pre-preg pinholes.. driving me crazy


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roger sbk composites
roger sbk composites
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found a picture of the first part fast cooked

roger sbk composites
roger sbk composites
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thanks to the endless help from more poweri decided to try out the VARI-PREG fabric from eassy composite i originaly got eassy preg and vari preg for a costumers part but i was able to sneack a bit of vari preg to see if a good result was posible fromt hat more affordable fabric and the results are acceptable tiny viods because of layup mistake but this was a rushed test and also some breather made contact inside with the carbon it jumped the release film so dryed that spot out but in conclusion i think the vari-preg fabric works fine when you take you time...total time consumed in this airtube was 24 hours 
  

here is where the breather made contact with the c.f



morepower
morepower
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That is not bad.... As you say, you need to get your layup techniques down a little more.. You need to have total control over the oven too... That will give you consistent results too... But not too bad.. VTF/easy preg would/should give a better finish still.. But cost is always part of the equation when you are making parts for sale... You need to juggle to get the most profitable way of making a part which the customer is happy with.... 
fgayford
fgayford
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You have bridging for sure. You can see how some of the resin has tried to fill the voids and puddled in the gaps.
You must maintain full vac or pinholes will appear. The voids would probably have air trapped which would boil and froth the resin.
When you place your carbon always press in the potential bridge areas first and slowly move away from them as you use your heat gun to lightly warm the prepeg. warm the bridge area and press in over and over as you lay down the rest of the areas.
Hope this helps.

PS: I have been doing more and more prepreg and have discovered for myself a trick of the trade I will share.
It used to drive me crazy trying to get the plastic sheets off of the prepreg.
I used to try putting a blade or pin or twizers in between the layers to seperate them.
TIP: Use a big sowing pin. (I actually use a dentists pick-sharp pin end) lay your prepreg sheet down and scratch at 90 degrees from a corner and the stuff peels up instantly, make like your going to drag a deep scratch through the prepreg. If it doesn't lift off make a bunch of quick scratching motions and it will. The only hinderance to this is the prepreg gets too warm.  
Hope this helps.
Fred
combustioncraig
combustioncraig
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Hey I am new here but I am mechanical engineer and here are my thoughts.  You have bridging for sure like everyone else has pointed out.  I would try using a heat gun to get the prepreg pliable (but sticky trade offsErmm) and a tool like the lil'chizlers (or any Vinyl wrap applying tools) to push the Prepreg down into the voids.  It is also recommended to debulk after the first layer and then every 4-5 later after that. Doing so gets expensive quick unless you are using some sort of RVB (reusable vacuum bag).  You also might be able to order just sheets of epoxy resin (at least you can here in the USA).  This is a less ideal option as you will have very resin rich areas that are weaker but if you are just going for surface finish it might be a option (make sure the resins have the same cure rate as your prepreg).  Hope this plus slower the ramp rate/ longer dwell time at low temp cures the problems.  Also lacquer and clear coat may become your new best friends if you continue to have problems.     

On a side note I am going to be doing a test with some low temp epoxy prepreg for a autoclave and add a thin sheet of epoxy resin (same resin and same supplier) and see how it affects the surface finish.  I am doing this because after using easy composites surface layer prepreg(resin rich stuff) I thought I might try it.  If it does work this will save a ton of money but I am not too hopeful.  I will do some ultrasonic testing and cut a few layers apart to see if the interior layers are full of pin holes as well just to prove the concept.        
roger sbk composites
roger sbk composites
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hey guys i have some updates... i found that bridging was the problem and also my layup as in plain weave i tried to do all at once and was imposible unlike twill... here are some other i have managed to pull out and clear coat


here is a test
 someother tests
here is my radiator shroud of my bike i did with the same autoclave fabric with debulking ect. and very slow cooking for 14 hours and was almost perfect

and i finaly got around to making the oven and the key is in the slow cooking and slowing everything down and full vacuum i now debulk all my parts for about 3 hours in between layer and debulk another 3 hours BEFORE i actualy cook them i will start testing parts of this oven shortly
and i've also started using VARI-PREG system from easycomposites.. as a surface layer so lets see how the tests come out on the new oven stay tuned
Edited 11 Years Ago by roger sbk composites
Djekouk
Djekouk
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Nice to see progress mate, got any more pics of ur oven? Inside oven? 
Regards
roger sbk composites
roger sbk composites
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yeah sure...  after two hours of tunning the oven... and drilling venting holes i finaly got it stable and i had to add a second air heater and also brake little tabs on the termostat that the original airheaters bring to be able to adjust it behond the limits... thats untill the controler gets here... also you have to bypass the fan ... fan needs to stay on and only the heating elements be controled



untill the controler gets here i wont be doing any overnight stuff i also plan on putting a braker switch board for all this just in case... and well this is only 50% of the way stable oven ... "EMPTY" now i need to see what it does full of molds because it can easy take an entire motorcycle fairing set 
Djekouk
Djekouk
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Cool design :-)
morepower
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Get one of these too... It can be used on the parts you cook as a check of the actual temp of the mould/part as it cures. You can also use it now as you set up the oven.. I checked mine in at least 6 different locations front to back and top to bottom..

http://www.ebay.com/itm/ET72-Maverick-RediChek-Remote-Wireless-Meat-Probe-Thermometer-6-Taste-Settings-/300934234856?pt=LH_DefaultDomain_0&hash=item46111402e8

It is very basic for an oven but you will see once set up works very well...
GO

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