Stability Control of Induction Furnaces in Casting of Automotive Engine Blocks

In the automotive industry, the casting of engine blocks (โดยทั่วไป HT250/GJL-250 หรือ HT300/GJL-300 grade Grey Cast Iron) represents a “high-precision” sector. Facing the high-speed demands of automated molding lines (such as DISAMATIC or HWS), ที่ core conflict lies in how to eliminate the fluctuations caused by the “intermittent melting” nature of induction furnaces and provide a supply of molten iron that is as “continuous and stable” as that of a Blast Furnace or Cupola.

ฉัน. Extreme Consistency Control of Composition and Temperature

In mass production, minute differences in each batch of molten iron can lead to uneven hardness, machining difficulties, or shrinkage porosity in castings. The key to control is transforming “variables” เข้าไปข้างใน “constants.”

1. Refined Charge Management (การควบคุมแหล่งที่มา)

Induction furnaces operate on the principle of “garbage in, garbage out” and lack the metallurgical reaction capabilities of cupolas. ดังนั้น, charge management is the cornerstone of stability.

• Cleanliness Control: Automotive castings are sensitive to gas porosity. Oil, moisture, and rust on Steel Scrap must be strictly controlled. For Bales, density and internal inclusions must be monitored.
• Batching ความแม่นยำ: Automatic batching systems must be used to ensure the ratio errors of Pig Iron, การส่งคืน, and Steel Scrap are controlled within ± 1%.
• Trace Element Tracking: Grey iron is extremely sensitive to trace elements (เช่น, ของ, ป.ล, อัล). A supplier archive for trace elements must be established to avoid accumulation effects that degrade graphite morphology.

2. “Heel Melting” and Process Discipline

To maintain consistency across continuous batches, the furnace must never be fully emptied.

• Heel Melting Operation: Always maintain 30%~50% liquid iron (the heel) in the furnace.
  • การทำงาน: Shortens the melting time for the next batch and, ที่สำคัญกว่านั้น, uses the old molten iron as a Buffer to significantly dilute the compositional fluctuations of the new charge.
• Full Power & เครื่องทำความร้อนอย่างรวดเร็ว: If grey iron stays in the high-temperature zone too long, the nucleation cores (Nuclei) will dissolve/fade, leading to an increased chill tendency. The strategy is: Melt with high power, tap immediately upon reaching temperature, and strictly prohibit holding the iron for long periods.

3. Closed-Loop Temperature Control

• เป้า ความแม่นยำ: The pouring temperature window is usually extremely narrow (เช่น, 1420°C ± 10°C).
• Tap Temperature Compensation: Considering the temperature drop in the transfer ladle (typically 30–50°C), the furnace tapping temperature must be adjusted via a dynamic compensation algorithm based on transfer distance and ladle status (Cold Ladle vs. Hot Ladle).

ครั้งที่สอง. Configuration Schemes for Automated Molding Lines: Duplexing & Multi-systems

Automated molding lines (such as vertical parting lines) are characterized by continuous and high-speed iron consumption (เช่น, 300-500 molds/hour). A single induction furnace cannot simultaneously satisfy the demands of Melting (Batch process) and Pouring (Continuous process).

1. Core Concept: Decoupling Melting and Holding

Separating the “ละลาย” function from the “Supplying” function is key to achieving a continuous flow.

2. Typical Configuration Schemes

ก. “One-to-Two” หรือ “Multi-supply-One” Duplexing

This is the most mainstream high-efficiency configuration.

• Mode: Multiple high-power Mains or Medium Frequency Melting Furnaces + 1 large capacity Holding/Pouring Furnace.
• Workflow:
  • Melting furnace melts at full speed and adjusts composition.
  • Iron is tapped into a transfer ladle.
  • Iron is poured into the large holding furnace (เช่น, ก 10-20 ton Channel Induction Furnace or Pressurized Pouring Furnace).
• ข้อดี:
  • Homogenization: The holding furnace acts as a massive “mixing pool.” Even if there are slight Carbon/Silicon fluctuations between melting batches, they are leveled out upon entering the large pool, outputting extremely stable iron.
  • Buffer: During melting furnace maintenance or charging, the holding furnace inventory allows the molding line to continue production for 20-30 นาที.

บี. Butterfly Configuration

Suitable for ultra-large-scale production.

• Layout: 2-3 Melting furnaces arranged around a rotating intermediate transfer device or automated charging car.
• Power Distribution: การใช้งาน “Dual-Power” หรือ “Tri-Power” systems (เช่น, one power supply unit feeding two furnace bodies). One melts at full power while the other holds or sinters, achieving seamless switching with minimal power grid fluctuation.

3. Integration of Automated Pouring

At the end of the induction furnace duplexing scheme, an Automatic Pouring Machine (เช่น, Pressure or Bottom-pour type) เป็นสิ่งจำเป็น:

• Stream Inoculation: The auto-pourer is equipped with a precise stream inoculation device to ensure consistent inoculant dosage per mold (error < 2%), which is critical for the graphite morphology of grey iron.
• Visual Positioning: Utilizes laser vision systems to automatically adjust flow rate based on the pouring cup liquid level, keeping the pouring cycle perfectly synchronized with the molding line.

III. Key Process Control Techniques

To guarantee the stability of the systems mentioned above, the following monitoring methods must be introduced:

สรุป

For automotive engine block casting, “ความมั่นคง” is not just a technical indicator; it is an economic one.

By utilizing a configuration of “Multi-furnace Melting + ใหญ่ ความจุ Holding/Homogenization + Automatic Pouring,” combined with strict “Heel Melting” และ “Precise Inoculation” กระบวนการ, the discreteness of single-batch melting can be eliminated. This satisfies the rigorous requirements of automated production lines for “Zero Defect, Continuous Flow” molten iron.