When it comes to combating vibration in a threaded fastener assembly, our usual weapons of choice are mechanical locking hardware. A lock washer or lock nut adds friction to a threaded joint, deterring loosening and keeping things firmly in place. This solution works just fine for many applications, but what about cases with heavy, sustained vibration? What about other sources of loosening, such as thermal expansion of the fasteners, or flexing of the fastened materials? In such cases, we turn to thread locking compounds – special adhesives that are applied to a bolted joint, which glue the fastened materials together. Let’s dive into thread locking compounds below!
Thread Locking Compounds Explained
Most of the consideration given to specifying threaded joints is centered around strength, addressing potential joint failure by simply prescribing a stronger fastener than the stress load presented by the application. The ‘strength’ expected of a threaded fastener assumes that every part of the joint is in perfect condition – tight, square, free of corrosion, and installed correctly to begin with. Usually, an engineer will over-specify a fastener in order to provide a safety factor in their strength assumptions, making up for some of the potential imperfect conditions found in the real world.
Environmental and operational factors all tend to work against the resilience of a fastener, in a number of ways. Heat causes materials to expand and then contract once cool again, vibration causes fasteners to loosen, corrosion causes fastener surfaces to degrade, and so on. Even with mechanical friction or tension hardware added (such as lock washers or nylon-insert lock nuts), a joint can still loosen just enough that its clamping force becomes compromised. In such cases, changing our thread locking approach from mechanical means to adhesive compounds is in order.
Adhesive thread locking compounds (referred to from here as simply ‘threadlockers’) are fluid glues that are applied between male and female threads. As the coated threads are engaged, the locking compound flows into all of the void spaces between the two pieces, and expands to dispel any trapped air within the joint. The fastened materials act as a catalyst, starting an anaerobic chemical reaction that cures the thread locker into a hardened glue. Once hardened, the thread locker provides both full thread surface area engagement between the fasteners, as well as much higher friction required to loosen the joint.
Maximum surface engagement is a feature of thread lockers that should not be understated. In a standard threaded joint, as low as 15% of the threaded surface area is all that is engaged. Machining tolerances between male and female threads need to leave so much free play in order to compensate for manufacturing variances but also result in large portions of the threads floating in free air, allowing for minimal friction between components and therefore comparatively low resistance to loosening. Threadlocker compounds fill this space and adhere to the entirety of mating surfaces.
Do you have an application where you might envision using thread locking compounds over mechanical means? E&T Fasteners offers expert support and product selection between these options and more! Contact us to discuss your application, or to see our standard fastener offerings, visit our product selection here.
Common Specifications and Selection
To recap the above section, thread locking compounds have two primary benefits: thread lockers are a less expensive option compared to mechanical locking hardware, and offer a higher degree of locking engagement and strength even under higher vibration conditions. When selecting a thread locker for an application, it’s helpful to start your review with these benefits in mind. If the extra labor and material cost of locking hardware is of interest to avoid, and if your application has moderate to significant environmental and operational risks of loosening fasteners, then you’ll definitely benefit from pursuing thread locking compounds.
Threadlockers are available in a variety of grades and strengths, ranging from low strength reusable formulas, all the way up to near-permanent single-use strengths.
In the context of thread lockers, ‘permanent’ means that the compound cures into an extremely resilient resin, which will take significant torque (and in some cases heat plus breaking compounds) in order to disassemble. Once disassembled, the joint will need to be fully cleaned to remove old compounds.
To select a thread locker, follow this selection sequence:
- New or already-assembled fastener? Some compounds are intended to be applied to existing threaded joints, with penetrating properties aimed at breaking into assembled threads.
- Is frequent disassembly required? Usually larger diameter hardware (over 1” diameter) is considered to not require disassembly, and so threadlocker compounds in this category offer much higher strength and permeance, some even requiring the use of heat to disassemble.
- Determine the fastener material – threadlockers work by inducing an electrochemical reaction with the base fastener’s material, and so the material serving as this reaction’s catalyst is important. Some materials react directly and instantly, while others may require a heat source and a primer in order to start the reaction.
- Determine the diameter – typically, lower strength thread lockers correlate with smaller diameter hardware. Consult the thread locker manufacturer’s sizing data to confirm size compatibility.
- Confirm strength – threadlocker strength is measured by break-away and prevailing torques, and is also influenced by temperature (where higher ambient or operating temperature will de-rate the strength). For example, Permatex Large Diameter Threadlocker RED has the below performance values, pulled from their technical data sheet found here:
Once you’ve selected a thread locker, you have one last decision to make: do you want to apply the thread locker yourself, or would you like to specify the thread locker to be pre-applied when you order fasteners? It is a common option to have large fastener orders include pre-applied thread locker, saving you time and risk of errors out in the field.
Many thread lockers are marketed specifically into automotive applications, and as such you’ll find that most retail packaging will mention engine, chassis, or drive-train type uses. When purchasing a thread locker for any other application, it’s therefore important to rely on technical specifications to gauge suitability, namely permanence (strength), material types, and temperature. It’s also worth noting that seemingly similar applications may have other factors that change which thread locker to select. For example, a vehicle engine-grade ‘medium strength’ thread locker to be used in a marine engine application might not be the ideal choice. Instead, it may be better to select the superior ‘high strength’ grade due to the additional demands added by seawater, significant hull vibration, and higher risks associated with any failure occurring while at sea.
E&T Fasteners is here to help you navigate fastener and accessory options. Price quotes, availability, lead times, delivery confirmations, unique application suggestions – whatever your need, we’re here to take your call or email. For support and advice from our fully trained staff, speak with an E&T sales representative today.
With sales and support teams spanning the Continental US, E&T Fasteners is here to serve your hardware, fastening, and component needs both domestically and internationally. We are a stocking distributor of metallic, plastic, and exotic alloy fasteners, backed by our technical staff directly experienced in your unique applications. We can assist your specifying and selection efforts, providing engineered solutions, record-fast lead times, and stellar customer service from quote through delivery