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

Check both the Grainger and McMaster Carr listings. They both have
fairly reasonably priced ($90- $400) temperature controlers that can be
programed with ramp rates and hold times. Add in a solid state relay
and a thermocouple (another $40) and you can build a nice curing oven.
They are simple to set up and use. Eurotherm is one brand name that I
remember from my lab days........ http://www.eurotherm.com/
===============
Leon McAtee
Building bents for kids and experimenting with my first bent trike

Make your oven out of urethane foam insulation. Line it with aluminum
foil. Install 100 watt lightbulbs as needed to get the desired heatup
rate. I used 8 or 10. Put aluminum foil reflectors over the bulbs to
keep them from shining directly on the part and creating hot spots.
This is the oven I used to bond some honeycomb repairs to a Gulfstream
G-II flap, a 250° cure process. Of course, I used a hot bonder to
control and monitor it, but a simple thermostat would work just as well.

The biggest factor in your heatup rate will be the mass of your mold.
Less massive will make life easier. You'll need to have thermocouples
right on the part you're curing.

Don't use vacuum with a bladder. Apply pressure. About 2 atmospheres.
Make sure you consolidate your layup by applying pressure at
elevated temperature for a few hours before the cure cycle.

I have two Vision R-40's.

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
>


--
J Kimmel

www.metalinnovations.com

"Cuius testiculos habes, habeas cardia et cerebellum." - When you have
their full attention in your grip, their hearts and minds will follow.

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.

Good info, thanks.

This post brings up a couple of questions...

1. Do I need breather with a bladder (to allow the air to be forced
out)?
2. Is there any concern with vapors building up in the oven and
causing a fire?
3. Perhaps it would be a good idea to put 2 bars in the bladder and
then put the whole thing in a vacuum bag so that the mold only sees
approximately 1 bar? This would keep the fumes out of the oven too.
4. Can thermocouples be joined together to "average" without using
software?
5. What is a very affordable PID controller (preferably under $100)
that will allow the ramp rate (up and down) to be set?

Thanks again folks.

Joe

wrote:
> Good info, thanks.
>

> 5. What is a very affordable PID controller (preferably under $100)
> that will allow the ramp rate (up and down) to be set?
>
> Thanks again folks.
>
> Joe
>
Try e-bay item 7546821715. I have one which I have used a couple of
times and am satisfied with.

Dan, U.S. Air Force, retired

"Dan, U.S. Air Force, retired" > wrote in message news:1KiYe.29212$dm.24132@lakeread03...
> wrote:
>> Good info, thanks.
>>
>
>> 5. What is a very affordable PID controller (preferably under $100)
>> that will allow the ramp rate (up and down) to be set?
>>
>> Thanks again folks.
>>
>> Joe
>>
> Try e-bay item 7546821715. I have one which I have used a couple of times and am satisfied with.
>
> Dan, U.S. Air Force, retired

47 bucks delivered with the thermocouple! Does it do PID? Heck of a deal it looks like...

..Blueskies. wrote:
> "Dan, U.S. Air Force, retired" > wrote in message news:1KiYe.29212$dm.24132@lakeread03...
>
wrote:
>>
>>>Good info, thanks.
>>>
>>
>>>5. What is a very affordable PID controller (preferably under $100)
>>>that will allow the ramp rate (up and down) to be set?
>>>
>>>Thanks again folks.
>>>
>>>Joe
>>>
>>
>> Try e-bay item 7546821715. I have one which I have used a couple of times and am satisfied with.
>>
>>Dan, U.S. Air Force, retired
>
>
> 47 bucks delivered with the thermocouple! Does it do PID? Heck of a deal it looks like...
>
>
I'd be able to answer if I knew what PID is.

Dan, U.S. Air Force, retired

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

In article . com>,
wrote:


> 5. What is a very affordable PID controller (preferably under $100)
> that will allow the ramp rate (up and down) to be set?
>

>
> Joe

A stand alone, full PID with ramp and soak? Several hundred dollars, I'm
afraid. Keep an eye out on ebay, but the one Dan referenced isn't such a
beast.

Again, I have absolutely no idea what your requirements are as far as
accuracy and precision. If you can clarify those, you might find that
you need less sophistication. Also, as someone else mentioned, you might
find PC based software to do the work of a temperature controller. I
don't know what's out there in that regard.

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
> :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.
>
> 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

GREAT explanation Richard. That's exactly the way I understood it too
(and why I am trying to be pretty careful with my ramp rates). If you
ramp up too fast then it could cure before it has a chance to get rid
of the voids. I'm not exactly sure what happens if you ramp up too
slow but it must be a bad thing :)

Also, if I use a bladder I'm assuming I still have to use breather
cloth so that the air has a chance to go somewhere? If so how do you
keep the prepreg from "losing" some of the resin to the breather cloth?
Should I use a peel-ply that breathes the trapped air but still
doesn't allow the resin to get lost to the breather cloth? Is there a
peel ply that is stretchy enough to expand when the bladder expands?

Good discussion folks, we're all learning lots.

Joe

On Wed, 21 Sep 2005 17:49:49 -0500, "Dan, U.S. Air Force, retired"
> wrote:


>>
>> 47 bucks delivered with the thermocouple! Does it do PID? Heck of a deal it looks like...
>>
>>
> I'd be able to answer if I knew what PID is.
>
>Dan, U.S. Air Force, retired

in control system parlance PID is proportion, integral and derivative.

they are used when the state of the process being monitored cant be
directly measured but must be inferred or calculated as the integral
of some calculation. one that comes to mind is the inference of a flow
rate from the upstream pressure and downstream pressure differential
of a fluid flow through a known diameter aperture plate.

Stealth Pilot

Should I be considering this method in building my fuel tanks? It's my
understanding that the higher cure temp, the higher delaminating temp.
Or am I reading too much into this?
Lou

In article >,
Stealth Pilot > wrote:


>
> in control system parlance PID is proportion, integral and derivative.
>
> they are used when the state of the process being monitored cant be
> directly measured but must be inferred or calculated as the integral
> of some calculation. one that comes to mind is the inference of a flow
> rate from the upstream pressure and downstream pressure differential
> of a fluid flow through a known diameter aperture plate.
>
> Stealth Pilot

PID control algorithms may well be used in conjunction with indirect
process monitoring, but that isn't my understanding of what PID means.

PROPORTIONAL --

You want to heat a pot of water to 170 degrees F with an electric
heating element. If you turn off the burner at 170, the water temp will
coast to 200. So you decide to scale back the power, beginning at 150.
The difference between target temperature ("set point") and the
beginning of scaling back power is called the "proportioning band."
Typically, the power to the burner is cycled off and on. 9 seconds on, 1
second off. Then 8 seconds on, 2 seconds off, etc. Even when the
temperature is above the target, you still get a couple of seconds of ON
time and 8 seconds of OFF time, just to minimize PIO -- Pilot Induced
Oscillation.

Now, you've got less initial overshoot, and smaller oscillations around
the set point. (An ON/OFF controller is always shutting off too late and
coming back on too late, because it can't anticipate and correct for lag
time in the system.)

INTEGRAL --

But, proportioning controllers tend to stabilize below set point. How do
you fix that? With manual reset, or, automatic reset, calculated
mathematically as an integral. Integral compensates for droop before it
exists.

DERIVATIVE --

We're still stuck with that pesky initial overshoot, the largest
magnitude deviation from set point, before the oscillations dampen out
to an acceptable level. (Tempering of chocolate requires very minimal
deviation, and the process requires many hours. Overheating and then
cooling a chocolate bar destroys the temper, and thereby the texture, so
don't do it!) The derivative function, obviously, watches the RATE of
change as the process temperature enters the proportioning band and
begins to approach the set point. To anthropomorphize, "where am I,
where am I going, and how fast am I getting there, and how quickly can I
react?" You start pulling the power back on downwind, at the latest,
planning a carefully controlled deceleration to stall speed two inches
off the ground. As things change, you keep fine tuning things.

Sorry for waxing pedantic on this one.

In article om>,
wrote:

> GREAT explanation Richard. That's exactly the way I understood it too
> (and why I am trying to be pretty careful with my ramp rates). If you
> ramp up too fast then it could cure before it has a chance to get rid
> of the voids. I'm not exactly sure what happens if you ramp up too
> slow but it must be a bad thing :)
>

The more I think about this, and based on what Richard and others have
said, the more I think that you don't need a sophisticated controller,
particularly in light of your financial constraints. Maybe a
well-insulated box, (oven) with the correct size heater, would work
fine. You might have to experiment a bit with heater size to fine tune
it. And, you could put in three small heaters with external switches.
Use all three for heat up, two for holding temp, and one for
decelerating the down ramp. A bit of experimenting with different
wattages might do the trick nicely.

"Smitty Two" > wrote in message ...
> In article >,
> Stealth Pilot > wrote:
>
> >
> Sorry for waxing pedantic on this one.

Spoken (written) very clearly, no apologies needed....

On Thu, 29 Sep 2005 18:32:03 -0700, Smitty Two
> wrote:

>In article >,
> Stealth Pilot > wrote:
>
>

>
>Sorry for waxing pedantic on this one.

so why didnt you step in and answer the guy's question?

In article >,
Stealth Pilot > wrote:

> On Thu, 29 Sep 2005 18:32:03 -0700, Smitty Two
> > wrote:
>
> >In article >,
> > Stealth Pilot > wrote:
> >
> >
>
> >
> >Sorry for waxing pedantic on this one.
>
> so why didnt you step in and answer the guy's question?

I'm not positive which question you're talking about, because I don't
remember all the details of our little saga. Recumbent bike guy came in
here looking for temperature control info for his custom carbon fiber
bicycle. Someone suggested sitting and watching, with a thermometer and
a switch, so I brought up the shortcomings of ON/OFF controllers and
suggested he might need a PID controller. (Based on subsequent
discussion, I've reconsidered that, and said so.)

I think it was Dan who had an inexpensive controller from ebay. He was
asked whether it was a PID type, and by looking at the picture, I could
tell it wasn't, and I said so. When Dan said he didn't know what a PID
controller was, I didn't interpret that as him asking for a detailed
explanation. I thought I did answer the relevant question, which was,
"is the ebay model such a beast?"

Which brings me to my best attempt at trying to answer your question: I
actually thought that the nitty gritty details of what PID controllers
do was outside the scope of RAH and beyond the participants' interest.
But since your explanation seemed incomplete, I wanted to offer a little
clarification in case anyone was still actually reading this thread!