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PEXa Pipe Extrusion: Innovative heating technology based on infrared radiation

Articles
1
PEXLINK conveyor oven - 4-strand conveyor oven
featuring a specifically designed guide and deflection system

Floor heating, radiator connections, hot and cold water piping: PEXa pipes are used for many different applications. However, PEXa pipe extrusion still belongs to the most demanding processes encountered in the extrusion industry. Manufacturing companies are presented with significant challenges. One of the challenges is the cross-linking process of the involved polyethylene. iBA GmbH, headquartered in Melle (Germany) offers an efficient and innovative technical solution based on infrared heating. The system is called PEXLINK.

Unique 4-strand conveyor oven

The core element of the heating process is the unique conveyor oven which enables the process in the first place and ensures the specific high production quality. The perfect tuninig of the extruder and the extrusion die provides a good melt homogeneity at a very low mass temperature which is imperative for the crosslinking process that takes place after the pipe has passed the extruder. The innovative 4-strand conveyor oven features 12 infrared units and a specifically designed guide and deflection system to achieve the correct cross-linking of the polyethylene. The required exposure to radiation has a direct influence on the haul-off speed. A very short exposure permits a high haul-off speed. When the pipe subsequently passes several infrared units, it is possible to increase the exposure period. As a result, the haul-off speed can be increased to a maximum of 36 m/min.

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PEXLINK conveyor oven – Infrared units are the prerequisite for the optimum cross-linking of polyethylene

During the pipe's passage through the oven, the thermally activated peroxide which is regularly distributed inside the pipe wall decomposes following an optimum wavelength distribution of the infrared radiation. Highly reactive components are produced (radicals). They spilt hydrogen atoms from the polyethylene chains. In the now free spots the cross-linking process takes place through a recombination with other polyethylene chains.

The particular advantage of the infrared heating process is that heat radiation penetrates the material much deeper that pure thermal convection. As a result, a perfectly round pipe with a good geometry can be produced. Even smallest tolerances and an ovalness of less than 0,3 mm which is far below standard requirements can be adhered to. Gaseous reaction products are instantly removed by an integrated extraction system which aspirates them directly from the oven and all neighboring line parts.

Intelligent cooling system

In order to protect the pipe from overheating during the cross-linking proces, an air cooling system has been integrated. This is an intelligent cooling system which protects the pipe from burning and ensures the safe handling of the pipe material.

This specific PEXa process stands for the complete cross-linking inside the pipe wall as the pipe is perfectly cross-linked „in a hot state", i.e. above the melt temperature. Due to the high cross-linking degree, the required long-term pipe properties, namely a very high flexibility and ease of installation are achieved already with small wall thickness sizes. PEXLINK technology stands for a long-term temperature resistance and a proven lifespan of more than 50 years. PEXa pipes are permanently suitable for exposure to high (+95° C) and low (-60° C) temperatures and they are extremely pressure-resistant.

David Brinkmann, Marketing

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