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Glass filters are often used in the field of medical technology and chemical analysis to separate particles of a defined size out of liquids. Depending on the application, different pore width from 1.6 μm to 500 μm are necessary. Glass materials are particularly suitable, because a high purity, the chemical resistance and a high thermal resistance of the filter are necessary. Traditionally, these glass filters are produced by conventional sintering. In the new investigations, selective laser sintering is investigated as an alternative method. The conventional sintering process allows defined pore sizes to be adjusted by varying the sintering time. The high purity of the glass filters can be achieved by a binder-free production. The material properties of the glass material, such as the chemical resistance or thermal stability is maintained by the sintering process. Typically, fused silica or borosilicate glasses are used as basis materials. High-temperature selective laser sintering (HT-SLS) is an additive manufacturing process for the production of silicate and porous components. This manufacturing technology allows complex and unconventional geometrics to be realized efficiently and flexibly. For this purpose, the volume model to be produced is first separated into the desired layer geometry and number of layers. In the subsequent specific process cycle, the glass powder is distributed by a squeegee on a building platform in a defined manner. A solid material layer is created by means of scanning CO2 laser radiation. After lowering the building platform and transporting the powder again, the component can be generated layer by layer. For the production of the glass filters by HT-SLS, initial investigations are carried out with synthetic and natural fused silica glass powders with particle diameters in the range of 19... 78 μm in spheroidized and vitrified form. A laser sintering furnace has been specially designed for the HT-SLS, which achieves process temperatures up to T = 1000 °C as well as low contamination of the glass powder. In addition, material-specific scan and parameter concepts are developed. A high component quality can be achieved by combining a hull-and-core scan strategy with a 180° scan field rotation each sintered layer. Also a bidirectional beam guide and a material-specific parameter concept is needed. The absorption of CO2 laser radiation and the heat-conduction of the powder are supported by the process-dependent plasma and the preheating of the building platform. The generated porous components are investigated with regard to the density and the bending strength. Component densities of ρ = 65 % and bending strengths of σ = 13.6 MPa are achieved. Basically, HT-SLS is an alternative method to the classical sintering process of glass powder to produce glass filters. In particular, an increase in efficiency with regard to the producible component geometry of the porous components can be achieved. This new technology offers a high degree of innovation, while at the same time requiring a high level of research.
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