metallurgical overhead crane

Common Faults and Practical Solutions for Metallurgical Overhead Cranes

Metallurgical foundry overhead cranes are critical core equipment in steelmaking production lines. Their operational stability directly determines the production efficiency of steel mills, and is closely related to the life safety of on-site operators. Sudden equipment failures and shutdowns will not only cause production line interruptions and capacity losses, but may also lead to safety accidents in severe cases.

Compared with general-purpose overhead cranes, metallurgical cranes operate long-term in complex working conditions with high temperature, heavy dust, and frequent cross-operation. They feature high working class, frequent operation cycles, and high full-load rate, which impose extremely high requirements on equipment structure, mechanical performance, and electrical control systems, resulting in a relatively higher failure rate. In addition, most on-site repairs in metallurgical scenarios require online maintenance, which puts forward strict requirements on fault location speed, maintenance efficiency, and solution reliability.

This article sorts out more than 10 typical faults in the structure and mechanical systems of metallurgical overhead cranes, analyzes the root causes combined with on-site working conditions, and provides actionable solutions, which can serve as a reference for equipment design optimization, on-site maintenance, and emergency troubleshooting.

1. Typical Structural Faults and Repair Solutions

Structural cracking and deformation are the most common types of failures in metallurgical overhead cranes, mostly caused by long-term alternating loads, welding residual stress, and working condition fatigue.

1.1 Weld Cracking Around Wheel Bearing Housing

Fault Performance: Cracks appear in the welds around the wheel bearing housing, accompanied by web plate tearing in severe cases.

Root Causes:

  • External factors: Defects in rail installation, such as foundation settlement and column deflection, cause excessive deviations in rail straightness, span, and height difference. During crane operation, horizontal guide wheels bear excessive lateral force, or wheel flange wear and rail gnawing occur on cranes without horizontal guide wheels.
  • Internal factors: Insufficient thickness of the web plate at the bearing housing connection, poor weld quality with missing welds or incomplete penetration, and excessive horizontal and vertical deviation of wheel assembly, which cause cracking under long-term alternating stress.

Solutions:

  1. Inspect and calibrate rail parameters, and check wheel assembly accuracy to adjust horizontal and vertical deviation.
  2. Remove the cracked welds and perform repair welding; drill crack stop holes at the end of web cracks before repair welding.
  3. Install stiffener plates to reinforce the web plate when structural strength is insufficient.

1.2 Weld Cracking Under Rail of Eccentric Rail Box Girder

Fault Performance: Weld cracking occurs between the web plate and the top cover plate under the rail, on eccentric rail box girders without T-shaped steel.

Root Causes: High wheel load causes excessive local compressive stress on the weld between the web and the cover plate. Since the trolley of metallurgical cranes operates in a relatively concentrated area, the welds in this area bear cyclic fatigue load for a long time, and the fatigue stress accumulates continuously, eventually leading to cracking.

Solutions:

  • For minor cracking: Remove the original welds for repair welding, and install triangular stiffeners on both sides of the web to disperse compressive stress.
  • For large-area tearing: On the basis of repair welding and stiffener installation, choose one of the following two schemes:
    1. Install thick steel plates under the rail to reduce the compressive stress on the weld.
    2. Replace with larger-size trolley rails to optimize the load transfer path.

1.3 Tearing at Main Girder and End Beam Connection

Fault Performance: Welds or base metal tear at the connection between the main girder and the end beam.

Root Causes: Sudden change of structural section at the joint without local reinforcement design; poor weld quality with incomplete penetration and insufficient weld height, leading to stress concentration and tearing under long-term load.

Solutions:

  1. Remove cracked welds and perform re-welding; drill crack stop holes at the end of base metal cracks before repair welding.
  2. Install reinforcing plates on the web plate to improve the structural strength of the connection part.

1.4 Wavy Deformation of Main Girder Web

Fault Performance: Irregular wavy deformation appears on the main girder web.

Root Causes:

  1. Unreasonable welding process leads to excessive welding residual stress.
  2. Insufficient reserved camber during web blanking, and wavy deformation occurs during flame straightening.
  3. Long-term overloaded operation causes local instability of the web plate.

Solutions:

  1. Implement standardized welding processes strictly to control welding stress.
  2. Reserve sufficient camber during web blanking, and carry out stress relief treatment after flame straightening.
  3. Strictly prohibit overloaded operation; install transverse stiffeners to improve web stability when deformation is obvious.

1.5 Lateral Bending Deformation of Main Girder

Fault Performance: Horizontal lateral bending deformation of the main girder, mostly occurring on eccentric rail box girders.

Root Causes: Mainly caused by welding residual stress; improper selection of supporting points during transportation and storage, or side-placed storage and transportation of the main girder will also cause lateral bending.

Solutions:

  1. Adopt reasonable welding process to control stress during the manufacturing stage.
  2. On-site deformation can be repaired by flame straightening.
  3. Standardize supporting points during transportation and storage, and side placement of the main girder is prohibited.

1.6 Camber Degradation of Main Girder

Fault Performance: The original upper camber of the main girder gradually decreases, affecting trolley operation performance and load-bearing safety.

Root Causes:

  1. Insufficient preset camber of the main girder during manufacturing.
  2. Insufficient stiffness reserve of the main girder in the design stage, resulting in permanent deformation and continuous camber decline after long-term load-bearing.

Solutions:

  1. Flame straightening can be used for repair when the camber drop is small.
  2. For girders with insufficient stiffness, π-shaped beams can be welded on the lower cover plate for reinforcement, which improves the strength and stiffness of the main girder simultaneously. The thermal stress generated by welding can also help restore the camber of the main girder.

2. Common Faults of Traveling Mechanisms and Troubleshooting

Traveling mechanism faults directly affect the traveling stability of the equipment, and are also the most frequent failures that affect the operation rhythm on site.

2.1 Vibration of Cab and Bridge During Operation

Fault Performance: Obvious vibration occurs in the driver’s cab or the whole bridge during crane operation.

Root Causes:

  1. Insufficient driving wheel load causes wheel slipping.
  2. Oil, water, ice or snow accumulated on the rail surface.
  3. Stuck rotation of the balance shaft of the bogie-type traveling mechanism, or foreign matter stuck in the bogie frame.
  4. Violent starting and braking, with too short acceleration and deceleration time.
  5. The natural vibration frequency of the long-span bridge is lower than 2Hz, causing resonance during operation.

Solutions:

  1. Adjust the wheel load distribution, and increase the number of driving wheels if necessary.
  2. Clean oil, ice and snow on the rail surface in time.
  3. Improve the lubrication of the balance shaft and remove foreign matter.
  4. Extend the starting and braking time, install speed regulating devices, or adopt soft-start motors.
  5. Install vibration damping devices on the cab mounting frame for long-span cranes.

2.2 Wheel Rail Gnawing of Bridge and Trolley

Fault Performance: Abnormal friction and wear between the wheel flange and the rail side, with increased running resistance.

Root Causes:

  1. Uneven wheel wear leads to large diameter difference between the two sides.
  2. Asynchronous transmission mechanisms on both sides, with mismatched motor parameters.
  3. Excessive horizontal deflection of wheel installation.
  4. Inconsistent opening and braking force of brakes on both sides.
  5. Oil or ice and snow on the rail surface aggravate slipping and offset.

Solutions:

  1. Unify wheel diameter, and adjust worn wheels to the driven wheel side.
  2. Prioritize motors of the same manufacturer and batch to ensure consistent speed.
  3. Calibrate the horizontal deflection of wheel installation.
  4. Adjust the brake clearance and braking torque to ensure synchronization on both sides.
  5. Clean oil, ice and snow on the rail surface.

2.3 Frequent Loosening or Damage of Mounting Bolts

Fault Performance: Mounting bolts at equipment connection parts loosen repeatedly, and even break and get damaged.

Root Causes:

  1. Insufficient coaxiality of connecting parts, and misalignment angle causes vibration.
  2. Insufficient structural strength of the mounting base, which deforms under load.
  3. Low machining accuracy of the base, resulting in uneven stress and structural deformation after bolts are tightened.

Solutions:

  1. Calibrate the coaxiality of connecting parts.
  2. Reinforce the structure of the mounting base.
  3. Install adjusting shims to compensate for machining errors and ensure uniform stress on the contact surface.

3. Transmission and Braking System Faults and Fixes

The transmission and braking system is directly related to the operation safety of the equipment, and faults must be checked and disposed of immediately.

3.1 Abnormal Noise from Crane Drum

Fault Performance: Abnormal sound occurs during drum operation.

Root Causes:

  1. Foreign matter left in the drum during machining or assembly.
  2. Broken mounting bolts of the drum coupling fall into the drum.
  3. Insufficient lubrication of the drum coupling due to oil shortage.
  4. Damaged coupling components or broken rollers.
  5. Worn and damaged drum bearings.

Solutions:

  1. Disassemble the drum to clean internal foreign matter and broken bolts, and reassemble the coupling.
  2. Fill lubricating oil to the coupling regularly.
  3. Replace accessories in time when the coupling or rollers are damaged.
  4. Replace new bearings when bearings are damaged.

3.2 Brake Failure, Load Slipping and Travel Drift

Fault Performance: Load slipping occurs in the hoisting mechanism, and travel drift occurs in the traveling mechanism, with significantly reduced braking performance.

Root Causes:

  1. Oil contamination on the surface of the brake wheel leads to insufficient friction.
  2. Excessive wear of brake shoes, with exposed rivets scratching the brake wheel.
  3. Improper adjustment of brake springs, or aged and failed springs.
  4. Misaligned brake installation, non-concentric brake shoe and brake wheel, resulting in single-side stress.
  5. Low machining accuracy of the brake wheel, with excessive circular runout.

Solutions:

  1. Thoroughly clean the oil on the surface of the brake wheel.
  2. Replace brake shoes with excessive wear in time.
  3. Adjust the braking force of the spring, and replace aged springs directly.
  4. Reinstall and calibrate the brake, and add automatic compensation and self-aligning structures.
  5. Re-machine or replace the brake wheel when the runout exceeds the standard.

4. Best Practices for Daily Operation and Maintenance

Most faults of metallurgical overhead cranes originate from long-term fatigue stress, insufficient installation accuracy, and lack of daily maintenance. In daily management, steel mills and maintenance teams should establish a regular inspection mechanism, focusing on monitoring rail accuracy, structural welds, brakes and transmission components.

It is also necessary to strictly standardize equipment operation, eliminate illegal operations such as overloading, violent starting and braking. Meanwhile, improving the fault judgment ability of maintenance personnel and adopting standardized maintenance procedures can effectively shorten downtime on the premise of ensuring safety, and guarantee continuous and stable production of steel mills.