Extrusion of peroxidic cross-linkable molded plastic parts

Abstract

The invention relates to a method for extruding peroxide-crosslinked plastic mouldings, preferably pipes, the plastic is heated in an extruder (2) and continuously fed to an extrusion die (15) for the production of pipes , and at least partial crosslinking of the plastic is achieved in the extrusion die by heating the plastic above a crosslinking temperature; the method comprises the following process steps: a) conveying the crumb or granular mixture to an extruder ( 2), comprising mixing of crosslinkable plastics with crosslinking agents and stabilizers or other components; wherein, b) through the cooperation of an external temperature regulating device (12) and an internal cooling device (14), The unmelted plastic in the extruder is controlled to a temperature above the melting temperature of the plastic, but below the crosslinking temperature of the plastic; wherein the crosslinking temperature exceeds the melting temperature by about 30%, thereby The plastic is conveyed in a molten state; c) the melting pressure in the extruder is 700-1500 bar before the molten plastic enters the extrusion die; and, d) an additional external heating device (16) will The temperature of the molten plastic in the extrusion die is brought to a value at least 15% above the crosslinking temperature and the plastic is placed in a partially crosslinked state, including greater than 60% crosslinking when the tube leaves the extrusion die.

Description

technical field [0001] The invention relates to a method for extruding peroxidatively crosslinked plastic moldings, preferably pipes. Background technique [0002] One such method is known, for example, from EP 0 999 030 A1. Pipes of peroxide-crosslinkable plastics are produced by this method. The pipe is made of polyethylene, and an organic peroxide is added as a cross-linking agent and an antioxidant. Polyolefins can also be used instead of polyethylene. In the method described in EP 0 999 030 a mixture of unmelted plastic and peroxide is fed to an extruder via a known addition hopper. The extruder feeds the plastic into the extrusion die, where the tube is finally produced and the crosslinking of the plastic is carried out. For this purpose, heat is applied in the region of the extrusion die, which brings about crosslinking of the plastic. The plastic and crosslinking agent are first melted in the extrusion die and heated above the crosslinking temperature. The mate...

AI Technical Summary

Problems solved by technology

Failure to maintain can lead to strong quality fluctuations during the manufacture of tubes or molded parts

[0003] and undesired crosslinking, which can lead to undesirable stresses and loads in the extruder or extrusion die

Possible consequences of damage to extrusion dies or extruders in addition to insufficient properties of the produced pipe

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