What does bonding sandwich panels mean?

Very typical applications are: cooling element sandwiches in truck superstructures and other vehicle structures, in partitions in high-rise construction, sanitary cabins, raised floors, movable room dividers, etc., can be designed as sandwich elements. The entire lightweight construction sector uses the sandwich bonding method.

In addition to the typical structure of a bonded sandwich, there are surface laminations similar to sandwich constructions. Here, the usual core layer is omitted in the sandwich. This is also referred to as a false sandwich.

The following have proven effective as face layers in sandwich bonding: coated or painted sheets of aluminum or steel, glass fiber reinforced panels (GFRP) based on polyester, epoxy resin and others, thermosetting laminated panels (DKS), thermoplastic plastic sheets made of ABS, PC, PMMA, and various wood materials.

Common core layers in sandwich bonding include: rigid insulating foams made of polystyrene, polyurethane, Foamglas®, and others, as well as fiber mats made of glass or stone wool, various wooden structures, and wood-based materials.

Lightweight elements in sandwich bonding are made from face layers of aluminum, galvanized steel, stainless steel, and other metals. As core layers in sandwich bonding, metallic and non-metallic honeycomb structures, high-strength rigid foams such as Foamglas®, or metallic corrugated materials are used.

The respective material combinations, the surface sizes, and requirement profiles determine the use of the type of adhesive in sandwich panel bonding.

For metallic bare surfaces made of aluminum, steel, stainless steel, zinc sheet, non-ferrous metals, etc., 2-component adhesives based on epoxy resin are preferred for sandwich bonding. Here, various epoxy adhesives are offered. These structural adhesives or sandwich adhesives based on EP are available in different processing times and joint conditions (harder, softer, elastomeric, etc.). These 2-component epoxy adhesives are also used in sandwich bonding with combinations of thermoset sheet materials made of GFRP, CFRP, and carbon.

Sandwich bonding of highly stressed connections made of aluminum and carbon mats, e.g., in aerospace, is preferably done with 2-component adhesives based on epoxy resin (EP).

For coated or painted metallic surfaces and other materials such as plastics and wood, 2-component adhesives based on polyurethane (PUR), such as technicoll 8301/8302, are preferred for sandwich bonding. These are also offered with different processing times and final properties in the cured state.

In sandwich bonding using core layers of rigid foams or mineral fiber mats and facing layers of coated or painted metals, as well as with thermosetting and thermoplastic plastic panels, 2-component adhesives based on polyurethane (PUR) are also effective. Other possible adhesives include foaming 1-component PUR adhesives, such as technicoll 8324. They react with the moisture in the environment and penetrate into the core layer of the foam material. These adhesives optimally fill the cavities and significantly improve the strength of the entire sandwich.

Small-area sandwich elements can also be executed with the faster-curing 2-component adhesives based on methyl methacrylate (MMA). Sandwich bonding in material combinations without metals and on lightly loaded surfaces can often also be carried out with dispersions (glues). Here it is important that one of the sandwich materials used is absorbent. Sandwich bonding for purely decorative applications, e.g., sheet materials made of plastics or wood with each other or onto painted, coated, or bare metals, can be well executed with contact adhesives based on polychloroprene or polyurethane.