IMPROVING BOLT CONNECTIONS

In wind energy units, bridges, and steel construction, bolted joints are an indispensable component. In addition to the material and the tool, different climatic conditions also have a great impact on the coefficients of friction and, therefore, on the entire bolt connection.

A unitless dimension that describes the relationship between tension and torque, the coefficient of friction is an important element for a secure bolt connection. It is determined by two factors: thread friction and head friction. Thread friction describes the characteristics that arise when bolt and nut threads meet. In contrast, head friction occurs where the lower side of the head of the bolt meets the surface of the joint. The load pressure that affects the surfaces is the tension, which is also responsible for the elongation of the bolt and the corresponding spring effect. Torque, on the other hand, affects

How can zinc flake coatings enhance the protection of bolted connections in the wind energy industry?

the surface of the thread and the contact area. It is divided into three partial torques: thread torque, head friction and the part translated directly into tension. This means that the tension ultimately achieved with prescribed torque is dependent on the coefficient of friction.

The challenges for bolted joints

Different factors such as material pairing, surface, lubrication and wear all effect a bolt connection. In addition, there are external influences such as the ambient temperature, humidity or rain, which can lead to elastic deformations. In the worstcase scenario, bolts can break or the required pre­tensioning force cannot be achieved. This results in construction site stoppages with high costs as well as time delays due to repairs or the replacement of bolt sets.

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