A Ladle Refining Furnace (LRF) is an important secondary steelmaking unit for refining molten steel after primary melting. Stable equipment operation is essential for maintaining production continuity, process reliability, and equipment service life.
For a 25-ton LRF system, effective maintenance should not be limited to the maintenance department. Operators also play an important role by using the equipment correctly, identifying abnormal conditions, and reporting defects before they develop into major failures.
This article summarizes key maintenance and repair practices for a 25-ton LRF steelmaking system, covering daily inspections, lubrication, cooling water, hydraulic systems, routine repairs, and major overhaul.
What Are the Key Maintenance Areas of a 25-Ton LRF?
The main maintenance areas of an LRF system include:
- Water-cooled furnace cover and cooling system
- Electrode arms, electrode clamps, and water-cooled cables
- Ladle car and tapping/slag-handling equipment
- Hydraulic system
- Mechanical transmission components
- Electrical connections and insulation
- Lubrication system
- Instrumentation, interlocks, and control components
Regular inspection of these systems helps identify wear, leakage, loose connections, overheating, and other abnormal conditions at an early stage.
Daily Maintenance and Inspection
Daily maintenance should be integrated into normal steelmaking operations.
1. Keep the Furnace Area Clean
The area around the LRF should be cleaned after each heat to maintain a safe and workable operating environment. Slag accumulating around the ladle rim should also be removed to ensure proper contact between the ladle and the water-cooled furnace cover.
The furnace cover should be inspected during shift handover. Slag buildup on the inner surface can become uneven and may affect the alignment of the cover.
2. Inspect the Electrode System
Before extending or replacing electrodes, inspect the electrode joints and connection threads for damage and ensure that the connections are properly tightened.
When the electrode is gripped by the electrode arm, the clamping position should remain at least 400 mm away from the electrode joint.
Before installing a new electrode, clean the contact surfaces of the electrode clamp to maintain good electrical conductivity. The electrode clamps and conductive arms should also be checked for burning, deformation, and abnormal wear.
3. Inspect the Ladle Car and Mechanical Components
The ladle car should be checked regularly for:
- Loose bolts and foundation bolts
- Abnormal operation of the electro-hydraulic brake
- Bearing, shaft sleeve, guide wheel, and chain condition
- Lubrication and wear of moving components
- Abnormal operating noise
The rail surface should be cleaned at every shift handover. Any solidified steel or material resulting from steel leakage should be removed promptly.
Approximately every six months, the ladle car drive should be inspected for wheel alignment and rail-climbing or wheel-flange contact problems. The drive unit should also be cleaned to prevent dust accumulation from affecting motor cooling and equipment operation.
How Should the LRF Water-Cooling System Be Maintained?
The water-cooling system is one of the most critical parts of an LRF because the furnace cover operates in a high-temperature environment.
Cooling-water flow meters, thermometers, pressure gauges, and other instruments should be checked regularly. Their local readings should also be compared with the values received by the control system.
Inspect all cooling-water pipes, hoses, and connections for looseness, blockage, or leakage. Cooling-water quality should meet the requirements for industrial treated water.
Monitor Water Temperature Carefully
The water-cooled furnace cover is divided into multiple cooling circuits. High-temperature areas require particular attention.
If the cooling-water temperature exceeds 55°C, the cause should be investigated promptly. Steelmaking operations should not continue when a cooling-water leak presents a significant safety risk.
What Are the Signs of Water Leakage in a Water-Cooled Furnace Cover?
Water leakage inside the furnace may be indicated by unusually long flames emerging around the electrode holes or furnace door. In some cases, the flame may appear yellow, indicating a change in the furnace atmosphere.
If water leakage is suspected:
- Stop power input.
- Raise the electrodes.
- Raise the furnace cover if necessary for inspection.
- Identify the suspected leakage circuit or location.
- Isolate the affected cooling-water supply.
- Repair or replace the damaged component after the heat is completed.
The exact response should follow the plant’s established operating and safety procedures.
Hydraulic System Maintenance
The hydraulic system should be inspected regularly to ensure reliable operation of the LRF’s hydraulic equipment.
The hydraulic oil temperature should normally remain within 35–55°C, with a maximum of 65°C according to the equipment maintenance requirements described here. The hydraulic tank level should also be monitored.
Regular inspection should cover:
- Hydraulic pumps
- Filters
- Valves and connections
- Accumulator nitrogen pressure
- Oil temperature
- Hydraulic oil level
- Signs of leakage
Filters should be inspected approximately once a month for blockage, while hydraulic valves should be checked for leakage and abnormal operation.
Lubrication of LRF Equipment
Correct lubrication is essential for reducing wear and extending component service life.
Maintenance personnel should follow the specified lubricant type, lubrication interval, and quantity for each lubrication point. Grease and oil must be kept clean and protected from contamination by dust, sand, water, acids, alkalis, or other foreign materials.
Before lubrication, clean the oil hole, grease nipple, or oil cup and check that the lubrication passage is clear.
Centralized Lubrication System
The 25-ton LRF system described here uses a centralized lubrication system for the electrode lifting guide rollers. An electric grease pump delivers lubricant through distributors to the designated lubrication points.
The lubrication pipes, distributors, and safety valves should be inspected regularly. Leakage from a distributor or safety valve may indicate blockage in the corresponding lubrication circuit and should be investigated promptly.
Electrical Connections and Insulation
Electrical connections in the high-current circuit require regular inspection.
The conductive arms, water-cooled cables, and secondary circuit connections should have clean, flat contact surfaces and secure bolted connections.
The connections between the conductive arms, water-cooled cables, and secondary circuit should be checked and tightened approximately every two weeks. The insulation condition of relevant components should also be inspected regularly.
Routine Repair and Periodic Maintenance
Minor repairs and intermediate maintenance are generally carried out during planned shutdowns or holidays.
Typical work includes:
- Checking and calibrating measuring instruments
- Inspecting measurement, alarm, and limit switches
- Checking automatic control and interlock functions
- Cleaning slag from the furnace cover and ladle rim
- Inspecting or replacing cooling-water pumps and valves
- Replacing damaged seals and gaskets
- Checking mechanical connections and fasteners
- Draining water from pipelines and distributors during extended shutdowns
For longer periods of equipment inactivity, carbon-steel connecting components should be cleaned and protected against corrosion where required.
When Should the Water-Cooled Furnace Cover Be Replaced?
After extended operation, the water-cooled steel tubes in the furnace cover may develop fatigue deformation, localized water seepage, or weld cracking.
For the equipment described in the maintenance manual, approximately 3,000 heats is used as a reference point for evaluating the condition of the furnace cover. This should not be treated as a universal replacement interval. Actual replacement should be determined by inspection results and the condition of the cooling tubes and welds.
Minor defects may sometimes be repaired by cleaning and welding. If deformation, leakage, or cracking becomes extensive, replacement of the furnace cover should be considered.
Major Overhaul of an LRF System
A major overhaul should be planned in advance and based on equipment condition, operating history, inspection records, and known defects.
Before the overhaul, the maintenance team should:
- Define the overhaul scope and schedule
- Review drawings and technical documentation
- Analyze equipment defects and failure causes
- Prepare spare parts, materials, tools, and testing equipment
- Develop appropriate maintenance procedures
- Implement required safety controls
During the overhaul, critical components should receive detailed inspection and measurement. All maintenance findings, measurements, repairs, and modifications should be documented and archived.
After maintenance, equipment should undergo the required single-machine and integrated test runs before being returned to production. The maintenance and operating teams should jointly verify equipment condition and performance before formal handover.
Safety Is an Essential Part of LRF Maintenance
Maintenance of an LRF involves high temperature, high current, heavy equipment, hydraulic systems, and lifting operations. Maintenance work must therefore follow the plant’s safety procedures and equipment-specific requirements.
Particular attention should be given to:
- Lockout and power-isolation procedures
- Work at height
- Lifting and crane operations
- Hot-work controls
- Confined or restricted work areas
- Coordination between maintenance and operating personnel
- Furnace-cover replacement
- Equipment testing and commissioning after maintenance
During test operation, maintenance personnel should remain on site and assign personnel to monitor equipment movement and operating conditions. If further adjustment is required, the equipment should be safely isolated before maintenance resumes.
