Chapter 5 - Environmental Testing

Question 1

Describe relative humidity.

Answer 1

It is a measure of the amount of moisture in the air compared to saturation level. Coating operations may be affected because of either too much or not enough relative humidity.

Question 2

What is the dewpoint temperature.

Answer 2

It is the temperature at which moisture begins to form on a steel surface. Temperature to which a volume of air must be cooled in order to reach saturation.

Question 3

Name some of the effects wind may have on a coating project.

Answer 3

Blowing abrasives
Causing excessive drift or overspray accelerating solvent of evaporation
contributing to the formation of dry spray

Question 4

What are some of the common errors when using an electronic hygrometer

Answer 4

Operator based and or equipment based. Operator based in accuracy examples are the reading was taken in direct sunlight the instrument was left in place too long or removed before it stabilized.
Equipment based erroneous reading are very likely due to calibration or equipment malfunction and therefore must be replaced.

Question 5

Explain the process for use of the sling psychrometer.

Answer 5

Saturate the sock with clean water.
Whirl the instrument rapidly for about 40 seconds.
Read the wetbulb temperature.

Ensure the sock is clean
Continue to sling until 3 consecutive readings are achieved

Question 6

Identify some of the defects that can be caused by incorrect application temperatures.

Answer 6

Failure to cure, too rapid solvent evaporation and poor film formation

Blistering, pin holing, cratering, dry spray and mud cracking.