heater control for curing oven

In article .com,
wrote:

I'm into recumbents and am exploring building a mold for a prepreg
carbon setup. This looks like an active site for composites.

Can anyone recommend a heater control to adjust the heating/cooling
ramp rate (5 degrees a minute, etc)? I'm obviously trying to keep
costs down so something surplus or homemade would be best.

Also, if I do a pressure bladder inside a female mold how do I apply
the vacuum between the composite and the inner mold line (so that the
bladder inflates)? Or should I just only apply pressure to the bladder
and not try to pull a vacuum on the mold?

Thanks airplane guys.

Joe

I don't know anything about composites, but I do know something about
temperature control. If that's critical to the process, I sure wouldn't
use anything like an oven thermostat. The hysteresis in those is way too
wide open.

For close control, you need a good PID controller hooked to an accurate
thermocouple or RTD probe. And, you need to "tune" it to your particular
usage. That involves setting the proportional, integral, and derivative
(PID) values in light of your requirements. Those would be different if
you were trying to heat a swimming pool with a hair dryer than they
would if you wanted to roast marshmallows on the sun.

Many PID controllers are "auto tuning" which means they can self-select
PID values, but they need time to "learn" your process. Until they have
time to do so, expect wide temperature fluctuations and significant
overshoot of your target temp. (And don't expect to auto tune an empty
oven and then use those values for one with parts in it.)

Omega, by the way, is a graphic arts company. They put out slick full
color glossy catalogs, but they don't manufacture temperature controls.
Peel the label off an Omega controller and you'll find the real
manufacturer, Love Controls or one of a handful of others. I don't mind
buying from distributors, but it irks me some to see distributors posing
as manufacturers.

By the way, I love the idea of carbon fiber bike frames. I think there
would be a great market for an electric recumbent that was set up for
practical short commuter use. Good luck.

KISS!

Assuming you are only doing these on a low production level basis,
(homebuilt!) and price is paramount, why don't you sit and watch a
thermometer and switch on and off the heater?

This has the advantage of being cheap, but is labour intensive. If you need
to use your hands for other things while the heating cycle is operating,
then even buying a few beers for a qualified mate to watch the dial and turn
on the heater could still be much cheaper. (As long as the beers are
supplied after a successful run!)

Hope this helps,
Peter

wrote in message
oups.com...
I'm into recumbents and am exploring building a mold for a prepreg
carbon setup. This looks like an active site for composites.

Can anyone recommend a heater control to adjust the heating/cooling
ramp rate (5 degrees a minute, etc)? I'm obviously trying to keep
costs down so something surplus or homemade would be best.

Also, if I do a pressure bladder inside a female mold how do I apply
the vacuum between the composite and the inner mold line (so that the
bladder inflates)? Or should I just only apply pressure to the bladder
and not try to pull a vacuum on the mold?

Thanks airplane guys.

Joe

In article ,
"Bushy Pete" wrote:

KISS!

Assuming you are only doing these on a low production level basis,
(homebuilt!) and price is paramount, why don't you sit and watch a
thermometer and switch on and off the heater?



Hope this helps,
Peter


Peter, I had occasion to learn about temperature control a few years
back when we were developing test equipment for food laboratories. More
sophisticated temperature control algorithms (e.g. PID) were developed
because On/Off controls, whether manual as you suggest, or automated in
some way, simply do not hold temperature. (That's why people who cook
use gas stoves. Turn an electric burner off and it will continue to
transmit massive amounts of heat energy to the food for another fifteen
or twenty minutes.) Unless your process is unaffected by temperature
overshoot and fluctuations of 20 degrees F or more, flipping the power
to an electric heater isn't adequate. The OP is building a bicycle, not
an airplane, but I'm sure he doesn't want his carbon fiber frame
disintegrating at 60 mph.

Smitty Two