In our last blog, you gained insight into troubleshooting polyurethane air entrapment. This week let’s look at troubleshooting voids in urethane adhesives.
Causes of Voids
Before de-molding, there could potentially be huge voids in the part or on the surface. The voids are visible with the naked eye and they occur at thin-walled sections.
Pot Life is Too Short – Air can be trapped for a short period of time when the batch is poured into the mold and displaces the air. Air then moves to the upper surface of the part. This process can take some time, and when the pot life is too short, the air bubbles don’t have reach the surface to self-release.
Mold Leaks – When mold leaks into the adhesive a void can easily be formed within this area. This typically occurs when the system has an extended pot life or a low viscosity.
Air Entrapment – Air is displaced from the mold when the batch is poured into the mold. A void will form when the air is trapped in different cavities and there are no mechanisms to allow the air to escape. This typically occurs in thin-walled areas when the viscosity is too high.
How to Fix These Voids
Mold & Vents Should be Redesigned – Since large voids occur when there isn’t proper ventilation, a new mold design may be necessary to improve ventilation.
Utilize Low Viscosity Urethanes – Air can easily escape when a low viscosity material is used. A system with an extended pot life and lower viscosity can decrease the void formation.
Reduce Splashing – Specifically when using large rollers, it’s best to tilt the mold before filling. You can also limit the amount of splashing when you pour down the side of the mold.
Use a Degassing Agent – The surface tension of the system can be reduced when a degassing aid is used. This allows air to escape with more ease. This will significantly reduce the formation of voids when higher viscosity materials are used.
Contact Resin Designs for Urethane Adhesives & Encapsulants
Resin Designs offers a range of products for various industries including aerospace, automotive and electronics. Entex 53051 is a clear, rigid polycarbonate bonder and encapsulant. This urethane is formulated, by use of two of the methods mentioned above, to minimize void generation. This material is low in viscosity, 400-900 cps mix viscosity, and contains a degassing agent which reduces surface tension allowing trapped bubbles to escape.