Guidelines for Mouting and Maintenance of Bearings in Hard Material Crushing Equipment

1.1 Processes used for crushing hard materials

These processes are used to reduce a material from its original size to a smaller, defined output size.

The main physical size reduction processes are:

shattering (breaking),

squeezing,

grinding.

Shattering (breaking) is used, as a rule, to reduce materials with grain sizes of > 50 mm in size. In squeezing and grinding processes, materials already reduced to grains sizes of 5-50 mm are reduced/ground to extremely small grains. The boundaries between squeezing  and grinding are fluid.

1.2 Machines used for crushing hard materials

Machines used for crushing hard materials can take materials with edge lengths of up to 2500 mm and reduce them to sizes of a few hundredths of a millimeter in a series of processes. In these machines - crushers, mills and presses - moderately to extremely

hard stones, other minerals, coal and sands are processed. Depending on the material and on the desired end product, the following machines may be used:

Jaw crushers

Cone crushers

Hammer crushers

Roller grinding mills

Roller presses (cylinder crushers) - Tube mills

Machines used for crushing hard materials must be characterized by a high efficiency and operational reliability, and they must be easy to maintain. As a famous rolling bearing manufacturer, FV are making their contribution to meeting these requirements.

2.1 Jaw crushers

2.1.1 Principle of operation of double toggle jaw crushers

The jaw crusher was invented in the middle of the 19th century, by an American named Blake. It is also referred to as double toggle jaw crusher.

Double toggle jaw crushers are used as coarse crushers and fine crushers. The principle of operation is intermittent. On a horizontal shaft with an eccentric centre section sits the pitman, which actuates the swing jaw through a double toggle lever system. The swing jaw is supported in sliding sleeves or rubber-bonded-to-metal bondings. Rolling bearings are installed in the pitman (inner bearings) and in the crusher frame (outer bearings).  

Industry Unit Mining & Processing

The crushers feed opening can span more than 2000 mm. The eccentric shaft speed is between 180 and 280 rpm, depending on the crusher size.

2.1.2 Eccentric-shaft support in double toggle jaw crushers and single toggle jaw crushers

The outer bearings (b) both in double toggle jaw crushers (Fig. 1) and in single toggle jaw crushers (Fig. 2) have to support the eccentric shaft in the frame. The outer bearings are more heavily loaded than the inner bearings as they have to transmit not only the crushing forces but also have to support the flywheel weight and transmit the loads resulting from the drive.

The inner bearings (a) support the pitman in double toggle jaw crushers and the swing jaw in single toggle jaw crushers. Due to the eccentric shaft, the inner bearings have a larger bore than the outer bearings.

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