Application Tips – Sealants
Sealants come in a wide variety of chemical base,however the three most common industrial sealants are
Silicones Polyurethane MS Polymer/Modified Silanes All are single component sealants that cure when exposed to moisture.Curing rate depends on humidity,environmental and substrate temperature and thickness of sealant. However,they differ in their final physical properties achieved after full curing such as temperature resistance,Weaterability,Surface Preparation required and paintaibility etc. One must choose based on the final properties desired.
Since sealants can fill large gaps upto 6mm, surface flatness and finish are not very critical.Instead clean surface becomes an important aspect to be considered for optimum performance.
Sealants seal by adhesion and not compression,hence surface preparation is very important for their successful performance. Ensure surface is dry,clean and free from any foreign particles by cleaning with a solvent based cleaner.
2-3mm seal provides best curing and final properties.
Curing of sealants (Silicones, Polyurethanes and MS Polymers) depend on two key factors, presence of humidity and bond line thickness. If humidity in the environment is low, sealant will cure very slowly.It is recommended to us a humidity oven/chamber to expose maximum moisture. In case of complex design or enclosed chamber where direct exposure of moisture is prevented, curing can get affected. A humidity chamber can help. Because sealants cure in presence of moisture,thicker beads take time to cure.Top 2mm layer can cure in roughly 24hours,subsequently every 1mm thickness takes anywhere around 24hours. Thus sealants forming more than 2.5mm thickness will take time to cure and must be considered appropriately for a high speed production line.
Most sealants can be dissolved using Loxeal CR5 cleaner that also works very well on modified epoxy adhesives.
Dispenser choice depends on the viscosity of the product. A higher viscosity will need dispenser with high advantage ratio (typically 18:1 or more) and lower viscosity can be handled with dispensers of lower advantage ratio (12:1 or less).