Coil Ovalization During Storage – Causes, Inspection, Repair & Prevention Guide for Roll Forming Machines

Coil Ovalization During Storage

Roll Forming Machine Troubleshooting & Repair Guide

Steel coil quality is one of the most important factors affecting the performance of any roll forming production line. One common but often overlooked issue is coil ovalization during storage.

Ovalization occurs when a coil loses its circular shape and becomes slightly flattened or distorted while stored in a warehouse, yard, or transport container. Even small deformation can cause major feeding problems once the coil is placed on an uncoiler.

For manufacturers producing roofing panels, purlins, decking, trims, or structural sections, coil ovalization can lead to:

• Feeding instability
• Entry guide misalignment
• Leveling issues
• Strip tracking problems
• Surface damage to panels
• Production downtime

Understanding how coil ovalization occurs and how to identify it early is critical to maintaining consistent roll forming production.

This guide explains the causes, inspection methods, repair options, and preventative practices used by experienced technicians.

Causes of Wear or Failure

Coil ovalization does not originate from the roll forming machine itself but from storage conditions, handling methods, and coil stacking practices.

Several factors contribute to coil deformation.

Long-Term Storage Pressure

Steel coils stored for long periods may gradually deform due to their own weight.

This is especially common with heavier coils used in:

• Structural deck production
• Purlin roll forming lines
• Heavy gauge roofing panels

When coils sit on hard surfaces without proper supports, the bottom section may flatten.

Improper Coil Stacking

Stacking coils directly on top of one another can compress lower coils.

The bottom coil absorbs the full weight of the upper coils, which may distort its shape over time.

This is common in:

• Small fabrication warehouses
• Import container storage yards
• Coil distribution depots

Soft Ground Storage

If coils are stored on soft ground, wooden pallets, or uneven surfaces, the weight distribution becomes uneven.

This creates localized pressure points that deform the coil.

High Temperature and Humidity

Extreme temperature changes can slightly soften steel structure over time.

Combined with weight pressure, this increases the risk of ovalization.

Transportation Pressure

Improper container loading or loose securing during shipping may cause coils to shift during transit.

This movement can deform the coil if pressure is applied to only one side.

Incorrect Coil Supports

Coils should be stored using cradles or V-shaped supports.

Flat storage surfaces increase the likelihood of deformation.

Why It Happened and What Caused It

From an engineering perspective, coil ovalization occurs because the steel strip layers shift under compressive load.

When a coil is wound, each layer supports the structure evenly. However, when pressure is applied unevenly:

1. Lower layers compress.
2. Upper layers shift slightly.
3. Coil tension changes internally.

This results in the coil no longer maintaining its round geometry.

Once placed on an uncoiler, this causes:

• Uneven unwinding tension
• Coil wobble during rotation
• Strip feeding instability

The issue becomes more severe with:

• Wide coils
• Heavy gauge steel
• Large diameter coils

How to Inspect the Problem

Inspection Procedure

Technicians should inspect every coil before loading it onto a roll forming line.

Step 1 – Visual Inspection

Look at the coil from the side.

A healthy coil should appear perfectly circular.

Signs of ovalization include:

• Flattened lower sections
• Uneven coil diameter
• Visible deformation in the outer wraps

Step 2 – Measure Coil Diameter

Use a tape measure or laser gauge.

Measure the diameter at several points around the coil.

Example measurements:

Top diameter – 1200 mm
Side diameter – 1180 mm

Any difference greater than 10–15 mm may indicate ovalization.

Step 3 – Check Coil Edge Alignment

Look at the coil edges.

Signs of distortion include:

• Edge layers shifting outwards
• Uneven coil sidewalls
• Slight telescoping

Step 4 – Check Coil Rotation on Uncoiler

Mount the coil slowly onto the uncoiler mandrel.

Rotate manually.

Observe for:

• Coil wobbling
• Uneven rotation
• Strip tension fluctuations

Step 5 – Strip Feeding Test

Feed the strip slowly through the entry guides.

Look for:

• Strip wandering left or right
• Sudden tension release
• Coil jumping on the mandrel

Step-by-Step Technician Guide – How to Fix

In many cases, slightly ovalized coils can still be used safely if corrected properly.

Method 1 – Coil Re-rounding

For mild deformation, the coil may be re-rounded.

Procedure:

1. Mount the coil on the uncoiler.
2. Apply slight back tension using the brake system.
3. Slowly rotate the coil several revolutions.
4. Use a coil leveling system if available.

This helps redistribute tension across the coil layers.

Method 2 – Controlled Unwinding

If deformation is moderate:

1. Unwind the first few meters of coil.
2. Remove distorted outer wraps.
3. Continue feeding once the coil becomes stable.

Outer wraps usually suffer the most deformation.

Method 3 – Recoiling the Material

If the coil is severely distorted:

1. Uncoil the entire strip.
2. Recoil it using a recoiler system.
3. Ensure even tension during recoiling.

This restores round geometry.

Method 4 – Reduce Uncoiler Speed

When running an ovalized coil:

• Reduce line speed
• Increase entry guide control
• Use strip tension monitoring

This minimizes feeding instability.

Preventative Maintenance Tips

Preventing coil ovalization is easier than repairing the problem.

Follow these storage best practices.

Use Coil Storage Cradles

Coils should always rest in V-shaped supports.

This distributes weight evenly across the coil.

Avoid Stacking Heavy Coils

Stacking increases compression pressure.

Where possible, store coils in single layers.

Rotate Long-Term Stored Coils

If coils remain in storage for several months:

• Rotate their position
• Rebalance weight distribution

Control Storage Environment

Ideal conditions:

• Dry warehouse
• Stable temperature
• Flat concrete floor
• No moisture exposure

Inspect Incoming Coil Deliveries

Before accepting coil shipments:

• Check coil roundness
• Look for transport deformation
• Document damage immediately

FAQ Section

What is coil ovalization?

Coil ovalization occurs when a steel coil loses its circular shape due to uneven pressure during storage or transport.

Can an ovalized coil damage a roll forming machine?

Yes. Severe ovalization can cause feeding instability, strip tracking issues, and increased stress on entry guides and leveling equipment.

How much ovalization is acceptable?

Minor deformation under 10 mm difference in diameter is usually manageable.

Anything larger may require correction.

Does coil ovalization affect panel quality?

Yes. It can cause:

• Wavy panels
• Oil canning
• Panel length variation

Can coil ovalization be repaired?

Yes. Techniques include re-rounding, removing outer wraps, or recoiling the material.

How do large factories prevent this issue?

Large coil processing facilities use:

• Coil cradles
• Climate controlled storage
• Automated coil handling systems

Machine Matcher Technical Support

If you are experiencing coil feeding problems, strip instability, or production issues caused by material defects, the Machine Matcher technical team can assist.

Our support includes:

• Roll forming machine troubleshooting
• Coil handling diagnostics
• Production line inspection
• Remote technical assistance
• Preventative maintenance planning

Submit your issue through the Machine Matcher Technical Support Desk

Provide details including:

• Machine type
• Coil specifications
• Photos or videos of the issue
• Production speeds
• Panel profile being produced

Our technicians will review the information and provide step-by-step guidance.