Mengapa Kumparan Aluminium Cor-Rolled Menunjukkan Ketebalan dan Penyimpangan yang Tidak Merata (Ketidaksejajaran)?

Ketebalan tidak rata (gauge variation) and deviation (misalignment/“running off”) in cast-rolled aluminum coils are classic issues in cast-rolling production. Their root causes primarily lie in process stability, equipment condition, and input material quality​ during the cast-rolling process. Below is a detailed cause analysis and troubleshooting guide.

SAYA. Main Causes of Uneven Thickness

1. Nozzle Block and Feeding System Issues
   • Nozzle Clogging or Damage: Localized dross buildup inside the nozzle or wear on the lip can cause uneven flow of molten aluminum across the width, leading to strip-like thickness variations after solidification.
   • Unstable Metal Feed: Significant fluctuations in the headbox level or an unstable flow control system (stopper, launder) result in varying flow rates to the nozzle.
2. Rolling Mill System Issues
   • Poor Control of Roll Thermal Crown: Uneven cooling water distribution across the cast-rolls or improper water temperature control leads to unreasonable thermal expansion (thermal crown) of the roll barrel (center vs. edges), directly affecting the cross-directional thickness profile of the strip (misalnya, thicker center/thinner edges, or vice versa).
   • Roll Wear or Surface Defects: Memakai, lubang, or aluminum pickup on the roll surface are directly imprinted onto the strip, causing periodic or localized thickness changes.
   • Rolling Force Fluctuations: Unstable hydraulic screw-down system, servo valve malfunction, or abnormal pressure sensors prevent a constant rolling force from being maintained.
3. Process Parameter Fluctuations
   • Variation in Cast-Rolling Zone Length: Unstable process temperatures (pouring temperature, roll surface temperature) cause the solidification point (cast-rolling zone) to shift, disrupting the stable balance between casting and rolling.
   • Speed Mismatch: Poor synchronization between the cast-roll speed and the pulling (coiling) speed creates uneven forces on the strip in the rolling zone.
4. Input Material Influence
   • Molten Aluminum Quality: Inconsistent temperature, high gas content, or poor cleanliness of the melt adversely affect the uniformity of solidification and rolling.

II. Main Causes of Deviation (Misalignment/Running Off)

1. Poor Input Strip Shape
   • Wedge-Shaped Cross-Section: If the cast-rolled strip itself has inconsistent thickness across its width (one edge thicker than the other), the subsequent tension will naturally pull it toward the thicker side, causing misalignment.
2. Equipment Alignment and Parallelism Issues
   • Non-Parallel Roll Axes: The axes of the upper and lower cast-rolls are not parallel, forming a “V-shape,” which generates a lateral force pushing the strip to one side during rolling.
   • Misaligned Guide or Tension Rolls: The axes of guide rolls and tension rolls throughout the line are not parallel or level with the cast-roll axes, forcing the strip off the centerline.
   • Misaligned Coiler: The coiler mandrel is not centered with the production line centerline.
3. Process and Control System Issues
   • Uneven Roll Gap on Both Sides: Inconsistent screw-down settings on the drive side and operator side of the rolls.
   • Uneven Cooling on Both Sides: Significant difference in cooling intensity on the two sides of the cast-rolls leads to different metal flow and shrinkage rates.
   • Faulty Automatic Center Position Control (CPC) System: Malfunctioning photoelectric detector, slow response, or failure of the hydraulic steering mechanism.

AKU AKU AKU. Systematic Troubleshooting Approach and Steps

Melangkah 1: Rapid On-Site Diagnosis

1. Observe the Pattern: Is the thickness variation periodic or random? Does the misalignment occur suddenly or increase gradually? This helps determine if it’s a mechanical equipment issue or a process fluctuation problem.
2. Measure and Confirm: Use a micrometer to measure thickness at multiple points across the strip width. Plot a thickness profile to confirm if it’s a “wedge” atau “mahkota” type variation.

Melangkah 2: Targeted Investigation and Adjustment (Prioritized Order)

• For Uneven Thickness:
  • Inspect and clean the nozzle block, ensuring the lip is intact and unclogged.
  • Stabilize the Process: Focus on monitoring and stabilizing headbox level, pouring temperature, Dan cast-roll cooling water​ (flow and temperature).
  • Inspect the Rolls: Measure roll surface temperature distribution; check for damage. Regrind rolls if necessary.
  • Check the Hydraulic System: Verify the stability and response of the screw-down system pressure.
• For Misalignment:
  • Pertama, check and adjust alignment: Work backward from the coiler to ensure all guide rolls, tension rolls, and the cast-rolls are parallel and level.
  • Check for strip wedge: If a wedge exists, address the thickness unevenness using the methods above.
  • Test the CPC system: Manually trigger the steering action to check if it operates correctly.

Melangkah 3: Establish Preventive Measures

• Standardize Operations: Develop strict standards for nozzle installation, pemanasan awal, and process parameter setup.
• Implement Regular Maintenance: Schedule regular checks for roll crown/profile, bearing clearance, and calibration of all roll system parallelism/alignment. Maintain hydraulic and control systems.
• Enhance Process Monitoring: Implement real-time monitoring and logging of key parameters (level, suhu, kecepatan, tekanan) to facilitate problem tracing.

Core Recommendation:

For thickness unevenness, prioritize checking the “nozzle block” Dan “roll thermal crown control.” For misalignment, prioritize checking “roll system alignment” Dan “strip wedge.”​ These two issues are often interrelated; solving thickness unevenness is fundamental to correcting misalignment. It is advisable to start with the easiest-to-adjust process parameters (misalnya, headbox level, cooling water) and progressively delve into checks