Break it down

08 May 2008

A broken end on a blow bar results in damage to the rotor. Inspecting the rotor and bars before each

A broken end on a blow bar results in damage to the rotor. Inspecting the rotor and bars before each shift can help prevent serious damage.

Equipment downtime can often make the difference between profit and loss. Proper and diligent maintenance practices, which should be preventive and done on a daily or weekly basis, can help minimise this.

Indeed, without proper maintenance a good crusher can be ruined in as little as six weeks. However, and surprising as this may seem, overdoing maintenance can also cause problems. A good quality crusher will last between 10 to 15 years, but finding the right balance with maintenance can prolong active service life to 20 or even 25 years.

The most important step is to follow the manufacturer's maintenance schedule and procedures, establish a sensible maintenance and repair schedule, and stick to it.

Common themes

Different crusher types require different maintenance, but there will also be common themes. The most obvious common component on mobile machines is the diesel engine, and here it is important to make sure connections between the engine and air cleaner are tight. It is a good idea to run a duct from the air intake to a clean area 5 to 10 m away from the crusher, because dust ingestion is a big problem in crusher operation. Without proper air filtration, a new engine can be ruined in a matter of days or even hours.

An oil-sample analysis programme can also save you a lot of engine grief. It will expose air cleaner problems by identifying any high silica content or other contaminants in the oil.

It is also important not to over-grease shaft bearings ” it causes the bearings to overheat. Big bearings don't require as much grease ” just follow the manufacturer's schedule. Manufacturers know what their equipment needs so don't improvise.

Wear parts

Wear parts are expensive. But breakdowns are much more expensive. It is therefore important to replace all wear parts regularly, including side liners, rotor shoes, manganese apron, manganese blocks on the apron, impact plates, seals and so on. Always keep wear parts in stock, especially crusher wear liners and blow bars so there are no delays when they need replacing.

Impact crushers have blow bars, which, if not replaced on time, could end up damaging the rotor itself ” a very expensive replacement! This happens when the blow bars are worn down to the extent that material being crushed wears on the rotor surface itself.

Blow bars themselves are expensive so turning them can save money and prevent breakdowns. Many users recommend turning the bars every 25000 tonnes or so when crushing concrete and limestone. Manganese steel bars can be used in this application, because it is softer than high chrome steel, so is less likely to break. The downside is that manganese bars will wear faster, so have to be turned more often.

High chrome bars should be used for crushing asphalt, and should be turned every 15000 to 20000 tonnes, depending on how abrasive the material is and how much aggregate is in it.

When changing blow bars it is also worth performing other maintenance tasks. For example, it is a good idea to change liners if they are fairly worn, so the crusher does not have to be shut down again soon after.

Another important wear part is the sideliner. These are square plates bolted to the crusher inside walls on both sides of the rotor. These can normally be unbolted and turned through 90° or 180°, rather than replaced every time. It is also worth looking at wear plates outside the rotor zone. These will last longer and can sometimes be switched with highly worn plates to give a longer life from the whole set.

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