Slip resistance

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.

Definition and Meaning
Slip resistance describes the maximum shear force that a screw connection can transmit across the interface surface before relative slippage of the components occurs. It is influenced by the coefficient of friction, clamping force, geometry, number, and strength of the fasteners, as well as by the surface finish of the mating parts.

Consequences of Exceeding the Limit
If the slip resistance is exceeded, relative rotational movement occurs, resulting in a loss of clamping force, increased bolt load, the risk of loosening, and possible damage to contact surfaces.

Calculation according to VDI 2230
VDI 2230 Part 1 enables the mathematical design of bolted joints, taking into account the elastic elements recommended therein. The use of spring-loaded securing elements, such as tension washers or NSK-L washers, increases resilience and improves the maintenance of preload force, especially with short clamping lengths.

Effect with short clamping lengths
Spring-loaded fasteners significantly increase resistance to slip and are particularly advantageous in lightweight construction, where short clamping lengths and compact designs are common.

Technical, economic, and environmental advantages:

  • Number of screws: Reduction while maintaining the same level of safety
  • Material: Savings due to smaller cross-sections
  • Weight & CO₂: Contribution to reducing the carbon footprint, particularly in the automotive and aerospace sectors

Conclusion and Outlook
Spring-loaded fasteners, such as lock washers per DIN 6796 for property class 8.8 or NSK washers, which are differentiated by property classes and applications, make a significant contribution to increasing slip resistance and thus to the functional safety of bolted joints. Including them in calculations in accordance with VDI 2230 enables optimized design, particularly under challenging design conditions such as short clamping lengths or dynamic loads. In the future, their use will become even more important in the context of resource-efficient designs and CO₂ reduction. When using multifunctional screw locking elements, this functionality—in addition to protection against loosening—is generally present and fundamentally improves the robustness of the screw joint.

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