Why do Bright Spots Appear on Wires Drawn by Dual-line Wire Drawing Machines?

Bright spots (including bright lines or streaks) appearing during the dual-line wire drawing process are typically related to material quality, dies, lubrication, or process parameters. The specific causes and corresponding solutions are as follows:

Common Cause Analysis

Cause 1: Die Problems
Wear or scratches in sizing zone: Poor surface finish or localized wear in die bore causes uneven metal flow, forming bright spots.
Poor lubrication: Insufficient lubrication or contaminated lubricant leads to direct metal-die friction and localized overheating.
Improper die material: Non-uniform grain structure or coating peeling in carbide dies creates bright streaks.
Cause 2: Lubrication Issues
Low lubricant concentration: Over-diluted or degraded drawing fluid reduces lubrication effectiveness.
Contaminated lubricant: Impurities (metal chips, oxide scales) scratch wire surfaces.
Improper lubrication method: Uneven spray or inadequate lubricant penetration.
Cause 3: Process Parameter Problems
Excessive drawing speed: High speed breaks lubricating film, increasing friction.
Overly high reduction rate: Excessive single-pass deformation causes stress concentration.
Unstable tension: Imbalanced tension between dual spools creates uneven stretching.
Cause 4: Material Issues
Wire rod surface defects: Existing scratches/oxides expand into bright spots during drawing.
Material inconsistency: Composition/hardness variations cause non-uniform deformation.

Solutions

1. Die Inspection and Repair
Polish/replace dies: Microscopically inspect sizing zones; polish or replace if damaged.
Use premium dies: Prefer PCD or nano-coated dies for better wear resistance.
Verify die compatibility: Ensure die geometry matches wire specifications.
2. Lubrication System Optimization
Adjust concentration: Maintain 5%-15% concentration (as recommended) and monitor pH.
Filter lubricant: Install magnetic/centrifugal filters to remove debris.
Improve lubrication: Increase spray pressure or use ultrasonic mist lubrication.
3. Process Parameter Adjustment
Reduce speed: Test incrementally to find maximum spot-free speed.
Lower reduction rate: Limit to 15%-25% per pass (material-dependent).
Balance tension: Calibrate spool tensions for uniform stretching.
4. Raw Material Inspection
Check surface quality: Inspect for oxidation/scratches; pickle/polish if needed.
Control hardness: Ensure uniformity (e.g., copper rod HCP≤85); anneal if necessary.

Quick Troubleshooting

1. Observe spot patterns:
Periodic spots → Check dies/guide rollers for wear.
Random spots → Investigate lubrication/material issues.
2. Shutdown test:
Replace dies: If spots disappear, original dies were defective.
Adjust lubrication: Retest after parameter changes.

Preventive Measures

Regular maintenance: Inspect dies/lubrication every 8 hours; clean residue.
Process documentation: Record speed, tension, reduction rates for traceability.
Operator training: Standardize die installation and lubricant handling procedures.