How to check jaw crusher maximum feeding size standard

How to check jaw crusher maximum feeding size standard

1. Definition

Maximum feeding size (max feed size) is the largest single lump dimension allowed to enter the jaw crusher crushing chamber under normal continuous operation. It is NOT equal to the feed opening (gape) of the jaw crusher.

Gape: the distance between fixed jaw and movable jaw at the top feed position, the first dimension in PE model like PE600×900 (600mm = gape width).

2. Industry standard: 70%–80% golden rule

This is the widely accepted global standard for jaw crusher primary crushing:

Max allowable feed size = Gape × (0.7 ~ 0.8)

  • For hard rock (granite, basalt, iron ore): adopt 70%–75% (strict limit, prevent bridging)
  • For medium/soft rock (limestone, coal): can take up to 80%

Do NOT feed rock equal to 100% gape. The rock will get stuck, causing bridging, stalling, jaw plate damage or motor overload.

Example: PE600×900 jaw crusher, gape = 600 mm Max feed size = 600 × 0.8 = 480 mm (manufacturer nominal value is 500 mm for reference)

3. Three ways to verify the standard

Method 1: Check official manufacturer datasheet (most authoritative)

The product catalog, technical manual or nameplate directly marks the rated maximum feed size. This value is the official factory standard, prioritized over manual calculation.

Method 2: On-site physical measurement of gape

  1. Stop and lock the crusher; remove feed hopper if needed
  2. Measure the horizontal distance between fixed jaw tooth tip and movable jaw tooth tip at the fully open position (OSS at top) → get gape
  3. Multiply gape by 0.7~0.8 to get the safe maximum feeding size.

Method 3: Field lump dimension inspection

When checking raw ore stockpile:

  • Measure the longest side of the rock block (not shortest side)
  • Any block longer than the max feed size must be pre-broken or separated

4. Key influencing factors that change the standard limit

  1. Rock hardness & abrasiveness High compressive strength rock needs smaller max feed size; soft material can accept slightly larger blocks.
  2. Block shape Flat, elongated stones have a higher bridging risk. Reduce max feed size by 5~10% for flat slabs.
  3. Feeding method Continuous vibrating feeder feeding can follow 80% rule; intermittent loader feeding better stay under 75%.
  4. Jaw liner wear Worn jaw plates shrink the effective gape, so actual allowable feed size will drop during service life.

5. Consequences of exceeding maximum feed size

  • Material bridging at feed opening, production stop
  • Crusher stall, heavy shock load on flywheel, bearing and motor
  • Cracked jaw plates, broken toggle plate
  • Sharp rising current, belt slipping and burning

6. Practical site checking steps

  1. Confirm jaw crusher model and find gape dimension
  2. Check manufacturer rated max feed size from manual
  3. Calculate safe limit by 70–80% gape rule
  4. Sample and measure raw rock lump size
  5. If oversized lumps exist: add grizzly screen before crusher or pre-break big boulders