Institut für Werkstoffsystemtechnik Konstanz - WIK
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Zur Umsetzung "praxisnaher Modelversuche" ist am Institut für Werkstoffsystemtechnik (WIK) der HTWG Konstanz ein systemdynamisch optimiertes Zwei-Scheiben-Tribometer (ZST) entwickelt und aufgebaut worden. Im grundlegenden Aufbau entspricht das Tribometer einem klassischen Zwei-Scheiben-Modellprüfstand ähnlich dem Amsler Rad-Schiene-Prüfstand. Der Prüfstand ist jedoch sensorisch, aktorisch und dynamisch speziell auf die Simulationsprüfung von Zahnflankenkontakten von Kleingetrieben aus dem Automobilbereich ausgelegt. Das bedeutet, der Prüfstand kann die für Zweischeibenversuche typischen Parameter wie Anpresskraft und Probekörperdrehzahl hochdynamisch anpassen. Die Dynamik ist entsprechend so ausgelegt, dass die Anpassung mehrmals über eine Umdrehung der Probekörper erfolgen kann.
Steels for plastic injection moulds are available in different alloy compositions. Mechanical properties, such as wear resistance and hardness, are the most important properties of these steels. Corrosion resistance of these steels is also an important property, which is why there are high-alloy steel compositions.
The cooling and temperature control systems for moulds have different types of fluid circuits. There are open and closed systems, which has a direct influence on the oxygen content in the fluid. There are also different types of water, such as hard and soft water, and different types of additives, for example biocides or corrosion inhibitors.
The aim of this work is to investigate the corrosion behaviour of various typical plastic mould steels under high and low oxygen conditions. With these results, a mould tempering device will be developed that controls the oxygen content in a closed water-based liquid system. If this is successful, chemical additives can be dispensed with and good corrosion behaviour can be achieved, even for low and unalloyed steels.
Steels with different chromium contents typical for this application were selected for the tests. Heat treatment was carried out in a typical way for these steels. Corrosion behaviour was measured by open circuit and potentiodynamic measurements in soft water at 50°C. Oxygen-free and oxygen-saturated conditions were investigated.
Thermal shape memory alloys show extraordinary material properties and can be used as actuators, dampers and sensors. Since their discovery in the middle of the last century they have been investigated and further developed. The majority of the industrial applications with the highest material sales can still be found in the medical industry, where they are used due to their superelastic and thermal shape memory effect, e.g. as stents or as guidewires and tools in the minimal invasive surgery. Particularly in recent years, more and more applications have been developed for other industrial fields, e.g. for the household goods, civil engineering and automotive sector. In this context it is worth mentioning that for the latter sector, million seller series applications have found their way into some European automobile manufacturers. The German VDI guideline for shape memory alloys introduced in 2017 will give the material a further boost in application. Last but not least the new production technologies of additive manufacturing with metal laser sintering plants open up additional applications for these multifunctional materials. This paper gives an overview of the extraordinary material properties of shape memory components, shows examples of different applications and discusses European trends against the background of the most recent standard and new production technologies.
Martensitic stainless steels has a wide use, for example for blades, knifes or cutter. The best corrosion resistance of these materials is in hardened condition. For better mechanical properties a tempering is normally applied to increase the durability. The tempering is also reducing the hardness and finally the corrosion resistance. Austempering is meanly used at low alloyed steels and brings a good compromise between durability, hardness and corrosion resistance. For martensitic stainless steels, austempering is normally not a topic because of the very long tempering times.
This work shows first results of austempering of some standard martensitic stainless steels and the influence to corrosion resistance. For reference, hardened and also hardened and tempered specimens were investigated. The corrosions resistance was investigated by electrochemical methods.
Dass sich Stoffe bei Temperaturänderungen zusammenziehen beziehungsweise ausdehnen, ist eine uralte Erkenntnis. Diesbezüglich stechen Formgedächtnislegierungen heraus, da diese die verblüffende Eigenschaft besitzen, sich bei Temperaturänderung ungewöhnlich rasch zusamenzuziehen beziehungsweise auszudehnen. Eine physikalische Besonderheit, die sich auf vielfältige Weise nutzen lässt.
These days, medical applications of shape memory alloys (SMAs) can be found in cardiovascular devices, gastroenterology and urology as well as in the area of orthopedic implants, orthodontic devices and clinical instrumentation. Their functional properties combined with excellent biocompatibility increase the possibility and the performance of minimally invasive surgeries. Overviews of existing applications can be found in [1-2]. Within the medical field, most of the applications with shape memory (SM) material take advantage of the superelasticity of NiTi SMAs. In contradiction to the superelastic or mechanical SM effect, the application described in this study uses the thermal SM effect for a new medical implant. Before explaining the SM driven intramedullary bone nail in detail, a short introduction to the bone elongation technique is given.
The background of this application on based in the medical fact that normally any tissue reacts to an injury with repair and healing processes through multiplication of cells. If after a transverse osteotomy a strain stimulus is activated, for example by tensile stress, this multiplication of cells and new formation of tissue may be continued for any length of time. Due to this mechanism, even considerable loss of bone caused by fractures or congenital defective positions, may be compensated without bone grafts. The technique of callus distraction by means of external fixation or intramedullary nail stimulates the formation of callus in the bone gap. Callus is the repair tissue of the bone generated in the fracture gap in case of bone fracture or osteotomy. The gap to be bridged should not be wider than 1 mm per day [3]. The process starts with the exudation of callus around the ends of the broken bone. At first, callus is more like a fibrous tissue. Later it hardens due to deposition of calcium and eventually it is converted into true bone. Three weeks after severance, the vascular system is formed. An overview of current bone lengthening techniques, also called callus distraction, can be found in [3]. External systems are normally used for the extension of bones, the bone fragments being fixed on rings by wires. The decisive disadvantages of those external systems are primarily the considerable risk of infection due to protruding wires, noticeable discomfort for the patient because of the external rings, a coarse cosmetic result because of scarring, as well as rather long hospitalization.
Therefore, internal bone extension systems are of great interest to orthopedic surgery.
