Loctite 638: High-Strength Shaft-Hub Connection in Detail

LOCTITE 638 is an anaerobically curing adhesive for joining cylindrical metal components, such as shafts, bushings, and sleeves. Henkel specifies a joining gap of up to approximately 0.25 mm. We will check its suitability for your design and current availability upon request.

View LOCTITE 638 in the shop. Request a quote for LOCTITE 638.

Technical basis: Henkel data sheet, May 2024.The values ​​contained therein are typical test results and not a design guarantee.

Technical Data

Operating principle: Anaerobic curing

LOCTITE 638 cures anaerobically . Henkel describes the curing process as occurring between closely fitting metal surfaces in the absence of air.

Curing conditions:

• Air Exclusion: The adhesive must be enclosed between two closely fitting metal surfaces
• Metal contact: Active metals (steel, copper, brass) catalyze curing directly
• Passive metals: According to Henkel, LOCTITE 638 also hardens on stainless steel and coated surfaces. An activator can accelerate the curing process.
• Temperature: The curing time is temperature-dependent. Henkel's test data refers to defined temperatures.

Curing depends on the substrate, the joint gap, and the temperature. Henkel shows the development of the strength in the technical data sheet. For your application, the values ​​should be checked on the actual component.

Applications

Shaft-hub connections

The main application of Loctite 638: cylindrical joints between shaft and hub (gear, pulley, flywheel, coupling hub).

Whether LOCTITE 638 can supplement or replace an interference fit depends on the design and the load case. The specific connection must be technically verified.

Bearing Retaining

Securing rolling bearings in the housing (bearing seat) or on the shaft. The adhesive prevents migration and micro-movement of the bearing ring under vibration load.

Typical bearing seat applications:

• Electric motors: Securing bearing outer and inner rings
• Gearboxes: Securing bearings on input and output shafts
• Pumps: Fixing bearing housings under vibration load
• Fans: Securing against axial migration

Bonding of bushings and sleeves

• Secure plain bearing bushings in housing bores
• Fix spacer sleeves and spacer rings
• Repair of worn fits (tolerance compensation up to 0.25 mm)

Other cylindrical joints

• Rotor on shaft (electric motors)
• Encoders/sensors on shaft ends
• Thread inserts in light metal housings
• Pins and bolts in bores

Processing: Step by Step

1. Surface preparation

• For best results, clean all joining surfaces with a cleaner recommended by Henkel and allow to dry
• Select pretreatment according to manufacturer's instructions and material condition
• Remove rust and loose particles (abrasive fleece or wire brush)
• Activator if required: To accelerate curing, an activator provided by Henkel can be used according to the manufacturer's instructions.

2. Apply adhesive

• For sliding seats, apply the adhesive to the front edge of the outer part and to the inside of the counterpart, as Henkel describes
• For shafts: Apply in a ring around the fitting surface
• For bore: Distribute in the bore or wet the shaft
• Select the product quantity according to the manufacturer's instructions and ensure complete wetting of the bonding surfaces

3. Joining

• Assemble the components according to the intended joining method
• Slight rotational movement during assembly promotes distribution
• Wipe off excess adhesive at the joint exit points
• Align components and do not move them until sufficient handling strength is achieved

4. Curing

Do not move the parts until sufficient handling strength is achieved. The curing time depends on the substrate, the joint gap, and the temperature. The current Henkel specifications and testing on your specific joint are authoritative.

Disassembly: Loosening Shaft-Hub Connections

Despite high strength, joints bonded with Loctite 638 can be released:

• Thermally: Henkel suggests local heating to approximately 250 °C if necessary, followed by disassembly while warm. Suitability for the components must be verified.
• Mechanical: Henkel specifies standard tools for disassembly. If necessary, local heating can also be applied.

LOCTITE 638 and alternatives

The selection of an adhesive depends on the materials, the joint gap, the temperature, and the load. For other products, we compare the current manufacturer's data sheets with your requirements before recommending an alternative.

Discuss alternatives or applications

Frequently Asked Questions (FAQ)

Does Loctite 638 work on stainless steel?

Yes. Henkel explicitly lists stainless steel as a suitable substrate for LOCTITE 638. An activator can accelerate the curing process. The required handling strength should be tested on the specific joint.

Can I repair a worn fit with Loctite 638?

Henkel specifies joint gaps of up to approximately 0.25 mm for LOCTITE 638. For larger gaps, a product designed for this purpose should be selected based on the current manufacturer's data sheet.

How do I release a connection secured with Loctite 638?

Henkel specifies standard tools and, if necessary, local heating to approximately 250 °C followed by disassembly while still warm. The temperature limits of the components must be taken into account.

What is the difference between Loctite 638 and Loctite 243?

Henkel offers LOCTITE 243 as a medium-strength threadlocker for threaded connections and LOCTITE 638 as a high-strength adhesive for cylindrical connections. Both products cure anaerobically but have different applications. This information is based on the Henkel LOCTITE 243 datasheet and the LOCTITE 638 datasheet linked above.

Can I use Loctite 638 for threaded connections?

Henkel offers LOCTITE 638 as an adhesive for cylindrical parts. For threaded connections, a suitable threadlocker should be selected based on the specific requirements.