Qualitätssicherung bei der Herstellung von Gußeisen mit Kugelgraphit nach dem Meehanite-Verfahren – am Beispiel von Armaturen für die chemische Industrie

Quality Assurance in the Production of Nodular Cast Iron According to the Meehanite Process – with Particular Regard to Valves for the Chemical Industry The application of nodular cast iron for valves, specially for the chemical industry, has attracted particular interest. This is due to the fact that manufacturing methods have reached a high degree of perfection at reasonable costs. Interest is focused on ductile grades GGG-35.3 and GGG-40.3 per DIN 1693 and, with restrictions, on GGG-40 and GGG-50. Maintenance of the desired level and close tolerances of material properties in the casting is the main condition for industrial application. The most important factors in this respect are the manufacturing methods and quality assurance systems employed. Regarding these factors the Meehanite process offers optimum conditions. For control purposes it is important that the properties of the separate test bar and of the casting correspond. Tests carried out on a casting taken from routine production of a Meehanite foundry prove that this is possible. For approval of a foundry as a supplier of castings of this kind the application of a suitable manufacturing method and the presence of a reliable quality control system should be the main criteria.     

Durchstrahlungsbilder-Vergleichsreihe von Gußfehlern in Chemieapparaten aus Gußeisen mit Lamellengraphit

Reference series of radiographs of casting defects in chemical apparatus made of grey cast iron Chemical apparatus of grey cast iron as reaction vessels or storage tanks continue to be of major importance. When subjected to corrosive attack, they must not show excessive casting defects, otherwise the wall thickness will be reduced too much locally. Radiographic testing is generally used for the quality inspection of such apparatus. In order to evaluate casting defects in radiographs, a reference series of radiographs was produced and its system discussed. This series enables not only an evaluation of radiographs, but also makes it possible to fix quality requirements.     

Korrosion von grauem Gußeisen in konzentrierter Schwefelsäure

Corrosion of Grey Cast Iron in Concentrated Sulphuric Acid The Pauling process of regenerating spent sulphuric acid is an example of industrial application of the corrosion resistance of grey cast iron in boiling strong sulphuric acid. The corrosion behaviour of cast iron in boiling sulphuric acid depends on the corrosion potential. At a high corrosion potential, the material shows a stable passive state. In a study on the influence of the alloy components Si, Cu and Sn on the corrosion resistance of grey cast iron, the following results were derived: In the active state, cast iron containing more than 1,4-1,5% Si exhibits a corrosion maximum in 97% boiling sulphuric acid, whereas alloyed grey cast iron with low Si content displays in the active state better corrosion behaviour over the whole concentration range from 93–98% H₂SO₄. When the alloyed cast iron is in the passive state, corrosion resistance increases as the silicon content is reduced and the sulphuric acid concentration is raised.     

Bruchzähigkeit und Ermüdungs-Rißwachstum von Gußeisen

Fracture Toughness and Fatigue Crack Growth of Cast Irons Fracture toughness, elastic moduli and fatigue crack growth rates in air and in vacuum were measured for 17 different cast irons. The graphite shape in the cast irons varied from flakes to nodules, the matrix varied from ferrite to pearlite to martensite. In the fatigue crack growth rate tests, using fracture mechanics methods, it was observed that the fatigue crack growth rate increases significantly as the cyclic stress intensity range approaches the critical value for stable crack growth. This phenomenon was used to determine the fracture toughness of the cast irons. Such toughness data agree well with literature data on the fracture toughness of cast irons. An extensive review of the effects of strength on the fracture toughness of commercial cast irons is presented. In cast irons with flake graphite, cyclic loading results in a reduced modulus of elasticity. This is attributed to the rupture of the graphite flakes under cyclic loading.     

Definition,Messung und Anwendung bruchmechanischer Kennwerte von grauen Gußeisen

Definition, Measurements, and Application of Fracture Mechanical Properties of Grey Cast Irons Fracture mechanical properties were determined of cast irons with lamellar (GGL) and globular (GGG) graphite in a perlitic as well as a bainitic-austenitic matrix. Besides conventional and fracture mechanical tensile tests special attention was paid to fatigue crack growth. Ultrasonic loading appeared to be useful if at small amplitudes a large number of cycles is required for the observation of crack growth. A microscopic investigation of microstructure before and after cracking aided the interpretation of the origin of the measured properties. While the properties of the GGG-materials can be understood by the concepts of elastic-plastic fracture mechanics, lamellar graphite does cause a particular behavior. Notable is the non-linear elastic behavior, crack branching, and formation of satellite cracks, which provide difficulties in defining critical stress intensities K_c as well as the threshold for the start of fatigue crack growth δK_th. Stress induced transformation of residual austenite at the crack tip can retard crack growth by local increase in volume. Proposals are made for a reasonable definition of fracture mechanical properties as well as their application in design.     

Verwendung von statistischen Grundlagen für die Lebensdauervorhersage bei schwingender Beanspruchung

A concept to describe the fatigue lifetime by using statistical methods In order to spend time and money, cyclic loading tests have been usually undertaken with a relative small number of specimens. On the other hand, it is well established that fatigue life data, i.e. the cycle number of crack initiation N_i as well as the cycle number of total failure N_f show a scatter for a given load level. Therefore, fatigue live predictions must be undertaken using statistical methods. In this case it has to be taken into account that the quantity N_f consists of two parts, i.e. crack initiation and propagation. The first one has to be calculated in a statistical manner, whereas the second one with deterministic methods. Therefore, a superposition of statistical and deterministic parts has to be taken into account. Up to now it was estimated that in all cases the failure results from the same damage mechanism. In this case a scatter of fatigue life may be described by the Weibull distribution and characterised by the location parameter and the Weibull exponent. By using the correct density function, all fatigue life data N_i can be plotted in a failure probability P_v(N_i) vs. N_i plot. In case of some Al-alloys no linear dependence between P_v and N_i has been found, indicating that more than one type of defect spectrum may initiate the failure. Indeed, in AlMgSi cold worked specimens two types of cracks, e.g. surface as well as corner cracks, have been found that initiate the failure of the specimens. If was possible to correlate each type of crack with an individual Weibull distribution. By using this procedure, fatigue life can be estimated better than before.     

Verfestigung und Verschleißverhalten von weißen Gußeisen bei abrasiver Beanspruchung

Work Hardening and Abrasion Resistance of White Cast Irons White cast irons are frequently used against abrasive wear under extreme loading conditions. The microsructure and the mechanical properties of these alloys play an important role to control their wear rates. Regarding the mechanical properties, it has been reported that the bulk hardness alone is not enough to describe the wear behaviour. Generally, it has been shown that the work hardening induced by the wear process has an essential effect on the abrasion resistance. In this investigation, using a pin abrasion test, the wear behaviour of Ni-Hard 4 and high chromium white cast irons has been studied. The results of this study contribute to discuss the correlation mechanisms between work hardening and abrasive wear behaviour.     

Beizung von BIOHOCH®-Reaktoren als Vorbehandlung für eine Beschichtung

Pickling of Steel Tanks for Use in Biological Water Purification Plants as a Pretreatment to the Application of an Organic Coating High-level tanks made from structural steel, so called BIOHOCH®-Reaktoren for biological purification of chemical waste water, had to be protected against corrosion by an organic coating. After the usual pretreatment, which means cleaning of the steel surface by sand or furnaceslag blasting, pittinglike corrosion was observed in two cases. Therefore, the required grade of surface preparation was not available. Nevertheless, to get good preconditions for a sufficient service life, both tanks with a volume of about 20 000 m³ were pickled in such a manner, that the final furnace blasting operation furnished the presumed white metal state. The problematic nature of organic coatings, which has recommended the pickling of the steel surface, is discussed. The selection, realization and controlling of this treatment are specified.     

Untersuchungen Zum Temperaturwechselverhalten von Gußeisen - Teil II: Werkstoffwissenschaftliche und metallphysikalische Interpretation

Test examing the temperature shift behaviour of cast iron - Part II: Interpretation according to materials science and metallphysics The first part of this article discusses the most important influences on temperature shock behaviour of cast iron materials and experimental results of the examinations. The presented second article offers an interpretation of theoretical as well as practical examination results according to materials scientific views. A method will be presented determining the lifetime of thermal shock stressed components using activation-energy-stress diagrams and statisticall significant regression-relationships.     

Siliziumcarbid (SiSiC), ein neuer Werkstoff für den Apparatebau

Silicon carbide (SiSiC), a new material for mechanical engineering The state of the art of components made from SiSiC (=reaction sintered, free silicon-containing silicon carbide) is presented. Physical, mechanical properties, resistance against corrosion, methods of joining, costs, and future applications are discussed.     

Atomlagenabscheidung als Werkzeug für die Nanotechnologie

Atomic layer deposition ‐ a tool for nanotechnology The characteristic self‐limiting growth mechanism of atomic layer deposition (ALD) facilitates the control of film thickness at the atomic level and allows deposition on complex surfaces. These features make ALD to a very promising technique for future micro ‐ and nanotechnology. The precursor chemistry is a key issue in ALD.     

Glasartiger Kohlenstoff Sigradur® – ein Werkstoff für Chemie und Technik

Glassy Carbon Sigradur® – a Material for Chemistry and Technology Glassy carbon is a carbon modification characterized by its glasslike fracture behaviour. Raw material, manufacturing, microstructure, and studies on fracture mechanics are discussed and examples for the widespread application of glassy carbon are given.     

Abscheidung von Palladium und Palladiumlegierungen mit hohen Schichtdicken für die Mikrosystemtechnik

Deposition of Thick Palladium and Palladium Alloy Layers for Microsystems Technology Layers of metals and alloys deposited in microstructures usually require to be thicker than the 100 μm which is the approximate height of the structure. The deposited form of noble metals used in microsystems must be non‐stressed, ductile and free of cracks and pores. As the thickness of layers deposited from commercial noble metal electrolytes will rarely exceed 10 μm without loss of quality, developing an electrolyte system suitable for microsystems involves finding appropriate additives and deposition parameters. Details are given of deposit characterisation, the parameters of the deposition technology and some practical examples. Initial results are presented and discussed.     

Polymere Hochtemperatur-Verbundwerkstoffe für Anwendungen als Gleitelemente

High temperature polymer composites for applications as sliding elements Polymeric composites are nowadays frequently used for applications in which friction and wear are critical issues. Quite often, they also have to operate at elevated temperatures, so that the use of high temperature polymers is needed. This overview decribes on the example of sliding elements that can be used e.g in textile drying machines, how matrix, fiber and filler components of the composites can affect their friction and wear properties under sliding conditions against steel counterparts. As a good solution for a composite operating as a sliding element under extrem conditions, polyetheretherketone (PEEK) with 10 weight% of each, short carbon fibers, graphite filler, and polytetrafluoroethylene (PTFE) particles is suggested.     

Dünnschichten als Targets für den Schwerionenstrahl

Thin films targets For the understanding of the interaction between matter and matter ions are accelerated on a fixed target. The targets are self-supporting layers with a thickness between several nanometres up to centimetres. The self-supporting thin films are deposited in high-vacuum evaporation units on a soluble interlayer on a substrate, from which they can be removed. Typical materials are carbon, nearly all the metals, the transition metals and several rare earth materials. Beside the chemical purity fairly often an isotopic purity is required.