Shear Burr Formation — Root Causes

Why Burrs Form After Cutting PBR Panels & How to Eliminate Them

Shear burr formation is one of the most common post-cut defects in PBR (Purlin Bearing Rib) roll forming lines.

It appears as:

Sharp metal edge at cut end
Raised lip on panel bottom
Excessive edge roughness
Installer complaints during handling
Increased risk of injury
Coating cracking at cut
Premature corrosion at edge

Burr formation is not random.

It is always caused by:

Improper shearing mechanics.

This guide breaks down:

What causes burr formation
Mechanical vs material contributors
How blade clearance affects burr height
Hydraulic vs flying shear considerations
Step-by-step corrective actions

Because in roll forming:

A clean cut requires controlled fracture — not forced tearing.

What Is Shear Burr?

A burr is:

A raised edge of metal remaining after cutting due to incomplete or improper material fracture.

During shearing, the metal undergoes:

Elastic deformation
Plastic deformation
Crack initiation
Fracture propagation

If the fracture is clean and controlled:

Minimal burr forms.

If fracture is uneven or delayed:

Metal tears — leaving a burr.

Why Burr Formation Is Critical in PBR Panels

In roofing applications:

Panels are handled manually
Ends overlap
Fasteners installed near edges
Coated steel exposed at cut

Excessive burr causes:

Injury risk
Installation difficulty
Coating failure
Rust development

Clean shear quality is a production requirement — not cosmetic preference.

Primary Root Causes of Shear Burr Formation

Incorrect Blade Clearance (Most Common Cause)

Blade clearance = gap between upper and lower shear blades.

If clearance is too large:

Material stretches before fracture
Crack forms unevenly
Tearing occurs
Burr increases

If clearance is too tight:

Excessive compression
Blade wear accelerates
Coating damage increases

Correct clearance depends on material thickness and strength.

Engineering Rule of Thumb:

Clearance typically:

5–10% of material thickness per side
(depending on tensile strength)

Example:

0.5mm material → ~0.025–0.05mm per side

Improper setup is the leading cause of burr formation.

Dull or Worn Shear Blades

Blade wear leads to:

Increased plastic deformation
Delayed fracture
More tearing than shearing
Larger burrs

Signs of dull blade:

Rough cut edge
Increased cutting noise
Hydraulic pressure spike
Visible edge roll-over

Blade sharpening schedule must match production volume.

Blade Misalignment

If upper and lower blades are not parallel:

Uneven fracture propagation
Burr heavier on one side
Edge roll-over

Misalignment may result from:

Loose mounting bolts
Worn guide slides
Hydraulic ram imbalance

Always verify parallelism under load.

Excessive Cutting Speed

In flying shear systems:

High speed increases dynamic load
Vibration may occur
Fracture may become uneven

If burr increases at higher speed:

Cut timing or mechanical stability may be contributing.

Hydraulic Pressure Imbalance

If hydraulic pressure:

Is too low → incomplete fracture
Is inconsistent → irregular cut

Hydraulic systems must deliver smooth, consistent force.

Pressure fluctuations increase burr variability.

High Tensile Material

Higher yield strength steel:

Resists fracture
Requires higher force
Creates larger burr if clearance not adjusted

When switching from mild steel to higher tensile:

Blade clearance must be recalibrated.

Galvanized & Coated Steel Interaction

Zinc coating:

Softens fracture behavior
May tear slightly at cut
Exaggerates burr visibility

Pre-painted material may show coating flaking if clearance incorrect.

Types of Shear Systems & Burr Behavior

Stop-Cut Hydraulic Shear

Material stops
Blade descends
Controlled cut

More consistent burr control.

Requires precise clearance.

Flying Shear

Cut while material moving
Dynamic forces involved
Synchronization critical

More sensitive to timing and vibration.

Flying shear requires tighter maintenance discipline.

Diagnosing Burr Formation Step-by-Step

Step 1: Inspect Cut Edge

Look for:

Roll-over (rounded top edge)
Fracture zone
Burr height
Tear marks

A proper shear cut shows:

Clean fracture
Minimal burr
Small roll-over

Step 2: Measure Burr Height

Use calipers or micrometer.

Excessive burr typically:

0.05mm–0.1mm depending on tolerance

Step 3: Check Blade Clearance

Measure gap manually.

Compare to material thickness.

Adjust accordingly.

Step 4: Inspect Blade Sharpness

Look for:

Edge rounding
Micro chipping
Surface wear

Replace or sharpen if necessary.

Step 5: Verify Alignment

Ensure blades:

Meet squarely
Maintain uniform gap across width
Are parallel under pressure

Step 6: Monitor Hydraulic Pressure

Check:

Consistency
Pressure spikes
Response time

Irregular pressure increases burr variability.

Common Production Mistakes

❌ Increasing hydraulic pressure without adjusting clearance
❌ Ignoring blade sharpening schedule
❌ Switching material thickness without resetting clearance
❌ Allowing blade mounting bolts to loosen
❌ Ignoring asymmetric burr formation

Burr problems worsen progressively if not corrected.

Long-Term Prevention Strategy

✔ Maintain blade sharpening schedule
✔ Log material thickness changes
✔ Adjust clearance when changing gauge
✔ Monitor hydraulic system health
✔ Inspect shear alignment monthly
✔ Replace worn guides and bushings

Preventative shear maintenance protects panel quality.

Economic Impact of Burr Formation

Uncontrolled burr leads to:

Installer injuries
Field trimming
Customer rejection
Rust development
Warranty disputes
Increased scrap

Cut quality reflects overall machine precision.

Frequently Asked Questions

What causes excessive burr on PBR panels?

Usually incorrect blade clearance or dull blades.

Does thicker steel create more burr?

Yes — especially if clearance not adjusted.

Can higher hydraulic pressure reduce burr?

Not if clearance is incorrect.

Should blade clearance change with tensile strength?

Yes — higher tensile steel requires recalibration.

Is burr structural or cosmetic?

Primarily functional — affects safety and corrosion resistance.

Final Conclusion

Shear burr formation in PBR roll forming is a mechanical fracture control issue.

It originates from:

Incorrect blade clearance
Dull tooling
Misalignment
Hydraulic inconsistency
Material strength variation

A clean cut requires:

Proper clearance.
Sharp blades.
Parallel alignment.
Stable pressure.

In roll forming, the shear is the final operation.

Its quality defines the finished product.

And in roofing production, clean edges protect both reputation and safety.