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.
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.
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.
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.
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.
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.
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.
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.
If hydraulic pressure:
Is too low → incomplete fracture
Is inconsistent → irregular cut
Hydraulic systems must deliver smooth, consistent force.
Pressure fluctuations increase burr variability.
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.
Zinc coating:
Softens fracture behavior
May tear slightly at cut
Exaggerates burr visibility
Pre-painted material may show coating flaking if clearance incorrect.
Material stops
Blade descends
Controlled cut
More consistent burr control.
Requires precise clearance.
Cut while material moving
Dynamic forces involved
Synchronization critical
More sensitive to timing and vibration.
Flying shear requires tighter maintenance discipline.
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
Use calipers or micrometer.
Excessive burr typically:
0.05mm–0.1mm depending on tolerance
Measure gap manually.
Compare to material thickness.
Adjust accordingly.
Look for:
Edge rounding
Micro chipping
Surface wear
Replace or sharpen if necessary.
Ensure blades:
Meet squarely
Maintain uniform gap across width
Are parallel under pressure
Check:
Consistency
Pressure spikes
Response time
Irregular pressure increases burr variability.
❌ 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.
✔ 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.
Uncontrolled burr leads to:
Installer injuries
Field trimming
Customer rejection
Rust development
Warranty disputes
Increased scrap
Cut quality reflects overall machine precision.
Usually incorrect blade clearance or dull blades.
Yes — especially if clearance not adjusted.
Not if clearance is incorrect.
Yes — higher tensile steel requires recalibration.
Primarily functional — affects safety and corrosion resistance.
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.
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