Stripping Aircraft Paint With Starch

Hazardous waste disposal is the chief lacuna associated with the traditional methylene chloride based aircraft de-painting process. The EPA (Environmental Protection Agency) has banned it citing damage to operators and the environment. Aircraft maintenance units have therefore turned to environment-friendly processes of removing paint from aircraft surfaces.

One such method involves the use of crystallized corn starch acrylic polymer for stripping paint off aircraft surfaces. It is an abrasive, biodegradable, environment-friendly, and renewable medium. Wheat based starch was used earlier, but humidity affected it and its performance was not as good as the corn starch.

Compressed air propelled corn starch polymer dry spray is used in a light blasting machine in this PMB (plastic media blasting) process. The pressure of compressed air used to propel the starch spray varies between 30 to 40 pounds per square inch. Pressure in this range has been proved to be the most optimal.

It (as well as the hardness of the starch acrylic polymer) is high enough to make the starch particles to impinge with enough force on the aluminum paint-coated surface of aircraft and strip the paint from it. Both of these are at the same time low enough to prevent damage to the aircraft's aluminum layer under the top paint coat.

The above PMB process is akin to the sand blasting process used to clean metallic components. The entire paint stripping operation is conducted in an open blast room or closed big cabinet. The starch media is stored in the blast machine. Compressive air is injected into the blast machine from top. A blast hose is connected to the machine at its bottom at the end of which is a nozzle.

The painted aluminum aircraft sheets are carefully and properly cleaned of dust and carefully prepared by covering all unpainted surfaces. The thin painted ones among them ones are backed up to prevent damage to substrata. They are then kept in the blast room or cabinet.

The blast operator wears all protective gear including a mask and then operates the media valve in the blast machine. This causes the starch to flow out from the nozzle with the force imparted to it by the compressed air. The flow is directed at the painted surface with the nozzle at a specific angle to achieve a high paint stripping rate, but also to avoid damage to substrata.

At low nozzle inclination, the starch impinging force on the painted aluminum surface is low, so the paint stripping rate is also low. At high nozzle angles, the paint stripping rate is high, but so is the potential for damage to the substrata. The optimum nozzle angle is 45 to 50 degrees, but using slightly lower angles helps in avoiding substrata damage.

The substrata and the paint coating thickness, hardness, and adhesion properties also play a big role in the stripping. Moreover, other factors such as mass flow of starch particles and nozzle diameter also affect the effectiveness of the paint stripping. Computerized control of all the above factors goes a long way in ensuring economically viable paint stripping rates from aircraft.
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