What are the different types of structure for the flow channels of co-extrusion die heads? And what are their respective applications?

When manufacturing co-extruded profiles, different co-extrusion channel structures should be adopted according to the different shapes of the profile cross-section, the different co-extruded materials, and the size of the co-extruded coating. The commonly used surface co-extrusion channels in actual production include "straight-through type", "return type", "clothes hanger type" and "wood grain forming" co-extrusion channels.

The "straight-through type" co-extrusion channel is simple in structure and easy to process, but the pressures and flow rates of the melt on each surface during co-extrusion are mutually restricted, making it difficult to adjust them to be completely consistent. It is generally used for the extrusion of common co-extruded materials. The "return type" co-extrusion channel has sufficient material holding cavities and a long process, which can eliminate the uneven thickness of the co-extruded material caused by the difference in process length at each point. However, the melt chamber is large and the process is long, and it is generally not suitable for PVC with poor thermal stability and wood fiber reinforced PVC resins, to avoid material decomposition and color change, etc. In addition, because the co-extruded material has a lot of material storage in the channel during the production process, if the type or color of the co-extruded material is changed during production, a lot of waste will be produced. This type is mainly used for the extrusion of ASA and PMMA co-extruded materials with good fluidity and thermal stability. The "clothes hanger type" co-extrusion channel and the melt chamber are open, and the pressure and flow rate of the melt are easier to adjust and balance. This co-extrusion channel is suitable for the extrusion of all co-extruded materials.