The 5m rolling mill of the company’s thick plate factory is the first of its kind in China for a wide and thick plate production line. The oil film bearing is one of the main equipment of the thick plate rolling mill. Correctly understanding and mastering its features is a key link in improving thick plate production. The structure characteristics of the rolling oil film bearing were analyzed, and the lubrication system of the thick plate oil film bearing and the self-aligning mechanism of the bearing were briefly described. Combined with the problems encountered during the commissioning of the rolling mill, the self-aligning mechanism was analyzed and improved. At the same time, based on on-site experience, the phenomenon of a large number of spots appearing on the contact part of the supporting rod neck and the oil film bearing cone sleeve at the beginning of the operation was analyzed, and the assembly process was improved. Finally, the spots were eliminated.
Thick plate rolling mill; Oil film bearing; Self-aligning mechanism
The 5m wide thick plate rolling mill that was put into operation in March 2005 is the first of its kind in China for a wide and thick plate production line. There are very few similar rolling mills in the world. After the 5m thick plate rolling mill was put into operation, similar rolling mills of the same type have also been put into operation in China in recent years.
The parameters of the rollers and bearings of the Baosteel 5m thick plate rolling mill are as follows:
Rolling machine type: CVCPLUS four-roll reversible type.
Working roller size: Φ 1210/1110 × 5300mm.
Working roller bearing: four-row conical roller bearings.
Supporting roller size: Φ 2300/2100 × 4950mm.
Supporting roller bearing: MORGOIL oil film bearing.
The thick plate rolling mill has very high requirements for the accuracy and plate thickness deviation control of the rolled materials, and also puts forward corresponding requirements for various components of the rolling mill. The oil film bearing is a key component of the rolling mill. To meet the control technology of the rolled materials and the accuracy of the rolled materials, as well as the features of AGC (Roll Gap Automatic Control System) control, quick disassembly and assembly, etc., the supporting roller oil film bearing adopts the design of the American Morgan Company’s non-key thin-walled cone sleeve, hydraulic loading, bidirectional thrust bearing structure and combined lip seal technology.
1. Structural Characteristics Analysis
1.1 Meaning of MORGOIL Oil Film Bearing Model
80” – 76 – KLX – DT – LP – HB – S.
80” – The series number of the supporting roller diameter, indicating that the minimum diameter of the rolled material used by this bearing is 80” (≈ 2m);
76 – The percentage of the working length and diameter of the oil film bearing;
KLX – Non-key thin-walled cone sleeve
DT – Double thrust roller bearing
LP – Combined lip seal
HB – Hydraulic locking
S – Symmetrical roller.
1.2 Non-key Thin-Walled Cone Sleeve (KLX)
The cone sleeve rotates with the roller using one of three connection methods: long key, short key, or no key.
Long Key:
We install a key on the roller and a through-key slot on the thin-walled cone sleeve.
The slot opening weakens stiffness, causing oil film fluctuations under rolling force.
These fluctuations reduce rolled material accuracy and bearing capacity.
Short Key:
We replace the long key with two short keys on the cone sleeve.
This reduces the slot’s impact on accuracy, but the slot remains in the working area.
We improve but do not completely eliminate the issue.
No Key:
We open the key slot near the roller neck flange.
This keeps the contact cone surface slot-free.
We eliminate stiffness reduction and oil film fluctuations.
We thereby improve the bearing’s load-bearing capacity.
Morgan Company optimized the design of the cone sleeve based on the non-key cone sleeve, designing the cone sleeve with a thin-walled type. Under the same rolling conditions, the thin-walled design has the following advantages:
(1) The outer diameter size of the cone sleeve is reduced relatively. The reduction of the cone sleeve structure brings many advantages to the design of the entire rolling mill. The dimensions such as the bearing seat, the window of the rolling mill frame, and the height of the frame can all be reduced, saving investment.
(2) Compared with the keyless structure of the same working diameter, the diameter of the roll neck of the rolling mill can be increased, improving the bearing capacity.
1.3 Hydraulic Loading and Unloading (HB)
Traditional Mechanical Rapid Disassembly Mechanism
In the traditional loading and unloading process, we wind the steel wire rope around the locking key nut and use the crane to pull it, rotating the nut to push other parts axially for cone sleeve adhesion and bearing installation. However, during lifting, the crane hook rotates, and inappropriate rope specifications risk breakage. We cannot quantitatively control the locking force but rely on operator experience instead, which prolongs the crane occupation time and affects other processes.
Hydraulic Rapid Locking Structure (HB)
We retain the original structure’s advantages for overall rapid loading and unloading, replacing the nut and screw ring with a hydraulic piston mechanism. We simply connect the quick connector on the hydraulic moving cart to the piston and start the power supply, which installs the bearing in place with quantitatively controlled locking force. This method ensures accurate, fast, and safe loading and unloading, while also reducing the labor intensity of installation workers.
1.4 Bidirectional Thrust Bearing Structure (DT)
We designed the bidirectional thrust bearing structure to symmetrically arrange both ends of the rolling mill.
This arrangement effectively prevents axial movement of the oil film bearing.
Such movement would otherwise cause sealing failure due to the asymmetrical structure. At the same time, it improves the universality and interchangeability of the parts, and facilitates the spare parts management and installation and use by users.
1.5 Combined Lip Seal Technology (LP)
The working environment of the oil film bearing of the thick plate rolling mill is very harsh. The oil film bearing suffers from iron oxide scale, impurities, and high-pressure cooling water during rolling.
We therefore set strict sealing requirements.
Without effective measures, cooling water and impurities enter the bearings.
They deteriorate lubrication, affect oil film formation, and cause premature bearing damage.
They also emulsify the oil, shorten its life, and increase consumption.
We applied a combined lip seal device on Baosteel’s 5m mill.
Over one year of use, we have proven its excellent sealing performance.
We have seen no cooling water or impurities invade the bearings.
The device combines three water seals and two oil seals.
We arrange them to effectively seal both water and oil.
2 Lubrication System of Oil Film Bearings
The working mode is a dynamic pressure oil film bearing. The structure of the bearing lubrication system is shown in the figure. The system capacity is 490L/min, the maximum working pressure is 0.7MPa, and the supply temperature is 40℃.
3 Improvement of Oil Film Bearing Application Problems
3.1 Improvement of Self-aligning Mechanism
The self-aligning mechanism is one of the oil film bearing supporting designs. The self-aligning mechanism compensation pad of the 5m thick plate rolling mill is designed as an arc-shaped, with a radius of 3370mm.
We designed the arc-shaped pad to address a core rolling phenomenon.
The rolled piece’s deformation resistance bends the supporting roller and its axes.
This bending skews the conical sleeve relative to the bushing.
This skewing creates uneven axial gap distribution and inconsistent dynamic pressure.
We designed the pad to compensate for this bending deformation.
The pad guides the bearing seat to rotate with the roller’s deflection.
This rotation maintains the original conical sleeve-bushing gap.
During commissioning of the 5m thick plate mill, we found the AGC cylinder at the lower support roller bearing seat often tilted (see Figure).
The AGC cylinder is the mill’s largest cylinder, and its quality directly affects production line normal operation.
We analyzed the tilt and found the main cause: the lower support roller bearing seat tilts due to the rolled piece’s deformation resistance.
The self-aligning mechanism’s arc pad plate generates a horizontal force on the AGC piston rod.
This force tilts the cylinder piston, damages the seal, and causes direct friction between the cylinder body and piston.
This results in hydraulic oil leakage and prevents the AGC cylinder from functioning properly.
Through comprehensive analysis of the oil film gap and cylinder inclination, in order to ensure the normal operation of the AGC cylinder, the compensation pad plate of the self-aligning mechanism bearing seat was improved twice. The first improvement changed the arc-shaped compensation pad plate arc part to a flat surface. After one month of application, the cylinder piston inclination phenomenon did not show significant improvement. The second improvement that followed had a remarkable effect. During the application process over a period of more than half a year, this improvement effectively solved the problem of the cylinder block and piston inclination, and ensured that the oil film bearings always operated normally without any abnormalities.
3.2 Treatment of Roller Neck and Oil Film Bearing Cone Sleeve Spots
The taper of the 5m heavy plate mill support roller neck and the oil film bearing cone sleeve is 1:5.647.
At the early stage of operation, a large number of black spots appeared on the contact area between the support roller neck and the oil film bearing cone sleeve (see Figures 4 and 5).
These black spots severely impaired the geometric accuracy of the roller neck and the installation accuracy of the oil film bearing.
When grinding the rolls, we rely on the contact between the roll neck and the grinding machine bearing bush to achieve positioning. Based on this, we realize that the geometric accuracy of the roll neck will directly affect the grinding accuracy. In severe cases, it may even lead to the situation where the rolls cannot be ground.
3.2.1 Analysis of Spot Generation Causes
Due to the self-weight of the thick plate rolling mill support roller being 226 t and the rolling force being 100,000 kN, the contact stress between the inner surface of the cone sleeve and the conical roller neck surface of the support roller during operation is very large. Theoretically, there needs to be an appropriate locking force between them. If the locking force is slightly smaller, there will be a gap between the roller neck and the cone sleeve, providing a space for the lubricating oil to flow. We have found that due to chemical reactions, the lubricating oil will increase its acid value and reduce its dehydration capacity. These changes will eventually result in the formation of black spots of specific width and depth on the surface of the roller neck and the conical sleeve.
3.2.2 Treatment
We identified the blemish causes and immediately took action.
We focused on increasing the locking force during assembly.
However, after one operating cycle, we found the roller neck tightly stuck to the cone sleeve during disassembly.
Through further analysis, we discovered that the relative distance between the mechanical locking nut and the rotating outer threaded body is crucial for proper locking force.
We tracked this data and found each roller neck-cone sleeve pair has its own reasonable range.
Based on this, we improved the assembly process, established files for each pair, and checked surface contact conditions.
We corrected the data range and set it as the new assembly standard.
After over a year of production practice, we developed and standardized oil film bearing installation procedures.
These procedures basically eliminated the initial operation problems on the supporting roller neck and cone sleeve.
4 .Conclusion
The 5m thick plate rolling mill is the first special wide-width thick plate production line in China. The understanding and analysis of the structural characteristics of the oil film bearings of its main equipment are very necessary for better application and maintenance of the equipment. Currently, there is no comparable experience for the installation and application of large-sized oil film bearings in China. We recognize that there may be discrepancies between theoretical designs and actual operations. Therefore, we need to conduct further exploration, summarization, accumulation and continuous improvement in practice.
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E-mail: cykc@cykcgroup.com.cn