The ball mill makes more noise when the bearings are replaced
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After replacing the trunnion bearings in the ball mill, the vibration is even greater than before; seeking help from experts
It would be best if the original poster could post a photo, so that everyone can analyze the reasons, including whether the bearings are rolling bearings or sliding bearings
After replacing the rolling bearing at the free end of the ball mill’s trunnion, the vibration increased. The tooth surface meshing is fine; the reason for replacing the bearings was shaft wear (bearing seats), and the rear shaft was surfaced and adjusted so that there is no play. The small teeth have been reversed. The vibration is extremely strong now. The shaft reversal vibration has not changed.
Sir on the 2nd floor, it’s not possible to take photos on site; please analyze the reason. Thank you.
First, quality issues with the bearings and their assembly must be ruled out before other problems can be considered.
It might be due to an excessively small meshing clearance after the small teeth were replaced. {:2_44:}
Reply to 1# ysh730815: When only the small gear of the ball mill is replaced, it results in meshing between the new and old tooth surfaces, which naturally leads to increased vibration and noise. Moreover, the lifespan under such conditions is shorter than that when old teeth continue to mesh with each other. The problem can only be solved by replacing the large gear as well.
Vibrations are caused by loose foundation bolts.
This post was last edited by hcb081995 on 2011-4-20 09:46. Several technical challenges related to rolling bearings specifically designed for energy-saving ball mills. Edited on 2010-11-19 by Ruijing Imported Bearings. Qingdao Ruijing Electromechanical Equipment Co., Ltd. analyzed the drawback of using sliding bearings in ball mills, namely the high frictional resistance. Using rolling bearings instead of sliding bearings reduces the energy consumption of the mill, addresses issues such as bearing life and bearing sealing under high loads, and allows the power of the motor used in the mill to be reduced by 17–23%. I. Overview Ball mills are widely used in industries such as metallurgy, building materials, mining, and power generation. Their advantages include durability, a high crushing ratio, and strong adaptability to various types of materials. However, ball mills consume a large amount of energy, with an effective energy utilization rate of only 2%; moreover, traditional ball mills require complex maintenance that is time-consuming and labor-intensive. Traditional ball mills use sliding bearing shells, which result in high frictional resistance; the frictional power loss accounts for approximately 17–23% of the power required by the motors used in such ball mills, and this is a major factor contributing to the high energy consumption of traditional ball mills ； By replacing the bearing shells with rolling bearings, the frictional power loss of the main bearings can be reduced by 90%, thereby achieving energy savings. Since the 1970s, the domestic industry has been exploring ball mills with rolling bearings, but due to unresolved issues such as bearing manufacturing, lifespan, and bearing sealing, this technology has not been able to be widely adopted. II. Comparison of frictional torque between rolling bearings and sliding bearings 1. Frictional torque of rolling bearings: Frictional torque is a comprehensive practical performance characteristic of rolling bearings; it results from the combined effect of various factors, including rolling friction as well as sliding friction ； There is inter-solid friction as well as the viscous resistance of the lubricant. Based on a large number of measurements of friction torque, SKF’s Plam Gren department in Sweden has proposed the following method for calculating the friction torque of rolling bearings, which is based on empirical data: M = M0 + M1 (N.m). Here, M represents the friction torque (N.m), while M0 represents the friction torque that is independent of the load; this value depends mainly on the type of bearing, the viscosity and quantity of the lubricant, as well as the rotational speed of the bearing (N.m). Where: f0: a coefficient related to the bearing type and lubrication ； n: Bearing speed (r/min) ； v: Kinematic viscosity of the lubricant at the bearing operating temperature (mm2/s) ； M1: Mainly elastic hysteresis and frictional loss due to differential sliding at the contact surface. M1 = f1p1Dm, where f1 is a coefficient related to the bearing type and the load ； P1: Bearing load (N) when calculating bearing friction torque ； Dm: Diameter of the bearing ring (m); Dm = 0.5(d + D) ； d, D: Represent the diameters of the inner and outer raceways of the bearing, respectively. In the design of energy-saving mills, double-row self-aligning spherical roller bearings are used. According to relevant data, f0 = 6 and f1 = 5×10⁻⁴; therefore:
M0 = 160×10⁻⁷×10Dm = 9.6×10⁻⁵D³m (N•m)
M1 = 5×10⁻⁴×P1×10⁴×Dm = 5P1Dm (Nm)
Thus, M = M0 + M1 = 9.6×10⁻⁵D³m + 5P1Dm (N•m).
2. Frictional torque of sliding bearings: During the operation of conventional ball mills, the contact area between the shaft journals and the bearing shells is at least 75%, resulting in high frictional torque and significant energy consumption. Based on mechanical and tribological analysis, it is concluded that: P1: the load acting on the bearing (N) ； D: Hollow shaft diameter (m) ； μ: Coefficient of friction. The lubrication between the hollow shaft and the bearing shells is of the mixed-lubrication type. This includes adhesion, magic particle friction, as well as fatigue friction. The value for the listed polygon is: =2.55×10²P1D (N.m). 3. The ratio of frictional torque between rolling bearings and sliding bearings: Since D=Dm, when the diameter of the ball mill is 1.5 meters < φ < 4.5 meters, the diameter of the hollow shaft D is less than 2 meters, and the bearing load P1 is greater than 10 tons; that is, P1 > 10 and D2 < 10. The term on the left side of the above equation (can be ignored); the term on the right side. As determined through theoretical analysis, when rolling bearings are used in place of sliding bearings, the frictional torque of the mill is 2% of that of a conventional mill. However, taking into account various practical operating conditions such as manufacturing, installation, and lubrication, the value . is adopted. In other words, when rolling bearings are used for the main bearings, the frictional power loss is reduced by 90% compared to using sliding bushings. 4. Frictional power loss of the sliding support mill: As previously known, the friction torque T = 2.55×10²P1D (N.m). The frictional power loss between the journal of the hollow shaft and the bearing shells is given by; thus, the frictional power is equal to 2.67×10P1Dn, where n is the speed of the mill, in r/min. 5. Comparison of motor power requirements for the two types of mills: The motor power required for energy-saving mills and conventional mills is shown in Table 1. III. Overcoming technical challenges 1. Design and manufacturing of specialized rolling bearings: Ball mills are characterized by low speeds, heavy loads, and large sizes. Specialized bearings must possess sufficient load-bearing capacity as well as the ability to self-center, so as to meet the load requirements under both dynamic and static operating conditions, while also preventing issues caused by misalignment of the end covers and deflection during operation. By adopting standards such as ISO281, ISO76, ISO15, and GB/T6391, the calculation methods for the rated dynamic load, rated static load, and rated service life of specialized bearings were established. Strict requirements were set regarding the structural design, materials used, radial play, heat treatment, manufacturing processes, and acceptance criteria. Through collaborative efforts with large-scale specialized bearing manufacturers, the design and manufacturing challenges related to these extra-large rolling bearings designed for ball mills, which possess self-aligning capabilities, were ultimately overcome. ① Radial basic rated dynamic load of special self-aligning roller bearings: (1) GB/T6391──1995 bm: material-related coefficient ； The coefficients for calculation can be obtained by looking up a table ； i: Number of roller columns ； α: Contact angle ； Z: Number of rolling elements per column ； Lwe: Effective contact length of the rolling elements ； Dwe: Effective diameter of the rolling element ； Dpw: Pitch diameter of the rolling elements. ② Life calculation for specialized self-aligning roller bearings: Basic rated life: (2) GB/T6391──1995 Cr: Radial rated dynamic load ； Pr: Radial equivalent dynamic load ； (Hours) ③ Formula for checking the static load of special bearings: So: Safety factor ； Cor: Radial equivalent static load ； Por: Rated basic static load. 2. Application examples: Example: JNM2736 overflow mill, with a hollow shaft diameter (outer diameter) of D=1000 mm; the bearing load during operation is 170 t, and the rotational speed is n=21.7 r/min. Based on the load and diameter, and referring to international and domestic standard bearing series, this mill is designed with a double-row self-aligning spherical roller bearing S1000CAKF3/W33. The inner diameter of the bearing is d1 = 1000 mm, the outer diameter is d2 = 1400 mm, the width of the bearing is B = 260 mm, and rmin = 7.5 mm. By consulting tables, the required parameters are calculated; these values are then substituted into equation (1): the result is 8385 kN. From equation (2), we obtain 154741 hours, which is equivalent to 17.7 years (with 365 days per year). Additionally, through further calculations, it is found that Cor = 25700 kN, or 2570 tons. Since Por = X.oFr + YoFa, and after consulting relevant manuals and performing calculations, we get Por = 1700 + 4.11×272 ≈ 2817.9 kN, corresponding to a value of 9.12. It can be seen that this bearing has a long service life and a high safety factor. Under normal operating conditions, it can operate for 10 years without any problems. The basic parameters of the bearings selected this time are shown in Table 2: 3. “Flexible” sealing measures – To ensure a reliable sealing effect, this technology employs sealing measures that are completely different from conventional methods. Sealing is more important for rolling bearings than for sliding bearings. Sealing is necessary to prevent the leakage of lubricant as well as to stop harmful foreign substances from entering; otherwise, it can lead to abrasive wear of the bearing races, reduce the service life of the bearings, cause an increase in bearing temperature, and accelerate the corrosion of bearing components due to moisture and harmful gases, as well as speed up the aging of the lubricant. In powder-handling environments such as the mining industry, where conditions are poor and dust as well as slurry can get in, this is extremely detrimental to rolling bearings. For example, the hardness of iron ore is f=12–16, the hardness of the bearing raceways is HRC 61, and the hardness of the rollers is HRC 62; therefore, the presence of ore particles can cause severe abrasive wear. If the sealing issue is not properly resolved, it will cause wear on the bearings, resulting in additional stress that further accelerates wear and leads to failure due to wear. **This reduces the service life of the bearings and causes significant losses in production. The traditional sealing method involves pressing industrial felt at the shaft outlet; after operating for some time, the felt pad loses tight contact with the shaft, allowing materials, dust, and moisture to enter inside. Some use nitrile rubber rings for sealing, but factors such as the type of contact in this sealing mechanism, the pressing force applied, the lubrication conditions, the sliding speed, and the surface finish at the contact points all directly affect the friction torque and temperature rise of the bearing. The sealing device wears out during operation, and the rate of wear and failure depends on the performance of the sealing device itself as well as the operating conditions. When it fails due to wear or aging, it is difficult to replace, resulting in prolonged downtime. The nitrile rubber sealing devices for such extra-large bearings are produced in small quantities, are manufactured specifically, and are very expensive; as a result, these sealing devices are also not ideal. This technology uses sealing grease for sealing. Seal rings are designed at the shaft exits on both side end caps of the bearing housing; oil grooves are provided on the inner and outer sides of these seal rings. In addition, a seal sleeve is designed to work in conjunction with the seal rings. The oil grooves are filled with seal grease, which is a \"flexible\" material that allows it to fit tightly around the shaft under any conditions. It does not increase frictional resistance, and it is economical and simple. The performance is highly satisfactory. There is a certain taper from the end of the hollow shaft to the journal; when the bearing heats up, the lubricant becomes thinner and leaks out, which helps keep the interior of the bearing housing clean. 4. Technical features: ① This technology can be used to manufacture new grinders, as well as to technologically upgrade existing ball (rod) grinders. ② During the technical renovation, the transmission part and the cylinder section of the existing grinder are not altered; there is no need to machine the shaft shoulders on either side of the shaft, nor is it necessary to touch the bearing housing base plate. Instead, only new bearing housings are installed, along with additional seals, rolling bearings, and bearing bushings. ③ Cancel the light oil station of the ground coffee machine. Lubricant is applied once per quarter, which makes management convenient and keeps the site clean. ④ Under normal operating conditions, the main bearings do not need to be replaced for 10 years, and there is no need for routine maintenance, which saves a great deal of labor and resources. Production is not disrupted by the need to service the bearing shells. ⑤ After the technical upgrades, electricity consumption is reduced by 10–15%, lubricant usage is cut by 70%, resulting in an overall energy savings of over 15%. IV. Discussion on Performance and Existing Problems (I) Performance 1. Performance at Shougang Dashihe Mine: The MQ2736 unit in System 2, Mill 1 of Shougang Dashihe Iron Mine was modified, and it has been in operation for over 4 months now. The basic technical parameters are shown in Tables 3, 4, and 5. (II) Discussion on Existing Problems ① Improve the specialized structure to better withstand the impact on the bearings caused by the periodic vibration loads resulting from single-feed scoops. ② In the design of enterprises using multiple energy-saving grinders, an automatic fueling mechanism should be considered. ③ Add an automatic tracking and monitoring system for bearing operation. ④ The requirements for manufacturing and installation precision are higher than those of traditional grinders. In particular, the concentricity of the two end caps must be kept within 0.5 mm ； Strict limits are imposed on the total center distance and lateral parallelism of the bearing housings, with tolerances of 1 mm and 1.5 mm respectively ； The center heights of the two bearing seats should be kept at the same level as much as possible. Otherwise, it will affect the expected energy-saving effects. V. Conclusion The energy-saving upgrades implemented in the mills of metallurgical mining enterprises such as the Dashihe Iron Mine of Shougang Mining Company, the Nanfen Mine of Benxi Iron and Steel Company, and the Long** Mine of Xuanhua Iron and Steel Company demonstrate that the energy-saving technology for ball mills equipped with specialized rolling bearings has reached maturity. By summarizing the advantages and disadvantages encountered over the years in the process of technological upgrades, new approaches and methods have been proposed for design, manufacturing, and installation. We must work together as soon as possible with our peers in this industry to actively address the structural shortcomings, thereby making a contribution to energy savings and reduced consumption in the field of grinding in metallurgical mines.
M0 = 160×10⁻⁷×10Dm = 9.6×10⁻⁵D³m (N•m)
M1 = 5×10⁻⁴×P1×10⁴×Dm = 5P1Dm (Nm)
Thus, M = M0 + M1 = 9.6×10⁻⁵D³m + 5P1Dm (N•m).
2. Frictional torque of sliding bearings: During the operation of conventional ball mills, the contact area between the shaft journals and the bearing shells is at least 75%, resulting in high frictional torque and significant energy consumption. Based on mechanical and tribological analysis, it is concluded that: P1: the load acting on the bearing (N) ； D: Hollow shaft diameter (m) ； μ: Coefficient of friction. The lubrication between the hollow shaft and the bearing shells is of the mixed-lubrication type. This includes adhesion, magic particle friction, as well as fatigue friction. The value for the listed polygon is: =2.55×10²P1D (N.m). 3. The ratio of frictional torque between rolling bearings and sliding bearings: Since D=Dm, when the diameter of the ball mill is 1.5 meters < φ < 4.5 meters, the diameter of the hollow shaft D is less than 2 meters, and the bearing load P1 is greater than 10 tons; that is, P1 > 10 and D2 < 10. The term on the left side of the above equation (can be ignored); the term on the right side. As determined through theoretical analysis, when rolling bearings are used in place of sliding bearings, the frictional torque of the mill is 2% of that of a conventional mill. However, taking into account various practical operating conditions such as manufacturing, installation, and lubrication, the value . is adopted. In other words, when rolling bearings are used for the main bearings, the frictional power loss is reduced by 90% compared to using sliding bushings. 4. Frictional power loss of the sliding support mill: As previously known, the friction torque T = 2.55×10²P1D (N.m). The frictional power loss between the journal of the hollow shaft and the bearing shells is given by; thus, the frictional power is equal to 2.67×10P1Dn, where n is the speed of the mill, in r/min. 5. Comparison of motor power requirements for the two types of mills: The motor power required for energy-saving mills and conventional mills is shown in Table 1. III. Overcoming technical challenges 1. Design and manufacturing of specialized rolling bearings: Ball mills are characterized by low speeds, heavy loads, and large sizes. Specialized bearings must possess sufficient load-bearing capacity as well as the ability to self-center, so as to meet the load requirements under both dynamic and static operating conditions, while also preventing issues caused by misalignment of the end covers and deflection during operation. By adopting standards such as ISO281, ISO76, ISO15, and GB/T6391, the calculation methods for the rated dynamic load, rated static load, and rated service life of specialized bearings were established. Strict requirements were set regarding the structural design, materials used, radial play, heat treatment, manufacturing processes, and acceptance criteria. Through collaborative efforts with large-scale specialized bearing manufacturers, the design and manufacturing challenges related to these extra-large rolling bearings designed for ball mills, which possess self-aligning capabilities, were ultimately overcome. ① Radial basic rated dynamic load of special self-aligning roller bearings: (1) GB/T6391──1995 bm: material-related coefficient ； The coefficients for calculation can be obtained by looking up a table ； i: Number of roller columns ； α: Contact angle ； Z: Number of rolling elements per column ； Lwe: Effective contact length of the rolling elements ； Dwe: Effective diameter of the rolling element ； Dpw: Pitch diameter of the rolling elements. ② Life calculation for specialized self-aligning roller bearings: Basic rated life: (2) GB/T6391──1995 Cr: Radial rated dynamic load ； Pr: Radial equivalent dynamic load ； (Hours) ③ Formula for checking the static load of special bearings: So: Safety factor ； Cor: Radial equivalent static load ； Por: Rated basic static load. 2. Application examples: Example: JNM2736 overflow mill, with a hollow shaft diameter (outer diameter) of D=1000 mm; the bearing load during operation is 170 t, and the rotational speed is n=21.7 r/min. Based on the load and diameter, and referring to international and domestic standard bearing series, this mill is designed with a double-row self-aligning spherical roller bearing S1000CAKF3/W33. The inner diameter of the bearing is d1 = 1000 mm, the outer diameter is d2 = 1400 mm, the width of the bearing is B = 260 mm, and rmin = 7.5 mm. By consulting tables, the required parameters are calculated; these values are then substituted into equation (1): the result is 8385 kN. From equation (2), we obtain 154741 hours, which is equivalent to 17.7 years (with 365 days per year). Additionally, through further calculations, it is found that Cor = 25700 kN, or 2570 tons. Since Por = X.oFr + YoFa, and after consulting relevant manuals and performing calculations, we get Por = 1700 + 4.11×272 ≈ 2817.9 kN, corresponding to a value of 9.12. It can be seen that this bearing has a long service life and a high safety factor. Under normal operating conditions, it can operate for 10 years without any problems. The basic parameters of the bearings selected this time are shown in Table 2: 3. “Flexible” sealing measures – To ensure a reliable sealing effect, this technology employs sealing measures that are completely different from conventional methods. Sealing is more important for rolling bearings than for sliding bearings. Sealing is necessary to prevent the leakage of lubricant as well as to stop harmful foreign substances from entering; otherwise, it can lead to abrasive wear of the bearing races, reduce the service life of the bearings, cause an increase in bearing temperature, and accelerate the corrosion of bearing components due to moisture and harmful gases, as well as speed up the aging of the lubricant. In powder-handling environments such as the mining industry, where conditions are poor and dust as well as slurry can get in, this is extremely detrimental to rolling bearings. For example, the hardness of iron ore is f=12–16, the hardness of the bearing raceways is HRC 61, and the hardness of the rollers is HRC 62; therefore, the presence of ore particles can cause severe abrasive wear. If the sealing issue is not properly resolved, it will cause wear on the bearings, resulting in additional stress that further accelerates wear and leads to failure due to wear. **This reduces the service life of the bearings and causes significant losses in production. The traditional sealing method involves pressing industrial felt at the shaft outlet; after operating for some time, the felt pad loses tight contact with the shaft, allowing materials, dust, and moisture to enter inside. Some use nitrile rubber rings for sealing, but factors such as the type of contact in this sealing mechanism, the pressing force applied, the lubrication conditions, the sliding speed, and the surface finish at the contact points all directly affect the friction torque and temperature rise of the bearing. The sealing device wears out during operation, and the rate of wear and failure depends on the performance of the sealing device itself as well as the operating conditions. When it fails due to wear or aging, it is difficult to replace, resulting in prolonged downtime. The nitrile rubber sealing devices for such extra-large bearings are produced in small quantities, are manufactured specifically, and are very expensive; as a result, these sealing devices are also not ideal. This technology uses sealing grease for sealing. Seal rings are designed at the shaft exits on both side end caps of the bearing housing; oil grooves are provided on the inner and outer sides of these seal rings. In addition, a seal sleeve is designed to work in conjunction with the seal rings. The oil grooves are filled with seal grease, which is a \"flexible\" material that allows it to fit tightly around the shaft under any conditions. It does not increase frictional resistance, and it is economical and simple. The performance is highly satisfactory. There is a certain taper from the end of the hollow shaft to the journal; when the bearing heats up, the lubricant becomes thinner and leaks out, which helps keep the interior of the bearing housing clean. 4. Technical features: ① This technology can be used to manufacture new grinders, as well as to technologically upgrade existing ball (rod) grinders. ② During the technical renovation, the transmission part and the cylinder section of the existing grinder are not altered; there is no need to machine the shaft shoulders on either side of the shaft, nor is it necessary to touch the bearing housing base plate. Instead, only new bearing housings are installed, along with additional seals, rolling bearings, and bearing bushings. ③ Cancel the light oil station of the ground coffee machine. Lubricant is applied once per quarter, which makes management convenient and keeps the site clean. ④ Under normal operating conditions, the main bearings do not need to be replaced for 10 years, and there is no need for routine maintenance, which saves a great deal of labor and resources. Production is not disrupted by the need to service the bearing shells. ⑤ After the technical upgrades, electricity consumption is reduced by 10–15%, lubricant usage is cut by 70%, resulting in an overall energy savings of over 15%. IV. Discussion on Performance and Existing Problems (I) Performance 1. Performance at Shougang Dashihe Mine: The MQ2736 unit in System 2, Mill 1 of Shougang Dashihe Iron Mine was modified, and it has been in operation for over 4 months now. The basic technical parameters are shown in Tables 3, 4, and 5. (II) Discussion on Existing Problems ① Improve the specialized structure to better withstand the impact on the bearings caused by the periodic vibration loads resulting from single-feed scoops. ② In the design of enterprises using multiple energy-saving grinders, an automatic fueling mechanism should be considered. ③ Add an automatic tracking and monitoring system for bearing operation. ④ The requirements for manufacturing and installation precision are higher than those of traditional grinders. In particular, the concentricity of the two end caps must be kept within 0.5 mm ； Strict limits are imposed on the total center distance and lateral parallelism of the bearing housings, with tolerances of 1 mm and 1.5 mm respectively ； The center heights of the two bearing seats should be kept at the same level as much as possible. Otherwise, it will affect the expected energy-saving effects. V. Conclusion The energy-saving upgrades implemented in the mills of metallurgical mining enterprises such as the Dashihe Iron Mine of Shougang Mining Company, the Nanfen Mine of Benxi Iron and Steel Company, and the Long** Mine of Xuanhua Iron and Steel Company demonstrate that the energy-saving technology for ball mills equipped with specialized rolling bearings has reached maturity. By summarizing the advantages and disadvantages encountered over the years in the process of technological upgrades, new approaches and methods have been proposed for design, manufacturing, and installation. We must work together as soon as possible with our peers in this industry to actively address the structural shortcomings, thereby making a contribution to energy savings and reduced consumption in the field of grinding in metallurgical mines.
The issue is that the small teeth have been replaced while the large teeth haven’t; it will be fine after running in for a while