Effect of Synthetic Ester on the Performance of Cutting Fluid by Tapping Torque Test

January 17, 2023

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).

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.

Results and discussion

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 its two special effects, polyester has the highest inherent load capacity among the known ester compounds:

(1) Their polymerization properties, in addition, there are 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.

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.

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