For water-based Cutting fluid, its lubrication, rust prevention and cleaning performance is particularly critical. In order to improve the performance of Cutting fluid, several or even dozens of additives such as oiliness agent, extreme pressure agent, antirust agent and surfactant should be added to the water-based Cutting fluid. Triethanolamine is an important additive in water-based Cutting fluid. This paper will focus on the role and application of Triethanolamine in water-based Cutting fluid. 1. Properties of Triethanolamine Triethanolamine is also called amino triethanol, and its Molecular formula is C6H15O3N. Triethanolamine is widely used in industry, such as oil industry, petroleum processing industry, Textile manufacturing, rubber and environmental protection. Triethanolamine is produced by the reaction of ethylene oxide and ammonia, and its refined product is colorless viscous liquid. It has strong hygroscopicity and turns yellow brown in the air. Easily soluble in water and ethanol, slightly soluble in ethyl ether and benzene. PH=8-8.5, cannot evaporate with water vapor. 2. The role of Triethanolamine in water-based Cutting fluid 2.1 Synthesis of water-soluble oil based agents At present, most of the oil based agents with good lubrication performance are long carbon chain substances, which are mostly insoluble in water. To add them to water-based Cutting fluid, hydrophilic groups must be introduced into its molecular chain. Triethanolamine has three OH, which is well water-soluble. By controlling the ratio of raw materials, one OH in the molecule of Triethanolamine can react with the oiliness agent to produce water-soluble oiliness agent. Oleic acid is one of the important fatty acids, but it is insoluble in water. The chemical reaction between Triethanolamine and oleic acid (about 65 ℃) can produce Triethanolamine oleic acid. It is a commonly used water-soluble oiliness agent, and the higher the proportion of Triethanolamine contained, the better the water solubility. The maximum non seizing load PB of oleic acid Triethanolamine aqueous solution (5%) measured by four ball tester can reach 650N, and the friction coefficient measured by friction and wear tester is 0.071. When oleic acid Triethanolamine is added to Cutting fluid as an oiliness agent, it is easy to form a physical adsorption film between the tool and the chip (workpiece), which plays a lubricating role under low load. The experiment shows that oleic acid Triethanolamine and extreme pressure additive also have good synergistic anti-wear effect. Adding oleic acid Triethanolamine compound in the synthesis of borate ester and phosphate ester can significantly improve its extreme pressure lubrication performance, thus further improving its cutting performance. 2.2 Rust inhibitor Triethanolamine itself is a water-soluble rust inhibitor. It can effectively prevent steel from rusting in the short term when used alone, with a general concentration of 0.5% to 2%. Triethanolamine has synergistic antirust effect with Phenethyl alcohol amine, Sodium benzoate, borax, sodium carbonate and other water-soluble antirust agents, and the antirust ability of water-based Cutting fluid can be significantly improved by combined use. But Triethanolamine is corrosive to copper, and the addition of 0.05% ～ 0.1% benzotriazole can improve the corrosion resistance of copper. Oleic acid Triethanolamine is also a kind of rust inhibitor, which is suitable for rust prevention of Ferrous and aluminum alloy.
2.3 Surfactants
Surfactant plays a role of penetration, diffusion, stability and cleaning in water-based Cutting fluid, and is an indispensable additive for the synthesis of Cutting fluid and emulsion. Triethanolamine and fatty acid can synthesize an anionic surfactant. Surfactants with different ratios and different Fatty acid synthesis have different HLB values, which can meet the needs of different water-based Cutting fluid. These surfactants have good emulsifying ability. If they are used together with non-ionic surfactant Alkylphenol polyoxyethylene ether or Fatty alcohol polyoxyethylene ether, the emulsifying effect will be better.
Triethanolamine itself is also a non-ionic surfactant. Adding it to water can significantly reduce the surface tension of water. Adding Triethanolamine to the water-based Cutting fluid will help the Cutting fluid soak and penetrate into the cutting (grinding) interface, thus giving full play to the cooling and cleaning role of water-based Cutting fluid.
2.4 Stabilizers
Oiliness agent and extreme pressure agent added in water-based Cutting fluid are easy to be separated from water, thus reducing the role of Cutting fluid. A small amount of Triethanolamine can play a stabilizing role. For example, Boronic acid ester is a new type of extreme pressure and anti-wear agent, which is formed by the reaction of hydroxyl bearing substances with boric acid or its compounds. The main disadvantage of borate ester is that it is easy to hydrolyze. Adding a small amount of Triethanolamine in the synthesis of borate ester can inhibit the hydrolysis.
3. Application of Triethanolamine Cutting fluid
The BN type water-based Cutting fluid is compounded with additives such as oily agent (Triethanolamine oleate), antiwear agent (boric acid ester containing sulfur), antirust complex (Triethanolamine, urea, borax, sodium carbonate, benzotriazole, etc.), and is qualified according to the GB6144-85 Standard for Synthesis of Cutting fluid (IV). Among them, the lubrication and rust prevention performance are superior to national standards. After long-term use in the factory, the Cutting fluid has excellent performance, can significantly improve cutting efficiency and processing quality, extend tool life, reduce processing costs, and is harmless to operators with long service life.
4. Precautions during use
(1) Triethanolamine easily reacts with Nitrous acid to produce substances harmful to human body. Therefore, Triethanolamine Cutting fluid should be careful to use Sodium nitrite as rust inhibitor.
(2) When Triethanolamine type Cutting fluid is used as grinding fluid, a slight unpleasant smell will be produced. In order to overcome this shortcoming, the addition amount of Triethanolamine can be reduced, and a small amount of edible essence can also be added.
(3) When grinding hard alloy tools, it is not easy to use cutting fluids containing triethanolamine. Because Triethanolamine aqueous solution will leach cobalt from cemented carbide tools, thus affecting the tool performance and service life.
