Cutting fluid should have excellent cooling, lubrication, rust prevention, and cleaning functions. For water-based cutting fluids, their lubrication, rust prevention and cleaning performance are particularly crucial. In order to improve the performance of cutting fluids, several or even dozens of additives such as oiliness agents, extreme pressure agents, rust inhibitors, and surfactants need to be added to water-based cutting fluids. Triethanolamine is an important additive in water-based cutting fluids. This article focuses on the role and application of triethanolamine in water-based cutting fluids. 1. Properties of triethanolamine Triethanolamine, also known as tri (2-hydroxyethyl) amine, is an organic compound that can be regarded as a trihydroxy substitute of triethylamine, with the chemical formula C6H15NO3. Similar to other amine compounds, due to the presence of lone pair electrons on nitrogen atoms, triethanolamine has weak alkalinity and can react with inorganic or organic acids to form salts. Triethanolamine is generated by the reaction of ethylene oxide and ammonia water, and its refined product is a colorless viscous liquid. It has strong hygroscopicity and turns yellow brown in the air. Easily soluble in water and ethanol, slightly soluble in ether and benzene. PH=8-8 5. It cannot evaporate with water vapor. 2. The role of triethanolamine in water-based cutting fluids 2.1 Synthetic water-soluble oil based agent 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 fluids, hydrophilic groups must be introduced into their molecular chains. Triethanolamine has three - OH groups and good water solubility. By controlling the ratio of raw materials, one OH in the triethanolamine molecule undergoes a chemical reaction with an oily agent, resulting in the formation of a water-soluble oily agent. Oleic acid is one of the important fatty acids, but it is insoluble in water. The chemical reaction between triethanolamine and oleic acid (around 65 ℃) can generate triethanolamine oleate. It is a commonly used water-soluble oil based agent, and the higher the proportion of triethanolamine it contains, the better its water solubility. The maximum non seizure load PB value of triethanolamine aqueous solution (5%) can reach 650 N, and its friction coefficient is determined to be 0 071. Oleic acid triethanolamine, as an oily agent added to the cutting fluid, is prone to forming a physical adsorption film between the tool and the chip (workpiece), which plays a lubricating role at lower loads. Experiments have shown that triethanolamine oleate and extreme pressure additives also have a good synergistic anti wear effect. Adding oleic acid triethanolamine composite during the synthesis of borate and phosphate esters can significantly improve their extreme pressure lubrication performance, thereby further improving their cutting performance. 2.2 Rust inhibitor Triethanolamine itself is a water-soluble rust inhibitor. It can effectively prevent steel rust in the short term when used alone. Generally, triethanolamine with a concentration of 0.5% to 2% has a synergistic rust prevention effect with water-soluble rust inhibitors such as phenylethanolamine, sodium benzoate, borax, and sodium carbonate. Combined use can significantly improve the rust prevention ability of water-based cutting fluids. However, triethanolamine has a corrosive effect on copper, and adding 0.05% to 0.1% benzotriazole can improve its corrosion resistance to copper. Oleic acid triethanolamine is also a rust inhibitor, which is suitable for rust prevention of ferrous metals and aluminum alloys.
2.3 Surfactants
Surfactants play a role in penetration, diffusion, stability, and cleaning in water-based cutting fluids, and are essential additives for synthesizing cutting fluids and emulsions. Triethanolamine and fatty acids can be used to synthesize an anionic surfactant. Surfactants synthesized with different ratios and fatty acids have different HLB values, which can be suitable for the needs of different water-based cutting fluids. These surfactants have good emulsification ability, and when used in combination with non ionic surfactants such as alkylphenol polyoxyethylene ether or fatty alcohol polyoxyethylene ether, the emulsification effect is better.
Triethanolamine itself is also a non ionic surfactant, and adding it to water can significantly reduce the surface tension of water. Adding triethanolamine to water-based cutting fluid will help the cutting fluid to infiltrate and penetrate the interface being cut (ground), thereby fully utilizing the cooling and cleaning effects of water-based cutting fluid.
2.4 Stabilizer
The oiliness agents, extreme pressure agents, and other additives added to water-based cutting fluids are easily resolved by water, thereby reducing the effectiveness of the cutting fluid. Adding a small amount of triethanolamine can have a stabilizing effect. For example, organic borate esters are a new type of extreme pressure and anti wear agent, which are formed by the reaction of substances with hydroxyl groups with boric acid or its compounds. The main drawback of borate esters is their ease of hydrolysis. Adding a small amount of triethanolamine during the synthesis of borate esters can inhibit hydrolysis.
2.5 Adjusting pH value
PH value is an important indicator of water-based cutting fluid. If the pH value is too low, it is easy to breed bacteria, leading to cutting fluid corruption and workpiece and machine tool corrosion. A high pH value can harm the operator's skin and reduce lubrication performance. Triethanolamine is an ideal pH adjustment value for water-based cutting fluids. Adjusting the pH value of the solution with triethanolamine in the later stage of producing water-based cutting fluid will not cause other additives to gel and precipitate due to changes in pH value. When synthesizing phosphate and borate esters, triethanolamine can be used as an alkaline agent to neutralize the product.
3. Application of triethanolamine cutting fluids
BN type water-based cutting fluid is prepared by compounding additives such as oleic acid triethanolamine, anti-wear agent (sulfur-containing borate ester), and rust prevention complex (triethanolamine, urea, borax, sodium carbonate, benzotriazole, etc.), and passing the inspection according to the GB 6144-85 synthetic cutting fluid standard (IV). Among them, the lubrication and rust prevention performance are superior to national standards. After long-term use by the factory, this cutting fluid has excellent performance, can significantly improve cutting efficiency and processing quality, extend tool service life, reduce processing costs, and is harmless to operators, with a long service cycle.
4. Precautions during use
4.1 Triethanolamine is prone to chemical reactions with nitrite to produce substances harmful to the human body. Therefore, triethanolamine cutting fluids should be carefully used with sodium nitrite as a rust inhibitor.
4.2 When using triethanolamine cutting fluid as grinding fluid, it will produce a slight unpleasant odor. 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.
4.3 When grinding hard alloy tools, it is not easy to use cutting fluids containing triethanolamine. Because triethanolamine aqueous solution can leach cobalt from hard alloy cutting tools, thereby affecting their performance and lifespan.
