As a core transmission component in steel rolling production, the Rolling Mill Cardan Shaft undertakes the key mission of power transmission and angle compensation, and its operating status directly determines the continuity and stability of the steel rolling production line. The harsh conditions of heavy load, high temperature, dust, and vibration in the steel rolling scenario are likely to cause various faults in the cardan shaft. If timely diagnosis and troubleshooting are not carried out, it is very easy to cause production line shutdown and huge economic losses. Combined with the actual working conditions of steel rolling production, this article deeply analyzes the causes of common faults of the cardan shaft, summarizes the diagnosis methods, and provides scientific and efficient troubleshooting solutions, providing practical reference for equipment operation and maintenance of steel rolling enterprises.
The faults of the rolling mill cardan shaft are mostly concentrated in four categories: wear of core components, lubrication failure, seal damage, and assembly deviation. The manifestations, causes, and troubleshooting methods of different faults are significantly different. It is necessary to make accurate judgments and classify disposal to avoid aggravated component damage caused by blind maintenance.
I. Common Fault 1: Cross Shaft Wear and Abnormal Noise (Most Frequent Fault)
(1) Fault Manifestations
During operation, the cardan shaft produces obvious abnormal noise, mostly a periodic “clacking” sound, which intensifies with the increase of rotational speed; shutdown inspection can find that the cross shaft journal has wear and scratches, and in severe cases, the journal has elliptical deformation, the fit gap between the cross shaft and the bearing is too large, and there is obvious shaking during rotation; in some cases, it is accompanied by increased vibration of the cardan shaft, which further affects the dimensional accuracy of rolled steel products.
(2) Fault Causes
1. Insufficient Lubrication: In the steel rolling scenario with high temperature and much dust, the lubricating grease is easy to deteriorate and lose. The contact surface between the cross shaft and the bearing lacks effective lubrication, leading to dry friction or semi-dry friction, accelerating journal wear; some enterprises do not supplement lubricating grease regularly according to specifications, or the selected lubricating grease does not meet the working conditions (such as not selecting high-temperature extreme pressure lubricating grease).
2. Impurity Intrusion: The seal structure is damaged, and impurities such as dust, iron filings, and mud enter the fit part between the cross shaft and the bearing, forming abrasive wear during rotation, which intensifies the wear of the cross shaft journal and the inner ring of the bearing.
3. Excessive Angular Deviation: During installation, the offset angle of the transmission axis exceeds the rated compensation range of the cardan shaft (usually 15°-25°), resulting in uneven force on the cross shaft and excessive local load, leading to uneven wear and accelerated wear after long-term operation.
4. Overload Operation: The rolling force increases abnormally during steel rolling, or the equipment is started and stopped frequently, resulting in the torque borne by the cardan shaft exceeding the rated value. The cross shaft is in an overload state for a long time, accelerating fatigue wear.
(3) Diagnosis and Troubleshooting Methods
1. Diagnosis Method: Judge the fault location by listening to the abnormal noise (the abnormal noise comes from the cross shaft part), rotate the cardan shaft by hand to feel whether the fit gap is too large; use a vibration monitoring instrument to detect the vibration frequency of the cardan shaft, and if the vibration value exceeds the standard range, the cross shaft wear fault can be confirmed; observe the journal wear and bearing status after disassembly to further clarify the wear degree.
2. Troubleshooting Method: For mild wear (no obvious deformation of the journal, fit gap within the allowable range), clean the impurities in the cross shaft and bearing parts, replace with high-performance extreme pressure lubricating grease, adjust the transmission axis angle to ensure it is within the rated compensation range; for moderate to severe wear (excessive journal wear, elliptical deformation or bearing damage), it is necessary to replace the cross shaft and bearing assembly, perform lubrication treatment after re-assembly, and check the seal structure to avoid re-intrusion of impurities.
II. Common Fault 2: Bearing Failure
(1) Fault Manifestations
The temperature of the bearing part rises abnormally (exceeding 70℃), accompanied by a continuous and sharp “buzzing” abnormal noise during operation; in severe cases, the bearing seizes, causing the cardan shaft to be unable to rotate, directly leading to production line shutdown; after disassembly, it can be seen that the bearing balls are worn, the raceway has scratches, the inner and outer rings of the bearing are deformed, or the bearing lubricating grease is carbonized and blackened.
(2) Fault Causes
1. Lubrication Failure: Improper selection or aging and deterioration of lubricating grease, or insufficient lubricating grease filling, leads to poor internal lubrication of the bearing, increased friction between balls and raceways, generating a lot of heat and accelerating bearing damage.
2. Impurity Intrusion: After seal failure, impurities such as dust and iron filings enter the bearing, causing abrasive wear of balls and raceways, and at the same time aggravating lubricating grease pollution, further accelerating bearing failure.
3. Assembly Deviation: During assembly, the bearing is installed too tightly, resulting in too small internal clearance of the bearing and increased friction resistance during operation; or it is not aligned during installation, resulting in uneven force on the bearing and local wear and failure after long-term operation.
4. High Temperature Impact: High-temperature radiation in the steel rolling scenario leads to excessively high operating environment temperature of the bearing, accelerated aging of lubricating grease, decreased performance of bearing materials, and easy annealing of balls and deformation of raceways when in a high-temperature state for a long time.
(3) Diagnosis and Troubleshooting Methods
1. Diagnosis Method: Monitor the temperature of the bearing part with an infrared thermometer, and judge the bearing fault by combining with abnormal noise if the temperature rises continuously and exceeds the standard value; touch the bearing part by hand after shutdown to feel whether the temperature is abnormal, and rotate the cardan shaft to check for jamming; observe the bearing status after disassembly to confirm the failure degree.
2. Troubleshooting Method: After bearing failure, it is necessary to immediately replace it with a high-quality bearing of the same model and specification. Before replacement, clean the impurities inside the bearing seat and check whether the bearing seat is deformed; after replacement, fill with extreme pressure lubricating grease suitable for high-temperature working conditions to ensure sufficient lubrication; at the same time, check the seal structure, replace the damaged seal, strengthen high-temperature protection, and avoid the bearing being affected by high temperature and impurities again; if the fault is caused by assembly deviation, re-adjust the assembly position to ensure the bearing is aligned and the clearance is reasonable.
III. Common Fault 3: Seal Damage
(1) Fault Manifestations
Grease leakage occurs at the seal part of the cardan shaft, and the lubricating grease is seriously lost; the surface of the seal is damaged, aged, and deformed, unable to play a sealing role; a lot of dust and iron filings adhere to the seal part, and internal components (cross shaft, bearing) are prone to wear and rust.
(2) Fault Causes
1. Environmental Erosion: High temperature, dust, and corrosive media (such as cooling water, emulsion) in the steel rolling scenario erode the seal for a long time, leading to aging, hardening, and damage of the seal, losing its sealing performance.
2. Improper Assembly: The seal is installed crookedly or squeezed and deformed during assembly, or the seal is not installed according to specifications, resulting in too large seal gap and failure to achieve effective sealing; the selected seal is improper and not suitable for the high-temperature and heavy-load working conditions of steel rolling, resulting in shortened service life.
3. Component Wear: After the cross shaft and bearing are worn, the cardan shaft is eccentric during rotation, resulting in uneven force on the seal, and damage and leakage after long-term friction.
(3) Diagnosis and Troubleshooting Methods
1. Diagnosis Method: Observe whether there is grease leakage and dust adhesion at the seal part, and check whether the seal surface has damage and aging signs; disassemble the seal structure after shutdown to confirm the damage degree of the seal and whether the internal components are affected.
2. Troubleshooting Method: Replace the damaged seal with a high-temperature resistant, wear-resistant, and corrosion-resistant seal suitable for steel rolling working conditions (such as double-lip seal, labyrinth seal); ensure the seal is installed flat and without extrusion during assembly, adjust the seal gap to ensure the sealing effect; clean the impurities and oil stains at the seal part, regularly check the seal status, and replace it in time if aging or damage is found; at the same time, optimize the lubrication scheme to avoid leakage caused by excessive lubricating grease.
IV. Common Fault 4: Excessive Runout and Vibration of Cardan Shaft
(1) Fault Manifestations
The cardan shaft has obvious runout during operation, the vibration value exceeds the standard range, accompanied by obvious noise; in severe cases, the vibration is transmitted to the entire steel rolling equipment, leading to unstable operation of the roll and affecting the dimensional accuracy of rolled steel products; in some cases, the connection between the cardan shaft and the flange is loose, and even bolts are loose or fall off.
(2) Fault Causes
1. Assembly Deviation: The connecting flanges of the cardan shaft with the motor reducer and roll are not aligned, and the offset of the transmission axis is too large, resulting in uneven force on the cardan shaft during operation, generating runout and vibration.
2. Component Wear or Deformation: The fit gap between the cross shaft and bearing is too large after wear, or the intermediate connecting shaft is bent and deformed, leading to eccentricity of the cardan shaft during rotation and generating vibration.
3. Loose Connection: The flange connecting bolts are loose, missing, or the bolt tightening torque is insufficient, leading to insecure connection between the cardan shaft and the flange, resulting in runout during operation.
4. Unbalanced Dynamic Balance: After long-term operation of the cardan shaft, component wear leads to uneven mass distribution, decreased dynamic balance accuracy, and centrifugal force generated during operation, causing vibration.
(3) Diagnosis and Troubleshooting Methods
1. Diagnosis Method: Use a vibration monitoring instrument to detect the vibration value of the cardan shaft to judge whether the vibration exceeds the standard; check whether the flange connecting bolts are loose or missing, rotate the cardan shaft by hand to feel whether there is eccentricity or shaking; check whether the intermediate connecting shaft is bent and the fit gap between the cross shaft and bearing is too large after disassembly.
2. Troubleshooting Method: Adjust the assembly position to ensure the alignment of the cardan shaft with the flanges of the motor reducer and roll, and control the offset angle of the transmission axis within the rated range; replace the worn cross shaft and bearing, correct or replace the bent intermediate connecting shaft; fasten the flange connecting bolts, apply the tightening torque according to specifications, and make up for the missing bolts in time; perform dynamic balance detection and correction on the cardan shaft to ensure the dynamic balance accuracy meets the requirements and reduce vibration.
V. Fault Prevention and Precautions
1. Standardize Lubrication Management: Regularly check the lubrication system, select high-performance extreme pressure lubricating grease suitable for high-temperature and heavy-load working conditions of steel rolling, fill and replace lubricating grease according to the specified cycle. Some advanced production lines can be equipped with centralized automatic lubrication devices to extend the lubrication cycle and ensure sufficient lubrication of core components.
2. Strengthen Daily Inspection: Regularly check the seal structure, cross shaft, bearing, flange connection and other parts of the cardan shaft, monitor the operating parameters such as vibration and temperature, find abnormalities in time, and avoid the expansion of small faults.
3. Standardize Assembly and Selection: Strictly operate according to technical specifications during assembly to ensure flange alignment, proper seal installation, and reasonable bolt tightening torque; select the appropriate cardan shaft model according to the torque, rotational speed, temperature and other parameters of the steel rolling scenario to avoid faults caused by improper selection.
4. Do a Good Job in Environmental Protection: Strengthen seal protection for high temperature, dust, and corrosive media in the steel rolling scenario, regularly clean the dust and oil stains on the surface of the cardan shaft, and reduce environmental erosion on components.
Summary: The faults of the rolling mill cardan shaft are mostly related to lubrication, sealing, assembly, and working load. Accurate diagnosis of fault causes is the premise of efficient troubleshooting. By standardizing daily operation and maintenance, scientifically handling faults, and taking preventive measures, the fault rate of the cardan shaft can be effectively reduced, its service life can be extended, the stable and efficient operation of the steel rolling production line can be guaranteed, and solid support can be provided for steel rolling enterprises to reduce production costs and improve production efficiency.