Expert Advice about Anaerobic Adhesives

Henkel Australia’s Technical Engineers work in partnership with customers in a wide range of diverse markets. On a daily basis, the support team is questioned about the workings of Loctite anaerobic adhesives. There is a lot of interest in anaerobic adhesives clearly – but also a lot of confusion. Henkel’s Technical team have collected the most frequently asked questions about Loctite anaerobic technology and provided answers.

Henkel Australia’s Technical Engineers work in partnership with customers in a wide range of diverse markets. On a daily basis, the support team is questioned about the workings of Loctite anaerobic adhesives. There is a lot of interest in anaerobic adhesives clearly — but also a lot of confusion. Henkel’s Technical team have collected the most frequently asked questions about Loctite anaerobic technology and provided answers.

What are the different Threadlockers and their colors?

There are different grades of Threadlockers to refer to different strengths. In the case of Loctite for example, the purple threadlocker is low strength, the blue threadlocker is medium and the red threadlocker is high strength; the green threadlocker is a special wicking grade product that allows faster and deeper penetration through the assembled parts. The different colors refer to different strengths of the threadlocker.

What is the difference between a threadlocker and a thread sealant?

Threadlockers and thread sealants are each developed and formulated for specific purposes and applications. An anaerobic threadlocker locks and seals the threaded parts and shows higher locking and bonding strength.

On the other hand, an anaerobic thread sealant seals threaded parts tighter to withstand very high pressure of fluids but may have lower bonding and locking strength. It is very important that you always compare the different product specifications in detail in order to select the right product for your application. Thread sealants can withstand very high pressure from fluids.

How do I select the right Threadlocker to use?

Loctite offers a wide range of threadlockers with color-coded packaging to help users understand the different threadlocker grades for different applications. You should always refer to the technical data sheet for details on each product and match it carefully with your requirements. To get you started on some of the pertinent issues to consider, you can use the following quick guide to narrow down your choice for:

· What materials are used?

My earlier article with advise on anaerobic adhesives gives a list of active and inactive materials. These materials impact your choice of threadlocker and whether to use an activator/primer or not.

· Do you need the parts to be easy to disassemble later for servicing?

If so a low strength or medium strength threadlocker is the appropriate product since standard hand tools can be used for disassembly. If not, a higher strength threadlocker is suggested, but the assembly may still be loosened with heat and hand tools.

· What is the thermal resistance requirement for the assembly?

If the heat resistance required is in excess of 150oC, you may need to use high-temperature threadlockers. Loctite® 272 can be used up to 232 ?, If you want even higher temperature resistance, then the ultra high temperature products, such as Loctite ®2422 (medium strength) and Loctite ®2620 (high strength) should be used.

· Bolts and nuts of different sizes also require different threadlockers. The technical data sheets contain a guideline for which bolt sizes the threadlocker is suitable. In general, for small bolt/nut assemblies, a low or medium strength threadlocker is recommended over a high strength product to avoid the small bolts breaking during the process of disassembly.

Are there any conditions where anaerobic adhesives should not be used?

Anaerobic products are not recommended for use in assembly that includes thermoplastics, as it will soften their surface and cause a crack. Examples are ABS, Acrylic, PVC, etc.

What happens to the threadlocker material when I heat the part with a torch to disassemble it?

Threadlockers are thermoset polymers which means they will not melt like typical thermoplastic materials such as PET, polystyrene, hot-melts, and polyethylene-bags. The first thing to happen when you heat a part assembled with an anaerobic threadlocker is that the thermoset plastic actually gets harder and more dense because the heat drives more cross linking. As the temperature continues to rise, the plastic eventually becomes brittle and upon continued heating, the cured material will begin to degrade and char. This weakens the bonds and allows for disassembly.

Is it necessary to clean the surfaces before applying a liquid threadlocker?

It depends. Some threadlockers are formulated so they can be used on surfaces that are slightly oily or greasy, whereas others require a very clean surface. This is yet another factor to consider when selecting the right anaerobic threadlocker.

I cannot disassemble a part in which a threadlocker was used. What solvent will break the threadlocker down?

No solvent will wick into the joint to break the threadlocker down. You can only disassemble the parts by using hand tools, either at room temperature or after heating the assembly to high temperatures of around 250º. You are dealing with the thermoset plastics in the cured state and at high temperature they become brittle, allowing for easier separation of the parts. Solvents like methyl ethyl ketone and methylene chloride can be used to remove residual threadlocker only after disassembly.

Can I use a threadlocker for non-threaded assemblies like locking bearings or bushings in housings or on shafts?

Yes you can. Loctite has developed specific retaining compounds, but threadlockers have the same base chemistry and could be substituted in many cases. Inversely, you could use retaining compounds to lock threads as long as you’re cognizant of the fact that most will permanently lock threads.

Is there an electrically conductive threadlocker?

There are a handful of silver-filled electrically conductive epoxies but these are formulated to replace solder connections on a printed circuit board. These products are so dense that they probably wouldn’t fit between threads effectively.

What is the proper way to apply threadlockers for both thru and blind-hole application?

For thru-hole application, such as a nut and bolt combination, the threadlocker is applied just to the bolt, coating 3 or 4 threads, going all the way around the diameter, and then assemble. For blind-hole application, apply several drops of the product down the internal threads to the bottom of the hole.

Are threadlockers fungus resistant?

In general threadlockers will support fungus growth that is already present but will not promote growth otherwise. Many threadlockers conform to military specifications and these specifications (Mil-S-22473E, MIL-S-46163) specify that the polymerized compound will not support the growth of fungus when tested to the requirements of the military specification.

How do we define breakaway and prevailing torque?

When we apply a threadlocker to a bolt and finger tighten a nut to it, we let the assembly sit for 24 hours and allow it to cure fully. We then take a torque wrench and break the bond. The initial reading on the unseated assembly is the breakaway value (remember, this is not torqued to a specified value such as 11N.m (100 in lbs). This shows us the strength of the threadlocker alone. We then continue turning the torque wrench and the average torque used on the next four quarter-turns provides us with the prevailing torque value. This shows us how much friction or drag remains and needs to be overcome to continue turning the nut.

On the other hand, if, for example, we torque an assembly down to 11N.m (100 in lbs), and we use a threadlocker with a breakaway torque of 6N.m (50 in lbs), the breakloose value initially on this seated assembly is 17N.m (150 in lbs). The difference between what your torque this down to 11N.m(100 lbs) and what you breakloose at, 17N.m (150 in lbs) is 6N.m (50 in lbs) and this is referred to as torque augmentation.

The main function of any threadlocker is to maintain your torque. It has been determined that over time due to various factors such as vibration and side sliding, you may lose up to 30% of your torque. The goal is to choose a threadlocker that provides a breakaway value equivalent to 30% of your applied torque to compensate for this loss and to maintain your torque over time.

How do I determine how much volume of threadlocker I need to apply?

Normally the technical data sheets will help with that. In the case of Loctite®, we have developed a calculator to help you with this. You can find the threadlocker calculator on www.iLoctite.com.

What is the meaning of PST?

PST means “Pipe Sealant with PTFE”. Many thread sealants provide a lubrication effect for easier assembly when pipes and fittings are tightened.

Some thread sealants are liquid while others are a thick paste. Do the liquid sealants provide good sealing?

Yes. A more liquid thread sealant is used for hydraulic and pneumatic piping systems that normally have filters inside. These liquid sealants contain no fillers or particles and therefore there is no need to be concerned about clogging the filtering system or contaminating system fluids with the filler particles. Hydraulic and pneumatic threads are very fine and have a tight fit. Liquid sealants provide an excellent sealing in this case.

Can I use anaerobic thread sealant instead of an o-ring?

Yes, of course. Anaerobic thread sealants have big advantages over an o-ring on sealing as well as cost.

What is the advantage of using thread sealant over PTFE-tape?

Firstly, when assembled pipes, elbows, and tees are adjusted for the correct orientation, the PTFE-tape can cause leakage as it doesn’t effectively adjust to fill the newly generated gap. Secondly, in hydraulic and pneumatic pipe systems, shreds of PTFE-tape from the assembly process can migrate into the system and clog filters. When you use an anaerobic thread sealant, you can easily adjust the orientation of any parts as the sealant cures slow enough to do that. In addition hydraulic and pneumatic type thread sealant will not clog or foul the internal system.