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Hot Tips for Heat Measurement

(January 2001) posted on Fri Jul 27, 2001

A review of temperature-measurement tools and how to use them.

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By Rick Davis

While heat is an essential component of the garment-printing process, it is one of the most troublesome variables that we face as a screen printers. Not only must we maintain the right conditions in our dryers for each combination of garment, ink, and application we print, we also have to stay on top of the heat emanating from our flash-curing units.

Failure to regularly measure the performance of our flash units and dryers can have severe consequences. These include undercured prints with poor washfastness, over-gelled heat transfers that won't transfer and adhere correctly when applied to garments, overflashed underbases that prevent good adhesion with subsequent ink layers, scorched garments, and more.

To combat these problems, we need to regularly monitor the heat that our garments are exposed to during production. Several measurement devices are available to help us in this endeavor, and this month, we'll take a closer look at each of them and the areas of production they're best suited to measure.

Measuring devices

In screen printing, four temperature-measurement tools are typically used to gauge the performance of our equipment and determine the amount of heat our printed garments are exposed to. These tools include the following:

* temperature tapes--small adhesive strips that are affixed to garments and indicate the approximate temperature through a heat-activated color change

* non-contact pyrometers--electronic devices that read temperatures without physically contacting the material being measured

* on-contact pyrometers--electronic devices that read temperatures with a probe that physically contacts the material being measured

* doughnut probes--electronic devices designed to accompany the product through the dryer and continuously record heat conditions

Although none of these devices provide absolute temperature values, they help us establish important guidelines that lead to successful curing on the jobs we produce.

Measuring flash-curing temperature

Of the two heat-generating areas in print production, flash curing is probably the most difficult to control and, hence, very important to measure. The reason flash curing is so difficult to control is due mostly to the extreme temperature changes and the short time span in which the changes occur. These factors combine to make accurate temperature measurement on flash units a challenge. Compounding the problem is the fact that flash units come in a variety of configurations with different heat sources, including continuously operating infrared (IR) panels and quick-starting fused quartz elements that can jump from room temperature to 1400°F (760°C) in seconds.


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