What are blow bars?

Impact crusher blow bars (also called hammers) are the main wear item of horizontal shaft impact crushers and a major cost driver. The purpose of blow bars is to strike material entering the crushing chamber and throwing it against the impact wall causing the material to fracture into smaller particles (see also: how does an impact crusher work). In the process of striking the material blow bars wear out and need to be replaced. They are made out of cast steel with various metallurgical ingrediants optimized for a specific applications. Selecting blow bars that match your application is crucial for achieving a long wear life.

Metallurgical types of blow bars

Blow bars are manufactured in foundries- where they are cast to the manufactureres shape and metallugical specifications. While the crusher hammer shape can be easily copied the metallurgical composition is the actual secret ingredient.

What affects impact crusher blow bar wear?

Your blow bar wear life depends on the feed material chracteristics, crusher settings, and your overall crusher operation.

Feed material factors

• Feed size: feed size might affect your hammer selection. The bigger the feed the more breaking resitance you need from your hammers. Matensitic hammers with ceramic inlays have a good breaking resistance for primary crushing applications and recycled concrete.
• Abrasiveness: depends on the material characterastics. Rock with high silica content and asphalt are highly abrasive materials.
• Fines: large amounts of fines inside an impact crusher chew up your wearables quickly.
• Moisture: high moisture results in more wear. Take caution when using water for keeping the dust down onsite. Use as much as possible to keep the dust down but as little as possible to keep the wear down.

Crusher factors

• Crusher geometry and CSS (closed side setting): if your crusher settings are off you risk higher wear. In case you run an imapct crusher with 2 aprons both settings must be set correctly. RUBBLE MASTER impact crushers feature a single apron with 3 crushing stages that require only one setting to be set correctly.
• Rotor speed: the faster the rotor spins the more the material is hit.

Operational factors

The way how you run your impact crusher affects your wear life greatly.

• Fines management: the more fines entering the impact crusher the higher the wear. Fines inside an impact crusher is like sandblasting your consumables. If faced with excessive amounts of fines make sure your pre-screen grizzly stays open or try to seggregate fines with a mobile screening plant first (e.g. a mobile scalping screen). This becomes very important when processing sand & gravel, asphalt millings, or excavated materials with lots of dirt.
• Rock-on-rock crushing: if rock impacts rock you achieve a longer wear life out of your consumables. The key for rock-on-rock crushing is a constant and even flow of material. Doing your prep first and bringing in your crusher later allows you to feed the crusher steadily without interruptions. It is also recommended, to build an even pad so that there is no material shift on the left or right side of the feeder, which results in premature hammer wear on one side.
• Material prep: tramp iron and other uncrushables cause more wear on your hammers and you face a higher risk of breakage. .By sorting through your pile and feeding with an excavator you can set uncrushables aside before they go into your crusher.