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Release date: 2020-04-03 14:06:33
Roller mill is the main equipment used in grinding process. As the most important part of the mill, the performance of the grinding roller directly affects the grinding effect of the mill. In the process of grinding materials, material particles, abrasives and some impact loads will wear the surface of the grinding roller, which will affect the technical characteristics and service life of the surface of the grinding roller. It is very important to study the wear mechanism of the grinding roller and find the way to improve the wear performance of the grinding roller.
The mechanism of roller wear, the causes of roller wear and the preventive measures of roller wear will be showed in this paper.
Wear generally refers to the process of continuous loss or residual deformation of the surface material when two objects in direct contact move relative to each other. In the grinding mechanism of the roller mill, the wear of the grinding roller is mainly caused by the direct contact between the material and the surface of the grinding roller, which causes the material loss or residual deformation on the surface of the grinding roller.
Abrasive wear , also known as grain wear, refers to the phenomenon that the surface of the material is scratched or the surface material falls off during the friction process caused by the hard particles or hard protrusions on the contact surface. Its main feature is to form scratches along the sliding direction on the friction surface. The hard particles or projections can be either non-metallic or metallic. In the actual working condition, the size of abrasive particles or protrusions varies greatly from a few tons or larger and heavier rocks or minerals to a few microns of abrasive particles. Abrasive wear is the most common form of wear in production. According to statistics, the loss caused by abrasive wear accounts for about half of the total wear loss, so it is of great significance to reduce abrasive wear.
When the surfaces of two objects slide relative to each other, the adhesive contact is formed due to the adhesive effect. These adhesive joints are sheared and broken, and the sheared material may fall off into wear debris or from one friction surface to another. This kind of wear is called adhesive wear. According to the corresponding analysis, there is almost no adhesive wear in the wear of grinding roller.
The friction surface reacts with the surrounding medium to produce corrosion products. After further friction, these corrosion products will be worn away, and the material damage caused by such repetition is called corrosion wear. In the work of grinding roller, the surface friction will produce heat, which will cause the roller body temperature to rise, but the temperature rise can be controlled by the cooling system. In the process of contact and friction between the roller material and the material, there will be no corrosion products, so there is no corrosion wear form in the roller wear.
In the process of rolling contact between two objects, due to the effect of alternating contact stress, surface contact fatigue occurs, which makes the surface of material appear pitting or falling off. During the wear process of the grinding roller, the materials that pass through the grinding zone continuously and contact the surface of the grinding roller directly may produce alternating contact stress. It leads to a very small amount of contact fatigue on the surface of the grinding roller, and the phenomenon of pitting or falling off occurs.
Metallurgical defects such as non-plastic inclusions in metals have a serious impact on fatigue wear. Such as nitrides, oxides and silicates in steel. In the process of stress, the deformation cannot coordinate with the matrix to form a gap, which is the source of stress concentration. Under the action of alternating stress, cracks appear and propagate, leading to the early appearance of fatigue wear. Therefore, it is of great significance to select metal materials with less harmful inclusions to improve the anti fatigue wear ability of friction. The material factors of the grinding roller include chemical composition and mechanical properties. The surface layer shall be free of manufacturing defects such as pores, sand holes, cracks and uneven hardness.
In general, the wear resistance of materials increases with the increase of surface hardness. Once the surface hardness exceeds a certain value, the wear resistance will decrease. For the grinding roller, it is often involved in the rough machining of the surface, so it is necessary to consider the machining performance when improving the hardness. The core hardness of metal parts has a certain effect on fatigue wear. Under a certain external load, the higher the core hardness, the less the risk of fatigue crack. It bears a large radial force and needs a certain toughness of the roller body when the grinding roller works. The core is generally made of gray cast iron. Therefore, the hardness of its core should be increased reasonably. However, it can't be improved infinitely or the toughness is too low and it is easy to produce cracks. In addition, the thickness of the hardened layer of the outer white iron also has an effect on the fatigue wear resistance. The fatigue crack will appear at the joint of the hardening layer and the matrix, and the surface will be easily peeled off when the hardening layer is too thin. Therefore, the fatigue crack should be produced in the hardened layer to improve the fatigue wear resistance when choosing the thickness of the hardened layer.
It is sure to check whether the quality is qualified before installing the bearing. Good quality bearings are conducive to the smooth operation of the vertical mill. Installation should not be too tight and loose. If it is too tight, the wear will be accelerated and the gap between raceways will be reduced. As a result, the temperature is increased, and the bearing will be directly scrapped soon after use. The service life of the bearing is greatly reduced. At the same time, it will be difficult to dismantle it from the grinding roller due to over tightening when the bearing is damaged, which will bring further difficulties to the vertical grinding mill. If it is too loose, the gap between the grinding tracks will increase, and the grinding roller & the bearing cannot be closely connected. The phenomenon of engagement often occurs when the grinding roller rotates. They bite each other, and the bearing cannot be removed from the grinding roller again, which may damage the grinding roller.
When assembling, the bearing size should be checked first. After making sure there is no mistake, you can prepare for the next operation. Then it is necessary to carry out certain protective treatment to ensure that no pollutants such as dust and water stains will enter.
Always pay attention to time and temperature during assembly. The time and temperature required for different grinding rollers are different. The oxidized cortex produced by heating must be cleaned. At this time, the staff must wear special gloves to prevent scalding and other accidents.
After assembly, the inspection should be continued. In order to prevent the gap between the inner bearing and the outer diameter from increasing, which has a serious impact on the grinding roller.
Only when lubricating oil has excellent category and high cost performance can certain benefit be achieved. It is better to use industrial oil with high viscosity and good stability. At the same time, it is necessary to reduce the temperature of the bearing, adjust to the appropriate temperature and increase the oil pressure, and ensure the lubrication of the bearing. Meanwhile, in order to prevent bearing damage, affect the operation of the machine, reduce its service life, the amount of oil should be reasonable to reduce the running in between the grinding roller and the bearing.
The sealing property of the grinding roller also has a great influence on the bearing. Be sure to use special rotary oil for sealing. It can not only lubricate, but also prevent dust, water stains and wind dust from entering. It can play a good sealing role.
If the sealing effect is poor, the gas will enter the sealing area, and then enter the bearing area, which will cause unnecessary damage to the bearing, reduce the lubrication effect, and even cause the surface of the raceway to fall off.
Only by ensuring the sealing of the grinding roller, can the utilization rate of the bearing be increased, the service life be prolonged, the working environment of the bearing be ensured to be good and the track be free from any pollutant corrosion, so as to reduce the maintenance times of the grinding roller and ensure the normal operation.
With the progress of the times and the development of high technology, a new type of material cleaning device can be used. It adopts the working principle of belt conveyor and good driving system to collect the missing materials and prevent the equipment from being polluted.
For the roller grinding device, not only good configuration should be adopted, but also good maintenance work should be done. The mill device has been used for a long time. There must be a lot of dust and dirt on the parts of the corresponding grinding roller, and even a little scrap iron. Regular cleaning is required. For example, the roller shaft of the grinding roller shall be cleaned to ensure that there are no iron chips inside, otherwise serious damage will be caused to the machine. After all parts are cleaned, they can be scrubbed with diesel oil to ensure the quality of parts.
The oil hole must be purged with compressed air to ensure that the previously used oil is completely blown out, and then new dry oil is injected, repeat operation. Paying attention to the cleaning sequence when cleaning parts, making sure it is in order without missing, and keeping the daily parts clean and tidy.
Regular training of staff and real-time technical update of staff. To ensure the stability of personnel and technology in the whole construction process, so as to ensure the smooth progress of the whole project.
More details please contact:
E-mail: mkt@hcmilling.com
