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What is Thread Lock? – A Comprehensive Guide to Threadlockers

In precision engineering, ensuring the stability and integrity of fastened components is paramount. Enter thread lock, commonly known as threadlocker or by brand name Loctite, a pivotal player in ensuring the stability of bolts, nuts, and screws against the relentless forces of vibration and dynamic loads. This adhesive, skillfully applied to threaded fasteners, is more than just a bonding agent; it's a guardian against loosening, leakage, and the ravages of corrosion.

This article delves deep into the world of thread-locking compounds, exploring their purpose, application methods, and the myriad of options available. We'll decode the colour coding system that demystifies its strength and usage, and explore alternatives when a threadlocker isn't the best fit.

Whether you're a seasoned engineer or new to the field, understanding the role and application of thread lock is essential in ensuring the durability and efficacy of your engineering projects.


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Understanding Thread Lock

At its core, thread lock is an adhesive specifically formulated for application on the threads of fasteners like bolts, nuts, and screws. Its primary role is to prevent these threaded components from loosening, which is a common challenge in machinery and structures subjected to vibration and dynamic loads.

The fundamental principle behind thread lock is its ability to fill the minuscule gaps between the threads of fasteners. When applied, it acts as a thermosetting plastic, which, upon curing, forms a toughened bond. This bond effectively locks the threads in place, resisting the tendency to loosen under the influence of rotational forces or vibration.

Thread lockers are not just about preventing loosening though; they also provide a level of protection against corrosion. By sealing the thread interface, they shield the metal from moisture and other corrosive elements, thereby extending the lifespan of the fasteners and the integrity of the assembly.

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Different Types Of Thread Lock

Thread lockers are not one-size-fits-all solutions. They come in various formulations, each meticulously designed to cater to specific applications and environmental conditions. From the robust high-strength threadlocker that forms an almost unbreakable bond to the low-strength threadlocker variant designed for easy adjustability and disassembly, each type serves a unique purpose in the engineering toolkit.

High Strength Threadlocker: For permanent applications, resisting heavy loads and vibrations. Not easily removable.

Low Strength Threadlocker: Ideal for small fasteners and applications where regular disassembly may be required.

High Temperature Threadlocker: Specially designed for applications exposed to extreme temperatures, maintaining their bonding strength under thermal stress.

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A History Of Thread Locking Fluid

Thread-locking fluid has a rich history that dates back over half a century, solidifying (no pun intended) its place as a cornerstone in the world of mechanical fastening.

Its inception can be traced to the mid-1950s when American engineer and professor Vernon K. Krieble developed this innovative adhesive. Krieble's breakthrough in creating a solution that could effectively secure threaded fasteners against vibrational loosening was a significant milestone in engineering. His invention not only solved a widespread challenge of components loosening in mechanical assemblies but also laid the foundation for the establishment of Loctite, a company that would become synonymous with thread-locking technology.

Following Krieble's pioneering work, the use and popularity of thread-locking fluids soared, leading to a diverse range of products offered by numerous companies such as AccuLock, Precote 80 and Anu-Lok 180 each contributing to the evolution and enhancement of this indispensable tool in specific niche precision engineering tasks.

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Thread Lock Colour Coding

When it comes to distinguishing between the types of compounds, there are different thread lock colours which visually identify their strength and usage from permanent thread lock to re-usable. While this isn't a one-rule fits-all, it does provide a quick colour coding system that helps give insight into what adhesive has been used, especially if it comes to removal.

A Selection of the Most Common Thread Lock Colours Showing Their Attributes.

Here's a concise overview of the most common thread locker colours:

Red/Pink Thread Locker

Strength: High
Use: For permanent applications; requires heat for removal.
Ideal For: Heavy-duty fastenings where disassembly isn't anticipated.
Goes By: Precote 80

Yellow Thread Locker

Strength: Medium
Use: Easily removable and adjustable using standard tools; ideal for parts that require modifying post installation .
Ideal For: Applications requiring a balance of secure fastening and the ability to remove as needed.
Goes By: Anu-Lok 180

Blue Thread Locker

Strength: Medium
Use: Removable with standard tools; good for parts that might need adjustment or removal.
Ideal For: General-purpose applications needing balance between hold and removability.
Goes By: AccuLock

Green Thread Locker

Strength: Low/Medium (Penetrating)
Use: Seeps into pre-assembled fasteners. Often confused with retaining compound which is also green.
Ideal For: Enhancing the hold on pre-tightened fasteners or small screws.

Purple Thread Locker

Strength: Low
Use: Easily removable, avoids damage to small or delicate parts.
Ideal For: Small screws in delicate applications.

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How Do You Apply Threadlocker?

Applying threadlocking adhesive is a straightforward process, but it requires precision to ensure effectiveness. Here’s a detailed guide on how to apply thread locker correctly to threaded fasteners such as screws and bolts:

Cleaning the Oil and Debris Off of the Threads of a Screw.

Step 1: Selecting the Right Thread Locker

Before application, choose the appropriate thread lock type based on the fastener size and required strength. Consider factors like the material of the fastener, the environmental conditions it will be exposed to, and whether disassembly is planned in the future.

Step 2: Preparing the Fastener

For optimal adhesion, the fastener should be clean and dry. Use a cleaner or degreaser to remove any oil, dirt, or old adhesive residues from the threads. If the fastener is new, a simple wipe may suffice. Ensure the threads are completely dry before proceeding.

Applying Thread Lock to a Cap Head Screw.

Step 3: Applying the Thread Locker

Apply the thread locker directly to the male thread. The amount needed varies with the size of the fastener - typically, a drop or two is sufficient for most sizes. For larger fasteners, a continuous bead along the first few threads is recommended. Ensure that the thread locker is applied evenly.
If you're ever unsure about the application, Accu provides fasteners with pre-applied thread lock to make the application stress-free.

Step 4: Assembling the Components

Immediately after applying the thread locker, assemble the components by threading the fastener into its mating part. Tighten to the recommended torque setting. This action distributes the thread locker evenly across the thread surfaces.

Installing a Cap Head Screw With Thread Lock Applied.

Step 5: Curing Time

Allow the assembled parts to cure. The initial curing speed (to achieve handling strength) usually takes a few minutes to an hour, depending on the thread locker type. However, achieving full strength can take up to 24 hours. Make sure to check this and avoid subjecting the assembly to high loads or vibrations during this period.

Allowing Time for Thread Lock To Set.

Tips From Our Engineers

  • If any excess thread locker has spilt or smeared outside the assembly, wipe it off with a clean cloth.
  • Avoid using strong solvents on the fastened joint as they might affect the curing process leading to impacted reliability.
  • Do not apply thread locker to plastic fasteners unless the product is specifically formulated for plastic.
  • For fasteners that are frequently adjusted or will require disassembly with hand tools, consider a medium or low-strength threadlocker.
  • When dealing with high-temperature applications, ensure what you use is a heat-resistant thread lock and that its operational temperature is rated for such environments.

Patrick Faulkner

Lead Engineer

By following these steps, you can ensure a secure and reliable bond that will prevent the loosening of fasteners, thereby enhancing the safety and longevity of your mechanical assemblies. Alternatively, you can shop for screws with thread lock pre-applied with Accu.

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Alternatives to Thread Lock

While thread lockers are a popular choice for securing fasteners, there are alternative methods that can be equally effective in certain applications. Following on from our "Why Bolts Become Loose" article, these alternatives include locking nuts, anti-vibrational washers, and split pins, each serving a unique purpose in fastener technology. Let's explore how these alternatives compare to thread lockers:

Locking Nuts

  • How They Work: Locking nuts come with a built-in feature (like a nylon insert) that resists loosening under vibration and torque.

  • Advantages: They provide a reliable locking action without the need for additional chemicals. They're reusable and can be tightened and removed with standard tools.

  • Ideal For: Applications where regular maintenance or adjustments are required.

Anti-Vibrational Washers

  • How They Work: These washers, often made of spring steel, maintain a load and provide a locking action under vibration. They absorb and dampen the effects of vibration and shock.

  • Advantages: They're simple to install, remove and can be reused multiple times. They offer a mechanical means to maintain tension and resist loosening.

  • Ideal For: Situations where a physical barrier to vibration is needed, such as in heavy machinery.

Split Pins

  • How They Work: Split pins, are inserted through a hole in a bolt or shaft. Once inserted, the two ends of the pin are bent apart, preventing the nut from turning.

  • Advantages: They provide a simple and reliable method to prevent the nut from loosening. They're easy to inspect and indicate clear visual evidence of their presence and integrity.

  • Ideal For: Applications where safety is paramount, such as in automotive or heavy equipment.

Each of these alternatives to thread lock has its specific applications and advantages. The choice between using a thread locker or one of these alternatives depends on the requirements of the application, such as the need for removability, exposure to environmental conditions, and the type of load the fastener will bear. It's essential to consider these factors to select the most appropriate fastening method for each unique situation.

Images Showing Locking Nuts, Anti-Vibrational Washers and Split Pins.

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You're Now A Thread Locking Fluid Expert!

So, there we have it, you've learnt that thread lock is a crucial component in precision engineering, offering a reliable solution to secure threaded fasteners. Understanding its types, applications, and alternatives ensures the longevity and reliability of mechanical assemblies, crucial in maintaining high-performance systems.

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Q: What is the purpose of threadlocker?

A: Threadlocker is designed to prevent the loosening of threaded fasteners due to vibration or dynamic loads. It also provides additional corrosion resistance by providing a barrier to the surface of the coated threads.

Q: Does threadlocker need to cure?

A: Yes, threadlocker requires a curing period to fully set and achieve its maximum strength. This period varies depending on the product. Usually less than 24 hours but double check the curing speed before installation.

Q: Do you really need threadlocker?

A: Threadlocker is essential in applications where fasteners are exposed to vibration or dynamic forces. It ensures they are maintained in a fastened state offering stability and longevity.

Q: Can you unscrew thread lock?

A: Yes, low and medium strength threadlocker can be unscrewed with standard tools. High-strength varieties may require heat application north of 150°C for removal.

Q: What dissolves Loctite (a brand of threadlocker)?

A: Certain solvents such as brake cleaner and IPA can dissolve Loctite, but heat is often more effective for unscrewing high-strength thread lockers.

Q: Is thread lock like super glue?

A: No, thread lock is specifically designed for threaded fasteners and has different properties compared to super glue which is a general-purpose adhesive that hasn't undergone specific environmental testing for temperature, vibration and torque.

Q: Is thread lock permanent?

A: High-strength thread lock is considered permanent, while medium and low-strength varieties can be removed more easily.

Q: How long does threadlock last?

A: When applied correctly, threadlock can last several years, maintaining its effectiveness throughout its lifespan.

Q: Does threadlocker expire?

A: Threadlocker does have a shelf life, often a few years from the date of manufacture, after which its effectiveness may diminish.

Q: Can you use super glue as thread lock?

A: No, super glue is not suitable as a thread lock substitute. It lacks the specific properties required for securely fastening threaded components under load and vibration.

Q: What's the difference between red and blue thread lock?

A: Red thread lock is high-strength, used for permanent fastening, requiring heat for removal. Blue thread lock is medium-strength, suitable for applications where disassembly is possible with hand tools.

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