Plasmavorbehandlung und Beschichtung von Kunststoffolien. Teil 2: Experimentelle Ergebnisse der Plasmavorbehandlung von Kunststoffolien

Plasma Pretreatement and Coating of Polymer Films. Part 2: Experimental Results of the Plasma Pretreatment of Polymer Films The food packaging industry demands cheap polymer films possessing a high barrier against permeation of gases, moisture and flavor. Candidates for the most successful materials fulfilling these requirements are vacuum web coated b iaxial o riented p olypropylene (BOPP) films containing a thin inorganic barrier layer. For a good adhesion of the barrier layer on the BOPP films, the polymer film must be pretreated. The industry uses the Corona atmosphere plasma. This work is separated in three parts. The first part describes the experimental setup and the properties of vacuum web coated layers on polymer films [1]. The next part contains the results of the systematic modification of po } ymer surface by atmosphere and low pressure plasmas. The influence of the surface properties on the final functionality of the coated films is given. In the last part, the discussion of the results of the first and second part reveals systematic relations between the production parameters of the high barrier films and their final functionality. These results firstly reveal the adhesion mechanism of the inorganic barrier layers of the polymer films and the necessary surface properties of the polymer films, in order to get cheap high barrier films by vacuum web coating.     

Plasmavorbehandlung und Beschichtung von Kunststoffolien. Teil 3: Auswertung der experimentellen Ergebnisse und Diskussion

Plasma Pretreatment and Coating of Polymer Films. Part 3: Analysis of the Experimental Results and Discussion The food packaging industry demands cheap polymer films possessing a high barrier against permeation of gases, moisture and flavour. Candidates for the most successful materials fulfilling these requirements are vacuum web coated biaxial oriented polypropylene (BOPP) films containing a thin inorganic barrier layer. For a good adhesion of the barrier layer on the BOPP films, the polymer film must be pretreated. The industry uses the Corona atmosphere plasma. This work is separated in three parts. The first part describes the experimental setup and the properties of vacuum web coated layers on polymer films[1] The next part contains the results of the systematic modification of polymer surface by atmosphere and low pressure plasmas[2]. The influence of the surface properties on the final functionality of the coated films is given. In the last part, the discussion of the results of the first and second part reveals systematic relations between the production parameters of the high barrier films and their final functionality. These results firstly reveal the adhesion mechanism of the inorganic barrier layers of the polymer films and the necessary surface properties of the polymer films, in order to get cheap high barrier films by vacuum web coating.     

Beschichtung von Kunststoffen im Bereich Ophthalmik und Laserschutz

For achieving the desired manyfold requirements many types of technologies are used in the field of coating ophthalmic plastic lenses. In addition to the chemical coating PVD-processes are widely used for AR and scratchresistance. In the meantime plasmapolymerisation is used, too. The desired performances in the field of laser-safety-goggles can be realized only with coatings. This paper describes the aims of coatings, the theory about the interference-optic and the used coating-technologies together with the needed testingroutines.     

VAKUUMWAAGEN Teil 1: Einleitung und Makrowaagen

Balances destined for weighing of goods in vacuum are labeled as vacuum balances. Macrobalances are designed for loads above 100 g. For comparison of mass prototypes without influence of buoyancy, vacuum mass comparators were designed. Large vacuum balances are used for the determination of the specific or the atomic mass of gases. Electromagnetic vacuum precision balances are used to investigate chemical reactions at reduced gas pressure and for thermogravimetric analysis. Production processes can be controlled by means of load cells of various design.     

Mit Hochfrequenz angeregte Niederdruckplasmen: Prinzipien und Strukturierung von Halbleitern. Teil I

In two parts, the generation of cold plasmas by capacitive and inductive coupling as well as by absorption of whistler waves is outlined. In the third part, it is shown how the knowledge of these mechanisms can be exploited for modifying the surfaces of semiconductors.     

Spanende Bearbeitung von Hartlegierungen – Drehen und Schleifen. Teil II: Drehen von Hartlegierungen

Metal Cutting of Hard Alloys – Turning and Grinding. Part II: Turning of Hard Alloys Turning tests were carried out on selected hard alloys on iron (FeCr12C2.1, FeCr13Nb9MoTiC2.3, FeCr14Mo5WVC4.2) and cobalt basis (CoCr29W5C1.3) in a cutting speed range of between v_c = m/min and 180 m/min. Polycrystalline cubic boron nitride (PCBN) turned out to be a suitable tool material. Subsequent examinations focused on evaluating the mechanisms of chip formation, cutting tool wear and surface integrity of the workpiece. During turning of hard alloys the formation of chips is primarily influenced by the ductility and fracture toughness of the work material. While a ductile matrix enables the formation of highly deformable chips, the chips stemming from martensitically hardened alloys show low deformation. As the cutting depth increases shear and segmented chips are chiefly produced. Type and arrangement of the hard phases play a significant role. Adhesion is the main wear mechanism impacting the cutting face of the tool. Particularly, strong adhesion effects will arise during the machining of the work hardening alloy on cobalt basis. A high cobalt content of the metallic bonding phase of the PCBN cutting tool appears to be a disadvantage with this type of work material. When machining alloys on iron basis adhesion is promoted by the mechanical linking of alloy-specific hard phases to the cutting material binder. Abrasion primarily acts on the flank. The hard carbides of the work material produce typical grooves in the cutting edge zone of the tool. The flank wear increases as the carbide content goes up. As the cutting speed rises the tool wear ascertained passes through a minimum. Whereas the formation of built-up cutting edges predominates at lower speeds, a thermal softening of the PCBN binder takes place and is dominating at high cutting speeds. The location of the wear minimum depends not only on the cutting temperature but also on the strain hardening capability of the metal matrix. Raising the cutting speed will cause the cutting force to continuously reduce. The highest cutting forces are found for the Co-based alloy. The passive forces develop in line with cutting tool wear and vary with content and hardness of the hard phases involved. The selected process parameters also affect the surface near zone. With low cutting speeds and process temperatures the surface is mainly stressed mechanically. Carbides break or detach from the surrounding matrix. If the cutting speed and process temperature are increased the eutectic carbides (M₇C₃) are deformed together with the metal matrix. Microhardness profiles are indicative of near-surface strain-hardened zones after cutting of the Co-based alloy. Fe-based matrices do not show hardness changes worth mentioning. Although there are no new hardened zones noticeable even at maximum cutting speed, the matrix is nevertheless influenced thermally so that residual stresses will develop in the machined surface layer. In the lower cutting speed range the surface quality is characterized by flakes and material squeezing (Co-based alloy) and by spalling (Fe-based alloy). Only if the cutting speed is raised, a minor roughness is detected due to a potential deformation of eutectic hard phases.     

Spanende Bearbeitung von Hartlegierungen – Drehen und Schleifen. Teil I: Gefüge und Eigenschaften von Hartlegierungen

Metal Cutting of Hard Alloys – Turning and Grinding. Part I: Structure and Properties of Hard Alloys Hard alloys count among the materials that contain hard phases. This involves primary and/or eutectic hard phases embedded in a metallic matrix. The characteristics of the individual microstructural constituents may be combined to form a material featuring excellent wear resistance and a high resistance to fracture. For that reason, the material can be widely used in all applications where the wear resistance to abrasion is essential. In the event low operating temperatures are involved the component costs to service life ratio speaks for hard alloys on Fe basis. Above 600 °C heat resistant Ni and Co matrices are to be given preference. Carbides and borides of the transition metals are specially suited as hard phases. They attach well to the surrounding matrix. Nowadays, alloys of the FeCrC system are primarily employed for economic reasons. As nickel-based material the NiCrSiB alloying system is frequently employed. Hard alloys on cobalt basis usually belong to the CoCrWC (stellite) system. In many fields of application components of this material group require a largearea metal cutting technique (eg for barrel extruders, crushing rollers, valve seats). However, problems may be encountered during machining due to the high hardness and excellent wear resistance of this material. The structural difference between hard phases and metallic matrix causes different reactions to stresses exerted during the machining process. Process-related changes of the microgeometric surface characteristics and the physical condition of the surface zone of a material are paraphrased by the term “surface integrity”. To create a basis for assessing the machining influence on the multiphase component surface layer, the first part of the paper discusses manufacturing techniques, constitution of the microstructure and main properties of the individual structural components.     

Spanende Bearbeitung von Hartlegierungen – Drehen und Schleifen. Teil III: Schleifen von Hartlegierungen

Metal Cutting of Hard Alloys – Turning and Grinding. Part III: Grinding of Hard Alloys Straight surface plunge grinding tests were performed at a peripheral wheel velocity of v_c = 15 m/s on exemplary iron based alloys FeCr12C2.1, FeCr13Nb9MoTiC2.3 and FeCr14Mo5WVC4.2 both in soft annealed and hardened and slightly relieved microstructural condition. Vitrified bonded wheels of type SC 60 3/4 (SiC) and 2B252 M6 V240 (CBN) with a diameter of D_S = 300 mm were used as abrasive tools. When selecting the machining parameters due consideration was given to materials related aspects and an acceptable volumetric removal rate per unit width of Q_w′ = 4 mm³/mms was taken into account. Subsequent examinations focused on the analysis of the thermomechanical load imposed on the microstructure. The grinding of hard alloys by means of conventional abrasives is significantly influenced by the content and type of the hard phases present. Due to their excessive hardness primarily solidified M₇C₃ are highly resistant to the ingressing abrasive grains. Accordingly, maximum grinding normal forces are encountered with the FeCr14Mo5WVC4.2 alloy. However, the normal forces are also found to be higher in case of a hardened metal matrix, when SiC is used as abrasive or a wet grinding process is applied. As regards tangential forces they also show a tendency of being influenced by structure-specific hard phases. Process temperature and stress condition ahead of the grain cutting edges are of great significance for the behaviour of the hard phases during grinding. If the mechanical component is predominant, accumulations of near-surface eutectic carbides are destroyed. Individual stalk-like carbides often break in the phase center. However, in the event of thermal load an eutectic M₇C₃ may also be deformed plastically. Through the cleavage fracture of coarse primary M₇C₃ phases microcracks are initiated that in the end will grow into macrocracks. Carbide fragments broken off will impair the surface quality. In particular the metal matrix reacts strongly to the process heat generated. In case of dry grinding using SiC a rehardening zone has been detected near the surface. The alloy-specific austenizing temperature of approximated 1000 °C was exceeded. As the distance to the surface increased a tempered area with hardness figures below those of the basic structure was found. No rehardening will occur if CBN is used as abrasive. The residual surface stresses determined correlate with the extent of thermal and mechanical load imposed. Whereas an extensive crack network is evident after dry grinding when SiC has been used as abrasive, no surface cracks were detected when employing the CBN abrasive. Due to the excellent thermal conductivity characteristics of this grinding medium a thermal damage during dry grinding can be avoided. While the use of grinding fluid will improve the surface roughness, cracks may form due to the abrupt quenching effect, especially if hardened material is involved. Increasing the workpiece velocity will also contribute to reduce the risk of crack development, but, on the other hand, leads to a surface quality deterioration that cannot be accepted.     

Kondensation von Dampfgemischen—Teil 1

Zusammenfassung Bei der Kondensation str?mender Dampfgemische liegen im Vergleich zu reinen D?mpfen zwei wesentliche Unterschiede vor. Zum einen ?ndern sich bei der Kondensation eines Dampfgemisches die Zusammensetzungen und damit auch die Stoffwerte sowohl des Dampfes als auch des Kondensats l?ngs der Kondensationsstrecke, zum anderen kontrolliert der Stofftransport in der Gasphase meistens die gesamte Kondensationskinetik. Im Gegensatz hierzu ist die Kondensation eines reinen Dampfes nur durch W?rmetransport im Kondensat bestimmt. Die vorliegende Arbeit befa?t sich mit der Kondensation von Mehrstoffgemischen auf der Grundlage des Filmmodells. Die Analyse des Stofftransports und der Wechselwirkungen zwischen den Gemischkomponenten in der Gasphase beruht auf den Maxwell—Stefan-Gleichungen. Neben der exakten L?sung dieser Gleichungen werden in die Betrachtungen auch einige, N?herungsl?sungen einbezogen und durch Experimente getestet. Die auf dem Filmmodell beruhenden Rechenergebnisse stimmen mit den experimentellen Werten aus der Literatur meist gut überein, wenn eine einfache Str?mungsführung vorliegt, wie beispielsweise bei der Kondensation in einem senkrechten Rohr. Die exakte L?sung der Maxwell—Stefan-Gleichungen schneidet dabei besser als die N?herungsl?sungen ab. Bei komplexen Str?mungsführungen, wie in einem Rohrbündel mit Umlenkblechen, ist die übereinstimmung im allgemeinen schlechter. Hier sind Verfeinerungen sowohl bezüglich der Wechselwirkungen zwischen den Gemischkomponenten als auch der Berechnungen der für das Filmmodell ben?tigten bin?ren Stoffübergangskoeffizienten erforderlich.     

Abschirmung von Kunststoffen durch Beschichtung im Vakuum

Vacuum coating for shielding of plastics Shielding coatings can be deposited selectively on plastic housings by vacuum assisted processes. The mechanical properties of the polymer material are not affected. Uncoated areas maintain their visual appearance, i.e. refinishing operations are not required. Due to their high electrical conductivity, Aluminium and Copper films provide a high shielding effectiveness for electromagnetic waves. They are applied successfully to devices in a wide variety of industrial sectors if electromagnetic compatibility (EMC) has to be ensured. If applications under harsh environmental conditions are encountered, protective coatings deposited during the same vacuum cycle, are the best solution. Similarly, combinations of properties like shielding and solderability can be achieved by vacuum coating, e.g. with Copper / Tin layers. In case that for example transparency in the visual regime is specified in conjunction with dissipation of electrostatic charges or with attenuation of high – frequency interferences, indium tin oxide (ITO) films are well proven.     

Gießformherstellung durch Beschichtung von Modellen

Casting molds, produced by coating of prototypes A new method for the cost effective production of forming tools is introduced. These tools can be used for the production of prototypes and small series of products. The new method for the production of moulds and injection moulding tools consists of the following steps: ?coating of a positive model with a hard coating by physical vapour deposition (PVD)‐technologies ?deposition of a support coating, consisting of a metal coating, applied by an atmospheric plasma spraying technology ?embedding in a polymer removing of the positive model ?completion of the tool by adding the moulding equipment By using such a tool it is possible to produce more than 1000 parts of a polymer (enforced by glass fibre) or more than 1500 parts of a regular polymer.