Building A Hot Box??

[rxcomposite]

We built a curing oven before good enough for 350 degree. Closed box with doors, plywood construction with fiberglass wool insulation. The inside is lined with metal sheets.

Air is recirculating as Tom has suggested. Hot air is fed at the bottom (long) ducts with semi adjustable openings, collected at the top (hot air goes up) circulated outside the box by an cheap axial fan (like a turbocharger). The axial has the motor outside of the flow.

Heat was ordinary home gas fired furnace (can be quartz) located inside the closed loop system. Plumbing is metal sheet.

Control was a cheap programmable timer with a thermocouple feedback. It turns on and off the heater. Ordinary long probe thermometer was inserted in the holes provided to monitor hot spots in the oven. Control was good at +-3 degrees.

Well, must admit there were some tricks in tuning it but its good enough for pre preg curing.

[rxcomposite]

Here s a very ver quick sketch just to give you an idea.

[rxcomposite]

Resized. Would not upload

[CatBuilder]

Originally Posted by AndrewK

CatBuilder, as mentioned before to get a good result with thermoforming you need a solid mold, be vacuum bagging and a second pair of hands. With a batten mold you get a better result (fairer surface) with using smaller blocks of foam and kerf cuts for the topsides and strip planking in the bilge.

But if you want to give it a go you have to insulate the box, fiberglass wool or styrene will do. You must have fans, thermostats and lots of power around 4800 W, (two 2400W fan forced elements).

Andrew, can I use strip planking in the bilge even if I already have battens installed?
Can I use the kerf cuts in the bilge?

[Submarine Tom]

You shouldn't need nearly that much power (4800 watts) for 170 degrees F.

-Tom

[CatBuilder]

I cut some kerfs today with an organic vapor cartridge respirator on. While cutting the kerfs, I smelled that sweet smell that I had earlier when I got hydrogen cyanide poisoning from overcooking the foam.

I got out of the shop fast when I smelled this.

Is that smell something to worry about?

Do you all use a skill saw or table saw to cut 1" thick, A600 Corecell A foam regularly?

I was using a blade with many small teeth, marketed as a blade to use for cutting plastics.

[hoytedow]

First symptom of chronic cyanide poisoning is deafness.

[CatBuilder]

Originally Posted by hoytedow

First symptom of chronic cyanide poisoning is deafness.

What?



I found out from Gurit it's probably just the styrene I'm smelling from the cuts. It shouldn't be releasing any hydrogen cyanide when cut with a saw blade. Good to know. This stuff is pretty dangerous if you don't handle it properly.

[hoytedow]

Eh?

[Submarine Tom]

"While cutting the kerfs, I smelled that sweet smell that I had earlier when I got hydrogen cyanide poisoning."

You shouldn't smell anything with a proper fitting respirator on!

-Tom

[cthippo]

Depending on how much you have to do, a hot water heater, pump, and an old radiator might do the trick. The thermal mass of the water will be great enough that it's temp won't change quickly and therefore you can maintain the temp inside the box more precisely than you could with just heating the air.

[CaptBill]

If you plan to use your box much you may want to consider "heatpiping" your box. The heapipes enter the box with a section (about 1/3) extending to the outside. You heat the exterior portion of the heatpipe and the temp. is regulated for the length of the tube. Inside, the tubes should interface to a 'radiator' surface. This is good if you need isolation from the heat source and interior (no flames/fumes from source). This setup is excellent if you need to get uniform heat.

http://www.youtube.com/watch?v=LU4eynU6R-8

[Submarine Tom]

This is a great idea. A 5 gallon hot water tank would be ideal as you could set the thermostat on the tank to get your desired temperature in the box!

-Tom

[CatBuilder]

I agree. Somewhere, I remember hearing cthippo was in high school!?!?

I don't know if the info is fresh in his head, or what, but what a great idea.

I had always thought he was graduating college...

Anyway, thanks ct. I did decide to stop working on non-boat stuff (like building hot boxes) though and perfected (finally!) the bending of the foam without a hot box. Henny from fram.nl fame (and a couple others) suggested I use narrower strips. It worked!

Here's the link.

Is this right? (foam)