Coating process of multi-material composite sand mold 3D printing

Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during the pouring process, while the current sand mold 3 D printing technology can only fabricate a single material sand mold. The casting temperature field can not be adjusted by using single sand mold material with isotropous heat exchange ability during the pouring process. In this work, a kind of novel coating device was designed. Multi-material composite sand molds could be manufactured using the coating device according to the casting process demands of the final parts. The influences of curing agent content, coating velocity and scraper shape on compactness and surface roughness of the sand layer(silica sand and zircon sand) were studied. The shapes and sizes of transition intervals of two kinds of sand granules were also tested. The results show that, with the increase of the added volume of curing agent, the compactness of sand layer reduces and the surface roughness value rises. With the increase of the velocity of the coating device, the compactness of sand layer reduces and the surface roughness value rises similarly. In addition, the scraper with a dip angle of 72 degrees could increase the compactness value of the sand layer. The criteria of quality parmeters of the coating procedure are obtained. That is, the surface roughness(δ) of sand layer should be equal to or lesser than half of main size of the sand particles(Dm). The parameter H of the coating device which is the distance between the base of hopper and the surface of sand layer impacts the size of transition zone. The width of the transition zone is in direct proportion to the parameter H, qualitatively. Through the optimization of the coating device, high quality of multi-material sand layers can be obtained. This will provide a solution in manufacturing the multi-material composite sand mold.

Fabrication of in-situ synthesized ceramic reinforced Ni-based alloy composite coatings by reactive braze coating processing

In-situ synthesized ceramic such as TiC,Cr7C3 and Cr5B3 reinforced Ni-based alloy composite coating was fabricated on the surface of mild steel substrate by reactive braze coating processing with colloidal graphite,Cr,Ni,ferro-boron,Si and titanium powders as the raw materials at low temperature of 1000℃,and a new kind of coating materials was developed.By means of SEM,EDS,XRD and surface hardness tester,the microstructures,phases,hardness and wear-resistance of the coating were analyzed,respectively.The results revealed that the coating was mainly composed of the ceramic in-situ synthesized reinforcement phases of TiC,Cr7C3 and Cr5B3 and the binder phases in-situ synthesized of Ni31Si12 and(Ni,Fe)solid solution;The ceramic reinforcement phases of TiC,Cr7C3 and Cr5B3 were randomly distributed in the binder phases of Ni31Si12 and(Ni,Fe)solid solution;The coating had about 15vol%pores and can possibly be applied as a self-lubrication coating;The coating and the substrate were integrated together by metallurgical bonding;The coating had a hardness up to 91-94HR15N.

Material characterization and inter/intra-particle validation for DEM simulation of urea coating process

Particle coating is a common operation in the controlled-release fertilizer (CRF) industry,where a coating layer is appliedto the urea cores.A discrete element method (DEM) computer simulation was applied to model the coating process for the urea granules using measured model parameters.The accuracy of DEM input parameters for the coating material properties and the physical and mechanical characterizations of urea granules are crucial to the study of particle coating processes.Thus,to enhance the simulation accuracy,information on the material properties (urea granules) is required.In this study,the elasticity parameters,shear modulus ,coefficient of restitution (CoR),and coefficient of rolling and static friction (CoRF) and (CoSF) of urea granules are estimated experimentally in addition to the physical characteristics.The sensitivity of the angle of repose of the urea bed was investigated at different coefficients of friction.According to the obtained experimental value of the angle of repose,values of 0.2 and 0.3 for CoRF and CoSF,respectively,were adjusted to obtain consistent urea granules’ motion for simulation and the experiment.Moreover,the spray droplet sizes and velocity distributions were estimated using the video-imaging process technique.Based on this experimental characterization,elasticity parameters and spray properties were integrated into DEM simulation software as input data to perform numerical analysis of the coating process to compare simulation and experimental results,which show uniformity at three different pan speeds with a maximum deviation of 0.033 at 5 rpm.Also,consistency between DEM and experiment results was achieved in terms of average coating thickness (μm) of the selected samples and average intra-particle thickness variation ( CoV intra ).These results revealed that the coating film thickness is proportional to the rotation speed for the experiment and simulation.To enhance the inter-particle coating uniformity,the effects of the most significant parameters such as pan speed,filling ratio,particle size,spray rate,and spray angle,were examined.A low spray rate,filling ratio,and high pan speed improved the coating uniformity.The particle size and spray angle show considerable influence on the coating uniformity,where larger particle sizes and spray angles tend to reduce the inter-particle coating uniformity.

Molecular Dynamic Simulation on the Absorbing Process of Isolating and Coating of α-olefin Drag Reducing Polymer

The absorbing process in isolating and coating process of α-olefin drag reducing polymer was studied by molecular dynamic simulation method, on basis of coating theory of α-olefin drag reducing polymer particles with polyurethane as coating material. The distributions of sodium laurate, sodium dodeeyl sulfate, and sodium dodeeyl benzene sulfonate on the surface of α-olefin drag reducing polymer particles were almost the same, but the bending degrees of them were obviously different. The bending degree of SLA molecules was greater than those of the other two surfactant molecules. Simulation results of absorbing and accumulating structure showed that, though hydrophobie properties of surfactant molecules were almost the same, water density around long chain sulfonate sodium was bigger than that around alkyl sulfate sodium. This property goes against useful absorbing and accumulating on the surface of α-olefin drag reducing polymer particles; simulation results of interactions of different surfactant and multiple hydroxyl compounds on surface of particles showed that, interactions of different surfaetant and one kind of multiple hydroxyl compound were similar to those of one kind of surfaetant and different multiple hydroxyl compounds. These two contrast types of interactions also exhibited the differences of absorbing distribution and closing degrees to surface of particles. The sequence of closing degrees was derived from simulation; control step of addition polymerization interaction in coating process was absorbing mass transfer process, so the more closed to surface of particle the multiple hydroxyl compounds were, the easier interactions With isoeyanate were. Simulation results represented the compatibility relationship between surfactant and multiple hydroxyl compounds. The isolating and coating processes of α-olefin drag reducing polymer were further understood on molecule and atom level through above simulation research, and based on the simulation, a referenced theoretical basis was provided for practical optimal selection and experimental preparation of α-olefin drag reducing polymer particles suspension isolation agent.

Modelling the bed characteristics in fluidised-beds for top-spray coating processes

A particle sub-model describing the bed characteristics of a bubbling fluidised bed is presented. Atomisation air, applied at high pressures via a nozzle positioned above the bed for spray formation, is incorporated in the model since its presence has a profound influence on the bed characteristics, though the spray itself is not yet considered. A particle sub-model is developed using well-known empirical relations for particle drag force, bubble growth and velocity and particle distribution above the fluidised-bed surface. Simple but effective assumptions and abstractions were made concerning bubble distribution, particle ejection at the bed surface and the behaviour of atomisation air flow upon impacting the surface of a bubbling fluidised bed, The model was shown to be capable of predicting the fluidised bed characteristics in terms of bed heights, voidage distributions and solids volume fractions with good accuracy in less than 5 min of calculation time on a regular desktop PC. It is therefore suitable for incorporation into general process control models aimed at dynamic control for process efficiency and product quality in top-spray fluidised bed coating processes.

A study on reactive braze coating of (TiC+Cr_3C_2)/Fe composite coatings

A new hardfacing process, reactive braze coating process (RBCC) was studied, and (TiC+Cr_3C_2)/Fe composite coatings were prepared by RBCC using carbon, Cr_3C_2, iron, ferrochromium and titanium powder as the raw materials in vacuum braze furnace. The results show that TiC is in-situ synthesized in the coatings. The methods of introducing Cr_3C_2 have great effects on the distribution of TiC. Adding Cr_3C_2 directly to the raw materials for coatings, fine TiC particles aggregate into discoids parallel to the coating surface, whereas, in-situ synthesizing Cr_3C_2 in coatings, the aggregations of TiC are lumpish. During braze coating, Cr_3C_2 particles directly added dissolve and precipitate to become needle-shaped. The coatings have an even and smooth surface and are combined with their mild steel substrates by a metallurgical bonding.

Microstructure and Performance Analysis of Organic Coating under High Temperature and High CO_2 Partial Pressure

To evaluate the property of the organic coatings in oil and gas plants, the aging process was studied in high temperature and high CO_2 partial pressure environment. Correlations were developed between the macroscopic properties and microstructure of the organic coatings. The surface appearance, mechanical properties, and permeability of the organic coatings were measured. Furthermore, the crystal structure of the organic coatings was investigated through synchrotron radiation grazing incidence X-ray diffraction（GIXRD） on the BL14B1 beam line in Shanghai Synchrotron Radiation Facility. Combined with the Fourier transform infrared spectroscopy, the molecular structure of the organic coatings was investigated. The experimental results indicate that the thickness variation and weight loss of the organic coatings increase with the immersion time, and the penetration resistance of the coating obviously decreases as the temperature rises. Moreover, the degradation of the organic coatings with immersion time in high temperature and high CO_2 partial pressure environment is caused by the amorphization of the organic coatings as the groups and bonds of the organic coatings were not damaged.

Simultaneous removal of ethyl acetate, benzene and toluene with gliding arc gas discharge

The simultaneous removal of ethyl acetate, benzene and toluene with relatively low or high initial concentration is studied using a laboratory scale gliding arc gas discharge (GA) reactor. Good decomposition efficiencies are obtained which proves that the GA is effective for the treatment of volatile organic compounds (VOCs) with either low or high concentration. A theoretical decomposition mechanism is proposed based on detection of the species in the plasma region and analysis of the decomposition by-products. This preliminary investigation reveals that the GA has potential to be applied to the treatment of exhaust air during color printing and coating works, by either direct removal or combination with activated carbon adsorption/desorption process.

Evaluation of Susceptibility to Hydrogen Embrittlement—A Rising Step Load Testing Method

Hydrogen embrittlement (HE) is a dangerous reaction that puzzled the material world for a long time. Hydrogen embrittlement is a type of deterioration which can be linked to corrosion and corrosion-control processes. It involves the introduction of hydrogen into a component, an event that can seriously reduce the ductility and load-bearing capacity, cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Presently this phenomenon is not completely understood and hydrogen embrittlement detection, in particular, seems to be one of the most difficult aspects of the problem. Although the process cannot be understand completely, method such as baking can reverse the process of hydrogen embrittlement and RSL (Rising Step Load) testing presents an excellent way to test the susceptibility to hydrogen embrittlement in the steel and its alloys. Different specimens were made to facilitate the testing. This study determines the effect of coating process have on the brittleness of the material and use of RSL (Risisng Step Load) mechanical loading test method to qualify plating processes for the risk of internal hydrogen embrittlement. The paper introduces the different causes of the hydrogen embrittlement, especially the zinc coating process and the hot dip galvanizing process. Subsequently, hydrogen embrittlement prevention and testing are discussed, as well as the current McGill-established RSL (Rising Step Load) bend testing’s principle, potential set-up, tested specimens and some of the critical results. Finally, some of the future development of the hydrogen embrittlement prevention will be covered.

A moisture-resistant antireflective coating by sol-gel process for neodymium-doped phosphate laser glass

Using methyl triethoxysilicane as precursor, a moisture-resistant coating for neodymium-doped laser glass was developed by the sol-gel process. Colloidal silica was added in coating solution as modifier. The refractive index of this coating varied from 1.31 to 1.42. A porous antireflective （AR） silica coating with the index of 1.27 was coated on the moisture-resistant coating surface. The two-layer coating possessed transmission up to 99.1% at wavelength of 966 nm, surface root-mean-square （RMS） roughaess of 1.245 am, and roughness of average （RA） of 0.961 am. In the case of laser of 1053-nm laser waveleilgth and 1-ns pulse duration, the damage threshold of the two-layer coatings was more than 15 J/cm^2.

AN EXPERIMENTAL STUDY OF CO_2 LASER CUTTING OF METALLIC COATED SHEET STEELS

An experimental investigation is outlined for the CO 2 laser cutting process of metallic coated sheet steels, GALVABOND. It shows that by proper control of the cutting parameters, good quality cuts are possible at high cutting rate. Visual examination indicates that when increasing the cutting rate to as high as 5000 mm/min (about 100 times that suggested previously), kerfs of better quality can be achieved. Some kerf characteristics such as the width, heat affected zone and dross in terms of the process parameters are also discussed. A statistical analysis has arrived at a recommendatio on the optimum cutting parameters forprocessing GALVABOND.

Optimization of tracer coating parameters and their effects on the mechanical properties and quality of food-grade tracers for grain traceability

The purpose of this study was to optimize the coating process of food-grade tracers to manufacture tracers with good physical,mechanical and practical properties and an excellent appearance.The effects of the coating weight gain(1.00%-5.00%),coating solution spray rate(1.50-7.50 g/min)and tablet bed temperature(30℃-40℃)on the coating appearance quality,moisture absorption rate,friction coefficient,peak shear force,breaking rate,barcode recognition rate,transport wear rate and transport recognition rate were analysed using a Box-Behnken design(BBD)of response surface methodology(RSM).The experimental data were fitted to quadratic polynomial models by multiple regression analysis.The mathematical models of the barcode recognition rate,transport wear rate and transport recognition rate exhibited no statistically significant difference in these data.The optimum coating parameters were as follows:a 5.00%coating weight gain,spray rate of 5.47 g/min and tablet bed temperature of 35.42℃.Under the optimized conditions,the tracers had a good appearance(coating appearance quality),moisture resistance(moisture absorption rate),and frictional(friction coefficient),compression(peak shear force),and impact characteristics(breaking rate).

Self-Lubricating PEO Coating on an Al Alloy Produced by Vacuum Impregnation Post-treatment

The objective of this research was to develop a novel self-lubricating coating on an AA6061 aluminum alloy.Three coatings were prepared by the plasma electrolytic oxidation（PEO） process using 50-, 500-, and 1000-Hz pulsed direct current, respectively. The as-deposited coatings were then post-treated using two different methods, viz., ultrasonic vibration-aided vacuum oil impregnation（UVOI） and oil impregnation under ambient pressure（OIAP）. After posttreatment, an oil-containing, self-lubricating top layer was formed on the coatings. The effects of the coatings＇ surface morphologies and structures on their oil-holding capabilities were discussed. The results revealed that coatings prepared with higher frequency had a greater oil-holding capacity using OIAP post-treatment, while those prepared with lower frequency had a greater oil-containing capability using UVOI post-treatment. These phenomena are related to the morphologies of the coatings produced with various current modes. The tribological properties of the coatings before and after post-treatments were investigated by pin-on-disc sliding wear tests. Due to the formation of a lubricant-containing top layer, the post-treatment coatings had a lower friction coefficient and improved wear resistance compared with the asdeposited coatings. In addition, the coatings after UVOI treatment had better wear performance than those post-treated using the OIAP process. Among all coatings, the coating produced with a 50-Hz pulsed current followed by UVOI posttreatment achieved the lowest friction coefficient（0.03） and best wear resistance when sliding against a Si3N4 ceramic counterface. This study indicates that a novel self-lubricating coating can be prepared by a PEO process combined with vacuum oil impregnation post-treatment.

Effect of Radiant Spectral Characteristics on Performance of a Near-Infra-Red Heating Module

We simulated the heat transfer phenomena of the heating module that is primarily based on the radiant energy in the near-infra-red(NIR) domain.In the module,the power emitted by the lamp filament is distributed to the lamp glass,reflector,and the target medium,which are cooled by an air flow.The radiant heat transfer is simulated by using the ray-tracing scheme,in which the spectral characteristics of the emission and the materials are incorporated.The heat transport from the lamp glass to the cooling air is analyzed by using the finite volume method.As the lamp-filament temperature rises in the range of 3000-3400K,the NIR radiant power on the target medium increases.However,the lamp-glass temperature also rises,and the proportion of the NIR power to the entire radiation has a peak in the temperature range.The spectral distributions of the absorbed energies in all the components in the module are highly non-uniform,and a monochromatic model of the radiant heat transfer may result in a significant discrepancy.

Influence of annealing temperature of ZnO film as the electron transport layer on the performance of polymer solar cells

The surface morphology of Zn O films at different annealing temperatures and the performance of polymer solar cells(PSCs) with Zn O as the electron transport layer are studied.The low temperature sol-gel processed Zn O film has smoother surface than that in higher temperature,which results in the best photovoltaic performance with a power conversion efficiency(PCE) of 3.66% for P3HT:PC61BM based solar cell.With increasing annealing temperature,the photovoltaic performance first deceases and then increases.It could be ascribed to the synergy effects of interface area,the conductivity and surface energy of Zn O film and series resistance of devices.