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UV Curing

(November 2000) posted on Tue Nov 14, 2000

Bron Wolff discusses how you can assess and improve your UV-dryer performance by learning from his company's experience.

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By Bron Wolff

So what's the problem with low voltage? The problem is that when you vary the voltage and amperage provided to the lamp, you vary the radiant energy output (measured in millijoules) delivered by the lamp. If the lamp isn't delivering the proper energy to the print surface, it simply won't cure the ink.

To verify that you're getting sufficient curing energy from your system, you have to measure the energy output of the lamps using a radiometer. UV printing without a radiometer is like playing poker against a stacked deck. Radiometers make it easy to identify potential voltage drops. For example, by using a radiometer you'd quickly notice if a lamp-power setting of 200 watts and a belt speed of 70 ft/min gives you a different energy-output reading on different days, at different times of day, or at different times of the year.

Once we identified that voltage fluctuations were making it difficult for us to get a consistent cure, we invested in several step-down transformers. These units allow us to jack up incoming voltage levels when they fall below the levels we need to correctly operate our curing systems. However, due to component incompatibility and related concerns, several of our curing systems could not use step-down transformers, and we had to look for alternative solutions. So we turned our attention to the UV lamps.

Lamp concerns

Electricity is supplied to a UV lamp through a ballast, which is basically a transformer. The ballast takes the available voltage and converts it into the voltage supplied to the lamp. The incoming or primary voltage is directly proportional to the outgoing, or secondary, voltage to the lamp. The amount of voltage the lamp receives through the ballast directly affects the amount of energy (UV light) the lamp will generate.

Ballast manufacturers provide specification sheets for their products. As an example, consider a ballast for one of our old 72-in. lamps. It called for the lamp to use 2160 volts and 10 amps at a power density of 300 watts/in. However, in order to achieve the true 300 watts/in. over the entire 72-in. lamp, we needed to calculate the total power required for the lamp by applying Ohm's law, which states that volts x amps = watts. This gives us 2160 volts x 10 amps = 21,600 watts.


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