LOCTITE 640 High-Strength Slow-Cure Retaining Compound for Large Shafts, Bearings and Cylindrical Parts
LOCTITE 640 High-Strength Slow-Cure Retaining Compound for Large Shafts, Bearings and Cylindrical Parts
  1. LOCTITE 640 High-Strength Slow-Cure Retaining Compound for Large Shafts, Bearings and Cylindrical Parts
  2. LOCTITE 640 High-Strength Slow-Cure Retaining Compound for Large Shafts, Bearings and Cylindrical Parts

LOCTITE 640 High-Strength Slow-Cure Retaining Compound for Large Shafts, Bearings and Cylindrical Parts

Loctite 640: Ultra-High Strength Retaining Compound for Large Diameter Fittings

1. Product Overview

Loctite 640 is an ultra-high strength anaerobic retaining compound designed to securely bond and seal large diameter cylindrical assemblies. Engineered for extreme conditions, it provides robust performance in high-temperature and heavy-load environments. Loctite 640 is ideal for industrial maintenance, repair, and enhancement of mechanical assemblies, ensuring reliable and durable connections.

2. Key Features

Ultra-High Strength Bonding

  • Provides exceptional retention and sealing for large diameter fittings, ensuring a durable and reliable mechanical connection.

High-Temperature Resistance

  • Maintains strong bonding performance in temperatures up to 180°C (356°F), suitable for high-temperature applications.

Rapid Curing

  • Features a fast-curing formula to minimize downtime and expedite assembly and repair processes.

Chemical Resistance

  • Excellent resistance to oils, lubricants, and various chemicals, ensuring durability in harsh conditions.

Gap Filling

  • Effectively fills gaps between components, enhancing the structural integrity and strength of the assembly.

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 a variety of chemicals

4. Applications

Industrial Maintenance

  • Ideal for securing and sealing large diameter cylindrical components in machinery and equipment, particularly under high-load and high-temperature conditions.

Repair and Enhancement

  • Used for repairing and reinforcing fits between large cylindrical parts, improving the strength and longevity of the assembly.

Heavy-Duty Equipment

  • Suitable for applications involving heavy-duty equipment where strong and reliable bonding is required.

Automotive Industry

  • Provides dependable bonding and sealing in automotive assemblies, ensuring performance in demanding conditions.

5. How to Use

  1. Clean the Surfaces: Ensure surfaces are clean and free from oil, dirt, and other contaminants for optimal adhesion.
  2. Apply the Compound: Evenly apply Loctite 640 to the surface of one of the components.
  3. Assemble the Parts: Join the components and tighten to ensure the compound fills the gaps.
  4. Curing: Allow to cure for 10-30 minutes for initial set and up to 24 hours for full cure at room temperature.
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LOCTITE 640 Retaining Compound is a green, one-component anaerobic adhesive developed for high-strength bonding of large-diameter cylindrical metal components. Its low-viscosity formula flows into close-fitting joints between shafts, bearings, bushings, sleeves, keys, splines and housings. The deliberately slow curing profile provides additional positioning and assembly time, making it especially suitable for large components and active metals such as brass. Once confined without air between mating metal surfaces, it cures into a durable bond that helps prevent loosening, leakage and movement caused by vibration, shock and mechanical loading.

LOCTITE 640 Retaining Compound Benefits

LOCTITE 640 Retaining Compound offers high final strength while allowing more time to position large or complicated assemblies. Fast-curing retaining compounds may begin developing fixture strength before a large shaft, bearing or sleeve has been aligned completely. The slower curing behavior of LOCTITE 640 gives operators additional time to adjust component position and complete the assembly correctly.

The one-component format requires no resin-to-hardener measuring or mixing. This simplifies manual application and automated dispensing while reducing proportioning errors, preparation time and material waste. Its low viscosity promotes effective wetting of close-fitting surfaces and helps the adhesive spread around the full circumference of the cylindrical joint.

Positive fluorescence under ultraviolet light allows production teams to confirm adhesive presence and dispensing coverage with compatible inspection equipment. This feature supports process control in repetitive manufacturing and critical rotating-equipment assembly.

LOCTITE 640 Retaining Compound Applications

LOCTITE 640 Retaining Compound is suitable for retaining keys and splines, securing bearings against spin-out, fixing rotors onto motor shafts and bonding bushings or sleeves inside housings. It can also augment press fits, eliminate backlash and restore the fit of worn or slightly out-of-tolerance cylindrical components.

Typical application environments include electric motors, pumps, gearboxes, industrial machinery, power-generation equipment, automotive systems and maintenance workshops. Its extended positioning time makes it particularly useful for large-diameter parts and assemblies made from active metals that can accelerate the curing of conventional anaerobic adhesives.

The product can be applied to slip-fitted, press-fitted and selected shrink-fitted metal assemblies. Its maximum recommended diametrical clearance is approximately 0.1 mm. Components with substantially larger gaps or severe wear may require a dedicated large-gap retaining compound.

LOCTITE 640 Retaining Compound Technical Properties

LOCTITE 640 Retaining Compound is based on urethane-methacrylate technology and appears as a green liquid before curing. It has a typical specific gravity of approximately 1.2 at 25°C and a published viscosity range of approximately 450 to 750 mPa·s.

The current Henkel product information lists a typical fixture time of approximately two hours on steel. After 24 hours of curing at 22°C, published compressive shear strength on steel pins and collars is approximately 22 N/mm². Its fully cured service-temperature range is approximately -55°C to 175°C.

Laboratory testing also demonstrates resistance to motor oil, unleaded gasoline, brake fluid, water-glycol mixtures, ethanol and acetone under specified exposure conditions. These figures are typical technical values rather than guaranteed purchasing specifications. Actual curing and bond strength depend on substrate activity, joint clearance, temperature, surface cleanliness, adhesive quantity and activator use.

How to Apply LOCTITE 640 Retaining Compound

Clean and degrease the internal and external bonding surfaces with a compatible LOCTITE cleaner and allow them to dry. When the metal is inactive or the cure speed is unacceptably slow, apply LOCTITE SF 7471 or LOCTITE SF 7649 Activator and allow the solvent carrier to evaporate.

For slip-fitted assemblies, apply adhesive around the leading edge of the shaft and inside the collar. Use a rotating motion during installation to distribute the liquid evenly. For press fits, coat both mating surfaces thoroughly and assemble the components at a high press-on rate.

For shrink fits, coat the shaft with adhesive and heat the female component until sufficient installation clearance is available. Complete the assembly without disturbing the parts until adequate handling strength develops. High-strength cured joints may require localized heating to approximately 250°C before mechanical disassembly.

Why Choose LOCTITE 640 Retaining Compound?

LOCTITE 640 Retaining Compound combines high final strength, low-viscosity wetting, extended positioning time, temperature resistance and convenient one-component processing. It is a professional solution for large shafts, bearings, keys, splines, rotors, bushings and other close-fitting cylindrical metal assemblies.

Review the official Henkel LOCTITE 640 Technical Data Sheet and current Safety Data Sheet before qualification or production use. Explore our industrial retaining compounds for additional cylindrical metal bonding solutions.

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