Gluing
Aluminum composite surfaces can be bonded with suitable metallic or universal adhesives. When combining composite materials with other chemical groups, it is essential to use highly elastic adhesives (such as polyurethane-based single-component adhesives). Preliminary linear tensile tests are recommended to avoid deformation due to thermal differences.
In polyethylene (PE) core panels, butt-gluing is unfeasible due to the low surface energy of the polymer. Although special adhesives are available for polyethylene, the best technical solution is usually welding or mechanical fastening. For polyurethane or mineral cores, butt adhesives can be used, considering that the bond may fail under high shear or bending loads. For small parts or parts without high load requirements, double-sided adhesive tapes with maximum adhesion or Velcro-type snap fasteners for split joints can be used.
Welding
Welding of composite materials is carried out by hot air (t = 260 – 270 °C) using welding wire. This method heats and firmly joins the inner layer of the material. The quality depends on surface preparation, hot air purity, temperature and constant pressure.
The most efficient method is accelerated welding with fiber traction device, which guarantees uniform heating and high productivity. It is essential to bevel the ends of the material before soldering (according to the wire profile) and to perform the operation within 24 hours maximum to avoid reaction of the filler with oxygen. For PE cores, it is recommended to sand the surface before brazing. After cooling, the excess overlap is removed with a profiled knife inclined towards the surface.
Mechanical connection
Mechanical methods are similar to those used for plastics and sheet metal. The use of plastic, aluminum or stainless steel fasteners is recommended to avoid corrosion. If environmentally sensitive elements are used, they should be varnished or insulated with gaskets.
In facades and large advertising structures, safety depends on the strength of the joint. There are specific self-tapping screws for composite panels with a hardened steel drill bit tip, capable of drilling through the panel and the supporting structure (such as steel straps). Stainless steel screws are superior to galvanized screws, as the latter lose their zinc coating during screwing, reducing their service life to only 2-5 years.
Characteristics of technical screws:
- The fixing diameter at the base is smaller than the diameter under the washer to secure the thin aluminum layer.
- Double thread diameter for superior sealing.
- EPDM (ethylene propylene diene diene terpolymer) washer, the most weather resistant material.
- Consideration of linear expansion: the composite has a coefficient of 0.023 – 0.025 mm/m°C. Holes must be calculated according to temperature extremes to avoid deformation.
Riveting
Aluminum compatible rivets are used. In outdoor or humid areas, aluminum or stainless steel blind rivets should be used, leaving the necessary clearance for thermal movement of the sheet metal. Countersunk rivets are not suitable for outdoors as they prevent this movement. Cushioning pads can be used to prevent the rivet head from pressing unevenly on the surface.
Bolted joint
Indoors, wood or metal screws with various heads can be used. For countersunk screws, it is necessary to enlarge the hole beforehand to avoid local stresses. In exteriors, facade screws with sealing gaskets are required, avoiding over-tightening. Decorative plastic plugs can be used to hide the fasteners and unify the color.
Profiles
P-, U-, L- and H-profiles with snap-in systems are used for advertising and interiors. In exteriors, the panel should be mounted with gaps to allow for expansion. In large structures, it is recommended to fix the profile at several points with screws. Specialized profile systems are available for the installation of ventilated facades to ensure safety and material movement.
Attention: It is essential to install all panels in the same direction (following the markings on the protective film). Non-observance of this rule may cause visual shade variations depending on the light angle.