How does profile extrusion work?
Extrusion is a primary shaping process: a solid profile emerges from shapeless raw material in one continuous run. Eight stations determine the result:
- Raw material
The starting point is plastic granulate, for PVC often a powdery dryblend, plus additives such as stabilisers and colourants. Moisture-sensitive materials such as PA, ABS or TPU are dried beforehand to avoid streaks and bubbles.
- Plasticising in the extruder
A rotating screw conveys the material through a heated barrel: feeding, compressing, melting, homogenising. The melt is created by barrel heating plus frictional heat. PVC dryblend typically runs on twin-screw extruders, most other thermoplastics on single-screw machines.
- The die
The die distributes the melt onto the target contour. Important: the die opening is not identical to the finished profile, because the melt swells after exiting and shrinks while cooling. The tool anticipates this behaviour.
- Calibration
Right behind the die, calibration fixes the still-soft strand to its final dimensions, for profiles usually as dry calibration: vacuum draws the profile against cooled calibrator walls, often across several stages in series.
- Cooling
In the cooling section (water bath, spray cooling) the cross-section becomes dimensionally stable. Even cooling is quality-critical: unevenness creates internal stress and warpage.
- Haul-off
A caterpillar or belt haul-off pulls the strand through the line at constant speed. The interplay of extruder output and haul-off speed determines wall thicknesses and dimensional accuracy.
- Cutting or winding
At the end of the line the endless profile is sawn into fixed lengths or, for flexible products, wound onto rolls: the two delivery formats of profile extrusion.
- Fabrication
Optionally, further processing follows: punching, drilling, printing, adhesive tape, welding into frames or brush insertion, through to the ready-to-install component. Fabrication at Heller
What is co-extrusion (dual hardness)?
Co-extrusion is an extrusion variant in which two melt streams are united into one profile inside the tool. Typical is the dual-hardness compound: a rigid carrier, for example PVC-U or PP, is joined in a single pass with a soft sealing component of PVC-P or a TPE. The result mounts like a rigid profile and seals like a rubber lip.
The bond forms in the melt, not by gluing afterwards. The material pairing is decisive: both components must adhere chemically and exit at the same speed. At Heller, combining two hardnesses in one profile is part of the documented standard repertoire, produced on our own 20 lines in Herborn, Germany.
Extrusion versus injection moulding
Both processes melt thermoplastics, but they answer different tasks. Extrusion continuously creates endless goods with a constant cross-section; injection moulding fills a closed mould and creates individual, freely shaped parts.
| Criterion | Profile extrusion | Injection moulding |
|---|---|---|
| Geometry | constant cross-section, any length | freely shaped 3D parts |
| Tooling costs | comparatively low: one die contour plus calibration | high: closed cavity with ejectors, cooling, gating |
| Economical quantity | small to medium series already | usually larger series required |
| Typical products | sealing, protection, guiding profiles, hoses, round cords | housings, clips, complex mouldings |
| Delivery format | fixed lengths or rolls, fabrication possible | individual parts |
Industry rule of thumb: extrusion tools are considerably cheaper than comparable injection moulds, so custom profiles pay off earlier. Details in the tooling cost article.
When is extrusion the right process?
Extrusion is the first choice whenever your part has a constant cross-section: seals, edge protection, guiding and clamping profiles, cable ducts, hoses, round cords. As soon as the function varies along the length (bosses, ribs, screw domes), the path leads to injection moulding, or to a combination of an extruded profile plus fabricated features such as punching and drilling. Exactly that combination is what Heller covers in-house with extrusion plus fabrication.
Not sure whether your geometry can be extruded? That is what our design department is for: send a sketch and you will get an honest assessment.
