When San Joaquin Helicopters needed to improve the process for stripping and cleaning aircraft components and parts, the company turned to a baking soda-based abrasive. The abrasive has allowed the FAA-certified repair station to cut cleaning time by 50% or more, while also providing a substantial reduction in material costs and hazardous waste.

Baking soda crystals magnified.

San Joaquin Helicopters is an FAA-certified repair station in Delano, CA, that offers services for contracted helicopter maintenance. In 2005, Steve Randalls, director of maintenance, and Larry Bynum, component overhaul shop manager for the company, were trying to improve the process for stripping and cleaning aircraft components and parts. The challenge was to remove a polyurethane paint from a magnesium part without removing the chromate conversion coating. The process being used at the time was ineffective and time consuming. It consisted of putting parts in a paint stripping system for 16 to 18 hours, followed by a pressure washer rinse to remove the paint, which took another 15 minutes. Unfortunately, the stripper also removed the magnesium film treatment, and a new conversion coating had to be applied.

This chemical removal process also required that the solid wastes be pumped to a holding vessel to remove the sludge, and then the hazardous sludge had to be manifested and hauled away several times a week. Randalls was investigating options on the Internet when he came across a website explaining the benefits of using a baking soda-based abrasive for cleaning and depainting. Soon Randalls was in touch with a local California distributor representative, Bob Strohmeier of International Surface Preparation, who would demonstrate the process for him.

A dirty, corroded magnesium part before stripping.

A Carefully Engineered System

Initial tests showed that ARMEX® baking soda-based blast media manufactured by Church & Dwight Co., Inc., makers of ARM & HAMMER® products was effective in removing the paint and leaving the chromate conversion coating intact. The tests provided an early and obvious indication that the baking soda-based stripping process was going to eliminate costs and save time. But there was more work to be done. The team moved on to specify the necessary equipment and utilities to run the system.

There are a number of differences between stripping with a baking soda-based abrasive and a more conventional, harder grit, like plastic or glass beads. The baking soda particle is very soft, having a Mohs hardness of only 2.5. It is also extremely friable, so that upon impact the particle shatters completely, releasing all its energy on the surface. As the particle breaks apart, the smaller particles work to shear off the coating. The benefit inherent in this action is that it has a minimal impact on the surface material - in this case, the chromate coating. Baking soda-based abrasives can be used to strip in layers; they will not pit or peen a surface, nor will they cause crack closure. However, this breakdown of the particle and resulting dust can cause a whiteout in some glove box units, making it difficult to see the workpiece. A system engineered specifically for soda is required to ensure good visibility.

For San Joaquin Helicopters, Strohmeier recommended a BioBlast DBS 4848 - a fully contained glove box blast unit specifically designed to handle soda. The system drops more than 95% of the waste directly into a drum for easy disposal and sends only very fine particulate to the dust collector. Baking soda is a one-pass media, meaning it cannot be recycled.* The elimination of a recycling mechanism is a unique distinction of a soda blasting cabinet.

The blast unit was equipped with an Accustrip System Model 11SX with a Thompson Media Valve, using either a #4 ARMEX performance nozzle or fan nozzle, depending on the part, and operating at about 30 psi. A 50-hp compressor was sufficient to do the job, and an air dryer was included on the compressor to ensure the best quality air to run the system, which operates an average of 8 hours a day. A silencer was added to the dust collector to minimize noise.

ARMEX Maintenance Formula XL was chosen for this job because it contains a moderate flow aid and the largest particles available, making it good for penetrating painted surfaces.

The same magnesium part after stripping and cleaning with the baking soda-based blast media.

Successful Stripping

Overall, the new process is a success on many levels. There is no longer a bottleneck waiting for the parts to soak in a chemical.

“We’ve cut the cleaning time in half for most jobs and by 10 to 15% more on others. As for the hazardous waste issue, there is a related savings of about 60 to 70% in cost for the material, and we cut our waste stripper removal by more than two-thirds,” said Randalls.

In addition, the operators are no longer required to wear protective clothing and air-fed hoods because the media is benign and the whole process is contained.

San Joaquin has completely transitioned to the new process and has committed to a long-term overhaul project that it now can be assured of doing efficiently, safely and profitably.

For more information about baking soda-based abrasives, call 800.332.5424 or visit www.armex.com.

*Baking soda is environmentally benign and can be landfilled as a nonhazardous industrial waste. Some users choose to put it through their wastewater treatment system, as it is 100% water soluble and can act as a buffer, reducing the need for additional waste treatment chemicals.