Concealed-fastener color-coated steel panels, also called hidden-fastener or concealed-clip roofing panels, are profiled sheets roll-formed from color-coated steel. They are fixed to roof purlins with matching galvanized or aluminum alloy brackets rather than exposed screws. The connection sequence involves fastening the concealed brackets to the purlins, engaging the panel's female rib with the bracket's central rib, and then locking the seam with a seaming machine to create a tight joint between adjacent panels. SENBO produces these profiles on dedicated roll-forming lines and checks key dimensions such as rib height, effective width, and locking depth during production.
The main difference from standard color-coated steel roofing lies in the fastening method. Conventional panels are secured with self-tapping screws that pass through the panel surface, requiring sealant at each screw hole. Concealed-fastener panels rely on interlocking brackets instead, which means the surface remains free of penetrations. This approach improves waterproofing, reduces long-term corrosion risk at fastener points, and gives the roof a cleaner appearance.
| Profile Type | Rib Height (mm) | Effective Width (mm) | Unfolded Width (mm) | Material Utilization | Typical Applications |
|---|---|---|---|---|---|
| Jiaochi 760 (YX51-380-760) | 51–71 | 760 | 1000 | 76% | Large-span factories, airports, stadiums |
| Model 820 | 50 | 820 | 1000 | 82% | Small-to-medium span industrial plants |
| CC-750 (YX41-250-750) | 41 | 750 | Not listed | Not listed | Large-span venues; based on Australian technology |
| Performance Indicator | Parameter / Specification | Remarks |
|---|---|---|
| Base Material Grade | Q235B, Q345, high-strength steel (550 MPa class) | Depends on profile type |
| Common Thickness | 0.3–1.0 mm | Standard 0.5–0.6 mm |
| Typical Profiles | YX51-380-760 (Jiaochi 760), YX50-410-820 | Effective width 760 mm or 820 mm |
| Connection Method | Concealed clip-lock or seaming | No screw penetrations on the panel surface |
| Pull-out Resistance | ≥200 kg | Measured value for the panel clip |
| Single Panel Length | Up to 100 m | Supports thermal expansion and contraction |
| Application Scope | Large-span industrial plants, public buildings | Not suitable for curved roofs with radius R < 50 m |
Because the Concealed-fastener color-coated steel panel surface has no fastener penetrations, the system avoids a common leak path found in exposed-fastener roofs. In traditional systems, sealant at screw holes can age and crack over time, allowing water ingress. The Jiaochi 760 profile, with a rib height of 71 mm and rib spacing of 380 mm, helps rainwater move quickly from the valleys to the eaves. When the seams are closed with a seaming machine, the side interlock provides a continuous barrier against water entry. The absence of surface holes also reduces the potential for corrosion starting at fasteners.
The brackets that hold the panels to the purlins are designed to resist uplift. During a 5 MW color-steel-roof photovoltaic project at Shenzhen Bao'an International Airport, the on-site wind pressure reached 0.75 kN/m². Pull-out tests on the concealed clips recorded a pull-out strength of 200 kg, which met the safety requirements. The YX41-250-750 concealed-clip panel uses steel with a yield strength of at least 550 MPa and a locking depth greater than 5.2 mm. Each interlocking rib is anchored by a fixing clip, which improves the roof's ability to handle wind and snow loads.
The fixing clips allow the roof panels to slide along the slope as the metal expands and contracts with temperature changes. The panels remain engaged with the clips during this movement, so the connection between roof and structure stays stable. This allows continuous panel lengths beyond 100 meters without the need for transverse overlaps, which is useful for large-span roofs.
The system uses factory-prefabricated panels that interlock on site. Some concealed-clip profiles, such as the CC-750, do not require a specialized seaming machine, which can reduce labor and shorten installation time. Coil stock can be cut to length at the job site, enabling single panels over 100 meters and minimizing the number of end laps. This approach also lowers the risk of leakage at transverse joints.
The side interlock is formed mechanically with a seaming machine. The resulting joint is tight enough to resist water entry under normal conditions. Proper roof slope and drainage design also help move water away from the seams quickly.
Most concealed-fastener profiles are intended for straight or very large radius roofs. The minimum curvature radius depends on the panel profile and material thickness. For curved applications, check with the manufacturer before ordering.
Exposed fasteners require sealant at each screw hole. Over time, sealant can degrade and create leak paths. Hidden fasteners eliminate this maintenance point and reduce the risk of water entry and corrosion around screw holes.
Pull-out tests on the clips can be performed on site or in a laboratory. The measured value should be compared with the design wind uplift load for the building location. Suppliers can provide test data or assist with project-specific verification.
Before shipment, panels are checked for profile geometry, locking depth, surface coating condition, and dimensional accuracy. Mill certificates for the base steel should be available, along with reports for clip pull-out strength when required. During installation, spot checks on seam engagement and clip alignment help ensure consistent quality.
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