The effect of machined surface conditioning on the coating interface of high velocity oxygen fuel (HVOF) sprayed coating

Roughening the substrate surface is essential for thermal sprayed coatings. In this regard, sandblasting has established itself as an easy to use surface conditioning procedure. The quality of the obtained roughness depends on the conditions of the sandblasting material, adjusted parameters, and the kind of the process execution (manual or mechanical). These preconditions limit the reproducibility of the roughness obtained. Sandblasting causes residual compressive stress and may also lead to the inclusion of sand particles and notches in the roughened surface, which affects the interfacial properties of the coating, as well as the flexural strength of the coated parts. The hardness of the roughened surface plays, thereby, an important role. However, in order to reliably avoid these effects, microfinishing can be used as an alternative to generate a homogenous roughened substrate surface, control the induced residual stresses, and increase the reproducibility. In addition, the roughened surface pattern can be produced during the chip forming process of the to-be-coated parts. The utilization of the appropriate combination of machining processes and parameters should lead to the required surface pattern and thus to an enhanced coating adhesion and flexural strength of the coated part. The induced residual stresses and the quality of the obtained surface roughness have a significant influence on the coating adhesion and the lifespan of the coated parts. This paper aims to analyze, as a first step, the effect of the turning and microfinishing on the surface conditioning of the bearing steel 100Cr6 (AISI 52100). The investigation concludes by comparing the microfinished with the sandblasted surfaces with regard to the interface to and the adhesion of the WC–Co high velocity oxygen fuel (HVOF) sprayed coatings on them. Surface conditioning plays a decisive role by the induced residual stresses and the elimination of adhesion defects

Embedding behavior of ceramic particles in babbitt coatings and its effect on the tribological properties of low-pressure cold sprayed coatings

The low melting point of Sn-based Babbitt alloys often causes nozzle clogging in the low-pressure cold gas-dynamic spraying (LPCGDS) process, which impacts the process steadiness and the coating quality. Adding hard particles to the feedstock material eliminates this kind of interruption. A certain amount of these particles finds their way in the obtained coatings. These particles also trigger a kind of “hammering effect” due to their impulse forces. These forces are directly dependent on the mass and velocity of the impacting hard particles. However, these forces may lead to a decrease in the porosity and improve the adhesion of the obtained coating. In this study, the effect of the density and size of the hard particle was examined by three different hard materials, Cr3C2, Al2O3, and B4C, which have a material density of 6.68, 3.95, and 2.52 g/cm3, respectively. The used feedstock in this study is a powder mixture that contains 75 vol.% Babbitt and 25 vol.% of either B4C, Cr3C2, or Al2O3. The effect of the size distributions “particles with lower mass” was tested using two different Al2O3. The various hard particles show different embedding behaviors, as well as different effects on the coating build-up. It was found that the blended hard particles were enclosed with the Babbitt matrix, and their interface with Babbitt shows no clear evidence of pronounced diffusion. The size distribution of the blended hard particles has a direct effect on the splat formation and the obtained coating microstructure. It was found that the type of hard particles played a decisive role in the friction behavior. Nevertheless, the hard particle reinforced Sn-Sb-Cu-based composite coatings demonstrated a nearly constant coeffcient of friction throughout the load-interval

Microstructural characteristics in Babbitt coatings deposited by LPCS

Studies have already established that the mechanical properties of Babbitt coatings significantly depend on the microstructural characteristics, such as the amount and distribution of intermetallic compounds dispersed in a soft solid solution matrix. For Sn–Sb–Cu-based Babbitt coatings, the formation of SbSn- and CuSn-based precipitates has a substantial influence on the resulting microhardness and thus determines the maximum load carrying capacity. Thermal spraying of Sn-based Babbitt coatings results in a relatively more refined structure of these precipitates than in common manufacturing processes, such as casting, due to the thermal processing conditions. This study aims to evaluate the effect of the temperature of the propellant gas and substrate temperature on the microstructural characteristics of Sn–Sb–Cu-based Babbitt coatings deposited by low pressure cold spraying (LPCS). The deposits were examined for their phase composition, microhardness and mesoscopic structure. It was found that the coatings were mainly composed of Sb2Sn23, Sb0.49Sn0.51 and Sorosite (CuSn or CuSb0.115Sn0.835), regardless of the substrate temperature or temperature of the propellant gas to be investigated. For a gas temperature above 300 °C, an increased microhardness was observed, which correlates with the appearance of a more homogenous distribution of Sb0.49Sn0.51 dispersed in a soft Sn-rich solid solution matrix

Thermally assisted machine hammer peening of arc-sprayed ZnAl-based corrosion protective coatings

Structural elements of offshore facilities, e.g., offshore wind turbines, are subject to static and dynamic mechanical and environmental loads, for example, from wind, waves, and corrosive media. Protective coatings such as thermal sprayed ZnAl coatings are often used for protection, mainly against corrosive stresses. The Machine Hammer Peening (MHP) process is an innovative and promising technique for the post-treatment of ZnAl coating systems that helps reducing roughness and porosity and inducing compressive residual stresses. This should lead to an enhancement of the corrosion fatigue behavior. In this paper, the effect of a thermally assisted MHP process was investigated. The softening of the coating materials will have a direct effect on the densification, residual porosity and the distribution of cracks. The investigation results showed the influence of thermally assisted MHP on the surface properties, porosity, residual stresses, and hardness of the post-treated coatings. The best densification of the coating, i.e., the lowest porosity and roughness and the highest compressive residual stresses, were achieved at a process temperature of 300 °C. A further increase in temperature on the other hand caused a higher porosity and, in some cases, locally restricted melting of the coating and consequently poorer coating properties

Porosity characterization and its effect on thermal properties of APS-sprayed alumina coatings

In the thermal spraying process, the porosity of ceramic coatings contributes directly to the efficiency of the thermal insulation. The size, shape, and distribution of the pores determine the level of both thermal and sintering resistance. In this work, three different atmospheric plasma sprayed (APS) alumina coatings were fabricated with the same spraying parameters using alumina powders with fine, medium, and coarse particle size. The microstructure of the obtained coatings was analyzed regarding the obtained total porosity, pore size, and pore shape. It was found that it is expedient to divide the pore size range into fine, medium, and large sizes. The shape was characterized with regard to the circularity aspect. In this way, all types of cracks can be considered as oblate pores and were included in the calculation of the total porosity. In the case of using fine feedstock powder, the densest coatings were produced among all coatings, and the fraction of fine pores and cracks are thereby substantially higher. However, the total porosity increases with increasing feedstock powder size. A connection was also made between thermal insulation and porosity fraction which includes fine pores and cracks

The effect of argon as atomization gas on the microstructure, machine hammer peening post-treatment, and corrosion behavior of twin wire arc sprayed (TWAS) ZnAl4 coatings

In the twin wire arc spraying (TWAS) process, it is common to use compressed air as atomizing gas. Nitrogen or argon also are used to reduce oxidation and improve coating performance. The heat required to melt the feedstock material depends on the electrical conductivity of the wires used and the ionization energy of both the feedstock material and atomization gas. In the case of ZnAl4, no phase changes were recorded in the obtained coatings by using either compressed air or argon as atomization gas. This fact has led to the assumption that the melting behavior of ZnAl4 with its low melting and evaporating temperature is different from materials with a higher melting point, such as Fe and Ni, which also explains the unexpected compressive residual stresses in the as-sprayed conditions. The heavier atomization gas, argon, led to slightly higher compressive stresses and oxide content. Compressed air as atomization gas led to lower porosity, decreased surface roughness, and better corrosion resistance. In the case of argon, Al precipitated in the form of small particles. The post-treatment machine hammer peening (MHP) has induced horizontal cracks in compressed air sprayed coatings. These cracks were mainly initiated in the oxidized Al phase

Carbapenem resistance expressed by Gram-negative bacilli isolated from a cohort of Libyan patients

Background and objectives: Carbapenem-resistant Enterobacteriaceae (CRE) and other Gram-negative bacteria are among the most common pathogens responsible for both community and hospital acquired infection. The global spread of cephalosporinases in Enterobacteriaceae has led to the increased use of carbapenems resulting in the emergence and rapid spread of CRE. This has become an alarming public health concern, yet the condition in Libya remains unclear. The aim of this study was to obtain a better understanding of CRE strains prevalent in Libyan patients by investigating their phenotypic characteristics and antibiograms. Methods: Gram-negative bacterial species were collected from Misrata Central Hospital, Misrata Cancer Centre and Privet Pathology Laboratories. Clinical samples and swabs were obtained from hospitalised and non-hospitalised patients and from mechanical ventilation and suction machines. Patients who had received antibiotic therapy for at least three days prior to the study were excluded. The identification and characterization of the isolated species were achieved using the growth characteristics on MacConkey and blood agar, spot tests and API 20E or API 20NE biochemical testing systems. Screening for carbapenem resistance was performed using the disk diffusion method with carbapenem 10 μg and cephalosporin 30 μg disks and minimum inhibitory concentrations (MIC) determined using the Sensititre Gram-negative Xtra plate format (GNX2F). All strains demonstrating resistance or reduced susceptibility to one of the four carbapenems were subjected to carbapenememase activity detection using the RAPIDEC CARBA NP test, Modified Hodge test and carbapenem inactivation methods. Results: A total of one hundred and forty isolates representing fourteen bacterial species were isolated from 140 non-duplicated specimens. Clinical specimens included urine samples (96/140, 68.57%), sputum (15/140, 10.71%), surgical wound swabs (18/140, 12.85%), foot swabs from diabetes mellitus (DM) patients (6/140, 4.29%), ear swabs (3/140, 2.14%) and wound swabs (2/140, 1.43%). Thirty-four (24.29%) isolates demonstrated resistance to at least one of the four carbapenems with Klebsiella pneumoniae representing 73.53% (25 isolates) of all carbapenem resistant species, followed by 8.82% for Pseudomonas aeruginosa (3 isolates), 5.88% for both Proteus mirabilis (2 isolates) and Escherichia coli (2 isolates) and 2.94% for both Citrobacter koseri (1 isolate) and Rahnella aquatilis (1 isolate). The other isolates were either susceptible or cephalosporinase producers. Conclusion: This study has revealed the high rate of carbapenem resistance amongst Libyan patients and emphasizes the crucial need for accurate screening, identification and susceptibility testing to prevent further spread of nosocomial and community acquired resistance. This may be achieved through the establishment of antibiotic stewardship programmes along with firm infection control practices.National Research Foundation of South Africa; Libyan GovernmentWeb of Scienc

Welding fixture for railing : Product development project for a product adapted welding fixture for railings

Rapporten behandlar ett examensarbete för högskoleingenjörsprogrammet maskinteknik på Karlstad universitet. Examensarbetet handlar om produktutvecklingsprojekt där varje process i utvecklingen baserades på etablerade teorier och metoder. I projektet har använts metoder som datainsamling och intervju för att undersöka grundproblemet. Sedan har tillämpats Olssons kriteriematris för att identifiera alla krav på produkten. För konceptgenereringen har använts morfologiska matrisen för att hitta lösningsalternativ. Vidare har utnyttjats elimineringsmatris och relativ beslutmatris för att utvärdera varje koncept.       Arbetet har genomförts hos Nilssons Plåtindustri AB, Säffle. Projektets mål var att hitta en ny lösning för en svetsfixtur för räcke. Lösningen skall vara säkert och ergonomisk för svetsoperatören.   Detta räcke kan ha olika längder och formar beroende på tillämpningsområde. Den består av cirka 15 – 29 stålrör som svetsas ihop till ett helt räcke. I dagsläge sker svetsning manuellt på ett svetsbord. Detta kräver att svetsoperatören lyfter och om positionerar räcket för att kunna svetsa på alla sidor.   Projektet resulterade en svetsfixtur som positionerar samtliga delar av räcket i rätt orientering. För justeringsmekanism används en svetslägesställare som möjliggör att justera positionen av svetsfixturen. Lösningen anses vara effektiv och främjar en mer ergonomisk svetsprocess. Svetsfixturen är anpassat för tre olika varianter av räcke. Den är omställningsbar i flera riktningar vilket underlättar svetsprocessen av räcket. This report discloses a Bachelor of Science thesis for the mechanical engineering program at the University of Karlstad. The thesis covers a product development project where each process in the development was based on established theories and methods. There were certain methods that were used during the project, such as data collection and interview to analyze the main problem. Thereafter Olsson's criteria matrix was applied to identify all requirements for the product. In order to find a solution a morphological matrix was used. To evaluate and select a concept elimination and relative decision matrix were used. The assignment was held at Nilssons Plåtindustri AB in Säffle. The aim of the project was to find a new solution for the welding fixture for railings. the solution must be secure and ergonomic to apply for the operator. These railings may have different lengths and shapes depending on the application area. It consists of approximately 15 - 29 steel pipes that are welded together to form a complete railing. At the present, the welding process takes place manually on a welding table. This requires from the operator to lift and re-position the railing to be able to weld all sides. The project resulted in a welding fixture that positions all parts of the railing in the right orientation. For adjustment mechanism, a welding positioner is applied, which allows to adjust the position of the welding fixture. The solution is considered to be effective and promoted by an ergonomic welding process. It is adjustable in several directions, which facilitates the welding process of railings

Designing of polyethylene-based material modified by plasma discharge for water/oil separation

Produced water (PW) from petrochemical industries is one of the largest wastewaters generated in Qatar. Soluble and insoluble oil contaminants occur in this water and must be removed if water will be used or discharged into the land or sea. Adsorption is a common procedure used in the industry for a wastewater treatment and oily components removal. It is a simple, cost effective process. Currently there are many available natural and synthetic, particularly polymeric adsorbents. Polyolefins are pure hydrocarbon polymers, which due to an appropriate sorption efficiency of lowmolecular weight hydrocarbons can be used as suitable sorbents. However, polyolefins' based sorbents are commercially used only for removal of free oil. In this work, we have investigated a potential use of polyethylene as a filtration media in tertiary filtration of emulsified oil/water mixtures with respect to key parameters determining their adsorption ability. Polyethylene powders of various size and physical treatment were used. Emulsion formed from distilled water and commercial Diesel oil (DO) with a concentration below 200 ppm was used as a model of PW. The emulsions were prepared without emulsifier, and emulsification was insured by ultrasonication. The relationships between the sorption properties and surface composition and morphology of modified and unmodified PE powders were evaluated. Characterizations include the neat oil sorption, and sorption from emulsions, scanning electron microscopy, and profilometry. The PE adsorbents were further characterized by Brunauer-Emmett Teller surface area analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed in order to characterize the porosity, crystallinity and chemical composition of PE, respectively. Sorption experiments were carried out as a function of different weight dosage, initial oil concentrations, and contact time to obtain the optimum conditions for the adsorption process. The results showed that LDPE powder, at a dosage of 3 g treated with plasma, using initial oil concentration of 100 ppm and 720 min of contact time presented the most suitable conditions for the adsorption of oil from emulsified DO. The adsorption process renders LDPE a suitable adsorbent for the removal of oil from diluted oil emulsions with an oil removal efficiency exceeding 93.5%. Equilibrium studies have been carried out to determine the sorption capacity of LDPE for the adsorption of oil from diluted DO emulsions using the optimum conditions. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms. Equilibrium data were fitted very well with the Freundlich model. The pseudo first- and second-order kinetic models were used to describe the kinetic data and the rate constants of sorption were evaluated. The experimental data were fitted well with the pseudo-second-order kinetic model. The study confirmed the feasibility of using oil adsorbents based on plasma treated PE powders as potential adsorbents media for the removal of oil contaminants from P

Dual-modality multi-interface level sensors for monitoring oil separator and other storage tanks

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