Product Overview
LOCTITE 640 is a one-component, low-viscosity anaerobic retaining compound formulated for bonding cylindrical fitting parts—especially when longer assembly or alignment time is required (such as large diameter components or active metals like brass). It cures when confined between metal surfaces and excludes air, forming a strong bond that resists loosening, vibration and leakage. The product supports diametrical clearances up to approximately 0.10 mm and delivers high strength with good temperature resistance.
Key Features & Benefits
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Low viscosity for easy penetration into tight fits and large-bore assemblies.
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High strength—shear strength on steel around ~22 N/mm².
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Extended fixture/positioning time (~2 hours typical on steel) for large parts.
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Suitable for active metals (e.g., brass) and complex assemblies.
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Good temperature resistance—service range approximately –55 °C to +175 °C (–67 °F to +347 °F).
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UV fluorescing for inspection of correct application.
Application
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Surface Preparation: Ensure all mating metal surfaces are free from heavy contaminants, oils, and loose debris.
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Application: Apply LOCTITE 640 to the cylindrical surface, shaft or bore. Because of the long fixture time, you can assemble large components or align before bonding sets.
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Assembly: Fit the parts together, ensuring proper alignment and confinement of the adhesive between surfaces.
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Curing: The product cures in the absence of air; allow adequate time before subjecting the assembly to load. The long fixture time supports large assemblies and active metals.
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Disassembly / Repair: Where necessary, parts can be separated by applying heat or using mechanised tools. Always follow Henkel’s guidelines for safe disassembly.
Tips & Warnings:
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Do not exceed the recommended clearance for optimal strength.
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Ensure assembly remains clamped or supported during initial curing.
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For best performance on passive or plated metals, consult for potential activator use.
FAQs – LOCTITE 640
Q1: What makes LOCTITE 640 different from quicker curing retainers like 638?
A1: LOCTITE 640 offers a deliberately slower fixture time (~2 hours) which is beneficial for larger diameter components or those requiring longer positioning before cure.
Q2: Can it be used on brass or other active metals without primer?
A2: Yes, it is suitable for active metals such as brass and designed for assemblies needing longer set-up times.
Q3: What is the maximum gap it fills?
A3: Roughly up to 0.10 mm for recommended strength and performance.
Q4: What temperature range can it handle?
A4: It operates effectively from approximately –55 °C to +175 °C (–67 °F to +347 °F).
