Page 54 - Australasian Paint & Panel Magazine

SPRAY BOOTHS
Peter Belding of Junair explains how vital the correct booth temperature is, especially for clear coats.
DOES YOUR BOOTH GET HOT ENOUGH?
HOW LONG DOES it take to bake modern high solids clears?
On the paint company technical information sheets for most
high solids clear coats designed for baking, the typical bake time will be around 35 minutes at 60°C panel temperature. Note that this is panel temperature not air temperature.
Many years ago, I was one of the technical team supporting the introduction of Glasurit in South Africa. When we first launched Glasurit (21 and 54 lines), on our published technical data sheets there were two clear coat bake times:
30-35 minutes at 60°C and 15-20 minutes at 80°C panel temperatures. After a few months we deleted the shorter bake temp/time and established the standard bake time of 30 minutes at 60°C. It is clear from this example that the higher the panel temperature the shorter the bake time.
We all know hot air rises. The temperature
probe in most down draught spray booths is
located in or near the input plenum. Although the down draught ventilation system in a spray booth forces the hot air down into the spray booth cabin, the air in the input plenum is still hotter than it is in the cabin, and the air at the top of the spray cabin is hotter than it is compared to lower levels. During bake, the temperature at the top of the spray cabin (just under the ceiling filters) can be 15-20°C hotter than
the air temperature at floor height.
Modern high solids clear coat bake times are on average around 35 minutes at 60°C panel temperature (when using non accelerated products). In many booths I have come across here in Australia, the air temperature during bake is in the order of
54 PAINT&PANEL July / August 2018
60°C and some spray booths can take a long time to reach this temperature (there are a number of older booths that cannot reach this temperature at all during the bake cycle).
For the typical duration of a bake cycle the air temperature needs to be at least 10°C higher than the required panel temperature. In an average spray booth it is unlikely panel temperatures of 60°C on the side panels of a vehicle will be achieved (over 70 percent of the work in a body shop is on
panels below the glass line of
a vehicle – the panels closest to the floor where the cabin air is cooler), thereby requiring longer bake times.
To achieve short thorough clear coat bake times the air temperature in the spray cabin (during bake) needs to be 70°C and above. Junair Spray booths 5
Series booth with QADs is able to quickly (and safely) reach air temperatures in excess of 70°C and to achieve door, mudguard and sill panel temperatures of over 60°C.
Typical bake times for ‘non-accelerated’ high solids clears in a Junair 5 Series booth with QADs are around 20-25 minutes. After a 5-10 minute cool down, the vehicle can be de-nibbed, cut- polished, and bumpers can be refitted with no finger printing.
To increase the production capacity of your paint shop you need a modern high performance spray booth bake oven, which can also save you money by reducing energy costs.
Junair Spray booths can be contacted at:
Email: sales@junair.com.au Phone: 1300 881 411
“To increase the production capacity of your paint shop, you need a modern high performance spray booth bake oven.”
www.paintandpanel.com.au