What Is Anaerobic Sealer? The Ultimate Guide to Industrial Locking and Sealing
In the world of mechanical engineering, automotive repair, and industrial manufacturing, the integrity of a joint is paramount. Whether it is a bolt holding an engine block together or a pipe carrying high-pressure hydraulic fluid, the failure of a fastener or a seal can lead to catastrophic results. This is where anaerobic sealers come into play. But what exactly is an anaerobic sealer, and why has it become a cornerstone of modern assembly processes?
Anaerobic sealers and adhesives are a specialized class of chemicals that remain liquid until they are isolated from oxygen in the presence of metal ions. This unique “anaerobic” property—meaning “without air”—allows them to stay stable in their packaging while curing into a tough, thermoset plastic once applied between two metal surfaces. In this comprehensive guide, we will explore the science, applications, and benefits of anaerobic sealers to help you understand how they can optimize your assembly and maintenance workflows.
The Science Behind Anaerobic Technology
To understand what an anaerobic sealer is, one must first look at its chemistry. Most anaerobic products are based on acrylic monomers, specifically dimethacrylate esters. These liquids are formulated with stabilizers that prevent them from hardening as long as they are in contact with oxygen. This is why anaerobic bottles are typically only half-filled; the air gap in the bottle is essential for keeping the product in a liquid state.
The Curing Process: Two Essential Conditions
For an anaerobic sealer to transform from a liquid to a solid, two conditions must be met simultaneously:
- Exclusion of Oxygen: When a bolt is threaded into a nut or a flange is clamped down, the air is squeezed out. This lack of oxygen triggers the polymerization process.
- Presence of Metal Ions: Metals like iron, steel, copper, and brass act as catalysts. They provide the free radicals necessary to start the chemical reaction.
Because of this dual requirement, anaerobic sealers will not cure on plastic, glass, or rubber without the help of a chemical activator. They are specifically designed for metal-to-metal interfaces where tight tolerances exist.
The Four Main Categories of Anaerobic Sealers
Anaerobic technology isn’t just a single product; it is a family of solutions tailored for specific mechanical challenges. These are generally categorized into four main groups:
1. Threadlockers
Threadlockers are perhaps the most well-known type of anaerobic sealer. They are applied to the threads of fasteners (bolts, screws, and studs) to prevent loosening caused by vibration, shock, or thermal expansion. Unlike traditional mechanical locking devices like spring washers or nylon-insert nuts, threadlockers fill the microscopic voids between the threads, creating a 100% contact area that unitizes the assembly.
2. Thread Sealants
While threadlockers focus on preventing loosening, thread sealants focus on preventing leaks. These are used on tapered or straight pipe threads to seal against liquids and gases. They replace traditional methods like PTFE tape (Teflon tape) or pipe dope. Anaerobic thread sealants offer superior resistance to chemicals and high pressures, and they do not shred or block sensitive valves like tape can.
3. Retaining Compounds
Retaining compounds are used to secure non-threaded cylindrical parts, such as bearings, bushings, gears, and pulleys, onto shafts or into housings. They allow for “slip-fit” assemblies rather than “press-fit” or “shrink-fit” assemblies. By filling the gaps between the parts, they increase the load-bearing capacity and prevent fretting corrosion.
4. Anaerobic Gasket Makers
Also known as Form-in-Place Gaskets (FIPG), these sealers are used between flat metal flanges. They eliminate the need for traditional pre-cut gaskets. Because they do not shrink or relax over time, they maintain a constant clamping force and provide a leak-proof seal that is highly resistant to temperature and pressure.
Key Benefits of Using Anaerobic Sealers
Integrating anaerobic sealers into your manufacturing or repair process offers several distinct advantages over mechanical alternatives or other adhesive types.
Vibration Resistance
Mechanical fasteners are prone to “transverse sliding,” where vibration causes the threads to move slightly, eventually leading to a loss of tension. Anaerobic threadlockers physically “glue” the threads together, making the assembly immune to vibration-induced loosening.
Corrosion Prevention
When two metal surfaces are in contact, moisture and chemicals can seep into the gaps, leading to rust and galvanic corrosion. Because anaerobic sealers fill 100% of the internal space, they create an airtight seal that protects the metal from the environment, ensuring that parts can be disassembled easily years later.
Improved Structural Integrity
By filling the microscopic peaks and valleys of metal surfaces, anaerobic adhesives distribute the load more evenly across the entire joint. This reduces stress concentrations and can allow engineers to use lighter or smaller components without sacrificing strength.
Cost Efficiency
While the initial cost of a bottle of sealer might seem higher than a box of washers, the long-term savings are significant. Anaerobic sealers reduce the need for specialized inventory (like multiple sizes of gaskets), prevent costly leaks, and extend the service life of machinery by preventing premature failure.
Factors to Consider When Choosing an Anaerobic Sealer
Not all anaerobic sealers are created equal. To select the right product for your application, you must consider several technical factors.
Strength and Torque
Anaerobic products are usually color-coded by strength:
- Low Strength (Purple): Used for small screws and parts that require frequent adjustment or disassembly with hand tools.
- Medium Strength (Blue): The most common grade. It secures fasteners firmly but allows for disassembly using standard hand tools.
- High Strength (Red): Designed for permanent assemblies. Disassembly usually requires localized heating (to approximately 450°F / 230°C) to soften the plastic.
- Wicking Grade (Green): A low-viscosity liquid that can be applied to pre-assembled fasteners by “wicking” into the threads.
Gap Filling Capability
Anaerobic sealers are designed for tight-fitting parts. Most threadlockers can fill gaps up to 0.005 inches, while specialized retaining compounds can fill gaps up to 0.015 inches or more. If your tolerances are larger than this, the sealer may not cure properly because it will remain in contact with too much oxygen.
Temperature Resistance
Standard anaerobic sealers are typically rated for environments up to 300°F (150°C). However, high-temperature formulations are available that can withstand temperatures up to 450°F (230°C) or higher. Always check the technical data sheet for the specific thermal limits of the product.
Substrate Material
As mentioned earlier, the cure speed depends on the metal. “Active” metals like copper and brass result in the fastest cure. “Passive” metals like stainless steel, aluminum, or plated surfaces (zinc, chrome) result in a slower cure. In cases involving passive metals or cold temperatures, an anaerobic primer or activator may be required to speed up the reaction.
Application Best Practices
To achieve the best results with an anaerobic sealer, proper application is critical. Following these steps ensures a reliable and long-lasting bond.
1. Surface Preparation
The most common cause of failure is surface contamination. Oil, grease, and dirt can prevent the sealer from making contact with the metal ions. Clean the parts thoroughly using a solvent-based degreaser. For critical applications, ensure the parts are dry and free of any residual cleaning agents.
2. Proper Dispensing
When applying a threadlocker, apply a few drops to the leading threads of the bolt. For a blind hole (a hole that does not go all the way through), apply the sealer to the bottom of the hole as well. This prevents air pressure from pushing the liquid out as the bolt is inserted. For gasketing, apply a continuous bead to one flange surface, ensuring you encircle all bolt holes.
3. Assembly and Curing
Assemble the parts immediately after application. Once the parts are tightened, avoid moving them. Most anaerobic sealers reach “fixture strength” (where the parts can be handled) in 10 to 30 minutes, but full cure typically takes 24 hours. If you need to put the equipment back into service sooner, [Contact Our Team](https://www.incurelab.com/contact) to discuss fast-curing options or primers.
Common Myths and Misconceptions
Despite their widespread use, there are still several misconceptions regarding anaerobic sealers.
Myth: More Is Always Better
Using excessive amounts of sealer does not improve the bond. In fact, excess liquid that stays outside the joint will never cure because it remains exposed to air. This “squeeze-out” can migrate into sensitive areas of a machine. Only use enough to fill the engaged area of the joint.
Myth: They Can Be Used on Plastic Pipes
Anaerobic sealers are formulated for metal. Many plastics can be stressed or even dissolved by the chemicals in anaerobic adhesives (a process known as stress cracking). For plastic fittings, use specialized non-anaerobic sealants designed for polymers.
Myth: They Are Impossible to Remove
Even “permanent” red threadlockers can be removed. By applying localized heat with a blowtorch or heat gun, the thermoset plastic is broken down into a powdery state, allowing the fastener to be unscrewed. Medium and low-strength versions require no heat at all.
Comparing Anaerobic Sealers to Other Technologies
How do anaerobic sealers stack up against other common industrial adhesives? Let’s compare them to RTV Silicones and Cyanoacrylates (Super Glues).
Anaerobic vs. RTV Silicone
RTV (Room Temperature Vulcanizing) silicones cure by reacting with moisture in the air. They are excellent for large gaps and flexible joints. However, unlike anaerobic sealers, they are not suitable for tight-fitting metal threads or cylindrical assemblies because they require air/moisture to cure, which is absent in a tight metal joint. Furthermore, silicones can squeeze out and clog internal passages, whereas uncured anaerobic liquid can simply be wiped away or flushed through a system.
Anaerobic vs. Cyanoacrylates
Cyanoacrylates cure almost instantly when they contact moisture on a surface. They are great for bonding rubber and some plastics but lack the vibration resistance and high-temperature stability of anaerobic sealers. Cyanoacrylates are also brittle, whereas anaerobic sealers are designed to handle the mechanical stresses of industrial machinery.
Industrial Applications of Anaerobic Sealers
The versatility of anaerobic sealers means they are found in almost every sector of industry.
Automotive and Transportation
From engine assembly to chassis bolts, anaerobic threadlockers ensure that the constant vibration of the road doesn’t vibrate a vehicle apart. They are also used in transmissions and differentials to seal flanges against gear oil.
Aerospace
In aerospace, weight reduction is key. Anaerobic retaining compounds allow for lighter press-fits and help secure critical components in flight control systems where failure is not an option.
Heavy Machinery and Mining
Large-scale equipment used in mining and construction is subject to extreme forces. High-strength anaerobic sealers prevent the loosening of massive bolts on crushers, excavators, and conveyor systems.
Power Generation
In turbines and pumps, anaerobic thread sealants prevent the leakage of steam, cooling water, and lubricants, ensuring the efficiency and safety of power plants.
Conclusion: The Essential Tool for Modern Engineering
So, what is an anaerobic sealer? It is a sophisticated chemical solution to the age-old problem of mechanical failure. By understanding how these products work—curing only in the absence of air and the presence of metal—engineers and technicians can create assemblies that are stronger, more reliable, and more resistant to the rigors of industrial use.
Whether you are looking to prevent a small screw from backing out of an electronic device or ensuring that a high-pressure pipeline remains leak-free, anaerobic technology provides the performance you need. By selecting the correct strength, viscosity, and temperature rating, you can significantly improve the quality and longevity of your work.
If you are unsure which anaerobic sealer is right for your specific industrial application, it is always best to consult with experts who understand the nuances of adhesive chemistry and mechanical requirements. Choosing the right product today can prevent a costly failure tomorrow.
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