What is a Hammer Crusher?

A hammer crusher (also called a hammer mill crusher) is a type of Prallbrecher that uses high-speed rotating hammers to crush materials into smaller sizes. It is widely used in mining, metallurgy, cement, chemical, power plants, and construction industries for crushing medium-hard and brittle materials.

Typical materials processed by hammer crushers include:

• Kalkstein
• Kohle
• Gypsum
• Clay
• Glas
• Salt
• Dolomit
• Gangue
• Some metal ores (with suitable designs)

A hammer crusher is especially popular for primary and secondary crushing because it can produce relatively fine output in a single stage.

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Main Parts of a Hammer Crusher

A hammer crusher mainly consists of the following components:

1. Rotor

Die rotor is the rotating core part of the machine.

• A heavy-duty shaft supports several hammer discs.
• The rotor rotates at high speed (usually hundreds to thousands of revolutions per minute).
• Hammers are mounted around the rotor.

The rotor provides the impact energy needed to break the material.

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2. Hammer Heads

Die hammer heads are the crushing tools attached to the rotor.

They are usually made from:

• High manganese steel
• High chromium alloy
• Composite wear-resistant materials

The hammer heads strike the incoming material with high velocity and gradually wear during operation.

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3. Crushing Chamber

The crushing chamber is the working area where material is broken.

It includes:

• Rotor assembly
• Impact plates
• Grates or screens
• Liner plates

Material enters the chamber and is repeatedly impacted until it reaches the required size.

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4. Impact Plate / Liner

The impact plate receives secondary impacts from the material.

Its functions:

• Increase crushing efficiency
• Protect the crusher body
• Improve material fragmentation

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5. Grate Plate (Screen)

The grate controls the final product size.

• Smaller particles pass through the openings.
• Larger particles remain inside for further crushing.

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6. Feeding Opening and Discharge Opening

Feed opening:

• Material enters from the top or side.

Discharge opening:

• Crushed material exits from the bottom.

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How Does a Hammer Crusher Work?

The working principle is based on high-speed impact crushing.

The crushing process happens in several steps:

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Step 1: Material Feeding

Large rocks or raw materials enter the crusher through the feed hopper.

Example:

A limestone block of 300 mm size enters the machine.

↓

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Step 2: High-Speed Hammer Impact

The electric motor drives the rotor to rotate rapidly.

When the rotor spins:

• Hammer heads move at high speed.
• They strike the incoming material.
• The impact force breaks the material.

The main crushing forces are:

• Impact force
• Compression force
• Shearing force

↓

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Step 3: Secondary Crushing

After the first impact:

• Broken pieces hit the impact plate.
• They bounce back toward the rotating hammers.
• Repeated impacts further reduce the particle size.

This repeated collision creates finer particles.

↓

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Step 4: Size Control and Discharge

When particles become small enough:

• They pass through the grate openings.
• Finished products leave the crusher.

Oversized particles stay inside and continue being crushed.

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Hammer Crusher Working Principle (Simple Diagram)

        Feed Material
             ↓
       ┌───────────┐
       │           │
       │   Rotor   │
       │  ↻ ↻ ↻    │
       │  Hammer   │
       │  ↓ ↓ ↓    │
       │   ★★★     │ ← Impact Crushing
       │           │
       │  Grate    │
       └────┬──────┘
            ↓
     Finished Product

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Types of Hammer Crushers

1. Single Rotor Hammer Crusher

Features:

• One rotor
• Simple structure
• Lower investment
• Einfache Wartung

Applications:

• Limestone crushing
• Coal crushing
• Cement plants

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2. Double Rotor Hammer Crusher

Features:

• Two counter-rotating rotors
• Higher crushing capacity
• Better crushing of sticky materials

Applications:

• Kohle
• Clay
• Soft ores

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3. Reversible Hammer Crusher

The rotor can rotate in both directions.

Advantages:

• Even hammer wear
• Longer service life
• Reduced maintenance time

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Hammer Crusher Advantages

1. High Crushing Ratio

A hammer crusher can achieve a crushing ratio of approximately:

10:1 to 25:1

This means it can reduce large feed materials into much smaller products in one stage.

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2. Produces Fine Product

Compared with jaw crushers, hammer crushers usually produce:

• More cubic particles
• Less flaky material
• Smaller final size

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3. Simple Structure

Advantages:

• Fewer moving parts
• Easy operation
• Lower installation cost

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4. High Efficiency

Because crushing happens through direct impact:

• Energy is used efficiently.
• Material reduction is fast.

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Hammer Crusher Disadvantages

1. High Wear Rate

Hammer heads directly contact hard materials, so they wear quickly.

Wear parts include:

• Hammer heads
• Liners
• Grate plates

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2. Not Suitable for Very Hard Rocks

Hammer crushers work best with materials below approximately:

• Mohs hardness: 5–6

They are not ideal for:

• Granite
• Quartzite
• Very hard metallic ores

For harder materials, jaw crushers, cone crushers, or impact crushers are usually preferred.

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3. Moisture Problems

Wet and sticky materials may:

• Block the grate
• Reduce capacity
• Cause material buildup

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Hammer Crusher vs Backenbrecher

Feature	Hammer Crusher	Backenbrecher
Crushing method	Impact	Compression
Main part	Hammer head	Jaw plate
Product size	Finer	Coarser
Crushing ratio	Higher	Nach unten
Wear cost	Higher	Nach unten
Hard rock ability	Limited	Excellent
Typical use	Limestone, coal, gypsum	Granite, ore, construction rock

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Applications in Mineral Processing

In a mining plant, a hammer crusher is often used after primary crushing:

Example:

Gold Ore Processing Plant

Raw Gold Ore
      ↓
Jaw Crusher
      ↓
Hammer Crusher
      ↓
Ball Mill
      ↓
Gravity Separation / Flotation
      ↓
Gold Concentrate

Hammer crushers are commonly used when the ore is relatively soft and a fine feed size is required before grinding.