A new wax-based underbody coating from Daubert Chemical (Chicago, Illinois) has reportedly shown promise in withstanding exposure to sodium chloride (NaCL) as a corrosive agent on the steel beams used in truck and trailer manufacturing operations.
The Nox-Rust 1210HP†, a hydrophobic wax-based coating that repels water molecules, was designed as a corrosion-inhibiting solution for medium and heavy duty manufacturers, the company explains. The coating—which hardens upon cooling to form a dry, wax-like film—is best applied to clean, untreated steel such as I-beam cross members, slider boxes, and kingpin assemblies.
Following inquiries from original equipment manufacturers (OEMs) regarding trailer chassis construction, the company’s developers set up a study involving the wax coating by utilizing a 1,000-h salt fog test.
“Questions about the use of chassis components have arisen among truck and trailer OEMs in recent years,” says Mike Duncan, the company’s executive vice president of technology. “As we discussed the topic with our customers, we realized that nobody has done a definitive study on the subject, and that’s when we decided to undertake formalized testing.”
Salt Spray Exposure Tests
To test the coating, the company turned to the ASTM B1171—used to assess the corrosion resistance of surface coatings.
The salt spray testing specified in the standard effectively serves as an accelerated corrosion test, which approximates the long-term protection of a coating while also predicting its failure rate.
After 1,000 h of exposure to the saline spray, the clean steel sample with the wax-based coating showed very little deterioration. As shown in the image, the black beam that was tested with the salt spray looked nearly identical following the test—with only very small signs of zinc oxide, or white rust.
According to the company, the new coating is a potential alternative or enhancement option to use with galvanized steel beams, in which zinc coatings protect against corrosion.
Science of the Wax Coating
The hot-dipped, zinc coating used in many galvanizing processes is known as a sacrificial anode. In other words, it corrodes first—in preference to the metal substrate that it is designed to protect.
However, the company explains that its wax-based coating—which requires only minimal surface preparation—offers an additional advantage of hydrophobicity. This prevents the oxidation that can be caused by moisture contacting the metal beneath the protective layer of coating.
Another benefit from the wax coating is that it is self-healing. When using the product, a residual anticorrosive barrier of the wax-based material is retained, even after machinery operations have taken place. This is significant, the company says, because many trailer assembly processes—such as attaching landing gear, slider suspension boxes, wing plates, lighting brackets, and more—often require major welding, grinding, and drilling operations.
These operations pose the potential to dislodge the existing coating while also causing pieces of metals to become airborne. As a result, if the coating is removed, the steel substrate is vulnerable to corrosion—both from oxidation, as well as a galvanic reaction from dissimilar metals coming into contact with the other.
But when using the wax-based coating, tests have shown that the anticorrosive barrier remains in place, even after any assembly operations. Moreover, the company explains that the coating is also available as a smaller, touchup solution that can be applied in tandem with other corrosion protection strategies, particularly in areas where the original coating was significantly disturbed in the assembly process.
“The larger and smaller molecules fit tightly together like layers of marbles, with the nanoscale chemical layer adhering tenaciously to the surface,” Duncan explains. “Even if the coating’s outer layers are dislodged, the foundational layer continues to suppress the oxidation process.”
The wax-based coating adheres directly to fresh welds, providing residual oxidation and galvanic suppression during the application of screws, bolts, and other mechanical fasteners. While applying the coating to clean, untreated steel is recommended for optimum performance, the coating is also tolerant to oily or slightly rusted surfaces, Duncan says.
Corrosion Mitigation, Not Elimination
According to Duncan, eliminating corrosion entirely with the exclusive use of galvanized steel components or the wax coating is difficult. However, he believes the new wax coating can greatly enhance the mitigation process.
“You simply can’t take corrosion out of the equation,” Duncan says. “But you can successfully manage corrosion on all exposed metals, including galvanized, very cost-effectively with hot-melt, wax-based coatings.”
†Trade name.
Source: Daubert Chemical, www.daubertchemical.com.
Reference1 ASTM B117-16, “Standard Practice for Operating Salt Spray (Fog) Apparatus,” (West Conshohocken, PA: ASTM International, 2016).