Railway steel beam trusses require frequent maintenance to address two primary issues: deterioration of the hot-dip galvanized coating (a standard corrosion-prevention treatment) and loosening of bolted joints.
Aluminum beam trusses offer a clear advantage. Their natural corrosion resistance significantly reduces maintenance requirements. However, because aluminum is relatively soft, the applied bolt tension (preload) must be carefully limited to avoid damaging the bearing surfaces.
This restriction poses a challenge. Most fasteners—including self-locking types—resist loosening by relying on preload to create a clamping force. This force is maintained by friction at the threads, bearing surfaces, and at the interface between the clamped components. When only limited preload can be applied, the resulting friction is also low, making joints more susceptible to loosening.
To maximize the maintenance-free benefits of aluminum beam trusses while ensuring reliable locking under limited preload, HARDLOCK® nuts were adopted. The HARDLOCK® nut features a unique two-part design: the Convex nut applies the target preload, while the Concave nut engages a wedge interface, generating a transverse locking load across the bolt shaft. This transverse locking load is independent of preload and mechanically prevents loosening.
Stainless steel HARDLOCK® nuts with GEOMET® coating were selected to prevent galvanic corrosion between dissimilar metals, ensuring reliable long-term performance with minimal maintenance.