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LOCTITE 638 High-Strength Retaining Compound for Shafts, Gears, Pulleys, Bushings and Sleeves
Loctite 638: High-Strength Retaining Compound for Tight Fits and Extreme Conditions
1. Product Overview
Loctite 638 is a high-strength anaerobic retaining compound designed to securely bond and seal cylindrical assemblies. Ideal for applications requiring a tight fit, Loctite 638 provides excellent performance under extreme conditions, including high temperatures and heavy loads. This product is particularly suited for use in industrial maintenance and repair, as well as enhancing the strength and reliability of mechanical assemblies.
2. Key Features
- High Strength Bonding
- Provides strong retention and sealing of cylindrical components, ensuring a durable and reliable fit.
- High-Temperature Resistance
- Maintains performance in temperatures up to 180°C (356°F), making it suitable for high-temperature environments.
- Rapid Curing
- Quick curing time minimizes downtime, allowing for faster assembly and repair processes.
- Chemical Resistance
- Excellent resistance to oils, lubricants, and other chemicals, ensuring long-term durability in challenging conditions.
- Gap Filling
- Effectively fills gaps between components, enhancing structural strength and integrity.
3. Product Specifications
- Chemical Type: Methacrylate
- Color: Green
- Viscosity: 1,000 – 2,000 mPa·s (cP)
- Cure Time: Initial cure in 10-30 minutes; full cure in 24 hours at room temperature
- Maximum Gap Filling: Up to 0.25 mm (0.010 inches)
- Operating Temperature Range: -55°C to +180°C (-67°F to +356°F)
- Shear Strength: 20 N/mm²
- Breakaway Torque: 24-34 Nm (M10 bolts)
- Prevail Torque: 10-22 Nm
- Chemical Resistance: Excellent resistance to oils, lubricants, and various chemicals
4. Applications
- Industrial Maintenance
- Ideal for securing and sealing mechanical components in machinery and equipment, particularly in high-load and high-temperature environments.
- Repair and Enhancement
- Used for repairing and reinforcing fits between cylindrical parts, improving the strength and longevity of the assembly.
- Heavy-Duty Equipment
- Suitable for applications involving heavy-duty equipment where robust and reliable bonding is required.
- Automotive Industry
- Provides reliable bonding and sealing in automotive assemblies, ensuring performance under demanding conditions.
5. How to Use
- Clean the Surfaces: Ensure surfaces are clean and free from oil, dirt, and debris to achieve optimal adhesion.
- Apply the Compound: Evenly apply Loctite 638 to the surface of one of the parts.
- Assemble the Parts: Join the parts and tighten to ensure the compound fills the gaps.
- Curing: Allow to cure for 10-30 minutes for initial set and up to 24 hours for full cure at room temperature.
LOCTITE 638 Retaining Compound Benefits
LOCTITE 638 Retaining Compound provides maximum room-temperature strength for demanding cylindrical assemblies. The ready-to-use liquid requires no resin-to-hardener mixing, simplifying manual application and automated dispensing while reducing preparation time, proportioning errors and material waste.
Its high-viscosity consistency provides controlled application and useful gap-filling capability. Henkel recommends the product for bond gaps that can approach approximately 0.25 mm, making it suitable for components with larger clearances than those normally bonded with low-viscosity retaining grades.
The formulation cures reliably on active metals such as mild steel and passive substrates such as stainless steel and plated surfaces. It also tolerates minor contamination from cutting oils, lubricants, corrosion-prevention oils and protective fluids. Thorough cleaning is still recommended when maximum consistency and strength are required.
Positive fluorescence under ultraviolet light allows production teams to inspect adhesive presence and application coverage using suitable UV equipment. This supports quality control in repetitive manufacturing and critical cylindrical assembly processes.
Applications for LOCTITE 638 Retaining Compound
LOCTITE 638 Retaining Compound is ideal for locking bushings and sleeves into housings or onto shafts. Other typical applications include retaining gears, pulleys, sprockets, bearings, collars, rotors and cylindrical components used in motors, pumps, gearboxes and industrial machinery.
The adhesive can be used for slip-fitted, press-fitted and selected shrink-fitted assemblies. By filling the microscopic spaces between mating parts, it helps distribute loads across the complete joint, improve torque transmission and reduce relative movement between components.
Its high-temperature capability and oil tolerance support applications in automotive manufacturing, power generation, fluid-handling equipment, electric motors, industrial maintenance and remanufacturing. Regional versions may also carry approvals for selected hydrogen-gas, potable-water or industrial processing applications. Buyers should confirm that the required approval applies to the specific regional packaging supplied.
LOCTITE 638 Retaining Compound Technical Properties
The uncured material is a green urethane-methacrylate liquid with a typical specific gravity of approximately 1.1 at 23°C. Published viscosity is approximately 2,500 mPa·s at 25°C, providing a high-viscosity application profile suitable for controlled beads and larger cylindrical clearances.
The official product information lists a typical fixture time of approximately four minutes. After 72 hours of curing at 23°C, published compressive shear strength is approximately 29 N/mm² on steel pins and collars, 28 N/mm² on stainless steel and 17 N/mm² on aluminum.
The listed operating-temperature range is approximately -55°C to 180°C. Laboratory testing also demonstrates resistance to motor oil, petrol, brake fluid, water-glycol mixtures, ethanol, acetone, biodiesel and diesel exhaust fluid under specified conditions. These results are typical technical values rather than guaranteed purchasing specifications.
How to Apply LOCTITE 638 Retaining Compound
Clean and degrease all internal and external bonding surfaces with a compatible LOCTITE cleaner, then allow them to dry. When passive metals, low temperatures or large clearances slow curing, apply LOCTITE SF 7649 or another approved activator and allow the solvent carrier to evaporate.
For slip fits, apply adhesive around the leading edge of the shaft and inside the female component, then assemble with a rotating motion. For press fits, apply a continuous bead to both mating surfaces and assemble at a high press-on rate. For shrink fits, coat the male component and heat the female part sufficiently to permit free assembly.
Do not disturb or load the assembly until adequate handling strength develops. High-strength cured joints may require localized heating to approximately 260°C before mechanical disassembly. Store unopened containers in a dry location, preferably between 8°C and 21°C.
Why Choose LOCTITE 638 Retaining Compound?
LOCTITE 638 Retaining Compound combines rapid fixture development, high final strength, oil tolerance, high-temperature performance and dependable curing on active and passive metals. It is a professional choice for retaining shafts, gears, pulleys, bushings, sleeves, bearings and other cylindrical components.
Review the official Henkel LOCTITE 638 Technical Data Sheet before qualification or production use. Explore our industrial retaining compounds for additional cylindrical metal bonding solutions.
