Fastener Anti-Loosening Technology & Selection Guide for Vibration Conditions

In industrial MRO maintenance, bolt loosening is a common cause of abnormal noise, leakage, precision drift and even shutdown. Especially under vibration, impact and temperature fluctuation conditions, ordinary tightening is prone to self-loosening. This article provides practical technical specifications from anti-loosening principles, mainstream solutions, selection and installation.

Core Anti-Loosening Principle

The essence of thread loosening is axial preload attenuation and tangential micro-slip accumulation. Anti-loosening design should focus on three aspects: increasing friction resistance, limiting relative rotation, and chemical locking filling.

Comparison of Common MRO Anti-Loosening Solutions

• Spring washer: Anti-loosening by elastic expansion, low cost; prone to fatigue fracture in vibration environments, only suitable for light load and low-frequency vibration.
• Lock nut (all-metal/nylon insert): All-metal lock nuts (e.g., Spiralock) generate wedge effect through thread deformation, high temperature resistance and aging resistance; nylon insert lock nuts hold threads tightly via nylon ring, detachable and reliable, suitable for medium vibration.
• Thread locking adhesive (anaerobic): Pre-applied or on-site coating, fills thread gaps after curing, with anti-loosening, sealing and rust prevention functions; adjustable strength (medium strength detachable/high strength permanent locking), suitable for engines, gearboxes, hydraulic systems and other strong vibration parts.
• Belleville washer/anti-loosening washer: Belleville washer maintains stable preload, anti-loosening washer prevents rotation through tooth engagement, suitable for heavy load and high-frequency impact.

Selection & Torque Control for Vibration Conditions

1. Material & Strength Grade: Prioritize Grade 8.8 and above high-strength bolts with matching nuts in vibration environments; stainless steel (304/316) has weak anti-loosening performance, requiring locking adhesive or all-metal lock nuts.
2. Torque Specification: M6 (Grade 8.8) standard torque 8–11 N·m; M8 18–24 N·m; torque reduced by 15%–25% after adhesive application; use torque wrench for recheck and anti-loosening marking at key positions.
3. Installation Taboos: Threads must be clean and oil-free (degreasing required for anaerobic adhesive); avoid over-tightening (easy bolt fracture); do not mix different anti-loosening solutions in vibration areas (e.g., spring washer + nylon nut).

MRO Maintenance Recommendations

Daily inspection focuses on bolts near vibration sources; regular retightening cycle: high-frequency vibration equipment every 3 months, ordinary equipment every 6 months; prioritize stocking nylon insert lock nuts, medium-strength anaerobic adhesive and Belleville washer components for quick repair.