Ester lubricants are widely used in automobile and marine engine oil, compressor oil, hydraulic oil, Gear Oil and grease, and metalworking fluid formulations because of their low toxicity and biodegradability. As early as the 19th century, the natural esters in animal fats such as whale oil and lard or vegetable oils such as rapeseed oil and castor oil were used as lubricants. The earliest record is that the axle was lubricated with animal fats in 1400. Synthetic oil was developed in World War II, and its low-temperature lubricant was esters synthesized from long-chain alcohols and acids. Subsequently, esters and aviation gas turbines were greatly developed together. In 1960, pentaeryl alcohol polyesters began to be used as low-temperature lubricants because of their low volatility, high flash point and good thermal stability. Today, we will discuss the influence of synthetic ester on the lubricating performance of aluminum alloy Semi Synthetic Cutting Fluid.
Experimental part 1) Selection of synthetic ester and formula of cutting fluid The synthetic esters selected in the experiment are fatty acid monoesters (A), polyol esters (B1, B2), and polyesters (C1, C2, C3, C4). 2) Experimental methods
● Tapping torque test The tapping torque test is carried out on the Microtap G8 II tapping torque testing machine. In this experiment, the rotating speed is 1000r/min. The tap is YMW/M6 formed tap, and the test plate is 6061Al. The existence of lubricant will have an impact on the torque value. The better the lubricating property of oil is, the smaller the average torque value is, and vice versa. ● Friction and wear test The four ball friction and wear test was carried out on the MS-10A four ball friction and wear tester produced by Xiamen Tianji Automation Co., Ltd. The standard used in the test was GB/T 3142. Experimental conditions: room temperature; The rotating speed is (1450 ± 50) r/min, and the maximum non seizure load pB and sintering load pD are tested. The wear scar diameter was measured under 196N constant load for 30min, and then the wear scar diameter D of three stationary balls was measured. ● Particle size distribution experiment Malvern MS 2000 particle size analyzer is used for particle size distribution of cutting fluid, and the particle size measurement range is 0.02~2000 μ m。 Before the test, automatically adjust the optical path, set the measuring position and accurately control the temperature. The whole measurement is automatically completed and the test results are recorded. Experimental conditions: room temperature; The experimental water is distilled water; The shading is 10%. ● Rust prevention test The rust proof test adopts the iron filings rust proof method, namely IP287 method. Take about 2g of cast iron chips dried in an oven at (105 ± 2) ℃, evenly distribute them at 90mm, and draw 35mm between them × On the filter paper in the 35mm test area, put the filter paper into the Petri dish, use a pipette to suck 2mL of the tested liquid, drop it evenly on the cast iron scraps, cover the Petri dish cover, place it for 2h under the condition of (20 ± 2) ℃, clean the iron scraps and filter paper with tap water, dry the filter paper, and observe the corrosion of the filter paper surface. ● Conventional test of cutting fluid Refer to the national standard GB/T6144-2010 Synthetic Cutting Fluid, mainly including the appearance, rust prevention test, corrosion test, defoaming test, etc. of the cutting fluid. Results and discussion 1) Study on Lubrication Performance ● Tapping torque test The tapping torque tester simulates the process of metal tapping. When the tapping bit processes threads on a metal plate with holes drilled in advance, the torque value can be measured. The metal plates can be made of different materials as required. 6061Al is used in this experiment. Generally, the average value of 5 tests is measured. The test result can be expressed as a simple torque value or effective percentage - the ratio of the average torque value of the reference solution to the torque value of the fluid to be tested. It can be seen from Table 2 that seven synthetic esters show different lubricating effects. Under the same dosage conditions, the lubricating properties of polyesters, polyol esters and monoesters are better than those of blank samples, and the lubricating properties of polyesters are better than those of polyol esters and monoesters. This is because the lubricating properties of ester compounds are determined by their molecular structures. The lone electron pair of the oxygen atom in the ester chain tends to form an electrostatic bond with the metal surface. Under a given relative molecular weight, the more ester groups, the greater the polarity of the ester molecule, and generally the higher the affinity between the ester and the metal. Due to two special effects, polyester has the highest inherent load capacity among the known ester compounds: (1) their polymerization properties, plus many ester side groups on each polymer chain; (2) Ester side groups appear in pairs. These two effects together make it have a high affinity with the metal surface, sometimes called "caterpillar effect". Within the polyester family (in addition to product viscosity), for typical esters, the lubricity also depends on the polarity of the polyester type. The more ester groups in ester copolymers, the higher their inherent lubricity. ● Research on anti-wear extreme pressure performance Table 3 shows the antiwear extreme pressure properties of synthetic esters. It can be seen that seven synthetic esters show different extreme pressure lubrication properties, that is, under the same dosage conditions, the extreme pressure lubrication properties of polyesters, polyol esters and monoesters are better than the blank samples, and different synthetic esters have different extreme pressure lubrication properties, which is due to the different thickness of the adsorption film formed on the metal surface by different synthetic esters. Synthetic esters have high polarity because of the lone electron pair of the oxygen atom of the ester chain. Polar molecules are very effective lubricants because they generate physical bonds on the metal surface (that is, they stick better on the surface than mineral oil). Most metal oxide surfaces are partially hydroxylated under the presence of water vapor. This hydroxylated surface acts as the donor or recipient of hydrogen atoms in the process of participating in hydrogen bonding, Therefore, the absorption of hydrogen atom acceptors, such as synthetic ester lubricant, will lead to the protection of wear surface and reduce friction. Therefore, synthetic ester is a better lubricant than non-polar mineral oil. 2) Influence of Lubricant on Other Properties of Cutting Fluid ● Particle size distribution Under certain conditions of emulsifier compatibility, the influence of synthetic ester on the emulsification performance of the emulsification system was investigated. The results are shown in Table 4. It can be seen that the seven synthetic esters can be well emulsified by the selected emulsifiers, the particle size of the diluent is about 100 nm, and the emulsion system is stable. ● Rust resistance The IP287 method was further used to investigate the influence of different synthetic esters on the antirust performance of the emulsion system. The results are shown in Table 5. It can be seen that the seven synthetic esters have no effect on the antirust performance of the antirust system of the formula system. ● Conventional test of cutting fluid According to the formula, seven synthetic esters were added to the formula, and their conventional properties were investigated. Conclusion: According to the processing characteristics of aluminum alloy, seven kinds of synthetic esters were selected to be used in the cutting fluid formulation system, and the lubricating performance, antirust performance, corrosion resistance and defoaming performance of the system were tested. The results showed that the synthetic ester showed excellent lubricity in the cutting fluid, and the lubricity of the polymer ester was better than that of the polyol ester and the fatty acid monoester. After the synthetic ester was introduced into the cutting fluid formulation system, it had no effect on the antirust, lubricating and defoaming properties of the system, and could be used in the processing of aluminum alloy materials.
