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Reasonably cheap 220¦C resin system needed.
3

Reasonably cheap 220¦C resin system needed.

Reasonably cheap 220¦C resin system needed.

(OP)
We have an automotive part with high volume fraction (about 68%) of UD IM carbon and a service temperature of 220°C (430°F). It is currently all 0° fibres in a ring about 300 mm across.

Being automotive it's quite sensitive to cost and needs a fairly low cycle time. So, a lot of the usual resins we would use in aerospace are ruled out (BMI, cyanate ester, PI). At the moment a two-part epoxy is used, but the long, stepped cure makes it too expensive and its Tg is too low.

In addition it sees significant interlaminar shear at the max temperature, and needs an ILSS of about 100 MPa (14.5 ksi). We could change geometry to reduce the shear a bit but 75 MPa would be awkward and 50 MPa would be pretty much infeasible; it might be a goer but the size increase would make 50 MPa a very poor choice. So, a low porosity is desirable but not essential as long as it doesn’t compromise the strength too much.

On the plus side it doesn't need to be tough and damage tolerant and doesn't need resistance to the usual chemicals, 'just' fairly standard automotive lubricating oils. Also it doesn’t matter if it’s prepreg, infused, wet filament wound, dry wound, microwave cured, etc., (braiding might work but we don't think a non-0° UD layup would be useful), and one part, two part resin doesn’t matter. In fact a thermoplastic could be used and it doesn’t need to have good bonding characteristics except to the fibres. The fibres will probably need to be continuous and circumferencial, but you never know, short fibre filled resin mght not add too much weight. However, we do need that temperature resistance and a shear strength of 50 MPa would be very problematic. Also, it’s concealed and so effectively can’t be seen, so the ugliest brown phenolic would work if only it was strong enough (and an orange benzoxazine is ok). Also it doesn’t need to have a low coefficient of thermal expansion so something like a polyester might be ok in spite of (rumours of) misbehaviour on cure.

A reasonably fast cure, temperature resistant, epoxy would work well. The right benzoxazine might be very appropriate. Anyone know of any possible candidates that we could look into?

PS: I said that BMI, cyanate ester and PI were ruled out; that's only true if they are indeed too much money. My cost data is often approximate and at least two years out of date, but at the moment does indicate that those resins are a bit too dear. Each ring will weigh probably about 250 g/10 oz (depends on properties) and about 2000 or 3000 are forecast to be needed in 2014 and maybe 70000 by 2017.

I think that sums it up passably well. I haven't been able to share details of the usage. Apologies.

All suggestions welcome (most especially stuff we haven't thought of).

RE: Reasonably cheap 220¦C resin system needed.

RP,
A bit more information exerpted from an article on plastic fluepipe liners.
B.E.

The ASTM D 5364 standard specifies minimum flame
resistance and corrosion resistance requirements. Two
different vinyl ester resins were identified that meet these
requirements without the addition of a flame retar-dant
synergist, (antimony compound, etc.). A brominated
bisphenol A epoxy vinyl ester (BBVE) resin and a
brominated epoxy novolac vinyl ester (BNVE) resin were
chosen. Both of these resins are commercially available.

RE: Reasonably cheap 220¦C resin system needed.

Look into the phenolic resins. They have been around for a long time. Do not have any cost information for you.

RE: Reasonably cheap 220¦C resin system needed.

Phenolic molding compounds may meet your needs. They are cheap, and were among the first plastics. High pressure compresion molding is used to form parts. It is used for many electrical parts.

RE: Reasonably cheap 220¦C resin system needed.

Phenolic resins have lousy chemical resistance. They may meet your temperature needs (but probably won't). I would try again with epoxy or epoxy-vinyl ester. Have you been in touch with big vendors? Huntsman, Dow ....

RE: Reasonably cheap 220¦C resin system needed.

(OP)
berkshire: Vinyl esters are resins that I don't know enough about. Thanks for the hints. I'll try the check them out a bit more based on those links. Currently I can't find any that go to a high enough temperature (that's 220°C/430°F service).

Hansmeister & CompositePro: the phenolics I've checked include offerings from Hexcel, Cytec, Gurit, Parker (Electrical—they still seem to have trouble getting their name right for their non-electrical markets) and Lewcott. The strongest RT/dry ILSS was 55 MPa, which is probably not enough. Also the temperature tolerance seems questionable (as CoryPad says). If you're aware of an offering from someone that might fit the bill do please share.

I've not yet contacted vendors directly partly because I felt that I didn't know enough about the possibilties. A vendor can get it in their mind that they might just sell you something that might do you and attempt to guide you down that path (especially if it's reassuringly expensive, as the advert says). It's usually a bit difficult when dealing with materials that you're not so familiar with. Once I've scoped out a few more possibilties I'll contact the sales departments directly.

RE: Reasonably cheap 220¦C resin system needed.

If you require uni-directional IM carbon fiber at a service temperature of 430F, your mechanical strength requirements must be pretty severe. The aerospace industry has spent decades researching and developing materials for this use. The options are pretty well known, and you listed them. You can get BMI resins for $50-$60 per pound. Prepreg will be more like $80-$100 per pound. Cyanate resins are more than $100 per lb.

Since your resin content is pretty low and your fiber is relatively expensive, it seems you can't save much with cheap resin. It reminds me of the constant pressure that the large prime contractors put on prepreg manufacturers to reduce the price of prepregs. Aerospace prepregs sell for $50 to $100 per pound while fabricated structures often cost $300 to $1000 per pound.

RE: Reasonably cheap 220¦C resin system needed.

RP,
Here are a couple of suppliers of vinyl resins in commercial quantities. You can check with them to see if they can give you a resin with a heat curve to match your requirements. It does look to me, that you are banging the corners of the box.
You may find what you need in resins made for autoclave tooling.
B.E.

http://www.ashland.com/products/derakane-epoxy-vin...

http://www.ccponline.com/
www.reichhold.com/documents/927_DIONFR9300.pdf

RE: Reasonably cheap 220¦C resin system needed.

(OP)
Thanks 'Pro and berkshire.

As to the ring fibres, it turns out that actually glass might be strong enough but is a bit too flexible (there are apparently some tight radial tolerances). We think the resin is failing before any fibres (possibly failure is in ILSS; analysis is a bit ambiguous as to the direction of the principal shear relative to the fibres). The main dislike of the more normal high temperature resins is actually the typical long duration cure cycle.

I'm begininning to think we may have to bite the bullet and up the resin grade even if its cure is expensive. (Cheapest resin isn't necessarily cheapest cure, of course, so BMI might be ok; it seems to be the duration more than the peak temperature that costs.)

One of the other materials they've selected for part of the structure is Thermotar insulation which seems to be a sheet moulding compound. There are very few clues on the web that Google will tell me for what the resin might be. It has relativly low mechanical duty but the same temperature and doesn't seem to be appallingly low strength (seems to be about 350 MPa/50 ksi flexural strength, 600 MPa/90 ksi compression, both RT; good for 200°C-ish at reduced but not silly strength). Any help on that would be welcome.

Thanks again.

RE: Reasonably cheap 220¦C resin system needed.

2
Rp,
There is an article in todays Composites Technology Magazine which may give you food for thought. It looks like they may have the temp part covered but not the low cost.
It may also include some of the resins you ruled out, but it does not hurt to look.
B.E.

RE: Reasonably cheap 220¦C resin system needed.

(OP)
Thanks berkshire. That and the part-i are interesting articles. The last time I saw an article about such matters it was dated 2004!

Pthalonitriles look intriguing but seem stuck in the lab for now (as they were in 2004!); none of the companies mentioned (Maverick, Renegade or JFC) are making much of them. I'll recommend that the people concerned look at them if dotting is and crossing ts; I doubt if they'll find much but a phone call is cheap.

The other 'sure thing' resins temperature-wise may be ok. I guess it's dependent on cost.

NB: Masterbond claim 500°F use for some of their epoxies. This looks dubious. Maybe for uses where you can exceed Tg some of the time?

PS: looks like that grade of Thermostar may be BMI resin.

RE: Reasonably cheap 220¦C resin system needed.

(OP)
Thanks AeoN909. Looks like it's probably a little bit on the weak side but Tg might be adequate and it should be cheap and cure quite fast (probably a hybrid of polyester and urethane?). I've passed on to interested parties.

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