Alternative filling material

[homefire]

Try it ! You will Like it.

[BKY1337]

@kt315:

Cottonfibers as additive to the epoxy resin , to make it more rigid and tough.

@homefire:

Do you use this PU-Foam as filling material for your coils?

[Goaty]

I checked my epoxy , its probably enough to fill 1cm in the housing. I need to mix two epoxies together i hope this works.
I think this will fix the coils and then i can fill the rest with acrylic mass or hotglue or anything.
Do you think this works?
If not what about Polyester Resin? I can get 1kg for 6 euros.

I made a few things with epoxy in the past and i saw that it is very fragile. Can it break inside the housing without filling material (Microballoons)?
And can acrylic mass or silicone/hot glue influence the depht from the coil?

If you have two different epoxy resins you would better off mixing each one separately with its own hardener and pouring them into the coil housing individually. Allow the first mix to "go off" and cool down before mixing the second lot.
You will get better adhesion if the first mix is not fully set before adding the next layer. If you leave it too long you can get an amine blush on the surface which reduces the adhesion. Pouring in thinner layers is a good way to prevent heat build-up from causing problems, especially with faster hardeners.
In general, epoxy resin is stronger and more water-resistant than polyester but both are quite brittle without reinforcing fibres. Microballoons bulk up the mix and make it lighter but do not strengthen it.
Glass fibres are the best way of strengthening the mix and can even be used with the micro-balloons - chopped strand or rovings would work OK. The higher the ratio of fibre to resin the stronger the resultant mix as long as all of the fibres are wet out with the resin.
Also, epoxy is generally safer to use with other plastics, even polystyrene foam, whereas polyester will soften and dissolve many of them. It is a definite no-no with polystyrene foam!
Just remember when using epoxy - stick to the recommended resin/hardener ratio, mix very, very thoroughly and do not build up in thick layers where the exotherm heat can not escape (especially in warm climates)
You can top up your coil housing with polyester but it will add weight and it does not bond particularly well to most epoxies.

PS I have not had much experience with making metal detector coils but have been repairing both polyester and epoxy surfboards for around 30 yrs.

[Hyena]

Goaty: Did you really mean epoxy? I filled with epoxy thick layers and never got got it hot.


BKY137: Polyester is different story. Yes, it is really cheap, but it is also really hot b*tch. If you fill volume like fist, it get so hot, you can not touch it. If you fill central space of your cover with this, I think you will need to print new cover because this may melt it. Try cheap way and you will see.

[BKY1337]

Thanks a lot, i wont use my old resin , i bought a new one 750g , 1,14 g/m³

I think cotton fibres , or just selfmade cottonflakes will do the same as glassfibres and they are much lighter.
I have rovings because i made limbs for a compound bow two years ago. Im not sure about the cotton and i will use strands from the roving too.

I need 456g epoxy and my housing weights 200g , everything together has 656g plus the fibres.

[bernte_one]

Hello BKY

dont use two different types of epoxi, chemicals wont work together

as filling material for big space like in middle from coil use Bimsstein (1€ / st,. bei Connys Container oder mc geiz....)
you can cut it into smaller pieces with a carpet knife

as filler for mix with epoxi i take microballons 0,2-0,5mm, or Cotton flakes
for Ultra stable coil you can also mix glas fibre pieces (glasfaserschnitzel, liegt im Baumarkt beim Estrich), with Cotton flakes and epoxi

shield the coil housing with a layer from mixture of graphit powder and clear laquer (chaep variant of emv35)

dont use pu epoxi, shrinking rate ist to high it willleave a gap between housing wall

[homefire]

Yes, with no serious issues. LOL Do the foam before the shell is together. Just trim off the spouge.

[Tinkerer]

http://www.westsystem.com/ss/product-selection-chart

Use the 410 or 407 low density filling

You can also use the 423 graphite powder for shielding.

[Goaty]

Goaty: Did you really mean epoxy? I filled with epoxy thick layers and never got got it hot.

Yep! but it depends on lots of other factors - hardener speed, ambient temperature, how fast heat can conduct away into the surrounding mould/container. If it takes off in a thermal runaway it will really wreck things. Then the only thing you can do to try to control it is by blowing air over it to try to take some of the heat out of it.

BKY137: Polyester is different story. Yes, it is really cheap, but it is also really hot b*tch. If you fill volume like fist, it get so hot, you can not touch it. If you fill central space of your cover with this, I think you will need to print new cover because this may melt it. Try cheap way and you will see.

Similar factors to epoxy but, unlike epoxy, you can control it by the amount of catalyst you add. Too much catalyst and you'll have it smoking, too little and it will set very slowly, if at all, and stay sticky on the surface. It pays to use a chart to get the catalyst quantities right.

Also, I should mention that normal polyester laminating resin tends to stay sticky on the surface once it has set. This is good for adhesion if you want to add subsequent layers but not good for sanding. A nice smooth, non sticky surface can be obtained by using a filler resin, which is just laminating resin with a wax dissolved in styrene monomer added. As this sets a film of wax forms on the surface and keeps it smooth and non-sticky but it needs to be sanded if you want to add extra layers of resin.

Both types of resin shrink on curing but I think that fillers can help to reduce this but haven't looked into it!

I agree with homefire - the pressure pack foam is good stuff and can be trimmed easily once set but don't overfill when using it as it continues to expand slowly & steadily for some time after it is applied. Also, the remainder of the contents of the can do not keep for long once some of it has been used and the applicator nozzle blocks and is difficult to clean out so it can be wasteful.

[sinclairuser]

i use this, http://uk.rs-online.com/web/p/pottin...ounds/7031231/
in quantities we use it is light its water proof and removable if needed, that ad is for a large size the smallest one is about £12 from toolstation and will do 3 coils easy.
i have tried allsorts but like this stuff best.

[Altair]

i use this, http://uk.rs-online.com/web/p/pottin...ounds/7031231/
in quantities we use it is light its water proof and removable if needed, that ad is for a large size the smallest one is about £12 from toolstation and will do 3 coils easy.
i have tried allsorts but like this stuff best.

Are you use it for pulse technology MD only or also for VLF?

[jladre]

How about a filling material for pi coil?? Im looking for a bit heavy so that my coil will not float in water. Epoxy seems to ruins the coil performance.

[homefire]

Poor a little in the housing apply with brush. Let Cure. Keep adding layers until your happy.

https://www.lowes.com/pd/Plasti-Dip-...3-5fd3c27b2c4b

[BKY1337]

Does the epoxy resin interact with the aluminium foil shielding?
I have heard that the resin contains NaOH and its corrosive for aluminium.

[kt315]

Poor a little in the housing apply with brush. Let Cure. Keep adding layers until your happy.

https://www.lowes.com/pd/Plasti-Dip-...3-5fd3c27b2c4b

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