Crusher Blow Bars

During material crushing in an impact crusher, wear is produced when the elements press against each other, such as liner, blow bars, and crushing material. During this process, small materials from each element become detached, causing the surface to wear away. The primary factor in wear for crushing applications is abrasion. Material fatigue is also a factor as the wear material is subjected to numerous pressure and impact stresses. There are several factors that influence the wear behavior of an impact crusher. The following are some of the factors that affect the wear lifetime of crusher blow bars:

Material-related factors:

• Abrasiveness
• Breakability
• Grain shape
• Fine-particle proportion
• Moisture content
• The proportion of unbreakable elements

Machine-process-related factors:

• Crushing ratio
• The ratio of the upper to the lower impact toggle
• Rotor speed
• Type of loading
• Screening mesh of the prescreen
• Contamination in the crushing chamber

Operation-related factors:

• Continuity of feed
• Correct adjustment of machine parameters
• Replacement of wear parts in due time
• Selection of the right blow bars

There are 3 situations that need to change crusher blow bars:

1. Normal wear. In order to avoid damage to the rotor, blow bars should be replaced before they are worn through.
2. Blow bar break. When a chrome blow bar crushes iron steel, it easily breaks; Some “problem” blow bars (Casting shrinkage cavity) also easily break; Other reasons results.
3. When one face is used, the blow bar can be turned around to use the other face.

There are 6 steps to changing crusher blow bars:

1. Open the impact crusher as per the instruction manual;
2. Switch off the system components and diesel generator;
3. Secure the rotor;
4. Visually inspect the wear limit on all blow bars;
5. Visually check the blow bars for cracks and protrusions;
6. Turn around or replace the blow bars as necessary

Notes on change crusher blow bars:

• For rough cleaning of the crushing chamber, it is recommended to fill the crusher for several minutes with clean, coarse material;
• Always use suitable lifting gear and tack;
• At least two people should take part in installing and removing crusher blow bars;
• Improper replacement of the blow bars can lead to crusher damage;
• Completely extend the crusher gap before blow bar replacement in order to prevent a collision between the blow bars and toggle after new blow bars have been installed;
• Only operate the rotor if the blow bars have been correctly installed;
• Always replace blow bars in sequence;
• Before making the final setting, briefly operate the machine at the highest rotational speed, then check the wedge clamps; tighten the screws if necessary;
• Replace all blow bars even if only one of them is broken;
• A non-secured rotor can lead to severe injuries, observe safety instructions;
• Always use conical spring washers with the clamping bolts of the tensioning devices. Retighten the clamping bolts after approx. two operating hours.

There are many reasons why your impact crusher blow bars are breaking on a regular basis. We have compiled a list of the most common causes of blow bar failure and the solutions to those problems.

 

Study case 1

Problem: Excessive penetration on the blow bar

Causes:

• The rotor speed is too slow.
• Increases risk of blow bar breakage.
• The blow bar is under-utilized before changing.
• Increased rotor wear.

Solution:

• Increase the rotor speed.
• Change to 4 high blow bars.

 

Study case 2

Problem: Poor penetration on the blow bar means the top of the blow bars is worn down flat.

Causes:

• The rotor speed is too high.
  • Wear rates will be excessive.
  • Reduced output.
  • Creates a lot of fines

Solution:

• Reduce the rotor speed.
•  Change configuration to 2 high and 2 low blow bars.

 

Study case 3

Problem: Wear on the sides of the blow bar

Causes:

• A high percentage of fines in the feed or overfeed causing fines to be pushed outside.
• Crusher chamber contaminated with caked material causing friction wear.

Solution:

• Reduce the speed of the feeder so wear becomes even across the surface of the blow bar.
• Clean chamber daily after each shift.

 

Study case 4

Problem: Blow bar wearing excessively to one side

Causes:

• The machine on uneven ground – material falling to one side
• The machine isn’t choke-fed.
• Feed dropped onto one side of the feeder when using a recirculating option.

Solution:

• Ensure the machine is on level ground.
• Continuous loading.

 

Study case 5

Problem: Blow bar is damaged or broken.

Causes:

• Incorrect blow bar for an application. (E.g. Chrome)
• There is steel or rebar in the feed.
• The feed size is too large.

Solution:

• Select the correct blow bar.
• Control feed size.
• Remove steel or rebar.

What material is best for your impact crusher blow bars? What material has the longest service life of a blow bar? These depend on the working conditions of your machine. There are two main aspects of the working conditions: the wear resistance and crushing difficulty of the material being crushed; and the type of material being crushed.

There are four kinds of material that we used in manufacturing crusher blow bars. Different materials suit different impact crusher working conditions.

1. High Manganese. This material is widely used in crusher jaws, crusher cones, and crusher shells, not common in impact crushers. However, when crushing less abrasive and large feed material(such as limestone), the manganese blow bars are the best choice.
2. Martensitic Steel. Martensitic steel lies between manganese and chrome steel. It’s used if the impact load is too little to harden the manganese steel, and good wear resistance is required along with good impact stress resistance.
3. Chrome Steel. Chrome steel is the common material in casting HSI blow bars because it has a very good hardness. Regularly, chrome steel typically has a hardness of 60 to 65 HRC. And if we increase the elements’ “Mo” content, it also can get very toughness and wearable, not easy break.
4. Metal Matrix Composites. This combination makes HSI blow bars very wear-resistant but at the same time very impact-resistant. With blow bars made of composites from the surface of ceramics, the working life can reach three to five times that of simple martensitic steel blow bars.

 

What material do you crush?

Every material has unique characteristics in terms of hardness, abrasion, and breaking characteristics. The harder the material, the more you need to watch your feed size.

MATERIAL	HOW MUCH DOES IT WEAR? ABRASIVENESS	HOW EASY DOES IT BREAK? CRUSHABILITY
CONCRETE	low	easy
ASPHALT	high	easy
LIMESTONE	low	easy
GRANITE	high	medium
BASALT	medium	medium
GRAVEL	low	easy

 

What material of crusher blow bar is the best choice for crushing concrete?

Qiming Casting’s advice: Martensitic blow bars with ceramic inlays.

What material of crusher blow bar is the best choice for crushing asphalt?

Qiming Casting’s advice: Chrome steel or chrome steel blow bars with ceramic inlays.

What material of crusher blow bar is the best choice for crushing limestone?

Qiming Casting’s advice: In primary crushing, we suggest martensitic blow bars with
ceramic inlays; In secondary crushing, we suggest chrome steel or chrome steel blow bars with ceramic inlays.

What material of crusher blow bar is the best choice for crushing basalt?

Qiming Casting’s advice: In primary crushing, we suggest martensitic blow bars with
ceramic inlays; In secondary crushing, we suggest chrome steel or chrome steel blow bars with ceramic inlays.

What material of crusher blow bar is the best choice for crushing granite?

Qiming Casting’s advice: In primary crushing, we suggest martensitic blow bars with
ceramic inlays; In secondary crushing, we suggest chrome steel or chrome steel blow bars with ceramic inlays.

What material of crusher blow bar is the best choice for crushing sand & gravel?

Qiming Casting’s advice: In primary crushing, we suggest martensitic blow bars with
ceramic inlays; In secondary crushing, we suggest chrome steel or chrome steel blow bars with ceramic inlays.