Nomex Core

[granite]

I am thinking of making some parts of a light weight racing dingy out of a carbon nomex sandwich.
I have had some experiance building with vaccum bagging carbon over foam cores.
Does anyone have any experiance with Nomex honeycomb, what are the pitfalls and is it worth it?

[Karsten]

The best is to use prepregs. You just stick them on the nomex, vacuum bag and toss the whole thing into the oven. If you want to wet laminate the skins you obviously can't apply resin to the nomex because it will jut flow into the cells.

The best way to do it is to spread out a plastic sheet on your workbench. Calculate the amount of resin you need and spred half of what you need for the first ply onto the plastic sheet. Then you put on the first ply, wet it out, put more resin on, lay down the second ply...

After the laminate is wetted out on the plastic sheet you put the whole sticky mess onto the nomex core and remove the plastic. There should be enough resin to ensure good bonding to the core.

[granite]

Thanks for the answer, Pre preg is out of the question

From what you have said I think the procedure would be,

Wet out first skin on mould with slight excess of resin to bond to the core, put the nomex core in place and vac down.

Then wet out the outside skin on the plastic sheet and lift in place on to the core, then vac that lot down.

My worries would be that the laminate would not consolidate well as it would not be getting any pressure in the center of the cells and it could end up with a dimpled outer skin if the laminate sags.

[John ilett]

I think that for the inner skin you can use a layer of glass or carbon tissue/vale and let cure. Then the laminate and vacuum bag.

I think if you are using only one layer of carbon or glass that the extra weight of the resin in a tissue layer may defeat the purpose and intended weight saving expected from using nomex.

[granite]

Originally Posted by John ilett

I think that for the inner skin you can use a layer of glass or carbon tissue/vale and let cure. Then the laminate and vacuum bag.

I think if you are using only one layer of carbon or glass that the extra weight of the resin in a tissue layer may defeat the purpose and intended weight saving expected from using nomex.

That was one worry if I had to upp the laminate spec compared to a foam core then I would regain any weight lost by the change in core material.

Is the tissue vital for bonding? what sort of weight is it?

[John ilett]

I think the tissues are heavy on the resin quantity.

A freind of mine was working with a small aircraft builder who used this method with the tissue so it must be a structurally sound option being an aircraft.

Personally I think that while nomex is a quality core, it should be left to automotive and aerospace guys using pre pregs etc. For boats/boatbuilders and the methods they generally use there is reasonable risk the part could fail due to bonding or other problems. Air expansion/contraction shows cells on the surface. Water can get in if the inner skin is not 100% sealed. Foam is not that bad at all and is a very safe option.

The 3.3m foam core moth hulls we build at Fastacraft have a finished hull weight of around 9.5kg painted.

[marshmat]

We use honeycomb (Nomex-type) cores in the solar cars and have done so for some time. The stuff works extremely well with prepreg cloths (heat-cured). They are extremely stiff with very high ultimate strength in all directions.
BUT.... Nomex doesn't work too well for wet layup. To properly bond the skins to the core requires a 10mil thin film of a special adhesive that, under heat and vacuum, congeals around the cell edges to join them to the skins. Wet-layup with this core, regardless of what you use as the fabric, tends to just encourage all the resin to flow into the cells; thus your cells are full of resin and your cloth is dry. The undersaturated cloth then allows water into the cells. A closed-cell foam, that cannot absorb resin, is a much more reliable option if you are doing wet layup; good foabs exist with similar weight and structural properties to Nomex.

[gggGuest]

2658 is Nomex Phil. ISTR he used prepregs. Davro would know I think.

[granite]

thanks for the answers guys, I think the obvious answer is to give Nomex a miss and stick with foam core

I still fancy trying to get some off cuts for a bit of experimentation though

Phil

[Coretex]

We work with a wide rnages of honeycombs, including Nomex. Have you considered Polypropylene Honeycomb? It is now very popular in the USA and Europe for boat work and is replacing Nomex, Balsa and Foam in many areas.

It's key benefits are

1. Much cheaper than Nomex
2. Good mechanical properties
3. Excellent impact and sound absorption
4. Perfect for wet enviroments - Nomex and Balsa do not fair well
5. Excellent for wet layup - the core comes with a tissue veil welded to the core - so you get excellent delamination properties
6. The core can be moulded and heat formed into complex chapes - or the flat sheet can be back face slotted to follow hull profiles etc

As I said, we work with many honeycombs - and we rate PP very highly for marine and wetlayup use

Good luck!

www.CoretexGroup.co.uk

[grob]

Coretex,

Is the Polypropylene Honeycomb core suitable for Twintex, has anyone used it with Twintex in the past.

Gareth

[Coretex]

Hi Gareth,

Yes, we already supply a PP cored panel with Twintex skins ready fused to the core. It can be used as is or heated form and moulded to shape.

Also, automotive clients use the raw PP core and raw Twintex to layup in mould and fuse together in heated tools. Seems to work well either way

Coretex

[grob]

Thanks

Ideally we would like to use raw PP core and raw twintex in the mold as you describe, However our experience (with nidacore) is that the core melts in the mold with the heat required to process the twintex properly. Is your core somehow different.

Gareth