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What are Flush Rivetted Sign Blanks

Flush riveted sign blanks – also referred to within the sign industry as hidden rivet or invisible rivet sign blanks – are aluminium sign panels where the rear-mounted sign channel is mechanically fixed to the sign face using industrial rivets that sit flush with the front surface of the panel. Once finished, the rivets are not visible from the face of the sign, preserving a clean, uninterrupted visual appearance while providing a permanent mechanical fixing.

At Sign Trade Supplies, flush riveted sign blanks are manufactured using a Bollhoff industrial hydraulic riveting system, a process widely recognised in engineering and fabrication sectors for delivering consistent, high-strength fastenings.

This article is written for professional sign manufacturers and explores the process, materials, history, use-cases, compliance considerations (including UK highways signage), and how flush riveted blanks compare to bonded alternatives such as Stykra tape systems.

How Flush Riveted Sign Blanks Are Manufactured

 

Panel and Channel Construction

A typical flush riveted sign blank consists of:

  • Sign face: 3mm aluminium composite or solid aluminium panel

  • Rear stiffener: Aluminium sign channel profile (commonly extruded channel)

  • Fixing method: Industrial rivets applied from the face side

The aluminium channel provides rigidity, wind-load resistance, and a mounting interface for posts, frames, or clamps.

The Bollhoff Hydraulic Riveting Process

Flush riveted blanks are produced using a Bollhoff hydraulic riveting machine, which differs significantly from manual or pneumatic riveting methods.

Process overview:

  1. The sign face and rear aluminium channel are precisely aligned and clamped.

  2. A rivet is hydraulically driven from the face of the panel, through the 3mm aluminium, and into the channel profile behind.

  3. Hydraulic pressure expands and forms the rivet within the channel, mechanically locking the two components together.

  4. The rivet head sits flush with the sign face, requiring no surface finishing.

This controlled process ensures:

  • Consistent rivet deformation

  • Repeatable structural strength

  • No surface distortion or oil-canning of the panel

Rivet Types and Materials

What Are the Rivets Made Of?

For flush riveted sign blanks, rivets are typically:

  • Steel alloy rivets 

  • Selected for corrosion resistance, thermal compatibility, and longevity

Why Rivets Instead of Screws or Pop Rivets?

  • Rivets create a permanent mechanical joint

  • No risk of loosening over time due to vibration or thermal cycling

  • Flush finish cannot be achieved reliably with standard pop rivets

Industry History and Context

Historically, sign channels were attached using:

  • Screws or bolts (visible fixings)

  • Standard pop rivets (often visible or telegraphing through the face)

  • Adhesive bonding systems

Flush riveting emerged as a response to:

  • Increasing aesthetic expectations for highway and commercial signage

  • Stricter wind-load and durability requirements

  • The need for long-term performance without maintenance

Industrial riveting systems such as those from Bollhoff allowed sign manufacturers to adopt engineering-grade fastening techniques previously seen in automotive and aerospace applications.

Use Cases for Flush Riveted Sign Blanks

Flush riveted blanks are particularly well suited to:

  • Highway and road traffic signs

  • Motorway gantry signage

  • Permanent directional signage

  • Urban wayfinding systems

  • Large-format external signs subject to wind loading

They are commonly specified where:

  • Long service life is required (10–20+ years)

  • Visual appearance must remain pristine

  • Failure or delamination would pose safety risks

What Problems Do Flush Riveted Blanks Solve?

Structural Integrity

  • Provides a true mechanical fixing between face and channel

  • Resistant to peel, shear, and tensile forces

Aesthetic Quality

  • No visible fixings on the sign face

  • Ideal for reflective graphics and digitally printed faces

Environmental Durability

  • Unaffected by UV exposure

  • No adhesive degradation

  • Excellent performance in freeze–thaw cycles

Potential Problems and Constraints

While flush riveted blanks are highly robust, there are constraints to consider:

Manufacturing Constraints

  • Requires specialist hydraulic riveting equipment

  • Higher capital investment than bonding-only setups

Design Constraints

  • Minimum panel thickness typically required (commonly 3mm)

  • Channel placement must be predetermined – less flexibility post-production

  • Application of graphics must be completed after channels have been rivetted in place making it slightly harder to apply even pressure across the panel. This can alos stop standard Rollsroller application tables to be used.

Bonded vs Riveted Sign Blanks

Sign Trade Supplies offers both flush riveted blanks and bonded blanks using high-performance systems such as Stykra bonding tape.

Comparison Table

Feature Flush Riveted Blanks Bonded Blanks (e.g. Stykra)
Fixing method Mechanical (rivets) Adhesive bonding
Strength Very high, permanent High, but application-dependent
Aesthetics Great (flush rivets do not protrude but are visible) Excellent (no fixings visible from face)
Long-term durability Exceptional Very good (when specified correctly)
UV resistance Yes Yes
Failure mode Extremely rare Rare, but usually caused by improper application
Equipment required Hydraulic riveting system None
Speed of production Moderate Fast
Rework Not possible Not possible

Buyer Choices and Specification Considerations

When choosing between bonded and riveted blanks, buyers should consider:

  • Design life of the sign

  • Environmental exposure (coastal, high UV, high wind)

  • Panel size and wind loading

  • Client or authority specifications

  • Installation method and access

Common Buyer Mistakes

  • Assuming all bonded systems and tapes are equal

  • Underestimating wind loading on large panels

  • Selecting bonded blanks where permanent mechanical fixing is specified

  • Mixing materials that introduce corrosion risk

  • Using rivetted blanks where signs will be viewed in close proximity. (flush rivet indentations will likely be seen)

Compliance with UK Highways Signage Standards

TSRGD 2016

In the UK, traffic signs must comply with the Traffic Signs Regulations and General Directions (TSRGD) 2016.

While TSRGD primarily governs:

  • Sign design

  • Size

  • Reflectivity

  • Placement

It implicitly requires that signs:

  • Are structurally sound

  • Remain legible and secure for their intended service life

  • Do not present a hazard due to failure or detachment

Why Flush Riveted Blanks Are Common on Highways

Flush riveted sign blanks are widely used for Highways England / National Highways signage because:

  • Mechanical fixings provide predictable long-term performance

  • They are resistant to adhesive ageing concerns

  • They meet the durability expectations of long-term infrastructure assets

While bonding systems may be acceptable in some applications, flush riveted construction is often preferred or specified for:

  • Large-format signs

  • High-speed road environments

  • Permanent installations

Summary

Flush riveted sign blanks represent a premium, engineering-led approach to sign manufacture. By combining a clean, invisible finish with permanent mechanical strength, they offer a solution ideally suited to highways, infrastructure, and long-life external signage.

For sign manufacturers, understanding the differences between riveted and bonded systems – and specifying them appropriately – is critical to performance, compliance, and reputation.

Sign Trade Supplies supports both approaches, enabling manufacturers to choose the right solution for each application rather than forcing a one-size-fits-all method.