Detailed Introduction to Issues in the Rolling Process

The aluminum foil rolling stage is the core process determining its final quality and faces numerous technical challenges. Below is a detailed introduction to the issues encountered in this stage:

1. Shape Control Problem

This is one of the most central and challenging problems in aluminum foil rolling.

• Manifestation: Uneven elongation of the aluminum foil across its width, leading to the formation of waves. Common types include:
  • Edge Waves: The edges of the strip elongate more than the center, causing wrinkles at the sides.
  • Center Buckle: The center of the strip elongates more than the edges, causing a bulge in the middle.
  • Ribbon Buckle: Periodic waves located between the edge and the center.
  • Compound Buckle: Multiple wave types occurring simultaneously.
• Causes:
  • Roll Thermal Crown and Wear: During rolling, the work rolls expand thermally due to friction and deformation heat (thermal crown), and wear unevenly, causing the actual roll gap profile to deviate from the preset one.
  • Poor Shape of Incoming Material: The slab from casting or hot rolling itself has shape defects, which are amplified in subsequent rolling passes.
  • Mismatched Process Parameters: Improper settings for rolling force, tension, bending force, and coolant distribution fail to compensate for uneven deformation during rolling.
• Impact: Leads to poor flatness of the foil, making it prone to wrinkling, tracking issues, or even breaking in downstream processes (such as slitting, lapisan, laminating), severely affecting yield and subsequent processing performance.

2. Thickness Precision and Uniformity Problem

The thinner the foil, the higher the requirement for thickness precision (misalnya, double-zero foil requires thickness tolerance within ±5%).

• Manifestation: Longitudinal (lengthwise) thickness variation or transverse (widthwise) uneven thickness distribution (misalnya, thicker in the center, thinner at the edges).
• Causes:
  • Mill Stiffness and Vibration: Micro-vibrations of the mill system during high-speed rolling affect roll gap stability.
  • Roll Eccentricity: Minor geometric eccentricity in backup or work rolls causes periodic thickness variation.
  • Rolling Oil Film Thickness Variation: The oil film thickness, influenced by speed, suhu, and pressure, directly affects the actual reduction. Its fluctuations cause thickness changes.
  • Incoming Gauge Variation: Thickness deviations in the incoming slab are inherited by the final product.
  • AGC System Response: Insufficient detection accuracy or control response speed of the Automatic Gauge Control system.
• Impact: Uneven thickness directly affects the foil’s mechanical properties, sifat penghalang, and appearance uniformity. In applications, overly thin spots easily form pinholes or rupture, while overly thick spots waste material.

3. Surface Quality Problems

• Manifestation:
  • Rolling Oil Stains/Contamination: Rolling oil not completely removed by air knives or degraded oil residue left on the foil surface.
  • Scratches/Dents: Foreign particles or damage on the surface of deflector or tension rolls leave linear or point-like defects on the foil.
  • Bright/Dark Bands: Transverse stripes of uneven gloss, often related to roll surface condition or uneven cooling.
  • Blocking/Sticking: After coiling, layers locally bond together due to oil film breakdown or excessive pressure, causing surface tearing during uncoiling.
• Causes: Cleanliness of the rolling environment, quality and filtration of rolling oil, roll surface condition, coiling tension control, dll..
• Impact: Affects the foil’s appearance, dapat dicetak, laminating strength, and its suitability for high-end packaging (misalnya, makanan, farmasi).

4. Pinhole Problem

Pinholes are microscopic holes penetrating the foil, a key indicator of its barrier properties.

• Causes:
  • Foreign Inclusions: Hard particles like oxides or carbides not completely removed from the aluminum melt, which are pressed in and later dislodge during rolling, creating holes.
  • Dust in Rolling Environment: Airborne particles settling on the strip surface and being rolled in.
  • Improper Process Parameters: Excessive pass reduction or tension causing the material to tear at weak points.
• Impact: Severely compromises the foil’s barrier properties against moisture, oksigen, dan ringan, rendering it unsuitable for high-end packaging and electronic material applications.

5. Rolling Oil and Cooling Control Problems

Rolling oil serves the simultaneous functions of lubrication, pendinginan, and cleaning.

• Problems:
  • Oil Degradation: Prolonged use leads to oxidation and polymerization of the oil, increasing its viscosity and degrading its lubricating and cooling performance, making oil stains more likely.
  • Insufficient Filtration Precision: Inability to effectively filter out aluminum fines and impurities from the oil, leading to surface defects.
  • Uneven Cooling: Affects the distribution of the roll’s thermal crown, thereby impacting shape control.
• Impact: Directly linked to surface quality, shape control, and rolling stability.

6. Speed and Tension Coordinated Control Problem

Foil rolling, especially finishing, operates at very high speeds (hingga 1500-2500 meters per minute).

• Masalah: During high-speed starts, stops, acceleration, and deceleration, maintaining constant tension in the strip between mill stands and during coiling is extremely difficult. Tension fluctuations immediately cause gauge variation, shape changes, or even strip breaks.
• Impact: This is key to ensuring continuous, stable production and improving yield.

Singkatnya, aluminum foil rolling is a multi-variable, strongly coupled, high-precision dynamic process. The aforementioned problems are often interconnected; a fluctuation in one parameter can trigger multiple quality issues. The core of modern aluminum foil mills lies in using advanced sensor networks, high-precision actuators, and intelligent control systems to monitor, model, and compensate for these problems in real-time to achieve stable production of high-quality products.