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Metalworking fluid emulsions


A metalworking fluid (MWF) Soluble Oil (Conventional Oil) emulsion stability study was set up, comparing the properties of a Naphthenic base oil, versus three paraffinic type base oils of similar viscosity, ca. 20 cSt (100 SUS) at 40 °C, see Figure 1. NYNAS™ T 22 is a good example of the quintessential “100/100” metalworking fluid oil, having a viscosity of 100 SUS at 100 °F. As Group I oils we picked a traditional SN 100 oil, and the NYBASE®


Droplet size distribution experiments The Soluble oil (milky) emulsion droplet size distribution (DSD) was determined at three different times; at mixing, after one day, and again after seven days. The droplet size was measured at high dilution by a Malvern Mastersizer 3000 E.


100, which belongs to a New Range (NR)


of Group I replacement products. These have been designed to have Kinematic Viscosity (KV), Viscosity Index (VI) and Aniline Point (AP) closely matching those of existing Solvent Neutral Group I base oils. The properties of these new products are described in a previous publication [1] and more information is available on www.nynas.com. In this study, further work on model metalworking fluid emulsions was undertaken to search for more likenesses versus Group I. The last test oil was a conventional Group II base oil of similar viscosity.


The solvency, as indicated by the aniline point (AP), varies across the base oils studies: 1. Naphthenic NYNAS™ T 22 (~100 SUS), AP = 76 °C 2. SN 100, AP = 100 °C 3. NYBASE®


100, AP = 101 °C


4. HP4, a Group II base oil, 20 cSt @ 40 (4 cSt @ 100 °C), AP = 108 °C


Standard emulsifiers (surfactants), Span 80 (Sorbitan monooleate), with a Hydrophile-Lipophile Balance (HLB) number of HLB 4.3 and Tween 80 (Polyethylene glycol sorbitan monooleate), HLB 15, were utilized to make nine different blends with HLBs ranging from 9 to 13, in half-steps. Butyldiglycol was employed as solubiliser (co-emulsifier, coupling agent).


All emulsion concentrates were of the same oil content, with surfactants to make up the required HLB value. The concentrate was added to the water at ca. 5 v/v-%, and sonicated at low power for three minutes.


Figure 2. Droplet Size Distribution at HLB 12, soft water (0 °dH).


In Figure 3, the droplet size distribution statistical mean value is plotted versus HLB. These graphs typically will show an “U”-shaped minimum where the emulsion droplet size, is the smallest, and hence at which HLB the most stable emulsions are formed. Similar plots were obtained for the Group I, NYBASE® new range Group I replacement, and Group II formulations.


An increase in mean droplet size over time is observed: Day 0 (Blue bar), Day 1 (Red bar) and Day (7 Green bar) in general show increasing value with time (larger droplet size). Since a gradual increase of droplet size would be the earliest warning sign and the first steps towards coalescence and emulsion break-up, this is very interesting information.


The droplet size distribution varies over two orders of magnitude, from very small (1 µm or less) to close to 100 µm, see Figure 2. The smaller the droplet size, the more stable the emulsion.


Figure 1. From left: NYNAS™ T 22, SN 100, NYBASE®


100 and HP4 Continued on page 16


LUBE MAGAZINE NO.139 JUNE 2017


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