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Tech Tip: Sealants & Adhesives

Enhance your employees’ product and industry knowledge with PTDA’s Tech Tips. This library of online tips, hints and techniques may be used to educate new and current employees on power transmission/motion control (PT/MC) products, technologies and concepts and serve as reference and reminder for more experienced staff. Tech Tips are based on the expertise of PTDA member companies and content from PTDA’s Power Transmission Handbook®, the definitive resource and training tool on PT/MC products.

Visit the full library of Tech Tips for additional products.

What are Formed-In-Place gaskets (FIP) and what are the two most common types?

Formed-In-Place gaskets (FIP) are applied as a bead of sealant to one of the unassembled flange surfaces. Upon assembly, the bead conforms to the imperfections of the mated flanges, then cures and forms a durable seal. The two most common types of FIP sealants are:
1. Anaerobic FIP sealants: Optimized for close-fitting rigid metal flanges. Provide a unique combination of high shear strength and environmental resistance. 

2. RTV Silicone FIP sealants: High elongation elastomers optimized for flexible flanges such as stamped covers. RTV silicones cure through a reaction with atmospheric moisture to cure. They offer a unique combination of high gap-fill temperature resistance and a strong, flexible adhesive. 

What is the root cause of mechanical failure, and how are adhesives and sealants engineered to increase the performance and reliability of typical machinery equipment components (i.e. fasteners, fittings, flanges and bearings)?

Adhesives and sealants are effective because they address the "root cause" of mechanical failure; the innter space between components. Inner space includes the clearance that exists between threaded assemblies, in the unfilled space in press fits, and in the surface imperfections between flanges. Machinery adhesives solve the problem of mechanical failures caused by the clearance between close-fitting parts in assemblies by filling this space with a thermoset plastic engineered to provide predictable properties of adhesion, elongation, and environmental resistance.

How do anaerobic retaining compounds stop fretting corrosion?

Fretting corrosion is the micro movement of a bearing on a shaft and results in pitting of the surface as small areas are welded together, then ripped apart due to movement. An anaerobic retaining compound fills all the inner space between two surfaces preventing movement. If the space is gone, the part cannot fret. Note that the space is not due to any defects, but is inherent due to spaces formed by surface roughness, as even ground bearings have a measurable surface roughness providing a space for movement.

Should you use an anaerobic primer on a cast iron surface?

In general they are not required. Anaerobic materials cure by reacting with the surface of active metal like steel, cast iron or brass. However if the gaps are large (exceed 0.005”) the primer is useful to ensure the anaerobic materials cure.

What is the root cause of mechanical failure that anaerobic materials solve?

The root cause of fastener loosening, pipe and gasket leakage and bearing loosening is inner space between components.  In order for parts to fit together designers have to leave clearance space. Once assembled, this space is no longer required and the source of issues. Anaerobic materials fill this inner space stopping leaks and vibration loosening.

Why Use Adhesives in Threaded Assemblies or Press Fits?

There's typically only 20 percent to 30 percent metal-to-metal contact in threaded assemblies and press fits.  This means that 70 percent to 80 percent of the inner space is air which can cause potential loosening, leak paths and catastrophic mechanical failure.  Adhesives fill this inner space and "lock" the parts together to prevent failures commonly caused by loosening and leaks.  

What is an Anaerobic Adhesive?

Anaerobic adhesives cure in the absence of air and in the presence of metal. The most common anaerobic adhesive is used as a threadlocker to prevent fasteners from vibrating loose, but anaerobic adhesives are also used as pipe sealants to secure pipe fittings, gasket makers to seal rigid flanges and retaining compounds to mount bearings.

Using an anaerobic threadlocker stop leaks

The most common reason people use an anaerobic threadlocker is to stop vibration loosening.  It does this by filling all the gaps between the nut and bolt, which has the bi-product of sealing the threaded connection preventing leaks.  This property is utilized in automotive applications where an exhaust manifold bolt enters the engine block and penetrates the water jacket.  This is a potential leak path that the threadlocker seals.

The information provided in Tech Tips is not meant to be all-encompassing, but rather to draw attention to and provide information about the particular subjects covered. All suggestions and recommendations contained in Tech Tips are based upon information that is believed to be accurate to the best of the experience and knowledge of PTDA’s contributing members, but are made without guarantee or representation as to results. PTDA and Tech Tip contributors expressly disclaim any warranties or guaranties, express or implied, as to the accuracy or completeness of any information published in Tech Tips, and disclaims and makes no warranty that the information in Tech Tips will fulfill any of your particular purposes or needs. PTDA and Tech Tip contributors disclaim liability for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on Tech Tips.
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