External wall aluminum plastic panels are composites of aluminum alloy panels, plastic core layers, and back panels. Their coefficient of thermal expansion is influenced by both the aluminum alloy and the plastic core layer. The coefficient of thermal expansion of aluminum alloy is approximately twice that of steel, while the coefficient of thermal expansion of the plastic core layer is even higher, approximately four times that of aluminum alloy. This difference causes the different layers of the external wall aluminum plastic panel to expand or contract to varying degrees when temperatures change. If not properly matched to the building structure, this can easily lead to deformation problems such as bulging, warping, and joint cracking, especially in high-rise buildings or areas with large temperature differences.
Matching external wall aluminum plastic panels with the building structure requires coordinated optimization in three aspects: material selection, structural design, and installation technology. In terms of material selection, priority should be given to materials with similar coefficients of thermal expansion. For example, if the main building structure is steel, the significant difference in the coefficients of thermal expansion between steel and aluminum alloy can easily lead to the external wall aluminum plastic panel bulging due to temperature stress if directly fixed. At this point, elastic connectors or flexible transition layers can be used to absorb differences through material deformation, or an aluminum keel system can be used, whose coefficient of thermal expansion is closer to that of the external wall aluminum plastic panel, reducing interface stress.
During the structural design phase, space must be reserved for thermal deformation of the external wall aluminum plastic panel. Rigid fixing is not recommended during installation; instead, floating connections, elongated screw holes, or telescopic side rib designs should be used to allow the panel to expand and contract freely with temperature changes. For example, the side ribs can be connected with plug-in connectors to form a telescopic structure, which can both reinforce the strength of the aluminum panel and absorb thermal stress deformation caused by small temperature differences. Simultaneously, sufficient joint width must be left between panels to avoid mutual compression due to dimensional expansion. Joint design should also consider the elasticity of the sealant; a weather-resistant sealant with high displacement capacity should be selected. The better the elasticity, the stronger the ability to withstand joint displacement deformation, and the more adaptable it is to the thermal expansion and contraction of the external wall aluminum plastic panel.
The installation process is crucial for deformation control. During construction, environmental conditions must be strictly controlled to avoid operation in high-temperature direct sunlight or low-temperature conditions, reducing immediate deformation caused by temperature differences. When fixing external wall aluminum plastic panels, screws should not be overtightened, especially at the weaker edges; excessive tightening will hinder the release of thermal stress and exacerbate deformation. For large-area external wall aluminum plastic panel curtain walls, a segmented installation and zoned fixing method can be adopted to distribute overall deformation into localized, minor adjustments, reducing risk. Furthermore, the installation sequence must be reasonable: first install the main load-bearing components to form a stable system, then install the external wall aluminum plastic panels to avoid uneven stress on the panels due to structural instability.
The thermal expansion of external wall aluminum plastic panels is also closely related to the panel size. The larger the panel size, the more significant the change in joint size during temperature changes, and the higher the risk of bulging. Therefore, the area of individual panels should be controlled as much as possible during design, or the overall rigidity can be improved by adding horizontal and vertical reinforcing ribs. For extra-long panels, segmented installation with intermediate gaps can be used to provide buffer space for thermal deformation.
During the maintenance phase, the joints, fasteners, and sealant of the external wall aluminum plastic panel must be inspected regularly. If cracks are found in the joints, aging of the sealant, or loosening of the fasteners, they should be repaired promptly to prevent moisture infiltration and internal corrosion, which could further weaken the structural stability. Especially in humid or rainy areas, drainage design should be strengthened to prevent water accumulation from exacerbating deformation.
Thermal expansion matching of the external wall aluminum plastic panel must be considered throughout its entire lifecycle, including materials, design, construction, and maintenance. By selecting matching materials with similar coefficients of thermal expansion, allowing for deformation allowance, optimizing installation processes, and conducting regular maintenance, deformation risks can be effectively controlled, ensuring the long-term stability and aesthetics of the external wall aluminum plastic panel curtain wall, and meeting the building's functional and safety requirements.
