BIG PARTS!

"I believe within the coming year(s) we will want to increase the size, efficiency and through put of the large parts system.  I am looking for the best way to heat and cure parts of large size(up to 10,000 lbs.)

We have to pre heat to get the mil build required by our process 8-16 depending on the customer.

We coat with an epoxy that requires 15 min at 350 metal temp.

Infrared does not seem to be the best way to get even temperature increase especially given we coat inside and out and line of sight is an issue."

skip says Sure! I use to do armored plate 4 inch thick. No it did not work. The chemical resistant coatings never stuck to the uncured powder. I digress.

1~Your blessed with a low quantity of work.

2~Although very heavy the work is one heck of a HEAT SINK. Anything heat sensitive like on automotive air conditioning compressors...by the time the powder cures, the plastic parts within the electric clutch were melted.

3~Your really not going to cure that powder unless that heat sink is up to temperature. So 350 deg F. for 15 minutes. A heat soak. I built a p-coat line for NASCAR frames with full cage. Made a big-o-batch oven and 800,000 btu packaged Midco burner, used an explosion relief latch on the door and a 4" I-beam with a few 4" open complement trolleys with work hangers and manually pushed the frame in after p-coating with a portable gun/hopper unit. No booth. Maybe did about 14 frames a year. Cooked 'em all day, cooled 'em all night. Parked the line under the carport outside. Did a lot of small part overflow work using racked push carts and short run 'pain-in-the-butt' jobs.

4~Infrared; It's a cold but sunny day. You go to the beach to grab a suntan. Your covered with goosebumps because your cold all day and you go home with a sunburn, and you never got warm...think about it. Plus your only going to heat what I.R. sees. Any heat creeping around to the dark side will be by conduction. A problem already identified by your post.

5~A conveyorized line. A 8" power and free? Overhead or in the floor power and free. How about a towline/drag line. This [power and free] may save building floor space and limit the size of the equipment.

6~"Help!..I will paint big part 6'w x 7'L x 4'h and weight 3800lbs, we have a big oven with a burner of 3.o mbtu's how much time we need to have this part in oven to not over cure powder. There is any formula to calculate this? skip is guessing here but....

Sure btu's are always in hours. I have not done this in years but my work sheets are in the basement. I'll have to go back and dig them out. In the mean time let me plug along with a guess. I'm not remembering the coefficient of heat for oven panels or oven floors panel, steel castings, or air. Regardless. The conveyorized oven at 350 deg F. is about 68' x 26' x 10', 3 pass, 60 minutes @ 3 fpm. Say 12 works at 3800 each = 45,600 / hr. plus 30 lb /foot conveyor = 5,400 lb/hr. Exhaust about 252 cfm to keep her sweet. 2 work openings at 6'-6" x 4'-6" so 58.5 sq ft.

Heat the oven panels, the oven floor, the conveyor in lbs/hr, the work in lb/hr, the work hangers in lb/hr, the exhaust air in cfm/hour, and the work opening spill in cfm/hour. Use a bottom entry oven to eliminate this spill. Say 12 works /hour at 3800 lbs at 3 fpm at 350 deg F. I did this as a S.W.A.G. and came up with 2,131,111 btu. So 3,000,000 btu is about right. Maxon Oven Pac?

An 8 mil to 16 mil build your going to have to preheat the work and p-coat hot. Or double layer. You might want to immersion dip zinc phosphate as that crystal build up is substantial and really provides a good bedding for a thick mil p-coat. I can't say if the build will enhance p-coat to 8 to 12. The zinc will come out of the bath feeling like a cat's tongue. See my other posts about immersion pretreatments. The question remains. "How Good Is Good"  "What determines a good p-coat job for your customer?"

skip.

Last edited by skip (12/15/2009 - 02:22 PM)