PA66GF25 Thermal Break Strips
Polyamide material is the most commonly used for thermal bridge breaking. Polyamide 66 is a semi-crystalline polymer (25% glass fibre) with good mechanical and chemical resistance properties, due to the uniform packing of the molecules in the crystalline region.
This polyamide absorbs the water contained in the humidity of the environment. As the water content within the polymer matrix increases, there is a dimensional increase and changes in the mechanical properties of the polymer.
Its main qualities are:
· Resistant to corrosion and most chemicals.
· The residues from its calcination are not toxic and are not harmful to the environment.
· Physically tested after being used in carpentry systems for the last 3 decades.
· Low thermal conductivity coefficient.
· Thermal expansion coefficient close to that of aluminium.
· Melting point higher than the temperatures of the lacquering oven.
· Good resistance properties, even up to temperatures of 200° C.
· Resistant to impact and ageing.
· Resistant to UV radiation due to its carbon black content and the intrinsic properties of the polymer and processing method.
Thermal insulating profiles made of polyamide PA 66 GF25 have significant advantages.
Firstly,The coefficient of linear thermal expansion (linear elongation coefficient) of the polyamide profiles is equivalent to the aluminum profile. Therefore, the polyamide profile is not subjected to internal stresses after it is pressed to aluminum profile. This is one of the most important advantages of using the polyamide material as a thermal barrier.
Secondly, the deflection temperature of the polyamide profiles under load is high. Even at 200° C for about 15 minutes, no deformation occurs. Therefore, it can easily be heated in the ovens at the powder coating process.
Thirdly, polyamide profiles do not emit toxic gases in case of fire. They are environmentally friendly.
In addition, dimensional stability and resistance to chemicals of polyamide thermal barriers are high.
Thermal break assembly for aluminium profiles
Thermal break assembly in aluminum profiles takes place in 4 stages.
2- Insertion of thermal barriers into aluminium cavities
3- Curling (Rolling, crimping)
4- Shear strength test
Aluminum profiles have cavities where thermal break strips are inserted. Knurling on the neck of this cavities is performed with the aim of increasing the shear strength. If the knurling process is not performed with sufficient care, the thermal break strips are not sufficiently connected to the aluminum profile cavities and the composite profiles cannot reach the desired values in the shear stress test. Knurling machines work on the principle of carrying out 2 hardened special discs on aluminum profile. In a suitable knurling process, sharp teeth must be formed on the aluminum profiles. This ensures sufficient adhesion between the plastic insulating bars and the aluminum profiles.
Discussed for knurling should be periodically replaced. Before the process, ensure that the discs are correctly aligned vertically and horizontally with the aluminum housing.
Insertion and rolling of thermal break strips
It is possible to apply and tighten the thermal insulation barriers to the duct in aluminum profiles thanks to advanced machines. For a good compaction, the most suitable settings for the dimensions of the profiles are made automatically or manually on the machine. During the compaction process, the print settings should be carefully adjusted in order to avoid twists and breaks. Problems such as rotation, breakage or poor jamming are often caused by pressure from discs that are not correctly adjusted to the profile.
Shear strength test
Adhesion of heat barriers to aluminum profiles is measured by shear test. The EN 14024 standard specifies the requirements. Different factors contribute to the formation of a composite aluminum profile (combined with a thermal insulation barrier) with a high shear resistance. A good knurling is the most important one. In some polyamide thermal barriers there is a wire on the foot . This wire has no significant contribution to shear strength. Likewise, it is not possible to increase the shear strength by further pressing on the rolling process if there is not adequate knurling. The most important factor is a good knurling for a sufficient shear strength.
Coating of thermal breaks and resistance to heat
One of the most important features of polyamide thermal barriers is that it can be subjected to the heating, which is the final stage of electrostatic powder coating process. Composite (thermal barrier inserted) profiles shall be heated at a temperature of 180° C - 200° C not exceeding 20 minutes. If this limit is exceeded, the stability of the profiles is not guaranteed. Again, if this time is exceeded, the possibility of bubble appearing on the thermal barriers increases. In addition, profiles should be supported in the middle in horizontal production lines in order to prevent sagging.
Improving thermal insulation of aluminium windows and facades
Companies that develop aluminum windows and façade systems choose different thermal insulation barriers or design a custom profile for them in order to provide better thermal insulation systems considering the principles of thermal insulation. In order to understand these principles, we need to know the ways in which heat is transferred.
The transfer of heat from one substance to another takes place in three different ways: conduction, radiation and convection.
Conductive materials conduct heat directly from one side to another, that is called a thermal bridge as it is in our case with aluminium profiles. Heat is conducted btw inner and outer sides of the window or facade. The main task of using thermal break strips is to prevent direct transmission of heat through metal profiles. In this respect, insulated aluminum profiles are used in every application where thermal insulation is required. For the same reason, we prefer 24mm or 34mm heights for thermal breaks instead of 14.8mm, to minimize the transfer of heat through conduction. If the plastic profile is thin and long, the heat passes to the other side more difficult.
In a well-designed aluminum window and facade system, the thermal gap should be wider with respect to the direction of heat transfer. This is accomplished with thermal barrier profiles with higher profile heights. The longer the thermal insulation barrier, the greater the insulation gap and the better the insulation.
The transfer of heat by convection means the transfer of heat within liquids and gases. This is an important point in aluminum system design. We said that thermal cavities were created with thermal insulation barriers. When this gap is too large, it will be easier for the air to circulate inside and carry the heat. Therefore, when long thermal insulation barrier profiles are used, flags are used on the profiles in order to divide the gap into sections. When the insulation gap exceeds 24mm, thermal flags are added to the thermal insulation barrier profiles to prevent the transfer of heat by convection. Likewise, partitioning of the gaps in our chamber (hollow) insulating bars minimizes the transfer of heat through convection.