LOCTITE 640 High-Strength Retaining Compound – Extended Positioning Time

High-strength retaining compound with extended positioning time

LOCTITE® 640 is a green, one-part anaerobic retaining compound for close-fitting cylindrical metal assemblies. Its low viscosity and slower cure provide additional positioning time for large-diameter components and active metals such as brass, while delivering high strength after cure.

Key benefits

• Extended assembly time for positioning larger cylindrical components
• High-strength retention for slip fits and press fits
• Low-viscosity liquid flows into close-fitting joints
• Service temperature range: -67°F to 347°F (-55°C to 175°C)
• Typical fixture time on steel: 2 hours
• Fluoresces under UV light for inspection and quality control

Common applications

• Retaining bearings and helping prevent spin-out
• Securing keys, splines, bushings, and sleeves
• Retaining rotors on motor shafts
• Augmenting press fits and restoring worn or out-of-tolerance assemblies
• Eliminating backlash in cylindrical metal assemblies

Technical details

• Technology: acrylic
• Chemical type: urethane methacrylate
• Appearance: green fluorescent liquid
• Components: one part; no mixing required
• Cure: anaerobic
• Viscosity at 77°F (25°C): 450–750 mPa·s (cP)
• Specific gravity at 77°F (25°C): approximately 1.2
• Maximum diametrical clearance: less than 0.004 in. (0.1 mm)
• Typical compressive shear strength after 24 hours at 72°F (22°C): 3,190 psi (22 N/mm²), ISO 10123
• Full cure: typically 24 hours under suitable conditions

Application guidance

Clean and dry both mating surfaces. Apply adhesive around the leading edge of the pin and inside the collar, then assemble with a rotating motion for complete coverage. For inactive metals, larger gaps, low temperatures, or unacceptably slow cure, use LOCTITE® SF 7471 or SF 7649 activator according to its instructions. Do not disturb parts until sufficient handling strength is reached.

Standards and limitations

North American production is tested to applicable requirements of Mil-R-46082B and ASTM D5363; confirm any required approval for the specific application. Do not use in pure oxygen or oxygen-rich systems or as a sealant for chlorine or other strong oxidizers. The product is not normally recommended for plastics, especially thermoplastics that may stress-crack; verify compatibility before use.