Abstract
This paper investigates the surface film adsorption and lubricity of two different types of potential environmentally friendly cold metal forming lubricants: soybean vegetable oil in water VO/W emulsions and triblock copolymer aqueous solutions. The lubricants have different visual appearance, surface film adsorption characteristic, lubricity and surface cleaning behaviour. The effects of concentration, temperature and emulsification ultrasonic energy (for VO/W emulsion) are studied. The result shows that the soybean VO/W emulsions have stronger adsorption, superior lubricity and anti-wear property compared to the copolymer solutions. The effect of temperature is investigated at 30 °C and 65 °C which are below and above cloud point of the aqueous copolymer solutions. Both lubricants show improved friction and anti-wear property at 65 °C. However, tenacious residual film remained on the discs surface after surface cleaning indicates lower cleanability of the soybean VO/W emulsions compared to the copolymer solutions, postulating the need for extra post-processing cleaning operations after cold forming process with VO/W emulsion lubricant.
Highlights
Lubricating oils have evolved rapidly from the conventional mineral oil based lubricants to synthetic oils and aqueous solutions to the extent that more than 10,000 different lubricants are currently in use [1]
Adsorption and desorption behaviour were characterised by means of quartz crystal microbalance (QCM)
The increase in the mass sensed by QCM in rising stage indicates the strong polar nature of the molecules preventing the film to desorb from the surface, unless with high hydraulic current as the roll-up force [43]
Summary
Lubricating oils have evolved rapidly from the conventional mineral oil based lubricants to synthetic oils and aqueous solutions to the extent that more than 10,000 different lubricants are currently in use [1]. Water based lubricants are low cost environmentally-friendly substitutes for mineral oil based lubricants. Two types of water based lubricants namely oil in water O/W emulsions [2,3,4,5,6] and aqueous copolymer solutions [7,8,9,10] have been studied. Biodegradable, non-toxic, and environmentally friendly vegetable oil [11] with superior tribological properties than conventional mineral oil [12,13,14] is a potential mineral oil substitute. The study of the lubricity of different vegetable oils suggests that a small concentration of vegetable oil
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