Sealing problem - how to avoid defects?

By Bogdan Grebenyuk, Product Manager at Thermevo
on June 1, 2018
For a long time the standard width of a thermal break was 4,25 mm, then it was replaced by 4,2mm, and now the standard size of a thermal break is 4,05mm. To avoid undersealing, modern aluminium profiles are designed for both 4,2 and 4,05 mm breaks. Technically, with sufficient supplies, you can use both widths and get perfect results. But practice shows that the defect rate of automated sealing of 4,2mm profile can reach 50%.
During the day, a worker can be supplied with thermal breaks by different manufacturers and of different widths. Both a profile and a thermal break have their tolerances that add extra 0.5 mm in width. One can not estimate a thermal break's width by simply looking at it. Sometimes a batch of thermal breaks width is measured before starting work. It helps estimate the effort or - in worst scenario - a defect rate.


When a thermal break enters the groove in spurts, a profile is being milled; that results in polyamide hewing and cohesivity index rate decrease. Even if we can fit the thermal break into the groove, in places where the polyamide head is, sealing would result in defects.

Needless to say, that we can avoid the problem by manually fitting a thermal break. But manual operations take considerable time and therefore are not acceptable for big manufacturing companies. The standard practice is to make an additional measurement of a thermal break. If the cause of defect is thermal break quality, the entire batch is rejected, a supplier is subject to a complaint of defective production. If the problem is in the aluminum, the complaint is addressed to a profile provider.

Though problems with a thermal break fitting into a profile, can be caused by many different reasons.


Stored in a humid environment, the polyamide easily absorbs moisture. A thermal break, filled with moisture, increases in volume. It is impossible for a human eye to distinguish a thermal break, filled with moisture from a well-dried one. And even if a wet thermal break fits into a profile well, a problem may emerge while coating.

Modern manufacturing solves wet profile problem by measuring the sample of a batch. Quality control specialist cuts a piece of a thermal break and weighs it to measure the moisture percentage. If the moisture percentage exceeds the normal value, the entire batch is sent to the drying chamber.

Profile quality
Even when 4,2 mm thermal break is well dried and accurately made, it can jerk into a faulty aluminum profile with different width through the length. It's a bad situation in general, but all in all, we must admit that with a 4,05 mm thermal break we will receive a profile of sufficient quality because it is more versatile and eliminates errors in the aluminum profile.

And if we take into consideration that the thermal performance of 4,2 mm and 4,5 mm thermal breaks made of the same material are consistent, we would say that using a 4,2mm thermal break gives us no advantage, while a 4,05 mm thermal break helps decrease defect percentage without quality loss.

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