When it comes to industrial adhesives, choosing the right one is crucial for optimal performance and safety.
Loctite 620 and Loctite 638 are two high-performing adhesives widely recognized for their strength and reliability in engineering and manufacturing.
This article offers an in-depth comparison between these two products, providing insights into their unique features, differences, and applications, helping you decide on your specific bonding needs.
What is Loctite 620?
Loctite 620 is a retaining compound designed to bond cylindrical fitting parts. It’s formulated to provide robust and durable bonds, especially in assemblies where disassembly is not intended.
With a high-temperature resistance of up to 200°C, Loctite 620 excels in environments that experience thermal cycling. Its viscosity is relatively high, which makes it ideal for applications requiring a thicker adhesive layer.
This product is also known for filling diametrical gaps up to 0.15 mm, enhancing the load transmission and uniform stress distribution across the bonded area. Its green color aids in application visibility.
Commonly used in fitting bushings, bearings, and oil seals, Loctite 620 is a go-to for permanent, high-strength bonding.
What is Loctite 638?
Loctite 638, another powerhouse in the retaining compound category, is engineered for the same purpose as Loctite 620 but with some distinctive features.
It is primarily designed to bond cylindrical fitting parts where maximum strength is required. Loctite 638 is characterized by its lower viscosity than 620, making it more fluid and accessible to apply in thin layers.
It can fill gaps up to 0.25 mm, providing excellent adhesion even in slightly larger voids. This product also boasts high-temperature resistance, though somewhat lower than 620, at up to 180°C.
Its green color and rapid curing time make it a preferred choice for fast-paced environments where time and strength are of the essence. Loctite 638 is often utilized in securing gears, rotors, and press fits.
How are they different?
Viscosity
• Loctite 620: This adhesive has a higher viscosity, meaning it’s thicker and suitable for applications requiring a more substantial adhesive layer. It’s beneficial for more significant gaps and when the adhesive needs to stay in place before curing.
• Loctite 638: In contrast, Loctite 638 has a lower viscosity, making it more fluid and suitable for thinner adhesive layers. This property makes it easier to apply in tight spaces or where a sleek bond line is needed.
Gap Filling Capacity
Loctite 620: Capable of filling gaps up to 0.15 mm, Loctite 620 is adept at bonding parts with minimal clearance. Its gap-filling ability ensures strong adhesion and uniform stress distribution.
Loctite 638: With a gap-filling capacity of up to 0.25 mm, Loctite 638 can handle larger voids between components, making it versatile for a broader range of applications with more significant gaps.
Temperature Resistance
Loctite 620: It boasts a higher temperature resistance of up to 200°C, making it more suitable for applications exposed to higher temperatures or thermal cycling.
Loctite 638: While still resistant to high temperatures, 638’s limit is around 180°C, slightly lower than 620, making it more suitable for environments with moderately elevated temperatures.
How are they similar?
Primary Use
Both Loctite 620 and 638 are designed to bond cylindrical fitting parts. They are used in applications where a strong, permanent bond is essential, such as securing bearings, bushings, and cylindrical parts.
Chemical Composition
Both products are anaerobic adhesives, meaning they cure in the absence of air and the presence of metal ions. This property makes them ideal for metal-to-metal bonding applications.
Color and Application Visibility
The green color of both Loctite 620 and 638 ensures easy visual identification during application, which is beneficial for quality control in manufacturing processes.
High Strength and Durability
Both adhesives offer high strength and durability, ensuring the bonded parts remain secure even under stress or vibration. They are reliable choices for applications demanding high bond strength.
What’s better about Loctite 620?
Loctite 620’s higher viscosity makes it more suitable for applications requiring a thicker adhesive layer, providing better control during application and reducing the likelihood of adhesive flow on vertical surfaces.
Its ability to withstand temperatures up to 200°C gives it an edge in environments with extreme thermal variations. The 0.15 mm gap-filling capacity, while less than that of 638, is ideal for precision applications where tighter tolerances are necessary.
Furthermore, the high strength of Loctite 620 ensures reliable bonding in heavy-duty applications. It’s particularly effective in scenarios where disassembly is not planned, ensuring long-term durability and stability of the bonded components.
What’s better about Loctite 638?
Due to its lower viscosity, Loctite 638 excels in versatility and ease of application. This property makes it an excellent choice for applications where ease of application and quick flow into narrow spaces are crucial.
Its ability to fill gaps up to 0.25 mm allows it to be used in a broader range of applications, particularly where there’s a slightly larger clearance between parts.
Loctite 638’s rapid curing time is a significant advantage in fast-paced industrial environments where production speed is critical.
Additionally, its slightly lower temperature resistance still makes it suitable for most industrial applications, balancing performance and versatility.
Who should get Loctite 620 (and why)?
Loctite 620 is ideal for engineers and technicians working in high-temperature environments or requiring a thicker adhesive layer for gap filling.
It’s particularly well-suited for automotive, aerospace, and heavy machinery applications, where components are subject to extreme temperatures and require a durable, long-lasting bond.
Additionally, its higher viscosity makes it a preferred choice for vertical or overhead applications where adhesive flow needs to be controlled.
Loctite 620 is the go-to adhesive for scenarios demanding high precision and reliability, especially in permanent assembly processes.
Who should get Loctite 638 (and why)?
Loctite 638 is the adhesive for applications requiring fast, efficient bonding with easy application. Its lower viscosity and ability to fill more significant gaps make it suitable for various industrial and manufacturing processes.
It’s particularly advantageous in electronics, general manufacturing, and maintenance, where rapid assembly and versatility are key.
Loctite 638’s rapid curing time significantly benefits production lines by prioritizing speed without compromising bond strength.
This adhesive is ideal for professionals seeking a reliable, easy-to-use solution for everyday bonding challenges in dynamic industrial environments.