In an autoclave operation does the clave vacuum out air before pumping in nitrogen?
Not normally. I reckon that if you are adding 100psig to the vessel, which is at 0 psig. There would be relatively little AIR in there, so it’s pointless to pump out.
In general, no, you just add N2.
That makes sense. For some reason i was actually wondering about this earlier whilst driving my van.
Some one has offered me a very small autoclave for sale that doesnt have a nitrogen feed on it and i was wondering if that would have much or any effect on things.
This clave that i have been offered is only about one and a half foot dia and about two and a half foot length.
I need to purchase a heat source to heat the autoclave and that can be computer controlled. I found a company that sells the software, and they have all the controls but i am thinking of rigging our own controlls because i don’t really have $40K to buy their controlls.
So that is good news, no need to vacuum out the clave before pumping in nitrogen.
Next question. What is used to pump the nitrogen into the clave? And what is used to cool the clave?
How robust is this autoclave going to be? I don’t mean to discourage you but I’m not sure how easy it would be to program an autoclave for specific cure cycles. To a design the control system for an autoclave you’d need graduate knowledge of convection conduction as well as computer controls. Just because you have a heat source doesn’t mean that the heat will effectively be transferred to the laminate stack.
Good luck on your project though and please post your progress here!
Correct. We have to do a lot of heat mapping on sample parts before establishing a cure program, and even the location of the tooling inside the autoclave. Sometimes over 20 tc’s are needed on the test parts to get a good idea of temperature distribution.
Autoclaves are not for the inexperienced!
Re Nitrogen:
We don’t use N2 in our autoclave (as far as I know no one in NZ does), the cost is just too high. We do have an air drier to remove moisture in the air.
Re Temperature control:
A lot of work can be done to get a real good set up, which is very important if you are making certified products but if you are making car parts for example it’s not as critical. However a 5degC difference can be the difference between one end curing and the other not.
The key to good temperature distribution is air flow around the autoclave and the parts. We have fan forced heating and try to place parts in the center of the clave lifted off the floor. We test our autoclave yearly and can get less than 1degC difference anywhere inside (a local airline gets 5degC in theirs).
Most of our cooks are not for certified parts so we run a std cycle where we cure at 125C for 2hrs after holding at 80C for 2hrs. The recommended cycle is 120C for 60min, the dwell and over temp and extra time prevents exotherming and ensures the part is fully cured. But we need to modify it for thicker laminates, thick metal tools, big parts etc. As Tet said it takes trail and error to get what works, and a bit of Autoclave Black Magic(ABM).
Don’t be put off, just expect some failures and set backs but I urge you to give it a go.
1.0 To cool the clave we have 2 cooling pumps that turn on the cool down cycle, we got rid of our cooling tower because it was just taking up too much space. also we the blower on with the door open to vent out all hot air (that is if we don’t exceed around 300 degrees) as for rigging your own controls… i supported that mentality on saving 40k until last year when the work we were doing was getting too precise. our home made controls just weren’t cutting it, example passing certain government specs. we had to go pro. you have 2 options… either new controls from one of those bored charge you up the ass California companies or a better option… researching and hiring a local systems integrator… probably charge you per hour but ifs he’s legit he will tune your controls well enough. These guys usually have links attached on big company websites…
To cool the clave we have 2 cooling pumps that turn on the cool down cycle, we got rid of our cooling tower because it was just taking up too much space. also we turn the blower on with the door open to vent out all hot air (that is if we don’t exceed around 300 degrees) as for rigging your own controls… i supported that mentality on saving 40k until last year when the work we were doing was getting too precise. our home made controls just weren’t cutting it, example passing certain government specs. we had to go pro. you have 2 options… either new controls from one of those bored charge you up the ass California companies or a better option… researching and hiring a local systems integrator… probably charge you per hour but ifs he’s legit he will tune your controls well enough. These guys usually have links attached on big company websites… sorry for b[FONT=Tahoma]abbling
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While this thread is old I’m sure someone will read it in the future wondering about this same thing.
I am not 100% sure on how precise you could get it but if you used a program like Labview and some national instruments data acquisition systems you should be able to do anything you need to do. You could make the heaters and whatever else use PID and using an analogue output controller it shouldn’t be a problem. I would think this would be less than $40k.
As long as you are good in LV, and your PID equipment can handle it, I don’t see what the issue would be. Fine control is the same, for good software, or just a good PID. In the end, you are ramping up in pressure and temp, and recording what happens. You can fine tune any PID to adjust for issues, ± 1psi or ±1 deg in temp. Biggest problem is having a certified boiler vessel with tons of equipment and fittings on it 
I’m currently looking at building an oven where I can cure out of autoclave prepregs. I’m thinking about using an arduino board and software, as purchasing labview is pretty expensive outside of the university setting.
for an oven, just use a few quick acting heaters and a good PID. No need for computer control, since you can get ramping and setpoints for a cure cycle in a PID controller. Maybe use the ardunio for recording purposes.