Loctite 603 Retaining Compound

LOCTITE 603 is an acrylic technology adhesive based on urethane methacrylate chemistry, supplied as a green liquid with low viscosity and positive fluorescence under UV light for inspection purposes. It is a one component system requiring no mixing and cures anaerobically when confined in the absence of air between close fitting metal surfaces. A secondary cure can be achieved using an activator when required. The product is designed specifically for retaining applications and delivers high strength bonding for cylindrical fitting parts, particularly in conditions where consistently clean surfaces cannot be guaranteed. It prevents loosening and leakage caused by shock and vibration and is typically used for retaining roller bearings or oil impregnated bushings into housings.

The product is registered to NSF Category P1 for use as a sealant where there is no possibility of food contact in and around food processing areas (regional approval). In its uncured state, LOCTITE 603 has a specific gravity of 1.1 at 25 °C. Brookfield viscosity measured using RVT at 25 °C with spindle 1 at 20 rpm ranges between 100 to 150 mPa·s (cP), while EN 12092 - MV viscosity at 25 °C after 180 seconds at a shear rate of 277 s⁻¹ ranges from 90 to 180 mPa·s (cP). Flash point details are available in the Safety Data Sheet (SDS).

Cure speed depends on substrate type, bond gap, temperature, and activator usage. On steel pins and collars tested according to ISO 10123, shear strength develops progressively over time. Cure performance varies between steel, aluminum, and zinc dichromate substrates. Bondline gaps of 0.05 mm, 0.1 mm, and 0.2 mm influence cure rate and final strength development. Where cure speed is slower than desired or when larger gaps are present, application of Activator SF 7471™ or SF 7649™ significantly improves cure performance compared to no activator. Temperature also affects curing behavior, with strength development measured at 5 °C, 22 °C, and 40 °C demonstrating accelerated cure at elevated temperatures.

After full cure, the material exhibits a coefficient of thermal expansion of 80 × 10⁻⁶ K⁻¹ (ISO 11359-2), coefficient of thermal conductivity of 0.1 W/(m·K) (ISO 8302), and specific heat of 0.3 kJ/(kg·K). Typical performance after 24 hours at 22 °C shows compressive shear strength of ≥22.5 N/mm² (3,260 psi) on steel pins and collars according to ISO 10123, while after 30 minutes at 22 °C, compressive shear strength reaches ≥13.5 N/mm² (1,960 psi).

Environmental resistance testing after curing for 1 week at 22 °C demonstrates stable compressive shear strength performance. Hot strength testing at elevated temperatures shows percentage strength retention relative to 22 °C baseline. Heat aging evaluations at 120 °C and 150 °C indicate strength retention over exposure periods up to 5000 hours. Chemical and solvent resistance testing at 23 °C reveals percentage of initial strength retention after exposure to various environments: motor oil (MIL-L-46152) at 125 °C maintains 100% strength up to 1000 hours; unleaded petrol at 22 °C retains 100%, 90%, and 85% strength after 100, 500, and 1000 hours respectively; brake fluid at 22 °C retains 100%, 90%, and 80%; water/glycol 50/50 at 87 °C retains 100%, 90%, and 80%; ethanol at 22 °C retains 100%, 100%, and 75%; and acetone at 22 °C maintains 90% strength across 100, 500, and 1000 hours.

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 other strong oxidizing materials. When aqueous washing systems are used for pre-cleaning, compatibility between washing solution and adhesive must be verified, as certain aqueous washes may affect cure and performance. It is generally not recommended for plastics, especially thermoplastic materials where stress cracking may occur, and substrate compatibility testing is advised.

For assembly, all internal and external surfaces should be cleaned with a LOCTITE cleaning solvent and allowed to dry. If the substrate is an inactive metal or cure speed is insufficient, apply LOCTITE SF 7471™ or SF 7649™ activator and allow to dry. For slip fitted assemblies, apply adhesive to the leading edge of the pin and inside of the collar, using a rotating motion during assembly for full coverage. For press fitted assemblies, apply adhesive to both bond surfaces and assemble using high press-on rates. For shrink fitted assemblies, coat adhesive onto the pin and heat the collar to create clearance before assembly. Parts should remain undisturbed until sufficient handling strength is achieved. For disassembly, localized heat of approximately 250 °C should be applied and parts separated while hot. Cured residue can be removed by soaking in LOCTITE solvent combined with mechanical abrasion such as a wire brush.

Storage should be in unopened containers kept in a dry location, ideally between 8 °C and 21 °C. Storage below 8 °C or above 28 °C may negatively affect product properties. Material removed from the container during use may become contaminated and should not be returned to the original container. Standard engineering conversions include (°C × 1.8) + 32 = °F, N/mm² × 145 = psi, MPa × 145 = psi, N/mm × 5.71 = lb/in, N × 0.225 = lb, mm ÷ 25.4 = inches, µm ÷ 25.4 = mil, kV/mm × 25.4 = V/mil, N·m × 8.851 = lb·in, N·m × 0.738 = lb·ft, N·mm × 0.142 = oz·in, and mPa·s = cP.