heater control for curing oven

wrote:
Dan,

Does this unit allow you to set the ramp both going up and coming down?
Does it work with a solid state relay? How easy are the directions to
follow (assuming I can't read Chinese!)?

PID is described in the message below.

Joe


It's a basic temperature controller. You set the temperature you
want, the internal relay closes turning on your heater, if the
thermocouple says it's too high the internal relay opens so it's
basically an accurate thermostat. Since it comes without instructions I
have no idea what the relay specs are so I drove another relay with it.

There are two vertical 5 pin barrier strips on the back. The left pin
out is: 1-ground, 2 and 3 - 110 VAC, 4 and 5 are relay out. The right
pin out is: 6 and 7 - alarm, 8 - NC, 9 and 10 are the thermocouple.

I haven't tried the alarm function so I haven't bothered to figure
out how to set it. The power requirement is 100 VAC 50 cycles but it
operated rather nicely on 60 cycle for the half hour I tested it.

I still haven't gotten around to building my li'l oven yet. One of
these days I'll get around to procrastinating.

Dan, U.S. Air Force, retired

Yaa, you would think that an I/O card (with the TC voltage coming in
and the voltage to the relay going out) could do this pretty easily and
you could just put in the "curve" you want in your PC program and it
would know how to get you there. Basically a PC software driven PID
using a cheap I/O card off the RS232.

I did a brief look but couldn't find anything though so it's no doubt
harder than I'm imagining it.

I did find some cool stuff on guys doing their own coffee roasting with
hot-air popcorn poppers They're using PIDs too.

Joe

If you want to try to "roll your own" you might check out basic stamps
- and the clones. I'm pretty sure that you could find some freeware
for these that does what you need.

http://www.parallax.com/
====================
Leon McAtee
having lots of fun with my bent trike............but need to get back
to work on the Quickie.

" wrote in
oups.com:

If you want to try to "roll your own" you might check out basic stamps
- and the clones. I'm pretty sure that you could find some freeware
for these that does what you need.

http://www.parallax.com/
====================
Leon McAtee
having lots of fun with my bent trike............but need to get back
to work on the Quickie.



Also, look at PixAxe micro-controllers. Much cheaper than Basic Stamp.
Lot'a of free software and support web sites. Programming is in "basic"
like the Basic Stamp.

Otherwise have you looked at eBay. I've picked up several programmable
controllers for cheap, compared to new prices.

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

In article ,
Richard Riley wrote:

On Sat, 24 Sep 2005 23:22:04 -0700, Smitty Two
wrote:

: Unless your process is unaffected by temperature
vershoot 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.

I've worked with a lot of carbon pre-preg, and none of them were
*that* sensitive to temperature variations in curing. Of course, my
oven had a big enough thermal mass that it didn't do ANYTHING quickly
-it was 8'x6'x25' and 6000 watts of heating element.

Like I said, I have zero experience with composites and have no idea how
touchy they are. I agree that your setup has plenty of inherent
temperature stability. The OP wants ramping control on the way up and
again on the way down. Even taking target temperature fluctuation out of
the picture, he sure isn't going to get that with a light switch.

Does carbon fiber cure with different mechanical properties if it's
cured in different ways? We do some heat treating of machined components
at work, and there are pretty specific recipes for obtaining different
properties in various metals. Besides different times and temps, the
cool down ramp is also important, varying from hours to seconds (oil
quenching.)

"Richard Riley" wrote ...

not for the cure
itself, but so you have a reasonable amount of time in the temperature
range where things are soft and move easily, but not yet curing.

Ramp up and down don't affect strength, they affect accuracy - getting
things to the right shape on the way up.

Richard,

I've never been involved in this. Are you saying the thing sags into the
mold by gravity or are you taking it out of the oven and manipulating it?

Rich

"Richard Isakson" wrote ...

Richard,

I've never been involved in this. Are you saying the thing sags into the
mold by gravity or are you taking it out of the oven and manipulating it?

Wait a minute, I'm being dumb. Since you're vacuum bagging it, it's pushed
into the mold by air pressure.

Rich

Thanks Richard,

I've seen samples of small parts made this way and they looked like very
nice parts but I've never played with this type of thing.

Rich