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Test results question trailer coating effectiveness

Steel Coatings

CHICAGO _ Daubert Chemical, a manufacturer of specialty coatings and adhesives, announced the results of comparative corrosion resistance testing that reveal the limitations of galvanized steel and its inability to withstand exposure to the most common corrosive agent, sodium chloride. In salt spray exposure tests following American Section of the International Association for Testing and Materials (ASTM) B117 standards, Daubert compared galvanized steel I-beams to I-beams coated with Daubert’s Nox-Rust 1210HP wax-based coating.

The company performed the experiment in response to its OEM customers’ inquiries regarding the viability of galvanized components in trailer chassis construction.

“Questions about the use of galvanized steel chassis components have arisen among truck and trailer OEMs in recent years,” Mike Duncan, Ph.D., vice president technology for Daubert Chemical, said. “As we discussed the topic with our customers, we realized that nobody had done a definitive study on the subject, and that’s when we decided to undertake formalized testing.”

Also known as salt fog testing, the ASTM B117 is a standardized method used to assess the corrosion resistance of various surface coatings and is often used in side-by-side comparisons that demonstrate the relative effectiveness of different coatings. Salt spray testing is an accelerated corrosion test that approximates the long-term protective efficacy of a coating and is equally effective at predicting its failure rate.

The test results showed that after 1,000 hours of exposure to the saline spray, the galvanized steel I-beam underperformed in comparison to the I-beam coated with Nox-Rust 1210HP wax-based coating. The continuous salt spray exposure caused the galvanized sample to begin visibly shedding its protective zinc coating in the form of zinc oxide, also known as white rust.

The zinc coating used in the galvanizing process is known as a sacrificial anode because it corrodes first, in preference to the metal substrate it is designed to protect. In contrast, a wax-based coating like Nox-Rust 1210HP is hydrophobic and repels water molecules, preventing the oxidation that can be caused by moisture contacting the metal beneath its protective layer.

Using galvanized metals for trailer construction presents other problems as well. Galvanized steel is only protected as long as the zinc coating is in place. Trailer assembly processes, such as attaching landing gear, slider suspension boxes, wing plates, lighting brackets and the like, often includes welding, grinding and drilling operations that can dislodge the zinc coatings on galvanized steel, causing hazardous particulate matter to become airborne. Once the protective zinc is removed, the steel substrate is vulnerable to corrosion due to both oxidation and galvanic reaction from contact with dissimilar metals.

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