Kraftschluss

Kraftschluss, or force closure, is a principle in mechanical engineering describing a connection in which load transmission between two components is achieved primarily by friction forces generated by a preload on the contact surfaces. It contrasts with Formschluss (form closure), where the geometry of the parts themselves prevents relative movement.

The mechanism relies on a normal contact force, typically produced by clamping, pressing, or an external preload. The friction force that resists sliding is proportional to the normal force and the coefficient of friction, up to a limit. In practice, the amount of load or torque that can be transmitted before slip occurs depends on μ, the distribution of contact pressure, surface finish, and the contact area. Friction pairs are common in components designed to transmit motion or power without relying on perfect geometrical matching.

Applications of Kraftschluss include friction brakes and clutches, friction couplings, band brakes, and certain machine-tool fixtures and clamping devices. It is especially useful when minor misalignments, damping of vibrations, or rapid engagement are advantageous and when exact form-fit closure is impractical.

Advantages and limitations: Kraftschluss allows transmission without highly precise shapes and can accommodate slight misalignments. However, it is susceptible to wear, heat generation, and changes in friction due to lubrication, temperature, or surface wear. It can slip under higher loads, and stiffness and fatigue must be considered in design and maintenance.

Relation to other closures: Some connections employ a combination of Kraftschluss and Formschluss to achieve both load transmission and positional stability. The concept is a standard topic in mechanism design and machine element literature.