On 07/01/2011 11:15 AM, Gunner Asch wrote:
On Fri, 01 Jul 2011 07:39:48 -0500,
wrote:

For a project I am working on, I need to heat a roller.

The roller in question is a tube about eight feet long, horizontal,
about five inches in diameter and .049" thick aluminum wall. It turns on
a 3/4" axle and is supported on three spiders at the center and ends, so
that air can flow through.

The whole machine is always indoors, in ~70F room-temperature
conditions. For other reasons it can't be used in drastically colder
temperatures.

I need to be able to heat this whole thing to maybe 120F to 150F,
automatically. That is, I want to set a temperature and forget it. The
wattage I am guessing might take 1000 watts, and it must be electric
(dry) heat--propane will not help, as it gives off water vapor.

Are there any cheap UL-listed devices around built for doing this? I can
construct a "fan box" to use a separate fan to circulate the air if need
be. I really just need the heater circuit and elements... The fan motor
may not be able to withstand 150F so it will be separated from the
hot-air loop, but that's not a problem.

I know that there are industrial-devices known as 'drying-room heaters'
but they are way overbuilt and too expensive for my meager budget. There
must be something cheap and available that I can abuse reasonably-safely
to do this. I'd prefer lowering the operating temperature of a device
built for higher temps, than raising the temperature of something meant
for lower temps....

I have looked at a bunch of toaster-ovens and the lowest "warm" setting
for the food seems to usually start at 150F. I have a multimeter with
some thermal probes so I can test temps fairly decently and I know a bit
about electronics but don't know if there's any easy way to recalibrate
the heat to a lower temp.

Why not run a heating element down the center of a hollow roller? Or
put a series of elements in an enclosure snuggly above the roller that
directs heat At the aluminum roller and heats it up? It shouldnt be
hard to do.

The first solution would require slip rings -- but those are as close as
your nearest car alternator. The second is a bit indirect -- but it
sounds like it'd work great, particularly if you could keep the roller
painted black.

The OP hasn't chimed in yet on why he was asking for the UL listing
thing -- neither of those solution meets that criteria, but I'm not sure
you can get there from here anyway.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html