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FEATURE
FASTENINGS & ADHESIVES
Patrick Faulkner, lead engineer at Accu,
looks at the common causes of assembly
failure and how thread locking solutions
can improve fastener performance
F
asteners are continuously exposed to conditions which can compromise joint integrity, such as vibration, fluctuating
loads, thermal stress and material deformation. Even small losses in preload can lead to movement, reduced performance or complete assembly failure. While traditional thread locking solutions are effective, they can be inefficient in high-volume production as each fastener must be individually coated before being used. Pre-applied thread lock solves this limitation by providing a precisely factory-applied solution that is ready to use immediately.
Why assemblies fail The reliability of assembly depends on maintaining secure fastenings. The loosening of these fasteners is one of the common causes of assembly failure but, being a gradual process, this often goes unnoticed until a component fails. The most effective approach is therefore to understand the factors that cause it. There are five primary causes: • Vibration is one of the most persistent contributors. In most assemblies, components are exposed to vibration, which can gradually reduce preload tension. As micro-movements occur at the jointed surfaces, tension is progressively lost, resulting in a reduction of clamping force and ultimately leading to the fastener loosening.
• Dynamic load, where shifting or uneven load distribution across an assembly introduces fluctuating stresses, is also another cause of loosening. This can lead to movement within the joint itself, causing the fastener to loosen as the system responds to changing loads.
• A sudden shock or impact loading can also introduce unexpected stresses. These transient forces can cause an immediate
Pre-aPPlied th re Preventing as
reduction in tension, resulting in a significant loss of bolt preload.
• The stability of a fastened joint also depends on the long-term performance of the material. When torque is applied, the fastener relies on the clamped materials to maintain their dimensions and structural properties for the fastening to hold. If materials degrade, wear away or corrode, fasteners can become loose.
• Lastly, creep plays an important role in fastener loosening. Creep refers to the slow deformation of material under sustained stress, often driven by high static loads or thermal cycling. This mechanism can cause a gradual redistribution of stress within the joints, leading to a progressive loss of clamp force that often goes unnoticed until significant loosening becomes apparent.
What are thread locks? Thread lock is a liquid adhesive used on the threads of fasteners like bolts, nuts and screws to help prevent them from loosening over time. It works by filling the very small gaps between the threads of fasteners. When applied, it cures into a thermosetting plastic which forms a toughened bond, helping to lock the fastener in place and resist loosening caused by vibration, movement or other external forces. This is not a one-size-fits-all solution so
thread lock is available in different types for various applications. For example, high-strength thread lockers are used for permanent assemblies that must withstand heavy loads and strong vibration. Low-strength thread lockers are designed for small fasteners where regular disassembly may be required. High-temperature thread lockers are specially designed to maintain their bonding strength in environments exposed to thermal stress. Thread lock must be manually applied to
each fastener. While effective, this process can be time-consuming and impractical in large- scale applications. Pre-applied thread lock helps to overcome these limitations by integrating the compound directly onto the fasteners during manufacturing, ensuring consistent application.
advantages of pre-applied thread locks Pre-applied thread locks offer many advantages over manually applied liquid formulations, with the most immediate benefit being significant time savings as it eliminates the need for on- site application and curing during assembly. As the thread locking compound is applied to fasteners before delivery, fasteners arrive fully ready for installation while still achieving full locking performance. This approach also enhances consistency as
the application is controlled in a manufacturing environment rather than relying on manual application variability. Coverage, quantity and technique will vary between users. Therefore, pre-applied thread lock ensures that each batch of fasteners meets the same specification and delivers consistent performance. Unlike liquid thread lock, which can be sticky
Pre-applied
thread locks offer many advantages
3 DESIGN SOLUTIONS SEPTEMBER 2026 6
and messy to work with, pre-applied coatings are dry to the touch. This eliminates the risk of spillage during handling and reduces complications during installation, resulting in a cleaner and safer work environment. Pre-applied thread lock also protects against
corrosion. By sealing the thread interface against moisture and contaminant ingress,
www.designsolutionsmag.co.uk
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