Three main types of crushers
In practice, three main principles are used for crushing concrete and stone: the jaw crusher, the cone crusher, and the impact crusher. Each type operates in a different way and therefore places different demands on the bearing construction.
The jaw crusher is mostly used for the primary reduction of concrete and rubble. The material is compressed between a fixed jaw and a moving jaw. The motion of the movable jaw is generated by an eccentric main shaft. This construction creates high forces and heavy shock loads when hard pieces of concrete end up between the crusher plates.
The cone crusher is often used for further reduction after the material has already undergone an initial crushing step. A conical breaking mantle rotates eccentrically within a fixed bowl. This causes the material to be continuously compressed and reduced. The load here is very high but relatively uniform.
The impact crusher works according to a different principle. Here, a rotor with hammers or blow bars rotates at high speed. The material is accelerated by this rotor and flung against impact plates. The fracture occurs due to the impact energy. This primarily creates dynamic loads and strong vibrations.
Bearing constructions in crushers
The main bearings of crushers must be able to absorb high forces and withstand shock loading. Therefore, heavy-duty roller bearings are usually applied, such as spherical roller bearings or cylindrical roller bearings. These bearings have a high load-carrying capacity and can handle misalignment relatively well.
In some crushers, particularly cone crushers, plain bearings or bronze bushings are also used. These bearing constructions work with a hydrodynamic lubrication film whereby the moving parts remain separated from each other by an oil film. Plain bearings can handle very high loads, but place high demands on the quality of the lubrication.
Why bearings often fail
Bearings in rubble crushers rarely fail due to a single cause. Usually, there is a combination of heavy loading, contamination, and lubrication problems.
Shock loading plays an important role. Concrete and rubble often contain hard inclusions such as reinforcement steel or large stones. When such pieces suddenly end up between the crushing parts, very high peak loads occur. These can cause damage to the bearing raceways.
In addition, contamination constitutes a major problem. Crushing plants produce a lot of dust, including cement dust and sand. When these particles enter bearings, they act as an abrasive and cause accelerated wear.
Insufficient lubrication can also lead to damage. Due to the high load, a strong lubrication film is necessary to prevent metal-on-metal contact. When the viscosity of the lubricant is too low or when the lubrication is insufficiently replenished, wear increases rapidly.
Hydraulics in rubble crushers
In addition to the mechanical construction, hydraulics also play an important role in modern crushing plants. Hydraulic systems are used for setting the crusher gap, protecting the machine against overload, and opening the crusher for maintenance.
The hydraulics are exposed to heavy loads in this process. When an unbreakable object ends up in the crusher, the pressure in the system can suddenly rise sharply. Relief valves must absorb these peak pressures to prevent damage to the machine.
Temperature also plays a role. Due to the high pressures and internal losses, hydraulic fluid can heat up significantly. When the temperature becomes too high, the viscosity decreases and the lubricating effect of the oil is reduced.
Additionally, contamination poses a great risk. The dusty working environment of rubble crushers ensures that dirt particles easily enter the hydraulic system. These particles can cause wear to pumps, valves, and cylinders.
Protection of bearings and hydraulics
Due to the extreme conditions in which rubble crushers operate, the choice of lubricants is of great importance. Modern lubrication technology can play an important role in reducing wear and preventing unexpected downtime.
For heavily loaded bearing points in crushers, Eurol has developed a special Schmierfett: Eurol Grease CS-2/103-S. This grease is based on Eurol SYNGIS Technology, a technology aimed at maximum wear protection under extreme conditions. The grease offers very strong anti-wear and anti-corrosion properties and is furthermore exceptionally water-resistant, which is important in environments where water, mud, and cement dust are present.
Additionally, the grease contains a special polymer technology. These polymers do not adhere to the metal surface of the bearing, but instead encapsulate dirt particles with a protective coating. As a result, hard particles such as sand or dust become less abrasive and can cause significantly less damage to the metal bearing surfaces.
When this Schmierfett is combined with a shear-stable hydraulic fluid, such as Eurol Hykrol EXL ISO-VG 46, and the specially developed Eurol Additive-S, a very robust protection of both the bearing constructions and the hydraulic system is created. The additive provides extra wear protection for, among others, hydraulic pumps and other heavily loaded components in the hydraulic circuit.
This combination of Schmierfett, hydraulic fluid, and additive technology can contribute to a significant extension of the service life of critical components and helps to prevent unexpected downtime of crushing plants.
In modern installations, this approach can be further strengthened by condition monitoring with sensors. By monitoring, for example, temperature, vibrations, and the condition of lubricants, the technical state of bearings and hydraulic systems can be continuously followed and maintenance can be planned in a timely manner. This further increases the reliability of the crusher and can limit costly downtimes.
Author: Bart van Hoorn, Head Technology & Innovation.
