ANAEROBIC ADHESIVES – A PRIMER
The term ‘ANAEROBICS’ has been given to the class of single component Adhesives and
Sealants that are stable in the presence of air and cure to a solid polymer (plastic) in the absence
of air. Metals greatly accelerate the process of curing, which is why Anaerobics are
predominantly used for metal bonding.
Polymer chemistry permits formulation of anaerobic adhesives of various strengths and
viscosities. This has given rise to a range that is extensively used for:
1. Locking and sealing of threaded parts to prevent self-loosening, seizure due to corrosion
and leakage through the threads.
2. Co-axial bonding (retaining) of cylindrical parts such as bushes, ball bearings, collars,
shafts, gears, cup plugs, oil seals and knobs.
3. Sealing of flat mating surfaces, eliminations of traditional gaskets.
4. Mounting of keys in key ways to prevent wallowing and loosening.
5. Impregnating porous castings, welds and powder metal parts to prevent leakage and
improve machinability. To improve and some time make electroplating possible on
In all of the above applications an anaerobic adhesive / sealant of the right strength and viscosity
fills the space between the two mating parts as a liquid and then hardens / cures to a solid
polymer. It is this property of the anaerobic adhesives – the ability to wet and fill the ‘inner
spaces’ - that is exploited.
Anaerobic Adhesives have excellent properties which make them a useful engineering adhesive.
They can be formulated in high and low strength grades. They exhibit good resistance to the
common industrial fluids such as oil, coolants, greases and Lubricants. They also have excellent
working temperature range, normally from -40oC to + 150oC, though special grades are available
for temperatures + 210oC on the ‘hot’ side and -50oC on the ‘cold’ side. This represents 99% of
the applications where machines may be found and hence Anaerobics Adhesives have become
indispensable in assembly of machine elements.
Some of the common terms used in specifying Anaerobic Adhesives and their meaning:
1. Viscosity:- Measured with Brookfield Viscometer using specific spindles or any
other rota - viscometer and at various rpms, generally at 20 and 2.5 rpm for
thixotropic fluids or else only at 2.5. Sometime a different rpm and spindle
number is specified. The TDS of the grade gives detailed information. Some
anaerobic adhesives are liquids yet non-sag in nature and this is exploited in many
applications where application to the vertical surfaces is required.
2. Break Away Torque:- Tested as per BIS 13055, it is the torque measured at the
first relative movement of a bonded M10 nut and bolt where the bolt tension is
zero (Unclamped bolt). This is indicative of the adhesion strength of the grade.
The value thus obtained is the value by which the normal opening torque would
3. Break Loose Torque is the torque required to unseat a clamped bolt (Bolt under
tension). It is equal to the torque at which a normal bolt would have opened plus
the value of the Break Away Torque for the size and engagement length.
Both Breakaway & Break Loose Torque are indicative of the locking
ability of the adhesive
4. Prevailing Torque:- This is the maximum resistance offered when an unclamped
bolt is rotated through 360o. Tested as per BIS 13055. It is an indication of
cohesive strength of the polymer formed. It is not an indication of the locking
ability of the adhesive and is rarely used these days.
5. Service Temperature:- This is the useful service temperature range. At the
maximum the strength of the adhesive can be as low as 40% of the RT strength.
At subzero temperatures the polymer may become very brittle for certain
applications. However, special grades are available to address these extremes.
6. Curing Time:- Handling strength means that at least 20% of the strength has
been achieved. Usually the parts can be handled after elapse of such time for other
assembly operations. Functional strength means that at least 90 % of the strength
has been achieved. The assembly can be subjected to loads. Full strength is
achieved in 24 – 72 hours. The values tabulated in spec sheets are for M10
phosphated Nut and Bolt assembly. Factors which can influence cure speeds are
material surface; Copper and Copper alloys will give faster cures, inactive
surfaces like zinc cadmium, SS will give slower cure speeds.
7. Gap Filled:- Anaerobics are meant for assemblies which have small gaps, like
threaded connections, bushes and bearing fits, and machined and rigid face joints
like gear box haves. Typical gap filling range is 0.01mm to 0.5 mm, though with
the use of activators one can go up to 3mm also. The best strengths and results are
obtained at 0.025 mm gap. Also higher the gap longer will be cure time.
8. Shear Strength: Tested on a pin and collar assembly as per the procedure laid
down by BIS 13055. It is indicative of the bonding strength and can be used to
estimate the retaining strength of co-axially bonded joints. Steel and phosphated
steel give the best results. For zinc plated surfaces, stainless steel, copper etc the
strengths will be lower. For example for brass the strengths can be as low as 40%
of what is obtained on Mild Steel.
9. Pressure Sealed: Tested as per BIS test Jig for Hydraulic pressure resistance.
Used as indication of the sealing prowess of Anaerobics as a thread sealant or a
Anaerobics can be applied to a part in many ways
1. For a threaded part directly from the bottle which is provided with a nozzle. In
case of high volume application a small quantity can be poured in a polyethylene
cup and the fastener dipped directly in it. Automatic applicators are also available.
For a blind hole application in the hole is necessary.
2. For retaining applications directly from the bottle or from a dispensing valve all
around the male part. On assembly, a slight clock and anti-clock wise twist may
be given for even spread. A piece of sponge wetted with Anaerobics can also be
used for application to the male and also to the hole. The sponge however may
have to be changed from time to time as it may get hard due to the polymerizing
adhesive. For automatic application in hole a roto-spray is the best option.
3. For a flat surface, a 3 to 5 mm thick bead may be applied on the surface manually.
Care must be taken to ensure that the bead is applied before the mounting holes
on the flange. The adhesives may be applied using a roller or a using screen
printing techniques. Robotic x-y tables and arms fitted with dispense valves are
the best option for in-line production.
In all cases care may be taken to avoid excess contamination of the adhesive by metals.
Polyethylene cups may be cleaned or discarded from time to time, sponge pieces may be
changed and screens wiped clean with solvents.
Disassembly of the parts has to done using the tools they were used to assemble or the
tools normally used: Wrenches for threaded joints, bearing pullers or Bull-Arbor type
press for co-axial joints and a chisel type tool for face joints. It is, therefore, extremely
important that the adhesive with the right strength be used for the joint.
In some cases of high temperatures may be needed. At a higher temperature the polymer
becomes soft and is easier to break. Solvents are not useful in disassembling parts bonded
with Anaerobics, A) there is not much gap for the solvent to penetrate and act, and B)
Anaerobics cure to a crossed linked polymeric structure and solvents have little or no
effect on the polymer.
While still liquid the Anaerobic Adhesives can be wiped off using a cloth wetted with
Ketonic solvents, like Acetone. For larger spills the adhesive should be soaked up in a
piece of paper or a piece of cloth and disposed off in accordance with the local laws.
STORAGE AND PACKAGING:
Anaerobic Adhesives will come in 5ml to 250 ml bottles which will have nozzles for
application. Bulk will be one or two litre bottles to be used with dispensing systems.
Pastes grades will come in 50 ml or 250 ml squeeze tubes or 300 ml cartridges. Bulk will
come in squeezable bags or bellows for dispensing systems. All packaging will have
higher volume than contents. This required for storage stability.
Adhesives must be stored under +30oC Celsius for maximum shelf life. Temperature
accelerates chemical reactions hence higher temperatures during storage will seriously
affect the adhesives. An example of improper storage will be storing at the top shelf
under of a rack placed under an asbestos sheet roof. The temperatures at such a place can
go up to +65oC during summers (In India) and will cause polymerization (hardening) of
the adhesive. Refrigeration is not necessary. Storage place may also be dark.
What are the different threadlockers and their colors?
These are different grades of threadlockers; colour refers to different strengths. For
example, the purple threadlocker is a low strength, blue is medium and red is high
strength; the green threadlocker is a special wicking grade product that allows faster and
deeper penetration through the assembled parts.
On what kind of materials can I use anaerobic adhesives (threadlockers, thread
sealants, retaining compounds and gasket makers)?
Generally, anaerobic adhesives are recommended for use on metal surfaces. Some
materials are more active than others and depending on the types of materials used the
curing may be faster or slower.
What is the difference between active and inactive materials?
Active and inactive materials are classified as followed:
When do I need to use an activator?An activator achieves two things:
a. Accelerates the cure of the anaerobic adhesives on active materials at lower
temperatures or for inactive materials at room or elevated temperature.
b. Cleans the parts to be assembled, replacing the need to use solvents for surface
Can MyTLok anaerobic adhesives (threadlockers, thread sealants, retaining
compounds and gasket makers) be used on plastics?
We do not recommend that anaerobic adhesives be used on many types of plastics since
the adhesives may cause stress cracking of the soft plastics. However, for some plastics
of higher densities such as Acetal (Delrin®) the adhesives can be used without the
It seems that threadlockers and retaining compounds are similar in performance,
can they be used interchangeably?
Even though these two groups of adhesives appear to be similar, they are designed for
specific purposes and applications. The retaining compounds may be used for
threadlocking but the threadlockers should not be used to replace retaining compounds.
What is the difference between a threadlocker and a thread sealant?
Again, threadlockers and thread sealants are designed for specific purposes and
applications and should not be used interchangeably. A threadlocker adhesive locks and
seals the threaded parts with stronger locking/bonding strength and sometimes with
friction control.. On the other hand, a pipe sealant seals threaded parts to withstand very
high pressure but with lower bonding/locking strength. For locking you need bonding,
which is not provided by thread sealants.