With the development of glass curtain walls, metal curtain walls have also flourished in recent years. Compared with glass curtain walls, metal curtain walls have enriched the artistic expression of curtain walls and improved the performance of curtain walls. For the selection of decorative aluminum plates in metal curtain walls, we should correctly understand and select them reasonably, make the best use of materials, and ensure project quality and artistic decoration effects. 

1. Single-layer curtain wall aluminum panel 

In foreign countries, it is mostly made of pure aluminum plate, and the thickness of the plate is 3mm ~ 4mm. In my country, LF21 alloy aluminum plate (American grade 3003) is mostly used, and the thickness of the plate is 2.5 mm. The strength of LF21 alloy aluminum plate is nearly twice that of pure aluminum plate. Although the thickness of the aluminum plate is 0.5 mm thinner than that of pure aluminum plate, the strength of the plate surface is still greater than that of pure aluminum plate, and the weight of the plate is reduced. 

During the production process of a single-layer aluminum plate, the four sides are bent at right angles according to the design requirements. Generally, the four peripheries of the corner can be directly bent by 90 ° without slotting. If the four peripheries of a 2.5 mm thick aluminum plate are slotted, the thickness of the bending corner of the aluminum plate will affect the firmness. Some manufacturers report that there have been cracks in the aluminum plate without slotting and the bending corner is not straight and slightly curved, which affects the appearance. This is related to the status of LF21 alloy aluminum plate. The semi-hard state (1/2 Y) should be selected instead of the hard state (Y). If the material is good, there will be no corner cracks. When the periphery of the aluminum plate is not grooved at a 90 angle, the slightly curved corner cannot form a straight corner, but it does not affect the appearance of the curtain wall. There is no need to groove around the periphery to reduce the thickness of the aluminum plate and reduce the strength of the bending corner for the sake of right angles. After the four sides of the aluminum veneer are bent to 90, the adjacent sides of the four bent corners should be welded together, and the weather-resistant sealant joints between the aluminum plates should not be lower than the surface of the aluminum plate. 

In order to strengthen the strength of aluminum plate surface, reinforcing ribs must be installed on the back of aluminum plate. The reinforcing ribs are generally made of aluminum square tubes or angle aluminum of the same alloy. Welded on the back of single-layer aluminum plate with electric bolts, welded aluminum alloy bolts, put them into the holes of reinforcing ribs, and fastened with aluminum nuts. Electric bolt welding does not destroy the external facing of single-layer plate, and installs reinforcing ribs, so that the single-layer aluminum plate can maintain sufficient rigidity and flatness. 
Since the single-layer aluminum plate is easy to bend and can meet the needs of today's ever-changing exterior wall decoration, its appearance has enriched the processing, forming and installation structure forming of the aluminum plate curtain wall. The flatness of the aluminum plate of the veneer curtain wall depends on the quality of the manufacturer. The aluminum flat sheets of modern manufacturers are better than those of small old-fashioned manufacturers. Manufacturers that can press aluminum plates with wide plate surfaces are better than those that produce narrow widths. Southwest Aluminum Processing Factory, the largest and most advanced aluminum plate manufacturer in my country, can produce aluminum plates with a width of 2.8 m. Plate, its flatness and finish have won the national gold medal. 

The surface treatment of single-layer aluminum plate can't be anodized. Because the material composition and oxidation bath of each batch of aluminum plate are different, the surface color difference of aluminum plate after oxidation is large, and the overall effect of curtain wall is extremely poor. Generally, electrostatic spraying is used, which is divided into powder spraying and fluorocarbon spraying. The raw materials of powder spraying are polyurethane, epoxy resin and other raw materials with high retention pigments, and dozens of different colors can be obtained. 

Fluorocarbon spraying uses fluorocarbon polymer resin as a metal topcoat, which is generally divided into three or four coats (spraying three or four times). The commonly used brand is: KANAR500. The thickness of the paint on the surface of the aluminum plate is 40 μ ~ 60 μ. It can withstand corrosion, acid rain and various air pollutants, is not afraid of strong ultraviolet radiation, has good extreme heat and cold resistance, can maintain uniform color for a long time, and has a long service life. However, the hardness, collision resistance and abrasion resistance of the paint layer are worse than powder spraying. 

2. Aluminum composite panel (aluminum-plastic panel) 

Aluminum composite panel is a pure aluminum plate with two inner and outer layers of 0.5 mm thick, and the middle interlayer of polyethylene (PE) or polyvinyl chloride (PVC) or other petroleum by-products with a thickness of 3mm ~ 4mm. It is continuously rolled at high temperature and made by hot pressing. The surfaces of the inner and outer aluminum plates are fluorocarbon surface roller paint, and the thickness of the paint layer is generally about 20μ. The advantages of this product are: The surface is smooth, flat, beautiful, and has a certain strength. The main producing areas are: Germany, the United States, Japan, South Korea, and several domestic companies have imported equipment and have been mass-produced. The disadvantage of composite aluminum plates is: only 0.5 mm thick pure aluminum plates on both sides., laminated in the middle, so the strength is not high. At the same time, because the aluminum plate is very thin, when partially overheated, the expansion of the middle laminate can cause the aluminum plate to bubble. In addition, if burned, the middle laminate will produce harmful and toxic gases. 

In recent years, a large number of aluminum composite panels from various countries have been introduced from abroad. Some instructions have many advantages, but no shortcomings can be seen. Some people believe in foreign advertisements. Some aluminum composite panel manufacturers claim that their composite panels are simple to process. As long as there are ordinary woodworking tools, it can be processed and formed, but it is not the case. 

The processing requirements of aluminum composite panel are very strict and difficult. When bending, the aluminum composite panel must be grooved around the board, cut off a certain width around it, cut off one side of the aluminum plate and part of the glue layer, and then bend the aluminum plate to 90. If the groove is cut by hand, it is difficult not to scratch the aluminum plate, and the bending corner is the weakest link of this curtain wall panel. Now, many places can see that the corner of the composite aluminum plate is cracked, and rain and water will accelerate the delamination of the aluminum plate from the plastic. In order to ensure that the grooving depth does not scratch the outer panel of the composite plate. 

In the United States, aluminum composite panels are not used in high-rise curtain wall buildings, but only used for interior decoration or exterior walls. Aluminum composite panels are embedded in aluminum materials. 

3. Honeycomb aluminum composite panel 

Honeycomb aluminum composite panelHoneycomb aluminum plate for short, which is a variety of honey nest-shaped sandwiches made of different materials between two aluminum plates. The thickness of the two aluminum plates is different. It is generally 1.0 mm ~ 1.5 mm, and the thickness of the inner plate is 0.8 mm ~ 1.0 mm. The total thickness of the honeycomb plate is 10mm ~ 25mm. The middle honeycomb sandwich materials are: aluminum foil nest core, fiberglass nest core and mixed paper nest core. The shape of the honeycomb generally includes: corrugated strip, regular hexagonal, rectangular, cross-shaped, hypercurvature. The sandwich material needs special treatment, otherwise its strength is low and its life is short. 

Honeycomb aluminum plate is better with aluminum foil core, and its surface flatness is good, and its strength and stiffness are better than those of aluminum veneer. The reinforcing ribs on the back of aluminum plate should be set according to the design requirements. When using honeycomb aluminum plate, it should be designed and calculated according to the height, wind load and earthquake load of different buildings, different areas and curtain walls, and then according to the design requirements, the thickness of aluminum plate and honeycomb thickness should be selected, and different types of blocks should be manufactured according to the design requirements, which can meet the following main indicators: wind pressure index, air tightness index, water tightness index, impact resistance index, plane deformation, heat preservation and sound insulation index. 

There should be no leakage point after processing of honeycomb aluminum panel, otherwise rainwater will flow into the honeycomb core after installation. First, it will destroy the nest core, and second, it will cause water leakage. Therefore, during processing, the outer aluminum veneer of aluminum honeycomb panel is wider than the inner aluminum veneer. It is bent inward at an angle of 90 to fully cover the honeycomb and then glued or welded. Because honeycomb panels have better strength, better heat insulation and sound insulation properties, this kind of aluminum panel is mostly used for metals with higher requirements for the above performance. 

4. Conclusion 

As a non-load-bearing building enclosure functional structure, metal curtain wall should select corresponding decorative aluminum plates for specific and different buildings to ensure the engineering quality and use function.