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Expert Advice About Anaerobic Adhesives
Wed 09 Sep 2009 - 10:32
Expert Advice About Anaerobic Adhesives
By [http://ezinearticles.com/?expert=C._S._Woo]C. S. Woo
Below are a collection of questions and answers with regards to anaerobic adhesives.
Q: What exactly is meant by "anaerobic" in relation to adhesives?
A: These are products that cure only in the absence of air. They are designed for metal-to-metal assemblies although they can sometimes be used with other materials as well. The presence of metal ions accelerates the cure of these products. When you assemble parts with these adhesives and you have excess liquid squeeze out, this will not harden due to the exposure to air. Simply wipe the excess away with a common solvent like acetone or isopropyl alcohol. Anaerobic adhesives are typically used for applications of threadlocking, pipe sealing, gasketing and retaining.
Q: On what kind of materials can I use anaerobic adhesives?
A: Generally, they can be used effectively 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.
Q: What is the difference between active and inactive materials?
A: The following table groups active and inactive materials:
Active -
Brass
Copper Bronze
Manganese Iron
Kovar
Monel®
Nickel
Steel
Inactive -
Annodized Aluminum
Cadmium
Chrome
Gold
Inconel
Magnesium
Plated parts
Galvanized Steel
Stainless Steel
Titanium
Aluminum
Zinc
Silver
Black Oxide
Magnetite
Q: How fast do anaerobic adhesives cure?
A: In general, it takes 24 hours to fully cure but the parts are basically fixed in under 10 minutes depending on the grade of the adhesive. As they come in many different formulations, it is important to refer to the specification sheets for the correct curing time.
Q: What is the pH of Anaerobic Materials?
A: PH is only applicable to materials that are soluble in water. Anaerobic adhesives are not and therefore have no PH value.
Q: If anaerobic adhesives cure in the absence of air, how come they don't cure in the sealed bottle?
A: The bottles are made off specially formulated oxygen-permeable polyethylene, which allows air to pass through the wall of the bottle to maintain stability of the liquid product inside. The bottle is not fully filled with adhesive to ensure air is in the bottle, ensuring stability.
Q: Do you recommend using anaerobic adhesives on plastics?
A: These type of adhesives are generally not used with plastics as they will create stress cracks with some plastics, including many thermoplastics like ABS and polycarbonate. If the adhesive is used for a metal-to-metal assembly but in close proximity to plastic, there is the possibility of excess liquid product or vapor affecting the plastic. In the case of compatible plastics like acetals, the anaerobic adhesives are simply not the best family of products for effectively locking and/or sealing of these plastics. Instead often Cyanoacrylates are used if they meet the other application parameters.
Q: Can the curing time of anaerobic adhesives be accelerated via heat?
A: Yes, you can heat cure anaerobic adhesives to achieve faster curing time. Typically you can heat cure these products at 250°F (121°C) for about one hour or at 150°F (65°C) for about three hours. The one trade off is that you will probably reduce your ultimate strength. Whenever you accelerate the cross-linking of the polymer, you can reduce its ultimate strength. Test whether this is appropriate for your application.
Q: Do I need to use a primer with anaerobic adhesives?
A: I do recommend to use a primer with these products when applied to assemblies where both parts are classified as inactive metals. These metals lack the presence of iron or copper content and thus, lack the active metal ions required to fully cure the product in 24 hours. If on the other hand both or at least one part is an active metal, such as plain steel, brass, bronze, copper or iron, there is no need to use a primer to ensure full cure.
Q: Are anaerobic adhesives compatible with rubber parts that they may be exposed to in the liquid state prior to cure?
A: There are no long-term studies for these type of adhesives and compatibility with various elastomers. There is a general consensus that liquid anaerobic adhesives can negatively impact some elastomers in the form of swelling, cracking and weight change in case of prolonged contact. Customers should carefully test products for compatibility. Some dispensing equipment designed for anaerobic adhesives use Viton O-rings and seals because this material is considered compatible with them for a reasonable amount of time. Once an anaerobic adhesive cures, there are no compatibility concerns at all between rubber hardware and the cured, very inert anaerobic adhesive.
Q: Can anaerobic adhesives be used on oil-impregnated parts?
A: Yes. They can be used on oil-impregnated parts. Just wipe the part clean prior to applying the product. Select an anaerobic adhesive with better oil cutting action, which will cure, bond and seal effectively.
C.S. Woo is a Henkel Loctite Technical Customer Service Manager, Asia Pacific - http://www.iLoctite.com/press Since 1953 Loctite® has been the world's leading brand of engineering adhesives and sealants. It also stands for innovative technologies, superior performance, cost savings, and strong partnership with its customers. For more expert advice and resources on anaerobic adhesives visit http://au.iloctite.com/en/mechanical-threadlocking#
Article Source: http://EzineArticles.com/?expert=C._S._Woo http://EzineArticles.com/?Expert-Advice-About-Anaerobic-Adhesives&id=2705823
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