Coating Thickness Distribution Research Articles

Remanent Magnetic Field Scanning of Coating‐Graded Hybrid Foams

The manufacturing of hybrid materials such as nickel/polyurethane (Ni/PU) hybrid foams and 3D printed hybrid materials with the aid of electrochemical coating of lightweight structures leads to new materials, which can be used as crash absorbers, but also for lightweight design applications. Optimizing the coating quality of the developed hybrid materials necessitates a characterization on different scales regarding the coating thickness distribution. The ferromagnetic properties of the nickel coating enable a remanent magnetization of the produced hybrid foams and a subsequent measurement of resulting magnetic fields, so that the time‐consumption of a coating distribution determination could be enormously reduced by automating the quantification method. Previous studies have shown, that the local strength of these fields correlates with the deposited mass thus the coating thickness. The here presented automated measurement gives useful information about the homogeneity and the local coating thickness distribution according to an appropriate calibration. In order to optimize the coating quality of the newly developed hybrid materials, improved deposition conditions, as well as semi‐automated characterization methods, are studied to establish a large‐scale industrial production and a higher applicability of hybrid materials in the near future.

DEM-DDM investigation of the intra-tablet coating uniformity for tablets with different shapes

Coating uniformity is important for the quality, safety, and efficacy of tablets in the pharmaceutical industry. Among the various research methods, discrete element method (DEM) is a powerful tool for numerically investigating the coating process in particle level, increasing the understanding of coating uniformity and improving related processes. In this study, the combination of DEM and discrete droplet method (DDM) is applied for the simulation of tablet coating process, including the intra-tablet coating uniformity of differently shaped tablets. The biconvex tablets are described by multi-super-ellipsoid approach in this study. In order to obtain the coating thickness distribution on each tablet, two particle surface-based meshing methods are proposed. The proposed intra-tablet DEM-DDM coating model is subsequently verified by the qualitative comparison with both theoretical models and experimental results from other literature. Finally, the influence of tablet shape on the intra-tablet coating uniformity is investigated, including tablets with different aspect ratios and height ratios.

Dynamic Numerical Simulation of Curved Surface Coating Trajectory Based on STL Slicing Algorithm

The thickness of the coating on the surface of a workpiece is an important factor in determining the quality of spraying. However, it is challenging to estimate the distribution of film thickness accurately before the actual spraying process. This lack of estimation hinders the optimization of spraying process parameters and trajectory. To overcome this, a numerical simulation of surface spray coating thickness was conducted to provide guidance for the actual coating process. The research consists of three main parts. Firstly, the spray trajectory of the spray gun is determined using the proposed Stereo Lithography (STL) model slicing algorithm. Secondly, a two-phase flow spray model and collision adhesion model are established to construct the spray film model. The surface mesh is determined, and the spraying process parameters are set. Finally, numerical simulation is conducted to analyze the dynamic spraying trajectory and the distribution of coating thickness. The results show that the coating thickness distribution on an arc surface is thicker in the middle and thinner on the edges. The distribution is symmetric with respect to both the transverse and longitudinal directions of the arc surface. The coating thickness distribution at both ends is not as uniform as in the middle section. The concave part of the free surface has the largest coating thickness, while the coating thickness distribution on the convex part is not as uniform as on the relatively flat part. This method of simulating the coating thickness distribution on complex surfaces provides a solid foundation for further optimization of spraying process parameters and trajectory, ultimately improving the qualification rate of workpiece spraying processing.

Method of 3D Coating Accumulation Modeling Based on Inclined Spraying.

In the process of repairing the surface of products in aviation, aerospace, and other fields by spraying, accurate 3D cumulative-coating modeling is an important research issue in spraying-process simulation. The approach to this issue is a 3D cumulative-coating model based on inclined spraying. Firstly, an oblique spraying layer cumulative model was established, which could quickly collect the coating thickness distribution data of different spray distances. Secondly, 3D cumulative-coating modeling was conducted with the distance between the measuring point and the axis of the spray gun and the spraying distance between the measuring points as the input parameters, and the coating thickness of the measuring point as the output parameter. The experimental results show that the mean relative error of the cumulative model of the oblique spraying layer is less than 4.1% in the case of a 170~290 mm spraying distance and that the model is applicable in the range of -80~80 mm, indicating that the data on the oblique spraying coating proposed in this paper is accurate and fast. The accuracy of the 3D cumulative-coating model proposed in this paper is 1.2% and 21.5% higher than that of the two similar models, respectively. Therefore, the approach of 3D cumulative-coating modeling based on inclined distance spraying is discovered, demonstrating the advantages of fast and accurate modeling and enabling accurate 3D cumulative-coating modeling for spraying process simulation.

High power pulsed magnetron sputtering tailored low temperature CrAlN + MoWS coatings for dry tribological contacts

Gears are used in a variety of applications, for example, in automotive and aerospace industries. In these applications, gears are exposed to harsh conditions such as high Hertzian pressures. In many cases, lubricants are used to achieve a reduction in the coefficient of friction and, thus, in the wear of the components. Nevertheless, in some applications, the use of a lubricant is difficult, for example, in vacuum environments. One promising approach is the application of solid lubricants by using triboactive elements. The present study shows the potential of a process combining high power pulsed magnetron sputtering (HPPMS) and direct current magnetron sputtering (dcMS) for the deposition of CrAlN + MoWS coatings. In HPPMS/dcMS processes, especially, the share of HPPMS leads to higher ionization of the coating plasma and, therefore, to higher coating thicknesses on the teeth of gears. One major challenge in coating processes is the adjustment of the deposition temperature, since steels used for gear applications are temperature sensitive. Therefore, starting from an established coating process with a high coating temperature, the coating process was adjusted by reducing the number of used cathodes. By reducing the count of used dcMS cathodes, the share of HPPMS cathodes within the coating process was increased. Furthermore, segments of gears were coated in order to determine the coating thickness at different distances from the head of the gear tooth. A sufficient coating thickness distribution on the flank of the gear tooth is crucial for friction reduction and wear protection when used in gearboxes. The reduction of used cathodes led to a decrease in the coating temperature from a maximum coating temperature of Tmax = 281 °C to Tmax = 214 and 197 °C. It was shown by nanoindentation measurements that the effect of soft annealing was eliminated by reducing the coating temperature. At the same time, coatings deposited with increased HPPMS fraction led to a reduced coefficient of friction as well as lower wear volumes for pin-on-disk measurements in a dry tribological contact with an uncoated 100Cr6 counterpart. Moreover, these processes exhibited a good coatability of the gear tooth with a relatively high coating thickness even near the gear tooth root. The present study shows the potential of increasing the share of HPPMS during the deposition of coatings for dry-running applications. By increasing the HPPMS content, the tribological behavior as well as the coating thickness distribution on gears can be significantly improved.

Particle coating growth behaviors in a spray fluidized bed based on Gas-Liquid-Solid Quasi-Three-phase DEM numerical simulation

Wet granulation processes are widely used in chemical, food, pharmaceutical, and various other industrial processes. During the process of particle coating growth, particle fluidization state and liquid characteristics have an impact on the layer's thickness and homogeneity. In this study, discrete element, liquid bridge, and droplet motion models were combined to investigate the impact of injection gas velocity, droplet diameter and injection liquid viscosity on the particle growth ratio and coating thickness distribution, and the particle growth mechanism was investigated. The particle growth area, which is the area where the number of coated particles exceeds 0, was significantly expanded by decreasing the droplet diameter and increasing the gas velocity at appropriate ranges. The frequency of droplet and particle collisions increased, and average relative liquid content decreased with increasing particle growth area. By accelerating the injection of gas and reducing the viscosity of the injected liquid, the fluidization condition of the particles, which primarily affected the particle cycle frequency, could be enhanced. The improvement of particle growth area and particle cycle frequency allowed more particles to participate in growth and improved the quality of the grown particles. The proportion of small particles dramatically grew while the proportion of large particles reduced. The standard deviation of particle diameter decreased, and particle growth became more uniform.

Variable Velocity Coating Thickness Distribution Model for Super-Large Planar Robot Spraying

This study proposed a dynamic optimization method for spray gun flow to address the issue of uneven film thickness in the acceleration and deceleration section of the z-shaped spray trajectory in large plane ship segments. The method takes into account the acceleration and deceleration section of the spray trajectory and improves the film thickness distribution. The study first established a static vertical spray coating growth model of the spray gun without considering the acceleration and deceleration of the spray trajectory. Then, we used an integral method to optimize the coating uniformity and established a film thickness distribution model. The optimization of spray speed and spray spacing is crucial in the use of variable flow spray guns. It is assumed that the acceleration and deceleration sections of the spraying trajectory are linear and symmetrical, which forms the basis for establishing a mathematical model for the variable flow spray gun. To determine the flow of the spray gun at different speeds in the acceleration and deceleration sections, the pattern search method was adopted. A section of a ship was used as an example for this study. In this study, we utilized numerical simulations to compare the uniformity of paint film thickness when using a spray gun with a constant flow versus variable flow. The results indicate that when taking into account the acceleration and deceleration section of the spray trajectory, the film thickness was more uniform with a variable flow. These findings demonstrate the feasibility and effectiveness of the proposed method.

Unified theoretical framework for black carbon mixing state allows greater accuracy of climate effect estimation

Black carbon (BC) plays an important role in the climate system because of its strong warming effect, yet the magnitude of this effect is highly uncertain owing to the complex mixing state of aerosols. Here we build a unified theoretical framework to describe BC’s mixing states, linking dynamic processes to BC coating thickness distribution, and show its self-similarity for sites in diverse environments. The size distribution of BC-containing particles is found to follow a universal law and is independent of BC core size. A new mixing state module is established based on this finding and successfully applied in global and regional models, which increases the accuracy of aerosol climate effect estimations. Our theoretical framework links observations with model simulations in both mixing state description and light absorption quantification.

The Effect of Design and Size of the Fluid-Bed Equipment on the Particle Size-Dependent Trend of Particle Coating Thickness and Drug Prolonged-Release Profile

The focus of the current work is to study and demonstrate the impact of the design, the scale, and settings of fluid-bed coating equipment on the differences in pellet coating thickness, which in case of prolonged-release pellets dictates the drug release. In the first set of coating experiments, the pellet cores were coated with the Tartrazine dye with the aim of estimating the coating equipment performance in terms of coating thickness distribution, assessed through color hue. In the second set, drug-layered pellets were film-coated with prolonged-release coating and dissolution profile tests were performed to estimate the thickness and uniformity of the coating thickness among differently sized pellets. In both study parts, film coating was performed at the laboratory and the pilot scale and essentially two types of distribution plate and different height adjustments of the draft tube were compared. The dye coating study proved to be extremely useful, as the results enable process correction and the optimal use of the process equipment in combination with the appropriate process parameters. Preferential film coating of larger drug-containing pellets was confirmed on the laboratory scale, while on the pilot scale, it was possible to achieve preferential coating of smaller pellets using rational alternatives of settings, which is desirable in terms of particle size-independent drug release profile of such prolonged-release dosage forms.

Experimental analysis on the influence of the tool micro geometry on the wear behavior in gear hobbing

Gear hobbing is a well-established manufacturing process for cylindrical spur gears. The cutting edge of a hobbing tool is, among others, characterized by the cutting edge radius and the form-factor K. The magnitude of these parameters is ideally chosen based on the machining conditions given by the workpiece and cutting material and the cutting parameters as well as the gear and tool geometry. However, the influence of the cutting edge geometry on tool life and wear behavior is hardly known, which complicates an optimized tool design. Furthermore, the preparation process regarding the coating thickness distribution on the wear behavior is equally relevant. Therefore, the objective was to identify the influence of the cutting edge radius, the form-factor K, and the preparation process on the wear behavior of gear hobbing tools made of powder metallurgical high-speed steel (PM-HSS). Fly-cutting trials were performed as an analogy process for gear hobbing in order to study the wear behavior and identify the respective tool lives. The trials indicated that the form-factor K influences the wear behavior, while a variation of the cutting edge radius did not have a significant effect. A homogenous coating thickness could extend the tool life significantly.

Nondestructive Thickness Measurement of Thermal Barrier Coatings for Turbine Blades by Terahertz Time Domain Spectroscopy

Owing to its high penetrability with dielectric materials, terahertz time domain spectroscopy (THz-TDS) is a promising nondestructive measurement technology. The coating thickness deviation and defect of thermal barrier coatings (TBC) will affect its thermal insulation performance and lifetime. In this work, THz-TDS was applied to measure the coating thickness distribution of TBC. The refractive index was obtained by THz-TDS transmission mode. To avoid the normal incidence THz signal loss, the THz signal was reflected from the TBC with a 10° incident angle, which also made the measurement result insensitive to the unevenness and tilt of the TBC sample. In the experiment, the yttria-stabilized zirconia (YSZ) TBC was measured by THz-TDS to estimate the thickness distribution. To validate the thickness measurements, metallography was introduced to correlate the TBC thickness result. The measurement deviation was within 12.1 µm, i.e., 3.45% for the THz-TDS and metallography result. A piece of turbine blade was measured by THz-TDS and a eddy current test. The maximum deviation was 8.48 µm, i.e., 2.36% of these two methods. Unlike the eddy current test, the THz-TDS thickness result was not affected by the cooling holes. The effectiveness of the nondestructive thickness measurement of TBC for turbine blades by THz-TDS was verified.

An Indirect Evaluation Method of Mold Coating Thickness in AlSi Alloy Permanent Mold Casting Production

Permanent mold casting produces the second most aluminum cast parts among all casting processes. In this process, mold coating changes the heat transferred from the molten metal to the mold by acting as an insulating layer. Moreover, the coating thickness is a significant variable regarding the coating’s thermal resistance, which strongly influences the microstructure of cast parts and the thermal shock on expensive molds. However, in casting production, coating peeling-off and repeated recoating result in an inhomogeneous coating thickness distribution. Due to the high working temperatures of the molds, no efficient online coating thickness measurements exist. We propose an indirect evaluation method based on the as-cast surface corresponding to the coating area. Our experiments analyzed as-cast and coating surfaces at nine different coating thicknesses. The results show a close correlation between the as-cast surface roughness parameter of arithmetical mean height Sa and the coating thickness. Based on this correlation, we can derive the coating thickness from the corresponding as-cast surface analysis. Furthermore, the coating peel-off area and other casting surface defects are easily recognized in these surfaces. In our next work plan, an affordable optical camera and proper light conditions will be tested by taking photos of as-cast surfaces, and an algorithm for the real-time automatic evaluation will be developed.

Design of a three-nozzle for air spraying based on jet interference effect and numerical study of spraying process

Due to the problems of many round-trip time and low spraying efficiency when using single-nozzle, a three-nozzle structure is studied in this paper. The spraying process is numerically simulated by the method of computational fluid dynamics. The discrete phase model is used to predict the trajectory of droplets. The interference flow field is formed due to the entrainment of jet. Paint droplets are transported to the target under the action of gas flow field. The geometry of three-nozzle has a significant influence on the characteristics of the interference flow field. The influence of different distance (L) and axis angle (θ) between two adjacent paint holes on the interference gas flow field and coating thickness distribution are analyzed by changing the structure of three-nozzle. Numerical simulation results show that small L and θ result in strong interference effect, while the paint is mainly concentrated in the central region of the target, which is easy to cause overspray. With the gradual increase of L and θ, the strength of interference gradually decreases and the paint gradually spreads to both sides. However, the strength of interference would become very small when L and θ get too large, which is easy to cause an uneven coating film. According to the numerical simulation results, the best spraying effect can be obtained when L = 40 mm and θ = 30°. Compared with single-nozzle and double-nozzle, the effective coating film width of three-nozzle has increased by 414.3% and 176.9%, respectively, which improves the spraying efficiency.Article HighlightsFor the problem of low efficiency of single nozzle, this paper studies a three-nozzle based on jet interference effect.The coating film thickness distribution model is established based on numerical simulation, which avoids expensive and time-consuming experiments.Compared with single-nozzle and double-nozzle, the effective film width of three-nozzle has increased by 414.3% and 176.9%, respectively, which improved the spraying efficiency

Investigation of the Structural Coating Homogeneity in Open‐Porous Nickel/Polyurethane Hybrid Foams Produced by Flow‐Controlled Electrodeposition

In today's world, the saving of raw materials together with the reduction of emissions necessitates the development of new, customized and application‐oriented materials which fulfill various requirements at the same time. Metal foams achieve a high strength combined with low weight. The present work deals with a flow‐controlled production technique for hybrid foams to deposit a nanocrystalline nickel (Ni) layer on pre‐treated, open‐porous polyurethane (PU) foams. The analysis of the resulting coating thickness distributions with gravimetric and microscopic methods shows the qualitative and quantitative influences on the local deposition by varying the process parameters. For the first time, the coating thickness distribution of Ni/PU hybrid foams is investigated regarding the analysis of a global and local homogeneity. The comparison of experimental data with simulated flow velocity profiles leads to an estimation of the correlation between flow velocity, anode distance, and coating thickness distribution, which represents the mass transport. The correlations show, that the coating process is strongly controlled by the electrolyte's flow velocity as well as the distribution of the electric field.

Research on Film-Forming Characteristics and Mechanism of Painting V-Shaped Surfaces

Painting a V-shaped surface, which is widely found in various facilities and equipment, often results in poor coating quality, which may be caused by an insufficient understanding of film-forming characteristics and mechanism. In this study, computational fluid dynamic (CFD) simulations were carried out for in-depth research on the film-forming characteristics and mechanism of painting V-shaped surfaces. The mathematical model of film formation was established with the Euler–Euler method, and the unstructured grids and adaptive-mesh refinement were adopted to discretize the computational domain. By solving the model, the coating thickness distribution law and flow-field characteristics of spraying a V-shaped surface were obtained. When painting a V-shaped surface with an angle less than 180°, the coating thickness distribution appeared as two peaks, instead of the single peak that appeared when painting a flat wall. As the V-shaped angle decreased, the coating thickness became thinner. The peak position gradually shifted to both sides, and the thickness distribution became wider. Analysis of the spray flow-field characteristics revealed the thickness distribution mechanism, by whichthe geometric characteristics of the V-shaped surface changed the near-wall distribution of the flow field. When the V-shaped angle decreased, the pressure peak at the center of the V-shaped surface and the eccentric pressure peaks that formed on both sides increased. The near-wall paint fluid was confined between the central pressure peak and the off-center pressure peak, resulting in paint droplets depositing between the pressure peaks and double-peak distribution of the coating thickness forming on the V-shaped surface. The spraying experiments verified the correctness of the numerical simulations, film-forming characteristics, and corresponding mechanism, which are of great significance for efficient and high-quality spraying on V-shaped surfaces.

Automated visualization of steel structure coating thickness using line laser scanning thermography

This paper proposes a line laser scanning thermography system for automated visualization of coating thickness distribution within a steel structure. In the proposed system, a line laser scans the coated steel structure and generates heat energy on the coating surface; the resultant heat response is measured using an infrared camera. Thereafter, the proposed coating thickness visualization algorithm quantifies and visualizes the coating thickness distribution over the entire scanned surface. The proposed system achieves (1) noncontact and nondestructive inspection of invisible coating thickness; (2) automated coating thickness inspection of steel bridges; (3) quantification and visualization of coating thickness via algorithms based on laser-induced heat transfer analyses within the coating layer. The performance of the proposed line laser scanning thermography system was validated through laboratory and field tests. The coating thickness was quantified and visualized with an accuracy of approximately 20 μm.

Feature-based modeling for industrial processes in the context of digital twins: A case study of HVOF process

Industrial process modeling is currently undergoing a fundamental transformation, leading towards interconnected close-loop twins of models, i.e., the parametrically-controlled real-world physics model, and its corresponding digitalized virtual system model. Between these models, a highly time-sensitive mutual validation mechanism and a coherent and consistent control strategy are applied, which demand complex virtual-and-real world model-based information mapping and synchronization. Thus, this research proposes a semantic conceptual framework for industrial process modeling in the context of digital twins. Based on a hierarchical structure of digital twins, this framework modularizes the modeling process in terms of the semantic information modules of physics in the real-world phenomena, and clarifies inter-module associations and near-real-time data transmission coupled with virtual analysis in CAE environment so that the time-sensitive phenomenon information objects distributed on virtually-separated sub-level physics models can be supported for representing the real-world process comprehensively. Advanced feature concept is adopted to construct the digital models as the basic compositions of any virtual industrial process. The related feature definitions are extended in this work so that the common characteristics in the concept of digital twins could be generically and concisely represented. To validate the modeling method, the digital model of a prototyped High-velocity Oxygen-fuel (HVOF) coating process system was constructed as the case study. The data from the nozzle trajectory, the flame, and the in-flight particle behavior, and the transient thermal performance of the coating layer and substrate were synchronously incorporated for simulating the transient phenomena of the substrate component temperature and coating thickness distribution on the substrate surface. The final simulation result validates that the feature-based digital model is able to comprehensively reflect the real-world scenario on the virtual side. To illustrate how the developed model provides meaningful feedback to the real-world control, a general digital twin setup of the model is given at the end of the case study.

Sustained-release capsules coated via thermoforming techniques

Capsule coatings have a wide range of applications as they afford protection to active pharmaceutical ingredients. However, few studies have focused on capsule coating owing to the sensitivity of hard gelatin shells to solvents and high temperature. In the present study, we aimed to coat capsules using two thermoforming coating techniques: vacuum forming coating (VFC) and centrifugal forming coating (CFC). Rheological and mechanical properties were investigated to comprehensively elucidate the processes and mechanisms underlying the two coating techniques. The corresponding coating integrity and drug release behavior were characterized and compared. Herein, we observed that a lower temperature was more suitable for the VFC process than the CFC process. The drug release rate decreased with the film thickness increased. Both optimal VFC and CFC capsules revealed a 24 h sustained-release property following Fick's diffusion law. The coating thickness distribution was more homogeneous for the VFC capsule than the CFC capsule. With the advantage solvent-free of functional capsule coatings, thermoforming coating techniques are convenient and efficient solutions for small-scale personalized coating of oral solid preparations.

Influence of residual stresses in hard tool coatings on the cutting performance

During the hard machining of powder metallurgical high-speed steel, finely dispersed carbides in the steel expose the tools to both thermal and mechanical load. This can influence the cutting performance and cause damage to the tools such as premature abrasive and adhesive wear. Thin hard coatings like TiAlN deposited by physical vapor deposition are widely used in order to improve the tool performance. High power pulsed magnetron sputtering (HPPMS) results in technical benefits, such as a more homogeneous coating thickness distribution on the tools compared to direct current magnetron sputtering (dcMS). The advantages of HPPMS can be combined with the high deposition rates of dcMS leading to a higher economic efficiency conducting a dcMS/HPPMS hybrid process. Adding silicon to the coating system TiAlCrN results in TiAlCrSiN leading to a nanocomposite coating architecture with improved mechanical properties. The influence of the residual stresses on the mechanical properties and on the roughing performance of nanocomposite coatings is of high interest and was therefore investigated in the present study. Four different TiAlCrSiN hybrid coatings deposited with four different substrate bias potentials were examined for this purpose. The residual stresses and the mechanical properties including the resistance against crack formation as well as the compound properties of the coatings on cemented carbide were investigated. Finally, the roughing performance of the coated cemented carbide tools were tested by milling the powder metallurgical high-speed steel HS6-5-3C. For the coatings investigated, it can be concluded that a compressive residual stress state of approx. -2 GPa ≤ σ ≤ −3 GPa leads to the highest resistance against crack formation, and thus to the best cutting performance.

Correction of thickness uniformity of multilayer fluoride coatings on steep spherical substrates using shadowing mask combinations in planetary rotation systems.

In this study, the deposition angle parameter was introduced into the traditional deposition model to eliminate the coating thickness errors caused by large deposition angles and differences in the microstructures of coatings from the expected values. Based on the different thickness distributions of MgF2 and LaF3 coatings, a method that involves switching shadowing masks and a stepwise numerical optimization algorithm were proposed to control each coating thickness distribution accurately. When designing shadowing masks for a multilayer antireflective (AR) coating with a wide incident angle range, the correlation between the thickness distributions of the MgF2 and LaF3 layers was added to the merit function to ensure consistency in the two distributions. Two-layer deep-ultraviolet (DUV) AR fluoride coatings and a six-layer DUV low-polarization antireflection fluoride coating at 193 nm were fabricated on spherical substrate holders using thermal evaporation. In the experiment, when the ratio of the clear aperture to the radius of curvature was increased from -1.68 to 1.63, the thickness uniformities of the MgF2 and LaF3 layers of the two-layer DUV AR coatings on the fused silica substrates increased to a minimum of 98.49%. Owing to the transmission spectra and the incidence angle-resolved transmission, uniform optical performance and low-variation polarization transmittance were also achieved for the 193 nm AR coating deposited on the fused silica substrates.