A jaw crusher is the cheapest machine in the plant to buy and one of the most expensive to get wrong. Oversize it and you tie up capital in a unit that runs half-empty; undersize it and the whole line is throttled at the first stage, forever.
1. Start from the feed, not the machine
The first number you need is the 80% passing size of the run-of-mine feed after blasting, not the largest boulder someone once saw. If the mine can commit to a blasting pattern that keeps the feed below 600 mm, a 750×1060 machine will do a job that otherwise needs a 900×1200.
2. Set the reduction ratio deliberately
A single jaw crusher comfortably achieves a 3:1 to 6:1 reduction. Ask for 10:1 and you get a machine that stalls, wears its plates unevenly and produces a slabby product the next stage cannot handle.
If your feed is 600 mm and you need 80 mm product, that is roughly 7.5:1 — too much for one jaw. Open the discharge setting and let a cone take the work, or add a second stage.
3. Correct the capacity table for your ore
Published capacities assume a bulk density around 1.6 t/m³ and a medium-hard ore. Granite, basalt and dense iron ore typically reduce throughput by 15–30%. The same table assumes continuous, controlled feed — not a loader dumping in surges.
- Bulk density below 1.4 t/m³: the crusher is volume-limited, so the tonnage figure is optimistic.
- Compressive strength above 250 MPa: derate capacity and expect faster plate wear.
- Clay or high moisture: check for packing in the chamber; a smooth-jaw design may be needed.
4. Match the chamber and plates to the duty
A deep symmetrical chamber handles slabby feed and gives a better product shape; a shallower chamber gives more capacity at the cost of shape. Reversible plates are worth the small premium — a change-out in a primary station usually costs a full day of production.
5. Design the primary stage around the circuit
A jaw crusher almost always runs in open circuit. That makes the product curve matter more than the average size: too many fines overload the secondary, too many slabs and you recycle. If the next stage is a cone, a 120–150 mm setting is usually right; if it is a mill, a coarse 80–100 mm product keeps grinding efficiency high.
The mistakes we see most often
- Selecting on tonnage alone.
- Ignoring the feeder.
- Closing the setting to “make the product”.
- Leaving no room for maintenance.
The best primary crusher is the one whose discharge curve the rest of the plant was designed around — not the one with the biggest number in the brochure.
