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morepower
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TomDesign (05/12/2016)
so guys i simply need to make big owen correct? any help what is needed?Yes.. You can make it as simple or as complex as you want.. The better is it insulted the less power it needs is obvious. But there are a few things you need to do and not cut corners. You need a duct with a fan that is driven independently of the heater element. You can still run a cheap heater but you need to rewire it to let the fan run from its own power cable. Also use a fan that can take higher temperatures as most chinese heaters have a thermal cut out on the fan motor that will not let you run at the temperatures you want.. http://www.ebay.co.uk/itm/High-Temperature-Extractor-Fan-VA-16-2-/221929876966?hash=item33ac0d2de6:g:WOEAAOSwj0NUfHGaThe duct needs to force air to flow through the whole oven. So I have it pulling air from the front of the oven across the door. It is ducted to the back corner and blows up to the roof of the oven so the air has to go corner to corner.. The box can be MDF and expanded foam insulated (kingspan) if you want and just use a sliding door of MDF. It will lose some heat if you do this (I have but I have a lot of old sheets and blankets draped over the door to keep the heat in as much as possible). Then you need to have a controller as it makes your cure repeatable with every cure cycle.. you can get ramp and dwell controllers from eBay if you want to just get going. They are called re-work station controllers and do need some thought as the timers work in seconds not minutes or hours. Plus you need to add a on off switch to the control panel or the controller will not work, I think the Omega ones do this too, but their instructions are better than the ALTEC PC410 instructions. Wire the controller to a relay (mine is 40amp) to turn the heater element on and off. http://www.ebay.co.uk/itm/Altec-Pc410-Temperature-Controller-Panel-For-Bga-Rework-Station-Rs232-Module-O-/122009754612?hash=item1c68591bf4:g:dmsAAOSwImRYIlZw After that all you need is to plumb in some vacuum pipes....
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TomDesign
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so guys i simply need to make big owen correct? any help what is needed?
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morepower
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With out of autoclave pre-pregs getting better there is less need for an autoclave for almost all the work we as either small businesses or hobbyists do. The added strength given is not that great so adding one more layer or not making a part that is quite so structural is the compromise. How many meters of material would we need to use to make the cost of the autoclave worth while?
The one thing that does seem important is the ramp and dwell controller for OOA's. I know some get great results without one but having one does take out human error where the oven is concerned. Plus the cost of a controller is only a small one which could be paid for with one or two items that fail due to user error.
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Hanaldo
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I only really do smallish things. Anything bigger than say 0.5sqm I will usually infuse, just due to the cost of prepreg. Unless it is a super complex part in which case pre-preg is quicker, easier and has less risk of failure. And no, an autoclave is a pressurised oven made for regular pre-pregs so you can apply pressures of 80-150+ psi. You want out-of-autoclave pre-preg (what Easy Composites sell); this just cures under vacuum pressure and so only requires an oven with an active vacuum source.
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TomDesign
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so Hanaldo like wings door panels or mirrors best pre pregs as infusion i think real pain with temperatures and etc? autoclave i guess simple owen and from outside vacuuming pump? correct?
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Hanaldo
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Well my advice would be to really think about whether you need an autoclave or not... I think they are fairly redundant these days. Obviously still have their place in F1 and aerospace, but for anything else OOA pre-preg will do a great job. Infusion is definitely a pain compared to pre-preg. If I could do everything in pre-preg I certainly would!
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TomDesign
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any advise guys to me that want to build autoclave and to start using pre pregs as i think infusion is real pain?
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Hanaldo
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Another thing I worked out was specifically with the PID controller I'm using (an Omega CN7800). For whatever reason, the ramp setting don't work on this controller if you don't give it an initial dwell point. So I used to tell it to ramp up to 55 degrees over an hour, but it would heat straight up to 55 in like 2 minutes and then just hover around there for the hour duration. Initially I thought the ramp control just wasn't any good, but then I noticed that when it ramped up to the next stage of 75 degrees it would take the appropriate amount of time. So now I tell it to ramp up to 20 degrees over 2 minutes, hold that for 2 minutes, then ramp up to 55 over an hour. This works perfectly and helped greatly with the finish. So that's one of the things I would say might catch a few people expecting perfection on their first run. You need to know your oven, you need to know how your controller works (which takes a bit of watching, don't just set it and expect it to work as you want it to), and you need to know your moulds.
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Hanaldo
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The ones I get caught on are the complex tricky pieces, as the moulds tend to vary a bit in thickness. In some places they can be as much as 20 or 25mm thick, in others they are between 5 and 10. Simply the draw back of wet laid moulds and overlapping layers of CSM. These moulds take a bit of figuring out, and I've worked out they usually need a much much slower ramp and dwell cycle. I suppose you need to cater for the thickest part and it doesn't matter what the thinnest parts are. I have recently started adding aluminium powder to the resin when I build these moulds, and this helps ALOT. I do recommend it to anyone having difficulty with an OOA pre-preg that is known to work well normally.
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morepower
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Hanaldo (22/11/2016)
morepower (21/11/2016)
Hanaldo, I think it is most want to have a material where the guidelines given work 100%, 100% of the time regardless of what oven they have or how they run the schedule. It does take some work and needs to be done correctly with a controller. Do that and work on the timings and ramp rates a little and it does work perfectly as you and I know. If I could just say do A, B, C and D then it works that would be great. But you cannot allow for people doing it manually or the small lay up issues people 100% right with your lay up and bagging and then it is all down to the oven and the controller. I think a ramp and dwell controller is as important as any other part of the process. Yeh I agree. I think it's impossible for any given instructions to work straight off the bat, especially when most of us have made our own ovens and they are all completely different. You also have different mould materials, different thicknesses, etc. For whatever reason, I need to start EasyPreg at 35 degrees and ramp it up quite slowly to 55 degrees and give it a decent dwell there. Then I can take it up to 80 or 90 for the rest of the cycle and it won't have any issues. Although every mould is different and takes some figuring out, I never count on the first piece working perfectly. I think thats one of the things no one thinks about. It is trying to find a schedule that works with all of your moulds. I think the one I have has been a good compromise as it works with all of my moulds. But I would imagine it could be different with alloy moulds or ones which are much thicker.
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