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Water-miscible coolants: monitoring is key!

During machining processes, water-miscible metalworking fluids can get contaminated in different ways: by dirt, guideway and hydraulic oil, metal fines and even from unknown substances. Daily inspections can go a long way to increase process stability and minimize health as well as environmental risks.

The contamination may directly influence the main quality aspects of the product, like performance, foam building or skin tolerance. That is why it is strongly recommended to regularly monitor the coolant.

Daily visual checks

The first – and most fundamental – step is the daily check of the fluid level in the coolant tank. This is a prerequisite for proper metalworking fluid use. In machining centers with low fluid level, insufficient supply of the feed pump may lead to a higher emulsion temperature, air suction and increased foaming. Additional possible consequences can be insufficient cooling of the work piece, reduced tool life, reduced performance, and as a result a lower surface quality.

The second, equally important daily check is the visual inspection of the color and stability of the coolant. In case changes can be detected, such as a discoloration or a floating oil layer on the surface, this could be an early warning sign indicating that the quality of the emulsion is unstable.

Tramp oil can also form a floating oil layer – a problem that needs to be handled by continuously removing this layer, for example with an oil skimmer.


Take a sample from the nozzle


Initial filling of machine

Since it is often difficult to reach the metalworking fluid in the tank, it is advisable to take a sample from the nozzle. Once changes in the coolant are detected, the next step is to investigate potential causes. Depending on the underlying cause, the corrective measures can vary widely.

While the daily visual checks are a prerequisite, they are not enough when it comes to the monitoring and measuring of the most important parameter – the concentration of the emulsion. There is no stable process without a stable concentration! The emulsion concentration is important for the cutting performance, corrosion protection, as well as foam building, skin compatibility and sump life. The concentration should be checked whenever the coolant tank gets filled up. Several countries such as Germany, the United Kingdom and the USA request a periodical monitoring of the metalworking fluid.