Abstract
ABSTRACT The number size distributions of submicron oil mist particles generated by three industrial metal (steel) machining processes—lathe machining, cutting, and grinding—were measured using an electrical mobility analyzer and an optical particle spectrometer. The measured number concentration of ultrafine particles (UFP; ~30 nm diameter) reached 107 particles cm–3 during each machining process. The condensation of thermally evaporated oil vapor was considered to be a major route of ultrafine particle generation during lathe machining and grinding, which used an oil-in-water emulsion and an insoluble lubricant oil, respectively. Cutting, which did not use lubricant oil, also produced a steep increase in the number concentration of UFP; these particles may have formed from residual oil-in-water emulsion on the surface of the workpiece after lathe machining. A simplified numerical simulation was used to quantify the particles arising from machining and leakage when the apparatus was opened. Although local ventilation effectively reduced the concentration of the oil mist in the apparatus and prevented the diffusion of this substance when the apparatus door was opened, leakage was observed when the workpieces were exchanged; this leakage was attributed to entrained particles on the workpieces. Hence, countermeasures to prevent entrained oil mist are necessary to improve the air quality in working environments.
Highlights
Oil mist is generated in machining plants, which consume large amounts of oil for lubricating and cooling cutting tools and workpieces
Industrial Metal Machining Processes We investigated the oil mist generated by three typical machining processes: lathe machining (Fuji Corp.), gear cutting (Kashifuji Works, Ltd.), and gear grinding (Reishauer)
The number concentration of particles in the range of 300–500 nm increased once the machining process started and the ventilation was turned on, which occurred every 50 s (Fig. 4(c)); this periodic increase was observed by both OPC1 (Fig. 4(a)) and the EEPS (Fig. 4(b))
Summary
Oil mist is generated in machining plants, which consume large amounts of oil for lubricating and cooling cutting tools and workpieces. Oil mist emissions during the machining process increase the airborne particle concentration in the working environment and are associated with occupational health problems such as inflammation of skin, laryngeal cancer, asthma, and bronchial hyperresponsiveness (Mackerer, 1985; Robertson et al, 1988; Kubasiewicz et al, 1991; Ahrens et al, 1991; Massin et al, 1996; Kazerouni et al, 2000; Greg et al, 2001; Simpson et al, 2003). The Japan Society for Occupational Health recommends that the mass concentration of oil mist be maintained below. 3 mg m–3 (Japan Society for Occupational Health, 2017); such mass-based regulations do not account for the effects of oil mist generated by gas-phase nucleation processes. The UFP are considered to be associated with adverse health effects (Oberdörster, 2001; Donaldson et al, 2002)
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