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Short wave infrared explained

Tuesday, February 27, 2018 - 09:00
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One of the most common questions about infrared that we get asked is what difference does wave length (short wave vs medium wave) make when curing paint. To explain this, it is best to first understand what infrared is and how it works.

Infrared energy/radiation is part of the Electro Magnetic Spectrum, which includes radio waves, x-rays, ultra violet, gamma rays…light…the list goes on. Each of these radiation types has different characteristics and functions.

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Infrared creates heat in an object by causing molecular motion / excitement which creates heat. That’s why infrared energy from the sun can travel 93,000,000 miles and not warm the air. It only creates heat in objects / surfaces…anything that is made of molecules / atoms. For example, the air outside an aircraft at 36,000 ft is around -56c / -68.8F, highlighting this point.

You sometimes hear people in the automotive refinish industry saying “short wave heats from the inside out” when drying / curing paint, which is obviously a false statement. The paint itself is made of molecules, so infrared can not magically pass through it, without absorption, so the first thing that will heat up is the paint itself.

I like to compare what effects infrared energy has on everyday objects when I am giving a training session. For example, compare a wooden park bench to the hood of a car in summertime. Given the same amount of infrared energy from the sun, the wooden bench is at a lower temperature than the metal hood of a car. Both are made of different molecules and that effects the temperature reached.

Short wave infrared energy penetrates deeper into an object, so in the case of paint curing, both the molecules in the paint and molecules in the substrate (normally mild steel) generate heat. Wet paint heat build is different to dry paint as the temperature is held back as liquids evaporate. As a result of this, you get a 2 way cure, radiated energy heating the paint and conducted energy / heat, transferred via conduction from the substrate. Medium wave, which includes catalytic systems, will certainly cure paint but it tends to be a top down cure, thus taking longer to produce a good cure.

Generally speaking, short wave infrared is twice as fast as medium wave, whilst using half the energy.

If you would like to find out more about infrared paint drying / curing, you can obtain a copy of “The Infrared Handbook” from B-TEC Systems by visiting

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