VEGETABLE OIL STRUCTURE AND ANTIOXIDANTS
Five vegetable oils: canola, soybean, corn, cottonseed and sunflower oils were characterized with respect to their composition by gas chromatography and viscosity. The compositions of the vegetable oils suggest that they exhibited substantially different propensity for oxidation following the order of: Canola < corn < cottonseed < sunflower ≈ soybean The effect of molecular structure of five different vegetables oils including: corn, soybean, canola, cottonseed and sunflower oils with no antioxidants added on the oxidative stability was calculated and the following order of oxidative stability would be expected: canola < corn < cottonseed < sunflower ≈ soybean. Soybean oil, which is one of the most commercially interesting of the vegetable oils in Brazil, was determined to be the most susceptible to oxidative degradation of those oils evaluated. Therefore, soybean oil was selected to be used for a study to evaluate the ability of an antioxidant to stabilize a vegetable oil relative to two commercially formulated petroleum quench oils: Micro Temp 157, a conventional oil, and Micro Temp 153B, a fast oil. The antioxidants selected for this study were Irganox L57 and Irganox L109. In addition, the potential for combinations of L57 and L109 to provide a synergistic improvement over either antioxidant individually was also examined. The results of this work showed following order of oxidative stabilization: L109 > L57 over 60 hours of accelerated testing. No synergism using a blend of L109 + L57 was observed with performance increasing with increasing amount of L109. As expected all of the antioxidant combinations evaluated were better than soybean oil with no antioxidant. However, none of the vegetable oils evaluated exhibited the oxidative stability obtained for either petroleum oil. Cooling curve analysis results were surprising since increasing viscosity observed for vegetable oils with deceasing stability did not exhibit any large effect on cooling rates or times. The reasons for this have not been definitively shown thus far.
Epoxidized Soybean Oil: Evaluation of Oxidative Stabilization and Metal Quenching/Heat Transfer Performance
Vegetable and animal oils as a class of fluids have been used for hundreds of years, if not longer, as quenchants for hardening steel. However, when petroleum oils became available in the late 1800s and early 1900s, the use of these fluids as quenchants, in addition to their use in other industrial oil applications, quickly diminished. This was primarily, but not exclusively, due to their generally very poor thermal-oxidative instability and the difficulty for formulating fluid analogs with varying viscosity properties. Interest in the use of renewable fluids, such as vegetable oils, has increased dramatically in recent years as alternatives to the use of relatively non-biodegradable and toxic petroleum oils. However, the relatively poor thermal-oxidative stability has continued to be a significant reason for their general non-acceptance in the marketplace. Soybean oil (SO) is one of the most highly produced vegetable oils in Brazil. Currently, there are commercially produced epoxidized versions of SO which are available. The objective of this paper is to discuss the potential use of epoxidized SO and its heat transfer properties as a viable alternative to petroleum oils for hardening steel.
Inverse determination of boundary conditions during boiling water heat transfer in quenching operation
Abstract Heat transfer equations describe in most general terms the relationship of temperature, time and space coordinates. In order to achieve a solution matching a given phenomenon, unicity conditions of the solution have to be determined. One of them is the heat transfer coefficient. In complex heat transfer processes, to which belong quenching operation, that coefficient is being determined experimentally or numerically. This paper presents a technique for identifying the local heat transfer coefficient when cooling hot bodies in water during quenching. A dynamic method was applied, using inverse solution of the heat transfer equation. In that solution, a temperature experimentally determined during sensor cooling is set in the equation. The paper presents the results of measurements and calculations as well as a discussion of results for various cooling conditions and positions of the active surface of the sensor.