What are the Common Problems Faced by Mineral Sizers
Introduce
Mineral sizers are indispensable components in the crushing process. Their purpose is to reduce the particle size of the material and prevent overloading during the crushing stage, which is the most energy-consuming link in the mineral processing. The reduction of energy consumption helps to achieve more effective crushing and output.
The crushing process is divided into three main stages: primary, secondary and tertiary. At the primary stage, primary mineral sizer is used to reduce the size of the mining materials (from 1000-500 mm blocks to 300-100 mm). Then the materials are transformed into particles suitable for transportation on the conveyor belt and enter the secondary mineral sizer to reduce the blocks from 300-100 millimeters to 100-38 millimeters.
Some industry applications require three-stage crushing. The third crushing produces the product ready for grinding, which is the process of the next stage (producing an average of 12 millimeters of material). In the case of crushing very fine products, four-stage crushing may be required.
During operation, mineral sizer typically exhibits various failure modes, starting with the most common ones, including: lubrication issues; Bearing and gear failure; Misaligned, unbalanced or unstable bases; A bent or deformed shaft; Problems caused by mechanical loosening, etc. There are more specific issues, such as: wear or deformation of the crushing cavity plate; Blockage; Interference, etc.
Now let’s take a detailed look at what common problems mineral sizers face?
Mechanical failure of Mineral sizer
The malfunction of the broken component
During operation, the crushing teeth of the primary mineral sizer and the crushing tooth plates of the secondary mineral sizer may experience excessive wear, which will seriously affect the crushing efficiency and result in the particle size of the material failing to meet the expected standard. Moreover, the crushing teeth or tooth plates may also break. Once a break occurs, the crushing process has to be interrupted and the machine needs to be stopped for replacement. This not only takes a lot of time but also increases the maintenance cost.
Bearing failure
Bearing failure is mainly manifested as abnormal temperature rise, intensified vibration and increased noise. It is generally caused by insufficient lubrication, contamination or overload operation. If the lubrication is insufficient or the lubricating oil is contaminated, it will accelerate the wear of the bearing, and then cause abnormal noise and vibration. In severe cases, the bearings may get stuck, causing the entire mineral sizer to fail to operate normally.
Gear failure
Gear faults often present as tooth surface wear, broken teeth or deformation of the gear ring, mainly due to installation errors, material fatigue or foreign object jamming. If these malfunctions occur and are not dealt with in time, they will trigger a chain reaction, causing the mineral sizer to shut down and affecting the crushing efficiency. Bearing damage may also cause the shaft system to shift, which in turn aggravates abnormal gear meshing and forms a vicious cycle.
Faults caused by handling materials
Material blockage
Material blockage mainly occurs in the feeding port, crushing chamber or discharge port area. When the moisture content of the material is too high, its viscosity is too great or the feeding speed is too fast, it is easy for accumulation to form in the crushing chamber, causing the mineral sizer to overload and shut down. For instance, when dealing with ores with a mud content exceeding 15%, sticky materials will adhere to the surface of the crushing plates and toothed rollers, gradually forming a hard accumulation layer that eventually blocks the material flow channels. Local overload caused by uneven feeding can also lead to blockage, which is manifested as a sudden increase in mineral sizer current, intensified vibration and abnormal noise.
Crushing cavity plate wear and tear
When Mineral sizer processes high-hardness materials for a long time, the crushing cavity plates will suffer severe wear due to repeated impacts and friction. When manganese steel liners are used to process iron ore, the monthly wear can reach 20-30mm, leading to uncontrolled crushing particle size and reduced production capacity. The wear forms include uniform surface wear, local pits and edge curling. Among them, the wear at the tooth top of the toothed liner will significantly reduce the crushing efficiency. When the thickness of the liner wears down to 60% of its original size, it must be replaced in a timely manner; otherwise, it may cause secondary faults such as the breakage of the toothed roller or material leakage.
Foreign object jamming
When hard metallic foreign objects are accidentally mixed into the raw ore materials, it is very easy for them to get stuck in the gap between the toothed rollers of mineral sizer. Once these metal foreign objects get stuck in the gap between the toothed rollers, they will impede the normal rotation of the toothed rollers and the passage of materials, which will cause the entire mineral sizer equipment to suddenly jam within a short period of time, seriously affecting the continuity of the production process and the stability of equipment operation.
Over-crushing or uneven crushing
Over-crushing usually results from improper parameter Settings of the mineral sizer or changes in material properties. When the spacing between the toothed rollers is too small or the rotational speed is too high, it will cause the material to be repeatedly crushed, resulting in excessive fine powder. When handling limestone, if the gap between the toothed rollers is set less than the minimum size of the material discharge port, qualified products will continue to be under pressure, resulting in energy waste and an increase in dust. Uneven crushing is manifested as an overly wide particle size distribution in the output, which not only contains coarse particles that do not meet the standards but also generates excessive fine powder. This is mostly caused by uneven wear of the toothed rollers, feeding segregation or fluctuations in rotational speed.
A malfunction caused by a system issue
Failure of the lubrication system
When the viscosity of the lubricating oil is improperly selected, the oil supply is insufficient or the oil passage is blocked, it will cause the bearings and gears to be in a state of boundary lubrication. Experimental data show that for every 10℃ increase in bearing temperature, its fatigue life will be shortened by 50%. A certain iron ore beneficiation plant failed to replace the winter oil in the mineral sizer lubrication system in time, which led to a sharp increase in the viscosity of the lubricating oil at -15℃, resulting in insufficient pressure of the oil supply pump and eventually causing the main bearing to seize up. In addition, lubricating oil contamination is also a common problem. When the content of metal particles in the oil exceeds 0.1%, it will accelerate pitting on the tooth surface of gears and scratches on the raceways of bearings.
Electrical control system failure
The electrical faults of Mineral sizer are mostly manifested as motor overload, sensor failure and abnormal PLC program. Motor overload is usually caused by material blockage or mechanical jamming. When the load current exceeds 1.2 times the rated value, the thermal relay will act within 20 seconds to cut off the power supply. Sensor failures include signal loss of the rotational speed sensor and reading deviation of the temperature sensor, etc. A certain processing plant once had a temperature sensor installed in an improper position, resulting in the monitored value being 30℃ lower than the actual bearing temperature, thus delaying the opportunity for fault handling. PLC program errors may cause malfunctions of the mineral sizer, such as abnormal opening of the feed gate leading to material overflow, or sudden closure of the discharge port causing a sudden increase in pressure in the crushing chamber.
Summary
As key equipment in the Mineral processing process, the operational stability of Mineral sizers directly affects the overall production efficiency and energy consumption level. Therefore, corresponding preventive measures and maintenance strategies need to be formulated for different types of faults. A regular inspection system should be established, with a focus on monitoring the wear of the crushing teeth, bearings and gears, and replacing the aged parts in a timely manner.
