Dec 14, 2018
Thread-locking compounds made by Loctite, Permatex and other companies all work pretty much the same: they are anaerobic compounds that cure/harden in the absence of oxygen. If you apply thread-locking compound to the bare threads of a bolt and let it lie on your work bench, it will stay liquid for hours. Maybe days. But thread a nut onto that bolt so that the threads squeeze out the oxygen, and the liquid will turn to a semi-solid plastic within 10 to 20 minutes.
The cure-time of thread-lock depends on the type of metal and the cleanliness of the metal. "Active" metals like mild steel or steels used in nuts and bolts that are oil-free cure quickly, often within 20 minutes. "Inactive" metals like aluminum, titanium or stainless steel will eventually cure, but can take an hour or more. Curing of thread-locking compound on inactive metals can be speeded by using Cure & Prime products which speed up the chemical reaction. Contamination, like dirt, grease, oil--even the residual coating of machine oil on brand new bolts--slows the curing process dramatically.
Something I often forget when using thread-locking compounds is that I can use the component immediately because I probably mechanically torqued/tightened the nut or bolt to specification during assembly. Loctite and other products do NOT "tighten" fasteners. They merely keep properly torqued fasteners from vibrating loose. Technically, a properly torqued fastener shouldn't come loose anyway because the clamp-load on the threads literally stretches the bolt microscopically enough to spring-load the fastener and hold it in place. Thread-locking compound is just insurance that it won't come loose due to vibration.
A couple other things I have to remind myself: When Loctiting a nut on a bolt, put a drop or two of thread-locking compound on the threads where the nut will be once it is fully torqued. Don't put the thread-locker on the tip of the bolt and use the nut to smear it down the length of the bolt.
Another point to remember is that when installing a bolt in a blind hole, put drops of thread-locking compound into the bottom of the hole. When the bolt is threaded into the hole the air and Loctite trapped in the bottom will "escape" upward along the threads before they're cinched tight. Air willmovze up and out first, followed by thread-locking compound, ensuring the threads are well-treated for a secure bond once the bolt is torqued and the threads are tight, creating an oxygen-free environment. At least that's the recommendation of both Loctite and Permatex for installing bolts with thread-lacking compound in blind holes. Personally, I dribble a drop or two of thread-locking compound down one side of the threads of the blind hole, then add the recommended drops to the bottom of the hole. But that's just me.
I'll add a few more thread-locking tips in my next blog. Like, where do you use "Red" Loctite, and how do you take it apart after you realize Red was the wrong type of Loctite to use in that particular spot? Because Red is nearly the same thing as welding...