryer, both non- and on-contact pyrometers are automatically excluded as options. These tools can tell you the ink-film temperature when the garment exits the dryer, but they cannot tell you the peak temperature or the duration of exposure.
The most simple tool for measuring temperature within the dryer is heat tape, which has been a standard in many shops for years. One or more strips of the tape are affixed to the garment surface near the print before the garment is passed through the dryer. When the garment exits the dryer, a heat-sensitive ink on the label shows the highest approximate temperature reached during the curing process. Once again, however, the strip only tells us how hot it got inside the dryer, not how long the print was exposed to that temperature.
To enlighten us more about the conditions inside our dryers, the best tool we have at our disposal is the doughnut probe. This device rides through the dryer alongside our garments and measures the temperature of either the ink film or the belt at any point within the chamber.
Doughnut probes continuously record temperature data throughout the drying chamber. Not only do they inform us about what peak temperatures were reached, they also tell us how long prints are exposed to the various temperatures within the chamber.
We can download the data collected by a doughnut probe into a personal computer and use it in a spreadsheet program to plot a chart that shows hot and cool spots in the dryer. In IR dryers, these fluctuations in temperature could indicate poor airflow or failing heating elements. In gas forced-air dryers, cool spots may mean clogged air knives. As with the flash-curing unit, we can use an on-contact pyrometer to measure the actual temperature of any radiant heat panels within the dryer.
Even if you had to purchase each of the tools discussed in this article, you could still end up spending less than $500. That's a pretty modest investment for devices that could save you hundreds or thousands in miscured printed garments. But you'll only get the full benefit of these tools by making them part of regular monitoring and maintenance procedures for your flash-curing units and dryers and using them whenever job characteristics (inks, substrates, print type) change. Next month, the discussion continues with a look at how these tools can be used when applying heat transfers to garments.
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