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Bonding Technology In Cars: Adhesives Instead Of Rivets, Screws and Welding

Adhesives are increasingly used in modern automotive production. They allow different materials to be permanently bonded in an energy-efficient manner and without the need for other auxiliary parts.

The specialty chemicals company Degussa AG (Dusseldorf, Germany) supplies materials that are used in innovative bonding technology to design the vehicle of the future to be even safer and more economical.

In modern vehicle construction practically all components can be bonded using industrial structural adhesives. The benefits of structural adhesives are particularly evident when different materials need to be bonded to each other. This is even more important when dealing with a mix of lightweight construction materials, where bonding would not be possible without adhesives. Cost-savings (e.g. replacement of mechanical fasteners with adhesives) provide an additional advantage. A medium-class vehicle requires welding at approximately 5,000 points, each costing around five cents. More than half of these can be replaced by adhesive joins, saving around 70 euros per vehicle. In addition, using one kilogram of adhesive reduces the vehicle weight by 25 kilograms and adhesive-bonded vehicle bodies are more rigid, allowing thinner sheet metal to be used.

Car body rigidity substantially improved

Direct glazing using moisture-curing polyurethane systems provides a good example of glass-metal bonding, which is commonly used. This multifunctional bonding holds the glass windshield in place even if the vehicle is involved in an accident, improves the rigidity of the automotive body and allows for process automation.

Degussa has successfully marketed AEROSIL® fumed silica and PRINTEX® brand pigment blacks for windshield adhesives for many years. They enable the production of easy to process, strong and UV-stable adhesive products. Those are then applied with pinpoint accuracy to the body components using automated glue guns.

The copolyester DYNACOLL® increases rapid curing and cuts assembly time.

A further development that is progressing well is the use of structural adhesives for bonding metal. These solutions again yield significant improvements in terms of body rigidity and crash behavior. They also offer the advantage of reduced weight, versatile design options and structural rigidity. All these advantages should significantly increase the market prospects for these plastic/metal combinations in the future.

Good wet and dry adhesion

At present, single-component epoxy resins or two-component polyurethanes are used for structural adhesives. This demands that the adhesives provide a great deal of functionality even under adverse outdoor conditions, something that can only be achieved by adding suitable chemical additives. For example, when used in structural adhesives silanes such as DYNASYLAN® increase wet and dry adhesion (“adhesion promotion”). At the same time they improve resistance to solvents, heat, humidity and weathering. They also optimize the mixing behavior of the adhesive components and make processing very much easier.

Hot melt adhesives for interior ecology

Similarly, adhesive technology offers advantages in the passenger cab, where diverse materials such as textiles, leather and plastics are bonded to one another. Apart from commercial viability, ecological aspects in particular play a significant role when selecting an adhesive for this area of the vehicle.

Customized hot melt adhesives based on DYNAPOL® S and DYNACOLL® satisfy these sophisticated requirements: They achieve a maximum adhesive strength very rapidly, enabling the next stage of processing the adhesive-bonded components to take place immediately. Solvent-free adhesive reduces unpleasant evaporation in new cars, an occurrence known as fogging.

Debond “at the press of a button”

One of the biggest challenges in the chemical industry is to manufacture an adhesive bonding that can be undone. This is because whereas car bodies made from welded steel can be easily melted down, vehicles manufactured from a mix of adhesive-bonded materials remain a problem today from the recycling point of view. What is needed is an adhesive that will lose its adhesive properties on command, as it were.

This is precisely what the adhesive additive MagSilica®, produced by the internal start-up company Degussa Advanced Nanomaterials, accomplishes. Adhesives containing MagSilica® can be heated using an alternating magnetic field, and as a result they cure much faster than conventional products. Bonds created using this process can be undone using very selective heating, which results in the adhesive bond “switching off” again.

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