Untersuchung der Verteilung und Intensität filamentierter Barrierenplasmen für die Behandlung von Oberflächen

The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit.     

Ein verbessertes Verfahren für die Auswertung von Treppenstufenversuchen

An Improved Method for the Evaluation of Staircase Tests The assessment of the endurance limit by a time- and cost-saving methode - taking into account the mean, the scatter and the confidence limits - is an important engineering challenge. Among the many methods used up to now, only the staircase method developed by Dixon and Mood in 1948 specifies the confidence limits of the mean and standard deviation. Based on certain considerations it has to be doubted, however, wether the method of Dixon and Mood evaluating the “less frequent occurrence: failures or runouts” gives reliable estimates and confidence limits. Using a large numer of staircase tests, randomly computer-generated by way of the Monte Carlo-method, the evaluation method of Dixon and Mood was examined. An important result was that the estimate of the standard deviation is always too small and the use of the “less frequent occurrence” does not result in optimum confidence limits. The method was therefore improved considering all accurrences: failures and runouts in the evaluation. The new method for the evaluation of the estimate of means, standard deviations and their confidence limits is outlined. Moreover, an optimum way to plan staircase tests is explained. Finally a practical application of the new method is presented.     

Herausforderungen an Füge‐ und Oberflächentechnik für zukünftige Leichtbaukonstruktionen im Automobilbau

For the reduction of the weight of vehicle hot‐rolled magnesium alloys as well as carbon fiber reinforced plastics (CFK) shall be integrated into the body structure. Both light weight materials electrochemically are not compatible with galvanized steels or aluminium alloys, unless great efforts of corrosion protection measures are taken. From electrochemical investigations an oxidceramic surface layer deposited by plasmachemical oxidation can be recommended as a promising solution. The low‐porous oxidation deposit with limited insulation effect can be painted by e‐coat in high quality after joining in the body shop and before the full paint system will be deposited. In opposite to magnesium CFK parts have, however, electrochemically a very noble character causing galvanic corrosion of attached metallic parts when the carbon fibers are not fully embedded in the matrix or damaged by the cutting. Only joining elements made from stainless steels or titanium alloys (e. g. Ti‐6Al‐4V) are suitable for the joining of CFK by screwdriving and riveting technology to avoid galvanic corrosion. From view of compatibility of materials, a severe anodic corrosion risk can be eliminated by isolation through adhesive bonding in the flanges and an additional sealing to prevent from electrolyte ingress.     

Anwendungen der Oberflächentechnik in der Raumfahrt

Ever more challenging missions for the scientific investigation of space as well as the increasing use of satellite‐based services in the fields of telecommunication, navigation and earth observation require the development of more efficient, more economical and more resistant space technologies and systems in the future. A study of the VDI Technology Center on behalf of the German Aerospace Center points out, that nanotechnology, in particular in the range of surface technologies, could supply significant contributions and technological breakthroughs for the development of future space travel systems. Applications of friction and wear reducing layers, thermal protection layers, magnetoelectronics, x‐ray astronomy and thin film technologies for space structures are presented.     

Plasmachemische Mikrostrukturierung von polymeren Oberflächen für Pharmazie und medizinische Diagnostik

The plasma masking technology is a method applied to get locally selective, physical‐chemical structuring on nearly all plastic surfaces in the micrometer range. Such generated chemically functionalised, polymer‐based surface structures are suited for use as biochips and will promote the application of low priced polymer materials with appropriate modified surfaces. Provided with a biochemical treatment for analytical methods, they are used in medical diagnostics and pharmaceutical drug research. This technique supports the increasing application of high throughput screening systems (HTS) including micro arrays for genomics and proteomics as well as the development of cell biochips.     

Wissenstransfer Oberflächentechnik

Knowledge Transfer in Surface Technology »Wissenstransfer Oberflächentechnik« (knowledge transfer in surface technology) aims at existing and expected potentials of modern surface technology for the german economy. The main goals are knowledge transfer, acceleration of innovation and growth of competitiveness and technological performance capability. The target group mainly consists of Small and Medium Enterprises orientated to innovation. This initiative is untertaken by the VDI‐Technology Center Düsseldorf on behalf of the German Ministery of Education and Research. Preliminary results are already available.     

Beurteilung der Zuverlässigkeit von Schmiermitteln für die Feinwerktechnik

Assessment of the Reliability of Lubricants for Precision Machinery. The critical examination of the reliability of lubricants for instruments and precision machinery needs first the recognition of all the parameters influencing the efficiency of the lubricants. Afterwards these parameters have to be classified according to their significance of the application of the instruments and precision machinery. These numerous influences cause unexpected and very complicated interactions which often can only be recognized, if the instruments and precision machinery are tested under practical conditions. The very small quantities of lubricants used in the instruments and precision machinery require new techniques for examining the lubricated bearings. A well equipped laboratory and a serious planning of the tests as well are therefore indispensable.     

Einsatztiefe der Industriellen Plasma‐ Oberflächentechnik im Maschinen‐ und Anlagenbau

The following article summarizes the main results of a market study about the use of Industrial Plasma‐Surface Treatment (IPS) in the German machinery and plant manufacturing branch conducted by the VDMA surface technology group. The results of the survey verify that during the past 20 years plasma‐based processes have become a state‐of‐the‐art technology. Today, more than 50 % of companies in the machinery and plant manufacturing industry employ IPS. Most of them prefer surface treatment of their products on a job coating basis. Merely some of the large suppliers have already acquired coating machines. The technology is particularly popular with manufacturers of precision tools and printing and paper equipment. The dominating argument for using plasma‐supported surface treatment within all segments of machine and plant construction is wearing protection of highly stressed tools. Other advantages of the technology are reduction of friction and the protection of metal against corrosion. At present a higher diffusion rate of IPS into the markets seems to be limited due to high costs and a qualification lag in the potential application sectors. Continuing public relation campains by suppliers, policy and assosications will achieve an improved level of utilisation in the near future.     

Laserakustik für Schicht‐ und Oberflächenprüfung

Laser‐acoustics for Testing Coatings and Material Surfaces A laser‐acoustic test method is presented, which can be used for the non‐destructive characterization of coatings and material surfaces. The method measures the dispersion of surface acoustic waves induced by short laser pulses. The technique is based on the fact that the propagation velocity of the wave depends on the frequency in coated and surface modified materials. Measuring the dispersion of the surface acoustic wave enables to determine important properties of the material surface. Three examples demonstrate that the laser‐acoustic method can solve very different problems of surface engineering. The wear resistance of diamond‐like carbon film with a thickness of few nano‐meters was evaluated. The elastic modulus of thermally sprayed coatings which are typically some hundred micro‐meters thick was measured, which allows to conclude on the defect structure of the coatings. The depth of sub‐surface damage layers in semi‐conductor materials was determined, which are created when the wafer is sliced from the ingot.     

Oberflächentechnik. Korrosion,Verschleiß, Wechselwirkung zwischen Oberfläche und Grundwerkstoff

Metal finishing — corrosion, wear, interaction between surface and basic metal . The influence of the surface on the behaviour of metals by mechanical stress and chemical attack has been studied. The results described complete former publications [1]. There also are discussed the necessary fundamentals.     

Oberflächenspannungsmesstechnik für den Prozesseinsatz

Using Surface Tension Measurement in Applications When cleaning surfaces it is crucial for the process stability that the optimum surfactant concentration is maintained. The concentration of free surfactants can be measured by determining the surface tension. SITA Messtechnik has developed an innovative sensor based on the bubble pressure method. This sensor makes it possible to continuously measure surface tension with a high reliability. With this application for monitoring cleaning baths the potential to save money arises in regard to the use of raw materials, waste disposal and the costs resulting from undiscovered production failures.     

Streuung der Werkstoffestigkeit und die Wahrscheinlichkeit für das Versagen von Probenstäben an ausgesuchten Beispielen

Scattering of Strength and Probability to Failure of Smooth Test Bars – on Selected Examples . The influence of scattering of material properties (distribution density function f) and of the loading spectrum (distribution density function g) on the probability to failure is discussed. For the distribution density functions f and g, simple model functions (Gaussian function, δ-function) were used. It is shown that in typical design situations, a small reduction of the scatter of the material properties may reduce the probability to failure to some orders of magnitude. The width of the loading spectrum is shown to be less important compared to the width of the scatter of the material properties. For materials with a large scatter of properties e.g. ceramics, the probability to failure is really high, even if a large safety factor is used. A satisfactory reliability for designs made from such materials can be reached, if lower limits of strength can be guaranted – e.g. applying advanced methods of material testing. Under this special condition, the width of the loading spectrum and the safety factor gains a large influence on the probability to failure.     

Elektronenstrahl‐Randschichtbehandlung für die Herstellung verschleißbeständiger Auftragschichten auf nichtrostenden Stählen

Stainless steel components exposed to mechanical stresses are subjected not only to corrosion, but to abrasive wear. There are several possibilities for enhancing the wear resistance of stainless steels; however, such processes are very often associated with a reduction in corrosion resistance. This paper presents an electron beam surface treatment technology to significantly improve the wear resistance of austenitic steels (e.g. X6CrNiMoTi17‐12‐2) and duplex steels (e.g. X2CrNiMoN22‐5‐3), without a negative influence on the corrosion behavior. Fe‐ and Co‐additive wires were deposited thermally by electron beam cladding. The cladding layers produced were free of defects such as cracks and pores, and were well metallurgical bonded to the base materials. Microstructural analysis, hardness measurements, wear tests and corrosion tests were carried out. The wear rate k was reduced by a factor of 100 compared to the base materials for electron beam cladding with Fe‐based wire and by a factor of 10 with Co‐based wire. Corrosion resistance was preserved for the Fe‐based cladding layers and slightly increased (by a factor of 3) for the Co‐based cladding layers.