AIR MOVEMENT

Air movement or the lack of it, increases or decreases the affect of temperature, humidity and barometric pressure. Air movement is extremely important when applying water based paint. When the water evaporates from the paint it will hang just above the surface if there is no air movement, which prevents further evaporation. Ambient air pushed by a fan or blower, even without heat, will greatly help paint dry but especially water based paints.

TEMPERATURE

It is common knowledge that water evaporates faster as its temper-ature rises. And we know that at some point the water will boil causing all of the water molecules to transfer to a gaseous state.

oint the solvents.

RELATIVE HUMIDITY

The amount of water held in air is relative to the air temperature.  One cubic  foot of air at 94°F ( 34°C) holds twice the amount of water as air at 70°F ( 21°C). High RH is a common cause for drying complaints during he summer months. During periods of high humidity (>50% RH) adding some heat will help evaporation because warm air holds a lot more moisture than cold air.

parts need to be
clean and dry TO PAINT

There several methods to manage the drying process.

AMBIENT FLASH TIME
Drying can occur by evaporation if ambient conditions are correct - especially temperature and relative humidity. Some batch processes or slower conveyor lines provide enough flash time for drying. This practice is vulnerable to: a) seasonal fluctuation in humidity, b) constraints on product throughput, c) pockets of trapped wash solution.

AMBIENT AIR HANDLER OR FAN
Increasing the velocity of ambient air over a wet part will increase evaporation. Use a fan if the need is temporary or install a air handler if permanent. The direction, speed, volume and time of exposure will determine if this process will meet the production throughput requirement.

WARM AIR HANDLERS WITH LOW VELOCITY

If seasonality or throughput requirements are factors [See above ambient flash a) and b)], an air handler that supplies heated air maybe required. It is will accepted that warm air holds more water than cold air. Warm air in combination with velocity and volume will increase evaporation significantly.

HOT AIR HANDLER WITH HIGH VELOCITY

A drying system that delivers high velocity air is required if the parts do not drain well, have pockets that hold wash solution, or if more throughput is required. The velocity of the air is directed through nozzles or air knives to blow water out of pockets and dry the surface more quickly.

While driers are not substitutes for baking ovens, a high velocity drier with variable temperature controls may be used to force dry and partially cure some paints to a point of hardness that allows for quick handling and packing.