In jaw crushing operations, the "Gap"-technically known as the Closed Side Setting (CSS)-is the heartbeat of your production line. It determines the final product size, throughput capacity, and the wear rate of your jaw plates.
As a professional manufacturer of high-performance wear parts, Duma Machinery provides this guide to help you master gap adjustment while maximizing the lifespan of your liners.
1. What is the Jaw Crusher Gap (CSS)?
The CSS is the minimum distance between the fixed and movable jaw plates at the bottom of the crushing chamber during the closed stroke.
Why adjust it? As your Jaw Plates wear down, the gap increases, leading to oversized products. Regular adjustment compensates for this wear and maintains your target gradation.
2. Three Common Adjustment Methods
Method A: Shim/Gasket Adjustment (The Traditional Way)
Common in classic models like the PE series, this method uses a stack of steel plates (shims) behind the toggle seat.
Loosen the tension rod and backup bolts.
Add or Remove shims to change the position of the toggle seat.
Tighten everything back.
Pro Tip: Adding shims decreases the gap; removing them increases it.
Method B: Wedge Adjustment (The Efficient Way)
Found in modern high-performance crushers (e.g., Metso C-series style), this uses two sliding tapered wedges.
Activate the adjustment screw or hydraulic bolt.
Move the wedges relative to each other. This pushes the toggle seat forward or backward.
Benefit: This is much faster than the shim method and offers higher precision.
Method C: Full Hydraulic Adjustment (The Advanced Way)
Standard on premium mobile and stationary plants (e.g., Sandvik QJ series).
Operation: Controlled via a hydraulic panel or PLC.
Benefit: Allows for "one-touch" adjustment and provides overload protection. If uncrushable material (tramp iron) enters, the hydraulic system can automatically open the gap to prevent frame damage.
3. Critical Safety & Maintenance Steps
LOTO Protocol: Always follow "Lock-Out, Tag-Out" procedures. Ensure the crusher is empty and fully powered down before adjustment.
Tension Rod Synchronization: When you move the toggle seat to adjust the gap, you must adjust the tension rod spring tension accordingly. Failure to do so can cause the toggle plate to fall out during operation.
Calibration: After adjustment, run the crusher empty for 5 minutes and re-measure the CSS to ensure it meets your specs.
4. The Duma Advantage: Wear Control
Gap adjustment is a response to Jaw Plate wear. At Duma Machinery, our In-house Manufactured Jaw Plates (Mn18Cr2, Mn22Cr2) are engineered with a stable metallurgical structure.
Consistent Wear: Unlike low-quality castings, Duma plates wear uniformly, meaning your gap adjustments remain predictable and less frequent.
Precision Fit: Our 4,000+ patterns ensure that the seating surface is perfectly flat, preventing shim or wedge misalignment.
Duma In-house Manufactured Jaw Crusher Wear Parts
Verified Technical References
Metso Nordberg® C Series Manual: Industry standard for wedge-type adjustment.
ISO 13503-2: International guidelines for crushing machine safety and gap measurement.
Taggart's Handbook: "Crushing and Grinding Process Handbook," provides the mathematical link between CSS and reduction ratios.
Need Help Matching Your Gap Settings with the Right Jaw Plates?
Consult with Duma's engineers to select the ideal manganese grade for your rock hardness. Ensure your CSS stays stable for longer.
