How can we get the correct water mist?
Single-Component Polyurethane Adhesives often require some extra moisture in the form of a water mist, to accelerate their cure.
Often the Adhesive Manufacturer will prescribe a percentage of water to adhesive on their datasheet.
Fortunately, there is normally a fair bit of tolerance in the adhesive to water percentage (or percentage range), which you can be thankful for when applying the adhesive and then water mist by hand.
However, if the adhesive is being machined applied, you should expect that percentage to be very close to what the Adhesive Manufacture prescribes.
Here are the things we consider when specifying a water mist system, as part of an adhesive application system.
- Tip size (airless spray tip).
- Tip Positioning.
- Distance from the Tip(s) to the application surface.
- The number of Tips and spacing between the Tips.
- And the water pressure.
Each point must be considered in relation to the other points to get the correct water mist for the application. The first 4 points in the above list are probably the most significant to getting you into the right range, and then the 5th point – the water pressure gives a small amount of adjustment and fine-tuning within that range.
When selecting the right size Tip we need to focus on the output (ml per minute), and the fan angle, the fan/coverage will widen as you get further from the Tip (Tip manufacturer will typically offer helpful information around this), this in turn will govern the number of Tips that will be needed to cover the surface width.
Often when calculating the combined output of all the tips together, the output is greater (because of some overlapping) so this needs to be considered, and in some instances, a lower output Tip considered instead.