Expert Advice about Anaerobic Adhesives 1
A Henkel Asia Pacific Technical Customer Services Manager and expert in the use of anaerobic adhesives shares the questions he is asked most frequently by his customers and his responses covering issues from materials on which anaerobic adhesives can be used to accelerating the curing time and why the liquid anaerobic adhesives remain stable in their bottle.
Hello – my name is C.S. Woo and I have been working for Henkel, specializing on Loctite® products for 23 years. I am the Technical Customer Services Manager for the Asia-Pacific region and I am based in the Shanghai regional office. I have previously worked in the Japan and Korea offices of Henkel to support local customers in those markets.
C.S. Woo – specializing on Loctite® products for 23 years
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I get asked questions about anaerobic adhesives all the time. I have collected the most frequently asked questions about anaerobic technology and my answers in this article. I hope this is useful for you.
What exactly is meant by “anaerobic” in relation to adhesives?
Anaerobic adhesives are products that cure only in the absence of air. They are adhesives 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 an anaerobic adhesive 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.
On what kind of materials can I use anaerobic adhesives?
Generally, anaerobic adhesives 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.
What is the difference between active and inactive materials?
The following table groups active and inactive materials:
Active Inactive
Brass Annodized Aluminum
Copper Bronze Cadmium
Manganese Iron Chrome
Kovar Gold
Monel® Inconel
Nickel Magnesium
Steel Plated parts
Galvanized Steel
Stainless Steel
Titanium
Aluminum
Zinc
Silver
Black Oxide
Magnetite
How fast do anaerobic adhesives cure?
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 anaerobic adhesives come in many different formulations, it is important to refer to the specification sheets for the correct curing time.
What is the pH of Anaerobic Materials?
PH is only applicable to materials that are soluble in water. Anaerobic adhesives are not and therefore have no PH value.
If anaerobic adhesives cure in the absence of air, how come they don’t cure in the sealed bottle?
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.
Do you recommend using anaerobic adhesives on plastics?
Anaerobic adhesives are generally not used with plastics. Anaerobic adhesives 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.
Can the curing time of anaerobic adhesives be accelerated via heat?
Yes, you can heat cure anaerobic adhesives to achieve faster curing time. Typically you can heat cure these products at 250OF (121OC) for about one hour or at 150OF (65OC) 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.
Do I need to use a primer with anaerobic adhesives?
I do recommend to use a primer with most anaerobic adhesives 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.
Are anaerobic adhesives compatible with rubber parts that they may be exposed to in the liquid state prior to cure?
There are no long-term studies for anaerobic 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 anaerobic adhesives 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.
Can anaerobic adhesives be used on oil-impregnated parts?
Yes. Anaerobic adhesives 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.
[to be continued]
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Company Information
Loctite® is the world’s leading brand of engineering adhesives and sealants. Since the original invention of anaerobic adhesives in 1953, the Loctite® brand stands for innovative technologies, superior performance, cost savings, and strong partnership with its customers. Today, Loctite® is the flagship brand of Henkel adhesive technologies and offers over 5,000 unique products through a wide distribution network covering 125 countries. Industrial users across the globe trust Loctite® products to improve reliability of their assemblies and reduce overall costs.
For more than 130 years, Henkel has been a leader with brands and technologies that make people's lives easier, better and more beautiful. Henkel operates in three business areas – Home Care, Personal Care, and Adhesive Technologies – and is ranked among the Fortune Global 500 companies. In fiscal 2008, Henkel generated sales of €14,131 million and adjusted operating profit of €1,460 million. With more than 55,000 employees in more than 125 countries, people trust in brands and technologies from Henkel. Henkel – A Brand Like A Friend.
Information for editors: http://www.iLoctite.com/press