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Heißkanaldüsen Customer information Typ SLT/-DLT Hot runner systems for plastics filled with metal or ceramic powders The MIM (Metal Injection Molding) and CIM (Ceramic Injection Molding) technologies use injection molding process to produce metal and ceramic components which could not, or only with considerably more effort, be produced by machining. With these methods threedimensional components, e.g. for medical engineering products, can be molded in only one working step with no need of subsequent machining. Without well adapted hot runners it is hardly possible to ensure manufacturing process reliability. Metal and ceramic powder filled plastics are used in many different fields. Examples of use of MIM are components for consumer products like ballpoint pens or for medical engineering products. Products manufactured by CIM are in demand where ceramics are required for insulation, often in conjunction with high temperatures. Sample applications can be found in the lighting industry. Both of the processes are relatively easy to use and make it possible to produce components without subsequent machining. Complex components can be manufactured this way. An application example for the MIM technology is an implantable infusion pump used in pain management for chronically ill patients. This device, installed in the abdominal wall, is applied for the measured dispensing of pain medication into the human body. The base plate was formerly manufactured by machining from a special, relatively expensive titanium alloy. This method was not only time-consuming but also expansive because of swarf. However, to realize the idea of manufacturing this component by MIM was not so easy at the beginning. Although it is normally quite easy to manufacture three-dimensional components by injection molding, the difficulty in this case was that the base plate had a large diameter and significant changes in wall thickness. This problem has been solved by injection molding the component with three parallel hot runner nozzles. It has resulted in short flow paths and more even pressure distribution to yield a component which is manufactured in only one working step without the necessity of subsequent machining. Lower production costs are yet another compelling factor. With the MIM and CIM processes, a metal or ceramic powder is mixed with a binding agent, often polyethylene or polyoxymethylene, and a special wax, and then granulated. This mixture, called a "feedstock", can be processed by injection molding like any conventional plastic material. The plastic material is then removed from the molding, the so-called "green part", by heating. After debinding, this component has a porous structure because of the removal of the plastic material and is called the "brown part". By sintering of this brown part the metal and ceramic constituents are baked together to form a component with a homogeneous structure whose density and resistance does not differ from a conventionally manufactured steel or ceramic component. The advantages of e.g. a metal component, like high mechanical resistance and high conductivity, are combined with a relatively simple way of manufacturing. 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 Picture: The titanium alloy base plate (below) of an implantable infusion pump was formerly manufactured by a complex machining process. Today the MIM technology allows for scrap-free manufacturing without subsequent machining. (Photo: TiJet) 1.5. 16
Heißkanaldüsen Typ SLT/-DLT Customer information Hot runner systems for plastics filled with metal or ceramic powders Basically, conventional injection molding machines can be used for CIM and MIM. But if a manufacturer wants to use these processes on long term, wear-resistant cylinders, screws and non-return valves should be used because these components are submitted to an increased abrasion due to metal and, even to a higher extent, ceramic powders. Discussions with feedstock manufacturers and plastic processors have shown that 80 to 90% of the parts produced by using MIM and CIM are manufactured by means of a cold runner with a sprue rod. A big fraction of the sprue rod can be recycled, nevertheless it would be very promising to avoid this production step by using hot runner systems. A very homogeneous temperature control in the hot runner is required, since the materials have a very small processing window. Variations of the temperature lead to a segregation of binder and powder which results in shrinkage differences and finally in the formation of cracks in the component during the sintering process. For these applications, GÜNTHER Heisskanaltechnik GmbH recommends using its hot runner nozzles e.g. of the _HT type which are designed to meet higher requirements. The patented two-stage nozzle shaft guarantees an excellent isolation at the forward section of the shaft, providing for an extremely low heat loss between hot runner nozzle and cavity, and for a very homogeneous heat distribution within the nozzle. 1.5. 17 Material tube (25 W/mK) Heater Air (0,04 W/mK) Gap solidified plastic (0,2...1,2 W/mK) iA Picture: The two-stage shaft of the SHT type nozzle and the frozen plastic material which forms a "cap" around the nozzle provide for optimized isolation towards the cavity and therefore produce a homogeneous temperature profile in the nozzle. Melt Shaft made of titanium alloy (7 W/mK) Open nozzle tip (100 W/mK) In addition, the frozen plastic material forms a "cap" around the nozzle, thus providing thermal separation between hot runner nozzle and cavity. However, this feature produces quite the opposite effect for metal filled plastic materials because of the metal powder conductivity. In this case the mixture of plastic material and metal powder would draw the heat off the nozzle. That's why the supplier equip the nozzles used for MIM with special insulating caps made of a highly heat resistant plastics like polyetheretherketone (PEEK) or polyimide (PI) to provide thermal separation. A tubular titanium shaft located around the hot runner nozzle additionally improves the insulating effect. This is a certain distinctive feature of the products supplied by Günther, since most of the hot runner nozzles on the market have no two-stage shaft and achieve the sealing by direct metallic contact with the material tube in the mold insert. This leads to a very high heat loss which has to be compensated by a higher temperature in the hot runner nozzle. This causes an excessive rise of the temperature as well as temperature variations, and therefore the materials cannot be processed in a reliable way. With the MIM technology, the parts are often molded by direct gating, and not via a sub-runner. Nevertheless, a relatively large gating point must be used in this case to obtain the necessary throughput and to transfer sufficient heat into the gate point. This is necessary because the metal-filled material transfers some of the heat into the cavity, and the melt freezes quickly due to the high filler content. However, with the CIM technology a sub-runner is often used. Here, too, a large gate point is of importance in order to cause as little as possible shear stress and to transfer the melt as quickly as possible into the cavity. With regard to wear resistance, hot runners have to meet severe requirements, for both MIM and CIM. The products of Günther Heisskanaltechnik have nozzle tips made of hard alloy to provide reliable wear protection. For this reason high life times are possible with no need to change components of the nozzle. 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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