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How does an Impact Crusher work?

Ideal for recycling, primary and secondary crushing applications.

What are the benefits of an impact crusher?

Impact crushers reduce mineral materials such as concrete, asphalt and natural rock in size to produce a valuable commodity product. A fast spinning rotor throws the material against a solid stationary impact wall. The striking and impacting causes the material to shatter into smaller pieces. The result is a very homogenous and cubical product leaving the crusher box.

Maximum versatility


Good for processing reinforced concrete, asphalt, cinder blocks, sand & gravel, soft rock, and hard rock.

High reduction ratio

High Reduction Ratio

Ideal for producing a spec product without the need of a primary jaw crusher.

Superior finished material compaction

Superior Material Compaction

Material produced by an impact crusher is easier to grade and compact making it perfect for base and subbase.

Types of Impactors

There are 2 main types impact crushers - horizontal shaft impact (HSI) crushers and vertical shaft impact (VSI) crushers.

Horizontal Shaft Impactor (HSI)

The horizontal shaft impactors are the most common impactor type that can be used in recycling, primary and secondary crushing applications. This type impactor will take reasonable size pieces and produce small output material.

Vertical Shaft Impactor (VSI)

Vertical shaft impactors are designed to process already small material even smaller and are therefore used in a tertiary crushing application (e.g. producing manufactured sand).

What are the main components?

The crusher box includes a rotor with hammers (also called blow bars). Depending on the rotor style you will have either 3 bars or 4 bars. Hammers are cast iron replaceable wear parts that are actually in contact with the material. They are designed to withstand the many impacts of the material. The impact wall (also called apron) has several crushing stages and is armoured by thick wear plates.

Once the hammer hits the big material entering the crusher box it is thrown against the wall and starts ricocheting between hammers, wall and other material particles. As soon as the material is small enough the fit in between the rotor and the lowest crushing stage of the impact wall it will leave the crusher box at the bottom.

Diesel-electric direct drivetrain in a RUBBLE MASTER impact crusher

Drive systemX

On a mobile unit impact crushers are driven directly by a diesel-engine or indirectly driven by an electric motor or a hydraulic pump.

Rotor bodyX

There are different rotor body styles. Most common are 3-bar and 4-bar rotors. This example is a 4-bar rotor that can be operated in the following two operation modes:

  1. 4 high bars: this mode is for processing small materials (e.g. asphalt millings or gravel) or in a secondary crushing application (e.g. after a jaw crusher)
  2. 2 high & 2 low bars: this mode is a multi-purpose setup which is ideal for  primary crushing and recycling applications.

Inlet openingX

The inlet opening defines the overall feed-size. As a rule of thumb it is recommended that the maximum feed size is 80% of the inlet opening width.

A chain curtain prevents rocks being ricocheting back ensuring operator safety.

impact crusher inlet

Impact wall or apronX

The impact wall is typically hinged and can be adjusted hydraulically. The apron is typically armored with replacedable impact plates. Some crusher types need to replace the entire impact wall once it is worn out.

What materials can you process?

Impact crushers is a versatile crusher that can be used to process natural rock and recycle materials alike. Many people claim that you can't process hard rock with an impact crusher. This is not entirely true because it depends on the breaking characteristics of the rock and the feed size.

Concrete & asphalt recycling

Reinforced concrete, demolition material, asphalt millings, washout concrete, high PSI runway concrete, brick & masonry.

Natural rock

Soft & medium hard rock

Every rock is different even if it is the same type of rock. There is soft limestone and there is hard limestone. Please consult a crushing expert to verify your application.


Slag, railroad ties, glass, ivory, and pre-stressed concrete is also possible but need closer attention. Please consult a crushing specialist.

What size material can you produce?

The beauty of impact crushers is their versatility in terms of input material and output size. There are many different designs out there but generally speaking impact crushers can produce material from 3" down. The smaller the input material the harder it gets to crush. The output gradation can be adjusted through various settings.

Rotor Speed

The higher the speed the more fines are produced.

Crusher Geometry

Altering the distance between the rotor and the impact wall influences gradation and overall output size.

Simple settings

Hammer Setup

Common hammer setups are 2 high 2 low or 4 high hammers.

Changing The Impact Crusher Geometry

On most crushers this works hydraulically. The aprons need to be adjusted when you want to produce a different output material or when you need to readjust your crusher settings to accomodate the wear progress.

RUBBLE MASTER impact crushers use a simple design to change the crusher setup easily, quickly and safely within minutes. The unique proprietary crushing chamber design allows operators with limited impact crushing experience to operate our machine efficiently from day one.

Impact crusher hammers, wear liners, and impact plates are consumables and need to be replaced frequently.

Wear items are chewed up in the crushing process and need to be monitored and changed frequently. The higher the abrasion, hardness, and fines-content the faster the wear. The rotor body holds hammers in place through a sliding system (see picture) or they are lifted in and wedged in place.



Impact Crusher Models RUBBLE MASTER offers a large range of mobile Impact Crushers ranging from 90 to 385 TPH.
Inlet opening
RM 120X Mobile Impactor RM 120X
Impact Crusher
350 tph 385 TPH
1,160 x 820 mm 46" x 32"
298 kW 400 HP
44,000 kg 95,000 lbs
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RM 100GO! Tracked Impact Crusher RM 100GO!
Impact Crusher
250 tph 275 TPH
950 x 700 mm 37" x 28"
242 kW 325 HP
33,600 kg 74,500 lbs
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RM 90GO! Compact Crusher RM 90GO!
Impact Crusher
200 tph 220 TPH
860 x 650 mm 34" x 25"
194 kW 260 HP
28,400 kg 62,500 lbs
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RM 70GO! Compact Crusher RM 70GO! 2.0
Impact Crusher
150 tph 165 TPH
760 x 600 mm 30" x 23"
115 kW 155 HP
24,200 kg 53,400 lbs
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