Corrosion is an ongoing and costly issue for OTR fleets working in extreme mining environments. It causes immeasurable damage to mining equipment wheels and tires, negatively impacting equipment performance and making vehicles potentially unsafe for operators.
Corrosion occurs when a metal degrades to its natural state, through an electrochemical reaction with its environment. When iron, oxygen and water (air moisture) combine, the corrosion process is called oxidation. This reaction forms Fe2O3, known as iron oxide, ferric oxide, or rust. Rusting can be accelerated when iron is subjected to other minerals, chemicals and temperature fluctuations. The strength of wheel and rim components are compromised by rust and corrosion of contact surfaces. Oxygen, air and moisture not only corrode steel wheels, but they also react with rubber. With this type of corrosion, small particles of rust and dust can break off and clog valve cores, causing them to leak.
Corrosion of wheels leads to rough surfaces and tire beads that don’t seal properly. Exposure to oxygen also ages the inner liner, the thin layer of rubber inside the tire whose function is to keep air away from the carcass. As the inner liner ages, more and more air passes through it, leading to pressure losses that can average 2 psi per month in truck tires. As it passes through the rubber, the oxygen can also corrode and rust the steel cords.
Moisture is a key catalyst for the corrosion reaction, so it is vital to recognize and reduce the sources and amounts of water that wheels are exposed to, including:
Pooled water in tires that isn’t sufficiently removed before installation. It is impossible to get all the water out of a tire using a bucket, so some sites use a vacuum system.
Wet rims and components. Moisture accumulates on components when they sit out in the elements, unprotected, or when they are cleaned with a hose prior to mounting.
Moisture build-up in inflation hoses. Water traps should be used on compressors, and at inflation stations, to remove as much water as possible before the air enters the tire chamber.
Steam generated by the moisture and heat of operation. Exposure to steam magnifies corrosion.
Moist or wet storage areas. Always store rims and wheels in dry environments.
An effective way to stop wheel and rim corrosion is to add a corrosion inhibitor to the tire, prior to mounting. Corrosion inhibitors are coatings that are applied to the inside of the tire casing as part of the tire mounting process, either by the maintenance shop or by a tire service provider. In general, inhibitors are composed of fibers and/or fillers in a thick liquid suspension. Fibers may be textile filaments other material. Fillers can include small particles of crushed rubber or plastics. An inhibitor’s performance depends on its compounding properties, and each supplier creates specific formulations for particular applications. Although different suppliers may recommend different practices, corrosion inhibitors are usually poured into the tire prior to mounting, or injected while inflating the tire with a pneumatic pump system. Manufacturers provide tables that indicate the amount of inhibitor, or “dosage”, needed for particular tire sizes. After injection, the inhibitor spreads to cover the full inner liner of the tire (tread and sidewall area) within about the first hour of rolling. Supplementary inhibitor may need to be added during normal use of the tire. Inhibitors may also offer an extra barrier against loss of air through the casing, and some may provide an immediate seal around punctures.
Because of variations in the chemical nature of different corrosion inhibitors, and because they have not been an integral part of tire or rim design and development, caution should be taken to ensure that any selected inhibitor:
Is chemically compatible with tires, wheels, and any components that may come in contact with the compound.
Will perform properly over the range of warm and cold temperatures normally experienced during vehicle operation.
There is a broad range of corrosion inhibition products, suppliers, and applications in the market. When choosing an inhibitor, it is important to understand the amount of product you need so you can calculate its cost, which varies among products. But remember, without an inhibitor, you’ll pay the ultimate cost… of hazardous and harmful corrosion.
To learn about RIMEX’s premium corrosion inhibitor, RIMEXCEL, click here.
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