Anilox rolls are used as metering rolls in the flexographic printing process, delivering a precise quantity of ink to the plate roll (which contains the image to be printed). Anilox rolls are high precision parts with respect to their dimensional tolerances as well as to the engraved structures. The latter can nowadays be either very coarse in conjunction with a high volume of ink to be transferred or rather fine showing cell diameter of 20 µm, cell walls below 3 µm in thickness and cell depth of only 6 µm and below. Moreover, the market needs for high quality printing will lead more and more to the outer limits of these ranges, which can be matched only by tailoring the coating properties, as well as the interaction of the laser radiation with the sprayed surface. Besides the needs for extreme screen counts in conjunction with requirements of certain volumes of liquid to be transferred, new types of surfaces are needed to meet these requirements and providing a wear resistant coating and concurrent an easy to clean surface. Therefore this paper will give a review of the interaction of the laser with a thermally sprayed surface focussing on the main laser parameters, different coating materials, the application of sealants as well as the type of engravings with respect to the achievable screen counts and transferrable ink volumes.

Printing machines mirror the art of precise manufacturing and adjusting of fast moving and heavy components with an accuracy of few micrometers. In order to meet the challenge of fast and high quality printing combined with a long lifetime of the machines, the core components transporting the print substrate and the different kinds of ink and other liquids needs to be coated, what is done more and more by applying thermal spray processes. The main requirements cover wear and corrosion resistance as well as suitable wetting and special needs like the ability of laser engraving. Moreover, the coatings are post processed to achieve a sufficiently low surface roughness combined with an appropriate microstructure resulting in a fine structure if laser engraving is considered. This paper will give a review of applications, techniques and materials, which are well-established in printing industry in respect to the specific demands of the case of operation. This covers the surfaces in the printing unit namely the printing and blanket cylinders but also the inking and dampening systems.

For 20 years now, the HVOF-method has been an industrially-established process for the application of hard-metal coatings to prevent wear phenomena from happening. A successful application combines the typical process parameters, conditions of materials and, above all, constructive frame conditions. In the following, we will present investigations for coating uneven outlines/contours such as edges, cavities or uneven surfaces. Furthermore, constructive frame conditions will be deduced from these and compared to our practical experience. The distribution of the layer thickness and its accessibility with the spray jet will be discussed as well. Here, we will have a closer look on which mechanical properties the basic substance has regarding hardness

The suspension plasma spraying (SPS) technique implemented on DC plasma spray guns is a complex thermal spraying process. In order to gain a better understanding of this deposition technique a systematic “splat” study using a shutter mechanism and the line-scan test was conducted varying liquid feedstock properties (viscosity and surface tension) and injection parameters (stream velocity and mass-loading). Splat morphology revealed the degree of particle agglomeration within the droplet formed from the liquid/plasma interaction, as well as their impacting velocity and heating history. The droplet formation was correlated to the liquid feedstock injection velocity and its viscosity. A simple model was developed to explain the experimental results correlating suspension properties to suspension droplet fragmentation mechanism.

The triplex-torch design providing three stable arcs in power and geometry promises a stable, quasi-laminar plasma jet leading to an uniform plasma and thus an uniform particle distribution. Additionally, the three powder injectors lead to an extended powder feed rate, resulting in a lower spraying time. This paper deals with particle properties of YSZ (SM 204NS) with respect to their injection location and powder feed rate and the resulting coating microstructure and porosity levels. Concerning the injection conditions, the three powder jets can be clearly identified. Their location depends on the spraying distance and less pronounced on the injection velocity. Interestingly, if the different powder-sizes are grouped and the jet cross-section is plotted for the different size cuts, the position of each size cut varies. Thus, a local separation of the powder takes place in the jet. The powder feed rate was varied from 30 to 320 g/min. Accordingly to this variation, the particles mean temperature was lowered from 3050°C down to 2650°C, and the velocity values dropped from 230 m/s to 155 m/s. Regarding the achieved coating thickness, up to a powder feed rate of approximately 210 g/min the thickness is increasing with no dramatic change in the porosity values. More powder does not lead to a thicker coating but results in a significantly higher porosity. Moreover, the microstructure of the coatings obtained by using a higher feed rate exhibits more segmentation cracks.

The behaviour of plasma sprayed powder particles at impact is not adequately understood so that the microstructure of thermal barrier coatings cannot be predicted with the required accuracy. This is due to the complexity of the spraying process in which the shape of the impacting particles is influenced by the spraying conditions and the structure of the previously formed parts of the coating. In this paper we present some techniques to improve the understanding of coating formation. We investigate the impact of a single molten powder particle on a surface by performing splat tests, measuring the particle’s temperature, velocity, and diameter at the appropriate stand-off distance before the spraying process starts. The measured values are assigned to the splats. SEM-images of the splats are analysed by means of a image analysis algorithm. Thus we are able to evaluate the influence of particle properties on the splat shape. In order to get a better understanding of the mechanism of coating build-up, a three-dimensional series of cross sections is created. With this kind of examination the shape of splats can be characterised in three dimensions.

The innovative suspension plasma spraying (SPS) technique, in which the carrier gas used to inject particles (10…100 µm) into the plasma jet is replaced by a liquid feedstock, is currently under development procuring denser ceramic coatings due to the use of submicron particles. The suspension properties, as well as the most relevant injection parameters - injection angle and liquid velocity - are adjusted to improve the coating quality at acceptable deposition rates. In addition, the plasma jet instabilities are studied and correlated to the coating properties. In the present work, a feasibility study is conducted addressing the key factors influencing the coating morphological properties such as the porosity, cracks, molten-fraction and amount of over-spray. The experimental setup is adapted to different DC plasma torch architectures (Sulzer-Metco F4 and Triplex) operating under atmospheric conditions with the aim of correlating the plasma jet qualities to the properties of the feedstock under consideration. The metallographic probes and fractured surfaces of the resulting yttria stabilized zirconia (YSZ, 5 wt. % Y 2 O 3 ) coatings are analyzed by means of light microscopy and scanning electron microscopy (SEM).

The heat and momentum transfer of the plasma to the injected particles is an important issue in coating formation during plasma spraying. In this study, the plasma temperature and velocity of a Triplex-I torch was measured by means of an enthalpy probe system. Additionally, the properties of injected yttria-stabilized-zirconia powder of a fine sized fraction were recorded spatially resolved by using a DPV2000 system. The plasma temperature and velocity are decreasing by increasing the distance from 45 to 60 mm with respect to the torch exit by approximately 50% from initially 6200°C and 400 m/s, respectively. In contrast, the particles gain temperature up to the melting point at 70 mm stand-off distance as well as the velocity rises up to its highest value of 115 m/s at the maximum flow rate of the particles. Both, plasma and particle characteristics were used to obtain a deeper insight on heat- and momentum transfer of the plasma jet to the single particles.

The effect of argon carrier gas flow, ethanol- or water injection on the plasma-composition, -enthalpy and – temperature as well as on the entrainment from the ambient was investigated in comparison to the pure plasma condition of an Ar-H 2 -plasma. Additionally, the plasma gas flow rate and power levels were varied. The enthalpy, and thus the plasma temperature, as well as the composition and speed are determined by means of an enthalpy probe system. Spatial resolved data could be obtained by translating the torch via a robot so that a temperature and speed map shows the evolution of plasma features with increasing stand-off distance.

During plasma spraying in-flight particle characteristics are influenced by the many operating parameters associated with the deposition process. The distinctive temperature and velocity signals given by particles as they exit the plasma torch can be used to develop processing maps for defining the optimal operating envelope. Knowing the temperature and velocity history of the particles, the evolution of the microstructure, the amount of porosity and the phase composition can potentially be predicted. In this paper, the relationship of system parameters (stand-off distance, torch power, plasma gas composition and process gas flow) was correlated to in-flight particle characteristics of yttria stabilized zirconia and compared to the resulting coating features such as thickness, microstructure, porosity and phase composition. The appearance of the coating (i.e., color) was also compared after the deposition process. Yttria stabilized zirconia was deposited on grit blasted samples using an F4 (Sulzer Metco) plasma torch. Before depositing each sample on the substrate, the particle properties were measured at the desired stand off distance perpendicular to the particle jet covering an area of 18x18 mm 2 using the Tecnar DPV2000 inflight particle analyzer. The coatings were cross-sectioned for microstructure analysis, thickness measurements and deposition efficiency. Free standing films were used for mercury intrusion porosimetry. Grey levels of the coatings were obtained by optical microscopy and subsequent digital image recording. X-ray-diffraction analysis was also used to obtain the phase composition. Results showed that different particle temperature and velocity conditions lead to specific porosity and varying colors of the deposit. The color of the deposit was correlated directly to the amount of monoclinic phase in the as-deposit material.

For the application as a thermal barrier coating (TBC) the partially stabilized zirconia approaches some limits of performance, which hardly can be overcome in the near future. To further enhance the efficiency of gas turbines, higher temperature and a longer lifetime of the coating are needed for the next generation of TBC´s. This paper presents the development of new materials and concepts for application as TBC. Materials such as compositions with pyrochlore structure or doped zirconias are compared with new concepts like nanolayer between top- and bondcoat, metal-glass composites and double layer structures. One concept is to use new compositions in a combination with zirconia, as a double, multi or graded layer coating. In this case the benefits of zirconia will be combined with the promising properties of the new top-coating. For the concept of metal glass composites the influences of different plasma spraying processes on the microstructure are described. The quality of these coating systems are evaluated by a burner rig test.

This paper shows how in-flight particle diagnostics can be used to optimize parameter sets for new layer materials and to detect drift in the control of thermal spraying lines. It describes the equipment and methods used to measure the temperature, velocity, and diameter of spray particles in a plasma jet and explains how torch current, plasma gas composition, carrier and total gas flow, and stand-off distance are varied according to a statistical design plan to determine their effect. The results are presented in the form of process maps and data plots, from which several conclusions are drawn. Paper includes a German-language abstract.