Crushers are fundamental assets in the crushing process, which aims to reduce the particle size of the material to avoid overload in the grinding stage, which has the highest energy consumption in ore treatment. This reduction contributes to the greater effectiveness of grinding and leaching.
The crushing process is divided into three main stages: primary, secondary, and tertiary. In the primary stage, heavy machinery is used to reduce the size of the material coming from the mines (blocks from 1000 to 500 mm to 300-100 mm). Thus, the material is transformed into particles suitable for transport on conveyor belts and to feed the secondary crushing (reducing blocks from 300 – 100 mm to 100 – 38 mm), the semi-autogenous mill (SAG), or to form the stockpile for leaching.
In tertiary crushing, in a typical plant, the product ready for grinding is obtained, the next step in the process (producing aggregates of 12 mm on average). In cases of crushing for a very fine product, it may be necessary to perform quaternary crushing.
These assets tend to present various failure modes, from the most common, involving:
- Lubrication problems;
- Faulty bearings and gears;
- Problems caused by misalignments, imbalances, or even by unstable bases, bent or deformed shafts, mechanical looseness, etc.
There are also more specific failures, such as:
- Wear or deformation of the crushing chamber plates;
- Obstructions;
- Choking
Get to know the main types of crushers and their respective failure modes:
Types of Crushers
Roll Crusher
The family of roll crushers generally operates at low speed. Some of the most well-known models are the High Pressure Grinding Rolls (HPGR) and the Low Speed Sizer.
The HPGR uses two rotating rolls that turn in opposite directions. The crusher’s hydraulic cylinder system applies high pressure, promoting the comminution (reduction of grain) of the material as it passes through the rolls. Its application is indicated for processing diamonds and gold because crushing does not damage them and facilitates leaching. In fact, it is used for iron ores, replacing the SAG mill.
The Low Speed Sizer, on the other hand, is recommended for clayey or sticky materials. It consists of two toothed rolls wrapped in a crushing chamber. The system has high torque and low speed, generating few fines. However, it has a low reduction ratio.
Due to the mechanical composition of this crusher, the main failure modes are usually associated with the significant wear that the teeth undergo due to abrasion. In addition, breaks in the eccentric shaft can occur, mainly due to attempts to crush non-crushable materials.
Read a case of early detection of problems in the eccentric shaft at Vale here: Monitoring and Asset life of the HP 400 crusher (dynamox.net)
Jaw Crusher
The jaw crusher is used in primary crushing and is therefore usually installed near the mine. Crushing in this type of equipment occurs by compression and friction promoted by metal plates: one mobile and one fixed (jaws).
The mobile jaw moves and compresses the fragments against the fixed jaw, crushing them. These flow during the movement away until they are compressed again in the next interaction.
There are two types of jaw crushers: single or double shaft. In the single shaft crusher, the movement of the mobile plate occurs in a circular manner, making it more compact and with greater capacity. In the double shaft crusher, the movement is open and close.
The choice between one type or another of crusher is usually associated with the ore to be processed. The use of double shaft crushers is recommended when working with quartz, siliceous granites, siliceous ores, and itabirites.
Regarding possible failures, there is jaw wear (which is usually more severe in the single shaft crusher) and choking. This problem occurs when the output flow does not match the input volume, so there is a critical flow value.
Gyratory Crusher
The gyratory crusher can be used in both primary and secondary crushing. Its main advantage lies in its flexibility of use, as it allows to receive material directly from trucks, without the need for a scalper and feeder. This characteristic makes it ideal for operations that require speed and efficiency.
The gyratory crusher is also known for its high production capacity and low maintenance requirements. This is due to its robustness and the simplicity of its design. Some possible applications of the asset include:
- Ore crushing;
- Rock crushing;
- Aggregate crushing;
- Recycled material crushing.
Its composition consists of a movable element (cone) and a fixed element (mantle). The cone rotates eccentrically around an axis, approaching and moving away from the walls of the mantle in a circular recessive movement. Unlike the jaw crusher, the gyratory crusher must work with the crushing chamber 100% full and does not run the risk of choking.
One of the main failure modes of this type of crusher is the obstruction of the crushing chamber by oversize material. This obstruction mainly occurs due to the deformation of the concave plates of the crusher, caused by large ore or waste blocks (oversize material) present in the soil layers. They can be formed naturally or by the fragmentation of rocks, causing damage to loading and transport equipment.
Impact Crusher
The impact crusher uses the force of impact to reduce the size of the material. This reduction occurs both through the impactors and through the abrasion caused by contact with the housing or the impact bars.
The high operating speed of the impact crusher makes it equivalent to two to three stages of traditional crushers. This means that it can reduce the material more quickly and efficiently, although with higher abrasion wear.
The fragments generated by the impact crusher are finer than those obtained by jaw and gyratory crushers. This characteristic makes it ideal for processes where the generation of fines is not a problem and the production of cubic products is not necessary.
Thus, the main indications for use are with the crushing of phosphate, limestone, bauxite, clay minerals, barite, and coal.
In these crushers, the main failure modes involve:
- Failures in spare parts;
- Abrasion of wear parts;
- Mechanical failures caused by the entry of non-crushable material into the equipment.
Cone Crusher
The cone crusher operates on the same principle as the gyratory crusher. The difference lies in the long parallel surfaces of the mantle and the cone, which ensure a longer retention time for particles, providing more precise control over the final product’s particle size distribution.
These assets operate in secondary crushing and are called “standard” models. On the other hand, models that operate in tertiary crushing are called “short head“, which allow for better utilization of the chamber volume.
The versatility of the cone crusher allows for the fragmentation of materials into various sizes, from coarse to fine, allowing for variation in the particle size distribution of the crushed product. And, just like the gyratory crusher, cone crushers must also work with the chamber 100% filled, ensuring an efficient process and avoiding equipment choking.
The failure modes of the cone crusher are quite similar to those of the gyratory model. The most common problems involve inadequate lubrication and excessive wear of abrasion parts, which can lead to other failures.
How to Prevent Failures in Crushers?
The unplanned shutdown of an asset can have many causes and usually indicates that the machine has had some problem for some time. In the case of crushers, it is essential to detect this failure early on, as these machines are considered highly critical for the production process.
For this reason, continuous monitoring is essential. This can be done by installing vibration and temperature sensors, as well as through inspection routes. This combination allows for the detection of problems even in their early stages, both by analyzing abnormal vibration or temperature variations, and by visually identifying oil leaks, for example.
Dynamox offers a complete solution for online and continuous asset monitoring. In fact, it was possible to prevent an unplanned shutdown on a crusher by detecting that the bolts of the crankcase were damaged. Vibration analysis indicated this failure, and the technician, upon inspection, confirmed the problem. This diagnosis allowed for scheduling corrective maintenance and prevented losses in the production line.
Do you want to know how this diagnosis was made? Read here: Wireless Sensors identify breakage of Sandvik CH660 crusher (dynamox.net)