Extrusion International 2-2018

35 Extrusion International 2/2018 Comprehensive know-how The complex and demanding manufacture of PEXa pipes in a one-stage process involves a specific convey- ance technology for peroxide. The SAVEOMAT con- veyor station transports all required components to the production process at the correct time and subject to all safety regulations contained in the ATEX 95a. A com- plete leakage monitoring system and the encapsulation with inert gas provide safety at the highest level. The safety aspect, also in view of the safety of the operat- ing personnel, is observed throughout and extends also to integrated aspiration devices which are mounted in all relevant places along the extrusion line. The SAVEO- MAT multi-component dosing process which follows the static and dynamic mixing of all solid PE materials and the liquid peroxide mixture, assures that all com- ponents are homogeneously mixed which is in turn a prerequisite for a high-quality product. All of these fea- tures contribute substantially to avoiding complaints and claims for damages. A reduced consumption of raw materials, particularly of peroxide reduced by up to 10% and the creation, use and optimization of own recipes are further advantages of the continuously per- forming gravimetric SAVEOMAT multi-component dos- ing system. These benefits are supplemented by the long-standing expertise and the consultancy know-how offered by iBA on the optimum material composition and product recipes. Reliable high-performance process The perfect mixture of all process components is fol- lowed by their processing on a high-performance dou- ble-screw extruder L/D 27. A perfect combination of the extruder and the die offers a very good melt homoge- neity at very low melt temperatures, a prerequisite for the crosslinking process which takes place only after the product has passed the extruder. The core element of the extrusion line is the unique 4 strand infrared oven which features a specific guidance of the pipe. Higher speeds and higher outputs become possible due to this innovative ovenwhich is equippedwith 12 infrared units. An optimum retention time in the oven is selectable for different pipe dimensions. In the infrared oven, the ther- mal heating of the pipe and the optimum wavelength distribution of the infrared radiation make the peroxide which is regularly distributed inside the pipe wall split into highly reactive components (radicals). These release hydrogen atoms from the polyethylene chains and new combinations of polyethylene chains take up their place, thus carrying out the crosslinking process (see Picture 2). The particular advantage of infrared heating is that this kind of heat penetrates the material on a deeper level than mere heat convection. The result are perfect- ly round pipes and optimum product geometries. Very tight tolerances and an ovalness of less than 0,3 mm become possible, a figure which is far below set stan- dards. Resulting gaseous reaction products are instantly eliminated from the oven and all surrounding machin- ery equipment by an integrated aspiration unit. A PEXa production process offers a thorough crosslinking of the pipe wall as the pipe is completely crosslinked during its hot state, i.e. above the melt temperature. This achieves a crosslinking degree of at least 70%. The high crosslink- ing degree assures that the required long-term proper- ties for this kind of pipe are available already for small wall thickness sizes offering high flexibility and ease of installation. PEXLINK technology stands for a long-term Heat radiation in the infrared ovenmakes the peroxide disintegrate and form radicals. These radicals separate hydrogen atoms from the polyethylene chains. The resulting radicals in the polyethylene chain lead to a recombination with other polyethylene chains and thus the crosslinking process A NONCOLOUR TECHNOLOGY PERFORMANCE ADDITIVES FOR PACKAGING NPE - Orlando, FL - South Hall - Level 1 - Booth S19103 repi.com