Selecting and correctly using threadlockers | SILITECH

Threadlockers are essential for ensuring the reliability and safety of your bolted connections. Whether in technical equipment, furniture, vehicles, or industrial plants – they ensure that your connections remain tight and secure even under vibration, dynamic loads, or other influences. This article explains how to select and apply the right threadlockers to optimally protect your applications.

What are screw locks?

Threadlockers are specialized products that prevent bolted connections from loosening unintentionally. They increase the safety and durability of connections exposed to vibrations or other stresses. There are various types:

• Settling protection: Compensates for the settling behavior of the material and maintains the preload force (e.g. clamping washers, disc springs).
• Anti-loosening device: Prevents mechanical loosening through additional components such as lock nuts.
• Chemically bonded connections: Liquid threadlockers (e.g. Loctite, Permabond) form a chemical bond in the thread that withstands vibrations and seals at the same time.

Why do bolted connections fail?

Bolted connections can fail for various reasons:

• Dynamic loads: Vibrations or transverse loads loosen the connection.
• Static loads: Overloading or uneven forces.
• Relative motions: Movements between connected parts.
• Setting of the connection: Material fatigue or yielding under pressure.
• Insufficient clamping length: Screws are too short or the thread engagement is too shallow.

A real-world example: An ICE train lost a door while traveling at full speed because a locking nut in the door mechanism came loose, resulting in injuries to passengers. This demonstrates the importance of reliable screw locking devices.

How anaerobic adhesives work

Anaerobic adhesives are a special type of threadlocker used to secure and seal screws, bearings, or flanges. They only cure in the absence of air and upon contact with metal. Here's how it works:

• The adhesive is applied to the thread.
• When screwed together, it is sealed airtight between the metal surfaces.
• Metals such as iron or copper trigger a chemical reaction that causes the adhesive to harden – often within minutes to hours.

Important: The more metal ions the material provides (e.g., steel, copper), the faster the hardening process. For passive metals like stainless steel or aluminum, an activator can be helpful.

Advantages of screw locking devices

Threadlockers, especially anaerobic adhesives, offer numerous advantages:

• Single-component: No mixing required.
• Solvent-free: Environmentally friendly and safe.
• Easy handling: Easy to use.
• Disassembly possible: Depending on strength.
• Precise dosage: Precise application.
• Fabric bond in the thread: Vibration-resistant and durable.
• Corrosion protection: Protects the thread from rust.
• Safety and sealing in one: Saves time and material.
• Chemical and heat resistance: Stable from -55 to 150/180 °C.

These advantages help you save time and money and extend the lifespan of your products.

Tips for choosing the right product

When selecting the appropriate screw locking agent, you should consider the following points:

1. Application requirements

• Release: Does the fastening need to be removed frequently, occasionally, or never?
• Load: Is the screw subjected to high loads?
• Temperature: What are the minimum and maximum temperatures?
• Chemical exposure: Are there any influences such as oil or acid?
• Size: What thread size and spacing?
• Material: What material are the screws and components made of?

2. Determine strength

Screw locking devices are classified into three strength levels:

strength	Distance frequency	Distance difficulty	Vibration protection
Low	Regularly	Simply	none
Medium	Occasionally	Simply	Low to medium
High	Never	Difficult	Much

Loctite products indicate their strength by color: pink (low), blue (medium), red (high). Permabond products are marked with letters such as H (High), M (Medium), L (Low).

3. Check material compatibility

Ensure that the threadlocker is compatible with the materials of your fastener:

• Active metals (e.g., iron, steel, copper, brass): Promote hardening.
• Passive metals (e.g., stainless steel, aluminum, galvanized surfaces): Slow down the curing process – an activator or a special product (e.g., Loctite 270 or Permabond HM163) may be necessary.

4. Viscosity and flow behavior

• Low-viscosity (thin) products: Ideal for small screws or fine threads, also for subsequent securing.
• High-viscosity (thick) products: Better for larger screws or vertical applications, as they do not run.

The correct viscosity ensures optimal distribution in the thread.

5. Approvals and Standards

For certain applications, certifications such as NSF/WRAS (drinking water), DVGW (gas and water), or KBA (automotive) are required. Our products meet the necessary standards for your safety-critical applications.

Tips for use

Correct application is crucial for the effectiveness of the threadlocker. Here are some tips:

• Surface preparation: Ensure the threads are clean and free of dirt, grease, or contaminants. If necessary, use a cleaning agent such as Permabond CleanerA.
• Amount to use: Apply a small amount to the threads – usually one drop is sufficient. Avoid over-application.
• Application: Apply the adhesive to the male threads before inserting the female thread. For blind holes or cap nuts, apply it directly into the hole or nut.
• Tightening the fastener: Tighten the screw to the recommended torque specification. Avoid overtightening.
• Curing time: Allow sufficient time for the adhesive to cure before subjecting the assembly to stress. Refer to the information in the technical data sheet.
• Storage and handling: Store the products in their original containers at room temperature and keep them tightly closed.
• Safety instructions: Wear gloves and work in a well-ventilated area. Refer to the safety data sheet.

Conclusion