Design and Manufacturing of Steel-Reinforced PVC Windows
Profile extrusion, galvanised steel reinforcement, welded corners and quality control: how a high-performance PVC window is made.
Steel-reinforced PVC windows, sometimes called “metal-plastic” windows, dominate the renovation market. Understanding how they are made helps you recognise a quality product.
1. Extruding the profiles
PVC is heated and pushed through a die that gives it its shape. The resulting profile is hollow and divided into several chambers: these air pockets slow down heat transfer. Current profiles usually have five to seven chambers.
2. Galvanised steel reinforcement
PVC alone is slightly flexible, so a galvanised steel reinforcement is slid into the central chamber. It stiffens the frame, carries the weight of the glass and gives hardware screws a solid hold. Its section is matched to the window size and wind exposure.
3. Cutting and welding the corners
Bars are mitre-cut at 45°, then the corners are heat-welded: both ends are melted and pressed together. The weld bead is then trimmed. A welded corner is watertight and strong, with no visible screws or brackets.
4. Gaskets and hardware
Sealing gaskets are inserted into dedicated grooves, then the hardware is fitted: espagnolette, stays, hinges and locking points. This is also when anti-burglary mushroom cams can be added.
5. Glazing and beading
The insulated glass unit sits on setting blocks and is held in place by clip-in glazing beads. Proper blocking spreads the glass weight across the frame and prevents the sash from sagging.
6. Quality control
Serious manufacturers test air permeability, watertightness and wind resistance (the AEV classification in France). Also look for CE marking and, ideally, an NF-type certification.
What to ask your supplier
Number of chambers, presence and section of reinforcement, AEV rating and the Uw value of the whole window: these facts are worth more than any sales pitch.