Rust and Your Sweeper

That brown stain on your hopper, that bubble in the paint at the bottom of the inspection door. Signs that rust has come to beat on your sweeper.
Steel will always succumb to rust in a natural environment, but the problem is preventable. Understanding the rusting process, the problematic areas, and the ways to address trouble means your money-maker can stay on the job as long as possible.
Rust is the layman’s term for the electrochemical breakdown of iron-based metals called oxidation. In this process, surface molecules react with oxygen in the air and produce iron oxide. Iron and most steel will ultimately reduce to iron oxide and constituent elements given enough time.
Rust attacks the structural and chemical impurities in metal alloys at the molecular levels and the first sign of a problem show up as paint nicks, cracks, and scratches. Pure iron does not oxidize as aggressively. Just look at an old iron engine block, and you’ll see a thin surface layer of rust but little penetration into the metal. Unfortunately, iron isn’t a particularly suitable material to build sweepers out of. Adding carbon to iron creates steel, which offers dramatic improvements in flexibility, tensile strength, and formability. But by definition, this adds impurities. Impurities that accelerate rust.
The chemical process of rust corrupts the surface and reduces metal strength. All steel rusts, but at different rates depending on several factors, such as alloy components, thickness, the environment the steel has been in, and the type of heat treating the steel received. Nickel and chromium is often added to stave off the rust, but nothing is foolproof. The presence of any salt accelerates the effect. Road salts dissolved in water act as electrolytes, and when introduced to the effected site, make the exchange of molecular components much faster. This means dirty or salty water trapped somewhere on your sweeper makes that spot rust faster. It also explains why sweepers in northern climates, where salt is used in winter, are prone to rot.
After prolonged exposure, steel is converted to brittle iron oxide and holes form. Sweeper manufacturers do a lot to try to prevent corrosion. Aluminum components are becoming popular because of their lightweight, they also corrode, but at at a rate that is unnoticeable within a human lifetime. But those metals are expensive enough to be used sparingly. Modern sheet steel comes off the roll with highly durable coatings. Those are further augmented in the final assembly when the freshly made bodies are dipped in baths of anticorrosion agents applied before the painting process. Regular inspection and covering spots worn bare will keep rust from advancing and causing additional damage. Use primer and paint for light body rust, bed liner to repair hoppers and undercoating wear, and a rust neutralizer on the frame and subframe rust.

Levels of Rust Prevention
Sweeper decay is largely preventable and the best advice is the most obvious: Wash your sweeper every day to keep the sweeper clean of the road grime, salts, and dirt that lead to corrosion. The not-so-obvious advice is to also check drain holes along the bottoms of doors and toolboxes, which allow water to get out. Use a pipe cleaner to clear these holes, and keep your sweeper’s nooks and crannies dry.
Most surface rust happens when paint breaks down due to small damages. Structurally, surface rust is not a problem, but it’s best to correct surface rust as soon as you see it. Start by using an abrasive wheel or sandpaper to cut through the paint and corrosion until clean, bright metal is visible. Then apply primer, paint, and a clear coat.
If you don’t correct the rust when it was just surface rust, you’ll get the dreaded bubble, flaking away paint and exposing fresh base metal that begins to corrode. When rust penetrates the surface, it causes a rough, pitted area called scale. Correcting this means you have to get through the rust with a wire brush, grinding wheel, and sandpaper, followed by a coat of primer and paint.
When rust is left to to do its damage, eventually, the base metal flakes away and leaves holes. Now you’ve got a more significant problem, and you’ve got two options. You can completely replace the affected area, or you can cut the bad parts out and weld “patch panels” into place.
Just a little extra vigilance reduces rust to no more of a problem than any other regular maintenance issue. Of course, rescuing a rust bucket and replacing the hopper and components can be fun, but this is not for everyone.

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