Wear note
Coastal bolt corrosion
Salt air eats fasteners. Storage and grease notes matter.
By Mr Pieter Botha, Cone circuit adviser
Pieter Botha is the go-to adviser on mantle and concave geometry for secondary cone crusher circuits across Gauteng.
AuthorWhy this matters on the plant
Coastal air eats steel for breakfast, especially when it comes to crusher fasteners. I have seen more cone liner changes fail from rusty concave bolts than from worn-out manganese, so it pays to get this right from the start.
Why salt air is so aggressive
On the coast, especially around Durban or down the Cape, salt-laden humidity attacks exposed steel. This is even worse on the Highveld during a winter sea-mist, but true corrosion risk climbs as you get closer to the water. Fasteners on a cone’s top shell, such as concave bolts, sit right in the airflow, and small amounts of airborne sodium chloride can start pitting within weeks. If left unchecked, this weakens the bolt shank and head, and eventually makes removal a nightmare.
We have rescued more than one set of concave seats where the customer had to grind the heads off every bolt, which leads to wasted hours and possible damage to the shell. When you see orange stains around bolt holes, you know corrosion is already underway.
Best practice for storage and handling
Concave bolts often arrive at site on flatbeds or in bakkie bins, but leaving them outside for even a day or two near the coast is risky. I recommend storing all critical fasteners in a ventilated, covered container, never directly on the ground or concrete. Wet sand and sea air creep up from underneath.
If you must stage parts, keep the bolts in their original packaging or wrapped in plastic. Do not rely on the anti-rust film from the foundry, as it is rarely designed for coastal exposure longer than a month.
- Never store bolts outside or in open sheds
- Use covered, elevated racks or sealed bins
- Avoid direct contact with concrete or wet floors
- Inspect for rust spots before installation
Correct grease use on fitting
A light coat of anti-seize or marine-grade grease on the bolt threads and under the head is not just for easy removal later. It forms a barrier that slows down salt ingress, crucial for plants working within 50 kilometres of the sea or anywhere you see sea-mist.
Do not drown the threads in grease, as this can lead to under-torqued bolts if you do not adjust your torque values. The correct anti-seize product should be specified by the OEM, but in practice, a nickel-based product works better than copper types in coastal plants. Always wipe off old product and dirt before applying fresh grease.
Removing rusted bolts and avoiding repeat failures
If you are faced with rusted or seized concave bolts, resist the urge to force them out with an impact gun. This often leads to snapped shanks flush with the shell. Instead, use penetrating oil and allow it to work overnight, then try hand tools. If that fails, heat may be required but use caution to avoid shell distortion.
When fitting new concave sets, always replace the bolts, washers and nuts with OEM-profile parts. Reusing corroded hardware is false economy. Keep a campaign log and check bolt torque at the first maintenance shutdown after a week of running. Many coastal circuits now run a quarterly bolt check, and some use bolt caps for extra protection, which can add months to service life.
Related parts: Concave Set. You can also browse all parts and plant guides.
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