HOT RUNNERS | TECHNOLOGY
the melt-bearing pressure tube. This design ensures an absolutely homogeneous temperature profile over the entire length of the nozzle up to the gating area. The special screw technology with connecting nut allows free rotation of the nozzle until the screw connection is finally fixed and thus precise positioning of the connecting cables. This minimises the required installation space. The fully balanced manifold has an edge length of just 55 × 55mm. As a result, the overall flow path length and the melt volume to be exchanged in the system is reduced. This offers particular advantages when processing materials with critical residence times in applications with low shot weights. For use on small injection moulding machines, the system is only available as a complete hot half in a 4-drop version. The nozzle grid is 30 × 30mm. In order to realise higher-cavity systems with standard moulds, several of the 4-drop valve gate modules can also be used in combination with a common synchronous plate and a bridge manifold. A 16-drop system can be realised with a compact mould size of 256×346 mm. Since the bridge manifold can be kept simple, the general advan- tage of short flow path lengths remains even with such a configuration. FDU Hotrunner is a recently formed company to develop further and distribute the Flat Die Unit (FDU), an open hot runner nozzle system for injection moulds. The technology was originally a developmental synergy project of Haidlmair Group companies under its research and development department. With the FDU the plastic flows evenly into the cavity through a defined narrow gap, instead of a small pin gate. It is particularly suitable for use with polyolefins. The FDU is claimed to achieve significant
reductions in cycle times and injection pressures, resulting in higher productivity. Other advantages include optimum effect of holding pressure, shorter cooling times, reduction of shear, and improvements in part quality. It also offers benefits with the use of new and recycled materials. The company adds that the FDU is particularly suitable for the processing of regranulate. For example, clogs at the throat to the cavity are almost impossible with large slot geometry. Due to its large cross-sectional emitting area, the FDU causes considerably lower shear stress in the plastic melt, therefore critical materials and additives can be processed easily. Despite the large outlet cross- section to the cavity, the FDU has optimal tear-off behaviour and optimum heat balance, which provides a larger processing window. In addition, the specific pressure loss in the FDU
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nozzle is less than in a round die. The material is processed gently and depending on the material type, a higher internal mould pressure is available. A higher injection speed, higher level of in-mould pressure and larger outlet cross-section make the emphasis better and more effective in the compo- nent. This allows a reduced cycle time. The macromolecule chains of the regranulate are not degraded, meaning that the material and compo- nent properties are retained. Due to lower shear, there is almost no increase in the friction-induced melt temperature, which has a positive effect in processing.
With the FDU, there is no or extremely reduced deposit formation in the mould and reduced outgassing and odours on the injection moulding machine. General material fluctuations when processing recycled plastics are compensated by the large outlet cross-section of the FDU nozzle. This means that higher proportions of recycled plastic in components are possible, due to lower shearing of the melt by the FDU.
Hot runner cleaning SIPA has developed the Xactive-Cleaning process to cut dust in PET preform hot runner systems. In addition to mechanical or electrical issues that can affect the efficiency of a hot runner system, dust can also be a problem. Over time, PET powder builds up inside the cylinders of the actuators. Initially, this powder does not cause any problems, but as it accumulates, it inhibits the movement of the pistons, eventually severely compromising the quality of the preforms. If not treated, this accumu- lation can cause the system to seize up completely. SIPA has developed solutions that keep dust
production at low levels, especially when moulding systems are running with virgin resins. However,
Below: The XActive- Cleaning system from SIPA cuts dust in PET preform hot runner systems
November/December 2020 | INJECTION WORLD 51
IMAGE: SIPA
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