The vital Tolerance for Aluminium windows

By Bogdan Grebenyuk, Product Manager at Thermevo
on June 13, 2018
Close tolerance aluminium profiles glass fiber reinforced polyamide strips
Look at the new cars. The quality of supplies is getting better, and the gaps between parts are less. It's the result of the combination of calculation, high-tech equipment and the quality of supplied parts. The production of aluminium thermal break windows is utmost technologically sophisticated. Modern thermally broken aluminum window and curtain walls demand advanced technology to control with electronic devices and require high-quality components.
The window frame or sash profile consists of two extruded aluminum profiles which are separated from one another by polyamide thermal breaks PA 6.6.25 reinforced with glass fiber. A gluing thread or a glue wire, rolled and pushed in together with the insulation strip ensures a better adhesion after melting in the hardening furnace.

Each profile (aluminum frame, glass fiber reinforced polyamide strips, EPDM-gasket) has its tolerances, and the more practically feasible is the manufacturing company, the better is the precision of a profile. When the design engineer creates a new system, he or she focuses on this tolerance and can establish a system with minimal gaps.

Air and water tightness of windows are the most crucial things you want in a window. As you know, if you install the window poorly, you will get gaps letting in cold, drafts and water. The same principle applies if the tolerances of windows, doors or facades are poorly calculated, leave significant gaps, or just have poor tolerances themselves.

Earlier to ensure the efficiency of a gasket you had to do some wrap stock. Such approach provided that the seal is well established and performing its functions. Let's take an example. 10mm groove in the polyamide had a tolerance of +/- 0.5 mm for a seal. Now this tolerance is reduced to +/- 0.15 mm. It gives us optimization of the cross section of the seal and material savings, which ultimately affects its price.

The second issue is the quality of the finished construction, of which the best analogy is a tailor-made suit. When speaking of windows, this means that a profile of a frame or a sash has a thermal barrier rolled up between the two aluminium halves. If the tolerance is significant, then, in most cases, the rolled up profiles will be of very poor quality, because the rolling machinery is usually set up only once for a particular type and size and is rarely tampered with. Eventually, that leads to insufficiency to required shear strength in aluminium thermal break profile which in turn may result in a bad insulation against cold and draft window or sash hang.

Here is another example: two glass-reinforced polyamide strips in the aluminium window, each has their tolerances. If the tolerances are different, we will end up with parallel misalignment of the inner and outer surface of a profile that will inevitably affect the gasket and fittings.

A gasket is an important and the most sensitive element of a window with its requirements for tolerances and quality. It is exposed to ultraviolet light and must accept the dynamic loads from the wind and the opening / closing of a valve. In that case the bigger the tolerance, the greater the probability that the gasket may eventually reduce its performance, or even fall out of the groove. To avoid this, many manufacturers do the trick and make a seat in the seal wider, which leads to additional efforts when inserted into the slot and closing the window. As a result, it affects the performance and fittings life cycle duration.

Current market trends for thermal insulation systems dictate the size of components. Twenty years ago it was normal to use thermal insulation profile of 20mm width, and nowadays it's common knowledge to use 40mm wide multi-chamber profile.

For such systems, the tolerances are as fundamental. For example according to DIN 16941 2A tolerance for 10mm plastic profiles is +/- 0.5 and +/-0.8 mm for the size of 50mm. This is important because if we consider tolerances of aluminum profiles correctly, we can get the size of the leaf +/- 1.5 mm and it is guaranteed by blowing or fittings malfunction. Let's not forget about the foam elements, whether it is foamed polyethylene or polyurethane. The tolerance for these profiles is also critical, because if the section is bigger, there may be problems with installation, and if smaller, the heat transfer coefficient of the system will be worse.

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