Technical Concept – Anti-Seize: 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.
What are Anti-Seize Compounds?
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.
What is Anti-Seize made up of?
• 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 disulphide etc are common solid lubricants.
Types of solid lubricants used in Anti- Seize Compound.
Choosing Your Anti-Seize
There are two stages of lubrication.
High-quality grease: It serves as a base lubricant and can work up to 200 degrees C
Lubricating solids: These solid lubricants present in the grease serve up to 1,200 degrees C.
• 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 antennae 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 products 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.
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.
• 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 while using Anti –Seize.
• 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.