Mandrel Slipping Under Load – Causes, Inspection, Repair & Prevention Guide for Roll Forming Decoilers

Mandrel Slipping Under Load

Roll Forming Machine Troubleshooting & Repair Guide

Mandrel slipping under load is a common issue in decoilers used in roll forming production lines. The decoiler mandrel is designed to expand inside the coil core and hold the coil securely while the roll forming machine pulls the strip during production.

When the mandrel loses grip or slips inside the coil core, the coil may rotate unpredictably or fail to unwind correctly. This creates feeding instability and tension fluctuations that can affect the entire roll forming process.

If this problem is not corrected, it may lead to several production issues including:

• Strip tension fluctuations
• Coil jerking during unwinding
• Inconsistent feeding into the roll forming machine
• Coil core damage
• Production downtime
• Safety hazards for operators

For manufacturers producing metal roofing panels, cladding sheets, structural decking, purlins, trims, and other roll formed components, ensuring the mandrel grips the coil securely is essential for stable coil handling.

This guide explains the causes of mandrel slipping, inspection procedures, corrective actions, and preventative maintenance strategies used by experienced roll forming technicians.

Causes of Wear or Failure

Mandrel slipping under load typically occurs due to insufficient gripping force, worn components, or incorrect setup of the decoiler system.

Insufficient Mandrel Expansion

If the mandrel does not expand fully inside the coil core, it may fail to grip the coil securely.

This often occurs when the expansion mechanism is not adjusted correctly.

Worn Mandrel Segments

Mandrel segments gradually wear over time due to repeated coil loading and unloading.

Worn segments may lose friction contact with the coil core.

Hydraulic Pressure Loss

Hydraulic decoilers rely on hydraulic pressure to expand the mandrel.

If hydraulic pressure drops due to leaks or pump problems, the mandrel may lose grip.

Coil Inner Diameter Variation

If the coil inner diameter is slightly larger than expected, the mandrel may not expand far enough to secure the coil.

This mismatch may cause slipping during operation.

Coil Weight and Pulling Force

Heavy coils combined with high roll forming pulling force may exceed the gripping capacity of the mandrel.

This may cause the coil to slip during feeding.

Contamination on Mandrel Surface

Oil, grease, or debris on mandrel surfaces may reduce friction between the mandrel and the coil core.

Why It Happened and What Caused It

From a mechanical standpoint, the decoiler mandrel must generate sufficient radial friction force to hold the coil securely.

During roll forming production:

1. The roll forming machine pulls the strip forward.
2. The decoiler must allow the coil to rotate smoothly.
3. The mandrel must maintain a firm grip on the coil core.

If the friction force between the mandrel and the coil core is insufficient:

• The coil may slip relative to the mandrel.
• Rotation becomes unstable.
• Strip tension fluctuates.

These fluctuations can cause feeding problems and profile inconsistencies.

How to Inspect the Problem

Inspection Procedure

Proper inspection helps determine whether mandrel slipping is occurring and identify the cause.

Step 1 – Observe Coil Rotation During Operation

Watch the coil while the machine is running.

Signs of slipping include:

• Coil jerking during rotation
• Coil rotation not matching mandrel rotation
• Sudden strip tension changes

Step 2 – Inspect Mandrel Expansion

Expand the mandrel without a coil installed.

Ensure all segments extend evenly and fully.

Step 3 – Inspect Mandrel Surface Condition

Check mandrel segments for:

• Smooth surfaces
• Excessive wear
• Oil or grease contamination

These conditions may reduce grip.

Step 4 – Inspect Hydraulic System

Check hydraulic pressure levels and inspect hoses and cylinders for leaks.

Low pressure may prevent proper mandrel expansion.

Step 5 – Inspect Coil Core

Examine the coil inner diameter for:

• Deformation
• Oversized core
• Core damage

A damaged coil core may prevent proper mandrel grip.

Step-by-Step Technician Guide – How to Fix

Several corrective actions can restore proper mandrel grip.

Method 1 – Increase Mandrel Expansion

Adjust the expansion mechanism to ensure the mandrel fully expands inside the coil core.

Method 2 – Clean Mandrel Surfaces

Remove oil, grease, or debris from the mandrel segments to improve friction contact.

Method 3 – Repair Hydraulic System

Check hydraulic pressure and repair leaks or faulty components.

Restore proper expansion pressure.

Method 4 – Replace Worn Mandrel Segments

If mandrel segments are worn, replacing them may restore proper grip.

Method 5 – Use Mandrel Sleeves or Adapters

If coil inner diameter is too large, mandrel sleeves or adapters may improve grip.

Preventative Maintenance Tips

Regular maintenance helps prevent mandrel slipping issues.

Inspect Mandrel Segments Frequently

Check for wear and replace segments when necessary.

Maintain Hydraulic Systems

Ensure hydraulic systems operate at correct pressure levels.

Clean Mandrel Surfaces

Keep mandrel surfaces free from oil, grease, and debris.

Verify Coil Specifications

Confirm coil inner diameter matches decoiler specifications.

Train Operators on Proper Coil Loading

Correct coil positioning helps ensure proper mandrel contact.

FAQ Section

What causes mandrel slipping on a decoiler?

Mandrel slipping usually occurs due to insufficient expansion, worn segments, hydraulic pressure loss, or oversized coil cores.

How can I tell if the mandrel is slipping?

Signs include coil jerking, unstable rotation, and fluctuating strip tension during production.

Can mandrel slipping damage roll forming machines?

Yes. It can cause feeding instability and tension fluctuations that affect forming accuracy.

How can mandrel slipping be fixed?

Cleaning mandrel surfaces, increasing expansion pressure, repairing hydraulic systems, or replacing worn components may resolve the issue.

Do heavier coils increase the risk of slipping?

Yes. Heavier coils require stronger mandrel grip to prevent slipping.

Should damaged coils be rejected?

If the coil core is severely damaged and cannot grip properly, replacing the coil may be necessary.

Machine Matcher Technical Support

If your roll forming line is experiencing decoiler instability, coil slipping, or strip feeding problems, Machine Matcher technical specialists can help diagnose and resolve the issue.

Support services include:

• Roll forming machine troubleshooting
• Decoiler and mandrel diagnostics
• Coil handling inspection
• Production line performance evaluation
• Remote technical assistance

Submit your issue through the Machine Matcher Technical Support Desk:

Include the following information:

• Machine type
• Coil inner diameter and weight
• Photos or videos showing the slipping issue
• Profile drawing and production speed

Our technicians will review the information and provide step-by-step recommendations to restore stable production.