By Bernd Scholl, Head of Process Engineering Product Sectors, DELO Industrial Adhesives &  Dr. Ralf Hose, Head of Training, DELO Industrial Adhesives

Every year, more than 800,000 tons of adhesives are produced and used in Germany alone ? trend upwards. All over the world, it was even approx. 3.8 million tons in 2008. The joining method of bonding is definitely gaining ground. Almost everybody has already used adhesives in daily life ? from bonding of a bathroom towel rail that has fallen off to the handle of the coffee cup. Also in industrial production, adhesives are increasingly replacing many formerly used standard methods.

The time when they have only been used for bonding packagings or binding books has long been past. In innovative applications and production methods and processes, adhesives are in demand, as well. When bonding glass doors or glass furniture like living room tables or bathroom scales, different requirements are made on the adhesive. In the glass sector, for example, the adhesive is to be invisible and, therefore, make for a sophisticated design ? at the same time it must adhere reliable and be resistant to humidity and elevated temperatures. Therefore, transparent acrylates are used in such cases.

    Picture 1: Transparent acrylate adhesives used in bathroom scales and shower cabins

The continuously progressing light-weight construction has also contributed to the success of bonding technology as efficient joining method. Assembly groups are becoming smaller and smaller due to required miniaturization, foils and sheets are becoming thinner and thinner. Therefore, it is often not possible to connect them using conventional joining methods like screwing or welding. Welding does often not come into question due to the very high temperatures arising and the resulting heat stress on the components, and as many materials and material combinations cannot be welded.

In such cases, adhesives score that cure at room temperature or by irradiation with light. Heat-curing acrylates with typical curing temperatures between 100 °C and 180 °C also have a moderate heat influence on the bonded connection compared to welding. Further advantages of adhesives: They are often in the lead as regards the equalization of tensions, the damping of vibrations and absorption of dynamic loads.

Combination of several joining methods

 In some industrial areas with complex and apparently incompatible requirements, it often happens that combined joining methods are used to benefit from both methods. For example, in car body construction, bonding is combined with welding as good aging resistance and corrosion protection as well as good crash performance are required. Besides welding, other joining methods like clinching, screwing and riveting are suitable partners for hybrid connection.

In particular, the combination of riveting and bonding is used, for example, in aerospace industry to build the aircraft skin. In this application, the advantages of adhesives (even distribution of tensions, insulation and corrosion protection) and rivets (resistance to peel stress) come together.                                           Picture 2: Bonding is also used in aerospace industry

 Bonding in electronics and the consumer sector

 Many safety-relevant electronic applications can also not be imagined without adhesives ? for example, when casting safety sensors of sealing housings of airbag sensors. Sensors are normally installed where the parameters to be measured are: An oils pressure sensor, for example, is positioned directly in the oil circulation. As the signals are directed outwards via electrodes, the sensor must be sealed against the conditions at the point of measuring, e. g., temperature, pressure or aggressive substances, at their outlet. It is necessary to cover open contact areas reliably and protect them against corrosion ? and, therefore, to ensure the adhesive’s functional capacity.

For details, click the attached file.