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epoxy with fibres or alternative

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DYV1973

Mechanical
Aug 9, 2004
75
LS,

For creating a topcoat on an EPS250 part, we have experimented with hot spray polyurea. This material gave enough strength, but stiffness was to low. Product is round (diamters from 200 to 1000 mm), and the basic EPS is 40 mm. Application temperature is from 15°C to 55°C.

Now we are looking for a topcoat that gives also more stiffness, and we are thinking of epoxy or polyester with fibres. We are looking for an E of approx. 100 GPa, so aramide fibres could be a solution.

Can someone give me some advice about:

* which of both (polyester / epoxy) would be preferable
* can the epoxy/polyester with chopped fibres be sprayed easily (we would like to do it ourselves), and what kind of equipment would be needed
* what kind of tolerances can be achieved with spraying
* is there an alternative

Thanks.
DYV
 
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You will not be able to use Polyester resin; the styrene in the resin will dissolve your foam.
Epoxy resins will be a better choice.
To produce your own chopped fibers you will need a device called a chopper gun (Google it) you do not say what kind of production rates you want to achieve.

If they are low you may be better off using shopped strand mat in roll form and hand laying your part. This will also give you greater control of the thickness of your part.

Chopper guns are high speed production devices, they can, and do put out large quantities of material, and they also create a hell of a mess, so the spray areas need good industrial hygiene.
The tolerances produced by these machines depend entirely on the skill of the operator.
B.E.
 
Thanks Berkshire, I have found some on the internet. Both epoxy with chopped fibres and even polyurea with chopped fibres.

I will contact the supplier and see what comes out.

The production rate is not very high: lets say approx 5 m2 per week. But reducing man hours is important, so using a chopper instead of mats can be interesting.

DYV
 
You will get far more stiffness with less weight and coating thickness if you use a woven fiberglass fabric and wet-lay it on the surface. For 5 m2 it would probably also be faster than setting-up and cleaning-up after a chopper gun.

When you says stiffness do you mean flex in the surface coating or stiffness of the overall part?
 
With stiffness I mean the stifness of the overall part. But due to the fact that EPS does not give any stiffness, this should come from the top coating. In the EPS also some (electronic) components are integrated, which need to be covered with a coating for protection and also for the look.

The 5 m2 is the surface, but has a lot of radius and corners. Also applying the woven fabric will be time consuming.

If woven fabric gives more stiffness and thinner layers (thus weight), that would be an important criterium.

Will using woven fabric with epoxy, give a smooth layer, or do you need to apply some kind of thick coating on top? How bad are chances for allergic reactions when using epoxy?

DYV
 

DYV1973
I think a few more details of what the part looks like, and what you are trying to achieve, will help get you a better answer.
As soon as you say "thick coating on top". I feel you would be better off using a female mold, applying an in mold coating, then the glass/ resin, and pushing your styrofoam part into the wet resin/glass.
In this manner the surface smoothness would only be limited by the quality of the mold.
B.E.
 
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