Metal Processing Online Lecture: Types of Common Cutting Fluids

Aqueous solution

The main component of the aqueous solution is water, to which a small amount of additives having rust and lubrication effects are added. The aqueous solution has a good cooling effect and is used for general grinding and other finishing. The formulation is transparent and easy for the operator to observe. However, pure water tends to rust the metal and the lubrication performance is poor . Therefore, a certain amount of additives are often added to the aqueous solution to maintain both cooling performance and good rust resistance and certain lubricating properties.

2. Emulsion

The emulsion is obtained by diluting the emulsified oil with water. The emulsified oil is made up of mineral oil, emulsifier and additives. After being diluted with 95%~98% water, it becomes a milky white or translucent emulsion. The emulsion has a good cooling effect, but because of the large water content, the lubrication and rust prevention performance are poor. In order to improve its lubricating performance and anti-rust performance, a certain amount of oily, extreme pressure additives and anti-rust additives can be added to prepare an extreme pressure emulsion or an anti-rust emulsion. An emulsifier is a surfactant that is an additive that emulsifies mineral oil and water to form a stable emulsion. The surfactant consists of a hydrophilic polar group and a lipophilic non-polar group. The emulsifier is added to the oil and water. It can be aligned and adsorbed at the oil-water interface. The polar end is connected to the water, the non-polar end is connected to the oil, and the oil and water are connected to reduce the oil-water interfacial tension. It is stably dispersed in water with tiny particles to form a stable oil-in-water emulsion. This oil-in-water emulsion is applied during metal cutting, as shown in the figure below.

Schematic diagram of oil-in-water and water-in-oil emulsion

The low concentration emulsion has a good cooling effect and is mainly used for grinding, roughing, drilling and the like. The high-concentration emulsion has a good lubricating effect, and is mainly used for finishing cars, tapping threads, dumpling holes, and gear shaping.

3. Cutting oil

The main component of cutting oil is mineral oil, and a few use animal or vegetable oil or compound oil. Pure mineral oil does not form a strong lubricating film on the friction interface, and the lubrication effect is general. In practical use, oil additives, extreme pressure additives and anti-rust additives are often added to improve the lubrication and rust resistance. Animal and vegetable oils have good oil properties and are suitable for low-speed finishing, but they are prone to deterioration. Therefore, it is best not to use or use less, but other alternatives should be used, such as mineral oils containing extreme pressure additives such as sulfur and chlorine. For normal turning and tapping, oil can be used. Kerosene can be used when finishing non-ferrous metals or cast iron. Vegetable oil can be used when processing threads. Adding a certain amount of oily additives and extreme pressure additives to mineral oil can improve the lubrication performance under high temperature and high pressure. It can be used for finishing, reaming, tapping and gear processing.