I have been writing books, bulletins, magazine articles, and other forms of technical writing for more than 40 years, and there is one thing I know for sure when I think a subject is simple, most of the time, it is way more complex than I ever imagined. Trying to come up with material for sections of a book or a magazine article is often a challenge, as I want the subject matter to be interesting and helpful to the people reading the material.
In this month’s article, we are discussing the use of thread lockers and sealers. It is an area that many think they know everything there is to know about the subject but believe me; there is still a lot more to learn. Therefore, when writing technical information, I try to research the information as much as possible so you, the end user, can depend on the quality of the information you are reading.
I still use the same format for researching information I did for decades with GM. Find the subject expert and drain their brain of as much information as possible on the matter. For this article, I reached out to the engineers at Permatex and Loctite, the two largest producers of thread lockers and thread sealers on the planet. Both companies are OEM suppliers with vast engineering staffs dedicated to their products.
Let’s look at these products and what you need to know regarding when, where, and how to use them correctly.
Treaded fasteners have been around for more than 2000 years. Over 300 billion bolts and nuts are used yearly in the vehicle/aircraft assembly and repair industry. However, despite advances in fastener technology, problems still occur due to heat cycling, vibration, and material issues as a typical bolt/nut metal-to-metal contact area, which is as little as 15%.
Thread lockers are an “anaerobic adhesive” (Cure with a lack of oxygen) and are used to prevent nuts, bolts, and screws from loosening from vibration and stress. Tread lockers form a bond with the metal to prevent the bolt, nut, or screw from loosening when in use. “Monomers” provide a hard-setting product that locks the components together. When the “monomer” is combined with a compatible metal and if “oxygen is not present,” the product will change into a hard-setting end product locking the components together. If you lack a compatible metal or the oxygen is not eliminated from the threads, the product will not cure, meaning it will not function as a thread locker.
(Monomers + Active Metal Contact + Lack of Oxygen = Polymerization = Curing)
Some thread locker brands are identified by a part or ID number, while “most all” thread lockers can be identified by color. Six colors are typically used to identify today’s applications:
- Dark Red: High strength/High temperature, designed to be permanent (3/8 -1 1/2” 10-38 mm bolts)
- Red: High strength, designed to be permanent. (3/8 to 1” 10-25mm bolts)
- Orange: High strength, designed to be non-permanent or removable (1/4 to 1”, 10mm to 25mm bolts)
- Blue: Medium strength, designed to be removable. (1/4 to 3/4”, 6mm to 20mm bolts)
- Purple: Low strength, designed for tiny bolts and tiny screws. (#2 to 1/4”, 2.2mm to 6mm)
- Green: Low strength, designed to penetrate small screws like a set screw. (#2 to 1/2”, 2.2mm to 12 mm bolts) This product is also used as a sleeve and bearing retainer.
The companies also rate their products using three other terms, temperature range, prevailing torque, and breakaway torque. Breakaway torque is the amount of torque it takes to overcome the thread locker product to get threads to rotate once the product has cured. Prevailing torque is the amount of torque it takes to keep the fastener spinning once the bolt/nut turns.
Permatex provided the temperature ranges, breakaway, and prevailing torque for their products as follows:
- Dark red: -65 to 450° (-54 to 232°), breakaway torque 225 in-lbs, prevailing torque 200 in-lbs.
- Red: -65 to 300° (-54 to 150°) breakaway torque 275 in-lbs, prevailing torque 190 in-lbs
- Orange: -65 to 300° (-54 to 150°) breakaway torque 180 in-lbs, prevailing torque 160 in-lbs.
- Blue: -65 to 300° (-54 to 150°) breakaway torque 115 in-lbs, prevailing torque 50 in-lbs.
- Purple: -65 to 300° (-54 to 150°) breakaway torque 55 in-lbs, prevailing torque 20 in-lbs.
- Green: -65 to 300° (-54 to 150°) breakaway torque 225 in-lbs, prevailing torque 60 in-lbs.
THREAD LOCKER APPLICATION FACTS
1: A little goes a long way. The truth is, more thread locker does not equal more strength. The thread locker rides between the threads of the nuts and bolts. Any excess that is not contained in the treads will not cure. Many people think that the product is not curing because of what they are seeing, but remember that you cannot see inside the threads where curing is happening.
2: Thread lockers take 24 hours to cure fully. Loosening the bolt/ nut before that time will result in a connection that will not maintain the breakaway/prevailing torque values. If the bolt/nut is loosened before fully curing, the threads should be cleaned, recoated, and retightened. Curing time is different from “fixture time.” Fixture time is the time the assembled component must sit before being placed back into service. The time needed can be as little as a few minutes, but remember that for the product to fully cure will require much longer.
3: Thread lockers are designed to perform in the presence of oil and other contaminants, but you should always do your best to ensure the threads are clean and dry. Using the product on a dirty or contaminated surface can result in curing issues.
4: Thread lockers are not designed to cure when exposed to non-metallic threads. Steel, copper, or iron work the best. Aluminum, stainless steel, zinc, and magnesium do not promote curing as well as iron-based materials, but some curing will likely occur. If you are using the products on non-iron-based materials, you should always use a “surface prep activator,” which will etch the surface so the adhesive can work properly. Plastics and rubber components are not designed for standard thread lockers; as you have learned, the products require exposure to metal to activate the curing process.
- Cold temperatures slow the cure time for all thread lockers. Always use a surface prep activator to assemble the components in cold temperatures. The activators cut the cure time by typically 50% or more.
- Applying a new thread locker over the old one will lead to curing issues. The bolt or nut must be thoroughly cleaned to expose the metal for curing to occur.
- Applying heat may help you remove a nut/bolt previously installed with a thread locker.
- Through bolt assemblies, the thread locker should be applied to the bolt area where the nut and bolt meet when the assembly is fully tightened.
- For blind hole installations, the thread locker should coat the nut threads, not the bolt, as air pressure will force the thread locker from the threads as the bolt is tightened. Some technicians cover the bolt and nut, which will also work, but you are likely wasting some locker.
- The thread locker should always be shaken before use.
THREAD SEALANTS AND ANTI-SEIZE LUBRICANTS
Thread sealants are also a popular item in most automotive shops. Most thread sealants contain polytetrafluoroethylene (PTFE) and are designed for low-pressure systems with the idea of taking up the space between the male and female threads to prevent leakage. Like thread lockers, thread sealants are a form of anaerobic sealer. Three common versions are typically available:
- High Performance
- High Temperature
- Seal and lock
Most designs are compatible with metal, but some are not designed for plastic components unless it is listed as part of the product description.
Anti-seize products perform the function their name implies; they prevent the threads from seizing together. Three common types of anti-seize are on the market:
- Anti-seize: Typically, a blend of aluminum, copper, and graphite. Working temperature up to 1,600F. Initially designed for stainless steel fasteners, it also works on other metal types.
- Copper anti-seize: It contains flakes of copper for increased working temperatures up to 1,800F.
- Nickel anti-seize: Used where copper materials are not compatible. It is recommended for all metals with a working temperature of up to 2,400F.
Some anti-seize products are in paste form, while others are in dry form. Dry anti-seize products are typically used on splines, keyways, pins/cams/slides, and other mountings, while paste-type products are designed for bolts, nuts, and joints.
Anti-seize products should not be used on fasteners that require thread lockers, the threads to be coated with oil, or on an area where any gasket rides. To prevent galvanic corrosion, the type of anti-seize compound should match the type of metal the product is used on as close as possible. Like the other products discussed, a little goes a long way, so do not overuse the product. In addition, make sure the mating areas are clean before using the products.
Again, a big thank you to the engineers at Permatex and Loctite for their assistance with this article. Until next time remember, “The price of success is perseverance. The price of failure comes cheaper.”