Anaerobic adhesives—sometimes mistakenly called "anabolic" adhesives—are specialised bonding agents designed specifically for metal-to-metal assemblies. Unlike conventional glues, they remain liquid when exposed to air but cure into a solid, durable bond when oxygen is excluded and metal ions are present. Understanding how to select the right anaerobic adhesive for your application is essential for creating reliable, long-lasting assemblies.
Identify Your Application Type
The first step in choosing an anaerobic adhesive is determining what function your assembly must perform. Different applications demand different formulations:
- Threadlocking: Secures nuts, bolts, and screws to prevent loosening caused by vibration or mechanical stress.
- Thread Sealing: Creates leak-proof seals in threaded pipe connections carrying gases or liquids.
- Retaining: Fixes cylindrical parts—such as bearings or shafts—into housings to increase load-bearing capacity and prevent slippage.
- Gasketing: Replaces traditional gaskets in flange assemblies to provide pressure-resistant seals without the need for separate gasket materials.
Select the Correct Strength Grade
Anaerobic adhesives are colour-coded and categorised by their removal difficulty, which directly reflects their bond strength. Choosing the right grade ensures your assembly performs as intended without being over-bonded or under-bonded:
- Low Strength (Purple): Suitable for small screws or components that require frequent adjustment or easy removal with hand tools.
- Medium Strength (Blue): The most versatile and commonly used grade; ideal for standard machine parts that may need disassembly using conventional tools.
- High Strength (Red/Green): Designed for permanent assemblies where removal requires heavy-duty tools and elevated heat.
Account for Substrate Reactivity
The type of metal you're bonding significantly affects cure speed and bond reliability. Anaerobic adhesives depend on metal ions to initiate the curing process, so different metals react at different rates:
- Active Metals: Iron, copper, brass, and steel provide abundant metal ions, resulting in fast curing times and reliable bonds without additional treatment.
- Passive Metals: Stainless steel, aluminium, and zinc have fewer free ions and may require an activator or primer to accelerate the bonding process and ensure consistent results.
Match Viscosity to Gap Size
Anaerobic adhesives work best on close-fitting parts. The viscosity you select should match the gap between your surfaces:
- Low Viscosity (Thin): Best for small gaps or for "wicking" into already-assembled parts where the adhesive must flow into tight spaces.
- High Viscosity (Thick): Better suited for larger gaps or vertical surfaces where you need the adhesive to remain in place without sagging or dripping.
Consider Environmental Demands
Your assembly's operating environment plays a critical role in adhesive selection. Standard anaerobic formulations typically withstand moderate temperatures, but specialised grades are available for more demanding conditions. Most anaerobic bonds offer excellent resistance to oils, fuels, and industrial solvents once fully cured, making them ideal for harsh industrial environments.
By working through these five selection criteria, you'll choose an anaerobic adhesive that delivers the strength, reliability, and durability your assembly requires.