Wear note
Mn grade selection
Mn13 vs Mn18 is a plant decision, not a catalogue romance.
By Ms Amina Hassan, Impact and recycle specialist
Ms Amina Hassan supports demolition and recycling yards with practical guidance on blow bar alloys and wear part selection for impact crushers.
AuthorWhy this matters on the plant
Choosing between Mn13 and Mn18 manganese steel is not about picking the higher number from a catalogue. Here on South African plants, the right wear part grade depends on your actual material, feed conditions and crusher settings, not just the spec sheet.
Understand your feed and crusher settings
The question of Mn13 versus Mn18 starts at the rock face, not in a storeroom. I always ask: what are you crushing, at what closed side setting, and what is your target product? Mn13 has lower manganese content and is generally softer, which allows it to work harden under moderate impact. If your feed is relatively soft, well-graded and you’re running a jaw or impact crusher with a small closed side setting (say, 25 to 50 mm), Mn13 will work hard, last well and possibly be cheaper to run.
On the other hand, with hard, abrasive material, think Highveld dolerite, Karoo quartzite or heavily reinforced concrete demolition, you want Mn18 for its higher work hardening potential. Mn18 will become tougher under repeated impact, especially at wider settings (like 70 to 150 mm) and higher throughput. Don’t just default to Mn18 because it sounds stronger. If you’re feeding soft material, it may not harden fully and will wear quickly.
Balance impact and abrasion in blow bar applications
In impact and recycle yards, blow bar grade selection is a real-world decision. Mn13 blow bars are more forgiving if you have variable or poor feed discipline. They can tolerate a few surprises, like an unexpected chunk of rebar or a wet clay pocket, thanks to their ductility. Mn18, however, starts soft and only reaches its full hardness after heavy impact cycles.
If you’re crushing mainly brick, asphalt or limestone, stick with Mn13. When the feed turns nasty, hard concrete, granite, or basecourse with occasional tramp, Mn18 is worth the investment, provided your plant can keep choke fed and avoid excessive fines. In South Africa’s humid Durban climate, corrosion is another factor: both grades benefit from regular monitoring for localised wear.
Common mistakes with Mn grade selection
I’ve seen many plants jump straight to Mn18, expecting longer life by default. But if your closed side setting is too tight or you’re running at low tonnages, those blow bars may never harden up. You end up with soft, scalloped wear that eats through your liner budget. Over-sizing feed or running dry can cause early breakage even with Mn18.
Another mistake is mixing Mn grades in the same rotor. This upsets balance and creates uneven wear patterns. Always fit a full set from the same batch, and torque your liner bolts to the correct spec, as per OEM manual. Don’t guess, improperly torqued bolts can loosen during an Eskom power cut restart, leading to catastrophic liner loss.
- Never mix Mn13 and Mn18 on one machine
- Monitor wear patterns weekly, not monthly
- Keep rotor balanced at all times
- Check torque after each power cut event
Make the call with real data, not catalogue numbers
The right Mn grade comes down to how your plant runs, not just what the parts catalogue says. Before ordering, measure your actual feed size (using a shovel and tape, not thumb-suck) and run a wear profile on your current liners. Are you seeing gouging, pitting or smooth wear? Are your blow bars hard at surface when you tap with a chisel, or still soft after 200 hours?
If you’re unsure, get in touch through our contact form. Our stock covers both common grades, with full batch traceability. What matters is fitting the right grade, tensioning your screen decks properly and running a tight campaign plan. That’s how you get the best value per tonne, whether you’re on a bakkie in the Lowveld or shovel-testing on the Highveld.
Related parts: Blow Bar Kit. You can also browse all parts and plant guides.
What our Crusher Wear Parts customers say
Verified Google reviews