Reducing entrapped air in low density syntactic foam

[TymB]

I am requesting information about processes, materials and machinery for manufacturing low density (380-450 kg/m^3) syntactic foams.

I am intending to use glass microspheres and an epoxy matrix but alternative suggestions would be welcomed.

I have read the chapter in 'Polymeric Foams' D. Klempner (1991) about Syntactic foams but there are few details about actually mixing the resin and the microspheres to reduce entrapped air. The only mentions are of vacuum moulding, vibrating stirrers and vacuum mixers but I am unclear about how these would be applied.

Are there any techniques used with composites which could be applied to this problem?

The application is as an acoustic impedence matching material in an ultrasonic transducer.

Thanks, Tym

 

[Demon3]

Try Expancel (

http://www.expancel.com)

for microspheres that can be mixed with thermoplastics. They expand many times their original size to give a syntactic foam. I have seen this work.


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[TymB]

Thanks for the tip Demon3. I will investigate the expancell product. I am concerned about how accurately the density of the resulting foam can be controlled though.

In your experience what method did you use for mixing the spheres with the resin? My aim is to produce a foam without air inclusions (the only porosity should be introduced by the microspheres).

Many thanks, Tym

 

[Demon3]

Expancel made samples for me. I think they just extruded EVA with the beads in it then pressed the pellets into a sheet using pressure and heat. Depends how void free you need it I guess.


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell