Yes. You need to either get a cheap rework ramp and dwell controller and spend some time making it work how you want and accepting the compromises or get in touch with West or Omega for one of the better more suitable controllers. The only thing is then you need to work out the best ramp rate and staged cure for your materials.
I got my controller and SSR, switches, etc from Auber instruments. Pretty happy with it and it was very affordable, couple hundred bucks for the whole set up. They have wiring diagrams for basic setups, so if you spend brainpower on it you can figure out a controller set up without a huge background in electronics. I stripped the controls from a household convection oven and installed a box that runs the bake element. The bake element is waaaay more wattage than I need for a 1 or 2 hr ramp, so I still have to control from the air temperature rather than the actual mold temp. My mold is too thick to respond quick enough. If the element runs at full gas the oven temp gets over 600 degrees and things start smelling pretty bad. It’s surprising how little wattage you need for slow ramps in a normal size oven. With the Auber stuff I also wired switches individually for the element, fan, and oven light, plus I have a second “dumb” controller for reading temp from a second thermocouple. So I can monitor air temp and mold temp. Definitely took some time to build this, but it’s really nice having the PID controller. And it wouldn’t be too hard to adapt the set-up to a larger home-made oven or molds with integrated heat elements.
(link to the PID ramp/soak controller)
http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=4
Bringing this back from the dead, I’m thinking I may need a recommendation for a different prepreg fabric.
Right now I’m using 300 GSM 3k 2x2 twill from Rock West Composites while I wait for a new fabric from Hexel to arrive. I’m manufacturing some pieces for a motorcycle but they’re coming out rough with huge gaps in between the tow overlap. (And I’m having to use a LOT of fabric to achieve thickness that gives me enough strength to not worry about failure.)
I’m clearing them, which obviously helps, but the amount of clear required is exceptional, because I’m filling holes more than anything.
Here’s the resin data sheet.
https://www.rockwestcomposites.com/ckeditor_assets/attachments/122/Newport%20301%20Data.pdf
Following the data sheet, I’m ramping and dwelling as directed, so the 2 hour cycle times @250-300F are highly desirable, given the small oven I’m using (4’ cubed), and need to turn parts fairly quickly.
So, if anyone can give me some ideas as to a fabric that’ll give me a heavier weight (thickness) fabric better suited towards making cosmetic parts with a lower post work requirement, I’d sincerely appreciate it.
Oh, the molds are high a high temp epoxy system backed with woven glass, cured to 450F with a service temp of 400F.
I’ll upload some pics as soon as my phone stops being a jerk.
Cytec VTF261 or SHD DF212 are the only systems I’ve seen that deliver true pinhole free results from fibreglass tooling. I believe SHD have actually developed a new system that they say works even better, but morepower would be the one to speak to about that.
Personally I use Cytec VTF261, it’s outstanding performance just makes it worth the eye-watering price.
I’ve used gurit sc 110 and cytec vtf 261, both came out flawless with vacuum bagging and fiber glass molds.
So with a ton of clearing I’m getting beautiful pieces, but I’m struggling to get tight corner compaction in the same spots no matter what I do (ply thickness, orientation, bag positioning etc… none of it makes a difference.
Here’s a video of what it looks like out of the mold.
https://www.instagram.com/p/BHYF1QYjHOG/
are you using edge breathing? Also how long do you put it under vacuum before cooking it?
Its advisable to put thermal couples on your mould surface to see actual ramp rate and temp during cure. I’m guessing you’re using fiberglass tooling, so your tool is lagging and is likely colder than you want it to be. You may find that you need to increase your oven temp 5-10C.
I’ve never had anything come out looking so dry. Definitely log the temp on the part (i put a thermocouple on the outside of the bag, I compared to inside and there was only about 1 deg in it)
How good a vacuum do you have? And just to be certain, you are using non-perforated peel ply yeah?
Good question. I have two different prepregs and one calls for no perf and the other perf. Both call for edge breathing and a long preoven debulk. But that does look bad. I’d think it was a fast ramp rate or uneven heating?
Sorry, I meant to say perforated or un-perforated release film, not peel ply.
For prepreg you should only ever use un-perforated release film, as the small amount of resin you lose will definitely cause pinholes… But what you have is way more than pinholes!
I think you need to detail exactly what layup you’ve used, mould prep, bagging details and oven temp vs time info. Most prepregs want 28+inchHg vacuum and very little pressure lost on a drop test.
Bigtopgt,
So how have things turned out? Did you get the challenges with the rock west prepreg sorted or did you try a new system?
Hanaldo,
Regarding the vtf261. Do you build part thickness with a cheaper material for internal plies or do you use the vtf261 through and through?
Just to clarify in advance, the VTF261 is specifically the surfacing material. Cytec have their VTM264 backing ply material as well.
So to answer your question; no I generally don’t use the VTF261 through-out, I use the VTF261 as the surface layer and then the 400g VTM264 for the bulk. This is more to do with layup time rather than the actual material cost, doing one layer of 400 is just easier than 2 layers of 240.
I have also experimented with using a much cheaper product (completely unrelated to Cytec) for the backing layers, and surprisingly have had quite good success with that. I haven’t played around with it enough to be able to say it works as well as the VTM264, but what I can say is that the 2 different epoxy systems appeared to play well together and cured very strong. The crude testing I did on those panels didn’t reveal any performance issues, with no delimitation or obvious decrease in strength compared to the VTM264. Surface finish was also fine, the VTF261 didn’t appear to have any issues working with the cheaper material.
The main reason I played around with that is because I was interested in using uni-directional pre-pregs to back-up the VTF261.
Thanks for the advice, guys.
I’ll post an update when I get to my office.
So far, I’m using the wring release film (peel ply), at a minimum.
Oh wow… I have never had a part that bad even when I made a huge mistake when I forgot to connect my manifold to the vac pump and the bag lost vacuum over time.
That look like someone sold you a standard HT prepreg as OOA prepreg. I think it is a main problem of temperature over time.
This is what I get from the SHD material.
More power can you please remind me of the spec of material you use from SHD?
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