Vacuum Roll Grinding & Coating for Paper and Board Machines

Restore vacuum roll surfaces, protect fabrics and keep suction holes open

Vacuum and suction rolls operate under demanding conditions where surface wear, corrosion and contamination can gradually reduce their performance.

Worn or damaged roll surfaces can increase wire and fabric wear, cause marking, contribute to corrosion and allow suction holes to become blocked. These problems can affect both the lifetime of machine clothing and the ability of the vacuum roll to perform its intended function.

PR Rolls provides complete on-site grinding and coating of vacuum rolls and cylinders for paper and board machines.

Instead of removing large rolls and transporting them to a workshop, PR Rolls can restore the surface directly at the mill during a planned shutdown.

Depending on the condition and application, the complete restoration can include:

Grinding → Groove machining → Groove edge treatment → Surface preparation → HVOF coating → Non-stick treatment → Final surface finishing

The objective is not simply to apply a new coating.

The objective is to restore the complete functional surface of the vacuum roll – geometry, grooves, edges, coating and surface characteristics – while maintaining effective vacuum performance.

Why Vacuum Roll Surface Condition Matters

A vacuum roll has to perform several functions simultaneously.

The surface interacts continuously with the machine clothing while the vacuum system draws air through holes in the roll.

This means that both mechanical surface condition and airflow through the roll are important.

Over time, operating conditions can result in:

• Surface wear
• Corrosion
• Worn grooves
• Sharp or damaged groove edges
• Fabric or wire marking
• Contamination
• Blocked suction holes
• Uneven surface roughness

PR Rolls' technical material specifically identifies wire wear, fabric marking, corrosion and blocking of suction holes as problems addressed by its vacuum cylinder coating concept.

Restoring the roll therefore requires more than simply applying coating over the existing surface.

Grinding of Vacuum Rolls

Restore geometry before applying the functional surface

Grinding is the foundation of a successful vacuum roll restoration.

The existing roll surface may have developed wear, corrosion, scratches or other irregularities during operation.

PR Rolls uses precision grinding to restore the required surface condition before further machining and coating.

The surface roughness after grinding can be approximately Ra 0.4–0.8.

Grinding provides a controlled foundation for the following restoration stages.

This is an important part of PR Rolls' approach:

Do not simply cover the existing problem with a new coating – restore the underlying surface first.

Groove Machining & Groove Restoration

Vacuum rolls may contain grooves that form an important part of their functional surface.

Wear, corrosion and previous surface treatments can gradually affect the geometry and condition of these grooves.

As part of the restoration process, PR Rolls can perform precision groove machining directly on-site.

This allows groove geometry to be restored before the final coating and surface treatment are applied.

PR Rolls' documented vacuum cylinder restoration process specifically includes groove machining and groove edge treatment.

Groove Edge Treatment – Protect Wires and Fabrics

The interaction between the roll surface and machine clothing is not determined only by surface roughness.

Groove edges also matter.

Damaged, worn or unsuitable edges can contribute to mechanical interaction with wires and fabrics.

PR Rolls therefore includes groove edge treatment as part of its vacuum roll restoration process.

The objective is to create a functional transition between the coated roll surface and grooves while reducing conditions that can contribute to fabric wear or marking.

This connects directly with two of the main problems identified in PR Rolls' technical material:

wearing of wires and marking of fabrics.

HVOF Coating for Vacuum Rolls

Create a hard, wear-resistant functional surface

After grinding, groove restoration and surface preparation, PR Rolls can apply a wear-resistant coating using HVOF – High Velocity Oxy-Fuel thermal spraying.

HVOF creates a dense functional coating designed to provide high wear resistance under demanding operating conditions.

PR Rolls' technical documentation specifies a finished coating hardness of approximately:

1200 ±150 HV

with a typical coating thickness of:

100–150 µm.

This hard coating provides the mechanical foundation for a durable vacuum roll surface.

Non-Stick & Good Release Surface

Wear resistance alone is not always sufficient.

Vacuum rolls can also suffer from contamination and material build-up that interfere with their function.

PR Rolls' vacuum cylinder solution therefore combines the wear-resistant surface with a non-stick / good-release treatment.

The process includes both HVOF spraying and non-stick treatment, followed by final surface treatment.

This combination is designed to create a surface that provides both:

Mechanical durability
and
Reduced tendency for contamination to adhere.

Keep Vacuum and Suction Holes Open

A vacuum roll can only perform correctly if air can move effectively through the suction holes.

Contamination and surface build-up around the holes can gradually interfere with airflow.

PR Rolls specifically identifies blocking of suction holes as one of the problems addressed by its vacuum roll coating solution and “better ventilation – no blocking” as one of the intended benefits.

A correctly restored and treated surface can therefore help maintain cleaner hole openings and support the roll's vacuum functionality.

The goal is not merely a better-looking surface.

It is a surface designed to support the mechanical and airflow function of the vacuum roll.

Reduce Wire and Fabric Wear

Machine clothing represents a significant operating cost in paper and board production.

A worn, rough or damaged roll surface can create unnecessary mechanical interaction with wires and fabrics.

PR Rolls' vacuum roll restoration process addresses this through a combination of:

• Precision grinding
• Groove machining
• Groove edge treatment
• Wear-resistant HVOF coating
• Controlled surface roughness
• Non-stick surface treatment

The objective is to create a smooth, durable and functional contact surface.

PR Rolls' technical documentation specifically identifies longer wire lifetime and elimination of wire marking among the benefits of the treatment.

Corrosion Protection for Vacuum Rolls

Corrosion can gradually deteriorate vacuum roll surfaces and affect both surface geometry and functionality.

Simply polishing a corroded surface may not provide sufficient long-term protection.

The PR Rolls restoration process combines removal of the damaged surface with a hard functional coating.

This creates a renewed surface designed to withstand demanding paper-machine operating conditions while helping protect the underlying roll.

Corrosion is specifically identified among the problems addressed by PR Rolls' vacuum cylinder coating concept.

Complete Vacuum Roll Surface Restoration

This is where PR Rolls' offering becomes more than a coating service.

A typical project can include:

1. Inspection & Measurement
Evaluate the existing roll, wear, surface condition, grooves and suction holes.

2. Grinding
Restore geometry and remove the damaged surface.

3. Groove Machining
Restore the required groove geometry.

4. Groove Edge Treatment
Create suitable edges and transitions for interaction with the machine clothing.

5. Surface Preparation
Prepare the substrate for coating, including grit blasting where required.

6. HVOF Coating
Apply the hard, wear-resistant functional coating.

7. Non-Stick Treatment
Provide the required release characteristics.

8. Final Surface Treatment
Finish the surface according to the application requirements.

These stages closely reflect the process documented by PR Rolls for vacuum cylinder restoration.

Vacuum Roll Coating or Vacuum Roll Drilling?

These services solve different problems.

Vacuum roll grinding and coating is primarily used when the existing roll has problems related to surface wear, corrosion, fabric interaction, grooves, contamination or blocked suction holes.

Vacuum roll drilling is primarily used when the roll itself needs to be modified for new vacuum requirements, web stabilizers or dryer section optimisation.

PR Rolls provides both.

For dryer-section rebuilds, PR Rolls can drill or modify existing rolls to create the required vacuum conditions for web stabilisation.

For worn or deteriorated vacuum rolls, PR Rolls can restore the functional surface through grinding, groove machining and coating.

And in projects where both modifications and surface restoration are required, the services can be combined.

Combine Drilling, Grinding, Coating & Balancing

Some vacuum roll projects require more than one operation.

PR Rolls can combine:

Measurement → Drilling → Deburring → Grinding → Groove machining → Coating → Surface finishing → Field balancing → Verification

The existing vacuum-roll drilling page already describes a process that can include drilling, deburring, grinding, possible coating and balancing.

This allows an existing roll to be both mechanically modified and functionally restored during the same planned shutdown.

For the mill, this can provide an alternative to replacing the complete roll.

A grooved VAC-roll can also be modified to a drilled VAC-roll.

On-Site Vacuum Roll Restoration During a Short Shutdown

Large vacuum rolls can be difficult and expensive to remove from a paper machine.

PR Rolls' objective is therefore to complete the required restoration directly at the mill within the available shutdown window.

The original technical material explicitly identifies the target as eliminating the identified vacuum-cylinder problems on-site during a short shutdown.

Depending on the project, on-site execution can reduce:

• Roll dismantling
• Heavy lifting
• Transportation
• External workshop time
• Reinstallation requirements
• Overall maintenance lead time

This enables existing vacuum rolls to be restored and returned to production without unnecessary logistics.

Technical Characteristics

Typical characteristics of the vacuum cylinder coating include:

The exact specification should be determined according to the roll, application and operating conditions.

Benefits of Vacuum Roll Grinding & Coating

A correctly restored vacuum roll surface can provide several operational benefits:

• Longer wire and fabric lifetime
• Reduced fabric marking
• Improved wear resistance
• Improved corrosion protection
• Reduced contamination
• Reduced risk of blocked suction holes
• Improved ventilation and vacuum functionality
• Restored groove condition
• Extended vacuum roll service life
• Reduced need for component replacement

PR Rolls' original technical material specifically highlights longer wire lifetime, elimination of wire marks and better ventilation without blocking.

Frequently Asked Questions

What is vacuum roll coating?
Vacuum roll coating is a surface-engineering treatment designed to restore and protect the functional surface of a vacuum or suction roll. PR Rolls combines grinding, groove machining, HVOF coating and non-stick surface treatment according to the application.

Why are vacuum rolls ground before coating?
Grinding removes damaged material and restores the required geometry and surface condition before coating. PR Rolls' technical documentation specifies an after-grinding surface roughness of approximately Ra 0.4–0.8.

Can PR Rolls restore vacuum roll grooves?
Yes. Groove machining and groove edge treatment are specifically included in PR Rolls' documented vacuum cylinder restoration process.

Can coating reduce wire and fabric wear?
The objective of the PR Rolls treatment includes extending wire lifetime and preventing marking associated with the vacuum cylinder surface.

Can the coating help prevent suction holes from becoming blocked?
PR Rolls identifies blocked suction holes as one of the problems addressed by the treatment and improved ventilation without blocking as one of its benefits.

What is the difference between vacuum roll coating and drilling?
Coating primarily restores and improves the functional roll surface, while drilling modifies the hole pattern and vacuum functionality of the roll. Vacuum roll drilling is particularly relevant when adapting existing rolls for new stabilizers, vacuum requirements or dryer-section configurations.

Can drilling and coating be combined?
Yes. PR Rolls' existing vacuum roll drilling process can include drilling, deburring, grinding, coating and balancing as part of the same project.

Restore the Complete Function of the Vacuum Roll

A vacuum roll is more than a rotating cylinder.

Its surface condition, grooves, groove edges, suction holes and vacuum function must work together.

PR Rolls restores worn vacuum rolls directly at the mill through a combination of precision grinding, groove machining, groove edge treatment, HVOF coating and non-stick surface treatment. The objective is to reduce wear and marking of machine clothing, protect against corrosion and help maintain open suction holes and effective ventilation.

Where operating requirements have changed, PR Rolls can also modify the roll through precision vacuum roll drilling.

Restore the surface. Modify the vacuum function when required. Keep the existing roll in productive service.