Spare Parts

The roller core of the vertical mill has the following characteristics:
1. Supporting the roller: As the core supporting structure of the roller, the roller core of the vertical mill bears the weight of the roller, ensuring that the roller maintains the correct position and posture during the operation of the vertical mill, so that the roller can stably cooperate with the grinding disc to crush and grind the material. Through precise installation and positioning, the roller core ensures that the gap between the roller and the grinding disc is uniform, thereby achieving efficient and stable grinding operations.

2. Transmitting power: The roller core of the vertical mill is the key link in power transmission. It transmits power from drive devices such as reducers to the roller, driving the roller to rotate around its own axis. In this process, the roller core needs to have good transmission efficiency and torque transmission capacity to ensure that the roller can obtain sufficient mechanical energy to grind the material. At the same time, the roller core also needs to be able to adapt to different speed and load requirements to ensure that power can be transmitted stably under various working conditions of the vertical mill.

3. Bearing load: During the grinding process, the roller will be subjected to various forces, including the reaction force of the material, its own gravity, centrifugal force, and friction caused by the relative movement between the grinding disc and the roller. The roller core of the vertical mill needs to withstand these complex loads and transfer them to the basic structure of the mill in a reasonable manner. This requires the roller core to have sufficient strength and rigidity to prevent deformation, fracture and other failure forms under long-term load, and to ensure the structural stability and reliability of the roller core and even the entire roller.

4. Protect internal components: The roller core of the vertical mill is usually equipped with precision components such as bearings and sealing devices. The roller core can provide a stable and reliable working environment for these internal components and protect them from external factors. For example, the roller core can prevent dust from entering the bearing, avoiding the bearing from reducing its service life due to dust wear; at the same time, it can also play a certain role in heat insulation, reducing the impact of external heat on bearings and other components, and ensuring that they work within a suitable temperature range.

5. Auxiliary grinding: Although the roller core of the vertical mill itself does not directly participate in the process of grinding materials, its structure and surface characteristics will have a certain impact on the grinding effect. For example, some roller core surfaces are designed with special patterns or protrusions. These structures can increase the friction between the roller and the material, so that the material can be better squeezed and ground between the roller and the grinding disc, thereby improving the grinding efficiency and product quality. In addition, the rotation of the roller core will also drive the surrounding air to flow, forming a certain airflow field, which is helpful for the dispersion and transportation of materials and further optimizes the grinding process.

1. Design and drawing
According to the requirements of the vertical mill specifications, production capacity and material grinding characteristics, design a suitable roller core structure and determine its size, shape, material and other parameters. Draw a detailed two-dimensional drawing and mark the size, tolerance, surface roughness, technical requirements, etc. of each part as the basis for manufacturing.

2. Raw material preparation
Purchase suitable steel materials according to design requirements, such as 42CrMo, 35CrMo and other alloy structural steels, check the quality certification documents of the materials to ensure that the chemical composition and mechanical properties of the materials meet the requirements. Inspect the steel materials, such as non-destructive testing such as ultrasonic flaw detection and magnetic particle flaw detection, to find possible defects in the material, such as cracks, inclusions, etc. According to the size of the roller core, cut the steel into suitable blanks. The size of the blank should take into account the processing allowance. Generally, the allowance is 5-10mm on one side, depending on the specific processing technology and precision requirements.

3. Forging
The blank is heated to a suitable forging temperature range, generally 1100 - 1200℃, and forged with forging equipment such as air hammer and friction press. Through multiple upsetting and drawing processes, the internal structure of the steel is improved to make it more dense and uniform, and the strength and toughness of the material are improved. The forging ratio is generally controlled between 3 - 5. Forge a blank close to the final shape of the roller core, and reserve a certain processing allowance, generally 3 - 5mm on one side.

4. Heat treatment
The forged blank is heat treated, mainly including quenching and tempering, that is, high-temperature tempering after quenching. The quenching temperature is generally 850 - 880℃, oil-cooled quenching; the tempering temperature is 550 - 650℃, and the holding time depends on the size of the workpiece, generally 1 hour for every 25mm thickness. Quenching and tempering can make the roller core obtain good comprehensive mechanical properties and improve its strength, toughness and wear resistance. According to the needs, surface quenching and other treatments may be carried out to improve the hardness and wear resistance of the roller core surface. The surface quenching hardness is generally required to reach HRC50-55.

5. Machining
Rough machining: Use lathes, milling machines, drilling machines and other equipment to rough-machine the blank to machine the basic shape of the roller core, including the outer circle, inner hole, end face, keyway, etc., and reserve 0.5-1mm finishing allowance.
Finishing: Use high-precision grinders, boring machines and other equipment for finishing to ensure the dimensional accuracy and surface quality of the roller core. The dimensional tolerance of the outer circle and inner hole is controlled within ±0.01mm, and the surface roughness reaches Ra0.8-1.6μm. During the processing, various fixtures and measuring tools are required for positioning and measurement to ensure that the processing accuracy meets the design requirements.

6. Welding (if necessary)
If some parts of the roller core are connected by welding, such as the connection between the bearing seat and the roller body, welding process is required. Before welding, the welding part should be cleaned and preheated, and the preheating temperature is generally 150-200℃.
Use appropriate welding methods, such as submerged arc welding, gas shielded welding, etc. to ensure welding quality. After welding, perform non-destructive testing of the weld, such as radiographic testing, ultrasonic testing, etc., to check whether the weld has defects such as pores, slag inclusions, cracks, etc.

7. Surface treatment
In order to improve the corrosion resistance and wear resistance of the roller core, its surface can be treated, such as hard chrome plating, spraying wear-resistant coating, etc. The thickness of hard chrome plating is generally 0.02-0.05mm, which can improve the surface hardness and finish, and enhance wear resistance and corrosion resistance.
Spraying wear-resistant coatings, such as tungsten carbide coatings, with a coating thickness of 0.1-0.3mm, can significantly improve the wear resistance of the roller core surface.

8. Assembly
Assemble the processed components, such as roller shafts, hubs, bearing seats, sealing devices, etc. During the assembly process, the assembly process must be strictly followed to ensure that the installation position of each component is accurate.
For example, the installation of the bearing must ensure that the clearance between it and the shaft and the bearing seat meets the requirements, and the general clearance is 0.05-0.1mm. When installing the sealing device, pay attention to the installation direction and compression of the seal to ensure a good sealing effect and prevent lubricating oil leakage and dust from entering.

9. Inspection and testing
Appearance inspection: Check whether there are cracks, sand holes, pores and other defects on the surface of the roller core, and whether the surface roughness and appearance dimensions meet the design requirements.
Dimensional accuracy measurement: Use measuring tools such as calipers, micrometers, and three-coordinate measuring machines to measure the key dimensions of the roller core to ensure that the dimensional deviation is within the tolerance range.
Form and position tolerance detection: Detect the form and position tolerances of the roller core, such as cylindricity, coaxiality, and verticality. Generally, the cylindricity requirement is 0.01-0.02mm, and the coaxiality requirement is within 0.05mm.
Nondestructive testing: Ultrasonic testing, magnetic particle testing and other methods are used to conduct comprehensive nondestructive testing on the roller core to check whether there are defects such as cracks inside.
Static balance test: Static balance test is performed on the roller core to ensure that it will not vibrate due to imbalance during rotation, affecting the normal operation of the equipment. The allowable imbalance depends on the speed and weight of the roller core, generally within 5-10g・cm.

10. Painting and packaging
The roller core that has passed the inspection is painted, generally with anti-corrosion paint, with a paint layer thickness of 0.1-0.2mm to prevent the roller core from rusting during transportation and storage. After painting is completed, it is packaged according to transportation requirements, generally in wooden boxes, to ensure that the roller core is not damaged during transportation.

Pressure application: The vertical mill roller core applies pressure to the material through the grinding roller connected to it under the action of the hydraulic system or spring device. The hydraulic system or spring device can accurately adjust the pressure of the grinding roller on the material according to the properties of the material and the grinding requirements. For example, for materials with higher hardness, it is necessary to increase the pressure to achieve effective grinding; while for softer materials, the pressure can be appropriately reduced to avoid excessive grinding and energy waste.

Material grinding: The grinding roller rotates around the central axis of the vertical mill under the support and drive of the vertical mill roller core. At the same time, the material enters the grinding disc from the upper part of the vertical mill, and under the rotation of the grinding disc, the material moves to the edge of the grinding disc. When the material passes under the grinding roller, it is crushed and ground into smaller particles by the rolling and squeezing of the grinding roller. The gap between the grinding roller and the grinding disc can be adjusted according to the particle size requirements of the product. The smaller the gap, the finer the particle size of the material after grinding.

Material transportation: Under the joint action of the grinding roller and the grinding disc, the ground material continues to move to the edge of the grinding disc. After reaching the edge of the grinding disc, the material is blown up by the airflow at the high-speed rotating wind ring to form an upward airflow. The airflow brings the material into the upper powder selector of the vertical mill. Under the action of the powder selector, the coarse particles that do not meet the particle size requirements are separated and returned to the grinding disc for re-grinding, while the fine particles that meet the particle size requirements are discharged from the vertical mill with the airflow to become finished products.

Energy transfer: The vertical mill roller core is usually driven to rotate by an electric motor through a reducer. The power provided by the motor is transmitted to the vertical mill roller core through the reducer, and then transmitted to the grinding roller by the vertical mill roller core, so that the grinding roller can overcome the resistance of the material to rotate and grind. In this process, the energy transfer efficiency directly affects the grinding effect and energy consumption of the vertical mill. Therefore, the reasonable design of the structure and transmission mode of the vertical mill roller core is crucial to improve the energy utilization rate of the vertical mill.

1. Wear
Roller surface wear: This is one of the most common faults. Since the roller core is in direct contact with the material during operation, it is scour, squeeze and grind by the material, and the roller surface will gradually wear. The degree of wear depends on factors such as the hardness, particle size, feed amount of the material, and the material and surface treatment process of the roller core. After long-term operation, roller surface wear will cause the gap between the grinding roller and the grinding disc to increase, affecting the grinding effect, making the product particle size coarser, and the output to decrease.

Neck wear: The neck of the roller core is matched with the bearing, and it is easy to wear under high-speed rotation and heavy load conditions. Neck wear may be caused by poor lubrication, improper bearing installation, and the roughness of the neck surface does not meet the requirements. Neck wear will cause the bearing fit clearance to increase, making the grinding roller unstable, generating vibration and noise, and even causing bearing damage in severe cases, affecting the normal operation of the vertical mill.

2. Cracks and fractures
Fatigue cracks: The roller core of the vertical mill is prone to fatigue cracks under long-term cyclic loads. Especially in the stress concentration parts of the roller core, such as fillets, keyways, threads, etc., fatigue cracks are more likely to occur. Due to the sudden change of geometric shape, these parts will produce higher local stress when subjected to force. With the increase of running time, the stress continues to accumulate, and finally leads to the initiation and expansion of cracks. If fatigue cracks are not discovered and handled in time, they will gradually extend to the entire roller core, causing the roller core to break.

Overload fracture: When the vertical mill encounters a sudden overload during operation, such as large pieces of foreign matter mixed in the material, the feed volume is suddenly too large, etc., the load on the roller core will exceed its ultimate strength, resulting in the fracture of the roller core. In addition, during the start-up and shutdown of the vertical mill, if the operation is improper, a large impact load will also be generated, increasing the risk of roller core fracture.

3. Deformation
Thermal deformation: During the operation of the vertical mill, the roller core will increase in temperature due to frictional heat. If the cooling system is imperfect or fails, the roller core temperature is too high, which will cause it to thermally deform. Thermal deformation will change the shape and size of the roller core, affect the matching accuracy between the grinding roller and the grinding disc, and thus affect the grinding effect. At the same time, thermal deformation may also cause thermal stress inside the roller core, accelerating the generation and expansion of cracks.

Deformation under stress: Since the roller core is subjected to greater pressure and bending moment during operation, deformation under stress may occur when the material strength of the roller core is insufficient or the structural design is unreasonable. Especially at both ends of the grinding roller, due to the long cantilever, the stress situation is more complicated and deformation is more likely to occur. Deformation under stress will make the working surface of the grinding roller no longer flat, resulting in uneven grinding of materials and affecting product quality.

4. Bearing failure
Lubrication problem: The lubrication of the bearing is essential for its normal operation. If the quality of the lubricating oil is poor, the oil volume is insufficient, the oil film is broken or the lubrication system is blocked, the friction of the bearing will increase, overheating will occur, and the wear and damage of the bearing will be accelerated. In addition, impurities in the lubricating oil will also scratch the bearing surface and reduce the service life of the bearing.

Seal failure: The sealing device of the bearing is used to prevent the leakage of lubricating oil and the entry of external impurities into the bearing. If the sealing device is damaged or aged, the lubricating oil will leak, causing the bearing to lose lubrication. At the same time, impurities such as dust and materials from the outside will enter the bearing, aggravating the wear of the bearing and causing bearing failure.

1. Design
Reasonable design of structure: optimize the structural design of the roller core to avoid areas of stress concentration. For example, appropriately increase the fillet radius to reduce sharp corners; reasonably design the shape and size of the keyway and thread, and adopt a suitable transition method to reduce local stress.
Accurate calculation of load: During the design stage, accurately calculate the load that the vertical mill roller core bears under various working conditions, including material pressure, friction, impact, etc. According to the calculation results, reasonably select the material of the roller core and determine its size specifications to ensure that the roller core has sufficient strength and toughness to withstand the working load.

2. Manufacturing
Strictly control material quality: select reliable materials, such as high-quality alloy structural steel, and conduct strict inspections on the purchased steel, including chemical composition analysis, mechanical property testing, flaw detection, etc., to ensure that the material is defect-free and meets the design requirements.
Optimize manufacturing process: formulate a reasonable manufacturing process, such as strictly controlling the forging ratio, heating temperature and cooling rate during the forging process to improve the internal organization of the material and improve the density and uniformity of the material. In the welding process, appropriate welding process parameters are used to control welding heat input, reduce welding stress, and perform necessary post-weld heat treatment to eliminate welding residual stress.

3. Installation
Ensure installation accuracy: When installing the roller core of the vertical mill, strictly follow the requirements of the installation instructions to ensure the installation accuracy of the roller core. For example, the parallelism and gap between the grinding roller and the grinding disc should be accurately adjusted to make them uniform and consistent, so as to avoid uneven force on the roller core due to installation deviation and local stress concentration.
Fix the foundation well: The foundation of the vertical mill must be firm and reliable and able to withstand various loads generated during the operation of the vertical mill. Before installing the roller core, the foundation should be inspected and accepted to ensure that the flatness, verticality and embedding accuracy of the anchor bolts meet the requirements. At the same time, the connection between the roller core and the foundation should be firm to prevent loosening during operation, resulting in increased vibration and impact, and causing cracks and fractures.

4. Use and maintenance
Standardize the operation process: Develop detailed and standardized operating procedures, and operators should strictly follow the procedures to start, operate and shut down the vertical mill. During the startup and shutdown process, proceed slowly to avoid sudden loading or unloading and reduce impact loads. During operation, keep the feed rate, material particle size, moisture and other parameters stable to avoid large fluctuations and prevent the sudden increase of the load on the roller core due to changes in the material properties.
Strengthen daily monitoring: Establish a complete equipment monitoring system, and monitor the operating status of the vertical mill roller core in real time by installing monitoring equipment such as vibration sensors and temperature sensors. Pay close attention to parameters such as vibration values ​​and temperature changes. Once an abnormality is found, stop the machine for inspection in time to detect potential faults such as cracks at an early stage and take corresponding measures to deal with them.
Regular maintenance: Regularly maintain the roller core of the vertical mill, including checking the surface wear of the roller core, the tightness of the connecting parts, the working status of the lubrication system and the cooling system, etc. Clean the accumulated material and dust on the surface of the roller core in time, ensure that the cooling system is unobstructed, ensure that the quality and amount of lubricating oil meet the requirements, and regularly replace the lubricating oil and filter to reduce wear and prevent overheating, and extend the service life of the roller core.

Immediate shutdown: Once cracks or fractures are found in the roller core of the vertical mill, the operation of the vertical mill should be stopped immediately to avoid further deterioration of the fault and cause more serious equipment damage or production accidents. At the same time, cut off the power supply of the equipment and set up safety warning signs to prevent unrelated personnel from approaching.

Detailed inspection: Organize professional and technical personnel to conduct a comprehensive and detailed inspection of the roller core to determine the specific situation of the crack or fracture, including the location, length, depth, direction of the crack, as well as the degree of fracture, distribution of fragments, etc. Non-destructive testing technologies such as ultrasonic testing and magnetic particle testing can be used to accurately determine the extension range of the crack and potential defects. At the same time, check other components related to the roller core, such as bearings, seals, connecting bolts, etc., to see if there are any damage or abnormalities.

Analyze the cause: According to the inspection results, combined with the operation record, operation status, maintenance history and other factors of the vertical mill, analyze the causes of cracks and fractures. Is it due to overload, fatigue, material problems, manufacturing defects, or improper operation, poor lubrication, cooling system failure and other factors. After clarifying the cause, appropriate improvement measures can be taken to prevent similar problems from happening again.

Develop a repair plan: According to the specific situation of the cracks and fractures and the reasons analyzed, develop a reasonable repair plan. For smaller cracks, you can consider using repair processes such as welding repair, surface spray repair, patching repair, etc. However, for severe fractures or cracks that cannot be repaired, it is usually necessary to replace a new roller core. When formulating a plan, you must fully consider factors such as the strength, reliability, service life, and repair cost and time after the repair.

Implement repair or replacement
Repair treatment: If welding repair is used, choose appropriate welding materials and welding processes, and operate by welders with professional qualifications. Before welding, clean and pre-treat the cracked area, remove impurities such as oil and rust, and open a groove to ensure welding quality. During the welding process, strictly control the welding parameters, take appropriate preheating and post-heating measures, and reduce welding stress. After welding, non-destructive testing of the weld should be performed to ensure that the welding quality meets the requirements. For processes such as surface spray repair and patching repair, the corresponding specifications and requirements must be followed to ensure the bonding strength and wear resistance between the repair layer and the substrate.

Replacement of roller core: If you decide to replace a new roller core, you should choose a product with the same specifications and material as the original roller core or with better performance. During the replacement process, you must strictly follow the requirements of the installation instructions to ensure the installation accuracy of the roller core, such as the parallelism and gap between the roller core and the grinding disc. At the same time, the new roller core must be inspected and debugged as necessary to ensure its quality and performance.

Equipment debugging and acceptance: After repairing or replacing the roller core, the vertical mill is debugged as a whole. During the debugging process, closely observe the operation of the roller core, including whether the vibration, temperature, sound and other parameters are normal, check whether the matching between the grinding roller and the grinding disc is good, and whether the grinding effect of the material meets the requirements. After the debugging is completed, organize relevant personnel to conduct acceptance, and the acceptance content includes the operating performance, product quality, safety performance and other aspects of the equipment. Only when all indicators meet the requirements can it be officially put into production.

Record and summarize: Record the occurrence of cracks and fractures in the vertical mill roller core, inspection results, cause analysis, repair or replacement process, and commissioning acceptance in detail to form equipment files. At the same time, summarize the entire processing process, analyze the existing problems and deficiencies, and put forward improvement measures and suggestions to provide experience reference for future equipment maintenance and management.

1. Manual arc welding
Features: Flexible operation, welding can be performed in various positions, and the requirements for welding equipment and sites are relatively low. It is possible to select suitable welding rods according to the material and welding requirements of the roller core, and it has strong adaptability.
Application scenarios: Suitable for repairing smaller cracks, worn parts and some difficult-to-reach locations. For some parts with complex and irregular shapes, manual arc welding can be used for better welding repairs through the welder's operating skills.
Technical points: Before welding, the cracked parts need to be thoroughly cleaned, impurities such as oil and rust need to be removed, and appropriate grooves need to be opened according to the depth and width of the cracks. Select welding rods that match the material of the roller core, such as low-alloy steel welding rods or stainless steel welding rods. When welding, the welding current, voltage and welding speed should be controlled, and multi-layer and multi-pass welding should be used. After each layer is welded, the slag should be cleaned in time and hammered to eliminate welding stress. After welding, appropriate heat treatment, such as tempering, should be performed to improve the organization and performance of the welded joint.

2. Gas shielded welding
Features: Gas shielded welding includes carbon dioxide gas shielded welding and argon arc welding. This type of welding process has the advantages of fast welding speed, high deposition efficiency, good welding quality, and beautiful weld formation. The shielding gas can effectively isolate the air, prevent the weld metal from being oxidized and nitrided, and improve the mechanical properties of the weld.
Application scenarios: Suitable for parts with high welding quality requirements, such as crack repair on the surface of the roller core, surfacing of worn parts, etc. Gas shielded welding is more suitable for some occasions that require higher welding speeds and better weld formation.
Key points of the process: The welding part should also be cleaned and grooved before welding. Select suitable welding wire according to the material of the roller core, such as carbon steel welding wire, alloy steel welding wire, etc. During the welding process, the flow rate, welding current, voltage and welding speed of the shielding gas should be strictly controlled. For carbon dioxide gas shielded welding, attention should be paid to prevent the generation of pores; for argon arc welding, the purity and protection effect of argon gas should be guaranteed. After welding, the spatter and oxides on the weld surface should be cleaned in time.

3. Submerged arc welding
Features: Submerged arc welding has the advantages of large welding current, large penetration, fast welding speed, high production efficiency and stable weld quality. Since the arc is covered by flux during welding, the heat is concentrated, the welding quality is good, and the occurrence of welding defects can be reduced.
Application scenarios: Suitable for repairing large areas of wear, cracks, and areas that require a large amount of deposition. For example, when there is a large area of ​​wear on the surface of the roller core that needs to be repaired by surfacing, submerged arc welding is an ideal process.
Key points of the process: The welding area should be pretreated before welding, including cleaning and beveling. Select suitable welding wire and flux, and determine welding parameters such as welding current, voltage, welding speed, and wire feeding speed according to the material and welding requirements of the roller core. During the welding process, pay attention to maintaining the coverage thickness and uniformity of the flux to prevent the arc from being exposed. After welding, the flux and slag on the weld surface should be removed in time, and necessary inspections and heat treatments should be carried out.

Background: The roller core of the HRM vertical mill is made of ductile iron casting. After long-term use, due to factors such as rotation and vibration, extrusion and friction occur between the roller core and the pressure ring, and the material is swept by the wind, resulting in wear of the roller core.

Repair process:
Preliminary attempts: The company has tried J427 carbon steel welding rods and stainless steel welding rods for welding tests, using DC welding, pre-welding cleaning, preheating and post-welding insulation processes. However, the test found that although the hardness of the welding surface has improved, there are problems such as microcracks, hammering and falling, large amount of welding materials, long welding time, low efficiency, and limited cost reduction, which did not achieve the expected effect.

Determine the solution: The subsequent trial of stainless steel welding wire test found that ER316L (MIG) Φ1.2mm welding wire has the best welding effect. At the same time, the shielding gas was studied. By comparing Ar gas shielding welding, mixed gas (Ar+CO2) shielding welding and CO2 shielding welding, it was found that the mixed gas of Ar 78%~82%+CO2 18%~22% had the best and most stable quality after welding. Finally, it was determined that the welding material was ER316L (MIG) Φ1.2mm welding wire, and the shielding gas was (Ar+CO2) protective atmosphere. The ratio of the two was close to 4:1. AC welding technology and the original carbon dioxide gas shielding welding equipment were used as the process technology for roller core repair welding.

Welding operation: During the welding process, if cracks, unfused, slag inclusions, pores and other defects that affect the welding quality are found, the defects should be removed in time before continuing the repair welding; after each weld is completed, the weld should be hammered to eliminate stress, and the oxide scale and welding slag should be removed at the same time.
Insulation after welding: rock wool and electromagnetic heater are used for double insulation immediately after welding. The insulation process is insulation temperature 230~250℃, insulation time 2h; insulation temperature 200~230℃, insulation time 2h; insulation temperature 150~200℃, insulation time 1h; insulation temperature 100~150℃, insulation time 1h.

Repair effect: This technology can shorten the roller core welding time to less than 20h, the welding surface has high hardness, wear resistance and durability, and the maintenance quality is greatly improved. The shape of the roller core after welding and processing is as good as new, and the welding surface strength is higher than that of ductile iron, and the service life is longer than that of the newly cast ductile iron roller core. Through multiple user return visits, the roller core that was first repaired by welding using this technology is still in use for more than five years, with good results.

The wear standard of the roller core of the vertical mill usually does not have a fixed and unified value, and it will vary depending on the model of the vertical mill, the operating conditions, the material characteristics and other factors. It can be judged from the following aspects:

1. Amount of wear: Taking the HRM vertical mill of a certain company as an example, when the wear size of the roller core surface is less than 3mm, it is a light wear situation, and a relatively simple repair process can be adopted. When the wear size of the roller core surface is greater than 3mm, the repair process is relatively complicated, and operations such as welding positioning points may be required. For the MPS3350B vertical mill, the wear of the roller surface in the range of 0 to 39mm is the initial wear, 40mm to 79mm is the middle wear, 80mm to 99mm is the late wear, and more than 100mm is the excessive wear period. However, this is only the approximate standard of this specific model of vertical mill under its production conditions. The wear stage division of other models of vertical mills will be different.

2. Match clearance: During the use of the vertical mill roller body and the wear-resistant liner, once a fit clearance appears, the wear between the body and the liner will be aggravated. For example, the Smith 50 vertical mill, the theoretical matching rate between the roller skin and the roller body contact surface should reach more than 90%. If the matching area does not meet the requirements, the relative wear between the roller skin and the roller body contact surface will be caused during long-term operation. When the wear gap is formed and gradually increases, it will cause harm to the equipment itself, such as hot air carrying materials to produce material accumulation and scouring, which further increases the gap. Therefore, the size of the matching gap is also an important indicator to measure the degree of roller core wear.

3. Equipment operation status: When the roller core is worn to a certain extent, it will affect the normal operation of the vertical mill, resulting in a decrease in output, large mill vibration, and large power fluctuations. For example, in the late stage of wear of the grinding roller, due to the serious wear of the grinding roller and the grinding disc liner after long-term operation, the extrusion working surface between the grinding disc and the roller is uneven, the grinding capacity is reduced, and the production operation rate will be significantly reduced, the mill will vibrate greatly, and the power will fluctuate greatly. It is very easy to have problems and it is also easier to stop due to vibration. At this time, even if the wear amount has not reached the specified large value, considering the stable operation and production efficiency of the equipment, it is also necessary to evaluate and deal with the wear of the roller core.

The cost of repairing the wear of the roller core of the vertical mill varies depending on the repair process, degree of wear, equipment model and other factors. The following are the costs of several common repair processes:

Machining after welding: This process has a long repair cycle and high comprehensive costs. Involving gouging costs, metal flaw detection, metal composition analysis, welding materials and transportation and hoisting, the repair cost of a roller may not be less than 100,000 yuan. Moreover, welding can easily cause local thermal stress on the surface of the shaft, causing stress concentration and affecting the service life of the equipment.

Repair of polymer composite materials: Taking TONGLI Blue polymer composite materials as an example, its cost is generally calculated based on the amount of wear to calculate the material consumption, and then the repair cost is calculated. For example, 2211F polymer composite materials are about 12.5 yuan per cubic centimeter. The repair process using this material is simple and can be repaired online, which can save a lot of time and cost for disassembly and assembly operations for enterprises. For example, the roller wear of three Smith 50 mills of Zhonglian Cement was repaired with TONGLI Blue materials. The repair can be completed within 8 hours, and the cost is only 1/5 of the disassembly repair cost.

Laser cladding repair: The strength of the parts repaired by laser cladding can reach more than 90% of the original strength, and the repair cost is less than 1/5 of the replacement price. However, the process equipment cost is high, and the initial equipment investment may require hundreds of thousands of yuan or even higher, but in the long run, the repair of large key equipment can effectively shorten the maintenance time, increase the service life of the equipment, and have a high comprehensive benefit. For example, TONGLI charges 1,000 yuan to repair the wear of the vertical mill roller bearing. However, the specific cost will vary depending on the equipment model, wear area and depth.

Brush plating repair: The brush plating process is limited by the amount of wear. When the wear is greater than 0.3mm, the efficiency decreases exponentially, the service life is short, and for large vertical mill rollers, the brush plating efficiency is low. Its equipment cost is relatively low, such as a metal brush plating machine The price is about 9,300 yuan, but the labor cost of repairing a large vertical mill roller core is high, and the overall cost is not low, and the repair effect is not as ideal as some other processes.