Support

Elastic resilience has a significant influence on the preload force and sliding resistance of bolted joints. It is determined by the screw, the backing surfaces, and suitable spring elements. Lock washers conforming to DIN 6796 or NSK washers enhance this effect and reduce loss of preload, especially with short clamping lengths. Unsuitable elements are excluded; variants that comply with standards can be verified by measuring the residual spring force. See also Railway Engineer Technical Report.

Slip resistance refers to the maximum shear force that a screw connection can transmit before components begin to slip relative to one another. Especially with short clamping lengths, the use of spring-loaded elements such as tension washers (DIN 6796) or NSK washers significantly increases resistance to slippage. In addition to functional advantages, these elements also support lightweight design goals and CO₂ reduction. Evaluation is performed, for example, in accordance with VDI 2230 Part 1. See also Eisenbahningenieur Technical Report.

Screw connections with special hole geometries significantly alter the mechanical behavior of the joint due to their segmented contact area, negatively affecting surface pressure, pressure distribution, and elastic resilience while simultaneously promoting settlement, creeping, and loosening effects. Notches on the hole flanks and the absence of lateral screw guidance are particularly critical, which is why it is necessary to evaluate additional factors such as contact area, deflection, and resistance to loosening. Since no standard specifications exist, tested securing elements such as NSK L, NSK B, and NSK EL are recommended for mechanical and electrical applications.

Electrical screw connections ensure the transfer of current and mechanical clamping. A distinction is made between indirect current transmission via electrical contact glands and  directly current-conducting connections, known as electrically conductive screw connections. Settlement behavior, corrosion, and thermal influences require a targeted design using NSK washers. See also NSK-E Technical Report.<

Electrical contact glands transmit current via the clamped contact surfaces of the conductor materials, not via the screw. They require stable contact pressure and a minimal number of interface surfaces. NSK-E/EL washers offer elastic resilience, anti-loosening protection, and safety in accordance with standards—ideal for modern applications. See also NSK-E Technical Report.

First, the slackening phase occurs in the slackening mechanism of bolted joints. During slackening—or in the slackening phase of bolted joints—the preload force decreases due to embedding, relaxation, and creeping. The sliding resistance is maintained, so that operational forces continue to be transmitted through clamping. Embedding occurs through the plastic leveling of rough surfaces immediately after assembly. Relaxation and creeping lead to further force reduction over the long term. Screw connections can be secured against slackening using special screw locking elements or multifunctional screw locking elements.