Technical Concept- Anti-seize compounds | Problems occurred due to seizing | Choosing your Anti-seize
What is seizing?
When nuts and bolts are left in an assembled position for a long duration of time, they may get corroded due to exposure in surrounding or the threads may get damaged due to excessive pressure applied during tightening. It then becomes a tedious task dismantling the assembly. This condition of the damaged bolt is referred to as a seizure.
Frequently Asked Questions- Anti-seize
A Grease is best thought as a sponge full of oil where sponge is thickener which holds the oil and additives in place and have lubricating properties.
An anti-seize prevents or inhibits mechanical seizing.
Greasing are for bearings and anti-seize are for fasteners.
Don’t use anti-seize on exposed threads as it may attracts contaminates that may contribute to thread damage.
While installing the components wipe off excess anti-seize from the fasteners. Anti-seize should be applied where two metals meet, under the head of fastener and in the threads. for through hole clean the exposed thread area as it may attract contaminant leading to damage of threads.
Anti-seize should be used when two metals are involved (similar or dissimilar), when threads may be exposed to corrosion and fastener that frequently get removed.
Metal based anti-seize leave abrasive metallic oxides at higher temperatures which can potentially damage the threads. Metal free anti-seize do not generate abrasive oxides and are more suitable for applications involving higher temperatures or extreme vibrations.
A bolted joint, which experiences a high temperature or corrosive environment and requires future maintenance is a typical application of antisieze.It can used as thread sealing, thread locker and gasketing.
Nickel Anti-Seize has extremely high temperature capabilities and excellent chemical resistance. It is also suitable for seizure due to catalic corrosion.
Graphite helps operate with very low friction in sliding applications. Presence of Graphite in an antiseize helps reduce the torques required to operate the assembly.
Torque ratings on fasteners are based on their target clamping force. Anti-seize will act as a lubricant, the lubricating properties will significantly decrease the required torque to achieve the desired clamping force. Torque reduction varies with the material. When anti-seize are used without reducing the torque value it can strip the thread or stretch the bolt.
What is an Anti-Seize Compound?
As the word itself describes anti means restricts, Seize means getting fixed at a place. Using Anti-Seize Compound assures that when applied to bolts and gaskets during assembly, they can be tightened without thread damage and also dismantled easily.
Also when applied to bolts during assembly it prevents galling. Galling generally refers to cold welding of bolts in nuts due to excess pressure and friction caused during assembly. Anti-seize compounds serves the purpose of preventing dissimilar metals from getting corrodes in immensely corrosive surroundings and also enhances the performance of machinery.
Problems occurred due to seizing?
• Thread Stripping
Variation in the dimensions of thread such as major, pitch & minor diameters is stripping off a thread.
• Cross threading
When threads eventually cross the path that is supposed to follow, If forced it can typically ruin the threading of one or other, hence cross-threading.
If cross-threading occurred then it becomes very difficult to dismantle it.
When pressure is applied during installation, the friction causes bolt threads to seize to the threads of a nut or tapped hole. It is also known as “cold welding” or Galling
Once a fastener has seized up from galling it is typically impossible to remove without cutting the bolt or splitting. Later on by using cleaner – degreaser during maintenance one cannot dismantle the corroded bolted structure.
How is Anti-seize made ?
• Solid lubricants are dispersed in grease or a binder to form an anti-seizing compound. Anti-seize compound when applied creates a thick film which serves as a purpose of preventing contact between two mating surfaces. This reduces difficulty during dismantling and forms low friction coating.
• Graphite powders, copper, nickel, aluminium, molybdenum di-sulphide etc are common solid lubricants
Types of Solid Lubricants used in Anti- seize Compound
Which Anti seize compound to use ?
There are two stages of lubrication.
• It offers good corrosion protection for all steel.
• Copper-based formulas are restricted to 800 degrees C (However temperature may vary up to 1200 C)
• Copper on stainless steel causes inter-crystalline corrosion, which leads to crack and break in stainless steel parts.
• Aluminium as a base material for Anti-seize is good for use on stainless steel.
• Aluminium based formulas to 800 degrees C ( However temperature may vary up to 1200 C)
• When aluminium comes in contact with electrolyte it becomes an anode which is extremely small in volume compared to the large cathode of the steel. It usually deteriorates quickly and doesn’t leave protection at all on the steel surface.
• It is not recommended to be used on carbon steel.
• Nickel has a good anti-seize and corrosion protection and can be used for both steel and stainless steel
• They can perform well under medium temperature up to 1,400 degrees C.
• It’s on the list of carcinogens (Cancer producing products) and should not be used in workshops where direct or indirect contact is possible.
• Graphite is a superior conductor of electricity and high-temperature solid lubricant (up to 450 degrees C).
• In assemblies with electrical current flowing through a fastened joint such as the threads of spark plugs, ground screws, and antenna connections, anti-seize can be used with a minimum increase to resistance.
• Using such anti-seize will ensure current is transmitted by preventing corrosion.
• Graphite may be corrosive in the marine atmosphere; it also speeds up corrosion of ferrous alloys.
• Calcium fluoride and calcium oxide have a similar temperature resistance of nickel-based anti-seize product at 1,400 degrees F.
• Metal-free formulations are now utilized and have performance matching or exceeding traditional soft metal-based formulas
• It does not generate abrasive metallic oxides at high temperature
• The problem faced by industry nowadays is heavy metal discharge; Companies can be fined for the use of products that incorporate heavy metals due to bad effects on environmental of heavy metal discharge into lakes and rivers.
Applications Of Anti-seize compound
Anti-seize compounds are designated for the use and meet rating for use in specialized applications including the following:
Aerospace compounds are convenient for aerospace applications and will meet military specifications (MIL-SPEC), or military standards (MIL-STD).
Automotive compounds used for a variety of threaded fasteners along with brake callipers, spark plugs, and engine components are selected based on material and temperature compatibility.
3. Food Grade
Food grade compounds comprise those that have acknowledged National Sanitary Foundation (NSF) approval or are otherwise designed and applicable for use in processing equipment where food, beverages or pharmaceuticals contact may occur with anti-seize.
Used in chain sprockets, manifold tubes, pump gaskets.
Marine compounds are convenient for use on ships, dockyards or boats and resist oxidation.
Military-grade compounds are those who meet MIL-STD or MIL-SPEC ratings and are good enough for use in military applications.
Precautions to take while using Antiseize Compound
• A brush is most effective for applying a thin layer of anti-seize.
• A brush which has been used to apply a particular anti-seize compound, even if cleaned it should not be used to apply another because cross-contamination affects performance.
• It’s important to clean those bolts using cleaners, degreasers if they are oiled previously so that it doesn’t affect the frictional properties of anti-seize.