We all know unprotected ferrous substrates exposed to moisture and oxygen will eventually oxidize (rust). Manufacturers rely on metal and coatings technology to answer the age old question: how can oxidation be prevented or delayed to extend a metal product’s lifespan?
Coating cold-rolled and hot-rolled metal is one of the most effective ways to prevent oxidation. For typical exterior exposure, such as mufflers on tractors, combines, harvesters and balers, a primer and top coat system acts as a barrier film between metal and direct exposure to moisture and oxygen, thus preventing oxidation.
If a top coat is compromised and the underlying metal exposed, the primer coat acts as the backup defense to prevent the spread of rust on the substrate. A primer with a zinc additive is highly effective, as the zinc absorbs the oxidation, and thereby slows down the rusting on the substrate (this is why zinc primers are often called a “sacrificial” primer).
The Challenge of Coating Farm Equipment Mufflers
To perform as they were designed and resist corrosion, a coating system must maintain its film integrity. Friction and impact can break a coating’s film and expose the underlying metal to the oxidizing elements. Not all damage is visible, as micro-abrasions caused by friction, impact, or exposure to high temperatures also allow moisture to penetrate the coating and begin to cause oxidation on the substrate.
Farming and ranching equipment exhaust systems are at high risk for rust. As working machines, their inherent function makes them vulnerable to impact or friction. Furthermore, exhaust systems are typically operated at high temperature, which breaks down the film on a microscopic level and allows moisture to enter and corrosion to begin. A standard primer and top coat metal enamel system not formulated for high heat will breakdown quickly in an exhaust system. Visible signs of a failing coating on a muffler or exhaust system include peeling, bubbling, flaking, oxidation spots, pinholes, craters, chipping, cracking, color fade, chalking, and visible metal spots.
Once the coating on farm equipment exhaust is compromised, the moist and organic environment where these machines are used will allow oxidation to rapidly spread.
Coating Systems Optimized for High Temperature Performance
Specialty heat-resistant coatings are designed to maintain film integrity despite high operating temperatures and will better protect an agricultural machine’s exhaust system. The chemical formulation of these products includes binders and pigments resistant to high temperatures.
Rapid changes in temperature during use also place extreme demands on Ag equipment exhaust system coatings. During use, the very hot muffler may meet with snow, ice and water that cause the metal to rapidly cool and contract. The coating film must be “flexible” enough “move with” this rapid change in the metal to survive the rapid cooling without cracking. High temperature coatings undergo an extreme quench test, in which the coated metal is heated to high operating temperatures and then submerged in an ice bath to prove the integrity of the coating.
Repeated incidents of quenching can lead to a risk of rust over time, as the coating film must “open” when it is hot to move with the expanded metal. Therefore, high temperature coatings must strike a balance between flexibility and rigidity to prevent cracking while also maintaining a tight film.
Top quality exhaust coatings will have a combination of chemistries to reduce the opportunity for rust to form and propagate in these challenging conditions.