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#11
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#12
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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 |
#13
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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. |
#14
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" 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. |
#15
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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 |
#16
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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 |
#17
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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.) |
#18
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"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 |
#19
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"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 |
#20
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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 |
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