Compressed Air Blotter Test for Rubber Lining and Painting


Compressed Air Blotter Test

What is it checking for?

The background behind this specification, which is becoming more and more prevalent in engineering documentation, has to do with the presence of oil and water in the air stream. As you can imagine having oil sprayed onto a surface prior to painting would be terrible. It would immediately create fish eyes, lack of adhesion and all types of terrible things for the paint. Water  is just as bad as flash rusting can occur.

Rubber and hydrocarbons for the most part don’t get along. So the presence of oil on a surface will definitely have a negative impact on the adhesion and longevity of rubber on a steel sub straight.

Why would water be in the air line?

Humidity (water molecules suspended in the air) is found in the air all around us. When compressed the moisture forms into water. Most compressors are equipped with a water separator. But water separators are not all created equal. Based on the volume of blasting or painting, your air water separator may not be able to process the volume of water. Winter is a good gauge of if your water air separator is working for your setup. If your lines freeze in winter yours is not adequate for your work load.

Why would oil be in the air line in the first place?

Not all compressors are made the same. Piston compressors are more prone to oil in the air than screw compressors. Although all compressor designs offer various risk to oil in the air lines, there are many inline solution to capturing any residual oil left  in the air.

How is the testing done?

You can use a 4″ X 4″ clean cotton cloth. Spray for a duration of  1-5 minutes and look to see if you any oil or water. This only needs to be done once per shift as objective evidence for your client if required. Otherwise it’s good practice to monitor your compressor air as well as you oil separation for long term performance issues.

For the exact specification the standard would be according to ASTM D 4285

The net result of good clean air! 

A clean well blasted metal with no surface impurities will enable you to create a perfect adhesive bond that will ensure a rubber coating will last forever.

Good process equals good results…