Wire scratching during the bunching process is one of those problems that seems small at first glance, but it can quietly damage production yield, increase customer complaints, and disrupt downstream processes such as insulation extrusion. In many factories, wire scratches appear intermittently—sometimes only on certain bobbins, sometimes only after long runs—which makes the issue even more frustrating to troubleshoot.

From what we see across cable plants in Southeast Asia, China and India, scratch marks typically come from a combination of mechanical friction points, tension imbalance, and surface defects inside the machine. Below is a deeper technical breakdown based on real production experience and the typical equipment structure found in modern bunchers.

1. Understand Where Scratches Actually Come From

Most engineers immediately suspect the payoff or the die, but the scratch source can be anywhere along the payout–bunching–take-up path. The most common locations include:

• Groove rollers or ceramic pulleys

When a pulley develops micro-cracks, worn edges, or uneven glaze, the wire scrapes across the defect every rotation. These marks look like long, continuous scratches along the conductor.

• Entry guide or pre-twisting guide tube

If the guide eyelet is worn or slightly misaligned, it rubs the wire each time tension peaks.

• Back-twist or lay-plate area

This is a high-friction zone. If there is dust, oxidation from copper particles, or old lubricant residue, it forms a sandpaper-like surface.

• Payoff tension spikes

When one of the payoffs feeds wire at inconsistent tension, the wire briefly whips, hits a fixed point, and leaves scratches in short intervals.

Understanding the exact contact point is the first step—because scratches are always created by friction + pressure + movement.

2. Diagnose the Problem Systematically (Factory-Proven Method)

Instead of checking everything randomly, follow this real-world sequence used in many cable workshops:

Step 1: Run without wire (empty path test)

Listen for abnormal vibration or roller noise. If you hear rhythmic scratching sounds, a roller is worn.

Step 2: Run with white paper through the machine

A simple but extremely effective test. Paper reveals hidden sharp edges much faster than copper wire.

Step 3: Tension curve check

Observe payoff tension stability for at least 2–3 minutes. A single unstable bobbin often causes intermittent scratch marks.

Step 4: Stop at intervals and mark the cable

If scratches repeat every fixed length, the defect is almost certainly tied to one rotating element.

This structured method usually identifies the issue within 10–30 minutes.

3. Practical Fixes That Actually Work in Production

1. Replace or polish worn ceramic pulleys

Even a tiny chipped edge is enough to damage fine copper strands. Use diamond polishing rods to restore smoothness or replace the pulley entirely.

2. Clean the lay-plate and guide path regularly

Dust + copper powder creates abrasive friction. Cleaning every shift drastically reduces scratches.

3. Normalize payoff tension

Install or calibrate magnetic tension brakes. For high-speed bunchers, closed-loop tension control is ideal.

4. Upgrade guide eyelets to industrial ceramic (Zirconia)

Zirconia eyelets resist wear much longer than standard alumina ceramics and maintain surface smoothness for years.

5. Realign entry guides

A guide that is off by even 0.5 mm can force the wire into a side-wall friction path. Always recheck alignment after maintenance.

6. Lubrication—not too much, not too little

Too little → friction increases
Too much → dust sticks and creates abrasive slurry
Use thin-film synthetic lubricant suitable for copper wire processing.

4. When Scratching Happens Only at High Speed

If the issue appears only above 1,200–1,600 RPM, the cause is usually dynamic rather than static:

• Wire vibration from insufficient back-twist

Increase back-twist by 2–5% to stabilize wire entry.

• Rotor imbalance

An unbalanced rotor causes the wire to swing, touching surfaces it normally doesn’t.

• Take-up traverse instability

If the traverse is delayed or desynchronized, wire crosses unevenly and creates pressure scratches.

High-speed scratching is almost always linked to vibration + alignment shift.

5. Machine Condition Matters More Than Operators Think

Older bunching machines often develop internal clearance issues—micro-vibrations, loose bearings, off-center shafts. Even if they still run, their friction path is no longer the same as originally designed.

Regular checks should include:

• Lay-plate bearing wear

• Rotor balance

• Guide post rigidity

• Pulley axial alignment

• Traversing screw wear

Upgrading outdated machines can significantly reduce surface defects. For example, our DXCABLETECH Single-Twist Bunching Machines (internal link recommended here) use:

• High-hardness ceramic rollers

• Servo-controlled tension systems

• Anti-vibration rotor design

This ensures the wire moves along a clean, stable friction path—greatly reducing scratch risks.

6. Final Thoughts

Wire scratch issues are rarely random; they always point to a mechanical or tension-related root cause. The key is to identify the exact friction point, stabilize tension, and maintain clean, smooth guides and rollers. With systematic checks and consistent machine upkeep, scratch defects can be almost completely eliminated, improving both cable appearance and downstream extrusion performance.