Base Stocks Matter in Metalworking Fluids

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SHENZHEN, China – Research and development of metalworking fluids and other industrial lubricants often focuses on the chemical additives that contain. But formulators should pay more attention to selecting effective base stocks, an industry insider told a conference here last month.

Studies by the Lubrication Research Institute of the Guangzhou Mechanical Engineering Research Institute found that different base stocks are advantageous for different applications, Li Maosheng, a professor and senior engineer at LRI, told the CBI Base Oil Summit Sept. 12.

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Due to the obvious effect of additives and the promotion of additive companies, additive-related study has attracted more and more attention, Li said. In contrast, the number of base oil alternatives is limited, and the base oil is usually regarded as unchangeable. As a result, little attention has been paid to base oils.

Li contended that base stocks in metalworking fluids today have a significantly greater impact on industrial lube performance than they did in years past.

The Lubrication Research Institute is one of Chinas main centers for the study of industrial oils. It also has a commercial arm, Jetsun Lubrication Technology Co., which is one of Chinas largest suppliers of metalworking fluids. Li said the lubrication institute conducted a preliminary study recently of base stock performance in metalworking fluids and other industrial lubes. They concluded that base stocks should be selected based on characteristics such as viscosity, viscosity index, performance at different temperatures, oxidative stability and interaction with equipment and workpiece materials. But requirements can differ widely for different applications. LRI researchers looked specifically at requirements for fluids used in metal forming.

A low-viscosity oil with low surface tension will provide optimal permeability and cooling performance, so it is a relatively good choice as base oil, especially in processing soft metals like copper and aluminum, Li said. Base oils with too high viscosity have poor cooling performance and strong adhesion. They remove chips easily, but they are hard to clean. Thus, they should not be used as a cutting oil base stock.

Li said there are additional considerations when selecting a base stock for microemulsion metalworking fluids, because the oil is interacting not only with tools and workpieces but also with the water portion of the formulation. Naphthenic base oils perform well because they have low pour-points and help the microemulsion to maintain a low freezing point.

Low-viscosity paraffinic base stocks are also good choices, he said, because they are stable and allow good clean-up. Non-standard oils would seem a good choice, he said, but they make cloudy mircroemulsions – an undesirable characteristic in the eyes of end users. Tower oils meet most performance requirements at typical operating temperatures but tend to agglomerate during winter and therefore should not be used, Li said.

Li suggested that formulators of metalworking emulsions should consider the storage capabilities of base stocks that they choose. For example, he said, bottom oils and non-conventional oils tend to freeze when ambient temperatures fall below freezing. In comparison, naphthenic base stocks and tower oils maintain good liquidity during winters in northern China.

Li concluded by stating that the subject of base oil selection for metalworking fluids deserves further study.

Our study of base oil is only an attempt and is immature, he said. We hope we can explore and promote industry development together with others in the industry.

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