Experiments on Depron (KT) Foam pieces Thermal Forming, Rolling

8 April 2015

Rolling experiment.

Top two are 3mm with skin. Arrows are direction of visible bands. Both creased on concave side, left is better, the creases are smaller. Reduction in thickness in both pieces.
Bottom two are 5mm without skin. Arrows are direction of the longest length. No creases on concave sides, left is better, didn't snap. Resistance to reduction in thickness on the left piece.

Mission Statement

The purpose of conducting thermal forming experiment on Depron (KT) foam pieces is to appreciate its inherent characteristics (readily available from shops in Singapore), identify suitable technique/s to exploit the characteristics to the best advantage and applying them to making components for RC aircraft.

The Iron Experiment

Equipment:

• Normal clothes iron
• Aluminium kitchen foil
• Cotton fabric

Material:

• scrap 5mm Depron (KT) foam pieces

Methodology:

• Set temperature on iron
• Place foil above and below foam piece, shiny side to the foam
• Iron

 

Test 1 (cotton setting)

Result

Observation:

With a hiss, the foam melted and the foil bonded instantly.
On peeling of the foil, creases of foil were replicated on the foam.
Foam has been compressed/melted to paper thin.
The foam piece appears not to be homogeneous in density, resulting in some transparent areas.
Surface is very smooth and not bead-like.
The paper thin foam was rigid but brittle; the resilience of the foam was gone.
Creases were observed on the surface, these creases were the imprint of the aluminium foil.

Conclusion:

"Cotton" temperature setting was too high.

Test 2, 3 (wool and nylon respectively) 

Result

Wool at the bottom, Nylon at the top.

Observation:

Wool is similar to Cotton setting but slower. That's the piece at the bottom.

Nylon is too slow and the 5mm foam piece does not compress further than approximately 2mm. The piece at the top.

In either case, creases can be reduced by moving the aluminium foil, and the compressed surface is shiny.

Conclusion

Somewhere between "Silk" and "Nylon" might be appropriate.
Move the foil on every pass of iron.

 

 

 

 

 

 

 

Test 4 (introducing the cotton cloth)

Result

Observation:

The compressed surface took on the cross texture of the cotton fabric and is matte.
The heat transferred will bond the cloth to the foam.
The cloth may be peeled off.

Conclusion

The temperature of the iron to be at around wool.
Light pressure on the iron is useful for heat transfer and imprintment.

 

 

 

 

 

 

 

 

 

Application of the Iron experiment

This is a slice of the textured foam piece.
The leading edge was sliced with cutter.
This resulted in a flat-bottomed airfoil.










With additional thermal or cold forming (cold forming in this case), the same airfoil foam piece can be made into an under-cambered airfoil.

Further possibilities

It might be possible to iron on tissue by replacing the cotton cloth with coloured tissue and not peeling off the tissue; saves glue too.

Advantages

A 5mm foam is less than half of 1mm balsa. The iron method is quick to produce air-foiled wings that performs well and looks good and by virtue of its thickness has sufficient strength and is light. This method is also relatively clean, compared to the cleaning up of fine static-charged waste particles that resulted from sanding depron (which, is difficult and needs extreme care to avoid the sand paper digging into the foam).