Thermoplastic polyurethanes are demanding high-performance materials that can reach their full potential only by a precise and optimum processing.
All process steps in the processing of TPU (pre-drying, molding, post-treatment) are associated with a high consumption of energy. Follwoing the recommended processing parameters is very important.
The energy efficiency of the processing equipment is of great importance for economic and environmentally friendly processing.
Therefore, we recommend paying attention to modern, precise controlling and energy efficient machinery.
Optimum processing of Desmopan® is only possible on screw-type injection molding machines. Well plasticated, homogeneous melts can be produced with single-flighted, three-zone screws of normal length. If a high plasticizing capacity (throughput) is needed, longer screws can be used (Fig. 1).
Fig. 1 Injection molding screw for processing Desmopan
Due to the high shear stress, short-compression-zone screws are unsuitable. The high plasticisizing energy needed for TPU requires a high torque for the screw drive. Insufficient torque leads to fluctuations in the screw speed and thus to non-uniform homogenizing.
To a limited extent, higher cylinder temperatures may yield better results, although there is a risk of the material overheating. The nozzle and cylinder head should be designed in such a way that there are no dead corners in which the material can become lodged and thus become thermally damaged.
Accurate temperature control for the cylinder and nozzle heating system is essential.
Care must be taken to ensure that the nozzle is heated evenly over its entire length. Only in this way can local overheating or possible "freezing" of the melt be prevented.
Molten Desmopan® is neither corrosive nor abrasive. For this reason, there is no need for any special steel alloy or armor-plating of the screw.
Fig. 2 Injection molded gear shift knobs