Secrets Of Anaerobic Adhesives

By Jim Hayes | Nov 15, 2014




I suspect that the idea of employing anaerobic adhesives for fiber optics came from someone using Krazy Glue or the two-part adhesive made to fix a car’s rearview mirror after it fell off in the hot summer sun. Strange, that experience should have made them more cautious about its reliability, but I guess it didn’t.

After what was probably a lot of experimentation with a number of these fast-curing acrylic adhesives, several connector manufacturers introduced it as a quick-setting alternative to heat-cured epoxy. And quick they were!

The first anaerobic adhesives were sold as a two-part adhesive just like those rearview mirror versions. There was an adhesive that was injected into the connector with a syringe just like an epoxy and an accelerator solution to make the adhesive set almost immediately. The instructions were to dip the fiber into the accelerator solution then quickly insert it into the connector.

The first problem most installers faced was getting the fiber into the connector before the adhesive set. The adhesive would set in less than 30 seconds, often faster than installers could get the fiber inserted fully into the connector. The result was a ruined connector that had to be discarded.

Instructing students how to use anaerobic adhesive connectors was a frustrating experience for everyone. Many students would ruin connectors when trying to insert the fiber because the adhesive set before the job was complete. About half of the rest broke the fiber when trying to cleave it for polishing because the anaerobic adhesive does not leave a hard bead of epoxy on the end of the ferrule to physically support the fiber during cleaving and polishing.

Several options were used to make it easier to insert the fiber. One method was to not dip the fiber in the accelerator solution but to fully insert the clean, dry fiber and then apply the accelerator to the fiber sticking out the end of the ferrule. The accelerator could be applied either with a brush or a spray. Then you had to quickly pull the fiber back into the connector about ⅛ inch, rotate it and push the fiber back into the connector. That made the adhesive set quickly at the end, so the connector could be polished almost immediately, and the rest of the adhesive would set more slowly. Brushing the accelerator solution onto the fiber was less messy than spraying because you did not have to clean the overspray off the ferrule.

Another problem with the anaerobic adhesive was the large cost of a tiny bottle. I decided to investigate its origin and find a lower cost alternative. (Actually, the investigation involved carefully peeling the label off a couple of bottles to read the original Loctite label underneath.) Loctite 648 was the adhesive we had been using and you could buy a bottle at an industrial distributor for a fraction of the cost of the private-label versions sold for fiber optics. The accelerator was Loctite 7471 or 7649. Make a note of that.

Looking into this adhesive’s characteristics, I found it was not intended for fiber optics, but the manufacturer confirmed it bonded glass and ceramics well. With a little more research into this adhesive, I found out it would set in about 5 minutes without the accelerator with a much higher bond strength.

Some experimentation showed that you could do away with the syringe and just use the applicator tip of the adhesive to wipe a small film on the clean fiber, insert it leisurely into the connector, leave it on the bench for about five minutes and it was ready to polish.

That was a lot easier. It also did not leave excess adhesive inside the connector that might not harden. And, that cheap bottle of adhesive would probably be enough for 10,000 connectors.

So here is my recommendation on anaerobic adhesive termination. Do not inject the adhesive, just wipe it on the fiber. Insert the fiber and wait 5 minutes. If you are too impatient to wait that long, after inserting the fiber, use the method above to wipe just a bit of accelerator solution on the protruding fiber and have the fiber quickly bond on the end of the fiber.

I want to finish with one warning. It is normal to clean the fiber with isopropyl alcohol on a lint-free wipe. Be sure to use only pure 99 percent-plus isopropyl alcohol, not “rubbing alcohol,” which is 30 percent water. The water will slow or stop the curing of the anaerobic adhesive and adversely affect the bond strength.

Next month, the process continues.

About The Author

HAYES is a VDV writer and educator and the president of the Fiber Optic Association. Find him at

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