The wheat starch blasting process propels the media at less than a 35-psi nozzle pressure for most applications. The low pressure and relatively soft media have minimal effect on the surfaces beneath the paint. For this reason, wheat starch is well suited for stripping paints without risking damage to the substrate. Examples include removing paint from aluminum alloys and composites like graphite, fiberglass, and aramid (Kevlar™).

The wheat starch blasting process can remove a variety of coatings. Coating types range from resilient rain-erosion resistant coatings found on radomes and radar absorbing materials, to the tough polyurethane and epoxy paint systems. The wheat starch blast process has also been shown to be effective in removing vinyl coatings, sealants, and bonding adhesive flash while leaving the metal-to-metal bond primer intact. It has also been found effective in removing the paint from the cadmium-plated parts, while leaving the plating intact.

There are several process-specific requirements for wheat starch blasting systems. For instance, a moisture control system is needed to control the storage conditions of the medium. This is especially important when the system is shut down for an extended period of time, as moisture can severely affect the performance of the abrasive blast media. Another concern is the removal of blast contaminants from the wheat starch media. Low levels of dense particle contamination in the media may result in a rough surface finish on delicate substrates. To avoid this situation, spent wheat starch residue is dissolved in water and then either filtered or separated in a dense particle separator/centrifuge. The wheat starch media is recycled in the system and may be used for up to 15 to 20 cycles. The waste stream generated by wheat starch blasting is sludge from the recycling system. This system produces approximately 85% less waste sludge compared to chemical stripping.

• Wheat starch is a plentiful natural resource that is biodegradable.
• Waste generated from this process can be treated in a bioreactor.
• Waste volume requiring subsequent disposal is estimated to be only five percent of the original volume.
• The wheat starch blasting process can be used for removing coatings from both metallic and composite materials.
• This process is very controllable; it can be used to selectively remove one or more layers of coating.
• Wheat starch blasting does not cause fatigue to the substrate surface.
• Moderate stripping rates can be achieved while maintaining a gentle stripping action.
• Safe on soft-clad aluminum.
• Media is inexpensive and non-toxic.
• Reduces water use.
• Fully developed systems available.
• No size limitations on parts being stripped.

• High capital investment cost.
• Requires complex subsystems for media recovery and recycling and dust collection and control.
• Operator training required.
• Low levels of dense particle contamination in the media may result in a rough surface finish on delicate substrates.
• Waste material may require costly disposal as hazardous waste .
• Stripping rates are typically slow to moderate.
• Stripping rates are slow and inefficient as reported by WR-ALC/TIEDM.
• Operators must wear personal protective equipment.
• Media is moisture sensitive and may require an air dryer for humidity control.
• According to the Air Force Corrosion Program Office, wheat starch blasting is not considered to be a viable method of paint removal for Air Force aircraft. There may be some advantage in using this process on a limited basis to remove paint from aircraft composite or fiberglass components in an area where a very controlled environment can be assured. Due to the extreme moisture sensitivity of this process, humidity control to the extent required for very large aircraft such as the C-5 is almost impossible and not economically feasible.

The operating costs for wheat starch blasting systems have been estimated to be 50 % less than chemical paint stripping (i.e., methylene chloride).

Assumptions:

• Annual area of paints to be removed/year: 93,800 ft².
• Labor rate: $30/hr.
• Stripping rate for wheat starch blasting: 15 ft²/hr.
• Stripping rate for chemical stripping: 25 ft²/hr.
• Chemical procurement cost: $11.40/gal.
• Chemical stripping efficacy: 15.84 ft²/ gallon
• Media usage rate: 1 lb/ft².
• Wheat starch media cost: $1.70/lb.
• Hazardous waste generation rate: wheat starch blasting = 1.07 lbs/ft².
• Hazardous waste generation rate: chemical stripping = 5.52 lbs/ft²; this is based on a stripper requirement of 5,922 gal./yr. which is derived from the 15.84 ft²/gal rate and assuming about 1/3 remains after solvent evaporation, rinse water required is about 10 times the amount of stripper, the density of the stripper residue approaches 8.34 lbs./gal. (the density of water), and the weight of the primer and paint residue is about 6,998 lbs./yr. which is derived from the knowledge that a 17,424 ft² C-141B aircraft with two overcoats has about 1,300 lbs. of primer and paint on it.
• Hazardous waste disposal cost: $2/lb.

Annual Operating Cost Comparison for Wheat Starch Blasting and Chemical Stripping

Economic Analysis Summary

Annual Savings for Wheat Starch Blasting: $667,827
Capital Cost for Diversion Equipment/Process: $12,500,000
Payback Period for Investment in Equipment/Process: 18.7 years

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