24th International Colloquium Tribology - January 2024 73 Boundary Lubricant Additive Responses on Steel, Aluminum and Copper Using Twist Compression Tests (TCT) for Multimetal Lubricant Formulation Ted G. McClure 1 , Alexes Morgan 1 1 Sea-Land Chemical Co./ SLC Testing Services, Cleveland Ohio, USA 1. Introduction Materials and manufacturing processes continue to evolve quickly in response to changing industry requirements. Environmental pressures and sustainability are driving rapid vehicle electrification and lightweighting initiatives. This necessitates changes in the way vehicles are manufactured, the lubricants used in production, and fluids used in operation. Electric current and heat management are important considerations, which along with lightweighting, has led to an increase in aluminum and copper content of vehicles. [1][2] Lubricant additive availability is being altered by supplier consolidations, local regulations, global registration requirements, sustainability considerations, and supply chain disruptions. A trend towards multi-metal metalworking fluids has been driven by a desire by users for improved lubricant inventory management, efficient use of manufacturing assets, and an increase in multi-metal components being machined. [3] 1.1 Twist Compression Test (TCT) The Twist Compression Test (TCT) is a bench test that creates boundary conditions and lubricant starvation under high pressure and sliding contact; conditions leading to failures in many applications. It is used to evaluate the boundary lubrication performance of lubricants, including galling resistance of material couples. Figure 1: Twist Compression Test Schematic 2. Experimental TCT was used to evaluate the responses of boundary additives on AA5182-0 aluminum, 110-H02 copper, and AISI 1008 steel, when tested with D2 tool steel, according to ASTM G223-23 [4]. Boundary additive categories evaluated include conventional EP additives, esters, fatty acids, and amines. Specimens were cleaned with odourless mineral spirits, followed by n-heptane. An excess of lubricant was applied with disposable pipettes immediately before testing. All tests included three repeats. Data was collected at 50Hz. The TCT responses used in this analysis were the time until lubricant film breakdown (TBD), and average coefficient of friction (COF). TBD is used to rank lubricants in their ability to survive the test conditions and prevent adhesive wear and galling. Average COF ranks lubricants by friction level during the test. 2.1 Twist Compression Test Conditions Flat Specimens: AISI 1008 Cold Rolled Steel Tensile strength: 303MPa (44,000psi) AA5182-0 Tensile strength: 281MPa (40,756psi) C110 H02 Copper Sheet (99.9% Cu) Tensile strength: 260MPa (37,700psi) Annular Specimen: D2 Tool Steel, Approximately 62 Rc Hardness Lapped contact surface Interface Pressure: Cu: 48.3MPa (7ksi), AA: 20.7MPa (3ksi), 1008 Steel: 103.4MPa (15ksi) Speed: 10rpm (1.2cm/ sec) Dynamic tests (rotation before contact) run to failure: three repeats per test. 2.2 Test Lubricants Boundary additive categories evaluated include conventional EP additives, esters, fatty acids, and amines. Table 1 lists the additives and concentrations in naphthenic base oils that were tested. The viscosity of all lubricants was controlled near 38cSt at 40-°C by base oil blending. 74 24th International Colloquium Tribology - January 2024 Boundary Lubricant Additive Responses on Steel, Aluminum and Copper Using Twist Compression Tests (TCT) for Multi-metal Lubricant Formulation Table 1: Test Lubricants Code w/ w% Additive N 100.00 Naphthenic base oil blend: 38cSt @ 40°C Esters-Alcohol OAL 20.00 Oleyl alcohol ML 20.00 Methyl lardate EAR 20.00 Aromatic monoester EHS 20.00 2-ethylhexyl stearate GE1 5.00 Glycerol ester VO 20.00 Vegetable oil (22% erucic acid) VOB 20.00 Blown Vegetable oil (22% erucic acid) LO 20.00 Lard Oil EWS LAN 5.00 Lanolin POLY 10.00 Polymeric ester (saturated) Acids-Amines EA50 10.00 Poly fatty acid (AV=50) WGFA 5.00 WGFA(AV=46) TOFA 10.00 Tall oil fatty acid (AV=190) ISA 10.00 Isostearic acid (AV=185) FAH 10.00 Diacid (AV=271) OLAM 10.00 Oleyl amine OLDM 10.00 Oleyl diamine EP-Antiwear CP 10.00 Chlorinated paraffin; MCCP (55%Cl) SI 10.00 Sulfurized olefin (20%S inactive) SA 10.00 Sulfurized olefin (20%S active) P1 5.00 2-EH phosphate ester (AV=320) P2 5.00 C-18 phosphate ester, ethoxylated (AV=150) ZDDP 5.00 ZDDP (secondary) CSA 10.00 OB Calcium sulfonate, amorphous (TBN=400) CSC 10.00 OB Calcium sulfonate, crystalline (TBN=300) 3. Results and Conclusions Figure 2 is a graph of the TBD and average COF of each boundary additive, grouped by category, in the steel tests. Chlorinated paraffin (CP), ethylhexyl stearate (EHS), and tall oil fatty acids (TOFA) resulted in the longest TBD on steel, while the blown vegetable oil (VOB) and diacid (FAH) gave the lowest COF results. Figure 2: AISI 1008 Steel Test Results Summary Figure 3 compares the TBD and average COF for the aluminum tests, grouped by additive category. As a class, esters/ alcohol resulted in longer TBD results than the acids/ amines or EP/ AW additives. The longest TBD were for the long chain unsaturated esters (VO, ML, and LO). Methyl lardate and lard oil also resulted in the lowest average COF with aluminum. Figure 3: AA5182-0 Test Results Summary Figure 4 compares the TBD and average COF for the copper tests, grouped by additive category. The overbased calcium sulfonates resulted in the longest TBD results, while the diacid (FAH) gave the lowest average COF. Figure 4: C110 H02 Test Results Summary References [1] DuckerFrontier, 2020 North American Light Vehicle Aluminum Content and Outlook. [2] International Energy Agency (IEA), The Role of Critical Minerals in Clean Energy Transitions. [3] Canter, N (2022), “Metalworking Fluids: Current Options for Machining Multi-metal Alloys”, TLT March, 2022, pp. 44-56. [4] ASTM G223-23; Standard Test Method for Measuring Friction and Adhesive Wear Properties of Lubricated and Nonlubricated Materials Using the Twist Compression Test (TCT). Book of Standards Vol. 3.02.