Positive locking is a critical design feature that directly enhances the stability and reliability of mechanical joints. This is especially the case in applications that involve dynamic loads, extreme temperatures or high vibrations.
Positive locking mechanisms secure components and eliminate the risks of unintentional loosening or failure over time. In this article, we explore the concept of positive locking and highlight its importance in maintaining joint integrity.
Positive locking refers to a method of securing a joint through direct mechanical engagement between components, preventing relative movement without relying solely on friction or torque retention. This is achieved by incorporating features like interlocking teeth, pins, lock wire or specialised wire thread inserts with internal locking elements. These mechanisms prevent rotation and slippage in mechanical joints, even under harsh operating conditions.
Positive locking refers to a method of securing a joint through direct mechanical engagement between components, preventing relative movement without relying solely on friction or torque retention. This is achieved by incorporating features like interlocking teeth, pins, lock wire or specialised wire thread inserts with internal locking elements. These mechanisms prevent rotation and slippage in mechanical joints, even under harsh operating conditions.
Prevailing torque fasteners
Prevailing torque nuts and bolts are designed with deformed threads or specialised shapes that provide resistance to loosening. These fasteners create an interference fit, applying a constant friction force that resists rotational movement.
Locking tabs and plates
Locking tabs and plates are metal components fitted around the fastener heads. They feature tabs or extensions that can be bent against the flat surfaces of bolts or nuts, physically restraining them from rotating. In high-vibration environments where mechanical access allows, locking tabs are a secure solution.
Safety wire and lock wire
In critical mechanical joints, safety wires (also known as lock wires) are used to physically secure fasteners together. This involves threading a wire through holes drilled in the fastener heads and then twisting and anchoring the wire to prevent rotation. While not as integrated as other solutions, safety wires are common in aerospace and motorsport due to their effectiveness in preventing loosening.
Locking wire thread inserts
Wire thread inserts can incorporate locking features that apply radial pressure on the fastener’s threads. This internal locking action prevents fasteners from backing out due to vibration or thermal cycling. Such inserts are ideal for aerospace and automotive applications, where weight savings and durability are crucial.
High-vibration environments, such as in aerospace and automotive applications, subject mechanical joints to repetitive loading and unloading cycles. This can create movement in the joint which accelerates wear and introduces the risk of fatigue failure. Positive locking mechanisms eliminate the risk of vibration-induced loosening by mechanically engaging the joint, offering better resistance compared to friction-based solutions like standard thread torque.
Mechanical joints can also experience expansion and contraction due to temperature fluctuations, potentially leading to loosening or slippage. This can lead to misalignments or increased gaps between components that result in excessive wear and degradation. Positive locking features counteract these effects by maintaining firm engagement even under significant thermal stress, preserving the integrity of joints in critical applications like engine housings or structural assemblies.
For joints exposed to corrosive environments, maintaining tightness over time is vital to avoid galvanic or fretting corrosion that can significantly impact joint integrity. Positive locking mechanisms, such as wire thread inserts with anti-corrosion coatings, provide a dual benefit of preventing loosening and reducing exposure to corrosive elements. This ensures that joints remain functional and secure for longer periods, reducing maintenance frequency and increasing the lifespan of components.
Positive locking mechanisms are not just a feature, but a necessity in applications where joint integrity is critical. By preventing loosening due to vibration, thermal cycling, and corrosion, these mechanisms significantly extend the lifespan of mechanical joints, ensuring reliability and safety in demanding environments. Engineers must consider the right positive locking solution based on their application needs to protect joints from the common failure modes associated with dynamic and challenging conditions.
At KATO® Advanex, we understand the importance of durable and secure mechanical joints. Our range of high-performance wire thread inserts with integrated positive locking features offers engineers the confidence to design resilient and reliable connections for aerospace, automotive, and industrial applications. With extensive expertise and innovative products, KATO® Advanex is here to support your projects and help you achieve optimal joint integrity.
To find out more about our products or to get additional pricing information, contact a member of our team today.