As magical a liquid as anaerobics may seem, they are not necessarily suitable for every flange type. They are most suited for sealing rigid flanges, designed to achieve optimum stiffness between two parts, minimise movement between them and transmit forces from one to another. Typical examples of such flanges can be found in vehicles, including gearbox housings, bedplate to crankcase, water pump to engine block and cam cover to cylinder head.
Anaerobic FIP (formed-in-place) sealants are ideal for rigid bolted joints because they offer metal to metal contact, ensure correct bolt tension, add structural strength, offer high pressure resistance and extensive on part life when exposed to air, making multiple application methods possible.
When it comes to flexible flanges, however, your best choice are RTV (Room Temperature Vulcanising) elastomers. They are best suited to seal i.e. gearbox covers, timing chain covers, stamped sheet steel parts, thin-walled metal castings and oil pans. Normally, flexible flanges don’t support the function of the parts, so micro-movement can be tolerated and optimum clamp load distribution is not crucial.
You’ll usually find flexible flanges covering openings in housings, sealing liquids inside components or protecting them from external contamination, covering moving parts for safety etc.
While anaerobics remain liquid on parts for as long as they are exposed to oxygen, RTV elastomers will cure into rubbery solids by reacting with the moisture from the environment. So there is a considerable difference in on part life between the two, which is important to take into consideration when suitability of the manufacturing process is being decided.
In both cases – rigid and flexible flanges – there are certain design recommendations to be followed to make the flange best suited for either anaerobic or RTV elastomer FIP gasket. Details can be found in the Gasketing design guide which I am happy to share on request.