Continued from page 21 Soluble oils
Soluble oils, sometimes referred to as milky cutting fluids, consist of a mixture of mineral oil (typically 40-80%) and an emulsifier. This emulsifier allows the oil to mix with water, creating a milky emulsion. Soluble oils offer the advantages of both oil-based and water-based fluids, providing effective lubrication and cooling properties.
Semi-synthetic fluids
Semisynthetic fluids strike a balance between oil-based and water-based fluids. They typically contain a lower percentage of mineral oil (5-30%) and a higher percentage of water (up to 60%), along with performance-enhancing additives. Semisynthetic fluids offer good lubrication and cooling capabilities while being more cost-effective than fully synthetic fluids.
Synthetic fluids Synthetic fluids are fully synthetic formulations that do not contain any mineral oil. These fluids typically consist of an additised water base and are engineered to provide exceptional performance and solution longevity. Synthetic fluids offer superior cooling and corrosion protection, making them ideal for metalworking applications where heat removal is critical. The latest generation of synthetic fluids are formulated to provide outstanding lubricity with any metallurgy, avoiding the troubles generated by emulsions like instability or cleanability of machined parts.
In recent decades, there has been a noticeable shift away from the use of straight oils towards water-based fluids. This transition has been driven by advancements in additive systems, particularly in the field of wear protection. Water-based solutions have emerged as a more appealing option from both economic and logistical perspectives.
When comparing straight oils to water-based fluids in cutting applications, several performance factors need to be taken into consideration. One of the most crucial functions of a metalworking cutting fluid is heat removal or cooling. Excessive heat generated during the cutting process can lead to deformations in both the workpiece and the cutting tool, making effective heat removal essential.
Water proves to be an excellent medium for heat removal due to its properties. A simple comparison of heat capacities highlights this advantage. Mineral oil, commonly found in straight cutting oils, has a specific heat capacity of 1.67 Joules/g 0°C. In contrast, water boasts a significantly higher value of 4.18 Joules/g 0°C. This disparity in heat capacity is why many machine shops prefer the use of water-based fluids, as they provide superior cooling capabilities.
Improved logistics is another significant factor contributing to the continued adoption of water-based solutions. In large factories like car plants, which often have centralised systems with capacities exceeding 30,000 litres, utilising local water offers substantial benefits in terms of transport and storage. This is because only the concentrate portion of the fluid needs to be transported by road or rail, resulting in significantly reduced transportation and storage requirements for the overall fluid volume.
Nevertheless, it is important to consider several well-documented issues associated with the use of water-based fluids. When mineral oil, water, and triglycerides are present in a warm environment, they can create an ideal breeding ground for bacterial and fungal growths. These micro-organisms can lead to significant problems and pose health hazards.
Figure 1: Global consumption of metal working fluids by % type: Source: Kline Global Lubricant Additives 2020 Market Analysis and Opportunities
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LUBE MAGAZINE NO.181 JUNE 2024
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