Liquid silicone rubber (LSR) is primarily used in injection molding. Foamed molded parts made of LSR are almost nonexistent because the process reliability of LSR foam injection molding is currently not given. It makes sense to have suitable foaming processes for this material as well, because the density of this elastomer is about 1.15 g cm−3. With the injection molding process presented herein for foaming LSR, density reductions of up to 40% can be achieved. In this process, up to 3% by weight of water is added to the material. In addition, the hardness of the component changes, it becomes softer. Especially in the case of hardness, the process parameter mold temperature has a decisive influence, as it determines the pore size in the component. Herein, the structural properties of the silicone foam are now discussed as a function of the process parameters and additives for foaming. Thus, with the new process, material can be saved, the haptic properties of components can be changed, and a stable processing method for foamed components made of LSR is found.

No abstract

Due to their valuable properties (low weight, and good thermal and mechanical properties), glass fiber reinforced thermoplastics are becoming increasingly important. Fiber-reinforced thermoplastics are mainly manufactured by injection molding and extrusion, whereby the extrusion compounding process is primarily used to produce fiber-filled granulates. Reproducible production of high-quality components requires a granulate in which the fiber length is even and high. However, the extrusion process leads to the fact that fiber breakages can occur during processing. To enable a significant quality enhancement, experimentally validated modeling is required. In this study, short glass fiber reinforced thermoplastics (polypropylene) were produced on two different twin-screw extruders. Therefore, the machine-specific process behavior is of major interest regarding its influence. First, the fiber length change after processing was determined by experimental investigations and then simulated with the SIGMA simulation software. By comparing the simulation and experimental tests, important insights could be gained and the effects on fiber lengths could be determined in advance. The resulting fiber lengths and distributions were different, not only for different screw configurations (SC), but also for the same screw configurations on different twin-screw extruders. This may have been due to manufacturer-specific tolerances.

This paper presents the impact of accelerated aging on selected mechanical and thermal properties and VOC emission of polypropylene composites filled with glass fiber with different fiber contents. Due to their positive properties (good thermal and mechanical properties, low weight), glass fiber reinforced thermoplastics are becoming increasingly important. Fiber reinforced thermoplastics are mainly produced by injection molding and extrusion, whereby the extrusion compounding process is primarily used to prepare fiber-filled granulates while the injection molding process is used to manufacture products. In this study, short glass fiber reinforced thermoplastics (polypropylene) are produced on a twin screw extruder. Then, tensile test specimens are produced by injection molding. The glass fiber content is between 20 and 40 wt%. In order to investigate the long-term stability, the test specimens are artificially aged in accordance with ASTM 1980. The thermal, mechanical, and emission properties were evaluated by means of differential scanning calorimetry (DSC), tensile tests, and TDS-GC-MS analysis prior to and after accelerated aging. The objective of this study was to investigate the effects of thermal aging on crystallinity and mechanical properties and on VOC emission of glass fiber reinforced isotactic polypropylene.

Internal heat exchangers are often employed in solar thermal applications as well as in many other applications that involve heat, and, for the most part, consist of metallic materials (copper, stainless steel). Corrugated stainless steel tubes are easy to assemble, and are commonly used in various storage geometries. In order to significantly reduce costs, alternative materials, such as plastics, can function as excellent substitutes. Alternative heat exchangers for the following examinations using various materials and an extrusion process were produced. Subsequently, the heat exchangers were examined in regards to the heat they transfer. The heat transfer coefficient and the thermal conductivity of all materials were determined.