Contents
1. What a cold room sandwich panel actually is
A cold room sandwich panel is a structural insulating element built around three components: two metal facings — typically galvanised, pre-painted steel sheets — bonded to a rigid polyurethane (PU) or polyisocyanurate (PIR) foam core. The metal sheets carry the mechanical load and protect the core from moisture and damage; the foam core provides the thermal insulation that lets a cold room maintain –25 °C while the outside sits at +35 °C with single-digit heat flux through the wall.
The panel's edges are profiled rather than flat: a male tongue on one long edge mates with a female groove on the next panel, and a cam-lock or hook-lock mechanism pulls the two together. This edge geometry is what lets a cold room be assembled out of a few standard panel widths with a near-airtight seam, on site, by a small installation team. The same panel type — with adjusted thickness and skin specification — also serves as roof panel, partition wall and door blank.
2. The two production routes — continuous lamination vs discontinuous press
Continuous lamination (CL) is the high-volume route. Two coils of pre-painted steel feed into the line from either side, run through a series of forming rollers that shape the panel edges and the surface profile, and meet at the foaming station — where polyurethane mix is dispensed onto the lower skin. The two skins then close together over the rising foam, travel through a long heated double-belt press while the foam fills the cavity and cures, and exit the press as a continuous panel. A flying saw cuts the panel to the ordered length, the cut ends are sealed, and the finished panels stack onto an outfeed table.
Discontinuous press (DC) lines work one panel at a time. Pre-cut skins are placed in a fixed-size press, the foam is dispensed, the press closes for the cure cycle, and the panel is unloaded when cure is complete. DC lines have a much lower capital cost and are flexible — they can handle short runs, non-standard sizes, asymmetric panels and prototyping — but their cycle time is longer and per-panel throughput is far below a continuous line.
Practically, a panel manufacturer running serious volumes of standard cold-room panels invests in a continuous line; a manufacturer producing project-specific panels in smaller runs, or doors and custom geometries, runs a DC press. Many large panel plants run both, with the continuous line carrying the catalogue range and a DC press handling specials.
3. The continuous panel line, step by step
Coil decoiling and surface preparation. Upper and lower steel coils are decoiled, optionally protective film is applied, and the strips are pulled into the line at the line speed (typically 4–15 m/min for cold-room thicknesses). The strips travel through a heater that brings the substrate to the temperature window the system house specifies — usually 35–50 °C — which is critical for adhesion between the foam and the metal.
Edge profiling. Forming rollers shape the panel edges into the tongue-and-groove or cam-lock geometry. This step defines how the panels will fit together on site, and small dimensional errors here propagate into seam gaps and air leakage in service.
Foam dispense. The PU (or PIR) system arrives at the line as two separate components — the formulated polyol blend (Side A) and the isocyanate (Side B) — stored in temperature-controlled tanks. A high-pressure metering machine mixes the two at the prescribed ratio (commonly around 100 parts polyol to 130–160 parts isocyanate by weight) and dispenses the mix onto the lower skin through a moving lance that sweeps across the width of the panel. The dispense pattern, the line speed and the cream/rise times are tuned so that the foam fills the cavity uniformly without overflow.
Double-belt press cure. The upper skin closes onto the rising foam and both skins are pulled into the double-belt press: long top and bottom belts that travel with the panel, holding the assembly to its target thickness while the foam expands, gels and cures. The press is heated (typically 50–70 °C) to accelerate cure and to bond the foam chemically to the metal. Cold-room panels at 80–200 mm thickness typically need 6–12 minutes in the press depending on system reactivity and line speed.
Cut to length, sealing, stacking. A flying saw — synchronised with the line speed — cuts the continuous panel into the ordered lengths. The fresh cut edges are sealed (often with an edge-coating or a pre-applied film) and the panels stack on the outfeed table, ready for packaging.
4. The process parameters a panel line actually controls
Three parameter groups dominate the day-to-day quality of a sandwich panel:
Foam reactivity vs line speed. Cream time (when the mix starts to expand), gel time (when it becomes self-supporting) and rise time (when expansion stops) have to be matched to the line geometry. If gel time is too short, the foam sets before it fills the cavity and panel edges starve; if too long, foam continues expanding inside the press and produces internal pressure marks or skin bulges. Adjusting these typically means adjusting the polyol blend's catalyst level — work the system house does.
Free-rise density vs core density. The system has a free-rise density (what the foam would expand to with no pressure) and a higher in-panel core density (because the press holds it to a fixed thickness). The ratio between the two — commonly around 1.10–1.18 for cold-room systems — is a quality lever. Too low a ratio and the foam fails to pack the cavity; too high and you waste material. Continuous lines monitor this through fill weight checks.
Skin temperature, line temperature and press temperature. These three together govern adhesion. The foam bonds chemically to the metal during the cure phase; if any of the three temperatures drops out of range, the bond weakens and panels can delaminate under thermal cycling or transport stress. Temperature controllers and contact probes monitor this continuously on a well-run line.
5. Quality control and the EN 14509 standard
Sandwich panels for buildings are governed in Europe by EN 14509, which defines the product type, the required test methods and the declared performance characteristics. The thermal conductivity of the core (λ, W/m·K) drives the panel's insulation rating and is measured on the foam itself; values in the 0.021–0.024 W/m·K range are typical for modern blowing-agent systems. Compressive strength, shear strength of the bond, dimensional stability under elevated temperature and water absorption are the mechanical tests a panel must pass before it can carry a CE marking.
Fire performance is the parameter where PU and PIR diverge most sharply. Standard PU systems typically achieve a Euroclass B-s2,d0 or B-s3,d0 reaction-to-fire rating; PIR systems — produced from the same line with a different formulation tuned to a higher isocyanate index — typically reach B-s1,d0 or A2 with mineral additives. The choice between the two is driven by the building code at the installation site, by insurer requirements (FM Approvals is influential here), and by the project's overall fire engineering. The companion article PIR vs PUR Insulation Panels covers that comparison in detail.
In Türkiye, panel manufacturers selling into the domestic market reference TS-EN 14509 and the relevant fire and energy regulations; exporters to Europe certify to EN 14509 under CE marking. Whichever route a panel takes, the line-side and laboratory-side tests are the same — and the system house's role is to supply a polyurethane formulation that passes all of them while running cleanly on the customer's specific line geometry.