The ULAMEX Bi-Metal Self-Drilling Screw combines a hardened carbon steel drill tip with an A2 stainless steel body (1.4301 / AISI 304), enabling direct penetration through trapezoidal metal sheet roofing without pre-drilling. This bi-metal construction provides the best of both worlds: the drill tip’s hardness cuts through steel, while the stainless body resists corrosion over the decades-long service life of the PV installation.
Technical Specifications
| Parameter | Value |
|---|---|
| Construction | Bi-metal (two-material composite) |
| Body material | A2 stainless steel (1.4301 / AISI 304) |
| Drill tip material | Hardened carbon steel (case-hardened) |
| Drive | Hexagon head (8 mm AF) |
| Sizes | 6×25 / 6×38 mm |
| Drilling capacity | Steel sheet 0.7–1.5 mm |
| Sealing | EPDM bonded washer (pre-assembled) |
| Thread | Self-tapping thread for thin-gauge steel |
Installation Guidelines
Position the mounting bracket or PV rail clamp on the trapezoidal sheet crest (the raised rib — never in the valley). Place the bi-metal screw through the bracket hole and onto the sheet surface. Using a power drill with an 8 mm hex socket driver, apply steady downward pressure while running at medium speed (400–600 RPM). The hardened carbon drill tip will cut through the steel sheet without pre-drilling.
Once the drill tip penetrates, the self-tapping thread engages and pulls the screw into the sheet. The EPDM bonded washer compresses against the sheet surface, creating a watertight seal that prevents rain ingress at the penetration point. Do not over-tighten — the EPDM washer should be visibly compressed but not extruded beyond the washer rim. A light bulge at the washer perimeter indicates correct compression.
For trapezoidal sheet mounting, drive screws into the crest (high point) of the sheet profile, not the valley. Crest-fixed screws bear the clamp load in shear, while valley-fixed screws would be subject to pull-out under wind uplift. Use a minimum of two screws per mounting point for adequate load distribution.
Applications
- Trapezoidal sheet roof PV mounting — direct attachment of rail clamps and brackets to metal roofing without pre-drilling
- Standing-seam roof adapters — supplementary fixings for PV mounting brackets on metal roofs
- Industrial hall rooftop PV — large-scale installations on steel-sheet roofed commercial and industrial buildings
- Agricultural building PV — barn and shed roof installations on corrugated and trapezoidal sheeting
- Carport steel canopy mounting — fastening PV rail systems to steel carport structures
Material Properties
The bi-metal construction addresses a fundamental challenge: the drill tip must be extremely hard to cut through steel sheet, but a fully hardened screw would be brittle and corrosion-prone. By welding a case-hardened carbon steel drill point onto an A2 stainless steel shaft, the screw achieves drilling performance equivalent to a carbon steel screw with corrosion resistance equivalent to a full-stainless fastener.
The A2 stainless body provides the same atmospheric corrosion resistance as all other ULAMEX PV fasteners — the passive chromium oxide layer self-regenerates and protects the screw throughout its 25+ year service life. The drill tip, being embedded in the steel sheet after installation, is protected from atmospheric exposure by the sheet itself and the EPDM washer seal above it.
Compatibility
The ULAMEX bi-metal self-drilling screw is used with:
- Trapezoidal sheet clamps — PV rail mounting clamps designed for metal roof attachment
- PV mounting rails 40×40 and 80×40 — via trapezoidal sheet mounting brackets
- EPDM sealing washers — pre-assembled on the screw for watertight roof penetration
- Carport mounting systems — steel-to-steel connections in PV canopy structures
Why ULAMEX
ULAMEX is an EN 1090 certified B2B wholesaler supplying the complete PV mounting system for all roof types — pitched tile roofs (roof hooks), trapezoidal sheet roofs (self-drilling screws), and flat roofs (ballast systems). Both screw sizes stocked for immediate dispatch in bulk packaging with pallet delivery across Europe.
Frequently Asked Questions
Q: What does “bi-metal” mean in self-drilling screws?
Bi-metal means the screw is made from two different metals: a hardened carbon steel drill tip welded to an A2 stainless steel body. The hard tip drills through metal sheet, while the stainless body provides corrosion resistance. This combines the drilling ability of carbon steel with the durability of stainless.
Q: Can bi-metal screws drill through any thickness of steel?
ULAMEX bi-metal self-drilling screws are designed for thin-gauge steel sheet (0.7–1.5 mm), typical of trapezoidal roof panels. For thicker steel (above 2 mm), pre-drilling is required. Do not attempt to drill through structural steel members with self-drilling screws.
Q: Do I need to add a washer?
No. ULAMEX bi-metal self-drilling screws come with a pre-assembled EPDM bonded washer that seals the roof penetration automatically during installation. No additional washer is required.
Q: 6×25 or 6×38 — which length?
6×25 mm for standard single-layer trapezoidal sheet (0.7–1.0 mm) with a bracket or clamp. 6×38 mm for thicker assemblies, double-skin panels, or where the bracket adds additional stack-up height. The screw must fully penetrate the sheet with at least 3 complete thread turns engaged.
Need bi-metal self-drilling screws for trapezoidal roof PV? Request a Quote | +48 504 424 761 | [email protected]