Optimization of Boundary Lubrication Properties of Metalworking Lubricants Combining Mixture Design of Experiments (DOE) with Twist Compression Tests (TCT)
January 15, 2016
Environmental, health, and safety pressures, global competition, and productivity demands necessitate rapid changes in manufacturing processes and materials. Metalworking fluid (MWF) ingredients and formulations are changing in response. A need exists for systematic, efficient, MWF formulation techniques, and rapid, flexible test methods which correlate well with field performance. An example is combining mixture design of experiments (DOE) with TCT.
2 Mixture Design of Experiments (DOE)
Mixture DOE methods are used to quantify the relative contributions of ingredients to a response of mixtures, predict the response for any mixture of the ingredients, and optimize combinations for the response(s) . These methods may be used to develop robust, cost-effective MWF formulations.
3 Twist Compression Test (TCT)
The TCT is used to rank lubricant performance under boundary and E.P. conditions. This bench test correlates with field performance in severe metalworking operations. TCT creates a lubricant starvation condition, under high pressure, and sliding contact: a condition common to severe operations in areas where lubricant film failure is likely to occur . Lubricants are ranked by their time until film breakdown and COF.
Figure 1: Twist Compression Test Schematic
TCT has been used to compare E.P. additive responses in different base stocks . The wear track is used for analysis of tribofilms and lubrication mechanisms .
In order to lubricate under a variety of conditions and to take advantage of synergies, combinations of additives are commonly used. In this case three ingredients (factors) are investigated: a sulfurized olefin (25%S), high polarity olefin copolymer, and dioleyl hydrogen phosphite (DOHP) in mineral oil. TCT used to evaluate the 20 DOE samples at 55MPa using 1008 steel and D2 tool steel specimens.
5 Results and Conclusions
The contour graph below shows the TBD behaviour in the design space defined. The longest TBD values can be achieved by combining high levels of the polymer with DOHP and less sulfur carrier, or by including high sulfur levels with lower levels of DOHP and polymer.
Figure 2: Contour Plot; Time Until Breakdown (TBD)
 Cornell, J. A.: Experiments with Mixtures, 3rd Ed. Ch. 1-2. (2002)
 Schey, J. A.: Tribology in Metalworking, (1983) 211-212
 S. Asadauskas, G. Biresaw, T. McClure: Effects of Chlorinated Paraffin and ZDDP Concentrations of Boundary Lubrication Properties on Mineral and Soybean Oils, Trib Letters, 37 (2010), 111-121
 J. Baltrus, T. McClure, G Bikulčius, S. Asadauskas: Formation of Carbonaceous Nano-Layers under High Interfacial Pressures during Lubrication with Mineral and Bio-Based Oils, Chemija, vol 25 (2014), 3 161-170
Ted G. McClure 1), Robert Stubbs 2)
1) Sea-Land Chemical Co. / SLC Testing Services, Westlake, Ohio, USA
2) Sea-Land Chemical, Europe, Ltd., Byley, Cheshire, United Kingdom