Performance Evaluation of Vegetable Oil-Based Cutting Fluids in Mild Steel Machining

Vegetable oils are being investigated to serve as a possible replacement for non-biodegradable mineral oils, which are currently being used as base oil in cutting fluids during machining processes. In this present study, the performances of palm oil and groundnut oil were compared with that of mineral oil-based cutting fluid during machining operation of mild steel. Temperature of the workpieces as well as their chip formation rates using these vegetable oils as cutting fluids under different cutting speed (rev/min), feed rate (mm/rev) and depth of cut (mm) were compared with that of mineral oil and dry machining. The average temperatures of the workpieces were obtained at different depths of cut; 5mm, 10mm and 15mm under different cutting conditions. The temperature of the workpiece when groundnut oil was used as the cutting fluid was very close to that of the conventional oil, which was the lowest. Palm oil gave the overall highest chip thickness of 0.27 mm probably due to its better lubricating property. This was followed by that of the groundnut oil and the conventional oil as compared with dry machining of 0.17 mm thickness. Vitamin-C- rich-lemon fruit extract was used as an antioxidant to improve the oxidative stability of the vegetable oils. Viscosities of the various fluids were also analysed, and lowest average viscosity value of 28.0 Poise was obtained using groundnut oil. This shows that groundnut oil possesses better fluidity and faster cooling capacity than other oil samples. Samples lubricated with mineral-oil based fluid show fine microstructures, similar to what obtained using groundnut oil based cutting fluid. Fine surface morphology indicates improved surface roughness compared to using other cutting fluids. Based on these results, groundnut oil and palm oil are being recommended as viable alternative lubricants to the mineral oil during machining of mild steel. Keywords: Vegetable oils, cutting fluids, drilling operation, mild steel, coolants

High temperature oxidation of Pt-based alloys

High temperature oxidation of Pt84:Al11:Cr3:Ru2 (at.%) in air between 1150°C-1350°C, for up to 500 hours in both water-quenched and air-cooled specimens was investigated. Mass gains and thicknesses of the Al2O3 scales were measured. Surface and cross-section morphologies of the oxide scales were examined using a field-emission scanning electron microscopy with EDS. Cross-sectional examination was also done by cutting the samples in a cross beam FIB workstation. Phase identification was done with X-ray diffraction and Raman spectrometry. Room temperature stresses in the oxide scales were measured by using an argon-ion laser, and were found to be compressive and low. Well-adhering and protective external α-Al2O3 scales formed on all specimens, without spallation. Cross sections showed protrusions of the alloy into the scale; which allowed mechanical keying of the scale to the substrate, and were mainly responsible for the good adherence. No internal oxidation was observed. Parabolic scale growth kinetics were established, and rate constants and activation energies were deduced. Oxidation rates in both the quenching media were close at lower exposure temperatures, while at higher temperatures, the scale growth rate of the air-cooled specimens was faster. Microscopic observations showed that the oxide grain sizes increased with increased oxidation time at all temperatures, and the morphology changed from small flakes to large oxide grains with time. The growth mechanism of the α-Al2O3 scale was proposed to be mainly by inward diffusion of oxygen along the oxide grain boundaries, with some outward diffusion of aluminium ions along the short circuit paths. Oxidation of both water-quenched and air-cooled Pt84:Al11:Cr3:Ru2 (at.%) specimens followed the same trends, with water-quenched specimens displaying slightly better properties. Compared to most other Pt-, Ni-and Fe-based superalloys, the scales on Pt84:Al11:Cr3:Ru2 (at.%) specimens possessed slower growth rates, lower activation energies and room-temperature compressive stresses. Thus, Pt84:Al11:Cr3:Ru2 (at.%) possesses potential for high temperature applications

Evaluation of Mechanical Properties of Medium Carbon Steel Quenched in Water and Oil

Samples of medium carbon steel were examined after heating between 900ºC-980ºC and soaked for 45 minutes in a muffle furnace before quenching in palm oil and water separately. The mechanical behavior of the samples was investigated using universal tensile testing machine for tensile test and Vickers pyramid method for hardness testing. The microstructure of the quenched samples was studied using optical microscope. The tensile strength and hardness values of the quenched samples were relatively higher than those of the as-cast samples, suggesting improved mechanical properties. However, samples quenched in palm oil displayed better properties compared with that of water-quenched samples. This behavior was traced to the fact that the carbon particles in palm oil quenched samples were more uniform and evenly distributed, indicating the formation of more pearlite structure, than those quenched in water and the as-received samples

Inhibition of mild steel corrosion using Jatropha Curcas leaf extract

Jatropha Curcas leaf was investigated as a green inhibitor on the degradation of mild steel in 4 M HCl and 4 M H2SO4 aqueous solutions using gasometric technique. Mild steel coupons of dimension 2 × 1.5 cm were immersed in test solutions of uninhibited acid and also those with extract concentrations of 4 ml, 6 ml, 8 ml and 10 ml at 30 oC, for up to 30 minutes. The results showed that as the concentration of the extract increases, there was reduction in the corrosion rate. As the extract concentration increased from 4 ml to 10 ml at 30 minutes exposure, the volume of hydrogen gas evolved decreased from 19.1 cm3 to 11.2 cm3 in H2SO4 medium, while it reduced to 5 cm3 from 9 cm3 in HCl medium. Also, the metal surface-phytoconstituent interaction mechanism showed that 6 minutes is the best exposure time for the adsorption of the extract in both acidic media. The Jatropha Curcas leaf extract was adsorbed on the mild steel surface to inhibit corrosion, while the experimental data obtained at 30 minutes exposure in both acidic media were well fitted with the Langmuir adsorption isotherm. Hence, Jatropha Curcas leaf extract is a good and safe inhibitor in both acidic solutions

Hydrogen Storage Characteristics and Corrosion Behavior of Ti24V40Cr34Fe2 Alloy

In this work, we investigated the effects of heat treatment on the microstructure, hydrogen storage characteristics and corrosion rate of a Ti34V40Cr24Fe2 alloy. The arc melted alloy was divided into three samples, two of which were separately quartz-sealed under vacuum and heated to 1000 °C for 1 h; one of these samples was quenched and the other furnace-cooled to ambient temperature. The crystal structures of the samples were studied via X-ray diffractometry and scanning electron microscopy. Hydrogenation/dehydrogenation characteristics were investigated using a Sievert apparatus. Potentiostat corrosion tests on the alloys were performed using an AutoLab® corrosion test apparatus and electrochemical cell. All samples exhibited a major body-center-cubic (BCC) and some secondary phases. An abundance of Laves phases that were found in the as-cast sample reduced with annealing and disappeared in the quenched sample. Beside suppressing Laves phase, annealing also introduced a Ti-rich phase. The corrosion rate, maximum absorption, and useful capacities increased after both heat treatments. The annealed sample had the highest absorption and reversible capacity. The plateau pressure of the as-cast alloy increased after quenching. The corrosion rate increased from 0.0004 mm/y in the as-cast sample to 0.0009 mm/y after annealing and 0.0017 mm/y after quenching

Corrosion of food grinding discs in gastro-intestinal environment

The need for food size reduction before consumption has led to the use of motorized grinding machine which operates on energized rubbing of two grooved cast-iron discs, and this unintentionally results in tribological degradation and corrosion of grinding discs into the ground food. The objective of this study was to carry out an assessment of corrosion susceptibility of grinding discs from different manufacturing methods in simulated gastro-intestinal environment. Six grinding discs from three states in Nigeria were selected for this study, based on manufacturing methods namely: rotary, cupola, and pit furnaces. Experimental techniques used for the study included: X-Ray Fluorescence spectroscope for determination of chemical composition and X-Ray Diffractometer was used for phase identification. Corrosion susceptibility of grinding discs on interaction with pseudo-body fluid was studied using potentiodynamic polarization scan and product analysis (gasometric) methods in simulated gastro-intestinal environment, typical of human stomach, as electrolyte. The electrolyte contained 2 g/L NaCl acidified to pH of 1.7 with HCl and regulated at 37 °C. Optical microscopy of the electrochemical samples was done for corrosion damage assessment. The key finding from the study was that all the grinding discs contain iron and silicon as dominant alloy elements, which existed predominantly as iron carbide and ferrosilicon phases. Corrosion of the discs in simulated gastric solution was well profound irrespective of the manufacturing method, though, with varying degree among the discs. The outcome of this study is applicable to food industries where cognitive measures may have to be taken on materials selection to minimise the risk of food contamination from materials corrosion