A new high-output extrusion die for large HDPE or PP pipe (110 to 2000 mm OD) combines water-cooling of the melt before it leaves the die with air cooling inside the pipe has been developed by Cincinnati Extrusion. The combination can either double pipe output or reduce downstream cooling length by half. The Kryos die has three parts: melt distribution, melt cooling, and shaping. The cooling and shaping parts have a number of separate chilled-water cooling loops. The large-diameter cooling section in the middle of the die has several chilled-water spirals, which make the die so large that it's mounted in its own motorized C-clamp to remove it for die changes and cleaning. The elongated final shaping stage is sectioned lengthwise into segments that have both water-cooling loops and heating for tight temperature control to maintain uniform wall thickness of the pipe. In addition to water-cooling the melt, the Kryos die sucks ambient air through the cut end of the pipe, back through the hot pipe, and out a hole in the middle of the die. This air flow renews the layer of air next to the inside surface of the pipe, which otherwise heats up and acts as an insulator. Cincinnati Extrusion calculates that energy use with its KryoSys line is less than half that for standard pipe extrusion.
The Kryos die requires an air suction unit behind the die (drawing 3 kW ) and a water chiller for the die (5 kW ), but then needs only one 9-meter vacuum calibration tank (10.5 kW ) and four 6-meter spray cooling tanks (4 kW each). Cooling-water circulation and heat exchange in all the tanks add another 122 kw, for total energy use of 156.5 kW . In a standard pipe line, downstream cooling uses one 9-meter and one 6-meter vacuum calibration tank (10.5 kW each) and ten 6-meter spray cooling tanks (4 kW each). Much higher volume of cooling-water circulation and heat exchange takes 320 kw, for total energy use of 381 kW . Heat removed by KryoSys air cooling can also be easily recycled for further energy savings. Drying and preheating plastic pellets in the hopper, for example, reduces energy consumption at the extruder by another 10%. Machine components are arranged slightly differently with KryoSys. The extruder is placed off-center from the die to allow for the air hole and suction unit behind the die. The die then feeds melt via an IRIS 40 spiral distributor at the edge of the die. Downstream spray tanks are spaced 4 to 6 ft apart, so pipe passes through ambient air (without sagging). This balances internal and external cooling. With a Kryos die, the pipe also has to be cut by a swarfless cutter to avoid sucking fines back through the hot pipe and into the suction pump.
Extruding the pipe at a lower temperature and cooling it evenly inside can improve pipe quality by reducing residual stress. The great advantage of this particular pipe die is an innovative melt cooling system inside the die. Thanks to this system, it has become possible to start cooling the melt in the die, which allows a substantial reduction in the length of the cooling section. The lower melt temperature also brings about a significant increase in viscosity at the point of exit from the die, which counteracts sagging especially in thick-walled pipes. Moreover, KryoS features a large internal aperture, which allows air cooling of the extruded melt. The KryoSys system is rounded off by a highly efficient pipe cooling section. In this aggregate, the pipe is cooled simultaneously from the outside and the inside by an ingenious combination of water and air cooling, which permits a further shortening of the cooling section. Another advantage of KryoSys is the system's great in-production energy saving potential. Thanks to its direct drive, the Rapidex high-speed extruder operates with an extremely high level of energy-efficiency. Through a reduction in the number of vacuum and spray cooling baths required for the downstream aggregates and the optimized cooling system consisting of water and air cooling, energy consumption can be cut by up to 71kW (about 27 kW are saved by the reduction in the number of circulation pumps, and about 44 kW by the fact the less water is circulated). Another source of energy savings is utilization of the heat set free by the pipe cooling system in the die. With KryoSys, this energy can be used for material pre-heating. Thus the torque of the extruder can be reduced, resulting in energy savings of up to 95 kW. By combining all of these measures, a total reduction in energy consumption of roughly 186 kW can be achieved.
With energy costs of 0.10 EUR/kWh and 6,000 operating hours per year, this adds up to about 100,000 EUR in annual savings for a single extrusion line. Kryosys lines lend themselves to the production of smooth mono-layer and multi-layer PE or PP pipes with diameters ranging from 110 to 2,000 mm. They are also suitable for the production of corrugated pipes. Total investment cost for a KryoSys line is highly competitive compared to conventional extrusion equipment.
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