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Go to IR manufacturers for curing time specifics

Tuesday, April 25, 2017 - 07:00
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Well, someone had to do it and yes, that’s something that’s been in my monthly task list for over 30 years…But why do it?

Over 30 years ago, the big change in the automotive refinish industry was the introduction of the acrylic urethane/2K paint system, which was rapidly taking over from the air dry paints, lacquer/cellulous and synthetic enamels.

As a side note/history lesson for the younger readers: this big change in paint technology came about mainly because of World War II. After the war, the Germans were not allowed to produce explosives. Because the chemical ingredients prohibited in explosives were also used in nitrocellulose lacquer paint systems, they concentrated on developing an enamel system. A high-solids acrylic urethane/2K paint system was the result. That also explains why it’s called a 2K system and not 2C, as Component in German is spelled Komponent.

It seemed like overnight, the new paint systems and heated spray booths were being installed, although it did take several years. The new paint cured/dried due to a chemical reaction, which could be accelerated by using heat, so not only did we see the introduction of heated spray booths, but also the first ceramic medium wave infrared paint curing equipment was also being introduced. The first systems we saw were actually from paint companies and booth manufacturers. This was long before the more popular short wave, mobile units like Trisk, IRT etc, were hitting the streets in the late eighties, early nineties.

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One of the first medium wave IR ceramic systems Checking cure times and temperatures is vitally important.

Infrared equipment is undoubtedly a great tool for body shops, if it is used correctly. That’s why I had to spend so much time collating infrared paint curing information for the shops to use. Nearly all the paint companies provided urethane / 2K curing data, based on booth temperatures of around 60◦C / 140◦F. The problem was that data did nothing for the painter wanting infrared curing information, and the IR manufacturers were only supplying guidelines / ball-park curing times.

Short wave infrared not only produces a higher temperature than a convection oven but it is more effective in heating the substrate. But what is that temperature? And what is that curing time?

Remember that for many years, the average infrared units did not come with a built-in pyrometer to read temperature and via a control system, regulate that temperature.

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There are significant differences in the curing times of some popular primers that highlight why having the infrared data is important. For example, one primer we tested recently was ready to sand in 6 minutes, while another needed 5 minutes on half power, followed by 15 minutes on full bake. Being out on your curing time by 14 minutes can be the difference between a good quality cure and a re-do waiting to happen. Panel temperatures can easily exceed 180◦F when using infrared, so distance guidelines from manufacturers should be noted and observed. If you don’t have temperature control, which is a very handy tool to have, use distance suggestions as a minimum, and if in doubt, back off.

Paint companies are doing much better with supplying IR times on their TDS’s, but cannot do what the infrared manufacturer is supposed to do. Paint companies can only give an approximate guide time and sometimes, the variation between medium wave and short wave infrared times. Some even list distance used from painted panel, but that again, is something only the IR manufacturer should advise on. For example, you could have an infrared unit using 2000w emitters and another 850w. This makes a huge difference on where the IR unit is positioned. You could have a 1000w emitter that is 350mm / 13.77” long, but another 1000w emitter 800mm / 31.49” long, so that also makes a big difference in lamp intensity and at what distance, it’s designed to be used.

When I produce an infrared data sheet, all the necessary information is listed, including what product mixing ratio was used, the details of hardener, thinner/reducer and if relevant, the accelerator. I also list the specific infrared unit used for the test and of course, the distance used. This data is really only good for that manufacturer and not some sort of generic guide that can be used for any infrared unit.

And finally let’s look at banding. Infrared manufacturers advise a certain distance to be used from the paint job so that the thermal footprint / curing area is even. If for example you have a 3 cassette unit and each infrared cassette is throwing out a fan of energy, at a given distance, each of those fans join up. But if you move in too close, the fan size reduces which can cause cold stripes across the curing area, which is called banding.

For those interested in obtaining an infrared data sheet for your paint brand, feel free to contact B-TEC Systems or your local distributor. You could also try me, but I might be tied up in my next exciting project…Watching paint dry…yawn.
 

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