Buoyancy float - diesel tank

[banlawadam]

I'm a Mech Eng seeking a suitable material(s) as a small (45mm OD) cylindrically shaped flotation device for use in diesel fuel tanks. To date, I have looked at extruded closed cell polyethylene (PE) foam or machined billet PE (hollow). I have in my mind a low S.G. foam - preferably hard setting - that can be machined, extruded, cut, or otherwise formed into the desired shape. A suitable material must have a low S.G., be compatible with diesel fuel, and NOT absorb the diesel. These points will ensure the buoyancy force is maximised (per unit volume).

I'd appreciate any assistance you can provide. Kind Regards.

 

[patprimmer]

PE will absorb some diesel. This will be accelerated by the fact that it is foam.

You should be able to eliminate the diesel absorbtion by dipping the foam into epoxy resin, so giving it a diesel proof coating.

Plastic floats for petrol carburettors are usually hollow mouldings of nylon, polyester, or acetal.

These are usually moulded in pieces and welded together.
Tooling costs could be many thousands of US dollars.

It might be possible to extrude any of these materials as foam, but wether or not they will be closed cell foams, I couldn't say. The high surface area of foams makes them more susceptible to absorbtion and permeation, when compared to a hollow moulding of the same weight.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[strokersix]

Why not soldered brass? It may cost more than a molded polymer for high production volumes but it sure won't absorb fuel.

 

[banlawadam]

Thanks fella's. Our prototype floats included balsa wood coated in lacquer/resin, and machined PE. I'm aware of the brass floats and will investigate further. Rotational moulding is an option with plastics (e.g. PE), but according to an enquiry, I could not further reduce the wall section using this method beyond what I could get by machining. Granted moulding would be cheaper in the long run, and I have not totally dismissed this idea yet. Production batch quantities of the float would be in the "low hundreds", so any sort of die moulding is cost prohibitive.

What I had in my mind was a hard setting "closed" foam (low S.G.) that could be formed/machined/extruded into the required shape. I've seen something at some stage in the past, but am buggered if I can think what it is.

What makes it more difficult is that diesel is not the most benign substance going 'round.

Cheers

 

[patprimmer]

Rotationaly moulded PE could be treated with Fluorine to improve it's barrier properties.

The treat blow moulded PE fuel tanks and fuel drums with fluorine to improve the permiation to acceptable levels.

Rotational moulding uses very little pressure, so there might be porosity in the mouldings as well as permiability problems. Fluorine will not fix porosity.

I suggest any easy to work,low density foam, dip coated with a resin known to have good barrier properties to the diesel fuels.

You might consider making a prototype shape, then making cheap moulds from wood, fibreglass or even plaster of paris, then useing two pot self foaming polyurethane, then dip coating.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[aviat]

There are several liquidometers on the market that use cork.
SG 0.24 solid or 0.16 ground.

 

[patprimmer]

Good point

I never thought of cork. I expect that it would need to be dipped in a resin to seal it.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Compositepro]

You can make syntactic foam floats by mixing glass microballons with two part epoxy. The specific gravity can be as low as 0.5 and still have the mixture fluid enough to mold easily. Syntactic foams have relatively high compression strength and low absorption. I've seen glass microballoons sold in hobby shops. Emmerson and Cummings is one manufacturer. Or you could try to find an established float manufacturer.

 

[Chris1001]

An existing fuel tank float moulded application comprises hollow glass bead filled nylon 6 (I think). I'm not sure of the fuel though. I can provide further details if required.

 

[harrisj]

I'm a bit late joining this thread but FWIW I have a feeling that PP (polypropylene) is the mutt's nuts for diesel.

It's cheap, it can be machined, and you can weld it (ultrasonic / laser?) but I don't know if you can get it as foam.

I believe it's impervious to diesel but check with a supplier