Locking Mechanism and Applicable Scenarios of Track Bolt Anti-Loosening Washers
What is the locking mechanism of friction-increasing lock washers and which scenarios are they suitable for?
Friction-increasing lock washers (such as spring washers and rubber washers) generate continuous axial preload between the bolt and the connected part through their own elastic deformation, increasing the friction force between the thread pairs. At the same time, the protruding parts of the washer form a small biting force with the contact surface to further prevent bolt rotation. These washers are simple in structure and low in cost, suitable for ordinary-speed straight lines and sections with small vibrations. In these scenarios, the vibration load is mild, and friction increase is sufficient to resist bolt loosening.
What is the core advantage of mechanical locking washers and why are they suitable for switch areas?
Mechanical locking washers (such as tab washers and external tongue washers) form mechanical constraints by bending the tabs of the washer to fasten the bolt head and the edge of the connected part respectively, structurally preventing bolt rotation. Its locking effect is not affected by vibration intensity, making it a permanent anti-loosening method. Switch areas have severe vibration, complex stress, and dynamic loads from point machines, where friction-type washers are difficult to be effective for a long time. Mechanical locking washers can completely lock the bolts, avoiding the impact of loosening on switch conversion accuracy, so they are the first choice for switch areas.
What is the working principle of deformation-locking lock washers (such as wedge lock washers)?
Wedge lock washers consist of two washers with wedge-shaped bevels, which are installed with the bevels facing each other. After the bolt is tightened, the washers generate axial locking force. When train vibration causes the bolt to tend to loosen, the bolt drives the washer to move slightly along the wedge-shaped bevel, and the washer generates greater axial preload to lock the bolt in the reverse direction. This "the more vibration, the tighter" characteristic enables it to automatically compensate for preload loss. The locking mechanism of wedge lock washers combines friction and mechanical action, with far higher stability than ordinary washers.
Why are wedge lock washers preferred over spring washers for heavy-haul lines?
Heavy-haul lines have large train axle loads, and the vibration loads generated by wheel-rail impact are extremely strong. The elastic deformation of spring washers will decay rapidly, resulting in serious preload loss and inability to prevent loosening for a long time. The wedge structure of wedge lock washers can continuously provide dynamic preload compensation. Even if the bolt has slight loosening, it can immediately restore the locked state. In addition, wedge lock washers bear force more evenly and will not cause local stress concentration like spring washers, which can protect the contact surface of bolts and fish plates. Therefore, joint bolts on heavy-haul lines generally use wedge lock washers.
What are the key precautions for installing lock washers on-site?
Before installation, check the integrity of the washers; deformed or cracked washers are strictly prohibited. Friction-type washers must ensure that the contact surface is clean without oil or rust, otherwise the friction coefficient will be reduced and the anti-loosening effect will be lost. The bending angle of the tabs of mechanical locking washers must be in place, and they must tightly fasten the bolt head and the connected part without gaps. Wedge lock washers must be installed in pairs with the bevel directions facing each other; installing them in the wrong direction will completely lose the anti-loosening effect. After installation, re-inspect the bolt torque to ensure the washers function properly.