Coating Process Parameters Research Articles

Effect of high quality hybrid coatings and coating condition on the properties of continuous glass fiber reinforced polypropylene prepreg composites

AbstractDue to the difficulty in infusing resin into interiors of fiber bundles by prevalent pre‐impregnation methods like melt impregnation and the substantial polarity difference between glass fibers (GF) and polypropylene (PP), the application of continuous glass fiber reinforced polypropylene (CGF/PP) composites has been restricted. In this study, a hybrid emulsion is prepared to address the polarity difference through coating process. And further by optimizing coating process parameters, composites glass fibers with excellent performance can be obtained. The study demonstrates that the composite glass fiber with coating amount of 15.34% exhibits good bunching and flexibility. The monofilament tensile strength and interfacial shear strength (IFSS) are increased by 2.53% and 109.74%, respectively compared to the desized glass fiber (GF0). Furthermore, after the hot‐pressing process, the composites glass fiber bundles show fully filled gaps and a completely wrapped surface. This study lays the foundation for producing CGF/PP prepreg composites conveniently, efficiently, and commercially.

Prediction of the finished tablet coating variability in pan coaters by coupling CFD-DEM and Monte Carlo simulations: Method development and validation

We present a numerical approach to predict the long-term coating variability of tablets in pan coaters by combining coupled computational fluid dynamics-discrete element method (CFD-DEM) simulations with a Monte-Carlo method. In CFD-DEM simulations, the coater geometry, operating conditions, air flow and exact tablet shapes are directly simulated to obtain statistical distributions of tablet coating mass gain and circulation time through the spray zone. These short-term distributions (∼102 s) serve as input to a Monte Carlo (MC) method to efficiently predict the coefficient of variation in pan coaters for timescales relevant to commercial manufacture (∼104 s). These predictions achieved reasonable agreement with experimental coating thickness measurements via both the manual gauge and optical coherence tomography (OCT) from coating trials on L.B. Bohle film coaters at different scales. This method enables the application of digital tools as efficient alternatives to resource-intensive experimental trials in determining the appropriate coating process parameters.

Investigation of the Properties of Anti-Friction Coatings Deposited with Different Casting Methods.

This article presents the research results of depositing anti-friction coatings (Babbitt) using three different casting methods: static casting, flame soldering, and clad welding. Babbitt alloy coatings deposited with different casting methods are discussed and explained in terms of changes in the coating properties, such as the microstructure, hardness, strength, and chemical composition. The results showed significant differences in the aforementioned properties, depending on the chosen coating deposition method. The results of the tests confirmed the importance of using shielding gas during deposition to ensure the chemical composition of the coating. The analysis revealed that decreases in the amounts of antimony and copper in the Babbitt coating compared with the initial concentrations were influenced by selective evaporation, oxidation, and the coating process parameters associated with different coating methods. To maintain the desired balance of mechanical properties in Babbitt coatings, it is important to control the antimony and copper contents. Clad welding deposition using a non-consumable tungsten electrode and argon shielding gas achieved a chemically stable coating quite close to the initial chemical composition of the Babbitt alloy.

Anti-bacterial PVA@Ag/PVDF NF membrane made by filtration-coating plus in-situ reduction of NPs for dye removal

In this study, a filtration-coating method was developed to create a PVA layer on a PVDF membrane, and then silver nanoparticles (Ag NPs) were introduced by in-situ reduction to form an antibacterial PVA@Ag/PVDF NF membrane. The relationship between the rejection of dye by the membrane, the morphology of the coated PVA layer and its coating process parameters, such as polymer concentration, crosslinking ratio, vacuum pressure, and time, was investigated. The filtration-coating method facilitated the infiltration of PVA molecules into the porous channel of PVDF membrane, thus improved the stability of coated PVA. Meanwhile, it was observed that high vacuum pressure (1 bar), high polymer concentration (2%), and short filtration time (5 min) have a similar effect to low polymer concentration (1%) and long filtration time (10 min), which results in the formation of a dense layer structure (2–5 μm) on the membrane surface and leads to a high rejection rate but low flux. While filtration at low vacuum pressure (0.1 bar) leads to a thin PVA layer (<0.2μm), and PVA turns to appear on the entrance and surface of pore channel of membrane. The coated membrane showed a stable performance during 72 hrs filtration. Furthermore, Ag NPs were incorporated into PVA layer by the in-situ reduction method, the obtained membrane showed an enhanced dye rejection (92% for methyl blue), and a low salt rejection (NaCl 18%) and moderate flux (17.2 L·m−2·h−1 at 1 bar). Moreover, the composite membrane demonstrated excellent antibacterial properties (Staphylococcus aureus and E. coli). Overall, this work may present a novel approach to prepare new NF membrane.

A 2-dimensional modelling of the coating process of nickel on polyurethane foam via electrodeposition

A numerical model is proposed to investigate the electrodeposition coating process of open-porous polyurethane (PU) foams with nickel. The modelling approach is based on the mixture theory, which accounts for the multi-phase nature of the system comprising the porous foam structure and the electrolyte which consists of the deposition material in form of cations. The model takes into consideration various physical and electrochemical phenomena, including different ionic transport mechanisms, i.e. diffusion, convection and migration. By solving the governing equations numerically, the coating process and the relevant variables are predicted over time. The simulation results are compared with experimental data to assess the agreement between the model and the experimental results. The findings reveal that the numerical model provides valuable insights into the electrodeposition process and facilitates a deeper understanding of the underlying mechanisms and it can be used for optimizing the coating process parameters.

Spray-Coated MoO3 Hole Transport Layer for Inverted Organic Photovoltaics.

This study focuses on the hole transport layer of molybdenum trioxide (MoO3) for inverted bulk heterojunction (BHJ) organic photovoltaics (OPVs), which were fabricated using a combination of a spray coating and low-temperature annealing process as an alternative to the thermal evaporation process. To achieve a good coating quality of the sprayed film, the solvent used for solution-processed MoO3 (S-MoO3) should be well prepared. Isopropanol (IPA) is added to the as-prepared S-MoO3 solution to control its concentration. MoO3 solutions at concentrations of 5 mg/mL and 1 mg/mL were used for the spray coating process. The power conversion efficiency (PCE) depends on the concentration of the MoO3 solution and the spray coating process parameters of the MoO3 film, such as flow flux, spray cycles, and film thickness. The results of devices fabricated from solution-processed MoO3 with various spray fluxes show a lower PCE than that based on thermally evaporated MoO3 (T-MoO3) due to a limiting FF, which gradually increases with decreasing spray cycles. The highest PCE of 2.8% can be achieved with a 1 mg/mL concentration of MoO3 solution at the sprayed flux of 0.2 mL/min sprayed for one cycle. Additionally, S-MoO3 demonstrates excellent stability. Even without any encapsulation, OPVs can retain 90% of their initial PCE after 1300 h in a nitrogen-filled glove box and under ambient air conditions. The stability of OPVs without any encapsulation still has 90% of its initial PCE after 1300 h in a nitrogen-filled glove box and under air conditions. The results represent an evaluation of the feasibility of solution-processed HTL, which could be employed for a large-area mass production method.

A Study of PLA Thin Film on SS 316L Coronary Stents Using a Dip Coating Technique.

The dip coating process is one of the recognized techniques used to generate polymeric coatings on stents in an easy and low-cost way. However, there is a lack of information about the influence of the process parameters of this technique on complex geometries such as stents. This paper studies the dip coating process parameters used to provide a uniform coating of PLA with a 4-10 µm thickness. A stainless-steel tube (AISI 316L) was laser-cut, electropolished, and dip-coated in a polylactic acid (PLA) solution whilst changing the process parameters. The samples were characterized to examine the coating's uniformity, thickness, surface roughness, weight, and chemical composition. FTIR and Raman investigations indicated the presence of PLA on the stent's surface, the chemical stability of PLA during the coating process, and the absence of residual chloroform in the coatings. Additionally, the water contact angle was measured to determine the hydrophilicity of the coating. Our results indicate that, when using entry and withdrawal speeds of 500 mm min-1 and a 15 s immersion time, a uniform coating thickness was achieved throughout the tube and in the stent with an average thickness of 7.8 µm.

Preparation of CNTs-HfB2-SiBCN ceramic composite coatings with adjusted electrical conductivity

Aiming at the lack of stable and reliable electrode materials for high temperature wireless sensors, a solution was proposed to use SiBCN ceramic as thin film electrode. To optimize the conductivity of SiBCN coatings, different conductive fillers were incorporated into the precursor solution to prepare conductive SiBCN coatings and the relationship between the coating process parameters, surface morphology and conductivity was established. The results show that the microstructure of the composite can be adjusted in terms of the HfB2/CNT ratio to optimize the electrical conductivity. HfB2 and CNTs are evenly distributed in the coating by adding dispersants and ground SiBCN self-fillers. The electrical conductivity of SiBCN coatings can be greatly enhanced by adding HfB2 and CNTs fillers. Integrating conductive fillers such as HfB2 and CNTs can form a diafiltration path and the resistivity of the prepared coating has been determined to be as low as 0.13 ± 0.01 Ω m. The conductivity did not necessarily increase with an increasing amount of fillers. Adding a balanced amount of filler particles to the ceramic matrix is the requirement for optimizing the electrical conductivity of the coating.

A novel low-cost spray coating machine for PLA solution on tubular metallic geometries

Polymeric coating is one of the most used surface modification techniques on stents to reduce late stent thrombosis and restenosis. Coating process parameters must need to be rigorously controlled in biomedical applications. Spray coating is one of the most promising process used to recover commercial coronary stents, wherein uniform surfaces must be achieved. A novel low-cost spray coating machine was developed constructed using an airbrush with adjustable pressure (30 psi to 45 psi). Additionally, time and distance control systems were adapted for tubular samples, and a motor controlled their rotation. Polylactic acid (PLA) was deposited on 316L stainless steel tubes, using a spray coating technique for coronary stents purposes in order to achieve optimal film characteristics. Scanning electron microscopy was used to analyze the coating homogeneity. Other physical characteristics such as weight and surface roughness were measured to assess the feasibility of the proposed system.

Investigation of high entropy alloy coatings produced by electrical discharge machining

The exploration of High Entropy Alloys (HEAs) has attracted significant attention due to their multifaceted property profile, suitable for a diverse range of industrial applications. Traditional fabrication techniques, such as melting, have been met with efficiency constraints, necessitating the investigation of alternative approaches for HEA development. The present study examines the feasibility of Electrical Discharge Coating (EDC) as a new and alternative process for the potentially cost-effective fabrication of HEA coatings, with an emphasis on enhancing surface integrity. To provide empirical insights, the research focuses on the deposition of HEA coatings on substrates of X37CrMoV5-1 steel and aluminum, utilizing powder electrodes made of Fe-Co-Mn-Ni-Cr and Fe-Co-Mn-Ni-Cu. The influence of Electrical Discharge Coating (EDC) process parameters on the formation and quality of the High Entropy Alloy (HEA) coatings was evaluated by advanced microstructural characterization techniques. The results show that HEA coatings could be fabricated using EDC, achieving a coating thickness of more than 40 µm.

Simple and additive-free synthesis of highly reflective thin silver films and their application on large-scale surfaces

There is a growing demand for highly reflective coatings especially on non-conducting surfaces for use in various industries. Additionally, focus is arising on green production and cost reduction in terms of energy, time, etc., which require detailed investigation of coating process parameters. Therefore, in this work, silver thin films with high reflectance were synthesized on glass substrates in short durations at room temperature by electroless plating (ELP) method in one-step and without using any additives. Effects of deposition time, concentration of the reactants (AgNO3, Glucose, NaOH), and also the surface pretreatment and activation steps were investigated in detail to improve the reflectance and structural properties of silver films. Contact angle measurements were realized to examine the effects of each surface modification step. Surfaces subjected to etching, sensitization and Ag activation were found to yield more homogeneously distributed nanoparticles in short deposition period. Scanning electron microscopy (SEM) also showed smaller-sized spherulite-shaped crystals, forming a close packed structure with an optimum film thickness of ∼110 nm. The continuity of the silver coatings on the surface was verified by the low sheet resistance of 0.18 Ωsq−1. Atomic force microscopy (AFM) analysis revealed a smoother film structure with an RMS of 10.7 nm after sensitization. X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy analysis (XPS) analysis proved the growth of highly crystalline silver nanoparticles with high purity. All these morphological improvements led to high values of light (∼97%), near-infrared (99%) and solar (96%) reflectance for the coatings. Finally, based on the optimized concentrations and bath conditions, large-scale (700×500 mm2) first-surface mirrors were successfully produced (96.2%R and 0.25 Ωsq−1) by spray coating technique combined with ELP. Overall, the results indicate that the obtained films have potential usage in applications such as solar energy, electronics and aeronautics.

Coating Characteristics and Dynamics of Sponge Roller Coatings with Different Viscosities and Linear Speeds for Different Diameters of Rollers

Coating technology, as a common coating method, is widely used in many industrial fields, among which the mattress industry utilizes it to bond sponges to produce foam mattresses. The thickness of the coating on the sponge is crucial to the quality and performance of the mattress. Hence, this study took the CNCHK-10 high-performance intelligent sponge roller coating as a model; simulated the roller coating process under different viscosities and linear speeds using fluid simulation; analyzed the effects of different viscosities of the coating liquid and the linear speeds of the rollers on the thickness of the coating; and derived the relationships between the viscosity of the coating liquid and the linear speed of the rollers and the thickness of the coating. The relationship between the viscosity of the coating liquid and the linear speed of the roller and coating thickness was obtained. The results show that in the viscosity range of the glue, the viscosity is 1.5 Pa·s when the coating thickness is the smallest, and, at this time, the amount of glue is about 74.1927 g/m2; in the adjustment range of the roller linear speed, the linear speed is 20 m/min when the coating thickness is the smallest, and, at this time, the amount of glue is about 74.1931 g/m2. The results of the study can be used for determining the coating process parameters for a reasonable selection and control to provide a theoretical basis.

Influence of Powder Mass Flow Rates on Wear Resistance and Impact Toughness of Inconel 718 Surface Coatings

Optimum laser cladding processing parameters were obtained based on the study of various powder mass flow rates for the repair of 27SiMn steel parts using Inconel 718 powder. In this study, fusion coating process parameters were set according to the influence of powder mass flow rates on fusion coating properties. The cross-sectional microstructure, X-ray diffraction patterns, micro-hardness distribution, friction, wear properties, impact properties, and fracture morphology of the clad layers were investigated for the various process parameters. The results indicate that the volume fraction for the Ni3Fe phase increases and then decreases as the powder mass flow rate increases. The micro-hardness, friction properties, and impact properties of the samples followed the same trend as those of Ni3Fe. At powder mass flow rates up to 20 g/min, microstructures in the cladding layer tended to be uniform with microstructures with fine grains, and micro-hardness and impact toughness reached maximum values of 328.2 HV0.5 and 45.4 J/cm2, respectively, which show better mechanical properties and wear resistance.

Quantification of the Stability of ALD-Grown TiO2 Protective Coatings on Photoanodes for Solar Water Splitting

Semiconducting photoabsorbers used in photoelectrochemical applications often exhibit low stability under operating conditions. One strategy implemented in recent years to prevent corrosion of photoelectrodes is the application of thin films of titanium dioxide (TiO2), coated by atomic layer deposition (ALD). However, the stability of these coatings under photoelectrochemical conditions is also limited. We are using spectroscopic ellipsometry (SE) and in-situ atomic force microscope (AFM) characterization[1, 2] in order to quantify the influence of the coating process parameters and of post-deposition treatments on the degradation of these protective layers. Here we show our recent investigations under anodic operation in acidic environment. For fully amorphous TiO2 layers, a significant contributor to the corrosion is a purely chemical process, with an activation energy of 57 kJ/mol. Furthermore, the degradation rate doubles upon illumination under simulated sunlight. With increasing pH, the stability increases significantly. Partially crystalline protective coatings exhibit improved stability under operating conditions in sulfuric acid.

Numerical Simulation and Experiment on Pill Coating of Red Clover Seeds under the Action of Vibrating Force Field

In order to solve the problem of the low qualification rate of the pilling and coating of small-grain forage seeds, a vibration force field is introduced to the traditional vertical disk coating machine to promote the mixing of materials and improve the qualification rate of the pilling. Using the typical small-grain forage seed red clover as an example, we used the vibration force field after adding seed powder particles to a coating pot for the theoretical analysis of the force situation, using the discrete element software EDEM to construct a red clover seed simulation model with the coefficient of discretization as the evaluation index. We studied the effects of the rotational speed of the coating pot, the vibration frequency of the pot, the amplitude of the vibration of the pot, and the other operating parameters of the pot on the uniformity of the seed powder mixing, with the pelletization of the pass rate as the physical evaluation standard, using a one-way test to study the effect of operating parameters on the pelletization pass rate. We used the qualified rate as the physical evaluation standard, through a single-factor test, to study the influence of the working parameters on the qualification rate of the pilling. The results show that the simulation test evaluation index of the discrete coefficient and the physical test evaluation index of the pilling qualification rate with the change rule of the working parameters is consistent with the discrete coefficient, and can be used as an indirect evaluation index of the quality of pilling. To further determine the optimal combination of working parameters, a quadratic regression orthogonal design test was conducted with the discrete coefficients as the evaluation index, and the second-order regression equations of the red clover seeds were established and analyzed by ANOVA using Design-Expert software. The study shows that, when the rotational speed of the coating pot is 307.204 rpm, the vibration frequency is 2.526 Hz, and the vibration amplitude of the coating pot is 5.843 mm, the predicted coefficient of dispersion at this time is 8.1%. Simulation using the best combination of parameters to obtain the average value of the dispersion coefficient of 8.4%, relative to the predicted value of 3.7%, indicated that the optimization of the experimental regression model is accurate, and the results obtained for the vibration of small seeds under the conditions of the design of the pellet granulation coating machine and the optimization of the pelletization coating process parameters have a certain degree of reference significance.

Crack Formation Mechanisms and Control Methods of Laser Cladding Coatings: A Review

Laser cladding, a novel surface treatment technology, utilizes a high-energy laser beam to melt diverse alloy compositions and form a specialized alloy-cladding layer on the surface of the substrate to enhance its property. However, it can generate substantial residual stresses during the rapid cooling and heating stages, due to inadequate selection of cladding process parameters and disparities in thermophysical properties between the clad layer and substrate material, leading to the formation of various types of cracks. These cracks can significantly impact the quality and performance of the coating. This paper presents a comprehensive review of crack types and their causes in laser cladding coatings, and identifies that three primary sources of residual stresses, thermal stress, organizational stress, and restraint stress, are the fundamental causes of crack formation. The study proposes several strategies to control coating cracks, including optimizing the coating layer material, refining the coating process parameters, incorporating heat treatment, applying auxiliary fields, and utilizing numerical simulations to predict crack initiation and propagation. Additionally, the paper summarizes crack control methods for emerging structural materials and novel preparation processes. Lastly, the paper analyzes the prospects, technical approaches, and key research directions for effectively controlling cracks in laser cladding coatings.

Experimental analysis of anodic coating process parameters of Al 5754 alloy by response surface method

Aluminum 5754 alloy appears as a candidate material for many engineering applications in terms of its lightness and strength values. The surface properties of this alloy need to be improved for applications where there is surface damage such as friction and wear. In this study, Central composite design was applied to investigate the influences of anodic coating process parameters (voltage, coating time and grit size) on the response (i.e. surface roughness and coating thickness). The competence of the mathematical models recognized, and the importance of the regression coefficients were studied by ANOVA. The initial surfaces of the samples were sanded with 400, 800 and 1200 grit size and surfaces with 3 different roughnesses were obtained. Al 5754 specimens were anodic coated at 8 V, 12 V and 16 V voltages and combinations of time parameters of 10, 20 and 30 min The ANOVA results show that the designed models by RSM for average coating thickness and surface roughness are statistically important at the confidence level of 95%, and 80%, respectively. Maximum anodic coated layer of 29 μm was obtained at surface prepared with 1200 grit size, at 16 V of voltage and used for 30 min of anodizing time. The lowest roughness value of 0.676 μm was obtained at the surface was prepared with 1200 grit size, 8 V of voltage and anodizing time of 10 min.

A novel infrared stealth coating material IR-PAN with excellent infrared radiation feature fusion performance of vegetation background

In this work, to explore the optimal coating process parameters of superior infrared (IR) camouflage performance in vegetation background, the effect of IR unit materials with different substrate surface (Al and Foam) on the surface temperature and IR image at different temperatures were studied. Wherein, the emissivity values of IR unit range from 0 to 0.933, and the scope of the substrate thickness is 0.2–1.2 cm. Besides, in order to further improve the IR camouflage performance of such IR unit materials, an IR/AlN/SiC composite coating (IR-PAN) was prepared and the IR fusion effect was also evaluated by the temperature difference, IR radiation energy difference and the fusion effect of the thermal image between IR-PAN and the traditional coatings. Finally, the experimental results showed that the target background temperature difference, radiation energy difference and the infrared fusion effect of IR-PAN were better than the traditional coatings because of the addition of the underlying coating, which buffered the heat and reduced the difference between the target and background thermal inertia. The temperature difference reduced from 2.58 °C to 1.13 °C, the energy difference of infrared radiation decreased from 1.6 e−3 J to 8.3 e−7 J and more fusion of thermal images was observed. IR-PAN exhibited better corrosion resistance, higher thermal conductivity of 0.463 (about 0.25 higher than traditional epoxy resin coating), hardness of 6H, impact resistance of 50/kg·cm−1, adhesion grade 1 (better mechanical properties) and the optimum AlN content of 20%.

Characterization of the spray droplets and spray pattern by means of innovative optical microscopy measurement method with the high-speed camera

Liquid atomization plays an important role in the manufacturing of the pharmaceutical products. It is used in all production steps where liquid is applied. In some productions steps precise control over spraying parameters is essential. These steps include fluid bed granulation, film coating of tablets and pellet coating. Precise atomization of liquids enables control over the granule formation in granulation steps and film formation in coating steps. Atomization process includes breakup of liquid and formation of droplets, which is a complex and important phenomenon that should be carefully evaluated for each particular use. This study focuses on characterization of atomization process by the means of combining high-speed imaging, optical microscopy and continuous backlight illumination together with robust image processing algorithm. With pure water and three different hypromellose (HPMC) polymer dispersions that are frequently used for film coating of solid dosage forms, we successfully measured mean droplet size (Sauter mean diameter between 49 and 413 μm), droplet size distribution and droplet speed (in average 10–46 m/s). It was shown that the shape of cumulative volumetric droplet size distribution can be used to evaluate the successfulness of ligament breakup (i.e., formation of droplets) and by that the spray quality. Moreover, the obtained trends and empirical correlations between droplet size and other process parameters are useful in practice in order to select appropriate settings for optimal coating process parameters. Due to the simplicity of proposed method and data processing, the entire system is potentially suitable for near real-time coating monitoring and for rapid optimization of the atomization process.

Polyamide powder coating of copper substrates: Impact of process parameters on the surface properties, the adhesion strength and the interface microstructure

The aim of this work was to assess the impact of coating process parameters on the quality of biopolyamide coating on copper substrates obtained by conventional hot dipping fluidized bed coating process (CHDFB). The experiments carried out in this study allowed to understand the decohesion mechanism of virgin biopolyamide 11 before having assessed coating properties by chemical, mechanical and microstructural characterizations. The investigations showed that a higher thickness and better surface finishing were obtained for high preheating temperatures and intermediate immersion times mainly thanks to a higher heat energy stored by the metal support whereas long immersion times compromised the aspect. A laboratory-developed mechanical test was also carried out to determine the adhesion strength. This allowed to overcome the variability linked to the analyzed surface preparation or the local radius of curvature of pull-off and peel conventional adhesion tests respectively that could influence the adhesion strength data. It was concluded that, even if more severe metal preheating conditions improved the coating physical properties, they led to a worse adherence. Surface morphology and spectrometry analyses of the coating side facing the interface correlated to the mechanical test results allowed to highlight the growing formation of copper oxide and copper hydroxide compromising the coating adhesion. From all the results, the optimal process parameters were determined.