Vac Infusion of large parts (lots of questions)

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#1

So i am planning on doing vacuum infusion of some vehicle body parts in carbon fiber as some one off prototype work to use on my race car and as a means to get a good repeatable resin infusion process worked out for my future structural parts and projects. I have a lot of questions about the whole process as i have never made fiberglass molds off of existing parts or done large scale infusions like a car hood. I will try to ask the questions in a reasonable order from the plug preparation all the way down to the finishing of the components.
I should first clarify i have some experience in wet layup of Fiberglass CSM and carbon fiber, wet layup/ vacuum bagging of carbon fiber. These questions will be a little more specific and most regarding the infusion process. I have read through a good amount of infusion posts on this site and just need some clarification and advice.

So i will start at the plug. I am starting with the smallest component the trunk lid which is roughly 3’x3’(1mx1m). I will be painting and finishing the hood to a very nice finish as if it were going on the car. so i will have a very nice plug. attached to the plug will be a flange which i will attach to the underside of the lid to give an extra 4-6inches around the trunk lid which will serve as a flange for extra materials/ infusion space ect. First point of concern is the release system. in the past I have only ever use wax/pva system because I was never making cosmetic parts. I never really got a nice finish from a part using the pva in a brush on application. If i want the mold to have a really nice polished surface would it be worth the costly investment to go to a frekote system? especially if it is a one off part and i don’t intend to do production with the mold? Will going to a spray application of the PVA net a better finish? if i have to polish the mold no matter what I understand that it would be unnecessary to invest in a frekote system and just finish the surface of mold. that or just worry about all the finishing work on the resulting carbon fiber part.

To the Mold, first i will explain the process and materials i intend to use. i will use the US composites PE 404 tooling resin, 4-5 layers of 1.5 oz/sqft (461g/sqM) fiberglass Matt, PE Tooling gelcoat and potentially a wood back brace which will be glassed into the hood to provide stiffness.
first things first, if i brush on the gelcoat will i still be able to get a nice finish or does it need to be sprayed? do i really need a tooling gelcoat for a mold that will only see 1-2 uses? will one quart (1liter) of gelcoat be enough to cover a trunk lid that is about 3’x3’ (1mx1m)? Is it ok to do the first glass layer with the heavier glass matt or should i buy a thinner matt for the first layer? If I lay down say 3 layers, let it cure then lay down another 3 will that lessen the shrinkage caused by the PE resin? would 6 layers of glass require a wood bracing on the back for stiffness? can you polish gelcoat in the same way you would polish paint on a car?

Onto the infusion process and carbon part. My plan for the part is to use applied polyeramics SC779 infusion resin 300cps and has a 200f Tg, 2-3 layers of 5.7oz/sqyd (200g/sqM) 2x2 twill weave carbon, nylon coated peel ply mesh, infusion mesh, standard nylon bag film(not stretchy), between layer flow media like soric? MTI hose and ive got a big vacuum pump.
first few questions all regard the infusion process and release system. Will a standard brush on pva system work with infusion? will the pva cause a more dull finish on the surface of the part? I read through an entire post about in mold coatings to be sprayed down as like a surface clear coat, is that something worth doing on a part this large? i will be doing a car hood that is even larger. I read that if the part is not infused while the coating is still tacky you will have cosmetic issues. I would like the part to require as minimal finishing as possible but I had already planned on doing a clear coat on the part at the end for UV resistance. Is there a particular resin flow speed across the part i should be looking for or will the MTI hose do the regulating for me? Does the MTI hose need to completly encompass the part or can it be set up like a regular infusion that pulls from one side to the other? for the resin system should i choose the slowest hardener to ensure good wetting of the fabric? I do not have a way to do a higher temp post cure so it will be at room temp 75f. Time really isn’t a factor for me as this is all experimental so if it takes a week to cure thats not a problem. Do I always need to degass the resin before the infusion? when using MTI hose how do you know when to clamp off the feed line? do you have to cut the resin supply before it reaches the last bits of the hose? I understand you can calculate by weight for a close resin measurement but the feed pots and lines get added ect and if no resin escapes you have to cut it off at the right time correct? does spray adhesive effect infusion? I have never used it but see its necessity for an infusion process. how does print through happen when doing infusion? how can it be avoided?

for the construction of the part, do you think 2 layers of carbon would be enough for a fairly stiff hood/trunk lid? it has some contour and shapes that would promote stiffness but maybe 3 layers to be safe? The other point of construction i forgot to mention is I will be using 2in carbon tape around the edge of the part for improved chip resistance and a little stiffness. there wont be any underside ribbing on the part.It a race only vehicle and just needs to be as light as possible but stiff enough that one guy could pick up the part from one side without it collapsing on itself. with only 2 or 3 layers do i need a flow media between them like soric? Is the purpose of the flow media just to ensure that resin gets to the first layer? Is there a limit on how many layers you can infuse at once or is that dependent on other factors like the resin?
for finishing i plan on clear coating the part for UV protection. how do you prep a surface for clear? light sand with 400grit or so and spray clear right to it? how much can you rough up the surface before you hit the carbon fibers? do you have to use a special clear to avoid chipping if the part is a little flexible?

Thank you all in advance for any responses i really appreciate it. Here is the part (in process of being sanded painted ect.) and also the car just for fun. 1962 pontiac tempest. Also if there are any experienced composite guys in the Chicago area I would love to meet up and go over setups ect.

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#2

Holy hell, how do you re-size pictures?

#3

Did my questions seem to broad? I know it was a lot of questions and i am still digging through the forums to find more answers but any info is appreciated.

#4

I will answer today in the evening.

#5

Thanks DD, if you are answering i may as well tack on one more question about the MTI valve. I understand it is your product so you would recommend it as the best resin throttling device but if a guy were trying to save an extra dollar or two where he could can the same effect be achieved by slightly clamping the resin feed line? at 4$ per valve its not that expensive so i may just get them while i am at it.

#6

Yes pontiackid73, I noticed the mti valve throttled down my infusion to much

#7

So do you bother with any throttling at all? How large of parts are you doing?

#8

I retract my statement, I did not have a absolutely perfect vip so I can’t fully judge how the valve would have worked under a perfect scenario. I would like to try it again at some point

#9

I don’t use no mti hose I will stop flow mesh shy of spiral tube that slows down pretty well. As for post cure I can tell ya epoxy needs a post cure if your buling body parts otherwise your stuff will move like crazy in the sun. What epoxy are you using? I try to get the fastest curing epoxy as I can get as long as I can infuse from point a to b. as most member here know its hard to tell someone exactly what to do, size of part, epoxy flow mesh ect. It goes on with things that can fail.

#10

Does a post cure have to be done with the part still in the mold? My plan is to use applied polyamerics SC-779. I guess I can assemble a real simple oven If it needs to be post cured.

#11

I have an oven im outside of Chicago, bolingbrook

#12

id post cure in the mould, but get in touch with th resin supplier regarding post cure temp. you should be able to do a lower temp cure for longer, meaning you can get away wiyh a simple tent and a fan heater at about 60C, maybe 4 hours, but check to be safe

#13

Good idea zac i will give them a call, Tuff do you do composite work professionally? I’d love to come by sometime if that’s ok to check out your setup. I live in tinley park so your not far away at all

#14

Not full time we started building racecar body parts for are own use and them it took off as people loved the qualty of the parts so we bulid parts part time. All my stuff is infused.

#15

I cure out of mold usually between 24-48 before it hits the oven and I do a slow heat ramp.just have to make sure part is relaxed in oven and not stressed works well for racecar body parts. Anything with very critical dementions I’d vote for in mold cure.

#16

If you spry the PVA you will get very good results and you can be sure that it will release! If you can do the job in a spray cabin it will be perfect. You can easily polish the mould to high gloss.

The layup of the mould is fine, I would use the Optimold II resin for building the mould, nice to work and nearly no shrinkage.
A VE GTooling gelcoat is very easy to polish and gives you a perfect surface. I use about 1kg/m² per layer. If you want to polish I would invest in 2 layers of gelcoat.
It can be polished in the same way than a car paint.

I would use a foam core, I like the 3D Core. Very stiff. We just build a Radical SR3 in full carbon. Most panels a 1 layer 200g/m², 3mm 3D Core PET 100, 1 layer 200 g/m²
Thats imperssive stiff.
I would also use a external flow media on top, will be a lot lighter at the end.
Also the absolute pressure of the pump ist decisive. You should bve able to get below 10mbar of pressure. I would recommend to invest in the Greisinger pressure gauge.

You can use the standard PVA. Even if you are a novice I would recommend it.
I would also use the In Mould Coating from German advanced Composites. You have to wait until it is dry and you do not have a time window. It also gives you a UV protection. If you brush or spray 3 layers you have enough to polish the part.

On the hood I would use the MTI around the parameter and make 1 or 2 infusion lines in the middle.
Place the resin pot about 1m below the part and let it infuse until the part is completely filled. You can also use the MTI valve, that will regulate the amount of resin and close itself once the part is saturated.
You should also always degas the resin, if not you may have voids and pinholes.
You can use spray adhesive, but always as less as possible, then it is no problem.
Print through is minimized if you cure at Room temperature and then ramp the part as slow as possible.

Take the layup I wrote before. Put some tape to the flanges and where it is fixed. Do not use internal flow media if you want to save weight.

Hope that helped

Dominik

#17

There are a bunch of different ways to approach the series of questions you posted (all good questions to ask, btw) so i’ll touch on a few I hope will help you out from our experience.

Instead of brushing on PVA, consider dropping $20 on a HVLP gun from Harbor Freight and only use it for applying PVA. While these are not highly precise guns, it will do a great job of letting you get even coats down over larger parts evenly (much better than a brush).

We use mostly Duratec Products because it is readily available in our area and reasonably priced.

Once you have a mold for a part ready to use, we’ll wax, spray PVA (typically multiple light coats) and then spray in a Duratec Sunshield clear. Then, light use of AirTacII (was suggested as a fix to a few issues we got from using Super77 in the past) to tack the layers of carbon fiber in place.

I prefer envelope bagging when possible since it gets us closer to a fully sealed vacuum quicker. Pros who have done it for year can probably lay down a pleated bag and isolate leaks pretty quick but I fine that using envelope bags take away some of the headaches for those new to the process.

I second the suggestion to use a foam core for the wood construction. You will be surprised at how much more rigid the end product is.

i hope this helps with some areas and the best of luck to ya! We love the oddball classics so you have our vote on tossing this one some carbon fiber pieces.

I’m not sure if you have a build thread somewhere on the Internet. If you do I would love to watch the process.

#18

Thank you both DD and Munsey i appreciate the response. I have had to put things on hold for a bit as my work has me moving for the next 6 months but in that time I will still be working on the project here and there. Munsey I have not had an in progress of the build but Plan to do a big summary in the future and probably put it up on Pontiaczone.com and Yellowbullet.com. It is a drag car with 25.3 spec full tube chassis and will be one hell of a monster haha

Munsey do you mean I should use the foam core inside the laywer of the carbon fiber hood or in the fiberglass mould? Do you have to do anything different when infusing with the foam core or will the resin still flow on the top and bottom of the core? I’ve got a sheet of 1/4" divinicell that I have used in the past, its a closed cell foam I think 3lb/ft^3 density?

#19

Divinycell needs to be perforated and scored before you can infuse with it. You can just punch some holes an inch apart or so, then use a metal ruler to lightly score the surface between the holes.

Alternatively you can use infusion specific foam cores such as 3D PET or Soric.