Loctite 641 Retaining Compound

LOCTITE 641 is a one-component acrylic anaerobic adhesive formulated with methacrylate ester technology and designed for retaining cylindrical assemblies that may require later disassembly. The uncured material appears as a yellow liquid with medium viscosity and does not require mixing before application. It has a specific gravity of 1.07 at 25°C and viscosity values measured using Brookfield RVT at 25°C ranging from 1,215 to 2,750 mPa·s (cP) using spindle 2 at 2.5 rpm and 400 to 800 mPa·s (cP) at 20 rpm. According to EN 12092 - MV at 25°C after 180 seconds, viscosity at a shear rate of 277 s⁻¹ ranges between 90 and 180 mPa·s (cP). The product cures anaerobically when confined between closely fitting metal surfaces and can be accelerated using LOCTITE SF 7471™ or LOCTITE SF 7649™ activators when required. This retaining compound is primarily used for bonding bearings onto shafts and into housings, preventing loosening and leakage caused by shock and vibration while still allowing service removal when necessary. Cure speed depends on substrate material, bond gap, temperature, and activator usage. Shear strength development tested according to ISO 10123 demonstrates progressive strength build-up over time on steel, aluminum, and zinc dichromate surfaces. Larger bond gaps may reduce cure speed, while higher temperatures accelerate strength development. The use of activators significantly improves curing performance, particularly on inactive metals. After 24 hours curing at 22°C, LOCTITE 641 achieves a compressive shear strength of ≥6.5 N/mm² (940 psi) on steel pins and collars as tested under ISO 10123 standards. Physical properties of the cured adhesive include a coefficient of thermal expansion (ISO 11359-2) of 80 × 10⁻⁶ K⁻¹, thermal conductivity of 0.1 W/(m·K) as per ISO 8302, and specific heat of 0.3 kJ/(kg·K). Environmental resistance testing shows maintained strength after exposure to various industrial fluids. When aged under controlled conditions and tested at 23°C, the product retains performance after exposure to motor oil (MIL-L-46152) at 125°C, unleaded petrol at 22°C, brake fluid at 22°C, water/glycol 50/50 mixture at 87°C, ethanol at 22°C, and acetone at 22°C for durations up to 1000 hours depending on the environment. Heat aging tests at 120°C and 150°C demonstrate gradual strength reduction over extended exposure, while hot strength testing confirms performance across elevated temperatures. The product is not recommended for use in pure oxygen or oxygen-rich systems and should not be selected as a sealant for chlorine or strong oxidizing materials. Surface preparation is critical for optimal results; all surfaces should be cleaned using a LOCTITE cleaning solvent and allowed to dry. For inactive metals or where faster curing is required, an activator such as SF 7471™ or SF 7649™ should be sprayed onto the surface and allowed to dry before adhesive application. For slip fitted assemblies, adhesive should be applied around the leading edge of the pin and inside the collar with rotational movement during assembly. For press fitted assemblies, adhesive should be applied thoroughly to both bond surfaces and assembled using high press-on rates. For shrink fitted assemblies, adhesive should be coated onto the pin, and the collar should be heated to create sufficient clearance before assembly. Components should remain undisturbed until adequate handling strength is achieved. For disassembly, localized heating to approximately 250°C is recommended, followed by separation while the assembly is hot. Cured adhesive residue may be removed by soaking in LOCTITE solvent combined with mechanical abrasion such as wire brushing. Storage should be in unopened containers in a dry environment, with optimal storage temperature between 8°C and 21°C. Storage below 8°C or above 28°C may adversely affect product properties, and contaminated material should not be returned to the original container.