Glues II - Sticky Situations: Challenges (and Fixes) When Designing for Liquid Adhesives
Many designers instinctively avoid liquid adhesive, as we mentioned in Part I of this article (Glues I - The Sticky Truth About Adhesives). At Globex, we are not afraid to use liquid adhesive when the product requirements demand it – and we have proven experience of getting it right first time. Let’s break down some common pitfalls and how you can avoid them.
The Big Challenges (and Fixes) of Using Adhesives
1. Thermal Expansion Mismatch
The Issue: Dissimilar materials expand and contract at different rates, creating stress on the glue layer.
Real-World Example: An epoxy bond between aluminium and polycarbonate failed in freezing conditions due to mismatched expansion rates.
The Fix: Use flexible adhesives like polyurethane for materials with different thermal behaviours, and test them under real-world temperature swings. Using the same material, or similar materials, on each side of the glue joint is advised - and may affect where you choose to place the glue joint in your design.
2. Material Bonding Compatibility
The Issue: Not all glues stick to every material—some combinations just do not play well together. The likes of acetal, polyethylene and polypropylene are very difficult to bond to.
Real-World Example: Cyanoacrylate failed to bond a silicone gasket to a steel housing.
The Fix: Match the adhesive to the material. For silicone, silicone-based adhesives are your go-to; other plastics and metals require different adhesives. When making your initial material selections for your product design, you should consider whether there is even a remote chance of needing to glue it together, and select materials accordingly.
3. Application Problems
The Issue: Inconsistent glue application can lead to weak bonds, excess waste, or production delays.
Real-World Example: Manual application caused uneven glue beads, leading to leaks and a spike in defective products.
The Fix: Automate the application process for consistency if volumes are high enough, or use jigs and fixtures to guide manual efforts in lower volume. Semi-automated tools (manually held applicators with automated dispensing rates) can lead to significant improvements in terms of product quality and failure rates.
4. Environmental Sensitivity
The Issue: Some adhesives, like cyanoacrylates, react to humidity, which can ruin production or weaken the bond.
Real-World Example: High humidity in a factory in Malaysia caused cyanoacrylate to cure prematurely, jamming the dispensers.
The Fix: Use humidity-tolerant adhesives or adjust the production environment with dehumidifiers.
5. Testing and Quality Control
The Issue: Skipping thorough testing is an express route to field failures.
Real-World Example: Solar panel mounts fell apart under UV exposure because UV testing was overlooked.
The Fix: Don’t trust datasheets alone—they’re a guide, not a guarantee. Test adhesives under real-world conditions, including temperature swings, UV exposure, and mechanical loads. Simulate the extremes your product will face to ensure the adhesive performs when it counts. It is always cheaper (in direct costs and in reputational damage) to find issues before your customers do.
6. Applicator Maintenance
The Issue: Adhesive applicator mishaps can mean lost time, rework, and higher costs. It is very difficult to rework product that has is partially glued together, but not fully sealed or structurally bonded.
Real-World Example: Clogged dispensers on a hot-melt adhesive line caused production delays and wasted materials.
The Fix: Invest in proper maintenance and automation to minimize downtime.
Wrapping It Up
Globex has been around for 21 years, and our designers have well over 100 years of engineering experience combined. These six issues are the most common we’ve seen in that time, but there’s a host of other tips and tricks we’ve learned over many product development projects.
We can help you make the right design choices at the early stage, or help debug production problems, to get your project back on track. If your project is at risk of coming un-stuck, let’s chat!