LOCTITE® 638 High Strength Retaining Compound

Features and Benefits

Designed for bonding cylindrical fitting parts, particularly with narrow bond gaps up to 0.25mm (0.01"). Great for a fast cure on all metals, including passive substrates like stainless steel.
For a retaining compound offering high strength on all metals, including passive substrates, try LOCTITE® 638. You can expect high temperature performance and good oil tolerance, a fixture time of just four minutes, and gap fill of 0.15 mm to 0.25 mm (0.006" to 0.01"). It even tolerates minor surface contaminants, including industrial oils. A high viscosity product, it’s ideal for shafts, gears, pulleys, and similar cylindrical parts, and can also be used for high strength threadlocking and thread sealing applications. Operating temperature is-55°C to 180°C (-65°F to 355°F). LOCTITE 638 meets the performance requirements of KIWA GASTEC QA AR 214 for admixtures up to and including 100% hydrogen gas on metal threaded fittings – certifications are available in select countries.
  • Ideal for shafts, gears, pulleys and similar cylindrical parts
  • High strength on all metals, including passive substrates (e.g. stainless steel)
  • High temperature resistance
  • Fluorescent under UV for quality control
  • Hydrogen gas approval for sealing threaded metal fittings according to KIWA GASTEC QA AR 214
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Technical Information

Agency approvals / certificates / specifications DVGW (EN 751-1): NG-5146AR0619, NSF P1 Reg. No 123010, WRAS (BS 6920): 0511518
Application method Dispense system, Manual
Applications For close fitting cylindrical parts, For slip fitted parts, Retaining
Color Green
Cure type Anaerobic cure
Fixture time 4.0 min.
Gap fill 0.15 - 0.25 mm
Key characteristics Fluorescent, Oil tolerant, Strength: high strength, Temperature resistant, Viscosity: high viscosity
Operating temperature -55.0 - 180.0 °C (-65.0 - 355.0 °F )
Physical form Liquid
Recommended for use with Metal: steel
Shear strength, Steel 31.0 N/mm² (4500.0 psi )
Viscosity 2500.0 mPa·s (cP)

How to

Step by Step Guide

1. Preparation - Cleaning

Use LOCTITE® SF 7200 or LOCTITE® SF 790 to remove any old adhesive from parts. Use LOCTITE® SF 7063, SF 7064 or SF 7070 to degrease and clean surfaces prior to applying adhesive. For gaps larger than 0.5mm or worn out shafts, bearing seats or keyways, use LOCTITE® metal-filled compounds to rebuild the surfaces.

2. Preparation - Activation

If cure speed is too slow due to passive metals or low temperature (below 5°C), use activator LOCTITE® 7240 or LOCTITE® 7649 (see cure speed vs activator graph in the TDS). Allow to dry.

3a. Application - For Slip-Fitted Assemblies

Apply adhesive around the leading edge of the male component and the inside of the female component and use a rotating motion during assembly to ensure good coverage.

3b. Application - For Press-Fitted Assemblies

Apply adhesive thoroughly to both bond surfaces and assemble at high press on rates.

3c. Application - For Shrink-Fitted Assemblies

Apply the adhesive onto the shaft; heat the collar to create enough clearance for free assembly.

4. Disassembly

Apply localized heat to approximately 500°F/260°C; disassemble while hot. For corroded or seized parts, use LOCTITE® 8040 Freeze and Release.

Equipment

For manual assembly of adhesive the use of LOCTITE® Pro Pump or LOCTITE® Peristaltic Hand Pump is recommended to ensure a consistent application volume. For semi-automatic or fully-automated dispensing options contact our technical service team for advice.

Frequently Asked Questions