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

Feb 21, 2025

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. 

Mainly spherical roller bearings of series 222 are used as inner bearings, and series 223 bearings as outer bearings. In some machines, spherical roller bearings of series 231 and 232 as well as 240 and 241 have been used successfully. 

Outer bearing mountings usually consist of a locating bearing and a floating bearing. For inner bearing mountings a floating bearing arrangement (axial displaceability 1 to 2 mm) is preferably used. 

The bearings can be mounted either directly on the cylindrical or tapered shaft, or on adapter or withdrawal sleeves. 

The bearings are preferably fastened with hydraulic adapter sleeves.

2.1.3 Dimensioning of the bearings 

The required dynamic load rating, and thus the bearing size, is determined for double toggle jaw crushers and single toggle jaw crushers using the following formula:

and on experience gained with field proven bearing arrangements as well as tests, FV has developed the above formula. The bearings calculated using this formula are sufficiently dimensioned for crushers with a feed opening of up to approx 1200 x 800 mm. 

In the case of larger crushers the application of this formula may yield overdimensioned bearings. Therefore, the mean power required by the machine - ca. 60 to 70 % of N should be entered in the calculation instead of the power installed. in cases of doubt, the crusher manufacturer must be consulted about the mean power required. 

When specifying the exact bearing design, the crusher manufacturers' unique experience in the field has to be taken into consideration. 

2.1.4 Bearing seats (Mouting Fits)

We recommend to machine the bearing seats to tolerance h7 for the shaft (if adapter or withdrawal sleeves are used) and to H7/J7 for the housing bore. 

If the bearings are mounted directly onto the shaft, the latter should be machined to m6. 

2.1.5 Bearing clearance 

The FV spherical roller bearings for jaw crushers are normally supplied with clearance group CN (normal). 

2.1.6 Bearing lubrication 

We recommend to lubricate the FV rolling bearings in jaw crushers with a lithium soap base grease with EP additives and corrosion inhibitors, e.g. our rolling bearing-tested the grease Arcanol L186 V. 

2.2 Cone crushers 

2.2.1 Principle of operation 

Cone crushers, also referred to as gyratory crushers due to their gyroscopic motions during the size reduction process, were developed in the USA, where they were also first built and put into operation. 

The Symons brothers contributed considerably to the development of cone crushing machines. The basic principle of cone crushers has remained the same to this day. 

The principle of operation of cone crushers is continuous, and the crusher axis onto which the crushing cone is mounted revolves at a defined angle to the perpendicular. Depending on the crusher gap adjusted, cone crushers are used either for coarse crushing or fine crushing of materials, effected by the gyratory movement relative to the crusher shell. 

Cone crushers are designed for large throughputs and are primarily used in mineral processing and in quarries. 

The throughput can reach up to several thousand tons per hour, depending on the machine used and on the original size (approx. 8 to 300 mm) of the material to be crushed. 

The output size of the crushed material can range from 0 to 70 mm, depending on the crusher size. 

2.2.2 Crusher axis/crushing cone support 

Shafts in cone crushers are supported either in rolling bearings or in plain bearings, depending on the crusher type. 

Figs. 2 and Figs. 3 show cone crushers in which rolling bearings are used. in the lower section of the crusher shaft the bearing axis is vertical. In the upper section, the bearing arrangement supporting the crushing cone is eccentric, and the bearing axis is inclined relative to the perpendicular. The crushing cone performs a gyratory movement. 

The crusher shaft is driven via a pinion meshed with the ring gear at the base of the crusher shaft. 

Fig. 2 shows how the "inner system" (crusher axis) is radially supported in two successive special cylindrical roller bearings of NU design (a), and axial support is provided by a special-design double-row cylindrical roller thrust bearing (b) with a high load carrying capacity. The same bearing Arrangement is used in these crushers to support the "outer system" (crushing cone). 

As shown in Fig.3, the "inner system" is radially supported at the top position by two successive standard cylindrical roller bearings of NU design (a). To achieve an even distribution of the external load among both bearings, the bearings are adjusted to N11B. At the bottom position the "inner system" is supported radially and axially by a specialdesign tapered roller bearing (b) with a high lead carrying capacity. 

The crushing cone ("outer system") which is mounted onto the crusher axis is supported at the top position by a standard cylindrical roller bearing of NU design (c). To prevent the crushing cone from being lifted off by a gyroscopic moment, the cylindrical roller bearing is locked by means of an HJ angle ring. At the bottom position the crushing cone ("outer system") is radially and axially supported by a special- design tapered roller bearing (d) with a high load carrying capacity. 

2.2.3 Bearing dimensioning 

2.2.4 Bearing seats (Mounting Fits)  

Fig. 3: 

Radial cylindrical roller bearings: 

we recommend to machine the bearing seats to m6 (shaft) and N6 (housing bore). 

Cylindrical roller thrust bearings: 

we recommend to machine the bearing seats to j6 (shaft) and H6 (housing bore). 

Fig. 4: 

Radial cylindrical roller bearings: 

we recommend to machine the bearing seats to k6 (shaft) and N6 (housing bore). 

Tapered roller bearings: 

we recommend to machine the bearing seats to j6 (shaft) and N6 (housing bore).

2.2.5 Bearing clearance 

Taking into consideration the fit recommendations and the temperature difference between inner and outer rings, a special radial clearance was selected for the radial cylindrical roller bearings in Fig. 3, and C3 radial clearance for the cylindrical roller bearings in Fig. 4. 

2.2.6 Bearing lubrication 

Rolling bearings in cone crushers are very heavily stressed. 

The heat generated in bearings with a high percentage of sliding friction, e.g. cylindrical roller thrust bearings and tapered roller bearings, must be removed. Oil circulation lubrication is the best choice, Figs. 2 and 3. 

To keep the operating temperature within reasonable limits, and thus to achieve a viscosity ratio of x= v/v1 = 2, we recommend to use a rolling bearing-tested lubricating oil in accordance with ISO VG 220 or 320 specifications. 

Suitable are, e.g. doped oils of series 

- Shell Omala

- Mobil Mobilgear 

- Aral Degol 

It is important to observe the oil volume, oil cleanliness and oil change interval specified by the machine manufacturer.

2.3 Hammer crushers 

2.3.1 Principle of operation 

Single-shaft and double-shaft hammer crushers have been used for many decades to crush a variety of materials 

As primary and secondary crushers, they are used for crushing bulk materials, e. g. limestone, marl, coal, gypsum, clay, etc. 

Huge hammer crushers in quarries can reduce material with edge lengths of up to 2.5 m and weighing up to 5 tons to an output size of approx. 25 mm in one single operation. They can reach throughputs of up to 2500 t/h. 

In single-shaft crushers, the material is smashed against one or several jaw plates by rotating beater works (hammers attached to the rotor). The rough-crushed material is further reduced in size between the rotating hammers and the grinding tracks. The end product falls through the grid openings in the bottom plate of the crusher. 

In double-shaft hammer crushers, the material is first rough- crushed above the rotors and then reduced to their final grain size by the two counterrotating beater works. The end product falls through the grid openings in the bottom plate of the crusher. 

Hammer crushers work, depending on their size, at speeds ranging from approx. 200 to 2000 rpm. The required power can be 1000 kW and more.

2.3.2 Rotor support 

Operation under rugged operating conditions and shaft deflections require spherical roller bearings to support the rotating beater works, see example in fig. 5. 

Fig. 5: Double-shaft hammer crusher 

Bearings of series 222, 223, 231 and 232 are used which are fastened on the shaft using adapter sleeves or withdrawal sleeves. 

The outer rings of the spherical roller bearings are supported by means of special plummer block housings. 

The beater works of single-shaft and double-shaft hammer crushers are supported in a similar way. 

2.3.3 Bearing dimensioning 

Example: KHD Double-shaft hammer crusher HDS 1600x1980, Fig. 5

Operating data

2.3.4 Bearing seats (Mounting fits)

We recommend to machine the bearing seats to h7 tolerance for the shaft (sleeve fastening) and to H7 for the housing bore. 

2.3.5 Bearing clearance 

FV spherical roller bearings for hammer crushers are normally supplied with C3 radial clearance. 

2.3.6 Bearing Inbrication 

We recommend to lubricate spherical roller bearings in hammer crushers with a lithium soap base grease with EP- additives and corrosion inhibitors, e.g. our rolling bearing- tested the grease Arcanol L135V.