A study of the effect of cryogenic treatment on the performance of high speed steel tools and carbide inserts

Cryogenic treatment has been acknowledged by some as means of extending tool life of many cutting tool materials, thus improving productivity significantly. However real mechanisms which guarantee better tool performance are still dubious. This implies the need of further investigations in order to control the technique more significantly. Studies on cryogenically treated HSS tools show microstructural changes in material that can influence tool lives. However little research has been done on other cutting tool materials. Cryogenic treatment of carbides has yet to be extensively studied. This work aims to study the effect of cryogenic treatment on M2 and S400 as well as Carbide inserts of SNMS120408 and SNMG120412MP grades. The tools were cryo-treated for 24 hours. The flank wear tests, sliding wear tests and hardness tests were conducted. In the process of ascertaining these findings, it was shown in this study that in flank wear tests cryogenically treated tool showed an increase in tool life. However in sliding wear test, weight loss in case of cryogenically treated tools was found to be more indicating the fact that the tool becomes more brittle after cryogenic treatment due to transformation of retained austenite to martensite as well as due to carbide refinement. Microstructural analysis and SEM analysis were done to support the results obtained. Performance of cryogenically treated tools largely depends upon the cutting conditions. Hence design of experiment (DOE) was employed to study the effect of cutting parameters on tool wear and tool life equations were developed illustrating the significant factors that affect performance of cryogenically treated tools

Experimental Investigations on The Effect of Tungsten Content on the Machining Behaviour of Tungsten Heavy Alloys

The present work attempts to assess the machinability of tungsten heavy alloys (WHAs) with varying tungsten content in terms of different machining characteristics such as chip thickness, material removal rate, cutting force and surface roughness under varied cutting conditions. The feed rate is found to have major influence on the machining characteristics; whereas the effect of rake angle appears to be marginal. With increase in W content both cutting force and material removal rate increase whereas surface roughness decreases. Since WHAs are difficult to machine, an additional objective of the study is to optimize machining parameters. An optimal balance of the experimental cutting parameters using Grey relational analysis has been achieved, which can be effectively employed for the machining of the alloys with close dimensional tolerances and desirable surface finish

Machining and Tribological Characterisation of Uncoated and Coated Carbide Inserts while Turning Tungsten Heavy Alloy

Tungsten heavy alloys are high density alloys containing 80 to 98 wt.% tungsten and the balance is a matrix made of relatively low melting elements such as copper, nickel and iron. These alloys are used as radiation shields, CG adjusters and also in armour piercing ammunition. Machining these alloys to close tolerances and finish leads to excessive tool wear, surface damage and hence proves to be a challenging task. This study focuses on turning operation carried out under dry and wet cutting conditions using three different commercially available cemented carbide inserts. Three different feed rates have been used at a constant depth of cut and cutting speed. The best possible cemented carbide tooling solution for machining tungsten heavy alloys has been determined based on the surface finish obtained, chip geometry, cutting forces, and machining temperature. The observations made during machining are correlated to the tribological behavior of the inserts and the alloy with the help of pin-on disc tests. Coated cemented carbide inserts provide surface roughness values lower than 1 µm under finish turning conditions. On the other hand, PVD coated inserts give consistently better results over different feed rates and are found to experience lower tool wear for the specific cutting conditions. Analytical tool wear model suggests better tool life for the PVD coated insert

Evaluating the fabric performance and antibacterial properties of 3-D piezoelectric spacer fabric

The increasing need of on-demand power for enabling portable low-power devices and sensors has necessitated work in novel energy harvesting materials and devices. In a recent work, we demonstrated the production and suitability of three-dimensional (3-D) spacer all fibre piezoelectric textiles for converting mechanical energy into electrical energy for wearable and technical applications. The current work investigates the textile performance properties of these 3-D piezoelectric fabrics including porosity, air permeability, water vapour transmission and bursting strength. Furthermore, as these textiles are intended for wearable applications, we have assessed their wear abrasion and consequently provide surface resistance measurements which can affect the lifetime and efficiency of charge collection in the piezoelectric textile structures. The results show that the novel smart fabric with a measured porosity of 68% had good air (1855 l/m2/s) and water vapour permeability (1.34 g/m2/day) values, good wear abrasion resistance over 60,000 rotations applied by a load of 12 kPa and bursting strength higher than 2400 kPa. Moreover, the antibacterial activity of 3-D piezoelectric fabrics revealed that owing to the use of Ag/PA66 yarns, the textiles exhibit excellent antibacterial activity against not only Gram-negative bacteria E. coli but they are also capable of killing antibiotic methicillin-resistant bacteria S. aureus

Demographic profile and clinical characteristics of Fuchs' endothelial corneal dystrophy in a tertiary eye care center

Purpose: This study was performed to determine the demographic profile and clinical characteristics in patients with Fuchs' endothelial corneal dystrophy (FECD) reporting to a tertiary eye care center in India. It is a retrospective, single-center, observational study. Methods: The study included 280 patients (559 eyes) diagnosed with FECD presenting between January 2013 and December 2020. The data was collected from the electronic medical record system of the institute. Patient data included demographic features, clinical characteristics, investigations, and surgical interventions. Results: The mean age of the patients was 62 years. Late-onset FECD (95.7%) was more common than early-onset FECD (4.3%). Male: female ratio for late-onset FECD and early-onset FECD was 1:1.65 and 3:1, respectively. More than one-third of the patients had associated systemic history. Preexisting ocular diseases were seen in 5.9% of eyes. Blurring of vision was seen in 383 eyes (68.5%), 13 eyes (2.1%) had glare, and 163 eyes (29.2%) were asymptomatic. A total of 113 surgical interventions were done in 108 eyes (including repeat transplants). Only cataract surgery was done in 40 (7.2%) eyes, whereas penetrating keratoplasty, Descemet stripping endothelial keratoplasty, and Descemet membrane endothelial keratoplasty without or with cataract surgery (sequential or triple procedure) were done in 12 (2.1%), 47 (8.4%), and 14 (2.5%) eyes, respectively. Conclusion: Patients with FECD present mostly during the sixth decade. Posterior lamellar keratoplasty is the most common transplant procedure being performed on FECD patients

Graphene Oxide-Coated Surface: Inhibition of Bacterial Biofilm Formation due to Specific Surface–Interface Interactions

Graphene oxide (GO) is a promising and remarkable nanomaterial that exhibits antimicrobial activity due to its specific surface–interface interactions. In the present work, for the first time, we have reported the antibacterial activity of GO-coated surfaces prepared by two different methods (Hummers’ and improved, i.e., GO_H and GO_I) against bacterial biofilm formation. The bacterial toxicity of the deposited GO-coated surfaces was investigated for both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) models of bacteria. The mechanism of inhibition is different on the coated surface than that in suspension, as determined by measurement of the percentage inhibition of biofilm formation, Ellman’s assay, and colony forming unit (CFU) studies. The difference in the nature, degree of oxidative functionalities, and size of the synthesized GO nanoparticles mitigates biofilm formation. To better understand the antimicrobial mechanism of GO when coated on surfaces, we were able to demonstrate that beside reactive oxygen species-mediated oxidative stress, the physical properties of the GO-coated substrate effectively inactivate bacterial cell proliferation, which forms biofilms. Light and atomic force microscopy (AFM) images display a higher inhibition in the proliferation of planktonic cells in Gram-negative bacteria as compared to that in Gram-positive bacteria. The existence of a smooth surface with fewer porous domains in GO_I inhibits biofilm formation, as demonstrated by optical microscopy and AFM images. The oxidative stress was found to be lower in the coated surface as compared to that in the suspensions as the latter enables exposure of both a large fraction of the active edges and functionalities of the GO sheets. In suspension, GO_H is selective against S. aureus whereas GO_I showed inhibition toward E. coli. This study provides new insights to better understand the bactericidal activity of GO-coated surfaces and contributes to the design of graphene-based antimicrobial surface coatings, which will be valuable in biomedical applications

Multicenter Case–Control Study of COVID-19–Associated Mucormycosis Outbreak, India

We performed a case–control study across 25 hospitals in India for the period of January–June 2021 to evaluate the reasons for an COVID-19–associated mucormycosis (CAM) outbreak. We investigated whether COVID-19 treatment practices (glucocorticoids, zinc, tocilizumab, and others) were associated with CAM. We included 1,733 cases of CAM and 3,911 age-matched COVID-19 controls. We found cumulative glucocorticoid dose (odds ratio [OR] 1.006, 95% CI 1.004–1.007) and zinc supplementation (OR 2.76, 95% CI 2.24–3.40), along with elevated C-reactive protein (OR 1.004, 95% CI 1.002–1.006), host factors (renal transplantation [OR 7.58, 95% CI 3.31–17.40], diabetes mellitus [OR 6.72, 95% CI 5.45–8.28], diabetic ketoacidosis during COVID-19 [OR 4.41, 95% CI 2.03–9.60]), and rural residence (OR 2.88, 95% CI 2.12–3.79), significantly associated with CAM. Mortality rate at 12 weeks was 32.2% (473/1,471). We emphasize the judicious use of COVID-19 therapies and optimal glycemic control to prevent CAM