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How do I achieve desired threadlocker and pipesealant strength?

There are two main things to consider when troubleshooting a threaded adhesive application that isn’t performing to specs.

  1. Correct Adhesive Selection
  2. Proper Adhesive Application


First, check the manufacturer’s technical data sheet and compare the relevant properties to the specifications from your engineering or design group. Threadlocker formulations come in a wide range of strengths and viscosities for specific compatibility with straight, tapered, fine or coarse thread patterns in pipe, pipe fittings and fasteners like bolts and screws.

Choose appropriate sealant strength

Threadlockers come in a variety of strengths to serve applications that require a permanent lock, or to lock fasteners in place but still allow for disassembly.   If the listed strength does not match up with your experience with the product the following may help uncover the cause.

  1. Not strong enough: Insufficient sealant coverage will provide lower strength. Anaerobic threadlockers prevent loosening due to vibration by filling all the voids between the threads. For optimum results, make sure that the threads are covered.
  2. Not strong enough: High temperatures that go beyond the adhesive rating can interfere with the cured properties. Some manufacturers report values as Fahrenheit, other as Celsius. Check for conversion errors and confirm design specs with adhesive selection. Specialty, high temperature anaerobic threadlockers resist 230 °C but conventional threadlockers resist up to 150 °C.
  3. Too strong: If the strength is higher than expected, consider the diameter and engagement length of components.  Doubling the diameter will increase the strength six-fold!  For example if the torque required to break away an M4 fastener is 2Nm (17.5 in.lb), it will be 12Nm (106 in.lb) on M8 and 72Nm (630 in.lb) on M16.  Use this calculation to select a more appropriate strength threadlocker for your application.

Choose Adhesive for compatibility with substrates

Slow or passive substrates: Anaerobic adhesives & sealants cure in the presence of metal and absence of oxygen.  Some metals cause anaerobic adhesives to cure faster than others.

Very Fast Fast Slow Passive (Activator Required)
Brass
Copper
Magnesium
Steel
Nickel
Iron
Aluminum
Anodized aluminum
Cadmium finishes
Chrome finishes
Passivated metals
Stainless steel
Titanium
Zinc
Ceramics
Glass
Plastics
Painted finishes
Lacquered finishes

Using anaerobic sealants on plastics or other non metal surfaces is generally not recommended, however, an anaerobic activator will cause the product to cure.  Activators also speed the cure on slower substrates, but may reduce the strength of the cured threadlocker.

When you are satisfied with the adhesive choice, then review the application process to see if any of the following conditions exist and can be corrected.

Insufficient sealant applied to bond area

Threadlockers fill the natural voids between threads. The adhesive cures to lock the fastener and component into a single unit and prevent loosening due to vibration.  Any air pockets trapped in the bond area will interfere with the ability to achieve desired results. Some common applications and general guidelines follow:

  1. Parallel to Parallel pipe joints
    1. Apply a bead of sealant to the leading edge of the male part sufficient so that when the pipe is seated a small bead of ‘squeeze out’ is visible around the circumference of the assembled joint.
    2. Do not apply the sealant to the internal threads of the female pipe fitting to insure full coverage and to avoid pushing adhesive into the pipe as the joint is tightened to specs.
  2. Taper to Parallel pipe joints and Taper to Taper pipe joints
    1. Count back several threads from the leading edge and apply the sealant to the male pipe at the point where you expect the threads to engage.  The bead of ‘squeeze out’ around the circumference of the assembled fitting is your evidence of correct adhesive application.
  3. Fasteners
    1. Open hole: Apply the sealant to the threads of the fastener where it will engage with component.  Check for visible squeeze out around the circumference of the fastener assembly.
    2. Blind hole: Apply the sealant inside and at the bottom of the hole, taking care to fill the void before inserting the fastener. Air pockets at the bottom will be forced upwards as the fastener is tightened, and can create air pockets along the length of engagement and prevent a cure to full strength.

This covers some common scenarios encountered when bonding adhesives. Contact the manufacturer if you continue to experience difficulty achieving desired results.