The technical line in a quotation reads "1 mm DKP sheet" and buyers reasonably ask what the abbreviation stands for and how it differs from ordinary sheet. Several readings of the acronym circulate in the Turkish trade, but the material it describes is always the same: cold-rolled, low-carbon steel sheet suited to deep drawing and pressing. Almost every steel door body is formed from it.
What cold rolling changes
Steel is first hot rolled down to plate, which leaves mill scale on the surface and a wide thickness tolerance. Cold rolling pickles that plate and re-rolls it at room temperature. Three things change: thickness tolerance narrows, the surface becomes smooth and matt grey, and the metal work-hardens. Because hardening makes forming difficult, the sheet is annealed to restore formability.
Why doors use it
- Surface: paint and cladding need a flat substrate; powder coating will not bond to mill scale.
- Consistent thickness: deviation shows as waviness in the pressed leaf face.
- Formability: embossed panel doors are deep pressed, and low-carbon sheet takes that strain without cracking.
- Bending: frame profiles and leaf edges are folded at sharp angles, where harder sheet splits.
- Welding: low carbon content makes spot and MIG welding straightforward.
Our sheet panel door production depends entirely on that formability; pattern depth only comes out of the right sheet grade.
Choosing thickness
Leaf faces commonly run 0.8 to 1.2 mm with heavier gauge in frames. More thickness is not automatically better: thick sheet resists deep pressing, blunts pattern definition, adds weight and loads the hinges. Stiffness comes from internal reinforcement profiles and edge fold depth rather than from gauge, so comparing quotations on millimetres alone is misleading.
Oiled sheet and pretreatment
Cold-rolled sheet arrives with a thin protective oil film that must be removed before coating; residual oil prevents adhesion and blisters within the first year. A proper line runs degreasing, rinsing, phosphating or nano-ceramic pretreatment, then drying. Asking a supplier about the pretreatment line tells you more than asking about sheet gauge.
Compared with galvanised sheet
Galvanised sheet is cold-rolled sheet with a zinc coating that acts sacrificially and protects the steel even where scratched. In exchange, painting over zinc needs its own pretreatment and the coating is stressed in deep pressing. For interior and sheltered openings, cold-rolled sheet with a sound paint system is sufficient; for continuously exposed or humid locations a galvanised substrate is preferred.
Corrosion in practice
Steel rusting is not a defect; the coating system is what prevents it. The highest-risk points are cut edges, weld spots, around drilled holes and anywhere scratched during installation. Touch in installation damage before it spreads, and inspect annually in coastal and damp basement locations.
What to ask for in a quotation
Request the leaf outer and inner sheet gauge separately, the frame gauge, the number and layout of internal reinforcement profiles, whether the substrate is galvanised or plain cold-rolled, and the pretreatment steps before coating. Those five lines show the real difference between two offers. Tell us the exposure of each opening along with wall openings in centimetres and we will specify substrate and finish together. Where ratings apply, sheet and core follow the tested fire door system instead of free selection. Doors are crated and dispatched from Istanbul by truck or sea container.
