The heat is on at body shops to send vehicles out of the spray booth properly dried yet in a profitable time frame. A half-baked job is, well, just that.

With the low-VOC paints on the market, many of the traditional rules of the game are changing. It used to be that there were only two settings used in a job: painting and baking. Now multiple settings are common. And there is a battle waging between those who want to see drying temperatures around 140 degrees and those willing to push them 20, 30 or even 40 degrees higher.

While there is little spare time in a typical paint shop, with today's quick-bake systems, there is even less time spent on each job. In some cases, the name of the game is to find a system that will get the room up from normal temperature to 180 degrees in a matter of seconds - two minutes may be too long. More shops are looking at drying temperatures in the 180 to 200 degree range, depending on the paint used.

"The painter makes money, the car moves through the shop faster and the customer is happy," says Jimmy Lee Harris of Garmat USA, Englewood, Colo.

"All paint manufacturers are requesting a zero-perch time," he continues. Perch time is the time between finishing a paint job and the time that the bake cycle comes on. The term is used in spray booths and is commonly called "flash time" by paint firms. For years, it was common to have a perch time of 10 to 15 minutes on a car. Today, many paints require that the bake cycle come on as soon as the painting is completed.

Since the low VOC paints marketed by major firms are formulated with fewer solvents, the paint can be prone to a skinning problem if the outside temperatures are warm. Dye-back and solvent popping are the result and the end-product ends up with a loss of gloss or a milky-looking finish. Both problems can be avoided by using proper drying temperatures.

"Paint manufacturers want the surface temperature to rise as high and as fast as possible," Harris continues.

Chris Kane, sales manager for Spraybake Canada Ltd., Concord, Ontario, agrees. Their PowerBake system brings temperatures up to 185 degrees at the beginning of the cycle and keeps it there for six or seven minutes. "That brings the metal temperature to 140 degrees and gives a true bake cycle," he says. Once the temperature has been at 185 degrees for the six minutes, it is dropped back to 150-155 degrees - not 140 degrees.

"We've found that, for every 15-degree raise in temperature, you can cut the bake time by half," Kane says. So baking at 155 vs. 140 degrees will save a considerable amount of shop time. Use of programmable logic controller (PLC) technology allows them to set precise measurements at the beginning of the bake program. The unit's settings are pre-programmed with the major paint manufacturers' specifications for optimum curing times.

Spraybake distributes the Swedish IRT infrared system and Kane says it will allow drying and curing in 15 minutes vs. 45 minutes. "It's ideal for door dings and panel jobs," he says.

Team Blowtherm, Atlanta, Ga., has a similar system they call SmartCure that brings the vehicle temperature quickly to 199 degrees and then lets it drop to the 160 degree area.

"All paint manufacturers have a common denominator - their P-Sheet," says Rick Farnan, senior engineer in charge of Team Blowtherm's technical center. He is referring to the performance sheets published by the paint companies. The P-Sheet gives the recommended temperature of the metal. "But by metal temperature, they mean the surface temperature, not the temperature of the metal underneath," he continues.

"Once the surface temperature reaches 140 degrees, then the clock starts," Farnan says. The key point is to get that surface temperature to 140, not how long it takes. Farnan notes that during a summer day, the temperature in a spray booth at an Arizona shop may get to 140 degrees in four or five minutes. It might take the same system 20 minutes to do the same job during a cold Michigan winter.

"So to get to 140 degrees, you might have to set the dial on the booth to 165 or 180 degrees," Farnan says. That is because a lot of heat is absorbed by the booth's walls, by tire rubber, or lost through air movement.

Are booth temperatures around 140 degrees on their way out? Tom Dickinson, sales manager for Eagle Spray Booths, Sacramento, Calif., thinks not. "Our systems get to 120 degrees above ambient," he says. "We tell our customers never to bake over 140 degrees." The reason, he says, is that at temperatures over 160 degrees the bumpers start to melt.

"Sure, it cures quicker. But you may be melting parts and frying the computers," he says. Ruining chips in a vehicle is an expensive blunder. In fact, manufacturers warn that using infrared lamps can warp plastic and metals if used incorrectly. Correct procedure calls for rubber or thin plastic to be covered with foil tape or removed and replaced later.

Brian Jackson, custom booth estimator for Spray Booth Systems, Inc. (SBS), Fort Worth, Texas, agrees. "We typically quote a capability to go to 140 degrees." He, too, voices concern about the relatively low melting temperatures for the rubber and plastics on most vehicles.

However, Harris has little time for those who argue that high temperatures are a problem. "We use much higher temperatures in our industrial jobs," he says. As for computer components, he notes that vehicle manufacturers now are mounting computers in the engine compartment, where temperatures can reach 300 degrees and more, and there is no ill effect on the components. "People are stand-offish about high temperatures at first. But once they start to use them, they are very happy," Harris maintains.

The legal limit for paint booth temperatures is 199 degrees, set under the National Fire Code, which says booths must be operated at temperatures under 200 degrees. For that reason, Garmat rates its booths at 80-199 degrees. Harris says that raising the temperature from 80 to 190 degrees in about 90 seconds causes the solvent to boil to the body right away. "You get a beautiful flow-out," he says.

Blowtherm's Farnan also doesn't worry about setting a booth up at 199 degrees. "There is no reason to hold at 199 beyond 10 minutes," he says. "As soon as the surface temperature reaches 140, we drop the booth temperature to 165 and that holds the surface temperature."

Farnan says they started using the high-temperature process seven years ago with auto auction groups. "We've never had a problem with computer chips smoking," he says. Besides, he adds, the surface temperature on a black car left out on a Georgia parking lot during the summer will get to 180 degrees. That vehicle will be left out in the blazing sun for four or five hours, day after day, without harming the systems.

While he concedes that keeping a car in a booth set at 199 degrees for several hours might cause damage, Farnan says nobody recommends going longer than 10 minutes or so before dropping the temperature back.

On top of that, Garmat says the six to eight temperature settings provide considerable energy savings during the bake cycle of the vehicle. Research from Spies Hecker shows that infrared heat uses about one-fifth the energy that conventional heat uses. Most of those savings come because it takes about half the time to cure paint using infrared.

"Most of our painters are telling us they spray at 72 degrees and bake at 140 degrees," says Clay Rose, factory sales manager for Spray-Tech, Ontario, Canada. While he agrees that paints from different manufacturers will dictate different temperatures, he also says that it depends on an individual painter's preferences and on the type of shop.

Rose says their systems are all digitally controlled, with temperature settings to 110 degrees over ambient for spray and 180 degrees over ambient for bake.

Part of the confusion, Harris says, is figuring temperature. Paint booths work on ambient temperature. Paint manufacturers generally want a skin temperature of 140 degrees. "How you get there is up to the paint booth manufacturer," Harris says.

How a painter measures temperature also figures into the equation. The magnet gauges typically used in a paint shop actually measure the temperature of the vehicle's metal. However, Harris maintains the more important reading is the actual temperature of the paint. For this, an infrared or laser gun is required. "Metal temperature and skin temperature are not the same thing," Harris said. "All we are worried about are the top two mils of clear coat."

This is true even on custom colors or specialty jobs like a candy apple red. The color actually rests in the lower layers of paint. It is the temperature of the top-most clear that needs to be measured accurately.

Cure Times
Rose says a typical cure time is 38 to 40 minutes. While he agrees that bake times have dropped with the arrival of water-based paints, he notes that some painters are seeking the optimum in dryability. "A lot of painters are trying to reach the absolute optimum so the paint almost starts to cure when it comes out of the gun," Rose said.

"A production-style facility that moves a lot of vehicles through will see faster dry times. But you don't see that with the high-end shops," he says. "Where the customer is willing to pay top dollar, the shop is going to give the full, recommended cure time. Other places may try to squeeze an extra vehicle through every 48 hours."

Whatever the shop's quality orientation, "I tell people to bake no more than 40 minutes," Eagle's Dickinson says.

Warming up to the subject, Harris says that paint manufacturers like to see the temperature of the booth go from 80 to 180 degrees in about 90 seconds. "Then there is no way for the paint to skin over," he says, adding that some systems take as much as 40 minutes to get metal temperature to 140 degrees, whereas he would prefer to see optimum metal temperature reached in seven to eight minutes. "Once you get to 140 degrees, then you start to count the eight minutes curing," he says. Once the skin temperature reaches 140 degrees, it can be allowed to drop back. This way, he says, the car can be done in 17 minutes, as opposed to three-quarters of an hour.

Working with the paint manufacturers, Blowtherm has shortened drying cycles in its booths by 10 to 15 minutes. "By the time you've done four vehicles, you've picked up a full hour's time - the time it takes to do another car," Farnan says.

"Thirty-five to 45 minutes is plenty of time to do the job," agrees SBS's Jackson. "They can cure out a car regardless of whether it is a full paint job or just panels." Like several others, he says it is most important that a shop follow the recommendations of its paint manufacturer.

Jackson's greater concern is the cleanliness of the shop, not fretting about a few minutes of dry time one way or the other. "Our discussions with painters revolve around the environment in the paint booth," he says. "Our biggest worry is keeping the booth and the area around it clean and being sure the painter wears the right clothes."

Kane acknowledges that a painter might not want to use the higher temperatures for every job, although no negatives from the practice were noted in the Spraybake training centers. Perhaps the biggest drawback would be higher fuel bills. "Gas bills may be 30 to 35 percent higher," he says.

That is not deterring many painters. While all new systems come with the PowerBake option, Kane says they also are retrofitting a number of older units.

Before making any final decisions on temperatures or cure times, be sure to talk both to your paint company representative and to the people who manufactured your spray booth and drying equipment. This is no time for lukewarm results. They are sure to set you up with a sizzling program that will cook up some red-hot profits.

Curt Harler is a freelance writer based in Strongsville, Ohio.

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