How base oil selection determines
metalworking fluid emulsion stability
Prof. Thomas Norrby Nynas AB, Naphthenics TechDMS, Nynäshamn, Sweden
thomas.norrby@
nynas.com Dr. Pär Wedin Nynas AB, Naphthenics Research, Nynäshamn, Sweden Ms. Linda Malm Nynas AB, Naphthenics TechDMS, Nynäshamn, Sweden
Introduction
Metalworking fluids (MWF) are used to aid the process of metal machining, mainly by providing lubrication of the workpiece and tool, by providing cooling and corrosion protection.
Metalworking fluids can be generally categorized as being either • emulsions (“coolants”), which mainly cool and protect against corrosion, or
• neat oils, which can handle better high deformation, severe boundary lubrication and offer improved tool wear protection
In metal cutting, the metalworking fluid flow has another very important task, which is breaking and flushing away the chips and swarf as these form.
The make-up of a typical metalworking fluid emulsion is a dilution (not a “neat” oil!) of 5 to 10 volume-% mineral oil concentrate in water. This water could be tap water, with whatever water hardness the local source offers, or demineralised (Demin) or Reverse Osmosis (RO) water which is very soft. The mineral oils content is high, typically 60-70% of the concentrate, and the remainder being oil soluble additives: Emulsifiers, Lubricity additives, Corrosion inhibitors, Biocides, Antifoams and Mist suppressants. Applications for emulsions include use as cutting fluids, corrosion protecting fluids and hot rolling fluids. Emulsions are suitable for high-speed cutting operations where much more heat is generated.
Naphthenic base oils provide several advantages to MWF formulations. High solvency allows for the dissolution of high amounts of additives, and contributes to increased emulsion stability. In addition, a lower density difference between naphthenic oil and water compared to paraffinic oils also provides increased emulsion stability, as gravity has less of
a density difference to pull on. This also increases emulsion resistance to centrifugal forces during pumping.
Thus, there is an intimate relationship between the formulation chemistry and the performance of metalworking fluids. To investigate how key formulation parameters, such as selection of base oil, emulsifier system, and water hardness affects the emulsion stability, a series of emulsions were formulated where the base oil, the emulsifier type and Hydrophile-Lipophile Balance (HLB) value, and water hardness were parameters changed independently.
In this study, we set out to investigate how the emulsion droplet size distribution would vary as the result of formulating changes varied, and how that distribution changed over time. Results were obtained and analysed for Naphthenic, Group I and Group II base oils.
Experimental work Emulsion stability
Emulsion stability is key to metalworking fluid (MWF) usefulness- if the emulsion breaks, it has ceased to function. Investigations of the relationship between formulation and emulsion stability thus is a first step towards better understanding of the complex chemistry of a fully formulated MWF. Test parameter in the study were base oil type selection, water hardness and emulsifier chemistry and Hydrophile-Lipophile Balance (HLB) value selection. We sought to understand how the properties of the base oils, especially solvency (Aniline Point), and the water hardness (°dH) would influence emulsion stability over test period up to one week. A second step was to investigate a semi-synthetic formulation giving transluscent mictso-emulsions utilizing the same base oil slate.
14
LUBE MAGAZINE NO.139 JUNE 2017
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72