Baking Soda Solves Coating Build-Up Problem

Article From: Products Finishing, , from Church & Dwight Co., Inc.

Posted on: 6/1/1996

More than 1,700 carriers are cleaned quarterly without interrupting production...

Completing a coating removal project poses many challenges: time constraints, environmental and safety concerns, regulatory compliance and increasing labor costs are just a few. Some companies, however, are finding that these factors are bearing better, cheaper, faster and safer solutions.

The automotive industry is among those known for such challenges. Recently, a major Midwestern automobile manufacturer sought a better solution to a coating build-up problem at its assembly plant.

The manufacturer uses carriers to convey leaf springs through the manufacturing process. The various-sized leaf springs are used to connect the car body to the rear drive axle. The carriers (similar to paint hooks) are 12 inches long, weigh approximately five lbs and resemble large tuning forks. They are welded from 3/8-inch steel rod. The autophoretic rust-preventive coating applied to the springs during manufacturing builds up on the carriers. This build-up can cause coating residue or parts to fall off the carriers, disrupting plant production and impacting operating costs. With more than 1,700 carriers, effective cleaning is a significant concern.

Previously, the carriers were soaked in an acid bath, then manually pounded with hammers to remove the built-up coating. This method did not remove the coating completely, resulting in rapid buildup return. Furthermore, the labor intensive coating removal method prompted the manufacturer to delay cleaning until absolutely necessary. When cleaning was required, plant personnel would take 500 carriers out of service on weekends and replace them with spares.

Waste disposal and its associated costs were also an issue. The autophoretic coating combines organic polyvinyladene chloride or PVDC (similar to plastic food wrap) with trace amounts of hexavalent chromium. As a result, the mechanical removal process produced waste containing chromium, causing it to fail the Toxicity Characteristic Leaching Procedure (TCLP). Proper disposal of hazardous waste is significantly more costly than non-hazardous waste and requires extensive recordkeeping.

In evaluating alternative methods, pyrolysis (high-temperature burn-off) was not an option, as the PVDC can generate carcinogenic compounds when removed this way. On the other hand, typical blasting methods created the same disposal concerns as the manual removal method.

Several months ago, however, the manufacturer turned the cleaning challenge over to Geostrip Systems, Inc. of Livonia, Michigan, a certified contractor of the ARMEXTM Cleaning and Coating Removal Systems. Developed by Church & Dwight Co., Inc., this system uses a patented baking-soda-based technology to effectively clean and remove coatings and built-up residues. Now, the customer outsources the cleaning process to the contractor, who cleans all 1,700 hooks quarterly in a four-week period, with no production interruptions and no plant personnel involvement.

Geostrip Systems uses the Blast Cabinet Process, a containment system featuring either a Model 13P or 12X delivery device mounted on a mobile unit. The equipment is powered by a 185 cfm compressor. The operator uses a hand-held, No. 6 Hi-Pro nozzle and baking-soda-based Maintenance Formula XL with a rinse accelerator at blast pressures of 60 to 70 psi. Approximately 1,000 lbs of media is used to clean the entire stock of 1,700 hooks.

The result is a faster, more effective and environmentally sensible alternative to the plant's previous soak-and-pound method. The paint hooks are cleaned down to bare metal. Also, due to the speed and ease of this process, the hooks are maintained at a higher level of cleanliness, satisfying the customer and eliminating production problems related to coating build-up on the hooks.

In addition to these benefits, the system has solved the disposal concerns related to the cleaning process. With the previous mechanical cleaning method, the process residue failed the TCLP test for chromium at 18 mg/liter (the limit is 5.0 mg/liter). By contrast, the waste stream produced by the replacement tests at 2.3 mg/liter. Therefore, the waste does not need to be treated as hazardous and can be disposed in conventional landfills.

This has reduced waste disposal costs by a factor of 10. In addition, the customer does not need to track the waste as part of RCRA record-keeping requirements. This is a significant time and cost saving as the cleaning process generates approximately 1,000 pounds of dry, nonhazardous waste for every 1,700 carriers cleaned.

Cleaning Media Profile. The blast media is effective for paint removal due to its soft crystalline structure, which makes it an ideal mild abrasive. The soft, friable crystals break down on contact with the substrate, resulting in a more gentle cleaning process, even for fragile surfaces such as glass and brick. The process may be used on iron, steel, galvanized metal, ornamental brass and copper, aluminum, chrome and composite materials.

One advantage of a soft abrasive is the added capability to selectively remove coatings layer-by-layer. As a result, the operator can often remove the paint while leaving the underlying coatings intact. The system was originally developed to safely clean and strip the Statue of Liberty.

The cleaning media is non-toxic and non-hazardous as defined by EPA and OSHA, so it eliminates many safety and environmental restrictions. The media also poses no special disposal concerns and may even be beneficial as a buffer for wastewater treatment.

Unlike plain baking soda, the cleaning media has a larger, uniform grain size along with flow agents and rinse accelerators for improved performance. This helps keep the media free-flowing. It flows better and can be stored for long periods without handling problems. In addition, some formulations have rinsing agents to help facilitate cleanup.

Equipment Profile. When powered by an industrial air compressor, the media delivery system operates on 20 to 100 psi of air pressure and may be used to clean wet or dry depending on containment needs. It uses an atomized external water stream for media control, and has a flow control system that precisely and consistently meters small amounts of media (½ to 3-½ lbs/min) required for optimal performance. The rate of paint removal varies according to the equipment, media and substrate; however, a typical removal rate is between one and two sq ft per min.

The baking-soda-based process effectively solved the coating build-up problem for this Midwest manufacturer and saved significant time and money in plant operating and disposal costs. In the automotive industry, the system is ideal for cleaning and stripping a variety of other types of carriers, such as those used to convey auto bodies and parts through dip and spray processes. It is among a new generation of technologies for better, faster, cheaper, and safer ways to successfully meet everincreasing manufacturing and maintenance challenges.

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