Extrusion Asia Edition 2-2018

图4: 有缺点的铸铝加热器 Picture 4: Defective aluminium casting heating 图6: ISOWEMA® 应用 Picture 6: ISOWEMA ® application 图5:加热-冷却组合件 HK218 全保温，蓝色 Picture 5: Heating-cooling combination HK218 fully insulated, blue dustry. The thermal digestion of the ma- terials is effected by aid of electrical resis- tance heater elements manufactured in a vast range of configurations. Run by the owner since the turn of the century, the company has principally specialised in the application of extrusion technology. In the new construction of processing ex- truders the focus tends to be less on the ideal configuration of the heating and cooling of the extruder cylinder than, for example, on the screw geometry or the drive system. Without doubt, however, an exact tem- perature guidance of the molten plastic until it enters the shaping tool is of very great importance for optimum product quality. The requirements can vary greatly: For some processes standard heating-cooling combinations, in which several, narrow ceramic heater bands surrounded by a steel housing in con- junction with low pressure fans, are suffi- cient to achieve and maintain the set temperature values. (Pictures 1 + 2) For processes that involve a high degree of frictional heat, however, it is often very important to have powerful air cool- ing after the heating phase in order to swiftly dissipate the frictional heat gene- rated above the set target value away from the barrel. Here full ceramic heater bands made of a thermally conducting oxide ceramic with cooling ribs located on the rear provide very good results be- cause the heat band surface already pro- vides highly effective air cooling. Extreme cooling demands such as, for example, required for the extrusion of PVC tubing or profiles calls for the addi- tional use of flexible aluminium cooling elements to achieve a significant increase in the air cooling performance. (Picture 3) Without additional costs for a mould or a tool every diameter across a broad range of widths can be catered for. On larger extruder cylinders the perma- nent flush-fitting of the heating systems to the cylinder circumference is of great importance. The failure to ensure this re- sults in a non-uniform heating or cooling of the cylinder and this can even damage the heating elements, because the tem- perature control system, for example, fails to detect an air gap arising between the heater element and cylinder. This in turn puts the heater element under full load, which, however, still fails to reach the target temperature at the measuring point. This can lead to the complete ther- mal destruction of the heater element. Especially prone to this problem are here those systems with embedded heat resis- tors in aluminium. (Picture 4) The highly competitive nature of manu- facturing mass produced articles such as, for example, packaging film or also pro- ducts for the construction industry, as well as the requirement to reduce the "CO² footprint" have meant that full in- sulated versions of extruder heating sys- tems have been in demand. These work in conjunction with convector flap sys- tems to help prevent heat losses. This goes hand in hand with the reduction of activation periods of the heating ele- ments and the low thermal load of the surroundings - and not just during the production phase but also and principal- ly in the heating up and downtime pha- ses, which also results in energy savings, occasionally quite significant ones, for the operator of the extrusion machine. Therefore, investment made in new, up- to-date heating technology can already 21 Extrusion Asia Edition 2/2018