"steal the beam and replace the column"
-PVC insulation strip, a low-cost non-structural general plastic, is used to replace glass fiber and nylon 66 insulation strip, which have been recognized in Europe for decades. Because the linear expansion coefficient of PVC is far from that of aluminum alloy, and it has many defects such as low strength, poor heat resistance and poor aging resistance. This leads to the broken bridge aluminum profile composite PVC insulation strip. After actual installation and use, PVC insulation strips will become loose or even completely fall off in the broken bridge aluminum profile due to thermal expansion and contraction, which will lead to the loosening and deformation of windows, thus destroying the air tightness and water tightness of doors and windows, and even leading to the overall loosening and falling off of windows.
"Crossing the sea from the sky"
At present, in the engineering example of broken bridge aluminum doors and windows, many enterprises use imported nylon 66 insulation model windows to bid, and then use PVC insulation strips or domestic nylon insulation strips for actual processing after winning the bid, or mix imported nylon 66 insulation strips with PVC or other insulation strips. The imported nylon 66 insulation strip with trademark logo faces outward to "prove" the "quality grade logo" of the insulation strip used. This kind of "hiding the sky from the sea" has a strong concealment. The owner of the broken bridge aluminum doors and windows project can only identify the profiles before they are processed, because only in this way can two heat insulation strips be identified.
"fish in troubled waters"
The material of heat insulation strip is the basic guarantee of the quality of heat insulation doors and windows, but it is by no means a good guarantee. In order to reduce the cost, domestic nylon thermal insulation strips are processed and produced by using general mineral materials (commonly known as fillers) to replace glass fiber filled polyamide and nylon in whole or in part. This kind of insulation strip is incomparable to glass fiber reinforced nylon 66 insulation strip in mechanical strength, heat resistance and aging resistance.
"opportunism"
Some broken-bridge aluminum doors and windows enterprises have fully studied and mastered the great performance differences among PVC insulation strips, domestic nylon insulation strips and imported nylon 66 insulation strips, and adopted an economical and relatively safe compromise scheme. Low-quality and cheap PVC or domestic nylon insulation strips are used for window frame aluminum profiles, and high-quality imported nylon 66 insulation strips are used for window sash aluminum profiles. They think that the aluminum profile of window frame is fixed on the wall, even if there is quality risk, there will be no big problem, while the aluminum profile of window sash is movable and bears stress alone, so there can be no quality hidden danger.