Product Guide
Fixed vs Swing Jaw Plates: Choosing Between Mn13 and Mn18
Last updated September 2026 · By SKS Steel Zambia, Foundry & Machine Shop, Kalulushi
A jaw crusher has two jaw plates, and they do not wear the same way. Get the grade wrong on either one and you are either replacing plates too often or paying for toughness you do not need. Here is how to tell the two plates apart and choose between Mn13 and Mn18 manganese steel for each.
What Fixed and Swing Jaw Plates Actually Do
The fixed jaw plate is bolted to the stationary frame of the crusher. The swing jaw plate is mounted on the moving jaw, which drives toward the fixed plate to crush material and pulls back to release it. Every piece of feed passes between the two, but they do not take the same load.
Why the Two Plates Wear Differently
The swing plate does the active crushing stroke, so it sees more direct impact. The fixed plate takes more sliding and compressive wear as material is squeezed and dragged down the crushing chamber. That difference in wear mode is why the two plates can call for different grades, or at least different thicknesses of the same grade.
Mn13 vs Mn18: What's the Difference
| Property | Mn13 (13% manganese) | Mn18 (18% manganese) |
|---|---|---|
| Work-hardening response | Standard, hardens well under strong, repeated impact | Faster and deeper hardening response |
| Best suited to | Most general crushing duty, moderate to hard rock | Very hard or highly abrasive feed, primary crushing |
| Toughness | High | Slightly higher, better resistance to cracking under extreme shock |
| Typical use on this site | Default grade for most jaw plate orders | Requested for harder ore bodies or heavier feed sizes |
Neither grade is simply better. Mn18 costs more to produce and only pays for itself when the feed is hard or abrasive enough to push the extra manganese content to work. On softer rock, Mn18 does not reliably out-harden Mn13 in practice, since the work-hardening effect depends on impact energy, not just alloy content.
How to Choose the Right Grade for Your Crusher
Match the grade to what is actually going through the crusher, not to what you ordered last time:
- Quarried limestone, dolomite, most sedimentary rock: Mn13 is the standard choice for both plates.
- Hard igneous rock, granite, or ore with high silica content: Mn18 is worth the extra cost, at least on the swing plate.
- Primary crushing with large feed size and heavy impact: Mn18, or a thicker Mn13 section if budget is the constraint.
- Unsure which you are feeding it: send us the rock type or a sample and we will recommend a grade, the same way we do for blow bars and high-chrome parts.
Signs Your Jaw Plates Need Replacing
- Reduced output size consistency, where the crusher stops holding its set gap
- Visible grooving or scalloping on the plate face, especially near the bottom of the swing plate
- A noticeable increase in vibration or a change in crushing sound
- Metal loss changing the crusher’s closed-side setting outside spec
For a broader look at how wear part life varies across your equipment, see how often you should be replacing crusher wear parts.
Frequently Asked Questions
Yes. It is common to run Mn18 on the swing plate, which takes the harder impact, and Mn13 on the fixed plate, where cost savings make more sense. We can cast and machine plates to either grade per order.
No. Work-hardening depends on impact energy as much as alloy content. A Mn18 plate in a low-impact application may never harden past what Mn13 would achieve, so it does not automatically outlast it.
Yes. Send us your existing plate, worn or not, and we can take dimensions directly and cast a matching replacement.
Not Sure Which Grade Fits Your Crusher?
WhatsApp us your feed material and jaw plate dimensions and we will confirm the right grade and turnaround, or browse our Jaw Crusher Plates page.