Common Issues and Solutions in Steel Rolling Processes

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1. How to solve strip surface indentations?

• Stop production immediately when indentations are detected

• Identify the source by analyzing indentation pattern and periodicity

• Inspect work rolls, intermediate rolls, and backup rolls for surface damage

• Check scale breaker rolls if indentations show short periodicity

2. Causes of strip breakage:

• Material defects: Severe edge defects, improper pickling, thickness variations, shape problems

• Equipment failures: Electrical, control system, or hydraulic malfunctions; tension fluctuations

• Operational errors: Unnoticed strip deviation, improper pass schedule, excessive reduction

• Roll failures: Roll breakage or spalling

3. Procedure after strip breakage:

• Immediate shutdown

• Remove strip from mill stands and inspect rolls for damage

• Clean broken strip fragments from housing

• Check main drive shaft and safety pins for damage

• Carefully monitor first coil after roll replacement

4. Causes of thermal scratches:

• Insufficient emulsion flow during high-speed rolling

• Elevated roll temperature breaking emulsion oil film

• High-speed roll slippage causing friction

• Note: Thermal scratches are typically shallow with minimal texture

5. Thermal scratch control measures:

• Increase emulsion flow rate

• Lower emulsion temperature

• Verify roll diameter input accuracy

• Monitor work roll current differential

• Ensure consistent roll roughness

• Check adequate roll bending force

6. Causes of hard scratches:

• Excessive roll service time reducing surface roughness

• Over-reduction causing roll slippage

• Common in early passes (1-2) with heavy reduction

• Note: Hard scratches are deeper and more visible

7. Hard scratch control in passes 1-2:

• Replace rolls when roughness deteriorates

• Increase exit tension, decrease entry tension

• Apply reduction gradually to target thickness

• Avoid sudden speed reductions

• Adjust reduction amount if slippage marks appear

8. Pre-compression functions:

• Eliminates roll system clearance

• Ensures displayed rolling force reflects actual strip force

• Provides accurate roll gap indication

• Equalizes roll gap across strip width

9. Pre-compression procedure:

1. Select pre-compression mode on AGC computer

2. Zero rolling force at 20cm roll gap position

3. Apply initial light force (200T) to equalize cylinder position

4. Input target roll gap setting

5. Apply pressure incrementally

6. Maintain constant pressure with emulsion and 200m/min rotation

7. Stabilize when both sides show equal force

8. Complete pre-compression cycle