What maintenance is required for medium frequency electricity furnace equipment?

Why Maintenance Matters

Medium frequency furnaces operate in challenging environments. In smelting and forging workshops, dust, intense vibration, and corrosive gases are common. If dust accumulates on thyristor chips or other power cabinet components, surface discharge and insulation failure can occur. Cooling water systems can develop scale or leaks, leading to overheating and costly repairs. Without routine inspection, minor issues escalate into unplanned downtime and expensive component replacement.

A well-maintained furnace not only runs more efficiently but also consumes less energy and produces cleaner melts. For facilities using a lead refinery furnace or similar equipment to produce high-purity ingots, stable thermal conditions are essential to achieving 99.999% purity targets.

Daily Maintenance Checklist

1. Power Cabinet Inspection

Clean the interior of the power cabinet every day. Use compressed air to remove dust from the induction coil area, thyristor (SCR) heat sinks, and control boards. Pay special attention to the exterior of thyristor chips; wipe them carefully with alcohol if necessary. Dust buildup reduces electrical efficiency and can cause short circuits or surface discharge on high-voltage components.

2. Cooling System Verification

Before starting the furnace, confirm that both the power water pump and the furnace water pump are running. Check water pressure at multiple points: power cabinet pressure should read between 1.5 and 1.7 kg, while furnace cooling pressure should be between 1.5 and 2.0 kg. Verify water flow and temperature in each cooling circuit. Top up with deionized water if levels are low, and inspect filter press cloth for tears or clogging. Clean or ｒｅｐｌａｃｅ filters as needed to protect pumps and heat exchangers.

3. Temperature Monitoring of Electrical Components

Use an infrared temperature gun to check the operating temperature of SCR modules, resistance-capacitance protection resistors, and equalizing resistors. Record measurements at three stages during the melting cycle:

• First measurement: 5 to 10 minutes after reaching approximately one-third power during the initial furnace charge.
• Second measurement: when the furnace is nearly full and the melt approaches the target temperature.
• Third measurement: at the end of the final melt of the day, when the system is running at full power.

If any SCR shows abnormal temperature, immediately inspect the water pipe for kinks or blockages restricting flow. A clogged rectifier sleeve or folded hose can cause rapid overheating and device failure.

4. Mechanical and Connection Checks

Check cable screws and busbar connections for looseness caused by thermal cycling and vibration. Inspect water-cooled cables near the furnace for signs of wear, cracks, or contamination from iron filings and metal debris. Keep these cables clean to prevent electrical faults. Examine all water pipe joints for tightness and signs of leakage or seepage. Address any drip immediately to avoid water entering electrical compartments.

Weekly and Monthly Maintenance Tasks

1. Bolt Tightening and Structural Inspection

Once a week, tighten all bolts, nuts, and water hose clamps on the furnace frame, induction coil supports, and hydraulic connections. Thermal expansion and workshop vibration gradually loosen fasteners. A loose connection can lead to arcing, water spray, or coil displacement. Inspect contactors and relay contacts; ｒｅｐｌａｃｅ any that show pitting, burning, or poor contact rather than continuing to use them.

2. Capacitor and Reactor Inspection

Check the inverter resistance-capacitance protection trunking for any wires that have fallen or shifted. Loose wiring can short-circuit non-inductive resistors and damage KK inverter thyristors. If you notice one protection resistor running significantly hotter than the others, investigate whether its associated capacitor has failed open or the resistor itself is damaged. During startup, a healthy reactor should produce a slight hum; excessive buzzing or physical shaking may indicate winding looseness or core gap problems.

3. Hydraulic System Servicing

For furnaces equipped with hydraulic tilting or cover systems, check the hydraulic oil level weekly. Maintain the reservoir at least 80 percent full. Hydraulic oil should be changed every six months under normal operating conditions. Clean the suction filter screen monthly. Note that most hydraulic stations contain two filters; position them properly inside the reservoir on the mounting shelf, not resting at the bottom where they can draw in sediment and metal chips that damage the hydraulic pump.

4. Water Distributor and Nozzle Maintenance

In facilities with hard tap water or well water, scale and corrosion affect the water distributor inside the power cabinet. Inspect nozzles monthly for blockage or deterioration. If multiple nozzles are severely corroded, ｒｅｐｌａｃｅ the entire water distributor assembly as a unit. Welding individual nozzles back onto the manifold is not recommended, as it creates uneven flow and extended downtime. For open cooling systems, plan water distributor replacement approximately every three months. For fully closed-loop systems with treated water, replacement may only be needed every six to twelve months.

5. Pipe Sleeve Descaling

Scale buildup inside water-cooled pipe sleeves reduces heat transfer and raises component temperatures. Every three to six months, circulate a 20 percent dilute hydrochloric acid solution through the sleeves for 10 to 15 minutes to dissolve mineral deposits. After acid cleaning, flush thoroughly with clean water and blow dry with compressed air before returning the circuit to service. Residual acid will corrode the sleeves and shorten their lifespan.

Cooling System Best Practices

The cooling system is the lifeblood of a medium frequency induction furnace. Operators must verify water flow and pressure at the start of every shift. When using tap water or well water as a direct cooling source, scale accumulation is inevitable. Consider installing a closed-loop recirculating system with a heat exchanger and deionized water makeup. This dramatically reduces scaling, improves cooling stability, and lowers long-term maintenance costs.

In warm or humid climates, condensation can form on cold water pipes inside the power cabinet, especially during summer months. Condensation dripping onto control boards or thyristor modules causes electrical faults. If severe condensation is observed, improve ventilation in the electrical room, raise cooling water temperature slightly, or switch to a closed-loop system. Stop operation immediately if water is found inside the power cabinet.

ｒｅｐｌａｃｅ plastic cooling hoses at the first sign of aging cracks. A burst hose can flood the power cabinet within minutes, causing catastrophic damage to the inverter and rectifier sections.

Electrical System Care

The power supply system converts grid electricity into medium-frequency alternating current for the induction coil. Test capacitors and transformers periodically for capacitance drift, oil leaks, or abnormal heating. Clean dust from control units and check that cooling fans on heat sinks operate correctly. Calibrate temperature sensors and current transformers annually to ensure accurate process control.

Test the emergency shutdown circuit monthly. A functional emergency stop is critical for protecting personnel and equipment if a coil lining failure or water leak occurs during a melt. Verify that all indicator lights, alarms, and interlocks on the control panel respond correctly.

Seasonal and Environmental Considerations

Furnace rooms must be kept clean and well ventilated year-round. During winter, ensure that cooling water does not freeze in external piping. In summer, monitor ambient temperature in the electrical room; if it exceeds 35 degrees Celsius, add ventilation or air conditioning to prevent power component derating. In workshops near pickling or phosphating lines, corrosive gases accelerate deterioration of printed circuit boards and electrical contacts. Increase the frequency of cabinet cleaning in these environments, and consider positive-pressure ventilation or sealed cabinets for sensitive electronics.

Maintenance Records and Scheduling

Systematic record-keeping turns reactive repairs into predictive maintenance. Log daily temperatures, water pressures, and any abnormalities observed. Track the run hours since the last hydraulic oil change, filter replacement, and pipe sleeve cleaning. Compare month-to-month data to identify gradual degradation trends, such as slowly rising SCR temperatures or declining water flow rates. Addressing these trends during a planned maintenance window prevents unexpected failures during production.

Schedule a comprehensive inspection once every week or two weeks, depending on production intensity. During this inspection, perform all weekly tasks, review the maintenance log with operators, and plan parts procurement for upcoming monthly or quarterly services.

Conclusion

Consistent, thorough maintenance is essential for getting the best performance and longest life from your metal melting furnace. Daily cleaning, temperature monitoring, and leak checks prevent minor issues from becoming major failures. Weekly bolt tightening, hydraulic servicing, and capacitor inspection keep mechanical and electrical systems reliable. Seasonal awareness and detailed record-keeping further reduce downtime and repair costs.

By following the maintenance schedule outlined above, foundries and recycling plants can keep their medium frequency equipment running safely and efficiently for many years, maximizing return on investment and ensuring consistent product quality.