Product Description

LOCTITE 638 is an anaerobic acrylic (urethane methacrylate) retaining compound manufactured by Henkel. It is designed for bonding cylindrical fitting parts, particularly where bond gaps approach 0.25 mm and maximum room-temperature strength is required. The product cures when confined between close-fitting metal surfaces in the absence of air, preventing loosening and leakage caused by shock and vibration.

LOCTITE 638 works on active metals such as mild steel, as well as passive substrates including stainless steel and plated surfaces. It offers high temperature performance and oil tolerance, tolerating minor surface contamination from cutting, lubrication, anti-corrosion, and protection fluids. Typical applications include locking bushings and sleeves into housings and onto shafts.

Product Characteristics

Typical Curing Performance

Cure rate depends on several factors. On steel pins and collars at 23°C, tested per ISO 10123, shear strength develops fastest on mild steel, followed by stainless steel, then aluminum. Smaller bond gaps also cure faster — the manufacturer's data shows a 0.05 mm gap developing strength substantially faster than 0.15 mm or 0.25 mm gaps. Higher temperatures accelerate cure: at 40°C, strength development is faster than at 22°C or 5°C. Activators (Henkel SF 7471, SF 7649, or SF 7091) further accelerate cure speed compared with no activator, particularly useful for passive substrates like stainless steel.

Storage

Store product in the unopened container in a dry location. Optimal storage temperature is 8°C to 21°C — storage below 8°C or above 28°C can adversely affect product properties. Material removed from containers may become contaminated during use; do not return product to the original container.