Complete Analysis of Medium Frequency Melting Furnace Working Principles: From Basics to Efficient Application

1. What is a Medium Frequency Melting Furnace?

A medium frequency melting furnace is an industrial equipment that uses electromagnetic induction principles to heat metals, typically operating at frequencies between 50Hz and 10kHz. Its core function involves generating eddy currents within the metal through alternating current, achieving an efficient and environmentally friendly melting process. Compared to coal-fired furnaces, its thermal efficiency can be improved by over 40% (Source: International Heat Treatment Journal 2023). It is now widely used in foundry, metallurgy, and other industries.

2. Step-by-Step Analysis of Core Working Principles

Step 1: Power Conversion
Three-phase mains power is converted into direct current through a rectifier circuit, and then inverted by an inverter to generate medium frequency alternating current. Interestingly, this conversion can improve energy efficiency by 30% compared to traditional resistance furnaces.

Step 2: Induction Heating
When medium frequency current passes through the induction coil, it produces an alternating magnetic field. Eddy currents form inside the metal charge, generating Joule heat due to the metal's own resistance. Counter-intuitively, the heating depth is inversely proportional to the frequency—medium frequency furnaces are more suitable for rapid melting of small and medium-sized metal pieces.

Step 3: Electromagnetic Stirring
The alternating magnetic field pushes the molten metal to flow directionally. This automatic stirring action optimizes the uniformity of alloy composition. Our team found in a 2024 case study that properly controlling the stirring intensity can reduce composition segregation by 15%.

3. Comparative Analysis: Medium Frequency Furnace vs. Power Frequency Furnace

4. Common Operation Misconceptions Warning

⚠ Warning: Starting the furnace empty can cause coil arc-through! At least 20% of base charge must be reserved as a starting melt. For example, a factory once suffered coil insulation burnout due to an unauthorized empty furnace start, resulting in losses exceeding 500,000 RMB.

5. 5 Key Measures to Optimize Performance

1. Frequency Matching: Select frequency based on the metal type being melted (e.g., 500Hz-1kHz for steel).

2. Staged Power Control: Use full power during the heating phase, reduce to 60% during the holding phase.

3. Cooling Water Monitoring: Keep inlet water temperature stable within the 25-35°C range.

4. Lining Maintenance: Check lining thickness every 10 melts; replace immediately if wear exceeds 30%.

5. Electromagnetic Shielding: Add silicon steel sheets to reduce magnetic flux leakage and improve thermal efficiency.

Practical Operation Checklist

□ Confirm cooling water flow rate > 25m³/h
□ Check the output waveform of the power supply inverter module
□ Record power consumption and melting time for each melt
□ Verify molten metal temperature using an infrared thermometer
□ Clean oxides from the contact surface of the magnetic yoke

Frequently Asked Questions (Q&A)

Q1: What are the possible reasons for the medium frequency furnace tripping after startup?
A: Mostly due to rectifier bridge breakdown or coil-to-ground short circuit. Use a megohmmeter to check the insulation resistance.

Q2: How to reduce power consumption during the melting process?
A: Using spherical charge materials to increase packing density can shorten heating time by 20%.

Q3: How to adjust for uneven molten metal temperature?
A: Appropriately increase the frequency to enhance the electromagnetic stirring effect, but ensure it does not exceed the equipment's rated value.

Q4: Why must a new furnace lining be baked?
A: To remove moisture and water of crystallization, preventing sudden temperature rise from causing cracks and potentially leading to a furnace breakout accident.

Q5: Which is more economical, medium frequency furnace or electric arc furnace?
A: For annual production below 5,000 tons, choose a medium frequency furnace; above that, choose an electric arc furnace. Specific selection requires calculation based on local electricity prices.