How the jaw crusher adjusts discharge opening size

How the jaw crusher adjusts discharge opening size

The discharge opening (Closed Side Setting, CSS) is the minimum gap between the bottom of fixed jaw plate and swing jaw plate when the movable jaw swings to the closest position. Adjusting this gap directly controls the maximum particle size of finished crushed stone.

All adjustment methods share the same core mechanical logic: shift the horizontal position of the toggle seat at the machine rear → change the effective length of the toggle plate support → alter the swing limit of the swing jaw bottom → expand or narrow the bottom crushing cavity gap.

Three mainstream adjustment structures are widely used on jaw crushers: shim (gasket) adjustment, mechanical wedge block adjustment, and hydraulic automatic adjustment.

1. Core Mechanical Logic Behind All Adjustment Types

  1. Toggle plate sits between swing jaw bottom and rear toggle seat; its horizontal position determines how far forward the swing jaw can push.
  2. Push the toggle seat forward: the toggle plate shortens the swing jaw’s rear support distance, the swing jaw leans closer to the fixed jaw, CSS becomes smaller (finer output stone).
  3. Pull the toggle seat backward: the toggle plate extends the support distance, the swing jaw retreats, CSS becomes larger (coarse output stone).
  4. Tension spring & tie rod must be loosened before adjustment to eliminate pulling resistance on the swing jaw; retighten after setting to maintain stable reset movement.

2. Method 1: Shim / Gasket Adjustment (Traditional PE Series Jaw Crusher)

Structure Composition

Thick metal shims of uniform standard thickness (2mm, 5mm, 10mm), stacked between toggle seat and rear frame baffle.

Step-by-Step Adjustment Process

  1. Shut down the machine, cut off power, clear all stones inside the crushing cavity for safety.
  2. Loosen the lock nut of the rear tension spring to release pulling force on the swing jaw.
  3. Remove the side guard behind the toggle seat, take out or add shim plates.
    • Add more shims: Push toggle seat forward → narrow discharge opening, produce fine aggregate.
    • Remove shims: Pull toggle seat backward → widen discharge opening, produce coarse stones.
  4. Reinstall guard plates, retighten tension spring nuts to standard tension.
  5. Manually rotate flywheel to check swing jaw flexibility, then measure CSS with lead wire or gauge for verification.

Advantages & Disadvantages

  • Pros: Simple structure, low manufacturing cost, stable positioning, widely used on medium & large mining jaw crushers.
  • Cons: Labor-intensive, frequent disassembly required if frequent particle size changes are needed.

3. Method 2: Mechanical Wedge Block Adjustment (PEV / European Heavy-Duty Jaw Crusher)

The most popular modern manual adjustment structure, equipped with paired upper & lower inclined wedge blocks and adjusting screw handwheel at the machine rear.

Working Principle of Wedge Transmission

Two wedges are stacked slantingly: rotating the adjusting screw pushes the wedge set horizontally. The inclined surface converts horizontal thrust into forward/backward displacement of the toggle seat.

Operation Steps

  1. Power off and clean the crushing chamber, loosen all locking bolts on the wedge housing.
  2. Turn the adjusting handwheel clockwise: wedges squeeze each other, push toggle seat forward → CSS reduces.
  3. Turn counterclockwise: wedges slide apart, toggle seat retreats → CSS expands.
  4. After reaching target gap, fully lock all wedge fixing bolts to prevent position shift during crushing vibration.

Advantages & Disadvantages

  • Pros: Continuous stepless adjustment without adding/removing parts, easy fine-tuning, shorter downtime.
  • Cons: Wedge inclined surfaces wear gradually under long vibration, requiring regular lubrication.

4. Method 3: Hydraulic Automatic Adjustment (Intelligent New Jaw Crusher)

Hydraulic cylinder connects directly to the toggle seat, controlled by PLC touch panel with digital CSS display, no manual disassembly needed.

Adjustment Mechanism

High-pressure hydraulic oil pushes the piston rod to drive the toggle seat forward or backward. Real-time sensors feed back gap data to the control screen for precise digital setting.

Operation Flow

  1. Stop feeding raw stones, keep the crusher running idle.
  2. Input target CSS value on the touch screen:
    • Press “Close Gap”: Hydraulic cylinder extends, toggle seat moves forward, discharge opening narrows.
    • Press “Open Gap”: Cylinder retracts, toggle seat moves back, discharge opening widens.
  3. System automatically locks hydraulic pressure after adjustment; double-check CSS with measuring tools.

Advantages & Disadvantages

  • Pros: Ultra-fast adjustment (3–5 minutes), high precision, safe, suitable for production lines requiring frequent particle size switching. Hydraulic system also supports automatic overload release.
  • Cons: Higher equipment cost, regular hydraulic oil maintenance required.

5. Auxiliary Note: Toggle Plate Length Replacement (Rare Adjustment)

For old large jaw crushers, replacing toggle plates of different lengths can also change discharge opening size:
  • Shorter toggle plate → smaller CSS; Longer toggle plate → larger CSS.

    This method is only used for large-range fixed adjustment, not daily fine-tuning.

6. Safety & Maintenance Rules for Discharge Opening Adjustment

  1. All adjustment operations must be carried out with power cut and LOTO (Lockout Tagout) to avoid accidental startup injuries.
  2. After jaw plates wear down, the discharge opening will slowly expand; operators need to re-adjust the gap weekly to guarantee qualified finished particle size.
  3. After every adjustment, test the machine empty for 3–5 minutes to check abnormal vibration, noise or swing jaw jamming.
  4. Always measure CSS at left, middle and right three positions of the discharge outlet to ensure uniform gap width, avoiding uneven stone size.