Auto Service World
Feature   March 1, 2009   by Chuck Carman, Curriculum Developer CARS

“A” Is For Anaerobic

Knowledge: When dealing with today's sophisticated engineered automobiles, you just can't get enough of it. As the engineering and manufacturing processes have improved over the years, the impact of i...

Knowledge: When dealing with today’s sophisticated engineered automobiles, you just can’t get enough of it. As the engineering and manufacturing processes have improved over the years, the impact of incorrectly serviced components is greatly increased.

Gone are the days where one tube of silicone sealant would work on all jobs. Today, one must keep a variety of tubes and bottles on the work bench to accommodate the different jobs throughout the day. But, what exactly are they all for?

Anaerobic adhesives like thread lockers, thread sealants, retaining compounds and gasket makers are now used repeatedly in many applications. These require two conditions to cure properly. The first is known to most technicians: that is the absence of oxygen or air. The presence of oxygen prevents the anaerobic material from curing (solidifying) while in storage or during preparation. Therefore, they should not be used in an oxygen rich environment, with strong oxidizing substances or with chlorine. The second condition is that it requires metal ionization: it needs to come in contact with metal ions, especially those of active materials.

Anaerobic adhesives work best on active materials. When being used on inactive materials, a primer or activator may be required. These chemicals assist in cleaning the parts to be assembled. They not only accelerate the cure times in most scenarios-especially when the parts are cold, but also, they assist with the curing of inactive materials that have low metal ion content. Cure times vary between products, but generally they are cured well enough to go into service in twenty minutes (some as low as a minute-and-a-half) and are fully cured in twenty-four hours.

Anaerobic adhesives are not recommended for use on most plastics since, with softer plastics, they may cause stress cracking. Denser plastics such as acetal are not affected by this.

Thread locker adhesives fill the inner voids of a threaded clamp area (bolt/ nut, etc.) sealing and locking the parts together. These come in a wide variety for different applications-depending on what the components are made of, the bolt size and required torque (both installing and removal). Also, whether the components are oily when assembled and what temperature range they must operate in. These are colour coded, in most cases, for easy recognition. Purple is for low strength, less than 1/4-inch bolt size and can be easily disassembled. Blue is medium strength, 1/4-to 3/4-inch and still able to be disassembled with hand tools. Red is high strength 1/4-inch and up. These can still be loosened but heat may be required. Green is medium to high strength for fasteners between #2 to

1/2-inch however, what makes it unique is it is designed to be used for locking preassembled components; it has a low viscosity and wicks into place. It requires heating and hand tools for disassembly.

Thread sealants seal threaded parts together tighter to withstand very high pressures, however, they offer low locking strength. This replaces most sealing tapes or pipe dope. They will harden thus preventing any leakage caused by vibration.

Retaining compounds are used when securing press or slip fit non-threaded components together; such as a bearing into a shaft. Retaining compounds can be used as a thread locker, however, thread lockers should not be used as a retaining compound.

Anaerobic gasket makers are different than RTV silicone gasket material; they are used on rigid machined surfaces with tight tolerances. These flexible gasket materials are normally used in conditions with gaps less than 0.015-inch however, there are some that can span gaps up to 0.050-inch. These are commonly used in sealing timing chain covers, transmission and transaxle case halves. In some cases, a putty knife or plastic blade scraper can remove these gaskets however, in many

cases a technician will need to use a chlorinated solvent or paint stripping solvent to completely remove the adhesives.

While this is a general overview of the usage of these products, always follow the sealant requirements for each repair situation as directed by the service information. If more detailed information (such as material safety data sheets) is required, contact your supplier or the adhesive manufacturer.

For more information on automotive technology visit CARS OnDemand training


Active Materials

Iron, Bronze, Brass, Steel, Nickel, Manganese, Copper

Inactive Materials

Galvanized steel, Gold, Glass, Plastic, Zinc, Cadmium, Magnesium, Pure aluminium, Stainless steel, Anodized aluminium, Silver, Titanium, Plated parts, Ceramics, Composites, Paint coated parts

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