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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. 6 iA Heißkanaldüsen Typ SLT/-DLT Smallest cavity pitches with the new micro flat nozzle type SFT/NFT The given dimensions of the punch-out strip resulted in a grid dimension with a distance of 122 mm between double rows of nozzles and a nozzle pitch of 15 x 9.35 mm for the position of the gates. It was no problem to implement the required nozzle pitch of 9.35 mm. However, the distance of 15 mm between a pair of rows and the separate control of each gate necessitated developing a “twin flat nozzle” 3SFT60S. This “twin flat nozzle” 3SFT60S consists of a nozzle body incorporating two material tubes with hard metal tips and two separately controlled heating elements. It was decided to do without full balancing because of the low part weight and the consequently increased dwell time of the material in the hot runner system. Due to the low part weight and the minimal pitches, the calculation of the pressure drop in a partially balanced hot runner system Customer information has resulted in a very small pressure difference whith no negative impact on the production process. This complete hot runner system requires 66 control points, 64 for the individual cavities and 2 for the manifold. As a “Hot Half”, i.e. with the clamping plate, frame plate and cavity nesting plate, the system was completely wired, assembled and tested before delivery to the customer. www.guenther-hotrunner.com Subject to technical changes 7/12
Heißkanaldüsen Customer information Typ SLT/-DLT Stable and Material Saving Processing of Flame Retardant Polyamides with GÜNTHER Hot Runner Technology As a world leading supplier, Moeller GmbH (Bonn) pro- duces components and systems for automation, command and control devices. Diverse electrical and electronic components made of plastic are used in these systems. Fig. 1 Pushbuttons in command and control equipment (photo: Moeller GmbH) For a long time now Moeller has been using molds with hot runners for sprueless production of these parts. The advantages of hot runner technology over a conventional gating system include savings in material and a reduction in cycle time. When selecting a plastic for electronic components, it is often necessary to take account not only of the design requirements but also of statutory provisions and standards. In the electronics industry, for example, plastic components that are in direct contact with live parts must conform to the IEC Standard (International Electrotechnical Commission) etc. A further requirement is that the plastic must be capable of extinguishing itself after catching fire. Here, Standard 94 of the Underwriters Laboratories has established itself throughout the world as the authoritative standard for classifying flame retardance in plastics. The classification in standard 94 of UL depends on the rate of combustion, time needed for extinction, formation of drops and afterglow time. Depending on the component's function, the following criteria must be met: UL94 V2: Vertical test specimen; self-extinguishing up to 30s after withdrawal of the flame, drips of flaming particles allowed; afterglow max. 60s. UL94 V0: Vertical test specimen; self-extinguishing up to 10s after withdrawal of flame; no drips of flaming particles; afterglow max. 30s. Moeller usually uses PA66 reinforced with 25% fiber glass with flame retardant for housing of electrical or electronic components. This type of material complies with UL94-V2 combustibility grading as well as other standards. A lot of devices from Moeller are also used in areas subject to the ATEX directives (ATEX = Atmospheres Explosibles = potentially explosive atmospheres). Here the requirements set for flammability have recently been tightened so that these components must now meet the requirements in combustibility class UL94-V0. On account of this more stringent requirement Moeller has had to replace the type of plastic it had previously used in a lot of components by an appropriate one classified in conformance with UL94-V0. Depending on the polymer, various flame protection systems are necessary to make a plastic flame-retardant. In the case of the PA66 used here, red phosphorus is used to give flame retardancy. The combustibility class is usually influenced by the quantity of the flame protection system used. Depending on the quantity, the red phosphorus used here reacts more or less strongly to temperature. Accordingly overheating during processing can cause thermal damage to the flame retardant. The gases arising as a result can form deposits on the mold and lead to corrosion. Occasionally the gases can even inflame. The PA66 with 25% glass fibers originally used by Moeller (combustibility class in conformance with UL94- V2) could be processed easily with the existing hot runner system. However, after changing to a PA66-GF25 conforming to combustibility class UL-V0, serious problems arose when processing with this hot-runner system. In spite of the processing temperatures of 275…295°C being appropriate for the material, extremely severe deposits appeared on the molds. The molds had to be cleaned every 30,000 to 35,000 shots. In addition to cleaning the mould deposits, the mold inserts had to be replaced after every 250,000 shots because of corrosion. The reason for this heavy formation of deposits and corrosion in the mold was the significantly excessive rise in temperature in the hot runner nozzles in connection with the higher quantity of red phosphorus in the PA66. With a temperature of 290°C set at the control unit, temperatures of approx. 360°C were sometimes measured in the nozzles. This caused a reaction in the flame retardant. 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 7/12 Subject to technical changes iA 1.5. 7
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