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Why Does Epoxy AB Glue Crack? Causes, Mechanisms, and Solutions

Learn why epoxy AB glue cracks during or after curing. Discover common causes such as thermal stress, air bubbles, improper mixing, and effective solutions to improve epoxy adhesive performance.

11-06-26

Why Does Epoxy AB Glue Crack? Causes, Mechanisms, and Solutions

Epoxy AB glue is widely used in electronics, automotive, construction, and industrial bonding because of its high strength and chemical resistance. It is a two-component system: Part A contains epoxy resin, fillers, and additives, while Part B is the curing agent, typically amine- or anhydride-based.

Although epoxy adhesives form hard and durable thermoset materials after curing, users sometimes encounter cracking during or after curing. Understanding the root causes can help improve product performance and reduce failure rates.

1. The Chemistry Behind Epoxy AB Glue

When Part A and Part B are mixed, the epoxy groups react with the active groups in the curing agent to form a highly crosslinked polymer network. This crosslinking gives epoxy its excellent mechanical strength and chemical resistance.

However, the same high crosslink density can also make the material relatively brittle. The higher the epoxy value and crosslink density, the stronger but less flexible the cured adhesive becomes.

2. Main Reasons Why Epoxy AB Glue Cracks

A. High Brittleness After Curing

Cured epoxy is a thermoset material with high hardness. If the formulation has excessive crosslink density, the adhesive loses flexibility and becomes prone to cracking under stress, vibration, or thermal expansion.

B. Thermal Stress from Temperature Changes

Epoxy and the bonded materials often have different coefficients of thermal expansion. Repeated heating and cooling cycles create internal stress, which can lead to microcracks and eventually visible cracking.

This is especially common in:

Electronics encapsulation
Outdoor applications
High-temperature environments

C. Gas Bubbles and Voids During Curing

Many epoxy systems cure through addition-condensation reactions. During curing, by-products such as methanol, ammonia, or other gases may be generated. If the process is not well controlled, bubbles become trapped inside the adhesive.

These voids significantly reduce mechanical strength and act as stress concentration points, making the cured epoxy much more likely to crack under thermal or mechanical load.

D. Improper Mixing Ratio or Poor Dispersion

Incorrect A/B ratios or insufficient mixing can leave unreacted resin or curing agent in the adhesive. This creates uneven curing, weak spots, and internal stress, all of which increase the risk of cracking.

E. Excessive Cure Temperature or Fast Reaction

Some anhydride curing systems require high curing temperatures and long cure times. If the reaction proceeds too quickly or the temperature is too high, shrinkage stress can build up rapidly, leading to cracks.

3. How to Prevent Cracking in Epoxy AB Glue

Here are practical methods to improve reliability:

Optimize the Formulation

Control the epoxy value and crosslink density.
Choose curing agents that provide a balance between strength and flexibility.
Add suitable toughening agents or flexibilizers.

Reduce Bubbles and Voids

Mix Part A and Part B thoroughly and uniformly.
Degas the mixture under vacuum when possible.
Dispense slowly to avoid entraining air.

Control the Curing Process

Follow the recommended curing temperature and time.
Avoid excessive heat buildup in thick sections.
Use staged curing for large-volume encapsulation.

Improve Process Consistency

Use precise metering and mixing equipment.
Maintain consistent environmental conditions (temperature and humidity).
Ensure proper surface preparation of bonded parts.

4. The Role of Professional Dispensing Equipment

Accurate dispensing and mixing are critical for preventing cracking. Professional two-component dispensing systems can:

Maintain precise A/B ratios
Ensure uniform mixing
Reduce trapped air
Improve production consistency and yield

WEFILL TECH specializes in:

Two-component dispensing machines
Single-component dispensing machines
Two-component adhesive filling equipment
Single-component adhesive filling equipment

Our core focus is stable, reliable production performance for industrial adhesive applications.

Conclusion

Epoxy AB glue cracks mainly because of high brittleness, thermal stress, trapped bubbles, improper mixing, and uncontrolled curing conditions. By optimizing the formulation, reducing voids, and using precise dispensing equipment, manufacturers can significantly improve the durability and reliability of cured epoxy products.

Interested in Improving Your Epoxy Dispensing Process?

WEFILL TECH provides professional dispensing and filling solutions for epoxy and other industrial adhesives.

Website

https://www.wefilltech.com

info@wefilltech.com

We welcome you to visit, test our machines, and discuss your production needs.

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