loctite flange sealant 518

LOCTITE 518 is a single component anaerobic acrylic flange sealant based on dimethacrylate ester chemistry. It is supplied as a red, gel type, thixotropic material that cures when confined between close fitting metal surfaces in the absence of air. The product provides medium strength sealing and develops immediate resistance to low internal pressure after flange assembly. It works effectively on active metals such as mild steel as well as passive substrates like aluminum and tolerates minor contamination from industrial oils and fluids. Recommended gap performance is up to 0.25 mm and the material shows fluorescence under UV light for inspection.

The specific gravity at 23°C is approximately 1.1 and Brookfield viscosity at 25°C using spindle TC at 0.5 rpm is about 4,000,000 mPa·s. Instant sealing capability testing on annular steel flanges (50 mm ID, 70 mm OD) shows pressure resistance around 1.35 MPa at 0.05 mm gap, 0.14 MPa at 0.125 mm gap and 0.1 MPa at 0.25 mm gap, with pen roller application typically limited to 0.125 mm film thickness.

After 24 hours cure at 23°C, the glass transition temperature is about 100°C. Coefficient of thermal expansion is approximately 145 × 10⁻⁶ K⁻¹ below Tg and 160 × 10⁻⁶ K⁻¹ above Tg. Elongation at break is around 64%, tensile strength about 7.3 N/mm² and tensile modulus about 54 N/mm². Compressive shear strength on steel pins and collars is approximately 5 N/mm² after 1 hour and 24 hours at 23°C. Lap shear strength after 24 hours is about 8.4 N/mm² on grit blasted mild steel, 5.5 N/mm² on mild steel, 5.4 N/mm² on aluminum, 2.2 N/mm² on aluminum clad and 6.7 N/mm² on grit blasted mild steel bonded to aluminum. After 72 hours, lap shear strength on grit blasted mild steel can reach approximately 11 N/mm². Tensile strength on grit blasted mild steel pins is around 10 N/mm² and on aluminum pins about 13 N/mm².

Sealing tests confirm capability up to 0.25 mm induced gap on both mild steel and aluminum with resistance up to 1.3 MPa after 20 hours cure. The product has been evaluated for hot strength, low temperature performance down to -75°C and heat aging at elevated temperatures. Chemical resistance testing shows varying strength retention after exposure to synthetic motor oil at 120°C and 150°C, automatic transmission fluid, water/glycol mixtures, unleaded gasoline and diesel exhaust fluid depending on time and temperature conditions.

For best results, mating surfaces should be clean and free from heavy grease. The product is intended for close fitting flanges up to 0.25 mm gap and may be applied as a continuous bead, rolled film or screen printed layer. For gaps above 0.125 mm when using a roller method, application to both flange surfaces is recommended. Low pressure testing below 0.05 MPa can be performed immediately after assembly to verify sealing before full cure. Recommended storage temperature is between 8°C and 21°C in the original unopened container. The product is not recommended for use in pure oxygen or oxygen enriched systems or with strong oxidizing agents. Technical values stated are typical performance data for reference.