Aluminium thermal break windows: better surface?

By Bogdan Grebenyuk, Product Manager at Thermevo
on June 05, 2018
Polyamide is a perfect material for a thermal break in an aluminium profile. It has excellent strengths and heat properties. But there is one complexion with polyamide that only a few know. The polyamide thermal break profiles can absorb up to 6% of moisture from the air.
Mechanical, heat and electrical behavior of polyamide vary depending on moisture absorbing. The polyamide can absorb moisture from the air and give it back. Fed with moisture polyamide sometimes loses up to 50% of the original characteristics and changes linear dimensions. Moisture enters the polyamide during transportation or improper storage of thermal breaks.

A thermal break should be stored in a dry place, protected from moisture and extreme temperatures. Transportation must be carried out in a covered body, protected from rain or snow.

The polyamide can absorb 6% of moisture from the air.Chart 1 shows the relationship between the equilibrium moisture content and the polyamide humidity.

At high humidity, moisture absorbing is quickest possible.

Polyamide fed with moisture increases in the size and loses its strength, dielectric and thermal properties. The material becomes softer and more flexible. Moisture absorbing also leads to the bubbles in the thermal breaks which destroy its inside and make the surface of a profile rough.

Usually, up to 2% moisture in a thermal break is not crucial as it only shows itself in bubbles on the surface of a thermal break after coating.

It can even be mistaken for a decorative finishing of a profile, but in fact, it speaks about quality control problems. The higher the temperature, the more bubbles we see. Recommended temperature for polyamide profile in a coating oven is 2000 C. Chart 2 shows that 1% of moisture in a thermal break will not give this effect, but at higher humidity bubbles are imminent.

The bubbles result from water boiling, thereby exploding thermal break inside the body. This profile dramatically loses its bearing strength and must be sent for recycling, as using it in the profile system is absolutely unacceptable.

Enlargement of thermal break affects the tolerances of the assembled composite profile. It is not as evident in the small thermal break up to 20mm but becomes unacceptable for sizes from 34mm because the profile has its tolerances and adds extra 0.5 mm in width. As thermal break increases in proportion to the volume, the question of sealing larger break arises. The most disappointing is the fact that if you do not notice that the profile absorbed moisture and start rolling it, there can be the gap because thermal break gives moisture back into the environment.

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