Loctite 638 Retaining Compound 50ml

Loctite 638 is a green, one-component, high strength anaerobic retaining compound. It is a urethane methacrylate with a high viscosity, and it is fluorescent under UV light.

Henkel describes it as particularly suited to bond gaps that can approach 0.25 mm where maximum strength at room temperature is required. Typical uses include locking bushings and sleeves into housings and on shafts, on active metals and on passive surfaces such as stainless steel and plated parts.

Where this product is used

• Locking bushings and sleeves into housings and on shafts
• Cylindrical fitting parts where bond gaps can approach 0.25 mm
• Stainless steel and plated parts (passive surfaces)
• Parts with minor surface contamination from cutting, lubrication, anti-corrosion and protection fluids
• Hydrogen applications, where the GASTEC QA AR-214 requirement applies (regional approval)

Features

• High strength class
• One component, no mixing
• Cures on active metals and passive surfaces
• Tolerates minor oil contamination from cutting, lubrication and protection fluids
• 29 N/mm² compressive shear on steel after 72 hours at 23 °C
• 57 N·m breakaway torque on M10 black oxide bolts and mild steel nuts
• Conforms to GASTEC QA Approval requirement 214 (AR-214), a regional approval

Key specifications

Selecting the right option

Loctite 638 suits bond gaps that can approach 0.25 mm. For other retaining compounds see Loctite 609 Cylindrical Bonding Retaining Compound, Loctite 635 Retaining Compound, Loctite 680 High Strength Retaining Compound 50ml and Loctite 620 High Temperature Retaining Compound 50ml.

Using it

Henkel gives no fixture time. Strength is 13.5 N/mm² on steel pins and collars after 15 minutes at 23 °C, and cure rate depends on the bondline gap. Do not disturb the parts until sufficient handling strength is achieved.

Henkel states no operating temperature range. Cold strength is tested to -75 °C (it may work lower, but this is untested), and hot-strength values are not given.

To disassemble, use standard hand tools. If needed, apply local heat to about 250 °C and pull apart while hot; otherwise heat as much as practical and use mechanical aids.

Storage and handling

Store unopened in a dry location, with optimal storage at 8 °C to 21 °C. Storage below 8 °C or above 28 °C can adversely affect properties. The data sheet gives no shelf life.

Limits and safety

Not normally recommended for plastics. Not recommended for pure oxygen systems, or as a sealant for chlorine or other strong oxidising materials. The AR-214 conformity is a regional approval; confirm it suits your application. Read the safety data sheet before use.

Frequently asked questions

How strong is Loctite 638?

On steel pins and collars it reaches 29 N/mm² compressive shear after 72 hours at 23 °C (ISO 10123). On stainless steel it is 28 N/mm² and on aluminium 17 N/mm².

What gap does Loctite 638 suit?

Henkel describes it as particularly suited to bond gaps that can approach 0.25 mm, where maximum strength at room temperature is required.

How do I disassemble parts bonded with Loctite 638?

Use standard hand tools. If needed, heat locally to about 250 °C and pull apart while hot.

Is Loctite 638 hydrogen certified?

The data sheet states it conforms to GASTEC QA Approval requirement 214 (AR-214). This is a regional approval, so confirm it for your application.

What is the viscosity of Loctite 638?

2,500 mPa·s at 25 °C (Brookfield RVT, spindle 3, 20 rpm), classed as high.

What temperature can Loctite 638 take?

Henkel states no operating range. Cold strength is tested to -75 °C, and no hot-strength values are given.

Related products

See also: Loctite 609 Cylindrical Bonding Retaining Compound, Loctite 635 Retaining Compound, Loctite 680 High Strength Retaining Compound 50ml, Loctite 620 High Temperature Retaining Compound 50ml, Loctite 648 High Strength, High Temperature Retaining Compound 50ml.