Cost Compare PREPREG VS. INFUSION

General Composites Discussions Composites Talk
#1

I’m in need of some help getting numbers.

I know Prepreg is more costly. But there are a lot of advantages to be considered beside just pricing.

I know that to be a true cost compare you must include those things such as flow media, MTI hose or whatever other consumables that are used in the infusion but won’t be in a prepreg situation.

A.)disregard the fact an oven is needed, lets say you have one either way.

B.)let’s also assume your buying small quantities. No bulk discounts, partial pregreg rolls or by the yard/ft.

C.)I know there’s a place on here that’s selling it for $70/YD which sounds high but I think it’s possibly worth it.

D.)using that as a partial starting point would you agree that carbon cost would be somewhere in the $35/sqFT?

The major question:
What would infusion be with raw carbon costing $19/YD? I don’t know how to get the resin number? I’m not familiar with having to figure out how much resin is needed.

One more thing. Lets keep it K.I.S.S. method. I’m looking for a price per square foot, based on 1 layer.

Thanks in advance for assistance given.

#2

Getting the per lb. cost of your resin from your supplier will help on the infusion side of things, but don’t forget to add activator/initiator, cups and consumables to be fair.

Storage requires more utility with pre-preg unless your ignoring expiration.

Post curing cycles may determine the final separation in costs unless they are the same.

#3

Thanks for replying.

ok, but how do I know how many pounds per square foot of carbon? that’s really what’s really stumping me.

#4

If you know the gram weight or gsm of the dry weight of your pre-preg to compare, you’ll need to either weigh a square meter of CF on a good scale to be certain.

Your resin to cloth ratio content goal is what? 60/40 or 70/30 or what?

That will give you a WET weight to compare the pre-preg.

#5

This does a good job in comparing the two techniques in wind turbine blades.
They found that prepreg costs more upfront, but they can make more blades a year using prepreg than they could with infusion. Also prepreg resin is usually higher performing.
http://www.gurit.com/files/documents/6_Cost_Study_Infusion_vs_Prepreg.pdf

#6

yes, I know it. It’s Torray cloth 199GSM for comparison sake let’s just say 60/40 because I believe that’s what most normal grade prepreg is.

So there just isn’t a general calculation to follow? I know there can be a lot of different variables with resin types and other factors, but I’m just looking at a generalized estimated value.

For example your making a single layer panel that’s 1ft square, how much resin do you mix for infusion? 10grams? 50grams?

I know this is vague but it gets me in the ballpark. Only reason I’m asking is I’ve not done infusion.

Again, thanks so much for helping me out. I know it’s not typical request. I’m just evaluating paths to take.

#7

reading now. thank you.

#8

If you figure on an estimate of 50/50 fiber/resin you can figure out how much resin per square foot or yard or meter.

I found some 3K 2x2 Twill 50" Cytec T300 5.8 oz for $22/yd which equates to $1.80/sq ft

For resin I pay about $150, say $170 with shipping for a kit of 13.375lbs of resin which is

12.70/lb = $.79oz

so for 1 sq. ft. I need 5.8oz resin which = $4.58 per square foot of fabric.

I’ve found prepreg for as low as $35/yd at 50", if you buy the whole roll of aprox. 100 yards or so… a bit investment. But at that price it’s $2.80/sq. ft at a 60/40 FR.

At $70/yd of prepreg that’s $5.60/sq. ft.

In which case it’s not more cost effective. But with infusion you can use lower cost consumables for RT curing including non-nylon bag film. Prepreg requires some higher temp resistant materials. Granted the prepreg I had found and considered was a low temp 180-220 cure resin system. Plus you gotta figure on testing to get your setup right with the infusion and any possibilities of leaks that could happen and ruin the infusion. The prepreg is a bit more controllable and dependable and would probably result in better parts faster.

#9

whoa, Thank you for that. This is good info. One question though your price for infusion should technically include the “extra” consumables that are not present in a prepreg situation, correct? So I can just look up the price on flow media, spiral tube, vacuum tubing, seems as though most people use peel ply all the time but I wouldn’t think that’s always necessary.

I would almost bet by the time you add all those things it’s gonna be really close.

Again thank you so much for helping me out, this is a great start in my pathway search.

One other tidbit, the prepreg would obviously have be OOA material, cause let’s face it if you have a clave I personally wouldn’t even mess with infusion.

#10

of course I’m figuring out of clave… but prepreg still needs heated cure, not even oven but heatbox. Autoclave is well out of the scope for pricing. Though if I had a clave I’d be all about OOA cause it could be less costly than claving. Though to get similar results I’d probably do RTM with matched tooling, which not cheap. Application dictates process and materials right?

I think the flow media and tubing is probably pretty cheap and you might estimate it at like $.50/sq. foot or less. Peel ply would be the next biggest cost but, I figured since infusion/prepreg both need it, that I didn’t get too nitpickety. You could also think about spray tac for dry layup, which isn’t super expensive. Also release films, breathers, sealant tapes, wax/freekote releases, etc. Nitty gritty also gloves, rags, acetone, etc. The infusion can use low temp stuff so the price is less. Mostly it would be the bag for prepreg that is a little more costly.

#11

I am in total agreement with you, on this. With the $.50 added it marginally lower.
The other consumables virtually cancel each other out.

One question I do have that I don’t understand. Some use peeply on every part seems like. Why? That question goes far beyond what this topic is but I’m curious. In my experience, I’ve only ever used peelply when I know I need to use adhesive or something like that on that surface. Even still I’ve just scuffed it with grinder or whatever, and never experienced a glue joint failure. Mostly just wanting to know if I’m missing out on something?

Sent from my SAMSUNG-SGH-I747 using Tapatalk

#12

Oh, sorry I wanted to add one more thing.

I’m not necessarily looking for the cheapest route. I know it’s more expensive but I’m trying to justify that the small cost increase could be worth it because it’s “easier” to work with. Especially for me since I have worked with it and not infusion. But maybe I’m just wanting someone to agree that if you know it, and can aford it, go for it. ?

Sent from my SAMSUNG-SGH-I747 using Tapatalk

#13

This is interesting as in New Zealand dry fibre is almost exactly the same price as prepreg. Once you add in consumables prepreg is much cheaper to make parts from. In Auckland there are about 10 companies that have autoclaves that will cook parts for a small fee.

#14

Wish that were true here. Worst part is I can’t hardly find a company that sells by the yard for prepreg. They only do full rolls. And I’m just trying to start up. $3k is tough to do.

Sent from my SAMSUNG-SGH-I747 using Tapatalk

#15

I agree on starup costs… Maybe we should do a group by. I had gotten a quote to buy a 100 or 125 yard roll of twill prepreg for $35/yd. Too rich for my blood but I could use some yardage. Might be worth pitching in on a roll and then dividing it up? Something to think about.

As for the peel ply… if you infuse, you need it to keep the infusion media from sticking. If you do prepreg, I completely agree with you. I only use it if I know I’m going to do some bonding or painting. It’s great if you’re doing any finishing operations cause you don’t need to sand for paint or bond, and you also know that the surface will be clean and free of grease and fingerprints. Otherwise, why wast eh time and money?

For me though, what process is being used is dependent on some factors. Cost being important but, sometimes cost is outweighed by ease of layup and results. Infusion is great and I do it often because I can do a room temp cure and then post cure. If I had a heat box/oven at home I’d be more inclined to get some prepreg. That and a freezer. Having worked with prepreg some I know it’s fairly easy to work with, compared to dry layup and spray tac. Plus the results you get are very consistent. Infusion can be tricky; especially if you’re only going to make a few parts. It really just depends on the part, how many you want to make, and what you’re more comfortable with. Both methods have their merits and applications.

If you do know one method and it works than great but, it’s better to have more tools than one in your toolbox. Seems like a lot of companies use autoclave prepreg because that’s what they know. Then these new companies come along and get same or better results without the clave and leave the old methods behind. It’s ever changing.

I always say that composites are a black art.

#16

I’ve said it on here before in another thread. Try going to you local companies that work with prepreg, maybe a boat builder, aerospace company or auto part manufacturer and ask them for off cuts, end’s of rolls, expired or maybe nice new material or they’ll even tack on a bit extra on their next order for you. It may cost a small fee, or as I used to charge, some beers for the boys, take your best manners and smile maybe even some past work.

You might even make a new friend who will teach you something along the way and spin you small jobs. We had a file of guys we could get in for a quick job or if it wasn’t for us they could do it.

#17

I’ll do more research on that but that’s one off the issues. I’m going to be the only one. Yeah there are a couple boat repair places. And tracker boats are close but they don’t do carbon, let alone prepreg. But I’ll do more looking maybe in STL area?

Sent from my SAMSUNG-SGH-I747 using Tapatalk

#18

Sammy, I’m not clear on this calculation. The fiber cloth weighs 5.8 oz per square yard, so with a 50/50 mix the resin would be $4.58/sq yard, or $0.51/sq foot.

#19

I work with OOA pre pregs and infusion processing also.

For us, smaller carbon parts are far better done with pre pregs if tooling is suitable as the pre preg process is far less labour than infusion. It’s a simpler process without the extra pipes and plumbing of infusion and it’s less sensitive to vacuum leak issues so that’s safer with less risk of errors. Down side for us is most parts need hand finishing and painting whereas infusion can give you gloss gel coat finishes.

Larger jobs are often fglass and these suit infusion since the tooling may be too big for an oven/pre-preg or not suitable for the temp. The bigger job also justifies the extra plumbing work for infusion. Bigger laminates and material volumes are also labour intensive for wet laid work when infusion can wet out a full sandwich layup in just 1 hour once you start shooting resin in. (it may have taken 1-3 days of layup and prep though)

Pre pregs sound scary but it’s easy to do. You need freezer for storage (second hand $500), build your own oven with control system ($1000-$3000 depending on size), a vacuum pump and your away with simple and safe process. Getting OOA cosmetic parts is not easy though so be prepared for that.

#20

I have not had too many problems with cosmetic parts using OOA pre-preg carbon. Ok the pre-preg choice is key with Cytec selling VTF261 as possibly the industry standard for a cosmetic OOA pre-preg but if you tweak your breather stack and curing schedule you can get perfect parts… I have just tried a brand new material which is not for sale yet but the parts are flawless and it is now the flaws in the mould where the issues lie… This new material is priced at about $60 per sq/meter… (including sales tax at 20%) So that would be about $48 per meter if you are exporting it from the UK. For me pre-pregs make more sense and are cheaper and faster to process than infusion. Less consumables and the material costs are close enough now to make it minimal if you just look at cost of materials.