On 07/01/2011 08:49 AM, Paul Hovnanian P.E. wrote:
DougC 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.
Aim a hair-dryer down one end of the tube.
It took _six replies_ before someone figured out a mapping between "UL
Listed thingie that delivers 1000W at 150F and has a fan" and "hair
dryer". Good for you, Paul!
If one hair dryer doesn't do it, try two. Or three. Or whatever. Get
them from Goodwill if you're on that much of a budget.
It may be as simple as this (although a hair dryer fan might have problems
providing adequate flow with the back pressure.
You say you can use 120 to 150 F, but given this range, does the temperature
have to be uniform (within what limits) along the length of the roller?
That's an important consideration -- it'll be easy to end up with a warm
end and a cold end. You may need to do something a bit perverted, like
an inner somewhat insulating tube (PVC pipe that can stand hot water
would maybe do) with holes drilled at whatever intervals makes things
work. Put hot air into the inner tube, and drill your holes to keep the
temperature distribution of the outer tube constant.
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.
Its easy to construct a fan that will tolerate much higher temps. Just make
the impeller and housing out of whatever will tolerate the temps and
connect the motor using a suitably long shaft to keep it in a cooler
region. You can have the shaft pass through a heat shield (sheet metal with
a hole for the shaft) to protect the motor against radiated heat and draw
the incoming (cool) air over the shaft and through the motor to keep it
cool.
--
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