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Essential Guide to CNC Coolant Maintenance: Best Practices and Tips

What is CNC coolant and why is it important?

Metalworking coolants are soluble cutting fluids that are made up of a mixture of oil, emulsifiers and other chemicals which are mixed with water prior to use. They are used in the manufacture of metal components and are used to cool and lubricate the workpiece along with preventing chip accumulation that could compromise both tool life and surface finish.

What is the life expectancy of CNC coolant and can it go bad?

Good concentration control is the most important aspect in maintaining soluble cutting fluids. If your coolant is in a good, healthy condition, this will help you to maximise tool life, sump life surface finish and minimise the risk of skin irritation, corrosion, foaming and sticky residues. Using a hand refractometer is an easy method for measuring and maintaining good concentration control. All coolants are formulated to have a minimum and maximum operating range which is determined by the additives in the formulation and the materials and applications they are designed to work with.

What are the risks of poor coolant maintenance?

Poor maintenance of metalworking coolants can lead to several risks, affecting both the efficiency of the machining process and the health and safety of workers. Here are some potential risks associated with inadequate metalworking coolant maintenance:

  • Decreased Machining Performance - Insufficient coolant maintenance can result in a breakdown of the coolant properties, leading to reduced heat dissipation. This can cause an increase in cutting tool temperature, resulting in poor machining performance, tool wear, and reduced tool life.
  • Corrosion and Rust - Coolant systems are susceptible to bacterial contamination and the formation of undesirable by-products. Without proper maintenance, corrosion and rust may occur in metalworking equipment, leading to damage and reduced lifespan of machinery.
  • Microbial Growth - Stagnant or contaminated coolants can create an environment conducive to microbial growth. Bacteria and fungi can thrive in the coolant, leading to the formation of biofilms. This can cause foul odours, clog filters, and contribute to system corrosion.
  • Health Risks - Contaminated or degraded coolants may release harmful substances into the air, posing a risk to the health of machine operators. Breathing in mist or aerosols containing coolant contaminants can lead to respiratory issues and skin irritation.
  • Reduced Lubrication - Metalworking coolants often have lubricating properties to enhance the cutting process. Poor maintenance can lead to a loss of these lubricating properties, resulting in increased friction, heat, and wear on cutting tools.
  • Unstable Cutting Conditions - Inconsistent coolant properties can result in unstable cutting conditions, affecting the accuracy and precision of machining operations. This can lead to poor surface finishes and dimensional inaccuracies in machined parts.

To mitigate these risks, it is essential to follow manufacturer recommendations for coolant maintenance, including regular monitoring, filtration, and replenishment of coolant additives. Regular maintenance practices, such as cleaning, filtering, and microbial control, can help ensure optimal coolant performance and prolong the life of metalworking equipment.

How often to change CNC coolant?

This is largely dependent upon the type of machine, volume of work and the type of material being machined. However, it is considered good practice to carry out a full machine clean every 12 months. Before clean out, it is essential to run a system cleaner such as Cutwel CutClean SC through the machine for 24-48 hours beforehand in order to kill of bacterial and fungal infections, as well as clean down dirt and slime that may have accumulated and ensure the new charge of coolant is going into a sterile, clean environment.

How to mix CNC fluids correctly? 

When mixing a soluble cutting fluid which contains oil and emulsifier (emulsion or semi synthetic), it is vitally important to always add oil slowly to water and not vice versa. This is due to how the emulsifiers react with water. Adding water to oil can create an “invert emulsion” which will offer poor performance and instability issues, such as short sump life and increased risk of corrosion. Where possible, an automated mixing device such as a Mixtron should be used to ensure accurate and safe mixing of soluble cutting fluids.

Why does my CNC coolant smell? 

The rotten egg, sulphur or “Monday morning smell” often associated with soluble cutting fluids is caused by bacteria in the fluid. This can be caused by several factors including:

  • Using the wrong type of coolant for the materials/application.
  • Poor concentration control.
  • Poor housekeeping.
  • Heavy tramp oil contamination.

Light to moderate bacterial infections can be controlled by use of a suitable biocide such as Cutwel Bacteriacide, and by ensuring that a suitable systems cleaner is used when carrying out full fluid changes, such as Cutwel Cutclean SC.

Why is my CNC coolant foamy? 

Foam in soluble cutting fluids is usually caused by either chemical or mechanical means. 

Mechanical causes can include:

  • Blocked filters.
  • Significant fluid displacement.
  • Low fluid levels, causing air entrainment.

This will lead to the coolant foaming excessively and can compromise tool life and surface finish. 

Chemical causes include: 

  • Running the coolant at a concentration above that recommended by the manufacturer.
  • Using the wrong coolant type for the makeup water.
  • Machine type can also cause coolant to foam.

On occasion, the use of an antifoam agent, such as Cutwel Antifoam Ultra, can help to control foam until other parameters are checked and resolved.

How to remove tramp oil 

Tramp oil (caused by slideway oil, hydraulic oil etc.) can have a detrimental impact on soluble cutting fluids. As the oil floats to the surface, it cuts off oxygen entering the fluid, increasing the risk of bacterial infection or shortened fluid life. If tramp oil emulsifies into the coolant, this can lead to increased smoking and compromised tool life and surface finish. Tramp oil can be easily removed by use of an oil skimmer or by skimming off with a Freddy Coolant Vacuum.

How to dispose of CNC coolant 

  • Recycling and Reusing - Where possible, try to recycle or reuse cutting fluids. Some fluids can be filtered and reused using a Freddy vacuum, reducing the need for disposal.
  • Contact Local Authorities - Check with your local environmental agency or council for specific regulations and guidelines regarding the disposal of cutting fluids. Different regions may have different rules.
  • Licensed Waste Disposal Services – contact a licensed waste disposal service that specialise in handling industrial fluids. These services are equipped to manage hazardous waste and will ensure proper disposal in accordance with regulations.
  • Waste Transfer Note - When arranging for disposal with a waste management company, ensure that a Waste Transfer Note is provided. This document outlines the type and quantity of waste being transferred and is a legal requirement.
  • Treatment Facilities - Some areas may have specialised treatment facilities that can process and treat cutting fluids before disposal. Check if such facilities exist in your area.
  • Always check with local environmental agencies and follow their guidelines to ensure compliance with regulations. Improper disposal of cutting fluids can have serious environmental consequences and may lead to legal consequences as well.

Can you recycle CNC coolant? 

It is possible to filter and recycle soluble cutting fluids using a Freddy Coolant Vacuum. Unless particularly large volumes of waste coolant are being produced (100,000’s litres p/a) then the only viable option currently available is disposal via an authorised waste disposal carrier.

Is CNC coolant hazardous? 

Metal working coolants are hazardous. They can cause skin irritations, often primarily caused by dirty, contaminated coolant entering under small skin abrasions. This can be reduced by regularly filtering the fluid using a Freddy Coolant Vacuum which will help to remove contaminants. 

Another cause can by elevated concentration for prolonged periods. This can be easily rectified by checking coolant concentration at least weekly using a hand refractometer.

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