Heißkanaldüsen Typ SLT/-DLT Customer information

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Heißkanaldüsen Customer information Typ SLT/-DLT Nozzle design for injection moulding on tandem tools 50% of cycle time can be saved by switching from standard injection moulding production to tandem technology. A precondition here is the ideal adaptation of the melt flow path and the nozzles to suit the altered process. To produce glass-fibre reinforced polyamide covers, GÜNTHER Hot-Runner Engineering developed within a very short time a nozzle construction that offered the advantages of low costs, reliable heat management and easy installation. Objectives which even in normal economic circumstances would rank among the most important for a new process are of particular significance in times of crisis. These are to manufacture components in as short a time as possible and at costs as low as possible. The fact that tandem technology in injection moulding can reduce cycle time by up to 50% induced a major German manufacturer of motor tools to change over to this technology for the production of glass-fibre reinforced polyamide covers for work tools. Tandem technology makes use of the unproductive cooling time in injection moulding. Ideally this doubles the output from a standard machine. The process runs as follows: after closing the first parting level of the mould and injecting the melt, the second parting level opens during the cooling process, the parts fall out of the mould, the parting level closes and the melt is injected. While the components are cooling in the second level, work can be continued in the first level. The advantages for the process of this overlapping are shorter time requirements and lower costs. Fig. Mould with tandem technology: One challenge is the melt flow path from the first to the second parting level. www.guenther-hotrunner.com 7/12 Subject to technical changes iA Before the process changed over to this technology the assembly, which consisted of two differently-sized components, was produced on two injection moulding machines in two different moulds. In tandem technology the production of the assembly could be combined in one mould so that there was no longer any need for a second machine. Keeping mould costs low To implement the technology, the injection moulder got in touch with T/Mould GmbH & CO KG, Bad Salzuflen, the sole supplier of tandem technology, at the beginning of 2008. “A major challenge presented by such a project is to keep tool costs as low as possible”, explains Daniel Gersmann, who is the supplier's Project Consultant. “In the current project the main challenges were the design of the nozzle and melt flow path. The tandem technology side of the project did not present any great problems because the component geometry is relatively simple.” To find the best solution, injection moulders and suppliers of tandem technology drew on the know-how of Günther Heisskanaltechnik GmbH in Frankenberg (Eder). The hot-runner specialist developed a system for the application in which the functionality of the complete 2+2cavity mould could be produced with two nozzles. The alternative to this would have been a more complex hotrunner system with main manifold and sub-runners for injection for both components. The simple layout reduced the costs of the nozzle construction by more than half compared to the redirection system. Combination of hot-runner and cold-runner technology “Looking back, we actually built the system twice”, remembers Carlo Rasi, sales representative for the Frankenberg hot-runner specialist. “The first solution comprised a large hot-runner system with which the melt was conducted through main manifolds and sub-runners to the hot-runner nozzles; the transfer nozzle was constructed as a valve gate nozzle.” The original idea was that in addition to the nozzle in the first level, two nozzles with their heads lying against each other would be used in the second level. “However, this solution not only required a larger mould but also a larger injection moulding machine and would accordingly have increased costs. Furthermore”, continues Rasi “such a solution would not have been ideal because of the heat loss.” For any questions, please contact our Application Engineering department at + 49 (0) 6451 5008-31 or -63. The information is given in accordance with our present-day knowledge and is meant to provide technical background. 1.5. 24
1.5. 25 iA Heißkanaldüsen Typ SLT/-DLT Nozzle design for injection moulding on tandem tools To avoid these disadvantages, the hot-runner specialist in consultation with the heater supplier developed a special solution for the second level in the form of a transfer nozzle, which on the outside is identical to the suppliers' SHT nozzles with two-part shaft. Here, the basic idea of two nozzles was maintained and optimised so that they could be produced in just one component. Fig. The special nozzle design in the second parting level cuts costs and reduces the construction size. In the new system an open passage was fitted on the cold-runner side for the first parting level. During the injection into the first level a plastic plate with a defined wall thickness is formed which allows injection through to the second level. Before that this plate provides a closure between the first and second parting levels. When injecting into the second level, the melt pressure and enthalpy of the melt are sufficient to inject the melt jet through the plate to the transfer nozzle. Customer information Based on T-Mould's experience and the injection trials conducted in the hot-runner specialist's own pilot plant experimental facility, it was possible to define the wall thickness of the plate in a way that would ensure that the process would function perfectly as of the first shot. The process with the aid of the plastic plate has al-ready been in use in practice for a long time but so far usually with polymers that have not been reinforced. In the current case a semi-crystalline, glass-fibre reinforced material is used, which makes greater demands on process reliability. Low losses during thermal conduction In a very short time GÜNTHER and the heating supplier were able to find a solution in terms of the best possible way to heat the transfer nozzle. A two-component shaft with titanium cap as well as nozzle heating adapted for this application make it possible to minimise the heat loss in the nozzle so that only very little is lost in the conduction of heat to the nozzle tip. The nozzle heating consists of only one component so that there are no significantly cold areas. “A further challenge presented by this project was the short time available”, remembers Rasi. The individual parts of the nozzle were developed, designed and specially produced within four weeks. There was no time for any extensive tests before the installation of the nozzle assembly. Nevertheless the design functioned from the beginning without any problems occurring at all, which of course is very unusual for a completely new development. “From the first shot, the temperatures were a uniform 280 °C in the material manufacturer's default window. The pressure curves did not show any irregularities and there were no problems starting up again after an interruption in production. At no time were there any signs of damage to the material. The production of the new tandem tool commenced in the autumn of 2008; since then production has been running perfectly with a 40% reduction in manufacturing costs. In the meanwhile GÜNTHER has implemented more projects with the new nozzle design, which is basically suitable for every family of mould if there is not too great a difference in injected weights in the first and the second levels Dipl.-Ing. Jörg Essinger Applications Engineering Manager For any questions, please contact our Application Engineering department at + 49 (0) 6451 5008-31 or -63. The information is given in accordance with our present-day knowledge and is meant to provide technical background. www.guenther-hotrunner.com Subject to technical changes 7/12
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