What is a Jaw Crusher?

A Backenbrecher is one of the most common and important primary crushers used in mining, quarrying, and aggregate industries. Its main purpose is to reduce large rocks and ore into smaller pieces before further processing.

A jaw crusher works like a mechanical jaw: one fixed jaw and one moving jaw crush materials between them by applying strong compressive force.

Typical applications:

• Gold ore crushing
• Copper ore crushing
• Iron ore crushing
• Limestone crushing
• Granite and basalt crushing
• Construction aggregate production

A typical mining process is:

Run-of-Mine (ROM) Ore
          ↓
     Jaw Crusher
          ↓
   Secondary Crusher
          ↓
 Grinding Mill (Ball Mill / Wet Pan Mill)
          ↓
 Mineral Separation
          ↓
   Final Product

---

1. Basic Structure of a Backenbrecher

A jaw crusher mainly consists of the following parts:

1. Feed Opening

The top opening where raw ore enters.

Example:

• Large rocks from blasting:
  • 500 mm
  • 800 mm
  • even >1000 mm

enter through the feed opening.

The size of the opening determines the maximum rock size the crusher can accept.

Example:

PE 600 × 900 jaw crusher

means:

• Feed opening width = 600 mm
• Feed opening length = 900 mm

---

2. Fixed Jaw Plate

The fixed jaw is attached to the crusher frame.

Its function:

• Provides a rigid crushing surface
• Receives the force from the moving jaw
• Helps break the rock

The jaw plate is usually made from:

• High manganese steel
• High chrome alloy steel

because it experiences severe wear.

---

3. Moving Jaw Plate

The moving jaw is connected to the eccentric shaft.

It moves back and forth.

Movement:

Open position:

Fixed Jaw        Moving Jaw

|               /
|              /

     Rock


Closed position:

|             |
|  Crushed    |
|    Rock     |

When the moving jaw approaches the fixed jaw, the rock is compressed and crushed.

---

4. Eccentric Shaft

The eccentric shaft is the heart of the jaw crusher.

It converts rotary motion from the motor into the reciprocating motion of the moving jaw.

The shaft center is offset:

Normal shaft:

     O
     |
     |
     O


Eccentric shaft:

      O
       \
        O

When it rotates, the moving jaw moves forward and backward.

---

5. Flywheel

A large flywheel stores rotational energy.

Functions:

• Smooths the crushing action
• Reduces motor load fluctuation
• Maintains stable operation

Because crushing is intermittent:

Crush → Release → Crush → Release

the flywheel helps maintain continuous movement.

---

6. Toggle Plate

The toggle plate is located between the moving jaw and the crusher frame.

Functions:

1. Transfers crushing force

It pushes the moving jaw toward the fixed jaw.

2. Safety protection

If uncrushable material enters:

Example:

• Steel piece
• Very hard rock

the toggle plate can break first, protecting expensive components.

---

How Does a Jaw Crusher Work?

The crushing process has four main stages:

---

Step 1: Feeding

Large rocks enter from the top.

Example:

Raw rock size:
800 mm

The rock falls into the crushing chamber.

---

Step 2: Compression Crushing

The motor rotates the eccentric shaft.

The moving jaw moves toward the fixed jaw.

The rock is squeezed:

Moving Jaw →  ROCK  ← Fixed Jaw

        ↓

     Crushing

The applied force exceeds the rock’s strength.

The rock breaks.

---

The crushing action mainly uses compressive pressure:

• High force
• Small contact area
• High stress on the rock

The rock fails internally and fractures.

---

Step 3: Discharge Stroke

After crushing, the moving jaw moves away.

The crushed material falls downward.

The discharge opening controls the final size.

Example:

If CSS (Closed Side Setting):

CSS = 100 mm

then the product is approximately:

<100 mm

---

Step 4: Continuous Crushing

The cycle repeats:

Feed
 ↓
Compress
 ↓
Crush
 ↓
Release
 ↓
Discharge
 ↓
Repeat

Thousands of cycles occur per hour.

---

Types of Jaw Crushers

There are two main designs:

---

1. Single Toggle Jaw Crusher

Most common type.

Structure:

Motor
 |
Eccentric Shaft
 |
Moving Jaw
 |
Toggle Plate

Characteristics:

Advantages:

• Simple design
• Lower weight
• Lower maintenance cost
• Good for medium crushing

Disadvantages:

• More vertical movement
• Higher wear on jaw plates

Common use:

• Small and medium mines
• Aggregate plants

---

2. Double Toggle Jaw Crusher

Uses two toggle plates.

Structure:

          Moving Jaw

             |
          Toggle
          Toggle

             |
          Frame

Advantages:

• Higher crushing force
• Better for very hard rocks
• More durable

Disadvantages:

• Heavier
• More expensive
• Higher maintenance

Used for:

• Large mining operations
• Hard rock crushing

---

Jaw Crusher Crushing Mechanism

A jaw crusher uses three main crushing actions:

1. Compression

The dominant force.

Example:

A rock squeezed between two plates.

Plate → Rock ← Plate

Rock breaks

---

2. Bending

The rock bends until it fractures.

---

3. Shearing

Sliding movement between jaw plates creates additional breaking force.

---

Important Jaw Crusher Parameters

1. Feed Size

Maximum rock size entering the crusher.

Example:

Feed size:
<750 mm

---

2. Discharge Size (CSS)

Distance between jaws at the bottom.

Smaller CSS:

→ smaller product

Larger CSS:

→ larger product

---

3. Capacity

Measured in:

• tons per hour (t/h)

Example:

Small crusher:

10–50 t/h

Large crusher:

500–2000 t/h

---

4. Reduction Ratio

The ratio between feed size and product size.

Formula:

Reduction Ratio =
Feed Size / Product Size

Example:

Feed:

600 mm

Product:

100 mm

Reduction ratio:

600 ÷ 100 = 6:1

Typical jaw crusher:

3:1 to 8:1

---

Advantages of Jaw Crushers

✅ Simple structure
✅ High reliability
✅ Low operating cost
✅ Handles very large rocks
✅ Suitable for hard materials
✅ Easy maintenance
✅ Good energy efficiency

---

Disadvantages

❌ Product shape can be irregular
❌ Cannot produce very fine powder
❌ Wear parts require replacement
❌ Produces vibration
❌ Not suitable for wet sticky clay materials

---

Backenbrecher vs Cone Crusher

Feature	Backenbrecher	Cone Crusher
Crushing stage	Primary	Secondary/Tertiary
Crushing method	Compression	Compression + squeezing
Futtergröße	Very large	Mittel
Product size	Coarse	Fine
Cost	Nach unten	Higher
Wartung	Simple	More complex
Best for	First crushing	Final shaping

---

Example: Gold Ore Processing Plant

A typical gold plant:

Large Gold Ore
       |
       ↓
 Jaw Crusher
(800 mm → 100 mm)
       |
       ↓
 Cone Crusher
(100 mm → 20 mm)
       |
       ↓
 Wet Pan Mill / Ball Mill
(20 mm → fine powder)
       |
       ↓
 Gravity Separation
       |
       ↓
 Gold Concentrate