Plastics for Intake Manifold - Forced Induction

[sewell94]

Hi gang, I am designing a custom intake manifold and am pondering the different options for producing them. Aside from casting aluminum, I am considering carbon fiber and some sort of injection molding. Can anyone shed some light on the following?

1) Would carbon fiber work well for an intake manifold in a forced induction environement? My concern is the temp and pressures. The manifold would be made from several different individual layed up pieces and then grafted together to make the final product. So, another concern is the strength of the seems where the parts are grafted together.

2) What type of plastic or phenolics would be best if I went the injection molding route? Is there an ABS formula or hyrid mix with another component that would be strong enough, hold its shape under these conditions? Similar to the above scenario, the manifold would be grafted/glued/epoxied together from different individual components.

Thanks for any input.

 

[patprimmer]

Carbon fibre composite can be used for forced induction manifolds. The fibre will withstand high stress and temperature.

The problem will be the resin matrix, but epoxy and polyester resin suppliers should be able to give data comparing change of properties vs time and temperature.

Many current production manifolds are glass fibre reinforced nylon. Various types of nylon have different reactions to high temperature, with nylon 6 being used where the service is not so severe to nylon 6.6 for higher temperatures and or stress, and nylon 4.6 for things like turbo diesel manifolds.

The capital outlay for moulds to make injection moulded manifolds is so high that automobile manufacturers only invest for medium to high volume applications, so unless you have a use for quite a few hundred thousand manifolds each year, I doubt you can justify the cost.

If you want to go the carbon fibre route, you can do as you plan, and make pieces and laminate them together with resin and fibre overlapping the joint.

Another technique would be to make female moulds out of plaster or wood, use these to make male moulds from expandable styrene beads, then use epoxy resin and wrap the male mould with resin impregnated fibre, allow to cure, then dissolve the styrene out.

Glass fibre will work quite well, and will cost a lot less than carbon.

The details are a lot more involved than I could cover here, and frankly, from the content of your question, you have a LOT TO LEARN about the subject before you could tackle such a project

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[sewell94]

Pat, thanks for the input. You adressed the questions I asked. However, why would you assume I know nothing about the other points you raise? I am aware of the different layup techniques for composites as well as the capital outlay for injection molds. I kept those issue out of my question to stay on point. There are econimical ways such as sand casting for small volume. I also found a place that is very economical for injection molding and it's even cheaper if you have access to CNC to make your own molds, which I do. The comprimise is simpler molds making individual parts and bonding them together. Thanks again for the input but don't assume things you don't know.

 

[patprimmer]

sewell94

I made the assumptions based on your comments as follows:-

"I am designing a custom intake manifold". This strongly implies low volume. A few years ago, Ford in Australia could not justify the cost of tooling to make a plastic manifold for there most popular engine for this market.

"What type of plastic or phenolic". Phenolic is a type of thermoset plastic, but not even close to to being suitable for an intake manifold.

"Is there an ABS formula or hybrid mix with another component". ABS is not even suitable for wheel covers, and is clearly not in consideration for manifolds. To ask this question shows a lack of knowledge of it's properties.

It seems that you have reasonable knowledge of layup for laminates, and unless the custom manifold has more market potential than a moderate volume OEM manifold, this should be the best route.

If you can build a light weight shell glued together from several components, you can greatly increase the strength by filament winding over the thin shells.

Your most difficult area will be where the manifold bolts to the head. Injection moulded manifolds normally have a steel tube encapsulated at this point so that the steel restrains the crush from the bolt.

If the light shells were compression moulded from BMC, you might be able to incorporate a flange of sufficient strength. The flange will be very difficult to reinforce by filament winding.

As far as I know, and my info re thermosets and lay up techniques is somewhat out of date, epoxies are the strongest matrix, but vinyl ester based polyesters have the highest temperature resistance.

If you do go the injection moulded route, I think that glass fibre reinforced nylon is the only viable material when you consider temperature, vibration, steady load, impact and chemicals in the environment of the manifold.

Glass fibre reinforced nylons require moulds that fit within fractions of a thou if you want to eliminate flash.

Glass filled nylons also exhibit considerable difference in mould shrinkage, depending on glass fibre orientation. This is compounded by differential shrinkage due to differential cooling rates. All this needs to be taken into account at mould design stage.

Nylons do not glue well due to their good resistance to solvents, but they can be ultrasonic or vibration welded, and I believe that is how all OEMs do their multi piece manifolds. Some still do one piece lost core moulding techniques with bismuth tin alloy cores, but this is loosing favour, mainly for environmental reasons involving the handling of and disposal of the bismuth tin alloy.

The biggest in use problems are breakages from backfires and creep from under the bolt heads at the mounting flanges.

A lot depends on the size and complexity of the manifold, neither of which you indicate.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SBBlue]

Just out of curiosity, how high a temperature will the carbon-fiber composites tolerate?

I would think it would have to tolerate temperatures of at least 400 deg F and perhaps 500 deg F.

 

[GregLocock]

The carbon is OK, the trick is finding a resin that will live. I think your temperatures are a bit off, the cylinder head is going to be at 110 C max, I'd have thought (ignoring turbos and exhaust).

http://icb.nasa.gov/excp102.htm

is good for 600F

!




Cheers

Greg Locock

 

[patprimmer]

I think most epoxies are good to about 250 deg C, and vinyl esters go a bit higher, but I don't know the current state of the art.

So long as there is no oxygen available to it, I think the carbon will take red heat levels. What do F1 brake rotors take?

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ZoRG]

CF is no problem, the latest designs I have seen have moved to carbon-kevlar based setups, which might be for strenght, or bling-bling, I am not sure. Any place that works with carbon fiber can make a manifold for you, you just need to specify the heat ranges and pressure it must support. If you haven't worked with CF before, do not try a inlet manifold as your first project, you will problably fail.

I presonally don't think plastic is worth it for low quantities.

Go to

http://www.theoldone.com

have a look at their carbon fiber manifold, quite nice.